二ケイ酸リチウムセラミックオンレーの破壊強度に及ぼす象牙質即時封鎖の影響

Effect of immediate dentin sealing on the fracture strength of lithium disilicate ceramic onlays.

抄録

本研究は，即時象牙質封鎖法（IDS）がセラミックオンレーの破折強度に及ぼす影響を，遅延象牙質封鎖法（DDS）と比較して評価することを目的とした．ヒト上顎小臼歯20本を無作為に2群に分け（n=10），象牙質封鎖の方法によって比較検討した．口蓋垂を縮小し，標準的な中・奥歯顎口腔腔を作製した．IDS群の象牙質表面は，調製終了後（印象採得，仮封，37℃14日間保存前），ボンディングシステム（ALL-BOND 3®, ALL-BOND 3® RESIN）と流動性コンポジット（Te-Econom Flow）を用いて即時封鎖した．印象採得後，PRO-V FILL®を用いて暫間補綴物を作製した．ワックスパターンをミリングし、ヒートプレステクニック（IPS e.max Press）によりオンレーを作製しました。最終補綴物をレジンセメント（バリオリンクN）で接着した後，試験片をサーモサイクルで加熱した．万能試験機（Testometric M350-10KN）を用いて，1 mm/minで破断するまで破断強度を測定した．破壊強度の評価には，Student's t-testを用いた．破壊モードは実体顕微鏡を用いて観察した．IDS群の平均破壊強度（1335±335N）は，DDS群（931±274N）よりも統計的に有意に高かった（p＜0.05）．また，修復物の破損は，歯牙のごく一部が破損することが最も多かった．このin vitro試験の制限の範囲内で，IDSの使用によりセラミックオンレーの破断強度の向上が見られた．しかし，セラミックオンレーは両群とも生理的咀嚼力に十分耐えうる強度を有していた．

This study aimed to evaluate the effect of immediate dentin sealing (IDS) on the fracture strength of ceramic onlays when compared with delayed dentin sealing (DDS). Twenty extracted human maxillary premolars were randomly divided into 2 groups according to the dentin sealing technique (n=10). A standardized mesio-occlusal-distal cavity was prepared with reduction of the palatal cusp. The dentin surfaces of the IDS group were immediately sealed after finishing the preparation (before taking impressions, temporization, and 14-day storage at 37°C) using a bonding system (ALL-BOND 3®, ALL-BOND 3® RESIN) and flowable composite (Te-Econom Flow). Impressions were made and temporary restorations were fabricated using PRO-V FILL®. The wax patterns were milled and the onlays were fabricated by heat-pressing technique (IPS e.max Press). After bonding the final restorations with resin cement (Variolink N), the specimens were thermocycled. Fracture strength was measured using a universal testing machine (Testometric M350-10KN) at 1 mm/min until failure occurred. Student's t-test was used to evaluate the results of the fracture strength test. The failure mode was examined using a stereomicroscope. The mean fracture strength in the IDS group (1335 ± 335 N) was statistically significantly higher than that for the DDS group (931 ± 274 N) (p < 0.05). Fracture of the restoration with a small portion of the tooth was the most frequent mode of failure. Within the limitation of this in vitro study, there was an improvement in the fracture strength of ceramic onlays with the use of IDS. However, the ceramic onlays were strong enough to withstand the physiological mastication force in both groups.