Bioactivity of zinc-doped dental adhesives

Design of restorative materials should be focused on promoting not only adhesion but also dentine self-repair processes.     

Dynamic viscoelastic behavior of dental composites measured by Split Hopkinson pressure bar

The present study evaluated the dynamic viscoelastic behavior of commercially available dental composites by a Split Hopkinson pressure bar (SHPB) test machine. Five commercially available composite resins--namely, two conventional hybrid composites (Filtek Z100, Z100; Filtek Z250, Z250), a packable composite (Filtek P60, P60), a flowable composite (Filtek Flow, FL), and a nanofill composite (Filtek Supreme, SU)--were evaluated. By means of SHPB technique, the dynamic stress-strain curve, storage modulus, and loss tangent of the five dental composites were calculated. All specimens exhibited a nonlinear stress-strain curve in the loading process, which resulted not only from the viscoelasticity--but also from the plasticity--of matrix. In terms of storage modulus, no significant differences were exhibited among the five dental composites (p > 0.05). In terms of loss tangent, Z100 showed a significantly higher value than P60, FL, and SU (p < 0.05). Within the limitations of this investigation using SHPB, it was indicated that the loss tangent increased with increasing filler content.     

牙本质粘接剂的回顾、现状和展望

1955年，Buonocore将酸蚀剂技术应用于牙体粘接，从此粘接技术开始迅速发展。修复美容的社会需求和现代牙科“保存”意识的不断深化，是粘接技术不断成熟完善的巨大驱动力。     

Modeling of the viscoelastic behavior of dental light-activated resin composites during curing.

OBJECTIVE: Three models consisting of springs and dashpots were investigated to describe the viscoelastic behavior of a commercial light-activated restorative composite during curing. METHODS: Stress-strain data on Z100 were recorded by means of a dynamic test method performed on a universal testing machine. The model was tested by matching its response to experimental data and the material parameters, E (Young's modulus) and eta (viscosity), associated with the model were calculated. RESULTS: The universal testing machine generated reliable stress-strain data on the fast curing, light-activated resin composite during curing. The high polymerization rate of Z100 had a negative effect on the viscous flow capability of the material. A predictive model of the viscoelastic behavior of Z100 during curing was carried out, using the Maxwell model for the initial 3 min in the curing process and the Kelvin model for the remainder of the process. SIGNIFICANCE: Dental researchers analyzing shrinkage stress problems by mathematical modeling can obtain a good quantitative estimate of the shrinkage stress development of Z100 before the restoration is actually made.     

Antimicrobial properties of dental dentin-enamel adhesives

This study evaluated the antimicrobial activity of Universal Bond II adhesive and two experimental versions of Universal Bond II adhesives against the bacteria, Streptococcus mutans. The zones of bacterial inhibition produced by three samples of the adhesive (identified as Batches 1, 2, and 3) were measured and compared. Batch 1 contained 0.7% glutaraldehyde, Batch 2 contained 1.0% glutaraldehyde, and Batch 3 contained 0.45% glutaraldehyde (current Universal Bond II adhesive). The bacteria was swabbed over the surface of agar plates in two directions. The plates were divided into the following two groups: Group I-Batches 1, 2, 3 were placed into wells for 1 minute before being cured. Group II-Batches 1, 2, 3 were placed into wells for 20 seconds before being cured. Zones of microbial inhibition were measured in millimeters at the end of 24, 48, and 72 hours. All batches of the adhesive produced zones of inhibition against S. mutans. All batches of the adhesive maintained zones of inhibition throughout the 72 hours of the study.     

Disinfection effect of dental impression tray adhesives

Objectives

Iatrogenic infections are serious problems in dental offices. Impression tray adhesives are delivered in glass containers with a fixed brush attached inside the cap. Using the brush for application of the impression tray adhesive on a contaminated impression tray or prostheses, pathogen transmission by replacing the cap with the brush is possible.

Materials and methods

Bacterial strains (patient strains and in vitro strains) were supervaccinated on Columbia agar. The bacterial solution was diluted with TSB and aerobically grown, and starting concentration was 1?×?10⁷ cfu/ml. The stock solution was placed on Columbia agar. Alginate, polyether, and silicon impression tray adhesives were applied to the center of the particular blood agar plates and incubated for 48 h. The expansion of the inhibition zone assays were measured using a microscope.

Results

Twenty-one different bacterial strains were selected in the saliva samples of 20 patients. The growth inhibition for alginate impression tray adhesive was 1.1 % (±0.3) of the patient strains. The overgrowth of polyether impression tray adhesive was 30.6 % (±9.3) and for silicon impression tray adhesive 11.8 % (±5.0). In in vitro strains, alginate impression tray adhesive performed an inhibition of 0.7 % (±0.3). The overgrowth of polyether impression tray adhesive was 7.0 % (±1.6) and for silicon impression tray adhesive was 6.5 % (±1.3).

Conclusions

Using the fixed brush for application of the impression tray adhesive on multiple patients, a cross-contamination cannot be ruled out.

Clinical relevance

An application of the impression tray adhesive with a pipette and a single-use brush would eliminate the contamination.     

The influence of alloy composition on anaerobic adhesives in dental bonding

Objectives: Single-component anaerobic adhesives are in common use in the electronics and engineering industries. They are generally diacrylate monomers which do not require conventional sources of heat, light or chemicals for activation. Their advantages include activation by the bonding substrate, as well as inhibition of polymerisation until the necessary anaerobic environment is created. The aim of this experiment was to determine whether metal attachments could be successfully bonded to enamel in vitro by such adhesives.

Methods: Metal attachments capable of providing an anaerobic environment were fabricated from one of three alloys: stainless steel, copper or cobalt–chromium. They were bonded to prepared human enamel with one of four adhesives: Orthodontic Concise, as a control, and three anaerobic adhesives, Perma Metal, Permabond A134 and Loctite 326. The specimens were then bond tested in shear to failure after bench curing for one of four time periods.

Results: The results were analysed in terms of mean force to debond (N) and 95% confidence intervals. Kaplan–Meier survival probabilities and log-rank tests were performed for the 10 min test times.

Conclusions: Both Orthodontic Concise and the three anaerobic adhesives displayed a specificity towards different attachment alloys. Whereas Orthodontic Concise displayed the highest force to debond with stainless steel attachments, for the anaerobic adhesives this was true of the copper attachments. With stainless steel attachments, however, the force to debond with the anaerobic adhesives was similar to that observed with Orthodontic Concise and steel, at least after the relatively short 10 min bench curing time.     

后牙区牙种植手术导板准确性的初步研究

目的:减少种植定位的偏差,取得种植预期设计效果。方法:确定种植手术导板的厚度为4mm,孔径为2.3mm,计算其最大理论偏差;并根据从种植义齿(牙合)面到种植体顶端的距离,求得最大理论偏差。另通过在石膏模型上定位,测量种植体中心螺丝的中心出孔位置与手术导板中心出孔位置间的距离,求得实际偏差,由此比较理论偏差与实际偏差的大小。结果:后牙区种植手术导板实际偏差不明显,但游离组存在偏差的可能性较非游离组大。结论:种植手术导板是满足精确定位的前提,手术导板的固位影响手术导板的准确性。     

Degree of conversion and permeability of dental adhesives

The aim of this study was to analyse the extent of polymerization of different adhesive films in relation to their permeability. One adhesive of each class was investigated: OptiBond FL; One-Step; Clearfil Protect Bond; and Xeno III. Adhesive films were prepared and cured with XL-2500 (3M ESPE) for 20, 40 or 60 s. Polymerization kinetic curves of the adhesives tested were obtained with differential scanning calorimetry (DSC) and data were correlated with microhardness. The permeability of the adhesives under the same experimental conditions was evaluated on human extracted teeth connected to a permeability device and analysed statistically. The results showed that the extent of polymerization obtained from DSC exotherms was directly correlated with microhardness. An increased level of polymerization after prolonged light-curing was confirmed for all adhesives. Simplified adhesives exhibited a lower extent of polymerization and showed incomplete polymerization, even after 60 s. An inverse correlation was found between the degree of cure and the permeability. This study supports the hypothesis that the permeability of simplified adhesives is correlated with incomplete polymerization of resin monomers and the extent of light exposure. These adhesives may be rendered less permeable by using longer curing times than those recommended by the respective manufacturer.     

A statistical evaluation of microtensile bond strength methodology for dental adhesives.

OBJECTIVES: The purpose of this study was to determine the correlation between beams from the same tooth in a microtensile bond strength study and to examine their effect on the interpretation of results. METHODS: A flat occlusal dentin surface was exposed using wet 180, 240, and 320-grit SiC paper on caries-free human molar teeth. Adhesive was applied followed by 6mm of composite (CoreRestore2) applied in 2mm increments. Four adhesives were used: Optibond FL, light-cure, dual-cure, and self-cure Optibond Solo Plus. Nine beams (1 mm2) were obtained from fifteen teeth for each group, labeled to indicate the orientation of the beams to each other and stored in artificial saliva at 37 degrees C for 1 week or 3 months. Microtensile dentin bond strengths were determined using a non-trimming technique. Statistical comparisons between adhesive-storage combinations were performed using ANOVA. Analyses were performed assuming statistical independence between all beams and then repeated using a random tooth effect to account for correlations between beams from the same tooth. RESULTS: Significant correlations were found between beams. No pattern was observed in the correlations related to the orientations of the beams to each other. Conclusions regarding statistical significance of comparisons (at alpha=0.05) were sometimes affected by the incorrect assumption of independent beams. The degree of correlation was large enough to severely affect power and sample size calculations. SIGNIFICANCE: Analyses of microtensile dentin bond strength studies need to account for correlations between beams to avoid over-stating statistical significance of study results.     

Effects of MMP inhibitors incorporated within dental adhesives

Matrix metalloproteinase (MMP) inhibition has been shown to reduce adhesive bond degradation when applied as a pre-conditioner, adding to clinical steps in the placement of adhesives, but their incorporation within dental adhesives has not been fully explored. This study examined the effect of including 2 MMP inhibitors (BB94 and GM6001) within the primers of 3 commercially available adhesives. Fluorometric assay and zymography showed that adhesives with MMP inhibitors had high affinity toward both synthetic fluorogenic FRET peptides (95%) and dentin powder substrates, respectively. The immediate microtensile bond strength was enhanced for 2 types of adhesives following the addition of both inhibitors. However, no changes were detected between the control and the inhibitor groups following 3-month storage. The modified two-step etch-and-rinse and single-step systems showed less Rhodamine B penetration to the "hybrid layer" and to the "adhesive", respectively. The incorporation of BB94 and GM6001 within the primers resulted in the inhibition of dentin MMPs with improved initial bond strength and enhanced sealing ability.