To observe the clinical efficacy in patients treated with two different eruption blocking appliances.

Totally 40 children (21 boys, 19 girls), aged 6.5-8.5 years old, having premature eruption of permanent tooth were randomly divided into 2 groups, with 20 cases in each group: group A (wearing traditional band and loop appliance of eruption blocking during the whole day) and group B (wearing modified band and loop appliance of eruption blocking during the whole day). The patients had regular check every 3 months until the root of premature premolar developed 1/2. The efficacy of the two appliances was evaluated on the following aspects: space maintenance, losing ratio of bands, tooth mobility and prevalence of dental caries of the premolars.

The efficacy on space maintaining and eruption impaction were not statistically different (P＞0.05), but prevalence of dental caries of the teeth in group A was higher than that of group B (P＜0.05).

The modified band and loop appliance of eruption blocking is effective and good for tooth health.

To evaluate the tensile bonding strength (TBS) and antibacterial properties when an orthodontic adhesive was added with nanohydroxyapatite (nHAp).

Light cure orthodontic adhesive (Grengloo) was blended with 2% TiO₂ containing nHAp nanoparticles by 0%、10%、20%、30% (w/w), while the control was not blended with nHAp. Brackets were bonded to extracted premolars by these new adhesives. TBS of 5groups were determined, and the adhesive remnant index (ARI) scores were assessed. Composite discs specimen were prepared, incubated with bacterial suspension for 48 h, and tested for antibacterial properties.

No significant difference was found in ARI. The colony unit counts and lactate productionof the groups containing 2% TiO₂ were significantly reduced. The colony unit counts and lactate production were without relationship with nHAp. The tensile bonding strength drastically decreased when containing more than 10% nHAp.

nHAp might not enhance the antibacterial effects of Grengloo.

To analyze the influence of the zirconia ceramic surface roughness on microbial attachment.

The surface of zirconia ceramics was abraded progressively into three roughness levels of rough, medium rough and smooth surface by silicon carbide sand papers. Then the surface roughness, surface morphology and contact angle of zirconia ceramic were measured by atomic force microscopy and optical contact angle measuring device, which was followed by detecting the adhesive force of different roughness of zirconia ceramic by Streptococcus mutans UA159 preprocessed probe. At last scanning electron microscope and confocal laser scanning microscopy were used to observe biofilm formation after co-culture of zirconia ceramics and Streptococcus mutans.

For different roughness of zirconia ceramic surface, with the smoother degree of their surfaces, the contact angle decreases step by step, surface energy increases gradually, surface biofilm thickness decreases generally, and adhesive force between Streptococcus mutans and surface of zirconia ceramics decreases by degrees, whereas the biofilm bacteria mass of different roughness of zirconia ceramics does not have statistical difference.

Zirconia surface roughness affects the adhesion force of Streptococcus mutans which grows with the increase of surface roughness. The biofilm thickness and the mass of microorganisms lessened correspondingly with the decreasing of surface roughness, until it drops to a certain number, from where the biofilm thickness and the mass of microorganisms remains stable.