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Biomedical subjects

N R Robertson

Publications and source records attributed to N R Robertson.

18 recordsLinked to original sources
PubMed1992

Stresses induced by edgewise appliances in the periodontal ligament--a finite element study.

The quantification of stress in the periodontal ligament is an important concept, as stress in this tissue is transmitted to the alveolus, with subsequent bone remodelling and tooth movement. A number of clinical studies have suggested figures for such an optimal stress range. This study makes use of a finite element technique to determine the stress induced in the periodontal ligament in three dimensions when a maxillary canine tooth is subjected to an orthodontic force similar to that produced by an edgewise appliance. The maximum stress induced at the cervical margin of the periodontal ligament was 0.072 N/mm2, while the maximum stress induced at the level of the apical foramen was 0.0038 N/mm2. These results are discussed in the light of known clinical experience and compared with the stresses produced in the periodontal ligament by other orthodontic forces. The findings would suggest that even with 'perfect' edgewise mechanics it would be difficult to obtain canine movement by pure translation or 'bodily movement.'

Alveolar Process↗
PubMed1992

The Barry Project--a cephalometric assessment of treatment change in a consecutive sample of malocclusion.

This is the last of a three-part series examining the results of orthodontic treatment in a consecutive sample of malocclusion from a Welsh town. The cephalometric changes are compared for the different treatment regimes which were employed. Where the variables being examined were common to both radiographs and study cast records the treatment changes observed for the regimes were similar. Only limited 'skeletal' change, interpreted as a change in a few cephalometric measurements, was found to occur during treatment. Perhaps of most interest was the consistent reduction of 'A' point in the full fixed appliance group.

Cephalometry↗
PubMed1992

Bioprogressive brackets and pentamorphic arches.

The use of high torque values with no tip in preadjusted incisor brackets in the Bioprogressive system, in conjunction with narrow anterior rectangular archwires may produce crown spacing, root crowding and upright central incisors. The solution to these problems would seem either to reduce the time spent in rectangular wires or to change to a bracket with reduced torque, together with appropriate second order compensations in the archwire or the bracket.

Chromium Alloys↗
PubMed1975

Prognosis for infants with idiopathic respiratory distress syndrome.

Infants with the idiopathic respiratory distress syndrome admitted to the intensive care unit during January 1972 to September 1974 were reviewed. The overall mortality rate for infants whose birth weight was 1000 g or more was under 10%, and for those who established spontaneous respiration after birth it was less than 5%. The hyperoxia test was not a useful guide to prognosis. It was possible on the basis of the infants' ability to establish spontaneous ventilation after birth to divide them into two groups. In those who established adequate ventilation the mortality rate was 4-5%; in those who did not it was 57%. This test should be generally applied, since not only does it give an immediate guide to the severity of the disease, which is better than that provided by birth weight, gestational age, or the hyperoxia test, but it may be applied to infants born in and outside a hospital providing neonatal intensive care. Improvement in the outlook for infants with a bad prognosis will be achieved only by improvements in perinatal care designed to minimize severe intrapartum asphyxia in infants of low birth weight.

Birth Weight↗
PubMed1975

Immediate effects of alkaline infusion in infants with respiratory distress syndrome.

Nineteen infants with acidosis associated with RDS were studied following the infusion of: (1) 0.58M (7%) THAM over 30 seconds; (2) molar bicarbonate over 30 seconds; (3) molar bicarbonate over 2 minutes; and (4) molar bicarbonate over 5 minutes. PaC02 fell after THAM; PaC02 rose sharply after bicarbonate and remained elevated 10 minutes after infusion. The pH rose abruptly in all infants and remained significantly elevated 10 minutes after infusion. Pa02 changes were variable; no infant had immediate improvement in Pa02. The changes in osmolality, hematocrit, and colloid osmotic pressure describe the immediate osmotic hemodilution following the infusion of hypertonic base.

Acid-Base Equilibrium↗
PubMed1975

Pneumothorax in the newborn. Changing pattern.

The clinical course of pneumothorax and its allied conditions was studied in 34 newborn infants who presented over a 2 1/2-year period. We found an overall incidence of 3/1000 live births. 11 term infants without obvious pulmonary pathology presented early (9 within minutes of birth); 6 of these had aspirated meconium or blood. The remaining 23 were preterm infants with hyaline membrane disease (HMD) and accounted for 68% of the infants in this series. In contrast, they presented late (mean 45 hours) and 16 were on continuous distending pressure (CDP) or intermittent positive pressure ventilation (IPPV) at the onset of pneumothorax. 15% of all infants with HMD who required CDP/IPPV developed pneumothorax; this increased incidence was most evident in infants who received CDP only. All except 2 of the 11 term infants in the first group were managed conservatively and all survived. Wehn pneumothorax occurred as a complication of HMD in preterm infants, 14 of the 16 infants required intrapleural drainage. Persistence or recurrence of pneumothorax occurred in 9 infants, 7 of whom were receiving CDP/IPPV at the time. Lung expansion was affected only after replacement with a patent chest drain through the same incision or insertion of a second drain on the same side of the chest. All 5 deaths occurred in the group of preterm infants with HMD. 3 resulted directly form respiratory failure due to severe HMD complicated by pneumothorax. We emphasize the increasing importance of pneumothorax as a complication of HMD in preterm infants, particularly in those receiving CDP. Successful management depends on prompt diagnosis and treatment of pneumothorax, which may occur as unexplained sudden deterioration at any time during the course of illness in this group of high risk infants.

Drainage↗