Interaction of resin-modified glass-ionomer cements with moist dentine

OBJECTIVES: The objective of this study was to report on a novel phenomenon that occurs when resin-modified glass-ionomer cements (RMGICs) are bonded to moist human dentine. METHODS: Dentine surfaces from extracted third molars were abraded with 180-grit SiC paper. Ten teeth were prepared for each of the two RMGICs tested (Fuji II LC, GC Corp. and Photac-Fil Quick, 3M ESPE). RMGIC buildups were made according to the manufacturers' instructions. After storage at 37 degrees C, 100% humidity for 24 h, the bonded specimens were cut occlusogingivally into 0.9 x 0.9 mm beams. Dentine surfaces bonded with the two RMGICs were examined along the fractured RMGIC/dentine interfaces. Additional beams fractured within the RMGICS and at 3 mm away from the interfaces were used as controls. The fractured beams were examined using scanning electron microscopy (SEM), field emission-environmental SEM (FE-ESEM) and transmission electron microscopy (TEM). RESULTS: SEM and FE-ESEM revealed numerous solid spherical bodies along the RMGIC/dentine interfaces. By contrast, no spherical bodies could be identified within the RMGIC fractured 3 mm distant from the bonded interface. TEM and energy dispersive X-ray analyses performed on carbon-coated ultrathin sections showed that these solid spherical bodies consisted of a thin aluminum and silicon-rich periphery and an amorphous hydrocarbon core within the air voids of the original resin matrix. CONCLUSION: The spherical bodies probably represent a continuation of GI reaction and poly(HEMA) hydrogel formation that results from water diffusion from the underlying moist dentine. Their existence provides evidence for the permeation of water through RMGIC/dentine interfaces.     

Bonding of contemporary glass ionomer cements to dentin.

OBJECTIVE: The objective of this study was to investigate the microtensile bond strength (microTBS) of contemporary glass ionomer cements (GIC) to sound coronal dentin. METHODS: Three specimen teeth were prepared for each material tested: Fuji IX GP (GC), ChemFlex (Dentsply) and Ketac-Molar Aplicap (ESPE). GIC buildups were made according to the manufacturers' instructions. After being stored at 37 degrees C, 100% humidity for 24h, the teeth were vertically sectioned into 1x1mm beams for microTBS evaluation. Representative fractured beams were prepared for scanning (SEM) and transmission electron microscopic (TEM) examination. RESULTS: Results of the microTBS test were: Fuji IX GP (12.4+/-8.6MPa), ChemFlex (15.0+/-9.3MPa) and Ketac-Molar Aplicap (11.4+/-7.7MPa). One-way ANOVA and a multiple comparison test showed that ChemFlex had a statistically higher microTBS (p<0.05). SEM fractographic analysis showed that the predominant failure modes were interfacial and mixed failures. The GIC side of the fractured beams revealed dehydration cracks, a high level of porosity, and voids with an eggshell-like crust. TEM analysis of the demineralized dentin sides of the fractured beams revealed the presence of an intermediate layer along the GIC-dentin interface. This zone was present on the fractured dentin surface in the case of interfacial failure, and beneath GIC remnants in specimens that exhibited a mixed failure mode. SIGNIFICANCE: The findings suggest that the bonding of GIC to dentin is not weak and that the microTBS values probably represent the weak yield strengths of GICs under tension.     

Bond strengths of two conventional glass-ionomer cements to irradiated and non-irradiated dentin

This study evaluated the influence of irradiation on the dentin shear bond strength of two conventional glass ionomer cements (GICs). Thirty extracted molars were bisected in the mesio-distal direction. One-half of 20 teeth were irradiated with 60 Gy (5 days/week) for 6 weeks, and then GIC was placed on the irradiated dentin surface (Groups A1, B1). For the other halves of these tooth specimens, the GICs were first placed on their dentin surfaces and then the specimens irradiated (Groups A2, B2). The remaining 10 teeth were bisected and used as non-irradiated controls (Groups C1, C2). The GIC-dentin shear bond strengths were examined. Groups A2 and B2 had significantly lower bond strengths than groups A1, B1, C1, and C2 (p < 0.05). No significant differences were found among groups A1, B1, C1, and C2 (p > 0.05). In conclusion, irradiation may have an adverse effect on the bond strength of GICs depending on the application sequence.     

Microtensile bond strength of glass ionomer cements to artificially created carious dentin

In this laboratory study, the microtensile bond strengths of a conventional glass ionomer cement (GIC) and a resin modified glass ionomer cement (CRMGIC) to artificially created carious dentin and sound dentin were compared, and the ultrastructural morphology of the fractured interface was examined with a low-vacuum scanning electron microscope (SEM). The specimens were divided into 4 groups: 1) a conventional GIC (Ketac-Fil Plus Aplicap) placed on sound dentin; 2) a conventional GIC placed on artificially created carious dentin; 3) an RMGIC (Photac-Fil Aplicap) placed on sound dentin and 4) an RMGIC placed on artificially created carious dentin. Artificial carious lesions were created using a chemical demineralizing solution of 0.1 M/L lactic acid and 0.2% carbopol. GIC buildups were made on the dentin surfaces according to the manufacturer's directions. After storage in distilled water at 37 degrees C for 24 hours, the teeth were sectioned vertically into 1 x 1 x 8-mm beams for the microtensile bond strength test. The microtensile bond strength of each specimen was measured, and failure mode was determined using an optical microscope (40x). The fractured surfaces were further examined with SEM. Two-way analysis of variance showed that the mean microtensile bond strengths of a GIC and an RMGIC to carious dentin were significantly lower than those to sound dentin, and the mean microtensile bond strengths of Photac-Fil to both sound and carious dentin were significantly higher than those of Ketac-Fil Plus. Chi-square tests indicated that there was a significant difference in failure mode between the sound dentin and carious dentin groups. In sound dentin groups, cohesive failure in GIC was pre- dominant; whereas, mixed failure was predominant in carious dentin groups. SEM examination showed that the specimens determined to be cohesive failures under light microscopy in the Photac-Fil/Sound Dentin group were actually mixed failures under high magnification of SEM.     

Clinical effects of glass ionomer restorations on residual carious dentin in primary molars

PURPOSE: To evaluate the mineralization and morphology of residual (infected and affected) carious dentin following the restoration of vital primary molars with viscous glass-ionomer cement (GIC). METHODS: Encapsulated Fuji IX GP and Ketac-Molar Aplicap GICs were placed in cavities that were prepared using the atraumatic restorative treatment (ART) approach. Four suitable exfoliated teeth with intact restorations were sectioned and then examined by electron probe microanalysis (EPMA) and scanning electron microscopy (SEM). RESULTS: EPMA demonstrated the presence of fluorine and strontium that had penetrated into the underlying residual carious dentin from the adjacent GIC. The concentrations of these two elements, and those of calcium and phosphorous, varied with distance from the GIC/dentin interface. SEM showed varying degrees of dentin tubule destruction and intratubular (peritubular) dentin present immediately subjacent to the GIC/dentin interface. Incomplete removal of carious dentin was observed in all specimens, and GIC remained adherent to the tissue.     

Scanning and transmission electron microscopy of tubular structures presumed to be human odontoblast processes

Tubular structures interpreted as being odontoblast processes can be observed with the scanning electron microscope (SEM) on fractured dentin surfaces which have been demineralized and treated with collagenase. To confirm the nature of these structures, SEM preparations exhibiting similar tubular structures were subsequently examined with the transmission electron microscope (TEM). Newly-erupted human third molars were fractured buccolingually with heavy-gauge industrial nippers or sectioned mesiodistally with a Leitz saw microtome and fixed in glutaraldehyde. The exposed dentin surfaces were decalcified to a depth of approximately 500 microns and then treated with bacterial collagenase. Half of the specimens were critical-point-dried and coated for SEM. The other half were post-fixed and processed for TEM. After examination by SEM, the specimens were embedded and thin-sectioned for TEM. SEM observations of both the fractured and cut surfaces of dentin showed tubular structures running from the surface of the pulp to the dentino-enamel junction. When the SEM preparations were examined with TEM, the tubular structures were seen to be the inner sheath of the peritubular matrix, not odontoblast processes. In the specimens directly processed for TEM, the structures lying inside the sheath could be visualized clearly. In the outer two-thirds of the dentin, the tubules were essentially empty. Well-defined odontoblast processes were seen lying inside the sheath only in the inner dentin.     

Micro-tensile bond testing of resin cements to dentin and an indirect resin composite.

OBJECTIVES: Micro-tensile bond strength (microTBS) evaluation and fractographic analysis were used to compare four resin cement systems (AC: All-Bond 2/Choice; RX: Single Bond/RelyX ARC; SB: Super-Bond C & B; and PF: Panavia F) in indirect composite/dentin adhesive joints. METHODS: Flat dentin surfaces were created on extracted human third molars. The resin cements were used according to the manufacturers' instructions for bonding silanized composite overlays to deep coronal dentin. 0.9x0.9 composite-dentin beams prepared from the luted specimens were stressed to failure in tension. Dentin sides of all fractured specimens were examined by scanning electron microscopy (SEM) to examine the failure modes. In group PF, morphologic features that could not be resolved at the SEM level were further validated by transmission electron microscopy (TEM) examination of the SEM specimens. RESULTS: Statistical analyses revealed significant difference (p<0.05) among microTBS and failure modes in the resin cement groups. The two groups (AC and RX) with highest microTBS failed predominantly along the composite overlay/cement interface. Cohesive failure in resin cement was primarily observed in group SB that exhibited intermediate microTBS values. In group PF with the lowest microTBS, failure occurred mostly along the dentin surface. Globular resin agglomerates seen by SEM on PF-treated dentin were distinguished from silica fillers by TEM. SIGNIFICANCE: The bond between the processed composite and the luting resin cement was the weak link in indirect composite restorations cemented with AC or RX. Super-Bond C&B exhibited intermediate tensile strength and Panavia F is less reliable when used in conjunction with a self-etching primer for bonding indirect restorations to dentin.     

Effects of acid and cleansing agents on shear bond strength and marginal microleakage of glass-ionomer cements

The aims of the present study were to evaluate the effects of various dentin chemical pretreatments (a) on the shear bond strength of five glass-ionomer cements (GICs) and (b) on marginal microleakage of the five GICs used in association with resin composites in Class V restorations. The dentin treatments were: three acid agents (polyacrylic acid, tannic acid, orthophosphoric acid), three cleansing agents (Tubulicid blue solution, hydrogen peroxide, and sodium hypochlorite), and an aqueous solution as control. After dentin treatment, the test specimens were stored in water at 37 degrees C for 24 hr. Shear bond strength was determined with a universal testing machine at a cross-head speed of 0.5 cm/min. Sodium hypochlorite and polyacrylic acid significantly improved the adhesion of GICs to a different degree in the various materials. Regarding microleakage tests, 320 non-retentive cavities were prepared at the cementum-enamel junction in freshly extracted human teeth. The teeth were thermocycled, immersed in dye solution, and serial-sectioned longitudinally at three sites. Treatment with sodium hypochlorite was the most effective in reducing marginal leakage. The present results suggest that dentin treatment is an important step in all resin composite/GIC restorations.     

An in vitro model for assessment of fluoride uptake from glass-ionomer cements by dentin and its effect on acid resistance.

This investigation presents an experimental model for studying interactions of glass-ionomer cements (GICs) with bovine dentin slabs. Fluoride incorporation was studied with five serial abrasion biopsies, each being approximately 10 microns thick. The time of interaction was a very important parameter, indicating continuous fluoride release from the GIC and diffusion into dentin over a 30-day period. Expressed in mass per volume (mg F/cm3), the fluoride incorporation reached 12.0 mg at the first and 2.5 mg at the fifth layer, several times greater than the baseline of 0.27 mg/cm3 in bovine dentin. A subsequent test of acid resistance in a lactic acid buffer (pH 4.0), followed by microradiography of lesions, showed a characteristic 40-microns-wide acid-resistant zone on surfaces exposed to the GICs. In contrast, the untreated control surfaces had lesions demineralized evenly from the surface to the intact tissue, without the higher-density zone at the surface of the lesion. The model seems promising for screening fluoride incorporation into dentin from fluoride-releasing dental materials.     

Nanoleakage types and potential implications: evidence from unfilled and filled adhesives with the same resin composition

PURPOSE: To compare nanoleakage patterns of an unfilled (OS; One-Step), a 6 wt% spherical silica-filled (OSs; One-Step Plus) and a 15 wt% glass-filled (OSg) version of a two-step, acetone-based self-priming adhesive. Permeability of bonded dentin treated with OS and OSs was also examined. METHODS: Deep, coronal dentin from extracted third molars were etched and bonded using these adhesives. One-mm thick sections were immersed in 50 wt% ammoniacal silver nitrate (pH 9.5) for 24 hours. Unstained, undemineralized sections were examined by TEM. The permeability of dentin bonded with OS and OSs were investigated at 20 cm of H2O hydrostatic pressure and compared with the osmotic conductance determined with 4.8 M CaCl2 at zero hydrostatic pressure. Composite-dentin beams bonded with OS, OSs and OSg that were fractured after microtensile bond testing were examined by SEM. RESULTS: Two types of nanoleakage patterns were recognized along the resin-dentin interfaces. The reticular type consisted of discontinuous islands of silver deposits and was exclusively seen in hybrid layers. The spotted type consisted of isolated silver grains and was evident throughout the hybrid and adhesive layers in OS. These two patterns were seen to variable extents in the two filled adhesive versions OSs and OSg and their distribution was independent of one another. OS and OSs bonded dentin were permeable to fluid filtration. However, part of this fluid movement was due to the permeability of the adhesive layer, as demonstrated by osmotic fluid conductance in the absence of hydrostatic pressure. Fractographic analysis revealed denuded collagen fibrils within fractured hybrid layers that were indicative of incomplete resin infiltration.     

EFFECT OF ACID ETCHING OF GLASS IONOMER CEMENT SURFACE ON THE MICROLEAKAGE OF SANDWICH RESTORATIONS

The purposes of this study were to evaluate the sealing ability of different glass ionomer cements (GICs) used for sandwich restorations and to assess the effect of acid etching of GIC on microleakage at GIC-resin composite interface. Forty cavities were prepared on the proximal surfaces of 20 permanent human premolars (2 cavities per tooth), assigned to 4 groups (n=10) and restored as follows: Group CIE – conventional GIC (CI) was applied onto the axial and cervical cavity walls, allowed setting for 5 min and acid etched (E) along the cavity margins with 35% phosphoric acid for 15 s, washed for 30 s and water was blotted; the adhesive system was applied and light cured for 10 s, completing the restoration with composite resin light cured for 40 s; Group CIN – same as Group CIE, except for acid etching of the CI surface; Group RME – same as CIE, but using a resin modified GIC (RMGIC); Group RMN – same as Group RME, except for acid etching of the RMGIC surface. Specimens were soaked in 1% methylene blue dye solution at 24°C for 24 h, rinsed under running water for 1 h, bisected longitudinally and dye penetration was measured following the ISO/TS 11405-2003 standard. Results were statistically analyzed by Kruskal-Wallis and chi-square tests (α=0.05). Dye penetration scores were as follow: CIE – 2.5; CIN – 2.5; RME – 0.9; and RMN – 0.6. The results suggest that phosphoric acid etching of GIC prior to the placement of composite resin does not improve the sealing ability of sandwich restorations. The RMGIC was more effective in preventing dye penetration at the GIC-resin composite- dentin interfaces than CI.     

Effect of smear layer deproteinization with HOCl solution on the dentin bonding of conventional and resin-modified glass-ionomer cements

The effect of smear layer-deproteinizing pretreatment using hypochlorous acid (HOCl) on the micro-shear bond strengths (μSBS) of conventional and resin-modified glass-ionomer cements (GIC) to dentin was investigated and compared with demineralizing pretreatment with polyacrylic acid (PAA). Three GICs: Fuji IX GP Extra (restorative conventional GIC), GC Fuji II LC EM (restorative resin-modified GIC), and GC Fuji Luting EX (luting resin-modified GIC), were used. One hundred fifty human molars were divided into groups (n = 10) according to the cements and dentin pretreatments; no pretreatment (control), 10 s PAA pretreatment, and HOCl pretreatment for 5, 15, or 30 s. After 24 h, μSBS was tested and the data were statistically analyzed using a two-way ANOVA, followed by Tukey's post-hoc test. HOCl pretreatment significantly increased μSBS of conventional GIC compared to the control group. For resin-modified restorative GIC, 5 s HOCl deproteinization significantly increased μSBS, while longer application times did not. There was no significant difference between HOCl-pretreated and control groups of resin-modified luting GIC. PAA pretreatment increased the μSBS of all cements significantly. In conclusion, smear layer deproteinization with HOCl can enhance the dentin bonding of conventional GIC. However, the residual radicals may adversely affect the polymerization of resin-modified GICs.     

The physical and adhesive properties of dental cements used for atraumatic restorative treatment

Atraumatic Restorative Treatment (ART), a recently reported field dentistry technique, involves removal of carious debris using only hand instruments and placement of a glassionomer cement (GIC) restoration. While small ART-GIC restorations are effective short-term replacements for lost tooth form, many larger ART-GIC restorations are defective after two years. Presently, resin-modified GICs (R-M GIC) are available which require no special activation equipment and handle easily in field settings. This study measured the com- pressive, tensile, and shear bond strengths to enamel and dentin of a conventional ART-GIC (Fuji IX) and two R-M GICs (Fuji Plus and Advance) at a powder-to-liquid ratio of 3.6:1. The compressive strengths of the GICs tested were significantly different. Fuji IX had the highest compressive strength, and Advance had the lowest strength (p < 0.05). The tensile strength of the R-M GICs was greater than that of the ART-GIC. Fuji Plus showed the highest shear bond strength to enamel and dentin and was significantly different from both Fuji IX and Advance. A clinical protocol is presented followed by case reports where the ART technique was used for management of acute caries in a modern dental setting.     

Effect of fluoride-releasing filling materials on underlying dentinal lesions in vitro

Fluoride-releasing materials placed over carious tissue are assumed to enhance remineralisation of the underlying lesion. This remineralisation, however, also depends on the availability of calcium and phosphate, which may be supplied by the pulpal fluid. The aim of this study was to measure the fluoride release of glass ionomer cements (GICs) into underlying dentin and to measure the effect of the released fluoride on the remineralisation of the underlying dentinal lesions using transversal microradiography. Discs of fluoride-releasing GIC were placed on top of dentinal lesions in an in vitro model. The discs and the dentin slabs were covered completely by a protective layer of nail varnish, leaving only the pulpal side of the dentin slab open, and hence the dentinal tubules as the pathway for the incubation fluid to the GIC disc. Specimens were incubated in a remineralisation buffer. The materials tested were a conventional GIC, an experimental GIC that was designed to have a high fluoride release, and an inert material. Fluoride was found to penetrate through the dentin slab into the surrounding fluid. Fluoride uptake from the experimental GIC was higher than from the conventional GIC. Mineral content-depth profiles after 10 weeks' remineralisation revealed that in the outer 30 microm of the lesion a higher mineral deposition occurred for the experimental GIC than in both other groups. No differences in the overall change of integrated mineral loss were found for the tested materials. We conclude that high fluoride release from filling materials only results in superficially increased remineralisation of underlying demineralised dentin.     

A comparison of microtensile bond strengths of several dentin bonding systems to primary and permanent dentin.

OBJECTIVES: Limited information exists with regard to the adhesive ability of glass ionomer cements (GIC) and recently developed resin-based dentin bond systems to primary dentin. The aim of this study was to compare the microtensile bond strength of a conventional GIC (Fuji IX), a resin-modified GIC (Fuji II LC), and two resin-based dentin adhesives (Prime and Bond NT with NRC and Single Bond). The bonded interfaces were also observed using field emission electron microscopy(FE-SEM). METHODS: Microtensile bond test specimens were prepared on superficial dentin of primary and permanent molars. The specimens were bonded according to each manufacturer's instructions except for Prime and Bond NT/NRC which used Silux Plus resin composite instead of Dyract. Hour-glass shaped specimens were created (diameter of 1.2+/-0.02 mm) and stressed in tension at a crosshead speed of 1mm/min. Results were analyzed using two-way ANOVA and LSD test, fracture modes were analyzed using the Mann-Whitney U-test and Kruskall-Wallis test. Twelve specimens were prepared for each material on primary and permanent dentin. Samples were prepared in the same manner, then critical point dried, fractured and sputter-coated for the FE-SEM observations. RESULTS: Two-way ANOVA showed the overall bond strengths were greater for the permanent dentin compared with primary dentin. However, for individual material comparisons no differences among the bond strengths to primary and permanent dentin for Fuji IX (9.7, 12.2 MPa), Fuji II LC (16, 20.1 MPa), Prime & Bond NT/NRC (18.1, 21.6 MPa) and Single Bond (18.2, 21.6 MPa), were detected. However, Fuji IX bond strengths were significantly lower than the other systems tested when bonded to either primary or permanent dentin (p<0.05). Failure mode showed cohesive failure of GIC and mostly adhesive failure for the resin-based adhesives. The FE-SEM observations showed hybrid-like layer formation for the GIC materials and hybrid layer formation for the resin-based adhesives. SIGNIFICANCE: The materials tested would be suitable for bonding to either primary or permanent dentin, but the resin-modified GIC or resin-based systems are likely to provide a stronger bond than the conventional GIC, Fuji IX.     

Submicron hiati in acid-etched dentin are artifacts of desiccation.

OBJECTIVES: The submicron hiatus represents a potential space between the base of the collagen network and the mineralized dentin when dentin is acid-etched for bonding. These spaces were observed in SEM studies after acid-etched dentin specimens were critical point dried or dehydrated in hexamethyldisilasane. However, they have never been identified in TEM studies of dentin hybrid layers. This study critically examined the cause of submicron hiati formation using a silver staining technique to measure nanoleakage. METHODS: Two multi-step, total-etch adhesives (One-Step, Bisco; Single Bond, 3M) and two single-step, self-etching adhesives (Prompt L-Pop, ESPE; One-Up Bond F, Tokuyama) were examined. Flat dentin surfaces were bonded with these adhesives and a lining composite. In each adhesive group, 0.8mm thick slabs from the same bonded tooth were coated with nail varnish applied 1mm from the bonded interfaces. The varnish was either left to dry completely for 10min before immersing in 50wt% silver nitrate (AgNO(3)) for 24h (group D), or painted on blotted tooth slabs that were immediately dropped into the AgNO(3) solution (group M). After developing, undemineralized, unstained, epoxy resin-embedded sections were prepared for transmission electron microscopy (TEM) to identify the amount and distribution of silver uptake. RESULTS: Nanoleakage patterns were observed in all adhesive-bonded teeth, regardless of brand. Fine reticular silver deposits were also found in the underlying undemineralized dentin. In group D, submicron hiati were seen as tunnels of heavy silver deposits beneath hybrid layers. Specifically, a hiatus occurred between the undemineralized intertubular dentin and a cohesively fractured layer of the same matrix that was attached to the base of the hybrid layer. Hiati were completely absent in group M, regardless of the brand of adhesive. SIGNIFICANCE: Submicron hiati are artifacts created by desiccation during specimen processing, and should be referred to as such in future studies of bonded dentin interfaces.     

Technique sensitivity in bonding to vital,acid-etched dentin

Just as vital dentin is moist after removing the smear layer, avoiding collapse of the collagen matrix after acid-etching requires in vivo validation. This study hypothesizes that there is no difference between moist bonding performed in vitro or in vivo, and that excessive drying or wetting of vital acid-etched dentin produces inferior results. Resin-dentin interfaces bonded with a moist bonding technique (control), either in vitro or in vivo with Excite DSC (Vivadent), were examined with and without tracer penetration using transmission electron microscopy. Specimens bonded in vivo under excessively dry and wet conditions were also examined. The patterns of silver deposition were similar within the adhesive and hybrid layers created in vitro or in vivo. No hybrid layer was observed in vivo after excessive drying. Excessive wetting in vivo resulted in more extensive nanoleakage and water tree formation along resin-dentin interfaces.     

Bonding to root caries by a self-etching adhesive system containing MDPB

PURPOSE: To evaluate the bonding of an experimental antibacterial fluoride-releasing adhesive system (ABF) to normal and carious dentin in human teeth with Class V root caries. METHODS: Mesiodistal sectioning removed the buccal enamel, superficial dentin and much of the carious dentin in 21 extracted human bicuspids with root surface caries. The surfaces of normal coronal and root dentin, and caries-affected and caries-infected dentin were ground with wet 600-grit SiC paper to create a standardized smear layer. Tooth surfaces were treated with the ABF according to manufacturer's instructions, and then covered with excess resin composite. After immersion in 37 degrees C water for 24 hours, the restored teeth were horizontally sectioned into serial slabs that were trimmed into hourglass shapes to isolate the bonded area to the test substrates, and then their bond strengths were measured by the microtensile bond test, and the interfaces examined by SEM and TEM. The bond strengths were statistically compared with ANOVA and Fisher's PLSD (P < 0.05). RESULTS: The bond strengths of ABF to caries-affected and caries-infected dentin were significantly lower than those to normal coronal and root dentin. SEM micrographs revealed that the hybrid layers in caries-affected and caries-infected dentin were more porous compared to the hybrid layer in normal coronal and root dentin. TEM micrographs showed that bacteria that had invaded the dentin were embedded in this adhesive monomer in caries-infected dentin. CLINICAL SIGNIFICANCE: Although the bond strength of ABF adhesive system to root carious dentin is lower than that of normal dentin, the antibacterial and fluoride-releasing properties of ABF may contribute to prevent caries progression and inhibit secondary caries.     

Tubular occlusion prevents water-treeing and through-and-through fluid movement in a single-bottle, one-step self-etch adhesive model

Water entrapment occurs at resin-dentin interfaces of one-step self-etch adhesives. We hypothesized that by preventing water fluxes from dentin, any water entrapment would be attributed to incomplete removal of adhesive solvents. We tested this hypothesis by bonding to transparent carious dentin containing occluded dentinal tubules. An experimental single-bottle, one-step self-etch adhesive was applied to flat surfaces of caries-affected dentin surrounded by sound dentin, with or without pulpal pressure. Resin-dentin interfaces were examined with TEM after silver-impregnation. Although caries-affected dentin was highly porous, adhesive layers were devoid of silver deposits when tubules were occluded. Conversely, variable extents of water-treeing and water-droplets were identified from adhesive layers in bonded sound dentin. Water-treeing and water-droplet formation, being manifestations of evaporative and convective water fluxes, can be eliminated during bonding to occluded transparent carious dentin. However, the highly porous nature of this clinically relevant substrate after bonding may lead to potentially undesirable consequences.     

Possible role of cementoblasts in the resorbant organ of human deciduous teeth during root resorption

Human deciduous teeth undergoing physiologic root resorption were extracted and fixed with a mixture of formaldehyde and glutaraldehyde and processed for scanning (SEM) and transmission (TEM) electron microscopy, and for acid (ACPase) and alkaline phosphatase (ALPase) cytochemistry. The resorbant organ, rich in odontoclasts, cementoblasts, fibroblasts, and macrophages, formed prominent resorption lacunae in root dentin. SEM observations of resorption lacunae treated with trypsin solution showed islands of newly-formed cementum matrix in part of the resorbing dentin surfaces. Such cementum consisted of bundles of densely-arranged collagen fibrils and, in part, contained forming cementocytic lacunae and canaliculi. Active cementoblasts adjacent to odontoclasts on resorbing dentin surfaces showed cuboidal outlines and were characterized by the presence of numerous cisterns of rough endoplasmic reticulum, well-developed Golgi complexes, secretion granules, and many mitochondria. They sometimes formed a thin layer of cementoid and/or cementum matrix upon the resorbing dentin surface. These cementoblasts had ACPase-positive lysosomes in the cell bodies and exhibited intense ALPase activity along the plasma membranes of whole cell surfaces. These results suggest that, during root resorption, 1) active cementoblasts are present adjacent to active odontoclasts and 2) these cementoblasts are involved in remodeling the resorbing dentin surfaces.