[Strength of teeth to fracture by impact. Testing of fractural strength against impact force, using replication models of human permanent teeth].

Abstract

Traumatic injury anterior teeth is often encountered clinically. A number of clinical and statistical studies have so far been undertaken for the incidences, causes and ages in terms of the site of fracture. However, little has been attempted at fundamental estimation of the fractural resistance of anterior teeth that are susceptible to fracture. This has been studied in only an erect position of eruption by Nose or Chin. Changes in resistance of teeth in a twisted position or at different angles of eruption still remain unstudied. We took an interest in the relation between physicopositional conditions of human teeth and changes in their fractural strength against impact. Determination of the resistance of teeth to a variety of experimental conditions was attempted by use of an Izod-type tester. Epoxy resin replication models of human anterior teeth were used as experimental specimens, since human teeth were considered inappropriate because of their large individual differences and an anticipated difficulty in precise reproduction of the angles of eruption and torsion. The following results were obtained; (1) In the replication models of teeth erected positioned at 90 degrees vertically to the horizontal plane, the fractural strength against impact was highest for the maxillary cuspid model and was lowest for the mandibular central incisor model. (2) In the replication models of teeth with their mesial or distal incisal margin twisted 45 degrees medially, the fractural strength was reduced for all the teeth except the maxillary central incisors. (3) In comparison of the strength between the replication models with the mesial incisal margin twisted 45 degrees medially and those with the distal incisal margin twisted likewise am marked reduction in strength was found for the maxillary cuspid model prepared in the former condition of torsion. For the mandibular cuspid model, a relatively large reduction of the strength was found in the latter condition of torsion. (4) In comparison of the strength of teeth positioned at various angles, the strength was decreased by slanting either labially or lingually for all the replication models except the maxillary and mandibular cuspid models.