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The influence of plasticizer loss on the viscoelasticity of temporary soft liners
1Department of Restorative Sciences, University of Minnesota, Minneapolis, USA.
Purpose:
This study examined the changes in mechanical properties of temporary soft liners introduced by the differential loss of alcohol and plasticizer in different storage media.
Materials And Methods:
Four brands of temporary soft liners were used to prepare 128 specimens on Lucite LS substrates. Each group of specimens was stored in a different medium (air, 10% ethanol, water, and artificial saliva), selected to affect the levels of plasticizer and alcohol over time. Data on weight changes, plasticizer leaching, and recovery rate were recorded at the following intervals: baseline, 2, 7, 14, 28, 56, and 176 days. The storage media were periodically renewed except during the drying stage between day 56 and 176. Two-way analysis of variance and Duncan multiple-range tests were performed.
Results:
Plasticizer leaching occurs at higher levels in artificial saliva than in other storage media (P <.0001). The mean recovery rates exhibited a statistically significant increase (indicating reduced viscoelasticity) in more of the artificial saliva specimens than in all other test groups (P <.0001). Comparatively, the rates of recovery were lower in the 10% ethanol storage medium (except Lynal) with a statistically significant difference attained with the higher air-stored specimens in Tempo and Coe-Comfort (P <.0001). During the drying phase, weight changes in the 10% ethanol group were higher than those in the other storage media.
Conclusions:
The study supports the contention that alcohol may have been retained in the 10% ethanol group in a manner that extended the viscoelasticity of the material. The roles of alcohol and plasticizer content in the mechanical properties of temporary soft liners depend on the type of temporary soft liners and on the nature/duration of service desired. Storing dentures lined with tissue conditioners under dry conditions and those lined with true soft-liners in an ethanol humidor may be justified to extend serviceability by minimizing the loss of the component most relevant to viscoelasticity.