The effect of autoclave sterilization on the cutting characteristics of extracted teeth

Use of autoclaved teeth for preclinical laboratory exercises has been hindered by the perception that high-pressure steam affects their physical properties. The purpose of this study was to determine whether: 1) tooth hardness was affected by autoclaving and 2) faculty evaluators could determine these changes. 32 teeth were selected from those to be used for preclinical laboratories. 16 teeth were autoclaved at 260°F at 20 psi for 20 minutes, Teeth were randomly mounted in blocks and 4 faculty evaluators prepared two surface cavities in 14 randomly selected teeth (3 cavity preparations were made in each tooth). Before commencement of the study, each evaluator completed a bias questionnaire concerning their beliefs about the effects of autoclaving on the teeth. Changes in hardness of the teeth were determined by a Vickers´ hardness test and by differential thermal analysis. Mean hardness parameters were compared by factorial analysis of variance and Sheffe´s comparisons. Evaluation scores were compared by Spearman rank correlation coefficients. Mean hardness of enamel was not different between groups; however, dentin hardness was significantly lower in autoclaved teeth (p<0.05). Although autoclaved dentin was softer than control dentin, evaluators could not accurately determine a clinical difference. In addition, their beliefs were related to the hardness and brittleness scores in a negative direction, suggesting that when evaluators believed that autoclaved teeth would be softer and more brittle than controls their final determinations were influenced by that bias