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Biomedical subjects

R M Howell

Publications and source records attributed to R M Howell.

At least 37 records · Page 2Linked to original sources
PubMed1981

Early pulp changes after anterior maxillary osteotomy.

For purposes of examining the pulpal reaction to segmental osteotomy, six adult female Macaca fascicularis monkeys received identical anterior maxillary osteotomies involving the incisors only. The mobilized segment was displaced distally a distance of approximately 2 mm, then splinted in place for a week. The healing and revascularization of the bone proceeded well, with no ischemic areas visible on the microangiograms other than in the animal examined immediately after operation. The osteotomy site was bridged with new bone at three months. The majority of the pulps of the mobilized segment and all teeth examined distal to the segment remained vital. No degenerative change other than the temporary disappearance of sensory nerves was observed in the vital pulps of the segments. By the six-month period, the sensory nerve supply to the dental pulp had regenerated completely.

Animals↗
PubMed1980

Circular dichroic, infrared and other studies on the protein component of pig brain thromboplastin.

1. A four-step procedure used to isolate the protein component (apoprotein III) of pig brain thromboplastin yielded approximately 25 mg from 500g of brain. 2. In the absence of detergent, apoprotein III had an apparent mol.wt. of 360 000 by gel-filtration, and, after electrophoresis on polyacrylamide gels in the presence of sodium docecyl sulphate, it appeared as a major protein band of mol.wt.59 000, suggesting the existence of polymeric and monomeric forms. 3. Chemical analyses of apoprotein III revealed that hydrophilic and hydrophobic amino acids were present in a ratio of 3:2, together with approx, 9% (w/w) of carbohydrate. 4. The far-u.v.c.d. and i.r. spectral data indicated that, like other membrane proteins, apoprotein III has a high percentage of unordered structure with lesser amounts of alpha and beta-forms. 5. Relipidation of apoprotein III to restore clotting activity caused no extensive alteration in the c.d. and i.r. spectra, indicating that the phospholipid associates with a comparatively small hydrophobic segment. The constrained unordered conformation, which makes the major contribution to the c.d. spectrum, probably forms a separate domain in the aqueous phase. The absence of any increase in the amplitude of both negative c.d. extrema, following relipidation, contrasted with the substantial increase observed in a helix-forming solvent and raises the possibility that the more stable polymeric form of apoprotein III is retained as the active form in the lipid phase. 6. We suggest that as a consequence of cell membrane damage, the recognition and activation of factor VII may involve minor changes of conformation that are dependent upon the flexibility inherent in an unordered secondary structure.

Amino Acids↗
PubMed1979

Aggressive ossifying fibroma of the maxilla: review of the literature and report of case.

A case of a large aggressive ossifying fibroma of the maxilla has been presented. Review of the literature shows the literature shows the difficulty in establishing a definitive diagnosis through any single diagnostic modality. Much of this is due to the confusion surrounding classification of the tumor. Adjunctive radiographic and nuclear medicine diagnostic aids were utilized, as were clinical, laboratory, and histopathologic studies, in resolving the diagnostic questions posed by this large and aggressive tumor. Surgical intervention through conservative enucleation produced few operative or postoperative difficulties and minimal residual deformity. Differentiation of ossifying fibroma from other benigh and malignant neoplasms as well as fibrous dysplasia is important in the correct management of this lesion.

Adolescent↗
PubMed1977

Malignant transformation of ameloblastic fibro-odontoma to ameloblastic fibrosarcoma.

Two cases of malignant transformation of ameloblastic fibro-odontomas are presented, along with a review of the literature on ameloblastic fibrosarcomas. The occurrence of this malignant transformation of ameloblastic fibromas, ameloblastic odontomas, and ameloblastic fibro-odontomas appears to be more frequent than previously thought. This potential transformation alone does not justify radical treatment of all these benign lesions. If there is recurrence accompanied by a histologic pattern change toward a more unorganized fibrous stroma with displacement of the epithelial component, however, then more extensive treatment procedures appear to be indicated.

Adolescent↗
PubMed1976

Scanning electron microscopic and electrophoretic studies on clotting factor adsorbents.

Physical studies carried out on a range of protein and clotting factor adsorbents revealed marked morphological and charge differences. Their appearance in the scanning electron microscope could be used to classify the insoluble precipitates, calcijm phosphate, barium sulphate and citrate, as either amorphorous or crystalline. Surface charge is difficult to define but the present studies on the sparingly-soluble salts, based on calcium and barium, have revealed that they can be subdivided on the basis of the presence or absence of a charge reversal point in the pH-mobility curve. The anion component appeared to determine this characteristic; it was noted that phosphate and citrate ions had a marked effect and gave a biased negative potential at all pH values. We concluded that where a divalent cation is cohabiting with a trivalent anion, the greater potential-determining ability of the latter will dominate the overall charge at the surface of a particle, even below pH7 and the absence of a positive potential gives a monophasic pH-mobility curve. Differences in both the physical appearance and electrophoretic mobility of the adsorbents studied reflect the wide variation in their chemical composition, especially among the various forms of calcium phosphate which, unlike barium sulphate, can include substituted ions such as hydroxyl, in their crystal lattice. The definition of these characteristics allows their behaviour towards clotting factors to be more easily predicted.

Adsorption↗
PubMed1975

Scanning electron microscopic and electrophoretic observations on barium sulphate used to absorb clotting factors.

Electron microscopy and particle electrophoresis were found to be complementary techniques with which to complete the physical data from an earlier study on barium sulphates used to absorb clotting factors from serum. The differences revealed by scanning electron microscopy (S. E. M) in the physical shape of low and high density grades of barium sulphate particles appear to be of greater significance than charge as expressed by electrophoretic mobility, in determining whether or not precursor or performed factor Xa is eluted. This conclusion was based on the finding that at pH values close to 7, where the adsorption from serum occurs, all samples with the exception of natural barytes were uncharged. However as the high-density, or soil-grade, was found by S. E. M. to consist of large solid crystals it was suggested that this shape might induce activiation of factor X as a result of partial denaturation and consequent unfolding of the adsorbed protein. In contrast, uptake of protein into the centre of the porous aggregates revealed by S. E. M. pictures of low-density or X-ray grade barium sulphate may afford protection against denaturation and exposure of the enzyme site. The porous nature of particles of low-density barium sulphate compared with the solid crystalline forms of other grades accounts not only for its lower bulk density but also for its greater surface/gram ratio which is reflected by an ability to adsorb more protein from serum. Neither technique produced evidence from any of the samples to indicate the presence of stabilising agents sometimes used to coat particles in barium meals.

Adsorption↗