Influence of abutments and porcelain firing on strains around implants

It is speculated that porcelain firing cycles increase marginal misfit. This effect is imagined to increase strains around implants and it is supposed to be decreased by using abutments. Objectives: to evaluate the influence of porcelain firing cycles and the use of abutments on marginal misfit and on strains around implants. Methods: 20 titanium frameworks were fabricated simulating 3-element fixed partial dentures retained by 2 implants. Two groups were formed: conic abutment group presented 10 structures screwed to Branemark-type conic multi-unit abutments and UCLA group presented 10 structures screwed directly to the implants using non-engaging multi-unit UCLA cylinders. Frameworks were submitted to porcelain firing cycle simulation to evaluate marginal misfit and strains around implants. Strains were analyzed by strain gauges and misfit was analyzed by an optical microscope after each firing cycle and the results were confronted to the as-cast situation - control. The strains values were correlated with misfit values according to one-screw test at the as cast situation and after each firing cycle. Multivariate analysis was applied in sub divided parcel scheme and treatments were considered as parcel and firing cycles as sub parcel. Tukey's test was employed to multiple comparisons with 5% significance level. Results: There was no significant difference (p=0.601) on strains around implants due to the use of abutment (conic abutment: 580.06 ± 253.93gf; UCLA: 665.35 ± 173.99gf). A decrease on strains was observed due to firing cycles. Misfit analysis presented interaction between treatment groups and firing cycles (p=0.002). Lower misfit means occurred before frameworks were exposed to firing cycles (conic abutment: 118.07 ± 58.61µm; UCLA: 83.93 ± 25.63 µm). Conclusion: the presence of conic abutment on 3 elements partial fixed prosthesis cast in commercially pure titanium did not decrease strains around implants and porcelain firing cycles increased marginal misfit and decreased strains around implants.