Necrotizing tracheobronchitis in patent ductus arteriosus-dependent cyanotic congenital heart disease.

We report 2 patients with necrotizing tracheobronchitis (NTB) associated with patent ductus arteriosus-dependent cyanotic congenital heart disease. The pathologic findings suggest that hypotension and decreased tracheo-bronchial perfusion were the major contributing factors in the development of NTB. Necrotizing tracheobronchitis developed in infants with pulmonary atresia and Ebstein's anomaly with pulmonary stenosis. Both infants required prostaglandin E1 infusion from early infancy, and presented with sudden onset of dyspnea and hypercapnea. In one infant, NTB developed prior to mechanical ventilation. In the other infant, NTB developed after 4 days of mechanical ventilation. Care of both infants involved minimal pressures and FiO(2), adequate humidification, and optimal temperature of inspired gases; these factors probably did not play a role in the development or worsening of NTB. Both infants had hypotension and hypoxemia. These factors could have contributed to the development of NTB because of decreased perfusion pressure and tissue hypoxia. As the area of necrosis and its severity correlated with the area of blood supply served by the specific feeding arteries, we speculate that tissue hypoperfusion was the major cause of NTB.

[The clinical significance of plasma tissue plasminogen activator (t-PA) levels in severe acute or fulminant hepatitis].

We studied the tissue plasminogen activator (t-PA) levels in the plasma of patients with acute hepatitis (AH), severe acute hepatitis (AHs) and fulminant hepatitis (FH). Plasma t-PA levels were measured consecutively on the first, third and seventh days of hospitalization. Plasma t-PA levels were markedly higher in AHs and FH than in AH (p < 0.05, p < 0.01, respectively) on the first day, but did not differ significantly between AHs and FH on this day. The t-PA levels decreased markedly on the third and seventh days in AHs (both p < 0.05), but did not change from the first day to the third and seventh days in FH. The t-PA levels on the third and seventh days were higher in FH than in AHs (both p < 0.05). There was a significant increase in the plasma t-PA level before an episode of encephalopathy in FH compared with levels in AHs. These observations suggest that t-PA level may be useful as a prognostic parameter in patients with acute hepatic injury.

Study on high-strength plastic teeth. Tooth discoloration.

Conventional plastic teeth (CV teeth) are inferior to porcelain teeth in maintaining an adequate esthetic appearance with wear and discoloration, and thus have a shorter period of durability. Recently, high-strength plastic teeth (HS teeth) have been developed and applied to overcome the wear problems of CV teeth. Since HS teeth made of hard resin are still susceptible to staining with pigments, it has been observed that the esthetics of removable partial dentures made from such plastic teeth are gradually impaired in many patients. To investigate the susceptibility of HS teeth to pigments, we conducted an in vitro study by immersing three types of artificial teeth in three coloring liquids. It was found that the HS teeth tended to be less susceptible to the test pigments than the CV teeth to various degrees. In contrast, they showed markedly stronger susceptibility to the pigments than porcelain teeth. For all three artificial tooth types, daily tooth cleaning with an ultrasonic vibrator had a tendency to reduce the coloration in comparison with their counterparts without ultrasonic cleaning.

Study on the castability of Co-Cr alloy for cast plates. Part 3: Effects of alloy fusion temperature and the heating temperature of the cast ring.

Co-Cr alloy is used more frequently than Ni-Cr alloy as a non-precious alloy for cast plates in Japan. However, since the melting temperature of Co-Cr alloy is very high, about 1300 degrees C, and since it oxidizes easily, a vacuum-pressure casting machine capable of melting this alloy in a reduced atmosphere has recently been developed. Using this machine, the effects of fusion temperature and the heating temperature of the cast ring on the Co-Cr alloy were studied. It was found that in the vacuum-pressure casting method, both the fusion temperature of the Co-Cr alloy and the heating temperature of the cast ring had a significant effect (p < 0.01) on the castability of the Co-Cr alloy.

Wear of denture teeth by use of metal plates. Part 3: Abrasive wear of posterior teeth and wear of opposing metal plates.

An in vitro evaluation of abrasive wear resistance of high-strength denture (HS) teeth and wear of metal plates (Pd alloy) on the opposing side was conducted. A total of 8 types of teeth were used in the experiments including 3 types of HS teeth, 3 types of conventional plastic denture (PL) teeth, porcelain teeth and metal teeth (Pd alloy). Sliding-induced wear tests were conducted by sliding these teeth over the metal plates. Abrasive wear resistance of the teeth was evaluated in terms of wear depth and weight loss. A comparison of wear depth showed that the abrasive wear resistance of HS teeth was 4.7 times that of PL teeth, 0.7 times that of porcelain teeth and 8.3 times that of metal teeth. Weight loss showed that the abrasive wear resistance of HS teeth was 3.3 times that of PL teeth, 0.2 times that of porcelain teeth and 11.4 times that of metal teeth. The weight loss of the metal plates was minimal when they slid over HS teeth, but increased in the order PL teeth, porcelain teeth and metal teeth.

Wear of denture teeth by use of metal plates. Part 2: Abrasive wear of posterior teeth.

An in vitro study was conducted to evaluate the abrasive wear resistance of high-strength denture teeth (HS teeth). Eight types of specimen were used in the experiments; 3 types of HS teeth, 3 types of conventional plastic denture teeth (PL teeth), porcelain teeth and metal teeth. Sliding-induced wear tests were conducted by sliding the samples on a metal plate. The abrasive wear resistance of the samples was evaluated in terms of wear depth, weight loss and SEM observation. Comparison of wear depth showed that abrasive wear resistance of HS teeth was 4.7 times that of PL teeth, 0.7 times that of porcelain teeth and 8.3 times that of metal teeth. In terms of weight loss, the corresponding values were 3.3-fold, 0.2-fold and 11.4-fold, respectively.

Wear of artificial denture teeth by use of toothbrushes. Part 1: Abrasive wear of anterior teeth.

High-strength denture teeth (HS teeth) were developed in order to improve the hardness and wear resistance of conventional plastic denture teeth (PL teeth), while retaining their feature of easy occlusal adjustment. The objective of this study was to evaluate the abrasive wear resistance of HS teeth. We conducted wear tests and measured surface roughness using six types of anterior artificial teeth, i.e., three types of HS teeth and three types of PL teeth, the latter serving as the control. The results of the toothbrush abrasion test revealed that the HS teeth had about 5 times greater wear resistance than the PL teeth. It was also found that the type of artificial teeth and the number of abrasive wear-testing strokes had a significant (P less than 0.05) influence on the surface roughness of artificial teeth.

Studies on the castability of Co-Cr alloy for cast plates. Part 2: Effect of form of sprue attachment to the wax pattern.

Co-Cr alloy is used more frequently than Ni-Cr alloy as a non-precious alloy for cast plates in Japan. However, since the melting point of Co-Cr alloy is very high, about 1300 degrees C, and since it oxidizes easily, a vacuum-pressure casting machine capable of melting this alloy in a reducing atmosphere has recently been developed. Using this vacuum-pressure casting machine, the authors studied the effects on the castability of Co-Cr alloy due to the form of sprue attachment to the wax pattern. The results clarified that in the vacuum-pressure casting method, the form of sprue attachment to the wax pattern has a significant effect (p less than 0.01) on the castability of Co-Cr alloy.

Studies on the castability of Co-Cr alloy for cast plates. Part 1: The effects of sprue attachment direction to wax plates and the investment direction of refractory models.

Co-Cr alloy is used more frequently than Ni-Cr alloy as a non-precious alloy for cast plates in Japan. However, since the melting point of Co-Cr alloy is very high, about 1300 degrees C, and since it oxidizes easily, a vacuum-pressure casting machine capable of melting this alloy in a reduced atmosphere has recently been developed. Using this vacuum-pressure casting machine, the authors studied the effects on the Co-Cr alloy of the attachment direction of sprues and the investment direction of refractory models. The results clarified that in the vacuum-pressure casting method, sprue attachment direction and the investment direction of refractory models have a significant effect (p less than 0.01) on the castability of Co-Cr alloy.