Study Of Improving The Retention Of Short Cement-retained Abutment

Objective: Cement-retained implant-supported prostheses havebecome popular and exhibit potential advantages over screwretained restorations. These advantages include elimination ofprosthesis screw loosening, better esthetics,easier control ofocclusion, simplicity, lower cost, and passivity of fit. Because of thedesire to reduce the cost and maintenance associated withscrew-retained restorations, cement-retained restorations havegained favor among many practitioners. but it's utility is usuallylimited by inadequate occlusocervical dimension. To settle thisproblem, this study abstract experience from traditional prothetictheory,try to improve the retention of cement-retained abutment byredesign the shape and surface conditioning of abutment, in orderthat cement-retained abutment can be use even whenocclusocervical dimension is insufficient. The purpose of this studywas to test the retention of modified short abutment so that theeffect of redesign be tested.Materials and methods:63 BLB 4mm standard solid abutments areused. 3 of the abutments remain no modified as standard contrastgroup(SC) , other 60 are devided into 5 groups as: solidabutment;with 0 degree cavity in the middle of abutment producedby milling;with 0,5,8degree cavity in the middle of abutmentproduced by spark erosion technique;each group contains 12abutment in height of 3mm, 2.5mm ,2mm ,1mm. These abutmentswere mounted in acrylic resin blocks. master wax pattern wasdesigned on it, 5mm diameter wax loops added to the occlusalsurface vertically to allow for subsequent retention testing. the 63wax patterns were embedded in phosphate-bonded investment andcasted with Ni-Cr alloy. Castings were sand-blasted and inspectedfor surface irregularities using a stereomicroscope at 10×abutment shape. 0 degree abutments have the highest mean tensilestrengths while There was no statistical difference in the meantensile resistance to dislodgement between 5 degree and 8degree.Inspected under SEM, the surface of milled cancavity issmooth and no obvious change found before and after pull-out test.while the surface of spark erosion is rough and there are risinecomposite particles remained. The sand-blasted surface have meanweb-look change.more finer than that of spark erosion.Conclusions: The retention values of castings cemented to theresults suggest that each redesigned group can improve mean tensileresistance to dislodgements signifficently.the mean tensile strengthswere higher than that of 4mm standard abutment even when theheight of abutments were only 1mm, which can meet clinical needs.mean tensile strength was significantly different between differentsurface of spark erosion and milling with the same abutment shape.This trial improve the retention through making cancavity in themiddle of abutment and surface conditioning methods in the light oftraditional theory. And the result exhibited signifficent effect.sparkerosion has been reported as a method of improving the accuracy ofretainer ,it has not been reported as a method of surfaceconditioning in the literature.Computer controlled spark erosiontechnique can both improve the accuracy between abutment andcastings and rough the surface of retainers, its utility in implantaspect is worthy of more study.