Computer-Aided Rehabilitation of Maxillary Oncological Defects Using Zygomatic Implants: A Defect-Based Classification



Computer-Aided Rehabilitation of Maxillary Oncological Defects Using Zygomatic Implants: A Defect-Based Classification




Journal of Oral and Maxillofacial Surgery, 2015-12-01, Volume 73, Issue 12, Pages 2446.e1-2446.e11, Copyright © 2015 American Association of Oral and Maxillofacial Surgeons


Purpose

A complete maxillectomy for neoplastic lesions leads to serious oral dysfunction. Zygomatic implants for fixed bridge support are considered beneficial for maxillary defects after tumor resection.

Materials and Methods

This clinical study examined the management of patients with different maxillary defect types who underwent delayed rehabilitation using zygomatic implants and immediate prosthetic loading. Virtual preoperative planning and intraoperative navigation were performed in all cases.

Results

Five patients were treated with this new method. The total number of zygomatic implants positioned was 17. Four patients had immediate loading of a fixed prosthesis and 1 had delayed loading. One patient had 1 failed implant.

Conclusion

The use of preoperative virtual surgical planning and an intraoperative navigation system allows the surgeon to achieve safer implant positioning in a complex anatomic site. A systematic bone defect classification was created and a specific treatment protocol is proposed for each type of defect.

Oncologic bone resection for neoplastic lesions involving the maxilla leads to serious oral dysfunction with respect to speaking, swallowing, chewing, and quality of life. Defect classification systems enable clinicians to choose the type of rehabilitation and determine a functional prognosis. Since the publication of the study by Ohngren, many classification schemes have been proposed to describe the anatomic boundaries of maxillectomy defects.

A complete maxillectomy produces complex defects of the alveolar bone, palate, paranasal sinuses, and orbital floor. Loss of these anatomic structures has relevant functional and esthetic consequences. Reconstruction of this region should 1) prevent any communication between the oral cavity and the nasopharynx, 2) reconstruct the palatal surface, and 3) achieve facial symmetry and good facial morphology.

Several surgical reconstruction options exist, including nonvascularized grafts, local flaps, and microsurgical reconstruction with bone or soft tissues. However, in many cases, dental implants have been used to obtain functional restoration through mechanical retention of dental prostheses.

Implant placement and subsequent prosthetic rehabilitation are often difficult to obtain after maxillectomy because of a lack of bone alveolar tissue and gingiva. Dental implants can be considered a viable restorative option only when the basal maxillary bone is preserved.

Zygomatic implants are used to rehabilitate patients with insufficient bone volume for “traditional” dental implants. These implants are inserted into the zygomatic bone when alveolar bone is deficient after maxillectomy. However, the application of zygomatic implants in reconstructive surgery is often associated with various problems, including deficiencies of bone tissue and the presence of a reconstructive soft tissue flap.

In this clinical study, the authors examined the management of patients with different maxillary defect types who underwent delayed rehabilitation using zygomatic implants and immediate prosthetic loading. Clinical outcomes were assessed for implant failure and prosthetic loading.


Rehabilitative Protocol

During the preparation of this article, it became clear that none of the classifications addressed maxillary restoration using zygomatic implants. A systematic bone defect classification was considered and a specific treatment protocol is proposed for each type of defect.

Patients were categorized into 3 classes according to the site of the defect, the size of the defect, and residual masticatory function. Class I was defined as bilateral maxillectomy. Class II was defined as unilateral maxillectomy. In this class, 3 subclasses were identified according to the dental status of the unresected side: Class IIA included patients with dentition or partial dentition in the contralateral maxilla; Class IIB included patients without dentition in the residual maxilla; Class IIC included patients without dentition in the healthy maxilla with atrophied alveolar bone; Class III included patients whose anterior maxilla (premaxilla) was resected.

For patients in Class I, the treatment provided 4 zygomatic implants (2 for each zygoma; Fig 1 ). For those in Class IIA, rehabilitation was achieved through the insertion of 1 or 2 zygomatic implants on the resected side and 1 zygomatic implant on the unresected side. This implant was inserted in the contralateral zygomatic bone with a trajectory passing above the dental roots and below the nose ( Fig 2 ). For those in Class IIB, 2 zygomatic implants were inserted on the resected side and traditional implants were inserted in the alveolar bone of the healthy maxilla ( Fig 3 ). If the healthy side did not have sufficient alveolar bone height, then 2 zygomatic implants were inserted in this site instead of traditional implants (Class IIC; Fig 4 ).

Class I defect restored using a total prosthesis supported by 4 zygomatic implants.
Figure 1
Class I defect restored using a total prosthesis supported by 4 zygomatic implants.

Class IIA defect restored using a partial prosthesis supported by 2 zygomatic implants on the resected side and 1 zygomatic implant positioned in the contralateral maxilla.
Figure 2
Class IIA defect restored using a partial prosthesis supported by 2 zygomatic implants on the resected side and 1 zygomatic implant positioned in the contralateral maxilla.

Class IIB defect restored using a full-arch prosthesis supported by 2 zygomatic implants and standard implants in the unresected maxilla.
Figure 3
Class IIB defect restored using a full-arch prosthesis supported by 2 zygomatic implants and standard implants in the unresected maxilla.

Class IIC defect restored using a total prosthesis supported by 2 zygomatic implants on the resected side and standard zygomatic implants in the atrophied contralateral maxilla.
Figure 4
Class IIC defect restored using a total prosthesis supported by 2 zygomatic implants on the resected side and standard zygomatic implants in the atrophied contralateral maxilla.

For patients in Class III, the treatment provided 4 zygomatic implants for the edentulous patient ( Fig 5 ). Otherwise, the use of standard implants or a dental-supported prosthesis was contemplated.

Class III defect restored using a prosthesis supported by 4 zygomatic implants.
Figure 5
Class III defect restored using a prosthesis supported by 4 zygomatic implants.


Materials and Methods

From October 2013 through April 2014, 5 patients with maxillary defects owing to resections of neoplasms were recruited. The hospital's institutional review board approved this study protocol. Written informed consent was obtained from each patient and the study protocol conformed to the ethical guidelines of the World Medical Association Declaration of Helsinki—Ethical Principles for Medical Research Involving Human Subjects.

Patients were scheduled for treatment based on the extent of resection and residual bone. Clinical procedures were performed according to the specific treatment protocol proposed for each type of defect. In 4 patients, zygomatic implant positioning was delayed with respect to the maxillary resection. All patients underwent rehabilitation using zygomatic implants (Southern Implants, Irene, South Africa). Zygomatic implant length ranged from 27.5 to 52.5 mm according to the residual anatomy after resection.


Virtual Planning

Each patient in the study underwent preoperative computed tomographic (CT) scanning of the maxillofacial region. Digital Imaging and Communications in Medicine (DICOM) data extracted from the CT scan were imported into simulation software (SimPlant O&O; Dentsply Implants, Leuven, Belgium) for preliminary planning. This plan allowed the surgical team to simulate implant placement on a 3-dimensional (3D) model. While considering the anatomic structures and the bone resection performed, the surgical team interactively simulated the position and the length of the implant in each plane. Once the implant was positioned, its angulation could be modified and its dimensions adapted to obtain a better 3D position ( Fig 6 ).

Virtual implant positioning in a Class IIA defect case. The angulation of the implants can be adjusted according to the final prosthetic position and their dimensions can be adapted in the 3-dimensional model. The patient underwent a left maxillectomy for oral squamous cell carcinoma. The defect was initially restored using a temporalis muscle flap.
Figure 6
Virtual implant positioning in a Class IIA defect case. The angulation of the implants can be adjusted according to the final prosthetic position and their dimensions can be adapted in the 3-dimensional model. The patient underwent a left maxillectomy for oral squamous cell carcinoma. The defect was initially restored using a temporalis muscle flap.

In 3 cases, an intraoperative navigation system was used to control implant positioning. In 2 of these cases, CT data were imported into the navigation system software (ImplaNav, BresMedical, Ingleburn, Australia). A dental-supported reference tool for the passive tracking navigation system was used to connect the patient's position with the navigation system in real time. In 1 case, an active tracking navigation system was used for the intraoperative navigation guide. In this case, an active tracker was placed on the cranial skeleton.


Surgical Procedure

A full-thickness flap was performed in all cases to obtain zygomatic bone exposure. Implant drilling was performed using a straight or angled handle. The fixtures were placed with the handle at 30 rpm at a maximum torque of 50 N-cm or manually.

Zygomatic implants were used when in contact with the skin flap. This kind of zygomatic implant has a machined surface rather than spires in the third coronal portion of the fixture ( Fig 7 ). Figure 8 shows the design of the implant. Standard zygomatic implants were inserted to maintain contact with the oral gingiva and mucosa.

Intraoperative image showing implant positioning.
Figure 7
Intraoperative image showing implant positioning.

Zygomatic implant design.
Figure 8
Zygomatic implant design.

In these cases in which implant placement was performed under a navigation guide, during surgery, there was constant visualization of the drill trajectory in the 3D-reconstructed CT image and in the sagittal, coronal, and axial views ( Fig 9 ).

Intraoperative implant positioning control using a navigation system. The navigation screen allows the surgeon to view the drilling of the planned site and the angulation of the implant during the insertion.
Figure 9
Intraoperative implant positioning control using a navigation system. The navigation screen allows the surgeon to view the drilling of the planned site and the angulation of the implant during the insertion.

Deviation from the planned position was detected immediately, and precise implant placement was achieved. Postoperative radiographic evaluation confirmed the placement and angulation of the implant in the remaining zygomatic bone.


Prosthetic Procedure

In 4 of the 5 cases, right or angled conical abutments were mounted before suturing and not removed. At the time of surgery after the suture pickup, transfers were positioned and splinted with flow composite or resin. An impression was taken with a polyether impression material (Impregum Penta, 3M ESPE, St Paul, MN) using a custom-made tray, reproducing the dental arch, placed in occlusion. Within 72 hours, a screw-retained fixed bridge was delivered ( Fig 10 ).

Dental prosthesis fixed 72 hours after surgery.
Figure 10
Dental prosthesis fixed 72 hours after surgery.

A new definitive prosthesis could be placed after a 3-month follow-up if the prosthetist deemed it necessary. The definitive prosthesis could be a fixed bridge or an overdenture-retaining bar to facilitate oral hygiene.


Follow-Up

After 3 months, the prosthesis was unscrewed and implant stability was tested. Implant stability, pain, and inflammation of the peri-implant soft tissue were the parameters assessed. The same clinical outcomes were evaluated at each subsequent assessment at 6, 12, and 18 months. Postoperative radiographs (orthopantomogram and lateral head radiograph) were taken immediately after surgery, after 6 and 12 months, and then once every year ( Figs 11, 12 ).

Frontal radiographic outcomes of a Class IIA defect.
Figure 11
Frontal radiographic outcomes of a Class IIA defect.

Lateral radiographic outcomes of a Class IIA defect.
Figure 12
Lateral radiographic outcomes of a Class IIA defect.


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Computer-Aided Rehabilitation of Maxillary Oncological Defects Using Zygomatic Implants: A Defect-Based Classification Gerardo Pellegrino DDS , Achille Tarsitano MD , Francesco Basile DDS , Angelo Pizzigallo MD and Claudio Marchetti MD, DDS Journal of Oral and Maxillofacial Surgery, 2015-12-01, Volume 73, Issue 12, Pages 2446.e1-2446.e11, Copyright © 2015 American Association of Oral and Maxillofacial Surgeons Purpose A complete maxillectomy for neoplastic lesions leads to serious oral dysfunction. Zygomatic implants for fixed bridge support are considered beneficial for maxillary defects after tumor resection. Materials and Methods This clinical study examined the management of patients with different maxillary defect types who underwent delayed rehabilitation using zygomatic implants and immediate prosthetic loading. Virtual preoperative planning and intraoperative navigation were performed in all cases. Results Five patients were treated with this new method. The total number of zygomatic implants positioned was 17. Four patients had immediate loading of a fixed prosthesis and 1 had delayed loading. One patient had 1 failed implant. Conclusion The use of preoperative virtual surgical planning and an intraoperative navigation system allows the surgeon to achieve safer implant positioning in a complex anatomic site. A systematic bone defect classification was created and a specific treatment protocol is proposed for each type of defect. Oncologic bone resection for neoplastic lesions involving the maxilla leads to serious oral dysfunction with respect to speaking, swallowing, chewing, and quality of life. Defect classification systems enable clinicians to choose the type of rehabilitation and determine a functional prognosis. Since the publication of the study by Ohngren, many classification schemes have been proposed to describe the anatomic boundaries of maxillectomy defects. A complete maxillectomy produces complex defects of the alveolar bone, palate, paranasal sinuses, and orbital floor. Loss of these anatomic structures has relevant functional and esthetic consequences. Reconstruction of this region should 1) prevent any communication between the oral cavity and the nasopharynx, 2) reconstruct the palatal surface, and 3) achieve facial symmetry and good facial morphology. Several surgical reconstruction options exist, including nonvascularized grafts, local flaps, and microsurgical reconstruction with bone or soft tissues. However, in many cases, dental implants have been used to obtain functional restoration through mechanical retention of dental prostheses. Implant placement and subsequent prosthetic rehabilitation are often difficult to obtain after maxillectomy because of a lack of bone alveolar tissue and gingiva. Dental implants can be considered a viable restorative option only when the basal maxillary bone is preserved. Zygomatic implants are used to rehabilitate patients with insufficient bone volume for “traditional” dental implants. These implants are inserted into the zygomatic bone when alveolar bone is deficient after maxillectomy. However, the application of zygomatic implants in reconstructive surgery is often associated with various problems, including deficiencies of bone tissue and the presence of a reconstructive soft tissue flap. In this clinical study, the authors examined the management of patients with different maxillary defect types who underwent delayed rehabilitation using zygomatic implants and immediate prosthetic loading. Clinical outcomes were assessed for implant failure and prosthetic loading. Rehabilitative Protocol During the preparation of this article, it became clear that none of the classifications addressed maxillary restoration using zygomatic implants. A systematic bone defect classification was considered and a specific treatment protocol is proposed for each type of defect. Patients were categorized into 3 classes according to the site of the defect, the size of the defect, and residual masticatory function. Class I was defined as bilateral maxillectomy. Class II was defined as unilateral maxillectomy. In this class, 3 subclasses were identified according to the dental status of the unresected side: Class IIA included patients with dentition or partial dentition in the contralateral maxilla; Class IIB included patients without dentition in the residual maxilla; Class IIC included patients without dentition in the healthy maxilla with atrophied alveolar bone; Class III included patients whose anterior maxilla (premaxilla) was resected. For patients in Class I, the treatment provided 4 zygomatic implants (2 for each zygoma; Fig 1 ). For those in Class IIA, rehabilitation was achieved through the insertion of 1 or 2 zygomatic implants on the resected side and 1 zygomatic implant on the unresected side. This implant was inserted in the contralateral zygomatic bone with a trajectory passing above the dental roots and below the nose ( Fig 2 ). For those in Class IIB, 2 zygomatic implants were inserted on the resected side and traditional implants were inserted in the alveolar bone of the healthy maxilla ( Fig 3 ). If the healthy side did not have sufficient alveolar bone height, then 2 zygomatic implants were inserted in this site instead of traditional implants (Class IIC; Fig 4 ). Figure 1 Class I defect restored using a total prosthesis supported by 4 zygomatic implants. Figure 2 Class IIA defect restored using a partial prosthesis supported by 2 zygomatic implants on the resected side and 1 zygomatic implant positioned in the contralateral maxilla. Figure 3 Class IIB defect restored using a full-arch prosthesis supported by 2 zygomatic implants and standard implants in the unresected maxilla. Figure 4 Class IIC defect restored using a total prosthesis supported by 2 zygomatic implants on the resected side and standard zygomatic implants in the atrophied contralateral maxilla. For patients in Class III, the treatment provided 4 zygomatic implants for the edentulous patient ( Fig 5 ). Otherwise, the use of standard implants or a dental-supported prosthesis was contemplated. Figure 5 Class III defect restored using a prosthesis supported by 4 zygomatic implants. Materials and Methods From October 2013 through April 2014, 5 patients with maxillary defects owing to resections of neoplasms were recruited. The hospital's institutional review board approved this study protocol. Written informed consent was obtained from each patient and the study protocol conformed to the ethical guidelines of the World Medical Association Declaration of Helsinki—Ethical Principles for Medical Research Involving Human Subjects. Patients were scheduled for treatment based on the extent of resection and residual bone. Clinical procedures were performed according to the specific treatment protocol proposed for each type of defect. In 4 patients, zygomatic implant positioning was delayed with respect to the maxillary resection. All patients underwent rehabilitation using zygomatic implants (Southern Implants, Irene, South Africa). Zygomatic implant length ranged from 27.5 to 52.5 mm according to the residual anatomy after resection. Virtual Planning Each patient in the study underwent preoperative computed tomographic (CT) scanning of the maxillofacial region. Digital Imaging and Communications in Medicine (DICOM) data extracted from the CT scan were imported into simulation software (SimPlant O&O; Dentsply Implants, Leuven, Belgium) for preliminary planning. This plan allowed the surgical team to simulate implant placement on a 3-dimensional (3D) model. While considering the anatomic structures and the bone resection performed, the surgical team interactively simulated the position and the length of the implant in each plane. Once the implant was positioned, its angulation could be modified and its dimensions adapted to obtain a better 3D position ( Fig 6 ). Figure 6 Virtual implant positioning in a Class IIA defect case. The angulation of the implants can be adjusted according to the final prosthetic position and their dimensions can be adapted in the 3-dimensional model. The patient underwent a left maxillectomy for oral squamous cell carcinoma. The defect was initially restored using a temporalis muscle flap. In 3 cases, an intraoperative navigation system was used to control implant positioning. In 2 of these cases, CT data were imported into the navigation system software (ImplaNav, BresMedical, Ingleburn, Australia). A dental-supported reference tool for the passive tracking navigation system was used to connect the patient's position with the navigation system in real time. In 1 case, an active tracking navigation system was used for the intraoperative navigation guide. In this case, an active tracker was placed on the cranial skeleton. Surgical Procedure A full-thickness flap was performed in all cases to obtain zygomatic bone exposure. Implant drilling was performed using a straight or angled handle. The fixtures were placed with the handle at 30 rpm at a maximum torque of 50 N-cm or manually. Zygomatic implants were used when in contact with the skin flap. This kind of zygomatic implant has a machined surface rather than spires in the third coronal portion of the fixture ( Fig 7 ). Figure 8 shows the design of the implant. Standard zygomatic implants were inserted to maintain contact with the oral gingiva and mucosa. Figure 7 Intraoperative image showing implant positioning. Figure 8 Zygomatic implant design. In these cases in which implant placement was performed under a navigation guide, during surgery, there was constant visualization of the drill trajectory in the 3D-reconstructed CT image and in the sagittal, coronal, and axial views ( Fig 9 ). Figure 9 Intraoperative implant positioning control using a navigation system. The navigation screen allows the surgeon to view the drilling of the planned site and the angulation of the implant during the insertion. Deviation from the planned position was detected immediately, and precise implant placement was achieved. Postoperative radiographic evaluation confirmed the placement and angulation of the implant in the remaining zygomatic bone. Prosthetic Procedure In 4 of the 5 cases, right or angled conical abutments were mounted before suturing and not removed. At the time of surgery after the suture pickup, transfers were positioned and splinted with flow composite or resin. An impression was taken with a polyether impression material (Impregum Penta, 3M ESPE, St Paul, MN) using a custom-made tray, reproducing the dental arch, placed in occlusion. Within 72 hours, a screw-retained fixed bridge was delivered ( Fig 10 ). Figure 10 Dental prosthesis fixed 72 hours after surgery. A new definitive prosthesis could be placed after a 3-month follow-up if the prosthetist deemed it necessary. The definitive prosthesis could be a fixed bridge or an overdenture-retaining bar to facilitate oral hygiene. Follow-Up After 3 months, the prosthesis was unscrewed and implant stability was tested. Implant stability, pain, and inflammation of the peri-implant soft tissue were the parameters assessed. The same clinical outcomes were evaluated at each subsequent assessment at 6, 12, and 18 months. Postoperative radiographs (orthopantomogram and lateral head radiograph) were taken immediately after surgery, after 6 and 12 months, and then once every year ( Figs 11, 12 ). Figure 11 Frontal radiographic outcomes of a Class IIA defect. Figure 12 Lateral radiographic outcomes of a Class IIA defect. Quality-of-Life Assessment The Oral Health-Related Quality of Life Questionnaire (OHRQOL) is “a multidimensional construct that reflects (among other things) people's comfort when eating, sleeping, and engaging in social interaction; their self-esteem; and their satisfaction with respect to their oral health.” The OHRQOL is associated with functional factors, psychological factors, social factors, and experience of pain or discomfort. Oral health related quality of life-14 (OH-14 QOL) questionnaires were administered to each patient. A high score indicates low functional ability. The questionnaire was administered preoperatively (T0) and after prosthetic rehabilitation at 2 weeks (T1) and 6 months (T2). Results Five patients received this treatment (age range, 51 to 83 yr; mean, 61.8 yr). The follow-up period was 10 to 29 months (mean, 12 months). Four of the 5 patients had delayed implant placement with respect to primary maxillary resection. The mean interval from resection to implant positioning was 34 months (range, 29 to 61 months). One patient had implants placed at the same time as surgical bone resection. This patient underwent adjuvant radiotherapy 2 months after implant insertion. Table 1 lists the patient characteristics and the numbers of implants positioned in each case. According to the proposed classification, 2 patients were in Class IIA, 1 was in Class IIC, 1 was in Class I, and 1 was in Class III. The total number of zygomatic implants positioned was 17. Four patients had immediate loading of a fixed prosthesis and 1 had delayed loading. Table 1 Patient Characteristics and Implant Positions According to Type of Maxillary Defect Patient Number Age (yr) Diagnosis Class of Defect Zygomatic Implants Failure 1 56 OSCC IIA 3 2 77 OSCC IIC 4 1 3 62 ACC I 4 4 54 Mucoepidermoid carcinoma IIA 2 5 59 cleft III 4 Abbreviations: ACC, adenoid-cystic carcinoma; OSCC, oral squamous cell carcinoma. One patient had 1 failed implant. At approximately 8 months after loading, during a follow-up examination, unscrewing of the prosthesis was detected. After prosthesis removal, 1 implant had a rotation during contra-torque shunting. The fixture was unscrewed without local anesthesia and the prosthesis was replaced. No definitive prosthesis has been requested by the prosthodontist or the patient. To date, no peri-implantitis or local inflammation has occurred. Quality-of-Life Assessment Results from the OH-14 QOL questionnaire are reported using a score system. Information on QOL allows the assessment of patient-reported perceptions, thus improving the possibility of effective communication between physicians and patients. This leads to better knowledge of the impact of oral health on the daily activities of the patient and an evaluation of the clinical results obtained. The OH-14 questionnaire mean values at baseline and at T0, T1, and T2 are listed in Table 2 . Table 2 OH-14 QOL Questionnaire Mean Values at Preoperative, 2-Week, and 6-Month Evaluations T0 T1 T2 Mean value 25.5 19.4 15.5 Abbreviations: OH-14 QOL, oral health related quality of life-14; T0, preoperative; T1, 2-week follow-up; T2, 6-month follow-up. A mean of 10 points in QOL improvement was recorded between the T0 and T2 assessments. Discussion Extensive surgery for neoplasms of the jaws often produces serious functional, emotional, and social effects on patients. Currently, immediate reconstruction with local pedicled flaps or microsurgical flaps is often performed, somewhat decreasing postoperative functional impairment. However, even when reconstruction is performed successfully, it does not always guarantee functional restoration of mastication. Soft tissue flaps, temporalis muscle flaps, and fasciocutaneous free flaps do not offer the possibility of implant insertion. Although minor maxillary bone resections can be repaired easily, large defects often require complex rehabilitation. Some of these cases could be restored using standard implants with long abutments anchored in the zygoma area. In contrast, most extensive resections lead to complete loss of the alveolar bone with the consequent loss of support for the facial soft tissues in the lip and cheek areas. Moreover, in most cases, surgery is associated with adjuvant radiotherapy that can cause adjunctive impairment of the elastic properties of the facial structures. In patients in whom immediate reconstruction with a microsurgical bone flap after a subtotal maxillectomy is not possible, zygomatic implants could represent the only available option to obtain stable support for a viable prosthesis. The specific design of zygomatic implants allows their insertion even in cases of large bone defects because they obtain bicortical stability through the malar bone. There is agreement that placement of a zygomatic implant is more complex and difficult than conventional oral implant placement. Not only the dimensions of the implants, but also the anatomic intricacies of the curved zygomatic bone make this type of surgery a challenging procedure. Moreover, the presence of the orbital floor and the limited intraoperative visibility require great accuracy during the surgical insertion of implants. The surgical procedure can be simplified and facilitated using computer-assisted planning and surgery. A computer-based transfer of preplanned positioning can be achieved using drill guides. However, when applying this technique, precision depends largely on the ability to position the drill guide accurately on the underlying tissue. In contrast to the technique using drilling templates, a computer-aided surgical navigation approach offers constant intraoperative visualization of the tip of the drilling bur. This enables the surgeon to guide the drill precisely to control the implant axis and achieve better implant stability. A cadaver study reported an accuracy of 1.3 ± 0.8 mm in the implant versus planned position. This result appears to be better than the accuracy achieved using drilling templates. In the authors' experience, the use of preoperative virtual surgical planning and an intraoperative navigation system allows the surgeon to achieve safer implant positioning in a complex anatomic site. The rationale for proposing a new defect-based classification and algorithm is based on the opportunity afforded, using new techniques, to perform implant insertion in extreme bone deficiency. Classifications of maxillary bone defects described in the literature do not consider the functional aspect of residual dentition. The classification of Brown and Shaw considers the size of the defect in soft and hard tissues and the preferred method of microvascular reconstruction. However, it does not consider rehabilitative options when reconstruction is performed without bone-free flaps. Jensen et al in 1992 described available sites for implant placement in the facial skeleton and suggested a viable craniofacial site classification. The authors' new reconstructive algorithm could be considered a step forward, although their suggestions have not been widely adopted. Compared with the classification of Jensen et al, the present classification is simpler and more effectively considers the rehabilitative opportunities afforded by zygomatic implants and computer-assisted surgery for patients in whom bone reconstruction is not performed. For each type of defect, the authors' classification defines the number of zygomatic implants required to optimize functional and esthetic outcomes. To the authors' knowledge, no previous reported study has tested zygomatic implants in oncologic patients undergoing maxillectomy. In this study, the authors tested these newly designed zygomatic implants in various maxillary defects. This technique appears to be a safe procedure to obtain effective rehabilitation after extensive maxillectomy. Early prosthetic loading certainly allows the patient to have better functional outcomes and satisfactory masticatory function. A fixed bridge not removable by the patient for the first 3 months seems to promote osseointegration of the implants. Prosthetic screwing is advisable to obtain greater stability. This use of fixed treatment does not allow for patient removal and cleaning. It can cause problems from chronic inflammation. For this reason, the authors suggest maintaining an adequate distance between the implant emergence and the prosthesis to allow the patient to perform a daily accurate cleaning. The results of this series should be confirmed by further studies and longer-term follow-up. Acknowledgments The authors thank Claudio Carboni of the University of Bologna for his work, S.I.R. Srl (Verona, Italy), and Southern Implants (Irene, South Africa). Drs Pellegrino and Tarsitano contributed equally to this research. References 1. Okay D.J., Gender E., Buchbinder D., et. al.: Prosthodontic guidelines for surgical reconstruction of the maxilla: A classification system of defects. J Prosthet Dent 2001; 86: pp. 352. 2. Ohngren L.: Malignant tumors of the maxillo-ethmoidal region. Acta Otolarynogol 1933; 19: pp. 1476. 3. Davison S.P., Sherris D.A., Meland N.B.: An algorithm for maxillectomy defect reconstruction. Laryngoscope 1998; 108: pp. 215. 4. Sisson G., Toriumi D., Atiyah R.A.: Paranasal sinus malignancy: A comprehensive update. Laryngoscope 1989; 99: pp. 143. 5. Cordeiro P.G., Santamaria E., Kraus D.H., et. al.: Reconstruction of total maxillectomy defects with preservation of the orbital contents. Plast Reconstr Surg 1998; 102: pp. 1874. 6. Devlin H., Barker G.R.: Prosthetic rehabilitation of the edentulous patient requiring a partial maxillectomy. J Prosthet Dent 1992; 67: pp. 223. 7. Shirota T., Shimodaira O., Matsui Y., et. al.: Zygoma implant-supported prosthetic rehabilitation of a patient with a maxillary defect. Int J Oral Maxillofac Surg 2011; 40: pp. 113. 8. D'Agostino A., Procacci P., Ferrari F., et. al.: Zygoma implant-supported prosthetic rehabilitation of a patient after subtotal bilateral maxillectomy. J Craniofac Surg 2013; 24: pp. e159. 9. Malevez C., Abarca C., Durdu F., et. al.: Clinical outcome of 103 consecutive zygomatic implants: A 6-48 month follow-up study. Clin Oral Implants Res 2004; 15: pp. 18. 10. Brånemark P.I.: The Osseointegration Book from the Calvarium to the Calcaneus.2005.QuintessenceBerlin, Germany 11. Guerrero C.A., Sabogal A.: Zygoma Implants. Atlas of Surgery and Prosthetics.2009.Edit RipanoMadrid, Spain 12. Guerrero C.A., Sader G., Henriquez M., et. al.: Zygomatic implants with pentagonal design for the rehabilitation of the intermediate maxilla. Implant News 2012; 9: pp. 49. (in Portuguese) 13. Bedrosian E., Stumpel L., Beckely M.L., Indresano T.: The zygomatic implant: Preliminary data. Int J Oral Maxillofac Surg 2002; 17: pp. 861. 14. Schmidt B.L., Pogrel M.A., Young C.W., et. al.: Reconstruction of extensive maxillary defects using zygomaticus implants. J Oral Maxillofac Surg 2004; 62: pp. 82. 15. Pellegrino G., Basile F., Richieri L., et. al.: Large defect rehabilitation of upper jaw with zygomatic/oncologic implants. Preliminary results of a prospective study. Clin Oral Implants Res 2014; 25: pp. 491. 16. US Department of Health and Human Services: Oral Health in America: A Report of the Surgeon General.2000.US Department of Health and Human Services, National Institute of Dental and Craniofacial Research, National Institutes of HealthRockville, MDpp. 7. 17. Inglehart M.R., Bagramian R.A.: Oral Health Related Quality of Life.2002.Quintessence PublishingHanover Park, IL 18. Bennadi D., Reddy C.V.: Oral health related quality of life. J Int Soc Prev Community Dent 2013; 3: pp. 1. 19. Tarsitano A., Pizzigallo A., Ballone E., et. al.: Health-related quality of life as a survival predictor for patients with oral cancer: Is quality of life associated with long-term overall survival?. Oral Surg Oral Med Oral Pathol Oral Radiol 2012; 114: pp. 756. 20. Jensen O.T., Brownd C., Blacker J.: Nasofacial prostheses supported by osseointegrated implants. Int J Oral Maxillofac Implants 1992; 7: pp. 203. 21. Stella J.P., Warner M.R.: Sinus slot technique for simplification and improved orientation of zygomaticus dental implants: A technical note. Int J Oral Maxillofac Implants 2000; 15: pp. 889. 22. Chow J., Hui E., Lee P.K., et. al.: Zygomatic implants—Protocol for immediate occlusal loading: A preliminary report. J Oral Maxillofac Surg 2006; 64: pp. 804. 23. Vrielinck L., Politis C., Schepers S., et. al.: Image-based planning and clinical validation of zygoma and pterygoid implant placement in patients with severe bone atrophy using customized drill guides. Preliminary results from a prospective clinical follow-up study. Int J Oral Maxillofac Surg 2003; 32: pp. 7. 24. Van Steenberghe D., Malevez C., Van Cleynenbreugel J., et. al.: Accuracy of drilling guides for transfer from three-dimensional CT-based planning to placement of zygoma implants in human cadavers. Clin Oral Implants Res 2003; 14: pp. 131. 25. Watzinger F., Birkfellner W., Wanschitz F., et. al.: Placement of endosteal implants in the zygoma after maxillectomy: A cadaver study using surgical navigation. Plast Reconstr Surg 2001; 107: pp. 659. 26. Brown J.S., Shaw R.J.: Reconstruction of the maxilla and midface: Introducing a new classification. Lancet Oncol 2010; 11: pp. 1001.

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