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Biomedical subjects

J H Noar

Publications and source records attributed to J H Noar.

18 recordsLinked to original sources
PubMed2000

Three-dimensional analysis of the child cleft face.

OBJECTIVE: This study examined the facial surfaces of cleft children and unaffected children aged 8-11 years with the aim of identifying and assessing differences in their facial surface morphology. The investigation was carried out using an Optical Surface Scanner, an instrument that utilizes laser light to construct and archive a three-dimensional image of the face suitable for linear measurement and direct surface comparisons. DESIGN, SETTING, AND PATIENTS: Thirty-nine cleft lip and palate (CLP) patients and 25 unaffected subjects were voluntarily recruited from two southeast England hospitals. A range of linear facial measurements was compared. Three-dimensional differences between the cleft subgroups and the control group were visualized by superimposition of averaged cleft scans over the averaged control group images. RESULTS: Statistically significant dimensional differences (p < or = .05) in interocular width, nose base widths, mouth widths, and nose base/mouth width ratios were found between the cleft group and the control group. Qualitative differences over the whole of the face were readily demonstrated between the groups by superimposition. Face width and submandibular area depth differed consistently between the groups, the cleft face appearing narrower with a deeper submandibular area. CONCLUSION: Significant differences exist between the facial surface morphology of CLP patients and control subjects.

Analysis of Variance↗
PubMed1999

The physical characteristics of neodymium iron boron magnets for tooth extrusion.

Impaction and non-eruption of teeth is a common problem encountered in orthodontics and many techniques have been proposed for the management of this condition. It has been advocated that a system utilizing magnets would supply a continuous, directionally sensitive, extrusive force, through closed mucosa and thus provide not only a physiological sound basis for successful treatment, but also reduce the need for patient compliance and appliance adjustment. This ex vivo investigation examined in detail the physical characteristics of neodymium iron boron magnets employed in attraction in order to assess their usefulness in the clinical situation. Attractive force and magnetic flux density measurements were recorded for nine sets of magnet pairs with differing morphologies. The effect of spatial relationship on force was assessed by varying vertical, transverse and horizontal positions of the magnets relative to each other, and by altering the pole face angles. The data obtained suggest that magnets with larger pole face areas and longer magnetic axes provide the best performance with respect to clinical usefulness. It was possible to formulate a specific relationship between force and flux density for each magnet pair. This relationship can be used in the clinical management of unerupted teeth to predict the force between the magnets by measuring the magnetic flux density present at mucosal level. The results indicate that magnetic systems may, indeed, have a place in the treatment of unerupted teeth.

Biomechanical Phenomena↗
PubMed1999

The durability of parylene coatings on neodymium-iron-boron magnets.

A parylene coating is frequently used to prevent corrosion of neodymium-iron-boron magnets when they are used intra-orally. This in vitro study was designed to test the durability of parylene coating in a simulated oral environment. Single and double parylene-coated magnets were subjected to grinding and crushing forces in an industrial ball mill. The results demonstrate that abrasion and wear was visible around the edges after 1 hour of testing, with a breach of the coating noted under high magnification scanning electron microscopy (SEM). The conclusion of the study is that parylene coating is unlikely to withstand intra-oral forces. The shape of the magnets, the manufacturing process involved in their production, and the thickness of the parylene coating are important factors to consider with respect to the durability of magnets used in the mouth.

Boron↗
PubMed1999

Rare earth magnets in orthodontics: an overview.

Magnets have been used in dentistry for many years. They can be made to push or pull teeth. The force they deliver can be directed, and they can exert their force through mucosa and bone, as well as within the mouth. In orthodontics they are used for intrusion of teeth, tooth movement along archwires, expansion, retention, in functional appliances, and in the treatment of impacted teeth. New 'high energy' magnets are capable of producing very high forces relative to their size. Although magnets are potentially very useful there are a number of problems that severely affect their performance; the force produced between any two magnets falls dramatically with distance, significant irreversible loss in force is seen if the magnets are heated and a dramatic reduction in force is seen if the magnets are not ideally aligned to one another. In addition, magnets corrode badly in the mouth and a robust coating is required to protect them. This paper outlines the background to high energy magnets used in orthodontics, discusses the relevant physical and biological properties of them, and reviews their applications.

Biocompatible Materials↗
PubMed1998

Effect of chlorhexidine on multi-species biofilms.

With human saliva as an inoculum, microcosm dental plaques were grown on dental amalgam in a constant-depth film fermentor (CDFF) in the presence (suc +ve) and absence (suc -ve) of sucrose. The biofilms were then exposed to 0.2% chlorhexidine gluconate (CHG) for 1, 5, or 60 min and the survivors enumerated. Suc +ve biofilms had higher proportions of streptococci but lower proportions of veillonellae than suc -ve biofilms. Exposure to CHG for 1 min reduced the viable count of suc -ve and suc +ve biofilms by 53% and 89% respectively. In both cases, reductions were mainly attributable to killing of streptococci and actinomyces. After 60 min of exposure, 4% of the bacteria in the suc -ve and 2% in the suc +ve biofilms remained viable. This study has shown that large numbers of bacteria in microcosm dental plaques can survive a 1-min exposure to 0.2% CHG and that even after a 60-min exposure, substantial numbers of bacteria remain viable.

Bacteria↗
PubMed1997

Corrosion of the intra-oral magnets by multi-species biofilms in the presence and absence of sucrose.

The purpose of this study was to determine the corrosive effects of multi-species biofilms on intra-oral magnets in the presence and absence of sucrose. Using pooled human saliva as an inoculum, biofilms were grown on the surfaces of 90 neodymium-iron-boron (Nd2Fe14B) magnets in a constant depth film fermentor under aerobic conditions at 37 degrees C. The fluid phase was a mucin-containing artificial saliva (delivered at a rate of 0.72/litres day-1), and, after 15 days, 100 ml of 10% (w/v) sucrose was added (as three pulses of 33.3 ml) each day for a further 15 days. Six magnets with attached biofilms were removed periodically. On each sampling occasion the numbers of aerobes, anaerobes, streptococci, veillonellae and actinomyces in each biofilm, the pH of the fermentor effluent and the dry mass of the magnets were determined. Addition of sucrose to the fermentor resulted in a fall in pH (from a mean of 6.94 to a mean of 4.96), an increase in the proportion of streptococci and a decrease in the proportion of veillonellae comprising the biofilms. The decrease in mass of the magnets was 28-fold greater in the presence of sucrose than in its absence. The results of this study have shown that the presence of sucrose affects the microbial composition of multi-species biofilms growing on Nd2Fe14B magnets and results in a marked increase in corrosion of the magnets.

Bacteria, Anaerobic↗
PubMed1996

The physical properties and behavior of magnets used in the treatment of anterior open bite.

This investigation examined the magnetic flux and repulsive force of neodymium-iron-boron (Nd-Fe-B) magnets used in repulsion in the treatment of anterior open bite. Three different grades of magnets each of five different dimensions were used. Magnetic flux was measured by a Hall probe and the repulsive force by an Instron mechanical testing machine. Results showed that the different grades of magnet displayed similar magnetic flux with a relationship between thickness and flux. There was a significant difference between the flux measured at the end as opposed to the center of the magnet. The force between two magnets and the flux above each magnet was directly related. Using magnets in groups did not produce higher forces than using single magnets of an equivalent size. It was concluded that Nd-Fe-B magnets can be used to give predictable repulsive forces in the mouth.

Boron↗
PubMed1996

The performance of bonded magnets used in the treatment of anterior open bite.

This investigation examined the magnetic flux and repulsive force of neodymium-iron-boron (Nd-Fe-B) magnets based on Nd2Fe14B with acrylic coatings in different orientations. The flux was measured with a Hall probe and the force measured by electronic scales with the magnets mounted on a laboratory jack. Results show that there were no magnetic losses after embedding the magnets in acrylic bite-blocks, although there were significant flux losses when the magnet blocks were directly heated. The alignment of the magnets over each other was of the utmost importance and significantly affected the repulsive force between the magnets. When the magnets were mounted in an articulator to simulate jaw movement, the force levels between the magnets was further reduced as a result of the effects of the rotation of the articulator. It is concluded that Nd-Fe-B type magnets embedded in acrylic can be used to give predictable repulsive forces in the mouth. The dramatic reduction in force levels when the magnets are not in optimal alignment, however, makes their effectiveness in aiding intrusion of teeth doubtful.

Acrylic Resins↗
PubMed1996

A comparison of crown size dimensions of the permanent teeth in a Nigerian and a British population.

This investigation was undertaken to compare the mesio-distal and bucco-lingual crown dimensions of the permanent teeth in Nigerian and British populations. The study sample consisted of 30 pairs of study models of children from each of the two populations. The children were matched for sex. The mean age for the Nigerian and British samples was 12.5 +/- 1.4 years and 12.9 +/- 1.2 years respectively. No left-right side differences were observed (P > 0.05). The results indicate that the mesio-distal crown diameters were consistently larger in the Nigerian sample. With the exception of mandibular central incisors and maxillary canines there were no statistically significant differences in bucco-lingual crown diameters in the two populations.

Bicuspid↗
PubMed1996

Variability in recording and grading the need for orthodontic treatment using the handicapping malocclusion assessment record, occlusal index and dental aesthetic index.

This investigation evaluates three malocclusion treatment need indices, the Handicapping Malocclusion Assessment Record (HMAR), the Occlusal Index (OI) and the Dental Aesthetic Index (DAI), for reliability and inter-index correlation. Pretreatment study models of 30 cases (mean age 12.9 years, SD 1.2) were assessed using each index. All the indices demonstrated a high level of reliability and non could be selected over the other with regards intra-examiner differences. The DAI, however, was more time-saving (2.68 mins, SD 0.41) and simple to use. The highest correlation was between HMAR and OI (r = 0.87, P < 0.001) which is a reflection of the similarity in their design. This study also discusses the limitations of the three indices.

Adolescent↗
PubMed1996

A comparison between DAI and SCAN in estimating orthodontic treatment need.

This study was undertaken to assess the reliability and the correlation between two aesthetic indices, the Dental Aesthetic Index (DAI) and the Standardised Continuum of Aesthetic Need (SCAN Index) in estimating orthodontic treatment priority. The indices were applied to 53 randomly selected study models and records of orthodontic patients treated at Mount Vernon Hospital, Middlesex, UK. The patients ages at initial presentation ranged from 10.7 to 16.4 years (Mean 12.8 years, SD 1.0). The DAI and the SCAN Index were moderately correlated (r = 0.67) and the association was highly statistically significant (p < 0.001). The findings indicated that the two indices could be used consistently. The limitations of both indices are also discussed.

Adolescent↗
PubMed1995

Corrosion of intra-oral magnets in the presence and absence of biofilms of Streptococcus sanguis.

Intra-oral magnets are used in dentistry for a variety of purposes, and their susceptibility to corrosion is of great clinical importance. Although a number of in vitro models have been developed to study corrosion of intra-oral magnets, none have attempted to determine the possible contribution to corrosion made by oral bacteria, which are known to form a biofilm on intra-oral appliances. We have exposed demagnetized neodymium/iron/boron (Nd2Fe14B) magnets to an artificial saliva in the presence and absence of a biofilm of Streptococcus sanguils, one of the predominant organisms in the oral cavity. Over a 21-d period, a 3.2% decrease in the mass of the magnets was observed when S. sanguis was present, while in the absence of the organism the decrease in mass was 1.4%. We also examined the ability of poly(para-xylylene), a commonly-used coating, to protect the magnets against corrosion. No decrease in the mass of magnets coated with poly(para-xylylene) was detected over a 21-d period in the presence of S. sanguis. This study has shown that biofilms of S. sanguis cause appreciable corrosion of Nd2Fe14B magnets which is greater than that occurring in the absence of the organism, and that a coating of poly(para-xylylene) provides protection against such corrosion.

Biofilms↗
PubMed1992

A questionnaire survey of attitudes and concerns of three professional groups involved in the cleft palate team.

This study investigated the opinions of three of the professional groups who treat cleft lip and palate patients in the United Kingdom. Plastic surgeons, orthodontists, and speech therapists were asked to give their opinions regarding adolescents with a unilateral cleft of the lip and palate. A mail questionnaire investigating four main areas: treatment, facial appearance and speech, social and emotional aspects, and the perceived success of the specialists was sent to each subject. Nearly all the subjects reported that they worked as part of a cleft palate team and there was good agreement among the three groups. Although the professionals felt that they have been successful, they were not satisfied with the results of their treatment nor with the patients' overall facial appearance or speech. They also felt that the patients are emotionally and socially affected by their cleft and are teased. The subjects noted that they think patients feel similarly to themselves on all aspects. The significance of the results is discussed.

Adolescent↗
PubMed1991

Questionnaire survey of attitudes and concerns of patients with cleft lip and palate and their parents.

The self-perceived problems and concerns of patients with complete unilateral cleft lip and palate and their parents were investigated. Thirty-two patients ranging in age from 16 to 25 years (mean = 19.9 years) and their parents were sent questionnaires by mail. Twenty-eight patients and 30 parents completed the questionnaires. The results suggest that the patients were satisfied with the treatment they had received. They believed that the efforts of the members of the cleft palate team had been successful, and they were generally satisfied with their overall facial appearance and speech. There were, however, specific aspects with which they were less satisfied; their nose, lip, profile, speech, and teeth. They did not feel significantly socially or emotionally handicapped, although they noted that they had been teased and that they found relations with the opposite sex difficult. Their parents were also generally satisfied with all aspects of treatment and their child's appearance and speech. They identified those areas that their child was most concerned with, but did not fully appreciate how satisfied their child was with his or her facial features. The parents felt that their children were socially and emotionally affected by their cleft and felt their school results had also been affected.

Adolescent↗
PubMed1990

Project teeth relief: dental aid for rural Zambia.

For 10 weeks, at the end of last year, my wife and I went out to Zambia with Project Teeth Relief, a UK based charity providing dental care to the rural areas of Zambia. The aim of the charity is to provide emergency dental care, dental health education and training for local health workers in the rural areas where there are no dental services available. Dentists on long-term contracts and volunteers who will spend 2-3 months at a time in the rural area are needed urgently to go out to the country.

Adolescent↗
PubMed1990

Dental anomalies in cleft lip and palate: an unusual case.

A cleft palate case is reported in which there is an unusual pattern of hypodontia involving aplasia of the primary second molars, but development of the corresponding second premolars. This paper discusses some of the implications of this situation and stresses the need for very thorough clinical and radiographic examination.

Anodontia↗