Colour and chemical stability of bismuth oxide in dental materials with solutions used in routine clinical practice.

Bismuth(III) oxide is included as a radio-opacifier in dental materials, including hydraulic silicate cements, the material of choice for several endodontic procedures. It has been implicated in tooth discoloration after contact with endodontic irrigants, in particular NaOCl solution, To date, there has been no work on the chemistry: all reports have been of clinical findings only. The purpose now was to report the reactions leading to colour change from Bi2O3 in contact with solutions used in routine endodontic practice. Ten-gram portions of Bi2O3 were immersed in either water, NaOH, NaCl, NaOCl or HCl solution, either in the dark or exposed to visible light, and samples retrieved at 1, 4, 12 and 24 weeks. After washing, these were exposed to either added CO2 or not, for 1 week while drying, and under the same dark or light conditions. Changes in appearance were monitored by photography and colour measurement, and chemically by X-ray diffraction and Fourier-transform infrared spectroscopy. 24-week material was studied using electron paramagnetic resonance and Raman spectroscopy; NaOCl-treated material was also examined by scanning electron microscopy. With water, NaCl and NaOH, bismuth subcarbonate was formed. With or without added carbon dioxide, discoloration occurred from pale yellow to light brown when exposed to light, and to a lesser extent in the dark, intensifying with time. In contrast, exposure to NaOCl rapidly formed a dark brown-black sodium bismuthate. With HCl, white BiOCl was formed. Bi2O3 is not at all inert in this context as is commonly believed, denying its principle of use. Previously unreported solution-mediated reaction occurs readily even in water and NaCl solution, forming new compounds that discolour. In contact with NaOCl sodium bismuthate is formed; severe darkening occurs rapidly. The reactivity is such that Bi2O3 is not indicated for dental materials and should be withdrawn from use.

An in vitro investigation of pre-treatment effects before fissure sealing.

BACKGROUND: Fissure sealants prevent occlusal caries in permanent molars. Enamel preparation methods are used before fissure sealing. AIMS: To investigate effects of bioglass air-abrasion pre-treatment with and without an adhesive, on fissure enamel of permanent teeth, with respect to etchability, microleakage and microtensile bond strength. DESIGN: Half of the occlusal surfaces of 50 extracted premolars underwent bioglass air-abrasion. Dye was applied to the entire occlusal surface. Photographs were taken to score etched surface by dye uptake. Adhesive was applied to 25 of the bioglass-treated areas and all teeth were fissure sealed, sectioned, and evaluated using confocal microscopy. Buccal and lingual surfaces of a further eight premolars were acid-etched and randomly received: air-abrasion, adhesive, both, or none before sealant application for microtensile bond strength measurement in half of the samples immediately and half following 6 months of water immersion. RESULTS: Linear mixed models and multinomial logistic regression were used (P = 0.05). Bioglass air-abrasion significantly improved enamel etchability and reduced microleakage. The addition of an adhesive made no difference to either microleakage or microtensile bond strength. The combination of bioglass abrasion and adhesive led to more cohesive, rather than adhesive, failure. CONCLUSIONS: Bioglass air-abrasion improved enamel etchability and reduced microleakage irrespective of the adhesive use but neither pre-treatment affected the microtensile bond strength.

Origins of bone repair in the armour of fossil fish: response to a deep wound by cells depositing dentine instead of dermal bone.

The outer armour of fossil jawless fishes (Heterostraci) is, predominantly, a bone with a superficial ornament of dentine tubercles surrounded by pores leading to flask-shaped crypts (ampullae). However, despite the extensive bone present in these early dermal skeletons, damage was repaired almost exclusively with dentine. Consolidation of bone, by dentine invading and filling the vascular spaces, was previously recognized in Psammolepis and other heterostracans but was associated with ageing and dermal shield wear (reparative). Here, we describe wound repair by deposition of dentine directly onto a bony scaffold of fragmented bone. An extensive wound response occurred from massive deposition of dentine (reactionary), traced from tubercle pulp cavities and surrounding ampullae. These structures may provide the cells to make reparative and reactionary dentine, as in mammalian teeth today in response to stimuli (functional wear or damage). We suggest in Psammolepis, repair involved mobilization of these cells in response to a local stimulatory mechanism, for example, predator damage. By comparison, almost no new bone is detected in repair of the Psammolepis shield. Dentine infilling bone vascular tissue spaces of both abraded dentine and wounded bone suggests that recruitment of this process has been evolutionarily conserved over 380 Myr and precedes osteogenic skeletal repair.

Effect of loading on the microtensile bond strength and microleakage of a self-etching and etch-and-rinse adhesive in direct Class II MOD composite restorations in vitro.

The effect of loading on microleakage and microtensile bond strength of MOD composite restorations bonded with either self-etching or etch-and-rinse adhesive was investigated. MOD cavities were prepared in 28 extracted molar teeth. 14 teeth were bonded with a one-step self-etching adhesive (G-Bond) and 14 with an etch-and-rinse adhesive (Optibond Solo Plus) then restored with resin composite. For each adhesive, 7 teeth were loaded and 7 unloaded (controls). Loading was achieved with an axial force of 80 N at 2.5 cycles/s for 250,000 cycles. All the teeth were stored in 0.25% rhodamine solution for 24 h and sectioned in a bucco-lingual direction at the proximal boxes to examine microleakage then further sliced mesiodistally into beams for the µTBS test. Failure modes were determined using confocal and scanning electron microscopy. ANOVA assessed the effect of loading on microleakage and bond strength. After loading, restorations bonded with G-Bond exhibited significantly greater dye penetration compared to Optibond Solo Plus at both the axial walls and cavity floor. On the other hand, loading significantly reduced the µTBS of Optibond Solo Plus, whereas it had no significant effect on the µTBS of G-Bond.

An in situ study investigating dentine tubule occlusion of dentifrices following acid challenge.

OBJECTIVES: To investigate the dentine occlusion and acid resistance of dentifrices developed to treat dentine hypersensitivity. METHODS: This was a single centre, single blind, randomised, split mouth, four treatments, two period crossover, in situ study in healthy subjects. Subjects wore buccal intra-oral appliances each fitted with four dentine samples over four consecutive days with one study product applied per appliance; 8% strontium acetate in silica base, 1040 ppm sodium fluoride (Sensodyne(®) Rapid Relief), 8% arginine, calcium carbonate, 1450 ppm sodium monofluorophosphate (Colgate Sensitive Pro-Relief(®)), 1450 ppm sodium fluoride (control paste) and water. On days 3 and 4, two agitated grapefruit juice challenges (ex vivo) occurred for 1 min. At the end of each treatment day 1 dentine sample was removed from each appliance for scanning electron microscopy (SEM). The extent of tubule occlusion was measured using an examiner-based visual scoring index (three trained examiners). RESULTS: In total, 28 subjects ((12 males and 16 females with a mean age of 34.7 years (SD 8.41 years)) completed the study. On day 2, both test dentifrices demonstrated significantly better dentine tubule occlusion than water (p < 0.0001) and control paste (8% strontium p = 0.0003 and 8% arginine p = 0.0019). After 3 and 4 days of twice daily brushing with acid challenges on days 3 and 4 the strontium-based dentifrice demonstrated significantly better dentine occlusion than all other treatments (p < 0.0001). CONCLUSIONS: Strontium acetate and arginine-based dentifrice result in statistically significant dentine tubular occlusion compared to controls, but the arginine-based dentifrice is more susceptible to acid challenge. CLINICAL SIGNIFICANCE: Erosive beverages are an important aetiology in DH by exposing dentine tubules. Their consumption has increased significantly over the past decade in the UK. This 4-day in situ study investigated the properties of commercially available dentifrices designed to occlude dentine tubules and their resistance to an agitated acid challenge.

Durability of resin cement bond to aluminium oxide and zirconia ceramics after air abrasion and laser treatment.

PURPOSE: The erbium laser has been introduced for cutting enamel and dentin and may have an application in the surface modification of high-strength aluminum oxide and zirconia ceramics. The aim of this study was to evaluate the durability of the bond of conventional dual-cured resin cements to Procera Al(2)O(3) and zirconium oxide ceramics after surface treatment with air abrasion and erbium laser. MATERIALS AND METHODS: One hundred twenty Al(2)O(3) and 120 zirconia specimens measuring 3 × 3 × 0.7 mm(3) were divided equally into three groups, and their surfaces treated as follows: either untreated (controls), air abraded with Al(2)O(3) particles, or erbium-laser-treated at a power setting of 200 mJ. The surface of each specimen was then primed and bonded with one of two dual-cured resin cements (either SCP-100 Ceramic Primer and NAC-100 or Monobond S and Variolink II) using a 1-mm thick Tygon tube mold with a 0.75-mm internal bore diameter. After 24 hours and 6 months of water storage at 37°C, a microshear bond strength test was performed at a crosshead speed of 1 mm/min. Surface morphology was examined using a confocal microscope, and failure modes were observed using an optical microscope. The data were analyzed using the Kaplan-Meier nonparametric survival analysis. RESULTS: In the case of zirconia, air abrasion and Erbium:yttrium-aluminum-garnet (Er:YAG) laser treatment of the ceramic surface resulted in a significant reduction in the bond strengths of both resin cements after 6 months water storage; however, when the zirconia surface was left untreated, the SCP-100/NAC-100 group did not significantly reduce in bond strength. In the case of alumina, no treatment, air abrasion and Er:YAG laser treatment of the surface led to no significant reduction in the bond strengths of the three SCP-100/NAC-100 groups after 6 months water storage, whereas all three Monobond S/Variolink II groups showed a significant reduction. CONCLUSION: Er:YAG laser treatment of the zirconia surface did not result in a durable resin cement/ceramic bond; however, a durable bond between a conventional dual-cured resin cement and Procera All Ceram and Procera All Zirkon was formed using a ceramic primer containing the phosphate monomer, MDP, without any additional surface treatment.

Effect of resin coating and occlusal loading on microleakage of Class II computer-aided design/computer-aided manufacturing fabricated ceramic restorations: a confocal microscopic study.

OBJECTIVE: To evaluate the effect of resin coating and occlusal loading on microleakage of class II computer-aided design/computer-aided manufacturing (CAD/CAM) ceramic restorations. MATERIAL AND METHODS: Molars were prepared for an mesio-occlusal-distal (MOD) inlay and were divided into two groups: non-coated (controls); and resin-coated, in which the cavity was coated with a combination of a dentin bonding system (Clearfil Protect Bond) and a flowable resin composite (Clearfil Majesty Flow). Ceramic inlays were fabricated using the CAD/CAM technique (CEREC 3) and cemented with resin cement (Clearfil Esthetic Cement). After 24 h of water storage, the restored teeth in each group were divided into two subgroups: unloaded or loaded with an axial force of 80 N at a rate of 2.5 cycles/s for 250,000 cycles while stored in water. After immersion in 0.25% Rhodamine B solution, the teeth were sectioned bucco-lingually at the mesial and distal boxes. Tandem scanning confocal microscopy (TSM) was used for evaluation of microleakage. The locations of the measurements were assigned to the cavity walls and floor. RESULTS: Loading did not have a significant effect on microleakage in either the resin-coated or non-coated group. Resin coating significantly reduced microleakage regardless of loading. The cavity floor exhibited greater microleakage compared to the cavity wall. TSM observation also revealed that microleakage at the enamel surface was minimal regardless of resin coating. In contrast, non-coated dentin showed extensive leakage, whereas resin-coated dentin showed decreased leakage. CONCLUSIONS: Resin coating with a combination of a dentin-bonding system and a flowable resin composite may be indicated prior to impression-taking when restoring teeth with CAD/CAM ceramic inlays in order to reduce microleakage at the tooth-resin interface.

Flexural strength of glass fibre-reinforced posts bonded to dual-cure composite resin cements.

The aims of this study were to evaluate the flexural strength of two different types of glass fibre-reinforced posts bonded to dual-cure composite resin cements. Forty glass methacrylate-based fibre posts (GC Fiber Post) and 20 glass fibre inter-polymerizing network posts (everStick POST) were divided into three groups. Group 1 contained 20 GC posts that were bonded to a dual-cure composite cement (UnifilCore). Group 2 contained 20 Stick Tech posts that had adhesive applied (Scotchbond Multipurpose resin) and were bonded to a dual-cure composite resin cement (RelyX Unicem). Group 3 contained 20 GC posts that were pretreated with a silane-coupling agent before being treated with resin and composite, as in group 1. A 4-point bend test was carried out to failure on all of the groups. Failure modes were determined using scanning electron microscopy. Pretreatment of the post surface with the silane-coupling agent did not increase the flexural strength. The flexural strength of the Stick Tech post was significantly lower than the flexural strength of the GC post. The mode of failure for the GC Posts was adhesive, whereas the Stick Tech posts failed cohesively. Different flexural strengths and failure modes were observed among the two fibre post-resin systems.

Effect of resin coating on adhesion and microleakage of computer-aided design/computer-aided manufacturing fabricated all-ceramic crowns after occlusal loading: a laboratory study.

This study investigated the effect of resin coating and occlusal loading on adhesion and microleakage of all-ceramic crowns. Molars were prepared for an all-ceramic crown and were divided into two groups: non-coated (control) and resin-coated with Clearfil Tri-S Bond. Crowns were fabricated using CEREC 3 and cemented using Clearfil Esthetic Cement. After 24 h of storage in water, the restored teeth in each group were divided into two subgroups: unloaded, or loaded while stored in water. Mechanical loading was achieved with an axial force of 80 N at 2.5 cycles s(-1) for 250,000 cycles. After immersion in Rhodamine B, the specimens were sectioned and processed for microleakage evaluation by confocal microscopy, which was followed by further sectioning for microtensile bond testing. Loading had no significant effect on microleakage in either the resin-coated or non-resin-coated groups. Resin coating did not reduce the microleakage at the dentine interface but increased the microleakage at the enamel interface. All the beams fractured during slicing when non-coated and loaded. The bond strengths of non-coated and unloaded, resin-coated and unloaded, and resin-coated and loaded groups were 15.82 +/- 4.22, 15.17 +/- 5.24, and 12.97 +/- 5.82 MPa, respectively. Resin coating with Clearfil Tri-S Bond improved the bonding of resin cement to dentine for loaded specimens. However, it was not effective in reducing the microleakage, regardless of whether it was loaded or unloaded.

Evaluation of the surface roughness and morphologic features of Y-TZP ceramics after different surface treatments.

OBJECTIVE: This study aimed to investigate the effect of different energy intensities of the Er:YAG laser and of air abrasion with Al(2)O(3) particles on the surface roughness and morphologic characteristics of yttrium-stabilized tetragonal zirconia (Y-TZP) ceramics. BACKGROUND DATA: Surface roughness enhances the micromechanical interlocking of luting agents to ceramic surfaces. However, the most appropriate surface treatment for Y-TZP ceramics has yet to be determined. MATERIALS AND METHODS: Two Y-TZP materials were evaluated: Cercon Smart Ceramics and Procera Zirconia. Thirty plates from each ceramic material were randomly divided into five groups according to the surface treatment received (none [control], air abrasion, or irradiation with the Er:YAG laser at three different energy intensities [200, 400, or 600 mJ]). After the surface treatments, the ceramic plates were gold-coated and their surface roughness (Ra, microm) was measured using confocal microscopy. For each ceramic system, the surface roughness was analyzed through two-way ANOVA/Tukey's test, with a 5% significance level. Changes in the morphological characteristics of the ceramics were examined through light and scanning electron microscopy. RESULTS: For both zirconia-based materials, irradiation with 400 mJ or 600 mJ increased surface roughness and provided significant morphological changes. Air-abraded Cercon surfaces were rougher compared to the ones irradiated with 200 mJ of laser energy, whereas Procera surfaces irradiated with 200 mJ were rougher than the air-abraded ones. CONCLUSIONS: Higher laser power settings (400 and 600 mJ) cause excessive material deterioration, making them unsuitable as surface treatments for zirconia surfaces. Irradiation with 200 mJ provides mild surface alterations, with intermediary features between the effects of air abrasion and higher laser intensities.

Long-term durability of one-step adhesive-composite systems to enamel and dentin.

This study evaluated the long-term durability of three one-step adhesive-composite systems to ground enamel and dentin. Twenty-seven teeth were randomly divided into three groups of nine. The first group had its crowns sectioned to expose superficial dentin, which was then ground with 600 grit SiC paper. One of three one-step adhesives: a trial bonding agent, OBF-2; i Bond or Adper Prompt L-Pop was applied to the dentin of three teeth and built-up with the corresponding resin composite (Estelite sigma, Venus or Filtek Supreme). The second group of nine teeth had their enamel approximal surfaces ground with wet 600-grit SiC paper, then one of the three one-step adhesives was applied and built-up with resin composite. The bonded specimens were sliced into 0.7 mm-thick slabs. After 24 hours and one year of water storage at 37 degrees C, the slabs were sectioned into beams for the microtensile bond strength test. Failure modes were observed using optical and electron scanning microscopy. The third group of nine teeth had approximal wedge-shaped cavities prepared above the CEJ into dentin. Two-to-three grains of rhodamine B were added to each of the three adhesives prior to restoring the cavities with resin composite. After 24 hours storage, the teeth were sectioned and their interfaces examined with a laser scanning confocal microscope. The bond strengths of the three adhesive-composite systems to both enamel and dentin significantly lessened after one year of water storage, however, there was no significant difference between the materials.

Microtensile bond strength of resin-post interfaces created with interpenetrating polymer network posts or cross-linked posts.

OBJECTIVE: The purpose of this study was to evaluate the microtensile strength of composite bonded to interpenetrating polymer network (IPN) or cross-linked glass fibre posts and to observe the failure modes by using light and scanning electron microscopy. METHODS: Twenty posts containing IPN resin matrix and 20 posts containing cross-linked epoxy polymer matrix were used for testing. One half of the posts from each type was treated with Stick Resin, the other half was treated with OptiBond. Composite resin was used to build up a block on the bonding surface. Tensile strength data was analysed statistically using the non-parametric Kaplan-Meier survival analysis. The distribution of failure modes as a function of post type/bonding agent was evaluated using the chi(2) test. RESULTS: The mean tensile strength values were lower for the groups bonded with OptiBond and higher for the groups bonded with Stick Resin (p = 0.017), the type of post used had no statistical significance (p = 0.263). All the IPN posts showed cohesive failure within the post The cross-linked posts demonstrated a higher number of adhesive failures and lower number of cohesive failures within the post (chi(2) = 0.0001). CONCLUSIONS: Stick Resin was more effective than OptiBond in bonding composite cores to fibre posts. Post fracture was the failure mode of IPN posts, debonding of the composite core was the failure mode of most of cross-linked posts. These different failure modes may appear clinically in endodontically treated teeth restored with the post types tested in this study.

Microtensile bond strength of resin-post interfaces created with interpenetratingpolymer network posts or cross-linked posts

Objective: The purpose of this study was to evaluate the microtensile strength of composite bonded to interpenetratingpolymer network (IPN) or cross-linked glass fibre posts and to observe the failure modes by using light and scanningelectron microscopy. Methods: Twenty posts containing IPN resin matrix and 20 posts containing cross-linkedepoxy polymer matrix were used for testing. One half of the posts from each type was treated with Stick Resin, theother half was treated with OptiBond. Composite resin was used to build up a block on the bonding surface. Tensilestrength data was analysed statistically using the non-parametric Kaplan-Meier survival analysis. The distributionof failure modes as a function of post type/bonding agent was evaluated using the ÷² test. Results: The mean tensilestrength values were lower for the groups bonded with OptiBond and higher for the groups bonded with Stick Resin(p = 0.017), the type of post used had no statistical significance (p = 0.263). All the IPN posts showed cohesivefailure within the post The cross-linked posts demonstrated a higher number of adhesive failures and lower numberof cohesive failures within the post (÷² = 0.0001).Conclusions: Stick Resin was more effective than OptiBond in bonding composite cores to fibre posts. Post fracturewas the failure mode of IPN posts, debonding of the composite core was the failure mode of most of cross-linkedposts. These different failure modes may appear clinically in endodontically treated teeth restored with the post typestested in this study (AU)

Operative dentistry and the abuse of dental hard tissues: confocal microscopical imaging of cutting.

We reviewed studies wherein the cutting of dental tissues, simulating interactions that would occur under clinical circumstances in the mouth, have been observed directly-first by real time, video rate, stereoscopic, three-dimensional scanning electron microscopy; and second and more conveniently, by video rate confocal optical microscopy. We have observed, directly, both the interactions of slow-moving cutting instruments emulating "chisels" and high-speed events, including the effects of rotary burs and air-propelled abrasive particles and soft powder slurries. The observational data contribute to our basic understanding of the functional behavior of dental tissues and formed a useful background for the practitioner of operative dentistry.

Micropermeability of current self-etching and etch-and-rinse adhesives bonded to deep dentine: a comparison study using a double-staining/confocal microscopy technique.

Water sorption decreases the mechanical properties and the bond strengths of resin-bonded dentine. The aim of this study was to evaluate the micropermeability of several self-etching and etch-and-rinse adhesives. Optibond FL, Silorane, Scotchbond 1XT, G-Bond, and DC-Bond were bonded under simulated pulpal pressure. A 10 wt% solution of ammoniacal silver nitrate and a 1 wt% solution of rhodamine B were injected into the pulp chamber at 20 cm of water pressure. The dentine-adhesive interfaces were examined using a confocal scanning microscope. Micropermeability was detected in all the adhesives. DC-Bond, G-Bond, and Scotchbond 1XT showed voids along the resin-bonded interface. Silorane and Optibond FL showed an adhesive layer that was free from water trees and micropermeability. The double staining technique is a method that gives accurate results in the study of the resin-dentine micropermeability. Each class of adhesive has a different distribution of micropermeability. The higher the micropermeability, the higher the risk of defects at the resin-dentine interface, which may represent the pathway for hydrolytic and enzymatic degradation of resin-dentine bonds over time.

Cyclic loading of endodontically treated teeth restored with glass fibre and titanium alloy posts: fracture resistance and failure modes.

The aims of this in-vitro investigation were to compare the fracture resistance and the failure modes of endodontically treated teeth restored with glass fibre-reinforced posts with those of teeth restored with titanium-alloy posts. A total of 60 single-rooted human mandibular premolars were endodontically treated. The teeth were divided into two experimental and one control group. Post spaces 9mm long were prepared in the roots of the experimental groups in which glass fibre-reinforced posts (Group A) and titanium-alloy posts (Group B) were cemented. In the control group (Group C), no post was inserted. The specimens were stored in normal saline for a period of three weeks before being intermittently loaded at an angle of 30 degrees degrees to the long axis of the tooth at a frequency of two loads of 40N per second. Log-rank test used for the overall analysis revealed that there was no significant difference of fracture resistance between teeth restored with glass fibre-reinforced posts (Group A) and titanium-alloy posts (Group B). The survival of the control group was found to be significantly inferior to that of the experimental groups. There was no significant difference in the number of failures between the two experimental groups. There was significantly more core and post failure for the glass fibre-reinforced posts, root and core failure for the titanium-alloy posts and core failure for the control group. The results suggest that post failures are more frequent in teeth restored with quartz fibre posts and root fractures are more frequent in teeth restored with titanium posts.

Crack closure on rehydration of glass-ionomer materials.

Moisture-sensitivity of immature glass-ionomer cements suggests that hydration-induced volumetric expansion might close and potentially heal established cracks. Crack closure in glass-ionomer cements (GICs) was observed following rehydration. Circular cavities were prepared in 15 teeth: 10 were restored with resin-modified GICs (5 with Fuji II LC and 5 with Photac-Fil) and 5 were restored with a conventional GIC (Fuji IX); all were dehydrated for 1 min with air and imaged immediately by confocal microscopy. Crack formation in each was located, after which water was placed on the surface and observed for 15 min via a CCD camera. Dehydration caused cracks with measurable gaps, while rehydration resulted in varying degrees of closure: closure was limited in the conventional GIC, and complete or near complete along part/s of the crack in the resin-modified GICs. In all, closure movement became imperceptible after the first 10 min. Statistical analysis indicated no significant difference between the closure behavior of all materials. However, the resin-modified GICs appeared to show a greater potential for closure of established cracks than the conventional GIC upon rehydration.

Density of dentinal tubules affects the tensile strength of root dentin.

OBJECTIVES: The aim of this study is to count the dentinal tubules in the coronal and middle-apical third of root dentin of teeth extracted due to the progression of periodontal disease, and to compare the Ultimate Tensile Strength (UTS) of the same areas. The research hypothesis was that root dentin areas with different densities of dentinal tubules would also show different UTS values. METHODS: From 10 caries free maxillary central, lateral incisors and canines, extracted for periodontal reasons from three patients, cylindrical specimens approximately 10 mm long were prepared parallel to the long axis of the root and then divided into two parts using a low speed diamond saw one from the coronal third of the root, (Group 1) and one from the middle-apical third of the root (Group 2). The density of the dentinal tubules of the specimens of the two groups was measured by means of a scanning electron microscope and the UTS of the specimens was measured by a microtensile test. One way ANOVA was used to assess the effect of specimen location (coronal specimens vs. middle-apical specimens) on UTS. The differences in the density of dentinal tubules between coronal and middle-apical specimens were also subjected to statistical analysis using one-way ANOVA. RESULTS: UTS values of middle-apical specimens were found to be significantly (p < 0.05) higher than those of coronal specimens. The results of the one-way analysis of variance showed that the number of dentinal tubules of the samples from the coronal part of the root groups was significantly higher than that of samples from the middle-apical part (p < 0.05). SIGNIFICANCE: These results suggest that high values of tensile strength of the dentin are associated with low densities of dentinal tubules and that apical areas of root dentin are more resistant to tension than coronal ones.

The morphology and stability of resin-modified glass-ionomer adhesive at the dentin/resin-based composite interface.

PURPOSE: To evaluate the interface with tooth structure, mode of failure and stability of Fuji Bond LC (FBLC) resin-modified glass-ionomer bonding system. MATERIALS AND METHODS: The study was in three main parts. The first part with interfacial characteristics of FBLC. The micropermeability of the FBLC/dentin interface of restored cavities in extracted teeth, after fluorescent dye was introduced into the pulp chamber, was assessed by confocal microscopy. In other teeth, confocal microscopy was also used to examine trhe failure of FBLC bonded to flat dentin surfaces, on shear loading. In the second part, cervical cavities restored with FBLC (with and without light-curing) and a resin-based composite were examined for stability of the interface over the first 15 minutes. In the last part of the study, a new fluorescent dye was mixed with FBLC for restoration of cavities and subsequent examination using 2-photon imaging techniques. RESULTS: FBLC adapted well to tooth structure, had an interface with dentin that was permeable to fluid and displayed the absorption layer. Shear loading at the dentin interface resulted in complex failure with areas of cohesive failure where the absorption layer was present. Light-curing of FBLC seemed to produce a stable restorative while "co-curing" resulted in an unstable situation, with the appearance of an emmisable exudate from the FBLC. Advanced fluorescent imaging of the material itself seemed to suggest that there was a movement of aluminum ions in a manner similar to other glass-ionomer cements. The presence of HEMA in the matrix of the cement associated with the absorption layer was also demonstrated.