The Journal of Adhesive Dentistry, 02/2005

To develop and validate a software program which automatically detects gaps of cylindrical fillings in bovine dentin by using an optical sensor (FRT MicroProf), evaluate 8 different adhesive systems with the defined parameters, and compare the results with that of SEM quantitative marginal analysis. An optical measuring head with strong wavelength dependency on its focal length splits white light into its colors. The surface height can be measured from the wavelength of the reflected light (resolution: x/y 1 to 2 µm, z 10 nm). A profile of the surface is taken by scanning the measuring point radially from the center of the filling over the restoration margins. An algorithm detects gaps and calculates their depths and widths. Eight adhesive systems (AdheSE, Clearfil SE, Excite, iBond, Optibond Solo Plus, Prompt L-Pop, Touch and Bond, Xeno III) were applied in cylindrical cavities (n = 8, Ø = 4 mm, depth 2.5 mm, C-factor 3.5) in bovine dentin together with Tetric Ceram. In the control group, no adhesive system was used. After 24 h of storage in distilled water at 37°C, the surface was polished with 4000-grit abrasive paper, and then epoxy resin replicas were produced. The evaluation criteria were as follows: the percentage of continuous margin along the entire margin (SEM, 500X) and the percentage of gap-free profiles to total profiles (FRT MicroProf), the latter being evaluated by using 100, 300 and 1000 profiles per sample. Two groups (Touch and Bond, Optibond Solo Plus) with 16 samples were selected to evaluate reproducibility and the occurrence of voids adjacent to the restoration margins. For each adhesive, a paired t-test was applied to evaluate the differences between both test methods for each adhesive. A linear regression analysis procedure was used to evaluate the overall agreement between the two test methods. The mean deviation between three consecutive measurements was 2.75%. Ten percent of all profiles showed voids adjacent to the restoration margins; 92% of the voids were excluded by setting the threshold value of the gap width at 20 µm. In less than 1% of the profiles, the concurrent presence of gap and void resulted in the nondetection of gaps. It was found that 100 profiles per sample are sufficient to characterize a sample as compared to SEM analysis. Except for the control group, the paired t-test did not reveal any statistically significant difference between the two test methods for either adhesive (p 0.05). Regression analysis for all 72 data points yielded R² = 0.72 (p 0.0001). The results of the quantitative marginal analysis by means of the FRT optical sensor are comparable to those obtained by SEM. The advantages of this method include (1) saving of operator time, (2) independence of operator's experience and bias, and (3) additional information about the gap width and depth. Keywords: marginal analysis, restoration, optical sensor, adhesive systems

The aim of this investigation was to determine the hydrolytic stability of conventional methacrylates in comparison with a new acrylic ether phosphonic acid and a bis(acrylamide) cross-linking monomer under acidic aqueous conditions and to confirm the potential of these new monomers as components in a self-etching enamel-dentin primer, based on shear bond strength measurements. Two new monomers were synthesized, an acrylic ether phosphonic acid and a bis(acrylamide). Characterization of the two monomers was carried out by ¹H-NMR, and ¹³C-NMR spectroscopy and of the phosphonic acid by ³¹P-NMR spectroscopy. The hydrolytic stability of these monomers was evaluated by ¹H-NMR spectroscopy or high performance liquid chromatography (HPLC), and was compared with the hydrolytic stability of conventional adhesive methacrylates, ie, MDP, 4-META, TEGDMA and GDMA. Shear bond strength to enamel and dentin was determined using the acrylic ether phosphonic acid and bis(acrylamide) formulated into what is now being marketed as a self-etching primer (AdheSE, Ivoclar Vivadent), and compared with the total-etch adhesives Prime & Bond NT (Dentsply) and Excite (Ivoclar Vivadent) and the self-etching systems One-Up Bond F (Tokuyama), Touch & Bond (Parkell), i-Bond (Heraeus Kulzer), Prompt-L-Pop (3M ESPE), and Clearfil SE Bond (Kuraray). Initial and 24-h bond strength values of AdheSE were compared with those after 16 weeks of storage at 42°C. Stability studies have shown that conventional methacrylate monomers undergo rapid hydrolysis under acidic aqueous conditions (up to 90% degradation after 16 weeks at 42°C). However, the newly formulated strongly acidic acrylic phosphonic acid and cross-linking bis(acrylamide) are stable under these conditions. Moreover, a self-etching enamel-dentin primer based on these new monomers showed high bond strength values. The shelf life of dental adhesives can be increased by using ether- or amide-linked polymerizable analogues instead of conventional, less stable ester derivatives. This should improve the performance of adhesive bonds made with these more hydrolytically stable comonomers. Keywords: self-etching primer, hydrolytic stability, methacrylate, phosphonic acid, bis(acrylamide)

To measure the buffering capacity of self-etching adhesive systems and to evaluate the effect of smear layer thickness on the mean gap width (GW) and microtensile bond strength (µBS) to dentin of these self-etching adhesives. Clearfil SE Bond (SE), Optibond Solo Plus Self-Etch Primer + Optibond Solo Plus (SO), Tyrian Self Priming Etchant + One Step Plus (TY) and as controls, Single Bond (SB) and ScotchBond Multi-Purpose Plus (SC) were used with Filtek Z250 Universal Restorative. The self-etching primers and 35% phosphoric acid (0.5 ml) were titrated by adding successive 0.05 ml drops of NaOH (1N). Thirty molars (n = 5) were sectioned in halves upon which thick (60-grit SiC) and thin (600-grit SiC) smear layer surfaces were produced. The adhesive application was randomized (n = 6) and a resin buildup was made. After 24 h, the resin-dentin sticks (0.8 mm2) were prepared. The GW on the sticks was measured at 400X magnification before the microtensile test (0.5 mm/min). The microtensile bond strength index was calculated including the relative failure type contribution. Data were analyzed by a two-way ANOVA and Tukey's multiple comparison. Simple linear regression was performed to determine whether correlation existed between µBS and pH, GW and pH, and µBS and GW. Only the factor "adhesive" significantly effected µBS (p = 0.001). TY had the lowest µBS values. Regarding GW, both main factors adhesive (p = 0.0001) and smear layer thickness (p = 0.03) were significant. The highest mean gap width was observed for SE and under a thick smear layer. A linear relationship was observed between the pH and GW and pH and µBS; however, a significant positive correlation was detected only between pH and GW (R = 0.99, p = 0.02). No relationship between µBS and GW was found (R = 0.04, p = 0.77). Although the smear layer thickness had no effect on resin-dentin bond strength, thick smear layers adversely affected the mean gap width. The µBS values were not affected by the acidity of self-etching primers; however, more aggressive self-etching primers showed the lowest mean gap width. The etch-and-rinse adhesive systems showed higher µBS and lower mean gap widths. Keywords: smear layer thickness, pH, microtensile bond strength, gap, dentin, self-etching, etch and rinse, adhesive system

The objective of this study was to verify the effect of cyclic compressive loading on the shear bond strength of an adhesive system following collagen removal. Sixty bovine teeth were divided into 4 groups based on the adhesive procedure used: groups 1 and 2 - etching with 35% phosphoric acid and application of the Single Bond adhesive system; groups 3 and 4 - after etching, a 10% sodium hypochlorite solution was applied for 1 min before the application of the adhesive. In all the specimens, a Z100 resin cylinder was built up over the bond area. Groups 2 and 4 were submitted to 500,000 cycles with a load of 100 N. The mean values for the shear bond test (MPa) were: group 1: 7.37 ± 1.15; group 2: 5.72 ± 1.66; group 3: 5.95 ± 1.21; group 4: 3.66 ± 1.12. There was no difference between groups 1 and 2 (p > 0.01). Between groups 1 and 3, 2 and 4, and 3 and 4 there was a significant difference (p 0.01). The majority of the specimens demonstrated an adhesive failure. The application of sodium hypochlorite on dentin decreased the values of shear bond strength, as did the load cycling in the group treated with sodium hypochlorite. Keywords: adhesive system, collagen removal, sodium hypochlorite, bond strength

Simple changes to bonding technique can improve resin-dentin bond strengths. The objective of this study was to evaluate the effects of multiple coatings of two all-in-one adhesive resins on both microtensile bond strength (µTBS) and nanoleakage. The mid-coronal occlusal dentin of extracted human molars was used. Two all-in-one adhesives - iBond (Heraeus Kulzer) and Xeno III (Caulk Dentsply) - were applied to 320-grit abraded dentin surfaces. In groups 1 and 3 during bonding, monomer application and solvent evaporation were done 1, 2, 3, 4 or 5 times on the dentin surface before light curing. In groups 2 and 4 after light curing the first layer, the adhesive was re-applied, the solvent evaporated, and the layer light cured. This was repeated from 2 to 5 times, followed by creation of composite buildups. After 24 h storage in 37°C water, the teeth were sectioned perpendicular to the adhesive interface to produce multiple beams of composite-bonded dentin, approximately 0.9 mm² in area. These were tested to failure in tension. Data were evaluated by three-way ANOVA (material vs coatings vs light curing) followed by multiple comparisons at α = 0.05. Additionally, nanoleakage of silver uptake and adhesive layer thickness were evaluated using transmission electron microscopy (TEM). The results indicated that bond strengths increased with the number of coatings (p 0.0001) with both adhesives, up to 3 layers, especially if each layer was light cured. Nanoleakage of silver tended to decrease with each coat in both adhesive systems. By simply applying more coats of adhesive, the strength and quality of dentin adhesion can be improved. Keywords: all-in-one adhesives, dentin bond strength, nanoleakage, multiple coatings

To evaluate the cumulative loss of mass of two-step solvent-based adhesives, examine the effect of prolonged application time on the resin-dentin microtensile bond strength (µTBS), and correlate the µTBS with the evaporation rate of adhesive systems. An ethanol/water based (Single Bond: SB) and an acetone-based system (One Step: OS) were employed. Approximately 16 µl of each product was transferred to a small glass container and placed in an analytical balance. The cumulative loss of mass (CLM) was determined in every minute for 5 min to the nearest 0.0001 mg and again after 20 min (n = 4). For the µTBS test, a flat superficial dentin surface was exposed in 24 human third molars by wet abrasion. The adhesives were applied to a delimited area of 52 mm² on wet surfaces, for 40, 90, and 150 s. Four teeth were assigned to each experimental group. Composite crowns were constructed incrementally. After storage in water at 37°C for 24 h, teeth were sectioned to obtain sticks with cross-sectional areas of 0.8 mm² to be tested in tension (0.5 mm/min). The CLM (%) for both adhesives was compared using a Student-t test at each minute (α = 0.05). The µTBS values were analyzed by two-way ANOVA and Tukey's test (α = 0.05). The CLM for OS was higher than for SB during the first 5 min, but these values were only statistically different at minutes 3, 4, and 5 (p 0.05). A CLM of approximately 50% was observed for both adhesive systems after 20 min. The factor application duration and the interaction between application duration and adhesive were significant (p 0.05). The increase in the application duration led to an increase in µTBS for both systems; however, the differences were only statistically significant for OS over the 150 s period (p 0.05). A strong correlation was found between the µTBS and the cumulative loss of mass of adhesives. Prolonged application times can increase the resin-dentin µTBS of two-step adhesive systems, but the application duration is dependent on the solvent present in the bonding system. Keywords: dentin bonding, priming time, microtensile bond strength, solvent evaporation

The aim of this study was to investigate the intra- and intertooth microtensile bond strength variability of two adhesive systems applied to dentin. Twenty human third molars were ground to expose a flat dentin surface. Two adhesive systems (Single Bond and One Step) were applied according to the manufacturers' instructions and composite resin crowns were constructed incrementally. After 24 h in distilled water at 37°C, each tooth was longitudinally sectioned in both "x" and "y" directions under 300 rpm to obtain sticks with a cross-sectional area of 0.8 mm². The sticks from each tooth were tested at a crosshead speed of 0.5 mm/min. The fracture pattern of each stick was microscopically analyzed after debonding (400X). A mixed model with adhesive as a fixed variable, tooth as a random variable, and bonded area included as a covariate, was employed for the data treatment. In this model, all observations have the same variance, which is the sum of two components: the variance of the random effect (intertooth) and the variance of the errors (intratooth). The intratooth variability was greater than the intertooth variability. The intratooth variability is higher than the intertooth variability. Sticks from the same tooth cannot be considered as an experimental unit, since it does not fulfill all ANOVA requirements. Keywords: adhesive systems, sticks, regional variation, microtensile bond strength, statistical analysis

Repair of worn, broken or discolored composite restorations can be accomplished using new composite material and dentin bonding systems. The purpose of this study was to investigate the effectiveness of self-etching adhesive systems for composite re-bonding procedures onto different composite substrates that had been aged for 6 years prior to testing. Two hundred cylinders (4 mm x 5 mm) of composite were fabricated using 4 hybrid composites [AeliteFil (Bisco), Prodigy (SDS Kerr), TPH (Dentsply Caulk), and Z100 (3M ESPE)] following manufacturers' directions and stored for 6 years in 1% NaCl solution. After aging, each specimen was wet polished through 600-grit SiC and randomly assigned to a self-etching bonding system (Adper Prompt L-Pop/Z100 [3M ESPE]; Tyrian One-Step Plus/AeliteFil [Bisco]; OptiBond Solo Plus SE/Prodigy [SDS Kerr], Xeno III/TPH [Dentsply Caulk]) or a total-etch control (Prime&Bond NT/TPH [Dentsply Caulk]) (n = 10 per group). Shear bond strengths (SBS) for repairs were evaluated after 48 h (crosshead speed = 0.5 mm/min) and were compared by two-way ANOVA (p = 0.05) with Tukey post-hoc tests. Significant differences (p = 0.05) were detected for the main effects (substrates and bonding systems), but the interaction was not significant. SBS for bonding systems were from highest to lowest: (1) Prime&Bond NT, (2) OptiBond Solo Plus SE, (3) Adper Prompt L-Pop, (4) Xeno III, (5) Tyrian One-Step Plus. SBS of the repair systems to Z100 were significantly lower than those to the other composite substrates. Self-etching systems can be used to repair aged composite, but the efficacy of repair of aged composite is system dependent. Keywords: self-etching, composite repair, re-bonding, bond strength

Nonrestored devitalized teeth are structurally compromised and represent one of the greatest challenges for the clinician. Restoration of endodontically treated teeth has been associated with the use of posts. Various post materials and designs have been introduced over the years; however, motivated by the desire to conserve the remaining sound tooth structure and thanks to properties of modern adhesive systems, clinicians have re-evaluated the dogma of traditional restorative dentistry and seek alternative methods to build up devitalized teeth. The use of direct Ultra High Molecular Weight Polyethylene (UHMWPE) fiber-reinforced post systems is becoming popular among clinicians because enlargement of the root canal space is not required and the risk of root perforation eliminated. This article presents an experimental clinical technique to reconstruct severely damaged endodontically treated posterior teeth using direct fiber reinforced post systems. Particular attention is paid to the incremental and curing techniques adopted to build up the restoration. The problems that clinicians can encounter in bonding to teeth that have undergone endodontic treatment are also analyzed. Questions that have yet to be answered by scientific research are presented. Keywords: adhesive system, composite resin, Class II restoration, devital teeth, post and core