In vitro load-induced dentin collagen-stabilization against MMPs degradation.

INTRODUCTION: Teeth are continuously subjected to stresses during mastication, swallowing and parafunctional habits, producing a significant reduction of the bonding efficacy in adhesive restorations. The purpose of this study was to evaluate the metalloproteinases (MMPs)-mediated dentin collagen degradation of hybrid layers created by using different demineralization processes, previous resin infiltration, and in vitro mechanical loading. METHODS: Human dentin beams (0.75×0.75×5.0mm) were subjected to different treatments: (1) untreated dentin; (2) demineralization by 37% phosphoric acid (PA) or by 0.5% M ethylenediaminetetraacetic acid (EDTA); (3) demineralization by PA, followed by application of Adper(™) Single Bond (SB); (4) demineralization by EDTA, followed by application of SB. In half of the specimens, mechanical loadings (100,000 cycles, 2Hz, 49N) were applied to dentin beams. Specimens were stored in artificial saliva. C-terminal telopeptide (ICTP), determinations (which indicates the amount of collagen degradation) (radioimmunoassay) were performed after 24h, 1 week and 4 weeks. RESULTS: Load cycling decreased collagen degradation when dentin was untreated or PA-demineralized and EDTA-treated. ICTP values increased when both PA-demineralized and EDTA-treated and infiltrated with SB dentin beams were loaded, except in samples that were subjected to EDTA treatment and SB infiltration after 4w of storage, which showed similar values of collagenolytic activity than the non loaded specimens. Load cycling preserved the initial (24h) ICTP determination at any time point, in all groups of the study, except in PA-demineralized and SB infiltrated dentin which showed an increased of collagen degradation values, over time. This same trend was observed in all groups without loading. INTERPRETATION: Mechanical loading enhances collagen's resistance to enzymatic degradation in natural and demineralized dentin. Mild acids (EDTA) lead to a lower volume of demineralized/unprotected collagen to be cleaved by MMPs. Load cycling produced an increase of collagen degradation when PA-demineralized dentin and EDTA-treated dentin were infiltrated with resin, but EDTA-treated dentin showed a constant collagenolytic degradation, over time.

A ZnO-doped adhesive reduced collagen degradation favouring dentine remineralization.

OBJECTIVES: The objective of the study was to determine the efficacy of a ZnO-doped etch and rinse adhesive in decreasing MMPs-mediated collagen degradation at the resin-dentine hybrid layer, and increasing bonding stability. METHODS: C-terminal telopeptide concentrations (ICTP) were determined after 24h, 1wk and 4wk in human dentine beams. Dentine was treated: (1) 37% phosphoric acid for 15s (PA), (2) PA-etched dentine infiltrated with Single Bond (SB), (3) PA-etched dentine infiltrated with ZnO doped SB (ZnO particles--10wt%--were added to the bonding resin) (ZnO-SB), and (4) Clearfil SE Bond primed-dentine was infiltrated with Clearfil SE bonding resin (CSE). Microtensile bond strength (MTBS) was assessed for the different groups at 24h and after 3months. Debonded dentine surfaces were studied by scanning electron microscopy. RESULTS: MMPs-mediated collagen degradation occurred in demineralized dentine (PA). Resin infiltration decreased collagen degradation. The lowest collagen degradation was found for Zn-doped SB, followed by CSE. When these adhesives were applied, ICTP values did not change throughout the study period. At 24h, similar MTBS was attained for all adhesives. Only SB decreased MTBS after three months. CONCLUSIONS: Addition of ZnO particles to SB produced a reduction in dentine collagen degradation and increased resin-dentine bonds durability. In Zn-doped adhesive interfaces, a calcium phosphate layer and tubular occlusion was encountered at the debonded interface. CLINICAL SIGNIFICANCE: ZnO particles addition into the bonding resin of SB makes a breakthrough to prevent the hybrid layer degradation and to preserve its bonding efficacy overtime.

Serum cathepsin K as a marker of bone metabolism in postmenopausal women treated with alendronate.

CONTEXT: Cathepsin K is a member of the cysteine protease family that cleaves both helical and telopeptide regions of collagen I, the major type of collagen in bone. Measurement of circulating levels of cathepsin K may be useful to assay the number or function of osteoclasts. OBJECTIVE: The aim of the study was to evaluate the role of serum cathepsin K as a biochemical marker of bone metabolism in patients with postmenopausal osteoporosis before and after treatment with alendronate. DESIGN, SETTING AND PARTICIPANTS: The study was a case-control and prospective study with postmenopausal osteoporotic women including a total number of 86 subjects. Serum cathepsin K was determined in 46 women with postmenopausal osteoporosis before and after 3, 6 and 12 months of treatment with alendronate. Basal serum cathepsin K levels were also compared between premenopausal healthy women (n=20), postmenopausal women without osteoporosis (n=20) and osteoporotic women. In addition, serum carboxyterminal cross-linked telopeptide of type I collagen (CTX), osteocalcin (OC) and bone-specific alkaline phosphatase (bALP) were measured. MAIN OUTCOME MEASURE: Changes in cathepsin K serum levels after alendronate treatment. RESULTS: Serum cathepsin K levels were higher in postmenopausal women with osteoporosis (9.4+/-11pmol/L) compared with healthy postmenopausal women (6.8+/-8.1pmol/L; p<0.01) and premenopausal women (6.3+/-5.0pmol/L, p<0.01). Serum cathepsin K decreases gradually after alendronate treatment (17% at 3 months, 22% at 6 months and 41% at 12 months, p<0.01). In contrast, the treatment resulted in early and sustained reductions in serum CTX. CONCLUSION: We conclude that serum cathepsin K seems to provide additional information on bone metabolism in postmenopausal women treated with alendronate.

The contribution of serum osteoprotegerin to bone mass and vertebral fractures in postmenopausal women.

Regulation of osteoclastic activity is critical for understanding bone loss associated with the postmenopausal period. In vitro and animal studies have revealed the role of OPG as a decoy receptor that neutralizes the effect of RANKL on the differentiation and activation of osteoclasts. However, the role of the OPG-RANKL system in postmenopausal osteoporosis is controversial. Thus, the aim of this study was to investigate the relationship among circulating levels of OPG, RANKL, bone turnover markers (BTM), bone mineral density (BMD) and vertebral fractures in postmenopausal women. We determined anthropometric parameters, circulating OPG and RANKL, BTM, estradiol, BMD by dual X-ray absorptiometry at the lumbar spine (LS) and femoral neck (FN), and pre-existing vertebral fractures in 206 ambulatory postmenopausal women of a mean age of 62 years (SD 7). Circulating OPG was significantly related to age (r =0.158; P =0.023), years since menopause (r =0.167; P =0.016) and BMD (LS Z-score: r =0.240; P =0.001, FN Z-score: r =0.156; P =0.025). Over half of the women had undetectable RANKL (n =113; 54.9%). There were no significant differences in clinical variables, BTM or BMD among women with detectable vs. undetectable RANKL. OPG was found to be independently associated with osteoporosis (OR: 2.9, 1.4-5.9) and prevalent vertebral fractures (OR: 2.5, 1.2-5.4). We conclude that serum OPG levels are independently associated with bone mass and prevalent vertebral fractures in postmenopausal women.

Susceptibility for postmenopausal osteoporosis: interaction between genetic, hormonal and lifestyle factors.

Although previous studies have established the importance of genetic, hormonal and lifestyle factors separately, the integral role of these factors on bone mass in postmenopausal women is still controversial. We examined the association of the collagen 1-alpha-1 gene (COLIA1) and vitamin D receptor gene (VDR) polymorphisms, s-IGF-I, s-25OHD and lifestyle factors with bone mineral density (BMD) in postmenopausal women. We determined anthropometric parameters, lifestyle factors, serum levels of IGF-I and 25OHD, the COLIA1 Sp1 (Mscl) and VDR (Bsml, Taql) polymorphisms by PCR and BMD by dual X-ray absorptiometry in 141 ambulatory postmenopausal Spanish women. There were significant linear correlations between S-25OHD and BMD and between s-IGF-I and BMD. BMD was statistically higher in active subjects. Of the three different polymorphisms, only the COLIA1 Sp1 polymorphism was significantly associated with BMD. In the logistic regression model, the COLIA1 Sp1 polymorphism, S-25OHD, s-IGF-I and physical activity variables were independently associated with osteoporosis. Our study shows that COLIA1 Sp1 polymorphism, S-25OHD and s-IGF-I serum levels and physical activity are independently associated with BMD in postmenopausal Spanish women.