A Study Of Mechanical And Biological Properties Of Orthodontic Latex Elastics

Objective To evaluate the mechanical properties of four kinds of orthodontic rubber elastics through static testing under air, water and saliva conditions, and to evaluate their biologic (cytotoxic) properties. Thus this may give the clinicians a guideline in selecting the proper elastics for treatment of orthodontic diseases.Methods Four kinds of orthodontic rubber elastics with the same internal diameter, which were commonly used in clinics, were included in the study. Samples were divided into 4 groups by manufacture. Group I, II, III, IV were obtained from TOMY, (JAPAN), ORMCO (GLENDORA, CALIFOTNIA), 3M Unitek (USA), SOUTH BALDEAGLE (Sheboygan, USA), respectively. The initial forces of the four kinds elastics were measured with a digital force gauge at 225%, 300%, 450% of the internal diameter elongation. The remaining forces of specimens with the three elongation distances were tested in air, water and saliva respectively for 24 hours and 48 hours. Then we tested the proliferation of human fibroblast influenced by elutes of four elastics using MTT method. Positive (polyurethane) and negative (tissue culture polystyrene)) toxicity controls were included. In addition, comet assay were performed to observe the influence of elutes on the cultured cells.Results At the extension of 14.4mm(225%), 19.2mm(300%)和28.8mm(450%), there were significant differences on initial forces among the four kinds of elastics. Among them, TOMY( group I )had the largest force and ORMCO ( group II) had the smallest force. At the time of 24 h and 48 h of insistence, three degrees of extension, water and saliva had a stronger degradation on the four kinds of elastics than those of air. And the change showed statistically significant different ( P<0.05; P<0.01) , however, there were no significant differences between water and saliva. (P>0.05).Except the special conditions, air had no influence on the force degradation of groups and there were no significant difference when compared to the initial forces. (P>0.05). The increase of extension length was not accompanied by the increase of mean percentage of force degradation of elastics under wet conditions and it did not show statistically different (P>0.05). At the extension of 225%, the mean percentage of force degradation of elastics were higher than those of 300% and 450%, and there are statistically different (P<0.05).Moreover, under wet conditions, the force decay was not changed at the different time(24h and 48h);at the extension of 300% and 450%, the...