Laminin and collagen IV distribution and ultrastructure of the basement membrane of the gingiva of the rat incisor

The continuous growth of the rat incisor is associated with renovation of the junctional epithelium and resorption of the periodontal ligament. The circumdental papilla separates the connective tissue suffering resorption from the rest of the gingiva. Laminin and collagen IV were detected by the immunoperoxidase technique on the basement membrane of all regions of the gingival epithelium of the rat incisor, except the internal basal lamina and the internal surface of the circumdental papilla. The internal basal lamina is formed by a granular electron-dense material, without the organization of a typical basal lamina. Areas of the internal surface of the circumdental papilla, negative for laminin and collagen IV, lack the basal lamina. These data suggest that these molecules are not components of the dento-epithelial junction of the distal surface of the rat incisor. In addition, the basal lamina is absent or fragmented on the internal surface of the circumdental papilla, adjacent to the areas of the connective tissue undergoing resorption.     

Scratch hardness and chipping of dental ceramics under different environments

OBJECTIVE: The goal of this program was to identify promising environments that could efficiently minimize machining-induced damage of dental materials. METHODS: Single point abrasion (SPA) scratch testing was used on five materials to determine the scratch hardness and amount of edge chipping as functions of chemical environment, including air, water, saline and glycerol solutions. Limited testing was also done under additional environments expected to promote chemomachining effects via crack growth promotion or debris removal. A conical diamond indenter and a conventional tungsten carbide machining tool were used in the scratch tests. One-way ANOVA analysis was used to determine statistical differences among the variables. RESULTS: There was a consistent trend across materials that the water and saline yielded the lowest values of scratch hardness, air the next lowest, and the tests performed in glycerol yielded the highest hardness values. The measured hardness values using the conical diamond tool in the glycerol environments were about twice the hardness values measured under water and saline solutions. Environmental effects on chipping were minimal, but a linear relationship between load and per cent chipping was determined for the WC tool within the 10-50 N test range. The choice of scratch tool strongly affected scratch hardness and chipping tendency. SIGNIFICANCE: The chemical environment had an effect on machining characteristics, but the effects were more dependent on tool interactions rather than material specific properties. As a result, it may not be possible to utilize a particular single environment to substantially improve the damage response of dental materials to machining operations. Improvements in damage resistance can be environmentally obtained, but only for shallow cuts (finishing operations).     

Evaluation of Stresses and Forces in Selected I-Bars Using the Finite Element Method

Purpose Three-dimensional models of half-round, tapered and full-round, untapered I-bar clasps of varying configurations and material properties were constructed. The purpose of this study was to examine the stresses and reaction forces produced within each model upon deflection to 0.01 in (0.254 mm), 0.02 in (0.508 mm), and 0.03 in (0.762 mm) at 1 mm from the tip using the finite element method. Materials and Methods Three-dimensional computer models of half-round and full-round clasps were constructed using solid eight-node brick elements. The half-round, tapered I-bar clasp model was 2.4 and 1.4 mm in diameter at the base and tip, respectively. The full-round, tapered I-bar clasp model was 1 mm in diameter. Three design groups were created for each clasp form. Group A had 25% of the total length in the straight anchor end of the I-bar clasp, B had 35%, and C had 50%. All models were 31 mm in length and had a radius of curvature of 5 mm. Different material properties were incorporated into the models. Each model was deflected at a point 1 mm from the tip to 0.01 in (0.254 mm), 0.02 in (0.508 mm), and 0.03 in (0.762 mm). Results The stresses and forces produced as a result of the deflection applied to each clasp were viewed and displayed graphically. The maximum von Mises stresses in megapascals and the reaction force in newtons (N) were recorded. Stresses varied in each clasp in the range of 0 to 154.3 MPa for the half-round, tapered I-bar clasp models, and 0 to 100.9 MPa for the full-round I-bar clasp models at 0.01-in deflection. Reaction force measured near the tip of the clasp models was between 1.60 N and 6.31 N for the half-round, and between 0.22 N to 2.13 N for the full-round I-bar clasp models. For all clasps studied, as the deflection increased, the location of stress within each group remained the same regardless of the material properties; however, the stress and force values increased linearly. Conclusions The location of maximum stress varied with the length of the anchor portion of the clasps studied. Maximum stresses were located on the flat side of the half-round, tapered I-bar clasp model.     

Effect of root canal filling material and level of surgical injury on periodontal healing in dogs

Abstract— Some divergencies in the literature about periodontal healing after surgical injury stimulated the development of this experiment. The root canals of dogs' teeth were negotiated and filled by the lateral condensation technique with two kinds of sealers: Sealapex and zinc oxide-eugenol cement. In the second session, the bone tissue was exposed and one cabity was made at the apical third of the root and another at the border between the coronal and middle thirds, both penetrating into the root canal. Six months later the animals were sacrificed and the specimens prepared for histopathologic analysis. The results showed that the kind of filling material and the level of the periodontal wound exposing the root canal can influence the healing process ( P <.01).     

An evaluation of commercial pastes for finishing composite resin surfaces

A study was conducted to determine the effectiveness of several commercial pastes in polishing the surfaces of composite resin material. Five samples of Concise composite resin contained within Plexiglas block holders were prepared using Mylar matrices. One block was disked only; three blocks were disked and polished, each with a different paste. The remaining block was the control. The surface roughness of all samples was measured with a stylus profile instrument. Five extracted teeth were prepared in the same manner with Concise composite resin and Mylar strip matrix. In each tooth, the surface was finished by disking only or by disking followed by polishing with one of three pastes. The fifth tooth was the control. The samples were examined by use of a scanning electron microscope. Quantitative evaluation of over-all computer data indicated that the smoothest surface was found immediately ater removal of the Mylar matrix and that pastes leave a rougher surface than is left with a disc.     

Dental Public Health for the 21st Century: Implications for Specialty Education and Practice

A panel of public health practitioners sponsored by the Health Resources and Services Administration met December 6–8, 1994, to examine current roles and responsibilities for dental public health workers and to recommend changes in education and training to meet challenges posed by an evolving health care system. Overall, at least the same number, if not more, dental public health personnel will be needed in the future. While some new roles were identified, the panel felt that only small numbers of personnel will be needed to fill these new roles. Not all of these roles necessarily require a dental degree. The panel felt that a need exists for more academicians for dental schools, schools of public health, dental public health residencies, and dental hygiene programs; oral epidemiologists and health services researchers; health educators; and specialists in utilization review/outcomes assessment, dental informatics, nutrition, program evaluation, and prevention. To meet these personnel needs: (1) dental public health residency programs should be structured to meet the educational needs of working public health dentists with MPH degrees through on-the-job residency programs; (2) the standards for advanced specialty education programs in dental public health should be made sufficiently flexible to include dentists who have advanced education and the requisite core public health courses; (3) flexible MPH degree programs must be available because of the rising debt of dental students and the decreased numbers of graduating dentists; (4) loan repayment should be available for dentists who have pursued public health training and are working in state or local health departments; and (5) standards for advanced education in dental public health should be developed for dental hygienists.     

Root surface conditioning with nicotine or cotinine reduces viability and density of fibroblasts in vitro

The purpose of study was to evaluate fibroblast attachment and cellular morphology on root surfaces chemically conditioned with nicotine or cotinine. A secondary objective was to determine if mechanical scaling and root planning of these chemically conditioned surfaces would alter cellular attachment. Root surface dentin specimens were prepared from uniradicular teeth of non-smoking patients. Specimens were randomly assigned to two experimental groups: no treatment (chemical conditioning only) and scaling and root planning after conditioning (SRPC). The concentrations of the tested substances were in the range of 0–1 mg/mL (nicotine) and 0–1 ?g/mL (cotinine). After a 24-h conditioning period, dentin slices were incubated with continuous lineage of fibroblastic cells from rat (McCoy cells) for another 24 h. Specimens were prepared for SEM analysis and microphotographs. The statistical analysis of the data indicated significant alteration of cellular morphology on fibroblasts that were grown on root surface exposed to nicotine concentrations greater than 1 ?g/mL. This effect of nicotine was not reduced by SRPC. On the other hand, in the SRPC group cellular density was greater. For cotinine-conditioned specimens, the greater concentrations also led to alteration on morphology, and these alterations were observed in the SRPC group as well. Cotinine did not induce significant changes on cellular density. The results indicated that fibroblasts are negatively influenced by nicotine present on the dentin substrate and also that scaling may reduce these effects. Cotinine treatment on root surfaces may alter cell morphology and density but these effects were less severe than that promoted by nicotine, and were not affected by scaling.     

Internal setting expansion of a dental casting investment measured with strain gauges

A study was undertaken to investigate the feasibility of using strain gauges to evaluate the internal setting expansion of dental casting investments. A strain gauge was invested in the center of a casting ring to determine the linear setting expansion at the site of the wax pattern. The findings suggest that strain gauges can be used to measure setting expansion internally more accurately than volumetric or external surface measurement techniques. It was also found that winged strain gauges were more stable in the investment than wingless strain gauges.     

Commissure Burn Splints: Literature Review and Prefabrication Technique Using a Visible Light–Cured Resin

Commissure burn splints reduce or eliminate the need for reconstructive surgery after injury to the perioral tissues. The literature describes the injury, immediate care, and splint treatment modalities. A technique to construct a prefabricated commissure burn splint from visible light cure resin and orthodontic wire is presented. Passive or dynamic retraction may be obtained by varying the tension of circumcranial orthodontic headgear or adjusting Velcro placed on a Velfoam strap.