Petra Hahn

Influence of resin cement viscosity on microleakage of ceramic inlays

OBJECTIVESnThe aim of the present investigation was to evaluate the effect of the different viscosities of two resin luting cements on microleakage of ceramic inlays at dentinal margins. The effect of the width of the space between inlay and tooth, on the quality of the marginal seal was also investigated.nnnMETHODSnMesial and distal class V cavities were prepared in 48 extracted third molars. The incisal margins of the cavities were in enamel and the cervical margins in dentin. Subsequently, Empress inlays with different cervical margin gap dimensions were fabricated. The mean cervical gap dimensions in the respective groups were as follows: group 1 (27 microm); group 2 (232 microm); group 3 (406 microm). Half the inlays in each group (16) were cemented with a low viscous resin luting cement, and half (16) with a highly viscous resin luting cement. The teeth were subjected to occlusal loading with synchronized thermal cycling in a masticatory simulator. Then, the specimens were immersed in basic fuchsin solution, and dye penetration along the cavity walls was measured. In addition, marginal adaptation was analyzed in the SEM at baseline and after loading, using a replica technique.nnnRESULTSnWith regard to dye penetration at dentinal margins, the highly viscous cement performed statistically significantly better at dentin/composite margins than the low viscous cement (p=0.0158). These findings are supported by SEM analysis.nnnSIGNIFICANCEnIt is assumed that polymerization stress within the luting cement could not be completely compensated for by larger luting spaces. Highly viscous luting cements are recommended for cementing class V inlays in larger luting spaces.

Effect of carbamide peroxide and hydrogen peroxide on enamel surface: an in vitro study

The aim of the study was to investigate changes in the micromorphologyl and microhardness of the enamel surface after bleaching with two different concentrations of hydrogen peroxide (HP) and carbamide peroxide (CP). Bovine enamel samples were embedded in resin blocks, and polished. Specimens in the experimental groups (nu2009=u200910) were treated with bleaching gels containing 10% CP, 35% CP, 3.6% HP, and 10% HP, respectively, for 2xa0h every second day over a period of 2xa0weeks. The gels had the identical composition and pH and differed only in their HP or CP content. The roughness and morphology of the enamel surface were analyzed using laser profilometry and SEM. Microhardness was measured using a Knoop hardness tester. The data were evaluated statistically. Specimens in the 10% HP group showed significantly higher roughness after bleaching compared to the control group (ΔRa, pu2009=u20090.01). Bleaching with 35% CP showed only a tendency to increase roughness (ΔRa, pu2009=u20090.06). Application of 10% CP or 3.6% HP had no significant influence on Ra. Enamel microhardness was significantly higher after application of 10% HP compared to the control (ΔMicu2009=u20098 KHN, pu2009=u20090.0002) and 35% CP (ΔMicu2009=u200920KHN, pu2009=u20090.01) groups. In summary, application of CP and HP showed only small quantitative and qualitative differences. In addition, the influence of bleaching procedure on the morphology and hardness of the enamel surface depended on the concentration of the active ingredients.

Two-year evaluation of a new nano-ceramic restorative material

The purpose of this prospective study was to evaluate the clinical performance of a new restorative material (Ceram·X) in combination with a new primer–adhesive (K-0127). One operator placed two Class I or II restorations in molars of 43 patients. One molar was restored with Ceram·X/K-0127, the other one with Tetric Ceram/Syntac Classic. At baseline, after 1 and 2xa0years, the restorations were evaluated by one evaluator using modified Ryge’s criteria. After 2xa0years, 31 patients were examined. One Ceram·X-restoration had to be removed for root canal treatment due to pulpitis. Thus, failure rate of Ceram·X was 3.2% and of Tetric Ceram, 0%. In both groups, no sensitivity, no recurrent caries, and no changes in surface texture were recorded after 2xa0years. One restoration in each group showed slight changes in color stability (score B). Marginal discoloration (score B) was found concerning three Ceram·X-restorations (10.0%) and two Tetric Ceram-restoration (6.5%). Marginal integrity was score B for four Ceram·X-restorations (13.3%) and for four Tetric Ceram-restorations (12.9%). No statistically significant differences were found (p>0.05). After 2xa0years of clinical service, 96.8% of Ceram·X/K-0127 and 100% of Tetric Ceram/Syntac Classic restorations were in place and performed clinically well.

Tensile bond strengths of four different dentin adhesives on irradiated and non-irradiated human dentin in vitro.

This study evaluated the influence of irradiation on dentin bond strength. Sixty irradiated and 60 non-irradiated human third molars were used. The irradiation dose of 60 Gy was fractionally applied over 6 weeks (2 Gy day(-1), 5 days week(-1). All teeth were prepared in a special manner allowing the simulation of intra-pulpal pressure and dentin perfusion. Dentin specimens with a thickness of 2.0 mm were obtained under standardized conditions. The specimens were randomly assigned to four experimental groups. Tensile bond strength of four different dentin bonding agents (Scotchbond 1, Solobond Plus, Prime&Bond 2.1 and Syntac) was evaluated using an Instron Universal testing machine. Pairwise comparison did not show any significant differences between the irradiated and non-irradiated groups. The influence of the different dentin adhesives was significant (P=0.0001; ANOVA). Compared with Solobond Plus and Prime&Bond 2.1, the use of Scotchbond 1 resulted in a significantly higher tensile bond strength in non-irradiated specimen (P< 0.05; closed test procedure based on Kruskal-Wallis test). Within the limitations of an in vitro study, it can be concluded that adhesive restoration procedures can be successfully used in patients irradiated for cancer of the head and neck.

Root lesions in a group of 50-60 year-old Germans related to clinical and social factors

Abstractu2002From a preventive point of view collection of data concerning carious and non-carious cervical tooth defects is definitely important. Consequently, the prevalence and distribution of different root lesions were studied and correlated with behavioral and biological factors in 50- to 60-year-old German individuals (n=298). Additionally, the data were correlated with characteristics concerning oral health and known risk factors such as gender, educational level, and presence of plaque. An interview included questions on sociodemographic and socioeconomic characteristics, dental and general health status, and various behavioral parameters. During clinical examination data concerning coronal and root lesions, restorations, probing depth, gingival bleeding, and dental plaque were obtained. The participants represented a social middle class population with a high awareness of dental health. Obviously, for the participants, known risk factors for root decay such as gender, educational level and plaque index were of minor importance. Factors correlating with root caries were: (a) number of missing teeth, (b) probing depth, (c) smoking habit, (d) regular dental attendance and (e) the reason for the last dental treatment. Additionally, the prevalence of non cariogenic lesions, primarily resulting from increased but wrongly performed oral self care, seems gradually to relieve carious root destruction.

A material model for internal stress of dental composites caused by the curing process

OBJECTIVEnTo compare the build-up of internal stresses in four different dental composites (Venus, Tetric Ceram, Ceram X mono and Filtek Supreme) during the curing reaction, based on the results of a former paper on polymerization kinetics, and to characterize the developing mechanical behavior for different modes of activation using experimental methods and simulation tools.nnnMETHODSnA four-parameter viscoelastic model combined with a curing model and a kinetic model was developed to simulate the mechanical behavior in three dimensions using the finite element software ABAQUS. In order to study the influence of slow polymerization behavior on the mechanical properties, the length of the activation period was doubled at half intensity of the curing light.nnnRESULTSnUsing a model which describes the complex interplay of stiffness, flowability, curing speed and activation intensity during the curing process gives deeper insight into the spatial and temporal build-up of stresses. An advantageous reaction kinetic or a lower stiffness can compensate for the effect of a higher polymerization shrinkage on the resulting peak stress. The evolution of stress is not directly proportional to the level of shrinkage of the composites.nnnSIGNIFICANCEnA material model which includes the developing mechanical characteristics of a curing dental composite can be used to develop and optimize dental materials and to assess the effect of different treatment strategies (i.e. mode of photo-polymerization, filling geometries, interfacial strength).

Kinetic model for the coupled volumetric and thermal behavior of dental composites

OBJECTIVEnThe volume and thermal behavior of dental composites during the curing reaction was analyzed for different modes of initiation using a combination of experiments and models for polymerization kinetics.nnnMETHODSnThe volume behavior of four dental composites (Venus, Tetric Ceram, Ceram X mono and Filtek Supreme) was studied with buoyancy measurements during the initiation and dark phase of the curing process. The volume and temperature development of the composites were described for different intensities of the photo-initiation with a mathematical model based on the mixed termination model for the polymerization reaction.nnnRESULTSnA good agreement between volumetric data and the model function was achieved. A non-linear regression of the experimental data with the model yields results for the adjustable parameters describing the kinetics of the polymerization reaction which are typical for comparable polymerization reactions. Using kinetic models of the polymerization reaction for analyzing the volume behavior of radically crosslinking curing dental composites, thermal and polymerization-specific components of the overall shrinkage of the composites can be distinguished and compared for different materials.nnnSIGNIFICANCEnWith the developed methodology, a more detailed insight into the curing process can be achieved which can contribute to the understanding of the build-up of internal stresses in dental fillings. These stresses can negatively affect the marginal integrity of the filling, which is a relevant precondition of long-term chemical, biological and mechanical stability.

Bond strength of composite resin to glass ceramic after saliva contamination

ObjectivesPurpose of this study was to investigate the effect of cleaning methods of glass ceramic specimens contaminated with saliva on tensile bond strength (TBS) to composite resin. Additionally, effect of water storage on bond strength was evaluated.Materials and methodsGlass ceramic discs (IPS Empress, Ivoclar-Vivadent, FL) distributed among five groups (nu2009=u200928) were etched with hydrofluoric acid, silanized, contaminated with human saliva, and in group W rinsed with water, group WS additionally silanized, group E rinsed with water and cleaned with ethanol, and group ES additionally silanized. Group C served as a control without contamination. Plastic screws were bonded to the glass ceramic discs using Variolink II (Ivoclar-Vivadent). TBS was measured after 24xa0h and after 150xa0days of storage. Failure modes were examined. ANOVA was applied to explore group effect on TBS. Pair-wise comparisons were calculated.ResultsThe mean TBS [in megapascals] were for W 46u2009±u200914, WS 55u2009±u20098, E 48u2009±u200911, ES 52u2009±u200910, and C 50u2009±u20098 after 24xa0h, and W 39u2009±u200911, WS 53u2009±u20099, E 48u2009±u20098, ES 48u2009±u200911, and C 50u2009±u20098 after 150xa0days. After 150xa0days specimens of group W showed significantly lower TBS compared to group C (pu2009=u20090.05). Additional silanization in group WS led to a significant increase of TBS compared to specimens of group W (pu2009=u20090.003). Adhesive fractures were observed only in specimens without second application of silane.ConclusionsThe cleaning of the contaminated glass ceramic surface by rinsing only did not result in a durable bond.Clinical relevancePre-silanized glass ceramic restorations need to be rinsed and treated with a fresh layer of silane after saliva contamination.

Influence of pressure application before light-curing on the bond strength of adhesive systems to dentin

This study evaluated the influence of defined pressure application before light-curing on the tensile bond strength (TBS) of two adhesive systems to wet and perfused dentin. Bonding sites were analyzed by scanning electron microscopy (SEM) to assess morphological changes. Dentin discs from 120 human third molars were prepared in such a way to allow simulation of intrapulpal pressure. The specimens were randomly assigned to 6 groups (n=20) according to different experimental conditions. The adhesive systems (Scotchbond Multi-Purpose and Syntac) were applied either to wet or perfused dentin. In the latter, compression was applied before adhesive light-curing . TBS was recorded using an universal testing machine. Qualitative examination of the bonding sites was performed by SEM after dissolving the dentin with 50% nitric acid. Pressure application prior to light-curing resulted in a remarkable decrease of TBS for Syntac, while no significant change was observed for Scotchbond MP. SEM analysis showed no considerable lengthening of the resin tags after pressure application. These findings suggest that application of adhesive systems to dentin under pressure before light-curing had no positive effect on TBS.