Deformation of cavities and resin fillings in loaded teeth.

The purpose of the present work was to study (1) the deformation of selected types of cavities in axially loaded human teeth and (2) the possible effect of this deformation on the restorative quality of fillings in the cavities. Recently extracted wet teeth without any visible structural defects were used throughout the study. Standard Class III and large Class III cavities were prepared in maxillary incisors, while Class I, m-o, m-o-d, and Class V cavities were made in maxillary first premolars. For the second part of the study several of the cavities, etched of non-etched, were filled with restroative resins. Mounted in a measuring microscope the teeth were loaded in a way simulating biting or chewing; cavities with fillings were accepted only when no marginal gaps could be found. The results showed a deformation of empty cavities proportional to the load up to 16 kg, the decrease or increase in diameter being 0.1-1.0 mum/kg, depending on the type of cavity. Loading and unloading of teeth with filled cavities resulted in permanent or transitory gaps. The dimensional instability of cavities in loaded teeth indicates a severe risk of percolation by several restoratives and of marginal fracture of brittle fillings.