Thermal cycling procedures for laboratory testing of dental restorations

Effect of chlorhexidine application methods on microtensile bond strength to dentin in Class I cavities

OBJECTIVE

To evaluate the influence of chlorhexidine with different application methods on the microtensile bond strength (microTBS) to dentin in Class I cavities.

METHODS

Flat dentinal surfaces with Class I cavities (4 mm long, 4 mm wide, 2 mm deep) in 50 molars were bonded with Adper Single Bond 2 etch-and-rinse adhesive system after: 1) Chlorhexidine (CHX) + rinsing + etching; 2) CHX + no rinsing + etching; 3) Etching + CHX + rinsing; 4) Etching + CHX + no rinsing; 5) Etching only as a control group. Resin composite buildups were constructed with Z-350 (3M ESPE) using a bulk method and they were polymerized for 40 seconds. For each condition, half of the specimens were immediately submitted to microtensile bond strength and half of the same group was submitted to 10,000 cycles of thermocycling between 5 degrees C and 55 degrees C before testing. The data were analyzed using the two-way ANOVA and Student t-test at a 95% significance level.

RESULTS

Chlorhexidine pretreatment did not affect the bond strength of specimens tested at the immediate testing period, regardless of the application method used, compared to the control group. However, after 10,000 thermocycles, a significant bond strength reduction was found in the control group. In general, the chlorhexidine application method did not demonstrate a significant difference among the groups treated with chlorhexidine. However, there was a significant difference after thermocycling in the groups treated with chlorhexidine before etching and no significant difference in the groups treated with chlorhexidine after etching.

CONCLUSION

Considering the amount of reduction in bond strength after thermocycling, the current study showed improved dentin bond strength with chlorhexidine when used after etching.

Comparison of shear bond strengths of orthodontic brackets bonded with flowable composites

This study evaluated the shear bond strengths of orthodontic brackets bonded to human premolars using five different combinations of flowable composites and one-step self-etching adhesives (n=12): (1) Adper Easy Bond+Filtek Supreme XT Flow; (2) Futurabond NR+Grandio Flow; (3) Clearfil S3 Bond+Clearfil Majesty Flow; (4) AdheSE One+Tetric EvoFlow; and (5) Transbond Plus Self Etching Primer+Transbond XT Light Cure Adhesive. After shear bond strength testing, adhesive remnant index (ARI) scores were given according to the amount of adhesive and resin remaining on the brackets. On shear bond strength, there were no statistically significant differences between Groups 2 and 4 and between Groups 3 and 5 (p>0.05). On ARI scores, the predominant ARI scores in Groups 1, 2, 3, and 5 were 4, 2, 5, and 4 respectively; in Group 4, they were 0 and 4. Results showed that some combinations of flowable composites and self-etching adhesives might not be suitable for orthodontic use due to their low shear bond strengths and high ARI scores -with the latter signaling the risk of damaging the enamel surface during debonding.

Marginal, Internal Fit and Microleakage of Zirconia Infrastructures: An In-Vitro Study

Fitting accuracy and microleakage dominate prognostic covariates for the long-term durability of crown restorations. The fitting accuracy and microleakage potential of zirconia infrastructures might be influenced by manufacturing technology.

Effects of thermocycling and light source on the bond strength of metallic brackets to bovine teeth

This study evaluated the effects of thermocycling and different light sources on the bond strength of metallic brackets to bovine tooth enamel using an adhesive resin. Bovine teeth were etched with 35% phosphoric acid gel for 20 s. After application of primer, metallic brackets were bonded to the buccal surface using Transbond XT, forming 8 groups (n=20), depending on the light source used for photoactivation (AccuCure 3000 argon laser - 20 s, Apollo 95E plasma arc - 12 s, UltraLume 5 LED - 40 s and XL2500 halogen light - 40 s) and experimental conditions without (Groups 1 to 4) or with thermocycling (Groups 5 to 8). Shear bond testing was carried out after 24 h of distilled water storage (Groups 1 to 4) or storage and thermocycling in distilled water (groups 5 to 8; 1,500 cycles - 5o/55oC). Data were subjected to two-way ANOVA and Tukey’s test (α=0.05). The Adhesive Remnant Index (ARI) was evaluated at ×8 magnification. No significant differences (p>0.05) in bond strength were found when the conditions without and with thermocycling were compared for any of the light sources. No significant differences (p>0.05) in bond strength were found among the light sources, irrespective of performing or not thermocycling. There was a predominance of ARI scores 1 in all groups. In conclusion, light sources and thermocycling had no influence on the bond strength of brackets to bovine enamel.

Microtensile bond strength of one- and two-step self-etching adhesives on sclerotic dentin: the effects of thermocycling

This study evaluated the effects of thermocycling on the microtensile bond strength (microTBS) of one- and two-step self-etch adhesives (SEAs) to sclerotic dentin. Two adhesives, Clearfil S3 Bond (S3), a one-step self-etch adhesive (1-SEA), and Clearfil SE Bond (SE), a two-step self-etch adhesive (2-SEA), were applied on cervical lesions in human premolars with sclerotic or normal dentin. After adhesive application, the lesions were restored and built up using a resin composite (Clearfil AP-X). After 24 hours in water storage, the restored teeth were sectioned into 0.7 x 0.7 mm composite-dentin beams. The beams were then aged with 0, 5,000 or 10,000 thermocycles. The use of two adhesives, two substrate types and three thermocycling regimens yielded 12 experimental groups of 14-19 beams each. The beams were subsequently subjected to microTBS testing at a crosshead speed of 1 mm/minute and statistical analyses were computed with three-way ANOVA and Tukey's post hoc test at p < 0.05. Three-way ANOVA showed statistically significant effects on bonding effectiveness by lesion type, adhesive system, thermocycling or combinations of the adhesive system and thermocycling (p < 0.05). With sclerotic dentin, although S3 and SE provided comparable microTBS after 24 hours of water storage, S3 showed significantly lower microTBS than SE after thermocycling (p < 0.05). Regardless of lesion type, the microTBS for S3 decreased significantly after 5,000 or 10,000 thermocycles, while the microTBS for SE showed a significant decrease only after 10,000 thermocycles. Regardless of the extent of thermocycling, the microTBS values for either SE or S3 bonded to sclerotic dentin were significantly lower than to normal dentin (p < 0.05). The results suggested that thermocycling had a significant negative effect on the bond strength of the two SEAs tested. In contrast to 2-SEA, 1-SEA might not be a good choice for sclerotic dentin when seeking durability of the resin-dentin bond.

Influence of decontamination procedures on shear forces after contamination with blood or saliva

INTRODUCTION

Despite rapid development in adhesive technology, contamination of bonding surfaces remains a major problem. The aims of this study were to evaluate the influence of contamination on bond strength and to investigate possible decontamination procedures.

METHODS

Four bonding systems were evaluated for their shear bond strengths under 5 bonding situations: control (without contamination and decontamination); contamination with blood; contamination with saliva; decontamination with water and air, and repriming after blood contamination; and decontamination with water and air, and repriming after saliva contamination. The 25 specimens of each group consisted of composite blocks bonded to bovine teeth. Shear forces were measured with a testing machine after thermocycling.

RESULTS

The 3 composite primers showed similar behavior. With the exception of Transbond SEP (3M Unitek, Monrovia, Calif) with saliva contamination, all contaminated samples showed greatly reduced shear forces. The control and decontaminated groups showed shear forces about 20 MPa. The resin-modified glass ionomer, however, did not reach clinically sufficient bond strengths in either setup.

CONCLUSIONS

Decontamination with water and air and repriming is sufficient after contamination with blood or saliva. Etching again is not necessary. The bond strength of Transbond SEP was not significantly altered by saliva contamination and can be recommended for conventional bonding procedures.

Estimation of the retainer height biomechanical contribution in posterior resin-bonded fixed partial dentures: a structural-thermal coupled finite element analysis

This study determines the RBFPD (resin-bonded fixed partial dentures) biomechanical aspects to retainer height using structural-thermal coupled finite element (FE) analysis under normal (37°C) and high (51°C) oral temperatures. Three RBFPD FE models with different retainer heights (100, 75, and 50% of the distance from 2 mm above the CE (cementum-enamel) junction to the occlusal surface) were created using image processing, contour stacking, and mapping mesh procedures. After FE model validation, the maximum first principal and von Mises stresses in the remaining tooth (σ(T)) and prosthesis (σ(P)), were recorded for all models under structural-thermal coupled analyses. The simulation results showed that the σ(T) and σ(p) values decreased with greater retainer height as a result of the increasing prosthesis stiffness and maximizing bonding area between the enamel and retainer at normal oral temperature (37°C). However, no significant stress differences were found according to the retainer height varying dimensions at high (51°C) temperatures. The RBFPD retainer height biomechanical response is dominated by the structural analysis result (at 37°C) and it is recommended that the prosthesis retainer have as great a height as possible to decrease the stress values.

The effect of zirconia surface treatment on flexural strength and shear bond strength to a resin cement

STATEMENT OF PROBLEM

Despite the expanded applications for zirconia in restorative dentistry, there is no clear recommendation in the literature regarding surface treatment before bonding.

PURPOSE

The purpose of this study was to evaluate the effect of mechanical surface treatment of yttria-partially stabilized zirconia on its flexural strength and the effect of mechanical and chemical surface treatments on its bond strength to a resin cement.

MATERIAL AND METHODS

For flexural strength evaluation, zirconia bars (4 x 5 x 40 mm) were prepared from zirconia blocks, finished using a diamond rotary cutting instrument, sintered, then assigned into 4 groups: (1) control (no treatment), (2) airborne-particle abrasion, (3) silicoating, and (4) wet hand grinding. After storage for 24 hours at 37 degrees C, flexural strength was determined using a 3-point bending test, and the results were analyzed using 1-way ANOVA (alpha=.05). For shear bond strength evaluation, zirconia rods (2.5 x 3 mm) were prepared from zirconia blocks, sintered, and assigned into 16 groups. Each group underwent a combination of the following mechanical and chemical treatments. Mechanical treatment included: (1) control (no treatment), (2) airborne-particle abrasion, (3) silicoating, or (4) wet hand grinding. Chemical treatment included: (1) control (no treatment), (2) acid etching followed by silanation, (3) silanation only, or (4) application of zirconia primer. Dentin specimens were prepared from extracted molars stored in 0.5% chloramine-T. Zirconia rods were bonded to dentin using a resin cement (Multilink Automix), then light polymerized. After storage, the specimens were loaded to failure with the notched shear bond test method in a universal loading apparatus. For artificial aging analysis, the groups that achieved the highest bond strength values were duplicated, stored at 37 degrees C and 100% humidity for 90 days, and thermal cycled before being loaded to failure. Results were analyzed using 2-way ANOVA (alpha=.05).

RESULTS

Airborne-particle abrasion and hand grinding significantly increased flexural strength. The highest shear bond strength values were achieved for the following groups: silicoated + silanated > hand ground + zirconia primer > airborne-particle abraded + silanated > zirconia primer > airborne-particle abraded + zirconia primer. Artificial aging resulted in significantly lower shear bond strength for the silicoated/silanated and the zirconia primer groups.

CONCLUSIONS

Mechanical modification of the surface increased the flexural strength of Y-TZP. The resin bond to Y-TZP was improved by surface treatment. A combination of mechanical and chemical conditioning of the zirconia surface was essential to develop a durable resin bond to zirconia.

Effect of artificial aging regimens on the performance of self-etching adhesives

This in vitro study was performed to compare the microtensile bond strengths (MTBS) of current self-etching adhesives to dentin and to evaluate the effects of artificial aging [(thermocycling (TC) and/or mechanic loading (ML)] on MTBS and on nanoleakage of self-etching adhesives. Two-step (AdheSE Bond, Clearfil Protect Bond, Clearfil SE Bond, Optibond Self-Etch) and one-step (Hybrid Bond, G-bond, Clearfil Tri-S Bond, and Adper Prompt L-Pop) self-etching adhesives were tested. Resin composite build-ups were created, and the specimens were subjected to 10(4) TC, 10(5) ML, and 10(4)/10(5) TC/ML. Non-aged specimens served as controls. In the control group, no significant differences were found among the MTBS of the one-step self-etching adhesives and among those of three two-step self-etching adhesives (AdheSE Bond, Clearfil Protect Bond, and Clearfil SE Bond) (p > 0.05). The MTBS of AdheSE Bond and Clearfil Protect Bond were higher than were those of all one-step self-etching adhesives and than those of Optibond Self-Etch. The MTBS of Clearfil SE Bond was higher than were those of two one-step self-etching adhesives (Adper Prompt L-Pop, G-bond) (p < 0.05). Compared with the non-aged controls, TC did not decrease (p > 0.05), but ML and TC/ML significantly decreased the MTBS of the adhesives tested (p < 0.05). Two-step self-etching adhesives tended to fail more cohesively in dentin. Transmission electron microscopy revealed different nanoleakage patterns in the adhesive and hybrid layers of all adhesives examined, and signs of additional silver-filled water channels were more readily detectable after TC/ML.

Effect of temperature variation on the cytotoxicity of cast dental alloys and commercially pure titanium

Cell culture system has been used to evaluate alloy cytotoxicity under different environments, testing the extracts, but the effect of temperature variation on the cytotoxicity of dental alloys has not been analyzed. Objective: The aim of the present study was to investigate if temperature variation could affect dental alloy cytotoxicity, testing alloy extracts in an epithelial cell culture system. Material and methods: Discs of Ni-Cr, Co-Cr-Mo, Ni-Cr-Ti, Ti-6Al-4V and commercially pure titanium (cp Ti) were cast by arc melting, under argon atmosphere, injected by vacuum-pressure. Discs were immersed in artificial saliva and subjected to different temperatures: 37°C and thermocycling (37°C/5°C/37°C/55°C/37°C). After thermocycling, extracts were put in a subconfluent culture during 6 h, and the number of cells and their viability were used to evaluate cytotoxicity in these temperatures. For each alloy, data from temperature conditions were compared by Student's t-test (α=0.05). Results: The cytotoxicity tests with alloy/metal extracts showed that Ni-Cr, Co-Cr-Mo, Ti-6Al-4V and cp Ti extracts (p>0.05) did not affect cell number or cell viability, while Ni-Cr-Ti (p<0.05) extract decreased cell number and viability when the alloy was subjected to thermocycling. Conclusion: Within the limitations of the present study, the Ni-Cr-Ti alloy had cell number and viability decreased when subjected to temperature variation, while the other alloys/metal extracts did not show these results.

One-component self-etching primer: a seventh generation of orthodontic bonding system?

The purpose of this study was to compare the bond strengths and to evaluate the debonding site using the adhesive remnant index (ARI) provided by a conventional acid-etch conditioner and a new self-etching adhesive system, Xeno IV (Dentsply Caulk). One hundred and eighty bovine lower incisors were randomly divided into six groups (n = 30). In groups 1, 2, and 3, Transbond XT (3M Unitek) composite was used to bond the brackets to enamel samples conditioned with 37 per cent phosphoric acid + XT primer (3M Unitek), Xeno IV + XT primer, or Xeno IV only, respectively. In groups 4, 5, and 6, the bonding procedures were performed using Fuji Ortho LC (GC Corp.) resin-modified glass ionomer cement unconditioned, enamel conditioned with 37 per cent phosphoric acid, or Xeno IV, respectively. All samples underwent thermocycling and then shear bond strength (SBS) testing was performed using a universal testing machine (Emic DL 10.000). Analysis of variance was applied. For the post hoc test, the Tukey's test was used. Kruskal-Wallis and Mann-Whitney U-tests were used to assess ARI scores. The results demonstrated no statistical differences between groups 1, 2, and 3. However, statistically significant differences were found between these samples and groups 4, 5, and 6. With regard to ARI score, the highest mean value was found in group 5 (Fuji Ortho LC + 37 per cent acid conditioning), whereas group 4 (Fuji Ortho LC + no conditioning) had the lowest SBS. Xeno IV self-etching bonding agent was able to bond orthodontic brackets in association with Transbond XT composite as well as with Fuji Ortho LC, thus maximizing bracket bonding.

Effect of fiber-reinforced composites on the failure load and failure mode of composite veneers

This study compared the initial and final failure loads and failure modes of indirect resin composite laminate veneers with and without fiber reinforcement. Forty intact lower canines received standard laminate preparations and were randomly assigned into four test groups (n=10). In Group 1, indirect resin composite veneers were repaired with two layers of preimpregnated bidirectional glass fiber weave and a restorative composite; in Group 2, with a layer of preimpregnated unidirectional glass fibers and a restorative composite; and in Group 3, with an experimental semi-IPN matrix composed of multidirectional short glass fibers. Indirect resin composite veneers without any fiber reinforcement were used as control (Group 4). All specimens were thermocycled and tested with a universal testing machine. On the final failure load, there were no statistically significant differences (p>0.05) among the test groups. Within each group, pairwise comparison of initial and final failure loads revealed statistically significant differences (p<0.05), except for Group 4 (p>0.05). On failure mode, unreinforced specimens showed instantaneous failure, whereas reinforced specimens mostly demonstrated elongated failure.

Effect of Configuration Factor on Shear Bond Strengths of Self-etch Adhesive Systems to Ground Enamel and Dentin

Despite recent improvements in self-etch bonding systems, a two-step etch and rinse system gave consistently higher shear bond strengths to both ground enamel and dentin and would be the best system to use clinically.

Push-out stress for fibre posts luted using different adhesive strategies

The influence of thermocycling on the bond strength of fibre posts cemented with different luting approaches was investigated. A total of 84 human incisors were selected for the study. Sixty teeth were assigned to one of the following adhesive/cement combinations for push-out bond-strength evaluation: group 1, XP Bond/CoreXFlow + DT Light-Post; group 2, Panavia F 2.0 + Tech 21; or group 3, RelyX Unicem + RelyX. Bonded specimens were cut into 1-mm-thick slabs and either thermocycled (40,000 cycles) or stored in artificial saliva (control specimens) before push-out bond-strength testing. Additional specimens were processed for quantitative interfacial nanoleakage analysis. Thermocycling decreased the bond strength in specimens of groups 2 and 3, but did not affect the specimens from group 1. No difference was observed among luting approaches in control specimens. Thermocycling resulted in increased silver nitrate deposition (i.e. interfacial nanoleakage) in all groups. Within the limitations of the study, the use of an etch-and-rinse adhesive in combination with a dual-cure cement to lute fiber posts is the most stable luting procedure if compared with a self-etch resin-based cement or a self-adhesive cement, as assayed by thermocycling of the bonded specimens.

Metal ceramic bond after multiple castings of base metal alloy

STATEMENT OF PROBLEM

Remelting previously cast metal can produce a critical change in metal-oxide composition at the dental alloy surface.

PURPOSE

The purpose of this study was to evaluate the effect of multiple castings on bonding of a single selected base metal and a dental ceramic, and to compare results from shear bond and 3-point-bending tests.

MATERIAL AND METHODS

Three groups of dental alloy (Remanium CSe) were prepared by mixing 50% fresh alloy to alloy remnants from previous castings. The specimens in the first casting group used 100% fresh alloy and served as control (C0). The second group consisted of equal amounts of fresh alloy and alloy remnants cast only once (C1). The third and fourth groups contained 50% fresh alloy and alloy cast twice (C2) and 3 times (C3), respectively. The bond load (N) between alloy and dental porcelain (VMK 95 Metal Ceramic) was evaluated, using shear bond and 3-point bending tests. The fracture surfaces of the specimens subjected to testing were analyzed using a stereomicroscope and scanning electron microscope. One-way ANOVA followed by the Tukey multiple comparison test was used for analysis of bond data (alpha=.01).

RESULTS

The mean shear bond load (SD) of C0 (738.0 (77.1) N) was significantly higher than that of C1 (577.8(139.4) N), C2 (494.8 (77.6) N), and C3 (480.5 (60.9) N). Mean peak load for the 3-point-bending test of specimens cast from C0 (39.8 (1.79) N) was significantly higher than for other groups (P<.01). No significant difference was found between C1 (24.4 (5.60) N), C2 (23.2 (4.03) N), and C3 (22.8 (1.79) N) in terms of the shear bond test and the 3-point bending test.

CONCLUSIONS

In general, there was agreement between the 2 bond strength tests to indicate that including re cast base alloy with fresh alloy for metal decreases metal-to-ceramic bond strengths. (J Prosthet Dent 2009;102:165-171)

A three-dimensional evaluation of microleakage of class V cavities prepared by the very short pulse mode of the erbium:yttrium-aluminium-garnet laser

The aim of this study was to evaluate microleakage along resin restoration in cavities prepared with an erbium:yttrium-aluminium-garnet (Er:YAG) laser, with and without acid etching, and to compare it with that in diamond-drilled cavities. Thirty intact molars were divided into three equal groups. In the teeth in group I, class V cavities were prepared with a diamond drill. Cavities in groups II and III were prepared with an Er:YAG laser (400 mJ/15 Hz for enamel and 250 mJ/10 Hz for dentine). The cavities in groups I and II were acid-etched and adhesive and flowable composite were applied to all cavities. The specimens were first immersed in dye for 24 h and then in 5% nitric acid for 72 h for softening. The fillings were extracted and photographed through a dissecting microscope. The leakage area was measured with specially designed software. The Kruskal-Wallis test showed that the best ranking was group II [mean range (m.r.) = 27.46], followed by group I (m.r. = 33.48) and, lastly, group III (m.r. = 45.15). The differences between groups I and III (P = 0.023) and between groups II and III were statistically significant (P = 0.080). The least microleakage was found in those cavities prepared by Er:YAG laser and subsequently acid-etched, whereas the most leakage was in the lased cavities that had not been etched; the traditional diamond-drilled acid-etched cavities produced medium leakage.

Effect of the C-factor and Dentin Preparation Method in the Bond Strength of a Mild Self-etch Adhesive

A course cut carbide bur should be avoided prior to a mild self-etch adhesive, because it adversely affected bond strength. In contrast, a fine cut carbide bur provided the best combination: high bond strength with low variability, which suggests more reliable bond strength performance.

Adhesive bonding of resin composite to various Ni-Cr alloy surfaces using different metal conditioners and a surface modification system

PURPOSE

This study evaluated the effect of three metal conditioners [Metal Photo Primer (MPP), Cesead II Opaque Primer (OP), Targis Link (TL)], and one surface modification system [Siloc (S)] on the shear bond strength (SBS) of a prosthetic composite material to Ni-Cr alloy.

MATERIALS AND METHODS

Rivet-shaped specimens were cast, and three surface treatments were evaluated: Polishing (P); sandblasting with either 50 microm (50SB) or 250 microm (250SB) Al(2)O(3). All products were applied to half of the specimens, while the other half remained without the materials. Veneering resin composite (8-mm diameter, 2-mm thick) was applied and light-exposed for 90 seconds in a laboratory light-curing unit. The specimens were stored in water at 37 degrees C for 24 hours, and half were subjected to 500 thermal cycles consisting of water baths at 4 degrees C and 60 degrees C. All specimens were submitted to SBS test (0.5 mm/min) until failure. Failure patterns were determined using optical and scanning electron microscope (SEM) analysis. Data were analyzed by ANOVA and post hoc Tukey's test (preset alpha of 5%).

RESULTS

The SBS values of OP and TL groups were higher than those of MPP and S within the 50SB treatment (p < 0.05). No significant difference in SBS was noted between OP and TL as well as between MPP and S. On the other hand, no significant differences were found among conditioners within the 250SB group (p > 0.05). The SBS values of MPP, OP, and S from the 250SB group were higher than those from 50SB (p < 0.05). No significant difference in SBS was noted among most groups with conditioners after thermocycling. The only exception was observed for MPP, which showed an increase in SBS after thermocycling (p < 0.05). Differences in SBS were noted among the groups with conditioners (p < 0.05), and no significant difference in SBS was noted between TL and OP groups, which showed the highest values among all within the P group. No significant difference was noted between MPP and S. Debonded surfaces showed adhesive failures predominantly located between metal surface and opaque resin.

CONCLUSIONS

The OP and TL conditioners and surface sandblasting with 250 microm Al(2)O(3) promoted the highest SBS between resin and the Ni-Cr metal surface.

Repairability of cross-linked biopolymers

Repair of biopolymers is a critical issue, especially with aged restorations. Obtaining a chemical bond to the repair surface might solve this problem. We hypothesized that certain repair liquids are suitable to establish a strong bond to an artificially aged dimethacrylate-based biopolymer for temporary restorations. Specimens made of a self-curing temporary crown-and-bridge material were prepared and thermocycled for 7 days (5000x, 5-55 degrees C). Cylinders made of light-curing composites (n=10) were bonded onto the specimen surface, either after grinding or after the application of 4 different experimental repair liquids (Bis-GMA:TEGDMA mixture=bonding, methylmethacrylate=MMA, bonding & acetone, bonding & MMA). A shear bond strength test was performed 24 hrs after repair. The highest bond strength was obtained with the bonding & acetone liquid (20.1+/-2.2 MPa). The use of MMA significantly affected the bond strength (6.8+/-1.9 MPa). MMA is inadequate as a repair liquid on aged composite-based biopolymers.

Influence of thermal stress on marginal integrity of restorative materials

The aim of this study was to evaluate the influence of thermal stress on the marginal integrity of restorative materials with different adhesive and thermal properties. Three hundred and sixty Class V cavities were prepared in buccal and lingual surfaces of 180 bovine incisors. Cervical and incisal walls were located in dentin and enamel, respectively. Specimens were restored with resin composite (RC); glass ionomer (GI) or amalgam (AM), and randomly assigned to 18 groups (n=20) according to the material, number of cycles (500 or 1,000 cycles) and dwell time (30 s or 60 s). Dry and wet specimens served as controls Specimens were immersed in 1% basic fuchsine solution (24 h), sectioned, and microleakage was evaluated under x40 magnification. Data were analyzed by Kruskal-Wallis and Mann-Whitney tests: Thermal cycling regimens increased leakage in all AM restorations (p<0.05) and its effect on RC and GI restorations was only significant when a 60-s dwell time was used (p<0.05). Marginal integrity was more affected in AM restorations under thermal cycling stress, whereas RC and GI ionomer restoration margins were only significantly affected only under longer dwell times.

Bond durability in erbium:yttrium-aluminum-garnet laser-irradiated enamel

This study sought to evaluate the influence of thermocycling and water storage on the microtensile bond strength of composite resin bonded to erbium:yttrium-aluminum-garnet (Er:YAG)-irradiated and bur-prepared enamel. Eighty bovine incisors were selected and sectioned. Specimens were ground to produce a flat enamel surface. Samples were randomly assigned according to cavity preparation device: (I) Er:YAG laser and (II) high-speed turbine, and were subsequently restored with composite resin. They were subdivided according to the duration of water storage (WS)/number of thermocycles (TCs): 24 h WS/no TCs; 7 days WS/500 TCs; 1 month WS/2,000 TCs; 6 months WS/12,000 TCs. The teeth were sectioned into 1.0 mm(2)-thick slabs and subjected to tensile stress in a universal testing machine. Data were submitted to two-way analysis of variance (ANOVA) and Tukey's test at a 0.05 significance level. The different periods of water storage and thermocycling did not influence the microtensile bond strength (microTBS) values in the Er:YAG laser-prepared groups. In bur-prepared enamel, the group submitted to 12,000 TCs/6 months' WS (IID) showed a significant decrease in bond strength values when compared to the group stored in water for 24 h and not submitted to thermocycling (IIA), but values were statistically similar to those obtained in all Er:YAG laser groups and in the bur- prepared groups degraded with 500 TCs/1 week WS (IIB) or 2,000 TCs/1 month WS (IIC). It may be concluded that adhesion of an etch-and-rinse adhesive to Er:YAG laser-irradiated enamel was not affected by the methods used to simulate degradation of the adhesive interface and was similar to adhesion in the bur-prepared groups in all periods of water storage and thermocycling.

Changes in the reflected and transmitted color of esthetic brackets after thermal cycling

INTRODUCTION

The objective of this study was to determine the changes in the reflected and transmitted color and the color parameters of esthetic brackets after thermal cycling.

METHODS

Four brands of plastic and 4 brands of ceramic brackets were investigated. Reflected color of the labial side of bracket was measured according to the Commission Internationale de l'Eclairage (CIE) LAB color scale before and after thermal cycling for 5000 cycles. Transmitted color was measured with the same measurement protocol. Color change was calculated with the equation: DeltaE*(ab) = [(DeltaL*)(2)+ (Deltaa*)(2)+ (Deltab*)(2)](1/2). Changes in color parameters such as lightness (CIE L*), chroma (C*(ab)), CIE a* and b* values were calculated as the value after thermal cycling minus the value before thermal cycling. One-way analyses of variance were performed for the changes in color and color parameters by the brand of bracket (alpha = 0.05), and the Tukey multiple comparison test was performed.

RESULTS

Changes in the reflected and transmitted color and the color parameters were influenced by the brand of bracket (P <0.05). Reflected color change was 1.4 to 6.4 DeltaE*(ab) units, and transmitted color change was 1.0 to 2.8 DeltaE*(ab) units. Kind of material (plastic or ceramic) and crystal structure of ceramic brackets did not influence color stability, but color stability was mainly brand-dependent.

CONCLUSIONS

Reflected color changes of 3 of 8 brands were in the clinically perceptible range (DeltaE*(ab) > 3.7). Therefore, color stability of esthetic brackets should be enhanced for long-term esthetic performance of these brackets.

Coronal microleakage of two root-end filling materials using a polymicrobial marker

The purpose of this study was to evaluate polymicrobial coronal leakage of mineral trioxide aggregate (MTA) and amalgam. There were 108 single-rooted teeth randomly divided into 3 groups of 32 teeth each and positive and negative control groups of 6 teeth and obturated with gutta percha and either Diaket (3M/ESPE, Seefeld, Germany), AH Plus (Dentsply, De Trey, Konstanz, Germany), or Ketac Endo (3M/ESPE). These groups were further divided into 2 subgroups of 16 teeth in which root ends were resected and obturated with either MTA or zinc-free amalgam. The samples have been incorporated in a dual-chamber leakage model with a polymicrobial marker of five facultative anaerobes on the coronal part. Leakage was observing during a period of 90 days. The least leakage was found in a combination of Diaket and MTA (76.9 +/-14.8 days) followed by AH Plus and MTA (66.1 +/- 18.7), Diaket and amalgam (60.0 +/- 23.1), AH Plus and amalgam (56.9 +/- 22.1), and Ketac Endo and MTA (42.1 +/- 17.8), whereas the greatest leakage was observed in the Ketac Endo and amalgam group (40.0 +/- 17.24). Samples filled with MTA showed significantly better sealing than samples filled with amalgam (p < 0.05).

Thermocycling Effects on Shear Bond Strength of a Self-Etching Primer

Objective: To determine the effects of thermocycling on shear bond strengths (SBSs) of a self-etching primer (SEP) after 0, 2000, and 5000 thermal cycles.

Materials and Methods: Brackets were bonded to bovine incisors with two etching protocols. In the control group (conventional method) teeth were etched with 37% phosphoric acid. In the experimental group, an SEP (Transbond Plus) was applied as recommended by the manufacturer. Brackets were bonded with light-cure adhesive paste (Transbond XT) and light cured for 20 seconds in both groups. The SBSs were measured after water storage at 37°C for 24 hours, after 2000 and 5000 cycles of thermocycling between 5°C and 55°C. Bond failure location was determined with the Adhesive Remnant Index (ARI).

Results: In the control group, SBSs did not show any significant differences among 0, 2000, and 5000 thermal cycles. However, in group SEP, SBSs decreased with 2000 and 5000 thermal cycles, and these decreases were significantly different from no thermocyling (P &lt; .001). A significant difference was observed between ARI scores of the control group with 5000 thermal cycles and group SEP with no thermal cycles (P &lt; .003). In addition, a significant difference was found between group SEP with no thermocycling and with 5000 thermal cycles (P &lt; .003).

Conclusion: The results of this study indicate that the SEP (Transbond Plus) provides clinically acceptable bond strength values compared with the conventional method after thermocycling.