Håkon Nordbø

Fluoride release and uptake in vitro from a composite resin and two orthodontic adhesives

The aim of this study was to investigate the fluoride release and uptake characteristics of a composite resin (Tetric) and two orthodontic adhesives (VP 862 and Saga Bond), with a type-II glass ionomer cement (Ketac Fil) as a control. Test specimens in 2 ml deionized water released fluoride over a period of 33 days. Ketac Fil released 54 and 15 times more fluoride than Tetric after 24 h and 1 month, respectively, whereas the two adhesives released amounts between these values. Specimen exposure to 1000-ppm NaF solution increased the 24-h fluoride release from all materials, with near pre-exposure levels reached after 2-3 days. Ketac Fil had a tendency to recharge not seen with the other materials. The ytterbium trifluoride filler in Tetric has a very low water solubility, and it is therefore suggested that the increases in fluoride release from Tetric after exposure to fluoride were most probably due to release of surface-retained fluoride.

Desorption of Salivary Proteins from Hydroxyapatite by Phytic Acid and Glycerophosphate and the Plaque-Inhibiting Effect of the Two Compounds In Vivo

The capacity of phytic acid and glycerophosphate to desorb salivary proteins from hydroxyapatite was studied in vitro. Phytic acid had a high capacity for desorption; the capacity of glycerophosphate was considerably lower. In vivo experiments showed that both substances were capable of reducing plaque formation; phytic acid had a greater effect. The results may offer an explanation of the cariostatic effect of these substances.

Saucer-shaped cavity preparation for composite resin restorations in class II carious lesions: Three-year results

This study determined the feasibility of saucer-shaped cavity preparations for composite resins in class II lesions. Saucer-shaped class II cavity preparations were restored with composite resin and subjected to clinical, radiographic, and replica cast evaluation (39 restorations) after 6, 18, and 36 months. The results indicated that the retention, resistance form, and wear resistance of the class II saucer-shaped cavity preparations were satisfactory after 3 years.

Chemical Plaque Control and Prevention of Extrinsic Tooth Discoloration in Vivo

Extrinsic discoloration of teeth has frequently been observed in connection with the use of chemical plaque-preventive agents. Preliminary investigations have indicated that oxidizing peroxymonosulfate may effectively reduce this discoloration without interfering with the plaque-preventive capacity of chlorhexidine. In the present experiment a 0.2% chlorhexidine and a 1% peroxymonosulfate solution were used for oral rinsing in a group of 50 military recruits. A double-blind experimental design was followed. The plaque-preventive capacity of chlorhexidine was maintained, and a marked reduction in extrinsic tooth discoloration could be observed.

Iron discoloration of acrylic resin exposed to chlorhexidine or tannic acid: a model study.

A clinical model was introduced to study the ability of chlorhexidine, tannic acid, and iron to discolor dental plaque formed on acrylic resin surfaces. None of the agents caused discoloration when applied individually five times daily during a 5-day period. However, exposure of the dental plaque to either chlorhexidine or tannic acid before the iron applications produced marked staining. Possible mechanisms, among which denaturation appears to be significant, are discussed. The use of a strong oxidizing agent, peroxymonosulfate, completely bleached the established discolorations.

The influence of resin coating on the shear punch strength of a high strength auto-cure glass ionomer

OBJECTIVES The aim of this study is to examine the influence of early water contact on the shear punch strength of a modern, high strength, auto-cure glass ionomer (Fuji IX GP). METHODS Specimens, 8.0mm in diameter and approximately 1.25mm thick, were prepared in metal washers, and allowed to remain covered by polyester strips for 7min, to ensure completion of the initial set. A minimum of 32 specimens was prepared for each set of experiments and they were divided into two equal groups. Following removal of the strips, the surfaces of the specimens in Group 1 were immediately coated on both sides with Fuji Coat LC and light cured for 10s. In Group 2 the specimens were left uncoated. All specimens were then placed in distilled water at 37 degrees C, and stored for periods of 24h, 1, 2, 5, or 8 weeks. The strength of the specimens was measured at each time interval in the shear mode by a punch test in a universal testing machine. RESULTS The mean strength of the coated specimens in Group 1, which had been protected against exposure to water, increased significantly on ageing from 67.1 (24h) to 78.0MPa (1 week), with no further significant change in strength. The mean strength of the specimens in Group 2 increased significantly from 75.7 (24h) to 83.3 (1 week) and 91.9MPa (2 weeks), with no further significant change in strength. Uncoated specimens were stronger at all points of time. The difference was statistically significant at 24h, 2, 5, and 8 weeks (P<0.05), but not at 1 week (P=0.061). Significance. The results suggest that, contrary to the usual instructions for placement of glass ionomer, early access to water will positively influence the shear punch strength of Fuji IX GP.

Auger electron spectroscopy of iron in dental pellicle from stainers and non-stainers

Stainers and non-stainers were selected on the basis of their individual tendency to develop extrinsic tooth discolorations from a chlorhexidine mouth rinse. Pellicle was allowed to form in vivo on dental enamel slabs in both stainers and non-stainers. The slabs were then exposed to chlorhexidine 0.2% and a neutral iron salt solution extraorally either once or until a brownish discoloration appeared from the stainers. The pellicle was examined for its content and distribution of iron by Auger electron spectroscopy (AES). Pellicle from stainers showed higher concentrations of iron than pellicle from non-stainers.

Ability of Chlorhexidine and Benzalkonium Chloride to Catalyze Browning Reactions in vitro

The use of chlorhexidine and benzalkonium chloride as plaque-controlling agents causes the formation of brownish discolorations in a high percentage of the persons involved (Hansen et al, J Clin Periodontol 6:153, 1975; Gjermo et al., J Periodontol Res 5:102, 1970). The presence of furfural in chlorhexidine discolored pellicles has recently been demonstrated (Nordb0 et al., Scand J Dent Res, 85:606, 1977). Furthermore, brownish colors are known to be produced in nature by a reaction between reducing sugars and amino compounds, designated the Maillard reaction, and furfurals are supposed to be intermediates (Berk, Bravermans Introduction to the Biochemistry of Foods, Elsevier, 1976, 149). The available data lead to the hypothesis that the presence of chlorhexidine or benzalkonium chloride may catalyze some sort of Maillard reaction in the pellicle, leading to the formation of brown pigments. The hypothesis was filrst tested in vitro by the following experiments: 0.25, 0.5 or 1.0 M furfural (Fluka A/G, Switzerland) was added to 3 ml centrifuged human saliva or to 0.25, 0.5 or 1.0 M glycine, in a total of 6 ml. In some of the series 22 mM chlorhexidine or benzalkonium chloride was added. In a parallel series ribose was substituted for furfural.

The clinical Performance of two groups of functioning class-II cast gold inlays

The length of service and the clinical performance of two groups of functioning class-II cast gold inlays in patients attending a private practice were assessed by conventional clinical and radiographic examination. In one group all inlays were older than 25 years (median age, 34 years), and they had an extended outline form. The impression technique was based on a thermoplastic material in a copper ring. In the other group, comprising inlays inserted during the past 25 years (median age, 16.5 years), the outline form was minimal and an elastic impression material in a copper ring was used. The inlays in the older group appeared to perform better than those in the younger group. In both groups recurrent caries appeared to be the predominant reason for repair.

Detection of microbial-derived fatty acids in carious dentin by gas chromatography and gas chromatography-mass spectrometry

The aim of the present study was to analyze the fatty acid content of carious and sound human dentin. Gas chromatography and gas chromatography-mass spectrometry revealed the presence of fatty acids of C10-C18 size in the carious dentin, whereas fatty acids of C16 size were present in minute amounts in three samples of the corresponding sound dentine controls. No fatty acids were detected in the other sound dentin control samples. The source of fatty acids was considered to be microorganisms invading the dentin during the progression of the caries lesion. The presence of bacterial fatty acids in carious dentin may serve as a marker for the pathological process and thus contribute to the understanding of the mechanisms involved.