Can surface protection prevent the loss of hardness on dentin and composite resin surfaces exposed to erosive challenges? / ¿Puede la protección de la superficie prevenir la pérdida de dureza en las superficies de dentina y resina compuesta expuestas a erosión?

Objective: This study investigated the effect of endogenous erosion on the microhardness of dentine and a nanofilled composite resin. Procedures for preventing erosion were also studied. Materials and Methods: 90 bovine dentine specimens were divided into three groups in accordance with the method for preventing: negative control, topical application of fluoride and resin-modified glass ionomer varnish. 120 composite resin specimens were distributed into four groups, which also included a resin sealant, among the preventive procedures. Specimens were then randomly divided into three sub-groups according to the exposure to simulate gastric acid solution and subsequent remineralization: negative control, 9 and 18 cycles. Surface analysis was carried out by measuring the Knoop hardness. The data obtained were statistically analyzed using 2-way ANOVA and Tukey test. Result: The mean hardness of dentine and of the composite specimens resin exhibited lower hardness after 18 cycles. However, the resin-modified glass ionomer varnish resulted in greater values compared to the other preventive procedures. Conclusion: A resin-modified glass ionomer varnish seems to be a promising method for minimizing the damage caused by endogenous acid, but its protection can be reduced depending on the intensity of the erosive challenge.

Objetivo: Este estudio investigó el efecto de la erosión endógena sobre la microdureza de la dentina y una resina compuesta de nanorrelleno. También se estudiaron los procedimientos para prevenir la erosión. Materiales and Métodos:90 muestras de dentina bovina se dividieron en tres grupos de acuerdo con el método para prevenir: control negativo, aplicación tópica de fluoruro y barniz de ionómero de vidrio modificado con resina. Se distribuyeron 120 muestras de resina compuesta en cuatro grupos, que también incluían un sellador de resina, entre los procedimientos preventivos. Las muestras se dividieron al azar en tres subgrupos de acuerdo con la exposición para simular la solución de ácido gástrico y la remineralización posterior: control negativo, 9 y 18 ciclos. El análisis de la superficie se realizó midiendo la dureza Knoop. Los datos obtenidos se analizaron estadísticamente mediante ANOVA de 2 vías y prueba de Tukey. Resultados: La dureza media de la dentina y de la resina de muestras compuestas exhibió una dureza más baja después de 18 ciclos. Sin embargo, el barniz de ionómero de vidrio modificado con resina resultó en valores mayores en comparación con los otros procedimientos preventivos. Conclusión: Un barniz de ionómero de vidrio modificado con resina parece ser un método prometedor para minimizar el daño causado por el ácido endógeno, pero su protección puede reducirse dependiendo de la intensidad del desafío erosivo.

Effect of the ceramic translucency on the long-term water sorption and solubility of resin cements

Aim: The aim of this study was to evaluate the influence of the translucency of ceramic on water sorption and solubility of resin cements over time. Methods: Lithium disilicate ceramic slides (15x15x1 mm), A1 in color and with different translucencies (high-medium-low) were manufactured; and a glass slide with similar dimension was used as control. Under every slide, 15 specimens (8x0.5 mm) from each resin cement were prepared: light-cured (RelyX Veneer); conventional dual-cured (RelyX ARC); and self-adhesive dual-cured (Rely-X U200). The specimens were then sub-divided according to the period of evaluation (immediately, after 6 and 12 months of storage) (n=5). To evaluate the loss or gain of mass, the specimens were dried until a constant mass was reached. Subsequently, they were divided according to the respective period of storage at 37°C in distilled water and weighed immediately following removal from water. After each period, specimens underwent a new dehydration. Values from water sorption and solubility were calculated and statistically analyzed (Anova 3-way/Tukey test). Results: The lower translucency resulted in greater water sorption and solubility for all cements, regardless of the experimental period. The self-adhesive dual-cured cement showed higher water sorption under all experimental periods and had worse values after 1 year aging. Differences among solubility could only be detected after aging, and the light-cured material had higher values after 6 and 12 months. Conclusions: It could be concluded that the low degree of translucency can negatively influence the passage of light and interfere on the durability of the resin cement. The conventional dual-cured resinous agent seemed to be less affected by such condition

Effect of Dental Erosion and Methods for its Control on the Marginal and Internal Adaptation of Restorations with Different Adhesive Systems / Efeito da Erosão Dental e de Métodos para seu Controle na Adaptação Marginal e Interna de Restaurações Confeccionadas com Diferentes Sistemas Adesivos

The dentin exposed to erosive challenges is often superficially protected to prevent progression of the lesion. This study investigated the marginal and internal adaptation of composite resin restorations made on surfaces that had first been treated with different methods for controlling erosion. Cavities with margins in dentin were prepared in bovine incisors (n=360) and were divided into three groups according to the method for controlling the erosive challenge: negative control, topical application of fluoride and resin-modified glass ionomer varnish. The specimens were then randomly divided into three sub-groups according to the exposure to simulated gastric acid solution (DES) (5% HCl, pH=2.2) and subsequent remineralization (RE): negative control, 9 and 18 cycles of DES-RE. Finally, teeth were divided into four groups, depending on the bonding agent used for composite resin restoration (n=10): conventional etch-and-rinse adhesive system (2 and 3 steps) and self-etching (1 and 2 steps). Front and internal images of the interface tooth/restoration were recorded in stereoscopic microscope (15x) to quantify the percentage of adhesive failures. Despite the promising results of the resin-modified glass ionomer varnish after 9 cycles; no protective material prevented increased internal defects after 18 erosive cycles. More continuous internal margins were noted with etch-andrinse acid systems after more intense erosion. The maintenance of internal margins in eroded substrates was positively influenced by the resinmodified glass ionomer varnish and, under the most aggressive challenge, by the use of etch-and-rinse adhesives systems. (AU)

A dentina exposta a desafios erosivos é muitas vezes superficialmente protegida para prevenir a progressão da lesão. Este estudo investigou a adaptação marginal e interna de restaurações de resina composta realizadas em superfícies que foram previamente tratadas com diferentes métodos para controlar a erosão. Cavidades com margens em dentina foram preparadas em dentes incisivos bovinos (n=360) e divididas em três grupos de acordo com o método de controle do desafio erosivo: controle negativo, aplicação tópica de flúor e verniz de ionômero de vidro modificado por resina. Os espécimes foram então divididos aleatoriamente em três subgrupos de acordo com a exposição à solução de ácido gástrico simulada (DES) (HCl a 5%, pH = 2,2) e posterior remineralização (RE): controle negativo, 9 e 18 ciclos de DES-RE. Por fim, os dentes foram divididos em quatro grupos, de acordo com o agente de união utilizado para a restauração da resina composta (n=10): sistema adesivo convencional (2 e 3 passos) e autocondicionante (1 e 2 passos). Imagens frontais e internas da interface dente/restauração foram registradas em microscópio estereoscópico (15x) para quantificar a porcentagem de falhas adesivas. Apesar dos resultados promissores do verniz de ionômero de vidro modificado por resina após 9 ciclos; nenhum material de proteção impediu o aumento de defeitos internos após 18 ciclos erosivos. Margens internas mais contínuas foram observadas com sistemas adesivos convencionais após erosão mais intensa. A manutenção das margens internas em substratos erodidos foi influenciada positivamente pelo verniz de ionômero de vidro modificado por resina e, sob o desafio mais agressivo, pelo uso de sistemas de adesivos convencionais. (AU)

Can surface protection prevent damage in margins of composite resin restorations after simulated endogenous erosion?

Aim: The study investigated the effect of using surface protection agents in the adaptation of external and internal margins of restorations subjected to simulated erosion. Methods: Cavities with margins in dentin were prepared in bovine incisors (n=120). Adhesive restorations were placed using a three-step etch&rinse adhesive system and nanofilled composite resin. The specimens were divided into four groups, according to the surface protection: negative control, topical application of fluoride (TAF), resin sealant and resin-modified glass ionomer varnish (RMGI varnish). Afterwards, they were divided into three sub-groups, according to the exposure to a simulated solution of gastric acid (DES) (5% HCl, pH=2,2) and subsequent remineralization (RE): negative control, 9 and 18 cycles of DES-RE. The evaluation of the tooth-restoration interface was performed on the internal and frontal images with the aid of a stereoscopic microscope (15x), and the percentage of continuous margins without adhesive failures was quantified. Results: In the external margins, only those groups with surface protection using sealants (resin and glass-ionomer) did not exhibit a significant decrease in the percentage of continuous margins after the erosive challenges. After 18 cycles of DES-RE, the use of resin-modified glass ionomer varnish resulted in the highest percentage of continuous margins. Conclusion: It was concluded that physically covering the surfaces with a sealing agent preserved the marginal adaptation of composite resin restorations exposed to endogenous erosive challenges

Bond strength of resin cements to a zirconia ceramic with different surface treatments.

This study evaluated the influence of surface treatments and metal primers on the bond strength of resin cements to a yttrium-stabilized tetragonal zirconia (Y-TZP) ceramic. Two-hundred and forty plates of Y-TZP ceramic were randomly assigned to 24 groups (n = 10) according to the combination of surface treatment (none, air abrasion with Al2O3 particles, Er:YAG laser irradiation), metal primer (none, Alloy Primer, Metal Primer II or Metaltite) and resin cement (Calibra [Bis-GMA-based] or Panavia F2.0 [MDP-based]). Fragments of dentin with a cylindrical edge (0.8 mm in diameter) were fixed to ceramic surfaces with the resin cements. The micro-shear bond test was carried out at a 1 mm/minute speed until failure, and the ceramic surfaces were examined after debonding. Bond strengths were analyzed through three-way ANOVA/Tukey test with a 5% significance level. Changes in topography after surface treatments were evaluated with scanning electron microscopy. Surface treatments significantly modified the topography of the Y-TZP ceramic. Air abrasion resulted in increased bond strength for both resin cements. However, air abraded and laser irradiated specimens presented higher bond strength with the Bis-GMA-based resin cement than with the MDP-based cement. Both cements presented similar behavior on untreated surfaces. The three metal primers yielded a significant increase in bond strength, regardless of the surface treatment and resin cement. Adhesive failures were the most prevalent. Air abrasion with Al2O3 particles and the application of metal primers increased bond strength to Y-TZP surfaces for both resin cements.

Y-TZP ceramics: key concepts for clinical application.

Compared to conventional ceramic systems, Yttrium-stabilized tetragonal zirconia (Y-TZP) ceramics have some superior mechanical properties, ensuring a broad application in dentistry. The current study aimed to present relevant information about Y-TZP ceramics gathered from peer-reviewed papers. A search of the English language peer-reviewed literature was conducted using the PubMed database between 1998 and 2008. Articles that did not focus exclusively on the clinical application of Y-TZP ceramic restorations were excluded from further evaluation. Selected papers describe the chief characteristics of zirconia ceramics and important clinical features, especially those related to cementation procedures. The literature shows that, although new substances and equipment for the surface preparation of zirconia ceramics are in development, the most promising luting protocol seems to be the use of air abrasion with aluminum oxide particles (silanated or not), followed by the application of resin cements or surface primers containing special reactive monomers. However, because zirconia ceramics have only recently been developed for dental applications, there is not enough clinical evidence to support any definitive cementation protocol.

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

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

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.

Microtensile bond strength of dual-cure resin cement to root canal dentin with different curing strategies.

The purpose of this study was to measure the bond strength of dual-cure resin cement at different regions of root canal dentin using three kinds of curing method. Thirty-six extracted bovine teeth were used. Each root was sectioned vertically into halves. Their pulpal dentin walls were polished flat and then applied with two dual-cure resin cements (Bistite II, Panavia F), and divided into three curing strategy groups: multi-direction light, one-direction light and no-light. The bonded specimens were sectioned perpendicularly to the long axis of the root into approximately 0.7 mm thick slabs within two-third of the root from the coronal end, and prepared for microtensile bond strength (muTBS) test. Knoop hardness of the cements was also measured. Within each curing strategy for both dual-cure resin cements, there were no significant differences between the muTBS values at the coronal third and mid third regions. The effect of curing method on bond strength and KHN was found to be dependent on the material.