Analysis of implant-supported cantilever fixed partial denture: An in vitro comparative study on vertical misfit, stress distribution, and cantilever fracture strength.

PURPOSE: To evaluate the vertical misfit, stress distribution around dental implants, and cantilever fracture strength of 3-unit implant-supported cantilever fixed partial dentures (FPDs) using frameworks made from different materials and manufacturing techniques. MATERIALS AND METHODS: Forty FPDs were fabricated and divided into 5 groups (n = 8) based on the framework material used: LAS Co-Cr (Conventional casting-laser welding); TIG Co-Cr (Conventional casting -TIG welding); OP Co-Cr (Conventional casting-one-piece); CAD Co-Cr (CAD-CAM); and CAD Zr (CAD-CAM ZrO2 ). The vertical misfit was evaluated before porcelain application (T1) and before (T2), and after thermomechanical cycling (T3) by stereomicroscopy. Cantilever fracture strength was tested with a 50 kN (5000 kgf) load cell at a crosshead speed of 0.5 mm/min. Qualitative and quantitative photoelastic analysis was performed to evaluate stress distribution at seven specific points in five FPDs (n = 1/group) subjected to occlusal loading. RESULTS: Only the molar showed interaction among the three factors (G × S × T; F(20.932) = 1.630; p = 0.044). Thermomechanical cycling (T2 vs. T3) had a significant effect on intra-group vertical misfit in molar, especially in LAS Co-Cr (Δ = 5.87; p = 0.018) and OP Co-Cr (Δ = 5.39; p = 0.007), with no significant effect in premolar (p > 0.05). Ceramic application combined with thermomechanical cycling (T1 vs. T3) caused a significant intra-group increase in vertical misfit in all groups, both in the molar and premolar (p < 0.05). OP Co-Cr was associated with greater vertical misfit and stress concentration. Frameworks manufactured by the CAD-CAM system exhibited lower vertical misfit and better stress distribution. FPDs with metal frameworks (>410.83 ± 72.26 N) showed significantly higher fracture strength (p < 0.05) than zirconia (277.47 ± 39.10 N), and the first signs of ceramic veneering fracture were observed around 900 N. CONCLUSIONS: FPDs with frameworks manufactured using a CAD-CAM system appear to be associated with lower vertical misfit and better stress distribution, although the section of the frameworks followed by welding may be a viable alternative. In addition, metal frameworks exhibit high fracture strength.

Evaluation of misfit and stress distribution in implant-retained prosthesis obtained by different methods.

This study evaluated the vertical misfit, passivity, and stress distribution after tightening the screws of different prosthesis. Two implants were used to simulate the rehabilitation of partially edentulous mandible space from the second premolar to the second molar. 40 three-element screw-retained fixed dental prosthesis with distal cantilever were fabricated and divided into four groups according to the method of production of framework (n = 10): G1 = conventional casting one-piece framework, G2 = conventional casting sectioned and laser welding, G3 = conventional casting sectioned and tungsten inert gas (TIG) welding and G4 = framework obtained by CAD/CAM (computer-aided design/computer-aided manufacturing) system. The vertical misfits (both screws tightened) and the passive fit (one screw tightened) were measured under a comparator optical microscope. The data was submitted to Shapiro-Wilk test to enable comparison with ANOVA followed by Tukey with Bonferroni adjust (α = .05). The qualitative analysis of the stress distribution was performed by the photoelastic method. The vertical misfit (both screws tightened) of the G2 (24 µm) and G3 (27 µm) were significantly higher than G4 (10 µm) (p = 0,006). The passive fit (for the non-tightened) of the G1(64 µm) and G3 (61 µm) were significantly higher than the G4 (32 µm) (p=0,009). G1 showed high stress between the implants in the photoelastic analysis and G4 presented lower stress. In conclusion, CAD/CAM method results in less vertical misfit, more passivity, and consequently better stress distribution to the bone.

Evaluation of misfit and stress distribution in implant-retained prosthesis obtained by different methods

Abstract This study evaluated the vertical misfit, passivity, and stress distribution after tightening the screws of different prosthesis. Two implants were used to simulate the rehabilitation of partially edentulous mandible space from the second premolar to the second molar. 40 three-element screw-retained fixed dental prosthesis with distal cantilever were fabricated and divided into four groups according to the method of production of framework (n = 10): G1 = conventional casting one-piece framework, G2 = conventional casting sectioned and laser welding, G3 = conventional casting sectioned and tungsten inert gas (TIG) welding and G4 = framework obtained by CAD/CAM (computer-aided design/computer-aided manufacturing) system. The vertical misfits (both screws tightened) and the passive fit (one screw tightened) were measured under a comparator optical microscope. The data was submitted to Shapiro-Wilk test to enable comparison with ANOVA followed by Tukey with Bonferroni adjust (α = .05). The qualitative analysis of the stress distribution was performed by the photoelastic method. The vertical misfit (both screws tightened) of the G2 (24 μm) and G3 (27 μm) were significantly higher than G4 (10 μm) (p = 0,006). The passive fit (for the non-tightened) of the G1(64 μm) and G3 (61 μm) were significantly higher than the G4 (32 μm) (p=0,009). G1 showed high stress between the implants in the photoelastic analysis and G4 presented lower stress. In conclusion, CAD/CAM method results in less vertical misfit, more passivity, and consequently better stress distribution to the bone.

Resumo Neste estudo foi avaliado desajuste vertical, a passividade e a distribuição de tensões após o aperto dos parafusos de diferentes próteses. Dois implantes foram usados ​​para simular a reabilitação do espaço edêntulo da mandíbula do segundo pré-molar ao segundo molar. Quarenta próteses dentárias fixas parafusadas de três elementos com cantilever distal foram confeccionadas e separadas em quatro grupos de acordo com o método de obtenção da infraestrutura (n = 10): G1 = fundição convencional estrutura monobloco, G2 = fundição convencional seccionada e soldagem a laser, G3 = fundição convencional seccionada e soldagem com gás inerte de tungstênio (TIG) e G4 = infraestrutura obtida pelo sistema CAD / CAM (computer-aided design/computer-aided manufacturing). Os desajustes verticais com ambos os parafusos apertados e os desajustes relativos à avaliação de passividade com um parafuso apertado foram medidos com microscópio comparador óptico. Os dados foram submetidos ao teste de Shapiro-Wilk para comparação com ANOVA seguida de ajuste de Tukey com Bonferroni (α = 0,05). A análise qualitativa da distribuição de tensões foi realizada pelo método fotoelástico. G2 (24 μm) e G3 (27 μm) apresentaram valores significativamente maiores que G4 (10 μm) (p = 0,006) de desajuste vertical (ambos os parafusos apertados). Os valores de desajustes nos G1 (64 μm) e G3 (61 μm), do lado não apertado, foram significativamente maiores que no G4 (32 μm) (p = 0,009). G1 apresentou maior tensão entre os implantes na análise fotoelástica e G4 apresentou menor tensão. O método CAD/CAM resultou em menor desajuste, maior passividade e melhor distribuição de tensões no osso.

Photoelastic analysis of mandibular full-arch implant-supported fixed dentures made with different bar materials and manufacturing techniques.

PURPOSE: To compare the stress distribution of mandibular full dentures supported with implants according to the bar materials and manufacturing techniques using a qualitative photoelastic analysis. MATERIAL AND METHODS: An acrylic master model simulating the mandibular arch was fabricated with four Morse taper implant analogs of 4.5×6mm. Four different bars were manufactured according to different material and techniques: fiber-reinforced resin (G1, Trinia, CAD/CAM), commercially pure titanium (G2, cpTi, CAD/CAM), cobalt­chromium (G3, Co-Cr, CAD/CAM) and cobalt­chromium (G4, Co-Cr, conventional cast). Standard clinical and laboratory procedures were used by an experienced dental technician to fabricate 4 mandibular implant-supported dentures. The photoelastic model was created based on the acrylic master model. A load simulation (150N) was performed in total occlusion against the antagonist. RESULTS: Dentures with fiber-reinforced resin bar (G1) exhibited better stress distribution. Dentures with machined Co-Cr bar (G3) exhibited the worst standard of stress distribution, with an overload on the distal part of the posteriors implants, followed by dentures with cast Co-Cr bar (G4) and machined cpTi bar (G2). CONCLUSION: The fiber-reinforced resin bar exhibited an adequate stress distribution and can serve as a viable alternative for oral rehabilitation with mandibular full dentures supported with implants. Moreover, the use of the G1 group offered advantages including reduced weight and less possible overload to the implants components, leading to the preservation of the support structure.

Influence of Temporary Cements on the Bond Strength of Self-Adhesive Cement to the Metal Coronal Substrate

This research evaluated the influence of temporary cements (eugenol-containing [EC] or eugenol-free [EF]) on the tensile strength of Ni-Cr copings fixed with self-adhesive resin cement to the metal coronal substrate. Thirty-six temporary crowns were divided into 4 groups (n=9) according to the temporary cements: Provy, Dentsply (eugenol-containing), Temp Cem, Vigodent (eugenol-containing), RelyX Temp NE, 3M ESPE (eugenol-free) and Temp Bond NE, Kerr Corp (eugenol-free). After 24 h of temporary cementation, tensile strength tests were performed in a universal testing machine at a crosshead speed of 0.5 mm/min and 1 kN (100 kgf) load cell. Afterwards, the cast metal cores were cleaned by scraping with curettes and air jet. Thirty-six Ni-Cr copings were cemented to the cast metal cores with self-adhesive resin cement (RelyX U200, 3M ESPE). Tensile strength tests were performed again. In the temporary cementation, Temp Bond NE (12.91±2.54) and Temp Cem (12.22±2.96) presented the highest values of tensile strength and were statistically similar to each other (p>0.05). Statistically significant difference (p<0.05) was observed only between Provy (164.44±31.23) and Temp Bond NE (88.48±21.83) after cementation of Ni-Cr copings with self-adhesive resin cement. In addition, Temp Cem (120.68±48.27) and RelyX Temp NE (103.04±26.09) showed intermediate tensile strength values. In conclusion, the Provy eugenol-containing temporary cement was associated with the highest bond strength among the resin cements when Ni-Cr copings were cemented to cast metal cores. However, the eugenol cannot be considered a determining factor in increased bond strength, since the other tested cements (1 eugenol-containing and 2 eugenol-free) were similar.

Resumo Esta pesquisa avaliou a influência dos cimentos temporários (contendo eugenol [CE]ou livre de eugenol[LE]) na resistência à tração de copingsde Ni-Cr fixados com cimento resinoso auto-adesivo sobre substrato coronário metálico. Trinta e seis coroas provisórias foram divididas em 4 grupos (n=9) de acordo com os cimentos temporários: Provy, Dentsply (contendo eugenol), Temp Cem, Vigodent (contendo eugenol), RelyXTemp NE, 3M ESPE (livre de eugenol) andTemp Bond NE, KerrCorp (livre de eugenol). Após 24 h da cimentação temporária, testes de resistência à tração foram realizados em uma máquina universal de ensaios, com velocidade de 0,5 mm/min. e célula de carga de 1kN (100 kgf). Em seguida, os núcleos metálicos fundidos foram limpos por meio de raspagem com cureta ejatos de ar. Trinta e seis copings de Ni-Cr foram cimentados sobre os núcleos metálicos com cimento resinoso auto-adesivo (RelyX U200, 3M ESPE). Testes de resistência à tração foram novamente realizados. Na cimentação provisória, Temp Bond NE (12,91±2,54) e Temp Cem (12,22±2,96) apresentaram os maiores valores de resistência à tração e foram estatisticamente semelhantes entre si (p>0,05). Diferença estatisticamente significante (p<0.05) foi observada apenas entre Provy (164,44±31,23) e Temp Bond NE (88,48±21,83)após cimentação dos copingsdeNi-Cr com cimento resinoso auto-adesivo. Além disso, Temp Cem (120,68±48,27) e RelyX Temp NE (103,04±26,09) mostraram valores intermediários de resistência à tração. Em conclusão, o cimento temporário contendo eugenol, Proxy, foi associado com a mais alta resistência de união do cimento resinoso, quando os copingsde Ni-Cr foram cimentados sobre os núcleos metálicos fundidos. Entretanto, o eugenol não pode ser considerado como um fator determinante no aumento da resistência de união, já que outros cimentos testados (1 contendo eugenol e 2 livres de eugenol) foram semelhantes.

Importance of a distal proximal contact on load transfer by implant-supported single adjacent crowns in posterior region of the mandible: a photoelastic study.

OBJECTIVE: This study aimed to evaluate the importance of a distal proximal contact on the load transfer to the posterior region of the mandible by non-splinted adjacent implant-supported crowns using photoelastic stress analysis. MATERIAL AND METHODS: A rectangular model (68x30x15 mm) was made of polymethylmethacrylate resin to simulate half of the mandibular arch. One model was completed with resin replicas representing the first premolar and second molar and with two 3.75 mm dia.x11 mm internal hexagon threaded implants replacing the second premolar and first molar. The other model was manufactured in the same way but without the second molar. Both models were duplicated using photoelastic resin. The roots of the teeth replicas were covered with a layer of polyether impression material to simulate the periodontal ligament. Two different vertical loads were applied to the crowns as follows: 1 - single static point load alternately applied to the crowns replacing the second premolar and first molar (50 N); 2 - simultaneous static point loads applied to both of the crowns replacing the second premolar and first molar (100 N). The resulting isochromatic fringe pattern in the photoelastic model was monitored and photographed. RESULTS: All loading conditions studied showed that the presence of the second molar has changed the load transmission and the pattern of stresses. CONCLUSION: Results showed that the presence of a second molar proximal contact can help minimize the stresses around the implants.

Importance of a distal proximal contact on load transfer by implant-supported single adjacent crowns in posterior region of the mandible: a photoelastic study

OBJECTIVE: This study aimed to evaluate the importance of a distal proximal contact on the load transfer to the posterior region of the mandible by non-splinted adjacent implant-supported crowns using photoelastic stress analysis. MATERIAL AND METHODS: A rectangular model (68x30x15 mm) was made of polymethylmethacrylate resin to simulate half of the mandibular arch. One model was completed with resin replicas representing the first premolar and second molar and with two 3.75 mm dia.x11 mm internal hexagon threaded implants replacing the second premolar and first molar. The other model was manufactured in the same way but without the second molar. Both models were duplicated using photoelastic resin. The roots of the teeth replicas were covered with a layer of polyether impression material to simulate the periodontal ligament. Two different vertical loads were applied to the crowns as follows: 1 - single static point load alternately applied to the crowns replacing the second premolar and first molar (50 N); 2 - simultaneous static point loads applied to both of the crowns replacing the second premolar and first molar (100 N). The resulting isochromatic fringe pattern in the photoelastic model was monitored and photographed. RESULTS: All loading conditions studied showed that the presence of the second molar has changed the load transmission and the pattern of stresses. CONCLUSION: Results showed that the presence of a second molar proximal contact can help minimize the stresses around the implants. .

Three-dimensional finite element analysis of the stress distribution on morse taper implants surface.

PURPOSE: This finite element analysis (FEA) compared stress distribution on external surface of different morse taper implants, varying implant bodies length and dimensions of metal-ceramic crowns in order to maintain the occlusal alignment. METHODS: Three-dimensional finite element (FE) models were designed representing a posterior left side segment of the mandible: group 0, 3 implants of 11 mm length; group 1, implants of 13 mm, 11 mm and 5mm length; group 2, 1 implant of 11 mm and 2 implants of 5mm length; group 3, 3 implants of 5mm length. The abutments heights were 3.5mm for 13 mm and 11 mm implants (regular) and 0.8mm for 5mm implants (short). Evaluation was performed on a computer program (Ansys software), with oblique loads of 365N for molars and 200 N for premolars, applied on ridges of cusps and grooves. RESULTS: Abutments with 0.8mm height generated less von Mises stresses compared with 3.5mm height. The use of short implants associated with bigger crowns concentrated higher stress distribution and stress values on the surface implants, principally on the vestibular side (oblique direction of the loads). The more distal implant concentrated higher stress. CONCLUSIONS: Moreover, these 5mm implants were positioned at the cortical bone level, which has higher elastic modulus and may have influenced at the stress distribution. However, despite the higher stresses, these implants were well able to withstand the applied forces.

Effect of toothbrushing with different toothpastes at commerciallypure titanium surface roughness / Efeito da escovação com diferentes dentifrícios na rugosidade superficial do titânio comercialmente puro

Objective: To evaluate the effect of brushing, using toothpastes with different fluoride concentrations, on the surface of commercially pure titanium (cp Ti). Methods: Discs (13x4mm) made of cp Ti, embedded in PVC rings and metallographically polished have their surface roughness measured. Tooth brushing simulations (50,400 cycles) were performed: speed of 80mm/s, distance of 10mm distance, at 240 cycles/min. Three toothpastes were tested: Prevident 5000 (Colgate-Palmolive Ind. e Com. Ltda., São Paulo, Brazil), Colgate Total 12 (Colgate-Palmolive Ind. e Com. Ltda., São Paulo, Brazil) and Tandy (Colgate-Palmolive Ind. e Com. Ltda., São Paulo, Brazil), with 5000, 1300 and 500ppm fluoride concentrations, respectively. The brushings had 7.14g and 14.28g of toothpaste, both for 50mL of deionized water. The surface roughness was reevaluated and data were analyzed by two-way ANOVA and Tukey?s test for the effect of brushing and toothpastes. Results: At the beginning, no significant difference (p=0.09) of roughness was noted among the experimental groups (Prevident, Colgate-Palmolive Ind. e Com. Ltda., São Paulo, Brazil): 0.160±0.019; Colgate Total 12 (Colgate-Palmolive Ind. e Com. Ltda., São Paulo, Brazil): 0.159±0.030; Tandy (Colgate-Palmolive Ind. e Com. Ltda., São Paulo, Brazil): 0.157±0.019) but roughness decreased after the 1st (p<0.05) (0.094±0.010) and 2nd (0.089± 0.012) brushings (p<0.05) with Prevident 5000 (Colgate-Palmolive Ind. e Com. Ltda., São Paulo, Brazil), with no significant difference between the 1st and 2nd brushings (p=0.16). Discs brushed with Colgate Total 12 (Colgate-Palmolive Ind. e Com. Ltda., São Paulo, Brazil) presented surface roughness similar (p=0.090) at the beginning and after the 1st brushing (0.133±0.029), and between the 1st and 2nd (0.113±0009) brushings (p=0.402); roughness after the 2nd brushing was statistically greater than at the beginning (p<0.05). Tandy (Colgate- Palmolive Ind. e Com. Ltda., São Paulo, Brazil) toothpaste caused a surface roughness significantly lower (p<0.05) after the 2nd brushing (0.113±0.010), compared to the 1st (0.147±0.020) and the starting point, which were statistically similar (p=0.090). Conclusion: The results suggest that brushing using toothpastes with fluoride causes a decrease in the surface roughness of cp Ti, mainly when greater fluoride concentrations are present.

Objetivo: Avaliar o efeito da escovação com dentifrícios contendo diferentes concentrações de flúor na superfície do titânio comercialmente puro (Ti cp). Métodos: Discos (13x4mm) de Ti cp, embutidos em anéis de PVC e polidos metalograficamente, tiveram a rugosidade superficial avaliada. A simulação da escovação (50400 ciclos) teve velocidade de 80mm/s, curso de 10mm, com 240 ciclos/min. Foram testados três dentifrícios: Prevident 5000, (Colgate-Palmolive Ind. e Com. Ltda., São Paulo, Brasil); Colgate Total 12 (Colgate-Palmolive Ind. e Com. Ltda., São Paulo, Brasil) e Tandy (Colgate-Palmolive Ind. e Com. Ltda., São Paulo, Brasil), com 5000, 1300 e 500ppm de flúor, respectivamente. As escovações tiveram 7,14g e 14,28g de dentifrício, ambas para 50ml de água deionizada. A rugosidade superficial foi reavaliada e os dados analisados por ANOVA - dois fatores e teste de Tukey quanto ao efeito da escovação e dos dentifrícios. Resultados: Inicialmente não houve diferença significante (p=0,09) na rugosidade dos grupos experimentais Prevident, (Colgate-Palmolive Ind. e Com. Ltda., São Paulo, Brasil): 0,160±0,019; Colgate Total 12 (Colgate-Palmolive Ind. e Com. Ltda., São Paulo, Brasil): 0,159±0,030; Tandy (Colgate- Palmolive Ind. e Com. Ltda., São Paulo, Brasil): 0,157±0,019), mas houve diminuição da rugosidade após a 1ª (0,094±0,010) (p<0,05) e 2ª (0,089±0,012) escovações (p<0,05) com Prevident 5000 (Colgate-Palmolive Ind. e Com. Ltda., São Paulo, Brasil), sem diferença significativa entre as demais (p=0,16). Discos escovados com Colgate Total 12 (Colgate-Palmolive Ind. e Com. Ltda., São Paulo, Brasil) apresentaram rugosidade semelhante inicialmente (p=0,090) e após a 1ª escovação (0,133± 0,029), e entre a 1ª e a 2ª escovações (0,113±0,009) (p=0,402); a rugosidade após a 2ª escovação foi significativamente maior que a inicial (p<0,05). O dentifrício Tandy (Colgate-Palmolive Ind. e Com. Ltda., São Paulo, Brasil) causou rugosidade superficial significativamente menor (p<0,05) após a 2ª escovação (0,113±0,010), comparada à 1ª (0,147±0,020) e a inicial, que foram semelhantes (p=0,090). Conclusão: Os resultados sugerem que a escovação com dentifrícios fluoretados diminui a rugosidade superficial do Ti cp, mais significativamente quanto maiores as concentrações de flúor presentes.

Photoelastic analysis of stresses transmitted by universal cast to long abutment on implant-supported single restorations under static occlusal loads.

OBJECTIVES: The aim of this study was to compare the stresses resulting from cemented or screw-retained dental prostheses using universal cast to long abutment by the photoelastic method. MATERIAL AND METHODS: A photoelastic resin model was fabricated to simulate a segment of the mandibular arch with resin replicas of a first premolar and a second molar, and two 3.75 × 11-mm implants replacing the second premolar and the first molar. Vertical static loads were individually applied on the occlusal surface of the premolar and the molar (5 kgf) and simultaneously on both crowns (10 kgf). RESULTS: Results found variable stress patterns around each implant and concentrated stresses in the individually loaded crowns. Force transfer characteristics of each situation and quantification of the isochromatic fringes were evaluated. CONCLUSIONS: Within the limitations of this study and based on the results obtained for implant-supported prosthesis with internal hexagon connection/universal cast to long abutment, it could be concluded that single adjacent screw-retained prosthetic restorations lead to higher stresses around the implants when compared with cement-retained restorations.

Effect of fluoride sodium mouthwash solutions on cpTI: evaluation of physicochemical properties

The effects of fluoride, which is present in different oral hygiene products, deserve more investigation because little is known about their impact on the surface of titanium, which is largely used in Implantology. This study evaluated the surface of commercially pure titanium (cpTi) after exposure to different concentrations of sodium fluoride (NaF). The hypothesis tested in this study was that different concentrations of NaF applied at different time intervals can affect the titanium surface in different ways. The treatments resulted in the following groups: GA (control): immersion in distilled water; GB: immersion in 0.05% NaF for 3 min daily; GC: immersion in 0.2% NaF for 3 min daily; GD: immersion in 0.05% NaF for 3 min every 2 weeks; and GE: immersion in 0.2% NaF for 3 min every 2 weeks. The experiment lasted 60 days. Roughness was measured initially and every 15 days subsequently up to 60 days. After 60 days, corrosion analysis and anodic polarization were done. The samples were examined by scanning electron microscopy (SEM). The roughness data were analyzed by ANOVA and there was no significant difference among groups and among time intervals. The corrosion data (i corr) were analyzed by the Mann-Whitney test, and significant differences were found between GA and GC, GB and GC, GC and GD, GC and GE. SEM micrographs showed that the titanium surface exposed to NaF presented corrosion that varied with the different concentrations. This study suggests that the use of 0.05% NaF solution on cpTi is safe, whereas the 0.2% NaF solution should be carefully evaluated with regard to its daily use.

Os efeitos do fluoreto, o qual está presente em diferentes produtos de higiene oral, necessita de maiores investigações, pois pouco se sabe sobre seus efeitos na superfície do titânio, o qual possui amplo uso na implantodontia. Este estudo objetivou avaliar a superfície do titânio comercialmente puro (cpTi) após exposição a diferentes concentrações de fluoreto de sódio (NaF). A hipótese testada neste estudo foi que diferentes concentrações de NaF aplicadas em diferentes intervalos de tempo seriam capazes de afetar diferentemente a superfície do titânio. Os tratamentos realizados foram: GA (controle): imersão em água destilada; GB: imersão diária por 3 min em NaF a 0,05%; GC: imersão diária por 3 min em NaF a 0,2%; GD: imersão quinzenal por 3 min em NaF a 0,05%; e GE: imersão quinzenal por 3 min em NaF a 0,2%. O tempo do experimento foi de 60 dias. A análise da rugosidade foi efetuada inicialmente e a cada 15 dias. Após 60 dias foi realizada análise de corrosão e polarização anódica. As amostras foram analisadas em MEV. Os dados de rugosidade foram analisados por ANOVA e não houve diferença estatisticamente significante entre grupos e entre tempos. Os dados de corrosão (i corr) foram analisados pelo teste de Mann-Whitney e foram encontradas diferenças significantes entre GA e GC, GC e GB, GC e GD, GC e GE. A MEV evidenciou que a superfície do titânio exposto ao NaF apresentou corrosão variando de acordo com a concentração. Com base nos dados encontrados conclui-se que o uso de solução NaF a 0,05% em cpTi é seguro, enquanto a solução NaF 0,2% para uso diário deve ser cuidadosamente avaliada.

Effects of chemical composition on the corrosion of dental alloys

The aim of this study was to determine the effect of the oral environment on the corrosion of dental alloys with different compositions, using electrochemical methods. The corrosion rates were obtained from the current-potential curves and electrochemical impedance spectroscopy (EIS). The effect of artificial saliva on the corrosion of dental alloys was dependent on alloy composition. Dissolution of the ions occurred in all tested dental alloys and the results were strongly dependent on the general alloy composition. Regarding the alloys containing nickel, the Ni-Cr and Ni-Cr-Ti alloys released 0.62 mg/L of Ni on average, while the Co-Cr dental alloy released ions between 0.01 and 0.03 mg/L of Co and Cr, respectively.The open-circuit potential stabilized at a higher level with lower deviation (standard deviation: Ni-Cr-6Ti = 32 mV/SCE and Co-Cr = 54 mV/SCE). The potenciodynamic curves of the dental alloys showed that the Ni-based dental alloy with >70 wt% of Ni had a similar curve and the Co-Cr dental alloy showed a low current density and hence a high resistance to corrosion compared with the Ni-based dental alloys. Some changes in microstructure were observed and this fact influenced the corrosion behavior for the alloys. The lower corrosion resistance also led to greater release of nickel ions to the medium. The quantity of Co ions released from the Co-Cr-Mo alloy was relatively small in the solutions. In addition, the quantity of Cr ions released into the artificial saliva from the Co-Cr alloy was lower than Cr release from the Ni-based dental alloys.

O objetivo deste estudo foi determinar o efeito do ambiente bucal na corrosão de diferentes ligas odontológicas, utilizando métodos eletroquímicos. Os índices de corrosão foram obtidos por meio das curvas de corrente-potencial e impedância eletroquímica (EIS). O efeito de saliva artificial na corrosão de ligas odontológicas foi dependente da composição. A dissolução dos íons ocorreu em todas as amostras e os resultados foram dependentes da composição da liga. Algumas mudanças na microestrutura foram observadas durante o estudo e influenciou o comportamento corrosivo das ligas investigadas. As ligas de Ni-Cr e Ni-Cr-Ti libertaram quantidade de 0,62 mg/L de íons Ni enquanto a liga de Co-Cr liberou entre 0,01 e 0,03 mg/L. As curvas potenciodinâmicas das ligas odontológicas mostraram que as ligas a base >70 wt% de Ni obtiveram curvas similares e a liga de Co-Cr apresentou a menor densidade de corrente e em consequência uma resistência alta a corrosão quando comparada as ligas à base de Ni. A baixa resistência à corrosão também levou a maior libertação de íons de níquel para o meio e a quantidade de Co liberado pela liga de Co-Cr-Mo foi relativamente pequena nas soluções. As quantidades de Cr liberada na saliva artificial pela liga de Co-Cr foi menor que a libertação de Cr pela liga à base de Ni.

Effect of fluoride sodium mouthwash solutions on cpTI: evaluation of physicochemical properties.

The effects of fluoride, which is present in different oral hygiene products, deserve more investigation because little is known about their impact on the surface of titanium, which is largely used in Implantology. This study evaluated the surface of commercially pure titanium (cpTi) after exposure to different concentrations of sodium fluoride (NaF). The hypothesis tested in this study was that different concentrations of NaF applied at different time intervals can affect the titanium surface in different ways. The treatments resulted in the following groups: GA (control): immersion in distilled water; GB: immersion in 0.05% NaF for 3 min daily; GC: immersion in 0.2% NaF for 3 min daily; GD: immersion in 0.05% NaF for 3 min every 2 weeks; and GE: immersion in 0.2% NaF for 3 min every 2 weeks. The experiment lasted 60 days. Roughness was measured initially and every 15 days subsequently up to 60 days. After 60 days, corrosion analysis and anodic polarization were done. The samples were examined by scanning electron microscopy (SEM). The roughness data were analyzed by ANOVA and there was no significant difference among groups and among time intervals. The corrosion data (i(corr)) were analyzed by the Mann-Whitney test, and significant differences were found between GA and GC, GB and GC, GC and GD, GC and GE. SEM micrographs showed that the titanium surface exposed to NaF presented corrosion that varied with the different concentrations. This study suggests that the use of 0.05% NaF solution on cpTi is safe, whereas the 0.2% NaF solution should be carefully evaluated with regard to its daily use.

Effect of laser welding on the titanium ceramic tensile bond strength.

UNLABELLED: Titanium reacts strongly with elements, mainly oxygen at high temperature. The high temperature of titanium laser welding modifies the surface, and may interfere on the metal-ceramic tensile bond strength. OBJECTIVE: The influence of laser welding on the titanium-ceramic bonding has not yet been established. The purpose of this in vitro study was to analyze the influence of laser welding applied to commercially pure titanium (CpTi) substructure on the bond strength of commercial ceramic. The influence of airborne particle abrasion (Al2O3) conditions was also studied. MATERIAL AND METHODS: Forty CpTi cylindrical rods (3 mm x 60 mm) were cast and divided into 2 groups: with laser welding (L) and without laser welding (WL). Each group was divided in 4 subgroups, according to the size of the particles used in airborne particle abrasion: A - Al2O3 (250 µm); B - Al2O3 (180 µm); C - Al2O3 (110 µm); D - Al2O3 (50 µm). Ceramic rings were fused around the CpTi rods. Specimens were invested and their tensile strength was measured at fracture with a universal testing machine at a crosshead speed of 2.0 mm/min and 200 kgf load cell. Statistical analysis was carried out with analysis of variance and compared using the independent t test (p<0.05). RESULTS: Significant differences were found among all subgroups (p<0.05). The highest and the lowest bond strength means were recorded in subgroups WLC (52.62 MPa) and LD (24.02 MPa), respectively. CONCLUSION: Airborne particle abrasion yielded significantly lower bond strength as the Al2O3 particle size decreased. Mechanical retention decreased in the laser-welded specimens, i.e. the metal-ceramic tensile bond strength was lower.

Effect of laser welding on the titanium ceramic tensile bond strength

Titanium reacts strongly with elements, mainly oxygen at high temperature. The high temperature of titanium laser welding modifies the surface, and may interfere on the metal-ceramic tensile bond strength. OBJECTIVE: The influence of laser welding on the titanium-ceramic bonding has not yet been established. The purpose of this in vitro study was to analyze the influence of laser welding applied to commercially pure titanium (CpTi) substructure on the bond strength of commercial ceramic. The influence of airborne particle abrasion (Al2O3) conditions was also studied. MATERIAL AND METHODS: Forty CpTi cylindrical rods (3 mm x 60 mm) were cast and divided into 2 groups: with laser welding (L) and without laser welding (WL). Each group was divided in 4 subgroups, according to the size of the particles used in airborne particle abrasion: A - Al2O3 (250 µm); B - Al2O3 (180 µm); C - Al2O3 (110 µm); D - Al2O3 (50 µm). Ceramic rings were fused around the CpTi rods. Specimens were invested and their tensile strength was measured at fracture with a universal testing machine at a crosshead speed of 2.0 mm/min and 200 kgf load cell. Statistical analysis was carried out with analysis of variance and compared using the independent t test (p<0.05). RESULTS: Significant differences were found among all subgroups (p<0.05). The highest and the lowest bond strength means were recorded in subgroups WLC (52.62 MPa) and LD (24.02 MPa), respectively. CONCLUSION: Airborne particle abrasion yielded significantly lower bond strength as the Al2O3 particle size decreased. Mechanical retention decreased in the laser-welded specimens, i.e. the metal-ceramic tensile bond strength was lower.

Evaluation of screw loosening on new abutment screws and after successive tightening.

This study evaluated the loss of the torque applied after use of new screws and after successive tightening. Four infrastructures (IE), using UCLA castable abutment type, were cast in cobalt-chromium alloy and new abutment screws (G1) were used in a first moment. Subsequently, the same abutment screws were used a second time (G2) and more than two times (G3). The values of the torques applied and detorques were measured with a digital torque wrench to obtain the values of initial tightening loss (%). Data were analyzed by ANOVA and Tukey's test (?=0.05). Significant differences were observed between the G1 (50.71% ± 11.36) and G2 (24.01% ± 3.33) (p=0.000) and between G1 (50.71% ± 11.36) and G3 (25.60% ± 4.64) (p=0.000). There was no significant difference between G2 and G3 (p=0.774). Within the limitations of the study, it may be concluded that the percentage of the initial torque loss is lower when screws that already suffered the application of an initial torque were used, remaining stable after application of successive torques.

Evaluation of screw loosening on new abutment screws and after successive tightening

This study evaluated the loss of the torque applied after use of new screws and after successive tightening. Four infrastructures (IE), using UCLA castable abutment type, were cast in cobalt-chromium alloy and new abutment screws (G1) were used in a first moment. Subsequently, the same abutment screws were used a second time (G2) and more than two times (G3). The values of the torques applied and detorques were measured with a digital torque wrench to obtain the values of initial tightening loss ( percent). Data were analyzed by ANOVA and Tukey's test (?=0.05). Significant differences were observed between the G1 (50.71 percent ± 11.36) and G2 (24.01 percent ± 3.33) (p=0.000) and between G1 (50.71 percent ± 11.36) and G3 (25.60 percent ± 4.64) (p=0.000). There was no significant difference between G2 and G3 (p=0.774). Within the limitations of the study, it may be concluded that the percentage of the initial torque loss is lower when screws that already suffered the application of an initial torque were used, remaining stable after application of successive torques.

O objetivo deste estudo foi avaliar a perda do torque inicial, quando usados novos parafusos de pilares e após sucessivos apertos. Quatro infra-estruturas (IE), utilizando pilares calcináveis tipo UCLA, foram fundidas em liga de cobalto-cromo, onde novos parafusos de pilares foram utilizados (G1) em um primeiro momento. Posteriormente os mesmos parafusos de pilares foram utilizados em um segundo momento (G2), e depois por mais duas vezes (G3). Os valores de torque e detorque aplicados foram mensurados a partir de um torquímetro digital para obtenção dos valores de perda do torque inicial ( por cento). Os dados foram coletados e submetidos à análise de variância e teste de Tukey (p<0,05). Foram observadas diferenças estatisticamente significantes entre os grupos G1 (50,71 por cento ± 11,36) and G2 (24,01 por cento ± 3,33) (p=0,000) and the groups G1 (50,71 por cento ± 11,36) and G3 (25,60 por cento ± 4,64) (p=0,000). Os maiores valores foram encontrados para o grupo G1. Não houve diferença estaticamente significante entre os grupos G2 e G3 (p=0,774). Dentro das limitações deste estudo, pôde-se observar que a porcentagem de perda de torque inicial foi menor quando os parafusos já haviam sofrido a aplicação do primeiro torque, se mantendo estáveis após os demais torques.

Comparative study of two commercially pure titanium casting methods.

UNLABELLED: The interest in using titanium to fabricate removable partial denture (RPD) frameworks has increased, but there are few studies evaluating the effects of casting methods on clasp behavior. OBJECTIVE: This study compared the occurrence of porosities and the retentive force of commercially pure titanium (CP Ti) and cobalt-chromium (Co-Cr) removable partial denture circumferential clasps cast by induction/centrifugation and plasma/vacuum-pressure. MATERIAL AND METHODS: 72 frameworks were cast from CP Ti (n=36) and Co-Cr alloy (n=36; control group). For each material, 18 frameworks were casted by electromagnetic induction and injected by centrifugation, whereas the other 18 were casted by plasma and injected by vacuum-pressure. For each casting method, three subgroups (n=6) were formed: 0.25 mm, 0.50 mm, and 0.75 mm undercuts. The specimens were radiographed and subjected to an insertion/removal test simulating 5 years of framework use. Data were analyzed by ANOVA and Tukey's to compare materials and cast methods (α=0.05). RESULTS: Three of 18 specimens of the induction/centrifugation group and 9 of 18 specimens of plasma/vacuum-pressure cast presented porosities, but only 1 and 7 specimens, respectively, were rejected for simulation test. For Co-Cr alloy, no defects were found. Comparing the casting methods, statistically significant differences (p<0.05) were observed only for the Co-Cr alloy with 0.25 mm and 0.50 mm undercuts. Significant differences were found for the 0.25 mm and 0.75 mm undercuts dependent on the material used. For the 0.50 mm undercut, significant differences were found when the materials were induction casted. CONCLUSION: Although both casting methods produced satisfactory CP Ti RPD frameworks, the occurrence of porosities was greater in the plasma/vacuum-pressure than in the induction/centrifugation method, the latter resulting in higher clasp rigidity, generating higher retention force values.

Comparative study of two commercially pure titanium casting methods

The interest in using titanium to fabricate removable partial denture (RPD) frameworks has increased, but there are few studies evaluating the effects of casting methods on clasp behavior. OBJECTIVE: This study compared the occurrence of porosities and the retentive force of commercially pure titanium (CP Ti) and cobalt-chromium (Co-Cr) removable partial denture circumferential clasps cast by induction/centrifugation and plasma/vacuum-pressure. MATERIAL AND METHODS: 72 frameworks were cast from CP Ti (n=36) and Co-Cr alloy (n=36; control group). For each material, 18 frameworks were casted by electromagnetic induction and injected by centrifugation, whereas the other 18 were casted by plasma and injected by vacuum-pressure. For each casting method, three subgroups (n=6) were formed: 0.25 mm, 0.50 mm, and 0.75 mm undercuts. The specimens were radiographed and subjected to an insertion/removal test simulating 5 years of framework use. Data were analyzed by ANOVA and Tukey's to compare materials and cast methods (α=0.05). RESULTS: Three of 18 specimens of the induction/centrifugation group and 9 of 18 specimens of plasma/vacuum-pressure cast presented porosities, but only 1 and 7 specimens, respectively, were rejected for simulation test. For Co-Cr alloy, no defects were found. Comparing the casting methods, statistically significant differences (p<0.05) were observed only for the Co-Cr alloy with 0.25 mm and 0.50 mm undercuts. Significant differences were found for the 0.25 mm and 0.75 mm undercuts dependent on the material used. For the 0.50 mm undercut, significant differences were found when the materials were induction casted. CONCLUSION: Although both casting methods produced satisfactory CP Ti RPD frameworks, the occurrence of porosities was greater in the plasma/vacuum-pressure than in the induction/centrifugation method, the latter resulting in higher clasp rigidity, generating higher retention force values.