Comparison between two methods to evaluate temperature changes produced by composite light curing units and polymerization techniques.

AIM: This study evaluated the temperature change into the pulp chamber during the light curing of composite resin by direct (bovine tooth) and indirect (matrix) methods. METHODS: Direct method: fifty standardized cavities (2x2x2 mm) were prepared in bovine incisors, which were randomly assigned to evaluation of the temperature changes in the pulp chamber. Indirect method: temperature changes were evaluated through a dentine slice of 1.0 mm thickness in a elastomer cubic mold (2x2x2 mm). Filtek Z250 composite resin (3M/ESPE) was photo-activated using three light curing units: quartz-tungsten-halogen (QTH) by continuous, soft-start or intermittent light modulations; light emitting diode (LED); and plasma arc-curing (PAC). Ten groups (N.=10) were established according to technique evaluation and photo-activation methods. All experiments were carried out in a controlled environment (37 °C and 50 ± 10% relative humidity). The temperature changes were recorded using a digital thermometer attached to a type-K thermocouple in contact with the dentin slice (indirect method) or in contact with the axial wall (dentin) of pulp chamber (direct method). The results were submitted to ANOVA and Tukey's test (α=0.05). RESULTS: Temperature changes were statistically higher for the matrix indirect method (2.56 ºC) than bovine teeth direct method (1.17ºC). The change temperature was statistically higher for the PAC (1.77 ºC) when compared to other photo-activation modes in bovine teeth direct method. CONCLUSION: The two methods of temperature evaluation were different, however indirect method detected the higher temperature increase. Higher energy density arising from the light curing units and polymerization techniques promoted higher temperature increase.

Assessment of the polymerization contraction stress of composites photoactivated by halogen light and light-emitting diode.

AIM: The aim of this study was to compare the polymerization contraction stress of composites photoactivated by two light sources: quartz tungsten halogen light (QTH) and light emitting diode (LED). METHODS: Glass rods were fabricated (5.0 mm X 5.0 cm) and one of the surfaces was air abraded with aluminum oxide. An adhesive was applied to this surface and photoactivated by LED. The glass rods were assembled to a Universal Testing machine (Instron - 5565) and the composite were applied to the lower rod using a manual instrument. The upper rod was placed closer, at 2 mm, and an extensometer was attached to the rods. The twenty composites were polymerized by either by QTH (N.=10) or LED (N.=10). Polymerization was carried out using two apparatuses positioned in opposite sides, which were simultaneously activated for 30 seconds. Contraction stress was analyzed twice: shortly after polymerization (t30s) and 30 minutes later (t30min). RESULTS: The contraction stress for all composites was higher at t30min than at t30s, regardless of the activation source. Z100 showed lower contraction stress values (P<0.05) compared to the other composites. Regarding to Charisma and TPH, the photoactivation source had no influence on contraction stress, except for Z100 at t30min. CONCLUSIONS: It was concluded that composite composition is the factor that most influence the polymerization contraction stress.

Radiopacity of root filling materials using digital radiography.

AIM: To evaluate radiopacity of root filling materials using digital radiography. METHODOLOGY: The sealers tested were AH Plus, Endofill, EndoREZ and Epiphany. Gutta-percha (Dentsply Maillefer) and Resilon cones were also tested. Acrylic plates, containing six wells, measuring 1 mm in depth and 5 mm in diameter, were prepared for the test, and filled with the materials. The test samples were radiographed together with an aluminium stepwedge calibrated in millimetres, according to ANSI/ADA Specification 57. For the radiographic exposures, digital imaging plates and an X-ray machine at 70 kVp and 8 mA were used. The object-to-focus distance was 30 cm, and the exposure time, 0.2 s. After the laser optic reading process, the software determined the radiopacity of the standardized areas, using grey-scale values, calculating the average radiographic density for each material. RESULTS: The decreasing values of radiopacity of the studied materials, expressed in millimetres of aluminium equivalent, were: Resilon (13.0), AH Plus(TM) (11.2), gutta-percha (9.8), Epiphany (8.0), Endofill (6.9) and EndoREZ (6.6). CONCLUSION: All materials had radiopacity values above 3 mm of aluminium recommended by ANSI/ADA Specification 57.

Influence of flask closure and flask cooling methods on tooth movement in maxillary dentures.

PURPOSE: This study investigated the tooth movement of standardized simulated dentures processed by traditional closure or the new Rafael Saide (RS) tension system when cooled in the curing water itself or in curing water followed by bench storage for 3 hours. MATERIALS AND METHODS: Forty stone casts were formed from a mold of an edentulous maxillary arch. The wax denture record bases were made on the casts; the height of the wax rim occlusion was 20 mm in the labial sulcus of the cast and 10 mm in the posterior region. The upper stone cast was mounted on a Mondial 4000 semi-adjustable articulator with wax rim interocclusal references in relation to the lower stone cast teeth. Metallic pins were placed in the incisal border of the maxillary central incisors (I), labial cusp of the first premolars (PM), and mesiolabial cusp of the second molars (M). The incisor-to-incisor (I-I), premolar-to-premolar (PM-PM), and molar-to-molar (M-M) transversal distances and left incisor-to-left molar (LI-LM), and right incisor-to-right molar (RI-RM) anteroposterior distances were measured before and after denture polymerization with an optical microscope with a tolerance of 0.0005 mm. For traditional closure, the dentures were flasked conventionally in standard metallic flasks, which were afterward placed in spring clamps. For the new RS system closure, the flasks were pressed between the metallic plates of the tension system after the final closure. The Clássico heat-polymerizing acrylic resin dough was packed in the flasks under a final packing pressure of 1.250 kg f. Twelve hours after flask closure, the dentures were polymerized in a moist heat-polymerizing cycle for 9 hours at 74 degrees C. The denture was deflasked after cooling in the water of the polymerizing cycle (groups A and C) or in the water of the polymerizing cycle and then bench-stored for 3 hours (groups B and D). Collected data were analyzed with analysis of variance and Tukey's test (p< 0.05). RESULTS: There was no statistically significant difference (p> 0.05) between the conventional and new RS system closure methods for the transversal distances after polymerization in all studied groups. The anteroposterior distances did not change with deflasking after water bath cooling. There were statistically significant differences (p< 0.05) in the anteroposterior distances with deflasking after water bath cooling and then bench storage for 3 hours. CONCLUSION: Tooth movement was similar in dentures processed by traditional closure and by the new RS tension system, with the exception of the anteroposterior distances when the flasks were cooled in their own curing water and bench-stored for 3 hours.

Halogen and LED light curing of composite: temperature increase and Knoop hardness.

This study assessed the Knoop hardness and temperature increase provided by three light curing units when using (1) the manufacturers' recommended times of photo-activation and (2) standardizing total energy density. One halogen--XL2500 (3M/ESPE)--and two light-emitting diode (LED) curing units--Freelight (3M/ESPE) and Ultrablue IS (DMC)--were used. A type-K thermocouple registered the temperature change produced by the composite photo-activation in a mold. Twenty-four hours after the photo-activation procedures, the composite specimens were submitted to a hardness test. Both temperature increase and hardness data were submitted to ANOVA and Tukey's test (5% significance). Using the first set of photo-activation conditions, the halogen unit produced a statistically higher temperature increase than did both LED units, and the Freelight LED resulted in a lower hardness than did the other curing units. When applying the second set of photo-activation conditions, the two LED units produced statistically greater temperature increase than did the halogen unit, whereas there were no statistical differences in hardness among the curing units.

Influence of number and position of flasks in the monomer release, Knoop hardness and porosity of a microwave-cured acrylic resin.

Simultaneous irradiation of multiple flasks may have deleterious effects on the polymerization of microwave cured-acrylic resins. This study evaluated the effect of the number and position of flasks in the monomer release, Knoop hardness and porosity of a microwave-cured acrylic resin. Samples were made of Acron MC(R) (AMC, GC Dent. Ind. Corp.) processed at 500 W. The following associations of the number and position of the flasks were tested: one simple flask centrally placed on the turning plate (I, control); two flasks, one in the centre (IIa) and the other peripherally placed in the plate (IIb); two flasks centrally, one above (IIIa) and the other below (IIIb). The processing time varied according to the number of flasks: 3 or 4.5 min for one or two flasks, respectively. For monomer release, each specimen (n = 12) was put in an assay glass tube containing 6 mL of deionized water that was changed daily. Monomer levels were obtained by spectrophotometry at 206 nm. For hardness test (n = 10), 12 indentations were made in the surface of each specimen. Immersing the polished specimens in permanent ink and counting the porous in a stereo light microscope verified the porosity. Monomer release was significant before 24 h: GI = 263.1(153.3)a, GIIa = 236.9(180.2)a, GIIb = 441.5(446.2)a, GIIIa = 1216.6(857.9)b. Tukey test showed no statistically significant differences among the groups for porosity and hardness. Monomer release was affected by the position of the flask (P < 0.05).

Effect of the photo-activation method on polymerization shrinkage of restorative composites.

This study measured the gap that resulted from polymerization shrinkage of seven restorative resin composites after curing by three different methods. Contraction behavior, according to the specimen region, was also characterized. The materials used for this study were Alert (Jeneric/Pentron, Wallingford, CT 06492, USA), Surefil (Dentsply Caulk, Milford, DE 19963, USA), P60 (3M Dental Products, St Paul, MN 55144, USA), Z250 (3M), Z100 (3M), Definite (Degussa-Hüls, Hanau, Germany) and Flow-it (Jeneric/Pentron). The composite was placed in a circular brass mold 7 mm in diameter and 2 mm in height. Photo-activation was performed by a) continuous light (500 mW/cm2) for 40 seconds; b) stepped light with low intensity (150 mW/cm2) for 10 seconds and high intensity (500 mW/cm2) for 30 seconds and c) intermittent light (450 mW/cm2) for 60 seconds. The top and bottom surfaces were then polished and after 24 +/- 1 hours, the contraction gap was measured by SEM at variable pressure (LEO 435 VP, Cambridge, England). Results were analyzed by ANOVA and the means compared by Tukey's test (5%). The results demonstrated 1) the continuous light method presented the greatest gap values (15.88 microm), while the other methods demonstrated lower polymerization shrinkage values (stepped light, 13.26 microm; intermittent light, 12.79 microm); 2) restorative composites shrunk more at the bottom surface (15.84 microm) than at the top surface (12.11 microm) and (3) the composites Alert (12.02 microm), Surefil (11.86 microm), Z250 (10.81 microm) and P60 (10.17 microm) presented the least contraction gaps, followed by Z100 (15.84 microm) and Definite (14.06 microm) and finally Flow-it (23.09 microm) low viscosity composite, which had the greatest mean value.

Effect of refrigeration on tensile bond strength of three adhesive systems.

The purpose of this study was to investigate the tensile bond strengths of three adhesive systems applied to dentin at refrigerated and room temperatures. Ninety bovine incisor teeth were obtained, embedded in self-cured acrylic resin, abraded on a lathe under water spray and polished to 400 and 600 grit to form standardized dentin surfaces before randomly assigning to six groups (n = 15). The adhesive systems Scotchbond Multi-Purpose, Single Bond and Prime & Bond NT were applied to dentin according to the manufacturers' instructions at refrigerated temperature (4 degrees C) and at room temperature (23 degrees C), before bonding resin-based composite (Z 100). The specimens were stored in distilled water at 37 degrees C for 24 hours and submitted to tensile bond strength tests on a universal testing machine (EMIC DL-2000) at a crosshead speed of 0.5 mm/min. The resulting data were statistically analyzed using analysis of variance and Tukey's test. No statistical differences were found when the adhesive systems were applied at refrigerated and room temperatures. Scotchbond Multi-Purpose and Single Bond had significantly stronger tensile bond strengths than Prime & Bond NT at room and refrigerated temperatures (p < 0.01). Scotchbond Multi-Purpose and Single Bond were statistically similar. No adverse effects upon tensile bond strength were observed when adhesive systems were taken directly from refrigerated storage.

Influence of loading types on the shear strength of the dentin-resin interface bonding.

Small differences in the shear bond test can make critical differences in the bonding strength values. The purpose of this study was to compare the influence of the orthodontic-looped wire, stainless steel tape and chisel systems used in shear bonding tests to verify the resistance in the dentin-resin interface. Forty-eight human teeth were used and divided in three groups. The teeth were ground until a flat smooth surface was achieved, that was delimited with an adhesive tape containing a hole of 4 mm diameter. After, the dentine surface was treated with Scotchbond Multi Purpose and the composite Z-100 was applied in layers, through a stainless steel mold. The samples were stored at 37 degrees C and 100% of relative humidity for 24 h and, then, submitted to 500 thermal cycles. After, they were taken to an universal test machine (Otto Wolpert) with crosshead speed of 6 mm/min. The results were statistically analyzed using a Tukey's test (p\lt 0.05). The orthodontic-looped wire determined the highest values of shear bond (13.33 MPa), following by chisel (7.81 MPa) and stainless steel tape (4.87 MPa). The debonding values depend on a complex stress combination produced during the loading of the samples. Small variations in test methodologies give statistically different values for shear bond strength. Different shear strength methods in vitro make the comparative clinical performance of the resin filling materials difficult.

Influence of curing tip distance on composite Knoop hardness values.

The purpose of this paper was to study the influence of curing tip distance on Knoop hardness values, at different depths, of two composites, Z100 and Silux Plus. Specimens (5 mm in diameter and 2.5 mm in height) were prepared in a copper mold, covered with mylar strip and polymerized for 40 s, at 3 tip-to-composite surface distances: 0 mm (surface contact), 6 and 12 mm, utilizing an XL 3000 curing unit, with 750 mW/cm2 power. The specimens were then stored at 37 degrees C for 24 h. Knoop hardness values were measured using a microhardness tester, with a load of 50 g for 30 s for each indentation. Four specimens were made for each distance and composite and eighteen indentations were made of each specimen. The results were submitted to analysis of variance and Tukey test at 5% significance level. The results indicated that 1) composite Z100: the larger the curing tip distance in relation to the composite, the lower the Knoop hardness values; 2) Silux Plus: increasing the curing tip distance did not produce a statistically significant difference in the Knoop hardness values; however, at 6 and 12 mm, the deeper layers showed lower Knoop hardness values in relation to the surface; 3) Z100: statistically superior in relation to Silux Plus at all three curing tip distances and at all depths (P < 0.05).

Correlation between light intensity and exposure time on the hardness of composite resin.

This study evaluated the correlation between light intensity emitted by the curing units and exposure time on the of degree polymerization of dental composites by measured Knoop hardness. Specimens with 5 mm diameter and 2 mm height were prepared in a copper mold, covered with a mylar strip and polymerized for 30 sec by curing units with 50, 130, 180, 220, 280 and 520 mW/cm(2), respectively. The output for all units was measured using a Curing Radiometer (Demetron). Other specimens were polymerized for 45, 60, 75, 90, 105, 120, 135, 150, 165 and 180 sec utilizing units of 130, 220 and 280 mW/cm(2). Knoop hardness values of the top and bottom surfaces were measured after 24 h. The results indicate that the curing units with higher light intensity presented improved values of Knoop hardness on the top and bottom regions. As expected, the top surface always presented improved Knoop hardness values in relation to the bottom, after exposure for 30 sec. The values obtained on the surface were statistically superior compared to the values on the bottom (p<0.05) for the intensity of 130, 220 and 280 mW/cm(2) after 30, 45 and 60 sec of exposure.

Effect of convergence angle and luting agent on the fracture strength of In ceram crowns.

This study compared the fracture strength of In ceram crown shapes fabricated with either 8 or 16 degrees total occlusal convergence; and attached with either a commercial zinc phosphate cement or a glass ionomer cement. Thirty crown shapes (8 mm diameter and 8.5 mm high) were fabricated for each preparation design on a brass master die with approximately the same dimensions as a premolar. In ceram crown shapes were luted on to the die using zinc phosphate or glass ionomer. The crown shapes were fractured in a testing machine (Instron) using a steel ball, 4 mm in diameter, that contacted the occlusal surface and the resulting data were statistically analyzed using a Mann-Whitney test. The results indicate that there is no statistical difference in the fracture strength values between preparations with 8 degrees total convergence compared with 16 degrees using the same cement. However, crown shapes luted with zinc phosphate on preparations with 8 and 16 degrees total occlusal convergence were significantly stronger than those luted using glass ionomer cements (p<0.05).

Effect of storage and acid etching on the tensile bond strength of composite resins to glass ionomer cement.

This in vitro study evaluates the effect of storage time and acid etching on the tensile bond strength of glass ionomer cement to composite resins. The bonded assemblies were stored at 100% relative humidity and 37 degrees C for 1 hour, 1 day, 1 week, 1 month and 3 months. The test specimen was loaded at tension to failure on an Otto Wolpert-Werke testing instrument with a crosshead speed of 6 mm/min. The results showed a significant statistical difference for etched Vidrion F when compared to etched Ketac Bond at all storage periods. The unetched samples were statistically similar at 3 months, with the highest values for Vidrion F.

Morphological effect of the type, concentration and etching time of acid solutions on enamel and dentin surfaces.

Thirty-six noncarious human molars were extracted and stored in saline. The buccal surfaces were ground wet on 400-grit silicon carbide paper to create a flat surface. The enamel and dentin surfaces were treated with 35% phosphoric acid gel, 10% phosphoric acid gel and 10% maleic acid gel for 15 and 60 seconds. Scanning electron microscope analysis showed that all the acid etchants modified the micromorphological appearance of enamel and dentin surfaces independent of the type of acid, the etching time and the concentration. On the enamel surface, the 35% and 10% phosphoric acid gels and the 10% maleic acid gel applied for 15 or 60 seconds preferentially removed the prism core material. In the specimens treated for 15 seconds with 10% maleic acid the prism core material was partially removed. On the dentin surface, the phosphoric acid gels (35% and 10%) and the 10% maleic acid gel applied for 15 and 60 seconds removed the smear layer and opened the dentinal tubule orifices; however, the dentinal surface etched for 15 or 60 seconds with 10% maleic acid gel showed residues of the smear layer.

Soldering and remelting influence on fatigue strength of cobalt-chromium alloys.

STATEMENT OF PROBLEM: For laboratory production, it would be economically advisable to reuse excess cobalt-chromium alloys in manufacturing partial denture frameworks. Furthermore, discrepancies in fit, modifications, repairs, and also economic factors could lead to soldering procedure on the metal framework. PURPOSE: This study evaluated the influence of soldering and remelting procedures on the fatigue strength of Steldent, Dentorium, and Biosil cobalt-chromium alloys, as new alloys and in a mixture of new and previously casted alloy and when submitted or not submitted to conventional soldering procedure. MATERIAL AND METHODS: The soldering procedure was conducted in rod specimens 1.7 mm in diameter made with new, or with a mixture of new and reused alloy (n = 10 per group). The results were compared with those of intact rods. The fatigue strength was carried out with a cyclic testing machine simulating the insertion and the removal of partial dentures. After failure, the fracture surface was examined with a scanning electron microscope. RESULTS: The soldered specimens revealed 1119 loading cycles before fracture. These means differed statistically from those of intact alloys, which disclosed 2733 cycles before failure (p < 0.05). Statistical analysis indicated that the soldering procedure reduced fatigue strength of all new alloys or those in a mixture of new and previously casted alloys. It was also found that the soldering procedure may cause premature failure of a removable partial denture. Photomicrographs from fracture surfaces revealed the presence of inclusions and voids. Conversely, there were no significant differences between new and reused specimens, soldered or not (p > 0.05), which suggested that it may be possible to reuse excess cobalt-chromium alloys without compromising the fatigue strength of the framework.

Influence of adhesive systems on the bonding of dental amalgam to glass ionomer cement.

STATEMENT OF PROBLEM: Dental amalgam restorations have traditionally been retained in cavity preparations by surgical procedures called retention form. In this procedure healthy dental structure is usually removed to create adequate retention. The increasing use of bonding systems for restorative procedures may result in more conservative cavity preparations. PURPOSE: The purpose of this study was to evaluate the tensile bond strength of the amalgam to glass ionomer cement under the influence of three adhesive systems (Panavia-EX, Vidrion F fresh mix, and Alpha Seal). MATERIAL AND METHODS: The bonded assemblies were stored in an environment of 100% relative humidity and 37 degrees C for 24-hour and 30-day storage periods. The test specimen was loaded in tension to failure on a universal testing machine with a crosshead speed of 6 mm/min. RESULTS: The results revealed that in the 24-hour period without acid etch fresh Vidrion F and Panavia Ex adhesives were stronger than autopolymerizing sealant. Panavia Ex adhesive was stronger in the 24-hour period with acid etch. CONCLUSIONS: The 30-day period with acid etch revealed no statistical difference among the adhesives. In the 30-day period without acid etch, the fresh Vidrion F adhesive recorded the greatest tensile bond strength.

Effect of topical fluoride application on the surface roughness of composites.

The influence of fluoride solutions on the surface roughness of polished and nonpolished composites with Sof-Lex discs was verified. Concise and Herculite XR samples were exposed to the action of 1.23% acidulated phosphate fluoride rinse, 1.23% acidulated phosphate fluoride gel, and 0.2% neutral phosphate fluoride rinse for 4 min each. The average roughness values obtained by perfilometer showed that all fluoride solutions produced surface alterations in the samples. In the unpolished samples, more roughness was produced in Concise etched by 1.23% acidulated phosphate fluoride rinse. In the polished samples, the 1.23% acidulated phosphate fluoride gel produced greater alterations in Herculite XR, and the neutral rinse in Concise samples.

Base deflection and microleakage of composite restorations.

The flexural deflections of human dentin, Herculite XR, Dycal, Vidrion F, zinc phosphate base, and combinations of composite-base were determined. The influence of the flexural deflections in the marginal microleakage was also determined for the composite-base combinations. The flexural deflection test for dentin showed no statistically significant differences between the two floor cavity depths studied. There were significant differences among cements when the thickness of the base was 1 mm whereas no differences occurred at 2 mm. The composite-base combinations did not present statistical differences. There were no statistically significant differences in the microleakage levels among loaded and non-loaded specimens; however, dye penetration was visually greater in loaded samples.

Chemical etching solutions for creating micromechanical retention in resin-bonded retainers.

This study introduced three chemical etching solutions capable of producing micromechanical retention in nickel-chromium and nickel-chromium-beryllium alloys used for resin-bonded retainers. The effectiveness of the chemical etching solutions was evaluated with tensile strength tests and photographs at various magnifications with a scanning electron microscope. Chemical etching with the CG-Etch solution produced suitable and uniform microretention whereas the other solutions were not effective on all metal alloys. Significant differences (p < 0.05) relating to tensile bond strengths were noted. The CG-Etch solution gave the highest mean bond strength compared with solutions II, III, and control groups.