In situ evaluation of surface roughness and micromorphology of temporary soft denture liner materials at different time intervals.

OBJECTIVE: To perform an in situ evaluation of surface roughness and micromorphology of two soft liner materials for dentures at different time intervals. BACKGROUND: The surface roughness of materials may influence the adhesion of micro-organisms and inflammation of the mucosal tissues. The in situ evaluation of surface roughness and the micromorphology of soft liner materials over the course of time may present results different from those of in vitro studies, considering the constant presence of saliva and food, the changes in temperature and the pH level in the oral cavity. MATERIALS AND METHODS: Forty-eight rectangular specimens of each of the two soft liner materials were fabricated: a silicone-based material (Mucopren Soft) and an acrylic resin-based material (Trusoft). The specimens were placed in the dentures of 12 participants (n = 12), and the materials were evaluated for surface roughness and micromorphology at different time intervals: 0, 7, 30 and 60 days. Roughness (Ra) was evaluated by means of a roughness tester. Surface micromorphology was evaluated by scanning electron microscopy. RESULTS: Analysis of variance for randomised block design and Tukey's test showed that surface roughness values were lower in the groups using the silicone-based material at all the time intervals (P < .0001). The average surface roughness was higher at time interval 0 than at the other intervals, for both materials (P < .0001). The surface micromorphology showed that the silicone material presented a more regular and smoother surface than the acrylic resin-based material. CONCLUSION: The surface roughness of acrylic resin-based and silicone-based denture soft liner materials decreased after 7 days of evaluation, leading to a smoother surface over time. The silicone-based material showed lower roughness values and a smoother surface than the acrylic resin-based material, thereby making it preferred when selecting more appropriate material, due its tendency to promote less biofilm build-up.

Influence of retentive areas associated to onlay preparations on the dimensional stability of silicone impression materials

This study evaluated the effect of retentive areas on onlay preparations on the dimensional alterations in condensation and addition silicone materials. A standard model with an onlay preparation was made. Each impression material was used through the double or simultaneous impression technique (n=25), resulting in a hundred impressions of the same model. Impressions were poured with type IV dental stone. Digital images were taken with a light microscope and the distances between the reference points created on the plaster dies were compared with the ones on the standard model. In the occlusal, mesial-medium and mesial-cervical segments, the double impression (DI) with condensation silicone presented similar values compared to the standard model. The values of the addition silicone with DI were similar to the standard model only in the mesial-occlusal segment. In the other segments (distal-cervical, distal-medium and distal-occlusal), all groups were statistically different from the control. It could be concluded that addition and condensation silicone impressions provided plaster dies with significant dimensional alterations in most of the evaluated areas when compared to the standard model. The retentive areas related to the onlay preparation influenced the dimensional stability of the addition and condensation silicone impressions.

Este estudo avaliou as alteracoes dimensionais de silicones de condensacao e adicao usados em duas tecnicas como resultado de areas retentivas de preparos do tipo onlay. Um modelo padrao foi feito e vinte e cinco moldagens realizadas com os dois materiais, atraves da tecnica de dupla impressao ou impressao simultanea, e cada material resultou em 50 modelos de gesso. Imagens digitais foram feitas com um microscopio de luz e as distancias entre os pontos de referencia criados no modelo de gesso foram comparados aos pontos de referencia no modelo padrao. Nos segmentos oclusais, medio-mesial e cervico-mesial, a tecnica de dupla impressao (DI) com silicone de condensacao apresentou valores similares comparados ao modelo padrao. Os valores do silicone de adicao com DI foram similares ao modelo padrao somente no segmento mesio-oclusal. Nos outros segmentos (disto-cervical, medio-distal e disto-oclusal), todos os grupos foram estatisticamente diferentes do controle. Pode- se concluir que moldagens com silicone de adicao e condensacao conferem modelos de gesso com alteracoes dimensionais significativas na maioria das areas avaliadas, quando comparadas ao modelo padrao. As areas retentivas relacionadas ao preparo de onlay influenciaram na estabilidade dimensional das moldagens atraves dos silicones de condensacao e adicao.