Mustafa Murat Mutluay

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.

On the fatigue behavior of resin-dentin bonds after degradation by biofilm

The durability of resin-dentin bonds is a growing concern in the placement of composite restorations. Most reported evaluations concerning the mechanical behavior of the bonded interface are conducted using static loading to failure only. They also do not account for the acid production of biofilms, which is one of the most common contributors to interfacial failures in vivo. In this investigation resin-dentin bonded interface specimens were exposed to S. mutans for 14 days and then subjected to quasi-static or cyclic four-point flexure to failure. Control specimens (without biofilm) were evaluated after aging for one and fourteen days. While no significant difference in flexure strength resulted from the duration of water aging (66.2 MPa vs. 56.9 MPa), biofilm exposure caused a significant reduction in strength (29.3 MPa; p ≤ 0.000). After water aging for one and fourteen days the apparent endurance limits were 13.0 MPa and 13.1 MPa, respectively. Biofilm treatment caused a significant (p ≤ 0.001) reduction in fatigue resistance of the interface, and the endurance limit was reduced to 9.9 MPa. Fatigue failure of the control specimens initiated within the resin composite adjacent to the interface, whereas failure of the biofilm treated specimens initiated within the hybrid layer and appeared attributed to the localized demineralization of dentin. Biofilm degradation is an important consideration in assessing the durability of resin-dentin bonds.

Fatigue of the resin–dentin interface: A new approach for evaluating the durability of dentin bonds

UNLABELLED There are concerns regarding the longevity of resin composite restorations and the clinical relevance of in vitro bond strength testing to the durability of dentin bonds in vivo. OBJECTIVE The objectives of this investigation were to: (1) develop a new method of experimental evaluation for quantifying the durability of dentin bonds, (2) apply this method to characterize the interfacial strength of a selected commercial system under both monotonic and cyclic loading, and (3) distinguish mechanisms contributing to the interface degradation and failure. METHODS A new method for fatigue testing the resin-dentin interface was developed based on a four-point flexure arrangement that includes two identical bonded interfaces. Cyclic loading of specimens comprised of coronal dentin bonded to a commercial resin composite and controls of resin composite was performed to failure within a hydrated environment. Scanning electron microscopy and nanoscopic dynamic mechanical analysis were used to evaluate failure mechanisms. RESULTS The fatigue strength of the resin-dentin interface was significantly lower (p≤0.0001) than that of the resin composite and reported for dentin over the entire finite life regime. Defined at 1×10(7) cycles, the apparent endurance limit of the resin-dentin interface was 13MPa, in comparison to 48MPa and 44MPa for the resin composite and dentin, respectively. The ratio of fully reversed endurance limit to ultimate strength of the interface (0.26) was the lowest of the three materials. SIGNIFICANCE The proposed approach for characterizing the fatigue strength of resin-dentin bonds may offer new insights concerning durability of the bonded interface.

Fatigue of the resin-enamel bonded interface and the mechanisms of failure.

The durability of adhesive bonds to enamel and dentin and the mechanisms of degradation caused by cyclic loading are important to the survival of composite restorations. In this study a novel method of evaluation was used to determine the strength of resin-enamel bonded interfaces under oth static and cyclic loading, and to identify the mechanisms of failure. Specimens with twin interfaces of enamel bonded to commercial resin composite were loaded in monotonic and cyclic 4-point flexure to failure within a hydrated environment. Results for the resin-enamel interface were compared with those for the resin composite (control) and values reported for resin-dentin adhesive bonds. Under both modes of loading the strength of the resin-enamel interface was significantly (p≤0.0001) lower than that of the resin composite and the resin-dentin bonded interface. Fatigue failure of the interface occurred predominantly by fracture of enamel, adjacent to the interface, and not due to adhesive failures. In the absence of water aging or acid production of biofilms, the durability of adhesive bonds to enamel is lower than that achieved in dentin bonding.

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.

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 Students 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.

Effect of carbodiimide on the fatigue crack growth resistance of resin–dentin bonds

UNLABELLED Recent studies have shown that ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) inactivates endogenous dentin proteases, thereby preventing collagen degradation and improving the durability of adhesive bonds to dentin. Bond durability is routinely assessed by monotonic microtensile testing, which does not consider the cyclic nature of mastication. OBJECTIVE To characterize the effect of an EDC pretreatment on the fatigue crack growth behavior of resin-dentin bonds. METHODS Bonded interface Compact Tension (CT) specimens were prepared using a three-step etch-and-rinse adhesive and hybrid resin-composite. Adhesive bonding of the treated groups included a 1 min application of an experimental EDC conditioner to the acid-etched dentin. The control groups did not receive EDC treatment. The fatigue crack growth resistance was examined after storage in artificial saliva for 0, 3 and 6 months. RESULTS There was no significant difference in the immediate fatigue crack growth resistance of the EDC-treated and control groups at 0 months. However, after the 3 and 6 months storage periods the EDC-treated groups exhibited significantly greater (p≤0.05) fatigue crack growth resistance than the control specimens. SIGNIFICANCE Although the EDC treatment maintained the fatigue crack growth resistance of the dentin bonds through 6 months of storage, additional studies are needed to assess its effectiveness over longer periods and in relation to other cross-linking agents.

Long-Term Durability of Dental Adhesives

The use of tooth-colored dental restorative materials, along with the adhesive techniques, has become routine in today’s dental practice. The longevity of adhesive restorations depends mainly on good bonding between restorative materials and tooth structure, which should be achieved in situ, within minutes. While bonding to enamel is reliable through micromechanical retention, bonding to dentin presents challenges due to its more complex collagenous structure. Progressive loss of resin-dentin bond integrity and reduction in bond strength have been extensively reported. This was attributed partly to the hydrophilic nature of the contemporary adhesives systems that causes unwanted water absorption, phase separation, and resin leaching and also to the endogenous collagenolytic enzymes that can slowly hydrolyze collagen. Current research in this field aims at increasing the durability of resin-dentin bonds by inhibition of the collagenolytic activity of dentin, as well as implementing bonding strategies which allow the use of more hydrophobic bonding agents.

Is the inactivation of dentin proteases by crosslinkers reversible

OBJECTIVE Inactivation of dentin proteases by crosslinkers has been suggested as a way to prevent the degradation of dentin collagen in the hybrid layer. However, it is not known if the inhibition is reversible. The aim of this study was to evaluate the inactivation effect of various crosslinkers on dentin protease activity over a period of 6 months. METHODS Demineralized dentin beams (1×2×6mm, n=10/group) were treated with (1) 1% glutaraldehyde (GA1), (2) 5% glutaraldehyde (GA5), (3) 1% grape seed extract (GS1), (4) 5% grape seed extract (GS5), (5) 10% sumac berry extract (S), (6) 20μM curcumin (CR20), and (7) 200μM curcumin (CR200) for 5min. Untreated beams served as control. The beams were incubated up to 6 months and incubation media were used to analyze solubilized telopeptide (ICTP and CTX) fragments as indicators of MMP- and cathepsin K-mediated degradation after 1, 3 and 6 months of incubation. The relative MMP activity of dentin beams was tested using a generic MMP assay. Data were analyzed using repeated-measures ANOVA, α=0.05. RESULTS All treated groups showed significant decrease in CTX release (32.2-469.5pg/mg dentin) and ICTP (1.8-47.6ng/mg dentin) fragments during the first month of incubation compared to control (1159pg/mg and 72.9ng/mg dentin, respectively). GA5, GS5 and CR200 maintained their inhibitory effect during 6-month incubation. The results were confirmed by dry mass loss and relative MMP activity following 6 months. SIGNIFICANCE The results of this study indicate that the long-term effect is both crosslinker and dose dependent.

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

Abstract 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.