The Journal of Adhesive Dentistry, 03/2019

Purpose: To compare after five-year simulated pulpal pressure (SPP) the degradation of adhesive-dentin interfaces created using two simplified adhesives applied with different bonding strategies. Materials and Methods: A two-step self-etch (CSE: Clearfil SE Bond) adhesive was used as a control multistep adhesive. The tested experimental materials were two simplified adhesives, a one-step self-etch (CS3: Clearfil S3 Bond) and a self-priming etch-and-rinse adhesive (SB2: Adper Single-Bond 2). Half of the bonded specimens were submitted to microtensile bond strength (µTBS) testing after 24 h. The other half submitted to SPP for five years before µTBS testing. Nonfractured sticks were evaluated using transmission electron microscopy (TEM). Scanning electron microscopy (SEM) was used to evaluate silver-nitrate nanoleakage within the interface. Data were statistically analyzed by two-way ANOVA and Tukey's test (p < 0.05). Results: Prolonged SPP induced bond-strength reduction for both SB2 and CS3. All bonding approaches showed increased nanoleakage after aging. The two simplified adhesives showed severe degradation at the resin-dentin interface. TEM revealed that the main degradation patterns for the etch-and-rinse adhesive SB2 was collagen breakdown, while polymer hydrolysis along with filler debonding was mainly observed in CS3. Conclusions: Simplified adhesives applied in etch-and-rinse mode are mainly characterized by hydrolysis and collagen degradation. In self-etch mode, simplified adhesives may principally show hydrolysis of the polymeric matrix and/or at the interface of fillers and coupling agent. The use of multistep self-etching adhesives may guarantee greater dentin bond durability compared to simplified adhesives. Keywords: aging, dentin, bond strength, electron microscopy, pulpal pressure

Purpose: To investigate the tensile bond strength of silane-containing universal adhesives and self-etch glass-ceramic primer to lithium disilicate glass ceramics (LS2). Materials and Methods: 960 rectangular LS2 bars (7 mm x 3 mm x 9 mm, IPS e.max CAD, Ivoclar Vivadent) were manufactured and divided into 4 groups (n = 240). Group 1 was etched with ~5% hydrofluoric acid (HF) for 20 s (VITA Ceramics Etch, Vita Zahnfabrik), group 2 was etched with ~5% HF for 20 s and silanized (ESPE Sil, 3M Oral Care), group 3 was pre-treated with a self-etching glass-ceramic primer (Monobond Etch & Prime, Ivoclar Vivadent, and group 4 received no pre-treatment. Three universal adhesives (iBOND Universal, Heraeus Kulzer; Scotchbond Universal Adhesive, 3M Oral Care; Futurabond U, Voco) were applied to the differently pre-treated surfaces, with Heliobond (Ivoclar Vivadent) serving as control. The bars from each group were paired and luted perpendicularly, forming a square bonded area of 9 mm2, using Variolink II (Ivoclar Vivadent) with a constant pressure of 10 N, followed by light curing (40 s at 800 mW/cm2, Elipar Trilight, 3M Oral Care). The resulting specimens were stored for 24 h at 37°C in distilled water. Half of the specimens of each group were submitted to tensile bond strength testing, the other half were thermocycled ([TC] 5000 cycles, 5°C/55°C, 30-s dwell time) before testing. Data were analyzed using three-way ANOVA (α = 0.05). Results: Group 2 (HF etched and silanized) and group 3 (self-etching glass-ceramic primer) reached significantly higher mean bond strengths than did groups 1 (only HF etched) and 4 (no pre-treatment). Conclusion: Additional silanization of HF-etched LS2 statistically signficantly improved the tensile bond strength of the silane-containing universal adhesive (Scotchbond Universal). The self-etching glass-ceramic primer Monobond Etch & Prime achieved mean bond strengths that did not differ significantly from HF-etched and silanized specimens. Keywords: silanization, universal adhesive, lithium disilicate ceramic, tensile bond strength, self-etch glass ceramic primer

Purpose: To compare the remineralization potential of Clinpro Tooth Crème (CTC C, 3M Oral Care) containing functionalized tricalcium phosphate (fTCP), Tooth Mousse (TM, GC) containing casein phosphopeptide amorphous calcium phosphate (CPP-ACP), and Tooth Mousse Plus (TMP, GC) containing casein phosphopeptide amorphous calcium phosphate with fluoride (CPP-ACPF) and their effects on the shear bond strength (SBS) of orthodontic brackets to enamel. Materials and Methods: In Part I of the study, 51 premolars were divided into 3 groups: 1: fTCP; 2: CPP-ACP; 3: CPP-ACPF. Artificial carious lesions were created and immersed in remineralizing solution for 30 days. Specimens were evaluated using Knoop microhardness and transverse microradiography. The percentage of surface hardness recovery (%SHR), change in lesion depth (∆LD), and mineral loss (∆∆Z) were analyzed using one-way ANOVA. In Part II of the study, 80 premolars were divided into 5 groups: A: brackets bonded to sound enamel; B: brackets bonded to demineralized enamel (DE); C-E: demineralized enamel immersed in remineralizing solution containing fTCP (group C), CPP-ACP (group D), or CPP-ACPF (group E) before bracket bonding. The SBS of half of the specimens were tested immediately, while the other half were tested after thermocycling. Data were analyzed using two-way ANOVA. Results: TMP showed significantly higher %SHR, ∆LD and ∆∆Z compared to the other groups (p < 0.05). Both control and TMP had the highest SBSs and demineralized enamel the lowest, irrespective of thermocycling. No significant difference in SBS was found between TM and TMP after thermocycling. Conclusions: Tooth Mousse Plus achieved significant remineralization of artificial enamel carious lesions without adverse effect on shear bond strength of orthodontic brackets to remineralized enamel. Keywords: calcium and phosphate-based agents, enamel bonding, orthodontic brackets, remineralization

Purpose: To investigate the use of a cold atmospheric plasma (CAP) source in a clinically realistic endodontic procedure to enhance the bond strength of a dental adhesive in root canal restoration. Materials and Methods: CAP was generated by a handheld DBD-jet prototype specifically designed for biomedical applications. Extracted monoradicular teeth were standardized through crown sectioning and root canal shaping before being embedded in epoxy resin cylinders using a custom molding procedure designed to ensure the accurate alignment of the specimens. Afterwards, the dentin surface was conditioned according to different protocols including (or not, in controls) chelating agents (EDTA or IP6) and CAP treatment (180 s). Then a self-etch adhesive was applied, followed by a luting material to seal the root canal. Both materials were light cured. Tooth sections were obtained from coronal and middle portions of the root canal, and the push-out test was used to evaluate the bond strength between the adhesive and dentin. Results: Push-out results demonstrated that plasma treatment greatly improved (> twofold) the mechanical properties of the adhesive-dentin interface along the whole length of the root canal. Contact angle measurements and SEM analyses showed that plasma treatment facilitated adhesive permeation into dentinal tubules, hence enhancing the effects of the bonding procedure. Conclusions: Although investigations on long-term bond stability after CAP treatment and clinical studies are required, the present study indicates that CAP devices may be useful in clinical endodontic treatment. Keywords: adhesion enhancement, adhesion to dentin, adhesive, cold atmospheric plasma, dental restorations, endodontic adhesion, push-out bond strengths, root canal therapy

Purpose: To present a new method for the closure of single-tooth gaps using metal-, ceramic-, and glass-fiber-free direct composite cantilever restorations. Materials and Methods: The new technique is described step by step in a case report, showing the creation and adhesive bonding of a single-retainer composite pontic. Furthermore, six cases are reported with radiological and clinical follow-up assessments over a period of one to three years after gap closure. Results: Excellent outcomes were observed clinically and radiologically. No failures due to material properties (such as composite fractures, chipping) or esthetic limitations through discoloration were observed. Due to good oral hygiene, no periodontal complications were found during the observation period. Conclusions: This new minimally invasive procedure expands the therapeutic spectrum for the management of single-tooth gaps. It does not require laboratory-fabricated restorations and can be considered when conventional treatments, such as fixed dental prostheses or implants, are not options for medical reasons or due to special patient preferences. Keywords: new restorative method, noninvasive technique, direct resin composite, cantilever design, direct composite buildups, single-tooth gap

Purpose: To evaluate the clinical performance of a flowable bulk-fill composite vs a compomer in Class II cavities of primary molars. Materials and Methods: In a clinical study, 100 restorations were placed in two randomly assigned comparable Class II cavities in 32 children (aged 6.7 ± 1.2 years) with at least one bulk-fill composite (Venus Bulk Fill, Heraeus Kulzer) and one compomer (Dyract eXtra, Dentsply). After caries excavation, the adhesive Scotchbond Universal (3M Oral Care) was applied in self-etching mode. According to the manufacturer's instructions, Venus Bulk Fill was used for the entire Class II cavity of primary molars without a cover layer. After visible-light curing, both restorations were finished and polished. Both restorative materials were evaluated at baseline and after one year, including esthetic, functional, and biological parameters, using the FDI criteria. The Mann-Whitney U-test was used to determine the difference in the complete scores at baseline and after one year (p < 0.05). Results: After one year, 99 restorations were reevaluated; one tooth had exfoliated physiologically. Concerning the esthetic parameters, Dyract eXtra showed slightly higher scores than Venus Bulk Fill. Both materials showed similar scores regarding functional and biological parameters. No severe postoperative sensitivities or side-effects were reported. There was no statistically significant difference between the performance of Venus Bulk Fill and Dyract eXtra for primary molars. Conclusion: The flowable bulk-fill composite Venus Bulk Fill can be considered as an alternative material for clinical use in primary teeth, but longer-term studies might still be needed. Keywords: Class II restoration, clinical study, compomer, flowable bulk-fill composite, one-step adhesives, pediatric dentistry, restorative materials

Purpose: To evaluate the bond strength (BS), nanoleakage, and marginal adaptation (MA) of three bulk-fill and one conventional composite, submitted or not to mechanical and thermal cycling. Materials and Methods: Ninety-six molars were selected and 4-mm-deep class I cavities were prepared and restored. Half of the teeth were submitted to mechanical and thermal cycling (MTC). Teeth were divided into 8 groups (n = 12), according to the composite used - Filtek Z350 XT (Z350), Tetric N-Ceram Bulk Fill (TET), Filtek Bulk Fill Posterior Restorative (FBF) and SonicFill (SF) - and aging, submitted or not to MTC. Fifty-six teeth (n = 7) were used for bond-strength testing, which was performed on stick-shaped specimens obtained from the restored area. Two sticks per tooth were selected to assess nanoleakage. For MA analysis, 40 teeth (n = 5) were sectioned parallel and perpendicular to the occlusal surface and resin-based replicas from the obtained surfaces were prepared. Fracture pattern, nanoleakage, and MA were evaluated using SEM. Quantitative analysis of nanoleakage and MA were performed with ImageJ software. Data obtained were submitted to two-way ANOVA and Tukey's test (ɑ = 0.05). Results: TET presented good MA and higher values of BS when compared to SF. Z350 and FBF presented poorer MA and lower BS, which was statically similar to the other groups. SF obtained the best MA values. Regarding nanoleakage, the highest values were obtained for TET, which differed significantly from the other groups, which presented similar results among themselves. Aging by MTC solely affected MA. Conclusion: Bulk-fill composites presented similar performance to the conventional nanocomposite and remained stable when aged. Keywords: bond strength, bulk-fill composites, composite resins, marginal adaptation, nanoleakage

Purpose: The purpose of the present in vitro study and survey was to compare the masking ability and the penetration capacity of three resin composite sealers as well as a resin infiltrant in shallow artificial caries lesions. Materials and Methods: Panels of artificial initial caries lesion with an average depth of 200 µm were created on buccal and lingual surfaces of 75 extracted human molars. Specimens were randomly assigned to 5 groups: ICON (DMG America), Biscover LV (Bisco), Optiguard (Kerr Hawe), Permaseal (Ultradent), and control (no treatment). Teeth were hemi-sectioned yielding two halves, each with a panel of artificial caries lesion. Lesions on one hemi-section were used to assess the esthetic improvement following caries lesion penetration with the 4 resins based on photographs evaluated using a 100-mm visual analogue scale (VAS) by 17 raters. Lesions on opposite hemi-sections were used to measure the resin penetration area percentage (PA%) and the resin penetration depth percentage (PD%) visualized using a confocal laser scanning microscope (CLSM, Leica). Results: ICON, Optiguard, and Permaseal yielded significantly greater average VAS scores compared to Biscover. The mean PA% and PD% were significantly higher for ICON, intermediate for Optibond and Permaseal, and significantly lower for Biscover. A moderately large positive correlation was noticed between the average VAS scores and the penetration measures. Conclusion: All the resin sealers (Biscover, Optiguard, and Permaseal) penetrated the artificial initial caries lesions. However, ICON resulted in the deepest penetration and the largest penetration area percentages. The masking ability of Optiguard and Permaseal of the artificial caries lesions was similar to ICON. Keywords: initial caries lesion, resin infiltration, resin composite sealers

Purpose: In order to provide an experimental basis for the use of baicalein (BAI) as an enzyme inhibitor to improve resin-dentin bonding durability, this study explored the effect of BAI on the expression of matrix metalloproteinases (MMPs) and cathepsins in human dental pulp cells (HDPCs). Materials and Methods: The effects of various concentrations of BAI on the viability and cell cycle arrest of HDPCs were investigated in vitro. qPCR and Western blot analysis were performed to determine the effects of BAI on the expression of MMP-2, MMP-9, cathepsin-B, and cathepsin-K in HDPCs. Thermocycling (aging) was performed to determine the effect of BAI on the microtensile bond strength of aged resin-dentin bonding. Results: Our results showed that BAI at concentrations below 25 μmol/l did not affect cell viability in HDPCs. Moreover, low concentrations of BAI effectively inhibited the expression of MMP-2, MMP-9, cathepsin-B, and cathepsin-K in HDPCs and improved the strength of aged resin-dentin bonding. Conclusion: BAI is a promising preconditioner for improving the durability of resin-dentin bonding by protecting against collagen degradation via the inhibition of MMPs and cathepsins. Keywords: baicalein, matrix metalloproteinases, cathepsins, human dental pulp cells, resin-dentin bonding

Purpose: To evaluate the bond strength to dentin produced by experimental adhesives formulated with an elastomeric methacrylate monomer (EMM) and an alternative initiator system based on a Thioxanthone derivative (QTX). Materials and Methods: A self-etching primer was used. For the bonding resin, a model adhesive (G1) was formulated containing bis-GMA/TEG-DMA/HEMA (co-monomeric blend) + CQ/EDAB (initiator system). The other groups were formulated by adding to this formulation: EMM only (G2), QTX (G3), or EMM and QTX (G4). Clearfil SE Bond was used as the commercial control group. Fifty bovine teeth (n = 5) were restored with each one of the five adhesives. After restorative procedures, half of the specimens were stored in distilled water at 37°C for 24 h. The other half was fixed on a metal stub and subjected to 200,000 mechanical (50 N loading at 2 Hz frequency) and 1000 thermal cycles (5°C and 55°C). Afterwards, specimens were serially sectioned into beams and tested in tension until fracture. Bond strengths were statistically analyzed by two-way ANOVA and Tukey's test (α = 5%). Results: After 24 h, significantly higher µTBS was observed for the formulation containing EMM and QTX (G4) when compared to Clearfil SE Bond (p < 0.05). No significant differences in µTBS were detected among the experimental groups after 24 h (p>0.05). After thermomechanical cycling, no significant differences were observed among groups. Conclusion: The addition of EMM and QTX can be considered as possible alternative in dental adhesive formulations. Keywords: adhesives, microtensile bond strength, thermomechanical load cycling, thioxanthone