Clinical versus laboratory adhesive performance to wet and dry demineralized primary dentin

Purpose: To evaluate the influence of dentin moisture on bond strengths of an etch-and-rinse bonding agent to primary dentin clinically and in the laboratory. Methods: The sample consisted of two groups of 20 caries-free primary second molars: molars in exfoliation period (clinical group) and extracted molars (laboratory group). Class I cavities were prepared in all specimens leaving a flat dentin surface on the pulpal floor. A two-step etch-and-rinse adhesive was vigorously rubbed on either dry (n= 5) or wet demineralized dentin (n= 5) under clinical or laboratory conditions. After restorative procedures, the teeth from the clinical group were extracted after 20 minutes. All samples were processed and underwent microtensile bond strength test and silver nitrate uptake evaluation under scanning electron microscopy. Results: Statistically higher bond strength values were observed when the bonding was performed under laboratory conditions and on a wet demineralized dentin. Most of the failures were adhesive and mixed irrespective of the experimental condition. Silver nitrate uptake occurred in all groups irrespective of the experimental condition. Resin-dentin bond strengths produced in the laboratory in primary teeth may overestimate those produced under clinical circumstances. (Am J Dent 2011;24:221-225).

Effects of Ultramorphological Changes on Adhesion to Lased Dentin-Scanning Electron Microscopy and Transmission Electron Microscopy Analysis

Dentin irradiation with erbium lasers has been reported to alter the composite resin bond to this treated surface. There is still a lack of studies reporting the effect of erbium lasers on dentin organic content and elucidating how laser treatment could interfere in the quality of the resin-dentin interface. This study aimed to evaluate the effect of erbium laser irradiation on dentin morphology and microtensile bond strength (lTBS) of an adhesive to dentin. Seventy-two dentin disks were divided into nine groups (n = 8): G1-Control (600-grit SiC paper); Er:YAG groups: G2-250 mJ/4 Hz; G3-200 mJ/4 Hz; G4-180 mJ/10 Hz; G5-160 mJ/10 Hz; Er, Cr:YSGG groups: G6-2 W/20 Hz; G7-2.5 W/20 Hz; G8-3 W/20 Hz; G9-4 W/20 Hz. Specimens were processed for cross-sectional analysis by scanning electron microscopy (SEM) (n = 3), transmission electron microscopy (TEM) (n = 2), and adhesive interface (n = 3). Forty-five dentin samples (n = 5) were restored and submitted to lTBS testing. ANOVA (alpha = 5%) revealed that G1 presented the highest lTBS values and irradiated groups did not differ from each other. TEM micrographs showed a superficial layer of denatured collagen fibrils. For SEM micrographs, it was possible to verify the laser effects extending to dentin subsurface presenting a rough aspect. Cross-sectional dentin micrographs of this hybridized surface revealed a pattern of modified tags with ringlike structures around it. This in vitro study showed that erbium laser irradiation interacts with the dental hard tissue resulting in a specific morphological pattern of dentin and collagen fibrils that negatively affected the bond strength to composite resin. Microsc. Res. Tech. 74:720-726, 2011. (C) 2010 Wiley-Liss, Inc.

Long-term effect of carbodiimide on dentin matrix and resin-dentin bonds

Objectives: To characterize the interaction of 1-Ethyl-3-[3-dimethylaminopropyl] carbodiimide Hydrochloride (EDC) with dentin matrix and its effect on the resin-dentin bond. Methods: Changes to the stiffness of demineralized dentin fragments treated with EDC/N-hydroxysuccinimide (NHS) in different solutions were evaluated at different time points. The resistance against enzymatic degradation was indirectly evaluated by ultimate tensile strength (UTS) test of demineralized dentin treated or not with EDC/NHS and subjected to collagenase digestion. Short- and long-term evaluations of the strength of resin-dentin interfaces treated with EDC/NHS for 1 h were performed using microtensile bond strength (mu TBS) test. All data (MPa) were individually analyzed using ANOVA and Tukey HSD tests (alpha = 0.05). Results: The different exposure times significantly increased the stiffness of dentin (p < 0.0001, control-5.15 and EDC/NHS-29.50), while no differences were observed among the different solutions of EDC/NHS (p = 0.063). Collagenase challenge did not affect the UTS values of EDC/NHS group (6.08) (p > 0.05), while complete degradation was observed for the control group (p = 0.0008, control-20.84 and EDC/NHS-43.15). EDC/NHS treatment did not significantly increase resin-dentin mu TBS, but the values remained stable after 12 months water storage (p < 0.05). Conclusions: Biomimetic use of EDC/NHS to induce exogenous collagen cross-links resulted in increased mechanical properties and stability of dentin matrix and dentin-resin interfaces. (C) 2010 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 94B: 250-255, 2010.

Photoinitiator content in restorative composites: Influence on degree of conversion, reaction kinetics, volumetric shrinkage and polymerization stress

Purpose: To determine the influence of rate of polymerization, degree of conversion and volumetric shrinkage on stress development by varying the amount of photoinitiators in a model composite. Methods: Volumetric shrinkage (with a mercury dilatometer), degree of conversion, maximum rate of reaction (RP(max)) (with differential scanning calorimetry) and polymerization stress (with a controlled compliance device) were evaluated. Bis-GMA/TEGDMA (equal mass ratios) were mixed with a tertiary amine (EDMAB) and camphorqpinone, respectively, in three concentrations (wt%): high= 0.8/1.6; intermediate= 0.4/0.8 and low= 0.2/0.4. 80 wt% filler was added. Composites were photoactivated (400 mW/cm(2) x 40 seconds; radiant exposure=16J/cm(2)). A fourth experimental group was included in which the low concentration formulation was exposed for 80 seconds (32 J/cm(2)). Results: For the same radiant exposure, conversion, RP(max) and stress increased with photoinitiator concentration (P< 0.001). When the low concentration group exposed to 32 J/cm(2) was compared with the high and intermediate groups (exposed to 16 J/cm(2)), RPmax Still increased with the photoinitiator concentration between all levels (P< 0.001) but conversion and stress did not vary (P> 0.05). Shrinkage did not vary regardless of the photoinitiator concentration or radiant exposure. For the photoinitiator concentrations used in this study. Polymerization stress was influenced by conversion but not by rate of reaction. (Am J Dent 2009;22:206-210).

Subcritical crack growth in porcelains, glass-ceramics, and glass-infiltrated alumina composite for dental restorations

The objective was to compare fracture toughness (K(Ic)), stress corrosion susceptibility coefficient (n), and stress intensity factor threshold for crack propagation (K(I0)) of two porcelains [VM7/Vita (V) and d.Sign/Ivoclar (D)], two glass-ceramics [Empress/Ivolcar (E1) and Empress2/Ivlocar (E2)] and a glass-infiltrated alumina composite [In-Ceram Alumina/Vita (IC)]. Disks were constructed according to each manufacturer`s processing method, and polished before induction of cracks by a Vickers indenter. Crack lengths were measured under optical microscopy at times between 0.1 and 100 h. Specimens were stored in artificial saliva at 37A degrees C during the whole experiment. K(Ic) and n were determined using indentation fracture method. K(I0) was determined by plotting log crack velocity versus log K(I). Microstructure characterization was carried out under SEM, EDS, X-ray diffraction and X-ray fluorescence. IC and E2 presented higher K(Ic) and K(I0) compared to E1, V, and D. IC presented the highest n value, followed by E2, D, E1, and V in a decreasing order. V and D presented similar K(Ic), but porcelain V showed higher K(I0) and lower n compared to D. Microstructure features (volume fraction, size, aspect ratio of crystalline phases and chemical composition of glassy matrix) determined K(Ic). The increase of K(Ic) value favored the increases of n and K(I0).

Factors Affecting Photopolymerization Stress in Dental Composites

Polymerization stress development results from the complex interplay of volumetric shrinkage, reaction kinetics, and viscoelastic properties. The objective of this study was to examine the relationships among volumetric shrinkage, degree of conversion, rate of polymerization (RPmax), and stress development for 2 model bis-GMA-based composites. Three irradiances were used 220, 400, or 600 mW/cm(2) - with exposure times adjusted to deliver the same radiant energy. Volumetric shrinkage was determined with a mercury dilatometer, degree of conversion and RPmax by differential scanning calorimetry (DSC), and polymerization stress with a low-compliance device (Sakaguchi et al., 2004b). Results indicated that polymerization reaction rate and shrinkage were not correlated. Irradiance was directly related to polymerization reaction rate and to stress development. The group with the highest stress/degree of conversion exhibited the lowest RPmax, so it can be assumed, within the limitations of this study, that the conversion was most closely related to stress development.

BisGMA/TEGDMA ratio and filler content effects on shrinkage stress

Objective. To investigate the contributions of BisGMA:TEGDMA and filler content on polymerization stress, along with the influence of variables associated with stress development, namely, degree of conversion, reaction rate, shrinkage, elastic modulus and loss tangent for a series of experimental dental composites. Methods. Twenty formulations with BisGMA: TEGDMA ratios of 3: 7, 4: 6, 5: 5, 6: 4 and 7: 3 and barium glass filler levels of 40, 50, 60 or 70 wt% were studied. Polymerization stress was determined in a tensilometer, inserting the composite between acrylic rods fixed to clamps of a universal test machine and dividing the maximum load recorded by the rods cross-sectional area. Conversion and reaction rate were determined by infra-red spectroscopy. Shrinkage was measured by mercury dilatometer. Modulus was obtained by three-point bending. Loss tangent was determined by dynamic nanoindentation. Regression analyses were performed to estimate the effect of organic and inorganic contents on each studied variable, while a stepwise forward regression identified significant variables for polymerization stress. Results. All variables showed dependence on inorganic concentration and monomeric content. The resin matrix showed a stronger influence on polymerization stress, conversion and reaction rate, whereas filler fraction showed a stronger influence on shrinkage, modulus and loss tangent. Shrinkage and conversion were significantly related to polymerization stress. Significance. Both the inorganic filler concentration and monomeric content affect polymerization stress, but the stronger influence of the resin matrix suggests that it may be possible to reduce stress by modifying resin composition without sacrificing filler content. The main challenge is to develop formulations with low shrinkage without sacrificing degree of conversion. (C) 2011 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

Effect of prolonged erosive pH cycling on different restorative materials

This in vitro study evaluated the effect of a prolonged erosive pH cycling on the superficial microhardness change (SMHC) and the erosive wear of different restorative materials. Eighty enamel specimens with prepared cavities of 1.5 x 1.5 mm were randomly divided into eight groups according to the restorative materials used for the fillings (RMGI - resin-modified glass-ionomer, CGI - conventional glass-ionomer, CR- composite resin, A - amalgam) and immersion media used (ERO - erosive medium or SAL - artificial saliva). During 35 days, half of the specimens were immersed in a cola drink (ERO), for 5 min, three times a day, and they remained in SAL between the erosive cycles. The other half of the specimens was immersed in SAL only, for the entire experimental period (control). Data were tested for significant differences by anova and Tukey`s tests (P < 0.05). Scanning electron microscopy images were made to illustrate the enamel erosive wear and restorative materials alterations. The mean SMHC (%) and mean erosive wear (mu m) of the materials were: RMGI-ERO (30/0.5); CGI-ERO (37/0.5); CR-ERO (-0.3/0.3); A-ERO (-4/0.3); RMGI-SAL (4/0.4); CGI-SAL (-6/0.4); CR-SAL (-3/0.2) and A-SAL (2/0.4). Scanning electron microscopy images showed pronounced enamel erosive wear on groups submitted to erosive pH cycling when compared with groups maintained in saliva. In conclusion, the prolonged pH cycling promoted significantly higher alterations (SMHC and erosive wear) on the glass-ionomer cements than the CR and amalgam.

Physical Properties and Interfacial Adaptation of Three Epoxy Resin-based Sealers

Introduction: The aim of the study was to evaluate the radiopacity, solubility, flow, film thickness, setting time, and adaptation to the root canal walls of 3 epoxy resin based sealers: AH Plus, Acroseal, and Adseal. Methods: Physical tests were performed following American National Standards Institute/American Dental Association`s requirements. For interfacial adaptation analysis, 30 maxillary canines were shaped by using Pro Taper instruments. The specimens were divided into 3 groups (n = 10): group 1, AH Plus; group 2, Acroseal; and group 3, Adseal. The sealers were mixed with rhodamine B dye, and the canals were filled by using the lateral compaction technique. The percentage of gaps and voids area was calculated at 2, 4, and 6 mm levels from the apex. Statistical evaluation was performed by using analysis of variance for physical analysis and nonparametric Kruskal-Wallis and Dunn tests for interfacial adaptation (P<.05). Results: No statistical differences were found for adaptation, percentage of voids, solubility, flow, and film thickness among the sealers (P>.05). AH Plus was significantly more radiopaque (P<.05). For the setting time, there were statistical differences among all the studied sealers (P<.05). Conclusions: AH Plus, Acroseal, and Adseal presented similar root canal adaptation, solubility, flow, and film thickness. Statistical differences were found for radiopacity and setting time (P<.05). (J Endod 2011;37:1417-1421)

Differential bonds degradation of two resin-modified glass-ionomer cements in primary and permanent teeth

Objectives: To evaluate the effect of chemical degradation on bond strength of resin-modified glass-ionomer cements bonded to primary and permanent dentin. Methods: Class I cavities of permanent and primary extracted human molars were restored with two resin-modified glass-ionomer cements: Fuji 11 LC and Vitremer, and stored in water for 24 h. Half samples were immersed in 10% NaOCl aqueous solution for 5 h. Teeth were sectioned into beams and tested for microtensile bond strengths. Results were analyzed with multiple ANOVA and Tukey`s tests (p < 0.05). Analysis of debonded surfaces was performed by SEM. Results: 24 h bond strengths for Vitremer and Fuji 11 LC were similar. For Fuji 11, bond strength values were higher for primary than for permanent dentin. Vitremer bond strength was similar for both. Chemical degradation did not affect Fuji I] LC bond strength to dentin. However, decreases in bond strength were found for Vitremer groups after NaOCl immersion. Signs of glass ionomer-dentin interaction were evident by SEM analysis for Fuji 11 LC specimens. Conclusions: Vitremer and Fuji II presented similar bond strength at 24. Vitremer dentin bonds were prone to chemical degradation. Fuji II LC-dentin bonds showed typical features of glass-ionomer dentin interaction at the bonded interfaces, and were resistant to in vitro degradation. (C) 2009 Elsevier Ltd. All rights reserved.

The effects of occlusal loading on the margins of cervical restorations

Background. Researchers have proposed the restoration of abfraction lesions, but limited information is available about the effects of occlusal loading on the margins of such restorations. Because abfraction is a well-recognized problem, the authors conducted a study to assess the effects of occlusal loading on the margins of cervical restorations. Methods. The authors prepared 40 wedge-shaped cavities in extracted premolars and restored them with a resin-based composite. They subjected specimens to occlusal loading (150 newtons, 101 cycles) on the buccal cusp, on the central fossa or on the lingual cusp, and they stored 1 the control group, specimens in deionized water. The authors used fluorescein to delimit marginal defects and evaluated the defects by using laser scanning confocal microscopy. Results. Results of chi(2) and Kruskal-Wallis tests (P < .05) showed that specimens subjected to occlusal loading had a higher percentage of marginal gaps (53.3 percent) than did the control specimens (10.0 percent). There were no differences between groups in marginal defect formation or in defect location, length or width. Conclusions. Occlusal loading led to a significant increase in gap formation at the margins of cervical resin-based composite restorations. Clinical Implications. The clinician cannot underestimate the effects of occlusal loading When restoring teeth with cervical wedge-shaped lesions. If occlusal loading is the main factor contributing to lesion formation, the clinician should identify and treat it before placing the restoration or otherwise run the risk that the restorative treatment will fail because of marginal gap formation.

Resistance to degradation of resin-modified glass-ionomer cements dentine bonds

Objective: To evaluate the effect of EDTA pre-treatment of dentine on resistance to degradation of the bond between dentine and resin-modified glass-ionomer cements. Methods: Sixty non-carious human molars underwent cavity preparations. Teeth were restored with Fuji II LC or Vitremer. Half of the cavities were restored following manufacturers` instructions whereas the other half was pre-treated with EDTA (0.1 M, pH 7.4) for 60 s. Teeth were stored in water at 37 degrees C for 24 h, 3 months or submitted to 10% NaOCl immersion for 5 h. Teeth were sectioned into beams (1 +/- 0.1 mm) and tested to failure in tension at 0.5 mm/min. Bond strength data (MPa) were analyzed by ANOVA and SNK multiple-comparisons tests (p < 0.05). Results: When EDTA was used for pre-treatment of dentine, higher bond strengths were observed for both cements. Degradation challenges produced a decrease in bond strength values only in the Vitremer group. This decrease was avoided when EDTA was used for dentine treatment before restoring with Vitremer. Conclusions: EDTA pre-treatment of dentine increases bond strength of resin modified glass-ionomers cements to dentine and improves resistance to degradation of the bond between Vitremer and dentine. (C) 2009 Elsevier Ltd. All rights reserved.

Fracture resistance of Class II glass-ionomer cement restorations

Purpose: To investigate in vitro the effect of retentive grooves, GIC type and insertion method on the fracture resistance of Class II glass-ionomer cement (GIC) restorations. Methods: Premolars were divided into 12 groups (n=10) according to three variables: retentive grooves [presence (PR) or absence AR)], GICs type [Ketac-Molar (KM), Fuji VIII (F8) and RelyX Luting (RX)], and insertion method [syringe injector (SI) or spoon excavator (SE)]. The specimens were subjected to fracture resistance test. Data were submitted to three-way ANOVA and multiple comparisons were performed using a Tukey test (P < 0.05). Results: Mean fracture resistance values (Kgf) +/- standard deviations (SD) were: KM (PR+SI) 65.66 +/- 2.5; KM (PR+SE) = 62.58 +/- 2.1; KM (AR+SI) = 57.11 +/- 1.9; KM (AR+SE) = 51.94 +/- 2.3; F8 (PR+SI) = 63.05 +/- 2.1; F8 (PR+SE) = 60.12 +/- 2.3; F8 (AR+SI) = 55.11 +/- 1.9; F8(AR+SE)=49.20 +/- 1.6; RX (PR+SI)=50.99 +/- 2.4; RX (PR+SE)=48.81 +/- 2.5; RX (AR+SI)=45.53 +/- 2.6; RX (AR+SE)=41.88 +/- 3.0. Statistically significant differences were observed among all the groups tested (P=0.001). There was significant difference when pooled means for GIC type were compared with retentive grooves (P=0.01) and when pooled means for retentive grooves were compared with insertion method (P=0.01).

Network structures of Bis-GMA/TEGDMA resins differ in DC, shrinkage-strain, hardness and optical properties as a function of reducing agent

Objectives. To evaluate the influence of different tertiary amines on degree of conversion (DC), shrinkage-strain, shrinkage-strain rate, Knoop microhardness, and color and transmittance stabilities of experimental resins containing BisGMA/TEGDMA (3: 1 wt), 0.25wt% camphorquinone, 1wt% amine (DMAEMA, CEMA, DMPT, DEPT or DABE). Different light-curing protocols were also evaluated. Methods. DC was evaluated with FTIR-ATR and shrinkage-strain with the bonded-disk method. Shrinkage-strain-rate data were obtained from numerical differentiation of shrinkage-strain data with respect to time. Color stability and transmittance were evaluated after different periods of artificial aging, according to ISO 7491: 2000. Results were evaluated with ANOVA, Tukey, and Dunnett`s T3 tests (alpha = 0.05). Results. Studied properties were influenced by amines. DC and shrinkage-strain were maximum at the sequence: CQ < DEPT < DMPT <= CEMA approximate to DABE < DMAEMA. Both DC and shrinkage were also influenced by the curing protocol, with positive correlations between DC and shrinkage-strain and DC and shrinkage-strain rate. Materials generally decreased in L* and increased in b*. The strong exception was the resin containing DMAEMA that did not show dark and yellow shifts. Color varied in the sequence: DMAEMA < DEPT < DMPT < CEMA < DABE. Transmittance varied in the sequence: DEPT approximate to DABE < DABE approximate to DMPT approximate to CEMA < DMPT approximate to CEMA approximate to DMAEMA, being more evident at the wavelength of 400 nm. No correlations between DC and optical properties were observed. Significance. The resin containing DMAEMA showed higher DC, shrinkage-strain, shrinkage-strain rate, and microhardness, in addition to better optical properties. (C) 2011 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

In situ effect of an erosive challenge on different restorative materials and on enamel adjacent to these materials

Objectives: This in situ study evaluated the effect of an erosive challenge on different restorative materials and on enamel restored with these materials, as well as the ability of these materials to protect the adjacent enamel against erosion. Methods: Ten volunteers wore palatal devices with eight bovine enamel blocks, randomly selected and distributed into two vertical rows, corresponding to the following groups: GI/GV, resin-modified glass ionomer; GII/GVI, conventional glass ionomer; GIII/GVII, composite resin; GIV/GVIII, amalgam. one row (corresponding to groups I-IV) was immersed in a cola drink and the other row (corresponding to groups V-VIII) was subjected to saliva only. The palatal device was continuously worn for 7 days and only half of the appliance (groups I-IV) was immersed in the soft drink (Coca-Cola (R), 150 mL) for 5 min, three times a day. The study variables comprised the wear (profilometry, mu m) and the percentage of surface microhardness change (%SMHC). Data were tested for significant differences by two-way ANOVA and Tukey`s tests (p < 0.05). Results: Considering the restorative materials, for %SMHC and wear, there were no differences among the materials and between the saliva and the erosive challenge. For enamel analyses, the erosive challenge promoted a higher wear and %SMHC of the enamel than did the saliva. There were no significant differences in wear and %SMHC of the enamel adjacent to the different restorative materials. Conclusion: This research data suggest that there is little %SMHC and wear of the studied restorative materials and none of them had a preventive effect against erosion on adjacent enamel, which showed a pronounced wear. (c) 2007 Elsevier Ltd. All rights reserved.