H.H. Messer

Stiffness of Endodontically-treated Teeth Related to Restoration Technique

Endodontically-treated posterior teeth are susceptible to fracture; consequently, full-occlusal-coverage restorations are recommended. We designed this study to examine the potential for alternative restorative techniques for pulpless teeth, using strain gauges mounted on extracted maxillary second premolars to measure strains generated by nondestructive occlusal loading. Cuspal stiffness was evaluated on the following sequentially performed procedures: unaltered tooth, completion of all endodontic procedures, appropriate restorative preparation, and restoration. The restorative procedures evaluated were: (1) amalgam, (2) cast gold onlay, (3) composite restoration with enamel etch, and (4) composite restoration with enamel and dentin etch. Finally, all teeth were loaded to fracture. Cast gold was the strongest restorative material tested (2.11 relative stiffness, compared with that of the unaltered tooth at 1.00), and amalgam was the weakest (0.35 relative stiffness). Composite restoration and enamel plus dentin etch were almost as strong as the unaltered tooth (0.87 relative stiffness), while enamel-etch-only yielded lower stiffness (0.51).

Differential sensitivity of normal human pulp and transformed mouse fibroblasts to cytotoxic challenge.

Six different lines of diploid cells from human pulp and one commonly used transformed-cell line, L929 (a continuous fibroblast line of mouse lung connective tissue origin), were challenged by sera changes, an agar-overlay toxicity test and transfilter-histochemistry-toxicity test. The normal diploid cells showed greater sensitivity than transformed cells in each test. Although a different parameter of cell toxicity was measured in each test, the data indicate greater toxic response in diploid cells by all measurements. These normal diploid human cells are more appropriate cells for toxicity testing materials for human use.

Preliminary results from disinfection of irreversible hydrocolloid impressions

The virucidal efficacy of germicides acting on an irreversible hydrocolloid surface is not known. Tests that are currently performed on germicides do not simulate the conditions under which the germicides are often used. One major concern for the dental profession is the disinfection of dental impressions, particularly irreversible hydrocolloid impressions. This study was designed to test the biocidal action of germicides against an enveloped virus on an irreversible hydrocolloid surface. The disinfection model, which was developed to simulate clinical conditions, specified the use of vesicular stomatitus virus, an animal virus amenable to safe handling. A 0.5% sodium hypochlorite spray inactivated the virus when the spray was allowed to remain on the impression 3 to 10 minutes. The iodophor disinfectant required a 3- to 10-minute immersion for total inactivation. Although 2% glutaraldehyde achieved total viral inactivation in less than 1 minute, the authors conclude that short disinfectant sprays, in general, are not an appropriate disinfection method.

Properties of Ca2+-, Mg2+-activated adenosine triphosphatase from rat incisor pulp

Abstract A plasma membrane fraction was prepared from pulps of freshly extracted incisors of rats using differential centrifugation at 35,000 g . Adenosine triphosphatase (ATPase) activity was measured by the release of inorganic phosphate from ATP. Assays were conducted at 37 °C for 30 min with 20 mM tris-HCl buffer plus 70 mM NaCl. Properties of the enzyme were as follows: pH optimum between 7.9–8.1; Ca 2+ or Mg 2+ alone activated the enzyme, with maximal activity at a divalent cation concentration of 5 mM; the enzyme was preferentially activated by Ca 2+ at low concentrations ( mM ) and by Mg 2+ at high concentrations (0.5 to 5.0mM); activity increased progressively up to 50 °C, and complete inactivation occurred at 70 °C; ATP, GTP and UTP were hydrolyzed at similar rates, while ADP and AMP were much less effective substrates; ouabain, tetracycline and fluoride in the dosages used did not inhibit ATPase activity.

Influence of in vivo-incorporated fluoride on collagen metabolism by mouse calvaria in organ culture

Abstract The synthesis and degradation of collagen by bones with high (0.107 per cent), moderate (0.041 per cent) and low (0.007 per cent) fluoride contents were assessed in organ culture, using half-calvaria of 5-day-old mice. Fluoride was incorporated into the half-calvaria before culture, during the entire period of bone formation. Collagen synthesis was measured by the conversion of [ 14 C]-proline to [ 14 C]-hydroxyproline, and collagen degradation by the release of hydroxyproline from bone. Fluoride inhibited the loss of hydroxyproline, both in control cultures and in the presence of parathyroid hormone. Calcitonin inhibited the release of hydroxyproline, and fluoride further reduced the loss from calcitonin-treated bones. Fluoride did not influence the conversion of [ 14 C]-proline to [ 14 C]-hydroxyproline, but enhanced the incorporation of newlysynthesized collagen into bone matrix, and reduced its subsequent loss by resorption. Parathyroid hormone suppressed collagen synthesis, and reduced the incorporation of [ 14 C]-hydroxyproline into bone matrix.

A comparison of Ca2+-, Mg2+-ATPase and alkaline phosphatase activities of rat incisor pulp.

SummaryA plasma membrane preparation derived from incisor pulps of 250-g rats was used as the source of alkaline phosphatase and an ATPase activated by either Ca2+ or Mg2+. Properties of the two enzymes were then compared under a variety of experimental conditions to determine if ATPase activity is clearly distinct from alkaline phosphatase activity. (a) The optimum pH for ATP hydrolysis was 8.0, compared with 10.2 forp-nitrophenylphosphate. (b) At the optimum pH, ATP hydrolysis required either Ca2+ or Mg2+ for activation, whereasp-nitrophenylphosphate hydrolysis did not require and was little influenced by the presence of divalent cations. (c) Alkaline phosphatase showed maximal activity at 40°C and ATPase at 50°C, with complete inactivation at 60°C and 70°C, respectively. (d) When the plasma membrane preparation was preincubated in the absence of substrate at varying temperatures of pH, alkaline phosphatase was less stable than ATPase at extreme pH and high temperatures. (e) Alkaline phosphatase activity was lost more rapidly than ATPase activity during storage at 4°C for up to 10 days. (f) Butanol extraction of the plasma membrane preparation to remove phospholipid destroyed ATPase activity and enhanced alkaline phosphatase activity approximately fivefold. On the basis of these comparisons it is concluded that ATP hydrolysis andp-nitrophenyl-phosphate hydrolysis are the result of separate enzyme activities.

Influence of Gastric Acidity on Fluoride Absorption in Rats

The rate of F absorption from the stomach is pH-dependent, with greater absorption at low pH. Since the rate of absorption is also strongly influenced by the rapidity of gastric emptying, we have compared the relative importance of gastric acidity and gastric emptying in overall F absorption. Male rats (350 g, n = 85) were pre-treated with cimetidine (to inhibit gastric acid secretion) or pentagastrin (to stimulate gastric acid secretion) or were untreated controls, and given 50 μg F by stomach intubation. The pH of the F-containing solution was varied in the cimetidine-pre-treated group (pH 1.5, 5.5, 8.5), and was 5.5 for the control and pentagastrin-pre-treated groups. Gastric emptying was measured by addition of 14C polyethylene glycol to the F solution as an unabsorbed marker of fluid movement. F absorption was measured after 10, 20, and 40 min. The rate of gastric emptying was unaffected by pre-treatment or pH of the intubating solution. Initially, F absorption was greatest at low pH. After 40 min, absorption was comparable in all groups, averaging approximately 70% of the initial dose. The extent of absorption from the stomach was inversely related to pH, but increased absorption from the small intestine compensated for the low gastric absorption at high pH.

A Comparison of the Antibacterial and Cytotoxic Effects of Parachlorophenoll

The antibacterial and cytotoxic effects of para chlorophenol (as 35% camphorated PCP and 2% aqueous PCP) were compared directly, using the agar overlay technique. Human pulp fibroblasts and L929 cells were grown to confluence in 60-mm petri dishes. Bacterial suspensions (S. aureus, E. coli) in agar were poured as a thin layer in 60-mm petri dishes. All were overlaid with agar. Cells were exposed to medicament via filter paper discs placed on the agar surface. After 24 hours, the zone of cell lysis (fibroblasts) or inhibition of bacterial growth was measured as diameter in mm. A dose-response relationship was observed for both fibroblasts and bacteria. The zone of inhibition for fibroblasts was larger than that for bacteria, indicating that the cytotoxicity of parachlorophenol exceeds its antibacterial activity.

Influence of calcitonin on bone phosphatases and phosphate release in organ culture.

Summary Calcitonin promoted an increase in both alkaline and acid phosphatase activities of half-calvaria from 5-day-old mice when the bones were cultured for 48 hr. Calcitonin inhibited the release of phosphorus from bones, relative to the release from control and parathyroid hormone-treated bones, and promoted an uptake of calcium from the culture medium. The results support the concept of a role for calcitonin in phosphate metabolism. This study was supported by Grant No. DE-01850, National Institute for Dental Research, Bethesda, MD.

A comparison of bone loss from different skeletal sites during acute calcium deficiency in mice

Severe Ca deficiency was produced by the combined stresses of a Ca-deficient diet and lactation in female mice. Alveolar bone loss was assessed by changes in alveolar crest height and in quantity of supporting trabecular bone. Changes in the femur were measured by changes in mineral content and in the cross-sectional area of the midshaft region, and in vertebrae by changes in mineral content. A similar decrease in bone was observed in all sites during progression of Ca deficiency with a similar increase during recovery. Maximum bone loss amounted to more than 50 per cent. Alveolar bone loss was characterized by a reduction in trabecular bone without loss of alveolar crest height.