Malcolm D. Jendresen

Time-dependent accuracy of elastomer impression materials. Part II: Polyether, polysulfides, and polyvinylsiloxane

T here are currently four basic types of elastomer impression materials in use in the dental profession: (1) silicone rubbers which polymerize by a condensation reaction, (2) polysulfide (mercaptan) rubbers, (3) polyethers, and (4) silicones which polymerize by an addition reaction. The latter have been introduced relatively recently and are also called polyvinylsiloxanes. The basic properties of these materials have been reviewed by Craig’ and Phillips.’ Two clinical advantages of these materials over reversible and irreversible hydrocolloids are that (1) multiple dies may be made from repetitive pours of a single impression and (2) the clinician can wait for an extended time period to pour the stone cast after making the impression. In addition, elastomers can be metal plated for the production of electrodeposited metal dies. There is disagreement in the literature regarding the superiority of dimensional stability between polysulfide rubbers and condensation silicones.:‘-” Polyether has been suggested as being more dimensionally stable when compared with its predecessors,‘. 7. ” and the polyvinylsiloxanes have recently claimed even superior accuracy and stability over polyethers.‘, ” The purpose of this study was to make a quantitative comparison of the accuracy and dimensional stability of representative products in each class by

Clinical Adhesiveness of Selected Dental Materials: An in-vivo study

An investigation was conducted to determine the clinical adhesiveness of some commonly used dental materials. Contact angle measurement data, obtained under clinical conditions, were used to calculate the in vivo-critical surface tensions for enamel, gold, stainless steel, and a resin polymer. The results of this study showed that the adhesive properties of the artificial surfaces studied were considerably modified in the oral environment. Thus, after two hours these solids with diverse original surface chemistries were observed to produce in vivo-critical surface tensions common to those recorded for enamel. The observed changes were attributed to be absorbed biofilm (acquired pellicle), which forms on all solid surfaces in the oral cavity.

Quality of fixed prosthodontics after 15 years

Interviews and/or clinical examinations by means of the California Dental Association quality evaluation system were carried out in a group of persons who had received extensive restorative treatments with fixed partial dentures 15 years before this study. The studied group consisted of 77 persons who agreed to participate from an original group of 150 persons selected at random from the Swedish Dental Insurance System records. Of the original group 20 had died, 17 were not traceable or not able to participate for medical reasons, and 36 declined to participate. Thirty-two per cent of the recorded reconstructions had been lost, and 8% partially lost during the 15-year period. Thirty-five per cent of the reconstructions were rated as Satisfactory, whereas the remaining ones had mixed clinical quality ratings. Failures and Not Acceptable quality ratings were found to be caused mainly by fractures, loss of retention, and/or dental caries.

Quality of extensive fixed prosthodontics after five years

A group of 150 patients who had received extensive restorative treatment 5 years prior to this study was selected at random from the Swedish Dental Insurance System records in Malmo. Of the 133 respondents to a questionnaire, 109 participated in a clinical evaluation of 891 restorations including 498 crowns, 232 pontics, 6 removable partial dentures, and 155 adjacent or opposing metallic restorations. The clinical evaluation was performed by two trained examiners by means of the CDA quality evaluation for dental care. Ninety percent of the crowns and pontics, 80% of the adjacent or opposing metallic restorations, and all six partial dentures were rated satisfactory. Twenty-three percent of the crowns, 49% of the pontics, 17% of the adjacent or opposing restorations, and half the partial dentures rated in the range of excellence. Not acceptable ratings for crowns included 3.4% T ratings and 6.6% V ratings. For pontics, the corresponding percents were 9.5% and 0.4%, respectively. T ratings were in most cases indicative of overcontouring, whereas V ratings for crowns were usually given because of secondary caries. Marginal periodontitis was mainly associated with not acceptable ratings but was also observed in connection with satisfactory restorations. Only 2% of the restorations had been lost during the 5-year period after insertion.

Clinical adhesiveness of the tooth surface

The clinical adhesiveness of tooth structure was determined for 43 individuals using intraoral contact angle measurements. There were no statistically significant differences in the critical surface tensions of wetting between groups of males and females nor between the three age groups tested. There was a statistically significant difference between individuals. The critical surface tensions for all the tooth surfaces measured were in the bioadhesive range of 32--50 dynes/cm. The formation of an organic film, pellicle, on the surfaces of teeth brings groups of different ages and sex to a common state of bioadhesiveness, allowing for the subsequent bacterial colonization and plaque formation as a clinical consequence.

Evaluation of detail reproduction for three die materials by using scanning electron microscopy and two-dimensional profilometry

This study evaluated the reproduction of detail by Fuji-rock artificial stone, Epoxydent epoxy resin, and Steady-plast polyurethane resin. A polyvinyl siloxane impression was made of a disk-shaped calibration model, with etched grooves ranging from 1 to 46 microns in depth. The die materials were poured in the silicone impression of the disk, then examined with a scanning electron microscope and two-dimensional profilometer. The results revealed that the artificial stone could not reproduce details smaller than 20 microns because of the size of the crystalline structure, whereas epoxy resin and polyurethane resin accurately reproduced details of 1 to 2 microns.

Time-dependent accuracy of elastomer impression materials. Part I: Condensation silicones

1. Although condensation silicone elastomers can be used to produce multiple dies from a single impression, one can expect changes in dimensions of dies produced from successive pours. 2. Putty/wash systems exhibit variable behavior among different brands. Some products produce a series of dies of increasing diameter over a 4-day period, while other brands may produce a series of dies whose diameters decrease as they are successively poured. 3. Light-body wash silicone impressions made in adhesive-lined custom acrylic resin trays produce dies which increase in diameter with time. 4. Putty/wash system, in general, show a greater eccentricity of dies than is seen with custom-tray/adhesive/wash systems, but there were some significant exceptions among the brands tested. 5. There does not appear to be any difference in behavior between single-wash and double-mix techniques in the condensation-silicone systems. 6. For maximum accuracy, the condensation-silicone systems should be poured as soon as possible after making the impression.

Quality of fixed prosthodontics after twenty-two years

After an observation period of 22 years, this study was conducted to clinically examine and interview patients who in 1984 and 1989 had participated in similar investigations regarding the quality, over time, of treatments with fixed partial dentures. The patients were examined by two standardized and experienced clinicians using the California Dental Association quality rating system, their results indicating that after 22 years the overall survival rates were 46.5% and 41.1% for the originally placed crowns and pontics, respectively. However, a continuing decrease of the crown quality rating was noted during the more than 20-year-long observation period. Restorative treatments with common types of fixed partial dentures can therefore be regarded as both safe and reliable over long periods of time.

Effectiveness of hardening films on die stone

1. Cyanoacrylate resins and resinous die hardeners effectively improved the hardness and abrasion resistance of stone dies. 2. Application of liquid resins followed by blotting and/or blowing with compressed air produced an improved surface without clinically significant dimensional change. The extent of film buildup was qualitatively related to the viscosity of the resin. 3. Application of multiple coats of resin or simply soaking the dies in resin without further blotting or other mode of removal of the excess produced a thick film which can obliterate surface detail.

A clinical method for the study of in-vivo adhesiveness of teeth.

For the present study a clinical method was developed to allow the direct or photographic recording of contact angles on solid surfaces within the oral cavity. This method, which was tested on four subjects, allows for relatively accurate and precise recordings of contact angles to be taken under relevant clinical conditions and without disruption of the surfaces in their normal state.