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Stress relaxation phenomena in polymeric orthodontic ligatures

Milewski Grzegorz

Engineering of Biomaterials

2021

Vol. 24, no. 162

2--6

Elastomeric products are applied in orthodontics mainly as elastic ligatures or chains and have become an alternative to wire ligation made of titanium alloy or stainless steel. Despite their popularity among the dentists and undoubtful advantages, some essential warnings are being raised regarding the degree of load loss. This relaxation phenomenon seems to be a dominant feature in the time-dependent behaviour of those elements in orthodontic procedures, such as dentition corrections or teeth extrusions. The aim of the paper was to examine and analyse the rheological properties of biocompatible orthodontic elastomeric ligatures. Five different polymeric orthodontic ligatures were examined in the following experiments: a simple relaxation test, relaxation simulating orthodontic extrusion and the two-steps relaxation process, which stands for so-called ‘secondary tightening’, resulting in the increase of the orthodontic force. The results of the relaxation experiments proved that among various descriptions of that phenomenon, the power-law descriptions fit the best time-dependent behaviour during orthodontic procedures. Power-law models give the most intensive initial relaxation, which is characteristic for elastomeric ligatures. The obtained results and analyses allow precise control of the treatment progress in the orthodontic extrusion procedure.

Experimental strength analysis of orthodontic extrusion of human anterior teeth

Milewski G., Hille A.

Acta of Bioengineering and Biomechanics

2012

Vol. 14, no. 1

15-21

The paper presents the strength tests, in terms of in vitro examinations, of restored mesial incisor crowns after endodontic treatment with modelled orthodontic extrusion procedure. The strength tests were carried out for 25 teeth randomly divided into groups with various degree of root reduction. The analysis was done for the following quantities: the force to fracture, the work to fracture, the energy of the first micro-crackings and breaking, the total displacement. Statistical analysis with the use of the Kruskal-Wallis test was done in order to assess the significance level in four tooth groups. Numerical simulations of periodontal ligament effort due to the orthodontic extrusion have also been carried out.