PubMed · 6928067
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I H Aas. 1980. [Root canals in permanent teeth].. https://pubmed.ncbi.nlm.nih.gov/6928067/
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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.
Secondary caries is one of the greatest causes for replacement of amalgam restorations. This study verified whether marginal defects in class I restorations could be a determining factor in the development of secondary caries. Fifty-five extracted premolars and molars whose occlusal surfaces were already restored with amalgam were selected. A macroscopic examination of these teeth was carried out to see whether there was a difference in the prevalence of caries beneath ditched and nonditched margins. To assess the presence of caries, a section was ground in each tooth so that the cut passed through a ditched margin and a better margin. This permitted assessment of the two types of margins that had been exposed to the same oral environment. Macroscopic examination revealed caries in 3.6% of the nonditched margins and caries in 20% of the ditched margins. Microscopic examination revealed caries in 47.06% of the nonditched margins and caries in 58.82% of the ditched margins. Statistical analysis supports the conclusion that the marginal defect itself is insufficient to determine the presence of secondary caries that surround the amalgam restoration on the occlusal surface.