PubMed · 296418
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C J Nogueira. 1979. [Inverted retained upper second premolar].. https://pubmed.ncbi.nlm.nih.gov/296418/
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Canine/premolar transposition is rare in both historic and prehistoric Homo sapiens with a known occurrence of less than 0.10%. This report describes a prehistoric population sample from one site (SCrI-3) on Santa Cruz Island, California in which the rate of C/P3 transposition is greater than eight percent, based on nine of 106 adult crania which exhibit the anomaly either uni- or bilaterally. As a means of investigating the etiology of this anomaly, the location of the canine root in adult crania was studied. Root location should indicate tooth bud origin, a factor likely to be under genetic control. In crania with normally erupted canines, the superior portion of the root averages 4.43 mm from alare, while this distance is 8.96 mm for anomalous roots. This difference suggests that during ontogeny the tooth buds for the canine and premolar arose in the wrong (or reversed) places, causing the teeth to erupt anomalously. It is suggested that inbreeding in a small island community resulted in a short-lived appearance of this anomaly at a high frequency.
Three-dimensional finite element models of a partially edentulated human mandible were generated to calculate the mechanical response to simulated isometric biting and mastication loads. The level of mesh refinement was established via a convergence test and showed that a model with over 30,000 degrees of freedom was required to obtain analysis accuracy. The functional loading cases included muscle loading based on an algorithm that assigns muscle forces in accordance with muscle cross-sectional area, while maintaining static equilibrium. Results were found for isometric application of unilateral and bilateral bite and mastication loading, and two different sets of displacement boundary conditions were imposed at the condyles. The mechanical response is shown in terms of displacements, principal strains, and a new measure called the 'mechanical intensity scalar'. For each load case studied, there was substantial bending in the molar region of the corpus and high tensile strains in the anterior portion of the ramus.
This study evaluated the clinical performance of a visible light-cured small particle bimodally filled hybrid condensable composite resin system that included a dentin bonding agent compared with an amalgam alloy in class II restorations of permanent teeth. A total of 108 restorations were placed in 34 patients. Fifty-three composite resin and 55 amalgam restorations were inserted. Each restoration was evaluated immediately after placement and then on an annual basis for a 3-year period using the Public Health Service (PHS) criteria. In addition, the Moffa-Lugassy scale was used to measure the loss of material on the occlusal surface of these materials. One hundred percent of the resin and amalgam restorations were evaluated, measured, and reasons for replacement were recorded over the 3-year period. There was no significant difference (p greater than 0.05) in the clinical performance of the composite resin and the amalgam when evaluated by the PHS criteria. Analyses of wear at each of the three annual recall periods did not reveal any significant difference (p greater than 0.05) between the two restorative materials when measured by the Moffa-Lugassy scale.