Contamination level of alginate impressions arriving at a dental laboratory.

The contamination level of alginate impressions delivered to a large dental laboratory in Sweden was determined. One hundred and seven consecutive alginate impressions were included during 7 days. Samples were taken and transferred into sterile physiological saline and analysed microbiologically for colony-forming units (cfu) as well as nonhemolytic, alpha-hemolytic, and beta-hemolytic colonies. After sampling, the clinics were contacted and asked to fill in simple questionnaires about their routines of disinfecting impressions. The questionnaire study revealed that about half of the clinics had some kind of disinfection routine, while the others rinsed in running water only. Seventy-two percent of the impressions yielded growth of bacteria, with a median number of 1.3x10(2) cfu. Thirteen per cent of the samples yielded >10(3) cfu, with a maximum number of 3.4x10(4) cfu. The majority of isolates were non- and alpha-hemolytic bacteria. Growth was recorded in 61.3% of disinfected impressions, and the numbers of bacteria in disinfected and nondisinfected impressions were similar. These findings raise the question of whether impressions need to be disinfected or if proper handling and hygienic procedures are sufficient to block the possible route of infection.

In vitro study of transmission of bacteria from contaminated metal models to stone models via impressions.

The purpose of this study was to determine the risk of microbiological transmission into the dental laboratory via impressions and dental stone models. Metal master models were contaminated with Bacillus subtilis and Streptococcus sanguis. Impressions in alginate, polyvinylsiloxane, and polyether were used, and models were cast in two brands of dental stone. Samples were taken from the impression surfaces before and after casting, and sections from the stone models were taken by a technique developed for this study. After incubation, the numbers of colonies were counted and the numbers of colony-forming units per milliliter were calculated. The reductions were statistically significant but considered to be clinically insignificant. The conclusion is that even after severe contamination, the risks to dental laboratory personnel are minimal. "Normal" hygienic procedures are recommended instead of disinfection.

The effect of different polishing techniques on the surface roughness of acrylic resin materials.

This study evaluated three methods of surface polishing on acrylic denture base materials. Specimens of three commercial heat-cured acrylic resin materials were finished using burs, sandpaper discs and rubber wheels, and polished with polishing soap, paste, or by application of a UV-light-activated resin sealant. The resulting surface roughness was examined by scanning electron microscopy as well as measured by means of a stylus profile Perthometer. Surface roughness was reduced by polishing. Polishing paste and UV-light-activated resin sealant were more, and equally, effective in reducing surface roughness compared to polishing soap. Polishing paste or UV-light-activated resin sealant may be used to create a smoother surface on acrylic dentures.

Fabrication of a custom-made impression tray for making preliminary impressions of edentulous mandibles.

Severe mandibular alveolar ridge resorption is usually observed in patients with long-term edentulism and/or ill-fitting dentures. In some of these patients, the genial tubercles project into the floor of the mouth as a high point in the anterior area of the mandibular residual ridge. The lingual flanges of mandibular stock impression trays usually impinge on the most prominent areas of the resorbed mandibular edentulous ridge (i.e., internal oblique lines and genial tubercles). It is suggested that a preliminary custom tray be made in such cases to pour an initial impression so that individual custom trays can be fabricated. An efficient method for constructing such a custom impression tray from readily available materials is described.

Weight and linear dimensional changes of reversible hydrocolloid duplicating materials: effect of storage and re-use.

Weight and linear dimensional changes of two hydrocolloid duplicating materials following setting in various environments were examined. Prior to the measurements, the sample materials were stored either in the sol or in the gel phase, for a period of 5 days, in order to evaluate the effect of ageing on their composition and behaviour. A 100% relative humidity environment produced the least change to the set material, and in this environment, the behaviour of the materials was not affected by their age. Results indicate that deterioration of the duplicating materials provoked by repeated or prolonged heating, is detectable, through their weight changes, even at an early stage.

Dimensional stability and reproduction of surface detail of tissue conditioning materials.

Four commercial tissue conditioners have been assessed in terms of their dimensional stability and ability to reproduce surface detail according to ADA specification #19 for impression materials. Results have been compared with those of a number of elastomeric impression materials. The tissue conditioners performed adequately and as such could be used as impression materials within 24 hours of their application. While they did not compare well with the elastomeric impression materials they comply with the limitations of the ADA specifications. It is suggested that standards specific to these materials should be developed.

Using cephalometry to evaluate maxillomandibular relationships in complete denture construction.

Long-term denture wearers undergo facial changes as a result of occlusal wear of the dentures and residual ridge resorption. This study examined 12 such patients, presenting with a clinical appearance of Angle's Class III occlusal relationships, to evaluate a clinical method of determining the correct mandibular position. Complete dentures were fabricated for each patient using standard clinical procedures, but acrylic resin blocks were left on the mandibular posterior bases instead of denture teeth. Ensuing changes in maxillomandibular relationships were recorded. After the stabilization of the mandibular relationship, the dentures were completed using mandibular posterior teeth. Patients were evaluated using cephalometric analysis before and after treatment. Results show that a careful procedure of denture fabrication allows the determination of the correct mandibular relationship, even in patients who have experienced extreme facial collapse.

[Behavior of hydrocolloid impression materials during disinfection for AIDS virus]. / Symperiphora ton ydrokolleidon apotypotikon ylikon kata ten apolymanse tous enanti tou iou tou AIDS.

The aim of this study is to investigate the dimensional changes of hydrocolloid impression materials agar type and alginates, when they are placed in fluids for AIDS virus sterilization as Sterile pack, alcohol 75%, sodium chloride 10% and Cidex for 40 min. It was found out that when the hydrocolloids were placed in alcoholic and Sterile pack fluids a great deal of changes happened (contraction and shrinkage) that made the sterilization in them impossible. The percentage of linear extention and imbibition noticed in hydrocolloids when they were placed in sodium chlorides and Cidex solutions showed that sterilization in them is usually possible. The best way of sterilization is to make a gypsum model from the hydrocolloid impression and place it in the furnace for 30 min in 60 degrees C.