The International Journal of Prosthodontics, 03/1994

The effectiveness of a newly developed anti-cross contamination device for a dental air-turbine handpiece was tested. The handpiece with or without the anti-cross contamination device was contaminated with two bacterial strains, Staphylococcus aureus and Streptococcus mutans, as well as two bacteriophage strains, T2 and MS2. After contamination with these microorganisms, the handpieces were disinfected with glutaraldehyde or replaced with newly autoclaved ones. Residual microorganisms inside the handpiece or an air/water supply hose line were collected and counted after overnight cultivation. The anti-cross contamination device effectively reduced the contamination level of an air-turbine handpiece to that of the negative control. No microbial contamination in the air/water supply hose line was detected with this device.

Stainless steel dies, simulating 0 to 80 microns of die spacing, were seated into a machined brass crown with Phosphacap, Panavia EX, and C & B Metabond. The seating discrepancy after 60 seconds was measured to determine the optimal cement space for best seating for each agent. The most complete seating for crowns luted with zinc phosphate cement was observed when at least 40 microns of cement space was provided. C & B Metabond and Panavia required 30 microns of die spacing.

The effect of increasing the occlusal vertical dimension on the mandibular postural relation was studied for eight subjects. Interocclusal rest space measurements were made weekly for 1 month prior and subsequent to increasing the occlusal vertical dimension by 3.5 to 4.5 mm interincisally using luted acrylic resin, complete-arch, fixed partial dentures. Interocclusal rest space measurements were made at the clinical rest position, which was established by requesting the subjects to close in maximum intercuspation and immediately relax their mandible. Interocclusal rest space measurements were also made at the more open resting position when the subjects were repeatedly instructed to relax and lapse into a semi-hypnotic condition termed elaxed resting posture. Initial speech difficulties and muscle discomfort subsided after 1 to 2 weeks. Analysis of variance using repeated measures showed no significant difference in interocclusal rest space after increasing the occlusal vertical dimension for both clinical rest position and relaxed resting posture. A significant difference was found between clinical rest position and relaxed resting posture (P = .001), and no interaction was determined between clinical rest position, relaxed resting posture, and time.

The purpose of this study was to demonstrate the ability of Kubelka-Munk reflectance theory to predict color parameters of veneer porcelain on various backings using colorimetric measurements. Tristimulus absorption and scattering coefficients were used to predict the respective tristimulus reflectance values of A1, D3, and translucent porcelain samples after they had been bonded to light and dark substrates using universal, opaque, and untinted shades of bonding resin. Observed and predicted reflectance values exhibited high correlation (r2 > or = 0.93 for each porcelain shade). Kubelka-Munk theory offers an accurate prediction for the resultant colorimetric reflectance parameters of veneer porcelain bonded to variously colored backings.

Current American Dental Association infection control guidelines recommend immersion disinfection of irreversible hydrocolloid impressions, and this study further defines the parameters for use of sodium hypochlorite. Sodium hypochlorite has been shown to be an effective disinfectant for impressions; however, it has not been fully evaluated for optimum immersion time and concentration. In this study, irreversible hydrocolloid impressions contaminated with different bacteria were immersed in varying concentrations of sodium hypochlorite for 1, 5, or 10 minutes. Dilute solutions of sodium hypochlorite (0.525% or 0.0525%) produced a 4-log10 (99.99%) reduction in colony-forming units of Staphylococcus aureus, Salmonella choleraesuis, or Pseudomonas aeruginosa after 1 to 5 minutes' immersion. Full-strength sodium hypochlorite (5.25%) required 5 minutes to produce a 4-log10 reduction of Bacillus subtilis. A 4-log10 reduction of Mycobacterium bovis was not obtained under any conditions examined.

The finite element method was used to model a 4.0 x 13.0-mm IMZ implant restored with a cast gold crown to examine the relationship between deflection of the prosthetic superstructure and stress concentrations in the retaining screw using both the polyoxymethylene intramobile element and the analogous titanium element under various loading conditions. A strong correlation was observed between the peak stresses in the screw and the deflection of the superstructure. Deflections and stress concentrations generally increased with increases of either the load magnitude or the load angle. Greater deflection and stress concentrations within the coronal retaining screw were predicted with the use of the resin IME than with the titanium element.

This study compared the dimensional accuracy of impressions and dies made from a metal model simulating prepared abutments and having gingival sulci of varying widths. Measurements of the abutments, impressions, and stone dies were made using a travelling microscope, and the number of defects in each impression was recorded. The impressions and dies made from abutments with narrower sulci showed greater distortions. Analysis of variance and the Fisher PLSD post hoc test indicated significant differences between the group having a sulcular width of 0.08 mm and the groups having larger sulcular widths for the impressions and for the dies (P < .05). The large coefficient of variation occurring groups having 0.08-, 0.13-, and 0.18-mm sulcular widths demonstrated the difficulty of consistently obtaining good impressions of abutments having such narrow sulcular widths. Between 50% and 90% of abutment impressions having sulcular widths of 0.08 and 0.13 mm had defects.

The purpose of this study was to determine stress corrosion fatigue characteristics of Optec-hsp porcelain. Disks (1 mm thick and 12 mm in diameter) were prepared according to the manufacturer's firing recommendations. Samples were subjected to dynamic loading at multiple constant stressing rates. Dynamic fatigue was measured using a biaxial flexural strength test in a circulating bath. Inert strength was determined in a moisture-free environment. The mean fracture strength for the dry (moisture-free) samples was 167.9 MPa. Linear regression analysis of log fracture strengths vs log time to failure was performed to obtain fatigue parameters. For Optec, the n-value was 26 (SE 1.9) and sigma f0 was 91.3 MPa (SE 1.2 MPa).

The tensile strength of connectors joining bars of palladium-silver alloy and formed using hydrogen/oxygen flame soldering was compared to those formed using conventional gas/oxygen soldering. As-cast specimens served as the control. No significant differences were found between the as-cast, hydrogen/oxygen flame soldered, or the natural gas/oxygen flame soldered specimens.

To investigate the effect of malocclusion on mandibular movement during speech, the Sirognathograph Analyzing System was used to analyze the form of the envelope of motion during speech, as well as the relationship between the envelope of motion and eccentric movement paths, in 10 normal subjects and 60 subjects having malocclusion. Location of the envelope of motion, and the relationship between the envelope of motion and eccentric movement paths, were closely related to specific malocclusions. It is suggested that analysis of the envelope of motion during speech has diagnostic value in speech function assessment and that its detailed analysis offers valuable information for diagnosis and initiation of dental treatment.

The difference in stress distribution in the bone around dental implants was determined under conditions where either two or four implants were placed in the interforaminal region of the mandible. The purpose was also to determine the influence of the height of the mandible on the stress distribution. The stress distribution around the implants was investigated using three-dimensional finite element models of the interforaminal region of two mandibles with two different stages of resorption. It was concluded that there is no reduction of the extreme principal stresses when the load is distributed over an increasing number of implants. There is a tendency for a gradual stress increase as mandibular height decreases.

Aluminum is one type of metal base material used as an alternative to acrylic resin. This study evaluated whether commonly used denture cleansers cause leaching of the metal base into the cleaning solution. Seven cleansers (Efferdent, Polident, Clorox, Clorox/Cascade, vinegar, Tartar and Stain Remover, and Ivory soap) and two controls (tap water and distilled water) were evaluated. One hundred thirty-five wax samples (30 x 30 x 1 mm) were cast in 99.4% pure aluminum. The 135 samples were randomly assigned to the nine cleanser groups. Each sample was soaked in a cleanser for 0.5, 1, or 8 hours, and the amount of aluminum present in each cleanser was then analyzed by atomic flame-emission spectrometry. The results indicated that all cleansers leached aluminum into solution in varying amounts. Tartar and Stain Remover and Clorox caused the greatest leaching, whereas Ivory soap and Efferdent leached the least.