UCSF

ABSTRACT

Reevaluating Our Orthodontic Treatment Goals: The Impact of Ideal Torque on Alveolar Bone Support

Stephanie Purnomo, DDS

OBJECTIVE: The purpose of this investigation was to: 1) develop a protocol to measure molar torque, taking into consideration both crown and root positions using 3D visualization software (InVivo5), test the reliability of using this analysis on a sample of adult patients; 2) Utilize this method to evaluate molar torque changes in relation to skeletal transverse jaw relationships and buccal bone coverage in patients before and after orthodontic treatment

METHODS: 32 adult patients were retrospectively selected from the UCSF orthodontic clinic. All were over 16 years old, with normal ANB angle between zero and five degrees, final CBCT records taken by August 2016, and initial records taken after August 2012. Initial and Final Dicom files were landmarked with 41 points, generating 16 different measurements utilized to measure molar torque, transverse jaw relationship, and the quality of bone surrounding the roots of maxillary first molars at 4 separate sites: the mesiobuccal and distobuccal root apex and furcation.

RESULTS: Intra- and inter- rater reliability of maxillary first molar torque values were excellent (r=0.98, 0.91) for right and left sides respectively (p<0.05). All other measurements demonstrated good intra and inter-rater reliability, with the exception of bone thickness measured at MBRF (mesiobuccal root furcation) and DBRF (distobuccal root furcation) on the left and right sides. There was a weak negative correlation between maxillary molar torque and the transverse maxillary deficiency prior to treatment (r=-0.03), indicating greater initial buccal crown torque when the maxillary width is narrow. There was a weak negative correlation between transverse deficiency and average change in torque throughout treatment (r=-0.17), indicating greater compensatory buccal crown torque after treatment when the maxillary width is narrow. Patients that experienced large molar torque changes during treatment demonstrated the largest changes in buccal root alveolar bone thickness (r=0.24). The percentage of root exposures were most pronounced in the mesiobuccal roots of both right and left first molars, at the level of the furcation.

CONCLUSIONS: This custom analysis is a repeatable and a reliable method for measuring whole tooth torque/ buccolingual inclinations. Orthodontic treatment in adults should be carefully evaluated to reduce risk of losing alveolar bone support in posterior teeth. In patients with larger skeletal maxillary transverse deficiency, a greater change in torque is observed, which is weakly correlated to changes in buccal bone thickness surrounding the roots of maxillary first molars.