An overview of orthodontic material degradation in oral cavity.

Various types of metallic orthodontic appliances are used in the management of malocclusion. These appliances are placed in oral environnent under many stresses and variations such as masticatory forces, appliance loading, temperature fluctuations, varieties of ingested food and saliva. These metals undergo electrochemical reactions with the oral environment resulting in dissolution or formation of chemical compounds. Various microorganisms and many aggressive ions containing oral environment can cause material degradation (corrosion) and its associated problems during long time exposure. Orthodontic alloys must have excellent corrosion resistance to the oral environment, which is highly important for biocompatibility as well as for orthodontic appliance durability. This article reviews various aspects of corrosion (surface degradation) of orthodontic alloys. It explores the emerging research strategies for probing the biocompatibility of materials. During orthodontic treatment, use of nickel free, better corrosion resistance alloys and less use of fluoride containing toothpaste or gel is expected.

Surface degradation of composite resins by acidic medicines and ph-cycling

This study evaluated the effects of acidic medicines (Dimetapp® and Claritin®), under pH-cycling conditions, on the surface degradation of four composite resins (microhybrid: TPH, Concept, Opallis and Nanofilled: Supreme). Thirty disc-shaped specimens (Ø = 5.0 mm / thickness = 2.0 mm) of each composite were randomly assigned to 3 groups (n = 10): a control and two experimental groups, according to the acidic medicines evaluated. The specimens were finished and polished with aluminum oxide discs, and the surface roughness was measured by using a profilometer. After the specimens were submitted to a pH-cycling regimen and immersion in acidic medicines for 12 days, the surface roughness was measured again. Two specimens for each material and group were analyzed by scanning electron microscopy (SEM) before and after pH-cycling. Data were analyzed by the Student's-t test, ANOVA, Duncan's multiple range test and paired t-test (α=0.05). Significant increase in roughness was found only for TPH in the control group and TPH and Supreme immersed in Claritin® (p<0.05). SEM analyses showed that the 4 composite resins underwent erosion and surface degradation after being subjected to the experimental conditions. In conclusion, although the roughness was slightly affected, the pH-cycling and acidic medicines caused surface degradation of the composite resins evaluated. Titratable acidity seemed to play a more crucial role on surface degradation of composite resins than pH.