ABSTRACT
Disinfection of dental impressions is a weak point in the dental hygiene chain. In addition, dental office personnel and dental technicians are endangered by cross-contamination.This study aimed to investigate the dimensional stability of two color-changing irreversible hydrocolloid materials [IH] after disinfection with glutaraldehyde.In this in vitro study, impressions were made of a master maxillary arch containing three reference inserts on the occlucal surface of the left and right maxillary second molars and in the incisal surface of the maxillary central incisors. Two types of color-changing irreversible hydrocolloid [tetrachrom, cavex] were used. Glutaraldehyde 2% was used in two methods of spraying and immersion to disinfect the impressions. The control group was not disinfected. Casts were made of type IV gypsum. The linear dimensional change of the stone casts was measured with a profile projector. For statistical analysis, Kruskall-Wallis and Mann-Witney tests were used [alpha=0.05].By immersion method, the casts fabricated from tetrachrom were 0.36% larger in the anteroposterior [AP] and 0.05% smaller in cross arch [CA] dimensions; however, the casts prepared after spraying of tetrachrom were 0.44% larger in the AP and 0.10% smaller in CA dimensions. The casts made from Cavex were 0.05% smaller in the AP and 0.02% smaller in CA dimensions after spraying and 0.01% smaller in the AP and 0.003% smaller in CA dimensions after immersion. Generally there were not significant differences in AP and CA dimensions of the experimental groups compared to the control [p > 0.05].Disinfection of the tested color-changing irreversible hydrocolloids by glutaraldahyde 2% did not compromise the accuracy of the obtained casts
ABSTRACT
A general process in implant design is to determine the reason of possible problems and to find the relevant solutions. The success of the implant depends on the control technique of implant biomechanical conditions. The goal of this study was to evaluate the influence of both abutment and framework materials on the stress of the bone around the implant by using three-dimensional finite element analysis.A three-dimensional model of a patient's premaxillary bone was fabricated using Cone Beam Computed Tomography [CBCT]. Then, three types of abutment from gold, nickel-chromium and zirconia and also three types of crown frame from silver-palladium, nickel-chromium and zirconia were designed. Finally, a 178 N force at angles of zero, 30 and 45 degrees was exerted on the implant axis and the maximum stress and strain in the trabecular, cortical bones and cement was calculated.With changes of the materials and mechanical properties of abutment and frame, little difference was observed in the level and distribution pattern of stress. The stress level was increased with the rise in the angle of pressure exertion. The highest stress concentration was related to the force at the angle of 45 degrees. The results of the cement analysis proved an inverse relationship between the rate of elastic modulus of the frame material and that of the maximum stress in the cement.The impact of the angle at which the force was applied was more significant in stress distribution than that of abutment and framework core materials