Camila Sabatini

Color stability of ten resin-based restorative materials.

UNLABELLED Despite significant developments to improve the optical properties of composites, color stability remains a challenge with changes still observed immediately after polymerization and after some time of storage. OBJECTIVE   This study aimed to evaluate the color change of ten commercially available resin composite systems immediately after polymerization, at 24 hours, and at 1 month of water storage. MATERIALS AND METHODS   Five discs of two thicknesses (1 mm/3 mm) in two shades (A3/Bleach) were made from ten commercially available brands of resin composite. Color measurements were recorded with a colorimeter and expressed in terms of the CIE L*a*b* scale. Color change was calculated between baseline and immediate polymerization (ΔE*(1) ), between immediate polymerization and 24 hours (ΔE*(2) ), and between 24 hours and 1 month (ΔE*(3) ). Values ΔE* ≥ 3.3 were considered clinically unacceptable as color shifts over this threshold value may be noticeable. The results were analyzed using a three-way analysis of variance (ANOVA) and Student-Newman-Keulss tests. A significance level of 0.05 was used for all tests. RESULTS   Color change was evidenced for all brands, shades, and thickness. The greatest color change was observed immediately after initial polymerization with ΔE* values ranging from 2.4 to 12.0. Color change after 24 hours and 1 month were significantly less than those observed after polymerization. Immediately after polymerization, only Tetric EvoCeram (Ivoclar-Vivadent, Amherst, NY, USA) showed changes below 3.3. At 24 hours, 20 out of the 40 groups including all materials in both shades and thicknesses showed changes above 3.3. At 1 month, color changes for all brands remained under 3.3. CONCLUSIONS   Overall, clinically relevant color changes (ΔE* ≥ 3.3) took place immediately after polymerization of current light-activated composites. These changes were predominantly attributed to shifts in the L* and b* parameters towards the dark and blue region, respectively. Color shifts continued at 24 hours with changes in the L* and b* parameters towards the light and yellow region, respectively. After 1 month, only minor changes under the 3.3 threshold took place. CLINICAL SIGNIFICANCE Ensuring an accurate color match of resin composite restorations to the surrounding tooth structure is a critical aspect of any esthetic restorative procedure. A better understanding of the changes taking place during the different stages of maturation and storage of composites may be of significant benefit to clinicians as this may help minimize shade mismatch issues.

Transdentinal Cytotoxicity of Carbodiimide (EDC) and Glutaraldehyde on Odontoblast-like Cells

OBJECTIVE To evaluate the transdentinal cytotoxicity of three different concentrations of carbodiimide (EDC) or 5% glutaraldehyde (GA) on MDPC-23 cells. METHODS Seventy 0.4-mm-thick dentin disks obtained from human molars were adapted to artificial pulp chambers. MDPC-23 cells were seeded on the pulpal surface of the disks. After 48 hours, the occlusal dentin was acid-etched and treated for 60 seconds with one of the following solutions (n=10): no treatment (negative control); 0.1 M, 0.3 M, or 0.5 M EDC; 5% GA; Sorensen buffer; or 29% hydrogen peroxide (positive control). Cell viability and morphology were assessed by methyltetrazolium assay and scanning electron microscopy (SEM), respectively. The eluates were collected after the treatments and applied on MDPC-23 seeded in a 24-well plate to analyze cell death, total protein (TP), and collagen production. The last two tests were performed 24 hours and seven days after the challenge. Data were analyzed by Kruskal-Wallis and Mann-Whitney tests (p<0.05). RESULTS EDC at all test concentrations did not reduce cell viability, while 5% GA did increase cell metabolism. Cell death by necrosis was not elicited by EDC or 5% GA. At the 24-hour period, 0.3 M and 0.5 M EDC reduced TP production by 18% and 36.8%, respectively. At seven days, increased TP production was observed in all groups. Collagen production at the 24-hour period was reduced when 0.5 M EDC was used. After seven days, no difference was observed among the groups. SEM showed no alteration in cell morphology or number, except in the hydrogen peroxide group. CONCLUSIONS Treatment of acid-etched dentin with EDC or GA did not cause transdentinal cytotoxic effects on odontoblast-like cells.

Matrix metalloproteinase inhibitory properties of benzalkonium chloride stabilizes adhesive interfaces

This study evaluated the effects of different concentrations of benzalkonium chloride (BAC) on the preservation of adhesive interfaces created with two etch-and-rinse adhesives and its inhibitory properties on dentin matrix metalloproteinase (MMP) activity. The following groups were tested with the adhesive systems Optibond Solo Plus and All-Bond 3: Group 1, adhesive without inhibitor (control); Group 2, topical 2.0% chlorhexidine (2.0% CHX); Group 3, phosphoric acid with 1.0%wt BAC (BAC-PA); Group 4, 0.25% BAC-adhesive (0.25% BAC); Group 5, 0.5% BAC-adhesive (0.5% BAC); Group 6, 1.0% BAC-adhesive (1.0% BAC); and Group 7, 2.0% BAC-adhesive (2.0% BAC). Composite cylinders were fabricated, and shear bond strength (SBS) was evaluated after 24 h, 6 months, and 18 months of storage. Extracts from concentrated demineralized human dentin powder were subjected to SDS-PAGE and incubated in the presence of 0.25, 0.5, 1.0, and 2.0% BAC. Overall, stable bonds were maintained for 18 months. Improved bond strengths were seen for 0.5% BAC and 1.0% BAC when bonding with Optibond Solo Plus, and for 0.25% BAC and 0.5% BAC when bonding with All-Bond 3. Zymographic analysis revealed complete inhibition of gelatinolytic activity with BAC. Benzalkonium chloride, at all concentrations, inhibited dentin proteolytic activity, which seems to have contributed to the improved bond stability after 18 months for specific combinations of BAC concentration and adhesive.

In Vitro Shear Bond Strength of Three Self- adhesive Resin Cements and a Resin-Modified Glass Ionomer Cement to Various Prosthodontic Substrates

OBJECTIVE To evaluate the shear bond strength (SBS) of three self-adhesive resin cements and a resin-modified glass ionomer cement (RMGIC) to different prosthodontic substrates. MATERIALS AND METHODS The substrates base metal, noble metal, zirconia, ceramic, and resin composite were used for bonding with different cements (n=12). Specimens were placed in a bonding jig, which was filled with one of four cements (RelyX Unicem, Multilink Automix, Maxcem Elite, and FujiCEM Automix). Both light-polymerizing (LP) and self-polymerizing (SP) setting reactions were tested. Shear bond strength was measured at 15 minutes and 24 hours in a testing device at a test speed of 1 mm/min and expressed in MPa. A Student t-test and a one-way analysis of variance (ANOVA) were used to evaluate differences between setting reactions, between testing times, and among cements irrespective of other factors. Generalized linear regression model and Tukey tests were used for multifactorial analysis. RESULTS Significantly higher mean SBS were demonstrated for LP mode relative to SP mode (p<0.001) and for 24 hours relative to 15 minutes (p<0.001). Multifactorial analysis revealed that all factors (cement, substrate, and setting reaction) and all their interactions had a significant effect on the bond strength (p<0.001). Resin showed significantly higher SBS than other substrates when bonded to RelyX Unicem and Multilink Automix in LP mode (p<0.05). Overall, FujiCEM demonstrated significantly lower SBS than the three self-adhesive resin cements (p<0.05). CONCLUSIONS Overall, higher bond strengths were demonstrated for LP relative to SP mode, 24 hours relative to 15 minutes and self-adhesive resin cements compared to the RMGICs. Bond strengths also varied depending on the substrate, indicating that selection of luting cement should be partially dictated by the substrate and the setting reaction.

Effect of a Chlorhexidine- containing Adhesive on Dentin Bond Strength Stability

PURPOSE The present study aimed to investigate a novel adhesive system containing 0.2% chlorhexidine digluconate (CHX) for its ability to improve the stability of the adhesive interface compared with the use of 2% CHX as a therapeutic primer. Furthermore, the study aimed to confirm the inhibitory properties of these CHX concentrations (0.2% and 2.0%) on dentin matrix metalloproteinase activity by gelatin zymography. METHODS Superficial dentin substrate for bonding was obtained from 120 non-carious human molars. A conventional adhesive Peak LC Bond and a CHX-containing adhesive Peak Universal Bond were used either in combination with 35% phosphoric acid (etch-and-rinse approach) or with self-etching primer (self-etch approach) for evaluation of the variables CHX treatment (2.0% therapeutic primer and 0.2% adhesive), adhesive approach (etch-and-rinse and self-etch), and storage time (24 hours and six months). A bonding jig was used to fabricate composite cylinders, which were stored for either 24 hours or six months, after which shear bond strength (SBS) was evaluated using a notched-edge testing device. A three-way analysis of variance and a Student t-test with a significance level of p<0.05 were used to analyze the data. Extracts from concentrated demineralized human dentin powder were subjected to sodium dodecyl sulfate polyacrylamide gel electrophoresis and incubated in the presence of 0.2% and 2.0% CHX. RESULTS No significant effect of CHX treatment, adhesive approach, storage time variables, or their interactions on mean SBS was demonstrated (p<0.05). No significant difference between the control and the CHX-treated groups was detected for either adhesive technique at 24 hours or six months (p<0.05). No significant variation in mean SBS was detected after six months of storage (p<0.05). Zymographic analysis revealed bands of enzymatic activity for the group demineralized with phosphoric acid and complete inhibition of gelatinolytic activity for the groups treated with 0.2% and 2.0% CHX. CONCLUSIONS CHX demonstrated inhibition of dentin proteolytic activity. However, when CHX was incorporated into a commercially available adhesive or used as a therapeutic primer, no difference in bond strength was observed at baseline or after six months of storage relative to the control group without CHX.

In Vitro Evaluation of Benzalkonium Chloride in the Preservation of Adhesive Interfaces

UNLABELLED Inhibition of endogenous dentin matrix metalloproteinases (MMPs) by benzalkonium chloride (BAC) decreases collagen solubilization and may help improve resin-dentin bond stability. OBJECTIVE This study evaluated the resin-dentin bond stability of experimental adhesive blends containing BAC and the stability of dentin matrices by assessing the mass loss and collagen solubilization from dentin beams pretreated with BAC. MATERIALS AND METHODS Twenty-five healthy molars were used for the bond strength evaluation of a two-step etch-and-rinse adhesive (Adper Single Bond Plus, SB) modified with BAC or not. The following groups were tested: 1) SB with no inhibitor (control); 2) topical 2.0% chlorhexidine + SB; 3) 1.0% BAC etchant + SB; 4) 0.5% BAC-SB; and 5) 1.0% BAC-SB. Microtensile bond strength (μTBS) and failure mode distribution under standard error of the mean were evaluated after 24 hours and six months of storage in artificial saliva (AS). A two-way analysis of variance and Tukey test with a significance level of p<0.05 was used for data analysis. In addition, 30 completely demineralized dentin beams from human molars were either dipped in deionized water (DW, control) or dipped in 0.5% and 1.0% BAC for 60 seconds, and then incubated in AS. Collagen solubilization was assessed by evaluating the dry mass loss and quantifying the amount of hydroxyproline (HYP) released from hydrolyzed specimens after four weeks of incubation. RESULTS The control group demonstrated lower μTBS than some of the experimental groups containing BAC at 24 hours and six months (p<0.05). When BAC was incorporated into the adhesive blend in concentrations of 0.5% and 1.0%, no reduction in dentin bond strength was observed after six months (p<0.05). Less mass loss and HYP release was seen for dentin matrices pretreated with BAC relative to the control pretreated with DW (p<0.05). CONCLUSION This in vitro study demonstrates that BAC contributes to the preservation of resin-dentin bonds by reducing collagen degradation.

Aging of adhesive interfaces treated with benzalkonium chloride and benzalkonium methacrylate

Inhibition of endogenous dentin matrix metalloproteinases (MMPs) within incompletely infiltrated hybrid layers can contribute to the preservation of resin-dentin bonds. This study evaluated the bond stability of interfaces treated with benzalkonium chloride (BAC) and benzalkonium methacrylate (MBAC), and the inhibitory properties of these compounds on dentin MMP activity. Single-component adhesive ALL-BOND UNIVERSAL, modified with BAC or MBAC at concentrations of 0, 0.5, 1.0, and 2.0%, was used for microtensile bond strength (μTBS) evaluation after 24 h, 6 months, and 1 yr. Beams produced from human dentin were treated with 37% phosphoric acid, dipped in 0.5% BAC, 1.0% BAC, or water (control) for 60 s, and then incubated in SensoLyte generic MMP substrate to determine MMP activity. A significant decrease in the μTBS after 6 months and 1 yr was observed for the control group only. No significant differences among groups were shown at 24 h. After 6 months and 1 yr, the control group demonstrated significantly lower μTBS than all treatment groups. When applied for 60 s, 0.5% BAC inhibited total MMP activity by 31%, and 1.0% BAC inhibited total MMP activity by 54%. Both BAC and MBAC contributed to the preservation of resin-dentin bonds, probably because of their inhibitory properties of endogenous dentin proteinases.

Inhibition of endogenous human dentin MMPs by Gluma

OBJECTIVE The objective of this study was to determine if Gluma dentin desensitizer (5.0% glutaraldehyde and 35% HEMA in water) can inhibit the endogenous MMPs of dentin matrices in 60 s and to evaluate its effect on dentin matrix stiffness and dry mass weight. METHODS Dentin beams of 2 mm×1 mm×6 mm were obtained from extracted human third molars coronal dentin. To measure the influence of Gluma treatment time on total MMP activity of dentin, beams were dipped in 37% phosphoric acid (PA) for 15 s and rinsed in water. The acid-etched beams were then dipped in Gluma for 5, 15, 30 or 60 s, rinsed in water and incubated into SensoLyte generic MMP substrate (AnaSpec, Inc.) for 60 min. Controls were dipped in water for 60 s. Additional beams of 1 mm×1 mm×6 mm were completely demineralized in 37% PA for 18 h, rinsed and used to evaluate changes on the dry weight and modulus of elasticity (E) after 60 s of Gluma treatment followed by incubation in simulated body fluid buffer for 0, 1 or 4 weeks. E was measured by 3-pt flexure. RESULTS Gluma treatment inhibited total MMP activity of acid-etched dentin by 44, 50, 84, 86% after 5, 15, 30 or 60 s of exposure, respectively. All completely demineralized dentin beams lost stiffness after 1 and 4 weeks, with no significant differences between the control and Gluma-treated dentin. Gluma treatment for 60 s yielded significantly less dry mass loss than the control after 4 weeks. SIGNIFICANCE The use of Gluma may contribute to the preservation of adhesive interfaces by its cross-linking and inhibitory properties of endogenous dentin MMPs.

Effect of phosphoric acid etching on the shear bond strength of two self-etch adhesives

Objective: To evaluate the effect of optional phosphoric acid etching on the shear bond strength (SBS) of two self-etch adhesives to enamel and dentin. Material and Methods: Ninety-six bovine mandibular incisors were ground flat to obtain enamel and dentin substrates. A two-step self-etch adhesive (FL-Bond II) and a one-step self-etch adhesive (BeautiBond) were applied with and without a preliminary acid etching to both the enamel and dentin. The specimens were equally and randomly assigned to 4 groups per substrate (n=12) as follows: FL-Bond II etched; FL-Bond II un-etched; BeautiBond etched; BeautiBond un-etched. Composite cylinders (Filtek Z100) were bonded onto the treated tooth structure. The shear bond strength was evaluated after 24 hours of storage (37ºC, 100% humidity) with a testing machine (Ultra-tester) at a speed of 1 mm/min. The data was analyzed using a two-way ANOVA and post-hoc Tukeys test with a significance level of p<0.05. A field emission scanning electron microscope was used for the failure mode analysis. Results: Both adhesives evidenced a significant decrease in the dentin SBS with the use of an optional phosphoric acid-etching step (p<0.05). Preliminary phosphoric acid etching yielded significantly higher enamel SBS for FL-Bond II (p<0.05) only, but not for BeautiBond. FL-Bond II applied to un-etched dentin demonstrated the highest mean bond strength (37.7±3.2 MPa) and BeautiBond applied to etched dentin showed the lowest mean bond strength (18.3±6.7 MPa) among all tested groups (p<0.05). Conclusion: The use of a preliminary acid-etching step with 37.5% phosphoric acid had a significant adverse effect on the dentin bond strength of the self-etch adhesives evaluated while providing improvement on the enamel bond strength only for FL-Bond II. This suggests that the potential benefit that may be derived from an additional etching step with phosphoric acid does not justify the risk of adversely affecting the bond strength to dentin.

Comparative study of surface microhardness of methacrylate-based composite resins polymerized with light-emitting diodes and halogen

Objective: The aim of this study was to evaluate the effect of polymerization with quartz-tungsten-halogen (QTH) and light-emitting diodes (LED) on the surface microhardness of eight commercially available light-polymerized, methacrylate-based composite resins, with different filler particle composition (microfill, minifill, nanohybrids, and microhybrids) immediately after polymerization, after 24 hours, and after three months of storage. Materials and Methods: Eighty disk-shaped specimens were prepared using a split Teflon mold (6 × 2 mm) and were irradiated with either the QTH (Elipar 2500; 600 mW/cm 2 ) for 20 seconds or an LED (Bluephase G2; 1,200 mW/cm 2 ) for 40 seconds. The microhardness values were recorded using a Vickers hardness tester at a 300 g load for 15 seconds, immediately after polymerization, after 24 hours, and after three months of dark aging in distilled water at 37°C. Statistical analysis was performed using a two-way analysis of variance (ANOVA) and the Tukey′s test. Results: The baseline values demonstrated a significant effect of the composite and the interaction composite-LCU on the microhardness (P < 0.05). At 24 hours, only the composite variable showed a significant effect on the hardness values (P < 0.05). After three months, the composite, LCU, and the interaction composite-LCU all demonstrated a significant effect on the microhardness (P < 0.05). Conclusions: The effectiveness of polymerization, measured in terms of surface hardness, was shown to be dependent not only on the type of light curing unit, but also on the type of composite. Moreover, the choice of composite was shown to affect the performance of the light curing unit.