Inflammatory and degenerative effects of induced osteoarthritis/rheumatoid arthritis models on temporomandibular joint of rats

OBJECTIVE

The present study compared three models of induction of osteoarthritis (OA) and rheumatoid arthritis (RA) in the temporomandibular joint (TMJ) of rats.

DESIGN

The induction method was by injection of complete Freund's adjuvant (CFA) + type II bovine collagen (CII). Twenty-four adult male rats were divided into four groups (n = 6): G1: Sham, 50 μL of 0.9% sodium chloride at the base of the tail and in each TMJ; G2: OA, 50 μL CFA+CII in each TMJ; G3: RA+OA, 100 μL of CFA+CII at the base of the tail and 50 μL CFA+CII in each TMJ; G4: RA, 100 μL of CFA+CII at the base of the tail. All injections were repeated 5 days later. Twenty-three days after the first injection, the animals were sacrificed and the TMJs were submitted to histomorphometric analysis and measurement of cytokines. The Kruskal-Wallis and Dunn tests were used (alpha=0.05).

RESULTS

The total thickness of the condylar cartilage increased in G2 in relation to the other groups, G3 and G4 reduced in relation to G1; and G2 and G4 reduced in relation to G2 and G3. The levels of IL-1β, IL-6 and TNF-α increased in the three induction models compared to G1. The level of IL-10 increased in G2 compared to the other groups and reduced in G3 and G4 compared to G1.

CONCLUSION

CFA+CII induced inflammation and degeneration compatible with RA (advanced chronic stage) when injected in the tail, and compatible with OA (acute stage or early disease) when injected only in the TMJ.

Comparison of the Accuracy of Different Transfer Impression Techniques for Osseointegrated Implants

The aim of this study was to evaluate 3 transfer techniques used to obtain working casts of implant-supported prostheses through the marginal misfit and strain induced to metallic framework. Thirty working casts were obtained from a metallic master cast, each one containing 2 implant analogs simulating a clinical situation of 3-unit implant-supported fixed prostheses according to the following transfer impression techniques: group A, squared transfers splinted with dental floss and acrylic resin, sectioned, and re-splinted; group B, squared transfers splinted with dental floss and bis-acrylic resin; and group N, squared transfers not splinted. A metallic framework was made for marginal misfit and strain measurements from the metallic master cast. The misfit between the metallic framework and working casts was evaluated with an optical microscope following the single-screw test protocol. In the same conditions, the strain was evaluated using strain gauges placed on the metallic framework. The data were submitted to one-way analysis of variance followed by the Tukey test (α = 5%). For both marginal misfit and strain, there were statistically significant differences between groups A and N (P < .01) and groups B and N (P < .01), with greater values for group N. According to the Pearson test, there was a positive correlation between the misfit and strain variables (r = 0.5642). The results of this study showed that the impression techniques with splinted transfers promoted better accuracy than the nonsplinted technique, regardless of the splinting material used.

Stress Evaluation of Implant-Abutment Connections Under Different Loading Conditions: A 3D Finite Element Study

This study evaluated the effects of axial and oblique occlusal loading on implant-supported partial dentures with different connection systems (external hexagon, internal hexagon, and Morse taper). Upon axial loading, all systems presented similar stress values. Stress values increased under oblique loading. Stress distribution changed for some of the internal connection structures. It can be concluded that oblique load increases stress on bone structures and prosthetic components. Internal connection system implants present more favorable stress distribution patterns than do external connection system implants.

Influence of the casting technique and dynamic loading on screw detorque and misfit of single unit implant-supported prostheses

OBJECTIVE

This study aimed to evaluate the influence of the casting procedure and cyclic loading of prosthetic frameworks on detorque of prosthetic screws and marginal misfit of single unit implant-supported prostheses.

MATERIALS AND METHODS

Twenty specimens were obtained, each one consisting of a set of an implant (external hexagon 3.75 × 13 mm - Branemark type), a prosthetic abutment (entirely calcinable or overcasted UCLA) and a prosthetic screw. After the specimens were obtained, the prosthetic screws were tightened with 30 Ncm torque and released 24 h later in order to evaluate initial detorque. The screws were retightened and marginal gaps were assessed. All specimens were submitted to 10(6) loading cycles, performed with 2 Hz frequency and 130 N load. The specimens were re-evaluated for marginal misfit and detorque after the mechanical loading (final marginal misfit/final detorque). The results were submitted to analysis of variance for repeated measurements, followed by Tukey HSD test (α = 0.05).

RESULTS

No statistically significant differences were found on detorque values of the prosthetics screws for all groups and intervals evaluated (p = 0.8922). The entirely calcinable abutments showed higher initial marginal misfit compared to the overcasted ones (p = 0.0438). There was no statistically significant difference on marginal misfit before and after mechanical loading for both groups (p > 0.05).

CONCLUSIONS

It can be concluded that the overcasted abutments showed lower misfit values when compared to the entirely casted abutments. No difference was observed on detorque values of prosthetic screws. After mechanical loading there was no difference on marginal misfit and detorque between the groups.

Adhesive bonding of resin cements to cast titanium with adhesive primers

The purpose of this study was to evaluate the effects of adhesive primer applications on the bond strength of resin cements to cast titanium. Four adhesive primers - Metaltite, Metal Primer II, Alloy Primer and Ceramic Primer - and their respective resin cements - Bistite II DC, Link Max, Panavia F 2.0, RelyX Unicem and RelyX ARC - were tested. Cast plates were prepared from titanium ingots (n=6 specimens/cement) and had their surfaces airborne-particle abraded with Al2O3 (50 μ m). Three resin cement cylinders were built on each bonded titanium surface, using a cylindrical translucent tubing mold and were subjected to micro-shear testing. Data were analyzed statistically by two-way ANOVA and Tukey's post-hoc test (α=0.05). The application of Metal Primer II and Ceramic Primer resulted in significant higher bond strength for Link Max and RelyX Unicem resin cements, respectively, than nonuse of adhesive primers. Panavia F 2.0 and RelyX ARC yielded high bond strength means with or without adhesive primers. The use of adhesive primers might increase the bond strength to cast titanium depending on the resin cement used.

The influence of master cast technique on the cast precision of implant-retained fixed prostheses

The aim of this study was to evaluate the precision of three different mold filling techniques in order to obtain a cast simulating a three-unit, implant-retained, fixed prosthesis. Thirty casts (n = 10) were obtained using three different mold filling techniques. Group 1 used a unique fulfillment technique, Group 2 used a two-step fulfillment technique, and Group 3 used a latex cylinder technique. Using a metallic matrix, a titanium substructure was created to simulate a three-unit fixed prosthesis used as reference to evaluate the marginal misfit and tension forces in each cast. The vertical misfit was measured by an optical microscope with an increase of 120X and by an analysis unit using the one-screw test. The tension was quantified using strain gauges. The strain results showed a statistical difference between Group 3 and the other groups. The Tukey test showed no difference between the different treatment groups (p = 0.05). All three techniques were deemed efficient; however, considering that the cylinder latex technique induced less force toward the implants, it is the preferable technique for daily clinical practice.

Efeito de agentes químicos de limpeza de próteses sobre as características superficiais de materiais reembasadores resilientes

Esse trabalho avaliou o efeito de agentes de limpeza sobre as características superficiais de materiais resilientes. Foram utilizados os materiais Luci Sof (Dentsply), Molloplast-B (Dentax) e Sofreliner (Tokuyama), e os agentes de limpezaHipoclorito de Sódio a 0,5% (Medicinallis - Farmácia de Manipulação) e Efferdent (Warner-Lamber Co). Foram confeccionados 20 corpos de prova de cada material. Os agentes de limpeza foram utilizados da seguinte maneira: 1) Hipoclorito de sódio a 0,5% (HA) a 37 ± 1 ºC, durante 20 min; 2) Peróxido Alcalino (PA) a 37 ±1 ºC, durante 15 min. Após as imersões,os corpos de prova foram lavados e imersos em água destilada a 37 ±1 ºC pelo período restante das 24 h (8x ao dia, durante 90 dias). A rugosidade superficial foi avaliada em rugosímetro Surfcorder SE 1700 (Kosaka- Laboratory Ltda),após 0 (T1), 180 (T2), 360 (T3) e 720 (T4) ciclos de higienização. Os resultados foram submetidos à ANOVA e teste de Tukey (5%). Para a imersão em HA, Luci Sof apresentou redução significativa dos valores de rugosidade superficial em T2, T3 e T4; e o material Sofreliner, em todos os tempos. Para a imersão em PA, Luci Sof apresentou redução significativa dos valores em T2, T3 e T4; Molloplast-B, redução significativa em T3; Sofreliner, aumento significativo em T4. Concluiu-se que a imersão em agentes químicos de limpeza, em geral, reduz a rugosidade superficial de reembasadores resilientes. Molloplast-B apresentou comportamento linear durante o estudo. Sofreliner, imerso em Hipoclorito, apresentou valores de rugosidade inferiores ao considerado mínimo para retenção bacteriana.

Análise fotoelástica da distribuição de tensões induzidas por infra-estruturas implanto-suportadas após soldagem a laser ou retificação de cilindros

O assentamento passivo de próteses fixas implanto-suportadas pode ser obtido por procedimentos laboratoriais. O objetivo deste estudo foi avaliar comparativamente a formação de tensões induzidas por infra-estruturas implanto-suportadas obtidas por duas técnicas através da análise fotoelástica. Dois grupos de infra-estrututas em titânio comercialmente puro foram obtidos sobre uma matriz metálica: I) três infra-estruturas confeccionadas pela técnica da soldagem de borda de cilindros e II) três infra-estruturas fundidas em monobloco e submetidas ao sistema de retificação de cilindros. Após análise em microscopia óptica, apenas a estrutura mais bem adaptada de cada grupo foi submetida à análise de tensões, em três seqüências de aperto dos parafusos protéticos. Após, a estrutura do grupo II sofreu secção e soldagem e foi novamente submetida à análise fotoelástica. Os resultados mostraram maior magnitude de tensões com a seqüência de aperto de parafusos da esquerda para direita e vice-versa, para ambos os grupos. A estrutura do grupo I induziu menor concentração de tensões, mesmo tendo apresentado maiores valores de desadaptação (165μm) comparada ao grupo II antes (54μm) e após secção e soldagem a laser (117μm). A técnica da soldagem de borda a laser, associada à seqüência de aperto do parafuso protético do centro para as extremidades, obteve melhores resultados formação de tensões para este tipo de reabilitação.

Influence of prosthetic screw material on joint stability in passive and non-passive implant-supported dentures

Objectives:

This study evaluated the influence of prosthetic screw material on joint stability in implantsupported dentures at two levels of fit.

Methods:

Ten mandibular implant-supported dentures were fabricated. Twenty cast models were fabricated using these dentures. Four groups (n=10) were tested, according to the vertical fit of the dentures [passive and non-passive] and prosthetic screw materials [titanium (Ti) or gold (Au) alloy]. The one-screw test was performed to quantify the vertical misfits using an optic microscope. The loosening torque for the prosthetic screws was measured 24 hours after the tightening torque (10 Ncm) using a digital torque meter. Data were analyzed by two-way ANOVA and Tukey’s test (α=0.05).

Results:

Overall, dentures with passive fit and Ti screws resulted in significantly higher loosening torque of the prosthetic screws (p<0.05). No significant interaction was found between fit level and screw material (p=0.199). The prosthetic screw material and fit of implant-supported dentures have an influence on screw joint stability. Ti screws presented higher joint stability than Au screws and minimum of misfit should be found clinically to improve the mechanical behavior of the screw joint.

The compatibility of denture cleansers and resilient liners

PURPOSE

Difficulty in cleaning resilient denture liners remains a material disadvantage. The purpose of the present study was to evaluate the effect of denture cleansers on hardness of resilient liner materials.

MATERIALS AND METHODS

Three resilient liners, Luci Sof (Dentsply), Molloplast-B (Dentax), and Sofreliner (Tokuyama), and two denture cleansers, Efferdent (Warner-Lamber), and 0.5% alkaline hypochlorite preparation were used. Twenty specimens of each material were prepared, measuring 25X15X3mm. Two denture cleansing approaches were used: 1) alkaline hypochlorite, for 20 minutes; 2) alkaline peroxide, for 30 minutes. This procedure was repeated 8 times a day, during 90 days. The specimens were evaluated before and after 360 and 720 cycles, to simulate 1 and 2 years of clinical cleaning procedures, respectively. The Shore A hardness was evaluated in a durometer (Teclock GS-709A), with a penetrating load of 10N for 1 second. Any macroscopic changes, such as loss of color or alteration in surface texture were recorded by one observer. All numeric data were subject to ANOVA with repeated measures followed by Tukey's test (alpha= 0.05).

RESULTS

All materials were significantly different, independently to time and treatment. Initially, Luci Sof and Sofreliner immersed in either hypochlorite or peroxide increased the hardness mean values significantly. These hardness mean values decreased significantly after 720 cycles. Molloplast-B showed no significant difference after the treatments, in any time.

CONCLUSIONS

Denture cleansers had no effect on hardness of the resilient denture liners evaluated after 2 years of in vivo simulated conditions of hygiene. Sofreliner was the smoothest material before and after all treatments.

Influence of laser-welding and electroerosion on passive fit of implant-supported prosthesis

This study investigated the influence of laser welding and electroerosion procedure on the passive fit of interim fixed implant-supported titanium frameworks. Twenty frameworks were made from a master model, with five parallel placed implants in the inter foramen region, and cast in commercially pure titanium. The frameworks were divided into 4 groups: 10 samples were tested before (G1) and after (G2) electroerosion application; and another 10 were sectioned into five pieces and laser welded before (G3) and after (G4) electroerosion application. The passive fit between the UCLA abutment of the framework and the implant was evaluated using an optical microscope Olympus STM (Olympus Optical Co., Tokyo, Japan) with 0.0005mm of accuracy. Statistical analyses showed significant differences between G1 and G2, G1 and G3, G1 and G4, G2 and G4. However, no statistical difference was observed when comparing G2 and G3. These results indicate that frameworks may show a more precise adaptation if they are sectioned and laser welded. In the same way, electroerosion improves the precision in the framework adaptation.

The Effect of Brushing on Surface Roughness of Denture Lining Materials

PURPOSE

The purpose of this study was to test the effect of brushing on surface roughness of two resilient liners (Luci Sof and Sofreliner) compared with an acrylic resin (QC 20).

MATERIALS AND METHODS

Twenty specimens of each material were prepared (25 mm x 14 mm x 3 mm). Ten specimens served as controls and were stored in distilled water and not brushed. The remaining ten specimens were subjected to mechanical brushing, using an MSEt plus machine to simulate brushing at a rate of 5.0 strokes per second (30,000 cycles). Surface roughness measurements were recorded before and after brushing. Random samples were analyzed using scanning electron microscope. Data collected were analyzed by a two-way analysis of variance using material and treatment as variables, followed by Tukey's test (alpha= 0.05).

RESULTS

Initial surface roughness of materials indicated that QC 20 was the smoothest (0.13 microm), and Luci Sof the roughest (0.68 mum). Sofreliner had an intermediate value (0.31 microm). All materials were significantly different. Mechanical brushing significantly increased surface roughness in all the materials. Although there was no statistical difference between QC 20 and Luci Sof after mechanical brushing (0.88 and 1.00 microm, respectively), both differed significantly from Sofreliner (7.74 microm).

CONCLUSION

The two resilient liners and the acrylic resin became rougher, to a greater or lesser extent, when subjected to mechanical brushing.

Tensile bond strength of dual curing resin-based cements to commercially pure titanium

OBJECTIVES

The aim of this study was to evaluate the tensile bond strength of dual curing luting resin cements to commercially pure titanium at 10 min and 24h after removal of the oxide layer.

METHODS

One hundred and twenty titanium discs were obtained by casting and polishing with silicon carbide papers. The titanium discs were sandblasted with 50 microm aluminum oxide, ultrasonic cleaned and bonded in pairs with the resin-based cements Panavia F and Rely X ARC at 10 min and 24h after the sandblasting. The tensile test was performed with a crosshead speed of 0.5mm/min in an Instron Universal testing machine.

RESULTS

The Rely X ARC reached the highest tensile strength value at 24h after sandblasting (18.27 MPa), but there was no statistically significant difference between the two dual curing resin cements for both times tested. All specimens showed a mixture of cohesive fracture in the resin cement and adhesive failure. However, the predominant failure mode for Panavia F was cohesive in resin cement, and the Rely X ARC exhibited a greater proportion of specimens with adhesive failure between the alloy and resin luting cement at 10 min and 24h.

SIGNIFICANCE

Both cements had, statistically, the same tensile bond strength. But in the fracture mode analysis, the adhesive predominant fracture mode of Rely X ARC cement indicates a premature clinical adhesive failure. On the other hand, the cohesive predominant fracture mode of Panavia F indicates a longer clinical adhesive bond with titanium.

Over-refractory casting technique as an alternative to one-piece multi-unit fixed partial denture frameworks

STATEMENT OF PROBLEM

Soldering has been suggested to achieve acceptable fit of multi-unit fixed partial denture (FPD) frameworks of 3 or more elements. However, distortion of the entire framework may occur.

PURPOSE

The purpose of this study was to evaluate marginal fit in 1-piece-casting FPD frameworks comparing 2 casting techniques: the conventional technique (CT) and the over-refractory technique (ORT). The techniques were evaluated on castings made from commercially pure titanium (CP Ti; Tritan), titanium-aluminum-vanadium (Ti-6Al-4V), and nickel-chromium (Ni-Cr; VeraBond II) alloys.

MATERIAL AND METHODS

A metal master cast including 3 preparations was created to simulate a 5-unit FPD. The metal cast was duplicated in vinyl polysiloxane for fabrication of 60 working casts. For the CT, 0.7-mm-thick patterns were waxed on the casts using an electrical wax-dipping unit. Patterns were removed from the preparations before investing. For the ORT, the silicone impressions were poured with an investment material (Rematitan for CP Ti and Ti-6Al-4V, and Talladium for Ni-Cr). The patterns were waxed on the refractory casts, and the assembly was invested. Both CT and ORT (n = 10), CP Ti, and Ti-6Al-4V frameworks were cast using an arc-melting titanium vacuum-casting machine. The Ni-Cr frameworks were cast using an automated centrifugal-casting machine. The mean marginal discrepancies of the frameworks were measured at the mesial, distal, buccal, and lingual interfaces. Marginal gap measurements were recorded 3 times for each surface to the nearest 0.5 microm using a traveling microscope (x50). The data were analyzed with 2-way analysis of variance, followed by the Tukey HSD test (alpha=.05).

RESULTS

Marginal discrepancies for the ORT specimens (82.8 +/- 1.7 microm for CP Ti; 64.4 +/- 1.3 microm for Ti-6Al-4V; and 77.2 +/- 1.5 microm for Ni-Cr) were significantly lower than those obtained for the CT specimens (106.3 +/- 2.6 microm for CP Ti; 75.7 +/- 0.8 microm for Ti-6Al-4V; 101.9 +/- 1.7 microm for Ni-Cr) (P < .05). For both techniques, marginal discrepancies were significantly different among the alloys evaluated, presenting the following order from greatest to least marginal discrepancy: CP Ti, Ni-Cr alloy, and Ti-6Al-4V (P < .05).

CONCLUSION

The ORT for multi-unit FPD frameworks demonstrated significantly lower marginal discrepancies than the CT.

Vickers hardness of cast commercially pure titanium and Ti-6Al-4V alloy submitted to heat treatments

The purpose of this study was to evaluate the effect of heat treatments on the Vickers hardness of commercially pure titanium and Ti-6Al-4V castalloys. Six-millimeter-diameter cylindrical specimens were cast in a Rematitan System. Commercially pure titanium and Ti-6Al-4V alloy specimens were randomly assigned to 3 groups (n=10) that received the following heat treatments: control (no heat treatment); treatment 1 (T1): heating at 750ºC for 2 h; and treatment 2 (T2): annealing at 955ºC for 1 h and aging at 620ºC for 2 h. After heat treatments, the specimens were embedded in acrylic resin and their surface was ground and polished and hardness was measured. Vickers hardness means (VHN) and standard deviations were analyzed statistically by Kruskal-Wallis test at 5% significance level. For commercially pure titanium, Vickers hardness means of group T2 (259.90 VHN) was significantly higher than those of the other groups (control - 200.26 VHN and T1 - 202.23 VHN), which presented similar hardness means to each other (p>0.05). For Ti-6Al-4V alloy, statistically significant differences were observed among the three groups: T2 (369.08 VHN), T1 (351.94 VHN) and control (340.51 VHN) (p<0.05). The results demonstrated different hardness of CP Ti and Ti-6Al-4V when different heat treatments were used. For CP Ti, VHN means of T2 group was remarkably higher than those of control and T1 group, which showed similar VHN means to each other. For Ti-6Al-4V alloy, however, VHN means recorded for each group may be presented as follows: T2>T1>control.

Effect of thermal treatments on tensile strength of commercially cast pure titanium and Ti-6Al-4V alloys

Heating titanium structures is assumed to relieve tensions induced by the casting process as well as possibly optimizing some mechanical properties. The aim of this investigation was to evaluate the effect of thermal treatments on tensile strength of commercially pure titanium (CP Ti) and Ti-6Al-4V alloy. Thirty dumbbell rods, with diameters of 3.0 mm at the central segment and lengths of 42 mm, were cast for each metal using the Rematitan System. CP Ti and Ti-6Al-4V specimens were randomly divided into three groups of ten: a control group that received no thermal treatment and two test groups. One (T1) was heated at 750 degrees C for 2 h and the other (T2) was annealed at 955 degrees C for 1 h and aged at 620 degrees C for 2 h. Tensile strength was measured with a universal testing machine (MTS model 810). Tensile strength means and standard deviations were statistically compared using a Kruskal-Wallis test at a alpha=0.05 significance level. No statistically significant differences in tensile strength were observed among CP Ti groups. For the Ti-6Al-4V alloy, the control and T1 groups revealed statistically higher tensile strengths when compared to the T2 group, with no significant difference between the control and T1 groups.

The influence of mold temperature on the fit of cast crowns with commercially pure titanium

Commercially pure titanium (CP Ti) has been widely applied to fabricate cast devices because of its favorable properties. However, the mold temperature recommended for the manufacture of casts has been considered relatively low, causing inadequate castability and poor marginal fit of cast crowns. This study evaluated and compared the influence of mold temperature (430°C - as control, 550°C, 670°C) on the marginal discrepancies of cast CP Ti crowns. Eight bovine teeth were prepared on a mechanical grinding device and impressions were used to duplicate each tooth and produce eight master dies. Twenty-four crowns were fabricated using CP Ti in three different groups of mold temperature (n = 8): 430°C (as control), 550°C and 670°C. The gap between the crown and the bovine tooth was measured at 50 X magnification with a traveling microscope. The marginal fit values of the cast CP Ti crowns were submitted to the Kruskal-Wallis test (p = 0.03). The 550°C group (95.0 µm) showed significantly better marginal fit than the crowns of the 430°C group (203.4 µm) and 670°C group (213.8 µm). Better marginal fit for cast CP Ti crowns was observed with the mold temperature of 550°C, differing from the 430°C recommended by the manufacturer.

Surface roughness and fatigue performance of commercially pure titanium and Ti-6Al-4V alloy after different polishing protocols

STATEMENT OF PROBLEM

Surface quality of cast metal is directly related to service performance under fatigue stress. Surface heterogeneities resulting from either finishing or polishing processes or by corrosive agents such as fluoridated solutions, can negatively affect fatigue life. Cast titanium frameworks are difficult to polish, and an accepted polishing protocol has not been established.

PURPOSE

This study evaluated and compared surface roughness of cast commercially pure titanium (CP Ti) and Ti-6Al-4V alloy submitted to conventional or electrolytic polishing, correlating the results with corrosion-fatigue strength testing performed in artificial fluoridated saliva. Specimens were also tested in air at room temperature to evaluate the effectiveness of the corrosion-fatigue test model.

MATERIAL AND METHODS

For each metal, 40 dumb-bell-shaped rods, 2.3 mm in diameter at the central segment, were cast. Conventional polishing was performed on 20 specimens of each metal following the manufacturer's instructions. A source of continuous electrical current was used for electrolytic polishing of the other 20 specimens of each metal, which were immersed in an electrolytic solution containing 5% fluoridric acid, 35% nitric acid, and 60% distilled water. Surface roughness, Ra (microm), was measured with a profilometer, and fatigue tests were carried out with a universal testing machine using a load 30% lower than the 0.2% offset yield strength. After failure, the fractured surfaces were examined using scanning electron microscopy. Surface roughness means were analyzed with a 2-way analysis of variance and the Tukey multiple comparisons test (alpha=.05).

RESULTS

Electrolytic polishing (0.24 +/- 0.05 microm) provided significantly (P <.05) lower surface roughness values than conventional polishing (0.32 +/- 0.06 microm). Regardless of the polishing protocol, surface roughness of Ti-6Al-4V alloy (0.25 +/- 0.06 microm) was significantly lower (P <.05) than that of CP Ti (0.31 +/- 0.05 microm), and the fluoridated environment did not influence fatigue performance. There was no correlation between fatigue performance and surface roughness.

CONCLUSION

Surface roughness of Ti-6Al-4V was significantly lower than that of CP Ti. For cast titanium frameworks, the electrolytic polishing regimen was found to be more effective than the manufacturer's polishing instructions with abrasives and rotary instruments. After polishing, differences in surface roughness values did not affect corrosion-fatigue performance.

Retention force and fatigue strength of overdenture attachment systems

This study evaluated retention force and fatigue resistance of two overdenture attachment systems. Twenty samples (O-ring and Bar-Clip) from two manufacturers (Conexão Sistemas de Prótese and Lifecore Biomedical) were prepared and divided into four groups: (i) Conexão/O-ring; (ii) Conexão/Bar-Clip; (iii) Lifecore/O-ring and (iv) Lifecore/Bar-Clip, with five samples in each group. They were submitted to mechanical fatigue test using a servohydraulic machine performing 5500 cycles of insertion and removal (f=0.8 Hz), immersed in artificial saliva. Retention force values were obtained three times (0, 3000 and after 5500 cycles) simulating the clinical service, using a tensile strength at 1 mm min(-1) and load cell of 1 kN. Data were analysed with analysis of variance and Tukey's test at 5% level. Results showed that Conexão/Bar-Clip specimens had significantly higher retention values than Lifecore/Bar-Clip (44.61 and 18.44 N, respectively), Conexão/O-ring specimens had significantly lower values than Lifecore/O-ring (13.91 and 19.75 N, respectively). Conexão/Bar-Clip values were always significantly higher than those of Conexão/O-ring group (44.61 and 13.91 N, respectively). Lifecore (O-ring and Bar-Clip) presented similar values (19.75 and 18.44 N, respectively). The systems evaluated showed satisfactory retention force values, before and after fatigue testing. Conexão/Bar-Clip specimens presented the highest values. A 5-year simulation of insertion and removal did not decrease retention values or fracture components.

Influence of chemical and mechanical polishing on water sorption and solubility of denture base acrylic resins

Influence of polishing methods on water sorption and solubility of denture base acrylic resins was studied. Eighty samples were divided into groups: Clássico (CL), and QC 20 (QC) - hot water bath cured; Acron MC (AC), and Onda Cryl (ON) - microwave cured; and submitted to mechanical polishing (MP) - pumice slurry, chalk powder, soft brush and felt cone in a bench vise; or chemical polishing (CP) - heated monomer fluid in a chemical polisher. The first desiccation process was followed by storage in distilled water at 37 ± 1ºC for 1 h, 1 day, 1, 2, 3 and 4 weeks. Concluding each period, water sorption was measured. After the fourth week, a second desiccation process was done to calculate solubility. Data were submitted to analysis of variance, followed by Tukey test (p<0.05). Means of water sorption (%) and solubility (%), respectively, were: CL-MP: 1.92 and 0.02; CL-CP: 1.98 and 0.52; QC-MP: 2.31 and -0.05; QC-CP: 2.32 and 0.25; AC-MP: 2.45 and -0.07; AC-CP: 2.43 and 0.41; ON-MP: 2.32 and -0.06; ON-CP: 2.34 and 0.27. Mechanical polishing promoted significantly lower solubility of acrylic resins; initially, water sorption values were higher for chemically polished samples, however, after 4 weeks all groups were similar.

Surface roughness of acrylic resins submitted to mechanical and chemical polishing

Surface roughness is extremely important as it influences micro-organism accumulation and consequently oral health. The aim of the present study was to evaluate the influence of mechanical polishing (MP) and chemical polishing (CP) on surface roughness of four heat-cured denture base acrylic resins. Twenty sample discs were prepared for each of the following acrylic resins: Classico (CL), QC 20 (QC), Acron MC (AC) and Onda Cryl (ON). The first two are boiling cured resins and the latter two are microwave cured. After curing and deflasking, samples were ground and subdivided into two groups: MP, which received pumice slurry, chalk powder, soft brush and felt cone, at a bench vice; and CP, which received fluid specifically for chemical polisher. Surface roughness was measured using a Surf Corder SE 1700 rugosimeter. Data collected were statistically analysed by analysis of variance followed by Tukey's test. Surface roughness means in mum were: CL-MP: 0.0350; CL-CP: 0.2298; QC-MP: 0.0307; QC-CP: 0.1792; AC-MP: 0.0312; AC-CP: 0.2700; ON-MP: 0.0321; ON-CP: 0.2949. It can be concluded that MP produced significantly smoother surfaces than CP and that surface roughness because of MP was not influenced by acrylic resin type, whereas this was not true of CP.

Evaluation of varying amounts of thermal cycling on bond strength and permanent deformation of two resilient denture liners

STATEMENT OF PROBLEM

Two problems found in prostheses with resilient liners are bond failure to the acrylic resin base and increased permanent deformation due to material aging.

PURPOSE

This in vitro study evaluated the effect of varying amounts of thermal cycling on bond strength and permanent deformation of 2 resilient denture liners bonded to an acrylic resin base.

MATERIAL AND METHODS

Plasticized acrylic resin (PermaSoft) or silicone (Softliner) resilient lining materials were processed to a heat-polymerized acrylic resin (QC-20). One hundred rectangular specimens (10 x 10-mm 2 cross-sectional area) and 100 cylindrically-shaped specimens (12.7-mm diameter x 19.0-mm height) for each liner/resin combination were used for the tensile and deformation tests, respectively. Specimen shape and liner thickness were standardized. Specimens were divided into 9 test groups (n=10) and were thermal cycled for 200, 500, 1000, 1500, 2000, 2500, 3000, 3500, and 4000 cycles. Control specimens (n=10) were stored for 24 hours in water at 37 degrees C. Mean bond strength, expressed as stress at failure (MPa), was determined with a tensile test using a universal testing machine at a crosshead speed of 5 mm/min. Analysis of failure mode, expressed as a percent (%), was recorded as either cohesive, adhesive, or both, after observation. Permanent deformation, expressed as a percent (%), was determined using ADA specification no. 18. Data from both tests were examined with a 2-way analysis of variance and a Tukey test (alpha=.05).

RESULTS

For the tensile test, Softliner specimens submitted to different thermal cycling regimens demonstrated no significantly different bond strength values from the control; however, there was a significant difference between the PermaSoft control group (0.47 +/- 0.09 MPa [mean +/- SD]) and the 500 cycle group (0.46 +/- 0.07 MPa) compared to the 4000 cycle group (0.70 +/- 0.20 MPa) ( P <.05). With regard to failure type, the Softliner groups presented adhesive failure (100%) regardless of specimen treatment. PermaSoft groups presented adhesive (53%), cohesive (12%), or a combined mode of failure (35%). For the deformation test, there was no significant difference among the Softliner specimens. However, a significant difference was observed between control and PermaSoft specimens after 1500 or more cycles (1.88% +/- 0.24%) ( P <.05).

CONCLUSIONS

This in vitro study indicated that bond strength and permanent deformation of the 2 resilient denture liners tested varied according to their chemical composition.

Evaluation of low-fusing ceramic systems combined with titanium grades II and V by bending test and scanning electron microscopy

The bond strength by three point bending strength of two metal substrates (commercially pure titanium or grade II, and Ti-6Al-4V alloy or grade V) combined to three distinct low-fusing ceramic systems (LFC) and the nature of porcelain-metal fracture by scanning electron microscopy (SEM) were evaluated. The results were compared to a combination of palladium-silver (Pd-Ag) alloy and conventional porcelain (Duceram VMK68). Sixty metal strips measuring 25x3x0.5mm were made - 30 of titanium grade II and 30 of titanium grade V, with application of the following types of porcelain: Vita Titankeramik, Triceram or Duceratin (10 specimens for each porcelain). The porcelains were bonded to the strips with dimensions limited to 8x3x1mm. The control group consisted of ten specimens Pd-Ag alloy/Duceram VMK68 porcelain. Statistical analyses were made by one-way analysis of variance (ANOVA) and Tukey test at 5% significance level. Results showed that the bond strength in control group (48.0MPa ± 4.0) was significantly higher than the Ti grade II (26.7MPa ± 4.1) and Ti grade V (25.2MPa ± 2.2) combinations. When Duceratin porcelain was applied in both substrates, Ti grade II and Ti grade V, the results were significantly lower than in Ti grade II/Vitatitankeramik. SEM analysis indicated a predominance of adhesive fractures for the groups Ti grade II and Ti grade V, and cohesive fracture for control group Pd-Ag/Duceram. Control group showed the best bond strength compared to the groups that employed LFC. Among LFC, the worst results were obtained when Duceratin porcelain was used in both substrates. SEM confirmed the results of three point bending strength.

Stress-relieving and porcelain firing cycle influence on marginal fit of commercially pure titanium and titanium-aluminum-vanadium copings

OBJECTIVES

This study evaluated: (1) the marginal fit of copings fabricated from commercially pure titanium (cp Ti) and titanium-aluminum-vanadium alloy (Ti-6Al-4V) after each firing cycle for a recommended porcelain; and (2) the effectiveness of a stress-relieving treatment on the fit. The results were compared with copings made with Pd-Ag alloy submitted to the recommended porcelain firing protocol.

METHODS

Bovine teeth were machined for metal-ceramic crowns and die casts were obtained for waxing patterns. The firing cycle of titanium porcelain was performed on cp Ti and Ti-6Al-4V copings obtained using the Rematitan System. A stress-relieving treatment (cp Ti treated and Ti-6Al-4V treated groups) was performed on original invested castings at the first porcelain firing temperature (800 degrees C). Fit (microm) was measured in the 'as cast' condition and after each porcelain firing cycle with a traveling microscope. The values were compared using the analysis of variance and Tukey's test (P<0.05), the Pd-Ag group was compared to titanium groups using Dunnett's test (P<0.05).

RESULTS

The marginal fit values in the as-cast condition (initial) were 84.43 microm for Ti-6Al-4V not treated, 76.35 microm for Ti-6Al-4V treated, 86.09 microm for cp Ti not treated, 97.66 microm for cp Ti treated and 58.11 microm for Pd-Ag group. The Ti-6Al-4V, cp Ti, and Pd-Ag groups exhibit significant differences in marginal fit values when the as-cast condition (initial) was compared with those after the recommended porcelain firing protocol (by Tukey's test at 5% probability level). No significant differences were observed between stress-relieving treated and not treated groups.Significance. The firing cycles used for porcelain build-up may worsen the fit of titanium copings to values that suggest no inferences to the detriment of clinical applications.

Fit of cast commercially pure titanium and Ti-6Al-4V alloy crowns before and after marginal refinement by electrical discharge machining

STATEMENT OF PROBLEM

Titanium has been suggested as a replacement for alloys currently used in single-tooth restorations and fixed partial dentures. However, difficulties in casting have resulted in incomplete margins and discrepancies in marginal fit.

PURPOSE

This study evaluated and compared the marginal fit of crowns fabricated from a commercially pure titanium (CP Ti) and from Ti-6Al-4V alloy with crowns fabricated from a Pd-Ag alloy that served as a control. Evaluations were performed before and after marginal refinement by electrical discharge machining (EDM).

MATERIAL AND METHODS

Forty-five bovine teeth were prepared to receive complete cast crowns. Stone and copper-plated dies were obtained from impressions. Fifteen crowns were cast with each alloy (CP Ti, Ti-6Al-4V, and Pd-Ag). Marginal fit measurements (in micrometers) were recorded at 4 reference points on each casting with a traveling microscope. Marginal refinement with EDM was conducted on the titanium-based crowns, and measurements were repeated. Data were analyzed with the Kruskal-Wallis test, paired t test, and independent t test at a 1% probability level.

RESULTS

The Kruskal-Wallis test showed significant differences among mean values of marginal fit for the as-cast CP Ti crowns (mean [SD], 83.9 [26.1] microm) and the other groups: Ti-6Al-4V (50.8 [17.2] microm) and Pd-Ag (45.2 [10.4] microm). After EDM marginal refinement, significant differences were detected among the Ti-6Al-4V crowns (24.5 [10.9] microm) and the other 2 groups: CP Ti (50.6 [20.0] microm) and Pd-Ag (not modified by EDM). Paired t test results indicated that marginal refinement with EDM effectively improved the fit of CP Ti crowns (from 83.9 to 50.6 microm) and Ti-6Al-4V crowns (from 50.8 to 24.5 microm). However, the difference in improvement between the two groups was not significant by t test.

CONCLUSION

Within the limitations of this study, despite the superior results for Ti-6Al-4V, both groups of titanium-based crowns had clinically acceptable marginal fits. After EDM marginal refinement, the fit of cast CP Ti and Ti-6Al-4V crowns improved significantly.

Effect of thermocycling on bond strength and elasticity of 4 long-term soft denture liners

STATEMENT OF PROBLEM

Two problems found in prostheses with soft liners are bond failure to the acrylic resin base and loss of elasticity due to material aging.

PURPOSE

This in vitro study evaluated the effect of thermocycling on the bond strength and elasticity of 4 long-term soft denture liners to acrylic resin bases.

MATERIAL AND METHODS

Four soft lining materials (Molloplast-B, Flexor, Permasoft, and Pro Tech) and 2 acrylic resins (Classico and Lucitone 199) were processed for testing according to manufacturers' instructions. Twenty rectangular specimens (10 x 10-mm(2) cross-sectional area) and twenty cylinder specimens (12.7-mm diameter x 19.0-mm height) for each liner/resin combination were used for the tensile and deformation tests, respectively. Specimen shape and liner thickness were standardized. Samples were divided into a test group that was thermocycled 3000 times and a control group that was stored for 24 hours in water at 37 degrees C. Mean bond strength, expressed in megapascals (MPa), was determined in the tensile test with the use of a universal testing machine at a crosshead speed of 5 mm/min. Elasticity, expressed as percent of permanent deformation, was calculated with an instrument for measuring permanent deformation described in ADA/ANSI specification 18. Data from both tests were examined with 1-way analysis of variance and a Tukey test, with calculation of a Scheffé interval at a 95% confidence level.

RESULTS

In the tensile test under control conditions, Molloplast-B (1.51 +/- 0.28 MPa [mean +/- SD]) and Pro Tech (1.44 +/- 0.27 MPa) liners had higher bond strength values than the others (P <.05). With regard to the permanent deformation test, the lowest values were observed for Molloplast-B (0.48% +/- 0.19%) and Flexor (0.44% +/- 0.14%) (P <.05). Under thermocycling conditions, the highest bond strength occurred with Molloplast-B (1.37 +/- 0.24 MPa) (P <.05). With regard to the deformation test, Flexor (0.46% +/- 0.13%) and Molloplast-B (0.44% +/- 0.17%) liners had lower deformation values than the others (P <.05).

CONCLUSION

The results of this in vitro study indicated that bond strength and permanent deformity values of the 4 soft denture liners tested varied according to their chemical composition. These tests are not completely valid for application to dental restorations because the forces they encounter are more closely related to shear and tear. However, the above protocol serves as a good method of investigation to evaluate differences between thermocycled and control groups.