Radiographic diagnosis of temporomandibular disorders

Impact of molar teeth distalization by clear aligners on temporomandibular joint: a three-dimensional study

BACKGROUND

Maxillary molar distalization is a common technique used in the non-extraction treatment of Angle Class II malocclusion that can effectively correct the molar relationship and create spaces for anterior teeth alignment. However, this approach may also impact the temporomandibular joint (TMJ) due to predictable changes in the posterior vertical dimension. Despite its widespread use, Class II malocclusions correction by molar distalization with clear aligners has not been investigated for their effects on the TMJ. Therefore, this study aimed to analyze the impact of sequential molar distalization using clear aligners on the TMJ.

METHODS

Three-dimensional CBCT scans of 23 non-growing patients (7 males, 16 females; mean age 29.8 ± 4.6 years) with skeletal class I or II malocclusion and a bilateral molar class II relationship treated by sequential upper molars distalization with orthodontic clear aligners (Invisalign, Align Technology, San Josè, Ca, USA). A total of 46 joints were examined before and after molar distalization using Anatomage InvivoDental 6.0.3. Linear and angular measurements of the mandibular joint were measured, including joint parameters, inclination, position, and the dimension of the condyle and articular fossa. In addition, 3D volumetric spaces of the joint were analyzed. All data were statistically analyzed by paired T test to determine the differences between the pre-and post-orthodontic procedures.

RESULTS

No statistically significant differences were found in all primary effects resulting from maxillary molars distalization by clear aligners on TMJ components measurements and joint spaces between T0 and T1. Meanwhile, statistically significant differences were observed in the linear position of the upper molars and the molar relationship parameter with at least P ≤ 0.05.

CONCLUSION

Treatment by sequential upper molars distalization with clear aligners does not lead to significant TMJ parameters changes in condyle and fossa spaces, dimensions, and positions.

Mandibular asymmetry and condylar position in children with unilateral posterior crossbite

The purpose of this retrospective study was to determine if condylar position in children with functional unilateral crossbites was different from that found in children with Class I noncrossbite malocclusions and if there was a change in condylar position after correction of the crossbite by palatal expansion. Mandibular asymmetry in children with functional unilateral posterior crossbite was also compared to that of a Class I noncrossbite group. Thirty-one children aged 6 to 14 years (mean, 9.3 years; standard deviation, 2.2) with functional unilateral crossbites were compared to 31 children aged 9.5 to 14.1 years (mean, 11.9 years; standard deviation, 1.3) exhibiting Angle Class I noncrossbite malocclusions. Pretreatment submentovertex radiographs were used to study mandibular skeletal, dental, and positional asymmetries with reference to cranial floor and mandibular coordinate systems. In addition, the anterior, superior, and posterior joint spaces were measured to determine differences between the groups with the use of pretreatment and posttreatment horizontally corrected tomograms of the temporomandibular joints. Finally, the distances of the mesiobuccal cusp of the upper first molar relative to the buccal groove of the lower first molar were measured in both groups before treatment. Univariate analyses revealed that the mandibles of children in the functional unilateral posterior crossbite group exhibited asymmetry in both anteroposterior and transverse dimensions when compared with the Class I noncrossbite group (P <. 05). These asymmetries were the result of a functional deviation of the mandible that was present in all subjects in the crossbite group. This deviation was manifested occlusally by a Class II subdivision on the crossbite side as indicated from the study model analysis (P <.05). Examination of condylar position as evidenced by horizontally corrected tomograms demonstrated a large standard deviation, resulting in an inability to detect any significant differences within or between groups at both T1 and T2 (P >.05). This study raised the question of the appropriateness of measuring joint spaces for routine diagnostic purposes.