A comparison of the wear resistance and hardness of indirect composite resins.

STATEMENT OF PROBLEM: Various new, second-generation indirect composites have been developed with claimed advantages over existing tooth-colored restorative materials. To date, little independent research has been published on these materials, and the properties specified in the advertising materials are largely derived from in-house or contracted testing. PURPOSE: Four second-generation indirect composites (Artglass, belleGlass, Sculpture, and Targis) were tested for wear resistance and hardness against 2 control materials with well-documented clinical application. Human enamel was also tested for comparison. MATERIAL AND METHODS: Twelve specimens of each material were fabricated according to the manufacturers' directions and subjected to accelerated wear in a 3-body abrasion, toothbrushing apparatus. Vickers hardness was measured for each of the tested materials, and energy dispersive x-ray (EDX) spectroscopy was performed to determine the elemental composition of the composite fillers. The statistical tests used for wear and hardness were the Kruskal-Wallis 1-way ANOVA test with Mann-Whitney tests and 1-way ANOVA with multiple comparisons (Tukey HSD). The Pearson correlation coefficient was used to determine the existence of a relationship between the hardness of the materials and the degree to which they had worn. The level of statistical significance chosen was alpha=.05. RESULTS: The control material Concept was superior to the other composites in wear resistance and hardness and had the lowest surface roughness. Significant relationships were observed between depth of wear and hardness and between depth of wear and average surface roughness. Enamel specimens were harder and more wear resistant than any of the composites. EDX spectroscopy revealed that the elemental composition of the fillers of the 4 new composites was almost identical, as was the composition of the 2 control composites. CONCLUSION: The differences in wear, hardness, and average surface roughness may have been due to differences in the chemistry or method of polymerization of the composites. Further research in this area should be encouraged. It was also apparent that the filler present in the tested composites did not exactly fit the manufacturers' descriptions.

A multicenter longitudinal clinical trial of a new system for restorations.

STATEMENT OF PROBLEM: A new method for fabrication of crowns and fixed partial dentures (Procera system) that involves electric discharge machining and copy milling has been developed. The metal used is unalloyed titanium, which can be processed as a single coping or multiple units joined to a pontic by laser welding. PURPOSE: The single-unit coping or the fixed partial denture (FPD) substructure is then veneered with a low-fusing porcelain. MATERIAL AND METHODS: In this article the clinical application of this technique was evaluated by six major universities in the United States. A total of 114 patients participated in this study, which involved 126 restorations (55 maxillary and 71 mandibular prostheses). There were 179 abutments, of which 73 were crowns and 53 were three-unit FPDs. Surface and color, anatomic form, and margin integrity were assessed 1 month after cementation and at 1 year with the California Dental Association (CDA) quality assessment evaluation system. RESULTS: No statistically significant differences in CDA scores between the 1 month evaluations and the 1 year assessments were found for surface and color (p = 0.68), anatomic form (p > 0.99), or margin integrity (p = 0.57). By use of the lowest ranking in the three categories as the overall quality of the restoration, only 3.3% (two crowns and two FPDs) were not acceptable at the 1-month visit and 4.5% (two crowns and three FPDs) were not acceptable at the 1-year evaluation. At-the 1-month visit 96.6% (114) of the restorations were considered to be satisfactory, whereas 95.5% (107 restorations) were evaluated similarly at the 1-year evaluation. CONCLUSIONS: The Procera system demonstrated, by use of the CDA criteria, its capability to produce quality prostheses that were rated satisfactory more than 95% of the time after insertion and maintained this high rating at least for 1 year.

Advanced education in prosthodontics.

1. The ADA Council on Dental Education Commission on Accreditation, using the Standards for undergraduate education and current National Board scores, does not believe there has been a deemphasis in prosthodontic knowledge and skill. This opinion is not shared by program Directors or representatives of the laboratory industry. The Council on Dental Education has a mechanism for periodic review in place. State Boards of Dental Examiners did not respond. 2. Teaching experience for residents or graduate students should be encouraged in advanced education programs in prosthodontics as an elective or be limited to no more than 10% of the curriculum time. 3. The American Board of Prosthodontics would not comment on any changes regarding the clinical or didactic knowledge of candidates. 4. Meaningful research is not possible within the current minimum 22-month program duration. 5. Accredited advanced education programs in prosthodontics are currently meeting the standard guidelines for clinical and didactic experiences. 6. Accredited advanced education programs in prosthodontics are currently satisfying the requirements on supervision and faculty; however, the data from the annual reports suggest a marked decrease in staff support and amount of time that program directors are devoting to the program. 7. Expanding the curriculum to include implant prosthodontics will require lengthening the curriculum time. 8. TMJ therapy and geriatric dentistry need to be better defined in the educational guidelines. 9. The criterion-based examination currently given by the American Board of Prosthodontics clearly delineates acceptable, marginal, and unacceptable levels of performance. 10. Program directors desire more "feedback" from the American Board of Prosthodontics on the performance of candidates.(ABSTRACT TRUNCATED AT 250 WORDS)

Facial surface coil for MR imaging.

A local-reception counter-rotating-current coil for magnetic resonance imaging at 1.5 T was developed. It consists of two parallel coaxial racetrack-shaped loops. The planes of the loops are orthogonal to the surface of the body, and the space between the loops is open. The separation between the loops allows the device to fit over the nose and mouth for oral-maxillofacial imaging without the threat of occlusion to the patient's air passages. The sensitivity of this coil is similar to that of conventional surface coils of the same dimensions. The two active current elements conform to other anatomic objects including the eyes and anterior portion of the neck.

Clip attachment for the mandibular staple implant.

A technique for making the staple implant superstructure has been described, which is simple, economically reasonable, and readily replaced with a minimum of difficulty. The procedure reduces both clinical and laboratory time compared with the use of precision attachments and ceramometal restorations. The size of the Rider clip generally allows sufficient space for the proper arrangement of denture teeth and the development of acceptable external contours of the prosthesis.

Effect of two clasping assemblies on arch integrity as modified by base adaptation.

(1) Altering clasp design can affect the way forces act on abutment teeth. (2) An RPI clasp design causes less distal displacement of the primary abutment tooth than circumferential clasp arms with a distal rest under the same conditions. (3) Forces applied on a mandibular distal-extension base will have a greater affect on the abutments on the same side of the arch than on crossarch abutments. (4) The influence of changes in clasp design is minimized when the bases are well adapted to the basal seat and fully extended.

Influence of tooth p roprioception on speech articulation.

Based on an analysis of the data obtained, the following conclusion can be made: 1. Time used to pronounce /S/ is increased for patients when their prostheses are not being worn. 2. There is a decrease in formant frequency when pronounciation of /S/ takes place without the prosthesis in place. 3. The amount of time span increase was less for overdenture group than for the complete denture group; the drop of formant frequency was not as greater as that of the complete denture group. 4. The precision of speech movement for the production /S/ is affected by the presence of tooth proprioception.

Prosthetic teachers: number and qualifications for undergraduate education.

A proposal has been made regarding the number and qualifications of undergraduate educators. To place this proposal in the proper perspective, certain philosophies, objectives, and methodologies of the teaching-learning experience were identified. These, of course, are partially unproven, conceptual innovations. The need exists to better qualify students in prosthodontics before they are graduated from a dental school. Unfortunately, schools seem to be taking a negative position on this problem. What better way to control a group than to govern the education of the individuals concerned.