The role of implant/abutment system on torque maintenance of retention screws and vertical misfit of implant-supported crowns before and after mechanical cycling.

PURPOSE: This study aimed to evaluate the role of the implant/abutment system on torque maintenance of titanium retention screws and the vertical misfit of screw-retained implant-supported crowns before and after mechanical cycling. MATERIALS AND METHODS: Three groups were studied: morse taper implants with conical abutments (MTC group), external-hexagon implants with conical abutments (EHC group), and external-hexagon implants with UCLA abutments (EHU group). Metallic crowns casted in cobalt-chromium alloy were used (n = 10). Retention screws received insertion torque and, after 3 minutes, initial detorque was measured. Crowns were retightened and submitted to cyclic loading testing under oblique loading (30 degrees) of 130 ± 10 N at 2 Hz of frequency, totaling 1 × 106 cycles. After cycling, final detorque was measured. Vertical misfit was measured using a stereomicroscope. Data were analyzed by analysis of variance, Tukey test, and Pearson correlation test (P < .05). RESULTS: All detorque values were lower than the insertion torque both before and after mechanical cycling. No statistically significant difference was observed among groups before mechanical cycling. After mechanical cycling, a statistically significantly lower loss of detorque was verified in the MTC group in comparison to the EHC group. Significantly lower vertical misfit values were noted after mechanical cycling but there was no difference among groups. There was no significant correlation between detorque values and vertical misfit. CONCLUSIONS: All groups presented a significant decrease of torque before and after mechanical cycling. The morse taper connection promoted the highest torque maintenance. Mechanical cycling reduced the vertical misfit of all groups, although no significant correlation between vertical misfit and torque loss was found.

Titanium in dentistry: historical development, state of the art and future perspectives.

Titanium is a metallic element known by several attractive characteristics, such as biocompatibility, excellent corrosion resistance and high mechanical resistance. It is widely used in Dentistry, with high success rates, providing a favorable biological response when in contact with live tissues. Therefore, the objective of this study was to describe the different uses of titanium in Dentistry, reviewing its historical development and discoursing about its state of art and future perspective of its utilization. A search in the MEDLINE/PubMed database was performed using the terms 'titanium', 'dentistry' and 'implants'. The title and abstract of articles were read, and after this first screening 20 articles were selected and their full-texts were downloaded. Additional text books and manual search of reference lists within selected articles were included. Correlated literature showed that titanium is the most used metal in Implantology for manufacturing osseointegrated implants and their systems, with a totally consolidated utilization. Moreover, titanium can be also employed in prosthodontics to obtain frameworks. However, problems related to its machining, casting, welding and ceramic application for dental prosthesis are still limiting its use. In Endodontics, titanium has been used in association to nickel for manufacturing rotatory instruments, providing a higher resistance to deformation. However, although the different possibilities of using titanium in modern Dentistry, its use for prostheses frameworks still needs technological improvements in order to surpass its limitations.

The effect of mechanical cycling and different misfit levels on Vicker's microhardness of retention screws for single implant-supported prostheses.

PURPOSE: The aim of this study was to evaluate the effect of mechanical cycling and different misfit levels on Vicker's microhardness of retention screws for single implant-supported prostheses. MATERIALS AND METHODS: Premachined UCLA abutments were cast with cobalt-chromium alloy to obtain 48 crowns divided into four groups (n = 12). The crowns presented no misfit in group A (control group) and unilateral misfits of 50 µm, 100 µm, and 200 µm in groups B, C, and D, respectively. The crowns were screwed to external hexagon implants with titanium retention screws (torque of 30 N/cm), and the sets were submitted to three different periods of mechanical cycling: 2×10(4) , 5×10(4) , and 1×10(6) cycles. Screw microhardness values were measured before and after each cycling period. Data were evaluated by two-way ANOVA and Tukey's test (p < 0.05). RESULTS: Mechanical cycling statistically reduced microhardness values of retention screws regardless of cycling periods and groups. In groups A, B, and C, initial microhardness values were statistically different from final microhardness values (p < 0.05). There was no statistically significant difference for initial screw microhardness values (p > 0.05) among the groups; however, when the groups were compared after mechanical cycling, a statistically significant difference was observed between groups B and D (p < 0.05). CONCLUSIONS: Mechanical cycling reduced the Vicker's microhardness values of the retention screws of all groups. The crowns with the highest misfit level presented the highest Vicker's microhardness values.

Influence of the implants inclination on the accuracy of the working cast / Influência da inclinação dos implantes na precisão do modelo de trabalho

The aim of this study was to evaluate the influence of the implants inclination on the accuracy of the working cast obtainedby two different pouring techniques. A metallic matrix containing two implants, positioned at 90 and 65 degreesin relation to the alveolar ridge, was submitted to the direct transfer impression technique. In CP group (conventionalpouring - n=10), the impressions were poured with dental stone type IV using the conventional technique. In EP group(experimental pouring - n=10), the analogs were embraced with latex tubes before the first pouring. After sixty minutes,these tubes were removed and the space was filled with the dental stone. The metallic matrix (control group) and thereplicas were evaluated regarding the implant/analog inclination and the vertical misfit between a framework and theimplants/analogs. The data were tabulated and analyzed using analysis of variance (ANOVA) and Tukey test at the 0.05level of significance. Regarding the analog inclination, both experimental groups differed statistically (p<0.05) from thecontrol group only in relation to the leaning analogs. Results demonstrated significant difference (p<0.05) between thecontrol group and the experimental groups when the reading of the vertical misfit was accomplished in the perpendicularimplant/analog with the retention screw in the leaning implant/analog and between the control group and the EP group in the opposite situation.Considering the inclination, perpendicular implants produced more accurate casts independentlyof the plaster pouring technique.

O objetivo deste estudo foi avaliar a influência da inclinação dos implantes na precisão do modelo de trabalho obtidoatravés de duas técnicas distintas de vazamento. Uma matriz metálica contendo dois implantes, posicionados a 90ºe a 65º em relação ao rebordo alveolar, foi submetida à técnica de moldagem de transferência direta. No grupo CP(vazamento convencional û n=10) os moldes foram vazados com gesso pedra tipo VI através da técnica convencional.No grupo EP (vazamento experimental û n=10) os análogos foram envolvidos com tubos de látex antes do primeirovazamento. Após sessenta minutos, os tubos foram removidos e o espaço foi preenchido com nova porção de gesso.A matriz metálica (grupo controle) e as réplicas foram avaliadas com relação à inclinação dos implantes/análogos eà desadaptação vertical entre uma supraestrutura e os implantes/análogos. Os dados foram tabulados e analisadospela análise de variância (ANOVA) e pelo teste de Tukey com nível de significância a 5%. Com relação à inclinaçãodos análogos, ambos os grupos experimentais exibiram diferença estatística (p<0.05) em relação ao grupo controleapenas para os análogos inclinados. Os resultados mostraram diferença significativa (p<0.05) entre o grupo controlee os grupos experimentais quando a desadaptação vertical foi observada no implante/análogo perpendicular com oparafuso de retenção localizado no implante/análogo inclinado e entre o grupo controle e o grupo EP na situaçãooposta. Considerando a inclinação, implantes perpendiculares produzem modelos mais precisos independentementeda técnica de vazamento do gesso.