Mulvay P G, Abbott P V
School of Dentistry, University of Western Australia.
Aust Dent J. 1996 Apr;41(2):134-9. doi: 10.1111/j.1834-7819.1996.tb05927.x.
Preparation of an endodontic access cavity through a full crown may affect its retention. This study was undertaken to investigate the effects on molar crown retention of endodontic access cavities and their subsequent restoration. Thirty human molars were mounted in resin, crown preparations were cut and their surface areas were determined. Vented metal copings were cemented with zinc phosphate and the forces required to displace each coping were measured using a tensile-testing machine. The copings were recemented, access cavities were cut and their surface areas determined prior to the displacement forces being re-measured. The copings were recemented, assigned to two groups, and the access cavities were restored--Group 1 with amalgam; Group 2 with glass ionomer (GIC). Displacement forces were re-measured and the copings were recemented. The occlusal margins of the access cavities were bevelled and restored again prior to displacement forces being remeasured. Mean displacement forces were - Group 1: Original (kg force), 37.86 +/- 3.97; After access cavity, 29.28 +/- 3.22; Amalgam, 50.21 +/- 4.71; Amalgam + bevel, 46.45 +/- 6.21. Group 2: Original, 42.77 +/- 4.49; After access cavity, 39.25 +/- 5.91; GIC, 48.11 +/- 3.55; GIC + bevel, 39.63 +/- 5.31. Statistical analyses with paired t tests showed that retentive values with access cavities were significantly lower than with intact crowns. Amalgam or GIC restorations increased retention beyond original values, significantly with amalgam. Bevelled occlusal margins decreased retention of crowns with restored access cavities but this was not significantly different from the original values. A significant relationship existed between total surface areas of the crown preparations, areas of the occlusal tables, and retentive values for crowns without access cavities. The access cavity area, as a proportion of the total area of the preparation, was related to the decrease in retention.
通过全冠制备牙髓治疗入口洞形可能会影响其固位。本研究旨在调查牙髓治疗入口洞形及其后续修复对磨牙冠固位的影响。将30颗人磨牙固定在树脂中，制备牙冠并测定其表面积。用磷酸锌水门汀粘结有排气孔的金属冠套，使用拉伸试验机测量使每个冠套移位所需的力。重新粘结冠套，制备入口洞形并测定其表面积，然后重新测量移位力。重新粘结冠套，分为两组，对入口洞形进行修复——第1组用银汞合金；第2组用玻璃离子水门汀（GIC）。重新测量移位力并重新粘结冠套。在重新测量移位力之前，将入口洞形的咬合边缘制成斜面并再次修复。平均移位力——第1组：原始（千克力），37.86±3.97；制备入口洞形后，29.28±3.22；银汞合金修复后，50.21±4.71；银汞合金修复+斜面，46.45±6.21。第2组：原始，42.77±4.49；制备入口洞形后，39.25±5.91；GIC修复后，48.11±3.55；GIC修复+斜面，39.63±5.31。采用配对t检验进行统计分析表明，有入口洞形时的固位值显著低于完整牙冠时。银汞合金或GIC修复可使固位力超过原始值，银汞合金修复显著提高。有修复入口洞形的牙冠，斜面咬合边缘会降低其固位力，但与原始值无显著差异。牙冠制备的总面积、咬合面面积与无入口洞形牙冠的固位值之间存在显著关系。入口洞形面积占制备总面积的比例与固位力降低有关。
