Thermal effects of the Er:YAG laser on a simulated dental pulp: a quantitative evaluation of the effects of a water spray

OBJECTIVES

To quantify the temperature increments in a simulated dental pulp following irradiation with an Er:YAG laser, and to compare those increments when the laser is applied with and without water spray.

METHODS

Two cavities were prepared on either the buccal or lingual aspect of sound extracted teeth using the laser. One cavity was prepared with water spray, the other without and the order of preparation randomised. Identical preparation parameters were used for both cavities. Temperature increments were measured in the pulp chamber using a calibrated thermocouple and a novel pulp simulant.

RESULTS

Maximum increments were 4.0 degrees C (water) and 24.7 degrees C (no water). Water was shown to be highly significant in reducing the overall temperature increments in all cases (p<0.001; paired t-test). None of the samples prepared up to a maximum of 135 J cumulative energy prepared with water spray exceeded that threshold at which pulpal damage can be considered to occur. Only 25% of those prepared without water spray remained below this threshold.

DISCUSSION

Extrapolation of the figures suggests probably tolerable limits of continuous laser irradiation with water in excess to 160 J. With the incorporation of small breaks in the continuity of laser irradiation that occur in the in vivo situation, the cumulative energy dose tolerated by the pulp should far exceed these figures.

CONCLUSIONS

The Er:YAG laser must be used in conjunction with water during cavity preparation. As such it should be considered as an effective tool for clinical use based on predicted pulpal responses to thermal stimuli.

An assessment of the cost effectiveness of a postal toothpaste programme to prevent caries among five-year-old children in the North West of England

OBJECTIVE

To assess the cost effectiveness of a postal toothpaste programme to prevent caries in 5-year-old children in the north west of England.

PARTICIPANTS

Birth cohorts of children aged 12 months were recruited from high caries risk populations in nine health districts.

DESIGN

The results of a randomised controlled trial to measure the effects of a postal toothpaste programme are used and related to the costs of running a similar programme. Children in the trial received free toothpaste on four occasions a year and a toothbrush once a year for four years from age 12 months to 5 years. When aged 5-6 years children were examined by trained, calibrated examiners using BASCD standards. Those who received toothpaste containing 1450 ppm F were found to have a significantly lower mean dmft than those who had not. The costs that would be incurred by a public dental service running such a postal toothpaste programme are identified, measured and related to the likely health improvement that could be achieved.

MAIN OUTCOME MEASURES

The cost per tooth saved and the cost per child saved from caries experience and extraction experience.

RESULTS

The estimated cost per tooth saved from carious attack was pounds sterling 80.83 and the cost per child of preventing caries experience was pounds sterling 424.38 and avoiding any extractions was pounds sterling 679.01. Analysis resulted in an overestimation of costs and underestimation of benefits.

CONCLUSION

The programme achieved a significant caries reduction in children who received the 1450 ppm F toothpaste and the costs are now available to those considering provision of treatment services in areas where children are at high caries risk.

Association between local mechanical factors and orofacial pain: survey in the community

OBJECTIVES

The aetiology of orofacial pain (OFP) is not well understood. We aimed to determine the relationship between OFP and local mechanical factors in an unselected general population sample.

METHODS

A cross-sectional population-based survey was conducted in the United Kingdom, involving 2504 participants (adjusted participation rate 74%). Postal questionnaire was used to collect information on OFP and local mechanical factors.

RESULTS

A significant association was found between OFP and a history of tooth grinding, facial trauma, the jaw getting stuck or locked, a clicking or grating sound in the jaw joint when opening or closing the mouth, difficulty in opening the mouth wide, and chewing of pens or biting finger nails. The jaw getting stuck or locked had the highest relative risk of 2.7 (95% CI: 2.3-3.2). A history of orthodontic treatment, having any type of dentures and using chewing gum were not associated with OFP. There was some evidence of heterogeneity between types of OFP and local mechanical factors.

CONCLUSIONS

Local factors play an important role in the aetiology of OFP.

The rational use of oral care products in the elderly

This review examines the evidence of the effectiveness of oral care products in preventing and controlling dental caries and periodontal disease in the ageing population. The strength of evidence is indicated using the following hierarchy: Type 1 (systematic reviews), Type 2 (randomised controlled trials), Type 3 (observational studies) and Type 4 (traditional reviews). Most of the evidence to support the effectiveness of fluoride products is extrapolated from studies involving children and adolescents. The few studies that have been performed in older adults suggest that fluoride toothpaste and, in the case of high caries risk individuals, the adjunctive use of other fluoride delivery systems, may be effective in preventing coronal and root caries. Some dentifrices containing triclosan have been shown to improve plaque control and gingival health and one, which contains triclosan/copolymer, reduces the progression of periodontitis in adults and high-risk individuals. Powered toothbrushes with an oscillation-rotation action are more effective in reducing plaque and improving gingival health than manual toothbrushes.

Factors associated with health care seeking behaviour for orofacial pain in the general population

OBJECTIVE

To describe the health care seeking behaviour associated with orofacial pain (OFP) and determine factors associated with such behaviour.

DESIGN

Cross-sectional population-based study using postal questionnaires.

PARTICIPANTS

Adults aged 18-64 years from a general medical practice in south-east Cheshire, UK (participation rate 74%).

RESULTS

Of the 2,504 respondents to the questionnaire 646 reported OFP, of whom 555 (86%) indicated whether or not they sought professional help. A total of 255 (46%) responded that they had sought advice. The majority had sought advice from their medical practitioner (57%) or dentist (51%), and 64% had taken medication because of OFP. The likelihood of seeking treatment increased linearly with age (p < 0.001) while gender, education and psychological distress did not show a significant association with seeking treatment. Persons who were regular dental attenders had an increased likelihood of seeking treatment for OFP (RR 1.4; 95% CI 1.1,1.8). Perception of illness had moderate association with healthcare seeking (RR 0.8; 95% CI 0.7,0.96). There was a significant trend of increasing RR with increasing total number of pain symptoms (p < 0.001), frequency of pain, duration of pain episodes, pain intensity and disability associated with pain. Participants who reported pain duration of more than three months had almost double the likelihood (RR 1.8; 95% CI 1.4,2.3) of seeking treatment. Decrease in self-reported control over pain and ability to decrease pain were both associated with an increased likelihood of seeking professional care (p < 0.001).

CONCLUSIONS

The strongest predictors of health care seeking behaviour were different characteristics of pain.

A randomised controlled trial of the effectiveness of providing free fluoride toothpaste from the age of 12 months on reducing caries in 5-6 year old children

OBJECTIVE

To assess the impact of regularly supplying free fluoride toothpaste regularly to children, initially aged 12 months, and living in deprived areas of the north west of England on the level of caries in the deciduous dentition at 5-6 years of age. A further aim was to compare the effectiveness of a programme using a toothpaste containing 440 ppmF (Colgate 0-6 Gel) with one containing 1,450 ppmF (Colgate Great Regular Flavour) in reducing caries.

DESIGN

Randomised controlled parallel group clinical trial. Clinical data were collected from test and control groups when the children were 5-6 years old.

SETTING

A programme of posting toothpaste with dental health messages to the homes of children initially aged 12 months. Clinical examinations took place in primary schools.

PARTICIPANTS

7,422 children born in 3-month birth cohorts living in high caries areas in nine health districts in north west England. Within each district children were randomly assigned to test or control groups.

INTERVENTIONS

Toothpaste, containing either 440 ppmF or 1450 ppmF, and dental health literature posted at three monthly intervals to children in test groups until they were aged 5-6 years.

MAIN OUTCOME MEASURES

The dmft index, missing teeth and the prevalence of caries experience.

RESULTS

An analysis of 3,731 children who were examined and remained in the programme showed the mean dmft to be 2.15 for the group who had received 1,450 ppmF toothpaste and 2.49 for the 440 ppmF group. The mean dmft for the control group was 2.57. This 16% reduction between the 1,450 ppmF and control group was statistically significant (P<0.05). The difference between the 440 ppmF group and control was not significant. Further analyses to estimate the population effect of the programme also confirmed this relationship.

CONCLUSION

This study demonstrates that a programme distributing free toothpaste containing 1,450 ppmF provides a significant clinical benefit for high caries risk children living in deprived, non-fluoridated districts.

Association between female hormonal factors and oro-facial pain: study in the community

The aim of this study was to determine the relationship between the prevalence of oro-facial pain (OFP) in the population and female hormonal factors. The cross-sectional population study was conducted in a general medical practice in the north-west of England. A random sample of 4000 adults aged 18-65 years were mailed questionnaires, of whom 2504 responded (adjusted participation rate 74%). Of these 1245 women provided information on both OFP and hormonal factors. For pre- or peri-menopausal women, there was no relationship between oral contraceptive use and OFP (age-adjusted relative risk (RR) 1.10; 95% confidence interval (CI) 0.81, 1.45), whilst a high score on a pre-menstrual symptom questionnaire was associated with an age-adjusted RR of 1.87 (95% CI 1.36, 2.57). Those who reported menstruating for 6 days or longer had moderate increase in risk of OFP (age-adjusted RR 1.39; 95% CI 1.01, 1.91). In post-menopausal women, there was a moderate relationship between hormone replacement therapy use and OFP (age-adjusted RR 1.46; 95% CI 1.02, 2.08). For women overall, there was an increased risk of OFP in those who reported ever having had painful periods (age-adjusted RR 1.47; 95% CI 1.20, 1.80), but no association was found with the number of children. This cross-sectional community-based study adds important information on the relationship between female hormonal factors and OFP. Women who report OFP are more likely to report symptoms associated with menstruation. This may indicate either the importance of hormones per se or identify a group of women who are more likely to report symptoms in general.

Sex hormonal factors and chronic widespread pain: a population study among women

OBJECTIVE

The observation of higher rates of chronic widespread pain, the cardinal feature of fibromyalgia, in women has led to hypotheses about the role of sex hormonal factors in the aetiology of symptoms. There is little available evidence from epidemiological studies on their importance or role.

METHODS

A population postal survey was carried out involving 1178 female participants living in south-east Cheshire in the north-west of England.

RESULTS

Amongst pre- and peri-menopausal women, the risk of chronic widespread pain was unrelated either to the length of the menstrual cycle or the usual length of period reported by participants. Risk was similar in current users and non-users of the oral contraceptive pill, and amongst users there was no relationship with duration of use. However, the reporting of chronic widespread pain showed a relationship with total score on a premenstrual symptom questionnaire. However, this relationship was explained by pain symptoms. Amongst post-menopausal women, reporting chronic widespread pain was not related to age at menopause. An increased (but non-significant) risk of chronic widespread pain was associated with current hormone replacement therapy (HRT), which may be a consequence of HRT being prescribed for menopausal symptoms.

CONCLUSION

This study, conducted on a large unselected population, has not demonstrated an association between sex hormonal factors and chronic widespread pain.

Complete genome sequence of a multiple drug resistant Salmonella enterica serovar Typhi CT18

Salmonella enterica serovar Typhi (S. typhi) is the aetiological agent of typhoid fever, a serious invasive bacterial disease of humans with an annual global burden of approximately 16 million cases, leading to 600,000 fatalities. Many S. enterica serovars actively invade the mucosal surface of the intestine but are normally contained in healthy individuals by the local immune defence mechanisms. However, S. typhi has evolved the ability to spread to the deeper tissues of humans, including liver, spleen and bone marrow. Here we have sequenced the 4,809,037-base pair (bp) genome of a S. typhi (CT18) that is resistant to multiple drugs, revealing the presence of hundreds of insertions and deletions compared with the Escherichia coli genome, ranging in size from single genes to large islands. Notably, the genome sequence identifies over two hundred pseudogenes, several corresponding to genes that are known to contribute to virulence in Salmonella typhimurium. This genetic degradation may contribute to the human-restricted host range for S. typhi. CT18 harbours a 218,150-bp multiple-drug-resistance incH1 plasmid (pHCM1), and a 106,516-bp cryptic plasmid (pHCM2), which shows recent common ancestry with a virulence plasmid of Yersinia pestis.

A cluster randomized controlled trial testing the effectiveness of a school-based dental health education program for adolescents

OBJECTIVES

This trial investigated the value of a school-based dental health education program in terms of changes in knowledge, reported behavior, and plaque scores.

METHODS

A total of 2,678 pupils with a mean age of 12.1 years attending 28 schools participated in a school-based dental health education program. The study used a cluster randomized controlled study design. The health service administrators stipulated that all participants receive the intervention; to meet this requirement, a rolling program of two six-month periods was utilized. During the first six months, half the adolescents received the intervention program, the other half acting as controls. Throughout a further six-month period, all participants received the intervention program. This research design allowed comparisons between participants receiving the program for six and 12 months. At baseline, six, and 12 months, a random subsample of 40 children in each participating school had their plaque scores recorded and a questionnaire was used to record their knowledge of dental health and reported dental behavior.

RESULTS

The analysis used the subjects clustered within the schools, which were the units of randomization. The intervention program produced statistically significant improvements (P < .001) in knowledge about periodontal disease and the frequency of sugar intake and dental caries in both assessment time periods. The reported frequency of brushing did not change, but the group who had received 12 months of the intervention were more likely (P < .05) to brush for over a minute. At six months the early intervention group had a statistically significant, 13 percent reduction in the mean proportion of sites with plaque compared with the late intervention group (P = .043). This difference was sustained at 12 months (P = .037).

CONCLUSION

This cluster randomized control trial demonstrated that the intervention program resulted in an improvement in knowledge of dental disease and an increase in the reported duration of brushing. These improvements were accompanied by a significant improvement in oral hygiene and a reported reduction in gingival bleeding.

Genome sequence of Yersinia pestis, the causative agent of plague

The Gram-negative bacterium Yersinia pestis is the causative agent of the systemic invasive infectious disease classically referred to as plague, and has been responsible for three human pandemics: the Justinian plague (sixth to eighth centuries), the Black Death (fourteenth to nineteenth centuries) and modern plague (nineteenth century to the present day). The recent identification of strains resistant to multiple drugs and the potential use of Y. pestis as an agent of biological warfare mean that plague still poses a threat to human health. Here we report the complete genome sequence of Y. pestis strain CO92, consisting of a 4.65-megabase (Mb) chromosome and three plasmids of 96.2 kilobases (kb), 70.3 kb and 9.6 kb. The genome is unusually rich in insertion sequences and displays anomalies in GC base-composition bias, indicating frequent intragenomic recombination. Many genes seem to have been acquired from other bacteria and viruses (including adhesins, secretion systems and insecticidal toxins). The genome contains around 150 pseudogenes, many of which are remnants of a redundant enteropathogenic lifestyle. The evidence of ongoing genome fluidity, expansion and decay suggests Y. pestis is a pathogen that has undergone large-scale genetic flux and provides a unique insight into the ways in which new and highly virulent pathogens evolve.

The use of fibre-optic transillumination in general dental practice

OBJECTIVE

To assess the use of fibre-optic transillumination (FOTI) as a diagnostic tool in general dental practice.

DESIGN

A cross-over quantitative study for the diagnosis of approximal carious lesions by two clinical methods with a qualitative component.

SUBJECTS AND METHODS

Seven GDPs were trained to use FOTI as an adjunct to their usual clinical examination to diagnose approximal caries. After 12 weeks of use in their practices four of the GDPs took part in two assessment sessions, set a week apart, using 29 volunteer patients. Each patient was examined on two separate occasions by each GDP using either their standard clinical examination technique alone or supplemented by FOTI examination. The order of the techniques was randomised. Radiographs of each patient were also examined separately. An experienced FOTI user also examined the patients to provide a benchmark. From standard charts the number of enamel and dentinal lesions on approximal surfaces was summed and comparisons made between the techniques. Six GDPs took part in one-to-one interviews.

MAIN OUTCOME MEASURES

Mean numbers ofcarious lesions recorded by each clinician using each technique.

RESULTS

There was a trend for all GDPs to find more enamel and dentinal lesions using FOTI, than with their standard clinical examination with or without radiographs. All GDPs found the FOTI technique a useful adjunct. They used FOTI in different ways and found a variety of uses for it other than caries diagnosis.

CONCLUSIONS

The

Mutation of the gene encoding the enamel-specific protein, enamelin, causes autosomal-dominant amelogenesis imperfecta

Amelogenesis imperfecta (AI) is a group of inherited defects of dental enamel formation that shows both clinical and genetic heterogeneity. To date, mutations in the gene encoding amelogenin have been shown to underlie a subset of the X-linked recessive forms of AI. Although none of the genes underlying autosomal-dominant or autosomal-recessive AI have been identified, a locus for a local hypoplastic form has been mapped to human chromosome 4q11-q21. In the current investigation, we have analysed a family with an autosomal-dominant, smooth hypoplastic form of AI. Our results have shown that a splicing mutation in the splice donor site of intron 7 of the gene encoding the enamel-specific protein enamelin underlies the phenotype observed in this family. This is the first autosomal-dominant form of AI for which the genetic mutation has been identified. As this type of AI is clinically distinct from that localized previously to chromosome 4q11-q21, these findings highlight the need for a molecular classification of this group of disorders.

The contribution of industry to the decline in dental caries

The contribution of the oral care industry to the reduction in dental caries extends beyond the provision of safe and clinically proven products containing fluoride. The industry has contributed to the scientific base that underpins the use of fluoride, delineated factors that influence the clinical performance of toothpaste, raised the public's awareness of dental health and provided funding to support both undergraduate and postgraduate students in clinical training and basic research.

Massive gene decay in the leprosy bacillus

Leprosy, a chronic human neurological disease, results from infection with the obligate intracellular pathogen Mycobacterium leprae, a close relative of the tubercle bacillus. Mycobacterium leprae has the longest doubling time of all known bacteria and has thwarted every effort at culture in the laboratory. Comparing the 3.27-megabase (Mb) genome sequence of an armadillo-derived Indian isolate of the leprosy bacillus with that of Mycobacterium tuberculosis (4.41 Mb) provides clear explanations for these properties and reveals an extreme case of reductive evolution. Less than half of the genome contains functional genes but pseudogenes, with intact counterparts in M. tuberculosis, abound. Genome downsizing and the current mosaic arrangement appear to have resulted from extensive recombination events between dispersed repetitive sequences. Gene deletion and decay have eliminated many important metabolic activities including siderophore production, part of the oxidative and most of the microaerophilic and anaerobic respiratory chains, and numerous catabolic systems and their regulatory circuits.

An SNP map of human chromosome 22

The human genome sequence will provide a reference for measuring DNA sequence variation in human populations. Sequence variants are responsible for the genetic component of individuality, including complex characteristics such as disease susceptibility and drug response. Most sequence variants are single nucleotide polymorphisms (SNPs), where two alternate bases occur at one position. Comparison of any two genomes reveals around 1 SNP per kilobase. A sufficiently dense map of SNPs would allow the detection of sequence variants responsible for particular characteristics on the basis that they are associated with a specific SNP allele. Here we have evaluated large-scale sequencing approaches to obtaining SNPs, and have constructed a map of 2,730 SNPs on human chromosome 22. Most of the SNPs are within 25 kilobases of a transcribed exon, and are valuable for association studies. We have scaled up the process, detecting over 65,000 SNPs in the genome as part of The SNP Consortium programme, which is on target to build a map of 1 SNP every 5 kilobases that is integrated with the human genome sequence and that is freely available in the public domain.

Dental fluorosis in permanent incisor teeth in relation to water fluoridation, social deprivation and toothpaste use in infancy

OBJECTIVES

To determine the prevalence and severity of fluorosis in permanent incisor teeth in young children in a fluoridated and a fluoride-deficient community and to establish what relationship, if any, there was between the occurrence of dental fluorosis and the reported use of fluoride toothpaste in childhood.

DESIGN

A prevalence study of children aged 8-9 years who had been continuous residents in fluoridated Newcastle or fluoride-deficient Northumberland.

METHOD

The permanent maxillary central incisor teeth were examined clinically and photographically by one examiner using the Thylstrup-Fejerskov index; the photographs were read blind to child identity and clinical score. A closed-response questionnaire enquired into the child's early experiences of toothbrushing and use of fluoride toothpastes. Social deprivation was measured by a Jarman score. The study took place in 1998.

OUTCOME MEASURE

Prevalence of dental fluorosis measured by the Thylstrup-Fejerskov index.

RESULTS

Complete data were available for 78% (n = 409) and 79% (n = 403) of eligible sampled children in the two areas, respectively. Clinical and photographic results agreed closely and had high reproducibility. The prevalence of fluorosis was 54% in the fluoridated area and 23% in the fluoride-deficient area when all grades (> 0) of fluorosis were included; percentage prevalence of mild to moderate fluorosis (> or = 3) was 3% and 0.5% in the two areas, respectively. Multivariate analysis indicated that area of residence (odds ratio = 4.5), Jarman score (odds ratio = 0.99 per Jarman unit) and type of toothpaste (odds ratio = 1.6) were statistically significantly related to presence or absence of fluorosis: the risk factors were--fluoridated area, affluence, and use of adult toothpaste.

CONCLUSIONS AND RECOMMENDATIONS

The prevalence of aesthetically important dental fluorosis was low, although higher in the fluoridated area. Use of a child's toothpaste (with lower fluoride concentration) could decrease risk in a fluoridated area. Adherence to the guidelines published by the British Society of Paediatric Dentistry is recommended.

An Examination of ‘Unidentified’Prevotella (Formerly PINLO) using RAPD-PCR and Partial 16S rRNA Gene Sequencing

Prevotella intermedia- and Prevotella nigrescens-like organisms (PINLO) have been described as organisms which are phenotypically and biochemically similar to P. intermedia and P. nigrescens and the species P. pallens was created to include some of them. Other PINLO groups which do not fit the definition of P. pallens exist, and in this study these 'unidentified' Prevotella sp. were compared with P. corporis, P. intermedia, P. nigrescens and P. pallens using commercial identification kits, GLC, RAPD-PCR and partial 16S rRNA gene sequencing. The Rapid ID 32 A and the RapID ANA II system both identified all 'unidentified' Prevotella as P. intermedia. Similarly they gave this identification to all the species tested (with the exception of P. corporis using the RapID ANA II system) clearly demonstrating biochemical similarities. Gas liquid chromatography (GLC) analysis of the volatile end-products of fermentation could not distinguish between strains. RAPD-PCR using arbitrary primer L10 demonstrated intra-species homogeneity within PINLO strains with amplification profiles which differed from other Prevotella species tested. Cluster analysis of the amplification profiles confirmed species divisions and yielded a distinct 'unidentified' Prevotella cluster. Comparison of partial 16S rDNA sequences displayed 98% sequence similarity between the 'unidentified' Prevotella strains, although 2 strains, HST 1156 and HST 2160 displayed 100% identity. The highest similarity between groups was seen between 'unidentified' Prevotella strains and P. corporis (approximately 94% similarity). The DNA techniques used here confirm that 'unidentified' Prevotella strains are distinct from the other species of Prevotella tested, including P. pallens. Partial 16S rDNA sequence comparisons suggested a close relationship with P. corporis.

Restorative treatment provided over five years for adults regularly attending general dental practice

OBJECTIVES

To investigate the distribution and type of restorative treatment, including re-treatment, provided for adults who attend annually.

METHODS

In 1991 a selected group of 24 general dental practitioners in the North West of England recruited 4211 of their regularly attending adult patients. Dentists recorded the reason for and type of treatment provided during the following 5 years.

RESULTS

Approximately 40% of the participants received treatment (restorations and/ or extractions) at each annual examination. Of the 2293 patients who attended every examination 1959 (85%) had received a restoration and/ or extraction during the 5 years. A total of 8187 teeth, 15% of those present at baseline, received treatment, 3030 (37%) for caries and 5157 (63%) for other reasons. The proportion of adults who received treatment by age group differed significantly with those aged 25-34 years (80%) being least likely and those 35-44 years of age (89%) most likely. Of the 1744 teeth restored in the first year of the study, 170 (10%) were retreated within 1 year and 402 (23%) during the subsequent 4 years. The 4 year survival of amalgam and tooth coloured fillings was 84% and that of crowns 92%.

CONCLUSIONS

This study documented the extent and type of restorative care provided for regularly attending adults during a 5-year period. The majority of treatment was provided for reasons other than caries. Of the teeth restored over the first year, 23% were retreated in the subsequent 4 years.

Cryopreservation and image enhancement of juvenile and adult dentine mineral

The inorganic component of bone and related hard tissues is generally described as sheets of uniform needle- and plate-like crystals. However, cryofixation has become the method of choice for ultrastructural studies of bone mineral when ladder-like arrangements of filaments contained within deformable microspheres about 1 microm in diameter are apparently the prime structural feature and are consistent with the optical image. The same methodology has now been applied to mature human dentine in caries-free juvenile and adult teeth. These were fixed, sliced, stained for mineral and examined optically or were snap frozen, fragmented under liquid nitrogen, freeze-substituted with methanol or acetone and embedded without thawing in Lowicryl K4M for electron microscopy. Others were processed by traditional transmission electron microscopy methods. To obtain maximum resolution, the electron micrographs were photographically printed as negatives and image-enhanced by digitisation using a Polaroid Sprint Scan 45 and laser printer. In both optical and cryopreparations of juvenile and adult dentine, mineral microspheres up to 1 microm in diameter, were present in the dentinal tubules and peritubular dentine. Within these objects, the mineral was primarily in the form of sinuous electron dense filaments, 5 nm thick, which had a characteristic periodicity. In these preparations needle-like and plate-like structures were rare. In contrast, after traditional transmission electron microscopy preparation although similar filamentous structures remained, the mineral more generally had the familiar form of needles measuring approximately 50 nm in the long axis. The cryopreserved calcified filaments were apparently particularly densely distributed in the intertubular dentine where their parallel ladder-like arrays often formed highly orientated struts and stays. It was concluded that early dentine mineral has the form of filamentous microspheres and as in bone (and other calcifying tissues and cells) has no specific association with collagen. It was also concluded that these structures compact and deform with maturity into a sub-structural framework which may relate to powerful biomechanical forces transmitted through the tissue. Needle- or plate-like mineral is probably rare in vivo in dentine, only becoming commonplace after extensive chemical processing.

Complete DNA sequence of a serogroup A strain of Neisseria meningitidis Z2491

Neisseria meningitidis causes bacterial meningitis and is therefore responsible for considerable morbidity and mortality in both the developed and the developing world. Meningococci are opportunistic pathogens that colonize the nasopharynges and oropharynges of asymptomatic carriers. For reasons that are still mostly unknown, they occasionally gain access to the blood, and subsequently to the cerebrospinal fluid, to cause septicaemia and meningitis. N. meningitidis strains are divided into a number of serogroups on the basis of the immunochemistry of their capsular polysaccharides; serogroup A strains are responsible for major epidemics and pandemics of meningococcal disease, and therefore most of the morbidity and mortality associated with this disease. Here we have determined the complete genome sequence of a serogroup A strain of Neisseria meningitidis, Z2491. The sequence is 2,184,406 base pairs in length, with an overall G+C content of 51.8%, and contains 2,121 predicted coding sequences. The most notable feature of the genome is the presence of many hundreds of repetitive elements, ranging from short repeats, positioned either singly or in large multiple arrays, to insertion sequences and gene duplications of one kilobase or more. Many of these repeats appear to be involved in genome fluidity and antigenic variation in this important human pathogen.

The genome sequence of the food-borne pathogen Campylobacter jejuni reveals hypervariable sequences

Campylobacter jejuni, from the delta-epsilon group of proteobacteria, is a microaerophilic, Gram-negative, flagellate, spiral bacterium-properties it shares with the related gastric pathogen Helicobacter pylori. It is the leading cause of bacterial food-borne diarrhoeal disease throughout the world. In addition, infection with C. jejuni is the most frequent antecedent to a form of neuromuscular paralysis known as Guillain-Barré syndrome. Here we report the genome sequence of C. jejuni NCTC11168. C. jejuni has a circular chromosome of 1,641,481 base pairs (30.6% G+C) which is predicted to encode 1,654 proteins and 54 stable RNA species. The genome is unusual in that there are virtually no insertion sequences or phage-associated sequences and very few repeat sequences. One of the most striking findings in the genome was the presence of hypervariable sequences. These short homopolymeric runs of nucleotides were commonly found in genes encoding the biosynthesis or modification of surface structures, or in closely linked genes of unknown function. The apparently high rate of variation of these homopolymeric tracts may be important in the survival strategy of C. jejuni.