| Objective:The development of material and technologies provides the basis for the minimally invasive veneers. This in vitro study aimed to explore the influence of three factors on the flexural strength of minimally invasive veneers including defect size (grade 1,2,3defect), preparatory width (1mm, 2mm,4mm)and prosthetic material (IPS e.max press porcelain laminate veneers, GC resin veneers):1. Comparing the flexural strength of minimally invasive veneer with different prosthetic material and different defect levels of maxillary central incisor, and observe the failure modes; 2. Comparing flexural strength of minimally invasive porcelain laminate veneer restoration for different prepare widths (1mm,2mm,4mm) of maxillary central incisor all with grade 2 defect, and observe the failure modes.Methods:1.42 extracted human maxillary central incisors were allocated into 6 groups (group 1A,2A,3A,1B,2B,3B) (n=7) to test for 2 variables:defect size and different prosthetic material. The labial surfaces of all teeth were divided into three equal portions by the maximum distance of mesial to distal and incisal to Gingival,the labial surface was divided into 9 regions. Define defect as grade 1,2,3 according to the defect involving 1,2,3 regions (Fig 1-1). gradel,2,3 defect was made for group 1A,1B; 2A,2B; 3A,3B respectively. The preparation was over all 1mm wide and 0.5mm depth with a chamfer margin in each group. Minimally invasive e-max porcelain veneer restorations and minimally invasive resin veneer restorations were completed in the mechanic center.2.21 caries-free human maxillary central incisors were made grade 2 defect and randomly divided into 3 groups (2Aa,2Ab,2Ac group) with 7 samples each. The preparatory width of group 2Aa,2Ab and 2Ac were 1mm, 2mm and 4mm to defect edge respectively. The depth of the preparation was over all 0.5mm with a chamfer margin in each group. Minimally invasive porcelain veneer restorations were completed in the mechanic center. Testing the flexural strength value used the universal testing machine after finishing restorations and luted with resin cement (Rely-X Veneer), observing the failure modes with stereomicroscope, data analysis performed using the SPSS 16.0 software. Groups were compared using the one-way ANOVA.Results:1. Defects size had effect on the flexural strength value of minimally invasive porcelain veneers complex. Mean (SD) flexural strength value of minimally invasive porcelain veneers complex were as follows:grade 1 defect (227.31 N (31.4)) revealed a significantly lower flexural strength value than the grade 2 defect (275.45 N (47.9)) and grade 3 defect (285.20 N (23.5)) (P<0.05), but there is not significant difference between grade 2 defect and grade 3 defect (P> 0.05), The main failure mode was the adhesive failure (71.43%). Defects size had not significant effect on the flexural strength value of minimally invasive resin veneers complex. Mean flexural strength of minimally invasive resin veneer complex from grade 1,2,3 defect were (205.00N (17.5)), (188.86 N (34.3)), (194.29 N (34.4)),the difference from 3 groups was not statistically significant (P> 0.05). Failure mode is fracture of the resin material. The flexural strength was no significant difference in group 1A and 1B. In grade 2.3defect, flexural strength value of minimally invasive porcelain veneer complex (2A,3A) is significantly higher than the value of resin veneer complex (2B,3B).2. Preparatory area had effect on the flexural strength value. Mean (SD) flexural strength value of minimally invasive porcelain veneer complex were as follows:4mm width preparation (368.25 N (33.9)) revealed a significantly higher flexural strength value than the 2mm width preparation (315.21 N (19.3)) and 1mm width preparation (227.31 N (31.4)) (P<0.05), Flexural strength value of 2mm width preparation is higher than the value of group 1mm width preparation,but the difference was not statistically significant (P>0.05). The main failure modes were adhesive failure (38.10%) and mixed failure (38.10%).Conclusions:1. When have 1mm wide preparation for the maxillary central incisor with small corner defect, flexural strength of minimally invasive porcelain veneer complex increases with the defect size,and all mean values obtained were higher than the average occlusal force of the up anterior teeth, could satisfy the need of the daily mastication. Adhesive force is an important factor to flexural strength of minimally invasive porcelain veneer restorations. Flexural strength of minimally invasive resin veneers was not related to the size of defect. The strength of hard resin was important factor to flexural strength of minimally resin veneers restoration. There is a fracture risk of the resin, because of the flexural strength of minimally invasive resin veneers does not exceed the average maximum occlusal force of the up anterior teeth.2. Flexural strength of minimally invasive porcelain veneer complex for maxillary central incisor with grade 2 defect increased with the Preparatory area, and were higher than the average occlusal force of the up anterior teeth. |
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