AIM To investigate a potential cause-effect relationship between dentinal microcracks and fracture resistance of mandibular incisors that had not been endodontically treated. METHODOLOGY Sixty mandibular incisors with circular-shaped canals were selected based on micro-computed tomographic scans to create a homogeneous sample. The cross-sectional images of the specimens were screened to identify and quantify the presence of dentinal microcracks. Then, teeth were embedded in polystyrene resin and subjected to axial compressive loading using a universal testing machine. After fracture, the roots were re-scanned and fractography analysis was performed by inspection of 3D models to verify crack propagation. Spearman's rank correlation was used to assess the correlation between the number of microcracks and force required to fracture. RESULTS Dentinal microcracks were detected in 79% of the specimens (n = 44). The incidence of microcracks varied between teeth from 6% to 42% of the total slices per sample (average of 14 ± 17%). The number of microcracks per sample varied from 0 to 1605, with an average of 412 ± 484 (median = 221 and IQR 25% = 15/75% = 658). The load at failure values varied from 227 to 924 N, with an average of 560.3 ± 168.1 N (median = 561 and IQR 25% = 458/75% = 694). The Spearman correlation coefficient (rho) equalled 0.065. CONCLUSIONS There was no cause-effect relationship between the number of dentinal microcracks and the fracture resistance of nonendodontically treated mandibular incisors. The presence and quantity of microcracks did not make these roots more prone to fracture.

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在实验室环境中，预先存在的微裂纹是否在根部的抗断裂性中起作用？

目的探讨牙本质微裂纹与未经牙髓治疗的下颌切牙的抗断裂性之间的潜在因果关系。方法学基于显微计算机断层扫描，选择了60颗具有圆形根管的下颌切牙，以产生均匀的样本。筛选标本的横截面图像，以识别和量化牙本质微裂纹的存在。然后，将牙齿嵌入聚苯乙烯树脂中，并使用通用测试仪进行轴向压缩载荷。断裂后，对根部进行重新扫描，并通过检查3D模型进行断层分析，以验证裂纹扩展。Spearman等级相关性用于评估微裂纹数与断裂所需力之间的相关性。结果在79％的标本中检出了齿状微裂纹（n = 44）。牙齿之间微裂纹的发生率从每个样本占总切片的6％到42％不等（平均14±17％）。每个样品的微裂纹数量在0到1605之间变化，平均值为412±484（中位数= 221，IQR 25％= 15/75％= 658）。失效值时的负载范围为227 N至924 N，平均为560.3±168.1 N（中位数= 561，IQR 25％= 458/75％= 694）。Spearman相关系数（rho）等于0.065。结论牙本质微裂纹的数量与非牙本质治疗的下颌切牙的抗断裂性之间没有因果关系。微裂纹的存在和数量并没有使这些根更容易断裂。牙齿之间微裂纹的发生率从每个样本占总切片的6％到42％不等（平均14±17％）。每个样品的微裂纹数量在0到1605之间变化，平均值为412±484（中位数= 221，IQR 25％= 15/75％= 658）。失效值时的负载范围为227 N至924 N，平均为560.3±168.1 N（中位数= 561和IQR 25％= 458/75％= 694）。Spearman相关系数（rho）等于0.065。结论牙本质微裂纹的数量与非牙本质治疗的下颌切牙的抗断裂性之间没有因果关系。微裂纹的存在和数量并没有使这些根更容易断裂。牙齿之间微裂纹的发生率从每个样本占总切片的6％到42％不等（平均14±17％）。每个样品的微裂纹数量在0到1605之间变化，平均值为412±484（中位数= 221，IQR 25％= 15/75％= 658）。失效值时的负载范围为227 N至924 N，平均为560.3±168.1 N（中位数= 561和IQR 25％= 458/75％= 694）。Spearman相关系数（rho）等于0.065。结论牙本质微裂纹的数量与非牙本质治疗的下颌切牙的抗断裂性之间没有因果关系。微裂纹的存在和数量并没有使这些根更容易断裂。每个样品的微裂纹数量在0到1605之间变化，平均值为412±484（中位数= 221，IQR 25％= 15/75％= 658）。失效值时的负载范围为227 N至924 N，平均为560.3±168.1 N（中位数= 561和IQR 25％= 458/75％= 694）。Spearman相关系数（rho）等于0.065。结论牙本质微裂纹的数量与非牙本质治疗的下颌切牙的抗断裂性之间没有因果关系。微裂纹的存在和数量并没有使这些根更容易断裂。每个样品的微裂纹数量在0到1605之间变化，平均值为412±484（中位数= 221，IQR 25％= 15/75％= 658）。失效值时的负载范围为227 N至924 N，平均为560.3±168.1 N（中位数= 561，IQR 25％= 458/75％= 694）。Spearman相关系数（rho）等于0.065。结论牙本质微裂纹的数量与非牙本质治疗的下颌切牙的抗断裂性之间没有因果关系。微裂纹的存在和数量并没有使这些根更容易断裂。结论牙本质微裂纹的数量与非牙本质治疗的下颌切牙的抗断裂性之间没有因果关系。微裂纹的存在和数量并没有使这些根更容易断裂。结论牙本质微裂纹的数量与非牙本质治疗的下颌切牙的抗断裂性之间没有因果关系。微裂纹的存在和数量并没有使这些根更容易断裂。