異なる熱処理を施した2種類のニッケル-チタン製回転機器の耐欠損性

resistance to fracture of two nickel-titanium rotary instruments made with different thermal treatments.

抄録

研究目的:

本研究の目的は，異なる熱処理を施したニッケルチタン製歯内療法用回転器具の耐欠損性を向上させるための効果を評価することである．

AIM: Aim of the study was to evaluate effectiveness of different heat treatments in improving Ni-Ti endodontic rotary instruments' resistance to fracture.

方法:

長さと形状が類似した24本の新しいNi-Ti製器具：M3器具12本，先端サイズ25，テーパー0.06（United Dental，中国，上海），M3 Pro Gold器具12本（United Dental，中国，上海）を60°湾曲人工根管でテストした．各グループは異なる熱処理を受けた．破折までのサイクルは，各インスツルメントについて計算した．グループ間の差は分散分析で評価した（有意水準はP<0.05とした）．

METHODS: 24 new NiTi instruments similar in length and shape: 12 M3 instruments, tip size 25 and .06 taper (United Dental, Shanghai, China), and 12 M3 Pro Gold instruments tip size 25 and .06 taper (United Dental, Shanghai, China), were tested in a 60° curved artificial root canal. Each group received a different heat treatment. Cycles to fracture were calculated for each instrument. Differences among groups were evaluated with an analysis of variance test (significance level was set at P<0.05.).

結果:

統計解析の結果、グループ間で有意差（p<0.0213）が認められた。M3プロゴールドは，M3インスツルメント（平均値＝748，SD±62）よりも有意に疲労に強かった（平均値＝1012，SD±77）．フラグメントの長さには、統計的に有意な差は認められなかった（p>0,05）。

RESULTS: Statistical analysis found significant differences (p<0.0213) between groups. The M3 Pro Gold instruments were significantly more resistant to fatigue (mean values = 1012, SD +/- 77) than M3 instruments (mean values = 748, SD +/- 62). No statistically significant differences were found between fragments' lengths (p>0,05).

結論:

柔軟性の向上と，製造工程中あるいは製造後の熱処理による内部欠陥の低減が，繰返し疲労と曲げ応力に対する耐性を向上させる要因である可能性がある．

CONCLUSIONS: An increased flexibility and the reduction of internal defects produced by heat treatments during or after manufacturing processes, may be responsible for improving resistance to cyclic fatigue and flexural stresses.