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The influence of a disinfectant solution containing glutaraldehyde on the dimensional stability of 2 alginate and 4 elastomeric impression materials has been investigated. Die models were measured using a computer-controlled method and compared to the master die to assess the three-dimensional change in the impression material. After an immersion time of 10 min, a dimensional change did not occur. When using immersion times longer than 10 min, the accuracy of the alginate materials was generally more affected by the disinfecting solution than that of the elastomeric impression materials.

Areas of elastomeric impression materials are deformed when impressions are removed from undercuts in the mouth. Bond strength between low and high viscosity impression materials is considered to be higher than the adhesion between impression material and teeth or gum (up to 50 N/cm2). Otherwise failure of impression may be due to failure of the bond between putty and wash elastomers. Bond strength of condensation putty and wash silicones was evaluated at about 70 N/cm2. Bond of putty and addition-cured wash silicones failed at about 130 N/cm2. Bond strength decreased to 34 N/cm2, when putty material was contaminated with saliva and dried before adding the wash elastomer. When putty silicones were rinsed and dried after contamination with saliva bond strength increased up to 80-90% that of fresh probes.

Traditional elastomeric impression materials, four recently developed "hydrophilic" silicones and a hydrocolloid have been tested for their accuracy of reproduction by use of indirect measurements via plaster dies and for their wettability by means of the sessile drop method. The new silicones are reproducing the original model as exactly as the traditional elastomers. The impression techniques have a stronger influence on the results than the impression materials. Although the new silicones are more hydrophilic than the traditional elastomers, they do not reach the wettability of a hydrocolloid. The results of the indirect measurements and the results of the contact angle measurements are corresponding to the results of other investigations and to literature data of bubble counts of plaster dies made of different impression materials.

The need for disinfection of dental impressions is generally postulated. While many disinfectants for elastomeric impression materials have been recommended for at least ten years, several authors recently described suitable disinfectants for alginate impressions. Disinfectants for reversible hydrocolloid materials are in the phase of practical testing, and show promising first results. Under practical and scientific aspects further investigations are necessary to evaluate standards and standardized testing procedures.

In a survey the methods and materials used for making complete dentures were collected from 603 dentists. The impression material most frequently used for primary impressions was alginate and elastic impression material for functional impressions. Compared with an earlier survey the percentage of dentist using needle point tracing for recording jaw relations increased from 6 to 40%. Remounting complete dentures was done by 64% of the dentists whenever required; 9% applied this method as a routine.

This study compares the accuracy of 23 impression materials. With each material seven impressions of a stainless steel master die were taken under standardized conditions. Characteristical dimensions of the master die and of the stone dies as well were determined by means of a CNC coordinate measuring device. Differences in prepared tooth heights ranged between -36 and +19 microns. The occlusal distances between prepared teeth were 2 to 54 microns greater on the stone dies than on the master die. Diameters differed by -89 to +52 microns. The two phase impressions tended to result in stone dies of reduced size, whereas single phase and double mix impression techniques produced larger stone dies than the master die.

The purpose of the present investigation was a comparison of three special articulation plasters and three impression plasters. As DIN 13911 does not refer to articulation plasters, the inspection as well as the testing of pouring time, setting time, setting expansion and compressive strength using standard and manufacturer's consistence as carried out conforming to the guidelines for impression plasters. None of the tested plasters could meet the requirements of inspection in all points. Considering the physical parameters all plasters are up to standard, while Alpa quickstone and Arti-Plaster exhibited very low expansion and high compressive strength values. Although the compressive strength standard needs redefining, the value of a standardized testing technique for dental plasters is evident.

Dental materials which are supposed to contact the oral, mucous membranes during their intended dental use may affect our patients health in different ways. Their local and systemic toxicity, and their allergenic and tumorigenic potential are reviewed and methods of biocompatibility testing discussed. Special emphasis is placed on impression materials, denture base resins and dental alloys.

A direct profilometric evaluation of impression materials, particularly elastic materials, has not been possible up to now. The optical fine scanner RM 600 Laser Stylus (Rodenstock) allows touch-free scanning of surfaces, thus providing a direct quantitative assessment of impressions made with elastic materials. To determine the suitability of various impression materials and methods for direct profilometric analyses, the accuracy of reproduction was verified by comparing the surface structures of elastomer and compound impressions as well as replicas with the original. With two exceptions in the replicas, the mean roughness values (Rz) obtained showed no significant differences. This result suggests that the materials used are suitable for direct profilometric evaluation.

The high fluid elastomer materials for making casts used for the double impression technique were studied with the so-called disc test in terms of their fluidity, diffusion, and layer thickness. The pressure exerted was also recorded at the same time. Our study showed that the low viscosity of the cast material and the application of small amounts were the prerequisites for obtaining the thinnest layer possible.

After casting one model with various procedures and materials, models were constructed of Duroc. the abutment distance of the Duroc model depended on the impression method and the impression material. In general, double-mix impressions were more accurate than corrective impressions. Corrective impressions could be improved by placing flow-off grooves in the primary impression.

Dimensional stability and mechanical properties of addition-silicone impression materials were tested after sterilisation with gamma rays. There were no clinically relevant changes to not sterilized materials.

Cross-linking of elastomeric impression materials is an exothermic process. In addition to the frictional heat produced during mixing, the reaction heat may increase the temperature by several degrees Centigrade in thermically isolated samples.

In addition to the impression material the type of the used impression tray influences the accurat dimensional transfer of the teeth position to the master cast. In total 80 impressions were taken from models of the upper- and lower jaw by using condensation silicone, hydrocolloid, solid and perforated stock trays and acrylic custom trays. After that the casts were measured. The highest conformity with the original could be achieved with a hydrocolloid stock tray. The custom tray for the upper jaw showed short differences to the original model. By using a custom tray for the lower jaw higher dimensional changes occurred. Besides the different impression material thickness, distorsions of the trays should be discussed.

Two reversible hydrocolloidal impression materials as well as two light-bodied polysulfide and silicone impression materials were tested with regard to their properties of coating plain ground dentin surfaces. With a wet surface, hydrocolloids produce flatter contact angles between dentin surfaces and the impression material, i. e. a more effective coating than polysulfide and silicone impression materials. The conditions are reversed with dry dentin surfaces and those pretreated with silicone oil. If the dentin surfaces of which an impression is to be taken are treated with silicone oil, coating is less effective with all impression materials tested.

By use of two different materials, the combination impression facilitates the preparation of models representing the oral situation without compression of the mucosa or tension at the abutment teeth. In addition, the original impression tray can be ground down without much additional effort and used for the determination of jaw relations. The otherwise necessary and additional preparation of bite blocks is no longer required.

The reproduction of elastic impression materials is described with a laser-technique. This technique allows a quantitative evaluation without touching and deforming the surfaces. Although it is possible to measure differences, clinically relevant differences between several elastomere and one hydrocolloid material are not found.

Ten frequently used hard plasters (Types 3 and 4 in accordance with DIN 13911) and 5 current modelling plastics have been investigated. Abrasion with testing forces of 1, 2 and 5 N were determined on samples 2 mm broad and about 12 mm long. The amount of abrasion could be calculated from the loss in weight. Only Kol-Dur and the plastics Diemet, Impredur and Alpha-Die are sufficiently reliable not to become damaged by abrasion on wax modelling (abrasion less than 5 micrometer). Hard plasters are not hard enough to resist abrasion. Taking into account the bending strength and modulus of elasticity, only Kol-Dur and Diemet can be recommended. Because of the improved dimensional stability of the hard plasters, Alca Dental Stone, Begolith, Duralit, Tewstone or Ferrodur can be recommended if the bending properties and a possible slight abrasion are taken into consideration. With the hard plasters, damage of more than 10 micrometer is easily possible.

In order to keep the degree of polymerisation of moulding materials as low as possible until they are applied, a lower working temperature for the first and second material is necessary. In addition, the preliminary impression is cooled in ice water so that the flow capacity of the correcting compound in the capillary cleft is improved and unreliable model reduction can thus be avoided.

The bending strength and modulus of elasticity of 15 materials were measured. 9 of them were hard plasters. Five were plastics with filling material, one a hard plaster with copper. On the basis of modelling calculation a bending strength of 20 N/mm2 is necessary. It is exceeded by 12 of the materials and not quite attained by 3 of them.