Efficacy and durability of bleaching with diode lasers: an in vitro study.

The aim of this in vitro study was to compare the efficacy and durability of bleaching with diode lasers over a 9-month period. This study evaluated 27 extracted teeth categorized into 3 bleaching groups (n = 9): 940-nm diode laser, 980-nm diode laser, and 40% hydrogen peroxide whitening gel (control). After the baseline color of the teeth was measured using a spectrophotometer, the teeth underwent dental prophylaxis and their color was measured again. Bleaching treatment was then performed. The color of the teeth was measured immediately after bleaching and 1 day (24 hours), 1 week, 1 month, 3 months, 6 months, and 9 months after bleaching. The Commission Internationale de l'Eclairage (CIE) L*a*b* color change (ΔE*) at each timepoint was calculated and compared using repeated-measures analysis of variance. All bleaching techniques effectively whitened the teeth to a clinically perceptible level (ΔE* > 3.3), and there were no statistically significant differences among the groups (P > 0.05). The mean ΔE* values of the laser groups were not significantly different from the mean value of the control group during the 9-month evaluation period (P > 0.05). However, statistically significant differences among the groups were noted when color measurements at the following timepoints were compared: immediately after bleaching vs 1 day; 1 day vs 1 week; and 3 months vs 6 months (P < 0.05). Use of a 940-nm diode laser, 980-nm diode laser, or conventional hydrogen peroxide gel provided equally effective bleaching. The color change remained clinically perceptible throughout the 9-month period.

Effect of surface treatment with laser on repair bond strength of composite resin to ceramic.

Background: Small chipping or fracture of ceramic restorations may be repaired by composite resin instead of replacing the restoration. This method is faster and cheaper compared to restoration replacement. Several strategies have been suggested to obtain a high repair shear bond strength (SBS). This study aimed to assess the efficacy of some new ceramic surface treatments (laser and universal adhesive) to enhance the repair bond strength of composite resin to ceramic compared to the conventional method. Materials and Methods: This in vitro study evaluated 80 IPS Empress Esthetic ceramic plates in eight groups (n = 10). The ceramic surface was polished with 320-grit silicon carbide paper under running water, rinsed with water spray for 10 s and dried. The samples were then divided into two subgroups for mechanical surface preparation with hydrofluoric (HF) acid and Er: YAG laser (2 W, 200 m J, 10 Hz, 10 s). Each group was divided into two subgroups for use/no use of silane. The conventional or universal adhesive was then applied on the samples in each subgroup. Composite cylinders were bonded to the ceramic surface using plastic tubes. The samples were stored in distilled water at 37°C for 24 h and subjected to an SBS test. Data were analyzed using one-way ANOVA (P < 0.05). Results: The interaction effect of variables on SBS was significant. Maximum SBS was noted in HF acid + silane + conventional adhesive group (mean: 12.0481 MPa). Minimum SBS was noted in the laser + conventional adhesive group (mean: 2.5766 MPa). Surface treatment with HF acid yielded significantly higher SBS than laser (P < 0.001). The interaction effect of conventional/universal adhesive and use/no use of silane on SBS was statistically significant. Conclusion: The repair SBS was higher in groups treated with HF acid compared to laser. Ceramic surface treatment with HF plus silane plus conventional adhesive yielded a higher SBS as well as HF plus Universal adhesive. Thus, the application of silane as a separate step can be omitted in the repair of ceramic restorations with universal adhesives.

Microshear Bond Strength of a Self-adhesive Composite to Erbium Laser-Treated Primary Enamel.

Introduction: Advances have been made in the composition of flowable composites in recent years and self-adhering composites, which do not require a bonding agent, have recently been introduced to the market. This study aimed to assess the microshear bond strength (µSBS) of a self-adhering flowable composite (Vertise) to primary enamel treated with a graphite disc with silicon carbide particles (SIC) and laser irradiation, the result of which was compared to that of a conventional flowable composite (Premise). Methods: In this in vitro, experimental study, 72 samples of sound primary enamel were evaluated. A smooth enamel surface was obtained using a graphite disc. Next, the erbium chromium yttrium scandium gallium garnet (Er,Cr:YSGG) laser was used for enamel surface treatment in half of the samples (n=36). All the samples were then randomly divided into 4 groups of (i) Premise flowable composite (PF) without laser (n=18), (ii) Vertise flowable composite (VF) without laser (n=18), (iii) PF with laser (n=18), and (iv) VF with laser (n=18). The teeth were then incubated at 37°C for 24 hours and were then subjected to thermocycling. The µSBS of samples was measured using a universal testing machine and reported in megapascal (MPa). Data were analyzed using SPSS via the two-way ANOVA and independent-samples t test at P<0.05. Results: The mean µSBS of VF was significantly higher to the laser-treated samples (13.60±5.47) compared with the non-treated samples (5.89±2.42) (P<0.001). However, no significant difference was noted in the µSBS of PF to the laser-treated (13.18±3.45) and non-treated samples (16.06±3.52) (P=0.058). Conclusion: The µSBS of the conventional flowable composite is higher than that of the self-adhering flowable composite to the enamel of primary teeth. Enamel surface treatment with laser irradiation increases the µSBS of self-adhering flowable composites.

Color stability of self-adhering composite resins in different solutions.

BACKGROUND: The success of composite resin restorations depends to a great extent on their color stability. However, discoloration is still a problem in composite resin restorations. OBJECTIVES: The aim of the study was to evaluate the effect of different staining solutions on the color stability of composite resins. MATERIAL AND METHODS: A total of 96 composite disks, 2 mm in height and 8 mm in diameter, were fabricated of 3 commercially available composite resins. The samples were divided into 4 groups of 8 and were immersed in 4 staining solutions: coffee, tea, soda, and artificial saliva. The color parameters of the samples were measured and recorded before as well as 2, 4 and 8 weeks after immersion by spectrophotometry, using the CIELAB color space. A color change (ΔE) ≤3.3 was considered the acceptable threshold for visual perception. The results were analyzed using the one-way analysis of variance (ANOVA) and Tukey's post hoc test (p < 0.05). RESULTS: All the composite resins in the study showed discoloration in all the staining solutions. The ΔE of VertiseTM Flow was the highest in the tea solution. The lowest ΔE occurred in the FiltekTM Z250 composite in artificial saliva. CONCLUSIONS: This in vitro study showed that the color stability of tooth-colored restorations can be influenced by dietary habits.

Effect of an Optical Whitening Toothpaste on Color Stability of Tooth-Colored Restorative Materials.

OBJECTIVES: This study aimed to assess the effect of an optical whitening toothpaste on color stability of microhybrid, nanofilled, and microfilled composite resins and resin-modified glass ionomer (RMGI) cement in comparison of two other toothpastes. MATERIALS AND METHODS: In this experimental study, disc-shaped composite samples were fabricated. The samples were then polished using silicon carbide papers. Twenty-seven samples of each material were fabricated and subjected to colorimetry using a spectrophotometer. Each group of material was then divided into three subgroups for the application of conventional whitening and whitening containing blue covarine toothpastes. One operator brushed the samples with an electric soft toothbrush with circular motion twice a day, each time for 30 seconds. Colorimetry was performed at 0, 1, 7, 30, and 90 days. STATISTICAL ANALYSIS: Two-way analysis of variance (ANOVA), one-way ANOVA, and Tukey's honestly significant difference (HSD) test were used for statistical analysis. RESULTS: The interaction effect of type of restorative material and time on ∆E was not significant at baseline or 1 day (p > 0.05). The effect of type of toothpaste on ∆E was not significant at baseline or 1 day (p = 0.78) but the effect of type of material was significant (p < 0.05). The toothpastes had significantly different effects on ∆E of Z250 at all time points (p < 0.05) except for ∆E0-30 (p = 0.106). The toothpastes had significantly different effects on ∆E of Z350 and Gradia at all time points (p < 0.05). The same was true for RMGI except for ∆E0-7 (p = 0.43) and ∆E0-90 (p = 0.52). The majority of color changes caused by toothpastes were not clinically perceivable (∆E < 3.3), except for ∆E0-90 by the whitening toothpaste (∆E = 9), ∆E0-90 by the conventional toothpaste for Z350 (∆E = 3.9), and ∆E0-1 by the whitening toothpaste for RMGI (∆E = 3.7). CONCLUSION: The color change of all composite samples was not clinically perceivable (<3.3) at all time points, which shows that the tested toothpastes do not cause a significant change in color of composite materials.

Effect of Addition of Nano-TiO2, Nano-SiO2, and a Combination of Both, on Antimicrobial Activity of an Orthodontic Composite.

AIM: This study aimed to assess the effect of addition of nano-titanium oxide (nano-TiO2), nano-silicon dioxide (nano-SiO2), and a combination of both, on antimicrobial activity of an orthodontic composite. MATERIALS AND METHODS: Molds measuring 0.64 × 0.5 mm were used for the fabrication of composite disks. For this purpose, 0.5% and 1% nano-TiO2, nano-SiO2, and a combination of both (0.5% nano-TiO2 and 0.5% nano-SiO2), were mixed with Transbond XT composite (3M Unitek). A total of 180 composite disks were fabricated for eluted component, disk agar diffusion (DAD), and biofilm inhibition tests. The colony counts of Streptococcus mutans (S. mutans), Streptococcus sanguinis (S. sanguinis), and Lactobacillus acidophilus (L. acidophilus) and the diameters of growth inhibition zones were measured at 3, 15, and 30 days after exposure to the materials. Data were analyzed using one-way ANOVA and a post hoc test. RESULTS: None of the nano-TiO2 and nano-SiO2 concentrations had any significant effect on the growth inhibition zone. All tested concentrations of nano-TiO2 and nano-SiO2 decreased the colony count of all bacteria. The composite sample containing both nano-TiO2 and nano-SiO2 had the greatest efficacy for reduction of S. mutans and S. sanguinis colony counts at all three time points. Also, 1% nano-TiO2 and 1% nano-SiO2 had similar effects on L. acidophilus in eluted component test. CONCLUSION: Addition of TiO2 and SiO2 nanoparticles conferred antimicrobial property to the tested orthodontic composite. CLINICAL SIGNIFICANCE: Using orthodontic composite containing nonoparticles with antibacterial activity may prevent dental caries.

Effect of Intracanal Medicaments on Pull-Out Bond Strength of Fiber Post Cemented with a Self-Adhesive System.

OBJECTIVES: This study aimed to assess the effect of four intracanal medicaments on pull-out bond strength of fiber posts. MATERIALS AND METHODS: A total of 65 single-rooted, single-canal teeth were selected and decoronated. Root canals were prepared and after rinsing were randomly divided into five groups (n = 13). G1: calcium hydroxide (CH), G2: CH plus chlorhexidine (CH+CHX), G3: triple antibiotic paste (TAP), G4: double antibiotic paste (DAP) were applied in the canals in the four groups. The control group (G5) received no medicament. After 4 weeks, the medicaments were rinsed off and the canals were filled with gutta-percha. Post space was then prepared in root canals for the placement of glass fiber posts and self-adhesive cement (Panavia F2). After cementation, they were subjected to pull-out bond strength test. STATISTICAL ANALYSIS: Data were statistically analyzed using one-way analysis of variance and Tukey test.Results The pull-out bond strength values were significantly different in the groups (p < 0.001). The highest values of bond strength were seen in G2, G1, and G3 (359.97 ± 81.26, 333.79 ± 98.96, 309.27 ± 78.07), respectively. There was no significant difference between G4 and G5 (p = 0.75). CONCLUSION: The results showed that CH, CH+CHX, and TAP enhanced the pull-out bond strength of fiber post to root canal wall as compared to the control group.

Apical Transportation of Mesiobuccal Canals of Maxillary Molars Following Root Canal Preparation with Two Rotary Systems and Hand Files: A Cone-Beam Computed Tomographic Assessment.

OBJECTIVES: This study aimed to compare the transportation of the mesiobuccal canal of maxillary molars following root canal preparation with HyFlex CM (HCM) and Edge Taper Platinum (ETP) rotary systems and stainless steel (SS) hand files using cone-beam computed tomography (CBCT). MATERIALS AND METHODS: This in-vitro study was performed on 48 maxillary molars in three groups of 16. The teeth were mounted in acrylic blocks, and root canals were prepared using HCM in group 1 (up to #30/0.06), ETP in group 2 (up to F3/0.06), and SS hand files in group 3 (up to #30). CBCT scans were taken before and after root canal preparation. The amount of canal transportation was measured at 0, 3, 6, and 9mm from the apex. Data were analyzed using Kruskal-Wallis and Mann-Whitney tests. RESULTS: The difference in canal transportation at 0 and 6mm from the apex was significant between the HCM and ETP groups (P=0.031 and 0.023) but none of the systems showed any significant difference with hand files at 0-and 6-mm levels (P=0.10, 0.56, 0.22, and 0.50), respectively. At 3mm from the apex, no significant difference was noted among the groups (P=0.30). At the 9-mm level, the amount of canal transportation was not significantly different between HCM and ETP (P=0.83) but they showed significant differences with hand files (P<0.001). CONCLUSION: ETP and HCM caused less canal transportation at the curvature of the mesiobuccal canal of maxillary molars compared to hand files. ETP showed superior efficacy in root canal preparation compared to HCM.

Influence of Primers and Additional Resin Layer on Zirconia Repair Bond Strength.

PURPOSE: To evaluate the influence of alloy/zirconia primer and 10-methacryloyloxydecyl dihydrogen phosphate (MDP)-containing resin layer treatments on the shear bond strength (SBS) of composite resin to zirconia after aging. MATERIALS AND METHODS: Sixty zirconia (Y-TZP) blocks were air-abraded (35-µm Al2 O3 ) and divided into 6 experimental groups (n = 10) in terms of primer/resin layer as follows: (1) control, without any primer or resin; (2) AP, Alloy Primer; (3) ZPP, Z-Prime Plus; (4) PL/ZPP, Z-Prime Plus with light polymerization; (5) AP+SEB, Alloy Primer along with light-cured bonding resin of a self-etch adhesive system (SE Bond); and (6) ZPP+SEB, Z-Prime Plus with SE Bond. After composite resin placement and light polymerization, the specimens were stored in distilled water (37°C for 4 months) and thermal-cycled for 6000 cycles. The SBS was tested with a universal testing machine. Statistical analysis of the SBS data was performed with one-way ANOVA, followed by HSD Tukey test (α = 0.05). RESULTS: There were significant differences between the groups (p < 0.001, F = 116.5). All the groups revealed significantly higher SBS than the control (p < 0.001). ZPP+SEB group exhibited the highest SBS (16.14 ± 2.52 MPa) and AP group the lowest SBS (7.00 ± 1.97 MPa) among experimental groups; both had significant differences with the other groups (p < 0.001). There were no significant differences between ZPP, PL/ZPP, and AP+SEB groups (p > 0.05). CONCLUSIONS: The bond strength between zirconia ceramic and composite resin was affected by different primers/resin layer. Applying an MDP-containing resin layer along with both primers resulted in significant enhancement of SBS. This improvement for Z-Prime Plus was significantly higher than that of Alloy Primer.

Effect of antimicrobial photodynamic therapy on microleakage of class cavities restored with composite resin.

OBJECTIVES: Disinfection of enamel and dentin following cavity preparation is a necessity. Considering the possible effect of antimicrobial agents on tooth structure and dental adhesives, this study aimed to assess the microleakage of composite restorations following disinfection of cavity walls with antimicrobial photodynamic therapy (aPDT). MATERIALS AND METHODS: Standard class V cavities were prepared in the buccal surfaces of 68 extracted human premolars. The teeth were then randomly divided into four groups (n = 17) for use of different adhesive systems (Adper Single Bond 2 or One-Step Plus) and disinfection with aPDT. The cavities were filled with Filtek Ultimate composite. After thermocycling and immersion in 0.5% fuchsine, the teeth were sectioned and evaluated under a stereomicroscope to determine the microleakage score. Data were analyzed using the Kruskal Wallis and Wilcoxon tests (P < 0.05). RESULTS: No significant difference was noted in microleakage in the occlusal and gingival walls among the study groups (P > 0.05). In each study group, microleakage in the gingival wall was significantly higher than that in the occlusal wall (P < 0.05). CONCLUSION: Methylene blue-mediated aPDT does not seem to contribute to the microleakage of class V resin-based dental restorations, independently of the composition of bonding agents used.

Effects of Erbium Family Laser on Shear Bond Strength of Composite to Dentin After Internal Bleaching.

Introduction: The aim of this study was to assess the effect of surface treatment with erbium: yttrium-aluminum-garnet (Er:YAG) and erbium, chromium: yttrium-scandium-gallium-garnet (Er,Cr:YSGG) lasers on shear bond strength of composite resin to recently bleached dentin. Methods: In this study, 40 extracted human premolars were selected. The teeth were cut 4 mm apical to the cusp tip and were randomly divided into four groups (n=10 in each group) for shear bond strength testing. For bleaching, 35% hydrogen peroxide (H2 o2 ) gel (Opalescence Endo, Ultradent, South Jordan, UT, USA) was applied to dentin surfaces of all specimens for 10 days. Before etching and bonding, in Er,Cr:YSGG and Er:YAG laser groups, dentin surfaces were irradiated with Er,Cr:YSGG and Er:YAG lasers, respectively. In Er,Cr:YSGG group, Er:YAG group and control group, composite restoration was performed immediately after bleaching while in common procedure group, composite restoration was performed after seven days. The teeth were then subjected to shear bond strength testing machine. The data were statistically analyzed using analysis of variance (ANOVA) and Tukey test. Results: The mean and standard deviation (SD) of shear bond strength was 4.3 ± 1.4 MPa for control group, 6.7 ± 2.0 Mpa for Er,Cr:YSGG group, 14.4 ± 3.7 Mpa for Er:YAG group and 19.4 ± 2.6 Mpa for common procedure group. Conclusion: The shear strength of composite to Er:YAG laser-treated bleached dentin was significantly higher than control group while significantly lower than common procedure.

In vitro evaluation of repair bond strength of composite: Effect of surface treatments with bur and laser and application of universal adhesive.

OBJECTIVES: This study aimed to assess the effect of surface treatment by bur and laser and application of universal adhesive on repair bond strength of composite resin. MATERIALS AND METHODS: A total of 120 composite blocks measuring 6×4×4 mm were fabricated of Filtek Z250 composite. All samples were subjected to 5,000 thermal cycles and divided into two groups for surface preparation by bur and by Er,Cr:YSGG laser (n = 60). The surfaces were then etched with orthophosphoric acid, rinsed with water and divided into three groups (silane, silane plus Single Bond and silane plus Single Bond Universal). Repair composite was then bonded to aged composite. Half of the samples in each group were stored in distilled water at 37°C for 24 hours and the other half underwent 5000 thermal cycles. All samples were then subjected to shear bond strength testing using a universal testing machine at a crosshead speed of 1 mm/minute. The data were analyzed using one-way ANOVA and Tukey's HSD test. Mode of failure was determined using a stereomicroscope. RESULTS: Bur preparation plus universal adhesive yielded the highest bond strength (30.16 µ 2.26 MPa). Laser plus silane yielded the lowest bond strength (5.63 µ 2.43 MPa). Bur preparation yielded significantly higher bond strength than laser (P < 0.001). Also, application of universal adhesive significantly improved bond strength compared to conventional adhesive and silane (P < 0.001). Bond strength after aging (5000 thermal cycles) had no significant difference with primary bond strength at 24 hours within each group (P = 0.182). CONCLUSION: Surface preparation of aged composite by bur and application of universal adhesive can improve the repair bond strength of composite. Application of silane (without adhesive) in the process of repair cannot provide adequately high repair bond strength.

In Vitro Comparison of Diagnostic Accuracy of DIAGNOdent and Digital Radiography for Detection of Secondary Proximal Caries Adjacent to Composite Restorations.

Introduction: Early detection of secondary proximal caries is critical for the preservation of tooth vitality. This study sought to assess and compare the diagnostic accuracy of DIAGNOdent and digital radiography for detection of secondary proximal caries adjacent to composite restorations. Methods: Sixty extracted molars including 30 teeth with carious lesions and 30 sound teeth were randomly selected. Class II cavities were prepared in all teeth and carious dentin was intentionally left in the gingival floor of cavities in 30 carious teeth. All cavities were restored with composite resin. The teeth were mounted in wax blocks (three teeth per block) and examined for caries using (DIAGNOdent kaVo Dental, Biberach, Germany). Digital radiographs using DIGORA photostimulable phosphor (PSP) plates (Soredex Corporation, Helsinki, Finland) were obtained from all teeth using the parallel technique and were evaluated by 4 observers. Repeated measure analysis of variance (ANOVA) was applied to calculate sensitivity and specificity values of the two diagnostic techniques. Receiver operating characteristic (ROC) curve was plotted for DIAGNOdent results and based on that, the cutoff points were determined. Results: The sensitivity and specificity values at the cut-off point of 10.5 were 0.622±0.038 and 0.822±0.077 for DIAGNOdent and 0.591±0.093 and 0.891±0.083 for digital radiography, respectively. The area under the ROC curve was 0.7 for DIAGNOdent. Weighted kappa revealed moderate to almost perfect intra-observer agreement (0.46-0.99). Intraclass correlation coefficient (ICC) for DIAGNOdent was calculated to be 0.88. Conclusion: No statistically significant difference was noted in diagnostic accuracy of DIAGNOdent and digital radiography for detection of secondary proximal caries adjacent to composite restorations. Thus, DIAGNOdent may be used as an adjunct diagnostic tool for detection of secondary proximal caries beneath composite restorations.

Effect of thermocycling and surface treatment on repair bond strength of composite.

BACKGROUND: Repair of composite restorations is a conservative method that can increase the longevity and durability of restorations while preserving the tooth structure. Achieving a suitable bond between the old and new composite is difficult. To overcome this problem, some methods have been recommended to increase the repair bond strength of composite.This study aimed to assess the effect of aging by thermocycling (5,000 and 10,000 cycles) and mechanical surface treatments (Er,Cr:YSGG laser and bur) on repair shear bond strength of composite resin. MATERIAL AND METHODS: Totally, 120 composite blocks measuring 6x4x4 mm were fabricated of Filtek Z250 composite and were randomly divided into three groups (n=40) based on initial aging protocol: (a) no aging: storage in distilled water at 37°C for 24 hours, (b) 5,000 thermal cycles, (c) 10,000 thermal cycles. Each group was then randomly divided into two subgroups (n=20) based on mechanical surface treatment (laser and bur). The laser and bur-prepared surfaces were silanized and Adper Single Bond 2 was then applied. The repair composite was bonded to surfaces. Half of the samples in each subgroup (n=10) were subjected to 5,000 thermal cycles to assess durability of bond. The remaining half were stored in distilled water at 37°C for 24 hours and all samples were then subjected to shear bond strength testing in a universal testing machine with a crosshead speed of 1mm/min. Data (in megapascals) were subjected to one-way ANOVA and Tukey's test (P=0.05). Mode of failure was determined under a stereomicroscope. RESULTS: Bur preparation significantly improved the bond strength compared to laser (P<0.001). Aging by 10,000 thermal cycles significantly decreased the repair bond strength of composite (P<0.001). No significant difference was noted in this regard between distilled water and 5,000 thermal cycles groups (P=0.699). Primary bond strength and bond strength after 5,000 thermal cycles in the same subgroups were not significantly different either (P=0.342). CONCLUSIONS: Aging by 10,000 thermal cycles significantly decreases the repair bond strength of composite and surface preparation by bur provides a higher bond strength compared to laser. Key words:Thermocycling, Composite, Repair, Laser.

Evaluation of the Diode laser (810nm,980nm) on dentin tubule diameter following internal bleaching.

BACKGROUND: The aim of this study was to evaluate the effect of diode laser irradiation and bleaching materials on the dentinal tubule diameter after laser bleaching. MATERIAL AND METHODS: The dentin discs of 40 extracted third molar were used in this experiment. Each disc surface was divided into two halves by grooving. Half of samples were laser bleached at different wavelengths with two different concentrations of hydrogen peroxide. Other half of each disc with no laser bleaching remained as a negative control. Dentin discs were assigned randomly into four groups (n=10) with following hydrogen peroxide and diode laser wavelength specifications; Group 1 (30% - 810 nm), group 2 (30% - 980 nm), group 3 (46% - 810 nm) and group 4 (46% - 980 nm). All specimens were sent for scanning electron microscopic (SEM) analysis in order to measure tubular diameter in laser treated and control halves. Data were analyzed by ANOVA and Tukey test (p<0.05). RESULTS: A significant reduction in dentin tubule diameter was observed in groups 1, 2 and 4. There was no significant difference between groups 1 and 2 and between groups 3 and 4 after bleaching. CONCLUSIONS: The SEM results showed that diode laser was able to reduce dentin tubule diameter and its effect on dentin was dependent on chemical action of bleaching material. KEY WORDS: Laser, diode, dentin, tubule, diameter.

Effect of organic acids in dental biofilm on microhardness of a silorane-based composite.

OBJECTIVES: This study evaluated the effect of lactic acid and acetic acid on the microhardness of a silorane-based composite compared to two methacrylate-based composite resins. MATERIALS AND METHODS: Thirty disc-shaped specimens each were fabricated of Filtek P90, Filtek Z250 and Filtek Z350XT. After measuring of Vickers microhardness, they were randomly divided into 3 subgroups (n = 10) and immersed in lactic acid, acetic acid or distilled water. Microhardness was measured after 48 hr and 7 day of immersion. Data were analyzed using repeated measures ANOVA (p < 0.05). The surfaces of two additional specimens were evaluated using a scanning electron microscope (SEM) before and after immersion. RESULTS: All groups showed a reduction in microhardness after 7 day of immersion (p < 0.001). At baseline and 7 day, the microhardness of Z250 was the greatest, followed by Z350 and P90 (p < 0.001). At 48 hr, the microhardness values of Z250 and Z350 were greater than P90 (p < 0.001 for both), but those of Z250 and Z350 were not significantly different (p = 0.095). Also, the effect of storage media on microhardness was not significant at baseline, but significant at 48 hr and after 7 day (p = 0.001 and p < 0.001, respectively). Lactic acid had the greatest effect. CONCLUSIONS: The microhardness of composites decreased after 7 day of immersion. The microhardness of P90 was lower than that of other composites. Lactic acid caused a greater reduction in microhardness compared to other solutions.

Bond strength of two resin cements to dentin after disinfection pretreatment: effects of Er,Cr:YSGG laser compared with chemical antibacterial agent.

OBJECTIVE: This study compared the effects of two disinfection procedures (2% chlorhexidine [CHX] solution versus Er,Cr:YSGG laser irradiation) on the shear bond strength of ED primer II/Panavia F2.0 (ED/P) and Excite DSC/Variolink N (Ex/V). BACKGROUND DATA: Different methods are used for cavity disinfection prior to adhesive cementation, which may influence the bonding ability of resin cements. METHODS: Flat dentin surfaces were prepared on 100 extracted premolars and randomly divided into 10 groups. In the eight experimental groups, indirect composite samples were cemented with either ED/P or Ex/V under three disinfecting conditions on the dentin surface as follows: (1) CHX application before ED primer II/ after etching, (2) wet laser irradiation (Er,Cr:YSGG laser, 20 Hz, 0.75 W, 15% water +15% air), (3) dry laser irradiation with no water and air cooling. The control groups had no disinfectant application. After 24 h water storage, bond strength test was performed. The data (MPa) were analyzed using two way ANOVA and Tukey tests. RESULTS: The lowest and highest bond strengths were obtained by dry laser and wet laser (10.18±2.67 and 17.36±2.94 for ED/P, 9.64±2.66 and 20.07±3.36 for Ex/V, respectively). For each cement, two-by-two comparisons of four groups revealed significant differences only for dry laser with others (p<0.001). CONCLUSIONS: The use of CHX and Er,Cr:YSGG laser at the low fluences with water/air cooling as the antibacterial agents does not adversely influence the bonding ability of the etch-and-rinse and the self-etch cements.

The effect of delayed placement of composite and double application of single-bottle adhesives on microleakage of composite restorations.

This study evaluated the effect of delayed placement of composite and double application of adhesive on microleakage of two-step, total-etch (single-bottle) adhesives. Standard Class V cavities were prepared in 140 sound premolars and randomly assigned into 10 groups (n = 14). Excite, Optibond Solo Plus, and Adper Scotchbond Multi-Purpose (as a control) were used. After the first layer of single-bottle adhesive was photocured, the adhesive was reapplied and photocured in four of the groups. A microhybrid composite was applied in five of the groups immediately after the adhesive was photocured; in the other five groups, the composite was placed after a three-minute delay. After 24 hours of storage in distilled water and thermocycling, the samples were placed in 1% methylene blue. All samples then were sectioned longitudinally and evaluated for microleakage at the occlusal and gingival margins under a stereomicroscope at 20x magnification. Data were analyzed using nonparametric tests. Delayed placement of composite significantly increased leakage at the gingival margins when single-bottle adhesives were used (p < 0.05). Double application of the single-bottle adhesives significantly reduced leakage at the gingival margin when placement of the composite was delayed. There was no significant difference between single and double application when the composite was placed immediately (p < 0.05).