Effects of Injury or Removal of the Articular Disc on Maxillomandibular Growth in Young Rats



Effects of Injury or Removal of the Articular Disc on Maxillomandibular Growth in Young Rats




Journal of Oral and Maxillofacial Surgery, 2014-11-01, Volume 72, Issue 11, Pages 2140-2147, Copyright © 2014 American Association of Oral and Maxillofacial Surgeons


Purpose

This study analyzed the effects of injury and removal of the articular disc on maxillomandibular growth in young rats.

Materials and Methods

Thirty 1-month-old male Wistar rats were divided into 3 groups: injury, removal, and sham operated. Unilateral injury of the articular disc, removal of the articular disc, or only surgical access was performed. The animals were sacrificed at 3 months of age. Specimens were submitted to radiographic incidences and cephalometric mensurations were performed using a computer system. Data were subjected to statistical analyses among groups and between sides in each group.

Results

There were degenerative changes of the condylar process in the injury and removal groups. Significant differences between sides were observed for length of the premaxilla, height of the mandibular body, and length of the mandible. Concomitant group comparisons showed significant differences in the height of the mandibular body ( P = .003) and the length of the mandible ( P = .001). There were important decreases to the height of the mandibular body and mandibular length in the injury group, whereas there was an important decrease only for the length of the mandible in the removal group. Specific measurements of mandibular ramus structures exhibited differences between the injury and sham-operated groups and between the removal and sham-operated groups.

Conclusion

Experimental injury and removal of the articular disc during the growth period in rats had deleterious effects on ramus structures and induced asymmetry of the mandible, with worse outcomes resulting from injury to the articular disc.

Mandibular deformities, especially mandibular asymmetries, have been associated with previous trauma to the temporomandibular joint (TMJ). Clinical studies have implicated prepubertal trauma as a cause of asymmetric growth of the mandible. This phenomenon can be explained by the presence of early condylar fractures that lead to disturbed growth of the fractured side, resulting in mandibular deviation. The mandibular condyle is considered the cornerstone of mandibular form and function and damage to this structure in growing children can adversely affect the growth of the jaw and the occlusion. Such changes would be a direct consequence of inflammatory or mechanical damage to the condylar cartilage.

In contrast, an association between internal derangement of the TMJ and the development of mandibular asymmetry has been suggested. In addition, children with temporomandibular disorders have exhibited a shorter mandibular corpus and vertical height of the ramus. Experimental studies have shown that surgical disc displacement can alter the growth of the mandible. This outcome would result in a retrognathic growth pattern.

The possibility of soft tissue changes in patients who have sustained injuries to the TMJ has been reported. An experimental model of indirect trauma to the TMJ has shown isolated injuries to structures such as the articular disc, condyle fibrocartilage, or temporal fossa. Soft tissue injuries of the TMJ can potentially lead to internal derangement, osteoarthrosis, and possibly fibrous ankylosis owing to disc displacement and condylar cartilage damage. Experimental disc perforation is initially followed by hypertrophy of the condylar cartilage and later by degeneration of the condylar surface. In addition, in growing rats, disc displacement or removal leads to an unfavorable outcome in the repair of condylar fractures, inducing condylar growth disorders. However, the role of trauma to the articular disc in maxillomandibular bone growth is not well understood.

The purpose of this study was to analyze the effects of unilateral injury and removal of the articular disc on maxillomandibular growth in young rats.


Materials and Methods

Thirty 1-month-old male Wistar rats were used for this study. All animals were fed with rodent feed (Labina, Agribands Purina, Paulínia, SP, Brazil) and water. They were divided into the following 3 groups: injury (n = 10), removal (n = 10), and sham operated (n = 10). The study was approved by the local subcommittee on ethics in animal experimentation (process 13/2009).

General anesthesia was induced with xylazine hydrochloride 10 mg/kg (Rompum, Bayer, Porto Alegre, RS, Brazil) and ketamine hydrochloride 25 mg/kg (Dopalen, Vetbrands, Paulínia, SP, Brazil). A single dose of benzylpenicillin 16,000 IU (Benzetacil, Fontoura-Wieth, Itapevi, SP, Brazil) was given, and the right side was shaved and cleansed with a povidone-iodine solution. A 1-cm preauricular incision was made, and blunt dissection was performed through the masseter muscle just below the zygomatic arch, with exposure of the lateral surface of the mandibular ramus. Injury to the articular disc was caused by using mosquito (Halstead) forceps, resulting in a crush in the anteroposterior direction. In the removal (discectomy) group, the articular disc and associated attachments were removed using a scalpel and forceps. The sham-operated group was subjected to exposure of the TMJ. In all groups, care was taken to prevent damage to the articular surfaces. The procedures were concluded by suturing in layers. Postoperative analgesia was provided with tramadol 0.3 mg/kg by injection. The animals were sacrificed at 3 months of age, and their heads and mandibles were carefully removed. After formalin fixation, radiographs with axial projections of the skull and lateral projections of the hemimandibles were obtained. These images were taken with a dental machine (Spectro II, Dabi-Atlante, Ribeirão Preto, SP, Brazil) at 56 kV and 10 mA, with an exposure time of 0.4 second for the skulls and an exposure time of 0.3 second for the hemimandibles. Periapical films were used (Dental Intraoral E-speed Film, Carestream Health, Rochester, NY).

The radiographs were subjected to a computerized cephalometric evaluation and digitized using an optical reader (Fotovix II, Tamron Co, Saitama, Japan). Measurements were obtained with Imagelab software (Softium Informática, São Paulo, SP, Brazil). Using skull radiographs, the following distances relative to the maxilla were measured bilaterally: the tympanic bulla (TB; the most anterior portion of this round structure of the skull base) to the mesial root of the first molar (the apex of this root) relative to posterior maxillary length; the TB to the infraorbital foramen (IF; the vertex of the image of this foramen) relative to maxillary length; and the IF to the incisal point (IP; the intersection of the lingual face of upper incisors with the midline) relative to the length of the premaxilla ( Fig 1 ). On hemimandible radiographs, the following distances relative to the mandible were measured bilaterally: the condylar process (CP; the highest point of this structure) to the angular process (AP; the apex of this structure peculiar to the rodent mandible) relative to mandibular ramus height; the distal face of the third molar (TM; intersection with the mandibular ramus) to the antegonial notch (AN; located on the mandibular base anterior to the mandibular angle) relative to mandibular body height; and the lower insertion of the incisor (II; the most anterior limit of the lower bone insertion of this tooth) to the CP relative to mandibular length ( Fig 2 ). Also, on the hemimandible radiographs, specific measurements relative to ramus structures were made. Initially, a line (A) tangent to the sigmoid notch and the most anterior point on the posterior aspect of the ramus was drawn. A perpendicular line (B) through the highest point on the condyle and then 2 additional perpendicular lines (C and D) were drawn tangent to the superior aspect of the coronoid process and the inferior border of the mandible. Using the horizontal line (A) and a perpendicular line to the top of the condyle, the height of the condyle (B) was recorded. The vertical height of the coronoid process (C) also was measured. The distance between perpendicular lines C and D was measured to determine the transverse width of the mandible (C-D). A line parallel to line A and bisecting line B measured the transverse width of the condyle (E; Fig 3 ).

Axial radiograph of the skull. Lines represent the measurements made. IF, infraorbital foramen; IP, incisal point; MR, mesial root of first molar; TB, tympanic bulla.
Figure 1
Axial radiograph of the skull. Lines represent the measurements made. IF, infraorbital foramen; IP, incisal point; MR, mesial root of first molar; TB, tympanic bulla.

Lateral radiograph of hemimandibles. Lines represent the measurements made. AN, antegonial notch; AP, angular process; CP, condylar process; II, insertion of incisor; TM, distal face of third molar.
Figure 2
Lateral radiograph of hemimandibles. Lines represent the measurements made. AN, antegonial notch; AP, angular process; CP, condylar process; II, insertion of incisor; TM, distal face of third molar.

Lateral radiograph of hemimandibles. White lines, reference lines; black lines, measurements made. B, condylar height; C, coronoid process height; C-D, transverse width of mandible; E, transverse width of condyle.
Figure 3
Lateral radiograph of hemimandibles.
White lines, reference lines;
black lines, measurements made. B, condylar height; C, coronoid process height; C-D, transverse width of mandible; E, transverse width of condyle.

To evaluate differences between mean values for the right and left sides in each group, the Wilcoxon signed posts test was used. The Kruskal-Wallis test was used to verify possible differences among the 3 groups when concomitantly compared and the Mann-Whitney test adjusted by Bonferroni correction was used to identify which groups differed from one another. SPSS 21.0 software (IBM Software Group, Chicago, IL) was used to conduct the analyses. The level of significance was set at 5% ( P < .050).


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Effects of Injury or Removal of the Articular Disc on Maxillomandibular Growth in Young Rats Leandro Giuseppim Toledo DDS , Samantha Christine X.B. Cavalcanti MS , Luciana Corrêa PhD and João Gualberto C. Luz DDS, MS, PhD Journal of Oral and Maxillofacial Surgery, 2014-11-01, Volume 72, Issue 11, Pages 2140-2147, Copyright © 2014 American Association of Oral and Maxillofacial Surgeons Purpose This study analyzed the effects of injury and removal of the articular disc on maxillomandibular growth in young rats. Materials and Methods Thirty 1-month-old male Wistar rats were divided into 3 groups: injury, removal, and sham operated. Unilateral injury of the articular disc, removal of the articular disc, or only surgical access was performed. The animals were sacrificed at 3 months of age. Specimens were submitted to radiographic incidences and cephalometric mensurations were performed using a computer system. Data were subjected to statistical analyses among groups and between sides in each group. Results There were degenerative changes of the condylar process in the injury and removal groups. Significant differences between sides were observed for length of the premaxilla, height of the mandibular body, and length of the mandible. Concomitant group comparisons showed significant differences in the height of the mandibular body ( P = .003) and the length of the mandible ( P = .001). There were important decreases to the height of the mandibular body and mandibular length in the injury group, whereas there was an important decrease only for the length of the mandible in the removal group. Specific measurements of mandibular ramus structures exhibited differences between the injury and sham-operated groups and between the removal and sham-operated groups. Conclusion Experimental injury and removal of the articular disc during the growth period in rats had deleterious effects on ramus structures and induced asymmetry of the mandible, with worse outcomes resulting from injury to the articular disc. Mandibular deformities, especially mandibular asymmetries, have been associated with previous trauma to the temporomandibular joint (TMJ). Clinical studies have implicated prepubertal trauma as a cause of asymmetric growth of the mandible. This phenomenon can be explained by the presence of early condylar fractures that lead to disturbed growth of the fractured side, resulting in mandibular deviation. The mandibular condyle is considered the cornerstone of mandibular form and function and damage to this structure in growing children can adversely affect the growth of the jaw and the occlusion. Such changes would be a direct consequence of inflammatory or mechanical damage to the condylar cartilage. In contrast, an association between internal derangement of the TMJ and the development of mandibular asymmetry has been suggested. In addition, children with temporomandibular disorders have exhibited a shorter mandibular corpus and vertical height of the ramus. Experimental studies have shown that surgical disc displacement can alter the growth of the mandible. This outcome would result in a retrognathic growth pattern. The possibility of soft tissue changes in patients who have sustained injuries to the TMJ has been reported. An experimental model of indirect trauma to the TMJ has shown isolated injuries to structures such as the articular disc, condyle fibrocartilage, or temporal fossa. Soft tissue injuries of the TMJ can potentially lead to internal derangement, osteoarthrosis, and possibly fibrous ankylosis owing to disc displacement and condylar cartilage damage. Experimental disc perforation is initially followed by hypertrophy of the condylar cartilage and later by degeneration of the condylar surface. In addition, in growing rats, disc displacement or removal leads to an unfavorable outcome in the repair of condylar fractures, inducing condylar growth disorders. However, the role of trauma to the articular disc in maxillomandibular bone growth is not well understood. The purpose of this study was to analyze the effects of unilateral injury and removal of the articular disc on maxillomandibular growth in young rats. Materials and Methods Thirty 1-month-old male Wistar rats were used for this study. All animals were fed with rodent feed (Labina, Agribands Purina, Paulínia, SP, Brazil) and water. They were divided into the following 3 groups: injury (n = 10), removal (n = 10), and sham operated (n = 10). The study was approved by the local subcommittee on ethics in animal experimentation (process 13/2009). General anesthesia was induced with xylazine hydrochloride 10 mg/kg (Rompum, Bayer, Porto Alegre, RS, Brazil) and ketamine hydrochloride 25 mg/kg (Dopalen, Vetbrands, Paulínia, SP, Brazil). A single dose of benzylpenicillin 16,000 IU (Benzetacil, Fontoura-Wieth, Itapevi, SP, Brazil) was given, and the right side was shaved and cleansed with a povidone-iodine solution. A 1-cm preauricular incision was made, and blunt dissection was performed through the masseter muscle just below the zygomatic arch, with exposure of the lateral surface of the mandibular ramus. Injury to the articular disc was caused by using mosquito (Halstead) forceps, resulting in a crush in the anteroposterior direction. In the removal (discectomy) group, the articular disc and associated attachments were removed using a scalpel and forceps. The sham-operated group was subjected to exposure of the TMJ. In all groups, care was taken to prevent damage to the articular surfaces. The procedures were concluded by suturing in layers. Postoperative analgesia was provided with tramadol 0.3 mg/kg by injection. The animals were sacrificed at 3 months of age, and their heads and mandibles were carefully removed. After formalin fixation, radiographs with axial projections of the skull and lateral projections of the hemimandibles were obtained. These images were taken with a dental machine (Spectro II, Dabi-Atlante, Ribeirão Preto, SP, Brazil) at 56 kV and 10 mA, with an exposure time of 0.4 second for the skulls and an exposure time of 0.3 second for the hemimandibles. Periapical films were used (Dental Intraoral E-speed Film, Carestream Health, Rochester, NY). The radiographs were subjected to a computerized cephalometric evaluation and digitized using an optical reader (Fotovix II, Tamron Co, Saitama, Japan). Measurements were obtained with Imagelab software (Softium Informática, São Paulo, SP, Brazil). Using skull radiographs, the following distances relative to the maxilla were measured bilaterally: the tympanic bulla (TB; the most anterior portion of this round structure of the skull base) to the mesial root of the first molar (the apex of this root) relative to posterior maxillary length; the TB to the infraorbital foramen (IF; the vertex of the image of this foramen) relative to maxillary length; and the IF to the incisal point (IP; the intersection of the lingual face of upper incisors with the midline) relative to the length of the premaxilla ( Fig 1 ). On hemimandible radiographs, the following distances relative to the mandible were measured bilaterally: the condylar process (CP; the highest point of this structure) to the angular process (AP; the apex of this structure peculiar to the rodent mandible) relative to mandibular ramus height; the distal face of the third molar (TM; intersection with the mandibular ramus) to the antegonial notch (AN; located on the mandibular base anterior to the mandibular angle) relative to mandibular body height; and the lower insertion of the incisor (II; the most anterior limit of the lower bone insertion of this tooth) to the CP relative to mandibular length ( Fig 2 ). Also, on the hemimandible radiographs, specific measurements relative to ramus structures were made. Initially, a line (A) tangent to the sigmoid notch and the most anterior point on the posterior aspect of the ramus was drawn. A perpendicular line (B) through the highest point on the condyle and then 2 additional perpendicular lines (C and D) were drawn tangent to the superior aspect of the coronoid process and the inferior border of the mandible. Using the horizontal line (A) and a perpendicular line to the top of the condyle, the height of the condyle (B) was recorded. The vertical height of the coronoid process (C) also was measured. The distance between perpendicular lines C and D was measured to determine the transverse width of the mandible (C-D). A line parallel to line A and bisecting line B measured the transverse width of the condyle (E; Fig 3 ). Figure 1 Axial radiograph of the skull. Lines represent the measurements made. IF, infraorbital foramen; IP, incisal point; MR, mesial root of first molar; TB, tympanic bulla. Figure 2 Lateral radiograph of hemimandibles. Lines represent the measurements made. AN, antegonial notch; AP, angular process; CP, condylar process; II, insertion of incisor; TM, distal face of third molar. Figure 3 Lateral radiograph of hemimandibles. White lines, reference lines; black lines, measurements made. B, condylar height; C, coronoid process height; C-D, transverse width of mandible; E, transverse width of condyle. To evaluate differences between mean values for the right and left sides in each group, the Wilcoxon signed posts test was used. The Kruskal-Wallis test was used to verify possible differences among the 3 groups when concomitantly compared and the Mann-Whitney test adjusted by Bonferroni correction was used to identify which groups differed from one another. SPSS 21.0 software (IBM Software Group, Chicago, IL) was used to conduct the analyses. The level of significance was set at 5% ( P < .050). Results Macroscopic examination of the specimens showed facial asymmetry with deviation of the mandible midline to the right side in the injury and removal groups. Atrophy and degenerative changes of the CP were noted in the injury ( Fig 4 ) and removal ( Fig 5 ) groups. These changes were primarily in shape, height, and contour, and findings represented regressive remodeling, with flattening arthrosis and erosions. The sham-operated group presented with smooth and round articular surfaces ( Fig 6 ). Figure 4 Macroscopic findings of the injury group showing an atrophic mandibular ramus on the right side. L, left side; R, right side. Figure 5 Macroscopic findings of the removal group displaying flattening and shortening of the condyle associated to ramus atrophy on the right side. L, left side; R, right side. Figure 6 Macroscopic findings of the sham-operated group, with side-to-side symmetry of the condylar heads. L, left side; R, right side. The mean values of the distances found on the axial radiographs of the skulls are presented in Table 1 . A significant difference between sides was observed only for the length of the premaxilla (IF-IP) measurement in the injury group ( P = .008). However, when comparing the maxillary measurements among groups, the Kruskal-Wallis test did not show differences in any of the measurements. Table 1 Distances Found on Axial Radiographs of the Right and Left Sides by Group Group Posterior Maxillary Length (mm; TB-MR) Maxillary Length (mm; TB-IF) Length of Premaxilla (mm; IF-IP) Right Left Right Left Right Left Injury 16.12 ± 0.43 16.18 ± 0.42 22.39 ± 0.55 22.60 ± 0.42 8.87 ± 0.25 9.31 ± 0.28 ∗ Removal 16.12 ± 0.78 16.33 ± 0.56 22.21 ± 0.42 22.49 ± 0.30 8.80 ± 0.54 9.06 ± 0.52 Sham operated 16.20 ± 0.48 16.13 ± 0.46 22.40 ± 0.60 22.52 ± 0.68 9.21 ± 0.23 9.16 ± 0.49 Note: Values are presented as mean ± standard deviation. Abbreviations: IF-IP, infraorbital foramen to the incisal point; TB-IF, tympanic bulla to the infraorbital foramen; TB-MR, tympanic bulla to mesial root of the first molar. ∗ P < .050 by Wilcoxon signed posts test for statistical significance between sides. The mean values of the distances found on the lateral radiographs of the hemimandibles are presented in Table 2 . A significant difference was found between sides for mandibular body height (TM-AN) in the injury group ( P = .012) and for mandibular length (II-CP) in the injury ( P = .008) and removal ( P = .005) groups. Table 2 Distances Found on Lateral Radiographs of Hemimandibles of the Right and Left Sides by Group Group Mandibular Ramus Height (mm; CP-AP) Mandibular Body Height (mm; TM-AN) Mandibular Length (mm; II-CP) Right Left Right Left Right Left Injury 8.64 ± 0.50 8.93 ± 0.43 6.51 ± 0.15 A 6.65 ± 0.16 ∗ 24.44 ± 0.45 A 25.96 ± 0.44 ∗ Removal 8.32 ± 0.45 8.53 ± 0.39 6.29 ± 0.28 B 6.40 ± 0.29 23.71 ± 0.99 A 25.58 ± 0.78 ∗ Sham operated 8.17 ± 0.52 8.61 ± 0.33 6.43 ± 0.12 B 6.49 ± 0.18 25.32 ± 0.44 B 25.27 ± 0.65 Note: Values are presented as mean ± standard deviation. Different superscript letters indicate statistically significant differences among groups by the Mann-Whitney test adjusted by Bonferroni correction ( P < .050). Abbreviations: CP-AP, condylar process to angular process; II-CP, lower insertion of incisor to condylar process; TM-AN, distal face of third molar to antegonial notch. ∗ P < .050 by Wilcoxon signed posts test for statistical significance between sides. When comparing mandibular measurements among groups, the Kruskal-Wallis test showed 2 significant differences: in mandibular body height (TM-AN; P = .003) and in mandibular length (II-CP; P = .001) measurements on the right side. Then, the Mann-Whitney test adjusted by Bonferroni correction showed differences in mandibular body height (TM-AN) between the injury and removal groups and between the injury and sham-operated groups and in mandibular length (II-CP) between the injury and sham-operated groups and between the removal and sham-operated groups ( Table 2 ). The mean values of the specific measurements relative to ramus structures found on the lateral radiographs of the hemimandibles are presented in Table 3 . A significant difference was found between sides for condylar height (B; P = .008) and for transverse width of the mandible (C-D; P = .046) in the removal group. Table 3 Specific Measurements Relative to Ramus Structures Found on Lateral Radiographs of Hemimandibles of the Right and Left Sides by Group Group Condylar Height (mm) Coronoid Process Height (mm) Transverse Width of Mandible (mm) Transverse Width of Condyle (mm) Right Left Right Left Right Left Right Left Injury 0.48 ± 0.08 A 0.52 ± 0.13 A 0.21 ± 0.02 A 0.22 ± 0.02 A 1.11 ± 0.05 A 1.26 ± 0.04 A 0.33 ± 0.12 A 0.34 ± 0.08 a Removal 0.41 ± 0.04 B 0.48 ± 0.02 ∗ A 0.21 ± 0.03 A 0.21 ± 0.01 A 1.18 ± 0.48 A 1.25 ± 0.34 ∗ A 0.35 ± 0.03 A 0.36 ± 0.02 B Sham operated 0.86 ± 0.32 C 0.88 ± 0.20 B 0.39 ± 0.09 B 0.40 ± 0.10 B 2.03 ± 0.13 B 2.08 ± 0.88 B 0.65 ± 0.26 B 0.67 ± 0.30 C Note: Values are presented as mean ± standard deviation. Different superscript letters indicate statistically significant differences among groups by the Mann-Whitney test adjusted by Bonferroni correction ( P < .050). ∗ P < .050 by Wilcoxon signed posts test for statistical significance between sides. When comparing specific mandibular measurements among groups, the Kruskal-Wallis test showed significant differences in condylar height (B; P < .001), coronoid process height (C; P = .006), transverse width of the mandible (C-D; P < .001) and transverse width of the condyle (E; P < .001) on the right side and condylar height (B; P < .001), coronoid process height (C; P = .001), and transverse width of the mandible (C-D; P = .001) and transverse width of the condyle (E; P < .001) on the left side. Then, the Mann-Whitney test adjusted by Bonferroni correction showed differences in condylar height (B), coronoid process height (C), transverse width of the mandible (C-D), and transverse width of the condyle (E) between the injury and sham-operated groups and between the removal and sham-operated groups and in condylar height (B) and transverse width of the condyle (E) between the injury and removal groups ( Table 3 ). Discussion The effects of injury or removal of the articular disc on the growth of the maxilla and mandible were analyzed in young rats. When the animals reached adult age, radiographic projections were obtained and used to perform cephalometry on a computer system. Statistical analyses showed changes in the mandible, resulting in asymmetry associated with injury or removal of the articular disc. To the best of the authors' knowledge, no previous studies in the literature have evaluated this aspect. Mandibular deformities resulting in a decrease in length and asymmetries have been related to condylar fractures. However, the present study detected actual asymmetry of the mandible associated with lesions of the articular disc, suggesting a complex process in the occurrence of sequelae related to trauma to the TMJ, such as ankylosis and osteoarthrosis. There was only an incipient difference between sides in the maxillary mensurations, but no difference among groups. A possible influence of the mandibular growth on maxillary growth and vice versa by occlusal intercuspation has been described but not confirmed. Although there are limitations to these findings because the lesions were on the TMJ, it was decided to include the results relative to the maxilla, aiming at a complete evaluation of maxillomandibular growth. Occlusal disturbances have been described as the main cause of maxillary asymmetry after experimental fractures and as a complication of condylar fractures. Cephalometric evaluations based on radiographs of the skulls and hemimandibles of dissected specimens using a computerized system have provided reliable measurements. In this study, the distances in the sham-operated group were similar to those in other studies. Mandibular distances between sides and in the concomitant comparison among groups were meaningfully different from the height of the body in the injury group and to its length in the injury and removal groups. Lower mean values observed for ramus height in the sham-operated group may suggest an effect of the surgical procedure itself, but there was no statistically significant difference ( P = 0.074). The effects of disc injury and removal on growth of the mandible in growing rats were similar to those reported in previous studies of experimental disc displacement. Injury to the articular disc resulted in worse outcomes, which were likely due to a more difficult remodeling process in the presence of an injury compared with complete removal of the articular disc. The remodeling process is an important component of the healing process associated with trauma to the TMJ. It is well known that healing after experimental microtrauma to the articular disc consists of formation of collagen fibers, and the original structure is not recovered. The possibility of a better response of the TMJ after discectomy than the perforation of the articular disc should be considered, taking into account experimental studies. Although the isolated discectomy might promote remodeling on the articular surface, experimental disc perforation can lead to osteoarthritis. Another possible effect of injury to the articular disc on mandibular growth would be the occurrence of pain and consequent functional deficit. Changes in innervation surrounding arthritic condyles after experimental disc displacement would indicate a possible mechanism of nociception. Also, an experimental study based on electrical stimulation in patients with chronic pain showed increased inhibition of muscle activity. Interestingly, when specific measurements of mandibular ramus structures were made, such as the heights of the CP and coronoid process and transverse widths of the mandible and condyle, there was a difference for all measurements between the injury and sham-operated groups and between the removal and sham-operated groups. This shows a deleterious effect of injury of the articular disc not only ipsilaterally, but also contralaterally. That this finding could be due to a refined mensuration method should be considered. Another possibility is that these changes had a localized effect, so as to have no influence on mandibular shape. The growing mandibular condyle is highly adaptive and responds to even slight alterations in its biophysical environment. Atrophic changes in the AP and shortening of the entire mandible were reported in a study in which the effects of unilateral removal or dissection of the masseter muscle on the facial growth of young rats were analyzed. Also, it is known that mandibular hypomobility can alter the form of the coronoid process. Features of atrophy and degenerative changes of the CP were the other important findings. The macroscopic appearance showed shortening and flattening of the articular surface in the injury group, with more intense findings in the removal group. Degenerative changes of the condyle have been reported in displaced CP fracture in growing rats and in disc displacement in growing rabbits. These findings show the importance of the integrity of the articular disc during normal condylar growth. After disc displacement in the growing individual, mandibular growth changes occur before the development of osteoarthrotic changes. Only cautious conclusions can be drawn regarding human subjects based in this type of experimental model. There are differences in the TMJ form and the surrounding muscular system between rodents and omnivores. In addition, the human TMJ disc possesses biochemical and biomechanical properties that are distinct from those in the rabbit. However, considering the findings of this study in the mandible, the authors suggest that children and adolescents with articular disc injuries should be closely monitored by maxillofacial surgeons. Injury and removal of the articular disc in young rats had important consequences on mandibular growth. There was induction of adverse effects on ramus structures and asymmetry of the mandible, with worse outcomes to the articular disc in the injury group. These results suggest that children and adolescents with articular disc injuries should be closely monitored by oral and maxillofacial surgeons. References 1. Skolnick J., Iranpour B., Westesson P.L., et. al.: Prepubertal trauma and mandibular asymmetry in orthognathic surgery and orthodontic patients. Am J Orthod Dentofac Orthop 1994; 105: pp. 73. 2. 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