Symphysis menti of the rabbit: anatomy, histology, and postnatal development.

A histologic and anatomic investigation of the symphyseal region in rabbits did not reveal a bony fusion between the two halves of the mandible; these two bones are united in the anterior part by a synchrondrosis, and a definite histologic suture with interdigitating bony rugosities and interposed connective tissue, in the posterior part. Functionally, the two parts are immobile and thus constitute one bone.

Effect of hydrogen peroxide and sodium perborate on the microhardness of human enamel and dentin.

The effect of 30% hydrogen peroxide and a paste of sodium perborate mixed with hydrogen peroxide at different temperatures and time intervals on the microhardness of human enamel and dentin was examined. Intact extracted human teeth were sectioned, embedded in acrylic resin, polished, and divided into four test groups related to surface treatment. The groups were 30% hydrogen peroxide at 37 degrees C, 30% hydrogen peroxide at 50 degrees C in an illuminated chamber, a paste of sodium perborate mixed with hydrogen peroxide at 37 degrees C, and a paste of sodium perborate mixed with hydrogen peroxide at 50 degrees C in an illuminated chamber. Teeth treated with distilled water at either 37 degrees C or 50 degrees C served as controls. The results indicated that treatment with 30% hydrogen peroxide reduced the microhardness of both enamel and dentin. This reduction was statistically significant after 5-min treatment for the dentin and after 15-min treatment for the enamel (p < 0.05). Treatment with sodium perborate mixed with hydrogen peroxide did not alter the microhardness of either the enamel or dentin at the tested temperatures and time intervals. It is therefore suggested that the use of high concentrations of hydrogen peroxide for bleaching purposes should be limited. Sodium perborate appears to be a less damaging bleaching agent.

The effect of parabens in a mouthwash and incorporated into a sustained release varnish on salivary bacteria.

OBJECTIVES: The purpose of this study was to evaluate the antimicrobial efficacy of parabens, in a mouthwash and in a slow release device, against cariogenic bacteria in the oral cavity. METHODS: Parabens were formulated in a mouthwash or in a topical slow release varnish preparation. In two separate studies, volunteers were asked to use the mouthwash or the slow release varnish applied in a personal night guard device. The levels of mutans streptococci (MS), Lactobacilli (LB) and total cultivated bacteria were measured before and after using the mouthwash or the slow release varnish. RESULTS: The mouthwash containing parabens had a minor and a short-term effect on MS and LB counts in human saliva. The use of slow release varnish containing parabens, applied in a night guard, had a prolonged antibacterial effect on both MS and LB counts. CONCLUSIONS: Parabens in a mouthwash had little effect on oral bacteria counts; however, paraben in the slow release device had a significant and an extended effect in reducing oral bacteria. Although substantial reductions in oral bacterial counts were recorded after the use of parabens in a slow release device, this effect could probably be enhanced by an improved pharmaceutical formulation.

Differentiation between major and milder acute mental stress by means of the leukocyte adhesiveness/aggregation test.

Following previous observations that the adhesive state of white blood cells in the peripheral blood increases during stress, we examined 645 volunteers in various conditions of anticipatory anxiety. The volunteer subjects included 465 controls in whom stress was related solely to impending venipuncture, 149 persons under moderate stress (students before delivering a graded lecture, patients before dental treatment, etc), as well as 31 individuals under major stress (eg, before induction of anesthesia in the operating room). The respective values of aggregated leukocytes in the peripheral blood were 5.2 +/- 3.8, 6 +/- 4.2, and 19.3 +/- 9.3% of aggregated cells, with a significant difference (p < .0001) between the third and the other two groups. In both discriminant analysis and multiple regression, the leukocyte adhesiveness/aggregation test (LAAT) was shown to be superior to the white blood cell count for the detection of major stress. The LAAT had a sensitivity of 0.8, compared with only 0.35 for leukocyte count for that purpose. We concluded that the LAAT could be a powerful tool for the diagnosis of major acute mental stress and for discrimination between conditions causing major stress and those conditions that are less stressful.

Esthetic repair of porcelain in a complete-mouth reconstruction: a case report.

This paper presents a relatively simple method of repairing a large porcelain fracture in a porcelain-fused-to-metal crown that is part of a multi-unit fixed partial denture. The technique involves fitting a "modified" porcelain-fused-to-metal crown over the original damaged crown following some preparation of the original crown. This technique is of special value when a permanently cemented multi-unit restoration is involved, eliminating the need to replace the entire restoration and providing a durable esthetic result.

Marginal leakage around V-shaped cavities restored with glass-ionomer cements: an in vitro study.

The object of this investigation was to assess the degree of marginal leakage around V-shaped cervical glass-ionomer cement restorations and compare it to that around composite resin restorations. Three different glass-ionomer cements and one composite resin control were assessed by means of dye penetration. Severe microleakage at the occlusal margins was found in 70% of the glass-ionomer cement restorations, but in only 10% of the composite resin restorations. A considerable amount of dye penetration was observed at the cervical margins of all restorations, including the controls. None of the glass-ionomer cements tested showed superiority in preventing marginal leakage occlusally or gingivally.

One-year clinical evaluation of an anterior composite resin.

An anterior composite resin was evaluated in a clinical study of 93 Class III and Class IV restorations placed in patients aged 12 to 50 years. The restorations were evaluated at baseline, 6 months, and 1 year. Sixty-four (79%) of the 81 restorations examined at the 1-year recall were unchanged. Marginal discoloration and changes in surface appearance and marginal adaptation accounted for most of the changes. All changes appeared in patients younger than 14 years, which may indicate that the patients had problems in oral hygiene. Replicas of randomly selected restorations showed smooth surfaces and well-sealed margins with a smooth transition from restoration to enamel. Some restorations showed marginal breakdown and a pitted irregular surface.

Effect of etching on leakage of sealants placed after air abrasion.

PURPOSE: The aim of the present study was to assess the microleakage of pit and fissure sealants in: 1) air-abraded molars with and without etching and 2) in preventive resin restorations (PRR) prepared with air abrasion or mechanically with a bur. METHODS: Forty molars with no or minimal occlusal caries were cleaned with pumice, washed, and assigned to four groups of 10 teeth each. In group A, the teeth were air-abraded and Helioseal was applied directly to the fissures without previous treatment. Group B was air-abraded and etched for 20 s prior to sealant application. In group C, caries was excavated with air abrasion, etched, and restored with Scotchbond Multipurpose, Z-100 and Helioseal. Group D was similar to C except that the fissures were prepared mechanically with a carbide bur at high speed. RESULTS: Group A was significantly different in both Y1 and Y2 measurements from all the other groups. No differences were observed between all the other groups. Acid etching should be a precondition before sealant application. Air abrasion and mechanical preparation resulted in the same amount of microleakage following acid etch.

Long-term electromyography as a possible diagnostic aid for detecting craniomandibular dysfunctions.

As there is a positive correlation between oral parafunctional habits and craniomandibular disorders, objective electromyographic findings on parafunctional jaw activities could be very interesting for the diagnosis and management of craniomandibular disorders. The described pocket-sized and battery-operated electromyographic measuring device fulfils the essential requirements for monitoring and recording parafunctional activity in a chosen time period. It is easy to handle and can therefore be operated by a trained patient. At the end of the registration the collected data are transferred to a computer for statistical or graphical analysis. With this device, long-term electromyography on patients in their usual environment is possible. Further studies on parafunctional behaviours applying long-term electromyography could increase the understanding of craniomandibular disorders.

EDTA enhancement of strontium uptake by intact human enamel.

The aim of this research was to study the effect of EDTA on the strontium uptake by intact tooth enamel. EDTA did not significantly affect the strontium uptake in an acid medium of pH 4.5. However, it caused a sharp rise in strontium uptake at pH 6.0. At such a pH, the stability constants of the Ca-EDTA complex are approaching a maximal value, and as a result of it a significant dissolution of the surface enamel, accompanied by a highly effective increase of the contact area for strontium uptake, is taking place. In all the experiments, treatment with strontium solution resulted in a decrease of the solubility and dissolution rate of enamel in an acidic environment. The resistance of enamel to acid attack was proportional to the quantity of absorbed strontium, reaching maximal values after treatment with strontium solutions in 10(-2) M EDTA at pH 6.0.

Dycal: physical properties and resistance to amalgam condensation.

Simulated clinical experiments showed that the hand condensation of amalgam on single or multiple layers of Dycal in Class II cavities does not cause significant fracture or displacement of the liner. Cyclic loading experiments demonstrated that the plastic deformation of Dycal decreases and its stiffness increases with each additional load cycle. This indicates that minor displacement of Dycal during amalgam condensation occurs mainly during the first thrusts with the condenser, and that its mechanical properties are improved by repeated condensation with heavy pressure. Cyclic loading tests may be of considerable value in the evaluation of the performance of liners during amalgam condensation.

Observations on cavity liners for composite resin restorations.

Adhesion or surface roughness and discoloration at the interface between pulpinsulating materials and composite resins were taken as indications for interaction between the resins and the insulating materials. Some interaction occurred between all insulating materials and resins investigated. After separation of the restorative resins, the interaction of Dycal with the different composite resins varied considerably and decreased in the following sequence: Opotow, Natural, and Adaptic. The interactions of ZOE with Natural and with Adaptic were similar and more pronounced than the interaction at the Adaptic-Dycal interface but less pronounced than at the Dycal-Natural interface. A very thin film of Tubulitec was found to adhere to the composite resins in some areas. The adherence of liners containing calcium hydroxide to dentin was found to be generally stronger than the bond between these liners and composite resins. Separation of the composite resins caused tears in the varnishes and frequently in Hydroxyline. Almost completely intact layers of the varnish Copalite were observed on dentin, but Zahnlack apparently dissolved to a great extent in the resins. Among the liners containing calcium hydroxide, Dycal and Tubulitec were found to give rise to a high pH in samples of saliva, but Hydroxyline did not. Porosity and a folded surface were observed for Hydroxyline, indicating the entrapment of the solvent beneath a dry superficial layer.

The residual ridge in partially edentulous patients.

The residual ridge which forms after the extraction of teeth is characterized by a loss of substance when compared with the dentulous ridge. The residual ridge shrinks in an apical direction and shifts lingually. This remodeling pattern takes place mainly at the expense of the bony crest, the buccal plate of the alveolar process, and the gingival tissues covering it. The lingual positioning of the residual ridge crest was observed in maxillary and mandibular specimens in all the regions of the jaws and regardless of the number of teeth missing. Cross sections of the residual ridge were square, parabolic, or tapered. The base of the pontic for a fixed partial denture should be made buccolingually as the mirror image of the crest of the residual ridge it is to contact, and it should follow mesiodistally the contour and length of the clinical crowns of the adjacent abutment teeth.

Reflectance spectra of composite resins on liners.

The reflectance spectra of two types of composite resins were determined on various backgrounds. It was found that the shade differences caused by different "whitish" liners were perceptible only for thin resin specimens and were smaller than those caused by varying the resin type and thickness. Employing a light brown liner gave rise to a difference in shade which was also perceptible on resin specimens of 2.5 mm thickness. Shade differences due to varying the thickness of the specimens were more pronounced on white than on black backgrounds. The clinical significance and the qualitative physical interpretation of the results were discussed.