Preserving the Neurovascular Bundle in Targeted Endodontic Microsurgery: A Case Series



Preserving the Neurovascular Bundle in Targeted Endodontic Microsurgery: A Case Series




Journal of Endodontics , 2021-03-01, Volume 47, Issue 3, Pages 509-519, Copyright © 2020 American Association of Endodontists


Abstract

Endodontic microsurgery encompasses the use of microscopy, specialized instruments, and advanced imaging with cone-beam computed tomographic (CBCT) imaging. This treatment modality results in high clinical success rates and facilitates the enucleation of osteolytic lesions, the resection of apical root canal complexities harboring persistent bacterial biofilms, and the evaluation of possible root defects and fractures. However, there is the risk of injury to important anatomic structures, particularly when treating posterior teeth. Neurovascular bundles are among these structures at risk for injury. Fortunately, high-resolution CBCT scans can be used to detect these structures that are known to have a high anatomic variability. In addition, CBCT information can be combined with high-resolution intraoral scans to plan, design, and fabricate surgical guides to be used in a targeted endodontic microsurgery (TEMS) approach. We report 3 cases with previous endodontic treatment having persistent apical periodontitis that were treated with TEMS to avoid damage to the neurovascular bundles at risk of injury. In the first case, the palatal root of tooth #14 was adjacent to the greater palatine artery. In the second case, the mental nerve exited through 2 separate foramina close to the predictive osteotomy site for the mesial root of tooth #19. In the third case, the posterior superior alveolar artery was in close proximity to the mesiobuccal root of tooth #14. Collectively, these cases illustrate the diagnostic value of CBCT imaging for detecting neurovascular bundles and the use of TEMS to mitigate the risk of injury to these important structures. Thus, the combination of CBCT imaging and TEMS can potentially minimize the risk of intraoperative complications and postoperative sequelae while increasing the predictability of endodontic microsurgeries in complex cases.

Significance

Clinicians need to be cognizant of vital anatomic structures such as neurovascular bundles while performing endodontic microsurgical procedures. The preoperative study of CBCT scans and careful planning, including the use of guides in TEMS, can reduce surgical complications such as hemorrhage and nerve injury even in complex cases.

Endodontic microsurgery (EMS) has classically been considered as a last resort for the management of failed endodontic treatment . Advancements in the field of endodontics, such as the dental operating microscope, cone-beam computed tomographic (CBCT) imaging, ultrasonics, microsurgical instruments, and calcium silicate–based biomaterials, have significantly improved the predictability and success of endodontic surgery , . A recent meta-analysis comparing the outcome of nonsurgical retreatment and EMS concluded that endodontic microsurgery has a pooled success rate of 92% in comparison to 80% for nonsurgical retreatment with no significant difference in long-term outcomes . In addition to a high success rate, EMS can also eliminate extraradicular biofilm, undebrided isthmuses, and apical canal complexities, which are typically not addressed by the nonsurgical approach , . Despite these clear advantages, EMS is often not considered as a first treatment option for root-filled teeth with persistent disease.

A survey on surgical trends revealed that 38% of endodontists have poor to fair comfort levels with mandibular molar surgery . Another finding from the survey was that 25%–30% of endodontists do not perform surgery in the mandibular premolar-molar region . Endodontists rate access and visualization among the more challenging aspects of the surgical procedure . Tooth position is also a significant factor affecting the success of EMS, with posterior teeth having poorer outcomes in contrast to anterior teeth . Although some of this hesitation may be related to the lack of proper training in surgical techniques, it can also be attributed to more difficult access and visualization in molar surgeries and the presence of apical root canal complexities . In addition, anatomic obstacles such as the presence of the neurovascular bundle or proximity of the maxillary sinus can also influence clinicians' decision-making process.

CBCT imaging is a critical step in the diagnosis and treatment planning of EMS procedures . Astute clinicians rely on the careful examination of high-resolution acquired CBCT slices to determine the relationship of the roots to important anatomic structures, such as buccal and lingual cortical plates, the maxillary sinus, the inferior alveolar nerve canal, and mental nerve foramina, among others. It is crucial for a clinician to visualize the location and path of the various anatomic structures such as neurovascular bundles as they traverse through the surgical field. Three-dimensional (3D) mapping of these structures allows a clinician to precisely plan both the surgical flap design and osteotomy. Unfortunately, the 3D reconstruction of the CBCT volume is seldom used for surgical planning purposes because it is fraught with artifacts and poor diagnostic value when visualized in the proprietary CBCT machine software package. This lost diagnostic value has a clear detrimental effect when trying to visualize the anatomic variations regarding the mental nerve, the posterior alveolar vascular channel, and the greater palatine neurovascular bundle. Third-party software may be needed to provide a 3D reconstruction of the volume so that these structures, which are known to have great anatomic variation , can be accurately visualized and traced ( Figs. 1–3 ). The knowledge gained can be directly applied toward EMS to avoid inadvertent damage to these important anatomic structures. Altogether, proper 3D reconstruction with advanced imaging software packages and the possible use of guides can increase provider confidence in endodontic surgery.

Anatomic variability in the GPNVB position can be detected in CBCT scans. ( A – D ) Four different cases are presented as examples of possible anatomic positions of the GPNVB in relationship to the palatal root of maxillary molars. ( i ) In the coronal slices, the position of the neurovascular bundle can be appreciated. ( ii ) The reconstructed 3D of the volume without further postprocessing has poor diagnostic value. ( iii ) However, the cinematic realistic 3D reconstruction using E-Vol DX software allows for excellent appreciation of anatomic structures facilitating surgical planning. MS, maxillary sinus; NF, nasal fossa.
Figure 1
Anatomic variability in the GPNVB position can be detected in CBCT scans. (
A
D ) Four different cases are presented as examples of possible anatomic positions of the GPNVB in relationship to the palatal root of maxillary molars. (
i ) In the coronal slices, the position of the neurovascular bundle can be appreciated. (
ii ) The reconstructed 3D of the volume without further postprocessing has poor diagnostic value. (
iii ) However, the cinematic realistic 3D reconstruction using E-Vol DX software allows for excellent appreciation of anatomic structures facilitating surgical planning. MS, maxillary sinus; NF, nasal fossa.

Anatomic variability in mental nerve foramen ( white arrows ) position and number can be detected in CBCT scans. ( A – D ) Four different cases are presented as examples of possible anatomic variations of the position and number of the mental foramen in ( i ) sagittal slices, ( ii ) unprocessed 3D reconstruction, and ( iii ) augmented 3D reconstruction using E-Vol DX software.
Figure 2
Anatomic variability in mental nerve foramen (
white arrows ) position and number can be detected in CBCT scans. (
A
D ) Four different cases are presented as examples of possible anatomic variations of the position and number of the mental foramen in (
i ) sagittal slices, (
ii ) unprocessed 3D reconstruction, and (
iii ) augmented 3D reconstruction using E-Vol DX software.

Anatomic variability in the PSAA position can be detected in CBCT scans. ( A – D ) Four different cases are presented as examples of possible anatomic positions of the PSAA in relationship to the maxillary molars. The examples shown demonstrate that the PSAA can be ( A ) completely enclosed in bone at the floor of the sinus, ( B ) transect the palatal root, ( C ) located with an apical lesion, or have a tortuous trajectory anastomosing with the greater palatine (traced in Di and Dii ). ( i ) In the coronal slices, the position of the PSAA can be appreciated. ( ii ) The reconstructed 3D image of the volume without further postprocessing has poor diagnostic value. ( iii ) However, the cinematic realistic 3D reconstruction using E-Vol DX software allows for excellent appreciation of anatomic structures facilitating surgical planning. ∗The PSAA location ( white arrow ). ∗∗The location of the GPNVB ( white arrow ). MS, maxillary sinus; NF, nasal fossa.
Figure 3
Anatomic variability in the PSAA position can be detected in CBCT scans. (
A
D ) Four different cases are presented as examples of possible anatomic positions of the PSAA in relationship to the maxillary molars. The examples shown demonstrate that the PSAA can be (
A ) completely enclosed in bone at the floor of the sinus, (
B ) transect the palatal root, (
C ) located with an apical lesion, or have a tortuous trajectory anastomosing with the greater palatine (traced in
Di and
Dii ). (
i ) In the coronal slices, the position of the PSAA can be appreciated. (
ii ) The reconstructed 3D image of the volume without further postprocessing has poor diagnostic value. (
iii ) However, the cinematic realistic 3D reconstruction using E-Vol DX software allows for excellent appreciation of anatomic structures facilitating surgical planning. ∗The PSAA location (
white arrow ). ∗∗The location of the GPNVB (
white arrow ). MS, maxillary sinus; NF, nasal fossa.

Targeted endodontic microsurgery (TEMS), also known as guided endodontic microsurgery , addresses some of these concerns associated with endodontic surgery on posterior teeth. This is particularly important when neurovascular structure trajectories are visualized in close proximity to the surgical site on a CBCT scan. Surgical guide fabrication is accomplished through merging of a CBCT scan and the optical scan of the arch being treated. Various software programs may be used to design the guide and then upload the file to a 3D printer for fabrication . Surgical bone trephines can be used to perform both osteotomy and root resection in TEMS. This approach not only ensures precise and conservative bone removal and root resection but also helps to reduce surgical time and postoperative healing complications . The aim of this case series is to present novel modifications for the guided EMS technique in challenging scenarios in which there is a high risk of trauma to the neurovascular bundle.


Case 1: Maxillary First Molar Palatal Root

A 63-year-old woman with a physical status category II according to the American Society of Anesthesiologists (ASA) presented to the Graduate Endodontics Clinic at the University of Texas Health at San Antonio (UTHSA), San Antonio, TX, for the evaluation of previously treated tooth #14. The tooth had been treated 2 years prior with nonsurgical root canal treatment followed by EMS for the mesiobuccal root. However, the patient reported the persistence of symptoms, requiring reevaluation because of the chief complaint of “biting tenderness.”

Clinical examination revealed a full-coverage crown on #14, and the tooth was tender to percussion. The teeth adjacent to #14 were vital and had no percussion or palpation tenderness. Tooth #13 through tooth #15 had physiological mobility, with probing depth measurements of less than 3 mm. The periapical radiograph showed a small radiolucent lesion associated with the palatal root of #14 ( Fig. 4 A ). A CBCT scan was acquired using Veraviewepocs 3D R100 (J Morita USA, Inc, Irvine, CA) revealing that the buccal roots of tooth #14 had intact lamina dura, but the palatal root had an approximately 3 × 3 × 3 mm low-density periapical area with an intact palatal cortical plate ( Fig. 4 B ). Imaging also showed a close proximity of the greater palatine groove to the palatal root ( Fig. 4 B ). The dynamic navigation through the acquired CBCT volume and its 3D reconstruction with E-Vol DX (CDT Software, Sao Jose dos Campos, SP, Brazil) imaging software allowed for tracing of the neurovascular bundle ( Supplemental Video S1 is available online at www.jendodon.com ). A minimally invasive pedunculated flap was planned to preserve the blood supply from the greater palatine artery ( Fig. 4 C ). Based on the clinical and radiographic findings, the diagnosis for tooth #14 was established as previously treated with symptomatic apical periodontitis. The risks and benefits of both nonsurgical and surgical treatment options were discussed in detail with the patient. The records acquired from the previous provider indicated that the palatal canal had a ledge that could not be bypassed. Therefore, nonsurgical endodontic retreatment of the tooth was deemed to be of little benefit. The patient provided written and oral consent to perform guided EMS.

A novel minimally invasive approach for palatal root resection adjacent to the GPNVB. Tooth #14 palatal root. ( A ) The preoperative periapical radiograph showing palatal root periapical radiolucency. ( B ) The location of the greater palatine groove housing neurovascular bundle in close proximity to the planned surgical site ( black arrow ) seen in a coronal slice of CBCT volume. ( C ) A diagrammatic representation of the palate showing the expected path of the GPNVB ( red and yellow solid lines ) and conservative incision design ( dotted black line ). ( D ) A surgical guide properly adapted on the maxillary arch with excellent retention. ( E ) Methylene blue dye used to mark the surgical site through the guide tube ( black arrow ). ( F ) A 6-mm biopsy punch with a modified semilunar cutting edge. ( G ) A small tissue flap retracted with a silk suture tied to the contralateral teeth. ( H ) A handpiece and trephine with adequate clearance and a neutral resection angle. ( I ) A single resorbable suture to tie the flap back in place. ( J ) The immediate postoperative radiograph. ( K ) The 3-day postoperative photograph showing good approximation of the incision line and minimal inflammation. ( L ) The 10-day postoperative photograph showing uneventful healing of tissues with no complications.
Figure 4
A novel minimally invasive approach for palatal root resection adjacent to the GPNVB. Tooth #14 palatal root. (
A ) The preoperative periapical radiograph showing palatal root periapical radiolucency. (
B ) The location of the greater palatine groove housing neurovascular bundle in close proximity to the planned surgical site (
black arrow ) seen in a coronal slice of CBCT volume. (
C ) A diagrammatic representation of the palate showing the expected path of the GPNVB (
red and yellow solid lines ) and conservative incision design (
dotted black line ). (
D ) A surgical guide properly adapted on the maxillary arch with excellent retention. (
E ) Methylene blue dye used to mark the surgical site through the guide tube (
black arrow ). (
F ) A 6-mm biopsy punch with a modified semilunar cutting edge. (
G ) A small tissue flap retracted with a silk suture tied to the contralateral teeth. (
H ) A handpiece and trephine with adequate clearance and a neutral resection angle. (
I ) A single resorbable suture to tie the flap back in place. (
J ) The immediate postoperative radiograph. (
K ) The 3-day postoperative photograph showing good approximation of the incision line and minimal inflammation. (
L ) The 10-day postoperative photograph showing uneventful healing of tissues with no complications.


Preoperative Treatment Planning and Procedure

An intraoral optical scan was obtained using the Trios 3Shape scanner (3Shape, Copenhagen, Denmark). The surface tessellation language (stereolithography) and Digital Imaging and Communications in Medicine files were merged in Blue Sky Bio implant planning software (Blue Sky Plan; Blue Sky Bio, Grayslake, IL) to design a surgical guide. The trephine port was positioned to avoid the greater palatine neurovascular bundle (GPNVB) and at an angle sufficient to prevent contact of the handpiece with the contralateral dentition. Modifications to the guide were made in MeshMixer (Autodesk Inc, San Rafael, CA), and the guide was printed using the FormLabs 2 3D printer (FormLabs Inc, Somerville, MA) with a proprietary Food and Drug Administration–approved surgical guide resin (Formlabs Photopolymer Resin, FormLabs Inc). The guide was postprocessed using the FormLabs washing station, and a final cure was completed in the Form Cure oven (FormLabs Inc) followed by autoclaving of the guide before use.


Surgical Procedure

The patient completed a 60-second presurgical mouth rinse with 0.2% chlorhexidine digluconate (Peridex; 3M ESPE, Seefeld, Germany). Profound anesthesia was obtained with local infiltration of 1 carpule (1.7 mL) of 2% lidocaine with 1:50,000 epinephrine (Benco Dental Supply Co, Pittston, PA) equivalent to 34 mg lidocaine. The entire procedure was completed with a surgical operating microscope (OPMI pico dental microscope; Zeiss, Oberkochen, Germany). Presurgical verification of seating and retention of the surgical guide was accomplished ( Fig. 4 D ). A microbrush soaked with methylene blue dye (Vista-Blue; Vista Dental Products, Racine, WI) was placed through the guide to transfer a circular mark onto the palatal tissue ( Fig. 4 E ). A 6-mm biopsy punch (6.0 mm Integra Standard Biopsy Punch; Miltex, York, PA) was modified with a high-speed bur to create a semilunar cutting edge ( Fig. 4 F ). The guide was removed, and the modified 6-mm diameter biopsy punch was used in a firm motion until it rested on bone followed by an incision directed laterally and anteriorly to create a semilunar incision over this area. A full-thickness flap of the small area of palatal tissue was elevated and tied to the contralateral side with a 4-0 silk suture (4-0 Perma-Hand Silk; Ethicon, Somerville, NJ) ( Fig. 4 G ). Guided osteotomy along with root resection was performed with a 4-mm diameter trephine bur (3i; Zimmer Biomet, Palm Beach Gardens, FL) at 1000 rpm ( Fig. 4 H ). Copious irrigation with sterile saline was directed over the trephine bur. The trephine bur was used in a pecking motion until the handpiece head reached the guide tube as incorporated into the guide planning. A Luxator Forte Elevator (Directa Dental, Upplands Väsby, Sweden) was used to remove the core consisting of bone, root-end, and periapical tissue. An Endo-Z bur (Dentsply Tulsa, Tulsa, OK) was used to smoothen the root end. Any remaining granulation tissue was curetted with a spoon excavator. The root end was stained with methylene blue dye (Vista-Blue) and inspected under 25× magnification to rule out the presence of any root fractures. Root-end preparation of the palatal canal was accomplished using JETip ultrasonic tips (B&L Biotech, Fairfax, VA) and filled with Endosequence BC Root Repair Material (Brasseler USA, Savannah, GA). The site was closed with a single 4-0 gut suture (4-0 Plain Gut, Ethicon) ( Fig. 4 I ). An immediate postoperative radiograph was taken showing adequate palatal root-end filling ( Fig. 4 J ). Inadvertent damage to the GPNVB was avoided as was evident by the insignificant amount of bleeding encountered during the surgery. The patient was instructed to take 600 mg ibuprofen and 325 mg acetaminophen every 6 hours for 3 days and as needed after the procedure. The patient was also instructed to rinse with 0.2% chlorhexidine gluconate (Peridex) twice daily for 2 weeks. The patient returned for a 3-day ( Fig. 4 K ) and 10-day ( Fig. 4 L ) postoperative visit with resolution of symptoms and no reported complications. The patient reported that no pain medications were necessary subsequent to the day of surgery.


Case 2: Mandibular First Molar

A 53-year-old man (ASA I) presented to UTHSA for the evaluation of pain related to the lower left tooth. The patient reported sporadic discomfort when chewing on the left side. A review of the patient's medical history revealed no systemic conditions or medications that could influence the treatment plan or outcome. Dental history indicated a previous root canal treatment performed 7 years prior on tooth #19. Clinical examination revealed a full-coverage restoration on tooth #19 with intact margins. Tooth #19 elicited tenderness upon the percussion test. All the other teeth in the lower left quadrant responded normally to thermal testing and had no percussion or palpation tenderness. Tooth #19 through tooth #21 had physiological mobility and periodontal probing depth measurements of less than 3 mm. Radiographic and CBCT imaging revealed overextended (2–3 mm) obturation with radiographic features consistent with a carrier-based material in both the mesial and distal root canals ( Fig. 5 A ). A small and localized low-density area at the apex of the distal root of tooth #19 was noted ( Fig. 5 A ). Based on the clinical and radiographic findings, a diagnosis of previously treated and symptomatic apical periodontitis was established for tooth #19. In addition to the well-reported high success rates of EMS compared with nonsurgical retreatment , the tooth had an appropriate full cuspal coverage with intact margins. Thus, the patient decided to pursue the surgical treatment modality.

The use of a double-barrel guide for simultaneous surgical management of both the mesial and distal mandibular molar roots. The risk of nerve damage to the accessory branch of the mental nerve was mitigated. Tooth #19 mesial and distal roots. ( A ) The preoperative radiograph showing overextended carrier-based obturation material. ( B ) The sagittal and axial CBCT slices showing the mental nerve ( black arrows ) and anterior accessory loop ( blue arrows ). ( C ) Blue Sky Bio rendering of the double-barrel guide. ( D ) The guide seated showing adequate clearance for the corner of the mouth. ( E ) The Luxator Forte Elevator used to easily remove the core. ( F ) The accessory mental nerve ( blue arrow ) in close proximity to the osteotomy site. ( G ) The osteotomy and resected root ends. ( H ) The immediate postoperative radiograph after retropreparation and retrofilling of the root end.
Figure 5
The use of a double-barrel guide for simultaneous surgical management of both the mesial and distal mandibular molar roots. The risk of nerve damage to the accessory branch of the mental nerve was mitigated. Tooth #19 mesial and distal roots. (
A ) The preoperative radiograph showing overextended carrier-based obturation material. (
B ) The sagittal and axial CBCT slices showing the mental nerve (
black arrows ) and anterior accessory loop (
blue arrows ). (
C ) Blue Sky Bio rendering of the double-barrel guide. (
D ) The guide seated showing adequate clearance for the corner of the mouth. (
E ) The Luxator Forte Elevator used to easily remove the core. (
F ) The accessory mental nerve (
blue arrow ) in close proximity to the osteotomy site. (
G ) The osteotomy and resected root ends. (
H ) The immediate postoperative radiograph after retropreparation and retrofilling of the root end.

A prominent accessory mental neurovascular bundle was identified exiting through an accessory mental foramen located in close proximity to the apical lesion ( Fig. 5 B ; Supplemental Video S2 is available online at www.jendodon.com ). Thus, in order to precisely perform a root-end resection without damaging the accessory branch of the mental neurovascular bundle, the positioning parameters of the surgical guide were modified and incorporated in the design. In addition, the surgical guide design was modified to fabricate a “double-barrel guide” ( Fig. 5 C and D ). This modified design facilitated guided osteotomy and root-end resection of both the mesial and distal root without the need for fabrication of 2 separate surgical guides ( Fig. 5 D ). Step-by-step planning for the surgical guide was performed similarly as for the previous case. The mandibular left quadrant was scanned with a Trios intraoral scanner followed by the merging of both Digital Imaging and Communications in Medicine and surface tessellation language files using BlueSky Bio software. Next, the guide was designed, printed using the FormLabs 2 printer, cured using the Form Cure oven, and autoclaved.

On the day of surgery, the patient completed a 60-second presurgical mouth rinse with 0.2% chlorhexidine digluconate (Peridex). Profound anesthesia was obtained with an inferior alveolar nerve block and lingual nerve block using 2 carpules (1.7 mL) of 2% lidocaine 1:100,000 epinephrine (68 mg lidocaine) (Benco Dental Supply Co, Pittston, PA), local infiltration of 1 carpule (1.7 mL) of 4% Septocaine 1:100,000 epinephrine (68 mg articaine) (Septodont, New Castle, DE), and 2 carpules (1.7 mL) of 2% lidocaine 1:50,000 epinephrine (68 mg lidocaine). A vertical releasing incision was made at the distobuccal line angle of tooth #22, and a full-thickness triangular, papilla-sparing mucoperiosteal flap extending to the mesiobuccal aspect of tooth #17 was reflected ( Fig. 5 E ). The flap design was then modified to include a small distal releasing incision on tooth #17. The accessory branch of the mental nerve was visualized, and this structure prevented further flap reflection ( Fig. 5 F ). A groove on the cortical plate was made distoinferiorly to prevent inadvertent slipping of the retractor. The surgical guide was seated, and adaptation was verified ( Fig. 5 D ). A 4-mm diameter trephine bur was used in a pecking motion until the full planned depth was reached through both guide tubes. After removal of the cores ( Fig. 5 G ), the portion of extended carriers apical to the osteotomies was subsequently removed with a Luxator Forte Elevator. Minimal bleeding was observed after the removal of the core and hemostasis controlled with local measures. The canals were retrogradely prepared using JETip ultrasonic tips followed by irrigation with saline and filling with EndoSequence BC Root Repair Material ( Fig. 5 H ). The site was sutured with 5-0 polypropylene (Perma Sharp Sutures; Hu-Friedy, Chicago, IL). One carpule (1.8 mL) of 0.5% Marcaine with 1:200,000 epinephrine (9 mg bupivacaine) (Benco Dental Supply Co., Pittston, PA) was administered for postoperative pain relief. Pressure was applied to the flap with saline-moistened gauze for 5 minutes. The patient returned for a 1-week postoperative follow-up with uneventful soft tissue healing and no reported paresthesia or other complications.


Case 3: Maxillary First Molar Mesiobuccal Root

A 38-year-old healthy (ASA I) woman presented to UTHSA for reevaluation of previously treated tooth #14. The patient complained of an intermittent dull ache on biting. Despite the nonsurgical management of the second mesiobuccal canal after retreatment, a persistent lesion was still present on the mesiobuccal root apex. Clinical findings revealed a full-coverage crown on tooth #14 with slight tenderness to percussion. Probing depth measurements were 3 mm or less, and all other teeth in the upper left posterior quadrant had no percussion tenderness, palpation tenderness, or pathologic mobility. Radiographic ( Fig. 6 A ) and CBCT imaging of tooth #14 revealed an intact lamina dura on the distobuccal and palatal roots of tooth #14 and a 4 × 4 × 3 mm low-density area at the apex of the mesiobuccal root immediately palatal to a branch of the posterior superior alveolar artery (PSAA) ( Fig. 6 B ). The trajectory of the PSAA and its branches was traced using E-Vol DX software ( Fig. 6 C ). Based on the clinical and radiographic findings, the diagnosis for tooth #14 was established as previously treated symptomatic apical periodontitis. Preoperative planning included an intraoral optical scan, a large-volume CBCT scan, and guide fabrication with a Formlabs 2 3D printer as performed in previous cases. The guide tube was moved bodily in a coronal direction and then angled apically to adequately resect the root while avoiding trauma to the PSAA and maxillary sinus.

A branch of the PSAA was immediately buccal to the root apex to be sectioned. The modification of guide tube positioning prevented significant complications. Tooth #14 mesiobuccal root. ( A ) The preoperative radiograph showing periapical radiolucency around the mesiobuccal root. ( B ) The sagittal view of the CBCT scan showing an undebrided isthmus despite instrumentation and obturation of the second mesiobuccal canal ( black arrow ). The PSAA branch passing through the cortical bone immediately buccal to the root apex ( blue arrow ). ( C ) The PSAA trajectory was traced using E-Vol DX software (visualized in red ). ( D ) The bone and root core in place after trephination with a guide. ( E ) An undebrided isthmus noted on the root segment ( black arrow ). ( F ) The immediate postoperative radiograph.
Figure 6
A branch of the PSAA was immediately buccal to the root apex to be sectioned. The modification of guide tube positioning prevented significant complications. Tooth #14 mesiobuccal root. (
A ) The preoperative radiograph showing periapical radiolucency around the mesiobuccal root. (
B ) The sagittal view of the CBCT scan showing an undebrided isthmus despite instrumentation and obturation of the second mesiobuccal canal (
black arrow ). The PSAA branch passing through the cortical bone immediately buccal to the root apex (
blue arrow ). (
C ) The PSAA trajectory was traced using E-Vol DX software (visualized in
red ). (
D ) The bone and root core in place after trephination with a guide. (
E ) An undebrided isthmus noted on the root segment (
black arrow ). (
F ) The immediate postoperative radiograph.

Subsequent to preprocedural mouth rinse with chlorhexidine for 60 seconds, profound anesthesia was obtained with local infiltration of 1 carpule (1.7 mL) of 4% Septocaine with 1:100,000 epinephrine (68 mg articaine) (Septodont, New Castle, DE) and 1 carpule (1.7 mL) of 2% lidocaine with 1:50,000 epinephrine (34 mg lidocaine). A vertical releasing incision at the distobuccal line angle of tooth #12 was made, and a full-thickness triangular, papilla-sparing mucoperiosteal flap extending to the mesiobuccal aspect of tooth #15 was reflected. The surgical guide was seated, and a 4-mm diameter trephine bur was used in a pecking motion until the full planned depth was reached, resulting in a well-defined bone/root-end core ( Fig. 6 D ) that needed to be gently luxated to be fully removed ( Fig. 6 E ) from the surgical site. Next, the root end and isthmus were retrogradely prepared using KiS ultrasonic tips (Obtura Spartan, Fenton, MO), and root-end filling (EndoSequence BC Root Repair Material) was placed ( Fig. 6 F ). The PSAA was avoided, and no significant bleeding occurred during the procedure. The site was sutured with 5-0 polypropylene (Perma Sharp Sutures). Pressure was applied to the flap with saline moistened gauze for 5 minutes. The patient returned for a 1-week postoperative suture removal and follow-up with no reported complications.


Discussion

The increasing number of surgeries being performed across various dental specialties including endodontics, periodontology, implantology, and oral surgery compounds the risk of trauma to the dentoalveolar neurovascular bundles . A study by Mainkar et al reported that mandibular premolar-molar periapical surgeries are associated with a 14% incidence of postoperative altered sensation. In addition, inadvertent damage to vascular channels and their anastomoses can lead to excessive hemorrhage and compromised postoperative healing . Advancements in imaging techniques, imaging software, and guided surgical techniques have provided ways to identify and reduce the risk of traumatizing these vital structures, as shown in this case series.

Guided surgical endodontic treatment is beneficial in cases with thick cortical plates, proximity to vital anatomic structures, and compromised access. In periapical surgery, excessive removal of bone has been reported to yield inferior surgical outcomes . Similarly, the length and angle of root-end resection are also critical prognostic factors for the success of endodontic surgery , . The use of 3D-printed surgical guides with the use of a trephine bur addresses most of these concerns because it results in conservative osteotomies and accurate root-end resection . Reports of guided EMS have been published in the literature substantiating the previously mentioned advantages of this procedure , , . In a study performed by Pinsky et al , it was shown that freehand surgery in comparison to guided surgery led to a larger osteotomy and deviated significantly more while doing the apicoectomy. In another in vitro surgical simulation scenario, TEMS was shown to provide efficient completion of osteotomy and resection with a more appropriate root-end resection volume and bevel angle when compared with nonguided EMS . In this case series, TEMS allowed for a precise 1-step osteotomy and root-end resection and avoided damage to critical neurovascular structures.

Clinicians hesitate in performing EMSs with a palatal approach because of difficult access and flap reflection and poor visualization of the root-end surface and canal. Surgeries with a palatal full-thickness mucoperiosteal flap are associated with postoperative discomfort and complications such as hematoma, eventually leading to jeopardized vascular supply of the flap . Reflection of a palatal flap can also be challenging because the tissues are firmly bound to the underlying bone . In addition, there is a high risk of severing the palatine neurovascular bundle, particularly if a posterior relieving incision is used . In addition, the greater palatine artery can also be damaged during osteotomy and root resection depending on the relative proximity of the palatal root end to the greater palatine artery. After careful examination of the 3D reconstruction of this case ( Supplemental Video S1 is available online at www.jendodon.com ), a novel and minimally invasive palatal flap was designed using a modified biopsy punch and in combination with guided EMS led to precise root resection, thereby minimizing the intraoperative time. Only a single suture was required to properly reposition and approximate the reflected tissue. For palatal approach surgery, the rapid soft tissue healing observed and the reduced postoperative pain were unprecedented, which could be attributed to the preservation of blood and nerve supply to the palatal flap. The patient did not require any additional pain medication after the day of surgery, and the postoperative recovery was uneventful. A thorough understanding of the GPNVB anatomy is critical to achieve a successful outcome with this technique. It has been demonstrated that there is great variation in the anatomy of the greater palatine groove, with 60% of cases having no groove, 34% with 1 groove, and 6% of cases having 2 grooves in the maxillary first molar region . As shown in this report, the location of the greater palatine groove on a CBCT scan might provide an indication of the path of the GPNVB. In Figure 1 A–D , we show examples of the various anatomic positions of this neurovascular bundle that can be estimated on CBCT scans. Regarding case 1, the location of the greater palatine groove was identified, and its trajectory was traced ( Supplemental Video S1 is available online at www.jendodon.com ), which aided in designing the surgical guide so as to avoid any damage to the GPNVB. However, in cases in which the greater palatine groove is not evident, the nerve bundle might be located in the overlying palatal soft tissues. In these cases, the GPNVB location can be assessed based on a patient's palatal vault height. It has been reported that its location in relation to the height of the palatal vault is at an average of 7, 12, and 17 mm from the cementoenamel junctions of the premolars and molars in shallow, average, and high palatal vaults, respectively .

The second case presented a scenario in which a prominent accessory branch of the mental nerve was identified on a CBCT scan. This accessory nerve bundle exits through the accessory mental foramen and is reported to have a prevalence of 5%–30% . The proximity of the mental nerve and its accessory branches to the surgical field have critical implications because inadvertent damage to the neurovascular bundle can lead to postoperative paresthesia . In Figure 2 A–D , we demonstrate examples of different positions and number of foramina of the mental nerve that can be identified in CBCT scans. In case 2, the accessory branch of the mental nerve exiting through the accessory mental foramen was identified on the preoperative CBCT scan through dynamic navigation through the acquired CBCT volume and realistic reconstruction of the 3D volume ( Supplemental Video S2 is available online at www.jendodon.com ). The findings from the CBCT scan were taken into account for surgical treatment planning to minimize the risk of damage to the neurovascular bundle. A distal releasing incision was also used to avoid excessive strain on the flap during the surgery . As soon as the accessory mental nerve was located, a groove was scored on the cortical plate to aid in placing the retractor and avoid any slippage to prevent damage to the nerve bundle . The double-barrel surgical guide expedited the procedure and aided in the removal of the thick cortical plate and root ends within a relatively short period of time.

The third case exhibited a scenario in which a branch of the PSAA was located immediately buccal to the root apex to be sectioned. The PSAA and the infraorbital artery give off extraosseous and intraosseous branches, which subsequently anastomose around the maxillary sinus . In Figure 3 A–D , we show examples of different anatomic positions for the PSAA trajectory in relation to the root apices of maxillary molars, including a case in which anastomosis occurs with the greater palatine artery ( Fig. 3 D ). Particularly for case 3, the sagittal view of the CBCT scan clearly shows the intraosseous branch of the PSAA in close proximity to the planned surgical site. In this case, the dynamic navigation through the CBCT volume and the visualization of the 3D reconstruction using E-Vol DX software allowed for visualization of the PSAA and its trajectory ( Fig. 6 C ; Supplemental Video S3 is available online at www.jendodon.com ). The design of a surgical guide averted significant complications, which may have arisen if the drilling path had not been properly planned. The mean distances from intraosseous anastomoses of PSAA to the alveolar ridge have been reported to be 17.7 mm for the second maxillary molar, 14.5 mm for the first maxillary molar, and 14.7 mm for the second maxillary premolar . Because the average location of the PSAA is 14.5 mm from the alveolar ridge in the maxillary first molar region, it seems that this case may be a more common finding, and careful assessment of the surgical site with a CBCT scan is crucial. A study by Nicolielo et al found that 20% of PSAA canals had diameters greater than 1 mm, which was large enough to cause significant bleeding risk if perforated. Therefore, damage of this structure should be avoided by all costs to minimize intraoperative complications such as hemorrhage and postoperative inadequate healing because of reduced vascularity.

The use of guided EMS has few inherent limitations. The characteristic shape of the trephine creates a not so flat resection pattern at the root end, which can be addressed by using an Endo-Z bur to flatten the root-end resection and remove any sharp edges, as was done in all the cases. Although it has been reported that the size of osteotomy with guided surgery might be too conservative in certain situations , we did not come across this problem in any of the cases because we used trephines of appropriate diameter. However, modification of the guide tube position in our cases, to avoid the neurovascular bundles, had likely caused a minor increase in the amount of root resection. Another reported disadvantage of guided procedures is the amount of time spent preoperatively in designing and fabricating the template ; however, this is compensated by the significant reduction in intraoperative time, which results in better healing and lesser patient discomfort. In addition, the time spent in the digital workflow of the guide design is significantly reduced as the surgeon becomes more versed in the digital planning. Lastly, the use of high-quality 3D printers with appropriate resin results in guides with high reproduction fidelity of the design that adapts very well to the reference dentition. Thus, it provides an accurate path to a precise osteotomy and root resection, while also minimizing time and risk of the collateral damage of important anatomic structures.


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Preserving the Neurovascular Bundle in Targeted Endodontic Microsurgery: A Case Series Gary Benjamin DMD , Amber Ather BDS, DDS , Mike R. Bueno DDS , Carlos Estrela DDS, PhD and Anibal Diogenes DDS, PhD Journal of Endodontics , 2021-03-01, Volume 47, Issue 3, Pages 509-519, Copyright © 2020 American Association of Endodontists Abstract Endodontic microsurgery encompasses the use of microscopy, specialized instruments, and advanced imaging with cone-beam computed tomographic (CBCT) imaging. This treatment modality results in high clinical success rates and facilitates the enucleation of osteolytic lesions, the resection of apical root canal complexities harboring persistent bacterial biofilms, and the evaluation of possible root defects and fractures. However, there is the risk of injury to important anatomic structures, particularly when treating posterior teeth. Neurovascular bundles are among these structures at risk for injury. Fortunately, high-resolution CBCT scans can be used to detect these structures that are known to have a high anatomic variability. In addition, CBCT information can be combined with high-resolution intraoral scans to plan, design, and fabricate surgical guides to be used in a targeted endodontic microsurgery (TEMS) approach. We report 3 cases with previous endodontic treatment having persistent apical periodontitis that were treated with TEMS to avoid damage to the neurovascular bundles at risk of injury. In the first case, the palatal root of tooth #14 was adjacent to the greater palatine artery. In the second case, the mental nerve exited through 2 separate foramina close to the predictive osteotomy site for the mesial root of tooth #19. In the third case, the posterior superior alveolar artery was in close proximity to the mesiobuccal root of tooth #14. Collectively, these cases illustrate the diagnostic value of CBCT imaging for detecting neurovascular bundles and the use of TEMS to mitigate the risk of injury to these important structures. Thus, the combination of CBCT imaging and TEMS can potentially minimize the risk of intraoperative complications and postoperative sequelae while increasing the predictability of endodontic microsurgeries in complex cases. Significance Clinicians need to be cognizant of vital anatomic structures such as neurovascular bundles while performing endodontic microsurgical procedures. The preoperative study of CBCT scans and careful planning, including the use of guides in TEMS, can reduce surgical complications such as hemorrhage and nerve injury even in complex cases. Endodontic microsurgery (EMS) has classically been considered as a last resort for the management of failed endodontic treatment . Advancements in the field of endodontics, such as the dental operating microscope, cone-beam computed tomographic (CBCT) imaging, ultrasonics, microsurgical instruments, and calcium silicate–based biomaterials, have significantly improved the predictability and success of endodontic surgery , . A recent meta-analysis comparing the outcome of nonsurgical retreatment and EMS concluded that endodontic microsurgery has a pooled success rate of 92% in comparison to 80% for nonsurgical retreatment with no significant difference in long-term outcomes . In addition to a high success rate, EMS can also eliminate extraradicular biofilm, undebrided isthmuses, and apical canal complexities, which are typically not addressed by the nonsurgical approach , . Despite these clear advantages, EMS is often not considered as a first treatment option for root-filled teeth with persistent disease. A survey on surgical trends revealed that 38% of endodontists have poor to fair comfort levels with mandibular molar surgery . Another finding from the survey was that 25%–30% of endodontists do not perform surgery in the mandibular premolar-molar region . Endodontists rate access and visualization among the more challenging aspects of the surgical procedure . Tooth position is also a significant factor affecting the success of EMS, with posterior teeth having poorer outcomes in contrast to anterior teeth . Although some of this hesitation may be related to the lack of proper training in surgical techniques, it can also be attributed to more difficult access and visualization in molar surgeries and the presence of apical root canal complexities . In addition, anatomic obstacles such as the presence of the neurovascular bundle or proximity of the maxillary sinus can also influence clinicians' decision-making process. CBCT imaging is a critical step in the diagnosis and treatment planning of EMS procedures . Astute clinicians rely on the careful examination of high-resolution acquired CBCT slices to determine the relationship of the roots to important anatomic structures, such as buccal and lingual cortical plates, the maxillary sinus, the inferior alveolar nerve canal, and mental nerve foramina, among others. It is crucial for a clinician to visualize the location and path of the various anatomic structures such as neurovascular bundles as they traverse through the surgical field. Three-dimensional (3D) mapping of these structures allows a clinician to precisely plan both the surgical flap design and osteotomy. Unfortunately, the 3D reconstruction of the CBCT volume is seldom used for surgical planning purposes because it is fraught with artifacts and poor diagnostic value when visualized in the proprietary CBCT machine software package. This lost diagnostic value has a clear detrimental effect when trying to visualize the anatomic variations regarding the mental nerve, the posterior alveolar vascular channel, and the greater palatine neurovascular bundle. Third-party software may be needed to provide a 3D reconstruction of the volume so that these structures, which are known to have great anatomic variation , can be accurately visualized and traced ( Figs. 1–3 ). The knowledge gained can be directly applied toward EMS to avoid inadvertent damage to these important anatomic structures. Altogether, proper 3D reconstruction with advanced imaging software packages and the possible use of guides can increase provider confidence in endodontic surgery. Figure 1 Anatomic variability in the GPNVB position can be detected in CBCT scans. ( A – D ) Four different cases are presented as examples of possible anatomic positions of the GPNVB in relationship to the palatal root of maxillary molars. ( i ) In the coronal slices, the position of the neurovascular bundle can be appreciated. ( ii ) The reconstructed 3D of the volume without further postprocessing has poor diagnostic value. ( iii ) However, the cinematic realistic 3D reconstruction using E-Vol DX software allows for excellent appreciation of anatomic structures facilitating surgical planning. MS, maxillary sinus; NF, nasal fossa. Figure 2 Anatomic variability in mental nerve foramen ( white arrows ) position and number can be detected in CBCT scans. ( A – D ) Four different cases are presented as examples of possible anatomic variations of the position and number of the mental foramen in ( i ) sagittal slices, ( ii ) unprocessed 3D reconstruction, and ( iii ) augmented 3D reconstruction using E-Vol DX software. Figure 3 Anatomic variability in the PSAA position can be detected in CBCT scans. ( A – D ) Four different cases are presented as examples of possible anatomic positions of the PSAA in relationship to the maxillary molars. The examples shown demonstrate that the PSAA can be ( A ) completely enclosed in bone at the floor of the sinus, ( B ) transect the palatal root, ( C ) located with an apical lesion, or have a tortuous trajectory anastomosing with the greater palatine (traced in Di and Dii ). ( i ) In the coronal slices, the position of the PSAA can be appreciated. ( ii ) The reconstructed 3D image of the volume without further postprocessing has poor diagnostic value. ( iii ) However, the cinematic realistic 3D reconstruction using E-Vol DX software allows for excellent appreciation of anatomic structures facilitating surgical planning. ∗The PSAA location ( white arrow ). ∗∗The location of the GPNVB ( white arrow ). MS, maxillary sinus; NF, nasal fossa. Targeted endodontic microsurgery (TEMS), also known as guided endodontic microsurgery , addresses some of these concerns associated with endodontic surgery on posterior teeth. This is particularly important when neurovascular structure trajectories are visualized in close proximity to the surgical site on a CBCT scan. Surgical guide fabrication is accomplished through merging of a CBCT scan and the optical scan of the arch being treated. Various software programs may be used to design the guide and then upload the file to a 3D printer for fabrication . Surgical bone trephines can be used to perform both osteotomy and root resection in TEMS. This approach not only ensures precise and conservative bone removal and root resection but also helps to reduce surgical time and postoperative healing complications . The aim of this case series is to present novel modifications for the guided EMS technique in challenging scenarios in which there is a high risk of trauma to the neurovascular bundle. Case 1: Maxillary First Molar Palatal Root A 63-year-old woman with a physical status category II according to the American Society of Anesthesiologists (ASA) presented to the Graduate Endodontics Clinic at the University of Texas Health at San Antonio (UTHSA), San Antonio, TX, for the evaluation of previously treated tooth #14. The tooth had been treated 2 years prior with nonsurgical root canal treatment followed by EMS for the mesiobuccal root. However, the patient reported the persistence of symptoms, requiring reevaluation because of the chief complaint of “biting tenderness.” Clinical examination revealed a full-coverage crown on #14, and the tooth was tender to percussion. The teeth adjacent to #14 were vital and had no percussion or palpation tenderness. Tooth #13 through tooth #15 had physiological mobility, with probing depth measurements of less than 3 mm. The periapical radiograph showed a small radiolucent lesion associated with the palatal root of #14 ( Fig. 4 A ). A CBCT scan was acquired using Veraviewepocs 3D R100 (J Morita USA, Inc, Irvine, CA) revealing that the buccal roots of tooth #14 had intact lamina dura, but the palatal root had an approximately 3 × 3 × 3 mm low-density periapical area with an intact palatal cortical plate ( Fig. 4 B ). Imaging also showed a close proximity of the greater palatine groove to the palatal root ( Fig. 4 B ). The dynamic navigation through the acquired CBCT volume and its 3D reconstruction with E-Vol DX (CDT Software, Sao Jose dos Campos, SP, Brazil) imaging software allowed for tracing of the neurovascular bundle ( Supplemental Video S1 is available online at www.jendodon.com ). A minimally invasive pedunculated flap was planned to preserve the blood supply from the greater palatine artery ( Fig. 4 C ). Based on the clinical and radiographic findings, the diagnosis for tooth #14 was established as previously treated with symptomatic apical periodontitis. The risks and benefits of both nonsurgical and surgical treatment options were discussed in detail with the patient. The records acquired from the previous provider indicated that the palatal canal had a ledge that could not be bypassed. Therefore, nonsurgical endodontic retreatment of the tooth was deemed to be of little benefit. The patient provided written and oral consent to perform guided EMS. Figure 4 A novel minimally invasive approach for palatal root resection adjacent to the GPNVB. Tooth #14 palatal root. ( A ) The preoperative periapical radiograph showing palatal root periapical radiolucency. ( B ) The location of the greater palatine groove housing neurovascular bundle in close proximity to the planned surgical site ( black arrow ) seen in a coronal slice of CBCT volume. ( C ) A diagrammatic representation of the palate showing the expected path of the GPNVB ( red and yellow solid lines ) and conservative incision design ( dotted black line ). ( D ) A surgical guide properly adapted on the maxillary arch with excellent retention. ( E ) Methylene blue dye used to mark the surgical site through the guide tube ( black arrow ). ( F ) A 6-mm biopsy punch with a modified semilunar cutting edge. ( G ) A small tissue flap retracted with a silk suture tied to the contralateral teeth. ( H ) A handpiece and trephine with adequate clearance and a neutral resection angle. ( I ) A single resorbable suture to tie the flap back in place. ( J ) The immediate postoperative radiograph. ( K ) The 3-day postoperative photograph showing good approximation of the incision line and minimal inflammation. ( L ) The 10-day postoperative photograph showing uneventful healing of tissues with no complications. Preoperative Treatment Planning and Procedure An intraoral optical scan was obtained using the Trios 3Shape scanner (3Shape, Copenhagen, Denmark). The surface tessellation language (stereolithography) and Digital Imaging and Communications in Medicine files were merged in Blue Sky Bio implant planning software (Blue Sky Plan; Blue Sky Bio, Grayslake, IL) to design a surgical guide. The trephine port was positioned to avoid the greater palatine neurovascular bundle (GPNVB) and at an angle sufficient to prevent contact of the handpiece with the contralateral dentition. Modifications to the guide were made in MeshMixer (Autodesk Inc, San Rafael, CA), and the guide was printed using the FormLabs 2 3D printer (FormLabs Inc, Somerville, MA) with a proprietary Food and Drug Administration–approved surgical guide resin (Formlabs Photopolymer Resin, FormLabs Inc). The guide was postprocessed using the FormLabs washing station, and a final cure was completed in the Form Cure oven (FormLabs Inc) followed by autoclaving of the guide before use. Surgical Procedure The patient completed a 60-second presurgical mouth rinse with 0.2% chlorhexidine digluconate (Peridex; 3M ESPE, Seefeld, Germany). Profound anesthesia was obtained with local infiltration of 1 carpule (1.7 mL) of 2% lidocaine with 1:50,000 epinephrine (Benco Dental Supply Co, Pittston, PA) equivalent to 34 mg lidocaine. The entire procedure was completed with a surgical operating microscope (OPMI pico dental microscope; Zeiss, Oberkochen, Germany). Presurgical verification of seating and retention of the surgical guide was accomplished ( Fig. 4 D ). A microbrush soaked with methylene blue dye (Vista-Blue; Vista Dental Products, Racine, WI) was placed through the guide to transfer a circular mark onto the palatal tissue ( Fig. 4 E ). A 6-mm biopsy punch (6.0 mm Integra Standard Biopsy Punch; Miltex, York, PA) was modified with a high-speed bur to create a semilunar cutting edge ( Fig. 4 F ). The guide was removed, and the modified 6-mm diameter biopsy punch was used in a firm motion until it rested on bone followed by an incision directed laterally and anteriorly to create a semilunar incision over this area. A full-thickness flap of the small area of palatal tissue was elevated and tied to the contralateral side with a 4-0 silk suture (4-0 Perma-Hand Silk; Ethicon, Somerville, NJ) ( Fig. 4 G ). Guided osteotomy along with root resection was performed with a 4-mm diameter trephine bur (3i; Zimmer Biomet, Palm Beach Gardens, FL) at 1000 rpm ( Fig. 4 H ). Copious irrigation with sterile saline was directed over the trephine bur. The trephine bur was used in a pecking motion until the handpiece head reached the guide tube as incorporated into the guide planning. A Luxator Forte Elevator (Directa Dental, Upplands Väsby, Sweden) was used to remove the core consisting of bone, root-end, and periapical tissue. An Endo-Z bur (Dentsply Tulsa, Tulsa, OK) was used to smoothen the root end. Any remaining granulation tissue was curetted with a spoon excavator. The root end was stained with methylene blue dye (Vista-Blue) and inspected under 25× magnification to rule out the presence of any root fractures. Root-end preparation of the palatal canal was accomplished using JETip ultrasonic tips (B&L Biotech, Fairfax, VA) and filled with Endosequence BC Root Repair Material (Brasseler USA, Savannah, GA). The site was closed with a single 4-0 gut suture (4-0 Plain Gut, Ethicon) ( Fig. 4 I ). An immediate postoperative radiograph was taken showing adequate palatal root-end filling ( Fig. 4 J ). Inadvertent damage to the GPNVB was avoided as was evident by the insignificant amount of bleeding encountered during the surgery. The patient was instructed to take 600 mg ibuprofen and 325 mg acetaminophen every 6 hours for 3 days and as needed after the procedure. The patient was also instructed to rinse with 0.2% chlorhexidine gluconate (Peridex) twice daily for 2 weeks. The patient returned for a 3-day ( Fig. 4 K ) and 10-day ( Fig. 4 L ) postoperative visit with resolution of symptoms and no reported complications. The patient reported that no pain medications were necessary subsequent to the day of surgery. Case 2: Mandibular First Molar A 53-year-old man (ASA I) presented to UTHSA for the evaluation of pain related to the lower left tooth. The patient reported sporadic discomfort when chewing on the left side. A review of the patient's medical history revealed no systemic conditions or medications that could influence the treatment plan or outcome. Dental history indicated a previous root canal treatment performed 7 years prior on tooth #19. Clinical examination revealed a full-coverage restoration on tooth #19 with intact margins. Tooth #19 elicited tenderness upon the percussion test. All the other teeth in the lower left quadrant responded normally to thermal testing and had no percussion or palpation tenderness. Tooth #19 through tooth #21 had physiological mobility and periodontal probing depth measurements of less than 3 mm. Radiographic and CBCT imaging revealed overextended (2–3 mm) obturation with radiographic features consistent with a carrier-based material in both the mesial and distal root canals ( Fig. 5 A ). A small and localized low-density area at the apex of the distal root of tooth #19 was noted ( Fig. 5 A ). Based on the clinical and radiographic findings, a diagnosis of previously treated and symptomatic apical periodontitis was established for tooth #19. In addition to the well-reported high success rates of EMS compared with nonsurgical retreatment , the tooth had an appropriate full cuspal coverage with intact margins. Thus, the patient decided to pursue the surgical treatment modality. Figure 5 The use of a double-barrel guide for simultaneous surgical management of both the mesial and distal mandibular molar roots. The risk of nerve damage to the accessory branch of the mental nerve was mitigated. Tooth #19 mesial and distal roots. ( A ) The preoperative radiograph showing overextended carrier-based obturation material. ( B ) The sagittal and axial CBCT slices showing the mental nerve ( black arrows ) and anterior accessory loop ( blue arrows ). ( C ) Blue Sky Bio rendering of the double-barrel guide. ( D ) The guide seated showing adequate clearance for the corner of the mouth. ( E ) The Luxator Forte Elevator used to easily remove the core. ( F ) The accessory mental nerve ( blue arrow ) in close proximity to the osteotomy site. ( G ) The osteotomy and resected root ends. ( H ) The immediate postoperative radiograph after retropreparation and retrofilling of the root end. A prominent accessory mental neurovascular bundle was identified exiting through an accessory mental foramen located in close proximity to the apical lesion ( Fig. 5 B ; Supplemental Video S2 is available online at www.jendodon.com ). Thus, in order to precisely perform a root-end resection without damaging the accessory branch of the mental neurovascular bundle, the positioning parameters of the surgical guide were modified and incorporated in the design. In addition, the surgical guide design was modified to fabricate a “double-barrel guide” ( Fig. 5 C and D ). This modified design facilitated guided osteotomy and root-end resection of both the mesial and distal root without the need for fabrication of 2 separate surgical guides ( Fig. 5 D ). Step-by-step planning for the surgical guide was performed similarly as for the previous case. The mandibular left quadrant was scanned with a Trios intraoral scanner followed by the merging of both Digital Imaging and Communications in Medicine and surface tessellation language files using BlueSky Bio software. Next, the guide was designed, printed using the FormLabs 2 printer, cured using the Form Cure oven, and autoclaved. On the day of surgery, the patient completed a 60-second presurgical mouth rinse with 0.2% chlorhexidine digluconate (Peridex). Profound anesthesia was obtained with an inferior alveolar nerve block and lingual nerve block using 2 carpules (1.7 mL) of 2% lidocaine 1:100,000 epinephrine (68 mg lidocaine) (Benco Dental Supply Co, Pittston, PA), local infiltration of 1 carpule (1.7 mL) of 4% Septocaine 1:100,000 epinephrine (68 mg articaine) (Septodont, New Castle, DE), and 2 carpules (1.7 mL) of 2% lidocaine 1:50,000 epinephrine (68 mg lidocaine). A vertical releasing incision was made at the distobuccal line angle of tooth #22, and a full-thickness triangular, papilla-sparing mucoperiosteal flap extending to the mesiobuccal aspect of tooth #17 was reflected ( Fig. 5 E ). The flap design was then modified to include a small distal releasing incision on tooth #17. The accessory branch of the mental nerve was visualized, and this structure prevented further flap reflection ( Fig. 5 F ). A groove on the cortical plate was made distoinferiorly to prevent inadvertent slipping of the retractor. The surgical guide was seated, and adaptation was verified ( Fig. 5 D ). A 4-mm diameter trephine bur was used in a pecking motion until the full planned depth was reached through both guide tubes. After removal of the cores ( Fig. 5 G ), the portion of extended carriers apical to the osteotomies was subsequently removed with a Luxator Forte Elevator. Minimal bleeding was observed after the removal of the core and hemostasis controlled with local measures. The canals were retrogradely prepared using JETip ultrasonic tips followed by irrigation with saline and filling with EndoSequence BC Root Repair Material ( Fig. 5 H ). The site was sutured with 5-0 polypropylene (Perma Sharp Sutures; Hu-Friedy, Chicago, IL). One carpule (1.8 mL) of 0.5% Marcaine with 1:200,000 epinephrine (9 mg bupivacaine) (Benco Dental Supply Co., Pittston, PA) was administered for postoperative pain relief. Pressure was applied to the flap with saline-moistened gauze for 5 minutes. The patient returned for a 1-week postoperative follow-up with uneventful soft tissue healing and no reported paresthesia or other complications. Case 3: Maxillary First Molar Mesiobuccal Root A 38-year-old healthy (ASA I) woman presented to UTHSA for reevaluation of previously treated tooth #14. The patient complained of an intermittent dull ache on biting. Despite the nonsurgical management of the second mesiobuccal canal after retreatment, a persistent lesion was still present on the mesiobuccal root apex. Clinical findings revealed a full-coverage crown on tooth #14 with slight tenderness to percussion. Probing depth measurements were 3 mm or less, and all other teeth in the upper left posterior quadrant had no percussion tenderness, palpation tenderness, or pathologic mobility. Radiographic ( Fig. 6 A ) and CBCT imaging of tooth #14 revealed an intact lamina dura on the distobuccal and palatal roots of tooth #14 and a 4 × 4 × 3 mm low-density area at the apex of the mesiobuccal root immediately palatal to a branch of the posterior superior alveolar artery (PSAA) ( Fig. 6 B ). The trajectory of the PSAA and its branches was traced using E-Vol DX software ( Fig. 6 C ). Based on the clinical and radiographic findings, the diagnosis for tooth #14 was established as previously treated symptomatic apical periodontitis. Preoperative planning included an intraoral optical scan, a large-volume CBCT scan, and guide fabrication with a Formlabs 2 3D printer as performed in previous cases. The guide tube was moved bodily in a coronal direction and then angled apically to adequately resect the root while avoiding trauma to the PSAA and maxillary sinus. Figure 6 A branch of the PSAA was immediately buccal to the root apex to be sectioned. The modification of guide tube positioning prevented significant complications. Tooth #14 mesiobuccal root. ( A ) The preoperative radiograph showing periapical radiolucency around the mesiobuccal root. ( B ) The sagittal view of the CBCT scan showing an undebrided isthmus despite instrumentation and obturation of the second mesiobuccal canal ( black arrow ). The PSAA branch passing through the cortical bone immediately buccal to the root apex ( blue arrow ). ( C ) The PSAA trajectory was traced using E-Vol DX software (visualized in red ). ( D ) The bone and root core in place after trephination with a guide. ( E ) An undebrided isthmus noted on the root segment ( black arrow ). ( F ) The immediate postoperative radiograph. Subsequent to preprocedural mouth rinse with chlorhexidine for 60 seconds, profound anesthesia was obtained with local infiltration of 1 carpule (1.7 mL) of 4% Septocaine with 1:100,000 epinephrine (68 mg articaine) (Septodont, New Castle, DE) and 1 carpule (1.7 mL) of 2% lidocaine with 1:50,000 epinephrine (34 mg lidocaine). A vertical releasing incision at the distobuccal line angle of tooth #12 was made, and a full-thickness triangular, papilla-sparing mucoperiosteal flap extending to the mesiobuccal aspect of tooth #15 was reflected. The surgical guide was seated, and a 4-mm diameter trephine bur was used in a pecking motion until the full planned depth was reached, resulting in a well-defined bone/root-end core ( Fig. 6 D ) that needed to be gently luxated to be fully removed ( Fig. 6 E ) from the surgical site. Next, the root end and isthmus were retrogradely prepared using KiS ultrasonic tips (Obtura Spartan, Fenton, MO), and root-end filling (EndoSequence BC Root Repair Material) was placed ( Fig. 6 F ). The PSAA was avoided, and no significant bleeding occurred during the procedure. The site was sutured with 5-0 polypropylene (Perma Sharp Sutures). Pressure was applied to the flap with saline moistened gauze for 5 minutes. The patient returned for a 1-week postoperative suture removal and follow-up with no reported complications. Discussion The increasing number of surgeries being performed across various dental specialties including endodontics, periodontology, implantology, and oral surgery compounds the risk of trauma to the dentoalveolar neurovascular bundles . A study by Mainkar et al reported that mandibular premolar-molar periapical surgeries are associated with a 14% incidence of postoperative altered sensation. In addition, inadvertent damage to vascular channels and their anastomoses can lead to excessive hemorrhage and compromised postoperative healing . Advancements in imaging techniques, imaging software, and guided surgical techniques have provided ways to identify and reduce the risk of traumatizing these vital structures, as shown in this case series. Guided surgical endodontic treatment is beneficial in cases with thick cortical plates, proximity to vital anatomic structures, and compromised access. In periapical surgery, excessive removal of bone has been reported to yield inferior surgical outcomes . Similarly, the length and angle of root-end resection are also critical prognostic factors for the success of endodontic surgery , . The use of 3D-printed surgical guides with the use of a trephine bur addresses most of these concerns because it results in conservative osteotomies and accurate root-end resection . Reports of guided EMS have been published in the literature substantiating the previously mentioned advantages of this procedure , , . In a study performed by Pinsky et al , it was shown that freehand surgery in comparison to guided surgery led to a larger osteotomy and deviated significantly more while doing the apicoectomy. In another in vitro surgical simulation scenario, TEMS was shown to provide efficient completion of osteotomy and resection with a more appropriate root-end resection volume and bevel angle when compared with nonguided EMS . In this case series, TEMS allowed for a precise 1-step osteotomy and root-end resection and avoided damage to critical neurovascular structures. Clinicians hesitate in performing EMSs with a palatal approach because of difficult access and flap reflection and poor visualization of the root-end surface and canal. Surgeries with a palatal full-thickness mucoperiosteal flap are associated with postoperative discomfort and complications such as hematoma, eventually leading to jeopardized vascular supply of the flap . Reflection of a palatal flap can also be challenging because the tissues are firmly bound to the underlying bone . In addition, there is a high risk of severing the palatine neurovascular bundle, particularly if a posterior relieving incision is used . In addition, the greater palatine artery can also be damaged during osteotomy and root resection depending on the relative proximity of the palatal root end to the greater palatine artery. After careful examination of the 3D reconstruction of this case ( Supplemental Video S1 is available online at www.jendodon.com ), a novel and minimally invasive palatal flap was designed using a modified biopsy punch and in combination with guided EMS led to precise root resection, thereby minimizing the intraoperative time. Only a single suture was required to properly reposition and approximate the reflected tissue. For palatal approach surgery, the rapid soft tissue healing observed and the reduced postoperative pain were unprecedented, which could be attributed to the preservation of blood and nerve supply to the palatal flap. The patient did not require any additional pain medication after the day of surgery, and the postoperative recovery was uneventful. A thorough understanding of the GPNVB anatomy is critical to achieve a successful outcome with this technique. It has been demonstrated that there is great variation in the anatomy of the greater palatine groove, with 60% of cases having no groove, 34% with 1 groove, and 6% of cases having 2 grooves in the maxillary first molar region . As shown in this report, the location of the greater palatine groove on a CBCT scan might provide an indication of the path of the GPNVB. In Figure 1 A–D , we show examples of the various anatomic positions of this neurovascular bundle that can be estimated on CBCT scans. Regarding case 1, the location of the greater palatine groove was identified, and its trajectory was traced ( Supplemental Video S1 is available online at www.jendodon.com ), which aided in designing the surgical guide so as to avoid any damage to the GPNVB. However, in cases in which the greater palatine groove is not evident, the nerve bundle might be located in the overlying palatal soft tissues. In these cases, the GPNVB location can be assessed based on a patient's palatal vault height. It has been reported that its location in relation to the height of the palatal vault is at an average of 7, 12, and 17 mm from the cementoenamel junctions of the premolars and molars in shallow, average, and high palatal vaults, respectively . The second case presented a scenario in which a prominent accessory branch of the mental nerve was identified on a CBCT scan. This accessory nerve bundle exits through the accessory mental foramen and is reported to have a prevalence of 5%–30% . The proximity of the mental nerve and its accessory branches to the surgical field have critical implications because inadvertent damage to the neurovascular bundle can lead to postoperative paresthesia . In Figure 2 A–D , we demonstrate examples of different positions and number of foramina of the mental nerve that can be identified in CBCT scans. In case 2, the accessory branch of the mental nerve exiting through the accessory mental foramen was identified on the preoperative CBCT scan through dynamic navigation through the acquired CBCT volume and realistic reconstruction of the 3D volume ( Supplemental Video S2 is available online at www.jendodon.com ). The findings from the CBCT scan were taken into account for surgical treatment planning to minimize the risk of damage to the neurovascular bundle. A distal releasing incision was also used to avoid excessive strain on the flap during the surgery . As soon as the accessory mental nerve was located, a groove was scored on the cortical plate to aid in placing the retractor and avoid any slippage to prevent damage to the nerve bundle . The double-barrel surgical guide expedited the procedure and aided in the removal of the thick cortical plate and root ends within a relatively short period of time. The third case exhibited a scenario in which a branch of the PSAA was located immediately buccal to the root apex to be sectioned. The PSAA and the infraorbital artery give off extraosseous and intraosseous branches, which subsequently anastomose around the maxillary sinus . In Figure 3 A–D , we show examples of different anatomic positions for the PSAA trajectory in relation to the root apices of maxillary molars, including a case in which anastomosis occurs with the greater palatine artery ( Fig. 3 D ). Particularly for case 3, the sagittal view of the CBCT scan clearly shows the intraosseous branch of the PSAA in close proximity to the planned surgical site. In this case, the dynamic navigation through the CBCT volume and the visualization of the 3D reconstruction using E-Vol DX software allowed for visualization of the PSAA and its trajectory ( Fig. 6 C ; Supplemental Video S3 is available online at www.jendodon.com ). The design of a surgical guide averted significant complications, which may have arisen if the drilling path had not been properly planned. The mean distances from intraosseous anastomoses of PSAA to the alveolar ridge have been reported to be 17.7 mm for the second maxillary molar, 14.5 mm for the first maxillary molar, and 14.7 mm for the second maxillary premolar . Because the average location of the PSAA is 14.5 mm from the alveolar ridge in the maxillary first molar region, it seems that this case may be a more common finding, and careful assessment of the surgical site with a CBCT scan is crucial. A study by Nicolielo et al found that 20% of PSAA canals had diameters greater than 1 mm, which was large enough to cause significant bleeding risk if perforated. Therefore, damage of this structure should be avoided by all costs to minimize intraoperative complications such as hemorrhage and postoperative inadequate healing because of reduced vascularity. The use of guided EMS has few inherent limitations. The characteristic shape of the trephine creates a not so flat resection pattern at the root end, which can be addressed by using an Endo-Z bur to flatten the root-end resection and remove any sharp edges, as was done in all the cases. Although it has been reported that the size of osteotomy with guided surgery might be too conservative in certain situations , we did not come across this problem in any of the cases because we used trephines of appropriate diameter. However, modification of the guide tube position in our cases, to avoid the neurovascular bundles, had likely caused a minor increase in the amount of root resection. Another reported disadvantage of guided procedures is the amount of time spent preoperatively in designing and fabricating the template ; however, this is compensated by the significant reduction in intraoperative time, which results in better healing and lesser patient discomfort. In addition, the time spent in the digital workflow of the guide design is significantly reduced as the surgeon becomes more versed in the digital planning. Lastly, the use of high-quality 3D printers with appropriate resin results in guides with high reproduction fidelity of the design that adapts very well to the reference dentition. Thus, it provides an accurate path to a precise osteotomy and root resection, while also minimizing time and risk of the collateral damage of important anatomic structures. Conclusion This case series presents the challenges associated with the anatomic variations of the GPNVB, mental nerve, and posterior alveolar artery in endodontic microsurgeries. The appropriate use of advanced imaging using CBCT scanning through dynamic navigation and 3D reconstructed volumes in association with 3D-printed surgical guides can help in treatment planning and to predictably perform EMS in scenarios in which there is a risk of trauma to the neurovascular bundle. This approach increases clinicians' confidence level while mitigating risks of inadvertent damage to vital anatomic structures and will enable them to deliver expedient treatment with more predictable healing and less risk of iatrogenic adverse events for their patients. Acknowledgments Gary Benjamin and Amber Ather contributed equally to this study. The authors deny any conflicts of interest related to this study. Supplementary Material   Supplemental Video S1 Dynamic navigation through the acquired CBCT volume of tooth #14 with identification and tracing of the greater palatine neurovascular bundle.   Supplemental Video S2 Dynamic navigation through the acquired CBCT volume of tooth #19 with identification of the mental nerve exiting through 2 separate foramina.   Supplemental Video S3 Dynamic navigation through the acquired CBCT volume of tooth #14 with identification and tracing of the posterior superior alveolar neurovascular bundle. References 1. Kim S., Kratchman S.: Modern endodontic surgery concepts and practice: a review. J Endod 2006; 32: pp. 601-623. 2. Setzer F.C., Shah S.B., Kohli M.R., et. al.: Outcome of endodontic surgery: a meta-analysis of the literature--part 1: comparison of traditional root-end surgery and endodontic microsurgery. J Endod 2010; 3: pp. 1757-1765. 3. Kang M., In Jung H., Song M., et. al.: Outcome of nonsurgical retreatment and endodontic microsurgery: a meta-analysis. Clin Oral Investig 2015; 19: pp. 569-582. 4. Signoretti F.G., Endo M.S., Gomes B.P., et. al.: Persistent extraradicular infection in root-filled asymptomatic human tooth: scanning electron microscopic analysis and microbial investigation after apical microsurgery. J Endod 2011; 37: pp. 1696-1700. 5. Wu M.K., Dummer P.M., Wesselink P.R.: Consequences of and strategies to deal with residual post-treatment root canal infection. Int Endod J 2006; 39: pp. 343-356. 6. Creasy J.E., Mines P., Sweet M.: Surgical trends among endodontists: the results of a web-based survey. J Endod 2009; 35: pp. 30-34. 7. Zhou W., Zheng Q., Tan X., et. al.: Comparison of mineral trioxide aggregate and iRoot BP plus root repair material as root-end filling materials in endodontic microsurgery: a prospective randomized controlled study. J Endod 2017; 43: pp. 1-6. 8. Song M., Kim S.G., Lee S.J., et. al.: Prognostic factors of clinical outcomes in endodontic microsurgery: a prospective study. J Endod 2013; 39: pp. 1491-1497. 9. Patel S., Brown J., Pimentel T., et. al.: Cone beam computed tomography in endodontics - a review of the literature. Int Endod J 2019; 52: pp. 1138-1152. 10. Monsour P., Huang T.: Morphology of the greater palatine grooves of the hard palate: a cone beam computed tomography study. Aust Dent J 2016; 61: pp. 329-332. 11. Katakami K., Mishima A., Shiozaki K., et. al.: Characteristics of accessory mental foramina observed on limited cone-beam computed tomography images. J Endod 2008; 34: pp. 1441-1445. 12. Pandharbale A.A., Gadgil R.M., Bhoosreddy A.R., et. al.: Evaluation of the posterior superior alveolar artery using cone beam computed tomography. Pol J Radiol 2016; 81: pp. 606-610. 13. Giacomino C.M., Ray J.J., Wealleans J.A.: Targeted endodontic microsurgery: a novel approach to anatomically challenging scenarios using 3-dimensional-printed guides and trephine burs-a report of 3 cases. J Endod 2018; 44: pp. 671-677. 14. Ray J.J., Giacomino C.M., Wealleans J.A., Sheridan R.R.: Targeted endodontic microsurgery: digital workflow options. J Endod 2020; 46: pp. 863-871. 15. Hawkins T.K., Wealleans J.A., Pratt A.M., Ray J.J.: Targeted endodontic microsurgery and endodontic microsurgery: a surgical simulation comparison. Int Endod J 2020; 53: pp. 715-722. 16. Jacobs R., Quirynen M., Bornstein M.M.: Neurovascular disturbances after implant surgery. Periodontol 2000 2014; 66: pp. 188-202. 17. Mainkar A., Zhu Q., Safavi K.: Incidence of altered sensation after mandibular premolar and molar periapical surgery. J Endod 2020; 46: pp. 29-33. 18. von Arx T., Hänni S., Jensen S.S.: Correlation of bone defect dimensions with healing outcome one year after apical surgery. J Endod 2007; 33: pp. 1044-1048. 19. Kim S., Pecora G., Rubinstein R.: Comparison of traditional and microsurgery in endodontics.Kim S.Pecora G.Rubinstein R.Color Atlas of Microsurgery in Endodontics.2001.W.B. SaundersPhiladelphia:pp. 5-11. 20. Popowicz W., Palatyńska-Ulatowska A., Kohli M.R.: Targeted endodontic microsurgery: computed tomography-based guided stent approach with platelet-rich fibrin graft: a report of 2 cases. J Endod 2019; 45: pp. 1535-1542. 21. Ahn S.Y., Kim N.H., Kim S., et. al.: Computer-aided design/computer-aided manufacturing-guided endodontic surgery: guided osteotomy and apex localization in a mandibular molar with a thick buccal bone plate. J Endod 2018; 44: pp. 665-670. 22. Pinsky H.M., Champleboux G., Sarment D.P.: Periapical surgery using CAD/CAM guidance: preclinical results. J Endod 2007; 33: pp. 148-151. 23. Grandi C., Pacifici L.: The ratio in choosing access flap for surgical endodontics: a review. Oral Implantol (Rome) 2009; 2: pp. 37-52. 24. Reiser G.M., Bruno J.F., Mahan P.E., Larkin L.H.: The subepithelial connective tissue graft palatal donor site: anatomic considerations for surgeons. Int J Periodontics Restorative Dent 1996; 16: pp. 130-137. 25. Moiseiwitsch J.R.: Avoiding the mental foramen during periapical surgery. J Endod 1995; 21: pp. 340-342. 26. Kqiku L., Biblekaj R., Weiglein A.H., et. al.: Arterial blood architecture of the maxillary sinus in dentate specimens. Croat Med J 2013; 54: pp. 180-184. 27. Nicolielo L.F., Van Dessel J., Jacobs R., et. al.: Presurgical CBCT assessment of maxillary neurovascularization in relation to maxillary sinus augmentation procedures and posterior implant placement. Surg Radiol Anat 2014; 36: pp. 915-924.

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