Inhibition of dentin matrix-bound cysteine cathepsins by potassium fluoride.

Matrix metalloproteinases (MMPs) and cysteine cathepsins (CCs) can break down unprotected type I collagen fibrils in dentin matrix. This study investigated the use of potassium fluoride (KF) as a potential inhibitor of MMPs and CCs in dentin. Demineralized dentin beams were divided into groups (n = 10 in each group) and incubated in artificial saliva (AS, control), either alone or with one of seven concentrations of KF (6-238 mM fluoride) for 1, 7, and 21 d. After 21 d, all groups were further aged in AS for 6 months. Total MMP activity was screened using the colorimetric MMP assay. The activities of MMP-2 and MMP-9 were investigated using gelatin zymography. At the end of each incubation, changes in loss of dry mass and CC-mediated or total dissolution of collagen peptides were measured via precision weighing, C-terminal crosslinked telopeptide of type I collagen (CTX), and hydroxyproline (HYP) assays. The beams were examined using scanning electron microscopy. After 21 d, total MMP activities, dry mass loss, and CTX release for the groups exposed to 179 and 238 mM fluoride were significantly lower compared with the control group. After 6 months, all groups showed similar total MMP activity, dry mass loss, and HYP release, and CTX levels were significantly lower when the fluoride concentration was ≥24 mM. Calcium fluoride (CaF2 )-like precipitates were observed over the beams. In summary, KF significantly inhibited the catalytic activity of dentin matrix-bound CCs but did not seem to be effective for MMP-mediated activity.

Effect of calcium fluoride on the activity of dentin matrix-bound enzymes.

OBJECTIVE: Matrix metalloproteinases (MMPs) and cysteine cathepsins (CCs) are two distinct enzymatic pathways responsible for the degradation of collagen fibrils in demineralized dentin. NaF and KF have been shown to inhibit salivary MMP-2, -9 and CCs. This study investigated the inhibitory effect of calcium fluoride (CaF2) on the dentin matrix-bound MMPs and CCs. DESIGN: Phosphoric acid (10%)-demineralized dentin beams (1 × 2×6 mm) were incubated at 37 °C in an 1 ml of artificial saliva (AS, control), or AS with 6, 12, 24, 48, 120. 179 and 238 mM F containing CaF2 (n = 10/group) for 1, 7 and 21 days. All groups were further incubated in AS only for 6 months. Total MMP activity, dry mass loss, CTX and hydroxyproline (HYP) analyses were performed after each incubation. The beams were examined under scanning electron microscopy (SEM). MMP-2 and MMP-9 activities were screened with gelatin zymography. Data were analyzed by using ANOVA and Tukey HSD tests (p = .05). RESULTS: The total MMP activity was similar for all groups after 21 days and 6 months. After 21 days, the cumulative mass loss and CTX levels were lower compared to control for the CaF2 ≥48 and CaF2≥120 mM, respectively (p < .05). After 6 months, no significant difference was detected in the dry mass loss and CTX compared to the control (p > .05), whereas HYP level was higher with F 24 and 238 mM groups. CaF2-like minerals were observed on the beams under SEM. There was no gelatinase inhibition in zymography. CONCLUSION: CaF2 does not prevent the degradation of demineralized dentin matrices due to the catalytic activity of MMPs and CCs.

Zinc Inhibits Collagenolysis by Cathepsin K and Matrix Metalloproteinases in Demineralized Dentin Matrix.

The enzymatic degradation of dentin organic matrix occurs via both the action of matrix metalloproteinases (MMPs) and cysteine cathepsins (CCs). Zinc can prevent collagen hydrolysis by MMPs. However, its effect on the activity of dentin-bound CCs is not known. The aim of this study was to investigate the effect of zinc on matrix-bound cathepsin K and MMP activity in dentin. Completely demineralized dentin beams were divided into test groups (n = 9) and incubated at 37°C in an incubation media (1 mL) containing ZnCl2 of 0.02 (physiological level, control), 0.2, 0.5, 1, 5, 10, 20, 30, or 40 mM. The dry mass changes of the beams were determined, and incubation media were analyzed for cathepsin K- and MMP-specific collagen degradation end products - CTX (C-terminal cross-linked telopeptide of type I collagen) and ICTP (cross-linked carboxy-terminal telopeptide of type I collagen) - at 1, 3, and 7 days of incubation. The mass loss of the beams decreased when the zinc level in the incubation media was ≥5 mM (p < 0.05). The release of liberated collagen degradation telopeptides decreased in accordance with the decrease in the mass loss rates of the beams. Cathepsin K-induced dentin collagen degradation can be strongly inhibited by zinc. Zinc levels of ≥5 mM can be considered as a reliable threshold for the stabilization of dentin matrices.

Color stability of bulk-fill and incremental-fill resin-based composites polished with aluminum-oxide impregnated disks.

OBJECTIVES: This study aimed to evaluate the color stability of bulk-fill and nanohybrid resin-based composites polished with 3 different, multistep, aluminum-oxide impregnated finishing and polishing disks. MATERIALS AND METHODS: Disk-shaped specimens (8 mm in diameter and 4 mm in thickness) were light-cured between two glass slabs using one nanohybid bulk-fill (Tetric EvoCeram, Ivoclar Vivadent), one micro-hybrid bulk-fill (Quixfil, Dentsply), and two nanohybrid incremental-fill (Filtek Ultimate, 3M ESPE; Herculite XRV Ultra, Kerr) resin-based composites, and aged by thermocycling (between 5 - 55℃, 3,000 cycles). Then, they were divided into subgroups according to the polishing procedure as SwissFlex (Coltène/Whaledent), Optidisc (Kerr), and Praxis TDV (TDV Dental) (n = 12 per subgroup). One surface of each specimen was left unpolished. All specimens were immersed in coffee solution at 37℃. The color differences (ΔE) were measured after 1 and 7 days of storage using a colorimeter based on CIE Lab system. The data were analyzed by univariate ANOVA, Mann-Whitney U test, and Friedmann tests (α = 0.05). RESULTS: Univariate ANOVA detected significant interactions between polishing procedure and composite resin and polishing procedure and storage time (p < 0.05). Significant color changes were detected after 1 day storage in coffee solution (p < 0.05), except Quixfil/Optidisc which was color-stable after 7 days (p > 0.05). Polishing reduced the discoloration resistance of Tetric EvoCeram/SwissFlex, Tetric EvoCeram/Praxis TDV, Quixfil-SwissFlex, and all Herculite XRV Ultra groups after 7 days storage (p < 0.05). CONCLUSIONS: Discoloration resistance of bulk-fill resin-based composites can be significantly affected by the polishing procedures.

NaF Inhibits Matrix-Bound Cathepsin-Mediated Dentin Matrix Degradation.

Matrix metalloproteinases (MMPs) and cysteine cathepsins (CCs) degrade the collagen fibrils of demineralized dentin. Sodium fluoride (NaF) has previously been shown to inhibit recombinant MMP-2 and MMP-9. This study aimed to evaluate the efficacy of NaF on the inhibition of dentin-bound MMPs and CCs. Dentin beams were completely demineralized in 10% phosphoric acid. The baseline total MMP activity and dry masses were measured. Beams were assigned to test groups based on similar MMP activity and dry mass (n = 10/group), and incubated in artificial saliva (control) or artificial saliva with NaF containing 6-238 mM fluoride for 1, 7 and 21 days. The dry mass loss and MMP activities were reassessed at each time point. The proteolytic activity was screened by gelatin zymography. ICTP and CTX released to the incubation medium were analyzed as indices of MMP and cathepsin K activity, respectively. The beams were examined under scanning electron microscopy. All NaF doses reduced the dry mass loss after 21 days (p < 0.05). NaF inhibition of the total MMP activity ranged between 5 and 80%. In gelatin zymography, the bands of MMP-2 and MMP-9 became less prominent with increasing NaF levels. NaF did not decrease the released ICTP (p > 0.05). Less CTX release was detected with F ≥179 mM (p < 0.05). CaF2-like minerals were observed on the beams. High levels of NaF may slow the degradation of the dentin matrix due to the inhibition of cathepsin K. Fluoride does not seem effective in the direct inhibition of proteolysis by dentin matrix-bound MMPs.

Stability and Marginal Bone Level Changes of SLActive Titanium-Zirconium Implants Placed with Flapless Surgery: A Prospective Pilot Study.

BACKGROUND: Immediately-loaded, narrow-diameter implants can be a less invasive alternative for the implant-supported fixed rehabilitation of narrow, posterior crests. PURPOSE: To determine the stability and marginal bone level (MBL) changes of narrow-diameter, titanium-zirconium (TiZr) implants placed with flapless surgery and loaded immediately in the posterior region. MATERIALS AND METHODS: Thirty-eight TiZr implants (3.3 mm diameter, 10 mm length, Roxolid, Straumann AG) were placed in the posterior crests of 14 patients with computer-guided flapless surgery as a support of 3-unit posterior bridges. Eighteen implants were loaded immediately, and 20 implants were loaded conventionally. The implant stability quotients were determined at the 1, 2, 4, and 8. weeks of healing before conventional loading, and at the 3, 6, and 12. months after loading by resonance frequency analysis. The MBL changes were measured by digital radiography. RESULTS: The surgical protocols were accomplished without any biological complications. There was no significant difference in the stability changes of TiZr implants between the loading groups (p > .05). The MBL changes were -0.18 ± 0.27 mm and -0.24 ± 0.27 mm at the 12. month of immediate and conventional loading, respectively, which was not statistically significant (p > .05). CONCLUSION: The stability and MBL changes of TiZr implants supporting posterior 3-unit bridges were clinically acceptable at the first year of loading.