MOD修復物の耐欠損性とギャップ形成：修復テクニック，ベベルの作成および水の保管の影響．

Fracture resistance and gap formation of MOD restorations: influence of restorative technique, bevel preparation and water storage.

抄録

このin vitro研究では，レジン複合材料MOD修復物の耐破折性とギャップ形成に及ぼす技法，ベベルの使用およびサーマルサイクルの影響を評価した．100本の上顎小臼歯に作製した標準的なMOD窩洞を24時間および6カ月間1000回の熱サイクルで保存し，耐破折性を測定した．サブグループ（n=10）は，面取りまたは非面取り準備と直接修復（アドパーシングルボンド/フィルテックZ250）および間接修復（Rely XARCでセメントしたプレポリマーフィルテックZ250）であった．健全歯10本とMOD調製品で修復物のない試料10本をそれぞれ陽性と陰性対照とした．試験片は，万能試験機を用いて，クロスヘッド速度0.5 mm/分で軸方向圧縮に供した．試験片の破壊形態は実体顕微鏡（40倍）で観察した．隙間の有無を評価するために，上記の方法で修復した24本のヒト第三大臼歯に近心箱型空洞を作製した．24時間後および6ヵ月後にSEM観察を行い，評価した．データは，ANOVAおよび多重比較検定により，有意水準0.05で統計的に解析した．24時間後，面取りした修復物は，面取りしていない修復物よりも高い破壊強度値を示し，すべてのグループが健全歯と同等以上の抵抗性を示した．6ヵ月後の破壊強度は，斜角付きインレーで最も高く，バットジョイントを用いた直接修復で最も低かった．熱サイクルにより，大半の群で耐欠損性が低下した．主な破断パターンは，材料の凝集破壊であったが，接着破壊は特にノン・ベベルド・レストレーションで経時的に増加した．SEM観察では，24時間後では各群間に差は認められなかった．しかし，6ヵ月後では，面取りした修復物にはギャップ形成が認められなかった．以上より，サーマルサイクルを伴う保存は耐欠損性を低下させ，ベベルは耐欠損性を改善し，一般に間接修復物は直接修復物より優れていないことが示唆された．

This in vitro study evaluated the effect of technique, use of a bevel and thermal cycling on the fracture resistance and gap formation of resin composite MOD restorations. Fracture resistance was measured on standard MOD cavities prepared in 100 upper premolars that were stored for 24 hours and 6 months with 1000 thermal cycles. Subgroups (n=10) were: beveled or non-beveled preparations and direct restorations (Adper Single Bond/Filtek Z250) and indirect restorations (prepolymerized Filtek Z250 cemented with Rely XARC). Ten sound teeth and 10 specimens with MOD preparations without restorations served as the positive and negative controls, respectively. The specimens were subjected to axial compression in a universal testing machine at a crosshead speed of 0.5 mm/minute. Failure patterns were analyzed by stereomicroscopy (40x). To evaluate gap presence or absence, proximal box cavities were prepared in 24 human third molars that were restored as described above. The specimens were evaluated under SEM examination after 24 hours and six months. Data were statistically analyzed by ANOVA and multiple comparison tests at the 0.05 level of significance. After 24 hours, the beveled restorations exhibited higher fracture strength values than the non-beveled restorations, and all groups showed resistance similar or superior to sound teeth. After six months, the highest fracture resistance was obtained for beveled inlays and the lowest values were observed for direct restorations with butt joints. Thermal cycling decreased fracture resistance in the majority of the groups. The main fracture pattern observed was cohesive failure in the material, but adhesive failures increased over time, especially in the non-beveled restorations. Under SEM examination, no difference was observed among the groups after 24 hours. However, after six months, the beveled restorations exhibited no gap formation. It was concluded that storage with thermal cycling decreased fracture resistance, bevels improved fracture resistance and, in general, indirect restorations were not superior to direct restorations.