The effect of mechanical loading on the cusp defection of premolars restored with direct and indirect techniques.

AIM: This study assessed the effect of fatigue load cycling on human premolars restored with MOD restorations (direct and indirect approaches) on cuspal defection, compared to intact teeth (unprepared) and unrestored teeth with an inlay preparation. MATERIALS AND METHODS: MOD inlay preparations were performed on sixty premolars with their roots embedded in acrylic resin. These teeth were divided into six groups (n = 10): (1) intact teeth; (2) unrestored and prepared teeth; (3) teeth restored with direct composite resin; (4) teeth restored with an indirect composite resin; (5) teeth restored with injected ceramic inlays (IPS Empress 2 (Ivoclar); (6) teeth restored with CAD/CAM inlays made of feldspathic ceramic (Vita Mark II). All of the indirect restorations were adhesively cemented. Strain-gauges were bonded to the buccal and lingual surfaces of the specimens. Compressive axial loading of 100N was applied on the occlusal face of the specimens to measure the cuspal deflection (microstrain) under compressive loading. These measurements were obtained before and after mechanical cycling (1 Hz, 37°C, 100,000x). RESULTS: Comparing the results obtained before and after fatiguing, the cuspal defection increased only in the CAD/CAM approach. The prepared tooth group had the highest cuspal defection, before and after mechanical cycling. CONCLUSION: The evaluated restoring approaches decrease the cuspal defection, consequently appear to improve the cuspal reinforcement.

Dimensional change of elastomeric materials after immersion in disinfectant solutions for different times.

AIM: The aim of this study was to evaluate the influence of immersion period in two disinfectant solutions on dimensional change of four elastomeric impression materials. MATERIALS AND METHODS: Four representative materials of each class of elastomers: Xantopren (polydimethylsiloxane-PDS), Express (polyvinyl siloxane-PVS); Permlastic (polysulfide- PS) and Soft Impregum (polyether-EP) were mixed according to manufacturers' instructions and then inserted into a metal matrix prepared according to the specification of ISO 4823. The molds were removed from the matrix after 7 minutes and immersed in disinfectant solutions (sodium hypochlorite 0.5 and 2% glutaraldehyde) for 5, 10, 20, 30 and 60 minutes (n = 7), except the control group, which was not immersed. Once removed from solutions, the test samples were washed in water for 15 seconds, dried and measured three times, using a comparative optical microscope, with accuracy of 0.0005 mm. The analysis of variance with three criteria and Tukey's test with significance level of 5% showed that differences in linear dimensions of the materials analyzed were not statistically significant (p > 0.05) after soaking in sodium hypochlorite 0.5 and 2% glutaraldehyde, for the tested periods of time. CLINICAL SIGNIFICANCE: Combinations of molding material and disinfecting solution can be used in the dental clinic for infection control, without changing the dimensional molds, for immersion periods not longer than 20 minutes.

Effects of horizontal misfit and bar framework material on the stress distribution of an overdenture-retaining bar system: a 3D finite element analysis.

PURPOSE: To evaluate the influence of horizontal misfit change and bar framework material on the distribution of static stresses in an overdenture-retaining bar system using finite element (FE) analysis. MATERIALS AND METHODS: A 3D FE model was created including two titanium implants and a bar framework placed in the anterior part of a severely resorbed jaw. The model set was exported to mechanical simulation software, where horizontal displacement (10, 50, 100, and 200 µm) was applied simulating the settling of the framework, which suffered shrinkage during laboratory procedures. Four bar materials (gold alloy, silver-palladium alloy, commercially pure titanium, and cobalt-chromium alloy) were also simulated in the analysis using 50 µm as the horizontal misfit. Data were qualitatively evaluated using von Mises stress, given by the software. RESULTS: The misfit amplification presented a great increase in the stress levels in the inferior region of the bar, screw-retaining neck, cervical and medium third of the implant, and cortical bone tissue surrounding the implant. The higher stiffness of the bar presented a considerable increase in the stress levels in the bar framework only. CONCLUSION: The levels of static stresses seem to be closely linked with horizontal misfit, such that its amplification caused increased levels of stress in the structures of the overdenture-retaining bar system. On the other hand, the stiffness of the bar framework presented a lower effect on the static stress levels.

Bond strength of fiber posts in different root thirds using resin cement.

PURPOSE: The aim of the study was to assess the in vitro bond strength (BS) of glass fiber posts (GF) and carbon fiber posts (CF) in the cervical, middle, and apical thirds of root canals cemented with RelyX-Unicem (RX) and Cement-Post (CP). MATERIALS AND METHODS: Forty maxillary canines were divided into 4 groups (n = 10) according to the cement and post used: group 1: GF and RX; group 2: CF and RX; group 3: GF and CP; group 4: CF and CP. The push-out test was applied in the cervical, middle and apical thirds of each specimen to assess bond strength of the cement/post complex to the root canal wall. The data obtained were submitted to ANOVA (Bonferroni test, p < 0.05), and fracture analysis was done with SEM. RESULTS: The GF posts presented the best results when cemented with RX and with CP (p < 0.05). RX presented the highest BS values for both GF and CF (p < 0.05). For all the groups, BS was higher in the cervical third, followed by the middle and apical thirds. Fracture analysis showed a predominance of cohesive fracture of posts for RX, and a predominance of adhesive fracture between dentin/cement, and mixed failure mode for CP. CONCLUSION: GF posts cemented with RX presented the highest BS values in all root thirds.

Effect of light-curing method and indirect veneering materials on the Knoop hardness of a resin cement.

This study evaluated the Knoop hardness of a dual-cured resin cement (Rely-X ARC) activated solely by chemical reaction (control group) or by chemical / physical mode, light-cured through a 1.5 mm thick ceramic (HeraCeram) or composite (Artglass) disc. Light curing was carried out using conventional halogen light (XL2500) for 40 s (QTH); light emitting diodes (Ultrablue Is) for 40 s (LED); and Xenon plasma arc (Apollo 95E) for 3 s (PAC). Bovine incisors had their buccal face flattened and hybridized. On this surface a rubber mold (5 mm in diameter and 1 mm in height) was bulk filled with the resin cement. A polyester strip was seated for direct light curing or through the discs of veneering materials. After dry storage in the dark (24 h 37 degrees C), the samples (n = 5) were sectioned for hardness (KHN) measurements, taken in a microhardness tester (50 gF load 15 s). The data were statistically analyzed by ANOVA and Tukey's test (alpha = 0.05). The cement presented higher Knoop hardness values with Artglass for QTH and LED, compared to HeraCeram. The control group and the PAC/Artglass group showed lower hardness values compared to the groups light-cured with QTH and LED. PAC/HeraCeram resulted in the worst combination for cement hardness values.

Fracture loads of all-ceramic crowns under wet and dry fatigue conditions.

PURPOSE: The aim of this study was to test the hypothesis that fracture loads of fatigued dental ceramic crowns are affected by testing environment and luting cement. MATERIALS AND METHODS: One hundred and eighty crowns were prepared from bovine teeth using a lathe. Ceramic crowns were prepared from three types of ceramic systems: an alumina-infiltrated ceramic, a lithia-disilicate-based glass ceramic, and a leucite-reinforced ceramic. For each ceramic system, 30 crowns were cemented with a composite resin cement, and the remaining 30 with a resin-modified glass ionomer cement. For each ceramic system and cement, ten specimens were loaded to fracture without fatiguing. A second group (n = 10) was subjected to cyclic fatigue and fracture tested in a dry environment, and a third group (n = 10) was fatigued and fractured in distilled water. The results were statistically analyzed using one-way ANOVA and Tukey HSD test. RESULTS: The fracture loads of ceramic crowns decreased significantly after cyclic fatigue loading (p

Dimensional accuracy of upper complete denture bases: the effect of metallic flask closure methods.

OBJECTIVES: To verify the dimensional accuracy of upper complete denture bases under the effect of different methods of metallic flask closure. MATERIALS AND METHODS: Wax record bases were assigned to six groups: 1-2: traditional clamp; 3-4: RS system; and 5-6: flask with screws. Flasks were immediately polymerised or bench stored for 6 h prior to polymerisation. Resin base-cast sets were sectioned at regions corresponding to the canines, first molars and posterior palatal zone. Gap discrepancies were measured at five points: right and left ridge crests, palatal midline, and right and left marginal limits of the flanges. An optical micrometer was used for measurement purposes. RESULTS: Data were submitted to anova, and the means compared by Tukey's test (alpha = 0.05). Results revealed significant differences in the flask closure technique, polymerisation time, section, and their interactions. Discrepancy values for the RS system and flask with screws were significantly lower than those related to the traditional clamp, regardless of whether resin polymerisation was immediate or delayed for 6 h. CONCLUSIONS: Flask closure methods should be considered when the denture base stability and comfort of the patient are being assessed during clinical use of the dentures.

NaOCl effects on primary and permanent pulp chamber dentin.

OBJECTIVES: The dentin quality of primary and permanent pulp chamber was inspected by Fourier-transformed Raman spectroscopy (FT-Raman) and scanning electron microscopy (SEM). Fragments of pulp chamber dentin were obtained from 20 human molar crowns (primary and permanent). METHODS: The fragments were assigned to 8 groups (n=5)-Primary teeth: G1, pulp chamber dentin; G2, pulp chamber dentin irrigated with NaOCl 1% (30 min); G3, pulp chamber dentin irrigated with NaOCl 1% (30 min) and etched by 35% phosphoric acid; G4, pulp chamber dentin etched by 35% phosphoric acid. Permanent teeth: G5, pulp chamber dentin; G6, pulp chamber dentin irrigated with NaOCl 1% (30 min); G7, pulp chamber dentin irrigated with NaOCl 1% (30 min) and etched by 35% phosphoric acid; G8, pulp chamber dentin etched by 35% phosphoric acid. The spectra were subjected to the Cluster analysis. The SEM images were scored. RESULTS: Inorganic content: There was a difference between primary and permanent dentin. The groups treated with NaOCl were statistically similar between them, but differed from the groups not treated. Organic content: There was no difference between primary and permanent dentin. The groups became similar after NaOCl and phosphoric acid treatments. The microscopic images showed the presence of calcospherites on permanent dentin and their absence on primary dentin. CONCLUSIONS: The NaOCl changed the inorganic content in both dentitions; regardless of the following phosphoric acid etching. However, the chemical changes caused by NaOCl were not detected by SEM when it was followed by etching.

The influence of 30-day-old Streptococcus mutans biofilm on the surface of esthetic restorative materials--an in vitro study.

OBJECTIVE: To evaluate the effects of Streptococcus mutans biofilm/restorative materials interaction on surface roughness, hardness and morphology of materials tested. METHODS: Empress 2 (E2), Filtek Supreme (FS), Vitremer (V) and Ketac Molar Easymix (KM) were tested. Twenty-five disks of each material were made and divided into three storage groups: (1) 100% relative humidity (n=5); (2) growth medium (BHI and 1% sucrose) (n=5); (3) S. mutans biofilm-growth medium (n=15). Before storage, hardness measurements were immediately obtained from group 1 specimens. After 30 days of storage, the specimens were cleaned in order to obtain the surface roughness and hardness values, besides morphology analysis by scanning electron microscopy. RESULTS: The surface roughness and hardness values obtained from E2 and FS specimens did not present statistically significant differences among the groups 1, 2 and 3 and between immediate and 30-day-old specimens of each material. However, group 3 specimens of V and KM showed statistically significant higher surface roughness means than other groups. Group 1 specimens of V and KM also showed higher hardness values than the immediate values. Group 3 specimens of V presented decreased hardness values compared with other groups. The scanning electron micrographs showed an increase in surface degradation from group 1 to group 3 for FS, V and KM. CONCLUSIONS: Thirty-day-old biofilm promotes a negative effect on the surface morphology of FS, V and KM, on the surface roughness of V and KM and on the hardness of V.

In vitro evaluation of surface roughness of 4 resin composites after the toothbrushing process and methods to recover superficial smoothness.

OBJECTIVE: This study evaluated the efficiency of repolishing, sealing with surface sealant, and the joining of both in decreasing the surface roughness of resin-based composites after a toothbrushing process. METHOD AND MATERIALS: Ten specimens of each composite (Alert, Z100, Definite, and Prodigy Condensable), measuring 2 mm in thickness and 4 mm in diameter, were made and submitted to finishing and polishing processes on both sides of the specimens using the Sof-Lex system. The specimens were then subjected to toothbrushing (30,000 cycles), and surface roughness (Ra) was analyzed with a Surfcorder SE 1700 profilometer. The upper surface of each composite was etched with 37% phosphoric acid, and the surface-penetrating sealant Protect-it was applied on 1 surface. The roughness of these surfaces was again measured. On the other side, the surface of the specimen was repolished, and the efficiency of this procedure was measured using the profilometer. The surface roughness resulting from the joining of the 2 methods was verified by applying, in the final stage, the surface-penetrating sealant on the repolished surface. Data were analyzed with analysis of variance and Tukey test (P <.05). RESULTS: Results showed that the lowest surface roughness values were obtained for Definite, Z100, and Prodigy Condensable after the repolishing process and after the repolishing plus sealing. For Alert, the joining of repolishing plus sealing promoted the lowest values of surface roughness. CONCLUSION: Of the resin-based composites, Alert demonstrated the highest values of surface roughness in all the techniques tested.

Microdureza de uma resina composta micro-híbrida submetida a diferentes tempos de exposição e aparelhos fotopolimerizadores (AU) / Microhardness of a microhybrid composite resin submitted to different exposition times and lightcuring devices

Introdução - A proposta deste trabalho foi avaliar o desempenho de três aparelhos fotopolimerizadores utilizados com tempos de exposição diferentes sobre a microdureza de um compósito, em diferentes profundidades (1/2/3mm). Material e Método - Foram utilizados os aparelhos Curing Light com 10/40 segundos, o Kreativ com 6/10/40 segundos e o Apollo 95E com 6/10 segundos. Cinco amostras foram confeccionados para cada aparelho, utilizando uma matriz metálica contendo 4 mm de diâmetro e 5 mm de altura. As amostras foram mantidas por 24h a 37 0 C até serem submetidos ao teste de microdureza Vickers. Foram realizadas seis impressões a cada milímetro. Resultados - A partir da análise estatística, usando o teste Kruskal-Wallis (p<0,0001), observou-se que, independente do tempo e aparelho, no 1 0 mm sempre se obteve melhor microdureza. Conclusões - Com 10 segundos, independente da profundidade, o Kreativ e o Apollo foram melhores que o Curing Light. Utilizando-se o teste Mann-Whitney com 6 segundos, os aparelhos Kreativ e Apollo tiveram no 1ºmm o mesmo grau de polimerização, sendo o Apollo significativamente melhor no 2ºmm e 3ºmm (p<0,0001). O mesmo foi observado para o Curing Light e o Kreativ, em relação ao tempo de 40 segundos, tendo o primeiro obtido melhores valores de microdureza no 2ºmm e 3ºmm (p<0,0001). O Curing Light, quando utilizado com 40 segundos, mostrou-se melhor do que os demais aparelhos testados

Introduction - The aim of this study was to evaluate the performance of 3 lightcuring devices used with different exposition times on the microhardness of a composite, Charisma-A3, in different depths (1/2/3mm). Material and Method - The used devices were the Curing Light with exposition time of 10/40 seconds, the Kreativ with exposition time of 6/10/40 seconds and the Apollo 9Ë with exposition time of 6/10 seconds. The light intensity of the devices was determined using a radiometer. Five specimens were confectioned for each device, using a metallic matrix contends 4 mm of diameter and 5 mm of height. After lightcuring, the specimens were kept for 24 hours at 37º C in specific incubator till they were submitted to the Vickers microhardness test. In order to do that, six impressions to each millimeter in a standardized depth of 3 mm were made. Results - From statistic analysis using the Kruskal-Wallis test (p<0,0001), it was observed that independent of time and device in 1ºmm always microhardness was gotten better. Conclusions - In relation to 10 seconds of polymerization, independent of the depth, the Kreativ and the Apollo were better than the Curing Light. Using the Mann-Whitney test, it was observed that with 6 seconds the devices Kreativ and Apollo had the same polymerization degree in 1ºmm, being Apollo significantly better in 2º mm and 3º mm (p<0,0001). The same was observed for the devices Curing Light and Kreativ in relation to the time of 40 seconds, with the first one getting better values of microhardness in 2ºmm and 3ºmm (p<0,0001). Curing Light device when used with exposition time of 40 seconds revealed to be the best

Effect of time and polymerization cycle on the degree of conversion of a resin composite.

The aim of this investigation was to verify the influence of 3 light curing units on the degree of conversion, using different irradiation conditions: 1) manufacturers' recommended times of photo-activation, 2) standardizing total energy density among the units and 3) standardizing energy density at the 450-490 nm wavelength range among the units and the effect of these irradiation conditions on the post-cure. Three light curing units were used: halogen, light emitting diodes (LED) and xenon plasma. Seven groups were tested (n=6). Twenty-four hours after the photo-activation procedures, half of the composite specimens were submitted to Fourier Transformed Infrared Spectroscopy analysis. The other half was analyzed after 1 month. The results were submitted to 2-way ANOVA and Tukey's test (5%). Twenty-four hour analysis revealed that the second set of irradiation conditions produced a similar degree of conversion among the LCUs. After 1 month, the conversion values were statistically higher for 20 seconds of halogen exposure (increased from 46.78 to 49.66%), 20 seconds of LED exposure (from 46.20 to 51.15%), 30 seconds of LED exposure (from 48.29% to 50.68%) and 3 seconds of PAC exposure (from 42.57 to 51.39%). The initial degree of conversion and post-cure depended on the photo-activation condition applied.

Avaliação da infiltração marginal em restaurações diretas e indiretas em compósito "condensável" e convencional / Evaluation of microleakage in direct and indirect restorations in condensable and convencional composite resin

Este estudo comparou o nível da infiltração marginal em restaurações diretas e indiretas, confeccionadas com compósitos convencional ou "condensável". Para isto, sessenta dentes bovinos recém-extraídos foram utilizados, nos quais cavidades padronizadas tipo slot foram confeccionadas na superfície mesial dos dentes com término 1mm abaixo da JCE (junção cemento/esmalte). As amostras foram divididas aleatoriamente em seis grupos (Grupo 1: restauração direta/Z100; Grupo 2: restauração direta/Surefil; Grupo 3: restauração indireta/alginato/Z100; Grupo 4: restauração indireta/alginato/Surefil; Grupo 5: restauração indireta/silicona por adição/Z100; Grupo 6: restauração indireta/silicona por adição/Surefil). Para a cimentação das restaurações indiretas foi utilizado o cimento resinoso de polimerização dual Rely X. Os materiais foram manipulados de acordo com as instruções dos fabricantes. Para avaliação da infiltração marginal, as amostras ficaram imersas em solução de azul de metileno tamponado a 2%, por quatro horas, em temperatura ambiente. Após serem lavados, foram seccionados para avaliação da penetração do corante na interface dente restauração, utilizando lupa estereoscópica com aumento de 63X. Os dados foram submetidos à análise estatística não paramétrica de Kruskal-Wallis. Não houve diferença estatística entre os dentes restaurados com Z100 e Surefil, para as três técnicas utilizadas. Tanto para o compósito Z100, quanto para o Surefil, as restaurações diretas apresentaram maiores níveis de infiltração marginal que as indiretas. Nas restaurações indiretas, independente das cavidades serem moldadas com alginato ou silicona por adição, não houve diferença estatística entre si

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.

Effect of resin liners and photoactivation methods on the shrinkage stress of a resin composite.

PURPOSE: This study was undertaken to evaluate the effect of three different photoactivation methods on the polymerization shrinkage stress of a resin composite using different resin liners. MATERIALS AND METHODS: Three photoactivation methods using a quartz-tungsten-halogen light were evaluated: continuous light, soft start, and intermittent light. Three lining groups were tested: one or three coats of adhesive, and flowable composite. The stress was measured using a universal testing machine. After the stress measurement, Knoop hardness numbers (KHNs) were evaluated to verify indirectly the degree of conversion of the composite using the three photoactivation methods. The data were submitted to analysis of variance and Tukey's test (p < .05). RESULTS: Intermittent light was always associated with statistically lower stress values when compared with continuous light. Statistical differences were not observed when continuous light and soft start were compared. The use of a flowable composite liner significantly reduced the stress generation when compared with the use of one adhesive coat. The three adhesive coats groups showed intermediate stress values. The hardness test showed no statistical difference between that achieved with continuous light and soft start. These two methods showed statistically higher KHNs when compared with results with intermittent light. CLINICAL SIGNIFICANCE: Photoactivation using intermittent light may lead to a significant reduction in shrinkage stress levels. This effect could be attributed to a significant reduction of the polymerization rate and/or a decrease in the degree of conversion. The use of a flowable composite liner reduced the stress levels when compared with levels when one coat of adhesive was used. This is possibly related to the higher thickness of the flowable composite layer.

Compressive strength recovery by composite onlays in primary teeth. Substrate treatment and luting agent effects.

OBJECTIVES: To evaluate 1% NaOCl treatment and two resin luting agent effects on compressive strength recovery in composite onlays on primary teeth and to analyze the fractures type. METHODS: Forty sound primary molars crowns were prepared in the standard machine and randomly divided into four groups (n=10): G1 (1% NaOCl/ 30 min+EnForce); G2 (without 1% NaOCl EnForce); G3 (1% NaOCl/ 30 min+Rely X); G4 (without 1% NaOCl+Rely X). The onlays were made using Z250 composite on plaster models. Ten sound teeth were used as control group (CG). All groups were submitted to compression mechanic test in a universal test machine INSTRON at 1mm/min cross-head speed. After that, the data (kgf) were submitted to ANOVA test (alpha=0.05). Finally, the fracture types were classified in a crescent scale (1-5) related with severity degree and submitted to Fisher's Exact Test (p<0.05). Scanning electronic microscope analysis was done in order to illustrate the fractures sites. RESULTS: The values of compressive strength of experimental groups did not differ each others neither from control group (p>0.05). The results from fracture type showed that types 5 and 4 fractures (most severe) present the highest percentage to experimental groups. Conversely, the CG showed higher percentage of fracture types 2 and 3. CONCLUSIONS: This research found that the composite onlays recovered the compressive strength compared to sound teeth, regardless of the substrate treatment and cement agent used. Nevertheless, no group showed similar type of fractures to CG, which had more frequency of less severe fracture types.

Temperature change and hardness with different resin composites and photo-activation methods.

This study verifies whether there is any temperature change during photoactivation of two resin composites (Filtek Z250 and Filtek Flow) with three different light curing methods (conventional halogen light curing unit, light emitting diodes curing unit and xenon plasma arc curing unit) and the relationship of temperature change with resin composite hardness. A type-K thermocouple registered the temperature rise peak in an elastomer mold during photoactivation. After photoactivation, the specimens were submitted to Knoop hardness test performed by an indenter (HMV-2000) under a load of 50g for 15 seconds. Both the temperature change data and results of the Knoop hardness test were submitted to ANOVA and Tukey's test at the 5% significance level. No statistical differences in temperature rise were recorded for the different composites following processing by light curing unit (p>0.05). The conventional halogen source produced statistically higher temperatures (p<0.05) than the other units. The plasma arc source promoted statistically lower (p<0.05) Knoop hardness values and temperature changes than the other light curing units.

Effect of cyclic compressive loading on the bond strength of an adhesive system to dentin after collagen removal.

PURPOSE: The objective of this study was to verify the effect of cyclic compressive loading on the shear bond strength of an adhesive system following collagen removal. MATERIALS AND METHODS: Sixty bovine teeth were divided into 4 groups based on the adhesive procedure used: groups 1 and 2--etching with 35% phosphoric acid and application of the Single Bond adhesive system; groups 3 and 4--after etching, a 10% sodium hypochlorite solution was applied for 1 min before the application of the adhesive. In all the specimens, a Z100 resin cylinder was built up over the bond area. Groups 2 and 4 were submitted to 500,000 cycles with a load of 100 N. RESULTS: The mean values for the shear bond test (MPa) were: group 1: 7.37 +/- 1.15; group 2: 5.72 +/- 1.66; group 3: 5.95 +/- 1.21; group 4: 3.66 +/- 1.12. There was no difference between groups 1 and 2 (p > 0.01). Between groups 1 and 3, 2 and 4, and 3 and 4 there was a significant difference (p < 0.01). The majority of the specimens demonstrated an adhesive failure. CONCLUSION: The application of sodium hypochlorite on dentin decreased the values of shear bond strength, as did the load cycling in the group treated with sodium hypochlorite.

Effect of the increase of energy density on Knoop hardness of dental composites light-cured by conventional QTH, LED and xenon plasma arc.

The aim of this study was to evaluate the effect of the increase of energy density on Knoop hardness of Z250 and Esthet-X composite resins. Cylindrical cavities (3 mm in diameter X 3 mm in depth) were prepared on the buccal surface of 144 bovine incisors. The composite resins were bulk-inserted and polymerized using different light-curing units and times: conventional QTH (quartz-tungsten-halogen; 700 mW/cm(2); 20 s, 30 s and 40 s); LED (light-emitting diode; 440 mW/cm(2); 20 s, 30 s and 40 s); PAC (xenon plasma arc; 1700 mW/cm(2); 3 s, 4.5 s and 6 s). The specimens were stored at 37 degrees C for 24 h prior to sectioning for Knoop hardness assessment. Three measurements were obtained for each depth: top surface, 1 mm and 2 mm. Data were analyzed statistically by ANOVA and Tukey's test (p<0.05). Regardless of the light source or energy density, Knoop hardness of Z250 was statistically significant higher than that of Esthet-X (p<0.05). Specimens cured with PAC had lower hardness than those cured with QTH and LED (p<0.05). Higher Knoop hardness was obtained when the energy density was increased for LED and PAC (p<0.05). No statistically significant differences (p>0.05) were found for QTH. Knoop hardness values decreased with the increase of depth. The increase of energy density produced composites with higher Knoop hardness means using LED and PAC.

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.