Comparison of unilateral chewing movements vs. dental guidance through the dental guidance ratio

Statement of problem. Limited knowledge exists about the interaction between dental morphology and mandibular excursive movements. Purpose. This study evaluated dental guidance in lateral excursive movement and its relationship to jaw motion in unilateral chewing. Material and methods. Three-dimensional mandibular movement paths (in lateral guiding movements and in the final part of a monolateral chewing stroke) were collected with automated infrared motion analysis in 22 subjects with complete, permanent dentitions. On 2 traces selected from the recorded movements, the angular values projected in all planes of space obtained from 2 lines tangent to a point at a distance of 2.5 mm from maximum intercuspation were used to calculate a canine and a molar dental guidance ratio (DGR). Descriptive statistics were computed for the DGRs in the 3 spatial planes. Results. Assuming masticatory movements of any given subject are restricted or guided by dental anatomy, a value below 100% of the DGR was expected. This was true for the frontal plane only, with mean values of approximately 80% (working-side movements, canines, and molars) and approximately 60% (nonworking-side movements for both molars and canines). In the horizontal and sagittal planes, mean values between 102% and 137% were found. Conclusion. Within the limitations of this study, masticatory movement was within the physical borders dictated by dental anatomy in the frontal plane only.