A review: Biodegradation of resin–dentin bonds

The Classification and Selection of Adhesive Agents; an Overview for the General Dentist

Adhesive agents are essential to most restorative procedures used in everyday practice. Depending on the clinical situation, the dentist will choose among a rapidly evolving variety of adhesive agents (bonding agents). Due to the availability of many adhesive agents, appropriate selection can take time and effort. Typically, a practitioner relies more on marketing and experience than in-depth material knowledge. The classification of adhesive agents may need to be clarified and easier to remember due to its lack of relevance to clinical procedures. This paper reviews the published literature retrieved from PubMed, Google Scholar, and Scopus by using specific keywords "adhesive agents", "classification", "dentin", "enamel", "universal", "self-etch", "etch-and-rinse", and "bonding". The titles and abstracts were screened, and the relevant literature was retrieved. The list of references from each identified article was examined to find other potentially relevant articles. Adhesive agents can be classified as etch-and-rinse, self-etch, or "multi-mode" according to their approach to interacting with the smear layer, and each approach can be further classified according to the number of clinical steps required during application. This article reviews the classification of current adhesive agents and discusses the properties that make a specific adhesive agent the optimal choice for a particular clinical indication. The review will assist the general dentist in understanding the various types of available adhesive agents and how they function. Overall, the review will facilitate decision-making and allow the selection of appropriate materials.

Shear-bond strength of different Self-Etching adhesive systems to dentin with or without laser irradiation before photopolymerization (A comparative Study)

This study aimed at comparing shear-bond strength (SBS) of different self-etching adhesive systems (Clearfil S³ Bond Plus, G-Premio BOND and IBond) to dentin without or with diode-laser irradiation before photo-polymerization and to determine the effect of storage and thermo-cycling on SBS of adhesive systems.

METHODS

The buccal surface of 84 extracted maxillary premolars was grounded to create flat surface. The specimens were allocated into 3 groups (n = 28) depending upon the adhesive systems, then each group was divided into two sub-group (I, II) (n = 14). After the placement of respective adhesive systems on the flat surface, adhesive system in group I was photo-polymerized immediately, while in group II, the adhesive systems were exposed to diode-laser before photo-polymerization. Composite cylinder (4 mm in diameter and 2 mm height) was built on the flat surface of each specimen. Then group I and II were divided into two sub-groups (n = 7) according to the storage time and thermo-cycling (1 day without thermo-cycling or 72 days with thermo-cycling) then all the specimens were stored in distilled water. The SBS was measured at the end of storage period. ANOVA, Duncan's Multiple Range Test and independent t-test "P ≤ 0.05" were used for data analysis.

RESULTS

G-premio BOND showed the highest mean value of SBS followed by Clearfil S³ Bond plus without significant difference between them, while IBond revealed the least mean value. Laser irradiation had positive effect on the bond-strength of all tested adhesive systems. The results also showed that the storage with thermo-cycling had negative effect on the bond-strength in groups without laser irradiation for all tested adhesive systems, while for groups with laser irradiation, the reduction in the bond-strength of all tested adhesive systems was not significant.

CONCLUSION

Diode-laser application prior to photo-polymerization of self-etch adhesive systems significantly increased the bond-strength to dentin and can increase the durability of composite adhesion.

Physicochemical, Mechanical, and Esthetic Properties of the Composite Resin Manipulated with Glove Powder and Adhesive as a Modeling Liquid

Composite resins with low flowability are usually handled and manipulated before insertion into the tooth preparation with gloved hands and/or using an instrument covered with a little amount of adhesive to facilitate modeling. We investigated if the modeling techniques (combined or not) affected physicochemical and esthetic properties of a composite resin. Specimens were fabricated and divided into groups according to the handling/modeling technique: Gloved-hands (composite was hand-manipulated with powdered latex gloves); Adhesive (adhesive was used in between the composite layers); Gloved-hands + Adhesive; Control (no adhesive and no touch with gloved-hands). The highest values for flexural strength (MPa), modulus of elasticity (GPa), and fracture toughness (MPa.m0.5) were obtained for Adhesive and Gloved-hands + Adhesive (p < 0.05); the lowest values were obtained for Control and Gloved-hands (p < 0.05). The Control group had the highest sorption. The Gloved-hands (p < 0.05) group had the highest solubility. Adhesive and Gloved-hands + Adhesive had a similar solubility (p > 0.05). The Control group (p < 0.05) had the lowest solubility. There was no statistical interaction between translucency vs. handling/modeling techniques and color stability vs. handling/modeling techniques. Adhesive as a modeling liquid protected the composite against sorption and solubility (if powdered gloves were used) and improved its physical/mechanical properties. Translucency and color stability were not correlated with modeling techniques.

Comparative Assessment of Different Pre-Treatment Bonding Strategies to Improve the Adhesion of Self-Adhesive Composites to Dentin

The aim of this study is to compare the adhesive interface formed in dentin, using self-adhesive composites applied with different bonding strategies, by testing the microtensile bond strength (μTBS) and ultramorphology through the use of light microscopy. Permanent, sound human molars were randomly allocated to six experimental groups. The groups included a negative control group, where only etching was performed via EtchOnly; a positive control group where an adhesive was applied, OptiBondFL (OBFL); and an experimental group where a primer was applied using a co-curing strategy together with a composite (Primer_CoCuring). The samples were sectioned into microspecimens for μTBS (n = 8) and into 1-mm thick slabs for light microscopy using Masson’s trichrome staining protocol (n = 3). The statistical analysis included a two-way ANOVA for μTBS data and Tukey’s HSD was used as a post-hoc test (significance level of 5%; SPSS v. 26.0). The results of the μTBS revealed that the self-adhesive composite (F = 6.0, p < 0.018) and the bonding strategy (F = 444.1, p < 0.001) significantly affected the bond strength to dentin. However, their interactions were not significant (F = 1.2, p = 0.29). Etching dentin with no additional treatment revealed the lowest μTBS (VF_EtchOnly = 2.4 ± 0.8 MPa; CC_EtchOnly = 2.0 ± 0.4 MPa), which was significantly different from using a primer (VF_CoCu = 8.8 ± 0.8 MPa; CC_CoCu = 6.3 ± 1.0 MPa) or using the full adhesive (VF_OptiBondFL = 22.4 ± 0.3 MPa; CC_OptibondFL = 21.2 ± 0.4 MPa). Microscopy images revealed that the experimental Primer_CoCuring was the only group with no collagen fibers exposed to the dentin−composite interface. Overall, the use of a primer, within the limitations of this study, increased the bonding of the self-adhesive composite and provided sufficient infiltration of the collagen based on light-microscopic imaging.

Influence of bonding agent application method on the dentin bond durability of a two-step adhesive utilizing a universal-adhesive-derived primer

This study investigated the effect of the bonding agent application method on the dentin bond durability of a two-step adhesive utilizing a universal-adhesive-derived primer. The bonding durability of a universal adhesive was compared with those of two conventional two-step adhesives by shear bond strength testing after thermal cycling. The primer was applied (with or without phosphoric acid pre-etching), and the specimens were divided into three groups based on the bonding agent application method used as follows: (i) strong air-flow application, (ii) gentle air-flow application, and (iii) gentle air-flow + second bonding application. The shear bond strength was determined after thermal cycling. All the factors (bonding agent application method, adhesive system, and storage condition) significantly influenced the dentin shear bond strength both with and without phosphoric acid pre-etching. The specimens exposed to gentle air-flow showed a higher shear bond strength than did those exposed to strong air-flow and gentle air-flow + second bonding. The bond durability of the tested adhesive systems was influenced by the bonding agent application method, and this trend was material dependent. The G2-Bond Universal exhibited the same or greater dentin bond durability to the other two-step adhesive systems.

Effects of Preheating and Sonic Delivery Techniques on the Internal Adaptation of Bulk-fill Resin Composites

CLINICAL RELEVANCE

The internal adaptation of resin composites that are recommended to be placed with the conventional insertion technique could be improved when the resin composites are preheated prior to their placement. SonicFill 2 and VisCalor bulk show the best internal adaptation when they are inserted as per the manufacurer's recommended techniques.

SUMMARY

Objective: To compare the effects of conventional (hand-placed), sonic, or preheated insertion techniques on the internal adaptation of bulk-fill resin composites.Methods and Materials: A total of 150 freshly extracted human third molars were used to prepare standardized cylindrical occlusal cavities. Teeth were divided into five main groups according to the resin composites: 1 incremental (Clearfil Majesty Posterior [CMP]) and four paste-like bulk-fill (SonicFill 2 [SF2], VisCalor bulk [VCB], Filtek One bulk-fill restorative [FBR], and Tetric EvoCeram bulk-fill [TEB]). Each main group was divided into three subgroups according to the placement technique: conventional, preheating, and sonic delivery (n=10). In the conventional placement technique, cavities were filled manually. In the sonic insertion technique, a specific handpiece (SonicFill Handpiece; Kerr Corporation) was used. In the preheating technique, a heating device (Caps Warmer, Voco, Cuxhaven, Germany) was used to warm the resin composites before placement. Internal voids (%) of the completed restorations were calculated with microcomputed tomography. Data was analyzed with two-way analysis of variacne followed by Tukey's multiple comparisons test (α=0.05).Results: All resin composites showed fewer internal gaps with preheating compared with the conventional placement (p<0.05). For all resin composites other than SF2, preheating provided fewer internal gaps than that of the sonic placement (p<0.05). Sonic placement led to fewer internal gaps compared with the conventional placement, but only for SF2 and FBR (p<0.05). For the conventional placement, the lowest gap percentage was observed with the incremental resin composite (CMP, p<0.05). Among all groups, the lowest gap percentages were observed for preheated VCB followed by sonically inserted SF2 (p<0.05).Conclusion: The best internal adaptation was observed in sonically inserted SF2 and preheated VCB, which were the manufacturers' recommended insertion techniques. Preheating considerably improved the internal adaptation of all resin composites, except for that of SF2.

Detection of the hybrid layer biodegradation initiation factor with a scanning electron microscope

The purpose of this study was to elucidate the origin of initiation of hybrid layer biodegradation. Ninety caries-free human third molars were divided into three surface groups: enamel, dentin, and NaOCl-treated dentin. (n = 30/group) Each group was divided into three subgroups (n = 10/group) of luting resin materials with etch-and-rinse; self-etch and self-adhesive systems. Resin composite blocks and sticks were fabricated and adhered onto dentin and enamel surfaces. The bond strength values were evaluated with micro shear test and statistical analysis were made. On the other hand, teeth were sectioned with a slow-speed saw into multiple beams. After thermocycling, samples were kept in 50% silver nitrate solution. Samples were analyzed with SEM in back-scattered mode. According to the micro-shear bond tests, higher bond strength values were observed in etch-and-rinse system. Bond strength values in self-adhesive and etch-and-rinse groups were significantly higher than self-etch groups in dentin surface and dentin surface treatment with NaOCl. Back-scattered scanning electron microscope results showed that, different degradation mechanism was observed. The present study indicates that, due to the acid etching in dentin, collagen biodegradation was observed within the hybrid layer. On the enamel surfaces, resin degradation was related with resin monomers in adhesive systems.

Effect of a Copaiba Oil-Based Dental Biomodifier on the Inhibition of Metalloproteinase in Adhesive Restoration

Aim

This study sets out to evaluate the antiproteolytic activity of copaiba oil-based emulsion at the resin/dentin adhesive interface union formed with conventional and self-etching adhesives systems.

Methods

At in situ zymography, 30 teeth were sectioned 2 mm below the enamel-dentin junction; a smear layer was standardized and subdivided into four groups. Gelatin conjugated with fluorescein was used and taken to the fluorescence microscope for evaluation. In cytotoxicity, the Trypan Blue method was used at four different time points. The tested groups were (G1) control with distilled water; (G2) 2% chlorhexidine (CLX); (G3) emulsion based on copaiba oil (EC) 10% + X; (G4) 10% EC + Y; and (G5) EC 10% alkaline. The zymographic assay used the same groups described, but in 30 seconds and 10 and 20 minutes. HT1080 cells were incubated and submitted to electrophoresis. The gel was analyzed using ImageJ software. Mann–Whitney and Kruskal–Wallis tests were used in the statistical analysis (p < 0.05).

Results

ECs showed higher cell viability in the cytotoxicity test and showed a significant difference in 10 and 20 minutes. In the zymographic assay, alkaline EC reduced 67% of MMP-2 activity and 44% of MMP-9 compared to 2% chlorhexidine. At in situ zymography in qualitative evaluation, all groups tested showed inhibition of activity in metalloproteinases.

Conclusion

EC showed activity in the inhibition of metalloproteinases in vitro and in situ, especially the alkaline one. The survey shows the possibility of using ECs, a product from Amazonian biodiversity, as a biomodifier in dentistry.

Bond durability of universal adhesives to intact enamel surface in different etching modes

This study aimed at determining the enamel bond durability of universal adhesives to intact enamel (IE) and ground enamel (GE) in different etching modes under thermal cycling (TC) and fatigue stresses. Two universal adhesives and a two-step self-etch adhesive were used. Enamel specimens were divided into four groups by treatment: (i) GE in etch-and-rinse, (ii) IE in etch-and-rinse, (iii) GE in self-etch, and (iv) IE in self-etch. Bonded specimens were subjected to TC, and then shear bond strengths (SBS) were conducted. SBS tests were also conducted after storage in 37°C water for 24 h (baseline). For shear fatigue strength (SFS) testing, bonded specimens were subjected to fatigue stress at a frequency of 10 Hz for 50,000 cycles. At baseline, all adhesives showed significantly higher SBS values with GE than IE in self-etch mode in contrast to in etch-and-rinse mode. After TC, the universal adhesives with IE showed lower SBS values than the baseline, regardless of the etching mode. Universal adhesives showed significantly lower SFS values with IE in etch-and-rinse, but not in self-etch mode. Phosphoric acid pre-etching or grinding of the aprismatic enamel may be helpful in establishing reliable initial and long-term bonds to enamel when using universal adhesives in self-etch mode.

Dual modified nanosilica particles as reinforcing fillers for dental adhesives: Synthesis, characterization, and properties

A facile procedure has been devised to develop a novel dentin bonding system containing poly (acrylic acid)-grafted-silanized fumed silica particles as reinforcing filler, with high stability of nanoparticle dispersion and enhanced bond strength and mechanical properties. In the first step, the silanization of fumed silica nanoparticles was performed in the following conditions: (i) ethanol-water solution with a pH of 5 and (ii) cyclohexane with a pH of 9 using trimethoxysilylpropyl methacrylate (γ-MPS) as a reactive silane coupling agent. FTIR and TGA analyses confirmed the presence of silane in the resultant structure and enhanced dispersion stability of modified particles was proved by a separation analyzer and also zeta potential analyses. In the second step, free radical polymerization of acrylic acid monomers in the presence of silanized nanoparticles was carried out and poly (acrylic acid) -grafted- silanized fumed silica were acquired. The flexural strength and fracture toughness of the adhesive containing 0.2 wt.% of the dual modified filler reached maximum of 70.4 MPa and 1.34 MPa m^1/2, respectively, showing average improvements of 74% and 179%, respectively, in comparison with the adhesive without filler. Flexural modulus values did not significantly change with increasing the filler content except the adhesive containing 5 wt.% having the lowest flexural modulus. The highest microtensile bond strength was also observed at 0.2 wt.% filler content showing the average improvements of 197% as compared with the neat adhesive. Energy dispersive X-ray (EDX) mapping confirmed a homogenous and uniform distribution of the fillers in the adhesive matrix containing 0.2 wt.% and 0.5 wt.% of filler while incorporation of 5 wt.% led to large particle aggregates. SEM images of the fracture surface of the adhesive with different filler contents subjected to fracture toughness test showed rougher surface and longer crack path by increasing filler concentration. The adhesive containing 0.2 wt.% of filler perfectly penetrated into the dentin tubules proved by the SEM micrographs in microtensile bond strength test.

Ageing of Dental Composites Based on Methacrylate Resins-A Critical Review of the Causes and Method of Assessment

The paper reviews the environmental factors affecting ageing processes, and the degradation of resins, filler, and the filler-matrix interface. It discusses the current methods of testing materials in vitro. A review of literature was conducted with the main sources being PubMed. ScienceDirect, Mendeley, and Google Scholar were used as other resources. Studies were selected based on relevance, with a preference given to recent research. The ageing process is an inherent element of the use of resin composites in the oral environment, which is very complex and changes dynamically. The hydrolysis of dental resins is accelerated by some substances (enzymes, acids). Bonds formed between coupling agent and inorganic filler are prone to hydrolysis. Methods for prediction of long-term behaviour are not included in composite standards. Given the very complex chemical composition of the oral environment, ageing tests based on water can only provide a limited view of the clinical performance of biomaterial. Systems that can reproduce dynamic changes in stress (thermal cycling, fatigue tests) are better able to mimic clinical conditions and could be extremely valuable in predicting dental composite clinical performance. It is essential to identify procedure to determine the ageing process of dental materials.

Immediate enamel bond strength of universal adhesives to unground and ground surfaces in different etching modes

The purpose of this study was to determine the immediate bond effectiveness of universal adhesives to unground and ground enamel surfaces in different etching modes, through shear bond strength (SBS) tests and scanning electron microscopy observations. Three universal adhesives, a conventional two-step self-etch adhesive, and a conventional single-step self-etch adhesive were compared. Human enamel specimens from lower anterior teeth were divided into four groups and subjected to the following treatments: (i) unground enamel in self-etch mode; (ii) ground enamel in self-etch mode; (iii) unground enamel in etch-&-rinse mode; and (iv) ground enamel in etch-&-rinse mode. Bonded assemblies were subjected to SBS testing. All the adhesives showed significantly higher SBS values in etch-&-rinse mode than in self-etch mode, regardless of whether enamel was unground or ground. The influence of the enamel surface condition on SBS was different in different etching modes. Without pre-etching, all tested materials showed lower SBS values in unground enamel than in ground enamel. In etch-&-rinse mode, no significant differences in SBS values were observed between unground enamel and ground enamel for any of the adhesives tested. Phosphoric acid pre-etching before application of self-etch adhesives to an unground enamel surface is essential to enhance initial enamel bond effectiveness.

The durability of adhesion to Er,Cr:YSGG laser-irradiated enamel

BACKGROUND AND AIMS

Adhesion durability of resin adhesives with Er,Cr:YSGG laser irradiated-enamel has been rarely investigated in the literature. Thus, the present study evaluated the influence of long-term water storage (12-month) on resin bond strength with the enamel irradiated with Er,Cr:YSGG laser irradiation deployed different settings.

MATERIALS AND METHODS

The flattened enamel samples of 35 bovine teeth, which were embedded into acrylic blocks, were randomly divided into 7 groups (n = 5), according to surface treatments using Er,Cr:YSGG laser with different parameters 6 W/20 Hz, 6 W/35 Hz, 6 W/50 Hz, 3 W/20 Hz, 3 W/35 Hz, 3 W/50 Hz or no laser treatment (Bur-treating as a control). Adper Single Bond 2 was applied to the prepared enamel and the composites were placed and cured. Resin-enamel sticks with an approximate cross-sectional area of 0.8 mm2 were obtained, and microtensile bond strength (µTBS) tests were performed at 24-hour and 12-month of water storage after bonding. The µTBS data were analyzed with two-way ANOVA and Tukey tests (p < 0.05).

RESULTS

24-hour water storage after bonding, the µTBS to laser-irradiated enamel in the 6W/ 20 Hz group was significantly lower than those of bur-treated. However, 3 W/50 Hz showed significantly higher µTBS than those of bur-treated. Two-way ANOVA revealed that 12-month water storage did not influenced µTBS.

CONCLUSION

It may be concluded that, initial bond strength to Er,Cr:YSGG laser irradiated-enamel might be significantly influenced by power and pulse frequency settings. However, resin bonding to laser-irradiated enamel was stable over 12-month water storage regardless of tested laser parameters.

Eighteen-month Clinical Study of Universal Adhesives in Noncarious Cervical Lesions

OBJECTIVE

To evaluate the clinical performance of Scotchbond Universal (3M Oral Care) and Prime & Bond Elect (Dentsply Sirona) in the restoration of noncarious cervical lesions (NCCLs).

METHODS AND MATERIALS

This was a randomized controlled clinical trial involving 63 subjects. Two hundred and three NCCLs were restored using Scotchbond Universal and Prime & Bond Elect using both an etch-and-rinse and a self-etch technique. Lesions were notch-shaped NCCLs, and the restorations were placed without any mechanical retention. Restorations were finished immediately after placement and scored with regard to retention, marginal discoloration, marginal adaptation, and secondary caries. Similar assessment of the restorations was performed 18 months after placement. Logistic regression was performed for each outcome separately with a compound symmetric variance-covariance structure assumed to consider a correlation of restorations within subjects. All analyses were conducted using SAS version 9.4 (SAS Inc).

RESULTS

One hundred and fifty-eight teeth (77.8% of the restorations placed) in 46 subjects (73% of subjects enrolled) were available for the 18-month follow-up. A statistically significant difference was reached only for the comparison Scotchbond Universal/self-etch (SU_SE) and Prime & Bond Elect/etch-and-rinse (PBE_E&R) groups ( p=0.01), where a restoration with SU_SE was 66% less likely to maintain a score of Alpha for marginal discoloration than a restoration performed with PBE_E&R.

CONCLUSIONS

Scotchbond Universal and Prime & Bond Elect presented acceptable clinical performance after 18 months of clinical service. However, Scotchbond Universal, when applied with a self-etch approach, did demonstrate a relatively high level of marginal discoloration when compared to the other groups.

Microtensile bond strength, 4-point bending and nanoleakage of resin-dentin interfaces: Effects of two matrix metalloproteinase inhibitors

Chronic degradation of hybrid layer collagen by matrix metalloproteinases (MMPs) jeopardizes resin-dentin interfacial integrity and limits the durability of dental restorations. The 4-point bending strength (BS) is a valid but uncommon method of testing the mechanical behavior of resin-dentin interfaces. The present study aims to analyze the influence of two matrix metalloproteinase inhibitors on microtensile bond strength (µTBS), BS and nanoleakage. A total of 48M were divided into three groups according to bonding procedure. Teeth were horizontally sectioned to produce a flat dentin surface. In the control group, etch-and-rinse Prime&Bond One (Dentsply) bonding was used; in the self-etch group, methacryloyloxydodecylpyridinium bromide (MDPB)-containing Clearfil SE Protect (Kuraray) was used; and in the benzalkonium chloride (BAC)-etch group, BAC-etchant (Bisco) was used. A Ceram.X-One (Dentsply) composite was built as three successive layers and was light-cured. Samples were sectioned to produce microrods that were randomly divided into two groups for analysis at baseline and after 6 months of water immersion (n = 32), plus one slab for nanoleakage analysis (n = 8) via scanning electron microscopy (SEM) and digital image analysis (Fiji). Data were analyzed using the Weibull distribution and a mixed-model ANOVA with a post hoc Tukey test. All groups showed deterioration of the initial bonds. The self-etch group had a worse baseline µTBS than the control but had the best BS after aging. BAC-etch did not improve bond stability of etch-and-rinse adhesive. The µTBS and BS test results after aging were moderately correlated. Mixed fractures prevailed with regard to µTBS, whereas adhesive fractures dominated with regard to BS. Nanoleakage was not eliminated in any group and increased after aging. MDPB self-etch resisted bond degradation better than etch-and-rinse adhesives, even after BAC-etching. Integrating BS in studies of µTBS and nanoleakage might provide more clinically relevant outcomes for predicting the performance of dental adhesives.

Influence of application method on surface free-energy and bond strength of universal adhesive systems to enamel

The aim of the present study was to determine the influence of different adhesive application methods and etching modes on enamel bond effectiveness of universal adhesives using shear bond strength (SBS) testing and surface free-energy (SFE) measurements. The adhesives Scotchbond Universal, All-Bond Universal, Adhese Universal, and G-Premio Bond were used. Prepared bovine enamel specimens were divided into four groups, based on type of adhesive, and subjected to the following surface treatments: (i) total-etch mode with active application; (ii) total-etch mode with inactive application; (iii) self-etch mode with active application; and (iv) self-etch mode with inactive application. Bonded specimens were subjected to SBS testing. The SFE of the enamel surfaces with adhesive was measured after rinsing with acetone and water. The SBS values in total-etch mode were significantly higher than those in self-etch mode. In total-etch mode, significantly lower SBS values were observed with active application compared with inactive application; in contrast, in self-etch mode there were no significant differences in SBS between active and inactive applications. A reduction in total SFE was observed for active application compared with inactive application. The interaction between etching mode and application method was statistically significant, and the application method significantly affected enamel bond strength in total-etch mode.

The innovative applications of therapeutic nanostructures in dentistry

Nanotechnology has paved multiple ways in preventing, reversing or restoring dental caries which is one of the major health care problems. Nanotechnology aided in processing variety of nanomaterials with innovative dental applications. Some showed antimicrobial effect helping in the preventive stage. Others have remineralizing potential intercepting early lesion progression as nanosized calcium phosphate, carbonate hydroxyapatite nanocrystals, nanoamorphous calcium phosphate and nanoparticulate bioactive glass particularly with provision of self-assembles protein that furnish essential role in biomimetic repair. The unique size of nanomaterials makes them fascinating carriers for dental products. Thus, it is recentlyclaimedthat fortifying the adhesives with nanomaterials that possess biological meritsdoes not only enhance the mechanical and physical properties of the adhesives, but also help to attain and maintain a durable adhesive joint and enhanced longevity. Accordingly, this review will focus on the current status and the future implications of nanotechnology in preventive and adhesive dentistry.

Adhesives Doped with Bioactive Niobophosphate Micro-Filler: Degree of Conversion and Microtensile Bond Strength

To evaluate the effect of incorporating niobium phosphate bioactive glass (NbG) into commercial etch-and-rinse adhesive systems, with and without silane, on their degree of conversion (DC) (%) and microtensile bond strength (μTBS). The NbG micro-filler was added to two etch-and-rinse adhesive systems: One Step (OS) and Prime & Bond (PB) at 40% concentration. The following groups were formed: control without glass addition OS; addition of unsilanized NbG (OSNbG); addition of silanized NbG (OSNbGS); control without glass PB; addition of unsilanized NbG (PBNbG); addition of silanized NbG (PBNbGS). The DC was determined using total Fourier spectroscopy reflection (FTIR/ATR). For μTBS testing, 48 human third molars (n=8) were restored and sliced to obtain specimens (0.8 mm2) and they were tested at two different time intervals: immediately and after 6 months. The fracture mode was evaluated with a stereoscopic loupe (40×) and by scanning electron microscopy (SEM). The data were subjected to ANOVA and Tukey tests (a=0.05). NbG addition did not compromise the adhesive system DC values (p>0.05). Furthermore, the NbG added to the adhesive systems did not affect μTBS values (p>0.05). Fracture occurred predominantly at the dentin-adhesive interface. NbG bioactive glass did not affect the DC or microtensile bond strength results.

Computer-aided Molecular Design of Water Compatible Visible Light Photosensitizers for Dental Adhesive

Dental adhesive resin undergoes phase separation during its infiltration through the wet demineralized dentin and it has been observed previously that the hydrophilic-rich phase is a vulnerable region for failure due to the lack of photo-polymerization and crosslinking density. The lack of photo-polymerization is mostly due to the partitioning of photo-initiators in low concentrations within this phase. Here, a computational approach has been employed to design candidate water compatible visible light photosensitizers which could improve the photo-polymerization of the hydrophilic-rich phase. This study is an extension of our previous work. QSPRs were developed for properties related to the photo-polymerization reaction of the adhesive monomers and hydrophilicity of the photosensitizer using connectivity indices as descriptors. QSPRs and structural constraints were formulated into an optimization problem which was solved stochastically via Tabu Search. Four candidate photosensitizer molecules have been proposed here which have the iminium ion as a common feature.

Dentin bonding performance using Weibull statistics and evaluation of acid-base resistant zone formation of recently introduced adhesives

Dentin bonding durability of recently introduced dental adhesives: Clearfil SE Bond 2 (SE2), Optibond XTR (XTR), and Scotchbond Universal (SBU) was investigated using Weibull analysis as well as analysis of the micromorphological features of the acid-base resistant zone (ABRZ) created for the adhesives. The bonding procedures of SBU were divided into three subgroups: self-etch (SBS), phosphoric acid (PA) etching on moist (SBM) or dry dentin (SBD). All groups were thermocycled for 0, 5,000 and 10,000 cycles followed by microtensile bond strength testing. Acid-base challenge was undertaken before SEM and TEM observations of the adhesive interface. The etch-and-rinse method with SBU (SBM and SBD) created inferior interfaces on the dentin surface which resulted in reduced bond durability. ABRZ formation was detected with the self-etch adhesive systems; SE2, XTR and SBS. In the PA etching protocols of SBM and SBD, a thick hybrid layer but no ABRZ was detected, which might affect dentin bond durability.

Effect of Partition of Photo-initiator Components and Addition of Iodonium Salt on the Photopolymerization of Phase-Separated Dental Adhesive

The polymerization kinetics of physically separated hydrophobic- and hydrophilic-rich phases of a model dental adhesive have been investigated. The two phases were prepared from neat resin containing 2-hydroxyethyl methacrylate (HEMA) and bisphenol A glycerolate dimethacrylate (BisGMA) in the ratio of 45:55 (wt/wt). Neat resins containing various combinations of popular photo-initiating compounds, e.g., camphoquinone (CQ), ethyl 4-(dimethylamino)benzoate (EDMAB), 2-(dimethylamino)ethyl methacrylate (DMAEMA) and diphenyliodonium hexafluorophosphate (DPIHP) were prepared. To obtain the two phases 33 wt% of deuterium oxide (D₂O) was added to the neat resins. This amount of D₂O exceeded the miscibility limit for the resins. The concentration of each component of the photo-initiating system in the two phases was quantified by HPLC. When combined with CQ, DMAEMA is less efficient as a co-initiator compared to EDMAB. The addition of DPIHP as the third component into either CQ/EDMAB or CQ/DMAEMA photo-initiating systems leads to comparable performance in both the hydrophobic- and hydrophilic-rich phases. The addition of the iodonium salt significantly improved the photopolymerization of the hydrophilic-rich phase; the hydrophilic-rich phase exhibited extremely poor polymerization when the iodonium salt was not included in the formulation. The partition concentration of EDMAB in the hydrophilic-rich phase was significantly lower than that of DMAEMA or DPIHP. This study indicates the need for a combination of hydrophobic/hydrophilic photosensitizer and addition of iodonium salt to improve polymerization within the hydrophilic-rich phase of the dental adhesive.

Effect of a functional monomer (MDP) on the enamel bond durability of single-step self-etch adhesives

The present study aimed to determine the effect of the functional monomer, 10-methacryloxydecyl dihydrogen phosphate (MDP), on the enamel bond durability of single-step self-etch adhesives through integrating fatigue testing and long-term water storage. An MDP-containing self-etch adhesive, Clearfil Bond SE ONE (SE), and an experimental adhesive, MDP-free (MF), which comprised the same ingredients as SE apart from MDP, were used. Shear bond strength (SBS) and shear fatigue strength (SFS) were measured with or without phosphoric acid pre-etching. The specimens were stored in distilled water for 24 h, 6 months, or 1 yr. Although similar SBS and SFS values were obtained for SE with pre-etching and for MF after 24 h of storage in distilled water, SE with pre-etching showed higher SBS and SFS values than MF after storage in water for 6 months or 1 yr. Regardless of the pre-etching procedure, SE showed higher SBS and SFS values after 6 months of storage in distilled water than after 24 h or 1 yr. To conclude, MDP might play an important role in enhancing not only bond strength but also bond durability with respect to repeated subcritical loading after long-term water storage.

Bond durability of contemporary adhesive systems to pulp chamber dentin

Objective: The purpose of this study was to evaluate long-term bond strengths of dentin adhesive systems, which include one-step self-etch adhesive systems (Optibond All-in-one, Kerr; Adper Prompt L-POP, 3 M ESPE), a three-step etch-and-rinse adhesive (Optibond FL, Kerr) and two-step self-etch adhesive (AdheSE Bond, Ivoclar), applied to pulp chamber dentin surfaces after 12-month water storage by using microtensile bond strength (µTBS) test.

Materials and methods: Dentin adhesive systems were applied to unprepared pulp chamber dentin surfaces according to manufacturer’s directions, respectively (n = 5). After applying adhesive systems, composite buildups were done incrementally. Bond strengths to pulp chamber dentin surfaces were determined using µTBS test after water storage for 24 h and 12 month. Kruskal–Wallis analysis and Mann–Whitney U-test for pairwise comparisons were used to determine statistical differences in µTBS between the groups at a significance level of 5%.

Results: There were no significant differences in µTBS between storage periods for tested adhesives regardless adhesive class.

Conclusion: Bond durability of tested adhesive systems, including one-bottle self-etch adhesives with pulp chamber dentin surfaces, may be considered stable after 12-month water storage. Therefore, one-step self-etch, also called “user-friendly” adhesives may perform and traditional three-step etch-and-rinse adhesives in the long-term when used for bonding to pulp chamber dentin surfaces.

Effect of simplified ethanol-wet bonding on dentin bonding durability of etchand-rinse adhesives

This in vitro study evaluated the effects of simplified ethanol-wet bonding technique on dentin bonding durability of two etchand-rinse adhesives to bovine dentin. Sixteen freshly extracted bovine incisors were divided into four groups according to bonding technique (water-wet or ethanol-wet bonding) and adhesive (Single Bond 2 or Prime & Bond NT). After etching and rinsing, dentin surfaces were left either water-moist or immersed in ethanol. Following adhesive application and composite build-up, bonded teeth were sectioned into sticks for microtensile bond strength (µTBS) testing conducted after 24-h and 12-month water storage. There were no significant differences in bond strength among the groups at 24 h. At 12 months, the bond strengths of adhesives to dentin were significantly decreased (p<0.05). Simplified ethanol-wet bonding did not improve the resin-dentin bonding durability of tested etch-and-rinse adhesives.

Polymerization behavior of hydrophilic-rich phase of dentin adhesive

The 2-fold objectives of this study were 1) to understand whether model hydrophobic- and hydrophilic-rich phase mimics of dentin adhesive polymerize similarly and 2) to determine which factor, the dimethacrylate component, bisphenol A glycerolate dimethacrylate (BisGMA) or photoinitiator concentration, has greater influence on the polymerization of the hydrophilic-rich phase mimic. Current dentin adhesives are sensitive to moisture, as evidenced by nanoleakage in the hybrid layer and phase separation into hydrophobic- and hydrophilic-rich phases. Phase separation leads to limited availability of the cross-linkable dimethacrylate monomer and hydrophobic photoinitiators within the hydrophilic-rich phase. Model hydrophobic-rich phase was prepared as a single-phase solution by adding maximum wt% deuterium oxide (D2O) to HEMA/BisGMA neat resins containing 45 wt% 2-hydroxyethyl methacrylate (HEMA). Mimics of the hydrophilic-rich phase were prepared similarly but using HEMA/BisGMA neat resins containing 95, 99, 99.5, and 100 wt% HEMA. The hydrophilic-rich mimics were prepared with standard or reduced photoinitiator content. The photoinitiator systems were camphorquinone (CQ)/ethyl 4-(dimethylamino)benzoate (EDMAB) with or without [3-(3, 4-dimethyl-9-oxo-9H-thioxanthen-2-yloxy)-2-hydroxypropyl]trimethylammonium chloride (QTX). The polymerization kinetics was monitored using a Fourier transform infrared spectrophotometer with a time-resolved collection mode. The hydrophobic-rich phase exhibited a significantly higher polymerization rate compared with the hydrophilic-rich phase. Postpolymerization resulting in the secondary rate maxima was observed for the hydrophilic-rich mimic. The hydrophilic-rich mimics with standard photoinitiator concentration but varying cross-linker (BisGMA) content showed postpolymerization and a substantial degree of conversion. In contrast, the corresponding formulations with reduced photoinitiator concentrations exhibited lower polymerization and inhibition/delay of postpolymerization within 2 h. Under conditions relevant to the wet, oral environment, photoinitiator content plays an important role in the polymerization of the hydrophilic-rich phase mimic. Since the hydrophilic-rich phase is primarily water and monomethacrylate monomer (e.g., HEMA as determined previously), substantial polymerization is important to limit the potential toxic response from HEMA leaching into the surrounding tissues.

Polymerization- and solvent-induced phase separation in hydrophilic-rich dentin adhesive mimic

Current dental resin undergoes phase separation into hydrophobic-rich and hydrophilic-rich phases during infiltration of the over-wet demineralized collagen matrix. Such phase separation undermines the integrity and durability of the bond at the composite/tooth interface. This study marks the first time that the polymerization kinetics of model hydrophilic-rich phase of dental adhesive has been determined. Samples were prepared by adding varying water content to neat resins made from 95 and 99 wt.% hydroxyethylmethacrylate and 5 and 1 wt.% (2,2-bis[4-(2-hydroxy-3-methacryloxypropoxy)phenyl1]-propane prior to light curing. Viscosity of the formulations decreased with increased water content. The photopolymerization kinetics study was carried out with a time-resolved Fourier transform infrared spectrometer. All of the samples exhibited two-stage polymerization behavior which has not been reported previously for dental resin formulation. The lowest secondary rate maxima were observed for water contents of 10-30 wt.%. Differential scanning calorimetry (DSC) showed two glass transition temperatures for the hydrophilic-rich phase of dental adhesive. The DSC results indicate that the heterogeneity within the final polymer structure decreased with increasing water content. The results suggest a reaction mechanism involving both polymerization-induced phase separation and solvent-induced phase separation for the model hydrophilic-rich phase of dental resin.

Effect of Postoperative Peroxide Bleaching on the Stability of Composite to Enamel and Dentin Bonds

This study investigated the effect of peroxide bleaching gel on the durability of the adhesive bond between composite material, enamel, and dentin created with the etch-and-rinse adhesive Gluma Comfort Bond (GLU) and with the self-etch adhesives Clearfil SE Bond (CLE), Adper Prompt (ADP), and iBond (IBO). The adhesives were applied to flattened enamel and dentin of extracted human molars and built up with a microhybrid composite (Charisma). After 25 eight-hour cycles of bleaching with a 20% carbamide peroxide bleaching gel (Opalescence PF 20), the shear bond strength was measured and compared with one-day and two-month control specimens stored in water. The data were analyzed using nonparametric Mann-Whitney and Kruskal-Wallis statistics (p&lt;0.05). Detailed fractographic analysis was performed using scanning electron microscopy. The bleaching gel significantly decreased the bond strength on both enamel and dentin for the simplified single-step self-etch adhesives ADP and IBO and markedly affected a fracture pattern of ADP specimens at the periphery of their bonded area. The results of our study indicate that the durability of adhesive restorations can be detrimentally influenced by carbamide peroxide bleaching and that different adhesives show varying sensitivity levels to the bleaching gel.

The effects of three dry-field techniques on intraoral temperature and relative humidity

BACKGROUND

The authors evaluated the effects of three dry-field techniques (rubber dam, Isolite i2 [Isolite Systems, Santa Barbara, Calif.] and Coolex [APT, Osaka, Japan]) on intraoral temperature and relative humidity (RH), compared with the effects of a nonisolated control on intraoral temperature and RH.

METHODS

The authors measured the room's temperature and RH and then placed dry-field devices in five participants' mouths and measured the intraoral temperature and RH for 20 minutes. They then removed the devices or turned off the vacuum system and measured intraoral temperature for an additional five minutes.

RESULTS

The authors found no significant differences in either intraoral temperature or RH at any time during the measurement period in the isolated control group (P > .05); the intraoral temperature was more than 30°C and RH was more than 95 percent. On the other hand, the use of dry-field techniques significantly reduced both intraoral temperature and RH when the rubber dam was in place or the vacuums were turned on (P > .05). The intraoral temperature and RH gradually increased after the authors removed the rubber dam or turned off the vacuums.

CONCLUSIONS

The results of this study revealed that all three dry-field techniques could reduce both temperature and RH effectively.

CLINICAL IMPLICATIONS

Both Isolite i2 and Coolex could provide environments similar to the room conditions used during in vitro specimen preparation for investigating the mechanical properties of dental restorative materials.