Lingual changes in ageing mice by light- and scanning electron-microscopy

Tongues from young, old and senescent Swiss-Webster white mice were compared. Sections and tissues were taken from the anterior, posterior, and ventral regions. The epithelium became atrophic and hyperkeratotic in the senescent animals. The filiform papillae were blunted, atrophic and disorganized across the entire dorsal surface in the older animals. The ventral aspect in the senescent animals had thinning epithelium, a hyperchromatic germinal layer, and a roughened, disorganized surface.     

Electron microscopic observations of the saliva-dependent aggregation of oral streptococci.

Cells of Streptococcus sanguis strain H7PR3 or Streptococcus mitis strain 26 aggregated in the presence of clarified whole saliva. Electron micrographs revealed the presence of two types of extracellular structures which were not detected in sections of control cells that were incubated without saliva, or in non-aggregating preparations in which cells were mixed with saliva plus ethylenediaminetetraacetate (EDTA). The sanguis-aggregating factor consisted of a round, globular component as well as an asymmetrical, fibrillar unit. The mitis factor appeared only as a globular structure. The dimensions and shapes of the aggregating factors were consistent with their known high molecular weights and, also, with the appearance of some of the intercellular matrix constituents of whole plaque.     

A virtual reality dental simulator predicts performance in an operative dentistry manikin course

This study was designed to test the ability of a virtual reality dental simulator to predict the performance of students in a traditional operative dentistry manikin course. Twenty-six dental students were pre-tested on the simulator, prior to the course. They were briefly instructed and asked to prepare 12 class I cavities which were automatically graded by the simulator. The instructors in the manikin course that followed were unaware of the students' performances in the simulator pre-test. The scores achieved by each student in the last six simulator cavities were compared to their final comprehensive grades in the manikin course. Class standing of the students in the simulator pre-test positively correlated with their achievements in the manikin course with a correlation coefficient of 0.49 (P = 0.012). Eighty-nine percent of the students in the lower third of the class in the pre-test remained in the low performing half of the class in the manikin course. These results indicate that testing students in a dental simulator, prior to a manikin course, may be an efficient way to allow early identification of those who are likely to perform poorly. This in turn could enable early allocation of personal tutors to these students in order to improve their chances of success.     

A new tricortical implant

We wish to introduce a new type of implant intended for use in the posterior maxilla when only 8 mm or less of the resorbed alveolar ridge is present, without the need for sinus lift procedures or ridge augmentation. The implant is called "Excalibur" and will be available in varying lengths with either an internal or external hex. The implant is supported at three points in the cortical bone due to the use of an apically positioned screw, which passes through the implant and the buccal and palatal cortices at 90 degrees to the long axis of the implant. The bicortical screw is inserted via a minimal full thickness flap or through a small incision in the gingiva at the proposed point of placement. The additional stability provided by this screw allows for immediate loading at the time of implant placement. In comparative tests with regular implants, the "Excalibur" was found to be far more resistant to forces applied to the implant resulting in far less stress on the neck of the implant, which was shown on the finite element modeling. Two clinical cases are presented: 1) Excalibur implants were placed in the posterior maxilla and four months after the surgical procedure the permanent prosthetic rehabilitation was completed. 2) Excalibur implants were placed at the time of extraction, with an immediate temporary acrylic bridge. Permanent prosthetic rehabilitation was begun four months later.     

Validated numerical modeling of the effects of combined orthodontic and orthognathic surgical treatment on TMJ loads and muscle forces.

Investigations of the changes in the mechanics of the craniomandibular system as a result of treatment have been limited by the lack of validated models of this system. The aims of this project were to (1) validate numerical model predictions of temporomandibular joint (TMJ) eminence morphology and muscle forces produced during molar biting and (2) use the validated models to calculate the changes in TMJ and muscle forces as a consequence of treatment involving orthognathic surgery. Ten volunteers participated; their combined orthodontic and orthognathic surgical treatments were completed. Three-dimensional anatomical data from each subject were used in computer models to predict the sagittal TMJ eminence morphology and joint and muscle forces for each subject, consistent with the neuromuscular objectives of minimizing joint loads and muscle effort. The actual shape of the eminence in each subject was measured with jaw tracking. Surface electromyographic recordings were a measure of the muscle forces involved in static molar biting. Model predictions were compared with measured data from the subjects for eminence shape (R(2) = 0.96) and for muscle activity ratios (R(2) = 0.98). The strength of these relationships validated the models for use in calculating changes in joint loads and muscle forces after treatment. The results suggested that the mechanics of the masticatory system are affected by the combined treatments. The TMJ loads increased in 8 subjects. The average increases in condylar and muscle forces were 4% relative to the applied bite force, but in 1 case the increases were up to 20%. Therefore, although average increases in the forces were small, some persons may experience biologically significant increases in joint and muscle forces as a result of treatment.     

Porous bovine bone mineral in healing of human extraction sockets: 2. Histochemical observations at 9 months

BACKGROUND: Porous bovine bone mineral (PBBM) has been used in ridge preservation procedures following tooth extractions. The aim of this study was to investigate histochemically tissue sockets grafted with PBBM at 9 months post-extraction. By using different histochemical stainings, characteristics of the newly formed bone; i.e., lamellar/woven ratio at different socket depths, were investigated and the arrangement of bone around the grafted material, as well as the nature of the amorphous organic material found in all specimens, were examined. METHODS: After extraction of 15 single-rooted maxillary teeth from 15 patients, socket sites were grafted with PBBM particles (250 to 1,000 mu). Primary soft tissue closure of the grafted site was established using the rotated split palatal pedicle flap technique. At 9 months, a cylindrical tissue specimen, 2.5 mm in diameter, was trephined from each previously grafted site followed by placement of a screw-shaped implant. Horizontal tissue section cuts, 5 mu wide, were prepared for histological examination. Histochemical staining included alcian blue, periodic-acid Schiff, Mallory trichrome, reticulin, Van Gieson, and picrosirius red (PSR). PSR stained slides were further evaluated morphometrically, using polarized microscopy to determine the amount of lamellar versus woven bone in superficial, mid and deep specimen section cut areas. RESULTS: All staining methods revealed that newly formed bone encircled and adhered to the grafted material in most specimens. Mallory trichrome staining showed osteoblasts present within an osteoid layer, lining the interface zone of PBBM particles and the new osseous tissue. Morphometric evaluation of the PSR stained slides disclosed a constant pattern of increased osseous tissue in a coronal-apical direction. An average of 17.1% osseous tissue with 1:12.9 lamellar/woven bone ratio was calculated in the superficial area. The average bone tissue fraction was 48.3% with a lamellar/woven ratio of 1:3.8 in the mid section area and in the deep area, it increased to 63.9%, with a lamellar/woven ratio average of 1:1.7. Differences between ratios at these sites were statistically significant (P<0.001). An amorphous organic substance was noted in most grafted particles. This material usually attached cell striae and harbored glycoproteins as revealed by periodic-acid Schiff and alcian blue stainings. Mallory trichrome staining showed denatured protein within the decalcified mineral particles; reticulin, Van Gieson stainings, and polarization of PSR stained sections refuted the existence of collagen in the grafted particles. CONCLUSIONS: Cancellous PBBM is a biocompatible filler agent in extraction socket sites and an acceptable graft for edentulous ridge preservation at sites prepared to receive endosseous implants. The osteoconductivity of PBBM was determined based on promoting osseous ingrowth and close integration with the newly generated bone. Grafted particles were not significantly resorbed at 9 months. Further studies are needed to determine the resorbable capability, as well as the nature and significance of the amorphous organic substance of PBBM observed in the grafted particles.     

Follicular gastritis associated with Helicobacter pylori

In order to understand the pathogenesis of gastric lymphoma, we investigated the association of H.pylori infection with lymphoid follicular hyperplasia. Eighty-four gastric specimens removed for gastroduodenal ulcer were histologically examined. The distribution and prevalence of H. pylori, neutrophilic and lymphocytic infiltration, mucosal atrophy, intestinal metaplasia, and lymphoid follicles were scored. The lymphoid follicles were more frequently observed in H.pylori positive cases. They indicated a positive correlation with the score of H. pylori. When follicular gastritis (FG) was defined as a case in which the secondary lymphoid follicles (Lf2) numbered two or more per one centimeter of mucosa in the pyloric gland area of the lesser curvature, twenty specimens out of the 84 (24%) fit that definition. All of the FG cases were H.pylori positive, and they displayed high H. pylori scores. It was supposed that most FG cases would ultimately lead to atrophic gastritis, whereas H.pylori would gradationally decrease or disappear in accordance with the aging and progression of intestinal metaplasia. The histological features of the FG cases, however, were similar to the background mucosal state of early-stage MALT-type gastric lymphoma. We may conclude that H. pylori infection is one cause of the FG, which may be a high-risk condition that gives rise to MALT-type gastric lymphoma.     

Influence of mixing disinfectant solutions into alginate on working time and accuracy

Possible transfer of pathogens from dental surgery to dental laboratory is of concern to the profession. This study investigates changes in the working time and accuracy of an alginate impression material when mixed with solutions of selected disinfectants rather than water. The results indicate that certain disinfectant solutions, when used as a water substitute, do not modify the working time of the alginate investigated beyond acceptable limits and have no significant effect on the dimensional accuracy of that material. The use of a 0.2 per cent solution of chlorhexidene gluconate is recommended as a water substitute for the alginate investigated.