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Biomedical subjects

A R Collett

Publications and source records attributed to A R Collett.

14 recordsLinked to original sources
PubMed2000

Orthodontic tooth movement after extraction of previously autotransplanted maxillary canines and ridge augmentation.

A case report is detailed in which autotransplanted maxillary canines were removed and the spaces closed. Substantial surrounding bone loss was associated with the upper right canine, and a bone graft was needed to reestablish normal dentoalveolar ridge morphology. Bone was taken from the maxillary tuberosity and placed in the canine extraction site, fixed with a bone screw, and covered with GoreTex. Seven months after placement of the bone graft, the GoreTex and stabilizing screw were removed to allow for consolidation of the bone. The upper left canine and lower second premolars were extracted, and fixed appliances were placed in both arches to align the teeth and close the spaces. Protraction of the upper right first premolar and retraction of the lateral incisor into the graft site were kept slow and constant with continued periodontal assessment. During the space closure, there was some concern that the bone in the graft site might resorb, leaving the teeth with compromised periodontal support. However, no significant periodontal attachment loss occurred despite ongoing concern about the amount of keratinized tissue. Perhaps the relatively slow rate of tooth movement provided for bone to be maintained and recreated ahead of the tooth. Almost complete closure of the upper canine extraction spaces was achieved. The upper premolars were substituted for the maxillary canines, and unfavorable prosthetic options were thus avoided. The lower arch was aligned, and the extraction spaces completely closed.

Adolescent↗
PubMed2000

Conservative management of lower second premolar impaction.

Lower second premolars account for approximately 24 per cent of impactions, excluding third molars, even though most reports in the literature relating to impacted teeth address the maxillary canine, with relatively few reports on the lower second premolar. Conservative management involves surgical exposure of the crown, however, subsequent premolar eruption is unpredictable. A case is described in which removal of a deciduous second molar was followed by eruption of an unfavourably inclined premolar located deep within the alveolus. Sufficient time must be allowed for eruption and in the present case 16 months elapsed before the tooth had erupted to the level of the occlusal plane.

Adolescent↗
PubMed2000

Current concepts on functional appliances and mandibular growth stimulation.

The mode of action of functional appliances, particularly in relation to stimulating mandibular growth, is a controversial subject. Many of the reports concerning growth effects of functional appliances have been characterized by poor methodology. In assessing functional appliances, results from prospective randomized clinical trials should be given prominence. On the basis of available evidence, it cannot be concluded that functional appliances are effective in stimulating and increasing mandibular growth in the long term. Although favourable growth changes have been reported following phase 1 therapy, they are generally not substantial and long term stability appears to be poor.

Cephalometry↗
PubMed1999

Smoking patterns in adolescent orthodontic patients and school children.

Smoking is known to be widely practised by young adults and teenagers, a fact that is of immediate importance to the orthodontic profession as it is now well accepted that smokers have poorer periodontal health than non-smokers. The aim of the present study was to determine the level of smoking in teenage orthodontic patients and compare it with that in the general teenage population and, further, to examine how these smoking habits are influenced by the subjects' attitudes. Patients were surveyed as to their smoking habits and attitudes. All were between 10 and 18 years of age and undergoing active fixed-appliance therapy. The same survey was distributed to a local primary (elementary) school and local secondary (high) schools. Of the 729 school respondents, 29 per cent were classified as smokers; of the 333 respondents in the orthodontic group, 11 per cent were classified as smokers. Although the level of smoking amongst orthodontic patients appears to be lower than that for the general adolescent population, significant numbers of patients smoke on a regular basis, and a small proportion of these is under 13 years of age. Because they have regular contact over a number of years with their adolescent patients, orthodontists are in a favourable position to reinforce non-smoking behavior.

Adolescent↗
PubMed1994

Mechanical properties of some polymer materials used for tooth positioners.

The chemical composition, thermal behaviour and mechanical properties of three tooth positioner materials, Urethane P1 (P1), White Rubber (WR) and Elastocryl (EL) were investigated. Infra-red spectrophotometry indicated the P1 polyurethane material to be of the polyether type, and EL to be a blend of poly(ethyl methacrylate) and poly(methyl methacrylate) while WR appeared to be filled cis-poly (isoprene) (natural rubber). The glass transition temperature (Tg) for EL was determined as approximately 10 degrees C, and for both P1 and WR the Tg was less than -50 degrees C. The stress relaxation behaviour was assessed in compression by measuring the stress variation with time. The results for all three materials conformed to the superelastic theory of rubber elasticity. EL exhibited both a more rapid rate and higher degree of stress relaxation than did P1 and WR. Recovery from deformation was assessed by compressing cylinders for given periods of time and then measuring the level of reduced residual strain of the material with time. All three materials exhibited significant residual strain (epsilon(t)) over 'clinically relevant' time periods, and the reduced residual strain (epsilon(t)/epsilon(O)) following deformation was greater for EL than P1 or WR. There was some indication that the three materials have some permanent set following deformation. It was concluded that, in considering desirable mechanical properties of tooth positioner materials, EL is the least suitable of the three examined, with none of the materials being ideal.

Butadienes↗
PubMed1993

Analyses of craniofacial and dental morphology in monozygotic twins discordant for cleft lip and unilateral cleft lip and palate.

The Michigan Cleft Twin Sample data was analyzed in order to investigate dental arch and craniofacial morphology. The present study consisted of 12 monozygotic twins discordant for either cleft lip or unilateral cleft lip and palate. Individuals having CL (repaired) alone did not differ from their unaffected counterparts in dental arch and skeletal morphology. Repaired UCLP subjects were characterized by having a shorter and more posteriorly positioned maxilla. Although reduction of dental arch width as a result of scar contraction following surgery was evident, the effects of scar tissue pull did not affect maxillary basal width.

Cephalometry↗
PubMed1993

Terminology of facial morphology in the vertical dimension.

Consideration of facial type plays an important role in the formulation of an orthodontic treatment plan and prognosis of treatment. Of particular importance is the vertical relationship, that is, whether an individual is long-faced (dolichofacial), or short-faced (brachyfacial). The vertical facial type provides a clue regarding the growth direction of the facial complex, and should be used with an anteroposterior classification to describe a patient's face. The potential for confusion in communicating vertical facial types exists due to the nature of the terminology in use. For example, the term dolichoprosopic as used in the Bimler analysis has an opposite meaning to the term dolichofacial. It would seem prudent that if such terminology is to be employed there should be some attempt at standardization, and at least an appreciation of the derivations of the terms, and their differences.

Cephalometry↗
PubMed1991

Eicosanoids: physiology update and orthodontic implications.

The eicosanoids are members of a group of substances comprising prostaglandins and leukotrienes which are released by a host of mechanical, thermal, bacterial and other insults and contribute importantly to the signs and genesis of inflammation (Brain and Williams 1990, Dusting 1989 Moncada et al. 1985, Salmon and Higgs 1987). In this review we examine the increasing number of reports on the actions of eicosanoids on the dentoalveolar complex. In addition, since it is desirable for the orthodontist to have a sound knowledge, not only of the roles of eicosanoids in tooth movement, but also of their basic general physiology, an overview of the latter area is presented.

Alveolar Process↗
PubMed1985

Prostanoids and adrenaline release: a study of [3H]adrenaline efflux from the rabbit isolated, perfused, adrenal gland.

[3H]Adrenaline was incorporated in an isolated perfused preparation of the rabbit adrenal gland and the effects of indomethacin, PGE2 and PGI2 on its release were investigated. Efflux of [3H]adrenaline was elicited by electrical stimulation of the splanchnic nerve (60 s at 5 Hz). Indomethacin (3 and 30 microM) had no effect on stimulation-induced efflux. PGE2 (30, 90 and 300 nM) reduced the efflux; with 90 nM PGE2 the inhibition amounted to approximately 30%. PGI2, in concentrations from 90 to 600 nM, was without effect. These findings indicate that release of [3H]adrenaline from the rabbit adrenal gland is not subject to modulation by endogenous adrenal prostaglandins; however, PGE2 may play a role in some pathological situations.

Adrenal Glands↗
PubMed1984

Catecholamine secretion from the rabbit adrenal gland is not modulated by a mechanism involving beta-adrenoceptors.

The possibility that catecholamine secretion from the rabbit adrenal gland is subject to modulation by a mechanism involving beta-adrenoceptors was investigated in an isolated perfused preparation of the gland. The adrenal catecholamine stores were radiolabelled with 3H-adrenaline and subsequently efflux of radioactivity was elicited by stimulation of an attached branch of the splanchnic nerve. The efflux of radioactivity evoked by nerve stimulation (1 min at 5 Hz) was not altered by isoprenaline (0.1 microM), metroprolol (0.1 microM) or (+/-)-propranolol (1 microM). Stimulation-induced efflux was reduced in the presence of a higher concentration of (+/-)-propranolol (10 microM); however, it was also reduced by (+)-propranolol (10 microM). These findings do not support the existence in the rabbit adrenal gland of a mechanism involving beta-adrenoceptors through which catecholamine secretion may be modulated.

Adrenal Glands↗
PubMed1984

Effects of adrenoceptor antagonists and neuronal uptake inhibitors on dimethylphenylpiperazinium-induced release of catecholamines from the rabbit isolated adrenal gland and guinea-pig atria.

Isolated rabbit adrenal glands were perfused with Krebs-Henseleit solution at 37 degrees C and the catecholamine storage sites were labeled with [3H]epinephrine. Release of radioactivity was evoked by 2-min periods of perfusion with dimethylphenylpiperazinium (DMPP, 100 microM). DMPP-induced efflux of radioactivity was decreased by desipramine (1 microM), cocaine (30 microM), phenoxybenzamine (1 and 10 microM), phentolamine (1, 3 and 10 microM) and propranolol (1 microM). The reduction in DMPP-induced efflux cannot be accounted for by interactions with alpha adrenoceptors, as prazosin (1 microM) and yohimbine (1 microM) were without effect. There also was no correlation between inhibition of DMPP-induced efflux and ability of the drugs to inhibit catecholamine uptake as phentolamine (1 microM) and propranolol (1 microM) did not affect the incorporation of [3H]epinephrine by the gland. In guinea-pig atria, in which the catecholamine storage sites had been labeled with [3H]norepinephrine, efflux of radioactivity was elicited by 1-min periods of contact with DMPP. DMPP-induced efflux of radioactivity from atria was decreased by desipramine (1 microM), cocaine (30 microM), phenoxybenzamine (1 and 10 microM), phentolamine (1 and 10 microM) and propranolol (1 microM) but not by prazosin (1 microM) or yohimbine (1 microM). The inhibition of DMPP-induced efflux in guinea-pig atria could not be correlated with alpha adrenoceptor antagonism or blockade of neuronal uptake. There were differences between the two preparations in the degree of inhibition of DMPP-induced release produced by the above drugs.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenal Glands↗
PubMed1982

Release of 3H-adrenaline from an isolated intact preparation of the rabbit adrenal gland: no evidence for release modulatory alpha-adrenoreceptors.

1 The possibility that catecholamine secretion from the rabbit adrenal gland is subject to modulation by a mechanism involving alpha-adrenoreceptors was investigated in an isolated preparation of the gland. 2 Intact left adrenal glands from the rabbit were perfused with Krebs-Henseleit solution through their vasculature. The adrenal catecholamine stores were radiolabelled with 3H-adrenaline and subsequently, efflux of the radiolabel was elicited by stimulation of an attached segment of splanchnic nerve (60 s at 5 Hz). In some experiments, efflux of radiolabel was elicited by perfusion with potassium-enriched Krebs-Henseleit solution (30 mM). 3 Radioactivity released in response to nerve stimulation was accounted for almost entirely by (3H)-adrenaline. Stimulation-induced (S-I) efflux was abolished by 0.1 microM tetrodotoxin and by omission of calcium from the perfusion medium and was reduced by approximately 55% by 100 microM hexamethonium. 4 S-I efflux was enhanced to approximately 150% of control S-I efflux in the presence of 10 microM phenoxybenzamine; however, 3 microM phentolamine and yohimbine in concentrations of 0.1 and 1.0 microM had no effect; in a higher concentration (10 microM) yohimbine reduced S-I efflux by approximately 50%. It is likely that the effect of phenoxybenzamine in enhancing S-I efflux is due to blockade of reuptake of 3H-adrenaline since cocaine (30 microM) enhanced release to a similar extent. 5 S-I efflux was not altered in the presence of the alpha-adrenoreceptor agonists noradrenaline (0.1 microM), clonidine (1 microM) or oxymetazoline (10 microM). 6 Release of radiolabel evoked by perfusion with 30 mM potassium solution was unaltered in the presence of phentolamine (3 microM) of clonidine (1 microM). 7 These findings do not support the existence in the rabbit adrenal gland of a mechanism involving alpha-adrenoreceptors through which catecholamine secretion may be modulated.

Adrenal Glands↗