不同残根处理术式和肩领设计对残根抗折力影响的实验研究

In vitro study evaluating the effect of different subgingival root exposure methods and ferrule designs on fracture resistance of residual root

目的探讨不同残根处理术式(牙冠延长术和正畸牵引术)及不同肩领高度对预成碳纤维桩核修复后残根抗折力的影响。方法将56颗完整的单根管下颌第一前磨牙行根管治疗后,于颊侧釉牙骨质界上1.0 mm处截冠,制备残根模型,随机分为7组,每组8颗。A组为对照组,根颈部不制备牙本质肩领;B、C、D组分别通过模拟牙冠延长术暴露残根颈部断面并制备一定高度的肩领(1.0、2.0、3.0 mm);E、F、G组分别通过模拟正畸牵引术暴露残根颈部断面并制备肩领(1.0、2.0、3.0 mm)。所有残根均采用碳纤维桩核联合铸造全冠修复。试件自全冠颈缘完成线下2.0 mm包埋于自凝塑料中,电子万能试验机以与牙长轴成150°、横梁位移速度1.0 mm·min-1于颊尖顶加载,测定折裂载荷及折裂方式。结果 A^G组试件的折裂载荷依次为(1.13±0.15)、(1.27±0.18)、(1.02±0.11)、(1.05±0.12)、(1.63±0.14)、(1.92±0.19)、(1.93±0.15)kN。残根颈部处理方式和牙本质肩领均对残根的抗折力产生显著的影响,且两因素间存在协同作用(F=33.396,P<0.001);在肩领高度相同时,采用模拟正畸牵引术组牙体的折裂载荷均显著高于采用模拟牙冠延长术组(P<0.001)。各组间折裂方式无统计学差异(P=1.00)。结论采用正畸牵引术暴露残根颈部断面,并制备1.0 mm以上高度的肩领,可以更好地提高残根的抗折力。

Objective To evaluate the effect of different subgingival root exposure methods, namely, crown lengthening or forced eruption, and different ferrule lengths on fracture resistance of a residual root restored with a carbon fiber post-and- core system. Methods Fifty-six extracted endodontically-treated mandibular first premolars were sectioned 1.0 mm coronal to the buccal cementoenamel junction. All the models were divided randomly into seven groups that each consist of eight roots. Group A was given non-ferrule as control. Simulated crown lengthening was performed for the dentin ferrule design in the cervical tooth structure for Groups B, C, and D with a ferrule length of 1.0, 2.0, and 3.0 mm, respectively. Simulated forced eruption was performed with a ferrule length of 1.0, 2.0, and 3.0 mm in the cervical tooth structure for Groups E, F, and G, respectively. After restoration with prefabricated carbon fiber post-and-core system, each specimen was embedded in a self-cured acrylic resin block from 2.0 mm apical to the margins of a cast Ni-Cr alloy crown, then loaded at 150° from the long axis in a universal testing machine at a crosshead speed of 1.0 mm＇min-1 until fracture. Data of failure loads and fracture mode were recorded and analyzed. Results Mean failure loads for Groups A to G were （1.13±0.15）, （1.27±0.18）, （1.02±0.11）, （1.05±0.12）, （1.63±0.14）, （1.92±0.19）, and （1.93±0.15） kN, respectively. The effects of root exposure method and ferrule design differed significantly, and two factors exhibited significant interaction （F=33.396, P〈O.O001）. When the ferrule lengths were the same, fracture loads in the simulated forced erup- tion groups were significantly higher than those of the simu- lated crown lengthening groups （P〈O.O01）. No statistical differences in fracture mode were observed among all groups（P=-I.O0）. Conclusion More than 1.0 mm ferrule placement on the apical crown margin by using forced eruption signifi- cantly increases fracture resistance.