Comparison of methods for measuring cuspal deformation in teeth

Objectives: The aim of this study was to compare two techniques of measuring cuspal deformation under occlusal load: Direct Current Differential Transformers (DCDTs) and strain gauges. The study investigated the relative dependence of the two techniques on the vertical orientation of the tooth in relation to direction of loading and differences in the patterns of change in response to a cavity preparation sequence. Methods: Strain gauges and DCDTs were attached to the buccal and lingual surfaces of extracted maxillary premolars and mandibular molars. Premolars were subjected to simulated occlusal loads at varying vertical angulations before and after MOD cavity preparation. Molars were tested at progressive stages of cavity preparation. Cuspal deformation was recorded as linear cusp displacement (in μm, using DCDTs) and as cuspal strains (using strain gauges) and relative stiffness. Results: Strain gauges were much less sensitive than linear displacement devices to vertical orientation of teeth, and computation of relative stiffness further reduced the effect of angulation. Strain gauges are much easier to use experimentally. DCDTs required precise three-dimensional adjustments for the testing of cuspal deformation. Patterns of change in cuspal flexure following cavity preparation were very different using the two techniques. Conclusions: Use of both devices simultaneously yielded much more information than when used alone, and showed that cusps do not deform as simple cantilever beams.