ヒト象牙質の力学的特性に及ぼす含水率と歯内療法の影響

Effects of moisture content and endodontic treatment on some mechanical properties of human dentin.

抄録

本研究の目的は、歯髄のない歯の象牙質と正常な歯の象牙質の機械的性質に有意な差があるかどうかを調べることである。象牙質の試料（n = 262）は、54本の抜歯したての正常な歯と24本の無髄歯から得た。これらの試料を異なる実験条件（湿潤、空気乾燥、乾燥、再水和）に供した。これらの試料の機械的特性を測定するために、圧縮試験、間接引張試験、衝撃試験を行った。得られたデータはすべてt検定で分析した。その結果、象牙質の脱水はヤング率、比例限界（圧縮）、特に極限強度（圧縮と引張の両方）を増加させることが示された。大幅な脱水は，静的圧縮荷重および間接的引張荷重下での象牙質試料の破壊特性を変化させた．乾燥象牙質の衝撃破壊エネルギーの測定では，有意な低下は認められなかった．本研究で得られた無髄歯象牙質の圧縮強さおよび引張強さは正常象牙質と有意な差は認められなかったが（p＞0.05），圧縮試験におけるヤング率および比例限度の平均値は低かった．無髄歯から採取した象牙質試料の50%は、圧縮試験において正常象牙質よりも大きな塑性変形を示した。本研究の結果は、歯内療法後の脱水がそれ自体で象牙質の構造を圧縮強度と引張強度の点で弱めるという理論を支持するものではない。しかし、無髄歯治療歯のその他の機械的特性は、正常な歯と同じではないかもしれない。

The objective of this study was to determine whether significant differences exist between the mechanical properties of human dentin from treated pulpless teeth and dentin from normal vital teeth. Dentin specimens (n = 262) were obtained from 54 freshly extracted normal vital human teeth and 24 treated human pulpless teeth. These specimens were subjected to different experimental conditions (wet, air dried, desiccated, and rehydrated). Compression, indirect tensile, and impact tests were conducted to measure the mechanical properties of those specimens. All data obtained were analyzed with t tests. The results showed that the dehydration of dentin increases the Young's modulus, proportional limit (in compression), and especially the ultimate strength (in both compression and tension). Substantial dehydration changes the fracture characteristics of dentin specimens under static compressive and indirect tensile loadings. The measurements of impact-breaking energies of desiccated dentin were not found to be significantly decreased. The compressive and tensile strengths of dentin from treated pulpless teeth obtained in this study do not appear to be significantly different from those of normal dentin (p > 0.05), while the mean values of Young's modulus and proportional limit in compression tests appear to be lower. Fifty percent of the dentin specimens from treated pulpless teeth exhibit greater plastic deformation than normal dentin in compression. The results of this study do not support the theory that dehydration after endodontic treatment per se weakens dentin structure in terms of compressive and tensile strengths. Other mechanical properties of treated pulpless teeth, however, may not be the same as those of normal vital teeth.