The investigation of biocompatibility and mechanical properties of denture base resins

U uvodnom delu doktorske disertacije opisuje se kompleksnost problematike korišćenja polimera za bazu zubne proteze, sa osvrtom na njihove opšte osobine, stepen biokompatibilnosti i njihove mehaničke karakteristike. Detaljno je opisana problematika ispitivanja stomatoloških materijala i napravljeno je poređenje i korelacija između in vitro i in vivo načina ispitivanja biokompatibilnosti. Drugi deo obuhvata ispitivanje čvrstoće polimera za bazu zubne proteze i analizu uticaja osobina materijala u odnosu na biološku sredinu u kojoj obavljaju svoju funkciju, i u odnosu na sile kojima su tokom funkcije materijali izloženi. Cilj doktorske disertacije je utvrđivanje stepena biokompatibilnosti i mehaničkih karakteristika toplopolimerizujućih, hladnopolimerizujućih i termoplastičnih akrilata za bazu zubne proteze. Istraživanje je obuhvatilo 3 komercijalna materijala iz grupe akrilata, koji se razlikuju po hemijskom sastavu i načinu polimerizacije. Ispitivanje biokompatibilnosti rađeno je u in vitro i in vivo uslovima. Ispitivanje na ćelijskim kulturama obuhvatalo je dve ćelisjke linije (MRC 5 i L929) sa dva načina kontakta između ćelija i materijala (direktan, indirektan) i dva načina određivanja biološkog ishoda (MTT test, Agar difuzioni test). Istraživanje urađeno in vivo obuhvatalo je test subkutane implantacije, na animalnom modelu pacova, i test iritacije oralne sluzokože na animalnom modelu hrčka. Oba testa rađena su u skladu sa standardom ISO 10993. Cilj in vivo istraživanja bio je ispitivanje reakcije tkiva na implantirani materijal, računajući i završnu integraciju ili dezintegraciju implantiranog materijala. Prednost in vivo istraživanja nalazi seu analizi uticaja materijala na sterilno živo tkivo, uz praćenje imunološke reakcije, kao dopuna prethodnom istraživanju na ćelijskim kulturama. Dopunski deo in vivo ispitivanja biokompatibilnosti određen je prema kliničkoj upotrebi ispitivanih materijala, zbog čega je odabran test oralne iritacije sluzokože. Sluzokoža bukalne kesice sirijskog hrčka sastoji se od pločasto slojvitog epitela sa orožavanjem, što je predstavljao dobar model za ispitivanje polimera za bazu zubne proteze, pošto zubna proteza naleže na sluzokožu nepca i rezidualnog alveolarnog grebena koja takođe orožava. Drugi deo disertacije obuhvatao je ispitivanje mehaničkih karakteristika, pri čemu su urađeni test zatezne čvrstoće, test savojne čvrstoće, test čvrstoće loma i mikrotvrdoće, uz dopunsku analizu pratećih parametara. Rezultati ispitivanja biokompatibilnosti pokazali su da su testovi biokompatibilnosti osetljivi na upražnjeni metodološki postupak. Ispitivanjem na ćelijskim kulturama nisu utvrđene značajne razlike u citotoksičnosti između toplopolimerizujućih, hladnopolimerizujućih i termoplastičnih akrilata. Takođe, rezultati su se razlikovali u odnosu na tip ćelijske kulture i način provere biološkog ishoda, što se slaže sa prethodnim navodima o kompleksnoj problematici njihovog međusobnog poređenja. Ispitivanjem biokompatibilnosti subkutanom implantacijom praćen je inflamatorni odgovor tkiva u vremenskom intervalu od 90 dana. Reakcija organizma na implantirani materijal posmatrana je kroz ćelijske i tkivne parametre, u skladu sa ISO 10993. Dodatno je urađena i analiza hrapavosti implantiranih materijala. Histološkom analizom utvrđena je razlika u inflamatornom odgovoru u odnosu na korišćeni materijal, kao i prema vremenskom intervalu implantacije. Test oralne iritacije sluzokože nije se pokazao kao dovoljno senzitivan za ispitivanje ovih vrsta materijala. Ispitivanjem mehaničkih karakteristika utvrđene su razlike između toplopolimerizujućih, hladnopolimerizujućih i termoplastičnih akrilata. Najveći stepen čvrstoće utvrđen je kod toplopolimerizujućih akrilata dok je najveća konzistentnost rezultata bila u grupi termoplastičnih akrilata. Prezentovano istraživanje predstavlja prvu detaljnu analizu biokompatibilnosti i mehaničkih karaktestistika polimera za bazu zubne proteze.The introduction describes the complexity of use of denture base materials, with regard to their general characteristics, biocompatibility and mechanical properties. Issues related to the testing of dental materials is described in detail and comparison is made between in vitro and in vivo methods of biocompatibility testing. The second part further covers the determination of strength of previously used materials, in relation to biological environment in which their function is conducted and in relation to the influence of masticatory forces which can contribute to their mechanical failure. The aim of the presented research was to assess the degree of biocompatibility and mechanical properties of cold curing, hot curing and thermoformed denture base materials. The research included three denture base materials, which differed according to their chemical composition and polymerization protocols. The biocompatibility testing was carried out in in vitro and in vivo conditions. The in vitro experiments covered two different cell lines (MRC 5 human lung fibroblasts and L929 mouse fibroblasts) with two types of contact (direct, indirect) and two different types of quantification of biological outcome (MTT assay and Agar overley test). The in vivo assessment of biocompatibility covered the subcutaneous implantation test, on the animal model of Wistar rat, and oral mucosa irritation test, on the animal model of sirian hamster. Both tests were conducted according to the ISO 10993. The aim of the in vivo investigation was to evaluate tissue reactions to the implanted materials, including the final integration or disintegration of the tested materials. The advantage of in vivo investigation included the possibility of monitoring the materials influence on living tissues, with the analysis of imunological response as an addition to the previously conductedresearchon cell cultures. The supplemental part of in vivo investigation was chosen according to the clinical use of the tested materials, which included the oral mucosa irritation test.The mucosa of hamster buccal pouch consists of stratified squamos epithelium, which is considered to be an adequate replacement for the human denture supporting tissues, which also consist of the same type of epithelium. The second part of thesis includes the determination of mechanical properties of denture base materials. It consists of four types of tests: tensile strength test, bending strength test, fracture toughness test and microhardness tests, followed by the analysis of corresponding parameters. The results of the biocompatibility tests showed that the biological outcome of the applied method is highly depended on the methodological procedure. The investigation conducted in vitro, on two different cell lines, did not show significant difference in cytotoxicity between hot curing, cold curing and thermoformed denture base materials. Also, the results were influenced by the type of cell culture and the evaluation method of biological outcome, which agrees with the previous allegations about the complexicity of their mutual comparison. The subcutaneous implantation test covered the inflammatory response in the time period of 90 days. The organism reaction to the implanted material was determined through the cell and tissue parameters of organism response, evaluation of which was conducted according to the ISO 10993. Additionally, the surface roughness of the implanted specimens of materials was also measured. The inflammatory response of the ogranism was influenced by the type of the implanted material and the time interval of implantation. The oral mucosa irritation test has proven not to be sufficiently sensitive for testing of this type of materials. Testing of the mechanical properties od denture base materials, revealed the difference between the cold curing, hot curing and thermofomed denture base materials. The highest strength was observed in hot curing materials, while the highest consistency of the results was observed in thermoformed resins. The presented investigation presents the first detail analysis of the biocompatibility and mechanical properties of the denture base materials, and as such presents a novelty in the field of dental materials characterization