| The preservation and restoration of residual crown and root has been a hot and difficult problem in oral prosthodontics.The factors such as the core material,the ferrule design,the amount of residual teeth,the crown to root ratio and so on can affect the fracture resistance and the prognosis of the endodontically-treated teeth restored with post-and-core system.For supragingival residual teeth,the complete uniform ferrule design,can effectively enhance the fracture strength;however,whether the lingual-lost oblique fracture could be saved and how to adequately restore such oblique fractures still needs to be determined.This in vitro study,which aimed in the oblique fracture roots,evaluated the effect of post materials,dentin collar wrapping,ferrule height and root neck treatment(orthodontic traction or crown lengthening)on the fracture resistance of such roots,so as to guide the clinical treatment of the residual roots.Part 1 Effect of ferrule wrapping on fracture resistance of endodontically treated mandibular premolars restored with two different post-and-core materialsObjective:To evaluate the effect of different post core materials and different ferrule designs on the fracture resistance of endodontically treated mandibular premolars.Material and methods:Thirty-two extracted mandibular first premolars were each sectioned perpendicular to the long axis at a point 2.0 mm occlusal to the buccal cementoenamel junction.The horizontal residual root models were prepared,with the residual root length(15±1.0)mm.All the roots were randomly divided into four groups.Groups A1 and B1 were given 2 mm complete ferrule design;The roots for Groups A2 and B2 were decoronated to create lingual to buccal residual oblique root models,with a 2.0 mm height of the lingual dentine wall coronal to the cemento-enamel junction,and the height of buccal surface at the cemento-enamel junction.Then Groups A2 and B2 were given the incomplete ferrule preparation,with 0.0 mm in buccal surface and 2.0 mm height in lingual surface.Roots in groups A1 and A2 were restored with cast post-and-core system,and those in group B1 and B2 were restored with prefabricated fiber post and core system.After restoration with a cast Co-Cr alloy crown,each specimen was embedded in an acrylic resin block to a height on the root 2.0 mm from the apical surface of the crown margin and loaded to fracture at a 135° angle to its long axis in a universal testing machine.Data were analyzed statistically using two-way ANOVA with Tukey HSD tests and Fisher's test,with a =0.05.Results:Mean failure loads(kN)for A1,A2,B1,B2 Groups were:1.33(S.D.0.19),0.73(0.09),1.04(0.15),1.01(0.21).Two-way ANOVA revealed significant differences for the effect of ferrule lengths(P = 0.000)but no differences for the effect of cervical treatment methods(P = 0.829).The teeth with 2 mm complete ferrule length in group A1 had the highest fracture loads restored with cast post-and-core restoration.However,In contrast,the mean fracture loads for group A2 with a 2.0 mm lingual and no buccal ferrule were lowest(P<0.05).Conclusion:When restored with cast post and core restoration,a 2.0 mm complete ferrule could significantly increase the fracture resistance of endodontically treated mandibular frst premolar.However,if restored with prefabricated fiber post and core system,the effect of ferrule wrapping and the location of ferrule preparation showed no differences on the fracture resistance of endodontically treated roots.The fiber-reinforced dowel-resin core system reduced the severity of the root fractures.Part ? Effect of different ferrule lengths on the fracture resistance of endodontically treated mandibular premolars restored with prefabricated fiber post-and-core system after simulated crown lengthening methodObjective:The purpose of this study was to evaluate the effect of ferrule design on the fracture resistance of endodontically treated mandibular first premolars after simulated crown lengthening method restored with a fiber post-and-core system.Material and methods:Twenty-four extracted and endodontically treated mandibular first premolars were decoronated to create lingual to buccal residual oblique root models,with a 2.0 mm height of the lingual dentine wall coronal to the cemento-enamel junction,and the height of buccal surface at the cemento-enamel junction.The roots were divided randomly into three equal groups.The control group had undergone incomplete ferrule preparation in the cervical root,with 0.0 mm buccal and 2.0 mm lingual ferrule lengths(Group F0).Simulated surgical crown lengthening methods provided ferrule preparations of 1.0 mm(Group CL/F1)and 2.0 mm(Group CL/F2)on the buccal surface,with ferrule lengths of 3.0 mm and 4.0 mm on the lingual surfaces,respectively.After restoration with a glass fiber post-and-core system and a cast Co-Cr alloy crown,each specimen was embedded in an acrylic resin block to a height on the root 2.0 mm from the apical surface of the crown margin and loaded to fracture at a 135°angle to its long axis in a universal testing machine.Data were analyzed statistically using one-way ANOVA with Tukey HSD tests and Fisher's test,with ?= 0.05.Results:Mean fracture loads(kN)for groups F0,CL/F1 and CL/F2 were as follows:1.01(S.D.= 0.26),0.91(0.29)and 0.73(0.19),respectively.One-way ANOVA revealed no significant differences for the effect of ferrule lengths(P = 0.099).The teeth with no buccal ferrule preparation in Group F0 had the highest fractre resistance.In contrast,the mean fracture loads for group CL/F2 with a 2.0 mm buccal and a 4.0 mm lingual ferrule created by simulated crown lengthening methods were lowest.Conclusions:For lingual-to-buccal oblique fractures,increased apical ferrule preparation after simulated surgical crown lengthening method,resulted in decreased fracture resistance of endodontically treated mandibular first premolars.Part ? Effect of different ferrule lengths on the fracture resistance of endodontically treated mandibular premolars restored with prefabricated fiber post-and-core system after simulated orthodontic forced eruption methodObjective:The purpose of this study was to evaluate the effect of ferrule design on the fracture resistance of endodontically treated mandibular first premolars after simulated orthodontic forced eruption methods restored with a fiber post-and-core system.Material and methods:Twenty-four extracted and endodontically treated mandibular first premolars were decoronated to create lingual to buccal residual oblique root models,with a 2.0 mm height of the lingual dentine wall coronal to the cemento-enamel junction,and the height of buccal surface at the cemento-enamel junction.The roots were divided randomly into three equal groups.The control group had undergone incomplete ferrule preparation in the cervical root,with 0.0 mm buccal and 2.0 mm lingual ferrule lengths(Group F0).Simulated orthodontic forced eruption provided ferrule preparations of 1.0 mm(Group OE/F1)and 2.0 mm(Group OE/F2)on the buccal surface and ferrule lengths of 3.0 mm and 4.0 mm on the lingual surfaces,respectively.After restoration with a glass fiber post-and-core system and a cast Co-Cr alloy crown,each specimen was embedded in an acrylic resin block to a height on the root 2.0 mm from the apical surface of the crown margin and loaded to fracture at a 135° angle to its long axis in a universal testing machine.Data were analyzed statistically using one-way ANOVA with Tukey HSD tests and Fisher's test,with a = 0.05.Results:Mean fracture loads(kN)for groups F0,OE/F1 and OE/F2 were as follows:1.01(S.D.= 0.26),0.96(0.25)and 0.76(0.20),respectively.One-way ANOVA revealed no significant differences for the effect of ferrule lengths(P = 0.012)but no differences for the effect of cervical treatment methods(P>0.05).The teeth with no buccal ferrule preparation in Group F0 had the highest fracture resistance.In contrast,the mean fracture loads for group OE/F2 with a 2.0 mm buccal and a 4.0 mm lingual ferrule created by simulated orthodontic forced eruption method were lowest.Conclusions:For lingual-to-buccal oblique fractures,increased apical ferrule preparation after simulated orthodontic forced eruption method,resulted in decreased fracture resistance of endodontically treated mandibular first premolars. |
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