Effect of extraction media and storage time on the elution of monomers from four contemporary resin composite materials.

INTRODUCTION: The purpose of this study was to examine the effect of different extraction media, including culture media, as well as storage times on the elution of monomers from modern dental composites. MATERIALS AND METHODS: FOUR CONTEMPORARY COMPOSITE MATERIALS WERE TESTED: (a) Clearfil Majesty Esthetic (Kuraray), (b) Esthet X (DENTSPLY), (c) Filtek Silorane (3M ESPE), and (d) Admira (Voco). Forty-eight specimens were made. The specimens were stored in 1 ml of (a) artificial saliva, (b) Dulbecco's Modified Eagle Medium (DMEM), (c) DMEM plus 10% fetal bovine serum (FBS), and (d) ethanol 75%. The specimens were analyzed after 24 hours and after 1 week of storage. HPLC Liquid Chromatography was performed to analyze the extracted solutions. The statistical package SPSS 18 was used for the statistical analysis of the results. RESULTS: All the materials tested released monomers that were consistent with the base composition of their resin matrix. Bisphenol-A (BPA) was detected in Clearfil Esthetic and EsthetX when ethanol 75% was used for storage. TEGDMA was released at a faster rate compared to the other monomers with most of the monomer eluted in the first 24 hours. The effect of storage solution and storage time on the elution of the same monomers varied between materials. CONCLUSIONS: There was a significant effect of time, storage solution, and material on the elution of the detectable unbound monomers. Unbound monomers were detected in culture media, which may lead to false-negative results in cytotoxicity tests of resin composite materials. BPA was detected in two of the tested materials.

Immediate vs delayed repair bond strength of a nanohybrid resin composite.

PURPOSE: To evaluate both the immediate and water-stored repair tensile bond strength (TBS) of a nanohybrid resin composite using different bonding protocols. MATERIALS AND METHODS: One hundred sixty half hourglass-shaped slabs were prepared. Eighty half-slabs were wet ground immediately after light curing using high-speed abrasive burs, while the other half-slabs were stored in water for one month (delayed) and then wet ground for repair. Each set of the 80 repaired slabs was split into two groups to be tested for TBS after 24 h or 1 month of water storage. For all repaired slabs, either immediate or delayed, four bonding procedures were used involving wet and dry bonding with a 3-step etch-and-rinse adhesive with or without silane pretreatment. TBS tests were performed at a crosshead speed of 0.5 mm/min. To determine the cohesive strength of the resin composite itself, which served as the reference, additional whole slabs were prepared and tested in tension after a 24-h (n = 10) and a 1-month storage period (n = 10). Failure modes were evaluated using a stereomicroscope at 40X magnification. Three-way ANOVA was run to test the effect of water storage, testing time, bonding protocols, and their interactions on the repair TBS, which was given as a percentage of the reference values. RESULTS: For the immediate repair groups, the repair TBS ranged from 40% to 61.9% after 24-h storage and from 26% to 53.1% after 1-month water storage compared to the TBS of the whole slabs. For the delayed repair group, the repaired TBS ranged from 47.2% to 63.6% for the 24-h repairs and from 32.2% to 44.2% for the test groups stored in water for 1 month. Three-way ANOVA revealed that water storage had no significant effect on the repair TBS (p = 0.619). Both testing time and bonding protocols had a significant effect on the repair TBS (p = 0.001). The interactions between the independent variables (water storage, testing time, and bonding protocols) had no significant effect (p = 0.067). CONCLUSION: The repair bond strength was consistently and highly significantly less than the cohesive strength of the composite. A delay of 1 month before carrying out the repair had no effect on the bond strength, irrespective of the bonding procedure used. Silane treatment did not improve the repair bond strength. In all instances, except for the immediate wet bonding plus silane procedure and delayed dry bonding, the bond strength of the repairs significantly dropped after 1 month of storage in water.

In vitro biocompatibility of modified potassium fluorrichterite and potassium fluorrichterite-fluorapatite glass-ceramics.

Potassium fluorrichterite (KNaCaMg(5)Si(8)O(22)F(2)) glass-ceramics were modified by either increasing the concentration of calcium in the glass (GC5), or by the addition of P(2)O(5) to produce potassium fluorrichterite-fluorapatite (GP2). The solubility of the stoichiometric composition (GST), GC5 and GP2 were measured using the standard test described in ISO 6872:1995 (Dental Ceramics). Ion release profiles were determined for Si, Ca, Mg, Na, K and P using inductively coupled plasma mass spectrometry and fluoride ion (F(-)) concentration was measured using an ion-selective electrode. The cytotoxicity of all compositions was assessed using cultured rat osteosarcoma cells (ROS, 17/2.8). Cell response was qualitatively assessed using scanning electron microscopy (SEM) and quantitatively using the Alamar blue assay. GST was the least soluble and also released the lowest concentration of ions following immersion in water. Of the modified compositions, GC5 demonstrated intermediate solubility but the greatest ion release while GP2 exhibited the highest solubility. This was most likely due to GC5 having the greatest proportion of residual glass following crystallisation. The mass loss exhibited by GP2 may have been due in part to the partial disintegration of the surface of specimens during solubility testing. SEM demonstrated that all compositions supported the growth of healthy ROS cells on their surfaces, and this data was further supported by the quantitative Alamar blue assay.

Effect of air-drying pressure and distance on microtensile bond strength of a self-etching adhesive.

PURPOSE: To investigate the effect of pressure and distance during air drying on the microtensile bond strength (µTBS) of a single-step self-etching adhesive to bovine dentin. MATERIALS AND METHODS: A total of 36 bovine molars was used in this study. Twenty-seven teeth were used for µTBS testing and 9 teeth for the evaluation of the resin/dentin interface. The teeth were divided into 9 groups according to the variation in solvent evaporation pressure and the distance from the dentin surface. The adhesive was applied according to the manufacturer's instructions. The pressure was adjusted using a pressure regulator and the distance was fixed by measuring the distance from the tip of the syringe to the flat dentin surface. Each tooth was restored with a composite crown 6 mm in height and was cut to produce composite/dentin rectangular sticks with a cross-sectional area approximately 1 mm2 and 12 mm in length. The sticks were tested in tension until failure at a crosshead speed of 0.5 mm/min. The fracture pattern was evaluated using a stereomicroscope under 40X magnification. For the resin/dentin interface, the samples were gold sputtered and examined using SEM operated at 20 kV. RESULTS: Two-way ANOVA showed that both pressure and distance from the dentin surface significantly affect the µTBS of the single-step self-etching adhesive (p = 0.001). The interaction of the two independent variables (pressure and distance from dentin surface) showed a significant difference (p = 0.001). CONCLUSION: On the basis of the µTBS data generated in this study, the single-step self-etching adhesive used proved to be technique sensitive.

Marginal gap, internal fit, and fracture load of leucite-reinforced ceramic inlays fabricated by CEREC inLab and hot-pressed techniques.

PURPOSE: This in vitro study was designed to evaluate and compare the marginal gap, internal fit, and fracture load of resin-bonded, leucite-reinforced glass ceramic mesio-occlusal-distal (MOD) inlays fabricated by computer-aided design/manufacturing (CAD/CAM) or hot pressing. MATERIALS AND METHODS: Fifty caries-free extracted human molars were prepared for standardized MOD inlays. Impressions of each specimen were made and poured using type IV dental stone. Dies were randomly divided into two equal groups. Twenty-five ceramic inlays were fabricated by the hot-pressed technique using IPS Empress leucite-reinforced glass ceramics, and the other 25 ceramic inlays were produced by CAD/CAM technology using ProCAD leucite-reinforced ceramic blocks and CEREC inLab facilities. Inlays were bonded to the teeth using a dual-cured resin cement. The specimens were stored in distilled water at 37°C for 24 hours and then thermocycled for 5000 cycles. The marginal gap measurements were taken with a stereomicroscope. Specimens in each group of inlay systems were randomly divided into two subgroups of 10 and 15 specimens each. Ten specimens in each subgroup were sectioned mesiodistally for evaluation of the internal fit. The fracture load of specimens in the second subgroup (n = 15) of the two inlay systems was determined under compressive load in a universal testing machine. Data were analyzed using Student's t-test at a significance level of p < 0.05. RESULTS: The mean marginal and internal gap size in both IPS Empress and ProCAD inlays were less than 100 µm; however, the marginal gap for the IPS Empress restorations was significantly higher than that of ProCAD restorations (p < 0.05). There was no significant difference in the mean internal fit or the fracture load between the two glass ceramic inlays (p > 0.05). CONCLUSIONS: The leucite-reinforced glass ceramic inlay restorations fabricated by CEREC inLab (CAD/CAM) and the hot-pressed technique provided clinically acceptable marginal and internal fit with comparable fracture loads after luting.

Prediction of osteoconductive activity of modified potassium fluorrichterite glass-ceramics by immersion in simulated body fluid.

Potassium fluorrichterite (KNaCaMg(5)Si(8)O(22)F(2)) glass-ceramics were modified by either increasing the concentration of calcium (GC5) or by the addition of P(2)O(5) (GP2). The stoichiometric composition (GST), GC5 and GP2 were soaked in simulated body fluid (SBF) along with 45S5-type bioglass as a control. After immersion, surface analyses were performed using thin-film X-ray diffraction (TF-XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and Fourier-transform infrared (reflection) spectroscopy (FT-IR). All compositions showed the formation of a calcium phosphate rich surface layer in SBF; GST, GP2 and the bioglass control within 7 days of immersion and GC5 after 14 days. It was concluded that all compositions were likely to be osteoconductive in vivo, with GP2 providing the best performance in terms of the combination of rapid formation of the surface layer and superior mechanical properties. This glass-ceramic system has potential as a load bearing bioceramic for fabrication of medical devices intended for skeletal tissue repair.

Biologic assessment of antiseptic mouthwashes using a three-dimensional human oral mucosal model.

BACKGROUND: The biologic safety profile of oral health care products is often assumed on the basis of simplistic test models such as monolayer cell culture systems. We developed and characterized a tissue-engineered human oral mucosal model, which was proven to represent a potentially more informative and more clinically relevant alternative for the biologic assessment of mouthwashes. The aim of this study was to evaluate the biologic effects of alcohol-containing mouthwashes on an engineered human oral mucosal model. METHODS: Three-dimensional (3D) models were engineered by the air/liquid interface culture technique using human oral fibroblasts and keratinocytes. The models were exposed to phosphate buffered saline (negative control), triethylene glycol dimethacrylate (positive control), cola, and three types of alcohol-containing mouthwashes. The biologic response was recorded using basic histology; a cell proliferation assay; 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide tissue-viability assay; transmission electron microscopy (TEM) analysis; and the measurement of release of interleukin (IL)-1beta by enzyme-linked immunosorbent assay. RESULTS: Statistical analysis showed that there was no significant difference in tissue viability among the mouthwashes, cola, and negative control groups. However, exposure to the positive control significantly reduced the tissue viability and caused severe cytotoxic epithelial damage as confirmed by histology and TEM analysis. A significant increase of IL-1beta release was observed with the positive control and, to a lesser extent, with two of the tested mouthrinses. CONCLUSIONS: The 3D human oral mucosal model can be a suitable model for the biologic testing of mouthwashes. The alcohol-containing mouthwashes tested in this study do not cause significant cytotoxic damage and may slightly stimulate IL-1beta release.

The influence of plastic light cure sheaths on the hardness of resin composite.

OBJECTIVE: This study investigated the influence of a disposable light cure sheath on both the surface hardness and hardness at varying thicknesses of resin composite. METHODS: A series of resin composite discs (Spectrum) were fabricated with varying depths up to 6 mm. The light curing units used were a standard halogen unit (Elipar Trilight) and an LED unit (Elipar Freelight 2). Recommended curing times from the manufacturer were followed. The disposable light-curing sheath (Cure Sleeve) was used with both light-curing units. Two additional groups without the sheath were employed as controls. Each specimen (n = 4) was subjected to hardness testing to evaluate hardness from 0 mm to 5 mm thick. A 200g load was applied for 10 seconds using a Vickers diamond indenter and six indentations were obtained from each specimen. Statistical analysis was performed using two-way ANOVA. RESULTS: The LED without a sheath achieved the highest surface hardness value (47.2 VHN +/- 5.5). There was no significant difference between the groups regarding surface hardness (p > 0.05). As the thicknesses of the resin composite increased, the hardness values decreased in all groups. The LED light curing unit, in combination with a sheath, demonstrated the lowest hardness values at a 5 mm thickness of resin composite (p < 0.05). CONCLUSION: All four different methods of light curing resulted in a significant reduction in hardness values with increasing resin composite thickness, which could compromise the mechanical properties of the resin composite. However, the use of the light cure sheaths still provided an acceptable depth of cure when used following the 2 mm increment rule. It was not until 3 mm that the use of the light cure sheaths compromised the hardness results. It is recommended that the curing depth should not exceed 2 mm, regardless of light curing method.

Fracture strength of minimally prepared resin bonded CEREC inlays.

PURPOSE: This study compared the structural integrity and fracture mode of teeth restored with traditionally and minimally prepared resin-bonded CAD/CAM inlays fabricated from the same material. METHODS: Forty intact maxillary premolars were used and divided into four groups. Two groups were prepared according to a traditional inlay preparation design (2.0 mm occlusal reduction, a 1.5 mm wide proximal box and divergent walls) and two groups were prepared according to a newly proposed minimal preparation design (round shaped cavity with 1.0 mm occlusal reduction, a U-shaped proximal box 1.0 mm wide and parallel walls). Two restorative systems were tested: a composite system comprised of Paradigm MZ100 (3M ESPE) blocks and RelyX Unicem (3M ESPE) resin cement and a ceramic system comprised of ProCAD blocks (Ivoclar-Vivadent) and Variolink II (Ivoclar-Vivadent) resin cement. The inlays were cemented according to the manufacturers' instructions. Each specimen was loaded axially to its occlusal surface at a crosshead speed of 0.5 mm/minute in a universal testing machine until fracture. The fracture load data were analyzed using ANOVA, comparing inlays of the same restorative material. Also, the mode of fracture of the inlays was recorded and analyzed using a non-parametric test (Kruskal-Wallis). RESULTS: In the composite system case, the mean fracture load and SD were 1322 N (+/- 445) for the traditional inlays and 1511 N (+/- 395) for the minimal inlays, while in the ceramic system case, those values were 1135N (+/- 450) for the traditional inlays and 1761 N (+/- 494) for the minimal inlays. Statistical analysis of the results showed that there was no statistically significant difference between the two designs for the composite system, while for the ceramic system, the minimally prepared teeth showed higher mean fracture strength. Non-parametric analysis (Kruskal-Wallis) of the mode of fracture showed that there was no statistically significant difference between traditionally and minimally prepared inlays for both systems (p > .05). CONCLUSIONS: Under the conditions of this experimental study, only the ceramic inlays, when prepared with a minimal preparation design, demonstrated a higher fracture strength as compared to the traditionally prepared teeth. Use of the proposed minimal preparation design did not compromise the immediate post-operative structural integrity of teeth restored either with resin composite or ceramic inlays.

Fracture toughness of a ceramic-resin interface.

OBJECTIVES: The purpose of this study was to compare the interfacial fracture toughness of smooth and roughened ceramic surfaces bonded with a luting resin using an optimized method of silane treatment. METHODS: Ceramic discs were prepared with four different surface preparations (n=20) consisting of (1) polished, (2) gritblasted, (3) hydrofluoric acid etched and (4) gritblasted and etched. The ceramic discs were then covered by a PTFE tape with a chevron shaped circular hole. The exposed surfaces were treated by an optimized silane treatment followed by an unfilled resin and then a luting resin. Specimens were then stored in distilled water at 37 degrees C for (A) 24h and (B) 30 days. The interfacial fracture toughness was measured, the mode of failure and fracture surfaces were also examined under a stereo-zoom microscope and a scanning electron microscope. RESULTS: One-way ANOVA showed that there was no statistically significant difference in the mean interfacial fracture toughness for groups A1-A4 (P>0.05). However, the mean interfacial fracture toughness for group B1 was significantly different from that for groups B2, B3 and B4 (P<0.05). Independent-samples t-test results showed that there was a significant increase in the G(Ic) mean value for groups B2 and B3 after 30 days water storage (P<0.05). The modes of failure were predominantly interfacial or cohesive within the resin. SIGNIFICANCE: It can be concluded that micro-mechanical retention by gritblasting the ceramic surfaces could be sufficient with no need for HF acid etching the ceramic surfaces when an appropriate silane application procedure is used.

Spectral reflectance and color of dentin ceramics for all-ceramic restorations.

OBJECTIVE: The study was conducted to observe the spectral reflectance curves, and evaluate the color coordinates (CIELAB) of VM7 dentin ceramics (VITA, Germany) across the whole 3D-MASTER shade system. METHODS: Three disc samples, 13 mm in diameter and 1.4mm in thickness, were produced for each shade by firing following the manufacturer's instructions. Each fired disc was ground to a thickness of 1.0 mm and both faces were polished. Spectral reflectance data in the visible spectrum under the standard illuminant D65 were collected at 1 nm intervals by using a computer-controlled spectrophotometer. Color coordinates, L*, a*, b*, C*, h, in the three-dimensional CIELAB color space were obtained. RESULTS: (1) Spectral reflectance in the short-wavelength range systematically decreased with increasing chroma number (M1, M2, and M3) when compared within the same value (lightness) group (1M, 2M, 3M, 4M, and 5M). (2) Spectral reflectance decreased systematically across the whole visible spectrum with increasing value group when compared within the same chroma group. (3) A negative relationship was recognized between lightness (L*) and chromaticity index a* (red-green direction). That is, a* coordinate increases from approximately 1 for the 1M1 sample to approximately 13 for the 5M3 sample, the corresponding lightness systematically decreased from 87 to 69. (4) With increasing a* coordinate, hue angle (h) significantly decreased from 85 degrees for the 1M1 sample to 69 degrees for the 5M3 sample. (5) Lightness apparently increased with increasing hue angle (h) throughout the whole range of the 3D-MASTER shade system. (6) A strong positive relationship between chroma (C*) and chromaticity index b* (yellow-blue direction) was found, demonstrating that the chroma of the present ceramic is mainly controlled by the b* coordinate. SIGNIFICANCE: Systematic variations in spectral reflectance and color coordinates of VM7 dentin were observed throughout the 3D-MASTER shade system and were suggested to be caused by the fine structure of the sample which can interfere with shorter wavelengths in the visible spectrum.

Mucotoxicity of dental composite resins on a tissue-engineered human oral mucosal model.

OBJECTIVE: Tissue-engineered human oral mucosal models have been developed for biocompatibility assessment of biomaterials. The aim of this study was to evaluate the biological effects of three different composite resin systems on a three-dimensional human oral mucosal model. METHODS: Full-thickness oral mucosal models were engineered by air/liquid interface culture of a human oral keratinocyte cell line on a lamina propria composed of oral fibroblasts seeded into a porous scaffold. The surface of the tissue models was exposed to three types of experimental composite resins: a TEGDMA-based, a UDMA-based, and a BisGMA/TEGDMA (80:20)-based composite resin for 24h. The response of the engineered oral mucosa to the test materials was assessed using routine histology, the Alamar Blue tissue viability assay and IL-1beta release measured by ELISA. RESULTS: Compared to the other materials tested, the TEGDMA-based composite resin caused significant damage to the oral mucosal model. Statistical analysis by one-way ANOVA followed by Tukey's analysis showed that there was a significant decrease in the viability of tissue models after 24h exposure to TEGDMA-based composite resin. Also exposure to TEGDMA-based composite resin significantly increased the amount of IL-1beta released from the oral mucosal model. CONCLUSION: The 3D human oral mucosal model has the potential to be a more relevant and more informative model than monolayer cell culture systems for biocompatibility testing of dental materials. The results obtained from multiple-endpoint analysis of the oral mucosal model indicate significant mucotoxicity of high TEGDMA-containing composite resins.

A clinical evaluation of a resin composite and a compomer in non-carious Class V lesions. A 3-year follow-up.

PURPOSE: To compare the clinical performance of a resin composite and a polyacid-modified resin composite (compomer) in non-carious cervical lesions using a one-step self-etch adhesive. METHODS: Thirty patients, each with two non-carious cervical lesions (60 restorations), received one composite (Pertac-II) restoration and one compomer (Hytac) restoration, both used in conjunction with a self-etch adhesive (Prompt L-Pop) and placed following the manufacturer's instructions. Evaluations were at baseline, 6, 12 and 36 months after placement for retention, margin adaptation, marginal discoloration, anatomic form, secondary caries and postoperative sensitivity. Statistical analysis with the Pearson Chi-square test was undertaken. RESULTS: Retention rates were 86.6% for composite and 86.7% for compomer at 36 months. 3.3% of composite and 6.7% of compomer restorations showed a deficiency in marginal adaptation. Both materials showed a slight marginal discoloration of 7.7%. More deterioration in anatomic form occurred with the compomer (11.5%) than the composite (3.8%). None of the restorations exhibited secondary caries or postoperative sensitivity problems. There was no significant difference in performance between the materials in any of the categories evaluated.

Cytotoxicity of resin monomers on human gingival fibroblasts and HaCaT keratinocytes.

OBJECTIVES: The aim of this study was to evaluate and compare the biological effects of three resin monomers on three human gingival fibroblast (HGF) cell lines and immortalised human keratinocytes. METHODS: Primary HGFs and HaCaT keratinocytes were cultured for 24h and grown to sub-confluent monolayers. Resin monomers were dissolved in dimethyl sulphoxide (DMSO) and diluted with culture medium. Cultures were exposed to different concentrations of monomers (10(-2) to 10mM) for 24h. Cell viability measured by Alamar Blue assay, and cell culture supernatant was examined for the presence of human interlukin-1beta (IL-1beta) using sandwich enzyme-linked immunosorbant assay (ELISA). TC50 values were calculated from fitted dose-response curves. RESULTS: All monomers showed toxic effects on the HGFs and HaCaT cells and inhibited chemical reduction of Alamar Blue in high concentrations. Statistical analysis of TC50 values by one-way ANOVA followed by Tukey's analysis showed that there is a significant difference in TC50 values between the cell lines (p<0.05), although the rank order of monomer toxicity remained the same for different cell lines. None of these monomers-induced IL-1beta release from HGFs and HaCaT cells. SIGNIFICANCE: Dental resin monomers are toxic to human gingival fibroblasts and HaCaT keratinocytes. However, they cannot induce IL-1beta release from these cells by themselves. Alamar Blue assay is a sensitive method for the evaluation of cytotoxicity and it can detect different sensitivities of different cell lines to the resin monomers.

Brittleness index of machinable dental materials and its relation to the marginal chipping factor.

OBJECTIVES: The machinability of a material can be measured with the calculation of its brittleness index (BI). It is possible that different materials with different BI could produce restorations with varied marginal integrity. The degree of marginal chipping of a milled restoration can be estimated by the calculation of the marginal chipping factor (CF). The aim of this study is to investigate any possible correlation between the BI of machinable dental materials and the CF of the final restorations. METHODS: The CEREC system was used to mill a wide range of materials used with that system; namely the Paradigm MZ100 (3M/ESPE), Vita Mark II (VITA), ProCAD (Ivoclar-Vivadent) and IPS e.max CAD (Ivoclar-Vivadent). A Vickers Hardness Tester was used for the calculation of BI, while for the calculation of CF the percentage of marginal chipping of crowns prepared with bevelled marginal angulations was estimated. RESULTS: The results of this study showed that Paradigm MZ100 had the lowest BI and CF, while IPS e.max CAD demonstrated the highest BI and CF. Vita Mark II and ProCAD had similar BI and CF and were lying between the above materials. Statistical analysis of the results showed that there is a perfect positive correlation between BI and CF for all the materials. CONCLUSIONS: The BI and CF could be both regarded as indicators of a material's machinability. Within the limitations of this study it was shown that as the BI increases so does the potential for marginal chipping, indicating that the BI of a material can be used as a predictor of the CF.

Evaluation of the marginal fit of three margin designs of resin composite crowns using CAD/CAM.

OBJECTIVES: To examine the marginal fit of resin composite crowns manufactured with the CEREC 3 system employing three different margin designs; bevel, chamfer and shoulder, by means of a replica technique and a luting agent. METHODS: Three master casts were fabricated from an impression of a typodont molar tooth and a full-coverage crown prepared with a marginal finish of a bevel, a chamfer and a shoulder. Each cast was replicated 10 times (n=10). Scanning of the replicas and crown designing was performed using the CEREC Scan system. The crowns were milled from Paradigm MZ100 composite resin blocks. The marginal fit of the crowns was evaluated with a replica technique (Aquasil LV, Dentsply), and with a resin composite cement (RelyX Unicem, Aplicap) and measured with a travelling microscope. Statistical analysis was performed using two-way ANOVA. RESULTS: For the replica technique the average marginal gaps recorded were: Bevel Group 105+/-34 microm, Chamfer Group 94+/-27 microm and Shoulder Group 91+/-22 microm. For the resin composite cement the average marginal gaps were: Bevel Group 102+/-28 microm, Chamfer Group 91+/-11 microm and Shoulder Group 77+/-8 microm. Two-way ANOVA analysis showed that there was no statistically significant difference between the three groups of finishing lines regardless of the cementation technique used. CONCLUSIONS: The marginal gap of resin composite crowns manufactured with the CEREC 3 system is within the range of clinical acceptance, regardless of the finishing line prepared or the cementation technique used.

The effect of variations in hourglass specimen design on microtensile bond strength to dentin.

PURPOSE: To correlate the microtensile bond strength (microTBS) of dentin bonding agents to dentin for different hourglass designs with the stress distribution across the adhesive interface utilizing finite element stress analysis (FEA). MATERIALS AND METHODS: Adper Scotchbond Multipurpose Plus dentin bonding agent was bonded to flat dentin surfaces in three experimental groups. A 5- to 6-mm layer of resin composite (Filtek Supreme, 3M ESPE) was built up incrementally. After 24 h water storage at 37 degrees C, the bonded teeth were sectioned into hourglass designs of circular, parabolic, and spline shape, with a ca 1 mm2 cross-sectional area at the bonded interface (n=30). The specimens were subjected to microTBS testing at a crosshead speed of 0.5 mm/min. The fracture surfaces were examined under SEM to determine the modes of failure. FEA models were constructed using the TOMECH program. A load of 100 N was applied and the stresses at the bonded interfaces were viewed using the FEMSYS visualization software. RESULTS: One-way ANOVA, Tukey's and Kaplan-Meier tests revealed significant differences in the microTBS for the three designs: 36.7 +/- 8.4, 21.4 +/- 7.9 and 13.8 +/- 4.3 MPa, for the circular, parabolic, and spline hourglass, respectively (p < 0.05). FEA stress distribution data in the adhesive layer showed significant differences among the three designs, which is consistent with the bond strength values. The spline hourglass design showed a three-fold increase in the local stress concentration at its narrowest cross section. CONCLUSION: The specimen geometry greatly influences the measurement of the microTBS. The results are consistent with the FEA predictions.

Influence of specimen designs on the microtensile bond strength to dentin.

PURPOSE: The purpose of this study was to examine the sensitivity of the microtensile bond strength (muTBS) to changes in the specimen design using three different dentin bonding systems, utilizing both experimental and finite element analysis (FEA). MATERIALS AND METHODS: Freshly extracted bovine central incisors were randomly divided into 9 experimental groups. Flat dentin surfaces were exposed and polished with 600-grit SiC papers. The dentin bonding agents (DBA) Adper Prompt L-Pop, Adper Scotchbond 1XT, and Adper Scotchbond Multi-Purpose Plus were bonded to the dentin surface. A 5- to 6-mm-thick layer of resin composite Filtek Supreme was built up incrementally. For each DBA, after 24 h in water, the bonded specimens were sectioned vertically into slabs of stick-, dumbbell- and hourglass-shaped specimens (n = 30). The muTBS test was performed at a crosshead speed of 0.5 mm/min and the fracture surfaces were examined under optical microscopy and SEM. FEA models of the three designs were developed using the TOMECH program and viewed using FEMSYS visualization software. RESULTS: One-way ANOVA, Tukey's and Kaplan-Meier tests revealed no significant differences between the bond strengths for the three designs for the same dentin bonding agent (p > 0.05). However, there were significant differences between the three adhesive systems when using one specimen design. FEA results showed no major differences between the three designs in the maximum stress within the adhesive layer, although the stress distributions for the hourglass shape followed a different pattern. CONCLUSIONS: The three different specimen designs had no influence on the bond strength to dentin within one adhesive system. FEA predictions are consistent with the results of the experiments.

The effects of different opacifiers on the translucency of experimental dental composite resins.

OBJECTIVE: The aim of this study was to evaluate the effects of different opacifiers on the translucency of experimental dental composite-resins. METHODS: Three metal oxides that are used as opacifiers were tested in this study: titanium oxide (TiO2), aluminium oxide (Al2O3) and zirconium oxide (ZrO2). Experimental composite-resins were fabricated containing 25wt.% urethane dimethacrylate (UDMA)-based resin matrix and 75% total filler including different concentrations of metal oxides (0, 0.25, 0.5, 0.75 and 1wt.%) blended into silane treated barium-silicate filler. The specimens (15.5mm diameter and 1mm thickness) were light-cured and tested in the transmittance mode using a UV/VIS spectrophotometer at wavelengths from 380 to 700nm under a standard illuminant D65. The color differences (ΔE* ab) between different concentrations of opacifiers were also measured in transmittance mode based on their Lab values. RESULTS: Statistical analysis by ANOVA and Tukey's test showed a significant decrease (p<0.05) in light transmittance with the addition of opacifiers to the experimental composite-resins. There was a linear correlation between different concentrations of TiO2 and Al2O3 and total transmittance. Total transmittance was also found to be wavelength dependent. The color differences for the concentrations of 0-1wt.% of the opacifiers were above 1 ΔE* unit, with Al2O3 showing the smallest color shift. SIGNIFICANCE: The type and the amount of the opacifiers used in this study had a significant effect on the translucency of the experimental UDMA-based dental composite resins. The most effective opacifier was TiO2, followed by ZrO2 and Al2O3 in decreasing order, respectively.

ADM guidance-Ceramics: Fracture toughness testing and method selection.

OBJECTIVES: The objective is within the scope of the Academy of Dental Materials Guidance Project, which is to provide dental materials researchers with a critical analysis of fracture toughness (FT) tests such that the assessment of the FT of dental ceramics is conducted in a reliable, repeatable and reproducible way. METHODS: Fracture mechanics theory and FT methodologies were critically reviewed to introduce basic fracture principles and determine the main advantages and disadvantages of existing FT methods from the standpoint of the dental researcher. RESULTS: The recommended methods for FT determination of dental ceramics were the Single Edge "V" Notch Beam (SEVNB), Single Edge Precracked Beam (SEPB), Chevron Notch Beam (CNB), and Surface Crack in Flexure (SCF). SEVNB's main advantage is the ease of producing the notch via a cutting disk, SEPB allows for production of an atomically sharp crack generated by a specific precracking device, CNB is technically difficult, but based on solid fracture mechanics solutions, and SCF involves fracture from a clinically sized precrack. The IF test should be avoided due to heavy criticism that has arisen in the engineering field regarding the empirical nature of the calculations used for FT determination. SIGNIFICANCE: Dental researchers interested in FT measurement of dental ceramics should start with a broad review of fracture mechanics theory to understand the underlying principles involved in fast fracture of ceramics. The choice of FT methodology should be based on the pros and cons of each test, as described in this literature review.