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Effect of thixotropic agents as additives on the mechanical properties of maxillofacial silicone elastomers

https://doi.org/10.1016/j.prosdent.2017.06.014Get rights and content

Abstract

Statement of problem

The incorporation of thixotropic agents to prevent slumping during the silicone packing procedure may alter some favorable mechanical properties of the silicone elastomers and could possibly influence the success of the prosthesis.

Purpose

The purpose of this in vitro study was to evaluate the effect of adding thixotropic agents on the mechanical properties of 3 commonly used silicone elastomers.

Material and methods

Specimens of 3 maxillofacial silicones (M511, Z004; Technovent Ltd, and A2000; Factor II Inc) were prepared according to the manufacturers’ instructions. Tear and tensile strength values and percentages of elongation and hardness were evaluated for each material with and without thixotropic agents. Data were analyzed using 1-way ANOVA and the Bonferroni post hoc test (α=.05).

Results

Results showed that the 3 types of silicone elastomers had significantly different (P<.001) tensile and tear strength and hardness values and percentages of elongation. Z004 silicone showed the highest tensile and tear strength followed by A2000 and M511, regardless of the addition of thixotropic agent. The addition of a thixotropic agent decreased the tear strength (P<.001) but not the tensile strength for all types of silicone. Percentage of elongation was the highest in M511 and the lowest in A2000 and was significantly higher (P<.001) for silicones with no added thixotropic agent. Hardness was highest in A2000 and lowest in M511. Adding a thixotropic agent decreased hardness significantly (P<.001) for Z004 and A2000 only.

Conclusions

The incorporation of thixotropic agents into the 3 maxillofacial silicone elastomers used in this study reduced some favorable mechanical properties, particularly tear strength and percentage of elongation. Z004 showed superior mechanical properties among the 3 tested silicones.

Section snippets

Material and Methods

Three commercial maxillofacial silicones were used in this study: M511 and Z004 (Technovent Ltd) and A2000 (Factor II Inc). Two thixotropic agents were used, M514 anti-slump agent (Technovent Ltd) and A-300-1 thixotropic agent (Factor II Inc). Silicone part A-to-part B mixing ratios were 10:1, respectively, for M511 and 1:1, respectively, for both Z004 and A2000.

For the tensile strength and elongation specimens, 180 wax patterns were made as dumbbell-shaped specimens to adhere to the conditions

Results

Mean tear and tensile strength values and percentages of elongation at rupture are shown in Table 2. The 3 types of silicone differed significantly (P<.001) in tensile and tear strength values, hardness, and percentages of elongation. The size of this difference depended on whether the thixotropic agent was added. Silicone Z004 showed higher tensile and tear strength followed by A2000 and M511, regardless of the addition of the thixotropic agent. Without the addition of the thixotropic agent,

Discussion

The null hypothesis for the mechanical properties was rejected, except for the tensile strength of all tested silicone types and hardness of M511, which demonstrated no statistically significant difference. The silicone rubber materials tested in this study were all systems which cross-link using an addition reaction. The base contained vinyl-terminated polydimethyl siloxanes, surface-treated silica fillers, and a platinum complex as catalysts. The cross-linker (part B) contained a

Conclusions

Within the limitations of this in vitro study, the following conclusions were drawn:

  • 1.

    The addition of thixotropic agents (at the level used in this study) to the 3 maxillofacial silicone elastomers reduced some mechanical properties, especially tear strength and percentage of elongation.

  • 2.

    Silicone Z004 showed superior mechanical properties among the 3 tested silicones; however, tear strength results had a relatively high (>25%) coefficient of variance, which would suggest that larger number of

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