Hydrophilic-interaction chromatography of complex carbohydrates.

Complex carbohydrates can frequently be separated using hydrophilic-interaction chromatography (HILIC). The mechanism was investigated using small oligosaccharides and a new column, PolyGLYCOPLEX. Some carbohydrates exhibited anomer separation, which made it possible to determine the orientation of the reducing end relative to the stationary phase. Amide sugars were consistently good contact regions. Relative to amide sugars, sialic acids and neutral hexoses were better contact regions at lower levels of organic solvents than at higher levels. HILIC readily resolved carbohydrates differing in residue composition and position of linkage. Complex carbohydrate mixtures could be resolved using volatile mobile phases. This was evaluated with native glycans and with glycans derivatized with 2-aminopyridine or a nitrobenzene derivative. Both asialo- and sialylated glycans could be resolved using the same set of conditions. With derivatized carbohydrates, detection was possible at the picomole level by UV detection or on-line electrospray mass spectrometry. Selectivity compared favorably with that of other modes of HPLC. HILIC is promising for a variety of analytical and preparative applications.

Dental caries prevalence and related factors in 5-year-old children in Hong Kong.

One thousand five Hong Kong kindergarten children with a mean age of 5.75 +/- 0.46 years were sampled for caries prevalence and related factors. Samples were drawn from a total population of approximately 9,000 5-year-old children. Caries examination was conducted after the teeth were cleaned professionally using a sickle probe (Ash #54) and diagnostic criteria of the World Health Organization. Thirty-seven percent of children were caries-free and the mean dmft of all children was 3.2 +/- 3.92. The components of the dmft were dt = 2.93, mt = 0.04 and ft = 0.23. The dmfs was 5.10 +/- 7.80 with ds = 4.67, ms = 0.12, and fs = 0.31. The caries distribution was skewed, 18% with more than 10 dmfs and the most severely affected child having 54 decayed surfaces. Seventy-two per cent had never visited a dentist. A statistically significant positive correlation was found between the father's profession and caries prevalence. The age of the child at the first visit and the frequency of visits to the dentist were related directly to parental income. The primary mandibular first molar ranked highest among the teeth that needed treatment, mostly extraction. (Pediatr Dent 15: 116-19, 1993).

Changes in power spectrum of electromyograms of masseter and anterior temporal muscles during functional appliance therapy in children.

This study applied frequency analysis to compare changes in the power spectrum density functions of surface electromyograms obtained from the paired masseter and anterior temporal muscles during therapy with three types of functional appliances, namely the Bionator, modified Fränkel type I, and Fränkel type III. Eighteen children were divided into three groups receiving either Bionator, Fränkel type I, or Fränkel type III therapy; a fourth group consisting of six children who received no therapy served as control. Before and after 3, 6, and 12 months of therapy, each child performed maximum voluntary isometric clenches in the position of maximum intercuspation. The mean frequency of the power spectrum was the variable studied. Children treated with the Bionator and Fränkel type I appliances showed greater changes in mean frequency than those treated with the Fränkel type III appliance. Although the muscles of untreated children also showed shifts of mean frequency to lower frequency values as a function of time, there was a greater downward shift of mean frequency in those treated with functional appliances. The downward shifts might have been associated with changes in muscle fiber lengths and/or recruitment patterns as a result of both treatment and normal growth.

EMG power spectrum patterns of anterior temporal and masseter muscles in children and adults.

The power spectrum of electromyograms (EMG) has been demonstrated to vary with muscles having different muscle fiber type compositions. This study investigated the variations in EMG power spectrum patterns of the masticatory muscles with age and gender by comparison of the mean power frequency (MPF) of the anterior temporal and masseter muscles in children and adults. Surface EMG signals were sampled bilaterally from the muscles when the subjects were performing maximum voluntary isometric clenches at maximal intercuspal position. The results indicated that MPF values were age-dependent (p less than 0.001), and sexual dimorphism was evident (p less than 0.001), with lower MPF values in male and adult muscles. While male adults had the lowest and female children had the highest MPF values, female adults had MPF values closer to values obtained from male children. These differences or similarities could be attributed to the degree of differentiation of the muscles during growth and development of the craniofacial morphology.

Real-time signal acquisition and analysis for clinical dental electromyography using a microcomputer-based system.

The Electromyographic (EMG) Signal Acquisition and Analysis System is an integrated hardware and software system that digitizes multichannels of amplified EMG signals and stores them in user defined disc files before analysis. The software runs on all IBM PC and its compatibles with the appropriate analogue-to-digital (A/D) conversion board. Both time and frequency domain analyses can be computed on-line. This system provides a low cost method of digitizing and analysing EMG signals on real-time for clinical dental electromyography.