BIOCOMPATIBILIDADE DE UMA RESINA ACRÍLICA E REEMBASADORES RÍGIDOS: ANÁLISE HISTOMORFOMÉTRICA EM RATOS

Abstract

The occurrence of adverse reactions in the mucosa caused by the use of removable dentures is very common. This fact raised an interest in this particular matter, and, because of that, a lot of studies have been done in order to determine the biological behavior of these materials, looking for materials that are biocompatible with the oral environment. Besides that, new techniques and treatments after-polymerization of denture base and reline resins are proposed in order to minimize the amount of released products and their effects in oral epithelium. Thus, the purpose of the current study was to test the biocompatibility of an acrylic base and hard chair-side reline resins, with an histopathological analysis in rats. The hypothesis that post-polymerization heat-treatments could reduce the cytotoxicity of these acrylic resins was evaluated. For this purpose, forty five adult female rats (Rattus Norvergicus Albinus Wistar), with 60 days old, weighing 150 g – 250 g, taken from the Biotério Central da Universidade Estadual de Ponta Grossa were used. This study received approval and is in accordance with the Comitê de Ética em Experimentação Animal (SCEEA-UEPG) recommendations, and, the animal manipulation rules of COBEA (Colégio Brasileiro de Experimentação Animal) were followed during the experiment. Palatal plates of heat-polymerized denture base acrylic resin Lucitone 550 (L) were custom-made and relined with Tokuyama Rebase II (TR), New Truliner (NT) or Kooliner (K) hard chair-side reline resins. For data comparison, five animals that did not receive the palates were kept under the same conditions during the experiment (control group). The plates embraced the palate area, in the region between the molars covering the occlusal and vestibular surfaces, being extended up to the first palatal fold. Half of the relined plates received a post-polymerization heat-treatment (immersion in water at 55°C for 10 min) and half of the acrylic resin denture bases received a similar post-polymerization heat-treatment, but for 60 min. The plates were cemented in the molar region with light-cured resin, thus being kept there for 14 days. The animals received a paste diet and water and libitum. Before and after the trial period, the rats were weighed individually on a precision scale. After 14 days, the animals of all groups were sacrificed by euthanasia. The palate of the animals were dissected, fixed in 10% buffered formalin for 48 h and decalcified in 4,17% EDTA for approximately four months. Then, the pieces were processed through a dehydration process to be embedded in paraffin, so that the back part of the palate lied down. The samples were cut with a microtome in sections of 5 μm and then stained with haematoxylin and eosin (H&E). Five histological cuts were done in each animal. Two standardized images from the central region of the cuts were made, referring to the rafe palatine, augmented 200x in order to verify histological changes. These include the thickness calculation of cellular compartment (TCC), total epithelial thickness (TET), and of keratin layer (TKC). Statistical analysis was performed using ANOVA (α = 0.05) test for comparison of weigh (g) of the animals at times 0 and 14 days of device using. There was no significant difference in weight change observed in the animals. For histological data comparisons from all groups it was performed one-way ANOVA (for type of palatal plate used). In one of the studies, the control group (without plates) was statistically compared to acrylic resin denture base plates submitted or not to the post-polymerization heat-treatment. In another study, the control group was statistically compared to palates fitted with relined plates submitted or not to the post-polymerization heat-treatment. Mean values from groups were compared with post-hoc Tukey with α = 0.05. Results from Keratin layer thickness from materials New Truliner, Tokuyama Rebase II and Kooliner without post-polymerization heat-treatment were statistically lower than control group (p<0.0001). For the same parameter, the heat-treatment significantly changed the results from Lucitone 550, reducing it. Means of connective tissue from resins Lucitone 550 and Tokuyama Rebase II whithout treatment were statisticaally higher than the control (p<0.01). The same means from Kooliner, without heat-treatment, were lower than the control (p<0.01). The heat-treatment was able to change the behaviour of resins Lucitone 550, Tokuyama Rebase II and New Truliner, reducing significantly the connective tissue thickness from both the former and augmenting that from the last material (p<0.01). Means of total epithelial thickness from resins Kooliner and New Truliner without heat-treatment were significantly lowers than the control (p<0.001 and p<0.01, respectivelly). As regards to the heat-treatment, it was responsable for change the behavior from materiais Lucitone 550 and Kooliner, augmented, in both cases, the thickness of this tissue (p<0.05 e p<0.001, respectivelly). Based on the results, it was possible to conclude that the use of individual impressions in Wistar rats, associated to plates with occlusal coverage on molars and the cementation with resin method developed in this study did not change their eating habits. Besides that, the post-polymerization heat-treatment proposed changed the biocompatibility of the materials evaluated, under the experimental conditions of this study.