Flexural strength of composites: influences of polyethylene fiber reinforcement and type of composite

MAIN PROBLEM: The microfill veneering of hybrid composite restorations has been indicated to improve esthetics. Also, polyethylene fiber reinforcement has been proposed for use in composite restorations in high-stress clinical situations. However, minimal information in the literature addresses the influence of such combinations on the resistance to fracture. The purpose of this study was to investigate the flexural strength of two composites, a microfill and a hybrid, the effect of their combination, and the influence of polyethylene fiber reinforcement. MATERIALS AND METHODS: Twenty-eight specimens were prepared using a standard metallic mold (20x2x2 mm) and divided into groups of seven each: Filtek Z-250 (3M ESPE, St. Paul, Minn., USA) (group I), Filtek A-110 (3M ESPE) (group II), Filtek Z-250 combined with Filtek A-110 (group III), and Filtek Z-250 combined with polyethylene fiber (Ribbond, Seattle, Wash., USA) (group IV). The specimens were stress-loaded to fracture in a three-point bending device according to International Standardization Organization (ISO) 4049. RESULTS: Data were analyzed using analysis of variance and Tukey's test at a 0.05 level of significance. No statistically significant differences were observed between groups I and IV. Group II, however, exhibited statistically lower resistance to fracture than the other groups. Group III presented intermediate results, showing statistically higher fracture resistance than group II but lower than group I. CONCLUSIONS: With the methodology employed, microfill composite presented the lowest flexural strength, but its association with hybrid composite increased the resistance to fracture. The combination of polyethylene fiber and hybrid composite did not present higher flexural strength than hybrid composite alone.     

Alumni perspectives on community-based and traditional curricula

In 1994, the University of Medicine and Dentistry of New Jersey-New Jersey Dental School (UMDNJ-NJDS) launched the Community-Oriented Dental Education (CODE) program. The CODE program provides senior dental students the opportunity to spend four days per week providing dental care in a community-based clinic. A survey of graduates of CODE (n = 55) and randomly selected graduates of the traditional curriculum (n = 110) was conducted via mail to determine attitudes relating to community service (CS), community-based learning (CBL), reasons for participating in their clinical program, perceived levels of clinical preparedness at graduation, and practice choices. A total of 111 surveys (66.9 percent) were returned to NJDS, with 84.6 percent of CODE alumni responding and 59.0 percent of traditional alumni (TA) responding. Of the 111 surveys returned, sixty-five (58.6 percent) were completed by TA, and forty-six (41.4 percent) were completed by CODE alumni. There were no differences among CODE and TA regarding attitudes toward CS and tendency to practice in underserved areas or to accept Medicaid payments. There were, however, some differences in attitudes toward CBL, reasons for applying or not applying to the CODE program, perceived impact of clinical education on graduates' preparedness, views of the extent to which the programs encouraged students to choose public or private areas of practice, and perceptions of how the desire to help communities influenced career and practice decisions. Some of these findings may be useful to schools as they plan extramural education programs.     

Hydrolytic stability of experimental hydroxyapatite-filled dental composite materials.

OBJECTIVES: The purpose of this study was to analyze the behavior in water, related to mechanical properties, of experimental composites for dental restoration. METHODS: The studied materials were composed of a visible-light-curing monomer mixture (Bis-GMA and TEGDMA or HEMA) and micrometric, nanometric or a mixture of both sizes hydroxyapatite particles as a reinforcing filler. Filler particles were modified with a coupling agent (citric, hydrosuccinic, acrylic or methacrylic acid or silane). The hydrolytic stability of the evaluated materials was studied through total elution and water-uptake tests. Percent net-mass variation was daily monitored and analyzed as a function of time. Mechanical performance was examined through flexural properties and Vickers hardness. Morphological surface changes were observed with scanning electron microscopy. ANOVA statistical analysis was performed (P<0.05). RESULTS: In general, the use of HEMA instead of TEGDMA did not substantially worsen the composite quality. Dental composites containing only nanometric particles of hydroxyapatite as a filler are unsuitable for clinical performance. Midway-filled composite resins loaded with micro-HAP particles, coated with citric, acrylic or methacrylic acid displayed low percent elution and water-uptake values. Mechanical properties were similar or even superior to those measured for silane treated particles. SIGNIFICANCE: More research is needed to further improve the interaction of nano-HAP particles with the polymeric matrix, either as a single filler or, preferentially, mixed with micro-HAP, that will allow to increase the total loading of reinforcing filler and, hence, to improve the mechanical properties.     

Capacity for training in clinical research: status and opportunities

The ability to base patient care on scientific evidence depends in part on the results of translational and applied research. The shortage of trained clinical researchers identified by several sources limits the availability of clinical research studies upon which to base evidence-based therapeutics. This premise suggests that the dental profession needs to train more clinical researchers and faculty to conduct clinical research and to teach its applications to practice. Increasing opportunities for clinical research training in a variety of settings should eventually increase the numbers of clinical researchers, raise faculty involvement in clinical research, and promote science transfer. This paper reports on the current status of clinical research in dental schools, specifies the diverse groups involved in the clinical research enterprise, and identifies underutilized opportunities and partnerships for clinical research training. Data on federal and nonfederal funding of clinical research and training programs are presented. Existing and novel mechanisms for expanding clinical research training throughout and across traditional as well as unconventional environments are explored.     

Visual-tactile examination compared with conventional radiography,digital radiography,and Diagnodent in the diagnosis of occlusal occult caries in extracted premolars

PURPOSE: This laboratory study compared visual-tactile examination with conventional radiographs, digital radiographs, and laser fluorescence in the detection of occlusal occult caries on extracted premolar teeth. METHODS: Extracted premolars without obvious caries or restorations were collected from school dental clinics. Occlusal surfaces of 320 extracted premolars were examined visually with an explorer, then examined using the KaVo Diagnodent unit and scored using specific criteria. The teeth were exposed using conventional and digital radiography, respectively. The radiographs were assessed for dentin radiolucencies beneath the occlusal surface. RESULTS: Of the 320 teeth used in this study, 302 were scored as sound by visual-tactile examination. Of these, 57 (19%) demonstrated dentin radiolucency on conventional bite-wings, and 245 (81%) were scored as radiographically sound. Thus, the sensitivity and specificity values of the visual-tactile examination compared with conventional radiography were 81% and 44%, respectively. In contrast, Diagnodent produced results of 82% sensitivity and 36% specificity when compared with conventional radiography. When compared to digital radiography, the sensitivity and specificity values of the visual-tactile examination were 90% and 44%, respectively. In contrast, when compared to digital radiography, Diagnodent showed a very low specificity of only 32%, although sensitivity was still high at 91%. Differences in specificity among the techniques were statistically significant (P < .03), whereas differences in sensitivity were not (P > .01). CONCLUSIONS: Although the diagnosis of occult dentinal caries may be further enhanced by the Diagnodent, a combination of visual-tactile examination and either conventional or digital radiography should identify over 80% of lesions.