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DEVELOPMENT OF OCCLUSION Introduction Ideal occlusion is not easy to learn as it is not a static condition but a changing function process, undergoing continued modifications and adjustments during the whole life of deciduous and permanent dentition. The achievement of normal occlusion is the result of so many interrelated variables starting from the prenatal developmental stages. The multiplicity and complexity of these factors are such that often malocclusion exists but occasionally there can be found a mouth without orthodontic problems. The active supervision of the developing dentition is a responsibility of the pedodontists. Seeing things from the beginning is the most advantageous. By making a detailed studies of dentition from initiation through eruption till functional occlusion, we may be able to obtain a clear concept of how occlusion develops and how its development can be guided. Occlusion is the approximation of upper and lower teeth, centric occlusion is the maximum intercuspation between upper and lower

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teeth. Centric relation is defined as the contact of teeth (U & L) in most retruded position of the mandible so that condyle is in its most posterior position with respect to glenoid fossa for the maximum comfort of the patient. The development of the concepts of occlusion: There are various trends in the development of the concept of occlusion. the trend ranges from static to dynamic. The various periods in the development of concept of occlusion are: -

Fictional period.

-

Hypothetical period.

-

Factual period.

Fictional period – 18th century: According to Talbot, concept of normal occlusion was that it was a historical event and passed in the decline of the species this hardly served as an inspirator for those to follow who were helpful of preventing, intercepting and treating developing malocclusion.

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Hypothetical period: a. Edward H. Angle in 1899 Put a hypothesis stating that in the normal occlusion, it will be seen that each dental arch describes a graceful curve, and that all the teeth in the arches are so arranged as to be in harmony with their follows int eh same arch, as well as with opposite arch. Each tooth helps to maintain every other tooth in these harmonies relations for the cusps to interlock and each inclined plane serves to prevent each tooth from sliding out of position. This basis created the impression of static relationship. b. Mathew Cryer and Calvin Case: 1905 According to them occlusion refers to the closure of the teeth, one upon the other, and normal dental relations, normal occlusion and typical occlusion refers to the standard anatomical occlusion. He rejected the first molar for the basis of normal occlusion. He told normal occlusion and normal facial lines are inseparable. He used nose, chin button areas in reference to the relative position of the teeth.

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c.

Lischer and Paul Simon: They broadened the concept of occlusion by relating the teeth to

the rest of the face and cranium. Lischer introduced the act of mastication as requisite part of the definition. Sinon made an approach to normal occlusion only through biometry i.e. the anthropometric approach. d.

Milo Hellman He showed a racial variations in normal occlusion. he studied the

number of skulls. But this still remained as static occlusion. Factual period: This concept divides the line between static and dynamic concept of occlusion. In 1930, Broadbent introduced an accurate technique of roentgenographic cephalometry, which eliminated most of the disadvantages

of

anthropologic

measurements.

He

followed

longitudinally the orofacial developmental pattern, tooth formation, eruption and adjustment.

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In his concept, he considered the psychologic rest position, which means that it is the position of mandible, where the muscles are in a relaxed position. It is constant throughout life. On the other hand, it may become smaller even disappear entirely. This is of utmost importance, because once it reduces, patients often complains atleast the tiredness in chewing muscles. The patients often complain of clicking of the joint too. This gives a concept of dynamic occlusion. This shows the evolutionary changes of occlusion

Anthrolopithecus

Ramapithicus

Evolutionary changes: The primitive cartilage of the jawless fish developed into the jaws of the palacoderm, and as evolution continued it developed into jaws of modern mammals.

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The mammalian dentition goes back to 75 million years. The dental formula of the early primates consisted of 2 incisors, 1 canine, 4 premolars, 3 molars. The theories behind this are: a. Theory of concrescence i.e. mammalian dentition was produced by the fusion of 2 or more primitive conical teeth. b. Theory of trituberculy Each mammalian tooth was derived from single reptilian tooth by a secondary differentiations of the tubercles and roots. c. Theory of multituberculy: The mammalian dentition is the result of reduction and condensation of primitive multituberculate teeth. Nolla C (1960) studied different stages of the permanent tooth development. He arbitrarily divided the development of each tooth into ten stages: 0 ďƒ  absence of crypt. 1 ďƒ  Presence of crypt.

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2  Initial calcification. 3  1/3rd crown completion. 4  2/3rd crown completion. 5  Crown almost completed. 6  Crown completed. 7  1/3rd root formed. 8  2/3rd root formed. 9  Root almost completed but open apex. 10  Root completed. In stage 6  most teeth being eruptive movements and in stage 8 most teeth pierce alveolar crest. The humans have two sets of teeth: a. Primary teeth. b. Permanent teeth. The dental formulae for primary dentition is 2102 and permanent teeth is 2123. Stages of occlusal development According to Barnett 1978 a. Ist stage (3years) – primary dentition. b. 2nd stage (6 years) – eruption of first permanent molars. c. 3rd stage (6-9 years) – exchange of incisors.

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d. 4th stage (9-12 years) exchange of canine and premolars. e. 5th stage (12 years) – eruption of 2nd molars. Post natal development of occlusion: Can be divided into (according to Vander Linden) 1. Birth to complete primary dentition. 2. First intertransitional period. 3. First transitional period. 4. Second intertransitional period. 5. Second transitional period. 6. Adult dentition. Birth to Complete eruption of primary dentition At birth the alveolar processes are covered by gumpads, which are firm and pink. The basic form of the arches is determined in intrauterine life around 4 months. Thus the gumpads are alveolar arches at the time of birth. They develop in two distinct parts, a labio-buccal and a lingual portion of these labiobuccal part is differentiated first and grows more rapidly and gets divided into ten segments by transverse grooves. Lingual portion which is differentiated later remains entirely smooth.

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The buccal part is divided into ten segment by transverse grooves, each corresponding to a deciduous tooth sac. It is papillomatous at first. The groove between canine and first deciduous molar crypts is important in assessing the relation of two pads. Their groove is referred to as lateral sulcus.

The lingual groove portion which develops later is separated by dental groove which is the site of origin of dental lamina. Lingual portion is limited lingually by gingival groove. In the upper jaw, gingival groove separates from the palate and is related to inner alveolar plane. The grooves are more clear in upper arch than the lower arch.

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The dental groove of the upper gum pad passes from the incisive papilla and moves laterally and lingually, to join the gingival groove in canine region and then continues distally and buccally across the segment of the gum pads corresponding to the first deciduous molar tooth crypt. The lower gum pad is U-shaped and is limited on the lingual aspect by a continuous groove. The gum pad is divided by transverse grooves into ten segments not as clearly as upper anteriorly gum pad is slightly everted. The lateral sulcus again passes at canine region. The size of the gumpads at birth is determined by the following factors: -

State of maturity of infant at birth.

-

Size at birth as expressed by birth weight.

-

Size of the developing primary teeth.

-

Purely genetic factors. The mandibular gum pad is distal to maxillary gum pad average

2.7mm in males and 2.5mm in females. The labial frenum varies in its attachment at birth and may be found at the crest of gum pad, high above the crest or even continuous with the incisive papilla.

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During the first year, gumpads grow rapidly in the lateral direction, with development of deciduous teeth, there is an increase in labio-lingual dimensions of the gum pad. Relationship of gumpads: At rest gumpads are separated by the tongue and protrudes over the lower gum pad to lie immediately behind lower lip. At this age, upper lip appears very short. The gum pads do not have a definite relationship when occluded. The antero-posterior movements vary and there are no lateral movement. The upper gum pad is wider than lower and when two are approximated, there is a complete overjet all around the lower gum pad. The lateral sulcus of lower is usually posterior to that of upper. The contact is only seen in first deciduous molar region. It is common for a vertical space to exist between upper and lower incisor segment even when they are pressed into occlusion. this appears to be linked with the position of tongue. At birth, the incisors are crowded and rotated in their crypts and as the gumpads grow during first year of life now they are in good alignment and spaced. Inspite of this incisors may erupt in irregular relation to each other. But, this however is temporary and later gets corrected by the tongue and lip pressure.

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Clinch (1934) in Jr of Orthodontics demonstrated the increase in the size of the alveolar arches from birth to the time just before the eruption of the incisors. The arches increase in both length and breadth. At birth no teeth are visible usually. The upper gum pad usually overlaps the lower anterior pad by about 0.5mm. At birth, the tooth buds of all primary teeth are present and in various stages of development. The incisors are somewhat crowded at this time for two reasons. 1. The arches have not yet complete rounded out anteriorly. Only during the first 8-12 after the birth are the jaws are capable of significant anterior apposition thereafter posterior growth and anterior displacement accounts for the increase in jaw size. 2. The development of posterior teeth takes later hence follicles are slower in achieving their complete size. Usually, by the end of first year, sufficient jaw growth has occurred that the primary teeth are seldom crowded or overlapped. Infact a normal desirable dentition at this stage will exhibit spacing. The extensive early transverse development of both jaws can be realized as mainly because of the presence of mid-palatine suture in maxilla and in mandible,

the

mandibular

synchondroses. 12

The

mandibular


synchondrosis calcifies at around 1 year of life but maxilla maintain its transverse growth potential till about 12 years of age. The growth in the both arches is not coordinated till the occlusion is established in the posterior region after which the development of both dental arches are coordinated. Characteristics of Primary dentition: The cardinal feature of primary dentition in contrast to the permanent teeth is that they drop almost vertically into the mouth requiring very little mesiodistal or bucco-lingual adjustments in their eruptive movement. At this age, the roots of primary cuspids and molars are not yet complete and the crowns of the permanent central incisors, lateral incisors, cuspids and first molars are in various stages of formation. By 30 months of age, 70% of all children have their primary dentition fully erupted but a great deal of variation exists. Eruption sequence of primary dentition according to ‘Bjork’.

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CI, LI, Ist molars, canines, 2nd molars.

Upper Lower

CI

LI

C

IM

IIM

(mth) 71/2 6

(mth) 9 7

(mth) 18 16

(mth) 14 12

(mth) 24 20

According to Logen and Kronfeld

Primary dentition can be broadly classified into two types: a. Spaced arches. b. Closed arches. Spacing was first described by Dellabarre in the year 1819 in the deciduous dentition between the ages of 4-6 years. The absence of spacing in the primary dentition is an indication that crowding of teeth can occur later when larger teeth erupt. If 6mm of total space is there no crowding develops. If 3-6mm, 20% may develop crowding. If less than 5mm, 50% may develop crowding. If no spaces, 70% may develop crowding. If crowding, 100% develop crowding. Spaces in primary dentition It is very common to find the physiological spaces in the primary dentition, with the most prevalent spaces mesial to the primary canines in maxilla and distal to the primary canine in the mandible. These spaces

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are called the primate spaces or simian spaces as they are commonly seen in the primates and are characteristics of the primary dentition. Boyko (1968) in American Jr. of Orthodontics found that 78% had bilateral primate spaces in both upper and lower arches, 98% of boys had bilateral primate spaces in the maxilla and 86% in the mandible. The primate (simian or primate) space is about 2mm and generalized interdental spacing is seen between teeth which measures about. These are also called as developmental or physiological spacs. Occlusal relationships of the second primary molars: The primary dentition is complete after the eruption of the 2 nd primary molars. This means that the location for the eruption of the permanent teeth in the future has already been determined at this stage. The relation of the distal surface of the maxillary and mandibular second primary molar is, therefore, one of the most important factors that influence the future occlusion of the permanent dentition. The mesiodistal relation between the distal surface of the upper and lower second primary molars is called the terminal plane when the primary teeth contact in the centric occlusion. the terminal plane can be classified into three types:

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Flush or vertical plane type: The distal surfaces of the upper and lower teeth are on the same vertical plane. This plane would produce end-on relationship of the first permanent molars. The change from a flush terminal plane to a mesial step plane is desirable. For the transition from end-on to Class I relation, the lower molars have to move forward by 3-5mm. This is achieved by two principles. 1. Early mesial shift : Occurs in children with spaced arches. Eruptive force of the first permanent molar is sufficient to mesialize the E and D in the arch to close the primate space. This occur in the early mixed dentition stage. 2. Late mesial shift : Occurs in children with closed arches. The first permanent molar drifts mesially by utilizing lee-way space of nance. This occurs in the late mixed dentition stage. Mesial step: The distal surface of the lower molar is more mesial to that of the upper. This is highly desirable as it would permit an immediate Class I first permanent molar relationship upon eruption. The mesial step most

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commonly occurs due to the early forward growth of the mandible, if the differential growth of the mandible continues it can lead to Angle’s Class II molar relation and if the forward mandibular growth is minimal it can establish Angle’s Class I molar relationship. Distal step: The distal step of the lower molar is more distal to that of the upper. The persistence of distal step would be consistent with establishing an Angles Class II first permanent molar relationship. Among Japanese children, the vertical type is the most prevalent and also Caucasian children. Alexander and Prabhu (1998), IJ of Ped. Dentistry, conducted a study on 1026, 3-4 years old children to assess the profile, occlusal relationships and presence of spacing or crowding of teeth in South India males had a higher incidence of straight profiles, but it was not statistically significant. 75% of both sexes had both physiologic and primate spaces and 3% population were devoid of spacing. The convex profiles were significantly correlated with flush and distal step terminal planes in both sexes. Foster T.D. and Hamilton in 1969 in Br. Dent. Jr. stated after the completion of the primary dentition, the ideal features are the following: 17


-

Spacing of incisor teeth.

-

Anthropoidal spaces.

-

Flush terminal plane.

-

Deep bite and decreased overjet.

First intertransitional period: This period is between the completion of primary dentition and the emergence of first permanent teeth and is marked by little obvious intraoral changes and multiple intrabony activities. The arches by this time are capable of significant growth leading to space for the first permanent molars, which is achieved posteriorly by tuberosity apposition in the maxilla and ramal resorpting in the mandible. During the early part of this period, the tooth buds for 1 st and 2nd premolar begin to form between furcations of the primary molar roots. The first permanent molar crowns are fully developed and roots are starting to form. At the stage there is some indication of the future occlusion. There may be excessive overbite and retrognathic tendency of the mandible.

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At 5-6 years of age, just before shedding of deciduous incisors, there are more teeth in the jaws than any other time. Description of occlusal contacts in primary dentition: All the maxillary teeth except the maxillary second molars occlude with two opposite teeth in the mandibular arch. The maxillary second molar only occludes with the mandibular second molar. All mandibular teeth except the central incisors occlude with two opposite teeth in the maxillary arch. The lower central incisors only occlude with the maxillary centrals. Each mandibular tooth is one-half cusp mesial to the corresponding maxillary tooth, there by establishing the following dental relationship. The primary maxillary cuspid occludes distally to the mandibular cuspid and mesially to the mandibular first primar molar. The maxillary first primary molar occludes between the distal aspect of the mandibular second primary molar. The contacts between the upper and lower teeth can be described as surface contact, or as cusp point contact with a fossa, groove or embrasure, or ridge contact with embrasure, or ridge contact with groove.

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Factors guiding normal occlusion in primary: The achievement of a normal occlusion is dependent upon a number of factors. Neuro-muscular considerations: The action of the muscles of mastication on TMJ and also tongue and cheek muscles are largely responsible for this relationship. These masticatory muscles are controlled by a system of complex-neuronal circuit consisting of sensory input to the CNS, and formation, generation of appropriate motor responses. Interdigitation occurs sequentially from the first teeth to erupt i.e. central incisors. As other new teeth appear the muscles learn to effect the necessary function occlusal movements. Since the primary occlusion is established during periods of ready developmental adaptation, there is less variability in occlusal relationship in primary when compared the permanent. The primary teeth are guided into their occlusal position by the functional matrix or muscles during very active growth of facial skeleton. The low cuspal height and ease of occlusal wear also make the primary occlusion more adaptable.

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When teeth are erupted and muscles are functioning, the arch formed by the crowns of the teeth is altered by muscular activities, although original arch form is not probably determined by the muscles. First transitional period: The first exchange of teeth begins around six years of age and is usually completed within two years. During this time span the permanent first molars erupt posterior to the primary teeth and this change usually goes unnoticed and the obvious exchange of eight incisors occurs. The chronology of exfoliation can be determinant of maturation in children and sequence of exfoliation can influence the order of eruption of succedaneous teeth. There is bilateral symmetry of tooth loss and the mandibular teeth exfoliate earlier than maxillary only the 2nd molars exfoliate at the same time. In girls, teeth exfoliate earlier than boys. This difference is greatest for canines especially. In the mandibular arch (10 months) and least for maxillary incisors (1-3 months). The rank of exfoliation of each tooth is the same for both sexes. In the mandibular arch the teeth are lost in order from anterior to posterior part of mouth but in maxillary, the posterior progression is disrupted by the canines which exfoliate after the first deciduous molars

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with the eruption of first permanent molars first of the three assaults on the excessive overbite occurs. As the upper and lower first permanent molars erupt, the pad of tissue overlying them creates a premature contact. The proprioceptive response leads to the increased eruption of deciduous teeth anterior to first permanent molar, thus reducing the overbite. The upper and lower first permanent molars display contrast pathways of eruption. The tooth buds of the lower first permanent molars are mesially and lingually inclined. The upper permanent first molar bud develop with a buccal and distal orientation. The mesiodistal relationship of the permanent molars is determined by the alignment of distal surfaces of 2nd primary molars. The later mesial shift occurs because of Lee-way space of Nance. The mesiodistal dimension of the primary molars is more than the mesiodistal dimensions of premolars. This difference of 1.7mm unilaterally in mandible and 0.9mm unilaterally in the maxilla. According to Moyers 1.4mm mandible unilaterally. The permanent incisors will start erupting in the early mixed dentition period. At 4 ½ years the crowns of permanent central incisors

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will be fully developed and located above and slightly lingual to the roots of primary incisors. Usually mandibular central incisors erupt first, followed by maxillary permanent central incisors. The mandibular incisors erupt lingual to the deciduous counterparts, while the maxillary permanent incisors appear as large bulges in the muco-buccal vestibule above the deciduous incisors before they erupt. Since the permanent incisors are larger than the primary incisors, inorder for the anterior tooth buds to fit within the jaws lingual to their antecedents, they must overlap and assume different vertical levels. In the maxilla, particularly the lateral incisors are situated behind the centrals and cuspids in addition to their labial position are located furthest from the occlusal plane. (The longer the root, the more away from the occlusal plane is the tooth bud). In the lower jaw, the cuspids are so inferior as to be almost at the mandibular border. The labial movement of the anterior teeth effects on the oblique resorption of the roots of the primary teeth. Within few months of appearance of the first permanent molars, the lower central incisors erupt. The upper centrals emerge a few months

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late followed by lower lateral incisors. The upper centrals are the last teeth to appear in the fist transitional phase. Because of the discrepancy in the mesiodistal crown width between the primary and permanent incisors, space available for the permanent teeth after the exfoliation of the antecedents is barely sufficient Mayne in 1969 has coined the term “Incisal liability” for this difference. It is 7.18mm in the maxilla and 5.06mm in mandible. This will be compensated by: -

The inter dental spacing of primary incisors.

-

Increase in the intercanine width (3mm by eruption of LI in maxilla and mandible and in maxilla further 1.5m by eruption of canines).

-

The average arch position of the maxillary central are 2.2mm anterior to the primary incisors.

-

Change of tooth axis of incisors. The interincisal angle is 150° in the primary dentition 123° in permanent dentition. When the mandibular lateral incisors emerge, not only they push

the primary lateral incisors labially but also more the primary cuspids distally and laterally, closing the primate space or an unusual resorption

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of the primary cuspid root. When the mandibular primary cuspids are lost prematurely, the anterior arch loses its stability and incisors may tip lingually by the hyperactivity of the mentalis muscle. This lingual tipping of incisors permits the developing cuspid to slide labially where it may erupt later in labioversion. In maxilla, there is a diastema often found between central incisors this may be because the central incisors often erupt with a slight distal inclination. The maxillary lateral incisors on the other hand, experience more difficulty in assuming their normal position, for as they are erupting, the developing crown of the maxillary cuspids lies just labial and distal to their roots. This position often causes the lateral incisors to erupt more palatally than central incisors. After the erupting cuspid has changed its course the lateral incisors correct itself and come into position besides the central incisors. Thus, as the end of first transitional phase the incisors are present sometimes slightly crowded in the mandible and spaced in the maxilla with more labial inclination than their antecedents. The first permanent molars are erupted usually with an end on relationship.

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Gellin and Haley (1982) Int. J. Dent. Child conducted a clinical study to determine if removal of the corresponding primary tooth is necessary when the lingual eruption pattern of permanent incisor is identified. They monitored 57 lingually positioned permanent central or lateral incisors in 44 children. They concluded that the spontaneous correction of lingually erupted mandibular incisor occurred in 95% of cases by the age 8 years, 2 months to 4 months. Ugly duckling stage: Children tend to look ensued during the time of exchange of their incisors, especially in the upper arch. Because of the presence of diastema the parents become worried; and often frenum is sacrificed in an effort to remove the cause of the space between the centrals. This transitional malalignment during the exchange period of upper incisors is called as ugly duckling stage, the term coined by Broadbent in 1937. This is corrected later when the canines erupted and the pressure is transferred from the roots to the crown of the incisors. If diastema is very much abnormal (> 4mm) investigations has to be carried out to rule out the presence of midline pathologies.

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2nd intertransition period: Almost 1 year gap between 1st and 2nd transitional period. During this in space dentition the end-on will correct to the Class I molar relation. Lo and Moyers in 1953, American Jr. Of Orthodontics, studied the sequence of eruption of maxillary and mandibular permanent teeth on a sample of 236 children. The most frequent in the maxilla was 6124537 appeared 48.72% of the time. There were 18 possible sequences. -

6124357 ďƒ  16.01%

-

6124573 ďƒ  11.87%

In mandible, 17 different sequences were noted: -

6123457 was found in 45.77%

-

6123475 were found in 18.64%

-

6124357 were found in 8.47% They reported the combination of eruption sequences of 6124537

in maxilla and 6123457 in mandible provides the greatest incidence of normal molar relationship.

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Nanda (1973) in Jr. of Dental Research, reported that most common sequence of tooth emergence is 6124357 in maxillary arch and 6123457 in the mandibular arch: The factors affecting the sequence of eruption: -

Endocrine (GH, TH).

-

Familial tendency.

-

Mental development.

Second transitional period: The primary cuspids and molars are shed and permanent cuspids and premolars erupt and 2nd permanent molars erupt. It is commonly occurs between the ages 10-12 years. Occasionally maxillary cuspid and second premolar will erupt simultaneously and mandibular cuspid and first premolar erupt simultaneously. The maxillary and mandibular 2nd permanent molars are the last teeth to erupt. They start erupting at the age of 12-13 years and this delay may be due to lack of space.

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The maxillary 2nd molar is tilled distally and buccally and mandibular 2nd molar is tilted mesially and lingually with the emergence of teeth, they are guided into occlusion by the “cone funnel� mechanism and not until contact is attained do these teeth start to upright. If the 2nd molar erupts before 2nd premolar, there is tipping of first molar thus reducing space for the erupting second premolar. The eruptive force of the 2nd molar helps in late mesial shift and it also acts as bite-opener. Adult dentition: Although after the exfoliation of last primary tooth, the dentition is considered as adult, it is only around the 20 th years when the 3rd molars have erupted and finished root development, the adult dentition is completed. 3rd molars show more variability in calcification and eruption than do any other teeth. There is evidence of ethnic differences. The finnish aquire their 3rd molars, later than middle American whites and south Indians show eruption as early as 13-14 years.

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Andrews – 6 keys to normal occlusion: Andrew during 1970s put forward 6 keys to normal occlusion. He considered the presence of these features essential to achieve an optimal occlusion. 1. Molar inter arch relationship. 2. Mesio-distal crown angulation. 3. Labio-lingual crown inclination. 4. Absence of rotation. 5. Tight contacts. 6. Curve of spee. Molar inter-arch relationship: The mesio-buccal cusp of the upper first molar should occlude in the groove between mesial and medial buccal cusp of the lower firt molar. The mesio-lingual cusp of upper first molar must be angulated so that the distal marginal ridge occludes with the mesial marginal ridge of lower second molar. Mesiodistal crown angulation: It is the line that passes along the long axis of the crown through the most prominent part in the center of labial or buccal surface. For the normal occlusion, the gingival part of long axis of the crown must be 30


distal to the occlusal part of line. Different teeth exhibit different crown angulation. The labio-lingual crown inclination: The crown inclination is determined from a mesial or distal view. If the gingival area as the crown is more lingually placed from the occlusal area, it is referred to as positive crown inclination and the opposite is referred to as negative crown inclination. The maxillary incisors exhibit a positive crown inclination, while the mandibular incisors show a very mild negative crown inclination. The maxillary and mandibular posterior have a negative crown inclination. Absence of rotation: Normal occlusion is characterized by absence of any rotation. Rotated posterior teeth occupy more space on the dental arch while rotated incisors occupy less space in the arch. Tight contacts: To consider an occlusion as normal, should be light contact between adjacent tooth.

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Curve of spee: A normal occlusal plane according to Andrew should be flat, with the curve of spee not exceeding 1.5mm.

Summary and Conclusion Guidance of eruption and development of the primary and permanent dentitions is an integral part of the speciality of pediatric dentistry. Early diagnosis and successful treatment of developing malocclusion can have both short term and long term benefits while achieving the goal of occlusal harmony, function and dental facial esthetics. The understanding of the normal occlusion indicate whether prevalence and interceptive orthodontic procedures can be applied or not.

References 1. White & Gardner – Book of orthodontics. 2. Moyers. 3. Vander Lindon – Development of occlusion. 4. McDonald – Text book of children through adolescence. 5. Graber – Text book of orthodontics. 6. Wheeler – Text book of Dental anatomy.

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CONTENTS INTRODUCTION DEVELOPMENT OF CONCEPTS OF OCCLUSION

a. Fictional Period b. Hypothetical Period c. Factual Period EVOLUTIONARY CHANGES STAGES OF OCCLUSAL DEVELOPMENT POST NATAL DEVELOPMENT OF OCCLUSION BIRTH TO COMPLETE DEVELOPMENT OF PRIMARY DENTITION RELATIONSHIP OF GUMPADS CHARACTERISTICS OF PRIMARY DENTITION SPACES IN PRIMARY DENTITION OCCLUSAL RELATIONSHIP OF 2ND PRIMARY MOLARS

a. Flush Or Vertical Plane Type b. Mesial Step c. Distal Step FIRST INTERTRANSITIONAL PERIOD DESCRIPTION OF OCCLUSAL CONTACTS IN PRIMARY DENTITION FACTORS GUIDING NORMAL OCCLUSION IN PRIMARY DENTITION

a. Neuromuscular Co-ordinations FIRST TRANSITIONAL PERIOD UGLY DUCKLING STAGE SECOND INTERTRANSITIONAL PERIOD SECOND TRANSITIONAL PERIOD ADULT DENTITION ANDREW’S SIX KEYS ON NORMAL OCCLUSION

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Development of occlusion 1/Dental implant courses by Indian dental academy