探讨隐裂牙的裂纹尺寸对于其折裂模式及临床风险的影响。

将纳入的50颗上颌前磨牙简单随机抽样法分为5组，前4组通过对试样进行测量调磨制备成隐裂牙模型，调模为颊尖斜度为59°、腭尖斜度为50°。隐裂牙模型根据不同的预裂纹尺寸进行分组，将牙冠近远中边缘嵴最外缘中点间的距离设为裂纹长度（a），该两点所在平面至近中釉牙骨质界最凸点的距离为裂纹深度（h），第1组至第4组的裂纹长度及宽度分别为（a/3-h/2）、（2a/3-h/2）、（a/3-h）、（2a/3-h）。第5组不做处理即对照组。所有试样采用压应力实验，记录抗折力、折裂模式及临床风险分级。采用单因素t检验比较各组间最大抗折力，利用统计图表对折裂模式分析，使用非参数秩和检验统计折裂试样临床风险等级。检验水准α=0.05。

每组抗折力分别为（1126 ± 126）、（974 ± 159）、（1114 ± 240）、（608 ± 105）和（1205 ± 216）N。第2组与第4组最大抗折力与其余各组比较差异均有统计学意义（P<0.05），其余各组间比较无统计学意义。对于折裂模式：所有试验组多发生偏向腭侧的斜折，每组冠折与冠根折各占的比例分别50%~50%、40%~60%、20%~80%、0~100%、100%~0。对于临床风险评估：所有隐裂牙组（第1~4组）同对照组（第5组）相比差异均有统计学意义（P<0.05）。对于隐裂牙组，第1组同第4组间比较差异有统计学意义（P = 0.003），其余各组间比较差异无统计学意义。第1组和第5组试样折裂后均可保留，第2组和第3组均有20%的试样发生了不可保留性冠根折。第4组临床评估风险最大，40%的试样为不可保留性的冠根折，并且折裂部位多位于根尖区。

隐裂牙的抗折力显著低于正常牙，易发生折裂。并且隐裂牙的折裂情况同其裂纹尺寸有着密切关系，裂纹尺寸越深越宽，越易发生冠至根尖区方向的折裂，临床风险逐渐增加。

To explore the fracture patterns of cracked tooth syndrome (CTS) models with different crack size in vitro, and to explore the clinical risk of cracked teeth.

A total of 50 maxillary premolars were randomly divided into five groups by simple random sampling. The first four groups were used as cracked tooth models, which was adjusted to the buccal cusp inclination 59° and the palatal cusp inclination 50° by cusp inclination measurements and grinding. All the cracked tooth models were grouped according to the set pre-cracked size, i.e., the distance between the center points of the outermost edge of the mesio-distal middle margin ridge was set to the crack length a, and the distance between the plane where the two points were located and the most convex point of the cemento-enamel junction of the mesial adjacent surface was the crack depth h. The four groups were divided into (a/3-h/2) , (2a/3-h/2) , (a/3-h) , (2a/3-h) , with Group Ⅴ as blank control. All samples were subjected to compressive stress tests to record the anti-folding force, fracture mode and clinical risk classification. Single factor t-test was used to compare the fracture resistance of each group. Statistical chart was used to analyze the fracture mode. Nonparametric rank sum test was used to calculate the clinical risk level of fracture samples. The significant level was set at 0.05 (α = 0.05) .

The fracture resistance of the four groups was (1126 ± 126) N, (974 ± 159) N, (1114 ± 240) N, (608 ± 105) N, (1205 ± 216) N, respectively. There was a statistical difference between the maximum resistance of group Ⅱ, Ⅳ and the other groups (P<0.05) . No significant difference was observed among the other groups. For the fracture pattern, more palatal oblique fracture rather than buccal fracture was observed in all experimental groups. The proportion of crown and crown-root fracture for each group was (50%~50%) , (40%~60%) , (20%~80%) , (0~100%) , (100%~0) , respectively. For clinical risk assessment, there were significant statistical differences between all CTS model groups (groups Ⅰ-Ⅳ) and the control (group Ⅴ) (P<0.05) . For CTS model groups, there was a statistical difference between group Ⅰand Ⅳ (P_1-4 = 0.003) . No significant difference was observed among the other groups. The samples of group Ⅰ may be reserved. A non-reservable crown-root fracture may occur to 20% samples of group Ⅱ and III, while the risk for group Ⅳ was 40%, with a high crack proportion in the apical area.

The teeth with CTS were easier to fracture than normal teeth due to their much lower anti-crack ability. The fracture pattern of teeth with CTS seemed to be related to the crack size. The deeper and wider the crack, the easier the crown-root fracture, the higher the clinical risk. gradually increases on this account.