Primary tooth emergence in Australian children: timing, sequence and patterns of asymmetry.

BACKGROUND: Information on the timing and sequence of human tooth emergence is valuable when analysing human growth and development, predicting the age of individuals, and for understanding the effects of genetic and environmental influences on growth processes. This paper provides updated data on the timing and sequence of primary tooth emergence in Australian children for both clinicians and researchers. METHODS: Twins were recruited from around Australia with data collected through parental recording of twins' primary tooth emergence. One twin from each pair was then randomly selected to enable the calculation of descriptive statistics for timing, sequence and asymmetry in tooth emergence. RESULTS: The first and last primary teeth emerged, on average, at 8.6 months and 27.9 months, respectively, with teeth emerging in the order: central incisor, lateral incisor, first molar, canine, second molar. Left-side antimeric teeth were more likely to emerge before their right-side counterparts but this was not statistically significant. At least 35% of all antimeric pairs had emerged within two weeks of each other, serving as a useful guideline for assessing symmetrical versus asymmetrical development. CONCLUSIONS: Primary tooth emergence in Australian twins is occurring later than reported previously for Australian singletons but is consistent with findings for singletons in other ethnic groups. The most common sequence of primary tooth emergence appears to be consistent in twins and singletons and has not changed over time.

Strong genetic control of emergence of human primary incisors.

Our understanding of tooth eruption in humans remains incomplete. We hypothesized that genetic factors contribute significantly to phenotypic variation in the emergence of primary incisors. We applied model-fitting to data from Australian twins to quantify contributions of genetic and environmental factors to variation in timing of the emergence of human primary incisors. There were no significant differences in incisor emergence times between zygosity groups or sexes. Emergence times of maxillary central incisors and mandibular lateral incisors were less variable than those of maxillary lateral incisors and mandibular central incisors. Maxillary lateral incisors displayed significant directional asymmetry, the left side emerging earlier than the right. Variation in timing of the emergence of the primary incisors was under strong genetic control, with a small but significant contribution from the external environment. Estimates of narrow-sense heritability ranged from 82 to 94% in males and 71 to 96% in females.

Cytokines in the oral mucosa of mice infected with Candida albicans.

Oropharyngeal candidiasis is associated with defects in cell-mediated immunity, and is commonly seen in immunocompromised patients. We have previously shown that T-cell-deficient BALB/c nude (nu/nu) mice are extremely susceptible to oropharyngeal candidiasis, and that recovery from a chronic infection is dependent on CD4 T lymphocytes. In this study we describe the local tissue cytokine profile in lymphocyte-reconstituted immunodeficient mice and their euthymic counterparts. Mice were infected orally with 108 cells of the yeast Candida albicans, and oral tissues sampled on days 0, 4, 8, and 14. Nude mice were reconstituted with 3 x 107 naïve lymphocytes following oral inoculation. Interleukin (IL)-6, interferon (IFN)-gamma and tumour necrosis factor (TNF)-alpha were identified in the oral tissues of infected euthymic mice recovering from oral infection, as well as naïve controls. TNF-alpha was identified in nude oral tissue on days 4 and 8, but only after lymphocyte reconstitution. No IL-2, IL-4 or IL-10 was detected in either euthymic or athymic mice at any time-point throughout the experiment. This study confirms the functional activity of T lymphocytes in reconstituted nude mice, and suggests that TNF-alpha may be an important mediator in the recovery from oropharyngeal candidiasis.

Primary role for CD4(+) T lymphocytes in recovery from oropharyngeal candidiasis.

Oropharyngeal candidiasis is associated with defects in cell-mediated immunity and is commonly seen in human immunodeficiency virus positive individuals and AIDS patients. A model for oral candidiasis in T-cell-deficient BALB/c and CBA/CaH nu/nu mice was established. After inoculation with 10(8) Candida albicans yeasts, these mice displayed increased levels of oral colonization compared to euthymic control mice and developed a chronic oropharyngeal infection. Histopathological examination of nu/nu oral tissues revealed extensive hyphae penetrating the epithelium, with polymorphonuclear leukocyte microabscess formation. Adoptive transfer of either naive or immune lymphocytes into immunodeficient mice resulted in the recovery of these animals from the oral infection. Reconstitution of immunodeficient mice with naive CD4(+) but not CD8(+) T cells significantly decreased oral colonization compared to controls. Interleukin-12 and gamma interferon were detected in the draining lymph nodes of immunodeficient mice following reconstitution with naive lymphocytes. This study demonstrates the direct requirement for T lymphocytes in recovery from oral candidiasis and suggests that this is associated with the production of cytokines by CD4(+) T helper cells.

Irradiation-induced oral candidiasis in an experimental murine model.

The aim of this experiment was to establish a mouse model of irradiation-induced oral candidiasis and to explore the cellular populations and mechanisms by which the infection is cleared from the oral mucosa. BALB/c mice received irradiation to the head and neck equivalent to 800 Rad using a Cobalt 60 gamma source. Both irradiated and non-irradiated mice were infected orally with 1 x 10(8) Candida albicans yeasts. Compared with untreated controls, irradiated animals developed a more severe infection of longer duration, with hyphae penetrating the oral mucosa. Monoclonal antibody depletion of CD4+ but not CD8+ T cells from the systemic circulation prolonged the infection in irradiated mice, but not in controls. Supernatants of submandibular and superficial cervical lymph node cultures from irradiated animals demonstrated significantly higher titers of interleukin-12, but similar levels of interferon-gamma compared with controls. Screening for cytokine production by an RNase protection assay detected only macrophage migration inhibition factor in irradiated and non-irradiated oral tissues from day 8 onwards. The results of this study demonstrate a requirement for CD4+ T cells in the recovery from oral candidiasis induced by head and neck irradiation in mice, and are consistent with a role for Th1-type cytokines in host resistance.

T cells augment monocyte and neutrophil function in host resistance against oropharyngeal candidiasis.

The purpose of this study was to identify the cell populations involved in recovery from oral infections with Candida albicans. Monoclonal antibodies specific for CD4+ cells, CD8+ cells, and polymorphonuclear leukocytes were used to deplete BALB/c and CBA/CaH mice of the relevant cell populations in systemic circulation. Monocytes were inactivated with the cytotoxic chemical carrageenan. Mice were infected with 10(8) C. albicans yeast cells and monitored for 21 days. Systemic depletion of CD4+ and CD8+ T lymphocytes alone did not increase the severity of oral infection compared to that of controls. Oral colonization persisted in animals treated with head and neck irradiation and depleted of CD4+ T cells, whereas infections in animals that received head and neck irradiation alone or irradiation and anti-CD8 antibody cleared the infection in a comparable fashion. The depletion of polymorphonuclear cells and the cytotoxic inactivation of mononuclear phagocytes significantly increased the severity of oral infection in both BALB/c and CBA/CaH mice. High levels of interleukin 12 (IL-12) and gamma interferon (IFN-gamma) were produced by lymphocytes from the draining lymph nodes of recovering animals, whereas IL-6, tumor necrosis factor alpha, and IFN-gamma were detected in the oral mucosae of both naïve and infected mice. The results indicate that recovery from oropharyngeal candidiasis in this model is dependent on CD4+-T-cell augmentation of monocyte and neutrophil functions exerted by Th1-type cytokines such as IL-12 and IFN-gamma.

Potential of 4 per cent silver fluoride to induce fluorosis in rats: clinical implications.

The Health Department in Western Australia uses a 40 per cent silver fluoride (AgF) solution for prevention and treatment of dental caries in children. Analysis of this solution has revealed high fluoride concentrations (75,000-120,000 mg/L), raising concerns of potential toxicity and prompting investigation of clinical protocols utilizing low-strength AgF in an animal model. A single topical application of 4 per cent AgF solution to Sprague-Dawley rats resulted in moderate to severe localized fluorosis in 24 per cent of animals. In a second experiment, caries was induced in rats aged 19 days; six weeks later, between one-four carious molar teeth from each rat were treated with 4 per cent AgF (atraumatic technique). A generalized form of fluorosis developed in the continually growing incisors of less than 10 per cent of animals which had one or two carious teeth treated, and in 70-90 per cent of rats which received AgF to either three or four carious teeth. These results confirm the potential of a 4 per cent AgF solution to induce fluorosis and support previous recommendations that AgF at its empirical concentration of 40 per cent should be withdrawn from clinical use.

Abnormally high fluoride levels in commercial preparations of 40 per cent silver fluoride solution: contraindications for use in children.

Although a 40 per cent solution of silver fluoride would be expected to contain 6 per cent fluoride (60,000 ppm), F-levels of 100,000 ppm and 120,000 ppm were found in 14 commercial samples analysed at The University of Western Australia in 1993 and 1994. To determine whether F-levels in 40 per cent AgF preparations have remained high, the present investigation was aimed at analysing different batches of commercial preparations obtained more recently. Fluoride ion analysis was carried out on 24 AgF samples using the Ion-Selective Electrode technique. Independent analyses of the same samples were carried out by a private chemical testing laboratory (Genalysis). Ten samples supplied by Agson Chemical Export were found to contain between 75,000 and 100,000 ppm F-: Genalysis reported 80,000 to 120,000 ppm. Fourteen samples supplied by Southern Dental Industries were found to contain between 70,000 and 120,000 ppm F-; Genalysis reported 88,000 to 108,000 ppm F-. These results confirm significantly higher than expected F-levels (ANOVA p < 0.05) in commercial preparations of 40 per cent AgF. The solutions tested were found to contain a mixture of ammonium fluoride, sodium or potassium fluoride, and silver fluoride. The additional presence of silver difluoride and hydrofluoric acid resulting from the manufacturing process has been suggested as an explanation for the much higher than expected levels of fluoride ion. In view of possible toxicity of 40 per cent AgF in young children, it is concluded that such a highly concentrated solution should not be used clinically; instead, lower strength AgF solutions should be investigated for their efficacy in caries treatment.

Safety issues related to the use of silver fluoride in paediatric dentistry.

Due to its exceedingly high fluoride content, 40% silver fluoride solution has the potential to cause fluorosis when used in young children. In vitro testing conducted in the present investigation indicates that application of 40% silver fluoride to deep carious lesions or its use as a 'spot' application agent could result in 3 to 4 mg of fluoride reaching the systemic circulation. As scientifically-based clinical trials on the safety of 40% silver fluoride have not been conducted, it would be appropriate for it to be withdrawn from further clinical use until proper testing and evaluation have been carried out. In view of the possibility that lower strength solutions of silver fluoride (1-4%) may be just as effective as 40% in 'arresting' deep caries, testing should focus on such solutions, particularly as the potential for toxicity from their fluoride content would be reduced by a factor of 10-40.

Unacceptably high levels of fluoride in commercial preparations of silver fluoride.

Instead of expected fluoride ion concentrations of around 60,000 ppm, commercial preparations of 40 per cent aqueous silver fluoride were found to contain 120,000-127,000 ppm. Information received from the Western Australian Chemistry Centre which provided independent confirmation of the higher than expected [F] indicates that the currently available commercial preparations contain silver difluoride rather than silver fluoride. In view of the potential of fluoride-containing products such as dentifrices (1000-1500 ppm F) and topical fluoride gels and solutions (6000-12,000 ppm F) to cause adverse effects if excessive quantities are ingested, any product that contains 120,000 ppm [F] should be regarded as carrying a high risk of toxicity when used on young children.

Paediatric dentistry discussion paper and case report. Management of small carious lesions in primary teeth: caries removal versus fluoride application and periodic 'observation' until exfoliation.

Differences in treatment rationale exist between dental practitioners with respect to the management of small carious lesions in primary teeth. Some do not consider it necessary to use a conventional restorative approach, preferring to apply topical fluoride and/or 'monitor' the lesion(s). This paper advocates the alternative approach which entails complete caries removal by mechanical means, the rationale being to eliminate the pool of cariogenic microorganisms and thereby protect sound teeth from succumbing to carious attack. A case is presented to illustrate the extent to which caries can progress and also involve other teeth if small cavitated lesions are simply treated by 'spot' application of fluoride. Clinical treatment of caries must be based on scientific knowledge of the microorganisms involved and an understanding of its transmissible and infectious nature.

An in vitro study of the distribution of silver and fluoride following application of 40 per cent silver fluoride solution to dentine.

An in vitro test system involving application of 40 per cent silver fluoride solution to prepared cavities of moderate depth in extracted teeth failed to demonstrate the passage of significant amounts of fluoride into the dental pulp, despite a very high concentration of fluoride (100,000 ppm) in the applied solution. The test system used may not be conducive to quantitative investigation of ionic transfer because of disruptions to pulp circulation and fluid flow through dentine following tooth extraction. For this reason, the results are inconclusive as to whether or not application of 40 per cent silver fluoride as a cavity varnish of liner and its use in the 'atraumatic' technique for treating deep caries, can be considered safe clinical procedures.

Pulp response in primary teeth with deep residual caries treated with silver fluoride and glass ionomer cement ('atraumatic' technique)

Histological assessment of the dental pulps of 55 carious primary teeth was carried out 3 to 58 months after treatment by the 'atraumatic' technique involving application of 40 per cent silver fluoride to residual caries followed by restoration with glass ionomer cement. Fifty of the 55 teeth examined showed a favourable pulpal response, inducing presence of abundant reparative dentine and a wide odontoblast layer. Histological comparisons were made between these teeth and others not treated with silver fluoride but restored with glass ionomer cement, amalgam or zinc oxide and eugenol. Possible mechanisms of the action of silver fluoride in arresting residual caries are discussed. The question of whether or not treatment of carious dentine with silver fluoride represents a biologically acceptable clinical procedure cannot be answered on the basis of pulpal histology alone. The very high concentration of fluoride in commercial preparations of silver fluoride raises several questions concerning its clinical safety.

Choice of toothbrush: a survey of dentists' personal preferences and recommendations for patients.

Data on dentists' choice of toothbrush brand/type for personal use and their recommendations for patients were obtained by means of a questionnaire. Seventy-nine per cent of dentists surveyed received free samples, with Oral-B comprising 33 per cent of all such samples, followed by Colgate (16 per cent) and Tek (13 per cent). Fifty-three per cent of dentists surveyed indicated they used all free samples received. Sixty-two per cent of dentists do not consider that different brushes differ significantly in their plaque-removing ability. Therefore, while an effective toothbrushing technique is important, selection of the 'correct toothbrush' from the wide range available may not be critical. The results of the present investigation provide information that is relevant to dental health education and can be applied at the chairside as well as at the broader community level.

Integration of basic biological sciences and clinical dentistry in the dental curriculum. A clinically orientated approach to teaching oral and dental anatomy.

Although dental curricula have undergone significant revision during the past three decades, the problem of linking basic science with clinical dentistry often remains an unmet challenge in dental education. This paper describes the content and method of presentation of a course in oral and dental anatomy which aims to integrate closely basic biological science and clinical dental practice. The course holds considerable promise for overcoming one of the major deficiencies of the horizontally structured curriculum by presenting basic science information and detailing its clinical relevance simultaneously. The academic background, clinical experience, and educational philosophy of the course co-ordinator and assisting teaching staff are undoubtedly important factors in determining the extent to which integration between basic and clinical science can be achieved.

Oral biology and the early introduction of clinical dentistry in the dental curriculum.

For the past nine years students entering the Dental School in the University of Western Australia have participated in an introductory clinical dentistry program closely integrated with oral biology. This paper outlines the content of the program and discusses its educational advantages. Changing attitudes in Australian universities toward the appointment of full professors in clinical disciplines also are discussed, and reference is made to the way in which these appointments are helping to achieve a closer correlation between basic science and clinical dentistry.

The role of oral biology departments in dental education.

This paper defines the scope of oral biology, examines patterns of organization and staffing of oral biology departments, discusses the rationale for including courses in oral biology in the undergraduate curriculum, and the organization and content of such courses. Future trends in oral biology are outlined and the conclusion is reached that until clinical departments can assume primary responsibility for ensuring that basic sciences are adequately correlated with clinical dentistry, the need for an oral biology department within a dental school will continue to exist. Furthermore, departments of oral biology must collaborate closely with the clinical departments to develop unified teaching programs that encourage the use of basic science material in solving clinical problems

Intracellular collagen in recurrent ameloblastic fibroma.

Electron microscopic examination of tissue from a twice recurrent ameloblastic fibroma revealed the presence of intracellular collagen fibres in fibroblasts active in protein synthesis. The intracellular fibres were morphologically identical to collagen fibres located extracellularly. The literature on intracellular collagen in biological systems and pathological states has been reviewed, and attention is focussed on collagen phagocytosis and degradation by fibroblasts which are currently considered to represent the basis of connective tissue remodelling and turnover.