Abstract:

Objective To investigate the changes of retention strength of magnetic attachment, precise attachment and semiprecise attachment after repeated dislocation in vitro. Methods Magnetic attachment (Magfit EX 600W), precise attachment (Mini-SG attachment) and semi-precise attachment (ERA attachment) were fixed on universal material test machine respectively. The retention strength of each attachment was measured initially and after repeated stretching (500 times, 1 000 times, 1 500 times and 2 000 times of stretching) with the speed of two times per second. The attenuation of retention strength of each attachment was observed and analysed. Results The initial retention strength of magnetic attachment, Mini-SG attachment and ERA attachment was 2.67 N, 7.30 N and 40.20 N respectively. There was no significant change in retention strength of magnetic attachment during 2000 times of stretching. The curve of retention strength of Mini-SG attachment was relatively smooth, and the retention strength exhibited a downward trend. The retention strength of ERA attachment decreased significantly during the first 500 times of stretching, and the curve of retention strength turned to be smooth later. The attenuation rates of retention strength of magnetic attachment, MiniSG attachment and ERA attachment were 0.75%, 45.75% and 69.95% respectively. Conclusion The retention strength of magnetic attachment may not be influenced by times of dislocation, and the initial retention strength and attenuation rate of Mini-SG attachment were smaller than those of ERA attachment. The results of this experiment provide reference for attachment selection for both dentists and patients.

Key words: magnetic attachment, precise attachment, ERA attachment, retention strength, attenuation