Adaptation and validation of the Wylie cephalometric analysis for three-dimensional assessment of canine occlusion in Labrador retrievers.

Introduction: In veterinary medicine, we lack a quantitative method for assessment and classification of occlusion. Current systems of occlusion classification are subjective, limiting the ability for precise treatment planning. Methods: A medical record search identified 146 head CTs from Labrador Retrievers from 2007-2022. 3D computer models of skulls were created from DICOM files. Thirty standardized anatomic landmarks were placed on each model to perform cephalometric analysis. A cohort of 96 dogs was used to establish breed-specific reference values, with assessment for sexual dimorphism prior to standardization. The remaining 50 dogs served as a validation cohort for the Wylie cephalometric analysis to quantify maxillomandibular length discrepancy. Facial angles analysis and three ratio-based measurements (MXPM4: MNM1, MXK9: MNK9, and MX: MN) were calculated for all samples. Results: Craniofacial measurements showed significant sexual dimorphism and showed allometric scaling with weight. There was no significant difference between normalization and validation groups. Wylie score clustered near zero (SD = 3), indicating minimal maxillomandibular discrepancy in dogs with normal occlusion. The mean ANB angle was 7.8° ± 1.5°. Ratio-based measurements assessing maxillary-to-mandibular relationships were as follows: MXPM4: MNM1 ratio was 1.1, the MXK9: MNK9 ratio was 0.9, and the MX: MN ratio was 1.0 across all individuals. The ratio-based measurements correlated strongly with the Wylie score. Discussion: Human cephalometric analyses can be adapted for use in canine patients. This study established a reference standard for cephalometric analysis in Labrador Retrievers as a representative of mesaticephalic canine skulls. The Wylie analysis and ratio-based measurements represent a quantifiable method of occlusion assessment.