The effect of energy application sequence on the microtensile bond strength of different C-factor cavity preparations.

This study investigated the effect of three equivalent radiant exposure energy application sequences (EASs): high intensity power (HIP: 1,177 mW/cm2, 40 seconds), low intensity power (LOP: 573 mW/cm2, 71 seconds) and ramp (RMP: 650 mW/cm2, 5 seconds, then the irradiance increases to 1047 mW/cm2, 37 seconds) on the microtensile bond strength (MTBS) in both low and high C-factor cavity preparations. Thirty Paradigm blocks (Z100) were mounted in stone, with their top surfaces parallel to the mounting block. High C-factor (HC = 3.8) Class I cavity preparations were then prepared in 15 of the Paradigm blocks using a computer-controlled specimen former. Low C-factor (LC = 1.8) Class II cavity preparations were prepared in the remaining 15 blocks by sectioning them perpendicularly using a slow-speed diamond saw. Five samples, one from each experimental group (3 EASs x 2 C-factors), were prepared and stored in the dark for 48 hours in distilled water at 37 degrees C prior to MTBS testing on the third day and on the remainder of the samples (n = 30). Mode of fracture was determined with a stereomicroscope at 20-40x magnification. The findings of this study indicated that HC, in combination with HIP, had significantly lower bond strength (27.54 MPa) than LC with HIP (51.39 MPa). On the other hand, there was no significant difference between high and low C-factors with the other EASs (LOP or RMP). There was also no significant effect for EAS (HIP, RAMP and LOP), with C-factor (HC or LC) held constant. The HIP-HC group had the highest percentage of adhesive (20%) and mixed adhesive (50%) failures (70% total). Adhesive and mixed adhesive failures occurred in other groups, but with lower percentages (RMP-LC: 40% total) (LOP-HC: 40% total).

Polymerization contraction force of packable composites.

The maximum rate of shrinkage force development and maximum contraction force was evaluated for four packable composites and a hybrid composite control. One of the packable composites demonstrated a significantly higher maximum force rate and maximum force than the other materials; the three remaining packable composites had maximum force rates and maximum forces that were statistically similar to the conventional hybrid composite control.

Effect of stepped light intensity on polymerization force and conversion in a photoactivated composite.

PURPOSE: This study evaluated the effect of stepped light intensity on the polymerization shrinkage forces and degrees of conversion of a hybrid composite. MATERIALS AND METHODS: Composite specimens were bonded between two steel rods (5.00 mm diameter, 1.25 mm apart, configuration factor = 2) mounted in a universal testing machine using a constant displacement mode. Polymerization contraction force was recorded for 300 seconds under four light exposure conditions: group 1: 40 s x 800 mW/cm2; group 2: 10 s x 100 mW/cm2 + 30 s x 800 mW/cm2; group 3: 60 s x 800 mW/cm2; group 4: 10 s x 100 mW/cm2 + 50 s x 800 mW/cm2. Maximum curing force (N300 s) and maximum force rate of the four groups were compared using one-way analysis of variance (ANOVA) (alpha = 0.05) and the Tukey test. Degree of conversion in all groups was evaluated at two depths (top surface and 2 mm) using Fourier transform infrared spectroscopy (FTIR). RESULTS: Mean maximum shrinkage forces and standard deviations (SD) were: group 1, 177 N (SD = 23); group 2, 172 N (SD = 11); group 3, 213 N (SD = 15); group 4, 197 N (SD = 17). Mean maximum forces for stepped and standard groups with the same duration (1 and 2; 3 and 4) were not statistically different; means for groups 2 and 3 were statistically different. Maximum force rates were not significantly different (p = .1548). Force:time curves were S-shaped. Specimens exposed to stepped curing exhibited longer delays before force was recorded. Mode of curing was shown not to contribute to overall cure, but both duration of cure and the depth (top surface vs. 2.00 mm) were significant with an interaction effect.

Metal surface treatment: characterization and effect on composite-to-metal bond strength.

This study evaluated the effect of four methods of metal surface preparation and the use of silane on the bond strength between resin and a Noble metal alloy. SEM Examination and x-ray energy-dispersive spectroscopy (EDS) of the various metal surface treatments was also performed. One-hundred metal disks were cast in a Noble metal alloy (Porcelain #76). Ninety disks were polished flat and the surfaces received one of four abrasive treatments (n = 20). 1) Roughening with a diamond bur at high speed; 2) Air abrasion with an intraoral sandblaster using alumina particles; 3) Air abrasion with KCP-2000 and 4) Air abrasion with an intraoral sandblaster using silanated silica covered alumina particles (CoJet-Sand). Half the specimens from each treatment group (n = 10) were silanated prior to bonding procedures (All-Bond 2 adhesive system, Pertac-Hybrid composite). Specimens were stored in distilled water at 37 degrees C and thermocycled prior to shear strength testing. The 10 remaining metal disks were used for scanning electron microscopy and x-ray energy-dispersive spectroscopy (EDS). Scanning electron microscopy examined the micromorphology of the metal surfaces produced by the four abrasive treatments and x-ray energy-dispersive spectroscopy (EDS) to evaluate changes in surface composition. Two untreated disks served as controls. One-way ANOVA and Tukey's HSD post-hoc test demonstrated that air abrasion with CoJet-Sand and silane resulted in significantly higher resin-to-metal bond strength than all other metal surface treatments, while roughening with a diamond bur produced the lowest bond strength. Resin-to-metal bond strength was similar for all other particle abrasive treatments with or without silane. Using silane significantly improved bond strength only for metal surfaces treated with CoJet-Sand. An increase in Al concentration was observed on metal surfaces sandblasted with aluminum oxide, and an increase in the concentration of both Al and Si was observed on surfaces air-abraded with CoJet-Sand.

Effect of ramped light intensity on polymerization force and conversion in a photoactivated composite.

PURPOSE: This study evaluated the effect of ramped light intensity on the polymerization shrinkage forces and degrees of conversion (DC) of a hybrid composite. MATERIALS AND METHODS: Composite samples were bonded between two steel rods (2.50 mm diameter, 1.25 mm apart, configuration factor = 1.0) mounted in a universal testing machine using a constant displacement mode. Polymerization contraction force was recorded for 250 seconds under four light exposure conditions: group 1, STD: (40 s x 800 mW/cm2); group 2, EXP: (150 mW/cm2 logarithmic increase to 800 mW/cm2 over 15 s) + (25 s x 800 mW/cm2); group 3, 2-STEP: (10 s x 150 mW/cm2) + (30 s x 800 mW/cm2); group 4, MED: (80 s x 400 mW/cm2). Maximum curing force (N250s) and maximum force rate of the four groups were compared using one-way analysis of variance (ANOVA) (alpha = 0.05) and the Tukey test. Degrees of conversion obtained with STD, EXP, and MED cure modes were evaluated at three depths (top surface, 1 mm, and 2 mm) using Fourier transform infrared spectroscopy (FTIR). RESULTS: Maximum rates of polymerization shrinkage force development and standard deviations (SD), in ascending order, were group 4, MED: 0.33 +/- 0.03 N/s; group 2, EXP: 0.35 +/- 0.06 N/s; group 1, STD: 0.44 +/- 0.03 N/s; and group 3, 2-STEP: 0.46 +/- 0.07 N/s. Maximum rates of polymerization shrinkage force development of group 2, EXP and group 4, MED were statistically equivalent and lower than those of group 1, STD and group 3, 2-STEP. Maximum shrinkage forces (+/- SD), in ascending order, were group 2, EXP: 20.4 +/- 2.5 N; group 4, MED: 25.8 +/- 1.0 N; group 3, 2-STEP: 27.4 +/- 5.8 N, and group 1, STD: 30.5 +/- 2.7 N. Maximum force of the EXP mode was statistically lower than MED, 2-STEP, and STD curing modes. The EXP ramp was successful in reducing the conversion rate at the top surface and at 1.0-mm depth, but it did not affect the total conversion compared to the STD 40-second cure mode. There was no difference in DC at the top surface and 1-mm depth with mode of cure. The MED cure mode resulted in a higher DC than the EXP mode at a depth of 2 mm. CLINICAL SIGNIFICANCE: Maximum shrinkage force and force rate exhibited during the first 250 seconds of polymerization were significantly lower using a ramped light intensity exposure. Ramped light intensity decreased conversion rate at the top surface and at 1.0-mm depth and did not affect the total extent of conversion compared to a standard 40-second, single-intensity cure mode. The slower conversion rate resulting from ramped light intensity helped to reduce the rate and maximum polymerization stress, but would not be expected to compromise the physical properties for the restorative material, since similar degrees of conversion were obtained.

Radiopacity of compomers, flowable and conventional resin composites for posterior restorations.

The objective of this study was to densitometrically determine the relative radiopacity (aluminum [Al]-equivalent values) of dentin, enamel, and 20 resin composite materials currently used for posterior restorations. Specimens 5 mm in diameter and 2 mm thick were fabricated from 20 materials (n = 7) for a total of 140 specimens. Human molars were longitudinally sectioned 2.0 mm thick to include both enamel and dentin. The optical densities of enamel, dentin, restorative materials, lead, and aluminum step wedge were obtained from radiographic images, using a transmission photodensitometer. The Al equivalent (mm) for each material was calculated from the linear regression equation of the log of normalized optical density and Al mm thickness obtained from the step wedge. A linear regression of the logarithm of normalized optical density and Al mm thickness was plotted (r2 = 0.9953), and the relative radiopacities, expressed as equivalent thickness of Al, were ranked ordinally. All materials tested, with the exception of an unfilled resin adhesive, complied with ISO Standard 4049, being at least as radiopaque as a 2.0 mm thickness of 99.6% pure Al. Four of six flowable composites had radiopacity values that fell between that of dentin and enamel, while two materials were more radiopaque than enamel. The three compomers tested had radiopacities greater than enamel. In addition, all traditional light- and chemical-cure resin composite materials tested were more radiopaque than enamel. All materials tested, with the exception of one adhesive resin, were at least as radiopaque as dentin and complied with ISO Standard 4049. Clinicians should be able to distinguish these restorative materials radiographically from recurrent decay, voids, gaps, or other defects that lead to clinical failure. Utilization of materials ranked more radiopaque than enamel would enable clinicians to distinguish the restorative material from tooth structure.

Effect of two abrasive systems on resin bonding to laboratory-processed indirect resin composite restorations.

PURPOSE: This study compared two methods of surface roughening or preparation, with or without the use of proprietary surface wetting agents, to evaluate their effect on resin cement adhesion to the following laboratory-processed, indirect restorations: Artglass (AG), belleGlass HP (BG), Concept (C), and Targis (T). Methods of surface roughening or preparation included microetching with aluminum oxide (AO): 50 microns at 34 psi and silanized silica coating, CoJet-Sand (CJ): 30 microns at 34 psi. Artglass and Concept were tested with and without the use of their respective surface wetting agents: Artglass Liquid (AGL) and Special Bond II (SB). MATERIALS AND METHODS: One hundred twenty specimens, each consisting of a pair of cylinders (7.0 x 3 mm and 4.3 x 3 mm) were fabricated. The larger cylinder or base was embedded in self-curing resin in a phenolic ring, and bonding surfaces were finished with 320-grit silicon carbide paper. Specimen pairs for each restorative material were randomly assigned to treatment groups (n = 10) and received the following surface treatments prior to cementation: group 1 (AG/AO/+AGL), group 2 (AG/AO/-AGL), group 3 (AG/CJ/+AGL), group 4 (AG/CJ/-AGL), group 5 (BG/AO), group 6 (BG/CJ), group 7 (C/AO/+SB), group 8 (C/AO/-SB), group 9 (C/CJ/+SB), group 10 (C/CJ/-SB), group 11 (T/AO), and group 12 (T/CJ). Specimen pairs were cemented with a dual-cure resin cement (Dual) and a standardized force of 1 MPa. Specimens were light-cured 40 seconds per side (80 s total), then thermocycled 300 times at between 5 degrees and 55 degrees C. Shear bond strengths (MPa) were determined using a Zwick Materials Testing Machine at a crosshead speed of 5 mm per minute. RESULTS: One-way analysis of variance (ANOVA) and Duncan's multiple range test (alpha = 0.05) by restoration type indicated no significant differences in shear bond strength between BG group 5 (29.8 +/- 5.8), BG group 6 (28.3 +/- 4.3), T group 11 (29.3 +/- 4.9), and T group 12 (29.0 +/- 4.4). Shear bond strength in AG group 3 (35.9 +/- 3.4) was significantly higher than in AG group 4 (32.4 +/- 4.0) and equal to that in AG group 2 (31.9 +/- 3.9) and AG group 1 (30.0 +/- 3.6). Shear bond strength in C group 10 (24.8 +/- 5.7) was equal to that in C group 9 (21.5 +/- 2.9), but was higher than in C groups 7 (19.4 +/- 3.1) and 8 (19.3 +/- 3.4). CLINICAL SIGNIFICANCE: Under the conditions of this study, the combination of CoJet-Sand and Artglass Liquid resulted in the highest bond strength for Artglass restorations. Microetching with CoJet-Sand or aluminum oxide followed by wetting with an unfilled adhesive was an effective surface pretreatment for dual-cure resin cementation of the four proprietary indirect resin-ceromer restorations tested.

Effect of composite type, light intensity, configuration factor and laser polymerization on polymerization contraction forces.

PURPOSE: To investigate the effect of composite type, light intensity, configuration factor and laser polymerization on polymerization contraction force. MATERIALS AND METHODS: Glass rods (10 pairs/group) were etched with HF acid, silanated, unfilled resin applied and light cured for 20 s. Rods were held vertically in chucks on a Zwick machine. A cylindrical matrix was filled with Silar chemical cure, Silux Plus microfill or Z-100 hybrid composite and the crosshead of the UTM positioned at an inter-rod distance corresponding to a specific ratio of bound to unbound composite surface area (configuration factor or C). Exposure time with the Demetron 401 conventional visible light curing unit (D401) was 40 s/side (80 s total). Exposure times for the ILT Model D5500 air cooled laser (LAC) and Model 5500ABL water cooled laser (LWC) was 20 s/side (40 s total). Experimental groups, n = 10 with constant factors in parentheses, included: (1) Silar chemical-cured (C = 3); (2) Z-100 hybrid (C = 3, D401, 100% intensity); (3) Silux Plus microfill (C = 3, D401, 100% intensity); (4) D401 100% light intensity = 476 mW (Z-100, C = 3, D401); (5) D401 50% intensity = 238 mW (Z-100, C = 3, D401); (6) D401 25% intensity = 119 mW (Z-100, C = 3, D401); (7-9) C = 5, 3 & 1 respectively (Z-100, D401, 100% intensity); (10) D401 with 13 mm tip = 391 mW/cm2 (Z-100, C = 3; D401); (11) D401 with Turbo Tip = 811 mW/cm2 (Z-100, C = 3; D401); (12) LAC = 265 mW, 689 mW/cm2 (Z-100, C = 3); (13) LWC = 365 mW, 1100 mW/cm2 (Z-100, C = 3). One Way ANOVA and Duncan's Multiple Range Test (alpha = 0.05) were performed separately for each variable. RESULTS: Homogeneous subsets by variable were: composite type Group 1 (25N) < Group 3 (65.8N) < Group 2 (90.4N); intensity Group 6 (73.9N) = Group 5 (77.7N) < Group 4 (90.4N); C-Factor Group 7 (81.8N) < Group 8 (90.4N) < Group 9 (103.4N); light source Group 12 (77.4N) = Group 13 (79.1N) < Group 10 (90.4N) = Group 11.(89.4N). The chemical-cured composite had the lowest maximum polymerization contraction force, the microfill was intermediate and the hybrid composite had the highest recorded force. Increases in light intensity increased the maximum force on the force/time curve. Maximum forces were inversely related to C-factor (C5 < C3 < C1) and directly related to composite volume in a non-rigid system which allowed compliance. Maximum force was not significantly different with the two tips tested on the conventional curing light. Forces obtained with laser polymerization were similar for the two laser groups, which were both statistically lower than the conventional light tested.

Surface treatment techniques for resin composite repair.

PURPOSE: To compare bond strengths of fresh resin composites to previously polymerized ("aged") composites following various surface treatments. MATERIALS AND METHODS: Eighty Pertac Hybrid (PH) and an equal number of Silux Plux (SLX) specimens were fabricated and stored for 1 week prior to surface treatment. The specimens were then polished and stored for an additional 24 hours prior to final surface treatment. The surface treatments included use of one of the following: (1) diamond bur (DB), (2) microetcher with 50 microns Al2O3@80 psi pressure (ME), (3) high-pressure air abrasion with 27 microns Al2O3@psi, (KCP), or (4) low-pressure silicate ceramic deposition using 30 microns particles@34 psi (CJ-S) with a microetcher. Half of the samples were treated with a silanating agent. Fresh resin composite (same type as used for the aged specimen) was bonded to the treated surfaces, and specimens were then stored 24 h and thermocycled 300 x at 5 degrees and 55 degrees C prior to testing for shear bond strength. Two-way ANOVA was used to determine significant differences between mean shear bond strengths for both composite materials. RESULTS: Significant differences were found between the groups for both surface treatment and silane use (P < 0.05). The interaction between the two main effects was also significant (P < 0.05). Overall, the highest bond strengths were found when the low-pressure silicate ceramic deposition system (CJ-S) was used, with or without silane.

Effect of desiccation on microleakage of five Class 5 restorative materials.

Resin-modified glass ionomers, combinations of resin and glass-ionomer chemistry, have resulted in materials with longer working times and command set by visible light activation. These materials are easier to use and more resistant to early moisture contamination and fracture. A glass-ionomer or resin-modified glass-ionomer restoration may be inadvertently desiccated by isolation of the same quadrant for subsequent restorative procedures. The present study is an assessment of the effects of desiccation on microleakage of three resin-modified glass-ionomers: Vitremer, Photac-Fil, Fuji II LC; a glass-ionomer, Ketac-Fil; and a microfill resin, Silux Plus. Fifty extracted molars were prepared with class 5 preparations buccal and lingual and randomly assigned to 10 groups (n = 10). Restorations were placed according to the manufacturers' specifications and finished wet after the manufacturers' specified setting interval. All samples were thermocycled 300 cycles between 50 and 500 degrees C. Samples were stored in water at all times until the five groups to be desiccated were air dried and stored dry for 45 minutes. Desiccated groups were then rehydrated for 24 hours prior to AgNO3 staining. Teeth were sectioned mesiodistally and four buccolingual sections (0.6 mm thick) through each class 5 restoration were obtained with a Silverstone-Taylor hard tissue microtome. Each section was scored on a scale of 0-4 for microleakage, and the highest score for dye penetration was used as the score for that restoration. An increase in microleakage was observed in all desiccated groups. Three materials showed a statistically significant increase in microleakage (P < 0.05) following desiccation. Microleakage increases following a brief period of desiccation corresponding to typical treatment times indicate that clinicians need to protect previously placed restorations from undue drying during subsequent dental treatment.