PubMed · 6955424
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Y Shapira, P Delivanis. 1982. Multiple-rooted mandibular second premolars.. https://doi.org/10.1016/s0099-2399(82)80360-9
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The optical phenomenon of Moire magnification can be used to provide real-time measurements of the position of an erupting human premolar, with a resolution of 0.1 micron or better. A new instrument for this purpose, which allows repeated measurements in the same individual, is described. Cyclic changes in the position of the erupting tooth in concert with the heartbeat, with a magnitude of 0.05-0.35 micron, can be discerned. An unusual cyclic rhythm, with a period of 20-50 s, was observed.
OBJECTIVES: The purpose of this research was to evaluate the wear patterns of three posterior composites (Clearfil Posterior. Occlusin and P-30) and two amalgams (New True Dentalloy, Solila Nova) after 5 years' clinical service. METHODS: Marginal wear was measured using the stepwedge technique which determines the maximal marginal wear by any one cusp together with the mean marginal value. The overall maximum depth of wear, occurring at any site on the occlusal surface, was determined using an impression technique with epoxy models. RESULTS: The mean values (+/- standard deviations) for the overall maximum wear were: New True Dentalloy, 203 +/- 98 microns; Solila Nova, 200 +/- 96 microns; Clearfil Posterior, 252 +/- 141 microns; Occlusin, 324 +/- 189 microns; P-30, 380 +/- 273 microns. These values were significantly different (ANOVA F = 2.86 P = 0.05). There was no correlation between the marginal scores and the overall maximum depth of wear (P > 0.05). There was no correlation between the marginal scores and the overall maximum depth of wear (P > 0.05). With some restorations the maximum wear occurred at the margins, marginal ridges or cavity extensions rather than sites of occlusal contact. CONCLUSIONS: After 5 years' service the overall wear of three posterior composites exceeded that of two amalgams; however, for a number of restorations the difference was not significant. Marginal wear values cannot be used to predict the overall maximal depth of wear.