Effectiveness of self-etching bonding systems on dentin after radiotherapy: perspectives on microtensile and microshear bond strength

OBJECTIVE

Self-etching dental adhesives bond with dentin through chemical reactions with calcium. This study assessed bond strength (BS) using microtensile (µTBS) and microshear (µSBS) tests on sound and post-radiotherapy dentin, with dental adhesives containing different functional monomers.

METHODS

Sound dentin (SD) and post-radiotherapy irradiated dentin (ID) were tested with two adhesive systems: Clearfil SE Bond (SE, 10-MDP-based) and FL Bond II (FL, containing carboxylic and phosphonic monomers with S-PRG bioactive particles). The tests occurred initially (24 h) and six months later; fracture mode was also analyzed (40x). Ninety-six human molars were randomly assigned (n = 12), and half were irradiated with a 70 Gy radiation dose. For µTBS test, teeth were bonded, restored and sectioned them into beams (0.64 mm2). The µSBS test used filled transparent cylindrical matrices with resin composite and light-cured them after dental adhesive applications. Three-way ANOVA and Tukey's test (p < 0.05) analyzed the data.

RESULTS

µTBS showed a significant substrate x adhesive interaction (p < 0.001), while µSBS was significant for all factors (p = 0.006). SE and FL performed better on SD and ID, respectively, in the µTBS test. As for µSBS, SE showed higher values on ID (p < 0.05). Lower BS values occurred for SD-FL and ID-SE after six months.

CONCLUSION

Dental adhesive performance varied based on substrate type and test method. FL was more stable for ID in µTBS, while SE excelled in µSBS.

CLINICAL RELEVANCE

As post-radiotherapy irradiated dentin becomes more vulnerable, self-etching systems based on functional monomer and bioactive ingredients may exhibit appropriate bonding to this altered substrate.

Stability of the Dentin-Bonded Interface Using Self-Etching Adhesive Containing Diacrylamide after Bacterial Challenge

Purpose/Aim: Acrylamides are hydrolytically stable at pH lower than 2, and were shown to preserve bonded interface integrity with two-step, total etch adhesives. The objective of this study was to leverage those two characteristics in self-etching primers containing the acidic monomer 10-MDP and test the microtensile bond strength before and after incubation with S. mutans incubation. Materials and Methods: Acidic primers (10 wt % 10-methacryloyloxydecyl dihydrogen phosphate─10-MDP; 45 wt % N,N-diethyl-1,3-bis(acrylamido)propane─DEBAAP, or 2-hydroxyethyl methacrylate─HEMA; 45 wt %, glycerol-dimethacrylate─GDMA) and adhesives (DEBAAP or HEMA/10-MDP/UDMA 45/10/45 wt %) were made polymerizable by the addition of 0.2 wt % camphorquinone, 0.8 wt % ethyl-4-dimethylaminobenzoate, 0.4 wt % diphenyliodonium hexafluorophosphate, and 0.1 wt % butylhydroxytoluene. Nonsolvated materials were characterized for flexural strength (FS), modulus (E), toughness, water sorption/solubility (WS/SL), contact angle, and vinyl conversion (DC). Viscosity was evaluated after adding 20 and 40 vol % ethanol to the primer and adhesive, respectively. The experimental materials or Clearfil SE Bond (CC─commercial control) were used to bond a commercial composite (Filtek Supreme) to the flat surface of human dentin. Microtensile bond strength (MTBS) was tested in 1 mm2 sticks for the 5 primer/bond combinations: CC (Clearfil Bond Primer and Bond), HH (HEMA/HEMA), DD (DEBAAP/DEBAAP), HD (HEMA/DEBAAP), and DH (DEBAAP/HEMA). Prior to testing, sticks were stored in water or biofilm-inducing culture medium with S. mutans for 1 week. Confocal images and FTIR-ATR evaluation evaluated the hybrid layer of the adhesives. Results were analyzed using Student's t-test (WS, SL, DC, contact angle, FS, E, toughness), one-way ANOVA/Tukey's test for viscosity, and two-way ANOVA/Tukey's test for MTBS (95%). Results: HEMA-based materials had lower contact angle (p = 0.004), higher WS (p < 0.001), and similar SL values compared to DEBAAP (p = 0.126). FS (p = 0.171) and E (p = 0.065) dry values were similar, but after one week of water storage, FS/E dropped more significantly for HEMA materials. Dry and wet toughness was greater for DEBAAP (p < 0.001), but it also had the greatest drop (46%). Clearfil bonds had the highest viscosity, followed by DEBAAP and HEMA, respectively (p = 0.002). For the primers, HEMA had the lowest viscosity (p = 0.003). As far as MTBS, all groups tested in water were statistically different when compared with HH (p < 0.001). After storage in biofilm, DH had the highest MTBS value, being statistically different from HH (p = 0.002), CC (p = 0.015), and DD (p = 0.027). Conclusions: The addition of a diacrylamide and its association with HEMA in self-etching adhesive systems provided greater bonding stability after bacterial challenge.

Twenty-month Performance of a Universal Bonding System on Simulated-challenged Dentin Substrates Pretreated with Chlorhexidine

OBJECTIVES

Since the use of dentin antiproteolytic agents with universal adhesives (UAs) can potentially degrade the bonding interface, this study evaluated bond strengths with and without chlorhexidine (CHX) on variously altered dentin surfaces for up to 20 months.

METHODS

Human molar specimens (n=20) were categorized by substrates as S=sound, E=eroded, and C=carious, and by pretreatment as W=water or CHX. These specimens were subjected to micro-tensile bond strength (μTBS) testing at 24 hours, 6 months, and 20 months, after 30 seconds of pretreatment with CHX or W, followed by self-etching and bonding (Adper Single Bond Universal, 3M ESPE). Modes of failure were assessed using optical microscopy (40×) and scanning electron microscopy (SEM), and the results were analyzed by 3-way ANOVA and Tukey's statistical tests (α=0.05).

RESULTS

Substrate (p<0.001), pre-treatment (p=0.0413), and time (p<0.0001) were statistically significant. The sound-dentin group in initial time (W=39.27/CHX=40.55) yielded the higher μTBS values (MPa) in comparison with altered substrates pre-treated with CHX (E-CHX=19.84; C-CHX=18.24) after 20 months, which showed the lowest values. Under SEM analysis, heterogeneous patterns appeared in the hybrid layer of the CHX-treated group, particularly in the altered substrates.

CONCLUSIONS

Bond strength to dentin decreased over a period of 20 months using UA with 10-methacryloyloxydecyl-dihydrogen phosphate (MDP) in self-etching mode. Substrates altered by erosion or caries have impaired adhesion and associated clinical use of UA with MDP and CHX should be avoided.

A randomized clinical study of the performance of self-etching adhesives containing HEMA and 10-MDP on non-carious cervical lesions: A 2-year follow-up study

OBJECTIVE

To evaluate the association of HEMA and 10-MDP in the clinical performance of self-etching adhesives in the restoration of NCCLs during 2-years.

MATERIALS AND METHODS

60 restorations were performed in 17 volunteers and randomized into three groups: G1 (n = 20) - Prime and Bond Universal (10-MDP); G2 (n = 20) - Optibond All-in-One (HEMA); and G3 (n = 20) - Clearfil SE (10-MDP and HEMA). No cavity preparation was performed. After 2 years, the restorations were evaluated using the modified USPHS criteria for retention, marginal adaptation/ staining, postoperative sensitivity and secondary caries. The results were analyzed using Fisher's exact test and Kruskal-Wallis test.

RESULTS

All groups showed 100% retention rate, except G1, who lost two restorations (p > 0.05). Regarding marginal adaptation, G1 showed greater deficiency, as only eight restorations (40%) remained intact (p < 0.05). Regarding marginal staining, G1 and G2 showed higher rate, as only 12 restorations (65%) in each one were free of staining (p < 0.05). All groups showed similar results for postoperative sensitivity and secondary caries (p > 0.05).

CONCLUSION

The association of HEMA and 10-MDP monomers in the self-etching adhesives did not influence the clinical performance of the NCCL restorations with respect to retention, postoperative sensitivity, and incidence of secondary caries. However, positively influenced the marginal adaptation and marginal staining at the 2-year follow-up.

CLINICAL SIGNIFICANCE

The association of HEMA and 10-MDP monomers in the self-etching adhesives positively influence the clinical performance of the NCCL restorations with respect to marginal adaptation and marginal staining.

A Retrospective Clinical Study on Factors Influencing the Failure of NCCL Restorations

Objectives

This retrospective study evaluated the factors influencing the clinical failure of noncarious cervical lesion (NCCL) restorations.

Methods

Patients were routinely treated by undergraduate or postgraduate students and randomly received a clinical recall evaluation. A retrospective study was performed with two experienced calibrated examiners to evaluate NCCL restorations, including the critical parameters of retention, caries, marginal discoloration, and marginal integrity. The factors related to the restoration included gender, age, arch site, tooth position, the presence of occlusal wear facets, caries risk, operator, adhesive strategy, and composite. The clinical failure comparison between the parameters and factors was performed using the binary logistic regression analysis.

Results

A total of 460 cervical restorations from 96 patients were evaluated. The adhesive strategy and the presence of occlusal wear facets were the most important factors influencing the parameter failure. Therefore, the highest failure was marginal integrity, in which the gingival marginal integrity failure was 50.7%, and the occlusal marginal integrity failure was 42.4%.

Conclusions

The main factors influencing clinical failure for partial loss, marginal discoloration, and marginal integrity were the adhesive strategy and the presence of occlusal wear facets. Therefore, marginal integrity was the most frequent failure parameter.

Performance of a Universal Bonding System Associated With 2% Digluconate Chlorhexidine in Carious and Eroded Dentin

CLINICAL RELEVANCE

Carious and eroded dentin represent clinical challenges. The use of a universal bonding system, in a self-etching mode, associated with chlorhexidine (CHX) seems to not improve its longevity. This may be attributed to the competition for calcium between the bonding agent functional monomer and CHX.

SUMMARY

Clinical efficacy of universal adhesives for the restoration of noncarious cervical lesions: A randomized clinical trial

Introduction

The efficacy of an adhesive agent is an important aspect in restoring noncarious cervical lesion (NCCL) as studies have proved that compromise in adhesive agent results in reduced bond strength. The purpose of this prospective randomized double-blind clinical trial was to evaluate the efficacy of the newly formulated "universal" dental adhesive in the restoration of NCCLs in permanent dentition using either a self-etch or a selective-etch approach.

Materials and Methods

The study was done following the consolidated standards of reporting trials. 100 NCCLs randomly divided into 2 groups were restored using G-Premio Bond adhesive and Genial flowable composite in selective etch mode and self-etch mode. Restorations were evaluated at 1 week, 6 months, and 12 months using modified US Public Health Service criteria for marginal staining, fracture, and postoperative sensitivity. Statistical analysis was performed using appropriate tests.

Results

Recall rates were 100%, 98%, and 78% at the evaluation time. The result showed that neither the self-etch nor the selective etch mode had significant difference in ALPHA/BRAVO/CHARLIE scores (P > 0.05). Percentage-wise comparison showed less changes reported in the selective etch group compared to self-etch group.

Conclusion

It was concluded that there was no statistical significance between the groups for the parameters evaluated, but selective etch performed better than self-etch group.

Modelling ATR-FTIR Spectra of Dental Bonding Systems to Investigate Composition and Polymerisation Kinetics

Component ratios and kinetics are key to understanding and optimising novel formulations. This warrants investigation of valid methods. Attenuated Total Reflectance Fourier Transform Infra-Red (ATR)-FTIR spectra of separate primers/adhesives were modelled using summed spectra of solvents (water, ethanol), methacrylate monomers (HEMA (hydroxyethyl methacrylate), Bis-GMA (bisphenol A glycidyl methacrylate), and 10-MDP (10-methacryloyloxydecyl dihydrogen phosphate)), and fillers, multiplied by varying fractions. Filler loads were obtained following their separation from the adhesives, by analysing three repetitions (n = 3). Spectral changes during light exposure at 37 °C (20 s, LED 1100-1330 mW/cm2) were used to determine polymerisation kinetics (n = 3). Independent samples T-test was used for statistical analysis (significance level of 5%). FTIR modelling suggested a primer solvent percentage of OBFL (Optibond FL) (30%) was half that of CFSE (Clearfil SE 2) (60%). OBFL included ethanol and water, while CFSE included only water. Monomer peaks were largely those of HEMA with lower levels of phosphate monomers. OBFL/CFSE adhesive model spectra suggested that both contained equal volumes of Bis-GMA/HEMA, with CFSE having 10-MDP. Filler levels and spectra from OBFL (48 wt.%) and CFSE (5 wt.%) were different. Both systems reached a 50% conversion rate within seconds of light exposure. The final conversion for OBFL (74 ± 1%) was lower compared to CFSE (79 ± 2%) (p < 0.05). ATR-FTIR is a useful method to investigate relative levels of main components in bonding systems and their polymerisation kinetics. Such information is valuable to understanding such behaviour.

Performance of MDP-based system in eroded and carious dentin associated with proteolytic inhibitors: 18-Month exploratory study

The aim of this study was to explore the impact of the interaction between an MDP-based universal adhesive system in etch-and-rinse mode and two proteolytic inhibitors on the longevity of restorations bonded to artificially-affected-dentin substrates. 90 sound human third molars were randomly distributed into three groups according to the substrate: N-no challenges-control (stored in artificial saliva), ACD-artificial caries dentin (6 h DE + 18 h-RE/5 days + 48 h RE) and ERO-artificial erosion dentin (3 × 5 min/5 days with orange juice). They were further redistributed according to dentin pretreatment: W- water (control), CHX-2% digluconate chlorhexidine and E64- 5 μM E64-Trans-Epoxysuccinyl-L-Leucylamido-(4-guanidino) butane, which resulted in the following 9 groups (n = 10): N-W, N-CHX, N-E64, ACD-W, ACD-CHX, ACD-E64, ERO-W, ERO-CHX and ERO-E64. All specimens were restored with Adper Single Bond Universal (Etch-and-rinse mode)/Filtek Z250. Sticks (0.64 mm²) were obtained and subjected to microtensile test (μTBS) in a universal testing machine at 0.5 mm/min for 7-days, 6 and 18-month analyses. Failure modes were classified using optical microscopy (40X). Data were statistically analyzed by three-way ANOVA and Tukey tests (p < 0.05). All individual factors (p < 0.0001) and interaction between factors were statistically significant (substrate X pretreatment (p = 0.00093); substrate X time (p = 0.01035) and pretreatment X time (p = 0.0035). Caries-affected substrate was the most compromised one, disregarding the pretreatment. CHX was mostly affected compared with E64 up to 18 months, possibly due to its calcium-dependent mechanism.

[Effects of various surface treatments on the bonding efficacy of noncarious cervical sclerotic lesions]

Noncarious cervical sclerotic lesions (NCSL) are dental cervical lesions with noncarious sclerotic dentine (NCSD), which appears smooth, hard, and either light yellow or dark brown. Most NCSLs are wedge or dish shaped and commonly occur in canines and premolars, leading to dental hypersensitivity and aesthetic defect. The principal treatment is composite resin restoration; however, many clinical problems, such as retention loss, should not be ignored. NCSL's bonding interface includes NCSD and enamel, and interface pre-treatment can promote the bonding effect. This review summarizes current surface treatment methods and their influence on the bonding effectiveness of NCSL to provide guidance for clinical practice.

Evaluation of gap formation at the composite resin-tooth interface after using universal adhesives: In vitro SEM study using the replica technique

The aim of this study was to evaluate gap formation after using two universal adhesives, Peak Universal Bond (P), which contains chlorhexidine and Adhese Universal (A), which contains 10-MDP monomer, and to compare them with two gold standard adhesives. The adhesives were tested in different etching modes, etch-and-rinse (ER) or self-etch (SE), and under thermomechanical loading (TML). Two identical Class V cavities were prepared in each of 30 human third molar teeth, and resin-composite restorations were made. Before and after TML, replicas of the restorations were prepared. Gap formation and their frequency according to the modified classification of Blunck and Zaslansky and the width of the maximum marginal gap (MG) were separately evaluated in enamel and dentin. Gap frequency did not differ significantly only in the enamel before TML, despite the use of different adhesives or etching modes. At both timepoints, the highest MG values were obtained with the Peak Universal Bond self-etch (PSE) group in enamel (6.2 μm before TML, 12.2 μm after TML) and the Peak Universal Bond etch-and-rinse (PER) group in dentine (21.3 μm before TML, 35.5 μm after TML). After TML, there was a significant increase of gap frequency for Adhese universal self-etch (ASE) group and MG values for PER, PSE, ASE groups at the resin-enamel interface, and gap frequency and MG values for all groups at the resin-dentin interface. Universal adhesive with 10-MDP monomer have beneficial effect on the resin-dentin interface, while chlorhexidine may reduce the resistance of the universal adhesive system to oral cavity conditions.

Chemical Interaction and Interface Analysis of Self-Etch Adhesives Containing 10-MDP and Methacrylamide With the Dentin in Noncarious Cervical Lesions

Objectives:

To characterize the chemical interactions and analyze the interface of adhesive systems containing 10-methacryloyloxydecyl dihydrogen phosphate (10-MDP) and N-methacryloyl glycine (methacrylamide) functional monomers with the dentin in noncarious cervical lesions (NCCLs) compared with artificial defects (ADs).

Methods and Materials:

Twenty human teeth with natural NCCLs on the buccal surface were used. Class V cavities, similar to NCCLs, were created on the lingual surface to serve as controls. Teeth were randomly allocated to two groups according to the functional monomer in the adhesive (N=10): G1, 10-MDP; and G2, methacrylamide. NCCLs and ADs were characterized by their mineral composition (MC) and degree of demineralization (DD) using micro-Raman spectroscopy, adhesive/dentin chemical interactions (CIs) were assessed with infrared photoacoustic spectroscopy, and interface morphology was evaluated with scanning electron and light microscopy. MC, CI, and DD data were submitted to Shapiro-Wilk and Student t-tests (p&lt;0.05).

Results:

Compared with ADs, dentin in NCCLs was hypermineralized (p&lt;0.05). In G1, CI, and DD in the first 2 μm, and adhesive projections in NCCLs and ADs interfaces were similar. Additionally, a thin layer of dentin collagen was observed in ADs, while it was hardly present in NCCLs. In G2, although CI could not be identified, changes in the mineral components were observed. The DD in the ADs and NCCLs were statistically similar, while SEM showed a lack of adhesion at NCCLs interface. DD and collagen exposure in the ADs and NCCLs were more pronounced than in G1.

Conclusions:

Results suggest that the G1 adhesive could be applied directly on the superficial sclerotic layer in NCCLs. In contrast, previous cavity preparation should be conducted to improve the micromechanical interaction of G2 with the dentin.