Effect of the C-factor and Dentin Preparation Method in the Bond Strength of a Mild Self-etch Adhesive

This study evaluated the effect of the C-factor and dentin preparation method (DPM) in the bond strength (BS) of a mild self-etch adhesive; the study also observed the SEM superficial aspects of the corresponding smear layer. For purposes of this study, 25 molars (n=5) were used in a bond strength test. The molars were divided into two parts (buccal and lingual): one part received a Class V cavity (C-factor=3) and the other received a flat surface (C-factor=0) with the same bur type (coarse diamond or carbide bur and fine diamond or carbide bur), both within the same dentin depth. Five teeth were prepared with wet 60-grit and 600-grit SiC papers. After restoration with Clearfil SE Bond, microtensile beans (0.8 mm(2)) were prepared and tested after 24 hours in a universal testing machine (0.5 mm/minute). An additional two teeth for each DPM were prepared for SEM evaluation of the smear layer superficial aspects. The BS values were submitted to one-way ANOVA, considering only the DPM (flat surfaces) and two-way ANOVA (C-Factor x DPM, considering only burs) with p=0.05. Although the DPM in the flat surfaces was not significant, the standard deviations of carbide bur-prepared specimens were markedly lower. The BS was significantly lower in cavities. The fine carbide bur presented the most favorable smear layer aspect. It was concluded that different dentin preparation methods could not prevent the adverse effect in bond strength of a high C-factor. A coarse cut carbide bur should be avoided prior to a mild self-etch adhesive, because it adversely affected bond strength. In contrast, a fine cut carbide bur provided the best combination: high bond strength with low variability, which suggests a more reliable bond strength performance.

Early and 24-hour bond strength and degree of conversion of etch-and-rinse and self-etch adhesives

Purpose: To evaluate early and 24-hour microtensile bond strength (mu TBS) and the degree of conversion (DC) of one representative adhesive system from each of the four current bonding approaches. Methods: 40 human molars were sectioned occluso-gingivally into two halves. Resin composite was bonded incrementally to flat, mid-coronal dentin, using the adhesives Adper Scotchbond MP (MP); Adper Scotchbond 2 (SB); Clearfil SE Bond (SE); and Adper Prompt L-Pop (LP) according to the respective manufacturer`s instructions (n= 10). One half was immediately sectioned into sticks and subjected to mu TBS test. As the sectioning process took approximately 1 hour, the results were designated as 1-hour bond strengths. The other half was stored in distilled water at 37 degrees C for 24 hours before being sectioned and tested. The DC of these systems was measured using Fourier Transform-Raman spectroscopy in three periods: immediately, 1 and 24 hours after polymerization. Data were analyzed with ANOVA and Tukey`s tests. Results: There were no significant differences between the 1-hour and 24-hour bond strengths (P> 0.05), or among the DC measured immediately, 1 hour and 24 hours after polymerization (P> 0.05). However, significant differences were observed among adhesives (P< 0.05). mu TBS values obtained, in MPa (1 hour/24 hour), were: SB (48.6 + 1.3/48.4 + 3.5) = SE (51.9 + 4.7/53.3 +/- 2.9) > MP (35.3 +/- 10.9/38.6 + 6.7) > LP (25.5 + 1.1/26.0 + 1.5). The DC, in percentage (immediately/1 hour/24 hour), were: SE (81/82/87) > MP (79/77/81) > SB (60/63/65) > LP (39/37/42).

In vivo Acid Etching Effect on Bacteria within Caries-Affected Dentin

Acid etching procedures may disrupt residual bacteria and contribute to the success of incomplete caries removal followed by adhesive restoration. This study evaluated the in vivo effect of acid etching on cariogenic bacterial activity within affected dentin after minimally invasive treatment of caries lesions. Twenty-eight carious permanent teeth received standardized selective caries removal and random acid etch treatment (E) or not (NE) prior to adhesive restoration. Baseline and 3-month dentin biopsies were collected. The number of bacteria and activity of total bacterial cells and Streptococcus mutans were determined by quantitative PCR and RT-PCR. No statistically significant differences were observed in total bacterial number and activity between E and NE treatments (p > 0.3008). For NE, however, the residual S. mutans bacterial cells were reduced (p = 0.0027), while the activity per cell was significantly increased (p = 0.0010) after reentry at 3 months after restoration. This effect was not observed in group E. Although no significant differences were found between groups, this study suggests that acid etching of affected dentin prior to adhesive restoration may directly or indirectly have an inhibitive effect on the activity of residual cariogenic bacteria. Further research is required to investigate this potential effect. Copyright (C) 2010 S. Karger AG, Basel

Compromised Bond Strength after Root Dentin Deproteinization Reversed with Ascorbic Acid

Introduction: The present study evaluated the effect of a reducing agent on the bond strength of deproteinized root canal dentin surfaces when using a self-adhesive versus dual-cured cement. Regional differences were also evaluated. Methods: A total of 45 bovine incisor roots were divided into 3 groups: irrigation with physiologic solution (control), 10-minute deproteinization with 5% NaOCl, and 10-minute deproteinization with 5% NaOCl followed by 10 minutes of 10% ascorbic acid. Fiber posts were cemented with either RelyX 0100 or RelyX ARC (with SingleBond 2 or Clearfil SE Bond). The push-out bond strength was evaluated after 24 hours of storage. Data were submitted to three-way analyses of variance and Dunnett 13 tests (alpha = 0.05). Results: No differences between cements were observed within the testing conditions, regardless of the adhesive (P < .05). Deproteinization reduced bond strengths. Subsequent treatment with ascorbic acid was capable of reversing bond strength value changes to levels similar to those of controls. Regional radicular differences were also found, where coronal > middle > apical. Conclusions: The reducing agent was capable. of reversing the effect of dentin deproteinization, and RelyX U100 behaved similarly to RelyX ARC. (J Endod 2010;36:130-134)

A Randomized Clinical Evaluation of a One- and Two-step Self-etch Adhesive Over 24 Months

Objective: To evaluate the performance of All Bond SE used in a one- or two-step protocol in a 24-month randomized clinical study. Methods: Thirty-three patients with two similarly sized non-carious cervical lesions participated in this study. A total of 66 restorations were placed, half using the one-step All Bond SE protocol (SE-1) and the other half using the two-step All Bond SE protocol (SE-2). The restorations were evaluated at baseline and after 6, 12 and 24 months following the modified USPHS criteria and analyzed by the McNemar`s test and Fisher`s exact test (alpha=0.05). Results: After 24 months, six SE-1 and four SE-2 restorations were rated as Bravo in marginal discoloration The retention rates for SE-1 and SE-2 were 84.8% and 90.9%, respectively, after 24 months. Compared to baseline, the retention rate for SE-1 was statistically lower. Conclusions: All Bond SE used in the one- or two-step protocol resulted in high retention rates after 24 months.

State of the art etch-and-rinse adhesives

Objectives: The aim of this study was to explore the therapeutic opportunities of each step of 3-step etch-and-rinse adhesives. Methods: Etch-and-rinse adhesive systems are the oldest of the multi-generation evolution of resin bonding systems. In the 3-step version, they involve acid-etching, priming and application of a separate adhesive. Each step can accomplish multiple goals. Acid-etching, using 32-37% phosphoric acid (pH 0.1-0.4) not only simultaneously etches enamel and dentin, but the low pH kills many residual bacteria. Results: Some etchants include anti-microbial compounds such as benzalkonium chloride that also inhibits matrix metalloproteinases (MMPs) in dentin. Primers are usually water and HEMA-rich solutions that ensure complete expansion of the collagen fibril meshwork and wet the collagen with hydrophilic monomers. However, water alone can re-expand dried dentin and can also serve as a vehicle for protease inhibitors or protein cross-linking agents that may increase the durability of resin-dentin bonds. In the future, ethanol or other water-free solvents may serve as dehydrating primers that may also contain antibacterial quaternary ammonium methacrylates to inhibit dentin MMPs and increase the durability of resin-dentin bonds. The complete evaporation of solvents is nearly impossible. Significance: Manufacturers may need to optimize solvent concentrations. Solvent-free adhesives can seal resin-dentin interfaces with hydrophobic resins that may also contain fluoride and antimicrobial compounds. Etch-and-rinse adhesives produce higher resin-dentin bonds that are more durable than most 1 and 2-step adhesives. Incorporation of protease inhibitors in etchants and/or cross-linking agents in primers may increase the durability of resin-dentin bonds. The therapeutic potential of etch-and-rinse adhesives has yet to be fully exploited. (C) 2010 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

Flat-Oval Root Canal Preparation with Self-Adjusting File Instrument: A Micro-Computed Tomography Study

Introduction: The aim of this study was to evaluate the root canal preparation in flat-oval canals treated with either rotary or self-adjusting file (SAF) by using micro-tomography analysis. Methods: Forty mandibular incisors were scanned before and after root canal instrumentation with rotary instruments (n = 20) or SAF (n = 20). Changes in canal volume, surface area, and cross-sectional geometry were compared with preoperative values. Data were compared by independent sample t test and chi(2) test between groups and paired sample t test within the group (alpha = 0.05). Results: Overall, area, perimeter, roundness, and major and minor diameters revealed no statistical difference between groups (P > .05). In the coronal third, percentage of prepared root canal walls and mean increases of volume and area were significantly higher with SAF (92.0%, 1.44 +/- 0.49 mm(3), 0.40 +/- 0.14 mm(2), respectively) than rotary instrumentation (62.0%, 0.81 +/- 0.45 mm(3), 0.23 +/- 0.15 mm2, respectively) (P < .05). SAF removed dentin layer from all around the canal, whereas rotary instrumentation showed substantial untouched areas. Conclusions: In the coronal third, mean increases of area and volume of the canal as well as the percentage of prepared walls were significantly higher with SAF than with rotary instrumentation. By using SAF instruments, flat-oval canals were homogenously and circumferentially prepared. The size of the SAF preparation in the apical third of the canal was equivalent to those prepared with #40 rotary file with a 0.02 taper. (J Endod 2011;37:1002-1007)

Studies of solute self-association by sedimentation equilibrium: allowance for effects of thermodynamic non-ideality beyond the consequences of nearest-neighbor interactions

A sedimentation equilibrium study of a-chymotrypsin self-association in acetate-chloride buffer, pH 4.1 I 0.05, has been used to illustrate determination of a dimerization constant under conditions where thermodynamic non-ideality is manifested beyond the consequences of nearest-neighbor interactions. Because the expressions for the experimentally determinable interaction parameters comprise a mixture of equilibrium constant and excluded volume terms, the assignment of reasonable magnitudes to the relevant virial coefficients describing non-associative cluster formation is essential for the evaluation of a reliable estimate of the dimerization constant. Determination of these excluded volume parameters by numerical integration over the potential-of-mean-force is shown to be preferable to their calculation by approximate analytical solutions of the integral for this relatively small enzyme monomer with high net charge (+ 10) under conditions of low ionic strength (0.05 M). (C) 2001 Elsevier Science B.V. All rights reserved.

Ultracentrifugal studies of the effect of molecular crowding by trimethylamine N-oxide on the self-association of muscle glycogen phosphorylase b

The suitability of sedimentation equilibrium for characterizing the self-association of muscle glycogen phosphorylase b has been reappraised. Whereas sedimentation equilibrium distributions for phosphorylase b in 40 mM Hepes buffer (pH 6.8) supplemented with 1 mM AMP signify a lack of chemical equilibrium attainment, those in buffer supplemented additionally with potassium sulfate conform with the requirements of a dimerizing system in chemical as we:ll as sedimentation equilibrium. Because the rate of attainment of chemical equilibrium under the former conditions is sufficiently slow to allow resolution of the dimeric and tetrameric enzyme species by sedimentation velocity, this procedure has been used to examine the effects of thermodynamic nonideality arising from molecular crowding try trimethylamine N-oxide on the self-association behaviour of phosphorylase b. In those terms the marginally enhanced extent of phosphorylase b self-association observed in the presence of high concentrations of the cosolute is taken to imply that the effects of thermodynamic nonideality on the dimer-tetramer equilibrium are being countered by those displacing the T reversible arrow R isomerization equilibrium for dimer towards the smaller, nonassociating T state. Because the R state is the enzymically active form, an inhibitory effect is the predicted consequence of molecular crowding by high concentrations of unrelated solutes. Thermodynamic nonideality thus provides an alternative explanation for the inhibitory effects of high concentrations of glycerol, sucrose and ethylene glycol on phosphorylase b activity, phenomena that have been attributed to extremely weak interaction of these cryoprotectants with the T state of the enzyme.

The validity of self-reported energy intake as determined using the doubly labelled water technique

In the 1980s the development of the doubly labelled water (DLW) technique made it possible to determine the validity of dietary assessment methods using external, independent markers of intake in free-living populations. Since then, the accuracy of self-reported energy intake (EI) has been questioned on a number of occasions as under-reporting has been found to be prevalent in many different populations. This paper is a review of investigations using the DLW technique in conjunction with self-reported EI measures in groups including adults, children and adolescents, obese persons, athletes, military personnel and trekking explorers. In studies where a person other than the subject is responsible for recording dietary intake, such as parents of young children, EI generally corresponds to DLW determined energy expenditure. However, in instances where the subjects themselves report their intake, EI is generally under-reported when compared with energy expenditure. It was originally believed that this phenomenon of under-reporting was linked to increased adiposity and body size, however, it is now apparent that other factors, such as dietary restraint and socio-economic status, are also involved. This paper therefore aims to present a more comprehensive picture of under-reporting by tying in the findings of many DLW studies with other studies focusing particularly on the characteristics and mechanisms for under-reporting. Awareness of these characteristics and mechanisms will enable researchers to obtain more accurate self-reports of EI using all dietary recording techniques.

Communication and health beliefs - Mass and interpersonal influences on perceptions of risk to self and others

This study investigated the impact of media coverage of a health issue (skin cancer) on judgements of risk to self and others and the role of related communication processes. Consistent with predictions derived from the impersonal impact hypothesis, the effects of mass communication were more evident in perceptions of risk to others rather than in perceptions of personal risk. Perceptions of personal risk were more strongly correlated with interpersonal communication. However, as suggested by media system dependency theory, the relationship between mass communication and beliefs was complex. The impact of mass communication on both personal and impersonal perceptions was bound to be moderated by self-reported dependence on mass mediated information. The effect of this two-way interaction 071 perceptions of personal risk was partially mediated through interpersonal communication. Results point to the interdependence of mass and interpersonal communication as sources of social influence and the role of media dependency in shaping media impact.

Assessing self- and peer-assessment: The students' views

Self- and peer-assessment are being used increasingly in higher education, to help assign grades to students' work and to help students to learn more effectively. However, in spite of this trend there is little in the published literature on how students view these methods. In this paper we present an analysis of the views of a large number of students (N = 233) who had just experienced self- and peer-feedback as part of one of their subjects. It is a rarely questioned commonplace in the literature that in order to gain benefit from peer and self-assessment schemes students first need training in the specific scheme being used; ideally they will play a role in devising the scheme. The intervention reported here, which involved a large (N = 233) group of students, included no such measures. The results show that students felt, nonetheless, that they benefited from the intervention. The results also present prima facie evidence that training or other measures to further involve the students in the peer and self-assessment scheme might be beneficial. Our analysis of students' views revealed eight general dimensions under which are grouped twenty higher order themes. The results both support and extend previous research and give a more detailed picture than previously available. The general dimensions found were: Difficult; Gained Better Understanding of Marking; Discomfort; Productive (including learning benefits and improved work); Problems with Implementation; Read Others' Work; Develop Empathy (with assessing staff); and, Motivation (especially motivation to impress peers). The practical implications of these findings are discussed.

Self-reported calcium intake and bone mineral content in children and adolescents

Objective: We examined the relationship between self-reported calcium (Cal intake and bone mineral content (BMC) in children and adolescents. We hypothesized that an expression of Ca adjusted for energy intake (El), i.e., Ca density, would be a better predictor of BMC than unadjusted Ca because of underreporting of EI. Methods: Data were obtained on dietary intakes (repeated 24-hour recalls) and BMC (by DEXA) in a cross-section of 227 children aged 8 to 17 years. Bivariate and multivariate analyses were used to examine die relationship between Ca, Ca density, and the dependent variables total body BMC and lumbar spine BMC. Covariates included were height, weight, bone area, maturity age, activity score and El. Results: Reported El compared to estimated basal metabolic rate suggested underreporting of El. Total body and lumbar spine BMC were significantly associated with El, but not Ca or Ca density, in bivariate analyses. After controlling for size and maturity, multiple linear regression analysis revealed unadjusted Ca to be a predictor of BMC in males in the total body (p = 0.08) and lumbar spine (p = 0.01). Unadjusted Ca was not a predictor of BMC at either site in females. Ca density was not a better predictor of BMC at either site in males or females. Conclusions: The relationship observed in male adolescents in this study between Ca intake and BMC is similar to that seen in clinical trials. Ca density did not enable us to see a relationship between Ca intake and BMC in females, which may reflect systematic reporting errors or that diet is not a limiting factor in this group of healthy adolescents.