The International Journal of Prosthodontics, 02/1997

The color accuracy of resin composite cements and their corresponding try-in pastes was assessed. Three shades of three brands were compared using the cements alone and in contact with a standard porcelain disk. There were significant differences in color between resin cements and their corresponding try-in pastes. The addition of a 1-mm-thick porcelain disk greatly reduced the apparent color differences. The color of resin cements changed over time, but not significantly. Baseline measurements of resin cement colors were compared and measurements made after 24 hours of storage. Color changes were statistically significant but not perceptible, and all samples became slightly darker with age.

Frictional resistance to the dislodging forces of a removable partial denture with and without resin composite retrofitted guide planes was compared in vitro. Six master mod els of four natural teeth, each simulating a Kennedy Class III modification 1 arch, were used. Guide planes were prepared, and 18 cobalt-chromium removable partial denture frameworks without clasps were fabricated. Three resin composite materials were applied to the guide planes as retrofitting materials. Following this, the resistance to dislodgment of the removable partial denture framework was evaluated under cyclic dislodgment, and the resistance to dislodgment before and after resin composite retrofitted guide planes was compared. The dislodgment force was recorded every 500 cycles. Testing was concluded when the dislodging force value reached 50% of the initial val ue. There was a significant difference between the dislodging forces with and without retrofitted guide planes. Higher dislodging forces were recorded when resin composite retrofitted guide planes were used. Z100 was the most effective retrofitting material under cyclic dislodgment, and Heliomolar and Herculite XR performed similarly.

This in vitro study investigated the retention of the four differenct color-coded ERA attachments prior to and after various levels of fatigue loading (at baseline, at 500 cycles, and after every 500 cycles up to 5,500 cycles). Samples were placed in the Instron testing machine for determination of initial retentive values and then cycled in a specailly designed fatigue machine and retested. The results of this study demonstrated that although there are fuor different retentive elements supplied by the manufacturer of the ERA system, there were only two significantly different groups: (1) the white attachments and (2) the orange, blue, and gray attachments (P < .05). After 500 cycles, there was a loss in retention of 60% for the white, 60% for the orange, 56% for the blue, and 54% for the gray. After 1,500 cycles there was no difference in retentive values for any of the four colored attachments (P < .05). Microscopic examination of worn spcimens supported the findings of the fatigue testing.

The authors measured the precementation space achieved in vivo with varying layers of die spacer. Two hundred and ninety-one castings were fabricated in the Advanced Education Program in Prosthodontics at New York University College of Dentistry, New York, New York. Each of four clinician groups applied one layer of Taub Die Hardener and from one to four layers of die spacer to within 0.5 to 1.0 mm of the dies; finishing line. The resultant castings were adjusted using GC Fit-Checker. After final seating of the casting, the Fit-Checker was removed, sectioned buccolingually, and measured using a micrometer at three locations (midocclusally, midaxially, and on the bevel) for a total of 657 readings. Only after data collection were the specimens identified by group. Analysis of variance demonstrated a significance for group and location. Post hoc one-way analysis of variance and Sheffe tes ts (P < .1) demonstrated that: (1) one or two layers of die spacer demonstrated smaller precementation spaces than three or four layers; (2) the midocclusal precementation space was greater than the midaxial precementation space; (3) on the bevel area where no die spacer was used, the most consistent and minimal precementation space was measured.

The dual ion-exchange technique has been shown to improve the strength of feldspathic dental porcelains by first replacing constituent alkali ions with smaller ions above the strain point, and then exchanging the smaller ions for larger ions at temperatures below the strain point. The strength increase is directly related to the thickness of the surface-exchanged layer. This study evaluated the thickness of the exchanged layer after dual ion exchange of a leucite-reinforced dental porcelain. Optec HSP porcelain disks were fabricated, submitted to a dual ion-exchange treatment, and indented at various loads before determining the biaxial flexure strength. The mean flexural strength for the ion-exchanged groups was significantly higher than for control groups, except when the depth of the median crack exceeded 138 um. Wavelength Disp ersive Spectrometry analyses on cross sections shoed that the mean potassium amount in the glassy matrix was significantly lower (P < .001) for the treated specimens than for the controls. The mean thickness of the exchanged lay er after dual ion exchange was estimated at 140 um.

The effect of fiber reinforcement of autopolymerizing poly(met hyl methacrylate) was investigated. The impact strength of continuous E-glass fiber-poly(methyl methacrylate) composite was determined. Rectangular test specimens (n = 10 per group) were modified by incorporating an additional fiber reinforcement of untreated E-glass fibers, silanized E-glass fibers, or aramid fibers in the test specimens. Controls were either unreinforced or reinforced from the middle of the test specimen only. The impact strength of the specimens was measured by using a charpy-type pendulum impact tester after the specimens had been stored in water at 37 degrees C for 4 weeks. After the impact strength test, the length of the delamination of poly(methyl methacrylate) from the fibers was measured and plotted to the impact strength of the test specimens by using a linear regression model. The impact strength of unreinforced autopolymerizing poly(methyl methacrylate) was 7.8 kJ/m to the second power, while incorporation of glass fiber reinforcement with a fiber concentration of 12.4 wt% increased the impact strength to 74.7 kJ/m to the second power (P = .000). The additional fiber reinforcement of the test specimen did not affect the impact strength (P = .363). Delamination negatively correlated with the impact strength of the test specimens (r = -.72, P = .000). The results of this study suggest that glass fiber reinforcement enhanced the impact strength of autopolymerizing poly(methyl methacrylate), while the use of additional fiber reinforcement made of aramid or glass fibers in the test specimens did not have an effect on the impact strength.

This study reports the results of a long-term evaluation of conical crown-retained dentures. One hundred fifty-two restorations that had been in place for over 10 years were analyzed. Restorations were divided according to the Kennedy classification. Abutment and periodontal health, occlusion, retention, and frequency of relining and repair were among the factors evaluated. Good prognoses of removable partial dentures were shown in Kennedy Classes I, II, and III arches. However, some of the restorations placed on only a few remaining abutments showed rather unfavorable situations with almost all of the factors evaluated.

This study compared the effect that the introduction of mixed dentition alveolar bone grafting and subsequent orthodontic treatment has had on the prosthodontic/reconstructive habilitation of patients with unilateral cleft lip and palate. Two groups, each consisting of 40 consecutive patients with unilateral cleft lip and palate, were compared at the end of their dental treatment. In the group treated prior to the advent of bone grafting, all subjects received a fixed partial prosthesis in the cleft area, and a total of 87 abutment tee were prepared for complete coverage crowns. In contrast, in the group of patients for whom the alveolus was restored by bone grafting, it was possible to obtain a complete dental arch without prosthodontic intervention in 36 patients (90%). Thirteen subjects in the bone grafting group had the crown anatomy of anterior teeth modified using resin composite or resin-bonded porcelain veneers. Two patients had a premolar transplanted to the anterior region of the dental arch. On average the dental treatment was completed 3 years earlier in the bone grafting group. Thus, alveolar bone grafting with subsequent orthodontic treatment, together with advances in dental materials, have markedly reduced the need for prosthodontic procedures and have also allowed the completion of the dental treatment at an earlier age.

This study made an in vitro comparative evaluation of the color variation of four types of acrylic resin for provisional fixed prostheses, as determined using computerized spectrophotometry, before and after a 20- and 30-day cycle of immersion in four staining solutions. The four acrylic resins used for provisional fixed restorations were: Cold Pac, Trim, Protemp, and Mixacryl II. Thirty-two specimens for each resin were divided into four subgroups of eight elements, immersed in the four staining solutions (synthetic saliva, synthetic saliva and tea , synthetic saliva and coffee, and synthetic saliva nad chlorhexidine in 0.12% water solution), and then placed in to four thermostatic baths at 37 degree C ± 1 degree C. All specimens were measured for each resin before immersion (baseline). After 20 and 30 days, the specimens were analyzed by computerized spectrophotometry and compared. All data wer analyzed with analysis of variance for repeated measures (P < .05). Only the Cold Pac resin was color stable in all staining solutions, while the others shoed color changes from the different staining solutions.

One hundred twenty pressed feldspathic ceramic crowns were luted to 20 steel dies using six different cementation modes. Fracture resistance was tested under an angle of 45 degrees and was determined as the maximal fracture load. Crowns were tested with luting agent only (groups A and C) and after etching with hydrofluoric acid, silanating, and the application of a bonding agent (groups B, D, E, and F). The resulting means were: phosphate cement 294.3 (A) and 282.2 (B); glass-ionomer cement 217.2 (C) and 255.4 (D); resin composite 382.2 (E) and 687.6 (F). Statistical analysis revealed significantly greater fracture resistance (P < .01) of resin luted crowns. Bonding to the die almost doubled the fracture resistance. Conditioning of the inner surfaces of the crowns did not improve the fracture resistance of crowns luted using ainc phosphate or glass-ionomer cements.

The bond strength of six commercial soft denture liners was evaluated by a two-phase tensile test. The soft denture liners investigated were VinaSoft, Prolastic, Flexor, Molloplast-B, Novus, and SuperSoft. The samples were fabricated by processing them (1) against polymerized poly(methyl methacrylate), and (2) against unpolymerized poly(methyl methacrylate). The soft denture liners were processed according to the manufacturers' recommendations. The samples were tested using an Instron Universal Testing Machine. The mode of failure, adhesive or cohesive, was also recorded. The bond strength when processed against unpolymerized poly(methyl methacrylate) ranged from 0.48 to 2.60 MPa, and when processed against polymerized poly(methyl methacrylate) the bond strength ranged from 0.94 to 2.56 MPa. A two-way analysis of variance (P = .05) revealed a significant increase in bond strength when the liners were processed against polymerized poly(methyl methacrylate), except for Novus, which had no change, and VinaSoft, which decreased. The Tukey interval between materials was .22 and between methods of polymerization was .08. Four of the six liners investigated demonstrated increased bond strength when processed against polymerized poly(methyl methacrylate). It was concluded that bonding can be influenced by the processing method.

To evaluate the relationship between the complaints of complete denture wearers and alveoloar bone resorption as well as the location of mental foramina, 96 patients were interviewed. All subjects had received new dentures at the Uni versity of Iowa between August 1985 and July 1990. Panoramic radiographs had been made for all the subjects before dentures were fabricated. The amount of estimated ridge resorption correlated significantly with the number of years females had been edentulous, but no correlation was found in males. The location of the mental foramen in relationship to the crest of residual ridge correlated negatively with the number of years both genders were edentulous. Subjective need for dental treatment, as expressed by sore gums or poor or fair chewing ability, were the most frequent complaints among the subjects. These complaints were more often recorded with the subjects who had lost more than 50% of their estimated original ridge height than with htose with less than 50% resorption, but this difference was not significant.