The Effect of Different Decontamination Methods on the Micro-Tensile Bond Strength of CAD/CAM Resin-Based Blocks to Resin Cement.

INTRODUCTION: This study evaluates the impact of decontamination methods on Microtensile bond strength (µTBS) between resin cement and resin blocks. METHODS: Twenty CAD/CAM resin blocks from two manufacturers were wet-polished, sandblasted, and ultrasonically cleaned. After blood and saliva contamination, blocks were divided into subgroups: control, water rinsing, acid etching, alkaline cleaning paste, or 10-MDP containing cleaner. Resin-based cement was then applied. After 24 hours, the blocks were sectioned to obtain bars for testing. Half of the specimens were tested immediately for µTBS, and the other half underwent artificial aging. The surfaces of the blocks were inspected with a scanning electron microscope (SEM). Three-way ANOVA was performed for µTBS values (α=0.05). RESULTS: In one of the substrates, the positive control subgroup obtained the highest value (56,01 MPa, SD:6,96) followed by 10-MDP cleaner and universal cleaning paste, when immediately tested, with significant differences respect to the water rinsing (p⟨0.041) and acid etching (p⟨0.048) groups. After thermocycling, higher values were found in the 10-MDP cleaner (47,57 MPa, SD:8,15), but differences were not significant. In the other substrate group, the 10-MDP cleaner subgroup showed highest bond strengths (64,46 MPa SD: 10,92) at the initial test. After thermocycling, 10-MDP cleaner (58,66 MPa, SD: 9,93) gave the highest µTBS value. Significant differences between water rinsing group and the rest of subgroups (p⟨0.001), and between 10-MDP cleaner and the positive control group (p⟨0.006) were observed. CONCLUSION: Cleaning after contamination improves bonding. 10-MDP containing cleaner can help to restore initial µTBS value and maintain it in the long-term.

Leadership education in prosthodontics: Development and impact of the Future Leaders in Prosthodontics (FLIP) workshops.

STATEMENT OF PROBLEM: The effectiveness of leadership education for prosthodontists is unknown. PURPOSE: The purpose of this survey study was to evaluate the self-perceived impact a 2- to 2.5-day leadership education workshop in prosthodontics had on participants' professional, leadership, and management development. MATERIAL AND METHODS: Participants who attended a leadership workshop for future leaders in prosthodontics (FLIP) were surveyed to assess their self-reported improvements in different leadership domains. The survey was administered to 89 participants using an online survey tool, and demographic data about participants were also collected. Results were tabulated for descriptive presentation. Where applicable, the Spearman correlation coefficients were calculated. RESULTS: Seventy-two individuals responded to the invitation for a response rate of 80.9%. Improvement in all 11 leadership capabilities assessed in the survey was noted by over 75% of respondents. Over 90% of respondents reported improvement in overall leadership, career management, team management, self-awareness, problem-solving, and conflict resolution. No significant (P>.13) relationships were found among demographic data such as age, sex, home continent, or primary career focus (academics or private practice). CONCLUSIONS: Within the limitations of this survey study, participants in a leadership workshop noted improvement in a variety of leadership capabilities.

The influence of cyclic stress on surface properties of soft liners.

Soft polymers used under tissue-supported prostheses have limited service life because of surface degradation. PURPOSE: This paper evaluates the changes in surface properties and softness of soft relining materials after cyclic loading in water. MATERIALS AND METHODS: 3 polysiloxane (Silagum AM Comfort, Molloplast B, Mollosil Plus) and 2 acrylic-based (Vertex Soft, Astron LC Soft) proprietary soft relining materials and a vinyl polysiloxane (Imprint 2 Garant) as the reference impression material evaluated. A stainless steel block for detail reproduction was used on the basis of the apparatus recommended by the ISO 4823:1992 test method for preparing a standardized surface. A control group from each material was only subjected to water immersion. Non-destructive cyclic loading was carried out with a strain of 16.6 % and a frequency of 1.6 Hz 200,000 times in distilled water at 37 °C. The specimens were then duplicated and compared with the controls using roughness measurements, detail reproduction and Scanning Electron Microscope. Shore A hardness values before and after cycling were also measured. RESULTS: After degradation in the form of mechanical cycling in water, loss of substance and loss of surface detail was observed. Surface properties and Shore A hardness values of acrylic-based soft liners changed significantly (p < 0.05). CONCLUSIONS: The chemical composition of the soft relining materials seemed to affect their potential of preserving the surface texture and softness after mechanical cycling. Mechanical cycling influences the surface degradation process leading to changes of the surface texture. Polysiloxane-based materials preserved their softness, surface texture and surface smoothness better under cyclic loading compared to acrylic resin -based plasticized materials.

Effect of pretreatment with collagen crosslinkers on dentin protease activity.

OBJECTIVES: This study evaluated the effect of dentin pretreatment with collagen crosslinkers on matrix metalloproteinase (MMP) and cathepsin K mediated collagen degradation. METHODS: Dentin beams (1mm×2mm×6mm) were demineralized in 10% H3PO4 for 24h. After baseline measurements of dry mass, beams were divided into 11 groups (n=10/group) and, were pretreated for 5min with 1% glutaraldehyde (GA); 5% GA; 1% grape-seed extract (GS); 5% GS; 10% sumac (S); 20µM curcumin (CR); 200µM CR; 0.l% riboflavin/UV (R); 0.5% R; 0.1% riboflavin-5-phosphate/UV (RP); and control (no pretreatment). After pretreatment, the beams were blot-dried and incubated in 1mL calcium and zinc-containing medium (CM, pH 7.2) at 37°C for 3, 7 or 14 days. After incubation, dry mass was reassessed and aliquots of the incubation media were analyzed for collagen C-telopeptides, ICTP and CTX using specific ELISA kits. Data were analyzed by repeated-measures ANOVA. RESULTS: The rate of dry mass loss was significantly different among test groups (p<0.05). The lowest 14 day mean dry mass loss was 6.98%±1.99 in the 200µM curcumin group compared to control loss of dry mass at 32.59%±5.62, p<0.05, at 14 days. The ICTP release over the incubation period (ng/mg dry dentin) ranged between 1.8±0.51 and 31.8±1.8. CTX release from demineralized beams pretreated with crosslinkers was significantly lower than CM (5.7±0.2ng/mg dry dentin). SIGNIFICANCE: The results of this study indicate that collagen crosslinkers tested in this study are good inhibitors of cathepsin K activity in dentin. However, their inhibitory effect on MMP activity was highly variable.

Fracture strengths of chair-side-generated veneers cemented with glass fibers.

INTRODUCTION: CAD/CAM (computer-aided design and computer-aided manufacturing) systems have refreshed the idea of chair-side production of restorations, but the fracture of ceramic veneers remains a problem. Cementation with glass fibers may improve the fracture strengths and affect the failure modes of CAD/CAM-generated ceramic veneers. Therefore, this study compared the fracture strengths of ceramic veneers produced at chair side and cemented with or without glass fibers with those of composite veneers. METHODOLOGY: Thirty intact mandibular incisors were randomly divided into three groups ( n = 10) and treated with CAD/CAM-fabricated veneers cemented with dual-cure composite resin luting cement (CRLC; Group 1), CAD/CAM-fabricated veneers cemented with a glass fiber network (GFN) and dual-cure CRLC (Group 2), and a direct particulate filler composite veneer constructed utilizing fiber and a restorative composite resin (Group 3). The specimens were tested with a universal testing machine after thermal cycling treatment. RESULT: The loads at the start of fracture were the lowest for traditionally fabricated composite veneers and higher for CAD/CAM-generated. Veneers cemented either without or with the GFN. The failure initiation loads (N) for the veneers were 798.92 for Group 1, 836.27 for Group 2, and 585.93 for Group 3. The predominant failure mode is adhesive failure between the laminates and teeth for Group 1, cohesive failure in the luting layer for Group 2, and cohesive laminate failure for Group 3, which showed chipping and small fractures. CONCLUSION: Ceramic material is a reliable alternative for veneer construction at chair side. Fibers at the cementation interface may improve the clinical longevity and provide higher fracture strength values.

Degradation in the fatigue strength of dentin by cutting, etching and adhesive bonding.

UNLABELLED: The processes involved in placing resin composite restorations may degrade the fatigue strength of dentin and increase the likelihood of fractures in restored teeth. OBJECTIVE: The objective of this study was to evaluate the relative changes in strength and fatigue behavior of dentin caused by bur preparation, etching and resin bonding procedures using a 3-step system. METHODS: Specimens of dentin were prepared from the crowns of unrestored 3rd molars and subjected to either quasi-static or cyclic flexural loading to failure. Four treated groups were prepared including dentin beams subjected to a bur treatment only with a conventional straight-sided bur, or etching treatment only. An additional treated group received both bur and etching treatments, and the last was treated by bur treatment and etching, followed by application of a commercial resin adhesive. The control group consisted of "as sectioned" dentin specimens. RESULTS: Under quasi-static loading to failure there was no significant difference between the strength of the control group and treated groups. Dentin beams receiving only etching or bur cutting treatments exhibited fatigue strengths that were significantly lower (p≤0.0001) than the control; there was no significant difference in the fatigue resistance of these two groups. Similarly, the dentin receiving bur and etching treatments exhibited significantly lower (p≤0.0001) fatigue strength than that of the control, regardless of whether an adhesive was applied. SIGNIFICANCE: The individual steps involved in the placement of bonded resin composite restorations significantly decrease the fatigue strength of dentin, and application of a bonding agent does not increase the fatigue strength of dentin.

Addition of benzalkonium chloride to self-adhesive resin-cements: some clinically relevant properties.

OBJECTIVE: The clinical survival rates of the adhesive restorations are limited due to the deterioration of resin-dentin bonds over time, partly due to the endogenous enzymatic activity of dentin. Recently, benzalkonium chloride (BAC) has been shown to effectively inhibit endogenous protease activity of dentin. This study evaluated the effect of different concentrations of benzalkonium chloride (BAC) on the degree of conversion (DC), vickers hardness (VH), setting time (ST) and biaxial flexural strength (FS) of two self-adhesive resin luting cements (RC). METHODS: Two RC SpeedCEM (Ivoclar-Vivadent) and BisCem (Bisco) were modified by addition of 0.1, 0.5, 1, 1.5, 2 wt% BAC. The luting cements without the addition of BAC served as control. The DC (FT-IR/ATR from the bottom of the resin disc), vickers hardness (from top and bottom of the light-cured specimen), setting time (ISO 4049) and biaxial flexural strength (0.6 × 6 mm discs) of the specimens were tested. Data were analyzed using ANOVA and Tukeys HSD. RESULTS: DC results were in the range of 70-80%, with some significant changes in BisCem (p < 0.05). VH values of both materials increased significantly compared to control, with no significant change as the BAC percentage increases. BAC addition influenced the ST differently for both materials. For BisCem, a gradual decrease (p < 0.05) was observed whereas, for SpeedCEM, a gradual increase was observed until 1% BAC (p < 0.05). For FS values, a gradual decrease was observed for both materials with increased amounts of BAC (p < 0.05), compared to the control group. CONCLUSIONS: BAC addition of up to 1% seems to be acceptable considering the properties tested. Clinical significance. Incorporation of benzalkonium chloride to self-adhesive resin luting cements during the mixing procedure does not significantly affect the degree of conversion or flexural strength of the luting agent and may be a good option to improve the durability of adhesive interface.

Effect of using proper light-curing techniques on energy delivered to a Class 1 restoration.

OBJECTIVES: To determine the effect of proper light-curing instruction on the radiant exposure (energy density) delivered by dentists using six dental curing lights to a posterior Class 1 restoration. METHOD AND MATERIALS: Twenty-five dentists attending a professional meeting were instructed to position a patient simulator (MARC-PS, BlueLight), as they would for a patient, and then to expose the simulated Class 1 maxillary second molar preparation for a specified amount of time. At this point, the dentists were unaware of the purpose of the experiment. Each participant used three different curing lights, and the irradiance and radiant exposure (J/cm2) delivered to the preparation was recorded. Participants were then informed of the purpose of the exercise, and given specific light-curing instructions and training using the patient simulator, after which they re-exposed the same preparation using the same curing lights. Pre- and post-instruction radiant exposure values were compared using one-way ANOVA (α = .05), and for each light among all operators using a two-tailed, paired Student's t test. RESULTS: There was a wide variation in the radiant exposure delivered by the dentists and by the six curing lights, from 2.9 to 15.4 J/cm2. Before receiving additional light-curing instruction, 68% of dentists delivered less than 10 J/cm2. The radiant exposure delivered increased significantly (P < .001) by up to 30%, as a result of training using MARC-PS. CONCLUSION: The results indicate that some of the dentists participating in the present study delivered an inadequate amount of radiant exposure before instruction. More energy was delivered after a short training session using the MARC-PS. Reinforcing the proper photo-curing techniques may improve the outcome when placing resin-based restorations.

Accelerated fatigue of dentin with exposure to lactic acid.

Composite restorations accumulate more biofilm than other dental materials. This increases the likelihood for the hard tissues supporting a restoration (i.e. dentin and enamel) to be exposed to acidic conditions beyond that resulting from dietary variations. In this investigation the fatigue strength and fatigue crack growth resistance of human coronal dentin were characterized within a lactic acid solution (with pH = 5) and compared to that of controls evaluated in neutral conditions (pH = 7). A comparison of the fatigue life distributions showed that the lactic acid exposure resulted in a significant reduction in the fatigue strength (p ≤ 0.001), and nearly 30% reduction in the apparent endurance limit (from 44 MPa to 32 MPa). The reduction in pH also caused a significant decrease (p ≤ 0.05) in the threshold stress intensity range required for the initiation of cyclic crack growth, and significant increase in the incremental rate of crack extension. Exposure of tooth structure to lactic acid may cause demineralization, but it also increases the likelihood of restored tooth failures via fatigue, and after short time periods.

Flexural strength,water sorption and solubility of a methylmethacrylate-free denture base polymer reinforced with glass fibre reinforcement.

A methylmethacrylate-free denture base polymer (Eclipse) in comparison to a conventional denture base polymer (Palapress vario) was evaluated after water saturation and Stick glass fibre reinforcement. The data were analysed with ANOVA at a = 0.05. Water-storage caused a decrease in the flexural strength and stiffness of the materials (p > 0.05). Conventional denture base material with fibre reinforcement gave highest flexural strength (201.1 MPa) compared to fibre reinforced Eclipse (79.1 MPa) (p < 0.05). Water sorption after 76 days was 2.08% (Palapress vario) and 1.55% (Eclipse). Fibre-reinforcement of methylmethacrylate-free material was not as successful as conventional denture base and needs to be further optimized.

Effect of phosphoric acid on the degradation of human dentin matrix.

This study determined if dentin proteases are denatured by phosphoric acid (PA) used in etch-and-rinse dentin adhesives. Dentin beams were completely demineralized with EDTA for 30 days. We "acid-etched" experimental groups by exposing the demineralized dentin beams to 1, 10, or 37 mass% PA for 15 sec or 15 min. Control beams were not exposed to PA but were incubated in simulated body fluid for 3 days to assay their total endogenous telopeptidase activity, by their ability to solubilize C-terminal crosslinked telopeptides ICTP and CTX from insoluble dentin collagen. Control beams released 6.1 ± 0.8 ng ICTP and 0.6 ± 0.1 ng CTX/mg dry-wt/3 days. Positive control beams pre-incubated in p-aminophenylmercuric acetate, a compound known to activate proMMPs, released about the same amount of ICTP peptides, but released significantly less CTX. Beams immersed in 1, 10, or 37 mass% PA for 15 sec or 15 min released amounts of ICTP and CTX similar to that released by the controls (p > 0.05). Beams incubated in galardin, an MMP inhibitor, or E-64, a cathepsin inhibitor, blocked most of the release of ICTP and CTX, respectively. It is concluded that PA does not denature endogenous MMP and cathepsin activities of dentin matrices.

Carbodiimide cross-linking inactivates soluble and matrix-bound MMPs, in vitro.

Matrix metalloproteinases (MMPs) cause collagen degradation in hybrid layers created by dentin adhesives. This in vitro study evaluated the feasibility of using a cross-linking agent, 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC), to inactivate soluble rhMMP-9, as an example of dentin MMPs, and matrix-bound dentin proteases. The inhibitory effects of 5 EDC concentrations (0.01-0.3 M) and 5 incubation times (1-30 min) on soluble rhMMP-9 were screened with an MMP assay kit. The same EDC concentrations were used to evaluate their inhibitory effects on endogenous proteinases from completely demineralized dentin beams that were incubated in simulated body fluid for 30 days. Decreases in modulus of elasticity (E) and dry mass of the beams, and increases in hydroxyproline content of hydrolysates derived from the incubation medium were used as indirect measures of matrix collagen hydrolysis. All EDC concentrations and pre-treatment times inactivated MMP-9 by 98% to 100% (p < 0.05) compared with non-cross-linked controls. Dentin beams incubated in 0.3 M EDC showed only a 9% decrease in E (45% decrease in control), a 3.6% to 5% loss of dry mass (18% loss in control), and significantly less solubilized hydroxyproline when compared with the control without EDC cross-linking (p < 0.05). It is concluded that EDC application for 1 min may be a clinically relevant and effective means for inactivating soluble rhMMP-9 and matrix-bound dentin proteinases if further studies demonstrate that EDC is not toxic to pulpal tissues.

The inhibitory effects of quaternary ammonium methacrylates on soluble and matrix-bound MMPs.

Matrix metalloproteinases (MMPs) bound to dentin contribute to the progressive degradation of collagen fibrils in hybrid layers created by dentin adhesives. This study evaluated the MMP-inhibiting potential of quaternary ammonium methacrylates (QAMs), with soluble rhMMP-9 and a matrix-bound endogenous MMP model. Six different QAMs were initially screened by a rhMMP-9 colorimetric assay. For the matrix-bound endogenous MMPs, we aged demineralized dentin beams for 30 days in calcium- and zinc-containing media (CM; control), chlorhexidine, or QAMs in CM to determine the changes in dry mass loss and solubilization of collagen peptides against baseline levels. The inhibitory effects of QAMs on soluble rhMMP-9 varied between 34 and 100%. Beams incubated in CM showed a 29% decrease in dry mass (p < 0.05), whereas beams incubated with QAMs showed only 0.2%-6% loss of dry mass. Significantly more solubilized collagen was detected from beams incubated in CM (p < 0.05). It is concluded that QAMs exhibited dentin MMP inhibition comparable with that of chlorhexidine, but required higher concentrations.

The anti-MMP activity of benzalkonium chloride.

OBJECTIVE: This study evaluated the ability of benzalkonium chloride (BAC) to bind to dentine and to inhibit soluble recombinant MMPs and bound dentine matrix metalloproteinases (MMPs). METHODS: Dentine powder was prepared from extracted human molars. Half was left mineralized; the other half was completely demineralized. The binding of BAC to dentine powder was followed by measuring changes in the supernatant concentration using UV spectrometry. The inhibitory effects of BAC on rhMMP-2, -8 and -9 were followed using a commercially available in vitro proteolytic assay. Matrix-bound endogenous MMP-activity was evaluated in completely demineralized beams. Each beam was either dipped into BAC and then dropped into 1 mL of a complete medium (CM) or they were placed in 1 mL of CM containing BAC for 30 days. After 30 days, changes in the dry mass of the beams or in the hydroxyproline (HYP) content of hydrolysates of the media were quantitated as indirect measures of matrix collagen hydrolysis by MMPs. RESULTS: Demineralized dentine powder took up 10-times more BAC than did mineralized powder. Water rinsing removed about 50% of the bound BAC, whilst rinsing with 0.5M NaCl removed more than 90% of the bound BAC. BAC concentrations 0.5wt% produced 100% inhibition of soluble recombinant MMP-2, -8 or -9, and inhibited matrix-bound MMPs between 55 and 66% when measured as mass loss or 76-81% when measured as solubilization of collagen peptide fragments. CONCLUSIONS: BAC is effective at inhibiting both soluble recombinant MMPs and matrix-bound dentine MMPs in the absence of resins.

Bond strength of soft liners to fiber-reinforced denture-base resin.

PURPOSE: This study evaluated bond strengths of four soft liners to fiber-reinforced (FR) and unreinforced poly methyl(methacrylate) (PMMA) denture-base resin. MATERIALS AND METHODS: The autopolymerized denture-base resin Palapress Vario (Heraus Kulzer GmbH, Hanau, Germany) was used as the substrate (15 × 15 × 5 mm³). The test group consisted of substrates reinforced with porous PMMA preimpregnated unidirectional glass fibers (Stick [StickTech, Turku, Finland]) (PMMA + FR group), and the control group was unreinforced acrylic resin (PMMA group) (n = 80 per group). One of four soft liners (Ufi Gel SC [Voco, Cuxhaven, Germany], Sofreliner Tough [Tokuyama Dental Corporation, Tokyo, Japan], Vertex SoftSil 25 [Vertex-Dental B.V., Zeist, The Netherlands], and Eversoft [Dentsply Austenal, York, PA]) was placed and cured between two substrates using a polyethylene ring (10 mm inner radius, 3 mm height). Tensile bond strength tests (crosshead speed = 10 mm/min) were performed, and the results were analyzed using analysis of variance followed by Tukey's test (p= 0.05). Fracture surfaces were categorized as adhesive or cohesive-mixed modes, and failure types were statistically analyzed using chi-square test. RESULTS: FR did not affect the bond strength results significantly (p > 0.05) except for Ufi Gel SC. Significant differences in bond strength were found among the reline materials (p < 0.001). FR specimens showed a significantly higher number of cohesive-mixed fractures compared to unreinforced specimens (p < 0.05), except for plasticized acrylic-based reline material (Eversoft [Dentsply Austenal]), which showed fewer cohesive-mixed failures with FR. CONCLUSIONS: The choice of appropriate reline material system with FR acrylic resin is important for the soft liner/denture-base polymer bond. Glass FR did not have a decreasing effect on the bond strength, except for Ufi Gel SC.