Experimental use of an acrolein-based primer as collagen cross-linker for dentine bonding.

OBJECTIVES: The objective of the present study was to investigate the long-term effect of 0.01% acrolein (ACR) aqueous solution, employed as an additional primer, on the mechanical durability and enzymatic activity of resin-dentine interfaces created with a simplified etch-and-rinse adhesive. METHODS: Dentine surfaces were etched with 35% phosphoric acid for 15s, rinsed and blot-dried. Specimens were then assigned to: Group 1: dentine pre-treated with 0.01% ACR aqueous solution for 1min and bonded with Adper Scotchbond 1 XT (SB1XT), a 2-step etch-and-rinse adhesive; Group 2: SB1XT was applied on untreated acid-etched dentine (control). Resin composite build-ups were made using Filtek Z250. Microtensile bond strength was tested by stressing sectioned specimens to failure immediately or after 1year of storage in artificial saliva at 37°C. Zymography and in-situ zymography assays were performed for examining dentine matrix metalloproteinase (MMP) activities. RESULTS: The use of 0.01% ACR as conditioning primer appeared to have contributed better to preservation of bond strength over time without affecting immediate bond strength. Zymography and in-situ zymography showed reduction in MMP activities after the application of ACR. CONCLUSION: Dentine collagen cross-linking produced by an ACR-based primer increases the longevity of resin-dentine bonds by reinforcement of the adhesive interface and reduction of dentine MMP activities. Further studies are required to evaluate the potential in vivo and in vivo cytotoxicity of ACR. CLINICAL SIGNIFICANCE: The acrolein-based primer is a potentially useful clinical bonding tool because it demonstrates good collagen cross-linking ability within a clinically-acceptable working time. Although a low ACR concentration was employed in the present study, the cytotoxicity of ACR should be tested prior to clinical use.

X-linked hypophosphatemic rickets: enamel abnormalities and oral clinical findings.

X-linked hypophosphatemia (XLH) is a genetic disorder related to alterations in bones and teeth formation, due to low levels of phosphate in blood. Oral findings in XLH have been enamel and dentine abnormalities, high pulp horns, large pulp chambers, and some cases of periapical abscesses related to teeth without caries or traumatic injuries. The aim of our study was to assess the presence of enamel alterations, such as microclefts and/or structure defects in patients with XLH and give guidelines of prevention of XLH dental complications. History taking, oral clinical and radiological examination in 10 young patients affected by XLH (average age of 9) and in 6 patients without XLH (average age of 8). Impressions were performed on the vestibular surfaces of teeth in order to obtain replicas. The replicas were analyzed using scanning electron microscope (SEM) and compared to replicas of control group. The images of replicas of XLH patients showed deep microclefts and irregular enamel surface structure compared to replicas of control group. The replica of a patient with spontaneous periapical abscesses showed numerous enamel crater-shaped depressions and deep microcleavages penetrating into the enamel thickness. In absence of caries or fractures, the abscesses pathogenesis may be related to microcleavages of the enamel and dentin, which allow bacterial invasion of the pulp. There could be a relationship between XLH disease and enamel abnormalities.

A SEM and non-contact surface white light profilometry in vivo study of the effect of a crème containing CPP-ACP and fluoride on young etched enamel.

The aim of this in vivo study was to evaluate the short and a longer term effect on enamel of the application of a crème containing 10% CPP-ACP and 900 ppm fluoride, in orthodontically planned, high caries-risk patients. Epoxy resin replicas of upper lateral incisors were obtained from polyvinyl siloxane (PVS) impressions, before and after etching. The right incisors were left untreated in order to control saliva remineralizing potential. The upper left surfaces were coated with a pea-size amount of the crème. Replicas were obtained at 3 weeks and 6 months and analyzed by SEM and non-contact surface white light profilometry. In the treated sample the profilometric roughness parameters at 3 weeks were statistically significantly lower than the control group values (p < 0.05). At 3 weeks SEM images of the enamel surface showed fewer irregularities. After 6 months, differences between test and control groups were not present on SEM images and profilometric values. CPP-ACP and fluoride crème had positive in vivo effects on enamel surfaces. Significant differences in surface roughness existed after a 3-week period of crème use.

Influence of air-abrasion executed with polyacrylic acid-Bioglass 45S5 on the bonding performance of a resin-modified glass ionomer cement.

The aim of this study was to test the microtensile bond strength (µTBS), after 6 months of storage in PBS, of a resin-modified glass ionomer cement (RMGIC) bonded to dentine pretreated with Bioglass 45S5 (BAG) using various etching and air-abrasion techniques. The RMGIC (GC Fuji II LC) was applied onto differently treated dentine surfaces followed by light curing for 30 s. The specimens were cut into matchsticks with cross-sectional areas of 0.9 mm(2). The µTBS of the specimens was measured after 24 h or 6 months of storage in PBS and the results were statistically analysed using two-way anova and the Student-Newman-Keuls test (α = 0.05). Further RMCGIC-bonded dentine specimens were used for interfacial characterization, micropermeability, and nanoleakage analyses by confocal microscopy. The RMGIC-dentine interface layer showed no water absorption after 6 months of storage in PBS except for the interdiffusion layer of the silicon carbide (SiC)-abraded/polyacrylic acid (PAA)-etched bonded dentine. The RMGIC applied onto dentine air-abraded with BAG/H(2)O only or with BAG/PAA-fluid followed by etching procedures (10% PAA gel) showed no statistically significant reduction in µTBS after 6 months of storage in PBS. The abrasion procedures performed using BAG in combination with PAA might be a suitable strategy to enhance the bonding durability and the healing ability of RMGIC bonded to dentine.

Effects of pH, ionic strength, and applied voltage on migration of dental monomers in an organic matrix.

OBJECTIVES: The application of an electric field has been shown to positively influence the bonding of dentin bonding systems (DBS) by improving adhesive impregnation into dentin. However, the mechanism responsible for this phenomenon has not been completely elucidated. The aim of this study was to clarify the effects of pH, matrix ionic strength, and applied voltage on the migration of commonly used DBS monomers in a model matrix (agarose gel). METHODS: Some common monomers examined were bis-GMA (2,2-bis[4-(2-hydroxy-3-methacryloyloxy propoxy) phenyl] propane); HEMA (2-hydroxyethyl methacrylate); 2-MP (bis[2-(methacryloyloxy) ethyl] phosphate); TCDM [di(hydroxyethyl methacrylate) ester of 5-(2,5,-dioxo tetrahydrofurfuryl)-3-methyl-3-cyclohexenyl-1,2-dicarboxylic acid]; and TEGDMA (triethylene glycol dimethacrylate). Agarose gels poured into a horizontal 10-well electrophoretic cell were used to mimic the collagen fibrils of the dentin organic matrix. The role of pH, matrix ionic strength, and voltage on monomer migration was assayed by modifying the experimental conditions. RESULTS: Results of experiments performed at pH 3.1, 6.3, 8.5, and 12.3; at low, medium, and high ionic strength; and at 50 and 100 V clearly showed that DBA monomer migration toward both the anode and the cathode can be affected by each of these parameters. SIGNIFICANCE: Migration of acrylic monomers toward the anode or cathode can be achieved as desired by selective choice of pH, ionic strength, and applied voltage. Additional studies are needed to evaluate the synergistic effects of DBS monomer blends on migration in an electric field.

MMP-2 assay within the hybrid layer created by a two-step etch-and-rinse adhesive: biochemical and immunohistochemical analysis.

OBJECTIVE: Degradation of hybrid layers (HLs) within resin-infiltrated dentine results from multiple degradation factors, including collagenolytic activity of specific matrix metalloproteinases (MMPs). Inhibition of host-derived MMPs may, therefore, slow the degradation of HL. The null hypothesis tested is that the presence of MMP-2 is similar regardless of chlorhexidine (CHX) pre-treatment or the use of an adhesive. METHODS: Powdered dentine prepared from extracted human teeth was divided into 4 groups: (G1) mineralised powder (control group); (G2) dentine powder treated with 1% phosphoric acid for 1 min; (G3) 1% phosphoric acid-etched dentine treated with Adper Scotchbond 1 XT (SB1XT; 3M ESPE); (G4) 1% phosphoric acid-etched dentine treated with 0.2% CHX followed by SB1XT. The concentration of detectable pro-MMP-2 and MMP-2 was assayed using a colorimetric assay system (QuantiSir). In addition, the presence of MMP-2 in the HL was assessed in 1 year-aged adhesive-dentine interfaces using an immunohistochemical approach under FEI-SEM/TEM. RESULTS: In dentine powder treated with 1% phosphoric acid (G2), MMP-2 level decreased compared to controls (G1); the application of SB1XT (G3) resulted in an increase of MMP-2, whilst 0.2% CHX before SB1XT application (G4), reduced MMP-2. The FEI-SEM/TEM analysis revealed MMP-2 distribution within the HL of aged interfaces showing increase MMP-2 patterns in the control group and minor labelling in the CHX-pretreated specimens. CONCLUSION: The results of this study support the use of non-toxic MMPs inhibitors, such as CHX, as an appropriate additional step in bonding procedures in order to increase the longevity of the adhesive restorations.

An in vivo study of the effect of a 38 percent hydrogen peroxide in-office whitening agent on enamel.

BACKGROUND: In an in vivo study, the authors tested the hypothesis that no difference in enamel surface roughness is detectable either during or after bleaching with a high-concentration in-office whitening agent. METHODS: The authors performed profilometric and scanning electron microscopic (SEM) analyses of epoxy resin replicas of the upper right incisors of 20 participants at baseline (control) and after each bleaching treatment with a 38 percent hydrogen peroxide whitening agent, applied four times, at one-week intervals. The authors used analysis of variance for repeated measures to analyze the data statistically. RESULTS: The profilometric analysis of the enamel surface replicas after the in vivo bleaching protocol showed no significant difference in surface roughness parameters (P > .05) compared with those at baseline, irrespective of the time interval. Results of the correlated SEM analysis showed no relevant alteration on the enamel surface. CONCLUSIONS: Results of this in vivo study support the tested hypothesis that the application of a 38 percent hydrogen peroxide in-office whitening agent does not alter enamel surface roughness, even after multiple applications. CLINICAL IMPLICATIONS: The use of a 38 percent hydrogen peroxide in-office whitening agent induced no roughness alterations of the enamel surface, even after prolonged and repeated applications.

Effect of two in-office whitening agents on the enamel surface in vivo: a morphological and non-contact profilometric study.

This study evaluated the morphological effects produced in vivo by two in-office bleaching agents on enamel surface roughness using a noncontact profilometric analysis of epoxy replicas. The null hypothesis tested was that there would be no difference in the micromorphology of the enamel surface during or after bleaching with two different bleaching agents. Eighteen subjects were selected and randomly assigned to two treatment groups (n=9). The tooth whitening materials tested were 38% hydrogen peroxide (HP) (Opalescence Xtra Boost) and 35% carbamide peroxide (CP) (Rembrandt Quik Start). The bleaching agents were applied in accordance with manufacturer protocols. The treatments were repeated four times at one-week intervals. High precision impressions of the upper right incisor were taken at baseline as the control (CTRL) and after each bleaching treatment (T0: first application, T1: second application at one week, T2: third application at two weeks and T3: fourth application at three weeks). Epoxy resin replicas were poured from impressions, and the surface roughness was analyzed by means of a non-contact profilometer (Talysurf CLI 1000). Epoxy replicas were then observed using SEM. All data were statistically analyzed using ANOVA and differences were determined with a t-test. No significant differences in surface roughness were found on enamel replicas using either 38% hydrogen peroxide or 35% carbamide peroxide in vivo. This in vivo study supports the null hypothesis that two in-office bleaching agents, with either a high concentration of hydrogen or carbamide peroxide, do not alter enamel surface roughness, even after multiple applications.

Dental enamel dissolution after alendronate treatment.

PURPOSE: To evaluate the effect of treatment with a bisphosphonate (alendronate) on human dental enamel dissolution in vitro. METHODS: The dissolution of each enamel sample was evaluated by monitoring the calcium release in 0.1M lactic acid solution at pH 4.5 (acidic solution) during dissolution tests, after topical alendronate treatment with 0.1M alendronate solutions at pH 5.0, pH 7.4 and pH 9.0. RESULTS: Data showed that alendronate treatment, both at pH 5.0 and pH 7.4, obtained a statistically significant reduction of enamel demineralization during dissolution test reaction time (45 minutes). The protective effect was not present after treatment at pH 9.

Effects of citric acid and EDTA conditioning on exposed root dentin: An immunohistochemical analysis of collagen and proteoglycans.

OBJECTIVE: Preservation of structural and biochemical properties of the root dentin matrix is crucial to favor healing and regenerative periodontal processes. Aim of this study was to evaluate the biochemical characteristics of collagen and chondroitin sulphate of root dentin surfaces exposed by periodontal disease after acid conditioning by means of an immunohistochemical technique. DESIGN: Human teeth scheduled for extraction due to periodontal reason were submitted to: (A) scaling and root planning; (B) ultrasonic instrumentation; (C) no instrumentation. Teeth were then exposed to: (1) 10% citric acid; (2) 17% EDTA; (3) no etching. A double immunolabeling technique was performed to identify type-I collagen and proteoglycans and analyzed under FEI-SEM. RESULTS: Use of 10% citric acid revealed intense labeling for collagen fibrils and proteoglycans; lower labeling was found after EDTA conditioning. Unetched specimens showed residual smear layer on the dentin surface resulting in no evident surface labeling. CONCLUSIONS: This study supports the hypothesis that manual or ultrasonic instrumentation alone is not able to expose the sound dentin matrix, whereas a subsequent acidic conditioning exposes collagen fibrils and associated proteoglycans. The immunohistochemical technique revealed that despite their acidity, both citric acid and EDTA were able to preserve the structural and biochemical properties of the exposed dentin matrix.

Appearance of the root canal walls after preparation with NiTi rotary instruments: a comparative SEM investigation.

The aim of this study was to evaluate, in vitro, with scanning electron microscope (SEM), the appearance of root canal walls shaped by three different rotary NiTi techniques and one conventional manual technique in human extracted teeth. Four different instruments were used: K3, Hero 642, RaCe and K-file. Each sample was irrigated with 5 ml of 5% NaOCl and 5 ml of 3% H2O2 and EDTA, Rc-Prep (1 ml). Each sample was prepared for SEM observation and analyzed in the coronal, middle and apical third, comparing its aspect with a predefined scale of four different parameters: presence of smear layer, pulpal debris, inorganic debris and surface profile. The apical third showed significantly more pulpal and inorganic debris, smear layer and a high number of surface profile irregularities. No significant difference was found at the coronal, middle and apical thirds between manual and rotary techniques for inorganic debris, smear layer and surface profile. Much pulpal debris were found in the apical third for K3 and RaCe compared with Hero 642 and K-file. In conclusion, mechanical rotary techniques with NiTi instruments produced quite similar results compared with a conventional manual technique using K-files. The present study demonstrated that dentin and pulpal debris, the morphology of smear layer and surface profile were only partially influenced by the type of endodontic instruments. The apical third was the anatomical area with greater amount of debris and smear layer.

Microleakage and marginal hybrid layer formation of compomer restorations.

The tested hypotheses of this study were that dentin enamel bonding agents (DBAs) proposed for compomers create a hybrid layer (HL) that seals the margins of Class V restorations and HL is free from voids or gaps on both enamel and dentin margins. For purposes of this study, Class V restorations (n = 70) were made in vitro at the CEJ in extracted third molars. Different systems (bonding agent + compomer) were selected. After finishing with discs, each margin was polished with diamond polishing paste for one minute, treated with a 2.5% NaOCl gel for 10 seconds and washed with deionized water to remove polishing debris and non-infiltrated collagen. All restorations were immersed in dye solution for 24 hours, then inspected along the margins. SEM analysis was used to evaluate the morphology of the marginal HL and microleakage tests to evaluate their ability to seal the margins of restorations. Marginal leakage was observed along the dentin and enamel margin. A thin marginal HL (0.5-1.2 microm) was detected only along the dentin margin of several bonding systems but not along the enamel margin. Porosities and gaps were detected along margins when no HL was observed. The results demonstrated that the tested bonding agents for compomers produced a thin marginal hybrid layer, especially along the dentin margin. Microleakage had a relationship with the morphology (gap, porosities and thickness) of this hybrid smear layer. In conclusion, the DBAs tested specifically developed for compomers did not ensure an intimate interfacial adaptation, because microleakage was detected along the enamel and dentin interfaces and the marginal hybrid layer was only partially homogeneous.

Morphological evaluation of enamel surface after application of two 'home' whitening products.

PURPOSE: The purpose of this study was to investigate the effect on enamel surface morphology of two commercially available bleaching products (AZ Whitestrips 6% hydrogen peroxide - Procter & Gamble; Platinum TWS 10% carbamide - Colgate Oral Pharmaceuticals) and their ability to prevent enamel demineralization in the presence of cariogenic solution, with or without saliva. MATERIALS AND METHODS: Forty sound teeth were used to obtain 90 enamel fragments. Lactic acid (pH = 4.4) was used as a demineralizing cariogenic solution. The specimens were randomized into eight groups: Group A: product A + cariogenic solution; Group B: product B + cariogenic solution; Group C: cariogenic solution; Group D: (control group) stored in deionized water; Group E: product A + deionized water; Group F: product B + deionized water; Group G: product A + saliva; Group H: product B + saliva. Scanning electron microscope (SEM) analysis was performed to detect the type of lesions induced by the treatments. A score rating system was used to perform a non-parametric statistical analysis. RESULTS: Our study confirms that enamel alterations (i.e. removal of intraprismatic core and presence of deep porosities and pits) occur as a result of the application of a cariogenic solution (lactic acid). The enamel surface presented a honeycomb surface only in untreated samples previously stored in lactic acid solution. Conversely, both products were able to prevent enamel alterations caused by exposure to lactic acid. Saliva treatment reduced the degree of enamel lesions of both treated and untreated groups. Treatment with product A achieved better preservation of enamel integrity. CONCLUSION: Whitening treatment conducted with two 'home' bleaching agents had no adverse effects on enamel surface morphology. Several morphological aspects suggest that the tested products may even prevent demineralization of the enamel surface after exposure to lactic acid.