Evaluation of Cleaning Methods on Lithium Disilicate Glass Ceramic Surfaces After Organic Contamination.

The purposes of this study were to 1) evaluate the effectiveness of different cleaning methods from a previously etched and silanized lithium disilicate glass ceramic (EMX) surface after contact with organic fluids (saliva or human blood) and 2) assess the effect of applying a new silane layer after the cleaning methods on the microshear bond strength (mSBS) of resin cement to EMX. EMX discs were etched with 5% hydrofluoric acid (HF) and properly silanized. Three control groups were created (n=10): control (without contamination), saliva positive, and human blood positive. Later, after new contaminations, the samples were distributed into four groups according to the cleaning method (n=20): air-water spray (AWS), 35% phosphoric acid, 70% alcohol, or Ivoclean cleaning paste. After the cleaning methods, subgroups were submitted to a new silane layer application, or not (n=10). All samples received a thin layer of a bonding agent and, subsequently, three light-cured resin cement cylinders were prepared on each EMX surface for the mSBS test. This test was performed on a universal testing machine at a vertical speed of 1 mm/minute until rupture. Contaminated and cleaned silanized EMX surfaces were assessed by scanning electron microscopy (SEM) (n=1). The noncontaminated control group showed an average mSBS of 18.7 MPa, and the positive saliva and human blood control groups yielded a 34% and 42% reduction in bond strength, respectively, compared to the uncontaminated control (p<0.05). For saliva-contaminated surfaces, all cleaning methods were effective and not different from one another or the control group (p>0.05). However, for human blood contamination, only Ivoclean cleaning paste was effective in restoring µSBS to uncontaminated control group levels (p>0.05). SEM images showed a clean surface (ie, with no contaminant residues) after the cleaning methods, regardless of the organic contaminant type. All the assessed cleaning methods were effective in removing saliva from the silanized EMX surface; however, only Ivoclean was able to restore the adhesion quality when the silanized EMX surface was contaminated with human blood.

Two methods to simulate intrapulpal pressure: effects upon bonding performance of self-etch adhesives.

AIM: To evaluate the effects of two methods to simulate physiological pulpal pressure on the dentine bonding performance of two all-in-one adhesives and a two-step self-etch silorane-based adhesive by means of microtensile bond strength (µTBS) and nanoleakage surveys. METHODOLOGY: The self-etch adhesives [G-Bond Plus (GB), Adper Easy Bond (EB) and silorane adhesive (SIL)] were applied to flat deep dentine surfaces from extracted human molars. The restorations were constructed using resin composites Filtek Silorane or Filtek Z350 (3M ESPE). After 24 h using the two methods of simulated pulpal pressure or no pulpal pressure (control groups), the bonded teeth were cut into specimens and submitted to µTBS and silver uptake examination. Results were analysed with two-way anova and Tukey's test (P < 0.05). RESULTS: Both methods of simulated pulpal pressure led statistically similar µTBS for all adhesives. No difference between control and pulpal pressure groups was found for SIL and GB. EB led significant drop (P = 0.002) in bond strength under pulpal pressure. Silver impregnation was increased after both methods of simulated pulpal pressure for all adhesives, and it was similar between the simulated pulpal pressure methods. CONCLUSIONS: The innovative method to simulate pulpal pressure behaved similarly to the classic one and could be used as an alternative. The HEMA-free one-step and the two-step self-etch adhesives had acceptable resistance against pulpal pressure, unlike the HEMA-rich adhesive.

Effects of surface treatments, thermocycling, and cyclic loading on the bond strength of a resin cement bonded to a lithium disilicate glass ceramic.

SUMMARY Objectives : The aim of this present study was to investigate the effect of two surface treatments, fatigue and thermocycling, on the microtensile bond strength of a newly introduced lithium disilicate glass ceramic (IPS e.max Press, Ivoclar Vivadent) and a dual-cured resin cement. Methods : A total of 18 ceramic blocks (10 mm long × 7 mm wide × 3.0 mm thick) were fabricated and divided into six groups (n=3): groups 1, 2, and 3-air particle abraded for five seconds with 50-µm aluminum oxide particles; groups 4, 5, and 6-acid etched with 10% hydrofluoric acid for 20 seconds. A silane coupling agent was applied onto all specimens and allowed to dry for five seconds, and the ceramic blocks were bonded to a block of composite Tetric N-Ceram (Ivoclar Vivadent) with RelyX ARC (3M ESPE) resin cement and placed under a 500-g static load for two minutes. The cement excess was removed with a disposable microbrush, and four periods of light activation for 40 seconds each were performed at right angles using an LED curing unit (UltraLume LED 5, Ultradent) with a final 40 second light exposure from the top surface. All of the specimens were stored in distilled water at 37°C for 24 hours. Groups 2 and 5 were submitted to 3,000 thermal cycles between 5°C and 55°C, and groups 3 and 6 were submitted to a fatigue test of 100,000 cycles at 2 Hz. Specimens were sectioned perpendicular to the bonding area to obtain beams with a cross-sectional area of 1 mm(2) (30 beams per group) and submitted to a microtensile bond strength test in a testing machine (EZ Test) at a crosshead speed of 0.5 mm/min. Data were submitted to analysis of variance and Tukey post hoc test (p≤0.05). Results : The microtensile bond strength values (MPa) were 26.9 ± 6.9, 22.2 ± 7.8, and 21.2 ± 9.1 for groups 1-3 and 35.0 ± 9.6, 24.3 ± 8.9, and 23.9 ± 6.3 for groups 4-6. For the control group, fatigue testing and thermocycling produced a predominance of adhesive failures. Fatigue and thermocycling significantly decreased the microtensile bond strength for both ceramic surface treatments when compared with the control groups. Etching with 10% hydrofluoric acid significantly increased the microtensile bond strength for the control group.

Influence of the volume of composite and photoactivation method on push-out bond strength and Knoop hardness of a resin composite.

AIM: The aim of this paper was to evaluate the influence of modulated photoactivation methods and volume of composite on Knoop hardness (KHN) and push-out bond strength (PBS) of Filtek Z350 to root dentin. METHODS: Three volumes (small, medium and large) of composite were bulk inserted in cavities prepared in 90 premolars. The specimens were photoactivated with continuous light, pulse-delay, or soft-start methods and submitted to PBS and KHN tests. The failure pattern was evaluated in stereomicroscope after the bond strength test. The data were submitted to two-way ANOVA and Tukey's test (P<0.05). RESULTS: Modulated photoactivation methods showed a higher PBS than continuous method (P<0.05). Medium volume of composite showed higher PBS than small and large volumes when photoactivated with continuous method (P<0.05). Pulse-delay significantly increased KHN for medium and large volumes in comparison to continuous method (P<0.05). Medium volume of composite showed KHN significantly higher than small and large volumes (P<0.05). CONCLUSION: The volume of composite influenced the PBS and KHN of resin composites. Pulse-delay showed the highest bond strength to dentin, as well KHN similar to the conventional method. The analysis of the failure pattern showed predominance of adhesive failure.

In vitro marginal fit of three all-ceramic crown systems before and after cementation.

STATEMENT OF THE PROBLEM: Full-coverage all-ceramic restorations are widely used. The impact of various classifications of luting agent on marginal discrepancies is not well understood. PURPOSE: The purpose of this study was to evaluate the cervical fit of all ceramic crowns (IPS e.maxPress, Cergogold, and In Ceram) on bovine teeth with two luting agents before and after cementation. MATERIALS AND METHODS: Ninety bovine incisors were embedded in resin. The coronal portions of the teeth were prepared to receive full-coverage crowns. Thirty crowns of 7.0 ± 0.5 mm height, 8.0 mm cervical diameter, and 4.2 mm incisal diameter were fabricated for each ceramic system. The crowns were seated on the teeth, and the marginal discrepancy was measured using a measuring microscope. Then, 15 crowns of each ceramic system were luted on the teeth with resin cement (Variolink II) or resin-modified glass ionomer cement (Rely X luting), and the marginal discrepancy was measured. The results were submitted to analysis of variance, t test and Tukey's test (p<0.05). RESULTS: The three ceramic systems showed cervical fits after cementation statistically inferior to cervical fits before cementation for the two cements. The IPS e.maxPress showed values for cervical fit statistically superior to Cergogold before cementation. No statistically significant difference was found between IPS e.maxPress and In Ceram and In Ceram and Cergogold. After cementation, no statistically significant difference was found for the three ceramics systems when luted with resin or resin-modified glass ionomer luting agents. CONCLUSIONS: Within the limitations of this study, it can be concluded that both cements studied increase the marginal discrepancy between the crown and the preparation for the three ceramic systems evaluated.

Effect of chemical and mechanical degradation on surface roughness of three glass ionomers and a nanofilled resin composite.

Nanofillers have been incorporated into glass ionomer (GI) restorative materials to improve their mechanical and surface properties. The aim of this present laboratory study was to compare the superficial roughness (Ra) of nanofilled GI (Ketac N100) with that of conventional GI (Fuji IX GP), resin-modified GI (Vitremer), and a nanofilled resin composite (Filtek Supreme) after pH cycling and toothbrush abrasion. Ten specimens of each material were made using Teflon molds, which were polished using aluminum-oxide abrasive disks. Three measurements of Ra were made of each specimen to serve as baseline values. The specimens were submitted to pH cycling for 10 days in a demineralization solution for six hours (pH 4.3) and were then stored in remineralization solution for 18 hours (pH 7.0). Ra measurements were recorded after the pH cycling. Specimens were then submitted to toothbrush abrasion in a brushing machine with a 200g load for 30,000 cycles at 250 cycles/min. The Ra values were then recorded. The surface morphology of specimens from each group was analyzed using a scanning electron microscope. Data were analyzed by analysis of variance, Tukey, and t-tests. After toothbrushing, only Fuji IX GP (1.10 ± 0.80) showed Ra values that were statistically different from those of the other materials evaluated. Ketac N100 (0.68 ± 0.16) showed intermediate Ra values, but it did not differ statistically from the results associated with Vitremer (1.04 ± 0.46) and Filtek (0.30 ± 0.15). Ketac N100 showed intermediate values of superficial roughness among the conventional glass ionomer cement, resin-modified glass ionomer cements, and the nanofilled resin after chemical and mechanical degradation.

Influence of glazed zirconia on dual-cure luting agent bond strength.

The current study evaluated the influence of a novel surface treatment that uses a low-fusing porcelain glaze for promoting a bond between zirconia-based ceramic and a dual-cure resin luting agent. Bond strengths were compared with those from airborne particle abrasion, hydrofluoric acid etching, and silanization-treated surfaces. Twenty-four yttrium-stabilized tetragonal zirconia (Cercon Smart Ceramics, Degudent, Hanau, Germany) discs were fabricated and received eight surface treatments: group 1: 110 µm aluminum oxide air-borne particle abrasion; group 2: 110 µm aluminum oxide airborne particle abrasion and silane; group 3: 50 µm aluminum oxide airborne particle abrasion; group 4: 50 pm aluminum oxide airborne particle abrasion and silane; group 5: glaze and hydrofluoric acid;group 6: glaze, hydrofluoric acid, and silane;group 7: glaze and 50 pm aluminum oxide airborne particle abrasion; and group 8: glaze,50 pm aluminum oxide airborne particle abrasion and silane. After treatment, Enforce resin cement (Dentsply, Caulk, Milford, DE, USA) was used to fill an iris cut from microbore Tygontubing that was put on the ceramic surface to create 30 cylinders of resin cement in each treatment group (n=30). Micro shear bond test-ing was performed at a cross head speed of 0.5mm/min. One-way analysis of variance, and multiple comparisons were made using Tukey's test (p<0.5). The bond strength was affected only by surface treatments other than silanization. The groups that utilized the low-fusing porcelain glaze with airborne particle abrasion or hydrofluoric acid showed bond strength values statistically superior to groups that utilized conventional airborne particle abrasion treatments with 50 or 110 pm aluminum oxide (p<0.001). The treatment that utilized low-fusing porcelain glaze and hydrofluoric acid showed bond strength values statistically superior to remaining groups (p<0.001). Treatment of zirconia ceramic surfaces with a glaze of low-fusing porcelain significantly increased the bond strength of a dual-cure resin luting agent to the ceramic surface.

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.

Three-point bending testing of fibre posts: critical analysis by finite element analysis.

AIM: To evaluate the effect of taper, specimen supports and the isotropic and orthotropic properties of the posts on flexure and stress response during three-point bending using finite element analysis. METHODOLOGY: A three-dimensional finite element model of a fibre post was created. The occlusal portion was cylindrical whilst the apical portion was tapered. Five different support positions were evaluated during a simulated three-point bending test: M1 - support distance of 10 mm centralized and no tilt; M2 - 10 mm centralized with tilt; M3 - 10 mm not centralized and no tilt; M4 - 10 mm not centralized with tilt; M5 - 6 mm not centralized with no tilt. A sixth post model (M6) was a centralized post without tapered section. The applied properties were elastic and orthotropic. RESULTS: Tilting the tapered posts to level them in the test setup had little effect on the outcome. Flexure increased when 50% of the bent portion involved taper (M1, M2). If only 20% of the bent post involved taper (M3, M4), the flexure values were close to M6 (no taper). The orthotropic properties also caused increased flexure compared to an isotropic post. Maximum stresses were only a little higher when 50% of the bend structure involved taper, whilst the orthotropic properties had little effect. CONCLUSIONS: Regardless of levelling, the flexural stress determination with tapered fibre posts in the three-point bending test was valid as long as the tapered portion was limited in length.

Effect of monomer content in the monomer-polymer proportion on the adaptation of complete denture bases.

AIM: This study verified the effect of the monomer/polymer proportion on the base adaptation of the complete upper dentures. METHODS: Thirty stone cast-wax baseplate sets were packed in metallic flasks and the acrylic resin polymerized in water at 74 °C for nine hours. Three transverse cuts were made through each stone cast-resin base set, corresponding to regions: A) canines (anterior); B) first molars (median), and C) posterior palate (posterior). Measurements were made using an optical micrometer at five points for each cut to determine base adaptation: left and right marginal limits of the flanges, left and right ridge crests, and midline. Data were analyzed using to ANOVA and Tukey's test (5%). RESULTS: In region A there was significant difference among the monomer-polymer proportions, with a greater value of misfit for the content -25% monomer group and lower for the manufacturer's proportion group. In region B there was significant difference between the manufacturer's content (lowest value) and the monomer contents of +25% and -25% (both statistically similar). In region C there was significant difference among the monomer-polymer proportions, with greater value for the -25% monomer group than for the manufacturer's proportion. There was significant difference when the regions were compared in relation to the same monomer content. The best adaptation was in the region A and the worst in the region C. CONCLUSION: The amount of monomer exerted different effects on the adaptation of the denture base. In all regions, the smallest misfit was observed when the manufacturer's recommended proportion was used and the greatest misfit was observed in the -25% monomer.

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.

Radiodensity and hardness of enamel and dentin of human and bovine teeth, varying bovine teeth age.

Studies have evaluated dental hard tissues characteristics from animal species in order to be used as a substitute for human teeth. The aim of this study was to evaluate the radiodensity and hardness of human and bovine enamel and dentin, varying bovine teeth age. Five specimens (1mm thick) were obtained from animals aged 20 (B20), 30 (B30), 38 (B38) and 48 (B48)months and from 20 to 30-years-old human third molars (H). The radiographic images were taken with a phosphor plaque digital system (Digora Optime). The radiodensity was obtained and Knoop hardness (KHN) was recorded (100g for 15s--5 indentations per specimen). Data were analyzed by one-way ANOVA following Tukey's HSD test and Dunnet's two-sided t-test. Radiodensity was similar within enamel groups, but bovine dentin presented higher radiodensity than human one regardless of age groups. Enamel-KHN showed differences between B20-B30 and B38-B48-H, and dentin-KHN was similar within all groups. Enamel was always more radiodense than dentin and also presented higher KHN (p=0.001). The use of bovine enamel or dentin should take into consideration the teeth age, but as a general rule it should be recommended to select older bovine teeth due to better chances to find greater similarity with human teeth.

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.

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.

Carbamide peroxide bleaching agents: effects on surface roughness of enamel, composite and porcelain.

This study examined the effect of 10 and 35% carbamide peroxide bleaching agents on the surface roughness of enamel, feldspathic porcelain, and microfilled and microhybrid composite resins. Standardized cylindrical specimens were prepared for restorative materials. Enamel samples were obtained from buccal and lingual surfaces of human molars. Samples from each substrate were divided in three subgroups (n=10), according to surface treatment: distilled water (control), and 10 and 35% carbamide peroxide. The 10% agent was applied 3 h daily and the 35% agent was applied for 30 min/week, at 37 degrees C, during 21 days. Control samples remained stored in distilled water, at 37 degrees C. Roughness measurements (Ra, microm) were made at 24 h and repeated after 7, 14 and 21 days of exposure. Data were analyzed using ANOVA (split-plot design) and Tukey's test (5% significance level). Samples from control groups showed no significant alteration during all test periods, while for exposure to 10% agent, only the porcelain presented a rougher surface after 21 days (p<0.05). For the 35% product, roughness means significantly increased during the first and second weeks for enamel (p<0.05), and after 21 days for porcelain (p<0.05) and for the microhybrid composite (p<0.05). Microfilled samples showed no significant alteration throughout the 21-day period, regardless of the surface treatment.

In vitro evaluation of the effect of core diameter for removing radicular post with ultrasound.

The removal of radicular posts for endodontic reasons as well as their replacement is a common procedure in dental practice. The use of ultrasound is becoming a standard practice since it reduces the stress to displace the core from the canal minimizing the risks of root fractures, perforations and further wearing of dental structure. Thus, the objective of this study was to evaluate the effect of a reduction in the core diameter when removing radicular posts with ultrasound. Twenty-four teeth were divided in two groups. Group I received posts with the dowel and core of the same diameter (1.7 mm) and group II received posts with the dowel diameter 2 mm larger (3.7 mm) than the core diameter. Zinc phosphate cement was used to cement the posts in all groups. Half of the samples of each group received ultrasonic energy for 8, 2 min for each face. All samples were submitted to traction on an Instron machine (model 4444). Data were analysed statistically with anova and the Tukey test, revealing significant differences (P < 0.05) between groups. The authors concluded that the mean tension necessary to displace the posts from the roots was reduced by 26% when ultrasound was applied. The reduction of the post-diameter reduced the necessary tension to remove them by 24% compared with larger posts.

[Effect of acrylic resin post-pressing time on dimensional change of total denture base]. / Efeito do tempo pós-prensagem da resina acrílica na alteração dimensional da base de prótese total.

The dimensional alterations of denture bases were verified in function of the acrylic resin post-pressing time. Twenty stone cast/wax base sets were confected for routine flasking procedure. Thermosetting acrylic resin (Clássico) was prepared according to the instructions of the manufacturer. After final pressing, the acrylic resin was submitted to polymerization in water at 74 degrees C during 9 hours, following the immediate, 6-, 12-, and 24-hour post-pressing times. The resin bases were fixed on the casts with instantaneous adhesive and the sets were laterally sectioned in the regions corresponding to the distal aspect of canines (A), mesial aspect of first molars (B), and posterior palatal zone (C). The gap between the stone cast and the resin base was measured with a comparative microscope at five referential positions for each kind of sectioning. Data submitted to ANOVA and Tukey's test showed that there was no statistically significant difference between the immediate and the 6-hour post-pressing times as well as between the 12- and the 24-hour post-pressing times. However, there was statistically significant difference between the immediate/6-hour groups and the 12-/24-hour groups.

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.

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).