Effect of potential remineralizing agents on acid softened enamel.

PURPOSE: To assess whether pastes containing casein phosphopeptide-amorphous calcium phosphate (CPP-ACP) and calcium sodium phosphosilicate (CSP) protect acid softened enamel against further erosive episodes. METHODS: Enamel slabs of bovine teeth with preformed erosion-like lesions were randomly assigned to five treatment groups (n = 15): A) CPP-ACP (MI Paste, GC America); B) CPP-ACP+Fluoride (CPP-ACP+F, MI Plus Paste, GC America); C) CSP (Tooth Revitalizing Paste, Oravive); D) fluoridated dentifrice (FD, Sensodyne Cool Gel, GSK); E) control (CO, unexposed to any product). Paste treatments (1:3 slurry in deionized water or undiluted product in the case of the CPP-ACP formulae) were performed between five cycles of alternating erosive challenge (0.3% citric acid, pH = 3.2) and remineralization in artificial saliva. Specimens were analyzed by Knoop surface microhardness (SMH). RESULTS: ANOVA indicated a significant (P< 0.0001) difference among the SMH values attained by acid softened enamel following the exposure to the pastes interspersed with erosion-remineralization cycles. Tukey's test ascertained that SMH values observed for the CPP-ACP+F and CSP groups did not differ from that of FD group, which were significantly higher than that found for the CO group. Specimens treated with CPP-ACP did not differ from any of the other groups.

Sodium bicarbonate solution as an anti-erosive agent against simulated endogenous erosion.

This study investigated whether sodium bicarbonate solution, applied on enamel previously exposed to a simulated intrinsic acid, can control dental erosion. Volunteers wore palatal devices containing enamel slabs, which were exposed twice daily extra-orally to hydrochloric acid (0.01 M, pH 2) for 2 min. Immediately afterwards, the palatal devices were re-inserted in the mouth and volunteers rinsed their oral cavity with a sodium bicarbonate solution or deionized water for 60 s. After the washout period, the palatal devices were refilled with a new set of specimens and participants were crossed over to receive the alternate rinse solution. The surface loss and surface microhardness (SMH) of specimens were assessed. The surface loss of eroded enamel rinsed with a sodium bicarbonate solution was significantly lower than the surface loss of eroded enamel rinsed with deionized water. There were no differences between treatments with sodium bicarbonate and deionized water for SMH measurements. Regardless of the solution used as an oral rinse, eroded enamel showed lower SMH than uneroded specimens. Rinsing with a sodium bicarbonate solution after simulated endogenous erosive challenge controlled enamel surface loss but did not alter the microhardness.

Influence of cavity preparation with Er:YAG Laser on enamel adjacent to restorations submitted to cariogenic challenge in situ: a polarized light microscopic analysis.

BACKGROUND AND OBJECTIVES: Er:YAG laser has been used for caries removal and cavity preparation, using ablative parameters. Its effect on the margins of restorations submitted to cariogenic challenge has not yet been sufficiently investigated. The aim of this study was to assess the enamel adjacent to restored Er:YAG laser-prepared cavities submitted to cariogenic challenge in situ, under polarized light microscopy. STUDY DESIGN/MATERIALS AND METHODS: Ninety-one enamel slabs were randomly assigned to seven groups (n = 13): I, II, III-Er:YAG laser with 250 mJ, 62.5 J/cm2, combined with 2, 3, and 4 Hz, respectively; IV, V, VI-Er:YAG laser with 350 mJ, 87.5 J/cm(2), combined with 2, 3, and 4 Hz, respectively; VII-High-speed handpiece (control). Cavities were restored and the restorations were polished. The slabs were fixed to intra-oral appliances, worn by 13 volunteers for 14 days. Sucrose solution was applied to each slab six times per day. Samples were removed, cleaned, sectioned and ground to polarized light microscopic analysis. Demineralized area and inhibition zone width were quantitatively assessed. Presence or absence of cracks was also analyzed. Scores for demineralization and inhibition zone were determined. RESULTS: No difference was found among the groups with regard to demineralized area, inhibition zone width, presence or absence of cracks, and demineralization score. Inhibition zone score showed difference among the groups. There was a correlation between the quantitative measures and the scores. CONCLUSION: Er:YAG laser was similar to high-speed handpiece, with regard to alterations in enamel adjacent to restorations submitted to cariogenic challenge in situ. The inhibition zone score might suggest less demineralization at the restoration margin of the irradiated substrates. Correlation between the quantitative measures and scores indicates that score was, in this case, a suitable complementary method for assessment of caries lesion around restorations, under polarized light microscopy.

Analysis of potential lubricants for in vitro wear testing.

OBJECTIVES: A critical testing aspect for a reliable two-body wear simulation may be the lubricity condition. The main hypothesis tested in this study was that, over the experiment duration, the presence or absence of lubricants would provide to a composite similar wear rates to those observed under human saliva lubrication. METHODS: Seventy specimens, fabricated from a minifill composite, were tested in a programmable logic controlled wear simulator with human saliva (HS), mucin-based artificial saliva (MC), carboxymethylcellulose-containing saliva (CM), deionized water (DW) or with no lubrication (UN). Wear depth was quantified at the end of 1000, 5000, 10,000 and 50,000 cycles and at each 50,000 through 250,000 cycles. RESULTS: Over all the test period, UN led to the greatest wear. Initially, lubrication resulted in no significant differences among the wear rates. Subsequently, up to 50,000 cycles, depths of wear provided by HS and MC were still similar, being the lowest, whereas DW yielded greater wear than CM. Later, interposition of CM and HS resulted in equivalent wear. At 250,000 cycles, wear of the composite ranked as follows: MC

Permeability of enamel following light-activated power bleaching.

This study sought to ascertain whether in-office photocured bleaching techniques would increase permeability to enamel. A 7.1 mm2 circular area located in the middle third of the coronal portion of 90 human canines was isolated by applying an acid-resistant varnish to the remaining surfaces of the tooth. According to a randomized complete block design (n = 15), specimens were treated using a 35% hydrogen peroxide bleaching product activated by an integrated LED/diode laser (LED/laser) source or a quartz tungsten halogen (QTH) light. Bleaching was accomplished by applying the 35% hydrogen peroxide agent to the enamel surface in three 10-minute sessions, conducted at one-week intervals over a period of three weeks. For the photocured bleached groups, a bleaching agent was applied to the specimen and irradiated with the LED/laser device or the QTH light for 30 seconds. Negative control groups were exposed to artificial saliva or irradiated by the LED/laser device or the QTH light. Specimens were subjected to a histochemical coloring method that employed copper sulfate and dithio-oxamide solutions. Three 300-microm thick sections taken from the exposed area were imaged in an optical microscope. Permeability was measured in the digitized images as the percentage of copper ions penetration over the total enamel thickness. Friedman's test (alpha = 0.05) showed significant difference among groups. Least significant difference test revealed that in comparison with the group treated with 35% hydrogen peroxide only, there was no significant increase in enamel permeability when bleaching was activated by either the LED/laser or QTH light devices but all bleached groups showed higher permeability than the unbleached/nonirradiated group.

Abrasive wear of resin composites as related to finishing and polishing procedures.

OBJECTIVES: Finishing and polishing procedures may cause topographical changes and introduce subsurface microcracks in dental composite restoratives. Since both of these effects may contribute toward the kinetics of wear, the purpose of this study was to assess and correlate the wear and surface roughness of minifilled and nanofilled composites finished and polished by different methods. METHODS: Specimens (n=10) made of a minifilled and a nanofilled composite were finished and polished with one of the four sequences: (1) tungsten carbide burs plus Al(2)O(3)-impregnated brush (CbBr) or (2) tungsten carbide burs plus diamond-impregnated cup (CbCp), (3) diamond burs plus brush (DmBr) or (4) diamond burs plus cup (DmCp). As a control, abrasive papers were used. After surface roughness had been quantified, three-body abrasion was simulated using the OHSU wear machine. The wear facets were then scanned to measure wear depth and post-testing roughness. All sets of data were subjected to ANOVA and Tukey's tests (alpha=0.05). Pearson's correlation test was applied to check for the existence of a relationship between pre-testing roughness and wear. RESULTS: Significantly smoother surfaces were attained with the sequences CbBr and CbCp, whereas DmCp yielded the roughest surface. Regardless of the finishing/polishing technique, the nanofilled composite exhibited the lowest pre-testing roughness and wear. There was no correlation between the surface roughness achieved after finishing/polishing procedures and wear (p=0.3899). SIGNIFICANCE: Nano-sized materials may have improved abrasive wear resistance over minifilled composites. The absence of correlation between wear and surface roughness produced by different finishing/polishing methods suggests that the latter negligibly influences material loss due to three-body abrasion.

Influence of Er:YAG laser on microhardness of enamel adjacent to restorations submitted to cariogenic challenge in situ.

OBJECTIVE: This study assessed the effect of the Er:YAG laser on enamel adjacent to restorations submitted to cariogenic challenge in situ, by microhardness analysis. BACKGROUND DATA: The influence of Er:YAG laser energy on secondary caries formation has been investigated in vitro. However, no research involving demineralization around cavities prepared with the Er:YAG laser under intra-oral conditions has yet been described. MATERIALS AND METHODS: Slabs of enamel were randomly assigned to seven groups (n = 12), according to the cavity preparation technique: groups I, II, and III--Er:YAG laser, 250 mJ, at 2, 3, and 4 Hz, respectively; groups IV, V, and VI--350 mJ, at 2, 3, and 4 Hz, respectively; group VII--high-speed handpiece (control). Cavities were restored and the specimens were fixed in intra-oral appliances and worn by 12 volunteers for 14 d. Sucrose solution was applied to each slab 6 times/d. Samples were removed, sectioned, and examined for microhardness at 100, 200, and 300 microm (factor distance), and 30, 60, and 90 microm (factor depth), from the restoration and enamel surface, respectively. RESULTS: Analysis of variance according to a split-plot model showed no difference among the cavity preparation techniques, among distances, or among depths, as well as no difference in the interaction between the factors of cavity preparation and distance. A significant difference was found in the interaction of cavity preparation and depth (p < 0.0001), as identified by contrast technique. CONCLUSION: The results revealed that the Er:YAG laser did not differ from conventional cavity preparation with regard to enamel microhardness.

Comparative study of the wear behavior of composites for posterior restorations.

This investigation sought to compare the abrasive wear rates of resin composites designed for posterior applications. Seventy-five specimens were fabricated with conventional hybrid (Charisma and Filtek Z250) or packable composites (Filtek P60, Solitaire II and Tetric Ceram HB), according to a randomized complete block design (n = 15). Specimens were finished and polished metallographically and subjected to abrasive wear which was performed under a normal load of 13N at a frequency of 2 Hz using a pneumatic device (MSM/Elquip) in the presence of a mucin-containing artificial saliva. Wear was quantified profilometrically in five different locations of each specimen after 1,000, 5,000, 10,000, 50,000 and after every each 50,000 through 250,000 cycles. A split-plot ANOVA showed a significant difference between the wear resistance of composites (alpha = 0.05). Tukey's test ascertained that while the composites Filtek Z250 and Charisma wore significantly less than any other of the materials tested, Tetric Ceram HB experienced the greatest wear rates. Filtek P60 and Solitaire II showed intermediate rates of material removal. The wear pattern of composites proved to be biphasic with the primary phase having the faster wear rate. In conclusion, packable resin composites may not have superior wear compared to conventional hybrid composites.

Rehardening of caries-like lesions in root surfaces by saliva substitutes.

OBJECTIVE: This study sought to evaluate whether root dentine caries-like lesions could be remineralised by saliva substitutes. METHODS: Root dentine slabs (3 x 3 x 2 mm) were cut from bovine incisors, ground flat, polished and pre-tested for Knoop microhardness (KHN) at five locations spaced 500 microm apart and 500 microm from the left edge of each sectioned piece. After 60 out of the 100 slabs had been selected based upon their KHN values, specimens were coated with wax except for their outer surface. Specimens were then cycled through a highly cariogenic challenge model to induce caries-like lesions, whose formation was confirmed by KHN measurements located 500 microm from the right edge of the specimen. According to a randomised complete block design, the experimental units (n = 15) were exposed to 1.5 ml of saliva substitutes, based on either mucin (MC) or carboxymethylcellulose (CM), to natural human saliva (HS) or to 100% relative humidity (RH) over 20 days. Remineralisation was verified by KHN measurements located 1000 microm apart from the right edge of the specimen. RESULTS: Analysis of variance indicated a significant (p < 0.0001) difference among the KHN values attained by the carious root dentine after exposure to the remineralising agents. Tukey's test ascertained that remineralisation was greatest with MC, intermediate with CM and least with HS, but rehardening did not reach the pre-caries lesion formation values. CONCLUSION: Saliva substitutes may provide partial remineralisation to preformed caries-like lesions in root dentine.

Fluoride release and secondary caries inhibition by adhesive systems on root dentine.

This study tested the fluoride-release rate and the root caries inhibitory effect of dental adhesives. In phase 1, the fluoride released from samples (n = 5) of the adhesives A (Optibond Solo), B (One-up Bond F), C (Prime & Bond NT), D (Tenure Quick), and also of the controls [+] (glass-ionomer cement) and [-] (non-fluoride releasing adhesive), was quantified on a daily basis during a pH-cycling, caries-simulating phenomenon. In phase 2, restorations were made in bovine root dentine slabs (n = 16) with the same adhesives associated with a non-fluoridated composite. Control [+] restorations were made entirely with glass-ionomer cement. Specimens were thermocycled and submitted to the pH-cycling regimen. Demineralization areas and the presence of the wall lesion (WL) and the inhibition zone (IZ) were determined by polarizing light microscopy in dentine adjacent to the restoration. The highest concentration of fluoride was released by the control [+]; adhesives A, B and C, also released fluoride. No detectable amount of fluoride was released by D or [-]. Smaller areas of demineralization were found with control [+], whereas the demineralization areas of adhesives A-D and [-] did not differ from each other. No WL was detected, and higher percentages of IZ were recorded to [+] and to adhesive A. Although some dental adhesives were able to release fluoride, they could not inhibit secondary caries development as well as the glass-ionomer cement.

Influence of the mineral content and morphological pattern of artificial root caries lesion on composite resin bond strength.

Dentine substrates with different mineral contents and morphological patterns were created by submitting root slabs to the following treatments: (A) immersion in artificial saliva during the experimental period (control), (B) demineralization for 32 h to induce caries lesion (demineralized group), and (C) demineralization for 32 h followed by remineralization for 8 d (remineralized group). The slabs were longitudinally sectioned, the mineral content was determined by cross-sectional microhardness, and the bond strength of an adhesive system/composite resin was assessed using a microtensile bond strength test. The dentine morphology after the treatments as well as the failure pattern of the debonded specimens was examined by scanning electron microscopy. Statistically significant differences were found in mineral content. Morphological analysis showed marked differences between the patterns of demineralized and remineralized substrates. The bond strength mean value of the control A did not differ from the group B, but was statistically higher than the group C. Since no linear relationship was found between dentine mineral content and bond strength values, it could be suggested that the morphological pattern may be more relevant than the mineral content to explain the bond strength of composite resin to dentine.

Efeito do clareamento caseiro sobre o equilíbrio mineral dos tecidos dentais: revisão da literatura / The effect of home bleaching on dental mineral equilibrium: a literature review

O tratamento clareador caseiro consiste na utilização de um gel á base de peróxido de carbamina, o qual permanece em íntimo contato com os tecidos bucais por certo período, diariamente, durante alguns dias ou semanas. Ao longo do clareamento, os processos de des/remineralização podem ocorrer na estrutura dental, alterando o conteúdo mineral do esmalte e da dentina. Neste artigo, revisam-se estudos que descrevem o processo dinâmico do clareamento, outros que discutem os efeitos do clareamento no equilíbrio mineral do dente e os possíveis fatores que levam às alterações no conteúdo mineral. A partir desses artigos, verifica-se que não existem ainda evidências que comprovem o efeito permanente do tratamento clareador sobre o equilíbrio mineral das estruturas dentais. Fortes evidências sugerem que fatores protetores, principalmente os componentes salivares, previnem perda mineral significativa e restabelecem o conteúdo mineral durante e após o tratamento clareador. Para favorecer a remineralização e minimizar a desmineralização durante o clareamento, a escolha do agente clareador parece ser de extrema importância. Nas características esperadas de agentes clareadores caseiros pode-se incluir o pH neutro e a presença de flúor e devem-se evitar altas concentrações de peróxido.

Home bleaching requires that a peroxide-based bleaching gel be in contact with intraoral tissues for a number of hours a day for several days. Throughout bleaching treatment, demineralization and remineralization events likely occur at the dental structure, affecting the tooth mineral content. Studies considering the bleaching dynamic process were reviewed and attention was given to those that discuss the effects of the treatment on the dental mineral equilibrium and the conditions that lead to alteration of the mineral content. There is no definitive conclusion whether home bleaching affects permanently or not dental mineral equilibrium. Strong evidence suggests that protective factors mainly salivary components prevent significant mineral loss and/or restore mineral content during and after bleaching treatment. To favor remineralization and minimize demineralization during bleaching, the choice of bleaching agent is important. Ideal characteristics of home bleaching agents include neutral pH and fluoride content. Furthermore, high concentrations of peroxide should be avoided.