Degree of conversion of resin blends in relation to ethanol content and hydrophilicity

The evolution of adhesive dentistry: From etch-and-rinse to universal bonding systems

OBJECTIVES

This review aimed at presenting the mechanisms and pitfalls of adhesion to enamel and dentin, advances in the materials science and in the development of strategies to improve hybrid layer (HL) longevity.

METHODS

Search of the literature was performed on PubMed, Scopus and Web of Science with keywords related to the structure of the dental substrate, HL degradation mechanisms and strategies to contrast them.

RESULTS

Albeit the advances in the dental materials' properties, HL degradation is still a relevant and current issue in adhesive dentistry. However, adhesive materials have become more resistant and less operator sensitive, and good adhesion is currently in the hands of every practitioner. Numerous novel strategies are being developed, able to improve the resistance of adhesive resins to degradation, their ability to infiltrate and chemically bond to dentin, to remove the unbound/residual water within the HL, reinforce the dentin collagen matrix, and inhibit endogenous metalloproteinases. Many of the strategies have turned to nature in search for powerful biomodifying compounds, and for the inspiration as to mimic naturally occurring regenerative processes.

SIGNIFICANCE

Extensive knowledge on the structure of the dental substrate and the complexity of adhesion to dentin has led to the development of improved formulations of dental adhesives and numerous valid strategies to improve the strength and longevity of the HL. Nevertheless, for many of them the road from bench to chairside still seems long. We encourage practitioners to know their materials well and use the strategies readily available to them.

Effect of irradiance and exposure time on the adhesive properties of universal adhesives after 2 years of storage

OBJECTIVE

This study aims to evaluate the effects of exposure time and irradiance on the dentin bonding properties (microtensile bond strength (μTBS) and nanoleakage (NL)) of the Clearfil Universal Bond Quick (CUQ) adhesive and Scotchbond Universal Adhesive (SBU) immediately and after 2 years of water storage.

MATERIAL AND METHODS

Hence, 128 human molars were randomly assigned to 16 groups based on adhesive strategy, irradiance/exposure times, and storage time for each universal adhesive tested. The adhesives were applied using the etch-and-rinse and self-etch strategies and were light-cured using four different irradiance/exposure times: 1400 mW/cm2 for 5 s (1400 × 5), 1400 mW/cm2 for 10 s (1400 × 10), 3200 mW/cm2 for 5 s (3200 × 5), and 3200 mW/cm2 for 10 s (3200 × 10). Then, each sample was restored and sectioned into a resin-dentin bonded stick to be tested for μTBS and NL (immediately and after 2 years of water storage). The mean μTBS and NL of all resin-dentin bonded sticks from the same hemi-tooth (factor time) were statistically analyzed using a three-way ANOVA and Tukey's test (a = 0.05).

RESULTS

Despite a significant decrease in the μTBS values for all groups after 2 years of water storage, the 3200 × 5 group showed higher μTBS values, whereas the 3200 × 10 group showed lower μTBS values for both universal adhesives tested. Although a significant increase in the NL values was observed for all groups after 2 years of water storage, the 3200 × 10 group showed higher NL values than the other groups (p < 0.001).

CONCLUSION

Results indicate that light-curing the adhesive layer with 14-16 J/cm2 led to an improvement in the stability of the resin-dentin adhesive interface. A longer exposure time (10 s) coupled with a higher irradiance (3200 mW/cm2) resulted in a greater degree of degradation of the adhesive interface.

CLINICAL SIGNIFICANCE

To guarantee better stability of the adhesive interface, clinicians could be preferred a light-cured universal adhesive layer with 14-16 J/cm2. Higher irradiances should be avoided.

The Use of Warm Air for Solvent Evaporation in Adhesive Dentistry: A Meta-Analysis of In Vitro Studies

Any excess solvent from dental adhesive systems must be eliminated prior to material photopolymerization. For this purpose, numerous approaches have been proposed, including the use of a warm air stream. This study aimed to investigate the effect of different temperatures of warm air blowing used for solvent evaporation on the bond strength of resin-based materials to dental and nondental substrates. Two different reviewers screened the literature in diverse electronic databases. In vitro studies recording the effect of warm air blowing to evaporate solvents of adhesive systems on the bond strength of resin-based materials to direct and indirect substrates were included. A total of 6626 articles were retrieved from all databases. From this, 28 articles were included in the qualitative analysis, and 27 remained for the quantitative analysis. The results of the meta-analysis for etch-and-rinse adhesives revealed that the use of warm air for solvent evaporation was statistically significantly higher (p = 0.005). For self-etch adhesives and silane-based materials, this effect was observed too (p < 0.001). The use of a warm air stream for solvent evaporation enhanced the bonding performance of alcohol-/water-based adhesive systems for dentin. This effect seems to be similar when a silane coupling agent is submitted to a heat treatment before the cementation of a glass-based ceramic.

Full analysis of the effects of modeler liquids on the properties of direct resin-based composites: a meta-analysis review of in vitro studies

OBJECTIVES

This study systematically revised the literature to answer the following question: do modeler liquids (MLs) affect the properties of direct resin-based composites (RBCs)?

MATERIALS AND METHODS

The review followed the PRISMA statement, and the search was conducted in PubMed, Scopus, Web of Science, Embase, and Lilacs databases. Studies were included if they investigated the properties of RBCs prepared using the restorative dental modeling insertion technique (RDMIT). The risk of bias was performed with the RoBDEMAT tool. Statistical analyses were conducted using Review Manager, and heterogeneity was assessed with the Cochran Q test and I² statistics.

RESULTS

From 309 studies identified, 25 met the eligibility criteria, and 23 were meta-analyzed. In total, 27 MLs and 23 RBCs were evaluated. Modeled and non-modeled RBCs showed similar results in terms of cohesive strength, flexural strength, load-to-fracture, modulus of elasticity, work of fracture, degree of conversion, solubility, weight change, microhardness, and color change. Sorption and roughness benefited from the use of MLs, whereas translucency and whitening index were more adequate in the non-modeled RBCs. Aging affected similarly the modeled and non-modeled RBCs. Most studies showed a moderate risk of bias.

CONCLUSIONS

Modeled and non-modeled RBCs performed similarly in most of the properties, and the use of non-solvated lubricants offered beneficial effects in some cases.

CLINICAL RELEVANCE

When a balance has to be made between the RDMIT and the conventional technique, our review supports the safe application of modeler liquids for the handling of composite increments during the sculpting fabrication of direct resin-based restorations.

Influence of Irradiance and Exposure Times on the Mechanical and Adhesive Properties of Universal Adhesives with Dentin

OBJECTIVES

This study evaluated the influence of irradiance/exposure time on the Knoop hardness (KHN) and polymer cross-linking density (PCLD), as well as microtensile bond strength (μTBS), nanoleakage (NL), and in situ degree of conversion (DC) of universal adhesives.

METHODS AND MATERIALS

Two universal adhesive systems, Clearfil Universal Bond Quick (CUQ) and Scotchbond Universal Adhesive (SBU), were light-cured using various irradiance/exposure times: 1400 mW/cm2 for 5 s (1400*5); 1400 mW/cm2 for 10 s (1400*10); 3200 mW/cm2 for 5 s (3200*5); and 3200 mW/cm2 for 10 s (3200*10). Adhesive disks from each group were used to measure PCLD by KHN. One hundred and twenty-eight human molars were randomly assigned to 16 groups according to the following variables: adhesive system vs adhesive strategies vs radiance/exposure times. After restoration, specimens were sectioned into resin-dentin sticks and tested for μTBS, NL, and DC. The data from PCLD (%), KHN, μTBS (MPa), NL (%), and DC (%) data were subjected to ANOVA and Tukey's test (α=0.05).

RESULTS

Significant reductions in KHN, μTBS, and DC (p=0.00001) values and an increase in NL and PCLD (p=0.00001) values were observed for 3200*10 when compared with other groups. Higher KHN, μTBS, and DC (p=0.000001) values were observed for 3200*5 in comparison with the other groups. The 1400*5 (7 J/cm2) and 1400*10 (14 J/cm2) groups showed intermediate values (p=0.000001).

CONCLUSION

Although similar results in terms of hardness, polymer cross-linking density and nanoleakage were observed when 5 seconds at 3200 mW/cm2 and 10 seconds at 1400 mW/cm2 groups were compared, the use of higher irradiance (3200 mW/cm2) for only 5 seconds showed better results in terms of bond strength and degree of conversion for both universal adhesives to dentin. The prolonged exposure time (10 seconds) at the higher irradiance (3200 mW/cm2) showed the worst results.

Influence of Instrument Lubrication on Properties of Dental Composites

Resin composites are one of the most commonly used materials in restorative dentistry. To improve their handling and facilitate restoration sculpting, clinicians began to lubricate modeling instruments with various substances like alcohol, unfilled resins, or even bonding agents. Although the technique is commonly present in daily clinical practice, it has not been precisely described in the literature and both application methods and lubricating materials vary across the available studies. This study aims to summarize the currently available knowledge about influence of instrument lubrication on properties of dental composites. Literature selection was conducted within MEDLINE, SCOPUS, and EBSCO databases. Instrument lubrication seems not to be indifferent for composite mechanical and optical properties. Moreover, various lubricants can differently affect the composite material, so the choice of lubricating agent should be deliberate and cautious. Available in vitro studies suggest possible incorporation of lubricant into the composite structure. Unfilled resins based on bisphenol A-glycidyl methacrylate (Bis-GMA) seem to be the best choice for the lubricant, as bonding agents containing hydrophilic molecules and alcohols carry a bigger risk of altering the composite properties. Further research is necessary to evaluate lubricants' influence in clinical practice conditions.

Effects of Immediate Coating on Unset Composite with Different Bonding Agents to Surface Hardness

OBJECTIVES

 This study evaluated the surface microhardness of composite, affected by surface coating with different dental adhesive systems.

MATERIALS AND METHODS

 A total of 100 composite discs were divided into five groups. Group 1 was uncoated (control group C), and groups 2 to 5 were coated with different adhesive systems (OptiBond FL: FL, OptiBond SOLO Plus: SOLO, OptiBond XTR: XTR, and OptiBond All in one: AIO, respectively). The Vickers microhardness (VHN) was measured without and with 500 thermocycles.

STATISTICAL ANALYSIS

 The data were analyzed using two-way ANOVA and Tukey's posthoc test at the 95% confidence level.

RESULTS

 At 24 hours, the VHN of C (59.96 ± 3.68) and FL (59.83 ± 4.54) were significantly higher than SOLO (51.73 ± 4.63) and AIO (51.45 ± 4.11). The VHN of XTR (54.96 ± 3.68) was not significant compared with that of C and all other groups. After thermocycling, VHN were significantly decreased in all groups. However, there were no significant differences among all groups.

CONCLUSIONS

 At 24 hours, composite coated with different adhesive systems have different effects to VHN. Thermocycling all adhesive resin systems coated on composite surface significantly decreased the VHN.

Characteristics of biofilm-induced degradation at resin-dentin interfaces using multiple combinations of adhesives and resins

OBJECTIVE

We aimed to evaluate morphological, mechanical and chemical characteristics at resin-dentin interfaces using multiple combinations of adhesives and resins after a short-term biofilm-induced degradation.

METHODS

Cervical cavities were prepared in bovine incisors, treated by Clearfil SE Bond 2 (SE) or FL-Bond II (FL), restored by Clearfil Majesty ES Flow (ES) or Beautifil Flow Plus (BFP) and grouped into SE-ES, SE-BFP, FL-ES and FL-BFP. After biofilm challenge, interfacial gaps and dentin wall lesions were examined by optical coherence tomography (OCT). Gap depth (GD), gap pattern scale (GPS) and dentin wall lesion depth (WLD) were evaluated from confocal laser scanning microscope. Microhardness of dentin lesions was measured with a Vickers microhardness tester. Chemical elements in resins and dentin wall lesions were analyzed by scanning electron microscopy and energy dispersive X-ray spectrometry (SEM/EDS). Morphological structures of interfacial gaps were observed by SEM.

RESULTS

OCT could detect adhesive-dentin-bonded and adhesive-dentin-debonded gaps. SE-containing groups showed significantly lower GPS than FL-containing groups. FL-BFP showed significantly lower WLD than FL-ES. Microhardness of dentin wall lesions was higher than that of outer lesions and they showed significant differences in FL-BFP. SE-BFP showed a lower GPS curve and higher intensities of Ca and P in the upper half of dentin wall lesions than other groups. From SEM, microgaps between filler and matrix, break and loss of matrix, separation of adhesive matrix with hybrid layer occurred at interfacial gaps.

SIGNIFICANCE

The morphological, mechanical and chemical characteristics of resin-dentin interfacial degradation depend on the component and chemistry of restorative materials.

Interfacial Adhesion of a Semi-Interpenetrating Polymer Network-Based Fiber-Reinforced Composite with a High and Low-Gradient Poly(methyl methacrylate) Resin Surface

The research aimed to determine the tensile bond strength (TBS) between polymerized intact and ground fiber-reinforced composite (FRC) surfaces. FRC prepregs (a reinforcing fiber pre-impregnated with a semi-interpenetrating polymer network (semi-IPN) resin system; everStick C&B) were divided into two groups: intact FRCs (with a highly PMMA-enriched surface) and ground FRCs (with a low PMMA gradient). Each FRC group was treated with: StickRESIN and G-Multi PRIMER. These groups were further divided into four subgroups based on the application time of the treatment agents: 0.5, 1, 2, and 5 min. Next, a resin luting cement was applied to the FRC substrates on the top of the photo-polymerized treating agent. Thereafter, weight loss, surface microhardness, and TBS were evaluated. Three-factor analysis of variance (p ≤ 0.05) revealed significant differences in the TBS among the FRC groups. The highest TBS was recorded for the intact FRC surface treated with G-Multi PRIMER for 2 min (13.0 ± 1.2 MPa). The monomers and solvents of G-Multi PRIMER showed a time-dependent relationship between treatment time and TBS. They could diffuse into the FRC surface that has a higher PMMA gradient, further resulting in a high TBS between the FRC and resin luting cement.

Detection and analysis of early degradation at resin-dentin interface by optical coherence tomography (OCT) and confocal laser scanning microscope (CLSM)

OBJECTIVE

To evaluate early degradation at resin-dentin interface using non-invasive swept-source optical coherence tomography (SS-OCT) and confocal laser scanning microscope (CLSM).

METHODS

Self-etch adhesives and resin-composites containing bisphenol-glycidyl-dimethacrylate (Bis-GMA), which is one of the most widely used monomers in restorative materials, were investigated in this study. Forty cervical cavities were prepared in bovine incisors and applied by the adhesive with/without Bis-GMA (AdhesiveBG/Adhesive), filled by the resin with/without Bis-GMA (ResinBG/Resin) and then challenged by cariogenic biofilm (37 °C, 24 h). Gap Formation and dentin demineralization around resin-composites were observed by SS-OCT and CLSM.

RESULTS

Three types of resin-dentin interfacial degradation could be detected from SS-OCT. Type I-dentin demineralization around resin without gap, showing feather-shaped dark zones without bright scattered lines at resin-dentin interfaces. Type II-dentin demineralization around resin with adhesive-dentin bonded gaps, showing feather-shaped dark zones with bright scattered lines at resin-dentin interfaces. Type III-dentin demineralization around resin with adhesive-dentin debonded gaps, showing edge-shaped dark zones with bright scattered lines at resin-dentin interface. From CLSM, the groups were compared in gap scale (GS), gap depth (GD), gap width (GW) and dentin wall lesion depth (WLD). Bis-GMA-containing adhesive groups showed significantly lower GS than Bis-GMA-free adhesive groups. Bis-GMA-containing resin groups showed significantly lower WLD than Bis-GMA-free resin groups. However, they did not show significant differences in GD and GW.

CONCLUSION

Three types of early degradation at resin-dentin interface can be noninvasively detected by SS-OCT. Bis-GMA-containing and Bis-GMA-free restorative materials show differences in gap scale and dentin wall lesion depth.

CLINICAL SIGNIFICANCE

SS-OCT can nondestructively detect early resin-dentin interfacial degradation. Gap scale can be used as a parameter to evaluate the risk factor of gaps.

Degree of Conversion Contributes to Dentin Bonding Durability of Contemporary Universal Adhesives

Clinical Relevance

The degree of conversion of contemporary universal adhesives positively correlates with the bond strength to dentin. The correlation is more marked after thermocycling, suggesting that a high degree of conversion is required for long-term dentin bonding durability.

SUMMARY

Purpose: The objectives of this study were to evaluate the micro-tensile bond strength (μTBS) of five contemporary universal adhesives to dentin after 24 hours and thermocycling (TC), to measure their degrees of conversion (DC) and to test the correlation between μTBS and DC.

Methods and Materials: Four commercially available universal adhesives, Prime&Bond universal (PBU), Ecosite Bond (EB), G-Premio Bond (GPB), and Clearfil Universal Bond Quick (UBQ), and one experimental adhesive, UBQ without an amide monomer (UBQ-A), were used in this study. For the μTBS test, midcoronal dentin of 50 human molars was exposed, ground using 600-grit SiC paper, and the adhesives were applied according to the manufacturers’ instructions. After resin-composite buildup and 24-hour water storage, one-half of the specimens were subjected to 15,000 thermal cycles. The specimens were sectioned into beams and stressed in tension at a crosshead speed of 1 mm/min until failure. The DC of adhesives applied to dentin was evaluated using attenuated total reflectance Fourier-transform infrared spectroscopy immediately after light-curing. All data were statistically analyzed at a significance level of 0.05.

Results: The highest μTBSs were obtained with UBQ, UBQ-A, and PBU, which were not significantly different from each other both after 24 hours and TC. The μTBS of GPB was lower compared with the aforementioned adhesives, but significantly only after TC, and the lowest μTBSs were obtained with EB. TC did not affect the μTBSs of UBQ, UBQ-A, and PBU significantly, but a significant decrease was observed with GPB and EB. The highest DC was obtained with PBU and UBQ, followed by 2-hydroxyethyl methacrylate–rich adhesives UBQ-A and EB, which exhibited significantly lower DCs. The DC of GPB could not be determined because the reference peak at 1608 cm−1 was not detected in its spectra. A significant positive correlation was shown between μTBS and DC after 24 hours (r=0.716) and TC (r=0.856).

Conclusion: μTBS and DC were positively correlated, more markedly after TC, which suggests that DC may be an important factor for bond durability.

The influence of nanofillers on the properties of ethanol-solvated and non-solvated dental adhesives

Objectives

The aim of this study was to evaluate the influence of different concentrations of nanofillers on the chemical and physical properties of ethanol-solvated and non-solvated dental adhesives.

Materials and Methods

Eight experimental adhesives were prepared with different nanofiller concentrations (0, 1, 2, and 4 wt%) and 2 solvent concentrations (0% and 10% ethanol). Several properties of the experimental adhesives were evaluated, such as water sorption and solubility (n = 5, 20 seconds light activation), real-time degree of conversion (DC; n = 3, 20 and 40 seconds light activation), and stability of cohesive strength at 6 months (CS; n = 20, 20 seconds light activation) using the microtensile test. A light-emitting diode (Bluephase 20i, Ivoclar Vivadent) with an average light emittance of 1,200 mW/cm² was used.

Results

The presence of solvent reduced the DC after 20 seconds of curing, but increased the final DC, water sorption, and solubility of the adhesives. Storage in water reduced the strength of the adhesives. The addition of 1 wt% and 2 wt% nanofillers increased the polymerization rate of the adhesives.

Conclusions

The presence of nanofillers and ethanol improved the final DC, although the DC of the solvated adhesives at 20 seconds was lower than that of the non-solvated adhesives. The presence of ethanol reduced the strength of the adhesives and increased their water sorption and solubility. However, nanofillers did not affect the water sorption and strength of the tested adhesives.

Solvent and HEMA Increase Adhesive Toxicity and Cytokine Release from Dental Pulp Cells

The aim of the present study was to evaluate the effect of the hydroxyethyl-methacrylate (HEMA) concentration and solvent content of dental adhesives on cell viability and cytokine (IL-1b, IL-6, IL-10, TNF-α) release by human dental pulp cells (HDPCs). HDPCs were obtained from fresh extracted human third molars. Experimental adhesives were prepared containing different concentrations of HEMA (0%, 10%, and 20%) with and without solvent (ethanol 10%). Cylindrical specimens were immersed on culture medium during 24 h to obtain the extracts. The cells were incubated with extracts (culture medium + components leached from the adhesives) of different adhesives, and cell viability and cytokine release were evaluated after 6 and 24 h of exposure. Adhesives containing HEMA promoted high cell viability reduction after 6 h of exposure; but after 24 h, the results were similar to the ones found among control group cells. These effects on cell viability were prominently increased with the addition of solvent. Although IL-1b release was not affected by exposure to eluates, other cytokines (IL-10, IL-6, TNF-α) were modulated by the different experiment conditions, directly influenced by the HEMA concentration and presence of solvent. Higher HEMA concentrations, combined with the presence of solvent, can promote significant reduction on HDPC viability, increasing the release of anti- and pro-inflammatory mediators.

Impact of Solvent Evaporation and Curing Protocol on Degree of Conversion of Etch-and-Rinse and Multimode Adhesives Systems

Objectives

This study evaluated the effect of air-drying time and light-curing time on the degree of conversion (DC) of three etch-and-rinse adhesive systems: ONE-STEP (OS) and ONE-STEP plus (OSP), Ambar (AMB), and two multimode adhesive systems: All-Bond Universal (ABU) and ScotchBond Universal (SBU) by Fourier transform infrared (FTIR) analysis.

Materials and Methods

The DC of each adhesive system was analyzed with six experimental different protocols: (1) immediate light curing for 10 s without solvent volatilization; (2) 10 s solvent volatilization with air stream plus 10 s light curing; (3) 60 s solvent volatilization with air stream plus 10 s light curing; (4) immediate light curing for 20 s without solvent volatilization; (5) 10 s solvent volatilization with air stream plus 20 s light curing; and (6) 60 s solvent volatilization with air stream plus 20 s light curing. FTIR spectra were obtained, and the DC was calculated by comparing the ratio of aliphatic/aromatic double carbon bonds before and after light activation (Bluephase 20i). The DC means were analyzed by three-way analysis of variance (ANOVA) and post hoc Tukey tests (α = 0.05).

Results

Three-way ANOVA showed statistically significant adhesive, air-drying, and light-cured time (p < 0.001). In general, there was a trend of increased DC when the adhesives were dried and cured for longer times, but that was not observed for all the adhesives tested. The acetone-based adhesive systems require an air-drying prior to light activation. The light-curing time of 20 s increases the DC of all materials tested.

Conclusion

The results suggested that the DC of the adhesive systems tested was material dependent. In general, the protocol with solvent evaporation for 10 seconds with air syringe plus 20 seconds of light curing finds the high values of DC.

Modulating pH through lysine integrated dental adhesives

OBJECTIVES

The objective of this study was to explore the effect of lysine integration to dental adhesives with respect to the polymerization kinetics, neutralization capacities in the acidic microenvironment, dynamic mechanical properties, and thermal properties.

MATERIALS AND METHOD

Lysine was incorporated into liquid resin formulations at 2.5 and 5.0wt % with additional water/ethanol co-solvents. The co-monomer system contained 2-hydroxyethyl-methacrylate (HEMA) and Bisphenol A glycerolate dimethacrylate (BisGMA) with a mass ratio of 45/55. The kinetics of photopolymerization, neutralization capacities, lysine-leaching, dynamic mechanical properties and thermal properties of the control and experimental adhesives were analyzed.

RESULTS

The degree of conversion of the experimental adhesive was increased substantially at 2.5wt% lysine as compared to the control. The experimental polymers provided acute neutralization of the acidic microenvironment. Approximately half of the lysine was released from the polymer network within one month. Under dry conditions and physiologic temperatures, the incorporation of lysine did not compromise the storage modulus. Comparison of the thermal properties suggests that the more compact structure of the control adhesive inhibits movement of the polymer chains resulting in increased T_g.

SIGNIFICANCE

Incorporating lysine in the adhesive formulations led to promising results regarding modulating pH, which may serve as one aspect of a multi-spectrum approach for enhancing the durability of composite restorations. The results provide insight and lay a foundation for incorporating amino acids or peptides into adhesive formulations for pH modulation or desired bioactivity at the interfacial margin between the composite and tooth.

Degree of Conversion and Oxygen-Inhibited Layer Effect of Three Dental Adhesives

This study investigated the effect of the oxygen-inhibited layer on the degree of conversion (DC) of three dental adhesives, comparing two different protocols. Quartz–tungsten–halogen (QTH) light curing and light-emitting diode (LED) were used to cure three adhesives: OptiBond All in One (OAIO), Adper Easy Bond (AEB) and ExciteF (EXF). The DC was calculated utilizing Fourier Transform infrared spectroscopy (FTIR) (n = 12). The two protocols used were as follows: (i) prevent the oxygen-inhibited layer using a Mylar plastic strip pushed onto each bonding adhesive; and (ii) polymerize samples without a plastic strip. The data was analyzed statistically by a three-way ANOVA, and Tukey Test (a = 0.05). The presence of an oxygen-inhibited layer reduced the DC of the adhesives by 64% for EXF, 46% for AEB and 32% for OAIO. This study suggests that there are differences among the oxygen-inhibited layers present for the adhesives tested.

Effect of Instrument Lubricants on the Surface Degree of Conversion and Crosslinking Density of Nanocomposites

PURPOSE

The surface degree of conversion and crosslink density of composites should not be affected by the use of instrument lubricants in order to provide long-lasting tooth restorations. This study aimed to analyze the effect of instrument lubricants on the degree of conversion and crosslink density of nanocomposites.

MATERIALS AND METHODS

Samples (N = 10) were fabricated according to the composites (Filtek Z350 XT, 3M ESPE, St. Paul, MN, USA; and IPS Empress Direct, Ivoclar Vivadent AG, Schaan, Liechtenstein and lubricants used (Adper Single Bond 2 and Scotchbond Multi-Purpose bonding agent adhesive systems, 3M ESPE; 70% ethanol, absolute ethanol, and no lubricant). Single composite increments were inserted into a Teflon mold using the same dental instrument. The composite surface was then modeled using a brush wiped with each adhesive system and a spatula wiped with each ethanol. The control group was fabricated with no additional modeling. The surface degree of conversion and crosslink density were measured by Fourier transform infrared spectroscopy and the hardness decrease test, respectively. Data were analyzed using two-way analysis of variance and the Tukey's test (p < 0.05).

RESULTS

Filtek Z350 XT showed statistically similar degree of conversion regardless of the lubricant used, whereas the use of adhesive systems and 70% ethanol decreased the degree of conversion for IPS Empress Direct. Only Scotchbond Multi-Purpose bonding agent decreased crosslink density for Filtek Z350 XT, whereas both adhesive systems decreased crosslink density for IPS Empress Direct.

CONCLUSION

Filtek Z350 XT appeared to be less sensitive to the effects of lubricants, and absolute ethanol did not affect the degree of conversion and crosslink density of the nanocomposites tested.

CLINICAL SIGNIFICANCE

Although the use of lubricants may be recommended to minimize the stickiness of dental instruments and composite resin, dentists should choose materials that do not have a negative effect on the surface properties of composites. Only the use of absolute ethanol safely maintains the surface integrity of nanocomposites in comparison with adhesive system and 70% ethanol.

Influence of Organic Acids from the Oral Biofilm on the Bond Strength of Self-Etch Adhesives to Dentin

Abstract: The aim of this study was to evaluate the microtensile bond strength of self-etch adhesive systems to dentin after storage in acids from oral biofilm. Three adhesive systems were used in the study: a two-step self-etch adhesive for use with a silorane-based resin composite (Filtek P90 adhesive system - P90), a two-step self-etch adhesive (Clearfil SE Bond - CSE) and a one-step self-etch adhesive (Adper Easy One - AEO). The bond strength of these products was evaluated by bonding resin composite (Filtek Z350 for CSE and AEO; and Filtek P90 for P90) to 90 bovine dentin tooth fragments, according to the manufacturer's instructions. After 24 h of water storage at 37 °C, the specimens were sectioned into beams (1 mm2) divided and stored in distilled water, lactic acid and propionic acid, for 7 and 30 days. After storage, the specimens were tested for microtensile bond strength. Data were analyzed by three-way ANOVA and Tukey´s test (α=0.05). CSE presented the highest microtensile bond strength after storage in distilled water for 7 and 30 days. The microtensile bond strength of all adhesive systems was lower after storage in lactic acid and propionic acid than after water storage. Significant difference was not found between storage times.

Hydrophilicity of dentin bonding systems influences in vitro Streptococcus mutans biofilm formation

OBJECTIVE

To evaluate in vitro Streptococcus mutans (S. mutans) biofilm formation on the surface of five light-curing experimental dental bonding systems (DBS) with increasing hydrophilicity. The null hypothesis tested was that resin chemical composition and hydrophilicity does not affect S. mutans biofilm formation.

METHODS

Five light-curing versions of experimental resin blends with increasing hydrophilicity were investigated (R1, R2, R3, R4 and R5). R1 and R2 contained ethoxylated BisGMA/TEGDMA or BisGMA/TEGDMA, respectively, and were very hydrophobic, were representative of pit-and-fissure bonding agents. R3 was representative of a typical two-step etch-and-rinse adhesive, while R4 and R5 were very hydrophilic resins analogous to self-etching adhesives. Twenty-eight disks were prepared for each resin blend. After a 24h-incubation at 37°C, a multilayer monospecific biofilm of S. mutans was obtained on the surface of each disk. The adherent biomass was determined using the MTT assay and evaluated morphologically with confocal laser scanning microscopy (CLSM) and scanning electron microscopy (SEM).

RESULTS

R2 and R3 surfaces showed the highest biofilm formation while R1 and R4 showed a similar intermediate biofilm formation. R5 was more hydrophilic and acidic and was significantly less colonized than all the other resins. A significant quadratic relationship between biofilm formation and hydrophilicity of the resin blends was found. CLSM and SEM evaluation confirmed MTT assay results.

CONCLUSIONS

The null hypothesis was rejected since S. mutans biofilm formation was influenced by hydrophilicity, surface acidity and chemical composition of the experimental resins. Further studies using a bioreactor are needed to confirm the results and clarify the role of the single factors.

Effects of quaternary ammonium chain length on antibacterial bonding agents

The objectives of this study were to synthesize new quaternary ammonium methacrylates (QAMs) with systematically varied alkyl chain lengths (CL) and to investigate, for the first time, the CL effects on antibacterial efficacy, cytotoxicity, and dentin bond strength of bonding agents. QAMs were synthesized with CL of 3 to 18 and incorporated into Scotchbond Multi-Purpose (SBMP) bonding agent. The cured resins were inoculated with Streptococcus mutans. Bacterial early attachment was investigated at 4 hrs. Biofilm colony-forming units (CFU) were measured after 2 days. With CL increasing from 3 to 16, the minimum inhibitory concentration and minimum bactericidal concentration were decreased by 5 orders of magnitude. Incorporating QAMs into SBMP reduced bacterial early attachment, with the least colonization at CL = 16. Biofilm CFU for CL = 16 was 4 log lower than SBMP control (p < .05). All groups had similar dentin bond strengths (p > .1). The new antibacterial materials had fibroblast/odontoblast viability similar to that of commercial controls. In conclusion, increasing the chain length of new QAMs in bonding agents greatly increased the antibacterial efficacy. A reduction in Streptococcus mutans biofilm CFU by 4 log could be achieved, without compromising bond strength and cytotoxicity. New QAM-containing bonding agents are promising for a wide range of restorations to inhibit biofilms.

Transdentinal cytotoxicity of experimental adhesive systems of different hydrophilicity applied to ethanol-saturated dentin

The aim of this study was to evaluate the transdentinal cytotoxicity of experimental adhesive systems (EASs) with different hydrophilicity and dentin saturation solutions on odontoblast-like cells. One hundred 0.4-mm-thick dentin discs were mounted in in vitro pulp chambers and assigned to 10 groups. MDPC-23 cells were seeded onto the pulpal side of the discs, incubated for 48h. The EASs with increasing hydrophilicity (R1, R2, R3 and R4) were applied to the occlusal side after etching and saturation of etched dentin with water or ethanol. R0 (no adhesive) served as controls. R1 is a non-solvated hydrophobic blend, R2 is similar to a simplified etch-and-rinse adhesive system and R3 and R4 are similar to self-etching adhesives. After 24h, cell metabolism was evaluated by MTT assay (n=8 discs) and cell morphology was examined by SEM (n=2 discs). Type of cell death was identified by flow cytometry and the degree of monomer conversion (%DC) was determined by infrared spectroscopy (FTIR) after 10s or 20s of photoactivation. Data were analyzed by the Kruskal-Wallis and Mann-Whitney tests (α=0.05). Dentin saturation with ethanol resulted in higher necrotic cell death ratios for R2, R3 and R4 compared with water saturation, although R2 and R3 induced higher SDH production. Photoactivation for 20s significantly improved the %DC of all EASs compared with 10s. A significant positive correlation was observed between the degree of hydrophilicity and %DC. In conclusion, except for R1, dentin saturation with ethanol increased the cytotoxicity of EASs, as expressed by the induction of necrotic cell death.

Cytotoxicity of adhesive systems of different hydrophilicities on cultured odontoblast-like cells

This study evaluated the cytotoxicity of experimental adhesive systems (EASs) on odontoblast-like cells. Paper discs (n = 132) were impregnated with 10 µL of each EAS-R1, R2, R3, R4, and R5 (in an ascending order of hydrophilicity), followed by photoactivation. R1 and R2 are nonsolvated hydrophobic blends, R3 represents a simplified etch-and-rinse adhesive system, and R4 and R5 represent simplified self-etch adhesive systems. Discs were immersed in Dulbecco's modified Eagle's medium for 24 h to obtain eluates applied on MDPC-23 cell cultures. No material was applied on discs used as control (R0). Cell viability [3-(4,5-dimethythiazol-2-yl)-2,5-diphenyl tetrazolium bromide assay], total protein (TP) production, alkaline phosphatase (ALP) activity, type of cell death, and degree of monomer conversion Fourier transform infrared (%DC-FTIR) were evaluated. Data were analyzed by Kruskal-Wallis and Mann-Whitney tests (α = 0.05). Considering R0 (control) as having 100% of cell viability, R1, R2, R3, R4, and R5 reduced the metabolic activity of cells by 36.4, 3.1, 0.2, 21.5, and 65.7%, respectively, but only R1 and R5 differed from R0. Comparing with R0, lower TP production was observed for R1, R4, and R5, while ALP activity decreased for R1 and R5. Necrotic cell death was predominant for all EASs, but only R1, R4, and R5 differed from R0. Only R5 presented a different apoptotic cell death ratio from R0. R1 presented the lowest %DC (ca. 37%), whereas R4 and R5 presented the highest (ca. 56%). In conclusion, R2 and R3 were not toxic to the MDPC-23 cells, suggesting that the degree of hydrophilicity or %DC of the EASs alone were not responsible for their cytopathic effects.

Solvent content and dentin bond strengths using water-wet, ethanol-wet and deproteinization bonding techniques

OBJECTIVES

To evaluate the impact of solvent content in two-step, etch-and-rinse adhesives on the dentin bond strengths obtained via water-wet, ethanol-wet or deproteinization techniques.

MATERIALS AND METHODS

A model photocurable Bis-GMA/HEMA blend was diluted in ethanol (7.5, 15 or 30 mass%) or acetone (15, 30 or 60 mass%) (low, medium or high solvent content, respectively). Viscosity of the solutions was measured with an oscillatory viscometer and data analyzed using ANOVA on Ranks (5%). Dentin bond strengths were evaluated using microshear bond test. After acid-etching and rinsing, the dentin was kept wet (water-wet), treated with ascending ethanol concentrations (ethanol-wet) or with 10% NaOCl solution (deproteinization). Composite cylinders built-up on the surfaces for the microshear test. Data from each bonding technique were submitted to two-way ANOVA and Fisher's LSD method (5%). Failure modes were classified under magnification and data analyzed using chi-square tests (5%).

RESULTS

Viscosity of ethanol-based agents was remarkably higher than acetone solutions. For the water-wet technique, lower bond strength was observed for the low compared with medium and high ethanol contents. For the ethanol-wet technique, the bond strength for both solvents types was low < medium = high solvent content. For the deproteinization technique, no significant differences were observed among groups. Significant differences in failure modes were observed between the bonding techniques. The ethanol-wet technique had more adhesive failures, whereas the other techniques showed a predominance of mixed failures.

CONCLUSIONS

The solvent content may interfere with the dentin bond strengths for the conventional and ethanol bonding techniques.

Effects of solvent drying time and water storage on ultimate tensile strength of adhesives

AIM

Simplified adhesives are a blend of monomers with solvents that are expected to evaporate before light curing. The aim of the present study was to evaluate the effects of drying time and water storage on the ultimate tensile strength (UTS) of three adhesives: Adper Single Bond 2 (ASB), One-Step Plus (OSP) and Clearfil S(3) Bond (CSB).

METHODS

Dumbbell-shaped samples from each adhesive were prepared in three groups: (a) air drying prior to light curing; (b) no drying equal to active air drying; and (c) 3-h drying. Each group was further divided into two subgroups of no storage or 7 days' water storage, prior to the UTS measurement (n = 10).

RESULTS

Material, drying-time, and storage had a significant effect on UTS, and the interactions of the factors were also significant (P < 0.05). OSP showed a higher evaporation rate under passive air drying, and OSP and CSB showed higher UTS values compared to ASB (P < 0.05). Air drying improved UTS in OSP and CSB, but not in ASB. Likewise, water storage only affected the UTS of OSP and CSB.

CONCLUSIONS

The effects of air drying and water storage period on UTS are material dependent. Whenever solvent evaporation improved the UTS of adhesive, water storage decreased it. The all-in-one self-etching adhesive can maximize its best properties when the solvent is dried for an extended period.

On the fatigue behavior of resin-dentin bonds after degradation by biofilm

The durability of resin-dentin bonds is a growing concern in the placement of composite restorations. Most reported evaluations concerning the mechanical behavior of the bonded interface are conducted using static loading to failure only. They also do not account for the acid production of biofilms, which is one of the most common contributors to interfacial failures in vivo. In this investigation resin-dentin bonded interface specimens were exposed to S. mutans for 14 days and then subjected to quasi-static or cyclic four-point flexure to failure. Control specimens (without biofilm) were evaluated after aging for one and fourteen days. While no significant difference in flexure strength resulted from the duration of water aging (66.2 MPa vs. 56.9 MPa), biofilm exposure caused a significant reduction in strength (29.3 MPa; p ≤ 0.000). After water aging for one and fourteen days the apparent endurance limits were 13.0 MPa and 13.1 MPa, respectively. Biofilm treatment caused a significant (p ≤ 0.001) reduction in fatigue resistance of the interface, and the endurance limit was reduced to 9.9 MPa. Fatigue failure of the control specimens initiated within the resin composite adjacent to the interface, whereas failure of the biofilm treated specimens initiated within the hybrid layer and appeared attributed to the localized demineralization of dentin. Biofilm degradation is an important consideration in assessing the durability of resin-dentin bonds.

Effects of functional monomers and photo-initiators on the degree of conversion of a dental adhesive

Besides functional and cross-linking monomers, dental adhesives contain a photo-initiator system for polymerization, thereby providing physico-mechanical strength to the adhesive-tooth interface. Few studies have investigated the effect of the functional monomer and polymerization-initiation system on the polymerization efficiency of the adhesive. Here, we tested the effect of two different functional monomers (MAC-10 vs. SR) and two photo-initiator systems, camphorquinone-amine (CQ) vs. borate (BO), on the degree of conversion (DC) of different adhesive formulations. The DC of the CQ-cured adhesive formulations was significantly affected by the MAC-10 monomer. This should be ascribed to the known inactivation of the amine co-initiator through acid-base reaction. However, the SR monomer did not decrease the DC, which could be attributed to a "gel effect" or the so-called "Trommsdorff-Norrish" phenomenon of enhanced DC with more viscous resins, and to the more favorable availability of CC double bonds. In contrast, the DC of the BO-cured adhesive formulations was not affected by any acidic monomer. It is concluded that the degree of conversion of an adhesive can be affected by the functional monomer, but this depends on the kind of photo-initiator system used. As bond durability depends, among other factors, on the strength and thus degree of conversion of the adhesive, potential interaction between adhesive ingredients and the photo-initiator system definitely needs to be studied further.

Mechanical properties and degree of conversion of etch-and-rinse and self-etch adhesive systems cured by a quartz tungsten halogen lamp and a light-emitting diode

The aim of the present study was to evaluate the degree of conversion (DC), elastic modulus (E), and flexural strength (FS) of five adhesive systems (only the bonding component of both Scotchbond MP-SBMP and Clearfil Protect Bond-CP; Single Bond 2-SB2; One-up Bond F Plus-OUP; and P90 System Adhesive: primer-P90P and bond-P90B) cured with a quartz tungsten halogen (QTH) lamp and a light-emitting diode (LED). Two groups per adhesive were formed (n=5), according to the light source (quartz tungsten halogen-QTH: Demetron LC; and light-emitting diode-LED: UltraLume 5). Bar-shaped specimens were evaluated using three-point bending. The DC was obtained by Fourier transform infrared spectroscopy (FTIR). SB2 and P90P exhibited better DC values for QTH curing. However, SB2 and P90P presented the worst results overall. The light source was statistically significant for all adhesives, except for P90B and OUP. Non-solvated adhesives presented the best E and FS values. It could be concluded that the DC and E values can be influenced by the light source; however, this interference is material dependent.

Effects of pH, ionic strength, and applied voltage on migration of dental monomers in an organic matrix

OBJECTIVES

The application of an electric field has been shown to positively influence the bonding of dentin bonding systems (DBS) by improving adhesive impregnation into dentin. However, the mechanism responsible for this phenomenon has not been completely elucidated. The aim of this study was to clarify the effects of pH, matrix ionic strength, and applied voltage on the migration of commonly used DBS monomers in a model matrix (agarose gel).

METHODS

Some common monomers examined were bis-GMA (2,2-bis[4-(2-hydroxy-3-methacryloyloxy propoxy) phenyl] propane); HEMA (2-hydroxyethyl methacrylate); 2-MP (bis[2-(methacryloyloxy) ethyl] phosphate); TCDM [di(hydroxyethyl methacrylate) ester of 5-(2,5,-dioxo tetrahydrofurfuryl)-3-methyl-3-cyclohexenyl-1,2-dicarboxylic acid]; and TEGDMA (triethylene glycol dimethacrylate). Agarose gels poured into a horizontal 10-well electrophoretic cell were used to mimic the collagen fibrils of the dentin organic matrix. The role of pH, matrix ionic strength, and voltage on monomer migration was assayed by modifying the experimental conditions.

RESULTS

Results of experiments performed at pH 3.1, 6.3, 8.5, and 12.3; at low, medium, and high ionic strength; and at 50 and 100 V clearly showed that DBA monomer migration toward both the anode and the cathode can be affected by each of these parameters.

SIGNIFICANCE

Migration of acrylic monomers toward the anode or cathode can be achieved as desired by selective choice of pH, ionic strength, and applied voltage. Additional studies are needed to evaluate the synergistic effects of DBS monomer blends on migration in an electric field.

Degree of Conversion of Etch-and-Rinse and Self-etch Adhesives Light-cured Using QTH or LED

The effect of QTH and LED curing lights on the degree of conversion of bonding agents is material dependent.

The effect of ageing on the elastic modulus and degree of conversion of two multistep adhesive systems

During the curing reaction, the monomers of dentine bonding systems should cross-link sufficiently to strengthen an adhesive so that it is clinically reliable. This study evaluated how different storage conditions (air vs. water storage) affect the elastic modulus (E-modulus) and degree of conversion (DC) of a three-step etch-and-rinse adhesive and a two-step self-etch adhesive. The biaxial flexural test and Raman microscopy were performed on resin disks made from the bonding agents Adper Scotchbond Multi-Purpose (SBMP; 3M ESPE) and Clearfil Protect Bond (CPB; Kuraray). The measurements were repeated after storage in either air or water for 15 and 30 min and for 1, 24, and 72 h. At time 0, the E-modulus was not affected by the adhesive system, whilst the degree of cure of CPB was higher than that of SBMP. Air storage increased the E-modulus at each ageing interval. Storage in water increased the E-modulus until it reached a maximum at 24 h, after which it decreased significantly at 72 h. No linear correlation between the percentage DC and E-modulus of the two adhesives was found when stored in water. The results of this study indicate that the mechanical properties and polymerization kinetics of SBMP and CPB are affected by storage time and medium.

Effect of deproteinization and tubular occlusion on microtensile bond strength and marginal microleakage of resin composite restorations

Dentin adhesion procedure presents limitations, especially regarding to lifetime stability of formed hybrid layer. Alternative procedures have been studied in order to improve adhesion to dentin.

OBJECTIVE

The aim of this study was to evaluate in vitro the influence of deproteinization or dentin tubular occlusion, as well as the combination of both techniques, on microtensile bond strength (microTBS) and marginal microleakage of composite resin restorations.

MATERIAL AND METHODS

Extracted erupted human third molars were randomly divided into 4 groups. Dentin surfaces were treated with one of the following procedures: (A) 35% phosphoric acid gel (PA) + adhesive system (AS); (B) PA + 10% NaOCl + AS; (C) PA + oxalate + AS and (D) PA + oxalate + 10% NaOCl + AS. Bond strength data were analyzed statistically by two-way ANOVA and Tukey's test. The microleakage scores were analyzed using Kruskal-Wallis and Mann-Whitney non-parametric tests. Significance level was set at 0.05 for all analyses.

RESULTS

microTBS data presented statistically lower values for groups D and B, ranking data as A>C>B>D. The use of oxalic acid resulted in microleakage reduction along the tooth/restoration interface, being significant when used alone. On the other hand, the use of 10% NaOCl alone or in combination with oxalic acid, resulted in increased microleakage.

CONCLUSIONS

Dentin deproteinization with 10% NaOCl or in combination with oxalate significantly compromised both the adhesive bond strength and the microleakage at interface. Tubular occlusion prior to adhesive system application seems to be a useful technique to reduce marginal microleakage.

One-year stability of resin-dentin bonds created with a hydrophobic ethanol-wet bonding technique

Dentin bonding performed with hydrophobic resins using ethanol-wet bonding should be less susceptible to degradation but this hypothesis has never been validated.

OBJECTIVES

This in vitro study evaluated stability of resin-dentin bonds created with an experimental three-step BisGMA/TEGDMA hydrophobic adhesive or a three-step hydrophilic adhesive after one year of accelerated aging in artificial saliva.

METHODS

Flat surfaces in mid-coronal dentin were obtained from 45 sound human molars and randomly divided into three groups (n=15): an experimental three-step BisGMA/TEGDMA hydrophobic adhesive applied to ethanol (ethanol-wet bonding-GI) or water-saturated dentin (water-wet bonding-GII) and Adper Scotchbond Multi-Purpose [MP-GIII] applied, according to manufacturer instructions, to water-saturated dentin. Resin composite crowns were incrementally formed and light-cured to approximately 5mm in height. Bonded specimens were stored in artificial saliva at 37 degrees C for 24h and sectioned into sticks. They were subjected to microtensile bond test and TEM analysis immediately and after one year. Data were analyzed with two-way ANOVA and Tukey tests.

RESULTS

MP exhibited significant reduction in microtensile bond strength after aging (24h: 40.6+/-2.5(a); one year: 27.5+/-3.3(b); in MPa). Hybrid layer degradation was evident in all specimens examined by TEM. The hydrophobic adhesive with ethanol-wet bonding preserved bond strength (24h: 43.7+/-7.4(a); one year: 39.8+/-2.7(a)) and hybrid layer integrity, with the latter demonstrating intact collagen fibrils and wide interfibrillar spaces.

SIGNIFICANCE

Coaxing hydrophobic resins into acid-etched dentin using ethanol-wet bonding preserves resin-dentin bond integrity without the adjunctive use of MMPs inhibitors and warrants further biocompatibility and patient safety's studies and clinical testing.

Influence of different initiators on the degree of conversion of experimental adhesive blends in relation to their hydrophilicity and solvent content

OBJECTIVES

The aim of this study was to compare the curing reaction of five experimental adhesive blends containing different photo-initiating systems. The hypothesis tested was that degree of conversion (DC) of resin blends is affected by resin type, solvent content and photo-initiating system.

METHODS

The experimental methacrylate resin blends were ranked from hydrophobic (R2) to hydrophilic (R3 and R4) and tested as neat, or solvated with 10% or 20% ethanol, or 10% ethanol and 10% water. Three different photo-initiators were used: IS-1=0.25% CQ (camphorquinone)+1% EDMAB (ethyl 4-dimethylaminobenzoate); IS-2=1.25% TPO (diphenyl(2,4,6-trimethylbenzoyl)-phosphine oxide); IS-3=0.25% CQ+0.50% EDMAB+0.50% TPO. DC of resin blends was measured with a differential scanning calorimeter. Data were analyzed with a three-way ANOVA.

RESULTS

Neat resin type influenced DC, as R4 showed the highest values compared to R2 and R3 (p<0.05). Solvent had a significant effect on DC (p<0.05): dilution of resin blends with 10% or 20% ethanol or 10% ethanol+10% water increased the DC of all resins, except for R4. Initiators influenced the polymerization since neat resins and mixtures solvated with 10% or 20% ethanol showed their highest DC values when polymerized with IS-1 or IS-3 (p>0.05), while IS-2 or IS-3 increased the DC values of resins diluted with 10% ethanol and 10% water (p<0.05).

CONCLUSIONS

Water-compatible photo-initiators such as TPO should be included in the hydrophilic solvated adhesive formulation to ensure an appropriate DC of the adhesive layer.

Effects of ethanol addition on the water sorption/solubility and percent conversion of comonomers in model dental adhesives

OBJECTIVES

This study evaluated the kinetics of water uptake and percent conversion in neat versus ethanol-solvated resins that were formulated to be used as dental bonding agents.

METHODS

Five methacrylate-based resins of known and increasing hydrophilicities (R1, R2, R3, R4 and R5) were used as reference materials. Resins were evaluated as neat bonding agents (100% resin) or they were solvated with absolute ethanol (95% resin/5% ethanol or 85% resin/15% ethanol). Specimens were prepared by dispensing the uncured resin into a circular mold (5.8 mm x 0.8 mm). Photo-activation was performed for 80s. The water sorption/diffusion/solubility was gravimetrically evaluated, while the degree of conversion (DC) was calculated by Fourier-transform infrared spectroscopy.

RESULTS

Water sorption increased with the hydrophilicity of the resin blends. In general, the solvated resins exhibited significantly higher water sorption, solubility and water diffusion coefficients when compared to their corresponding neat versions (p<0.05). The only exception was resin R1, the least hydrophilic resin, in which neat and solvated versions exhibited similar water sorption (p>0.05). Addition of ethanol increased the DC of all resins tested, especially of the least hydrophilic, R1 and R2 (p<0.05). Despite the increased DC of ethanol-solvated methacrylate-based resins, it occurs at the expense of an increase in their water sorption/diffusion and solubility values.

SIGNIFICANCE

Negative effects of residual ethanol on water sorption/solubility appeared to be greater as the hydrophilicity of the resin blends increased. That is, the use of less hydrophilic resins in dental adhesives may create more reliable and durable bonds to dentin.

Influence of drying time and temperature on bond strength of contemporary adhesives to dentine

OBJECTIVES

To evaluate the bond strength (microTBS) of self-etching adhesives in different solvent evaporation conditions.

METHODS

Flat dentine surfaces from extracted human third molars were bonded with: (1) 2 two-steps self-etching adhesives (Clearfil SE Bond-CSEB); (Protect Bond-PB) and (2) 2 one-step self-etch systems (Adper Prompt L Pop-ADPLP); (Xeno III-XIII). Bonded dentine surfaces were air-dried for 5s, 20s, 30s or 40s at either 21 degrees C or 38 degrees C. Composite build-ups were constructed incrementally. After storage in water for 24h at 37 degrees C, the specimens were prepared for microtensile bond strength testing. Data were analyzed by two-way ANOVA and Student-Newman-Keuls at alpha=0.05.

RESULTS

CSEB and PB performed better at warm temperature with only 20s of air-blowing. The bond strength increased when XIII was performed at warm temperature at 40s air-blowing. Extended air-blowing not affect the performance of ADPLP, except at 30s air-blowing time at warm temperature.

CONCLUSIONS

The use of a warm air-dry stream seems to be a clinical tool to improve the bond strength to self-etching adhesives.

Effects of residual ethanol on the rate and degree of conversion of five experimental resins

OBJECTIVES

This study examined the extent of ethanol retention in five comonomer blends of experimental methacrylate-based dental adhesives, containing (10, 20, or 30 wt.%) ethanol, after solvent evaporation, as well as observing the effect of residual ethanol and exposure duration on degree of conversion (DC). The null hypothesis that was tested was that residual, unevaporated ethanol has no effect on the rate or extent of DC of polymerized adhesive resins.

METHODS

A known mass of each mixture was placed in glass wells and evaporated for 60s. The mass of the mixtures before and after evaporation was measured, allowing calculation of the gravimetric ethanol loss/retention.

RESULTS

The concentration of retained ethanol increased significantly with ethanol concentration (p<0.01): 1.1-1.9 mole/L for 10% ethanol/90% comonomers, 2.2-3.5 mole/L for 20% ethanol, and 2.6-3.7 mole/L for 30% ethanol/70% comonomers. As ethanol is evaporated from solvated comonomer mixtures, the molar concentration of comonomers increases, reducing the vapor pressure of the remaining ethanol. Thus, the fractional loss of ethanol solvent decreases as the comonomer concentration increases. The DC of 10, 20, and 30 wt.% ethanol blends increased with ethanol concentration in four of the five experimental resins (p<0.05), increasing by 30-45% when 10 or 20 wt.% ethanol was added to neat resins, regardless of exposure duration. Depending on the resin system, inclusion of 30% ethanol lowered DC at 20s but increased DC after 40-60s of light exposure.

SIGNIFICANCE

Since 10 and 20 wt.% ethanol-resin blends increased the DC of solvated resins by 30-45% over neat resins, the test null hypothesis is rejected. Even with prolonged evaporation, 4-9% residual ethanol concentration can remain in 90/10 (wt./wt.) comonomer-ethanol mixtures. This is thought to be because comonomers lower the vapor pressure of ethanol. This amount of residual ethanol facilitates DC but lowers the rate of polymerization.