Dentin bonding: effect of tubule orientation on hybrid-layer formation

Effects of C-factor on dentin bonding using various adhesive systems

Aims and Background

This study evaluated the effect of C-factor on the bond strength of a resin composite to floor and wall dentin using various adhesive systems.

Materials and Methods

Four dentin substrates (flat wall, flat floor, cavity wall, or cavity floor) were prepared on human molars. Each specimen was restored with one of three adhesives; Clearfil SE Bond, Single Bond, or Clearfil tri-S Bond followed by buildup or filling using Z100 resin composite. The specimen was cut perpendicular to the bonded surface parallel to the floor or wall to obtain beams after light curing at 24,000 mJ/cm². The microtensile bond strength to wall specimens or the cavity floor was determined. Data were analyzed.

Results

All adhesive systems exhibited the highest bond strength to flat wall group (p < 0.05). The bond strength to the cavity group was significantly lower than that to the respective flat group regardless of the bonding system (p < 0.05). There was no significant difference in bond strength with Clearfil SE Bond and Clearfil tri-S Bond between the cavity wall and cavity floor (p > 0.05).

Conclusion

The findings suggested that the strength of bonding to the cavity floor and cavity wall was affected by C-factor regardless of the adhesive system. Bonding to flat wall was higher than flat floor regardless of the adhesive system. Self-etching system provided uniform bond to the cavity wall and cavity floor dentin. However, total etching system reduced bond to the cavity floor than to the cavity wall.

Phenotypic features of dentinogenesis imperfecta associated with osteogenesis imperfecta and COL1A2 mutations

OBJECTIVE

Dentinogenesis imperfecta (DI) requires dental treatment. This study investigated the characteristics of DI teeth associated with osteogenesis imperfecta (OI) and COL1A2 mutations.

STUDY DESIGN

Whole exome and Sanger sequencing were performed. Three primary teeth (called "OIDI teeth") obtained from 3 unrelated COL1A2 patients were investigated and compared with 9 control teeth from age-matched healthy individuals using colorimetry, micro-computed tomography, Knoop microhardness, energy dispersive X-ray spectroscopy, scanning electron microscopy, and histology.

RESULTS

All patients were identified with heterozygous glycine substitutions in COL1A2. The COL1A2 mutations, c.1531G>T and c.2027G>T, were de novo, whereas c.3106G>C was inherited. OIDI1, 2, and 3 teeth had a substantial decrease in dentin microhardness and lightness. OIDI2 enamel microhardness was significantly reduced, whereas OIDI1 and 3 had enamel microhardness comparable to that of control individuals. The OIDI1 pulp cavity was large; OIDI2 was narrow; and OIDI3 was obliterated. OIDI1 and 3 had significantly higher carbon levels than those in control individuals. Numerous ectopic calcified masses, sparse and obstructed dentinal tubules, dentin holes, and collagen disorientation were observed.

CONCLUSIONS

OIDI teeth had reduced lightness and variable pulp morphology. Weak dentin, mineral disproportion, and abnormal ultrastructure could contribute to the brittleness of OIDI teeth and adhesive restoration failure. Here, we expand the phenotypic spectrum of COL1A2 mutations and raise awareness among dentists seeing patients with OI.

Impact of Dentinal Tubule Orientation on Dentin Bond Strength

This study aimed to determine the impact of dentinal tubule orientation on dentin bond strength to provide a reference for clinical cavity preparation in resin-bonded restoration. Patients aged 13-16 years were selected, including 18 males and 21 females. Forty-eight human maxillary first premolars from orthodontic extractions were chosen to prepare the test models with the dentinal tubule orientations perpendicular and parallel to the bonding substrate. The test models in the vertical and parallel groups were divided into three groups: total-etching with 20% phosphoric acid, total-etching with 35% phosphoric acid and self-etching, with the dentinal tubule surfaces bonded with composite resin blocks in each group. After the standard test models of dentinal tubule-composite resin blocks were placed in distilled water and stored at 37°C for 24 h, shearing tests were performed using a universal material testing machine at a crosshead speed of 0.5 mm/min. The bond strength values in the vertical group were 19.33±1.59 MPa for the 20% phosphoric acid group, 21.39±2.34 MPa for the 35% phosphoric acid group, and 16.88±1.54 MPa for the self-etching group. The bond strength values in the parallel group were 24.53±1.99 MPa for the 20% phosphoric acid group, 25.16±2.88 MPa for the 35% phosphoric acid group, and 20.83±1.99 for the self-etching group. After using same total-etching adhesive, the shear bond strength of the parallel group was higher than that of the vertical group, and the difference was statistically significant (P<0.05). Regardless of vertical group or parallel group, the difference in the bond strength value between the total-etching groups and the self-etching group was statistically significant (P<0.05). It was concluded that the dentin bonding substrate which was parallel to the direction of the dentin tubule achieved an improved bond strength; the total-etching adhesives achieved higher bond strengths in dentin bond than the self-etching adhesives.

Effects of C-factor on bond strength to floor and wall dentin

This study evaluated the effect of C-factor on the bond strength of a resin composite to floor and wall dentin using two adhesive systems. Box-form cavities were prepared on human molars, following the walls of half of the cavities were removed to create flat dentin surfaces for bonding. Each specimen was then restored using one of two adhesives (Clearfil SE Bond or Clearfil tri-S Bond) and filled or built up using Z100 resin composite. After light-curing, the specimen was cut perpendicular to the bonded surface parallel to the floor or wall to obtain beams. The micro-tensile bond strength to the flat floor, flat wall, cavity floor, or cavity wall was determined. Resin composite bonded more strongly to the flat wall dentin than to the flat floor dentin, regardless of the adhesive system used. Bonding to the cavity wall was higher affected by C-factor than to the cavity floor.

Effect of 180-Day Water Storage on Bonding Effectiveness of Self-Adhesive Systems to Occlusal and Proximal Dentin

PURPOSE

This study aimed to evaluate the microshear bond strength (μSBS) values of adhesive systems to occlusal and proximal dentin submitted to water storage aging.

MATERIALS AND METHODS

Occlusal and proximal dentin surfaces were obtained from 90 molars, polished with 600-grit SiC and divided according to the type of adhesive system: one total-etch and two self-etch. Starch tubing was used to perform 1 mm² cylindrical composite resin restorations. The specimens were aged in distilled water during different storage times: 24 hours, 3 months, and 6 months (n = 10). The specimens were submitted to μSBS test. The μSBS values in MPa were subject to three-way ANOVA and post hoc Tukey test (p < 0.05).

RESULTS

There was no statistical difference in the μSBS values among the storage times (p = 0.72); however, the dentin region (p < 0.01) and the adhesive system (p < 0.01) significantly affected the μSBS. The proximal surface (14.7 ± 3.3 MPa) presented higher μSBS values than the occlusal dentin (10.9 ± 4.1 MPa). The all-in-one adhesive system (GB) achieved the highest μSBS mean (17.0 ± 1.7 MPa).

CONCLUSION

Both material and dentin surface factors affected the composite-dentin bond strength; however, the water storage did not influence bonding effectiveness over time.

Bond Strength of High-Viscosity Glass Ionomer Cements is Affected by Tubular Density and Location in Dentin?

This study evaluated the influence of tubular density of different dentin depths and location on the bond strength of high-viscosity glass ionomer cements (GIC). A total of 20 molars were selected and assigned into six experimental groups, considering two different high-viscosity GICs-Fuji IX (FIX) or Ketac Molar (KM), and dentin location-proximal, occlusal superficial, or occlusal deep dentin (n=10). Teeth were cut and a topographical analysis of four sections per group was performed to obtain data about the tubular density of each different dentin location and depths by laser scanning confocal microscopy (100×). Polyethylene tubes were placed over the pretreated surfaces and filled with one of the GICs. Microshear bond strength (µSBS) test was performed after storage in distilled water (24 h at 37°C). Failure modes were evaluated using a stereomicroscope (400×). Multilevel regression analysis was performed to compare the results at a significance level set at 5%. The tubule density was inversely proportional to the bond strength for both GICs (p<0.05). Adhesive/mixed failure prevailed in all experimental groups. Proximal (30036.5±3433.3) and occlusal superficial 29665.3±1434.04 dentin shows lower tubule density, resulting in a better GIC bonding performance (proximal: FIX-3.61±1.05; KM-3.40±1.62; occlusal superficial: FIX-4.70±1.85; KM-4.97±1.25). Thus, we can concluded that the lowest tubule density in proximal and occlusal superficial dentin results in a better GIC bond strength performance.

Influence of fluorescent dye on physical-mechanical properties of luting cements for confocal microscopy analysis

AIMS

To evaluate the influence of a fluorescent dye (rhodamine B) on the physical and mechanical properties of three different luting cements: a conventional adhesive luting cement (RelyX ARC, 3M/ESPE), a self-adhesive luting cement (RelyX U-200, 3M/ESPE), and a self-etching and self-adhesive luting cement (SeT PP, SDI).

MATERIALS AND METHODS

The cements were mixed with 0.03 wt% rhodamine B, formed into bar-shaped specimens (n = 10), and light cured using an LED curing unit (Radii, SDI) with a radiant exposure of 32 J/cm(2) . The Knoop hardness (KHN), flexural strength (FS), and Young's modulus (YM) analyses were evaluated after storage for 24 h.

RESULTS

Outcomes were subjected to two-way ANOVA and Tukey's test (P = 0.05) for multiple comparisons. No significant differences in FS or YM were observed among the tested groups (P ≥ 0.05); the addition of rhodamine B increased the hardness of the luting cements tested.

CONCLUSION

The addition of a fluorescent agent at 0.03 wt% concentration does not negatively affect the physical-mechanical properties of the luting cement polymerization behavior.

A Comparative Evaluation of the Retention of Tooth Coloured and Stainless Steel Endodontic Posts: An In-vitro Study

AIMS

This in vitro study evaluated: a) the retention of stainless steel posts of 1.5 mm diameter which were cemented with Zinc Phosphate cement versus Glass fiber posts with 1.1 mm, 1.3 mm and 1.5 mm diameters which were cemented with resin cement and b) the effect of change in diameter on the retention of Glass fiber posts with 1.1 mm, 1.3 mm and 1.5 mm diameters.

MATERIALS AND METHODS

Sixty extracted mandibular premolar teeth were endodontically treated and randomly assigned to four groups of fifteen teeth each. In Groups I, II and III glass fibre posts with diameters 1.1 mm, 1.3 mm and 1.5 mm were cemented by using resin cement. In Group IV, stainless steel posts with diameter 1.5 mm were cemented by using zinc phosphate cement. The specimens were tested for tensile loading at a cross head speed of 2.0 mm/min, on a universal testing machine.

STATISTICAL ANALYSIS USED

One way analysis of variance and Tukey's (post-hoc) test.

RESULTS

Mean tensile strength from highest to lowest was in the order of Group IV, Group II, Group III, Group I. Statistically significant differences were observed between the mean tensile strengths between Groups I and II, Groups I and III, Groups I and IV, Groups II and IV, Groups III and IV, while non significant differences were observed between Groups II and III.

CONCLUSION

Stainless steel posts were more retentive than glass fibre posts. Glass fibre posts with 1.3 mm or 1.5 mm diameters provided significantly greater retention as compared to 1.1 mm diameter posts.

Effect of remaining dentin thickness on bond strength of various adhesive systems to dentin

The aim of this study was to evaluate the effect of remaining dentin thickness (RDT) on resin composite bond strength to dentin surfaces when using various adhesive systems. One of three adhesives, Clearfil SE Bond, Single Bond or Clearfil Tri-S Bond, followed by Z100 resin composite were built up on flat dentin surfaces of human molars. The teeth were sectioned obtaining beams with crosssectional areas of approximately 1 mm(2). RDT was measured and microtensile bond strength was determined. Resulting data were categorized into four groups: RDT<2 mm; 2≤RDT<3 mm; 3≤RDT<4 mm; RDT≥4 mm. Clearfil SE Bond showed a correlation between µTBS and RDT. Single Bond showed no significant difference in µTBS for any RDT. The bond strength of resin composite to the different RDT flat dentin surfaces was affected by the adhesive system used.

Comparative evaluation of the effects of Nd:YAG laser and a desensitizer agent on the treatment of dentin hypersensitivity: a clinical study

Abstract Objective: The aim of this randomized longitudinal clinical study was to assess different treatment protocols for dentin hypersensitivity with high-power laser, desensitizing agent, and its association between high-power laser and desensitizing agent, for a period of 6 months.

BACKGROUND DATA

The literature shows a lack of treatment for dentin hypersensitivity, and lasers are contemporary alternatives.

METHODS

After inclusion and exclusion analysis, volunteers were selected. The lesions were divided into three groups (n=10): G1, Gluma Desensitizer (Heraeus Kulzer); G2, Nd:YAG Laser (Power Laser(™) ST6, Lares Research®) contact mode, laser protocol of 1.5 W, 10 Hz, and 100 mJ,≈85 J/cm(2), four irradiations performed, each for 15 sec, in mesiodistal and occluso-apical directions, totaling 60 sec of irradiation with intervals of 10 sec between them; G3, Nd:YAG Laser+Gluma Desensitizer. The level of sensitivity to pain of each volunteer was analyzed by visual analog scale (VAS) using cold air stimuli and exploratory probe 5 min, 1 week, and 1, 3, and 6 months after treatment. Data were collected and subjected to statistical analysis that detected statistically significant differences between the various studied time intervals of treatments (p>0.05).

RESULTS

For the air stimulus, no significant differences were found for each time interval. For the long-term evaluation, all groups showed statistical differences (p>0.05), indicating that for G2 and G3, this difference was statistically significant from the first time of evaluation (post 1), whereas in G1, the difference was significant from the post 2 evaluation (1 week). Comparison among groups using the probe stimulation showed significant differences in pain (p<0.001). Only in G1 and G3 did this difference become significant from post 01.

CONCLUSIONS

All protocols were effective in reducing dentinal hypersensitivity after 6 months of treatment; however, the association of Nd:YAG and Gluma Desensitizer is an effective treatment strategy that has immediate and long-lasting effects.

Effect of Tubular Orientation on the Dentin Bond Strength of Acidic Self-etch Adhesives

The effectiveness of self-etch adhesive systems is dependent on both the physical properties of the adhesive and the integrity of the adhesive-dentin interface. Most importantly, the integrity of the adhesive-dentin interface is affected by the tubule orientation of the intaglio dentin structure. The initial bond strength and potential durability of the self-etch adhesive interfaces to dentin are significantly affected by both the adhesive pH and occlusally-oriented tubule direction. The clinical relevance to the dentist is that the results reported for bond strengths by both manufacturers and independent researchers should be interpreted and compared based on the orientation of the dentin used for the measurements, particularly for those adhesives that are very acidic (pH lower than 2).

Influence of differently oriented dentin surfaces and the regional variation of specimens on adhesive layer thickness and bond strength

STATEMENT OF THE PROBLEM

Adhesive systems can spread differently onto a substrate and, consequently, influence bonding.

PURPOSE

The purpose of this study was to evaluate the effect of differently oriented dentin surfaces and the regional variation of specimens on adhesive layer thickness and microtensile bond strength (MTBS).

MATERIALS AND METHODS

Twenty-four molars were sectioned mesiodistally to expose flat buccal and lingual halves. Standardized drop volumes of adhesive systems (Single Bond [SB] and Prime & Bond 2.1 [PB2.1]) were applied to dentin according to the manufacturer's instructions. Teeth halves were randomly divided into groups: 1A-SB/parallel to gravity; 1B-SB/perpendicular to gravity; 2A-PB2.1/parallel to gravity; and 2B-PB2.1/perpendicular to gravity. The bonded assemblies were stored in 37 degrees C distilled water for 24 hours and then sectioned to obtain dentin sticks (0.8 mm2). The adhesive layer thickness was determined in a light microscope (x200), and after 48 hours the specimens were subjected to MTBS test. Data were analyzed by one-way and two-way analysis of variance and Student-Newman-Keuls tests.

RESULTS

Mean values (MPa +/- SD) of MTBS were: 39.1 +/- 12.9 (1A); 32.9 +/- 12.4 (1B); 52.9 +/- 15.2 (2A); and 52.3 +/- 16.5 (2B). The adhesive systems' thicknesses (microm +/- SD) were: 11.2 +/- 2.9 (1A); 18.1 +/- 7.3 (1B); 4.2 +/- 1.8 (2A); and 3.9 +/- 1.3 (2B). No correlation between bond strength and adhesive layer thickness for both SB and PB2.1 (r = -0.224, p = 0.112 and r = 0.099, p = 0.491, respectively) was observed.

CONCLUSIONS

The differently oriented dentin surfaces and the regional variation of specimens on the adhesive layer thickness are material-dependent. These variables do not influence the adhesive systems' bond strength to dentin. CLINICAL SIGNIFICANCE Adhesive systems have different viscosities and spread differently onto a substrate, influencing the bond strength and also the adhesive layer thickness. Adhesive thickness does not influence dentin bond strength, but it may impair adequate solvent evaporation, polymer conversion, and may also determine water sorption and adhesive degradation over time. In the literature, many studies have shown that the adhesive layer is a permeable membrane and can fail over time because of its continuous plasticizing and degradation when in contact with water. Therefore, avoiding thick adhesive layers may minimize these problems and provide long-term success for adhesive restorations.

Microtensile bond strength between crown and root dentin and two adhesive systems

STATEMENT OF PROBLEM

Since bonding agent effectiveness is usually evaluated on coronal substrates, available knowledge for judging the effectiveness of bonds to root dentin is insufficient.

PURPOSE

The objective of this study was to evaluate the bond strength of 2 adhesive systems to crown, cervical finish line, and post space dentin.

MATERIAL AND METHODS

Twenty bovine maxillary incisors were used in this study. Teeth were sectioned along the cemento-enamel junction using a low-speed diamond blade to separate the crowns and roots. Then the crowns and roots were each divided into 2 groups, according to the 2 adhesive systems tested (n=10). The facial enamel surfaces of the crowns were abraded with 600-grit silicon carbide paper to expose flat, midcoronal dentin surfaces. Drills and a diamond rotary cutting instrument were used in a low-speed handpiece to prepare post spaces in the root canals. The same diamond rotary instrument was used to prepare horizontally flat surfaces in the cervical areas, similar to the horizontal aspect of a shoulder finish line. Composite resin was placed incrementally into the post spaces, over the flat cervical shoulder areas, and on the coronal dentin. Bonded beam specimens (0.5 mm(2) of cross-sectional area) derived from crown, cervical finish line, and post space dentin, were prepared for microtensile bond testing and tested in tension. Data were analyzed using 2-way ANOVA and Tukey post hoc test (alpha=.05). Failure patterns of tested specimens were analyzed using scanning electron microscopy.

RESULTS

The mean tensile bond strength values (SD) (MPa) were: Single Bond-crown: 29.8 (4.0); Single Bond-finish line: 18.7 (4.3); Single Bond-post space: 17.0 (4.8); Clearfil SE Bond-crown: 30.1 (6.4); Clearfil SE Bond-finish line: 30.4 (5.3); and Clearfil SE Bond-post space: 17.0 (4.2). Bond strengths to post space dentin were lower than those to coronal dentin for both adhesives (P<.001). However, no significant difference was observed between coronal and finish line dentin for Clearfil SE Bond.

CONCLUSION

Bond strength was reduced when adhesives were used in bonding to post space dentin. Cervical finish line sites bonded using Clearfil SE Bond adhesive yielded bond strength similar to that of coronal dentin sites.

Use of fluorescent compounds in assessing bonded resin-based restorations: a literature review

OBJECTIVES

This work reviews fundamental concepts involved with fluorescent imaging in the dental materials field.

DATA

Fluorescent dyes have been widely used: incorporated into adhesive system components, placed in the pulp chamber and allowed to diffuse toward the restorative interface, as well as used as a visible tracer in microleakage tests.

CONCLUSIONS

Although use of fluorescent imaging has substantially contributed to the existing knowledge base, there is no standardized methodology used, and as a result, interpretation of study results as well as comparison of results among studies remains questionable.

Hybrid layer thickness and resin tag length of a self-etching adhesive bonded to sound dentin

OBJECTIVES

the purpose of this study is to employ optical microscopy to measure the thickness of the hybrid layer and the penetration (tags) of an aggressive self-etching adhesive system into sound dentin.

METHODS

occlusal cavities were prepared in 40 extracted human posterior teeth. The prepared teeth were randomly assigned to four experimental groups with 10 specimens each. The self-etching adhesive system Adper Prompt L-Pop was applied to the dentin surface as follows: Group 1: cavosurface enamel was etched for 60 s and dentin for 20 s with 35% phosphoric acid gel, immediately followed by application of the self-etching adhesive with a brush to the entire cavity for 15 s; Groups 2, 3, and 4: no pre-etching was performed, and the self-etching adhesive was applied to both enamel and dentin for 15, 30 and 45 s, respectively. After curing, the cavities were filled with composite resin Filtek Z250. Afterwards, the teeth were decalcified and the restorations were carefully removed for later embedding in paraffin. The specimens were serially sectioned at 6 microm of thickness and sequentially mounted in glass slides. These sections were stained with Brown and Brenn staining for posterior analysis and measurement of the hybrid layer and resin tags on a light microscope with a micrometric ocular 40/075. The results were submitted to analysis of variance at the 5% level.

RESULTS

whenever there was significance, the Tukey test was applied at the 5% level. The specimens receiving application of acid etching before the self-etching adhesive displayed a larger thickness of the hybrid layer; on the other hand, specimens receiving only application of the self-etching adhesive on dentin for 15, 30 and 45 s exhibited similar thickness of the hybrid layer. As regards the resin tags, no statistically significant differences could be found between the study groups.

CONCLUSIONS

it could be concluded that the increase in the time of application of the self-etching adhesive Adper Prompt L-Pop did not significantly influence the formation and thickness of hybrid layer, as well as its penetration into the sound dentin surface.

Permeability of marginal hybrid layers in composite restorations

The goal of adhesive dentistry is to restore the peripheral seal of dentin lost from removal of enamel. Unfortunately, the hybrid layer (HL) that is used to create that seal is permeable to small ions or molecules, even in the absence of detectable, interfacial gap formation via nanoleakage. This nanoleakage results from several mechanisms including incomplete infiltration of adhesive monomers into demineralized collagen matrix, presence of hydrophilic monomers, and insufficient removal of solvent or water that remains trapped inside the HL. These mechanisms lead to a porous interface with nanometer-sized channels that increase the permeability of the HL. The null hypothesis tested in this study was that water and acidic solution storage are able to alter in vitro the resin-dentin interface, further increasing the marginal hybrid layer (MHL) permeability. Class II cavities were made in vitro. The specimens were stored in water for 1 week and in lactic acid solution for 3 days. Polyvinyl siloxane impressions of restoration margins were taken before and after storage in water and lactic acid solution. Polyether replicas were obtained using the silicon impressions as molds. Replicas and original samples were observed under scanning electron microscopy. Lines of water droplets were detected on MHLs and overlying adhesive only after storage. Replicas obtained after acidic solution storage showed great numbers of irregularities such as gaps, voids, and degradation of the dentin-restoration surface margin, but also a great number of droplets. Dentin-restoration resin interfaces absorb water and are damaged by storage in dilute lactic acid. The presence of water droplets probably indicates water that flows out of the interface during the setting time of the impression and thus represents an index of marginal HL water permeability.

Effect of irradiation mode and filling technique on resin/dentin bonding strength in Class I cavities

Factors such as light-curing mode, filling technique and cavity configuration may affect the bonding strength to dentin. This study evaluated the effect of irradiation mode and filling technique on resin/dentin bonding strength on the buccal wall of Class I cavities in human teeth. Occlusal enamel was removed to expose a flat dentin surface. Occlusal cavities (4 x 3 x 3 mm) were prepared in dentin. The adhesive Single Bond was applied according to the manufacturer's instructions and TPH Spectrum composite resin was placed using the following: oblique incremental, horizontal incremental or bulk filling techniques. The composite resin was light-cured either by continuous (600 mW/cm2 for 40 s) or Soft-Start (250 mW/cm2 for 10 s + 600 mW/cm2 for 30 s) modes. Specimens of the control group were obtained by bonding the material to the flat exposed buccal wall of the cavity (C-factor = 1). The teeth were stored in water at 37 degrees C for 24 h and prepared for microtensile testing. Bonded beams of approximately 0.8 mm2 were obtained from the buccal wall and tested with a tension of 0.5 mm/min. Results were analyzed by two-way ANOVA, Tukey's test and Dunnett's test (alpha = 0.05). Incremental placement techniques with both irradiation modes produced higher bonding strength values than the bulk technique (p < 0.05). Bonding strength tested in the cavities had lower values than those obtained in flat dentin surfaces (control group) (p < 0.05), except for incremental fillings using stepped irradiation. Bonding strength to the cavity walls depends on the filling technique and on the irradiation mode of composite resins.

Effects of additional and extended acid etching on bonding to caries-affected dentine

This study evaluated the effects of additional and extended acid etching on microtensile bond strength ( micro TBS) of two adhesive systems to sound (SD) and caries-affected dentine (CAD). Flat surfaces of CAD surrounded by SD of 36 extracted carious third molars were assigned to four treatments (i): self-etching adhesive system (Clearfil SE Bond) applied to dentine surfaces following manufacturer's instructions (MI); (ii) after additional etching for 15 s (35% phosphoric acid, PA); (iii) total-etch one-bottle adhesive (Single Bond) applied to dentine surfaces following MI; or (iv), after etching for 45 s with PA. Composite 'blocks' were built on bonded surfaces and restored teeth were vertically sectioned to obtain bonded slices of 0.7 mm thick. Slices were trimmed to create hourglass-shaped specimens (cross-sectional area of 1 mm(2)), which were tested under tension in a universal testing machine. Additional CAD and SD samples were prepared for scanning electron microscopy observations. Additional and extended etching significantly increased micro TBS to CAD; however, micro TBS of both adhesives to CAD were significantly lower than to SD. Additional and extended etching can improve bonding to CAD; however, adhesives applied on SD showed the best results for bonding.

In vitro microleakage of adhesive-sealed dentin with lactic acid and saliva exposure: a radio-isotope analysis

OBJECTIVES

The aim of this study was to evaluate the dentin-protective potential of two dentin-bonding systems (Syntac and Clearfil SE Bond) on artificial saliva and lactic acid exposure.

METHODS

Radiochemical analysis in combination with polarization-microscopy was used in the current study. Different applications in MOD preparations in irradiated human molars were compared. Untreated cavities and cavities covered with flowable resin served as controls. Forty-eight specimens were immersed in artificial saliva (pH 7.5), 48 in lactic acid (pH 4). Activity of (32)P was measured between days 1 and 21 and loss of mineralized tissue was estimated.

RESULTS

In lactic acid, cavities sealed with single bond, double bond or bond plus cavity sealer application resulted in significantly lower mineralized tissue loss compared to negative controls (p < 0.05). Upon both saliva and lactic acid exposure, bonding plus sealer application proved to be the most protective treatment (p < 0.05).

CONCLUSIONS

Based on these in vitro findings it may be advisable to use a filled cavity sealer or a flowable resin to protect dentin from demineralization. The radiochemical analysis appeared to be valuable in evaluating the protective potential of bonding agents against dentin demineralization.

In vitro evaluation of the retention of composite fiber and stainless steel posts

PURPOSE

This study compared the tensile retentive strength of composite fiber-reinforced dowels luted with a resin cement to stainless steel dowels luted with zinc phosphate cement.

MATERIALS AND METHODS

The crowns of 40 extracted human mandibular premolars were removed with a separating disc 1-mm coronal to the cementoenamel junction. The teeth were randomly divided into 4 groups (n = 10). A post space was prepared in each specimen to a depth of 9 mm, using the drill supplied by the respective manufacturer. For the stainless steel post group, 1.25-mm-diameter posts were cemented with zinc phosphate cement. For the composite fiber reinforced groups, posts with diameters of 1.00, 1.25, and 1.50 mm were luted with a Bisphenol A-Glycidyl Methacrylate (BIS-GMA) resin bonding system (Jeneric/Pentron, Wallingford, CT) according to manufacturer specifications. The specimens were stored in a sealed container with a moist environment for 24 hours, placed in a fixture in an 801 Materials Test Systems (MTS) machine (MTS Systems Corp, Minneapolis, MN), and loaded in tension at a rate of 5.0 mm/min until failure. Differences among the 4 groups were determined using a one-way analysis of variance and Tukey-B post-hoc tests (alpha = 0.05).

RESULTS

The mean loads to failure ranged from 43.9 +/- 10.4 kg for the stainless steel dowel group to 19.9 +/- 5.7 kg for the composite fiber-reinforced 1.00-mm-diameter group. The stainless steel post luted with zinc phosphate cement provided significantly greater tensile resistance than all composite fiber dowel groups. The retention of the 1.00-mm composite fiber-reinforced post was significantly less than the remaining groups.

CONCLUSIONS

Under the conditions of this study, the stainless steel dowel luted with zinc phosphate cement provided significantly greater retention.

Molecular structure of acid-etched dentin smear layers--in situ study

It is commonly reported that acid etchants remove the smear layer, but to date, there has been no chemical evidence to support these observations. The purpose of this study was to determine the molecular structure of acid-etched carbide- and diamond-bur-created smear layers. This project tested the null hypothesis that such smear layers are totally removed with current etchants. Smear layer/demineralized/mineralized dentin interfaces were analyzed at 1- m intervals by micro-Raman spectroscopy. Features associated with the organic component were substantially broadened with loss of fine structure, and mineral peaks were clearly evident in the spectra of acid-etched smear layers. The organic features in the spectra of the EDTA-treated smear layer showed relative intensity ratios similar to demineralized dentin without contribution from the mineral phase. The disorganized collagen within the smear layer was not removed but was denatured by the acid treatment; the mineral was trapped in this gelatinous matrix and shielded from complete reaction.

The ultrastructure of a compomer adhesive interface in enamel and dentin, and its marginal adaptation under dentinal fluid as compared to that of a composite

OBJECTIVES

To visualise the ultrastructure of the interface of SCA compomer adhesive and of Optibond composite adhesive in enamel and dentin, and to relate the findings to the marginal adaptation of these two products in mixed class V restorations.

METHODS

The ultrastructure was investigated using a scanning electron microscope (SEM) with and without prior argon ion etching, an environmental SEM, a field emission SEM, a confocal laser scanning microscope, and a transmission electron microscope. The marginal adaptation was quantified in mixed class V restorations by using the replica technique and a SEM under simulated dentinal fluid before and after simultaneous mechanical and thermal loading.

RESULTS

The ultrastructure of the compomer adhesive interface differed from those of the composite. However, no significant difference was discerned as regards the percentage of "continuous margin" in the enamel marginal area before loading, and in the dentin area before and after loading (p < 0.05; unpaired t-test). Only after loading, the percentage of "continuous margin" in enamel was significantly (p < 0.05; unpaired t-test) better than that of the compomer.

SIGNIFICANCE

The results indicated that the ultrastructure of the adhesive interface allowed no clear conclusions to be drawn as to the quality of marginal adaptation.

A pilot study of confocal laser scanning microscopy for the assessment of undisturbed dental plaque vitality and topography

Confocal microscopy and vital fluorescence techniques were combined for the first time to investigate ex vivo human dental plaque. The vital fluorescence technique used discriminates vital from dead cells, while confocal laser scanning microscopy allows the optical sectioning of undisturbed biofilms leaving the samples intact during analysis. The concomitant use of both methods made an examination of the three-dimensional architecture of dental plaque possible. The topography of plaque biofilms that were allowed to accumulate in situ on glass and enamel was recorded. The distribution of plaque microflora vitality as well as its accumulation varied according to plaque age. A plaque thickness of up to 8, 35 and 45 microm was estimated ex vivo on enamel after 1, 2 and 3 days, respectively. Young and sparse plaque biofilms consisted mainly of dead material. Vital bacteria were observed on top of this dead layers.