The general pattern of physical development after birth is a continuation of the pattern of the late fetal period : rapid growth continues with a relatively steady increase in height and weight. But birth is a traumatic process and requires a dramatic set of physiologic adaptations. For a short period, growth stops and there is a small decrease in weight during the first 7 to 10 days of life.
An interruption in growth produces an effect in skeletal tissues that are forming at the time - the result is a noticeable line across both bones and teeth“neonatal line”. Its location across the surface of the primary teethvaries from tooth to tooth, depending on the stage of development at birth.
Primary as well as permanent teeth can be affected by: • illnesses during infancy and early childhood. The more severe is illness, the greater the impact and the more chronic the illness, the greater cumulative impact. • chronically inadequate nutrition, has an effect similar to chronic illness.
MATURATION OF THE ORAL FUNCTION During the eruption of primary dentition also the maturation of oral functions take place. The principal physiologic functions of the oral cavity are: • the respiration • swallowing • mastication • speech
THE RESPIRATION • Newborn infants are obligatory nasal breathers and may not survive if the nasal passage is blocked at birth. • Later, breathing through the mouth becomes physiologically possible. • At all times during life, respiratory needs can alter posture of mandible and tongue and so the basis from which oral activities begin.
THE RESPIRATION The nasal passage may be reduced by: • tonsilar hyperthrophy • deviation of nasal septum
THE RESPIRATION • nasal polyps • adenoids
THE RESPIRATION This situation can alter oral function and the result is : • alteration of growth of the facial skeleton • the characteristic appearance of the face and • resulting malocclusion.
THE SWALLOWING Next physiologic priority of the newborn child is to obtain milk and transfer it into the gastrointestinal system. This is accomplished by two maneuvers: • suckling (not sucking) and • swallowing
THE SWALLOWING The milk ducts of the mammals are surrounded by smooth muscle which contracts to force out the milk. To obtain milk, the infant doesn´t have to suck it from the mother´s breast. Instead, the infant´s role is to stimulate the smooth muscle to contract. This is done by suckling, consisting of small nibbling movements of the lips, a reflex action in infants.
THE SWALLOWING • In infants the anterior oral seal is created by contact of the tongue with lower lip. At this stage of development, tongue – to- lower lip contact is maintained most of the time. • Infant swallowing is characterized by active contraction of the lips, a tongue tip brought forward in to contact with lover lip and little activity of the posterior tongue or pharyngeal muscles.
THE SWALLOWING • As the infant matures, there is increasing activation of the elevator muscles of the mandible as the child swallows. • As semisolid and solid foods are added to the diet, it is necessary for the child to use the tongue in a more complex way to transport food posteriorly. • The suckling reflex and infant swallowing normaly disappear during the first year of life. • After the eruption of the primary molars, during the second year, drinking from a cup replaces drinking from a bottle or continued nursing at the mother´s breast. • A transition in the pattern of swallow leads to the acquisition of an adult pattern. This type is characterized by relaxed lips, the placement of the tongue tip against the alveolar process behind the upper incisors and posterior teeth brought into occlusion.
THE SWALLOWING If some sort of sucking habit (thumb sucking, finger or similary shaped object sucking) persist, there will not be a total transition to the adult swallow. After sucking habit is stopped, a complete transition to the adult swallowing may require some month.
THE SWALLOWING An anterior open bite or proclination of the upper incisors (which may be present if sucking habit persists a long time) can delay this transition. It is because of the physiologic need to seal the anterior space during swallowing.
THE CHEWING PATTERN • The chewing movements of a young child typically involve moving the mandible laterally as it opens, then bringing it back towards the midline and closing, to bring the teeth into contact with food. • An adult typically opens straight down, then moves the jaw laterally and brings the teeth into contact. The transition from the juvenile to adult chewing pattern appears to develop in conjunction with eruption of the permanent canines, at about age 12.
THE GENRAL PATTERN OF MATURATION Maturation of oral functions can be characterized in general as following from anterior to posterior. At birth, the lips are relatively mature, whereas more posterior structures are quite immature. As the time passes, greater activity by the posterior parts of the tongue and more complex motion of the pharyngeal structures are required.
THE SPEECH This principle of the front-to-back maturation is particularly well illustrated by the development of speech. • The first speech sounds are bilabial sounds (p) and (b), so the usual first word is likely to be “mama” or “papa”. • Somewhat later, tongue tip consonants like (t) and (d) appear. • The sibilant (s) and (z) sounds, which require that the tongue tip is placed close to palate come later. • The last sound (r) requires precise positioning of the posterior tongue.
ERUPTION OF PERMANENT TEETH The eruption of any tooth can be divided into several stages. The nature of eruption and its control before emergence of the tooth into the mouth are somewhat different from eruption after emergence. • Preemergent eruption • Postemergent eruption
Preemergent eruption Preemergent eruption: eruptive movement begins soon after the root begins to form. This supports the idea that metabolic activity within the periodontal ligament is the major part of, if not the only mechanism for, eruption. Two processes are necessary. 1. there must be resorption of bone and primary tooth roots 2. the eruption mechanism itself then must move the tooth in the direction where the path has been cleared.
Preemergent eruption • Although the two mechanisms normally operate together, in some circumstances they don´t. The bone resorption and the rate of tooth eruption are not controlled by the same mechanism. • Failure of teeth eruption because of defective bone resorption occurs in the syndrome of cleidocranial dysplasia. (there is also heavy fibrous gingiva and multiple supernumerary teeth)
Preemergent eruption • In a rare but now well documented human syndrome called “primary failure of eruption” affected posterior teeth fail to erupt because of the defect in the eruption mechanism. Bone resorption apparently proceeds normally, but the teeth simply do not follow the path that has been cleared.
Preemergent eruption • Normally, the rate of eruption is such that the apical area remains at the same place, while the crown moves occlusally, but if eruption is mechanically blocked, the proliferating apical area will move in the opposite direction. (lack of space within the dental arch, supernumerary tooth, cyst, tumor )
Postemergent eruption Postemergent eruption: once a tooth emerges into the mouth, it erupts rapidly until it approaches the occlusal level and is subjected to the forces of mastication. At that point its eruption slows and then as it reached the occlusal level of other teeth and is in complete function eruption stops.
Postemergent eruption • After that teeth erupt at a rate that parallels the vertical growth of the mandibular ramus. As the mandible continues to grow, it moves away from maxilla, creating a space into which the teeth erupt. Exactly how eruption is controlled so that it matches mandibular growth is not known. • some of the more difficult orthodontic problems arise when eruption does not coincide with growth.
Postemergent eruption • The amount of eruption necessary to compensate for jaw growth can be best visible in observing an ankylosed tooth. It appears to submerge because it remains at the same vertical level while the other teeth continue to erupt. It may be covered over again by the gingiva.
Postemergent eruption • During the adult life, teeth continue to erupt at an extremely slow rate. If an antagonist is lost at any age, a tooth can again erupt more rapidly, demonstrating that the eruption mechanism remains active.
ERUPTION OF PERMANENT TEETH • A change in the sequence of eruption is much more reliable sign of a disturbance in the development than a generalized delay or acceleration. • For example, a delay in eruption of maxillary canines to the age 14 is within normal if the second premolars are also delayed. But if the second premolars have erupted at 12 and the canines have not, something is probably wrong.
ERUPTION OF PERMANENT TEETH • Several reasonably normal variations in eruption sequence have clinical significance and should be recognized: 1. Eruption of second molars ahead of second premolars in mandibular arch. Early eruption of second molars can be unfortunate in the dental arch where room to permanent teeth is marginal. It tends to decrease the space for the second premolars and may lead to displacement or retention of premolars.
ERUPTION OF PERMANENT TEETH 2. Eruption of canines ahead of first premolars in maxilla. If maxillary canines erupt at about same time as first premolars, the canines probably will be forced labially.
ERUPTION OF PERMANENT TEETH 3. As a general rule, if a permanent tooth in one side erupts but its counterpart on the other side doesn´t within 6 month, a radiograph shold be taken to investigate the cause of the problem.