Mark P. Hector

Brief Communication: The London Atlas of Human Tooth Development and Eruption

The aim of this study was to develop a comprehensive evidence-based atlas to estimate age using both tooth development and alveolar eruption for human individuals between 28 weeks in utero and 23 years. This was a cross-sectional, retrospective study of archived material with the sample aged 2 years and older having a uniform age and sex distribution. Developing teeth from 72 prenatal and 104 postnatal skeletal remains of known age-at-death were examined from collections held at the Royal College of Surgeons of England and the Natural History Museum, London, UK (M 91, F 72, unknown sex 13). Data were also collected from dental radiographs of living individuals (M 264, F 264). Median stage for tooth development and eruption for all age categories was used to construct the atlas. Tooth development was determined according to Moorrees et al. (J Dent Res 42 (1963a) 490-502; Am J Phys Anthropol 21 (1963b) 205-213) and eruption was assessed relative to the alveolar bone level. Intraexaminer reproducibility calculated using Kappa on 150 teeth was 0.90 for 15 skeletal remains of age <2 years, and 0.81 from 605 teeth (50 radiographs). Age categories were monthly in the last trimester, 2 weeks perinatally, 3-month intervals during the first year, and at every year thereafter. Results show that tooth formation is least variable in infancy and most variable after the age of 16 years for the development of the third molar.

The accuracy of three methods of age estimation using radiographic measurements of developing teeth.

The accuracy of age estimation using three quantitative methods of developing permanent teeth was investigated. These were Mörnstad et al. [Scand. J. Dent. Res. 102 (1994) 137], Liversidge and Molleson [J. For. Sci. 44 (1999) 917] and Carels et al. [J. Biol. Bucc. 19 (1991) 297]. The sample consisted of 145 white Caucasian children (75 girls, 70 boys) aged between 8 and 13 years. Tooth length and apex width of mandibular canine, premolars and first and second molars were measured from orthopantomographs using a digitiser. These data were substituted into equations from the three methods and estimated age was calculated and compared to chronological age. Age was under-estimated in boys and girls using all the three methods; the mean difference between chronological and estimated ages for method I was -0.83 (standard deviation +/-0.96) years for boys and -0.67 (+/-0.76) years for girls; method II -0.79 (+/-0.93) and -0.63 (+/-0.92); method III -1.03 (+/-1.48) and -1.35 (+/-1.11) for boys and girls, respectively. Further analysis of age cohorts, found the most accurate method to be method I for the age group 8.00-8.99 years where age could be predicted to 0.14+/-0.44 years (boys) and 0.10+/-0.32 years (girls). Accuracy was greater for younger children compared to older children and this decreased with age.

The possible relation between mastication and parotid secretion in the rabbit.

Salivary flow has been recorded from conscious rabbits during 1 min periods whilst continuously chewing standard laboratory dry pellets or pieces of carrot and, in some animals, a mash of pellets with water. Flow was measured using contact drop recorders or a continuous flow recorder via Polythene tubes permanently inserted into one or both parotid ducts. Large variations in flow were obtained with unilateral recordings particularly during dry pellet chewing. Bilateral recordings showed that the flow was always greater on one side than on the other and that dominant secretion alternated from side to side in an apparently random manner. Rabbits chew unilaterally. Videotaped recordings of chewing movements showed that the greater secretion was always produced on the chewing side. To test the possibility that drying of the oral mucosa, or the prolonged hardness of the pellets may result in higher flow rates in animals with cannulated ducts than would normally be seen in intact animals, water was injected downstream into the mouth through a third cannula. This was inserted in an anterograde direction in the parotid duct on one side. Significant reductions in flow were recorded during dry pellet eating, but not during carrot eating. When animals were fed a soft pellet mash, salivary flow was significantly lower than with dry pellets. Recordings have been made from strain gauges attached to the ascending ramus of the mandible. Previous findings that dry pellets produce greater strain than carrots have been confirmed. It has also been shown that less strain is produced with soft pellet mash. The strain gauge data suggested that a relation exists between masticatory force and parotid salivary flow. The results are compatible with the hypothesis that intra‐oral mechanoreceptors may be involved in a masticatory‐salivary reflex.

Periodontal Mechanoreceptors and Parotid Secretion in Animals and Man

Parotid flow was determined in rabbits during feeding. The animals produced more saliva when chewing hard laboratory pellets than with carrots, confirming the findings of Gjörstrup (1980a). We showed that one gland always produced more secretion than the other, and that the dominant gland alternated from side to side with changes in the chewing side. Strain-gauge recordings revealed a remarkable similarity in pattern between mandibular strain and ipsilateral parotid flow. Together, these data suggest that chewing movements and chewing force are involved in the control of parotid secretion. In man, flow rates of parotid saliva collected with a Lashley cup and cannula were recorded. During intermittent clenching on a bite block, we found: (1) a positive correlation between rectified integrated masseter EMG and parotid flow; and (2) that anesthesia of various intra-oral nerves could reduce the flow almost to zero. Crushing a particle of breakfast cereal between two teeth resulted in a reproducible parotid flow which was reduced by infiltration anesthesia around one of these teeth. These data point to the involvement of periodontal mechanoreceptors in the control of parotid secretion in rabbits and man.

Precipitation of specific proteins by freeze-thawing of human saliva

Frozen saliva samples demonstrate a variable amount of precipitate on thawing depending on the type of secretion [submandibular-sublingual (SML) greater than parotid]. This precipitate has been resuspended using EDTA or removed by centrifugation by some workers and others do not mention it. Yet others collect the salivas into EDTA or centrifuge them before freezing. To determine the adsorption of proteins to hydroxyapatite, prior treatment with EDTA would be disadvantageous. The aim here was to determine if the protein pattern in parotid and SML saliva as demonstrated by sodium dodecyl sulphate gel electrophoresis is affected by the formation of precipitates. Portions of parotid and SML saliva were thawed and treated in the following ways: (a) mixed vigorously with a vortex mixer; (b) centrifuged to remove the precipitate; (c) mixed with EDTA (1 and 5 mmol final concentration for parotid and SML samples, respectively) to resuspend the precipitate. The samples were loaded on to gradient (5-20%) SDS gels and, following electrophoresis, the gels were stained with Coomassie brilliant blue R-250. The protein patterns obtained for (a) and (c) were the same. The centrifuged samples demonstrated loss of a specific band of less than 14 kDa, although this was less obvious in the parotid samples. The SML samples also showed a reduction in other lower molecular-weight proteins. This study demonstrates that precipitates in thawed frozen salivas contain specific proteins and that these samples require careful handling to avoid any alteration in the overall protein composition.

The effects of unilateral and bilateral chewing, empty clenching and simulated bruxism, on the masticatory-parotid salivary reflex in man.

In man, parotid flow has been recorded, using modified Lashley cups, in response to mechanical stimulation of the teeth by repeated chewing and clenching manoeuvres. The rectified and integrated masseter electromyographic activity was used as an indirect measure of the stimulus intensity where necessary. Following the observation that –empty clenching— failed to evoke a parotid salivary response, a series of three experiments has been undertaken to address the following questions. (1) Is a lateral component of force required to evoke a flow during empty clenching? (2) Does contralateral inhibition of salivary secretion explain this observation? (3) What is the threshold for the masticatory‐salivary reflex? The results suggest that: (i) empty clenching together with a lateral component of force does not result in a secretion above resting flows; (ii) there is no evidence for the existence of contralateral inhibition of salivary secretion; and (iii) the threshold for the masticatory‐salivary reflex is lower than 5% of comfortable chewing forces. We are still unable to offer an explanation for the lack of parotid secretion during empty clenching.

Impact of sleep nasendoscopy on the outcome of mandibular advancement splint therapy in subjects with sleep-related breathing disorders

AIM To evaluate the impact of positive sleep nasendoscopy, with simultaneous mandibular advancement, on the outcome of mandibular advancement splint therapy in 120 subjects with sleep-related breathing disorders. METHODOLOGY Overnight polysomnography and sleep nasendoscopy were performed prior to splint therapy. Follow-up sleep studies, with the appliance in situ, were undertaken for those patients with obstructive sleep apnoea. Subjective outcome measures assessed daytime sleepiness and snoring. RESULTS One hundred and seven (89 per cent) subjects completed the study. Follow-up sleep studies confirmed the efficacy of treatment, with patients showing a mean reduction in apnoea/hypopnoea index (from 18.9 to 4.9, p<0.001), Epworth sleepiness scale scores (from 11 to seven, p<0.001) and partner-recorded snoring scores (from 14 to eight, p<0.001). CONCLUSION Sleep nasendoscopy, with concomitant mandibular advancement to mimic the treatment effect, could be of prognostic value in determining successful mandibular advancement splint therapy.

Activities related to the occurrence of traumatic dental injuries in 15- to 18-year-olds.

OBJECTIVE To assess the activities related to the occurrence of traumatic dental injuries (TDI) in order to establish the relationship between gender, socio-economic status (SES) and major TDI related events, using classification and examination procedures suitable for epidemiological purposes, in a sample of 15- to 18-year-old students in Taiwan. METHODS A random sample of 6312 15- to 18-year-old senior high school students in southern Taiwan was selected. Each was examined with standard clinical procedures and a questionnaire. RESULTS The prevalence of TDI was 19.9%. The major TDI related events included sports and leisure activities (30.8%), eating (20.5%), falls (19.4%), traffic accidents (10.2%) and collisions (7.1%). Within TDI victims, sports and leisure related TDI were more prevalent among males (P = 0.001, OR = 1.640, 95% CI = 1.225, 2.195) and high SES adolescents (P = 0.014, OR = 1.991, 95% CI = 1.149, 3.449). The occurrence of non-accidental TDI was not related to age, gender and SES (P > or = 0.643). CONCLUSION Traumatic dental injuries have become an important issue in public health and dentistry. Prevention and treatment of TDI should be emphasised to the public, the health professional and the policy maker. Future investigations into the relationship between TDI related events and their determinants are indicated.

Oesophageal acid and salivary secretion : Is chewing gum a treatment option for gastro-oesophageal reflux?

The presence of acid in the oesophagus has been shown to stimulate salivary secretion, but the relevance of this oesophago-salivary reflex for acid clearance in physiological and pathological gastro-oesophageal reflux (GOR) is unknown. This study was designed to investigate the interrelation between oesophageal acid and both resting and stimulated salivary secretion. In 10 healthy volunteers, the acid clearance times after bolus infusion of 20 ml of 0.1 N hydrochloric acid were measured by means of ambulatory oesophageal pH monitoring. With a constant swallowing rate and resting salivary flow, the acid clearance time was significantly longer with dry as opposed to wet swallows (12.6 +/- 2.6 vs. 6.9 +/- 1.9 min; p = 0.01). When the salivary flow was doubled by chewing a gum base (26.0 +/- 3.4 vs. 13.2 +/- 2.0 ml/15 min; p = 0.005), the acid clearance time was markedly shortened (6.9 +/- 1.9 vs. 2.3 +/- 0.2 min; p = 0.02). As compared with water control, salivary flow, pH, and protein content were not affected by a bolus infusion of hydrochloric acid. This was true both for resting and gum-stimulated salivary secretion. Our study suggests that an oesophago-salivary reflex becomes effective only in prolonged episodes of GOR. This may explain why the water brash phenomenon is not regularly experienced by all reflux patients. Our study also suggests that chewing gum might be a non-pharmacological treatment option for some patients with symptomatic GOR.

An in vitro scanning microradiography study of the reduction in hydroxyapatite demineralization rate by statherin‐like peptides as a function of increasing N‐terminal length

Enamel demineralization is slowed by salivary proteins that inhibit calcium hydroxyapatite (HA) demineralization. Statherin (StN43), a 43-residue phosphorylated salivary protein with primary sequence similarities to osteopontin and caseins, binds calcium and HA. The aim of this study was to identify the minimum length of the functional domain of the statherin molecule required for cariostatic function by measuring the efficacy of peptides of progressively shorter length (i.e. containing only the N-terminal 21 (StN21), 15 (StN15), 10 (StN10), or 5 (StN5) residues) to reduce HA demineralization rates (RD(HA) ). Porous HA blocks were used as enamel analogues, and were exposed to 0.1 M acetic acid at pH 4 for 120 h, rinsed, and treated with StN21, StN15, StN10, or StN5 peptides (1.88 × 10(-5) M) for 24 h, then demineralized for a further 120 h. The RD(HA) was measured, before and after peptide treatment, using scanning microradiography. Hydroxyapatite blocks treated with StN21 and StN15 demonstrated a 50-60% reduction in the RD(HA) . However, no reduction in the RD(HA) was observed following treatment with either StN10, StN5, or buffer only. The mechanism by which statherin-like peptides reduce RD(HA) may be associated with their binding to HA surfaces. Comparisons with previously published binding energies of statherin to HA also suggest that statherin-like peptides containing 15 N-terminal residues or more, are required for binding, suggesting a link between binding and demineralization reduction.