Catabolism of threonine in mammals by coupling of L-threonine 3-dehydrogenase with 2-amino-3-oxobutyrate-CoA ligase.

There is doubt about the L-threonine 3-dehydrogenase (EC 1.1.1.103) and threonine aldolase (EC 2.1.2.1) catabolic pathways of L-threonine in mammals which are believed to produce aminoacetone and glycine plus acetaldehyde, respectively. L-Threonine 3-dehydrogenase in disrupted guinea-pig liver mitochondria was investigated in a reaction mixture containing L-threonine without and with CoA and oxaloacetate; L-[U-14C]threonine was included in four similar experiments for autoradiograms. Threonine aldolase was examined in similar mitochondria from liver and kidney. CoA reduced the aminoacetone formed from L-threonine to 10-14% and CoA plus oxaloacetate produced citrate (from CoASAc) in approximately equal amounts to the decrease in aminoacetone. Autoradiograms confirmed the decrease in aminoacetone with the simultaneous appearance of citrate and glycine. No evidence was obtained that threonine aldolase catabolised L-threonine at the concentration used to assay the dehydrogenase. It is concluded that 2-amino-3-oxobutyrate (precursor of aminoacetone), which is produced from L-threonine by L-threonine 3-dehydrogenase, undergoes CoA-dependent cleavage to glycine and CoASAc by 2-amino-3-oxobutyrate-CoA ligase. The results suggest that the coupling of these enzymes provides a new pathway for the catabolism of threonine in mammals.

Plasma calcium levels in pregnant Asian women.

Plasma calcium, phosphorus, alkaline phosphatase, total protein, and albumin were measured during pregnancy in a group of Asian women living in the south of England and in a control group. The Asian women had slightly lower mean plasma calcium concentrations than the control group. Exposure of Asian women to sunshine appeared to be low, and it was inferred that they probably had little endogenous synthesis of cholecalciferol as a result. Both Asian and control subjects ingested similarly low amounts of vitamin D. The Asian women consumed greater amounts of phytate and vegetable fibres than the controls, and it is suggested that these substances may reduce absorption of insoluble lipids (including cholecalciferol) and calcium in a setting where the dietary intake and endogenous synthesis of vitamin D are already borderline for the subject's requirements.

Comparison of wet and dry finishing of resin composites with aluminum oxide discs.

Samples of four composites (Herculite, Visio-Dispers, Silux, and Prisma-Fil) were finished with aluminum-oxide discs either wet or dry so that the effects of these two finishing procedures could be compared. The samples were evaluated for surface smoothness, color stability, and surface hardness. Surface smoothness was determined immediately after a sample was finished with a profilometer. Knoop hardness values were determined for each sample immediately after being finished and once a week for five weeks. Color stability was evaluated with a tristimulus colorimeter by the color of each sample being finished and once a week for five weeks. When surface smoothness was compared between the wet- and dry-finished samples, there was no significant difference between Prisma-Fil, Silux, or Herculite; however, the wet-finished Visio-Dispers was significantly rougher than the dry-finished. When surface hardness was compared, there was no significant difference in hardness values between the wet and dry samples when compared over time. When changes in color were evaluated, only Visio-Dispers had no significant change in color for both the wet- and dry-finished samples over the five-week evaluation period. Dry finishing of only one composite (Silux) produced a significant change in color. Dry finishing of composites was superior or equal to wet finishing in all tests except for the color change in Silux.

Dentoalveolar trauma.

Dentoalveolar injuries represent a serious dental problem for the patient. Time from injury to treatment is a major factor in the outcome of many of these injuries. To decrease dental pain and suffering and enhance the prognosis, medical personnel must recognize the presence of dentoalveolar injuries and consult with, or refer the patient to, a dentist as soon as possible.

Paresthesia from an overdenture abutment: report of case.

A case is reported in which paresthesia of the area supplied by the right mental nerve was associated with alveolar ridge resorption and a failing overdenture abutment. After surgical removal of the overdenture abutment, all signs and symptoms of the paresthesia resolved.

A preliminary study of the effect of eliminating requirements on clinical performance.

This study determined the effect of a clinical program driven by patient needs upon students' productivity, attitudes, and academic performance. A group of eight senior students, whose academic and clinical performance profile replicated that of the rest of the class, were chosen to participate in a year-long non-requirement clinic. The students were expected to attend all clinic sessions, and treat their assigned patients. Their performance was compared to that of classmates in the regular requirement-driven curriculum. The non-requirement group had significantly higher academic achievement and significantly outproduced their classmates. Non-requirement students had no state board failures, versus 17 percent in the regular curriculum, and reported significantly lower stress. This study suggests that predoctoral clinical programs can maintain quality and productivity in the absence of unit requirements.

Effects of reducing senior clinical requirements.

This study investigated the effects of reducing dental clinical requirements. Twenty-seven senior students participated in a modified system in which requirements were reduced to essential experiences, points were awarded for all procedures completed, and a total point requirement was created to ensure comprehensive care. The remaining seniors (N = 97), who operated under the conventional requirement system, served as controls. No significant differences were found between the groups in daily clinic grades, comprehensive examination performance, final senior-year grade point average, or number of procedures completed. A year-end questionnaire on stress and anxiety indicated that the experimental group perceived less stress and anxiety, were significantly more positive about their performance evaluations, and perceived significantly less pressure to complete procedures.

A comparison of four simulation and instructional methods for endodontic review.

The effects of four different endodontic self-instructional review formats (slide-tape, latent-image simulation, computer text simulation, and computer-assisted video interactive simulation) on senior clinical endodontic performance are compared. The senior class of 105 students was divided into eight groups of 13-14 academically equivalent students prior to initiating endodontic treatment in the 1985-86 academic year. With the exception of the control group, each participated in a program designed to review principles of endodontic diagnosis and treatment. All clinical endodontic cases were subsequently critiqued by a calibrated panel of two general dentist and one endodontist. Overall, students in the study group made fewer diagnostic errors compared with those in the control group, while the error reduction in clinical treatment was not significantly reduced between the two groups. No significant difference in error reduction was noted between the simulation formats. Student evaluations, as well as comparative developmental expenditures, are discussed.

A simulation program for reviewing endodontics.

To reduce repetitive endodontic errors by senior dental students, a formal review program was established. It consisted of a slide-tape and a written, latent-image simulation of an endodontic case requiring diagnostic and treatment decisions. Before undertaking any endodontic cases in the senior year, each student had to complete the program successfully. The program significantly reduced diagnostic errors in six categories for posterior teeth and in four of six categories for anterior teeth. Errors were also significantly reduced in eight of 12 treatment categories for posterior teeth and in five of 12 categories for anterior teeth. Students' opinions of the endodontic review program were quite favorable.

Necrotizing fasciitis of the head and neck: review of the literature and report of a case.

Necrotizing fasciitis is a rapidly spreading, life-threatening, bacterial disease. Mortality rates have been estimated to vary between 8.7% and 74%. Mortality depends on many factors, one of which is early recognition. Necrotizing fasciitis of dental origin has a low prevalence and as such presents diagnostic challenges for the dentist. The literature is reviewed, and a case history is presented.