A CBCT evaluation of root position in bone, long axis inclination and relationship to the WALA Ridge

Correct tooth position in all planes of space while respecting the boundaries of the underlying bone is important for stability of teeth after orthodontic treatment as well as the health of the supporting periodontium.1., 2. The aim of this study was to determine: 1) if mandibular posterior teeth are more centered over basal bone when they are more upright or close to WALA Ridge norms proposed by Andrews3; 2) if mandibular posterior teeth are more centered in alveolar bone when they are more upright or close to the WALA Ridge norms; 3) if the estimated center of resistance mandibular posterior teeth is most often centered in alveolar bone; and 4) if the WALA Ridge is located at or near the estimated center of resistance of mandibular posterior teeth. A sample of 34 pre-treatment CBCT scans and mandibular casts of patients ages 12–18 were included in the study. CBCT scans were digitized and analyzed using the Carestream 3D Imaging Software Version 3.5.7. Casts were digitally scanned using the Ortho Insight 3D scanner. The WALA Ridge horizontal measurements were made using the Six Elements™ software (MotionView, Chattanooga, TN). The WALA Ridge vertical measurements were obtained from the casts using a digital caliper. Coronal CBCT images were used to measure tooth positions of pre-treatment mandibular posterior teeth relative to surrounding bone. Centeredness of teeth within the bone was quantified and compared to their inclination and to the WALA Ridge location: D1, D2, D3 and D4. Data were analyzed using the JMP version 10 SAS Software. Descriptive statistics were used to calculate the mean, standard deviation, minimum, and maximum values for the distance between WALA Ridge vertical and CR, D2, D3 and D4 for each of the posterior teeth. Single linear regression analysis was performed to evaluate the relationship between both the long axis inclination and WALA Ridge variables compared to the D1, D2, D3, variables. No statistical significance was found for centeredness of mandibular posterior teeth over basal bone when they were more upright or approached WALA Ridge norms. No statistical significance was found for centeredness of mandibular posterior teeth in alveolar bone when they were more upright or approached the WALA Ridge norms. Significant differences were found for the mandibular posterior teeth center of resistance being centered in the alveolar bone regardless of the long axis inclination or WALA Ridge norms (p-value <0.05). Significant differences were also found for the Wala Ridge being located at or near the center of resistance of mandibular posterior teeth (p-value <0.05). 1) More upright mandibular posterior teeth based on long axis inclination or mandibular posterior teeth more closely related to the WALA Ridge landmark are not more centered over basal bone. 2) More upright mandibular posterior teeth based on long axis inclination or teeth more closely related to the WALA Ridge landmark are not more centered in alveolar bone. 3) The center of resistance of all mandibular posterior teeth can most often be found in the center of the alveolar bone regardless of inclination. 4) The WALA Ridge is located at or near the center of resistance for all mandibular posterior teeth. 5) The WALA Ridge may be a useful landmark for customizing mandibular arch form if teeth are tipped to an upright position.