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Biomedical subjects

P A Cook

Publications and source records attributed to P A Cook.

18 recordsLinked to original sources
PubMed1992

Effect of hygiene instrumentation on titanium abutments: a scanning electron microscopy study.

Implant abutments can be exposed to a variety of oral prophylaxis procedures. In this in vitro study, titanium abutments were subjected to five oral prophylaxis treatment modalities; a metal scaler, a plastic scaler, a rubber cup, a rubber cup with tin oxide, and an air-powder abrasive. The abutment surfaces were then examined under both light and scanning electron microscopes. The metal scaler was seen to roughen the titanium surface. All other modalities tested appeared to smooth the titanium surface by removing surface debris and rounding off the sharp machined grooves present on the untreated abutment surface.

Air↗
PubMed1992

The reliability of positioning pre-adjusted brackets: an in vitro study.

To investigate the reliability of bracket positioning, twelve operators, familiar with the straight-wire appliance, placed 0.022" straight-wire brackets on the anterior teeth of a typodont study model, on three different occasions. Bracket position was assessed using a Magiscan image analyser. Angular judgements by the operators were found to be less consistently identified than linear assessments. Slot angulation showed the largest variability and vertical bracket placement the least. The clinical implications of bracket misplacement are discussed.

Cuspid↗
PubMed1992

The Second Medical Research Council study of prognostic factors in nonseminomatous germ cell tumors. Medical Research Council Testicular Tumour Working Party.

PURPOSE: To assess prognostic factors in a large population of patients with metastatic nonseminomatous germ cell tumors (NSGCT) arising in gonadal or extragonadal sites. PATIENTS AND METHODS: Data from 795 patients treated with chemotherapy between 1982 and 1986 in 13 centers were analyzed. Particular emphasis was placed on exact tumor measurements (eg, size of nodal masses, number of lung metastases), and the diagnostic pathology was also reviewed. Cox regression analysis was performed on these data. The patients were treated with a variety of cisplatin-containing chemotherapy regimens, 86% of which included etoposide. RESULTS: With median follow-up of 45 months, overall 3-year survival is 85%. The independently adverse features proved to be (1) the presence of liver, bone, or brain metastases; (2) raised marker levels (alpha-fetoprotein [AFP] level greater than 1,000 kU/L or beta subunit of human chorionic gonadotropin [HCG] greater than 10,000 IU/L [corrected]); (3) the presence of a mediastinal mass greater than 5 cm in diameter; (4) the presence of 20 or more lung metastases; (5) increasing age; and (6) absence of undifferentiated teratoma (embryonal carcinoma) or fibrous tissue from the primary tumor. CONCLUSIONS: The first four factors were used to define a simple prognostic classification. A good-prognosis group having none of these features comprised 67% of our patient population and had a 3-year survival of 93%. The remaining 33% of patients having at least one of these features had a 3-year survival rate of 68%. These patient groups are currently the subjects of international randomized clinical trials.

Adult↗
PubMed1992

Medical Research Council prospective study of surveillance for stage I testicular teratoma. Medical Research Council Testicular Tumors Working Party.

PURPOSE: A prospective study of surveillance after orchidectomy alone in patients with stage I nonseminomatous germ cell testicular tumor (NSGCT) was performed to determine the relapse-free rate and to identify the histologic criteria that predict for relapse. PATIENTS AND METHODS: Three hundred ninety-six patients from 16 United Kingdom and one Norwegian centers were entered onto the study between January 1, 1984 and October 1, 1987 of whom 373 were eligible for analysis. In a previous retrospective study, we defined a prognostic index based on histologic criteria that identified a group of patients with a high risk of relapse. This index was based on the presence of venous and lymphatic invasion, undifferentiated cells, and the absence of yolk sac elements in the primary tumor. RESULTS: The 2-year actuarial relapse-free rate after orchidectomy was 75% (95% confidence interval, 71% to 79%), and the rate at 5 years was 73%. Five patients died of tumor or treatment-related complications, which resulted in a 5-year survival of 98%. The relapse-free rate in patients with three or four risk factors was 54%. CONCLUSIONS: This study confirms the safety of surveillance as a method of management and identifies a group of patients with a high risk of relapse. A prospective phase II study has been initiated to determine whether two courses of platinum-based adjuvant chemotherapy will prevent relapse in these high-risk patients.

Adult↗
PubMed1991

Membrane peptidases in the peripheral nervous system of the pig: their localization by immunohistochemistry at light and electron microscopic levels.

The presence and cellular localization of five membrane peptidases has been investigated in peripheral nerves, including those of the autonomic nervous system, in the pig. Endopeptidase-24.11 ("enkephalinase") peptidyl dipeptidase A, aminopeptidase N, aminopeptidase W and dipeptidyl peptidase IV were studied by both enzymic assays of membranes prepared from samples of nerve and by immunoperoxidase histochemistry at light and in two cases, endopeptidase-24.11 and aminopeptidase W, at electron microscopic levels. All five peptidases could be quantified by enzymic assay, though the activities were about 1% of those in renal microvilli and less than those of choroid plexus membranes. Endopeptidase-24.11 was associated with Schwann cell membranes in all types of nerve examined, including major nerves containing predominantly myelinated fibres as well as autonomic nerves, such as the vagus and splenic nerves and the sympathetic chain, staining being observed in membranes associated with myelinated and unmyelinated fibres. The Schwann cell location of endopeptidase-24.11 was confirmed by correlation with immunostaining for glial fibrillary acidic protein and by electron microscopy. This peptidase is known to have a wide repertoire of susceptible substrates among neuropeptides which was here shown to include vasoactive intestinal polypeptide (Km 268 microM, kcat 568 min-1), one of a number of neuropeptides present in peripheral nerve fibres. Three of the peptidases, peptidyl dipeptidase A, aminopeptidase N and dipeptidyl peptidase IV, were associated with microvessels of peripheral nerves. Aminopeptidase N was also observed in connective tissue elements, including the perineurium. Aminopeptidase W was unique among the five peptidases in having a neuronal localization. This was observed in unmyelinated and myelinated nerves and was supported by comparison with the pattern of staining observed for neurofilament protein and by electron microscopic immunoperoxidase staining. This observation was unexpected since aminopeptidase W has not been detected as a neuronal marker in the brain. Some possible roles for the membrane peptidases in peripheral nerves are discussed.

Animals↗
PubMed1989

Resorption of a first permanent molar.

A case is presented of an unerupted maxillary second premolar causing the severe resorption of a first molar tooth. This case underlines the need for adequate radiographic evidence before recommending the extraction of teeth for the relief of crowding.

Bicuspid↗
PubMed1989

The reliability of mandibular radiographic superimposition.

Using tracings from thirty pairs of serial cephalometric radiographs, the reliability of three outlines, commonly used for mandibular superimposition, was investigated. There were sizeable errors associated with all three groups, but tracings involving Björk's mandibular structures were found to be the least reliable. Despite the greater validity of the Björk structures for assessment of growth changes, in certain cases the use of the mandibular outline may be of greater value for the superimposition of tracings, especially when the time interval between the radiographs is short, or the patient has passed maturity and the growth rate has declined to a negligible level.

Adolescent↗
PubMed1989

A fluoride-containing composite resin--an in vitro study of a new material for orthodontic bonding.

The shear/peel bond strength of a new material, a 'hybrid' of a composite resin and a glass ionomer cement, was compared in vitro with the bond strengths of a composite resin and of a glass ionomer cement. The new material had a significantly greater bond strength than the other materials tested and its properties were very similar to the composite resin. Unlike the glass ionomer cement, etching of the enamel before applying the adhesive is required. The clinical indications for using this new cement are discussed.

Adhesiveness↗
PubMed1989

The Senior Registar Orthodontic Group.

The Consultant orthodontist is a key member of the orthodontic profession in the UK, and it is essential that trainee consultants receive the best education possible if orthodontics is to continue to advance as it has in recent years. The Senior Registar Orthodontic Group has an important role to play in that education.

Dental Staff, Hospital↗
PubMed1988

Tracing error with Björk's mandibular structures.

The tracing errors associated with the structures used in Björk's method of mandibular superimposition are investigated using multiple tracings of fifty lateral cephalometric radiographs. The horizontal error levels were much less than the vertical, midline structures more reliable than bilateral structures, and the lower third molar tooth germ more reliable than the inferior dental canal.

Cephalometry↗
PubMed1988

An in vitro study of the bond strength of a glass ionomer cement in the direct bonding of orthodontic brackets.

The shear/peel bond strength of a 'no-mix' composite orthodontic bonding resin was compared in vitro with that of a glass ionomer cement. The effect of pre-treatment of the enamel, with either phosphoric acid or polyacrylic acid, prior to using the glass ionomer cement was also assessed. The composite resin had a significantly higher bond strength than the glass ionomer cement. Simple prophylaxis and drying of the enamel achieved the best results when using the glass ionomer cement, whilst etching the tooth surface with phosphoric acid produced a significantly poorer bond to the enamel. Investigation of the site of failure showed the composite resin bonded very well to the tooth and less well to the bracket, whilst the glass ionomer adhered significantly better to the bracket base than to the tooth surface.

Acid Etching, Dental↗
PubMed1987

Methods of attachment for palatal arches: an evaluation.

Orthodontic appliances attached to the palatal surfaces of molar bands are commonly used to produce, or is an aid to, active tooth movement. The present paper describes a number of the systems available for achieving this attachment and investigates their advantages and disadvantages in clinical practice.

Adult↗
PubMed1986

Pin-modified facial inlay to enhance retentive contours on a removable partial denture abutment.

A procedure has been described that will, in many instances, eliminate the necessity for a full veneer crown. The periodontal health of the tooth is not compromised because the accentuated contour is generally remote from the gingival tissues. A single pin will assure sufficient retention and resistance to displacement for the small inlay if the walls of the preparation offer reasonable resistance form.

Dental Abutments↗