Evaluation Of Marginal Adaptation Of Zirconia Ceramic Crowns After Proximal Box Elevation Technique In Subgingival Defects:An In Vitro Study

ObjectivesTo evaluated the marginal adaptation of Zirconia ceramic crown in deep proximal subgingival defects after proximal box elevation(PBE).Materials and methodsEight intact,caries-free human molars were collected and prepared according to the criterion of Zirconia ceramic crown,settled margins to 1mm above the Cemento-Enamel Junction(CEJ),and polished with 25?m diamond bur.Then we prepared mesial and distal proximal boxes with the size of 4mm(in mesio-distal direction)×2mm(in bucco-lingual direction),and located margin to 2 mm beneath CEJ.One of the proximal boxes was elevated with Beautifil Flow Plus(SHOFU)and BeautiBond(SHOFU)to 1mm above the CEJ,and polished with Super-Snap Disk(SHOFU),then serves as group PBE;the other group boxes served as control group1,and named group subgingival defect;the buccal and lingual margins of crowns served as control group2,and named group buccal and lingual margins.After direct scanning impression,crowns were designed and made by computer.We took the probing with modified United States Public Health Service(USPHS)criteria,which marginal quality was classified as A,B,C and D.The silicone rubber gap impression which made by Honigum Light and MixStar Heavy,was evaluated the marginal shape with“fit”and“unfit”,and measured with criterion of AMD,MG,IG-400?m and O&U by sereomicroscope(×100).Statistical analysis was performed by SPSS20.0(USA).Results1.All the probing dates of USPHS were grade A.We divided grade A into grade A1 and grade A2,then found the percent of grade A1 in group PBE is 81.25%,and a statistically difference between others groups.2.3 special cases found in marginal shape assessment,2 cases in group PBE and 1case in group buccal and lingual margins,and served as“step edge”:when the probing dates of USPHS is perfect(A1),the evaluation of stereomicroscope found that the crown edge completely covered the shoulder edge.3.The dates of group PBE were less than other's,and a statistically difference between the group PBE and group subgingival defect,group PBE and group buccal and lingual margins were found in the value of AMD(P<0.05).4.No statistically significant difference of group subgingival defect and group buccal and lingual margins was observed(P>0.05).The dates of group buccal and lingual margins,except for the value of IG-400?m,always higher than group subgingival defect.5.There was no difference between the probing and silicone rubber gap impression when evaluated the marginal shape(P_?>0.05).A high consistency between the probing and silicone rubber gap impression in group subgingival defect and group buccal and lingual margins(Kappa?0.75),and low consistency in group PBE(Kappa=0.375<0.4,P_K>0.05).6.The A1 and A2 corresponding numerical value of silicone rubber gap impression had a statistically difference in AMD,MG,IG-400?m and O&U of group PBE and AMD and MG of group subgingival defect.Conclusions1.Within the limitations of this study,zirconia ceramic crown in deep proximal subgingival defects with PBE--bonded by BeautiBond,filled by Beautifil Flow Plus and finished by Super-Snap Disks--had no negative impact on marginal adaption.2.The“step edge”which the crown edge completely covered the shoulder edge can be observed in zirconia ceramic crown with PBE.3.In order to acquired perfect marginal adaption,we should pay more attention to adapt to anatomical structures,such as root furcation anatomy during the teeth preparation.