Effects of mixing method, thixotropic agent, and polymerization procedure on porosities in silicone elastomers used...

Air entrapment during silicone mixing and processing can result in porosities in maxillofacial prostheses, compromising esthetics, mechanical properties, and hygiene. However, the combined effects of mixing method, thixotropic agent (TA), and polymerization pressure on the presence of porosities have not been fully clarified.

The purpose of the present study was to evaluate the effects of polymerization pressure, mixing method, and TA amount on the pore formation of a facial silicone material.

Cylindrical silicone specimens (N=96) were fabricated using 2 mixing methods (manual or mechanical), 4 TA levels (0, 1, 2, 3 drops), and 2 polymerization conditions (with or without pressure). Porosity, pore number, and maximum pore diameter were measured by using microcomputed tomography. Data were analyzed with 3-way analysis of variance (α=.05).

Pressurization markedly reduced the porosity and pore number, regardless of the mixing method or TA amount (P<.001). Without pressure, mechanical mixing produced significantly fewer pores than manual mixing (P<.001). In manual mixing without pressure, adding TA decreased the pore number but increased the maximum pore diameter. No significant effect of TA was observed with mechanical mixing (P=.102).

Polymerization under pressure was the most effective method of minimizing porosities. In situations where pressure cannot be applied, mechanical or manual mixing with limited TA can reduce pore incorporation in silicone prostheses.