Influence of tooth surface conditions on enamel fluoride uptake after topical application of TiF4 in vitro.

Three groups of extracted human teeth were sectioned longitudinally into experimental and control halves. The enamel surfaces of the three groups of teeth were pretreated with 37% H3PO4 for 1 min, 0.5 M NaClO3 for 2 h, or water rinsing for 10 min. The experimental halves of the three groups received an application of 1% TiF4 for 1 min and were washed with deionized water. The tooth specimens were then immersed in synthetic saliva for 24 h at 37 degrees C before sampling for measurement of fluoride uptake. An acid etching technique was used to determine the uptake of fluoride by measuring both fluoride and calcium concentrations in the solution collected from each etched sample. A significantly higher uptake of fluoride was found in teeth rinsed in water and etched with 37% H3PO4 than in teeth pretreated in 0.5 M NaClO3. It seems that the organic components in enamel play an important role in the fluoride uptake after the topical application of TiF4.

Bonding strength of glass ionomers to dense synthetic hydroxyapatite and fluoroapatite ceramics.

The bonding strength of two glass ionomers, a resin-modified and a conventional one, to dense synthetic hydroxyapatite (HA) and fluoroapatite (FA) ceramics was compared by measuring the shear strength between the ionomers and the apatites. Before the glass ionomers were applied on the apatites, the surfaces of HA and FA plates were either fine-polished or acid-etched after fine polishing. Commercially pure titanium (CP Ti) plates were used as a control. The effects of polyacrylic acid (PAA) surface preconditioning on bonding strength were also studied. The results show that the ionomers bind to HA significantly more strongly than to FA in all cases. The resin-modified material showed a significantly higher shear strength to apatites than the conventional one. Acid etching increased the shear strength significantly for the conventional glass ionomer to both HA and FA, and 25% PAA preconditioning increased the shear strength significantly for the resin-modified glass ionomer to both HA and FA. It was concluded that glass ionomers seemed to bind to apatite chemically, and the bonding strength was influenced by the cohesive strength of the ionomers and the surface roughness of the apatites. The dense synthetic apatites seemed to be good test materials for bonding evaluations of glass ionomers to mineral tissue.

Flexure strength of resin-modified glass ionomer cements and their bond strength to dental composites.

The flexure strength of three resin-modified glass ionomer cements and one conventional glass ionomer cement and their bond strength to dental composites were studied by measuring the three-point bending and the shear strengths. The bond strengths between the dental composite and the resin-modified glass ionomer cements were dependent on the curing modes. Resin-modified glass ionomer cements bonded significantly more strongly to cured dental composites than dental composites bonded to cured resin-modified glass ionomer cements. However, the dental composites showed a significantly stronger bonding to the resin-modified glass ionomer cements than to the cured conventional glass ionomer cement, to which the dental composite did not adhere without acid etching. The flexure strengths of the resin-modified glass ionomer cements were significantly improved compared with the conventional one but were still significantly lower than that of the dental composites.

Titaniumtetrafluoride for treatment of hypersensitive dentine.

Dentine hypersensitivity in cervical areas and severe dentine sensitivity in teeth prepared for restorations were treated with a titaniumtetrafluoride solution. Patients included in the study complained spontaneously about the sensitivity in intact dentine surfaces. Thirty patients with at least one tooth on each side of the maxilla and/or mandible experiencing moderate or severe sensitivity in cervical areas participated. The degree of sensitivity was determined by scraping an explorer over the dentine surface and by air blast. At least one sensitive tooth on one side of the jaw was treated with titaniumtetrafluoride, and one on the contralateral side with a placebo solution. Results were recorded after one month, four, eight and twelve months, using the explorer and the air blast. A total of 102 teeth, of which 51 were controls, were treated. About 80% responded to the treatment with the titaniumtetrafluoride solution after one month and 55-84% thereafter. No response occurred in any of the placebo-treated teeth. Twenty patients with severe sensitivity in dentine of teeth prepared for crowns were also treated with the titaniumtetrafluoride solution when trying casts and crowns and before cementation. A total of 52 teeth were treated. Desensitizing effects occurred in 75% of the patients, with 36 of the 52 prepared teeth.

Influence of phytic acid on zinc phosphate cement.

The influence of phytic acid on the properties of zinc phosphate cement was studied by adding 2-13 wt% phytic acid to the liquid. Improved mechanical strength and stability were found for some cements prepared from commercial powders when liquids with increased phytic acid content were used. The results indicate that the formation of increased amounts of zinc phytate has a favorable effect on the properties of zinc phosphate cement.

Evaluation of biocompatibility of various ceramic powders with human fibroblasts in vitro.

Cell reaction to powders of ceramics was studied in vitro. Cultured human fibroblasts were exposed to different types of ceramic powders: zirconia (ZP), alumina (A), tricalcium phosphate (TCP) and hydroxyapatite (HA), at various concentrations. The cell viability at the different exposure times was measured by the colony formation (expressed as colony forming efficiency, CFE), neutral red uptake (NR) and colorimetric tetrazolium (MTT) reduction. Alumina and hydroxyapatite showed no cytotoxic effects at studied doses (1-500 mug/ml) while zirconia and tricalcium phosphate inhibited cell viability, with 50% of CFE reduction at the concentration of about 50 mug/ml. In order to study the cytotoxic mechanism of zirconia powder, two further experiments were included, viz. the cellular response to the sintered zirconia ceramic powders (CZP) which were obtained by crushing the sintered ceramic material; and the measurement of the degradation of zirconia ceramic plate in the different solutions, i.e., either in saline or in 0.02 M lactic acid (pH 2.72). Similar cell reactions were obtained for the CZP and ZP by using MTT and NR assays. Slow releases of ions from zirconia ceramic plate, yttrium in both solutions and zirconium and yttrium in lactic acid, were detected.

Abrasion of acrylic veneers by simulated toothbrushing.

The abrasion responses were tested on four acrylic veneer materials, K + B Plus, K + B 75, Isosit, and Ivocron. The studies were performed in two independent research laboratories. Two different brushing machines were used with an abrasive slurry. The results were used for comparing the degree of abrasion for the resin materials. Three analytical methods of measuring the degree of abrasive wear were used: surface profile measurement, microscopic evaluation, and measurement of loss of volume. Isosit showed the best abrasion resistance of the four materials tested.

Nickel allergy and nickel-containing dental alloys.

Test pieces from five cobalt-chromium casting alloys intended for use in removable partial dentures were attached to the skin of 10 women with known allergy to nickel. Patch tests were also performed with nickel and cobalt salts. Nine of the 10 women showed clear-cut or strong patch test reactions to the alloy with 7% nickel, one patient also to one of the other alloys (less than 1% nickel). In five patients with contact allergy reactions to both nickel and cobalt salts mild or marked responses to some of the other alloys were observed. Corresponding observations were made in three out of the five patients with contact allergy reactions to nickel salt but not cobalt salt.

Uranium content in porcelain denture teeth and in porcelain powders for ceramic crowns.

Some porcelain denture teeth and porcelain powders marketed in Sweden haven been analyzed for the content of uranium. The fission track method and the delayed neutron technique were the methods used. Compared to results published previously the content of uranium was generally found to be lower in the brands analyzed. The denture teeth contained 23-186 ppm for Anatoform, 35-137 ppm for Myerson, 15-45 ppm for Candulor G and 20-53 ppm for Vivopearl. The baked and fired porcelain powders showed values of about 2.8 ppm at most, those in the form of powder about 25 ppm at most. The radiation dose to the mucosa of the upper lip was calculated and is discussed.

The distribution of nickel in mice. An autoradiographic study.

Metallic restorations are corroded in the oral environment. Corrosion products penetrate into the tissues and are distributed throughout the body seeking certain organs and tissues as targets. The distribution patterns of nickel in albino mice were studied autoradiographically at various periods after an intravenous injection of 63Ni in order to locate the target organs and tissues of nickel. With short survival periods the highest uptake of 63Ni was found in the blood, kidney, urinary bladder, lung, eye and hair follicles. With long survival periods, 3 weeks, the distribution pattern was dominated by high uptake in the lung tissues, central nervous system, kidneys, hard tissues and skin. The distribution pattern in brown mice was similar to that in albino mice. However, the concentration in the eye and the skin was more pronounced. The importance of release of nickel from nickel containing dental alloys in nickel allergic patients is discussed.

Tissue accumulation of nickel released due to electrochemical corrosion of non-precious dental casting alloys.

Specimens of four non-precious dental casting alloys intended for use in the ceramic-metal technique were implanted subcutaneously in the neck region of mice. The animals were killed after 5 months. Organs and tissues were tested as regards the concentration of nickel by means of atomic absorption spectrophotometry. The study showed that due to electrochemical corrosion nickel was released from implants and accumulated in some tissues and organs.

Autoradiographic study of distribution patterns of metals which occur as corrosion products from dental restorations.

Radioactive chromium, cobalt, gold and mercury, all of which may occur as corrosion products from dental restorations, were injected in single doses via the tail vein of mice and an in vivo analysis of their distribution was performed using whole-body autoradiography. Gold seemed to be inert and went mainly to the liver and bones. The other elements studied were distributed widely in the body and remained for a long period of time in specific target organs and tissues.

Some thoughts on dental education.

It is suggested that immediately after dental school there should be a pre-registration year--a whole year of clinical training and instruction in general practice under the close supervision of a competent general practitioner/teacher. This year should end with a period of 3--4 weeks at the dental school for feedback discussion, seminars and some examinations. In order to involve every dentist, teacher, therapist, hygienist, assistant technician in a well-planned continuing educational program it seems necessary to introduce a compulsory system. It is also suggested that there should be a control system for the quality of care and individual professional performance. The demand for dental care increases. It is therefore highly desirable to utilize modern preventive measures on a broad scale, more effective and careful planning of the dental services for the individual patient and for the community as a whole and increased quality of treatment in order to reach a better prognosis and more ancillary personnel.