Resina para confecção de aparelhos ortodônticos: análise do efeito de soluções desinfetantes, convencionais e extratos de plantas, sobre propriedades mecânica e microbiológica

Abstract

Evidence of an association between infectious diseases and removable orthodontic appliances is commonly observed with oral microbiota being a precursor of infections, especially when cleaning is deficient. Objective: To evaluate the in vitro effect of plant extract solutions and conventional disinfectant solutions on: the flexural strength of test pieces made of orthodontic chemically polymerized acrylic resin using two polymerization techniques and on different protocols to remove Candida albicans and Candida parapsilosis biofilm from the surface of acrylic resin. Material and Methods: The flexural strength of groups of ten test pieces was evaluated using mechanical testing after immersion in solutions of the essential oil of Cymbopogon nardus, alcoholic extract of Hydrastis canadensis, alcoholic extract of Casearia sylvestris, 2% chlorhexidine gluconate, sodium bicarbonate, effervescent tablets and 1% hypochlorite. Protocols were difined as: protocol I was mechanical brushing of the test piece surface with a stiff-bristled toothbrush for one minute, three times a day for 30 days; protocol II was chemical disinfection by 10 minutes of immersion in 100 mL of the aforementioned solutions, three times a day for thirty days and protocol III was a combination of procedures I and II. For the microbiological assay, circular test pieces (n = 3) with C. albicans and C. parapsilosis biofilm were subjected to Protocols I, II and III. Cell structure and biofilm formation were evaluated by scanning electron microscopy and cell viability was assessed using the tetrazolium salt reduction method (XTT). Results: The flexural strength was reduced of all the test pieces immersed for 48 hours in plant extract and conventional solutions compared to an untreated control group (p-value <0.05). However, there were no statistically significant differences between the treated groups and the flexural strength remained within the required range. There was no significant difference between the two polymerization techniques in respect to the flexural strength of acrylic resin. The microbiological assay identified mature biofilm structures of C albicans and C. parapsilosis and individual cells fixed to the resin surface. Of the plant extracts, Casearia sylvestris and Canadian hydrastis had the greatest inhibitory action whereas Cymbopogon nardus and chlorhexidine gluconate had the least antimicrobial activity (p-value <0.05). Conclusions: Extracts of Casearia sylvestris and Hydrastis canadensis can be indicated as antifungal compounds for the disinfection of orthodontic appliances made of acrylic resin. Further studies should investigate the synergistic effect of treatment with plant extracts and properties of the acrylic resins on mature biofilm of C. albicans and C. parapsilosis and cell adhesion and the structure of monomicrobial and polymicrobial biofilms