Air abrasion to increase rebond strength
Pakshir HR, Zarif Najafi H, Hajipour S. Effect of enamel surface treatment on the bond strength of metallic brackets in rebonding process. Eur J Orthod 2012;34:773-7
Debonded brackets are a fact of life in clinical orthodontic practices. The problem is compounded because research has shown that rebonded brackets have significantly lower shear bond strength. The authors of this in-vitro study investigated the effect of 2 enamel surface treatments on the bond strength of metallic brackets in the rebonding process. The sample included 50 healthy maxillary first premolars extracted for orthodontic purposes. Brackets were initially bonded to the teeth and then debonded, removing any visible residual bonding material. The teeth were then randomly divided into 2 groups. The teeth in group 1 were etched with 37% phosphoric acid for 30 seconds, and the teeth in group 2 were air abraded with aluminum oxide particles before acid etching. New brackets were bonded to all prepared teeth, and the samples were embedded in acrylic blocks to facilitate shear bond strength testing with a mechanical testing machine in an occluso-gingival direction. After debonding, the samples were examined under a light microscope to determine bond failure sites via an adhesive remnant index. The authors found that the samples prepared with both air abrasion and acid etching exhibited greater shear rebond strengths than those with acid etching alone; however, the difference was not statistically significant. Despite the surface roughening effect caused by the air abrasion, it had no major benefit in increasing shear bond strength, but the air-abraded teeth had higher adhesive remnant index scores with greater percentages of adhesive remaining on the tooth surfaces. Future studies should focus on evaluating the prepared surfaces under a scanning electron microscope to determine whether any techniques might serve as an adjunct or a replacement for acid etching to increase shear bond strength during the rebonding process.
Reviewed by James K. Dillehay
Release of composite nano-dust in dental operatories
Van Landuyt KL, Yoshihara K, Geebelen B, Peumans M, Godderis L, Hoet P, et al. Should we be concerned about composite (nano-)dust? Dent Mater 2012;28:1162-70
Contemporary composites contain large quantities of silica nano-particles that can be released during common dental procedures, inhaled, and absorbed into the dental personnel’s bloodstream. The purpose of this study was to investigate the release of respirable composite dust. Seven commercially available composites (1 hybrid, 1 microhybrid, 4 nano-hybrids, and 1 nano-composite) were evaluated in vitro and in a clinical setting. Five standardized composite blocks for each composite type were ground in a custom-made box by using a dental bur. The dust was collected by an inhalable aerosol sampler, analyzed gravimetrically and semiquantitavely, and characterized by transmission electron microscopy (JEM-1200 EX-II; JEOL, Tokyo, Japan). An Aerocet-531 mass particle counter (Met One Instruments, Shanghai, China) was attached to the collar of a dentist to measure the composite dust released in a dental operatory in real time. The controls consisted of measurements without composite grinding. The results showed that respirable particles were released. Upon in-vitro grinding, 3 to 9 submicron respirable particles were released for each particle larger than 1 μm. The nano-composite Filtek Supreme XT (3M ESPE, Seefeld, Germany) and the microhybrid composite Gradia Direct (GC America, Alsip, Ill) released the highest amount of submicron particles and the highest percentage of nano-particles, respectively. In the clinical setting, peaks of high concentrations of dust were recorded during contouring with a diamond bur and finishing with a rough polishing disk, but they never exceeded the regulatory limit for exposure. More research is needed to determine the biologic relevance of these findings and whether water cooling or an intraoral aspirator sufficiently removes respirable dust. Since long-term effects of inhalable nano-dust composites are not known, dental personnel should take protective measures when working with composites.
Reviewed by Andreea Voinea-Griffin