The International Journal of Prosthodontics, 03/1996

Sodium hypochlorite is one of the disinfectants recommended for impressions, usually in a 1:10 dilution to minimize the negative effects on the impression material and poured gypsum cast. Dilution causes a loss of antimicrobial properties, however. Sodium hypochlorite is known to have enhanced antimicrobial properties at lower pH levels. This study evaluated the antimicrobial activity of sodium hypochlorite at progressively lower pH levels. A metal model of a dental arch was contaminated, and irreversible hydrocolloid impressions were made, cultured, disinfected (by immersion), and cultured again. Predisinfection and postdisinfection bacterial counts were compared. It was found that a 10-minute immersion in solutions reduced to pHs 7 to 11 consistently produced a 4-log (99.99%) or greater reduction in viable organisms. A pH of 10 was the only level that was consistently effective at decreased immersion times. It was effective in times of 3 minutes or greater.

Lowering the pH of sodium hypochlorite has been shown to greatly improve its efficacy as a disinfectant for irreversible hydrocolloid. This study evaluated the surface roughness and detail reproduction of gypsum casts recovered from impressions disinfected with sodium hypochlorite at altered pH levels. The experimental disinfectants were sodium hypochlorite 0.525% (10-minute immersion) at pH 11.5 (unaltered), pH 10, and pH 8. An additional group was tested at pH 10 for 5 minutes. There was a trend toward increased surface roughness as the pH was lowered, but a 5-minute immersion of impressions in sodium hypochlorite at pH 10 produced casts of equivalent surface roughness to impressions rinsed in water and poured immediately. The test for surface detail reproduction produced similar results.

Cross-sectional and longitudinal studies have identified that persons wearing overdentures require regular care and maintenance of the remaining dentition. This paper reports on a longitudinal study of the periodontal problems of 254 patients seen over a period of 12 years. At overdenture placement, baseline measurements and photographs were made by a single examiner. These measurements included evaluation of the restorations; abutment height above the gingival margin measured at midmesial, middistal, midfacial, and midbuccal; and periodontal probing depths measured at the same four sites. Oral hygiene and denture status were also evaluated. Patients were asked to return at 6-month intervals for evaluation using similar indices. Plaque and calculus were a common finding, especially in the mandibular arch. Serious periodontal problems were not common; however, it was clear that a high-risk group existed in this population. Bleeding on probing proved to be the most reliable clinical predictor of periodontal problems.

This study evaluated the effect of pH on Porphyromonas gingivalis lipopolysaccharide (LPS) affinity for polymethyl methacrylate, polyethyl methacrylate, and polyethyl and polyisobutyl methacrylate resins. Specimens were exposed to 1,010 endotoxin units LPS in potassium phosphate buffer at pH 6, pH 7, or pH 8. Control specimens were incubated in LPS-free water. Sequence I evaluated LPS uptake and release from resin when exposure and elution pH were identical, whereas Sequence II evaluated LPS release from resin when elution pH differed from exposure pH. A slightly acidic pH decreased LPS affinity for all resins compared to pH 7. A slightly alkaline pH increased LPS affinity for the polyethyl methacrylate resin but decreased LPS affinity for the others compared to pH 7. The pH may affect resin-LPS affinity by altering LPS molecular charge.

A technique is presented for fabricating an esthetic, cast glass-ceramic pontic for the partial veneer-retained fixed partial denture. After the framework is waxed to full contour, the pontic is sectioned from the remainder of the wax pattern and cut back on the occlusal, proximal, and lingual aspects. A cast glass-ceramic pontic is then fabricated. The pontic is returned to the master cast to complete the wax pattern for the type IV gold fixed partial denture superstructure. The pontic is fitted and then luted to the gold framework using an adhesive resin cement. The lost wax technique ensures a pontic with precise, anatomic form that restores proper contours and relationships. Additionally, this esthetic and durable pontic for partial veneer fixed partial dentures encourages conservative tooth preparation and promotes restorative materials that minimize wear of the opposing dentition.

All-ceramic restorations can solve many esthetic problems associated with implant-supported prostheses. This study evaluated stress concentration and distribution in implant abutments under normal masticatory forces using computer simulations. Two-dimensional finite element analysis was used to study four different abutment-restoration combinations using Branemark implants. The models considered two positions of the fastening screw, two positions of the crown margins, cemented versus screw-retained prostheses, and clinical loads of 200 N. Models having screws on top of abutments had the lowest stresses (3.1 to 4.8 MPa) and best stress distribution. Screw-retained prostheses and short crown margins increased overall stresses (9.9 to 11.4 MPa).

This investigation was conducted in an effort to elucidate the mechanism of the strengthening that occurs during processing of a heat-pressed dental ceramic (IPS Empress). The effect of processing on leucite content was determined via quantitative x-ray diffraction. A significant effect of processing was revealed by analysis of variance (P .0001). Post-hoc comparisons by Student-Neuman-Keuls and Duncan's Multiple Range tests revealed no difference in leucite content after perssing, but the leucite content was significantly higher (P .05) after a single surface colorant firing. A second colorant firing produced a further significant increase in leucite content (P .05), but no further increase in leucite content was observed following the remaining colorant and glaze firings. The increase in leucite after firing is consistent with the increase in flexural strength following firing observed by Dong et al in 1992.

Dentists and denture wearers have reported that the regular use of a denture cleanser causes whitening of dentures. The whitening effect of denture cleansers on acrylic resin dentures was investigated using four different types of agents on six different types of acrylic resin discs. The color values of the samples were measured using a reflectometer. The greatest whitening effect was seen on autopolymerizing acrylic resins for one of the denture cleansers with all the resins tested.

This prospective study analyzed the time and costs involved in fabricating implant prostheses in private practice and the factors affecting prosthesis design. Esthetics was the most commonly reported factor influencing the decision to use a fixed or removable prosthesis, while cosgt was infrequently cited. The single-tooth fixed implant requierd the least time to fabricate and had the lowest clinical fees, while the removable bar/clip prostheis had the highest fees and demanded the greatest amount of time to fabricate. Single-tooth fixed and individual attachment removable prostheses generated approximately half the hourly income produced by multiple-unit fixed and bar/clip removable implant prostheses, and the individual attachment design had the highest ratio of expenses to income.

This in vitro study evaluated the bond strength of metal frameworks cast using Ni-Cr, Ni-Cr-Be, Cu-Al, type IV gold, and noble metal ceramic alloy with and without tin electroplating. The castings were luted to human teeth using Panavia Ex resin. It was found that tin electroplating had a negative effect for theCu-Al and type IV gold alloys and a positive effect for gold for metal ceramic restorations. The best results were obtained using the Ni-Cr alloy.

Border molding is an important step in the fabrication of complete dentures. Conventional border molding using impression modeling plastic has been time-consuming and has resulted in a great variation in the shape of the recorded borders. This study compared the shape and variability of the vestibular impressions made with impression modeling plastic and a polyether impression material. Four prosthodontists each made five maxillary vestibular impressions using the two materials. All the impressions were made on one edentulous subject. The results showed significant differences at many locations along the border of the impressions. The borders of the impressions made with modeling plastic tended to be thicker and shorter than those made using polyether material. Use of the polyether material required less time to complete the border molding procedures and demonstrated a more consistent result in the shape of the vestibular impressions.

Osteoporosis is the most common metabolic disease and presents a major public health problem among the elderly. This retrospective pilot study was designed to determine the strength of association of spinal bone density and the density of selected mandibular sites as determined from panoramic radiographs. Panoramic films of known low bone density and high bone density women between the ages of 50 and 75 were evaluated. These films were randomized and then converted to digital images for density analysis. Significant differences were noted between the groups at the 95th percentile. Further study is needed to ascertain the value of panoramic radiology as an adjunct diagnostic tool in the screening of patients thought to be at high risk of developing osteoporosis.