Bond strength to different CAD/CAM lithium disilicate reinforced ceramics.

OBJECTIVE: To evaluate the microstructure and the influence of applying universal adhesive only versus universal adhesive with additional silane application on shear bond strength (SBS) to four different lithium disilicate ceramic (LDC) materials. MATERIAL AND METHODS: Specimens (n = 240, 1.5 mm thick) cut from four different CAD/CAM materials were polished and etched with 4.5% hydrofluoric (HF) acid according to manufacturers' instructions (20 s: IPS e.max CAD, n!ce; 30 s: Amber Mill, CEREC Tessera). For cementation, either universal adhesive only or silane + universal adhesive were applied before prefabricated composite cylinders were cemented using a dual-cure resin cement. SBS testing was performed either after 24 h or after 20,000 cycles thermocycling +2 months water storage. Surfaces were analyzed with stereomicroscope for failure mode and with scanning-electron microscopy for microstructure of the LDC. Statistical analysis of the data was performed with non-parametric tests at α = 0.001. RESULT: SBS values for non-aged specimens ranged from 29.08 to 17.87 MPa and for aged specimens from 22.24 to 3.01 MPa. SBS was significantly reduced when silane was omitted after aging, (p < 0.001). Failure mode was mostly mixed with some cohesive failures in the LDC. CONCLUSION: Bond strengths are highly affected by the CAD/CAM LDC and their microstructures. The application of silane after hydrofluoric etching is still essential to obtain long-term bonding, irrespective of the presence of silane in the universal adhesive. Water degradation can significantly affect long-term bonding to novel LDC. CLINICAL SIGNIFICANCE: When using a universal adhesive for bonding to LDC restorations, the best long-term bond is achieved if an additional application of silane precedes the universal adhesive.

Microstructural considerations for novel lithium disilicate glass ceramics: A review.

OBJECTIVE: To review the ultrastructural characteristics of novel lithium disilicate based glass ceramics (LDC), how their manufacturing process influences their structure and their clinical use. OVERVIEW: Lithium disilicate based glass ceramic has been successfully used for indirect restorations ranging from partial tooth coverage up to tooth replacement for over 20 years. It combines esthetic and mechanical properties, unlike any other indirect material which makes it an indispensable part of esthetic and restorative dentistry. Recently, novel LDCs have been introduced to the market. Parameters for their use and their microstructure are still not been widely known. This article will review these materials and highlight with high-resolution scanning electron microscopic images their structural aspects and their resulting clinical relevance. CONCLUSION: Restorations made from LDCs are reliable and can be predictably used only when proper guidelines and protocols during manufacturing and clinical use are followed. For novel LDCs manufacturing and long-term bonding protocols still must be established. Moreover, novel LDCs machinable blocks should be crystallized or heat-treated after milling for superior performance. CLINICAL SIGNIFICANCE: With more and newer etchable LDC materials entering the market, clinicians and technicians need to be aware of the differences in manufacturing and the resulting microstructure to ensure a successful treatment outcome that will last.

Effect of Luting Cement and Convergence Angle of the Preparation on the Internal Fit of Zirconia Restorations.

The objective was to evaluate the effect of luting agents and the preparation design on the internal fit of zirconia restorations. Sixty dies were prepared and divided in occlusal convergence angle of 6° (OC6) and 12° (OC12). CAD/CAM zirconia copings were fabricated (Lava All-Ceramic System). A zinc phosphate cement (ZPC); a glass ionomer cement (GIC); and a resin cement (RC) were studied. Specimens were sectioned and coping/die discrepancies were evaluated through Stereoscopic Microscopy. A closer fit was observed in OC12 when compared to OC6 (p < 0.001). For OC6 no significant differences were observed in between ZPC, GIC, and RC (p > 0.05). For OC12, a significantly closer fit was recorded on the ZPC subgroup when compared to the GIC subgroup (p < 0.001). Preparations of 12 degrees demonstrated a closer internal fit when compared to 6 degrees. Preparations of 12 degrees achieved better internal fit values with ZPC (Fortex) followed by RC (RelyX Unicem), and GIC (Ketac Cem). No differences were found when comparing different luting agents over 6° degrees preparations.

How Reliable a Bonding Strategy Is the Use of Universal Adhesives?

Universal adhesives (UAs) were introduced about 10 years ago as alternative bonding systems to clinicians' demand for versatility and user-friendly clinical techniques. Clinical studies have shown that the performance of UAs is dependent on the bonding strategy used.

Effect of a single-component ceramic conditioner on shear bond strength of precoated brackets to different CAD/CAM materials.

OBJECTIVES: To compare the shear bond strength (SBS) of the CAD/CAM material-bracket interface using three surface treatments: following manufacturers' instructions (MI), Monobond Etch & Prime (MEP) and 9.6% hydrofluoric acid plus silane (9.6% HF), after 24 h of water storage (24 h) and 10,000 cycles of thermocycling (TC). MATERIALS AND METHODS: A total of 126 crowns with four identical buccal surfaces were fabricated using seven different CAD/CAM materials: CEREC Blocs unglazed (CBU), CEREC Blocs glazed (CBG), IPS Empress CAD (EMP), IPS e.max CAD (EMA), VITA SUPRINITY PC (SUP), inCoris TZI (TZI) and VITA ENAMIC (ENA). A total of 504 APC Flash-Free (APC FF)-precoated brackets were bonded applying three surface treatments: (1) MI; (2) MEP and (3) 9.6% HF. SBS was performed after 24 h and TC. Results were analyzed by Kruskal-Wallis and Mann-Whitney U tests (p < 0.05). RESULTS: MEP conditioning yielded lower SBS results compared with MI and 9.6% HF for CBG (24 h and TC) and EMA (TC) materials. EMP conditioning with MEP after 24 h obtained lower SBS values compared with MI; however, after TC, SBS was similar to MI group and higher than with 9.6% HF. After TC for TZI ceramic, MI protocol (sandblasting) obtained higher SBS scores than MEP, but similar than 9.6% HF. Treatment of ENA with MI and MEP produced higher results than 9.6% HF after TC. SBS results were similar for CBU and SUP, regardless of the treatment. CONCLUSIONS: Although each CAD/CAM material requires specific surface treatment to obtain the highest SBS of APC FF brackets, the treatment with MEP is a valid orthodontic alternative for most of the materials tested. TC significantly decreased SBS for most of the materials. CLINICAL RELEVANCE: MEP can be considered a valid and promising product to condition most of the CAD/CAM ceramics evaluated for APC FF bracket bonding purposes, allowing a faster and safer procedure.

Bioactive Dental Adhesive System With tt-Farnesol: Effects on Dental Biofilm and Bonding Properties.

BACKGROUND: Composite dental restorations are commonly used to restore cavitated carious lesions. Unfortunately, the main reason for failure is the development of secondary caries adjacent to the restoration. To improve the long-term survival of restorations, antibacterial agents have been added into dental materials. In this study, we assessed the antibacterial and bonding capacity of a commercial universal dental adhesive incorporated with the antibacterial agent tt-farnesol creating 3 experimental adhesives: 0.38% (v/v), 1.90% (v/v), and 3.80% (v/v), plus a control (no incorporation of tt-farnesol). METHODS: The antibacterial activity was evaluated by assessing colony-forming units (CFU), biofilm dry weight (DW) and production of extracellular insoluble polysaccharides (EIP) at day 2, 3, and 5 of biofilm growth post surface treatment on the surface of composite disks. The effect of tt-farnesol on the chemical and bonding capacity of the adhesive system was assessed via pH analysis, degree of conversion (DC), and microtensile bond strengths to human dentin in both self-etch and etch-and-rinse application modes. A qualitative analysis of the effects of tt-farnesol on biofilm formation was evaluated using scanning electron microscopy (SEM). The sealing capacity of all adhesive systems tested was evaluated using confocal laser scanning microscopy (CLSM). RESULTS: The 3.80% (v/v) experimental adhesive exhibited the lowest CFU count and lowest production of EIP at day 5. DW and pH values did no exhibit statistical differences among all tested groups. Bond strengths and DC decreased with the incorporation of the antibacterial agent into the adhesive system regardless of the concentration of tt-farnesol. CONCLUSION: The incorporation of tt-farnesol into the adhesive system significantly reduced bacterial viability and production of EIP; however, the bonding properties of the experimental dental adhesives were altered.

PROA concept: prosthetic restoration with orthodontic appliance.

This paper describes an alternative computer-aided design/computer-aided manufacturing (CAD/CAM) technique for the creation of a combined prosthetic restoration with orthodontic appliance (PROA). This concept allows the use of orthodontic appliances such as brackets, attachments, or any other type of appliance over different types of prosthetic restorations. The PROA concept aims to mitigate problems associated with performing restorative treatment when orthodontic treatment is necessary. This proposed concept provides the clinicians with proper control and planning of the interdisciplinary treatment that will lead to the final tooth shape, form, and proportions while performing orthodontic tooth movements.

Effects of Light Attenuation through Dental Tissues on Cure Depth of Composite Resins.

OBJECTIVE: Polymerization of light-cured resin-based materials is well documented; however, the intensity of the activating light can be reduced by passage through air, dental structure, or restoration compromising the physical properties of the restoration. The aim of this study was to evaluate the depth of cure of different light cured composite resins polymerized directly or transdental, through enamel and enamel/dentin tissues. MATERIAL AND METHODS: Five composite resins were selected for this experiment: SureFil SDR, Dentsply (SDR), Filtek Supreme Plus, 3M ESPE (FSP), Aelite LS, Bisco (ALS), Filtek LS, 3M ESPE (FLS), and TPH, Dentsply (TPH). Thirty specimens of each material were prepared with 2- or 4-mm thickness. The specimens were light-cured (Elipar 2500, 3M ESPE) for 40 sec using three different protocols: direct or transdental, through a disc of enamel with 1 mm of thickness, and a disc of enamel and dentin with 2 mm of thickness. Eight Vickers microhardness (VH) measurements were taken from each specimen, four on top and four on bottom surface (Micromet, Buehler, 100 g per 15 sec). Data was analyzed with ANOVA three-way, Tukey HSD post-hoc (α = .05). RESULTS: Bottom surfaces of specimens exhibited statistically significant lower Vickers microhardness than the top surfaces for all composite resin evaluated, regardless of the curing conditions, except for the SDR when direct light-cured. Transdental light curing through enamel/dentin layer, significantly decreased VH (P<0.05) on the bottom surface of all composite groups. CONCLUSION: The results of this study showed that light-curing attenuation of dental structures negatively affect the micro-hardness of composite resins.

All-on-four rehabilitation using photogrammetric impression technique.

Conventional implant impression techniques may introduce distortions in the framework that can lead to a lack of accuracy of the prostheses. Misfit between the restoration and the implants facilitates the occurrence of biomechanical failures and prostheses complications due to inadequate stress dissipation. Digital impressions present an alternative to eliminate procedural distortions by improving the fit between the restoration and the implants. Among the different types of digital impressions, photogrammetry has emerged as an alternative for multiple implant impressions. This case report describes photogrammetric technique for a full-arch rehabilitation in All-on-four of a 68-year-old patient with a fixed implant-supported restoration on the mandible. Photogrammetric technique has demonstrated to be a successful digital alternative to conventional multiple-implant impression. Esthetics and function remained stable over a follow-up period of 1 year. No biomechanical or biologic complications were observed.

Toxicology of Pre-heated Composites Polymerized Directly and Through CAD/CAM Overlay.

OBJECTIVES: The aim was to compare cytotoxicity/genotoxicity of pre-heated composites polymerized through CAD/CAM overlays on isolated human peripheral blood lymphocytes. MATERIAL AND METHODS: A microhybrid (Z100, 3M ESPE) and nanofilled composite (Filtek Supreme Ultra, 3M ESPE) were heated in a heating unit (Calset, AdDent Inc.) at different temperatures: 37 oC, 54 oC, and 68 oC. A small amount of heated composite was placed in a cylindrical mold (6mm diameter; 0.65mm thick), covered with a Mylar sheet, pressed and light-cured directly and through 2 mm thick CAD/CAM ceramic-reinforced polymer (CRP)(LAVA Ultimate, 3M ESPE) or CAD/CAM lithium disilicate ceramic (LDC)(e.max, Ivoclar/Vivadent) overlay. After curing, the specimens were immediately placed in a prepared lymphocyte cell culture. Cytotoxicity was assessed using a dye exclusion method by simultaneous staining with ethidium bromide and acridine orange, aimed to determine percentages of viable, apoptotic and necrotic cells. Genotoxicity was studied using alkaline comet assay. RESULTS: For Z100, the highest percentage of viable cells is recorded at T1 (93.7%) after direct light curing, followed by light curing through CRP (92.3%) and through LDC (91.7%T1,T3). For Filtek Supreme Ultra, the highest percentage of viable cells is recorded while curing through CRP (91.0% T2), followed by LDC (90% T1,T3) and direct light curing (88.7%T2). CONCLUSION: For both tested materials, preheating the procedure at T1 and T2 may be the procedure of choice. In terms of genotoxicity, preheating at T3 may not be suggested.

In Vitro Biocompatibility of Preheated Giomer and Microfilled-Hybrid Composite.

OBJECTIVE: The aim of this study was to evaluate cytotoxic potencies of two light cured composite materials after heating on different temperatures and cured directly and through CAD/CAM overlay. MATERIALS AND METHODS: Composite materials (microfilled-hybrid Gradia Direct Posterior and Beautifil II) were heated in a Calset warming unit at three different temperatures (T1:37°C, T2:54°C, T3:68°C). A small amount of heated composite material was placed in a round mold (diameter 6mm; 0.65mm thick), covered with Mylar sheet, pressed and polymerized with Bluephase LED unit. One group of samples were polymerized directly, and the other group through 2mm thick CAD/CAM ceramic-reinforced polymer (CRP) and CAD/CAM lithium disilicate ceramic (LDC) overlay for 20 and 40 seconds. The polymerized samples were placed immediately after curing in a lymphocyte cell culture. The viability of peripheral blood lymphocytes was evaluated using a dye exclusion technique by simultaneous staining with ethidium bromide and acridine orange. Quantitative assessments were made by determination of the percentage of viable, apoptotic and necrotic cells. The Pearson chi-square test was used for statistical analysis. RESULTS: In case of 20 seconds polymerization, the highest number of viable cells polymerization were recorded when materials were heated at 37°C (T1), while in case of 40 seconds polymerization, the highest number of viable cells were recorded when the materials were heated at 54°C (T2). The samples polymerized through CAD/CAM overlays showed less cytotoxicity than samples polymerized directly. CONCLUSION: Apart from composite material composition, the cell viability was also influenced by curing time, temperature of pre-heating and polymerization pattern.

Effects of CO2 laser irradiation on matrix-rich biofilm development formation-an in vitro study.

BACKGROUND: A carbon dioxide (CO2) laser has been used to morphologically and chemically modify the dental enamel surface as well as to make it more resistant to demineralization. Despite a variety of experiments demonstrating the inhibitory effect of a CO2 laser in reduce enamel demineralization, little is known about the effect of surface irradiated on bacterial growth. Thus, this in vitro study was preformed to evaluate the biofilm formation on enamel previously irradiated with a CO2 laser (λ = 10.6 µM). METHODS: For this in vitro study, 96 specimens of bovine enamel were employed, which were divided into two groups (n = 48): 1) Control-non-irradiated surface and 2) Irradiated enamel surface. Biofilms were grown on the enamel specimens by one, three and five days under intermittent cariogenic condition in the irradiated and non-irradiated surface. In each assessment time, the biofilm were evaluated by dry weigh, counting the number of viable colonies and, in fifth day, were evaluated by polysaccharides analysis, quantitative real time Polymerase Chain Reaction (PCR) as well as by contact angle. In addition, the morphology of biofilms was characterized by fluorescence microscopy and field emission scanning electron microscopy (FESEM). Initially, the assumptions of equal variances and normal distribution of errors were conferred and the results are analyzed statistically by t-test and Mann Whitney test. RESULTS: The mean of log CFU/mL obtained for the one-day biofilm evaluation showed that there is statistical difference between the experimental groups. When biofilms were exposed to the CO2 laser, CFU/mL and CFU/dry weight in three day was reduced significantly compared with control group. The difference in the genes expression (Glucosyltransferases (gtfB) and Glucan-binding protein (gbpB)) and polysaccharides was not statically significant. Contact angle was increased relative to control when the surface was irradiated with the CO2 laser. Similar morphology was also visible with both treatments; however, the irradiated group revealed evidence of melting and fusion in the specimens. CONCLUSION: In conclusion, CO2 laser irradiation modifies the energy surface and disrupts the initial biofilm formation.

Reproducing Optical Properties of Anterior Teeth after Ultra-Conservative Preparation.

OBJECTIVE: Selecting the appropriate material is essential when restoring color and appearance of esthetically compromised anterior teeth. CLINICAL CONSIDERATIONS: Most of the conventional restorative techniques require tooth reduction in order to mimic optical properties of a natural tooth. Fortunately, bonding techniques associated with improvements on dental ceramics esthetics allow for highly conservative treatment options in which maximum preservation of dental tissues can be attained. An analysis of different ceramic materials available and different types of tooth preparation is presented in a format of a decision tree for treatment planning. CONCLUSIONS: The suggested decision-making aims to facilitate clinicians' selection of the most appropriate restorative technique for reproducing color and appearance of anterior teeth after ultra-conservative preparation and according to different clinical scenarios CLINICAL SIGNIFICANCE: The selection of the appropriate ceramic material for each case is of major importance, since the entire treatment plan will be determined based on the type of ceramic material that will be used for the final restoration. Each restorative material has a specific tooth preparation requirement, indications, and limitations that shall be respected for maximum esthetical outcomes. (J Esthet Restor Dent 28:267-276, 2016).

The influence of intrinsic water permeation on different dentin bonded interfaces formation.

OBJECTIVES: To determine the effects of intrinsic wetness on the formation of dentin bonding interfaces of four resin cement systems bonded to dentin under different pulpal pressures. METHODS: Thirty-six freshly extracted third molars were selected and processed for dentin µTBS. The teeth were randomly assigned into 12 experimental groups, according to the adhesive luting system [Adper Single Bond Plus (3M ESPE) combined with two luting agents RelyX ARC (3M ESPE) and heated Filtek Z250 Universal Restorative (3M ESPE), Clearfil CD Bond (Kuraray) combined with Clearfil Esthetic Cement (Kuraray), and RelyX Unicem 2 Automix (3M ESPE)] and pulpal pressure (0, 5, and 20 cm of simulated pulpal pressure). Leucite-reinforced glass-ceramic slabs (IPS Empress CAD, Ivoclar Vivadent) of 3mm thickness were bonded to dentin. The samples were stored in distilled water for 24h and then sectioned in X/Y directions across the adhesive interface to obtain specimens with a cross section of 0.8 ± 0.2mm(2). All sticks were fractured by tension at a crosshead speed of 1.0mm/min and the data were submitted to Kruskal-Wallis and Mann-Whitney Tests (α=0.05). Ultrastructural analysis of the interfaces was performed using Confocal Laser Scanning Microscopy (CLSM) and Scanning Electron Microscopy (SEM). RESULTS: The statistical analyses showed that pulpal pressure decreased µTBS for all groups. Significantly higher µTBS values were obtained in heated Z250 group restored without any pulpal pressure. CLSM showed that the uptake of water through the dentin tubuli and their anastomosis of lateral branches during the adhesive luting procedures prevented adequate formation of the dentin bonding interfaces. SEM showed that the luting film created is material- dependent and all adhesive failure occurred at the resin-dentin interface. CONCLUSION: The constant intrinsic wetness replenishment prevents adequate formation of the hybrid layer. CLINICAL SIGNIFICANCE: Intrinsic moisture during adhesive luting procedures significantly affects the interaction between luting materials and dentin subtract and decreases the quality and bonding strength of the resin-dentin bond.

Biomechanical analysis of engineered bone with anti-BMP2 antibody immobilized on different scaffolds.

Recently we have demonstrated the ability of monoclonal antibodies (mAb) specific for bone morphogenetic protein (BMP)-2 immobilized on different scaffolds to mediate bone formation, a process referred to as Antibody Mediated Osseous Regeneration (AMOR). One of the key properties of regenerated bone is its biomechanical strength, in particular in load-bearing areas. This study sought to test the hypothesis that the biomechanical strength of regenerated bone depends of the mode of regeneration, as well as the scaffold used. Four different scaffolds, namely titanium granules (Ti), alginate hydrogel, anorganic bovine bone mineral (ABBM), and absorbable collagen sponge (ACS) were functionalized with anti-BMP-2 or isotype control mAb and implanted into rat critical-size calvarial defects. The morphology, density and strength of the regenerated bone were evaluated after 8 weeks. Results demonstrated that scaffolds functionalized with anti-BMP-2 mAb exhibited varying degrees of bone volume and density. Ti and ABBM achieved the highest bone volume, density, and strength of bone. When anti-BMP-2 mAb was immobilized on Ti or ABBM, the strength of the regenerated bone were 80% and 77% of native bone respectively, compared with 60% of native bone in sites implanted with rh-BMP-2. Control interventions with isotype mAb did not promote considerable bone regeneration and exhibited significantly lower mechanical properties. SEM analysis showed specimens immobilized with anti-BMP-2 mAb formed new bone with organized structure bridging the crack areas. Altogether, the present data demonstrated that the morphological and mechanical properties of bone bioengineered through AMOR could approximate that of native bone, when appropriate scaffolds are used. © 2015 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 104B: 1465-1473, 2016.

Permeation of intrinsic water into ethanol- and water-saturated, monomer-infiltrated dentin bond interfaces.

OBJECTIVES: The aim of this study was to evaluate the formation of dentin bonding interfaces using the water-wet and the ethanol-wet techniques under simulated pulpal pressure, and to assess the effect of adhesive solvent and thermomechanical loading. METHODS: Flat dentin surfaces were restored under 20mm-simulated pulpal pressure following two bonding approaches (water-wet and ethanol-wet bonding) in combination with dental adhesives containing ethanol (Single Bond Plus and Scotchbond Multi-Purpose) or acetone (One-Step Plus and All-Bond 2) as solvent. Half of the restorations of each subgroup were subjected to thermocycling followed by cyclic loading (three teeth per group). Bond strength was measured using the microtensile bond strength test and fitted to a Weibull distribution (α=0.05). Ultrastructural analyses of the interface and leakage/nanoleakage evaluation were performed using confocal scanning microscopy (CLSM) and transmission electron microscopy (TEM). RESULTS: Water permeation through dentin tubules during adhesive application prevented adequate penetration of adhesive monomers into the demineralized collagen matrix in both bonding techniques, but more severely for water-wet bonding. Acetone-solvated adhesives showed worse bonding performance and hybridization than ethanol-based systems when applied in the ethanol-wet mode, both before and after thermomechanical challenge. SIGNIFICANCE: The ethanol-wet bonding technique helps to compensate for water permeation from dentin tubules during the bonding procedures to form more stable dentin bonds, especially when used in conjunction to ethanol-solvated systems.

Roughness and morphology of composites: influence of type of material, fluoride solution, and time.

This study evaluated the effect of fluoride solutions on surface roughness and morphology of composites in the short and long term. Specimens were randomly assigned to experimental groups (n=5) according to type of composite (nanofilled, microhybrid, microfilled) and immersion media (artificial saliva, 0.05% sodium fluoride solution, Fluordent Reach, Oral-B, and Fluorgard). Roughness was evaluated at time intervals: T 0 after 24 h in artificial saliva (baseline); T 60 after being in assigned immersion media for 1 min daily over 60 days; and T final after artificial aging (20,000 thermal cycles, 1,200,000 mechanical loading cycles, and continuous immersion for 1,825 min). Surface morphology was qualitatively analyzed by scanning electron microscopy (SEM) at T 60 and T final. Roughness data were submitted to analysis of variance for mixed repeated measures, Sidak, and Tukey tests at α=0.05. Micro-filled resin showed the highest roughness values. Fluoride solutions had no influence on roughness. Higher roughness values were observed after artificial aging. In SEM observations after the artificial aging, the specimens showed surface degradation, irrespective of immersion medium or type of composite. Nano-filled resin showed higher loss of resin matrix and protrusion of filler particles. Roughness was not influenced by fluoride solutions; however, it is material dependent and increases over time.

Dental floss selection and its impact on evaluation of interproximal contacts in licensure exams.

Ideal interproximal contacts between adjacent natural teeth or dental restorations are a critical factor for the health of the dental-alveolar complex. Interproximal contact tightness is a physiological entity affected by many patient-related and restorative parameters. This variation poses a challenge in defining the "clinically acceptable" contact area tightness (CAT) and therefore how students and clinicians should be trained to evaluate this parameter. The most widely used method to evaluate interproximal contacts is to pass dental floss between contact areas. Candidates for licensure exams are instructed to check contact areas with dental floss and are advised that this will be one of the crucial parameters to be evaluated in the overall restoration quality. The purpose of this study was to evaluate a standardized interproximal contact with six brands of dental floss. Thirty faculty members and thirty dental students at one U.S. dental school evaluated the tightness of a single interproximal contact on a typodont. The results showed that no difference was found between CAT evaluations by faculty and students, whereas significant differences were found between different floss brands. In light of the results, it is suggested that licensure boards should standardize the recommendation for which floss brand should be used in order to avoid inconsistencies in students' preparation.

Comparison of heat generated by alumina-toughened zirconia and stainless steel burs for implant placement.

PURPOSE: In current practice, two types of burs are typically used: stainless steel (SS) and alumina-toughened zirconia (ATZ). The present study evaluated the durability of these two burs in relation to osteotomy creation for implant placement. In addition, the effects of the two types of burs on a bone model were examined. MATERIALS AND METHODS: SS and ATZ burs were compared under controlled conditions in a swine rib osteotomy. The heat generated and time necessary for perforation were measured and analyzed with repeated-measures one-way analysis of variance. The burs and bone samples were evaluated using scanning electron microscopy. RESULTS: New ATZ and SS burs showed greater bone disruption compared to burs that had been used 80 times. Brand new burs of either material showed small manufacturing defects, which increased in number with use. No clinically or statistically significant differences were found between burs with respect to temperature and time for perforation. CONCLUSIONS: SS and ATZ burs can be used several times for implant site preparation under controlled conditions without reaching a temperature that is harmful to the bone. Both burs wear under repeated use, but not to an excessive degree. The duller burs produced smoother perforations than did the new ones.

Effect of low-elastic modulus liner and base as stress-absorbing layer in composite resin restorations.

OBJECTIVES: The aim of this study was to evaluate the effectiveness of liner and base materials to reduce the stress resulting from polymerization shrinkage. The null hypothesis tested was that the presence of low-viscosity liner and base materials under the composite resin restoration reduces the polymerization shrinkage stress. METHODS: A quasi-three-dimensional photoelastic model of a second premolar with a class I preparation was restored using four experimental groups (n=7): RC, resin composite (Filtek Z250); FLRC, flowable liner (Filtek Flow)+resin composite restoration; VLRC, resin-modified glass-ionomer liner+resin composite restoration; and VBRC, resin-modified glass-ionomer base+resin composite restoration. The maximum shear stresses (tau(max)) were calculated along the adhesive interface in 13 predefined and standardized point locations. Data were submitted to one-way ANOVA, followed by a Tukey's post hoc test (p<0.05). RESULTS: A significant difference was found among the experimental groups (p=0.001); therefore, the null hypothesis was rejected. The mean maximum shear stress was: 38.0kPa for RC, 52.1kPa for FLRC, 72.8kPa for VLRC, and 90.2kPa for VBRC. The polymerization shrinkage stress level from least to greatest was: RC