In vitro shearing force testing of two seventh generation self-etching primers.

OBJECTIVE: The purpose of this study was to evaluate the in vitro shearing force performance of orthodontic attachments using two self-etching primers (SEPs): iBOND and G-Bond. DESIGN: In vitro, laboratory study. MATERIAL AND METHODS: One hundred and eighty human molars were randomly divided into four groups and again into three sub-groups with 15 teeth each. Teeth were bonded with a stainless steel button (GAC International,Bohemia, NY, USA) using Transbond XT adhesive composite. The bonding agents were iBOND, G-Bond, Transbond Plus SEP and Transbond XT primer. Shearing force tests were carried out immediately, and at 24 hours and 3 months using a universal testing machine. Force to debond (N) and Adhesive Remnant Index (ARI) scores were evaluated and compared. RESULTS: Transbond XT primer required a higher immediate (P<0·05)force to debond when compared to the Transbond Plus SEP, iBOND and G-Bond.After 24 hours, mean force to debond for Transbond XT primer and Transbond Plus SEP showed significant increases. At 3 months, all four bonding agents demonstrated force levels to debond that were not significantly different from one another. Furthermore, comparison of ARI scores indicated a significant difference between the groups at all time points. CONCLUSIONS: iBOND and G-Bond may well sufficiently with stand the alignment and occlusal forces imparted by light archwires during immediate archwire tie-in and over the initial levelling and alignment phase.

Photoactivated disinfection of Streptococcus intermedius through dentin disc at clinically relevant intervals: an in vitro study.

In this present study we have tested the impact of porfimer sodium (Photofrin, AXCAN PHARMA Inc., Quebec, Canada) photoactivated disinfection (PD) on cells of Streptococcus intermedius in suspension. In order to provide basic data to support future clinical studies of PD in dentistry the study used exposure to Quartz-tungsten-halogen (QTH) dental curing light for clinically relevant time periods to activate Photofrin and measured its effectiveness under a variety of conditions including activation through dentin hard tissue. S. intermedius was grown in planktonic suspension for 48h. Nine groups were formed: three control groups (1-3) and six experimental groups (4-9). Groups 4-6 tested the use of Photofrin treatment combined with QTH light at various intervals of irradiation (5, 15 and 60s). Groups 7-9 were similar to groups 4-6 with the exception that irradiation commenced through a dentin disc. Following treatment, bacteria were plated. Colony counts were measured following 72h incubation at 37 degrees C. Statistical analysis was carried out by one-way ANOVA at a 95% confidence level. A significant reduction in S. intermedius colony counts was observed for all experimental groups and one control group. The reduction in numbers of colonies in the experimental groups varied from 79.28 to 99.40% with an average of 94.61%. Reduction in viable bacterial cells indicated a strong relationship between power density and irradiation interval. When curing light energy density was lower due to the irradiation through the 1mm dentin disc, prolonged irradiation interval enhanced bacterial kill. In conclusion, where direct irradiation is not possible for PD treatment, irradiation through dentin may still be done successfully within a clinically relevant interval.

Environmental influences on Actinobacillus actinomycetemcomitans biofilm formation.

Fresh clinical isolates of the periodontal pathogen Actinobacillus actinomycetemcomitans have an adherent, rough colony morphology that transforms into a minimally adherent, smooth colony phenotype during successive in vitro passage. The objectives of this study were: (1) to compare biofilm formation of the rough (RVs) and smooth variants (SVs) of several strains of A. actinomycetemcomitans grown under various environmental conditions and (2) to examine the dynamics of biofilm formation. A microtitre plate biofilm assay was used to evaluate biofilm formation of strains grown in broth with modified salt concentration and pH, and to evaluate the effect of pre-conditioning films. Scanning electron microscopy (SEM) was used to monitor microscopic changes in morphology. Dynamics of biofilm formation were measured in a flowcell monitored by confocal microscopy. The RVs generally produced greater biofilm than the SVs. However, medium-dependent differences in biofilm formation were evident for some rough/smooth pairs. The RVs were more tolerant to changes in salt and pH, and more resistant to chlorhexidine than the SVs. Horse serum virtually eliminated, and saliva significantly reduced, biofilm formation by the SVs in contrast to the RVs. SEM revealed no alteration in morphology with change of environment. In a flowcell, the RVs produced towers of microcolonies anchored by a small contact area, whereas the SVs produced an open architecture of reduced height. After 7 days in a flowcell, the rough to smooth phenotype transition could be demonstrated. In conclusion, strain, growth medium and conditioning film all affect biofilm formation. The RVs produce biofilms of unique architecture that may serve to protect the bacterium from environmental perturbations.

Evaluation of varied repair protocols applied to aged composite resin.

PURPOSE: This paper aims to examine varied surface treatments combined with adhesive bonding to ascertain the highest bond strength of the composite resin repair. MATERIALS AND METHODS: A total of 100 specimens was made using an increment technique. The prepared specimens were aged for 20 days in 37 degrees +/- 20 degrees C water and then kept for 24 h at room temperature. The samples were separated into 5 groups of 20, and each group then received a different surface treatment (control group, phosphoric acid, diamond bur, air abrasion, silane primer combined with a diamond bur treatment). The effect of each surface treatment on the bond strength was determined by a shear bond test. RESULTS: Specimens that received surface treatment with a diamond bur exhibited higher shear bond strengths than any of the other repaired groups (p < 0.05). Those treated with air abrasion had the second highest shear bond strengths, but without a statistically significant difference when compared to the control group (p > 0.05). Specimens treated with phosphoric acid showed virtually no difference compared to the specimens of the control group (p > 0.05). CONCLUSION: Statistical analysis revealed that surface treatment with a diamond bur results in higher shear bond strength than other tested methods.

A new model for nanoscale enamel dissolution.

The dissolution kinetics of human tooth enamel surfaces was investigated using nanomolar-sensitive constant composition (CC) and in situ atomic force microscopy (AFM) under simulated caries formation conditions (relative undersaturation with respect to hydroxyapatite = 0.902, pH = 4.5). Scanning electron microscopic (SEM) examination of the resulting etched enamel surfaces showed that deminerzalization, initiated at core/wall interfaces of rods, developed anisotropically along the c-axes. After an initial rapid removal of surface polishing artifacts, the dissolution rate decreased as the reaction proceeded in accordance with our recently proposed crystal dissolution model, resulting in hollow enamel cores and nanosized remaining crystallites, resistant to further dissolution. Generally, dissolution of minerals is regarded as a spontaneous reaction in which all the solid phase can be dissolved in undersaturated solutions. However, the dissolution of some biominerals may be suppressed when the crystallites approach nanometer size. This study shows that CC demineralization of enamel in acidic medium follows this new model that can be used to mimic carious lesion formation. In dissolution studies, nanosized enamel crystallites exhibit a remarkable degree of self-preservation in the fluctuating physiological milieu.