Effects of different re-wetting techniques on dentin shear bond strengths

Critical appraisal. Current usage of glutaraldehyde/HEMA

The use of glutaraldehyde/2-hydroxyethylmethacrylate (HEMA) combinations has been recommended for routine use in restorative dentistry by many authors and opinion leaders. Clinical restorative sites are colonized by bacteria that can contribute to postoperative sensitivity or recurrent caries. The structure of dentin allows for fluid conductance, which has been identified by Brännström as the cause of dentin sensitivity and as well, its water content challenges short- and long-term adhesion. The glutaraldehyde/HEMA combination is stated to be antimicrobial, a flocculating agent that strengthens collagen, and an agent that can create tubular occlusion, thereby reducing postoperative sensitivity by limiting fluid movement without affecting the strength of bonding or adhesive cements. This Critical Appraisal reviews five publications that deal with the various issues and clinical challenges described above, and provides suggestions for additional reading. A Bottom Line summary is provided.

Bond strength of newer dentin bonding agents in different clinical situations

This study compared the tensile bond strengths of different adhesive systems to different dentinal substrate conditions. The adhesive systems used were Adper Single Bond 2 total etch, XP Bond total etch, and two all-in-one adhesives, Adper Easy One and Xeno V. Ninety-six intact human premolars extracted on periodontal or orthodontic grounds were collected and stored in 0.9% physiologic saline for less than four weeks. Teeth were carefully cleaned to remove the soft tissue remnants. The occlusal surfaces were ground until the level of the dentinoenamel junction, exposing superficial dentin using a low-speed diamond disc. A standard smear layer was produced by wet sanding the dentin surface with 600-grit silicon carbide sandpaper for 40 seconds. The 96 specimens were embedded in autopolymerizing acrylic resin and divided into four groups of 24 each based on the dentin bonding agents used. Each group consisted of 24 specimens, which were further divided into two subgroups of 12 specimens each, moist dentin and dentin air-dried for 10 seconds. The regions of interest for adhesion were demarcated in each sample using adhesive tape, with a 4-mm–diameter hole isolating the peripheral region, and each adhesive system was employed. Four adhesive systems, two total etch and two self-etching adhesive, were applied to different dentinal substrates as per the manufacturers' instructions. Following the adhesive application, the specimens were restored with composite material using a metallic mold measuring 5 mm in diameter and 5 mm in height to keep the material in cylindrical form and were light cured per manufacturers' instructions. After being stored for 24 hours in distilled water at room temperature, the specimens were thermocycled for 550 cycles at temperatures ranging from 5°C to 60°C with a dwell time of 15 seconds in each bath and a transfer time of five seconds. The tensile bond strengths were determined using a Universal loading machine (Lloyd Universal Testing Machine) at a cross-head speed of 1 mm/min. On moist dentin, total-etch adhesives showed higher bond strength than did the all-in-one adhesives. Under the dry dentin condition, XP Bond exhibited significantly higher bond strength than did the Adper Single Bond 2 and two all-in-one adhesives, Adper Easy One and Xeno V.

Influence of fluoride- or triclosan-based desensitizing agents on adhesion of resin cements to dentin

Effect of desensitizers on the bond strength of resin cements to dentin was evaluated. Intact premolars (N = 90) were embedded in polymethyl methacrylate; dentin surfaces were exposed, and they were randomly divided into two main groups of cements (Duolink (D), Variolink II (V); n = 45 per group) and then into three desensitizer subgroups (n = 15 per subgroup). Teeth in controls (C) were treated according to cements' adhesion protocols; the other two groups received either fluoride- [Aqua-Prep F (F)] or triclosan-based [Seal&Protect (T)] desensitizers. Ceramic disks (Empress 2) were adhered; specimens were thermocycled (×5,000 cycles, 5-55 ± 1°C, dwell time 30 s) and subjected to shear bond strength test (MPa ± SD) in a universal testing machine (crosshead speed 1 mm/min). Failure types were classified using scanning electron microscope. For V, application of both desensitizers (29.6 ± 7.8 and 22.8 ± 2.8 for F and T, respectively) did not present significantly different results than that of the VC (21.2 ± 2.3; p > 0.05, one-way ANOVA). In D, F (20.6 ± 2.4) showed significantly higher results (p < 0.05) than those in T (16.1 ± 3.9) and DC group (15.2 ± 2.3). V showed significantly higher results than D (p < 0.05, Bonferroni). F and T did not negatively affect the bond strength results with D and V. Adhesive failures were more frequent with both T (84%) and F (66%) in D; cohesive failures in the cement (88%) were more commonly observed with F in V. Both F and T desensitizers can be safely used prior to final cementation but F in combination with V seems to be more reliable, considering both the bond strength and the failure types.

The influence of dental unit waterline cleaners on composite-to-dentin bond strengths

BACKGROUND

One approach to controlling dental unit waterline (DUWL) contamination by microorganisms is the addition of chemical cleaners to the treatment water. Yet, there is concern that these cleaners might affect the bonding of resin-based composites to enamel and dentin. The authors evaluated the influence of DUWL cleaners on composite-to-dentin bond strengths.

METHODS

The authors tested the strength of resin-based composite bonded to dentin in specimens treated with distilled water (control) or one of four cleaners. They tested a total-etch adhesive, a self-etching primer/adhesive and an experimental self-etching primer/adhesive. The authors stored the specimens for 24 hours at 37 C and tested them to determine their bond strengths.

RESULTS

The mean shear bond strengths (SBSs) varied according to the cleaner and adhesive used, ranging from 14.7 to 21.9 megapascals. However, the authors found no statistically significant differences and/or interactions between mean SBSs of specimens treated with the various DUWL cleaners and adhesives (P > or = .05).

CONCLUSIONS

The tested DUWL cleaners did not significantly influence composite-to-dentin bond strengths for the total-etch adhesive and self-etching primer/adhesives used in this study.

CLINICAL IMPLICATIONS

The conclusions imply that bonding of resin-based composites to dentin is not affected by the cleaners tested when they are used to treat DUWL contamination.

Shear bond strength of acetone-based one-bottle adhesive systems

The aim of this study was to assess the shear bond strength of four acetone-based one-bottle adhesive systems to enamel and dentin, and compare to that of an ethanol-based system used as control. Fifty human molars were bisected mesiodistally and the buccal and lingual surfaces were embedded in acrylic resin using PVC cylinders. The buccal surfaces were ground to obtain flat dentin surfaces, while the lingual surfaces were ground to obtain flat enamel surfaces. All specimens were polished up to 600-grit sandpapers and randomly assigned to 5 groups (n=20; 10 dentin specimens and 10 enamel specimens), according to the adhesive system used: One-Step (Bisco); Gluma One Bond (Heraeus Kulzer); Solobond M (Voco); TenureQuik w/F (Den-Mat) and OptiBond Solo Plus (Kerr) (control). Each adhesive system was applied according to the manufacturers' instructions. The respective proprietary hybrid composite was applied in a gelatin capsule (d=4.3mm) and light-cured for 40 s. The specimens were tested in shear strength with an Instron machine at a crosshead speed of 5 mm/min. Bond strengths means were analyzed statistically by one-way ANOVA and Duncan's post-hoc (p£0.05). Shear bond strength means (MPa) (±SD) to enamel and dentin were: Enamel: One-Step=11.3(±4.9); Gluma One Bond=16.3(±10.1); Solobond M=18.9(±4.5); TenureQuik w/F=18.7(±4.5) and OptiBond Solo Plus=16.4(±3.9); Dentin: One-Step=6.4(±2.8); Gluma One Bond=3.0(±3.4); Solobond M=10.6(±4.9); TenureQuik w/F=7.8(±3.9) and OptiBond Solo Plus=15.1(±8.9). In enamel, the adhesive systems had statistically similar bond strengths to each other (p>0.05). However, the ethanol-based system (OptiBond Solo Plus) showed significantly higher bond strength to dentin than the acetone-based systems (p£0.0001). In conclusion, the solvent type (acetone or ethanol) had no influence on enamel bond strength, but had great influence on dentin bonding, which should be taken into account when choosing the adhesive system.

Adhesive Dentistry and Endodontics: Materials, Clinical Strategies and Procedures for Restoration of Access Cavities: A Review

The complexity of restorative dentistry has increased greatly in recent years, with the myriad of products used in "adhesive dentistry." So too has the "simple" matter of restoring access cavities after completion of endodontic treatment. This review discusses current methods of "bonding" to tooth structure, ceramic materials, and metals, with emphasis on those aspects that are important to endodontics. Specific materials, procedures and major decision making elements are discussed, as well as how to avoid problems in compatibility between endodontic and restorative materials.

The effect of short-term calcium hydroxide treatment on dentin bond strengths to composite resin

The purpose of this study was to evaluate the influence of calcium hydroxide (Ca(OH)2) treatment on the bond strengths to dentin of a resin-based composite material. Two distinct dental adhesives, Prime & Bond (P&B) NT and Single Bond (SB) were used. One hundred and twenty-seven bovine incisors were mounted in acrylic, ground flat to expose middle dentin, polished to 600-grit, and randomly assigned to 10 groups: (i) 0 days, no Ca(OH)2, P&B NT; (ii) 7 days, no Ca(OH)2, P&B NT; (iii) 7 days, Ca(OH)2, P&B NT; (iv) 30 days, no Ca(OH)2, P&B NT; (v) 30 days, Ca(OH)2, P&B NT; (vi) 0 days, no Ca(OH)2, SB; (vii) 7 days, no Ca(OH)2, SB; (viii) 7 days, Ca(OH)2, SB; (ix) 30 days, no Ca(OH)2, SB; (x) 30 days, Ca(OH)2, SB. All specimens were stored in an incubator at 37 degrees C. Specimens were then retrieved and the dentin surface was rinsed with air/water spray from a triple syringe. Dentin was etched with 37% phosphoric acid (PA) for 15 s, rinsed, blot dried, and coated with adhesive according to manufacturer's instructions. The adhesive was light cured for 10 s, and Filtek Z250 was applied to the surface with a #5 gelatin capsule and light cured for 160 s. Shear bond strengths were measured for each specimen in an Instron unit at a cross-head speed of 0.5 mm min(-1). The data were subjected to anova and Duncan post-hoc tests. Mean shear bond strengths for P&B NT ranged from 8.02 to 11.79 MPa. There was no significant difference between P&B NT groups treated with or without Ca(OH)2 at any time interval. Mean shear bond strengths for SB ranged from 14.70 to 19.54 MPa. No significant difference was found between SB groups treated with or without Ca(OH)2 at 7 days. At 30 days, SB with Ca(OH)2 was significantly higher than SB without Ca(OH)2. Short-term Ca(OH)2 treatment had no detrimental effect on dentin bond strengths to the ethanol or acetone-based adhesive resin systems tested.

In vivo influence of residual moisture on microtensile bond strengths of one-bottle adhesives

PURPOSE

This study evaluated the microtensile bond strengths of three dentin adhesives applied on clinically moist dentin or on dentin that was dried with air for 5 seconds. The null hypothesis to test was that the level of residual moisture does not influence bond strengths when restorations are placed in vivo.

MATERIALS AND METHODS

Twenty-four premolars scheduled to be extracted for orthodontic reasons from patients between the ages of 15 and 23 years were restored with one of the following adhesive systems followed by a mini hybrid composite resin: Excite (Ivoclar/Vivadent), an ethanol-based dentin adhesive; Prime & Bond NT (Dentsply/Caulk), an acetone-based dentin adhesive; and Single Bond (3M ESPE), an ethanol and water-based dentin adhesive. After extraction, the specimens were sectioned with a slow-speed diamond saw in two perpendicular directions to obtain sticks with a cross-section of 0.7 +/- 0.2 mm2. The specimens were attached to a Geraldeli device and fractured using a universal testing machine at a crosshead speed of 1 mm per minute.

RESULTS

For each dentin adhesive, there were no statistical differences between means for dry dentin versus moist dentin. Single Bond and Prime & Bond NT ranked in the same statistical subset regardless of the moisture condition of the substrate. Both Excite, dry, and Excite, moist, resulted in statistically lower bond strengths than Single Bond, moist, but similar to those of Single Bond, dry, Prime & Bond NT, moist, and Prime & Bond NT, dry.

CLINICAL SIGNIFICANCE

In this study, the level of residual moisture did not influence microtensile bond strengths. Clinically, the degree of moisture left on the dentin surface upon rinsing off the etching gel may not be as relevant as previously reported in laboratory studies.

Effects of phosphoric acid and glutaraldehyde-HEMA on dentin collagen

The purpose of this study was to evaluate the effects of phosphoric acid (PA) and a proprietary glutaraldehyde-HEMA aqueous solution (Gluma Desensitizer; GD) on dentin collagen. Specimens of demineralized bovine dentin collagen were treated with either 37% or 50% PA for 1 or 5 min. An additional set of specimens was treated with 37% PA for 1 min followed by GD for 1 min. All specimens were washed with distilled water, lyophilized. reduced with standardized NaB3H4, hydrolyzed with 6 M HCl and subjected to amino acid and cross-link analyses. The results demonstrated that the treatment of demineralized dentin with PA under the conditions tested did not significantly alter the collagen cross-links. The GD-treated samples showed reduction of free lysine (Lys) and hydroxylysine (Hyl) residues, as well as a decrease in the levels of collagen reducible cross-links. In addition, unidentified reducible compounds were detected by high-performance liquid chromatography (HPLC) analysis. These compounds may be derived from cross-links formed between GD-derived aldehyde and Lys/Hyl of collagen. The findings indicate that PA treatment does not significantly affect dentin collagen amino acid and cross-link composition, and that GD treatment affects dentin collagen amino acid and cross-link composition.