Handout Paediatric Dentistry Children's Hospital at Westmead
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HANDOUT PAEDIATRIC DENTISTRY CHILDREN’S HOSPITAL AT WESTMEAD A/Prof Richard Widmer Head, Dental Department The Children’s Hospital at Westmead Cnr Hawkesbury Road & Hainsworth Street WESTMEAD NSW 2145 INTRODUCTION Paediatric Dentistry involves treating a complex range of dental problems in children, viz: dental caries, dento-facial trauma, periodontal conditions, orthodontic problems, and in many cases requires detailed assessment of the patient's medical and social status. Dental caries and periodontal disease are the two main dental disorders in children. Both are preventable. The use of community based water fluoridation and locally applied topical fluorides have significantly reduced the incidence of dental caries as has the wide-spread dissemination of preventive activities and information. As well gingivitis and periodontal, whilst not generally as destructive in children as adolescents and adults, has also been significantly affected by the strong preventive effort mounted both professionally and commercially. Water fluoridation, introduced to capital cities in Australia (except Brisbane) during the period 1961- 1978, remains the single most important community based strategy available, to decrease the caries burden. Approximately 2/3 of Australians have access to a fluoridated water supply, while around 1 per cent have access to water supplies with naturally occurring concentrations of fluoride above 0.5ppm. Although the magnitude of the reduction in dental caries attributable to water fluoridation - in the presence of other sources of fluoride - is considerably smaller than was the case previously, it is still estimated to confer and maintain an approximately 20-40 per cent reduction in decay within western populations. Reduction in caries in permanent teeth in children is likely to be towards the lower end of this range; while for primary teeth, the reduction is likely to be towards the upper end. Fluoride toothpaste (1000ppm or 400ppm) dominates the market. The lower strength toothpaste is recommended for children age 6 months to 10 years. Only a small ’pea sized’ amount is needed on the brush. 1. DENTITION The Primary dentition is composed of 20 teeth, all of which erupt prior to those of the permanent dentition. There are 8 incisors, 4 canines and 8 molars. The Permanent dentition consists of 32 teeth, the central incisors, lateral incisors, canines and bicuspids, which replace the primary teeth, and the first, second and third permanent molars, all of which erupt posterior to the primary teeth. The formation of the primary teeth begins in utero with the dental lamina formed around the 4th to 6th week from ectomesenchyme. Development of the permanent teeth is initiated at about the 20th week of embryonic life, with the permanent tooth buds arising from the dental lamina lingual to the primary tooth germs. The number and shape of the teeth are subject to strong genetic regulation. Disturbances in induction during this early morphogenetic stage may lead to numeric or morphological aberrations of the teeth. The calcification of the primary embryonic tooth follicles commences at around 3 to 4 months in utero. The primary incisors begin to calcify first and the second primary molars complete the calcification process by 12 months of post-natal development. Disturbances of the calcification process can result in a chronological hypoplasia of the enamel forming at that time. Thus the primary teeth can be a record of foetal development and can provide valuable information on the timing and extent of any inter-uterine insults; for example, such an event at 8 months gestation may leave an obvious horizontal hypoplastic defect on the second primary molars. Special studies quantifying the levels of environmental pollution have used exfoliated primary teeth as a measure of lead exposure. 2. MORPHOLOGY The teeth of the primary dentition have a cervical constriction. The enamel and dentine layers of the primary teeth are approximately equal in thickness and are generally thinner than in the permanent dentition. The primary teeth have varying numbers of roots, depending on their position within the dental arch; for example, if a toddler accidentally knocks out a primary anterior tooth, it is often a great surprise to parents that the tooth has a long root, as such roots are generally resorbed before exfoliation of the primary teeth, and not seen. In contrast the roots of the primary teeth are shaped like "ice tongs". They are more delicate and divergent than those of the permanent molars. Resorption of roots of primary teeth is usually physiological, whereas resorption in the permanent dentition is pathological. 3. ERUPTION OF PRIMARY TEETH At birth the gum pads are slightly indented, indicating the position of the developing teeth. The primary teeth begin to appear through the gum pads at about 6 months of age, their eruption being completed by around 2 years of age. There are no distinct differences between sexes and the normal range of eruption is relatively small. The primary central and lateral incisors erupt initially followed by the first primary molars, the canines and finally the second primary molars. There appears to be little connection between the normal eruption time of primary teeth and other developments such as skeletal maturity, body height or psychomotor maturity of the child. A genetic influence, however, has been shown in reports on familial trends towards early and late eruption. Also, severely delayed eruption or impaction has been reported as an inherited trait. The primary teeth do not erupt into the mouth in the same sequence in which they are formed in the alveolar bone. Thus at the age of 12 to 14 months when the primary incisors and the first primary molars have erupted, that is, numbers 1, 2 and 4, there is a space where number 3 has not yet erupted. This is often a worry to parents, who may need reassurance. Spacing between teeth is common in the early primary dentition and spacing between the upper incisors and canines and between the lower canines and first molars are known as primate spaces. A lack of such spaces in the primary dentition is an indicator that the permanent teeth may also be crowded. 4. ERUPTION OF PERMANENT TEETH In general, the age at eruption of permanent teeth is more variable than for primary teeth. There are sex and racial differences as well, in that girls are somewhat ahead of boys and that the teeth of Caucasians erupt at a later age than most other races. When the first permanent teeth start to appear at about 6 years of age the child moves into what is known as the mixed dentition. This lasts until all the primary teeth have exfoliated. The upper and lower incisor teeth are exfoliated first between 6 and 8 years of age. The remaining canine and bicuspid teeth are shed between the ages of 9 and 12. The initial permanent teeth to appear are the first permanent molars. These teeth erupt at the back of the mouth behind the last standing primary molars and are entirely new teeth without any primary teeth having been shed to make way for them. Parents are often surprised to know that they are there. They are the largest human tooth and are important in the establishment of the dental arch. They are never replaced and have to last a lifetime. A common finding with the next permanent teeth to arrive, the lower incisors, is for one or more to erupt lingually to the retained primary teeth. Occasionally, a dark bluish area of mucosal tissue is apparent before eruption of the tooth. This is an eruption cyst, and usually ruptures spontaneously, although a moderate level of discomfort can be reported. Parents need reassurance that this is usually only a variation on the normal eruption pattern. The permanent teeth, like the primary teeth, commence formation in utero but, unlike the primary teeth, do not begin calcification until the post-natal period and can thus provide a record of development post-partum. The initial teeth to calcify are the first permanent molars. Calcification of the crowns of the permanent teeth continues until about age 8 (excluding the 3rd molars, that is, wisdom teeth). Dental malformations can result from systemic or environmental insult such as a difficult, prolonged labour; calcium imbalance; prolonged high fevers; chemotherapy and radiation therapy. An understanding of the chronology of dental development allows an estimate of the child's age at the time of disturbance. When all the permanent teeth have erupted the child has what is termed the permanent dentition. Dental Occlusion The final relationship of the upper and lower permanent teeth is dependent on developmental processes of the cranial base, the jaws and the patterns of tooth eruption. These skeletal processes are under the dual influence of genetic and environmental factors. The growth and development of the craniofacial skeleton are principally by bony displacement at the facial sutures and surface remodelling of bones. The early relationship of the gum pads does not bear a relationship to the future dental occlusion. Initially, when a baby attempts to appose the gum pads, contact is mainly in the posterior region and this contact is not precise. During the first year of life, the relationship of the gum pads and erupting teeth begin to settle down and by the age of 16 months the first primary molars attain occlusal contact. Once this is established the jaws are normally closed to the same position each time. Once all the primary teeth have erupted, the alveolar bone develops and there is a considerable increase in facial height. This has a secondary effect on the palate resulting in an increase in palatal height. Individual variability in growth of the cranial base and the jaws is great and the co-ordination of development with the various components is not always perfect.