| ObjectiveIn this study, groups of different thicknesses and a heights of ferrule of endodontically treated premolars in vitro will be designed and be static fracture loaded,in order to investigate the influence of the dentin thickness and height on the fracture resistance, and to provide an experimental basis for the design of ferrule of premolars with fiber post-core and crown in clinic. MethodsSeventy-two single rooted human premolars extracted because of orthodontic treatment were collected in half a year and endodontically treated,then assigned randomly into three groups,which has twenty-four samples in each group.Name the groups by preparing the ferrule heights for Group A:1mm;Group B:2mm and Group C:3mm.Then each group was assigned randomly into three subgroups,which has eight samples in each subgroups.Name the subgroups by preparing the ferrule thickness for Group A1 / B1 / C1: 1 mm in buccal and lingual sides,0.5 mm in mesial and distal sides; Group A2 / B2 / C2: 1.5 mm in buccal and lingual sides,1 mm in mesial and distal sides; Group A3 / B3 / C3: 2 mm in buccal and lingual sides, 1.5 mm in mesial and distal sides. All the teeth were restored with fiber post and resin core and metal full crown.Then all the samples were embedded vertically in autopolymerizing acrylic resin,whose surfaces were 1.5mm below the CEJ.After that,each sample was loaded by the Universal load-testing machine,as the loading location to be 0.5mm below the tooth buccal cusp,the loading direction to be 30 degrees to the long axis,and the speed to be 1.0mm/min. All the fracture dates and modes were noted and analysised with SPSS17.0 software for statistical analysis. Result1. The average fracture loads of Group A/B/C showed a trend of increasing. The minimum average fracture load is group A1, and the max is group C3. Group A1 and A2 showed no statistical difference(P>0.05);groupA1 and A3, A2 and A3 showed statistically difference(P<0.05); The datas of subgroups in group B/C were statistically significant(P<0.05). As to longitudinally compare, group A1 and B1 / C1 were statistically difference(P<0.05),group B1 and C1 showed no statistical differences(P>0.05), A2 /B2/C2 and A3 / B3 / C3 were statistically differences(P<0.05). Two-factor factorial analysis of 9 sets of data, both factor a(thickness of ferrule) and factor b(height of ferrule) are effect on fracture resistance of teeth, and there are interaction between factor a and factor b(P<0.05).2. The fracture patterns of group A and group B1 / C1 are similar,which are above the neck or on the ferrule, The fracture modes of group B2 / C2 / B3 / C3 are mostly below the neck of the tooth,which mostly could not able to restore. ConclusionThere are influences of the thickness and height of ferrule on the fracture resistance of premolars, and they both have interaction.It can get a larger fracture resistance by remaining a higher/thicker ferrule,if there is little thickness/height of ferrule left in clinic. |
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