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In addition to lowered pH values, the molecular profile and concentrations of microbial-derived organic acids in carious dentin are important demineralization parameters involved in the induction, development and progression of dental caries. High-resolution proton ((1)H) NMR spectroscopy was employed to examine the organic acid status of primary root carious lesions. (1)H-NMR analysis of post-neutralized perchloric acid extracts of active carious lesions revealed that at an operating frequency of 600 MHz, the (1)H-NMR-detectable organic acid composition of carious dentin samples (mean molecular percentage content +/- standard error; the mean molecular percentage content is defined here as the mean of the concentration of each (1)H-NMR-visible organic acid/anion expressed as a percentage of total (1)H-NMR-detectable organic acid/anion level in each sample) was acetate 51 +/- 2%, formate 37 +/- 2%, lactate 5 +/- 1%, propionate 3 +/- 0.8%, pyruvate 2.4 +/- 0.3%, n-butyrate 1.2 +/- 0.2%; succinate 0.1 +/- 0.1%; iso-butyrate, n- and iso-valerate, and n- and iso-caproate (total) <0.2%. Further components detectable included alanine, glycine, choline, phosphorylcholine, trimethylamine oxide, methanol, glycolate and assorted saccharides. In view of their high dissociation constants (K(a)), our results demonstrate that formic and pyruvic acids (K(a) = 1.77 x 10(-4) and 3.20 x 10(-3) mol/dm(3), respectively) contribute substantially to the decreased pH values associated with active caries lesions (cf. lactate K(a) = 1.40 x 10(-4) mol/dm(3)), and hence the pathogenesis of primary root caries.

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High field proton (1H) NMR spectroscopy has been employed to evaluate the abilities of the antioxidant thiol drug N-acetylcysteine and exogenous cysteine to protect metabolites present in intact inflammatory synovial fluid samples against oxidative damage arising from gamma-radiolysis (5.00 kGy) in the presence of atmospheric O2. Although oxidation of urate to allantoin by radiolytically-generated *OH radical was readily circumventable by pre-treatment of synovial fluids with N-acetylcysteine (1.00 or 3.00 x 10(-3) mol x dm(-3)) or cysteine (1.00, 2.00 or 5.00 x 10(-3) mol x dm(-3)), both thiols offered only a limited protective capacity with respect to hyaluronate depolymerisation and the production of formate from carbohydrates in general. Radiolytic products generated from the added thiols (predominantly their corresponding disulphides) were simultaneously detectable in 1H Hahn spin-echo spectra of gamma-irradiated synovial fluids, permitting a quantitative evaluation of the radioprotective capacity of these agents. It is concluded that the multicomponent analytical ability of high field 1H NMR spectroscopy provides much useful molecular information regarding mechanisms associated with the radioprotectant actions of thiols in intact biofluids.

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The metal ceramic crown has become the most popular extra-coronal restoration in the armamentarium of the dentist, certainly within the UK. It combines the aesthetic qualities of porcelain with the strength of cast metal. This review discusses a number of issues relating to these crowns, and considers the principles of tooth preparation and marginal fit. The physical requirements of tooth preparation are considered in terms of shoulder width, emergence profile, shoulder angle and effects on the pulp. It also considers the teaching of metal ceramic crown preparation, the failure of metal ceramic crowns and the influence that preparation quality has on these failures.

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OBJECTIVES: The flexural strength, reliability and microstructure of a heat pressed ceramic system (Empress) was evaluated in comparison with three current frit materials used in ceramic crown and inlay construction. METHODS: Twenty bar specimens per material were constructed, overglazed and transverse tested at a crosshead speed of 0.5 mm/min. Etched and fractured bar specimens were viewed under a scanning electron microscope using secondary electron imaging. RESULTS: Mean strengths (MPa +/- SD) were: Empress, 117.3 +/- 31.7; Cerinate porcelain, 118.2 +/- 8.7; Corum porcetain, 92.9 +/- 13.3; and Alpha porcelain, 60.9 +/- 10.1. Results were highly significant (P < 0.001) with differences between all groups (P < 0.05) except Cerinate porcelain and Empress (P > 0.05). Weibull analysis of the results provided m-values and the predicted strength at the 1 and 5% probabilities of failure. Microstructural examination using secondary electron imaging showed leucite crystals 1.6-3.5 microns and associated microcracking in Corum porcelain and leucite crystal clusters (1.5 microns) in Empress. Cerinate porcelain exhibited a uniform distribution of fine leucite crystals (1 micron). Spherical porosity combined with crack pore combinations were noted in Vita Alpha porcelain. CONCLUSIONS: Empress glass ceramic was not stronger than Cerinate or more reliable than many of the frit materials. Uniform leucite distribution and fine crystal size may be associated with improved strength and reliability.

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OBJECTIVES: The biaxial flexural strength and reliability of four dental ceramics including: Empress glass ceramic (EM), Cerinate porcelain (CE), Corum porcelain (CO) and Alpha porcelain (AL) were compared. METHODS: Twenty disc specimens per material were prepared overglazed and tested. The piston on three ball test was used to test the specimens in a universal testing machine at a crosshead speed of 0.15 mm/min. Weibull analysis provided m-values and the 1 and 5% probabilities of failure. RESULTS: Mean strengths (MPa +/- SD) were: EM, 133.5 +/- 21.5; CE, 109.1 +/- 11.3; CO, 119.8 +/- 19.2; and AL, 68.2 +/- 9.9. There was no statistical difference between EM or CO and CO and CE strengths (P > 0.05). Weibull m-values included: EM, 6.60; CE, 10.20; CO, 5.27; and AL, 6.93. Cerinate had the highest m-value (P < 0.01) and good dependability. CONCLUSION: Empress was not stronger or more reliable than many of the frit materials.

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High field (400 and 600 MHz) proton NMR spectroscopy has been employed to investigate the thermally-induced autoxidation of glycerol-bound polyunsaturated fatty acids present in intact culinary frying oils and fats. Heating of these materials at 180 degrees C for periods of 30, 60 and 90 min. generated a variety of peroxidation products, notably aldehydes (alkanals, trans-2-alkenals and alka-2,4-dienals) and their conjugated hydroperoxydiene precursors. Since such aldehydes appear to be absorbed into the systemic circulation from the gut in vivo, the toxicological significance of their production during standard frying practices is discussed.

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The oxidative deterioration of glycerol-bound polyunsaturated fatty acids (PUFAs) in culinary oils and fats during episodes of heating associated with normal usage (30-90 min at 180 degrees C) has been monitored by high field 1H NMR spectroscopy. Thermal stressing of PUFA-rich culinary oils generated high levels of n-alkanals, trans-2-alkenals, alka-2,4-dienals and 4-hydroxy-trans-2-alkenals via decomposition of their conjugated hydroperoxydiene precursors, whereas only low concentrations of selected aldehydes were produced in oils with a low PUFA content, lard and dripping when subjected to the above heating episodes. Samples of repeatedly used, PUFA-rich culinary oils obtained from restaurants also contained high levels of each class of aldehyde. The dietary, physiological and toxicological ramifications of the results obtained are discussed.

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Root caries prevalence was recorded for a consecutive sample of dental patients (n = 146), aged over 55 yr and with at least 12 natural teeth. The mean root DFS score of the males (n = 49) was 6.34 +/- 4.55 and for the females (n = 97) 3.76 +/- 3.31 (P less than 0.001). The salivary levels of mutans streptococci, lactobacilli, and yeasts were determined in addition to salivary flow rate and buffering capacity. Subjects with greater than 1 root DFS had significantly higher salivary levels of mutans streptococci, lactobacilli, and yeasts. They also had fewer teeth and more exposed root surfaces. In step-wise multivariate analyses the factors significantly related to the root DFS score were the number of exposed root surfaces, number of teeth, sex and salivary yeast levels (R2 = 0.41). In the multivariate analyses salivary levels of mutans streptococci were not significantly related to any clinical measurement of root caries experience due to the greater strength of association between the root DFS score and salivary levels of yeasts. Subjects prescribed medicines with a reported xerostomic effect had significantly fewer active root lesions than those not prescribed such medicines and salivary levels of all microorganisms studied were significantly elevated in subjects prescribed medications containing sucrose.

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The depth of cure of three light-cured glass-ionomer cements was examined immediately after polymerization under the curing light and 12 hours after polymerization. The duration of illumination was also varied among groups to determine its effect on the depth of cure. Light-Cured Zionomer showed a greater immediate depth of cure than did either Vitrabond or XR Ionomer. All three materials demonstrated greater depth of cure 12 hours after application of the light source, indicating that they possess dual-curing characteristics. Increasing the duration of illumination from 30 to 60 seconds significantly (P less than .05) increased the depth of cure for all three materials.

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With increasing numbers of older people retaining their natural dentitions, dentists are becoming increasingly aware of the problem of dental caries occurring on exposed root surfaces--root caries. This study reports the prevalence of root caries in a selected older population, living in the community and attending a general dental practice in Bexhill, East Sussex. A total of 146 non-institutionalised people, aged at least 55 years with at least 12 teeth, were examined. Most of the subjects (88.4%) had evidence of root caries, males and denture wearers having more lesions than females and non-denture wearers, respectively. Active coronal caries was present in only 11.6% of the subjects, whereas active (soft or leathery) root caries lesions were present in 31.5% of the subjects. The teeth and surfaces most commonly affected by root caries were found to be similar to those seen in previous epidemiological surveys. The majority of active root caries lesions were within 1 mm of the gingival margin, while inactive lesions tended to be greater than or equal to 1 mm from the gingival margin. Colour of root caries lesions was not diagnostic of caries activity. A more detailed method of recording root caries lesions is also described.

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