The International Journal of Prosthodontics, 04/1991

This study was conducted to determine the effectiveness of a silicone disclosing medium, G-C Fit-Checker, as an aid in the improvement of marginal integrity. Standardized preparations were made on 42 freshly extracted premolars. Base metal alloy castings were finished externally and initially adjusted internally. The castings were placed on their respective teeth and the marginal opening was determined. They were then adjusted twice using the silicone material and remeasured. The preadjustment mean marginal opening was 92 microns and the postadjustment measurement 55 microns, yielding a mean reduction of 37 microns (SEM 3 microns) or 39%.

The authors previously reported on the strengthening effect of a thin Ni-Cr plate on an acrylic resin test specimen in the three-point bending test. This study evaluated the reinforcement of acrylic resin denture bases by measuring the strain distribution in the palate of a maxillary complete denture. It was found that this reinforcing technique led to a uniform distribution of strain in the palatal area of the maxillary denture and a reduction of strain in the midpalatal area.

In vitro measurements were made of the heat transferred to the pulp chamber during the direct fabrication of extracoronal provisional restorations. The temperature was monitored for the following four groups: (1) control - the provisional restoration was left on the tooth with no coolant used; (2) removal - the provisional restoration was removed upon initial resin polymerization; (3) in situ - the provisional restoration was left in place and cooled with an air/water spray; and (4) on/off - the provisional restoration was repeatedly removed and replaced upon initial polymerization while using an air/water spray. The intrapulpal temperature rises were as follows: control 7.08 degrees C, removal 2.39 degrees C, in situ 2.36 degrees C, and on/off 3.12 degrees C. The temperature rise for all cooling techniques was significantly lower than that of the control. No significant differences were found between the three cooling techniques.

Prosthodontic patients are generally a high-risk group relative to their potential to transmit infectious diseases as well as acquire them. There has been a recent increase in awareness of the need for cross-infection control measures to protect against possible routes of transmission frequently ignored in the past. This article is essentially a literature review of cross-infection control measures especially relevant to removable prosthodontic practice. Cross-contamination control measures are considered within the following categories: patient evaluation, personal protection, instrument and equipment contamination, clinical technique, impression handling, and laboratory asepsis.

The use of methyl methacrylates for cranial repairs has been well established. Procedures for sterilization of these materials include soaking in benzalkonium chloride, use of ethylene oxide gas, or cobalt 60 irradiation. Although ethylene oxide sterilization is the most common method, gas sterilization and degassing of these prefabricated implants may require almost as much time as fabrication. This study evaluated impact strength and linear dimensional change following steam autoclave sterilization of heat-processed methyl methacrylate. It was compared to an autopolymerizing methyl methacrylate for impact strength. No statistical difference was found in impact strength between nonsterile heat-processed methyl methacrylate and autoclaved heat-processed methyl methacrylate; however, both were significantly stronger than the autopolymerizing material. A statistically significant linear dimensional change of 1.211% between the autoclaved and nonsterile heat-processed methyl methacrylate was found, but was not considered clinically significant.

The restoration of anterior teeth for patients with excessive vertical overlap is often complicated by a lack of space for restorative materials. This situation often occurs in patients with worn anterior teeth. Two methods of creating adequate space to permit satisfactory restoration are presented.

While gold alloys are well accepted for metal ceramic restorations, the increasing cost of gold has limited their use. This study investigated the loss of a noble alloy during the fabrication of metal ceramic crowns. Weight losses resulting from (1) the casting process and cleaning of the casting, (2) sprue removal, (3) seating of the casting onto the die, and (4) preparation for porcelain addition were investigated using 323 crowns. The percentage weight losses were 8.92%, 17.59%, 34.03%, and 39.46%, respectively. Weight losses were generally higher for maxillary restorations, but metal ceramic restorations on anterior teeth registered significantly higher losses than those for premolars and molars.

The current proliferation of light-polymerized denture base resins and the continual modification of their formulations make standardized biocompatibility testing a necessity. The biocompatibilities of three light-polymerized denture base resins were compared using an in vitro epithelial cell culture system. The effect of varied lengths of polymerization of denture base resin on cell toxicity was examined. This study indicated that light-polymerized denture base resins have an effect on oral epithelial cells that appears to be related to the specific formulation of the material and not to the type of polymerization required. Varying the polymerization time or light-polymerization unit appeared to have little effect.

The current proliferation of light-polymerized denture base resins and the continual modification of their formulations make standardized biocompatibility testing a necessity. The biocompatibilities of three light-polymerized denture base resins were compared using an in vitro epithelial cell culture system. The effect of varied lengths of polymerization of denture base resin on cell toxicity was examined. This study indicated that light-polymerized denture base resins have an effect on oral epithelial cells that appears to be related to the specific formulation of the material and not to the type of polymerization required. Varying the polymerization time or light-polymerization unit appeared to have little effect.

Ten healthy young adults were examined for changes in occlusal contacts related to three head positions: supine, sitting, and head forward. The contacts were analyzed using T-Scan special research software, which measured the time moments of the first five occlusal contacts. Time moment is a descriptive term calculated from a formula that considers both spatial (where contacts are) and temporal (when contact occurs) aspects of tooth contact and provides a quantitative basis for comparing the dynamics of tooth contact. Paired head positions were analyzed for differences using Student's t test, and it appears that in healthy young adults, initial tooth contacts are substantially influenced by posture.

Following in vitro inoculation with C albicans or P aeruginosa, three impression materials - polysulfide rubber, irreversible hydrocolloid, and poly(vinyl siloxane) - were disinfected with either 0.1% or 0.02% chlorhexidine gluconate and a quantitative assessment of the microorganisms was made. Very few microorganisms were retained on the poly(vinyl siloxane) material immediately after microbial inoculation. The numbers of microorganisms on polysulfide impression materials diminished rapidly with time even without disinfection, and a 30-minute disinfection procedure resulted in total microbe elimination. With irreversible hydrocolloid, microorganisms persisted and disinfection procedures were considerably less effective. When the disinfection efficacy of three commercially available agents was compared using irreversible hydrocolloid impression material, chlorhexidine gluconate (0.2%) was found to be less effective than either glutaraldehyde (2%) or sodium hypochlorite (0.0125%); the latter two agents were comparable in their antimicrobial effect. Thus, a simple disinfection regime of 30 minutes with commonly available disinfectants may be effective in eliminating cross-contamination from impression materials.

A fixed-volume drop of liquid between a pair of parallel surfaces has been a common model for the denture-mucosa system. The reported one-term equation for the model, the derivation of which is suspect, implies that the acting force is inversely proportional to the square of the separation. Direct measurement of the force, however, showed that a better approximation is given by a two-term equation, with force varying as the inverse of the separation. The need for rigorous theoretical derivation is thereby emphasized. The experimental data suggest that a maximum retention force might occur for denture bases at separations of about 15 microns.