Page 168 - Clinical relevance of current materials for cranial implants

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Chapter 8
DISCUSSION
This in vitro study reports the leaching behavior of four representative PMMA-based materials which are used for medical devices. The following trends were observed: (I) the amount of leached monomers significantly differs for different PMMA-based materials (II) release patterns of residual monomers significantly differ for different PMMA-based materials (III) the novel PMMA-based material NextDent C&B MFH demonstrates a significantly lower total cumulative concentration of leached residual monomers but a higher initial release.
Kühn reports that Palacos R+G released approximately 185 μg MMA per g PMMA over a two week span into 5 mL water using specimens with a volume of 0.45 cm3 and area of 4.5 cm2. The accumulated release of MMA from 8 different PMMA-based materials ranged approximately between 185 and 470 μg/g. Palacos R contained approximately 4% residual monomers immediately following curing, this dropped to roughly 1.5% after 1 day.7 In this study, the specimens (volume: 18.85 cm3, area: 72.5 cm2) were placed in water after 20 ± 4 hours. The thickness of the specimens was 6 mm, since this is comparable with the human skull15,16. The specimen thickness has been shown to have a significant influence on the content of residual monomers11. It is unknown whether this has an effect on the leaching behavior of MMA. Literature reports a significant increase in leaching when a sample was put in a larger volume of extraction solution17. This, in addition to the difference in volume to surface ratio, may explain the lower values reported here in comparison to literature 7. These effects should increase the values found in our study compared to the study by Kühn7, as their extraction volume and specimen thickness were significantly lower. However, their reported values are significantly higher than ours, probably due to the previously mentioned effects. The actual monomer exposure for the patient in a clinical setting, where upon cooling down the medical device is immediately placed into the patient, is thus likely higher than the reported values in this study and may be more in line with the values reported by Kühn7.