Profile Characteristics of Cut Tooth Surfaces Developed by Rotating Instruments

Abstract

THE irregularity of the cut tooth surfaces resulting from the shaping of cavities would appear to have a twofold significance.First, these irreg- ularies should have some effect on the adaptation of the specified filling mate- rial to the cavity walls, and second, they may tend to undermine or weaken groups of enamel rods at the eavo-surface margins, thus resulting in a failure of the tooth structure surrounding the restoration rather than a failure of the restoration itself.In order to determine the significance that these irregularities may have in either case, it is desirable to know their magnitude as produced by various instruments.Appraisals of such surface roughness have been made previously by Street,6 and Peyton and Mortell.5These methods of evaluation have been somewhat qualitative since they rely on observation at right angles to a cut surface which has been previously treated to make the crests of the irregulari- ties more distinguishable.The eye is, however, more sensitive to the spacing of the irregularities rather than their height.2Lammie4 used a stylus-type surface analyzer which gives an average height rating for a given surface.Such recordings do not provide a profile of widely spaced irregularities.There- fore, the Proficorder, an instrument of different design, has been employed in this study. METHODThe Proficorder1' 3 is a mechanical-electronic instrument which provides a permanent magnified chart record of the shape, height, and spacing of sur- face irregularities.Vertical displaeements of a diamond stylus, whose tip has a radius of 0.0005 inch, react through a differential transformer type trans- ducer to modulate a carrier voltage whieh is fed into an amplifier and record- ing unit.The reference surface for the stylus tracer is an optical flat with deviation of no more than one-millionth of an inch, or one microinch (1 MU").Although both the vertical and horizontal scales have, independently, a wide range of magnifications, the degree of magnification on the horizontal scale was kept constant throughout this study while two vertical magnifications were used.This report represents the partial results of studies supported by Contract No. AF 18(600)-427 between the United States Air Force and the University of Michigan.