咬合接触様式と咬合調整が歯冠の摩耗と安定に及ぼす影響

Impact of the occlusal contact pattern and occlusal adjustment on the wear and stability of crowns.

抄録

目的:

臼歯部クラウンの摩耗，粗さ，破折力に及ぼす咬合接触状況および咬合調整の影響を検討する．

OBJECTIVES: To investigate the impact of the occlusal contact situation and occlusal adjustment on wear, roughness, and fracture force of molar crowns.

材料および方法:

CAD/CAM冠（右下第一大臼歯，n=64；4群à8，3Y-TZPジルコニアおよびレジンコンポジット）および対応する拮抗歯（右上第一大臼歯，3Y-TZPジルコニア）を作製した．クラウンは2つの咬合原理に従って製作された（T群．Peter K. Thomasのcusp-to-fossa tripodizationコンセプト（15点接触），Sigurd P. RamfjordとMajor M. Ashのfreedom in centricコンセプト（4点接触）である．半数のクラウンには，咬合調整が行われた（「T調整」グループと「RA調整」グループ）．すべてのクラウンについて，熱サイクル（TC）と機械的負荷（ML）を併用した（ML：1.2×10サイクル，50N，2Hz，口開き1mm，TC：2×3000サイクル，5/55°C）．クラウンと拮抗歯の咬合面における各接触点の摩耗面積と深さをデジタルマイクロスコープを用いて測定した．表面粗さ（R，R）は，摩耗部およびその外側（基準）で測定した（3Dレーザー走査型顕微鏡）．クラウンの破断力を測定した（統計学．統計：Levene-test，one-way-ANOVA，Bonferroni-post-hoc-test，被験者間効果，Pearson correlation，α=0.05).

MATERIALS AND METHODS: CAD/CAM crowns (lower right first molar, n = 64; 4 groups à 8, 3Y-TZP zirconia and resin composite) and corresponding antagonists (upper right first molar; 3Y-TZP zirconia) were manufactured. Crowns were constructed according to two principles of occlusion (group "T": Peter K. Thomas' "point-centric" cusp-to-fossa tripodization concept, with 15 contact points; group "RA" Sigurd P. Ramfjord and Major M. Ash, "freedom in centric" concept with four contacts). On one half of the crowns, occlusal adjustment was performed (groups "T adjusted" and "RA adjusted"). All crowns underwent combined thermal cycling (TC) and mechanical loading (ML) (ML: 1.2 × 10 cycles, 50 N, 2 Hz, mouth opening 1 mm; TC: 2 × 3000 cycles, 5/55°C). Wear area and depth of each contact point on the occlusal surfaces of crowns and antagonists were determined using a digital microscope. Surface roughness (R, R) was measured in and besides (reference) the worn area (3D laser-scanning microscope). Fracture force of the crowns was determined (statistics: Levene-test, one-way-ANOVA; Bonferroni-post-hoc-test; between-subjects effects, Pearson correlation, α=0.05).

結果:

レジン複合冠は，摩耗面積と深さの平均値が有意に高く（p＜0.001），破断力が低かった（p＜0.001）．レジン系コンポジットレジンの表面はTCML後に粗さが増加し，ジルコニアの表面は平滑化された．咬合設計は，摩耗深さ（p=0.012）および破折力（p<0.001）に有意な影響を及ぼした．接触点の少ないレジン複合冠（RA群）は，摩耗量が多く，破折力は小さかった．調整型レジン複合冠は，摩耗面積と深さが増加した（p＝0.009～0.013）．ジルコニアクラウンでは，調整により摩耗面積（p=0.013），摩耗深さ（p=0.008），破折力（p=0.006）が影響を受け，調整ジルコニアクラウンでは摩耗量が多く，破折までの最大荷重が小さかった．ジルコニアの摩耗深さは，咬合設計にも影響された（p＝0.012）．拮抗摩耗は，修復物材料，咬合接触様式，および調整によって影響を受けた．

RESULTS: The resin composite crowns yielded significantly higher mean values for wear area and depth (p < 0.001) and lower fracture forces (p < 0.001). Resin composite surfaces showed increased roughness after TCML while zirconia exhibited smoothened surfaces. The occlusal design significantly impacted wear depth (p = 0.012) and fracture force (p < 0.001). Resin composite crowns with fewer contact points (group RA) showed more wear and lower fracture force. Adjusted resin composite crowns showed increased wear areas and depths (p = 0.009-0.013). For zirconia crowns, the adjustment impacted wear area (p = 0.013), wear depth (p = 0.008), and fracture force (p = 0.006), with adjusted zirconia crowns exhibiting more wear and lower maximum forces until fracture. Zirconia wear depth was also impacted by the occlusal design (p = 0.012). Antagonistic wear was influenced by the restorative material, the occlusal contact pattern, and the adjustment.

結論:

調査した材料は，ジルコニアは調整に大きく影響され，レジン複合材料は接触設計と調整が大きく影響し，性能は大きく異なることがわかった．

CONCLUSIONS: The investigated materials show strongly varying performances with zirconia being significantly influenced by the adjustment, while for resin composites, contact design and adjustment had a major impact.

臨床的関連性:

この結果は，ジルコニアおよびレジン・コンポジット・クラウンの粗さ，摩耗および安定性を改善するために，咬合設計と調整を適合させる必要性を示している．

CLINICAL RELEVANCE: The results show the necessity of adapting occlusal design and adjustment in order to improve roughness, wear, and stability of zirconia and resin composite crowns.