Effect of Immersion on Plasticiser Leaching from Tissue Conditioners

Objective:  To compare the effect of immersion in distilled water (DW), artificial saliva (AS) and three food simulating liquids on the hardness of tissue conditioner formulations containing two different plasticisers

Methods: Materials used were poly(ethyl methacrylate) powder from Lucite International, acetyl tributyl citrate (ATBC) and butyl phthalyl butyl glycollate (BPBG) plasticisers, both from Vertellus Specialities Inc. Liquids were 95/5 v/v plasticiser/ethanol mixes, powder/liquid was 3g/1.6ml. Specimens (50x50x5mm) comprised a 3mm thick layer of tissue conditioner on a 2mm thick Perspex sheet. Shore A hardness (according to ASTM D2240) was measured prior to immersion in 100mls of either DW, AS, 3% acetic acid (AA), 25% ethanol (EtOH) or coconut oil (CO). n=2 per formulation/liquid.  Hardness was determined at regular intervals up to 84 days.  6 measurements were made per specimen, mean and standard deviation (SD) were calculated from the 12 measurements.

Results: Initial and final Shore A hardness values are given in the table below (SD).

Both formulations increased in hardness over the 84 days in all liquids to varying degrees, although it was highest in CO.  In all liquids ATBC increased in hardness more than BPBG.  Increase in hardness can be related to plasticiser/ethanol leaching, as ethanol content was the same any differences can be attributed to the different plasticisers.

Conclusions: ATBC is leached more easily than BPBG. Leaching of both plasticisers proved highest in CO indicating that tissue conditioners may have a shorter intra-oral lifetime in patients eating a high fat diet.