| Background and Objective: The guided veneer restoration procedure involves generation of a target restoration,usually a diagnostic wax-up,and the use of guidance techniques to obtain a definitive restoration that is consistent with the target restoration.The purpose of this experiment is to investigate the accuracy of different guidance techniques in guiding porcelain veneer restorations at each stage of tooth preparation and the morphological match between the final restoration and the target veneer restoration,and to explore the better guidance method applicable to the porcelain veneer restoration technique.Methods:(1)A virtual model was obtained by scanning a maxillary cast with space between the central incisors using intraoral scanning equipment.(2)The virtual model was designed with 11 and 21 porcelain veneers to close the interdental space to obtain a a digital additive veneer wax-up.(3)Twenty casts were 3D printed and randomly divided into 4 groups(5 casts per group containing a total of 10 abutment teeth).Group 1: freehand tooth preparation.Group 2: tooth preparation guided by a three-stage indicator template.Group 3: tooth preparation guided by self-limiting diamond burs.Group 4: tooth preparation guided by a rigid-constraint template.(4)After the preparation of the set-depth indicators in each group and after the completion of tooth preparation,optical scans were performed,and the models after set-depth and tooth preparation were matched with the digital diagnostic wax-up to measure the depth of set-depth markers and the amount of tooth preparation in each group.(5)Using CAD/CAM technology,porcelain veneers were fabricated,bonded on the model and scanned again,the final restoration model was fitted to the diagnostic model,and the morphological differences between the final restoration and the target restoration were measured linearly in each dimension.Results:1.The deviations of the indicator depth in the four groups were(76±19)μm、(95±17)μm、(65±14)μm、(54±15)μm,respectively,with statistical differences(P =0.0016).The deviations of the depth of preparation were(151±22)μm、(129±21)μm、(102±22)μm、(78±17)μm,respectively(P < 0.0001).The loss of tooth tissue was different among different tooth preparation methods,and significant difference was found between them(P < 0.05).2.The cervical third(124 ± 67 μm)and mesial third(85 ± 49 μm)of the definitive restorations were larger in volume than the target restorations,and the incisal third(-124 ± 78 μm)and incisal edge(-400 ± 160 μm)were smaller.The mean absolute deviation in the mesial third was significantly lower than that in the other sites(P<0.05).The restorations in group 4 were the closest to the predesigned wax-up at all sites except the cervical third,and the largest discrepancy was observed in group 2,but no significant differences were found between the groups(P >0.05).Conclusion:1.The accuracy of digital tooth preparation guidance technology is higher than that of traditional non-quantitative tooth preparation guidance technology in all stages of tooth preparation.All four guidance methods in this experiment resulted in additional dental tissue loss during the finishing phase.2.The digital preparation guidance technique does not improve the matching of the final restoration to the morphological contour of the target restoration,with deviations being greatest at the incisal crest and least in the middle third. |
