The acrylic resins based on polymethyl methacrylate (PMMA) have been among  the most popular materials regarding the realization of orthodontic and prosthetic devices for over 70 years. For  many years, however, there have been problems associated with the use of polymethyl methacrylates and their non beneficial effects, for patients and operators who have to use it everyday.Until a few years ago,these effects were considered an acceptable risk when compared to the benefits by devices manufactured with these materials, but the sensitivity and vigilance towards common issues such as health, tolerability and biocompatibility have grown and the risks of PMMA in the past, today are no longer acceptable, even by virtue of the development of countless new technologies in all areas of our industry.

Polymethyl methacrylate (PMMA) is a volatile substance with excellent solvent properties, it is easily absorbed by the body, it is irritating to skin, mucous membranes and  the respiratory tract. The greatest risk is for operators who should work with special protection. Actually the protection indicated in safety data sheets, as the use of butyl gloves to avoid contact with hands, make l the transformation of the material impractical in normal laboratory protocols. The consequence is that the working of the material is practically impossible without severe health risks for the operators.

As regards the use of the devices in the oral cavity it is now widely accepted that from matrices polymerized resinous material monomers responsible of for cytotoxic reactions can be a released. There are today polymerization systems that reduce the amount of residual monomer, but the best result that could be obtained is the following: with this system the potential risk to the health of patients can be reduced to an extremely low level, we add, not eliminated. To date, in terms of technical and scientific issues of the release of the residual monomer it has not been resolved yet and remains an integral part of the problems of the PMMA.

The greatest damage however for patients is undoubtedly linked to the direct use in the oral cavity of these materials, in fact, in vitro studies reported:  the majority of treated cells died from necrosis; whereas a small portion of cells died from apoptosis. In conclusion, the results demonstrated that these liquid forms of dental polymers and their major monomers cause cytotoxic reactions. The direct relining procedure that cures these materials in situ should be used cautiously.