PubMed · 3912217
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W Pavanello. 1985-05-15. [Cast posts in multirooted teeth].. https://pubmed.ncbi.nlm.nih.gov/3912217/
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Restoration of dental restorations with resin composite is hampered by shrinkage of the material during the polymerization process. In this study, we simulated the polymerization process in a detailed three-dimensional finite element model of a human upper premolar with a cusp-replacing restoration. It was analyzed how the stress patterns changed during polymerization and it was assessed whether immediate failure of the restoration is likely to occur and if so, which locations within the restoration are at highest risk and what the clinical implications of these findings are for clinical practice. It was found that the stresses increased rapidly during polymerization and decreased again in the post-polymerization phase. At the interface, tensile stresses relaxed to a higher degree than the shear stresses. Stress values in the composite material and at the interface with the tooth tissue were lower than the reported strength values suggesting that immediate failure is unlikely. The safety factor against mechanical failure of the interface, however, was relatively low indicating that the interface between the composite material and the tooth tissue is at a higher risk for failure than the bulk of the restoration. Stress relaxation was less effective in areas where the interface surface was irregular. In common practice, irregular interface surfaces are used to increase the retention of the restoration. This study indicates that the increased retention may be compromised to some extent by higher shrinkage stresses. The fact that stresses considerably decreased during the post-polymerization period suggests that mechanical loading should be limited during the first few hours after restoration.
Eruption of an inverted tooth is a rare condition. This case report describes the inverted eruption of a supplemental lower premolar in a 10-year-old Caucasian female. The tooth erupted in a downward direction and reached the lower cortical border of the mandible 2 years later. During an 8-year follow-up period, the tooth did not interfere with eruption of permanent teeth and the patient remained symptom-free. Considering clinical examination, medical and dental history as well as scientific evidence, the inverted eruption was most likely caused by a developmental abnormality with an inverted location of the tooth bud. This reported eruption of an inverted tooth is extremely rare and requires a radiographic follow-up to evaluate the relative position of this tooth in the jaw bone and its potential interference with neighbouring teeth or anatomic structures.
The purpose of this study was to calculate the temperature and thermal stress distribution as a result of hot/cold liquid in the mouth. This numerical study was carried out using three-dimensional finite element models and the tooth model was crowned with Au-Pd alloy, Ni-Cr alloy and porcelain. In the first part of the study, temperature changes as a result of hot/cold liquid in the mouth were calculated. In the second part, the thermal stresses caused by temperature changes were obtained. The tooth was assumed isotropic, homogenous, elastic and unsymmetrical. The authors using fortran 77 prepared all calculation programs. The distribution of temperature and thermal stress were plotted for some critical points.