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Biomedical subjects

G H Johnson

Publications and source records attributed to G H Johnson.

At least 19 recordsLinked to original sources
PubMed1992

Effect of admixed indium on properties of a dispersed-phase high-copper dental amalgam.

A new dental amalgam alloy containing admixed indium is available for clinical use. The purpose of this study was to conduct a full range of laboratory tests on two alloys containing differing amounts of admixed indium and on a similar alloy that did not contain indium. Results showed that less mercury was required to mix the alloys containing indium since admixed indium promotes wetting of the alloy. Back-scattered electron images showed the Ag-Hg matrix to be in good apposition to the Ag-Sn particles and to the Ag-Cu eutectic spheres, and there was no evidence of unreacted indium. The alloys containing admixed indium demonstrated improved resistance to creep and very little dimensional change upon setting. The early compressive strength was low for the alloys containing indium, but compressive strengths were significantly higher than those of the alloy without indium at 24 h and 7 d. Some improvement in resistance to marginal leakage and to corrosion was shown for the alloys containing indium.

American Dental Association↗
PubMed1992

Clinical performance of posterior composite resin restorations.

Two formulations of posterior composite resin (P-30 and Bisfil-P) were evaluated and compared to a high-copper, dispersed-phase amalgam (Dispersalloy). One hundred twenty-eight restorations were placed in 27 patients so that each patient received at least one of each material. After 3 years of clinical service, all three restorative materials produced clinically acceptable restorations, according to US Public Health Service and Leinfelder criteria. The amalgam restorations, however, underwent less wear (44 microns) than did the posterior composite resin restorations (60 to 74 microns). Stratification of data by type of tooth, class of restoration, and size of restoration produced the same ranking of wear from lowest to highest: Dispersalloy, Bisfil-P, and P-30. Resin restorations showed 45% more wear in molars than in premolars, and more wear was associated with moderately sized restorations than with conservative restorations. The surface texture of restorations of composite resin with porous strontium glass filler was nearly as smooth as that of enamel and was significantly smoother than that of the restorations of composite resin with zinc glass filler or of unpolished amalgam.

Analysis of Variance↗
PubMed1992

Clinical comparison of Class V resin composite and glass ionomer restorations.

Three techniques for restoring abrasion/erosion lesions were evaluated over a 2-year period: 1) glass ionomer restoration (Ketac-Fil); 2) composite restoration with a dentin bonding agent (Silux Plus, Scotchbond 2); 3) composite restoration with glass ionomer liner and a dentin bonding agent (Silux Plus, Vitrebond, Scotchbond 2). There were 116 lesions restored and 115 evaluated for color match, cavosurface discoloration, surface texture, caries development, and retention. Most restorations were rated clinically acceptable for color match, cavosurface discoloration, surface texture, and caries development when measured at 2 years. Glass ionomer restorations and composite restorations with a glass ionomer liner and a dentin bonding agent demonstrated better retention rates, 97.4% and 100% respectively, than the composite restorations with a dentin bonding agent only (86.8%) (Cochrane Q test, P = 0.07).

Aged↗
PubMed1992

Clinical evaluation of high-copper dental amalgams with and without admixed indium.

High-copper amalgam alloys containing 5% and 10% admixed indium, shown in previous studies to have improved properties and acceptable biological behavior, were evaluated in a clinical study designed to examine factors relating to clinical success. One hundred and seventy-five Class I and Class II amalgam restorations were placed in 25 patients. Each patient received all three dispersed-phase amalgams tested: without indium (Dispersalloy), with 5% indium (Indisperse 5), with 10% indium (Indisperse 10). After 30 months, 22 patients were recalled and 146 restorations evaluated. The margins of the indium-containing amalgam restorations incurred slightly less marginal breakdown, an effect that could be attributed to the addition of admixed indium and to the increase in silver-copper eutectic spheres which is found in these alloys. These amalgams also demonstrated a slightly darker appearance, and were slightly rougher than the non-indium-containing amalgam. These differences were minor; at 30 months, all restorations were well within the clinically acceptable range for each parameter evaluated.

Analysis of Variance↗
PubMed1991

An evaluation of dental stones after repeated exposure to spray disinfectants. Part I: Abrasion and compressive strength.

This study investigated the effect of repeated applications of spray disinfectants on gypsum surfaces. Types III and IV gypsum products were evaluated in combination with iodophor, acid glutaraldehyde, phenol, and water spray. Results demonstrated greater resistance to abrasion with increasing numbers of water or disinfectant spray applications. Acid glutaraldehyde spray decreased the compressive strength of type III stone by 26%, phenol increased the compressive strength of type IV stone by 18%, and iodophor had no significant effect on either stone relative to compressive strength.

Aerosols↗
PubMed1991

An evaluation of polishing agents for composite resins.

After the gross reduction and fine finishing of a composite resin restoration, selecting a system to create the smoothest polish is difficult because high magnification is necessary to compare the surface roughness. The surfaces of four anterior and posterior composite resins were compared using a Mylar strip, an unfilled resin as a glaze, polishing with three rubber polishers, and three different manufacturers' series of disks. This study suggested that pairing a specific composite resin with a matching polishing system produced the smoothest surface. Because of the differences in the size, shape, number of filler particles, and the type of resin, one system was incapable of creating the smoothest surface for all composite resins.

Acrylic Resins↗
PubMed1991

Marginal adaptation of castable ceramic crowns.

Tooth preparations and seating techniques of castable ceramic crowns differ from metal ceramic crowns. This study evaluated the variable effects of cementation on the marginal adaptation of Dicor, Cerestore, and porcelain-fused-to-metal crowns. The shoulder preparation was maintained for ceramic crowns, and a cavosurface bevel was designed for metal ceramic crowns. Crowns were made with a replication size of 10, placed on master dies, and the marginal openings measured with a Nikon Measurescope 20 instrument. Thirty crowns were cemented with zinc phosphate cement and the recommended clinical force. Marginal adaptation was not improved with a gingival bevel preparation or an increased seating force. The best marginal adaptation was recorded for Cerestore crowns.

Aluminum Oxide↗
PubMed1991

Clinical evaluation of direct esthetic restorations in cervical abrasion/erosion lesions: one-year results.

One hundred sixteen cervical abrasion/erosion lesions were restored with one of the following techniques: (1) glass-ionomer cement, (2) composite resin with a dentinal bonding agent, or (3) composite resin with a glass-ionomer cement liner and a dentinal bonding agent. The restorations were assessed at baseline and at 6 months and 1 year postrestoration for retention, caries, color match, marginal staining, and surface texture. No statistically significant differences were found in retention, caries, color match, or marginal staining. A statistically significant difference was found with regard to surface texture: glass-ionomer cement restorations demonstrated a rougher surface than did the composite resin restorations. A substantial number of restorations composed of composite resin with a dentinal bonding agent demonstrated a color shift towards mismatch when evaluated at 6 months. This difference was not significant at the 1-year followup.

Bisphenol A-Glycidyl Methacrylate↗
PubMed1990

The effect of immersion disinfection of elastomeric impressions on the surface detail reproduction of improved gypsum casts.

This investigation examined improved gypsum casts for surface roughness and line-detail reproduction after the immersion disinfection of elastomeric impression materials in an acid glutaraldehyde, an alkaline glutaraldehyde, and a phenol. Impressions were made of a surface roughness standard (Ra = 3.08 microns) that was custom made to include engraved grooves following American Dental Association specification No. 19. Mean surface roughness (Ra) values for all casts of all combinations of disinfectant treatments, impression materials, and improved gypsum stones were obtained with a surface analyzer. Untreated impressions served as controls. Data examined by an analysis of variance indicated that the addition silicone and polyether impression materials provided a surface roughness similar to the precision displacement specimen standard. The acid glutaraldehyde disinfectant demonstrated enhanced line-detail reproduction compared with the standard. Addition silicone and polyether impression materials combined with the acid glutaraldehyde provided the model system closest to the mean surface roughness of the reference standard. These combinations revealed differences in the surface roughness reproduction among the represented improved dental stones.

Calcium Sulfate↗
PubMed1990

The effect of tray selection on the accuracy of elastomeric impression materials.

This study evaluated the accuracy of reproduction of stone casts made from impressions using different tray and impression materials. The tray materials used were an acrylic resin, a thermoplastic, and a plastic. The impression materials used were an additional silicone, a polyether, and a polysulfide. Impressions were made of a stainless steel master die that simulated crown preparations for a fixed partial denture and an acrylic resin model with cross-arch and anteroposterior landmarks in stainless steel that typify clinical intra-arch distances. Impressions of the fixed partial denture simulation were made with all three impression materials and all three tray types. Impressions of the cross-arch and anteroposterior landmarks were made by using all three tray types with only the addition reaction silicone impression material. Impressions were poured at 1 hour with a type IV dental stone. Data were analyzed by using ANOVA with a sample size of five. Results indicated that custom-made trays of acrylic resin and the thermoplastic material performed similarly regarding die accuracy and produced clinically acceptable casts. The stock plastic tray consistently produced casts with greater dimensional change than the two custom trays.

Acrylic Resins↗
PubMed1990

Analysis of preoperative intracavitary cesium application versus postoperative external beam radiation in stage I endometrial carcinoma.

Two groups of patients with surgical Stage I endometrial carcinoma treated at the LDS Hospital in Salt Lake City are analyzed. Group 1 comprises 112 patients treated from 1974 through 1976, during which time preoperative intracavitary cesium was routinely used in all patients. Group 2 comprises 117 patients treated 1981 through 1983 under the treatment policy of hysterectomy without preoperative cesium. High risk patients from each group (grade 3 and/or deep myometrial invasion) generally received similar postoperative external beam pelvic radiotherapy (4500-5000 cGy). While 5-year actuarial disease-free survival rates were similar in each group (94% Group 1 vs 91% Group 2), multivariate analysis by the Cox Regression Method revealed that inclusion within treatment Group 2 carried independent adverse prognostic significance (p = 0.018). Other independent predictors of adverse 5-year disease-free survival included deep myometrial invasion and increasing histologic grade. Group 1 patients with grade 3 lesions had a superior 5-year actuarial disease-free survival (76% vs 53%) compared to those from Group 2. Group 1 patients with deep myometrial invasion also had a superior 5-year disease-free survival (84% vs 69%). The remaining low risk patients (grade 1 or 2, less than 1/3 myometrial invasion) had an excellent 5-year disease-free survival with or without preoperative cesium. Immediate preoperative intracavitary cesium was well tolerated, did not obscure pathologic findings and in our experience, reduced the probability of recurrence in high risk Stage I endometrial carcinoma patients.

Brachytherapy↗
PubMed1990

Preservation of all chordae tendineae and papillary muscle during mitral valve replacement with a tilting disc valve.

Mitral valve replacement was performed in 21 patients using a surgical technique that preserves the entire papillary muscle and chordal apparatus. With this technique, the anterior mitral leaflet is split from the center of the free edge toward the annulus. Bilateral incisions are made from the proximal end of this split to the two mitral commissures, detaching the anterior leaflet from the annulus. These two halves of the leaflet, with all chordae intact (corresponding to the anterolateral and posteromedial papillary muscles), are judiciously trimmed to remove areas of leaflet untethered by chordae tendineae and (when necessary) fibrous thickening; then swung posteriorly and sutured to the posterior mitral annulus using mattress sutures with pledgets. This surgical technique is expected to favor the preservation of left ventricular function and avoid occurrence of irreversible left ventricular dilation/dysfunction, and has been used successfully for calcific and degenerative etiologies, using both tilting disc valves and porcine bioprostheses. It is especially useful in the implantation of tilting disc and bileaflet mechanical prostheses because anterior subvalvular chordae tissue may interfere with the disc excursion and relocated to the posterior leaflet annulus.

Adolescent↗
PubMed1990

Sensitivity restored of Class V abrasion/erosion lesions.

The effectiveness of restorative treatment in reducing sensitivity associated with the Class V erosion/abrasion lesion was evaluated and the efficacy of three tooth-colored restorative materials in reducing sensitivity was compared. The 108 lesions were restored with either glass ionomer restorative material, composite resin with a dentin bonding agent, or composite resin with a dentin bonding agent and a glass ionomer liner. Composite resin with glass-ionomer liner restorations significantly reduced sensitivity to air and hot and cold water. Glass ionomer restorations and restorations with composite resin and a dentin bonding agent significantly reduced sensitivity but were also associated with increased sensitivity to air and cold respectively in 20% to 30% of the lesions restored when evaluated at 6 months.

Adhesives↗
PubMed1989

The accuracy and efficacy of disinfection by spray atomization on elastomeric impressions.

Five disinfectants applied by spray atomization were examined for possible dimensional distortion of elastomeric impression materials, polyether, polysulfide, and addition silicone, and the associated improved, type IV gypsum casts. The disinfectants did not affect, in a clinically significant manner, the three dimensions measured with an instrument accurate to 1 micron on improved gypsum casts that reproduced a stainless steel standard. The master cast represented two teeth of a fixed partial denture prepared for complete veneer retainers. The use of control casts from elastomeric impressions that were not treated with the disinfectants further supported previous investigations reporting the accuracy of dental casts as the function of the impression material. The use of a spray disinfectant will not appreciably alter the dimensional accuracy of improved stone casts made within elastomeric impressions. The most accurate stone cast system was produced by addition silicone impressions disinfected by a surface spray. It was also shown that four of the disinfectants applied by spray atomization were effective in disinfecting the surface of an elastomeric impression material contaminated with selected test organisms.

Aerosols↗
PubMed1989

Clinical evaluation of a nystatin pastille for treatment of denture-related oral candidiasis.

Nystatin has been formulated in the form of a flavored pastille (troche) as an alternative to the oral suspension. This parallel, double-blind, randomized, placebo-controlled study evaluated the acceptance and effectiveness of the nystatin pastille at two different dosages. Twenty-four subjects were selected on the basis of clinical signs of denture stomatitis and culture isolation of Candida spp. Each subject was randomly assigned to one of three treatment groups (A, 200,000 units; B, 400,000 units; and C, placebo). At entry, 7 days, 14 days, and at 10 days after cessation of treatment, the clinical condition was evaluated and Gram stain smears and imprint cultures were made and analyzed. The flavored pastille was well accepted by the subjects and both dosages were shown to be effective in significantly reducing or eliminating the Candida organism during active therapy. Data from the 10-day follow-up, however, demonstrated reinfection with the organism. Thus to resolve the condition, effective therapy must include treatment of the etiologic factors of denture stomatitis along with antimicrobial therapy.

Candidiasis, Oral↗
PubMed1989

A geriatric program in practice.

The geriatric patient represents an underutilized resource for the small animal practitioner. Thorough examination of the pet annually in detail allows detecting problems before they are too advanced. By using the systems approach to patient evaluation, one is better able to detect diseases and proceed with techniques to diagnose them. The use of in-house hematology and serum chemistry equipment benefits the pet and owner through rapid return of information and provides an added source of revenue for the practitioner. Developing and maintaining a system to reevaluate the geriatric patient is one of the most important aspects of a geriatric practice. Reminding clients that you care about their pet through routine scheduled evaluations develops loyal clients, which in turn generates additional hospital income.

Aging↗