Single-bottle adhesives behave as permeable membranes after polymerisation. II. Differential permeability reduction with an oxalate desensitiser

OBJECTIVES: This study examined the changes in hydraulic conductance and ultrastructure of dentine bonded with simplified etch-and-rinse adhesives to oxalate desensitiser pre-treated acid-etched dentine. METHODS: Human dentine disks were acid-etched, treated with an oxalate desensitiser (BisBlock, Bisco), and bonded with One-Step (OS), Single Bond (SB), OptiBond Solo Plus (OB) or Prime and Bond NT (PB). Similar disks from each group were acid-etched, and bonded without oxalate pre-treatment. Hydraulic conductance of the specimens was measured at 20 cm of water pressure and analysed with nonparametric statistical methods. Epoxy resin replicas of the smear layer-covered dentine and bonded dentine were examined with SEM for the extent of fluid transudation. Specimens bonded under perfusion were examined with TEM after tracer immersion. RESULTS: OB and PB exhibited a highly significant reversal of the reduced hydraulic conductance obtained with BisBlock on unbonded acid-etched dentine. Profuse water transudation across the bonded dentine was observed from the replicas. Adhesive interfaces were covered with spherical globules that interfered with dentine hybridization. Conversely, no significant difference in hydraulic conductance was observed in SB, between Bisblock pre-treated, unbonded and bonded acid-etched dentine. Significantly lower hydraulic conductance was shown on application of OS to Bisblock-treated acid-etched dentine. Water transudation was sparse, interfering surface globular structures were absent, and only angular subsurface crystals were seen in the dentinal tubules. CONCLUSIONS: Convective water fluxes through dentine may be reduced by applying Bisblock to acid-etched dentine before bonding with One-Step or Single Bond. However, reducing adhesive permeability with the use of oxalate desensitiser is not applicable to low acidity adhesives such as OptiBond Solo Plus and Prime and Bond NT.     

Effect of simulated pulpal pressure on dentin permeability and adhesion of self-etch adhesives.

OBJECTIVES: Dentin bonds made with one-bottle etch-and-rinse and self-etch adhesives are affected by the formation of interfacial blisters, porosities and deterioration. The first objective of this study was to evaluate the fluid flow through resin-dentin interfaces created by self-etching adhesives applied to deep dentin using a replica technique and by directly measuring dentin permeability (P). The second objective was to examine the effect of intrapulpal pressure on the microtensile bond strength of these adhesives. METHODS: A fluid-transport model was used to measure the fluid permeability (%P) through different adhesives. Impressions of bonded dentin were taken with a polyvinylsiloxane impression material to monitor fluid transudation from the surface of the adhesive. Positive replicas were fabricated for SEM examination. Two groups of resin-bonded specimens (pulpal pressure versus no pulpal pressure) were created for microtensile bond strength evaluation. Adhesive application was performed under 0 cm H(2)O. Pulpal pressure group was submitted to 20 cm H(2)O of pulpal pressure during build-up procedures. RESULTS: Clearfil Protect Bond exhibited the lowest permeability and fewest numbers of fluid droplets over the surface of the bonded dentin. G-Bond and Clearfil-S3 Bond were more permeable than Clearfil Protect Bond. One Up Bond F was the most permeable adhesive. A highly significant correlation was observed between the relative permeability of these adhesives (%P) and the number of fluid droplets on the adhesive surfaces. The application of pulpal pressure significantly reduced bond strength. SIGNIFICANCE: Resin-dentin bonds created by contemporary self-etch adhesives are susceptible to fluid permeation induced by pulpal pressure. HEMA-based adhesives showed the largest reductions in bond strengths after pulpal pressure application.     

Single-step, self-etch adhesives behave as permeable membranes after polymerization. Part III. Evidence from fluid conductance and artificial caries inhibition

PURPOSE: To test the hypothesis that formation of inhibition zones by bonded restorations in artificially-induced carious dentin lesions is related to the permeability of the self-etch adhesives. METHODS: Fluid conductance of four single-step self-etch adhesives (Prompt L-Pop, Etch&Prime 3.0, One-Up Bond F and Reactmer Bond), and a control two-step self-etch adhesive (UniFil Bond) were measured after sound dentin surfaces were:(1) acid-etched; (2) polished to produce smear layers; (3) bonded with the adhesive; each at 20 cm hydrostatic pressure (hp). Osmotic fluid conductance was also determined for the bonded dentin after immersion in 4.8 M CaCl2 at 0 cm hp. For artificial caries inhibition, a non-fluoride releasing (NFR) two-step self-etch adhesive (UniFil Bond) and a fluoride-releasing (FR) single-step adhesive (Reactmer Bond) were used in combination with a NFR composite (Metafil CX) or a FR restorative material (Reactmer Paste). Artificial caries were induced in these restorations, from which 120 +/- 10 microm thick sections and the effect of caries inhibition were quantitatively assessed with polarizing light microscopy and image analysis. RESULTS: Fluid conductance after bonding with the single-step adhesives Prompt L-Pop and Etch&Prime 3.0 were not significantly different from those recorded from smear layer-covered dentin. Although better seals were achieved with One-Up Bond F and Reactmer Bond, fluid conductance at 20 cm hp was significantly higher than the two-step self-etch adhesive UniFil Bond. Osmotic conductance at 0 cm hp were not significantly different from normal fluid conductance at 20 cm hp. The sizes of artificial carious lesions in UniFil Bond were significantly higher irrespective of whether a FR or NFR composite was used. Significant reduction in lesion size occurred in Reactmer Bond with the use of a NFR composite, and even more so with the use of a FR composite.     

In vivo and in vitro permeability of one-step self-etch adhesives

Adhesive dentistry should effectively restore the peripheral seal of dentin after enamel removal. We hypothesize that non-rinsing, simplified, one-step self-etch adhesives are effective for minimizing dentin permeability after tooth preparation procedures. Crown preparations in vital human teeth were sealed with Adper Prompt, Xeno III, iBond, or One-Up Bond F. Epoxy resin replicas were produced from polyvinyl siloxane impressions for SEM examination. Dentin surfaces from extracted human teeth were bonded with these adhesives and connected to a fluid-transport model for permeability measurements and TEM examination. Dentinal fluid droplets were observed from adhesive surfaces in resin replicas of in vivo specimens. In vitro fluid conductance of dentin bonded with one-step self-etch adhesives was either similar to or greater than that of smear-layer-covered dentin. TEM revealed water trees within the adhesives that facilitate water movement across the polymerized, highly permeable adhesives. Both in vitro and in vivo results did not support the proposed hypothesis.     

Dentin permeability: effects of crown preparation.

Sequential crown reductions of extracted human teeth were made to evaluate both regional differences in dentin permeability and the effects of tooth reduction. Two different methods of tooth reduction were used. In group 1, tooth reduction was nonuniform but was done in a manner similar to conventional crown preparations. Maximum, total crown permeability was measured using a pressurized fluid filtration technique after removing the smear layer. Regional reductions in permeability were accomplished by creating smear layers on mesial, distal, buccal, lingual, and occlusal surfaces sequentially. Between each step, changes in dentin permeability were measured. In group 2, tooth reductions were uniform and regional permeability was reduced by localized application of potassium oxalate. Both methods demonstrated increased permeability of dentin as the prepared surfaces approached the pulp chamber. Generally, the mesial surfaces were more permeable than the distal surfaces. The occlusal and lingual surfaces were the least permeable regions.     

In vivo fluid movement through dentin adhesives in endodontically treated teeth

Fluid transudation through simplified dentin adhesives can occur in bonded vital crown dentin, since these adhesives behave as permeable membranes after polymerization. The effect of adhesive permeability in endodontically treated teeth is unknown. This study examined the hypothesis that in vivo fluid movement through simplified adhesives occurs when they are applied to root canals. Dowel spaces were prepared in endodontically treated teeth with single root canals. Six adhesives were applied to the intra-radicular dentin of canal walls. Impressions were obtained with polyvinyl siloxane, and replicas were fabricated with the use of polyether impression material. Replica hemisections were gold-coated for SEM examination. Fluid transudation was evident on the adhesive surfaces of all simplified total-etch and self-etch adhesives. Conversely, most of the specimens bonded with the control three-step total-etch adhesive were devoid of fluid droplets. Permeability of simplified adhesives results in water movement, even in root-treated dentin. This may adversely affect the coupling of auto-/dual-cured resin cements.     

Effects of potassium oxalate on knoop hardness of etch-and-rinse adhesives

The objective of this study was to determine whether the hardness of etch-and-rinse adhesives may be affected by the pretreatment of acid-etched dentin with potassium oxalate desensitizer. Unerupted human third molars were cut into crown segments by removing the occlusal enamel and roots. The pulp chamber of these crown segments was connected to a syringe barrel filled with phosphate-buffered saline so that the moisture of dentin was maintained during the bonding procedures. Three etch-and-rinse adhesives-two two-step systems (Adper Single Bond 2 [SB], One-Step [OS]) and one three-step system (Adper Scotchbond Multi-Purpose [MP])-were applied to acid-etched dentin that had been treated (experimental groups) or not (control groups) with potassium oxalate (BisBlock). The Knoop hardness (KHN) of adhesives was taken at different sites of the outer surface of the adhesive-bonded dentin. The KHN of the three tested adhesives applied to acid-etched dentin treated with potassium oxalate was significantly lower than that exhibited by the respective controls (not treated with oxalate; p<0.05). Regardless of the adhesive, the treatment with potassium oxalate reduced the adhesives' KHN (p<0.05), with the OS system exhibiting the lowest KHN compared with the MP and SB systems.     

Single-bottle adhesives behave as permeable membranes after polymerization. I. In vivo evidence

Objectives: This study tested the hypothesis that single-bottle total-etch adhesives are effective in reducing dentine permeability under in vivo conditions. Methods: Crown preparations on vital human teeth were performed under local analgesia as part of the treatment plan for prosthetic rehabilitation. Four single-bottle adhesives (Single Bond, 3M ESPE; Excite DSC, Ivoclar Vivadent; Prime and Bond NT Dual-Cure, Dentsply DeTrey and One-Step, Bisco Inc.) were applied to the cut dentine after acid-etching. Polyvinyl siloxane impressions were taken, using an ultra-low viscosity impression material, of the smear layer-covered dentine before applying the adhesives to deep vital dentine, and after adhesive placement. Additional impressions were taken of the adhesive-sealed dentine following the removal of the provisional prostheses after a 7–10 day period. Epoxy resin replicas of the crown preparations were examined with scanning electron microscopy to evaluate the extent of dentinal fluid transudation during pre-bonded, immediately bonded and post-bonded periods. Results: Dentinal fluid transudation from localised areas that were close to the dental pulp was universally observed from all epoxy resin replicas, irrespective of the adhesive employed. The transudation of dentinal fluid from the control smear layer-covered dentine of each crown preparation was comparatively mild when compared to the extent that was observed after total-etching and application of the single-bottle adhesive. Dentinal fluid droplets were specifically located over the surface of the adhesive layer. Continuous transudation of dentinal fluid occurred even after the removal of the provisional prostheses, and was considerably more profuse in subjects who opted for the fitting of the permanent prostheses without the use of a local anaesthetic solution. Conclusion: Single-bottle adhesives, because of their lack of a comparatively more hydrophobic bonding resin layer, behave as permeable membranes after polymerisation. They permit the continuous transudation of dentinal fluid and do not provide a hermetic seal in vital deep dentine. Although the relatively slow rate of diffusion of dentinal fluid is unlikely to result in post-operative cold sensitivity, it may interfere with the optimal polymerisation of dual-cured or auto-cured composites or resin cements in both direct and indirect restorations.     

Correlation among dentin depth, permeability, and bond strength of adhesive resins

Correlations among dentin permeability, dentin depth, and dentin bonding of Scotchbond, Clearfil New Bond, and Superbond C&B were studied in bovine incisor crown segments. Since the dentin surface was prepared on deeper dentin, the permeability of the dentin increased both in the presence of, and especially after removal of, the smear layer. In general, the deeper the dentin, the lower the bond strengths of Scotchbond, Clearfil New Bond, and Superbond C&B. The higher the dentin permeability, the lower the bond strength of Superbond C&B, but there was no simple relationship in the case of either Scotchbond or Clearfil New Bond. The bond strength of Superbond C&B was much higher than those of Scotchbond or Clearfil New Bond at any depth of dentin. Superbond C&B should be considered as both an enamel- and dentin-bonding agent.     

Incompatibility of oxalate desensitizers with acidic, fluoride-containing total-etch adhesives

The use of oxalate desensitizers on acid-etched dentin prior to adhesive application can result in subsurface tubular occlusion by calcium oxalate crystals. However, the solubility of calcium oxalate increases in acidic solution. We hypothesized that total-etch adhesives can, depending upon their pH, interact with oxalate-desensitizer-treated dentin in an adverse manner. Acid-etched human dentin treated with 2 oxalate desensitizers (BisBlock and Super Seal) was bonded with 4 simplified total-etch adhesives: One-Step (OS), Single Bond (SB), OptiBond Solo Plus (OB), and Prime&Bond NT (PB). Composite-dentin beams were examined by SEM and TEM, both of which revealed numerous spherical globules on OB- and PB-bonded, desensitizer-treated dentin, but not in OS or SB samples. Bond strengths produced by OB and PB were significantly lower in oxalate-treated specimens than those produced by OS or SB. These surface globules may have interfered with hybridization of demineralized dentin with OB and PB resins and caused compromised bond strengths.     

Effect of iron gel on dentin permeability

This study evaluated in vitro the effect of an experimental gel containing iron on the reduction of hydraulic conductance of dentin. Thirty-six 1-mm-thick dentin discs obtained from extracted human third molars were divided into 3 groups of 10 specimens each. The groups corresponded to the following experimental materials: 1.23% acidulated phosphate fluoride gel, pH 4.1; 3% potassium oxalate gel, pH 4.1 (Oxa-Gel?); and iron sulfate gel (10 mmol/L FeSO4), pH 4.1. The gels were applied to dentin under the following conditions: after 37% phosphoric acid and before 6% citric acid. Data were analyzed statistically by ANOVA and Tukey's test at 5% significance level. There was no significant differences (p<0.05) among the groups in any of the conditions for hydraulic conductance reduction, except for smear layer presence. The active agents reduced dentin permeability, but they produced significantly lower (p<0.05) reduction in hydraulic conductance when compared to presence of smear layer. The effectiveness in reducing dentin permeability was not significantly different (p>0.05) among the gels. This study suggests that the iron gel promoted reduction in dentin permeability comparable to that of the other agents and thus may be considered a good clinical alternative for the treatment of dentin hypersensitivity.     

Microtensile bond strength of self-etching adhesive systems to differently prepared dentin

PURPOSE: To evaluate the microtensile bond strength (microTBS) of three self-etching adhesive systems with different degrees of acidity (Clearfil SE Bond, One-Up Bond F, and Xeno III) to dentin prepared with three different methods. METHODS: Forty-five extracted human third molars were ground flat to expose occlusal dentin and polished with 600-grit abrasive paper. All teeth were randomly divided into three groups according to the preparation method: baseline surface (AP#600), steel fissure bur (SB) and regular grit diamond bur (DB). Dentin surfaces were bonded with one of the three adhesive systems; then resin composite was incrementally built up. After storage in 37 degrees C water for 24 hours, specimens were cut and trimmed to create an hourglass shape with cross sectional area of approximate 1 mm2. All specimens were subjected to microtensile bond strength testing. The bond strength data were analyzed with one and two-way ANOVA and Dunnett Multiple comparisons test at P< 0.05. RESULTS: For Xeno III and One-Up Bond F, the microTBS to dentin prepared with the different methods were not significantly different. However, the microTBS of Clearfil SE Bond to dentin prepared with the diamond bur was significantly lower than the other preparation methods. Xeno III produced the lowest microTBS that were statistically different from the other adhesive systems when each preparation method was compared (P< 0.01). SEM observation of the prepared dentin surfaces showed that the diamond bur group produced a thicker smear layer that followed by steel bur and 600-grit paper. Therefore, the smear layer from diamond burs had a greater influence in decreasing microTBS of Clearfil SE Bond that has the weakest acidity self-etching adhesive systems evaluated.     

Effect of oxalate desensitizer on the durability of resin-bonded interfaces

Potassium oxalate desensitizers were previously shown to effectively reduce the immediate permeability of resin-bonded dentin. The current study evaluated whether the effect of the combined application of oxalate with etch-and-rinse adhesives interferes with the durability of resin-dentin bonds when using etch-and-rinse adhesives. The bond strength of resin-bonded dentin specimens composed of two-step or three-step etch-and-rinse adhesives (Single Bond, One-Step and Scotchbond Multi-Purpose, respectively) was tested immediately (24 hours) and after 12 months of water storage. The adhesives were used either according to the manufacturers' instructions (control groups) or after treating acid-etched dentin with a potassium oxalate gel (BisBlock, BISCO, Inc). The treatment of dentin with potassium oxalate was shown to negatively affect the baseline bond strength of resin-bonded dentin specimens, regardless of the adhesive used (p < 0.05). After storage, the bond strength of the resin-bonded interfaces was significantly reduced for all the tested groups (p < 0.001). Nevertheless, the rate of decreasing bond strength was significantly lower for oxalate-treated specimens than for the controls (p < 0.05).     

Aggressiveness of contemporary self-etching systems. I: Depth of penetration beyond dentin smear layers.

OBJECTIVE: This study examined, with the use of transmission electron microscopy (TEM), the aggressiveness of three self-etching adhesive systems in penetrating dentin smear layers of different thickness. METHODS: Dentin disks were produced from extracted human third molars. For the control group, the middle dentin surface was cryofractured to create a bonding surface that was devoid of a smear layer. The experimental teeth were polished with wet 600 or 60-grit SiC paper to produce bonding surfaces with thin and thick smear layers. They were bonded using one of the three self-etching systems: Clearfil Mega Bond (Kuraray), Non-Rinse Conditioner and Prime&Bond NT (Dentsply DeTrey) and Prompt L-Pop (ESPE). Bonded specimens were then demineralized and embedded in epoxy resin for TEM examination. RESULTS: For Mega Bond, thin authentic hybrid layers between 0.4-0.5 microm were found. Smear layer and smear plugs were retained as part of the hybridized complex. For Non-Rinse Conditioner/Prime&Bond NT, the authentic hybrid layers were between 1.2-2.2 microm thick. Smear layer and smear plugs were completely dissolved in dentin with thin smear layers, but were partially retained as part of the hybridized complex in those with thick smear layers. For Prompt L-Pop, authentic hybrid layers were 2.5-5 microm thick and smear layer and smear plugs were completely dissolved even in dentin with thick smear layers. SIGNIFICANCE: Contemporary self-etching systems may be classified as mild, moderate and aggressive based on their ability to penetrate dentin smear layers and their depth of demineralization into the subsurface dentin. The more aggressive system completely solubilized the smear layer and smear plugs and formed hybrid layers with a thickness approaching those of phosphoric acid conditioned dentin.     

Effect of periodontal root planing on dentin permeability

Abstract The purpose of this study was to quantitate the effects of root planing on the permeability of human root dentin in vitro. Unerupted 3rd molars were used. The crowns were removed and longitudinal slices made of the root. The hydraulic conductance of the root dentin was measured before and after root planing, acid etching and potassium oxalate application using a fluid filtration method. The results showed that root planing creates a smear layer that reduces the permeability of the underlying dentin, However, this smear layer is acid labile, Thus, root planing may ultimately cause increased dentin permeability and the associated sequelae of sensitive dentin, bacterial invasion of tubules, reduced periodontal reattachment and pulpal irritation.     

Effects of oxalate on dentin bond after 3-month simulated pulpal pressure

OBJECTIVES: Application of an acidic oxalate solution forms calcium oxalate within dentinal tubules and has been used to desensitize dentin and may also improve performance by reducing internal dentin wetness during bonding. The hypothesis tested was that oxalate restriction of dentinal fluid transudation when using an etch-and-rinse two-step adhesive will improve microtensile bond strength (muTBS) and reduce nanoleakage. METHODS: Occlusal dentin of 60 human molars were bonded (Adper Single Bond Plus, 3M ESPE) while one-half of each tooth received either a liquid (SuperSeal, Phoenix Dental) or gel (BisBlock, Bisco) oxalate treatment after acid etching. The restored teeth were placed under pulpal pressure for 3 months before forming cylindrical dumbbell specimens for muTBS and failure pathway determination. Additional teeth were prepared and stored in a similar manner for transmission electron microscopy (TEM) examination of nanoleakage after tracer immersion. RESULTS: The mean bond strength in the group with oxalate liquid and the control group was 27.06+/-7.14 and 36.18+/-9.07 MPa, respectively, and for the gel form of oxalate was 25.34+/-13.09 and 33.09+/-14.25 MPa, respectively. The control groups were significantly stronger than either oxalate group using t-tests (liquid p<0.00001; gel p=0.0032) or Weibull (liquid p=0.0002; gel p=0.0029) statistics. Oxalate groups also demonstrated more adhesive failure modes and nanoleakage. CONCLUSIONS: Under the conditions of this study, the application of oxalate with an etch-and-rinse two-step bonding system produced significantly lower long-term muTBS and enhanced nanoleakage.     

The influence of a dentin desensitizer on the microtensile bond strength of two bonding systems

A laboratory study evaluated the influence of a dentin desensitizer (D/Sense 2) on the microtensile bond strength of two adhesive systems: a self-etching primer (Bistite II SC) and a one-bottle adhesive (Prime & Bond 2.1). Sixteen crown dentin discs were obtained from extracted sound human third molars. Dentin surfaces were ground with 600 grit silicon carbide (SiC) abrasive papers to produce a standardized smear layer. Teeth were randomly divided into four groups (n=4). G1-D/Sense 2 + Prime & Bond 2.1; G2-D/Sense 2 + Bistite II SC; G3- and G4-dentin surfaces were bonded with Prime & Bond 2.1 and Bistite II SC, respectively, with no previous treatment with D/Sense 2. Eight mm high resin composite crowns (TPH Spectrum) were incrementally built-up on the treated surfaces. One sample from each group was prepared for evaluation of the hybrid layer on SEM. The specimens for the microtensile test were serially sectioned perpendicular to the adhesive layer to obtain 1 mm2 bounded sticks. Then, each stick was submitted to the microtensile test performed at a 0.5 mm/min crosshead speed. One-way ANOVA and Tukey test showed statistically significant differences among the groups (p<0.05). Values in MPa were: G1-17.85; G2-9.88; G3-35.16; G4-15.57. Based on the results of this study, it can be concluded that the D/Sense 2 desensitizer decreased the bond strength of Prime & Bond 2.1 and Bistite II SC bonding systems.     

Effect of different bur grinding on the bond strength of self-etching adhesives

This study compared the microtensile bond strength (MTBS) of three all-in-one adhesive systems and a two-step system using two types of burs to prepare the dentin surfaces. Flat coronal surfaces of 24 extracted human molars were produced using either regular-grit or superfine-grit diamond burs. Resin composite was then bonded to equal numbers of these surfaces using one of the four adhesives: Clearfil SE Bond (CSE), G-Bond (GB), SSB-200 (SSB) or Prompt L-Pop (PLP). After storage for 24 hours in 37 degrees C distilled water, the bonded teeth were sectioned into slices (0.7-mm thick) perpendicular to the bonded surface. The specimens were then subjected to microtensile testing and the bond strengths were calculated at failure. Bond strength data were analyzed by two-way ANOVA and the GamesHowell test for interaction between adhesive and type of cut dentin. The fractured surfaces were observed by SEM to determine the failure mode. In addition, to observe the effect of conditioning, equal numbers of the two bur-cut dentin surfaces of eight additional teeth were conditioned with the adhesives and observed by SEM. Based on the results, when CSE and SSB were bonded to dentin cut with a regular-grit diamond bur, the MTBS values were significantly lower than that of superfine bur-cut dentin; whereas, GB and PLP showed no significant differences in MTBS between the two differently cut surfaces. SEM observation of the fractured surfaces revealed a mixed mode (adhesive in some areas and cohesive in others in the same sample) of failure in all specimens except PLP, which showed cohesive failure within the adhesive for both types of bur preparation. Generally, SEMs of the conditioned surfaces using both types of burs showed partial removal of the smear layer for CSE, minimal for GB and SSB and complete removal for PLP. In conclusion, when cutting dentin, selecting the proper bur type is important for improving the bond strength of some self-etching adhesive systems.     

Evaluation of residual dentin after conventional and chemomechanical caries removal using SEM

The purpose of this in vitro study was to analyze the residual dentinal surfaces following caries removal using rotatory instruments and two chemomechanical methods (Papacárie and Carisolv), by scanning electron microscopy (SEM). Thirty primary incisors were divided into three groups, according to the caries removal method used, and their residual dentin was examined under SEM (15). After caries removal, 15 of these teeth were restored with Single Bond (3M) adhesive system and Z100 Filtek composite resin (3M). The tags of the replicas were observed under SEM. The chemomechanical caries removal methods (Papacárie and Carisolv) formed an amorphous layer, similar to the smear layer and few exposed dentinal tubules; the conventional caries removal method produced a smooth and regular dentinal surface, with typical smear layer and exposed dentinal tubules. All groups showed abundant tag formation. Scanning electron microscopy analysis revealed a difference between dentin treated with rotatory instruments and that treated with chemomechanical methods in spite of the occurrence of a similar tag formation in both groups.     

How can droplet formation occur in endodontically treated teeth during bonding procedures?

PURPOSE: The aim of this in vivo study was to clarify how blistering formation occurs along intraradicular dentin bonded interfaces. MATERIALS AND METHODS: Patients were selected and post space was prepared in vivo in endodontically treated teeth. Post space was etched, dried with ethanol, and bonded with one of the following adhesive systems: All Bond 2, XP-Bond, Clearfil SE Bond, Xeno III. The four adhesives were considered as representative of each bonding system class. An additional group was prepared with phosphoric acid treatment + application of Pre-Bond unfilled resin of All Bond 2, without the use of the primer agent. Etching was avoided for self-etching materials. Replicas of the post space were taken (1) after post space preparation; (2) after etching, rinsing, and drying; (3) after ethanol drying, and (4) after adhesive application. Replicas were analyzed with SEM and blisters were counted by independent observers. Statistical analysis was performed with Kruskal-Wallis ANOVA and Dunn's multiple comparison tests at p = 0.05. RESULTS: No blister formation occurred on replicas taken prior to adhesive application, while blister formation was evident in all replicas of bonded interfaces, irrespective of the adhesive system. No statistical difference in the number of droplets was found between All Bond 2, XP-Bond, and Clearfil SE Bond. Xeno III exhibited the highest number of blisters. Specimens bonded with Pre-Bond unfilled resin of All Bond 2 without primer application showed no blister formation. CONCLUSION: This study revealed that blister formation occurs only if the priming agent of the adhesive system was applied, thus supporting the hypothesis that blistering occurs due to adhesive phase separation or insufficient solvent evaporation.