Fracture resistance of extensive bulk-fill composite restorations after selective caries removal

Abstract This study evaluated the effect of selective carious tissue removal on the fracture strength and failure mode of composite restorations in molars presenting only the buccal cusps. Deep cavities were prepared on the occlusal surface, and the lingual cusps were removed. Carious lesions in the middle of the pulpal wall were artificially induced with acetic acid (pH = 4.5) for 35 days. The demineralized dentin was left intact or was completely removed prior to restoration with a bulk-fill composite (n = 10). Images of the specimens were obtained by optical coherence tomography (OCT) before and after the caries induction/removal. The mechanical resistance to fracture by axial compressive loading and the failure type and extension were determined. The pulpal wall/composite interface of the fractured specimens was analyzed by OCT. The data were analyzed for significance with t-tests (α = 0.05). The deepest cavities and a more frequent occurrence of pulpal exposure were observed more often for non-selective carious tissue removal. The protocol of carious tissue removal did not affect the fracture strength (p = 0.554). An increased occurrence of catastrophic failures involving the roots was observed for non-selective carious tissue removal. Some occurrences of restoration displacement or cracks throughout the resin-dentin were observed only for the selective carious tissue approach. Selective carious tissue removal is a feasible approach to extensively damaged teeth since it reduced the occurrence of pulpal exposure and root fractures, without compromising the fracture strength.

摘要 本研究评估了选择性龋坏组织去除法（selective carious tissue removal）对仅残留颊尖的磨牙复合树脂修复体的断裂强度与失效模式的影响。研究人员在牙合面制备深龋洞，随后去除舌侧牙尖。采用乙酸（pH=4.5）人工诱导牙髓壁中部形成龋损，诱导时长为35天。将脱矿牙本质保留原位，或在使用大块充填复合树脂（bulk-fill composite）修复前完全清除脱矿牙本质，每组样本量为10（n=10）。分别在龋损诱导/去除前后，通过光学相干断层扫描（optical coherence tomography, OCT）获取试件图像。测定试件在轴向压缩载荷下的抗断裂性能、失效类型及失效扩展范围。对断裂试件的牙髓壁-复合树脂界面进行光学相干断层扫描分析。采用t检验（α=0.05）对数据进行显著性分析。非选择性龋坏组织去除法（non-selective carious tissue removal）组的龋洞更深，牙髓暴露发生率更高。不同龋坏组织去除方案对修复体断裂强度无显著影响（p=0.554）。非选择性龋坏组织去除法组出现累及牙根的灾难性失效的概率更高。仅在选择性龋坏组织去除法组中观察到修复体移位或树脂-牙本质界面出现裂纹的情况。选择性龋坏组织去除法是治疗广泛受损患牙的可行方案，该方法可降低牙髓暴露与牙根断裂的发生率，且不会损害修复体的断裂强度。