Effect of several try-in attempts of crimped preformed metal crowns on their circumference.

AIM: To assess whether several try-in attempts change the circumference of preformed metal crowns (PMCs). METHODS: This in vitro, experimental study was performed on 68 PMCs of maxillary and mandibular molars that required crimping. First, a photograph was obtained of the gingival margin of each crown using a digital camera (fixed at a specific distance). Crown margins were then crimped using 114 pliers. The second photograph was obtained under the same conditions as the first one. After crimping, the crowns were removed using an excavator to assess the amount of crimping. This was repeated for the second time and a photograph was obtained after each time of PMC removal. The crown was crimped again and tried on the tooth and a photograph was obtained after completion of each phase. Photographs were saved in a computer and the circumference of the crowns was calculated using AutoCAD software. RESULTS: The reduction in circumference of the crowns following the first crimping was greater for the primary second molars than for the primary first molars and was on average 0.87%. After trying the crowns on teeth, the circumference of the crowns increased on average by 0.33%. This increase was 0.53% after trying the crowns for the second time. The reduction in circumference after the second crimping was 0.51%. There was an increase in circumference after re-trying of 0.35%. Changes in circumference of the crowns after the first (p = 0.037) and second (p = 0.00) try-in attempts were statistically significant. CONCLUSIONS: Re-crimping is necessary after trying the crown on tooth and prior to cementation.

Effect of aluminum on the hepatic mixed function oxidase and drug metabolism.

The effect of aluminum injection on the hepatic mixed function oxidase was examined in male Wistar rats. A cannula was surgically implanted in both the control and aluminum treated animals to provide a common port for aluminum injection. In addition, the control animals were pair-fed to the aluminum treated animals. The treated animals accumulated aluminum at about 0.1 mg/gm dry weight of liver/day. At 14 days, the cytochrome P-450 was decreased 20%, but the other components, cytochrome b5 and cytochrome reductases, were unchanged. By day 21 both cytochrome P-450 and cytochrome b5 were reduced 25%. Although NADPH cytochrome c reductase was not affected, the other flavoprotein, NADH cytochrome c reductase, was reduced. Drug metabolism, O-demethylation of p-nitroanisole and p-hydroxylation of aniline, was not affected at 14 days. However, at 21 days O-demethylation was not affected, but aniline hydroxylation was decreased, indicating an affect of aluminum on a specific isoenzyme of cytochrome P-450. Uniquely, the nonactivated glucuronyl transferase activity was fourfold greater in the aluminum treated animals. The increase was greater than cation activation and was similar to the detergent activated activity. Thus, aluminum infusion does produce specific alterations in microsomal function, including drug metabolism and conjugation.

QSAR analysis of drug excretion into human breast milk.

Breast feeding has increased by approximately 25% in the United States during the past decade and this trend appears to be continuing. The number of drugs available to lactating women is also growing at a rapid pace. The excretion of drugs into breast-milk presents a potential danger to infants. In spite of this, little is known about the excretion of drugs into breast-milk. The ability to predict which drugs are potential hazards would be very useful in the clinical setting. This study quantitatively correlates the human milk to plasma concentration ratio of various basic and acidic drugs (log M/P) with the square root of the molecular weight, the partition coefficient (log P) and the degree of dissociation (log U/D). For basic drugs there is a negative-dependence on both log P and log U/D. High lipophilicity favours protein binding and reduces the amount of drug available for diffusion into milk. Therefore, as log P increases, the log M/P decreases. The negative-dependence on log U/D indicates that the higher the degree of dissociation of the base in plasma, the greater the log M/P will be. This fits well with the concept of ion-trapping. A strong base is more likely to be transferred and then trapped in milk which has a lower pH than plasma. For acidic drugs there is a negative-dependence on both square root (MW) and log P. The negative-dependence on square root (MW) suggests that large molecules are less likely to be able to diffuse into the milk. A negative-dependence on log P appears to hold true for bases and acids. Log M/P decreases as log P increases. This is probably due to increased protein binding by lipophilic drugs through non-specific hydrophobic interaction with plasma protein.