Volumetric analyses of restorative crown preparations in simulated-premolar and -molar teeth

Abstract

Crowns or abutments of fixed partial denture tooth preparations to restore natural teeth or implant-supported restorations require tooth or abutment reduction in a tapered format.  Low angulations of axial wall taper to the long axis of the tooth or abutment have been shown to increase the restoration’s stability during masticatory function with large occlusal loads.  The tooth preparation and luting agent stabilize the restoration during these loading cycles to prevent dislodgement.  Restoration dislodgement represents a catastrophic failure of the prosthesis in function.  The preparation attributes contribute to prevent displacement failure and reduce luting agent tensile and shear stresses.  Low axial wall taper levels increase resistance to rotational displacement. Increasing axial wall angulations produces negative consequences including reduced rotational resistance, reduced surface area and increased volume of remaining tooth structure.  These three considerations have been shown to involve three variables: preparation vertical height, horizontal base width from rotational axis and rotational axis vertical height compared to the opposing axial resisting wall.  Natural tooth preparations are completed by a restorative dentist with a hand-held high-speed handpiece with cutting instruments within the oral cavity; while implant-supported custom abutments are prepared in a similar manner but machined outside the oral cavity.  As a result, the machined abutment is more controlled for ideal taper in inanimate materials compared to the intraoral tooth preparation on human vital tissues.  This experimental study will analyze the preparation of simulated-vital tooth premolars and molars for volume loss at ideal and non-ideal axial wall angulations with variation of vertical heights and vital pulpal tissue volumes.