不同洞型的离体牙根管治疗术后的抗折力与折裂模式的研究

Study of fracture resistance and failure pattern of endodontically treated teeth with different cavities in vitro in root canal therapy

目的量化研究3种典型洞型的离体牙根管治疗术后抗折力的关系,并对折裂模式进行评价。方法离体下颌前磨牙40个,随机等分为4组。A组:不作任何处理作为空白对照,B、C、D组制备不同洞型(牙合面洞、邻-牙合面洞、邻-牙合-邻面洞)并进行根管治疗术。万能测试仪加载头与牙长轴成45°角,以1 mm/min速度加载至牙齿折裂作为该牙的最大抗折力。将折裂模式分为"可修"和"不可修"2级,盲法评价,Stata 10.0软件数据统计。结果各组的最大抗折力分别为870.3±313.4,600.2±224.0,493.5±102.5和(262.6±100.0)N。秩和检验,差异有统计学意义(F=23.80,P=0.000 0)。以A组完整牙的抗折力为100%,B、C、D组抗折力分别降低到69.0%、56.7%、30.2%。各组均有折裂发生,"不可修"的折裂发生在A组和B组(分别为2和3)。结论根管治疗术后的牙齿抗折力会降低。牙齿折裂与否主要取决于外力的大小,而不是牙齿的状态。牙冠没有明显破坏时,一旦发生折裂可能累及牙根。

Objective This in vitro study quantified the relationship in root canal therapy between fracture resistance of teeth in vitro and three typical cavities of teeth,and evaluated the failure pattern.Methods Forty mandibular premolars were randomly divided into four groups.Group A was treated with nothing and served as control group.Group B,C,D were for preparation of three different cavities(occlusal,mesio-occlusal and mesio-occlusal-distio cavities) and were endodontically treated.A compress load given by an Instron machine was applied at the speed of 1 mm/min 45° to the long axis of the teeth until fracture.The failure pattern can be classified as 'reparable' and 'irreparable' with blind evaluation.Data were analyzed by Stata 10.0 software.Results The maximum fracture resistances of each group are(870.3±313.4)N,(600.2±224.0) N,(493.5±102.5)N and(262.6±100.0)N.There are significant differences among these groups in Rank sun test(F=23.80,P=0.0000).If the fracture resistance of group A with intact teeth was 100%,then the fracture resistances of group B,C,D were reduced to 69.0%,56.7%,30.2%,respectively.Tooth fracture occurred in every group.Irreparable failure patterns happened in group A and B(2,3respectively).Conclusions The fracture resistance of tooth reduced after root canal therapy.Tooth fracture largely depends on the load,not on the tooth state.When the crown has no significant damage,the root may be subjected to fracture.