Quantification of leucite concentration using X-ray diffraction.

OBJECTIVES: This study sought to evaluate the efficacy of using an X-ray diffractometer for the determination of leucite in Finesse, Ceramco II, and IPS Empress porcelains. METHODS: An internal standard, copper, was used. Two quantification methods are presented: (1) the generation of a calibration curve using peak height ratios; and (2) the generation of a calibration curve using peak area ratio. RESULTS: The leucite concentration obtained from the peak height versus concentration calibration curve was observed to be statistically different from leucite concentration obtained from the peak area versus concentration calibration curve. Other information obtained from X-ray powder diffraction include the lattice parameters and volume of the unit leucite cell. SIGNIFICANCE: The leucite contained in the dental porcelains (Finesse, Ceramco II, and Empress) has expanded a-lattice spacings and contracted c-lattice spacings relative to standard leucite. These changes in the lattice parameters resulted in a net expansion of the leucite cell volume.

Effect of varying fixture width on stress and strain distribution associated with an implant stack system.

The purpose of this investigation was to evaluate the dissipation of a force applied to an assembled stack of implant components. The stack consisted of a 10-mm threaded implant, a screw-retained abutment and a screw-retained gold crown. The dissipation of force was analyzed in relation to varying the implant diameter with and without a concomitant change in abutment diameter. Two experimental groups were evaluated. The first group consisted of 25 titanium screw-form implants (Implant Innovations, Inc.). These implants measured 10 mm in length and 3.25 mm, 3.75 mm, 4.0 mm, 5.0 mm, and 6.0 mm in diameter. The second group included 15 titanium screw-form implants (Nobel Biocare, Inc.) measuring 10 mm in length and 3.75 mm, 4.0 mm, and 5.0 mm in diameter. All implants were embedded in standardized photoelastic resin blocks. Points of interest were marked on each block using standardized templates to ensure consistency. Implants were restored using system-specific conical abutments and standardized single-unit restorations. A strain gauge was affixed to each abutment, and an eccentric load of 176 N was applied to the restoration. Periimplant stresses were measured using photoelastic analysis. Abutment strain was determined using an electronic strain indicator. Data were collated and compared using ANOVA and the Duncan multiple range statistical tests. When stress was analyzed at points on the resin-implant interface or a fixed distance from the interface, stress tended to decrease from the 5-mm-wide implant to the 6-mm-wide implant. Stress in relation to the 3.25-mm, 3.75-mm, and 4.0-mm implant was not as well defined, indicating the possibility that some deformation of implants was occurring. Increased abutment width resulted in decreased abutment strain. Therefore, using a wider abutment may be helpful in preventing preload reduction in clinical applications. This may reduce the incidence of loosening and fracture of abutment and restoration screws.

An investigation of new metal framework design for metal ceramic restorations.

STATEMENT OF PROBLEM: Metal ceramic restorations have been implicated in the discoloration of associated gingival tissues. Attempts to remedy this by altering the design of the metal frameworks for such restorations may lead to unacceptable decreases in fracture resistance. PURPOSE: This study evaluated a new metal framework design for metal-ceramic restorations. MATERIAL AND METHODS: Twenty artificial crowns were fabricated with various degrees of facial metal reduction; 0, 1, 2, and 3 mm. The study was conducted in two parts. The first part evaluated changes in light transmission into adjacent root tissue. A light box was fabricated so sample crowns could be illuminated on a mounted natural tooth. The root of the tooth remained outside the light box, and the light transmitted through the crowns into root tissue was measured with a light meter. The second part of the study evaluated changes in fracture strength. The sample crowns were subjected to a vertical load until fracture with use of an Instron machine at a crosshead speed of 1 mm per minute. The load at fracture was recorded. RESULTS: Results indicated a statistically significant increase in light transmission with 1 mm framework reduction or greater, and fracture strengths did not decrease with up to 1 mm of framework reduction. A 1 mm facial axial reduction of the metal framework may be indicated for anterior metal-ceramic restorations.

Directly placed esthetic restorative materials--the continuum.

Because new restorative materials have had little clinical testing, it is difficult to make specific material recommendations for the esthetic restoration of carious teeth. Although fluoride-releasing materials have long been used successfully to restore carious teeth, little clinical documentation has been presented to support their use to inhibit recurrent caries, and their use as an effective restorative material may be questioned. Glass ionomers, compomers, and resin-modified glass ionomers are esthetic fluoride-releasing materials designed to restore teeth by bonding to tooth structure. This article describes the continuum of directly placed esthetic dental restorative materials, the efficacy of amalgam replacement restorative materials, and the role that fluoride-releasing materials may play in the inhibition of recurrent caries in vitro and in vivo.

Gypsum compatibility of antimicrobial alginates after spray disinfection.

PURPOSE: This investigation examined the gypsum compatibility of two antimicrobial alginates after spray disinfection. Subjective compatibility evaluations were compared with objective quantitative profilometer readings of gypsum cast surface roughness. MATERIALS AND METHODS: COE Hydrophilic Gel Alginate, Jeltrate Plus, Antimicrobial Alginate, and their nonantimicrobial counterparts, Coe Alginate and Jeltrate Plus, were used in this study. After spray disinfection with water (control), Alcide LD, Biocide, OMC II, and 0.5% NaOCI, impressions of the American National Standards Institute/American Dental Association (ANSI/ADA) specification no. 18 detail reproduction die and impressions made simultaneously of a smooth glass die were cast in Microstone, Silky-Rock, and Die-Keen. Five specimens were made for each alginate/disinfectant/gypsum combination for a total of 300 samples each for both the subjective and objective analyses. For the subjective analysis of gypsum compatibility, the specimens made from the ANSI/ADA specification no. 18 test die were evaluated by using a 1-to-4 visual rating system at magnification x12. For the objective analysis, the arithmetic average surface roughness of each specimen made from the smooth glass die was recorded three times with a 200-mg skidless stylus instruments. RESULTS: The results of the ANSI/ADA specification no. 18 testing for gypsum compatibility showed that 11 of 60 possible combinations did not pass the test. All impressions made with nonantimicrobial COE Alginate passed the test regardless of the disinfectant/gypsum combination. The results of the three-factor analysis of variance for the subjective and objective analyses showed significant interactions between alginates, disinfectants, and stones at the P < .05 level. To further delineate these differences, unpaired t tests (P < .05) within brands for each disinfectant/gypsum combination were performed. CONCLUSIONS: The addition of 1% chlorhexidine diacetate to COE Hydrophilic Gel Alginate has decreased its compatibility with the dental stones and disinfectants tested when compared with its nonantimicrobial counterpart. In terms of gypsum compatibility, the nonantimicrobial COE Alginate was compatible with all disinfectant and gypsum combinations tested. The addition of 1.70% didecyldimethyl ammonium chloride to Jeltrate Plus Antimicrobial Alginate has increased its compatibility with all the dental stones tested. A strong positive correlation (r = 0.7398) was found between visual gypsum compatibility evaluation scores and surface roughness of gypsum casts.

Mercury in solution following exposure of various amalgams to carbamide peroxides.

Carbamide peroxide (CP) is an easily administered material for whitening teeth. Although toxicological research on CP alone has revealed no adverse health effects, possible oxidation and release of mercury from amalgams have not previously been investigated. This research evaluated the quantitative release of mercury from amalgams into solution by CP. CP preparations can generally be divided into two classes based on the presence or absence of carbopol, an oxygen-releasing inhibitor. Rembrandt (R), a 10% CP with carbopol and White and Brite (WB), a 10% CP without carbopol were used in this study. Four different types of amalgams [Dispersalloy (D), Sybraloy (S), Tytin (T) and Valiant Ph.D. (V)] were selected. Uniform samples of the four amalgams were prepared and stored at 37 degrees C for 1 week. Vials of saline (10 ml), R and WB were prepared. R and WB were mixed with saline to a 50:50 solution to reduce viscosity and facilitate stirring. Magnetic teflon coated stir bars were placed in all vials, and one amalgam specimen was placed in each non-control vial. After being stirred for 8 hours, solutions were analyzed for elemental mercury content using a Jerome Gold Film Mercury Analyzer. All background mercury levels were zero, but following the experiment there were significantly higher amounts of mercury in the CP solutions as compared to the 100% saline solutions. These results suggest there is an active oxidation of the amalgam releasing mercury ions into solution.

Dimensional stability of a mark made in a photoplastic wafer as a function of time.

This study investigates in vitro the dimensional stability of the Vishay's mark as a function of time. The Vishay was placed between a hardened, 1/2 inch diameter steel ball and a flat tungsten carbide cutting tool blank in an Instron testing machine. A compressive force of 10 pounds applied, and three separate marks made within the photoplastic wafer. The mark was displayed as a 10x image on the Vishay analyzer's monitor. The image was photographed, along with a standard, using a 35 mm camera tripod setup. To evaluate stability of the marks, photographs were taken at 1 hour, 1 day, 3 weeks, and 2.25 years after indentation. Each mark's image was measured three times with a Sigma-Scan digitizing software and reduced to real dimensions. The three marks were treated as a block and time as four repeated measures. An ANOVA was used to compare the mark sizes at these times. The four means across time were not significantly different (P = 0.34). Both Greenhouse-Geisser, and Huynh-Feldt epsilon correction factors for repeated measures were 0.34 which resulted in an adjusted significance level of 0.36. This indicates unequal correlations from one time to another, but does not affect the insignificant differences of these means. The Vishay photoplastic wafer can store mark size for at least 2.25 years in vitro.

The effect of trituration time on the mechanical properties of four high-copper amalgam alloys.

Several manipulative variables have been shown to influence the physical properties of dental amalgam. Variation in trituration time has been reported to affect creep, compressive strength, and diametral tensile strength in various amalgams. Recent classification of amalgam alloys by particle microstructure reveals four categories: single-composition lathe-cut; single-composition spherical; lathe-cut and eutectic admixture; and lathe-cut and single-composition spherical admixture. The effect of variation of trituration times has not been studied for these newer high-copper alloys. A representative from each classification was selected and physical properties tested, with varied times for trituration utilized. Results showed little compromise in laboratory values for the properties tested. Additional laboratory and clinical trials are warranted, but this study supports the premise that clinicians may vary trituration time to improve handling characteristics without significantly affecting mechanical properties.

Enamel reduction and the bond strength of resin-bonded retainers.

The authors investigated the shear bond strength of etched enamel retainers bonded to enamel reduced by different amounts. The depth of reduction in this study had no influence on bond strength.

Comparison of tinidazole given as a single dose and on 2 consecutive days for the treatment of nonspecific bacterial vaginosis.

Nonspecific bacterial vaginosis, defined as the presence of clue cells, was treated in a randomized, double-blind study with (1) tinidazole 2 g as a single dose (82 patients), (2) tinidazole 2 g on 2 consecutive days (84 patients), and (3) with placebo (81 patients). The cure rates, both clue cells and Gardnerella vaginalis absent, were 51, 74 and 4%, respectively. A closer clinical and microbiological evaluation showed the 2-day regimen to be superior.

An investigation of shear bond strengths of various resin-bonded inner surface rest seat designs for removable partial dentures.

Results and conclusions that can be drawn from this study are: All smooth, mesh, and seating preparation groups produced mean bond strengths significantly greater than that of the control group (p less than 0.01). The cast mesh rest seats exhibited significantly greater bond strengths at 24 hours (p = .0072). However, at 30 days, statistically significant differences between the three groups were not evident. Mean bond strengths for the electrolytically etched rest seat groups increased significantly at 30 days compared with the 24-hour means (p less than .05). These results suggest that an electrolytically etched resin-bonded rest seat can easily withstand the functional stresses exerted by a removable partial denture. The incorporation of seating preparation on an abutment tooth for an etched resin-bonded lingual rest seat seems to offer no advantage in terms of retentive strength.

The influence of contamination on the bond strength of an etched resin-bonded retainer.

This investigation examines the influence of potential sources of contamination on the resin bond strength of a base metal alloy. Sixty specimens were cast in a base metal alloy and etched. Composite resin cylinders were bonded to six groups of ten specimens each and tested for shear bond strength using a testing machine at a strain rate of .5 mm/min. Five of the test groups received a different set of treatments, and one of the test groups was a control group. An analysis of variance disclosed no significant differences in bond strengths among any of the test groups at a level of P less than .05.