Interceptive Guidance of Occlusion with Emphasis

on Diagnosis

by Ensi kolyaei

Burlington Orthodontic Research Project showed that: at age 3, 34% of kids enjoy a

normal occlusion while at age 12 only 11% have a normal intercuspation- a reduction

of 23% local factors are largely responsible, for example crowded dentition

results from a loss of arch length caused by the premature loss of primary teeth.

is an interceptive procedure designed to assist in the correction of hereditary tooth size/jaw size discrepancies.

Because the malocclusions of 66% of 3 year old kids are hereditary, serial extraction is an valuable adjunct to

interceptive treatment.

It is special true in the case of Class I malocclusions and to a lesser extent in the Class II malocclusions.

Class I malocclusions are ideal for serial extraction because the dentition is basically in a favorable

relationship and successful treatment is possible with a minimum of mechanotherapy

Serial extraction

1. True, relatively severe hereditary tooth size/jaw size discrepancy

2. Mesial step mixed dentition

developing into a Class I

permanent relationship

3 .Minimal overbite

4 .Minimal overjet relationship of

the incisor teeth

5.Facial pattern that is

orthognathic or with or with a

slight alveolodental

protrusion

The ideal condition for Serial Extraction

The signs of a true hereditary tooth size/jaw size discrepancy may be outlined as follows: 1. maxillary mandibular alveolodental protrusion without interproximal

spacing2. Crowded mandibular incisor teeth3. A midline displacement of the permanent mandibular incisors,

resulting in the premature exfoliation of the primary canine on the crowded side

4. A midline displacement of the permanent mandibular incisors with the lateral incisors on the crowded side blocked out, usually lingually but occasionally labially.

5. A crescent area of external resorption on the mesial aspect of the roots of the primary canines caused by crowded permanent lateral incisors.

6. Bilateral primary mandibular canine exfoliation, resulting in an upright positioning of the permanent mandibular incisors, this in turn incrreases overjet and/or the overbite as lower incisors retract

Hereditary Crowding

7. A splaying out of the permanent maxillary or mandibular incisors teeth caused by the crowded position of the unerupted canines8. Gingival recession on the labial surface of the prominent mandibular incisors9. A prominent bulging in the maxilla or mandible caused by the crowding of the canines in the unerupted position.10. A discrepancy in the size of the primary and permanent teeth, reducing the leeway space11. Ectopic eruption of the permanent maxillary 1st molars resulting in the premature exfoliation of the primary 2nd molars, which indicates a lack of development in the tuberosity area12. A vertical palisading of the permanent maxillary 1st, 2nd and 3rd molars in the tuberosity area, again indicating lack of jaw development.13. Impaction of the permanent mandibular 2nd molars in the absence of treatment

True hereditary tooth size/jaw size discrepacies must be

differentiated from crowded dentitions resulting from factors that

are more environmental in nature.

True hereditary crowding likely will be treated with the aid of

extractions and if discovered early, with serial extraction

However crowding resulting from environmental factors may be

treated without extractions.

1. Trauma that affects surrounding hard and soft tissues2. Iatrogenic malocclusion due to ill-conceived space management 3. Discrepancy in the size of individual teeth4. Discrepancy between mandibular tooth size and maxillary tooth size5. Aberration in the shape of teeth extra cusps6. Aberration in the eruptive pattern of the permanent teeth7. Transposition of teeth8. Uneven resorption of primary teeth9. Rotation of premolar teeth causing loss of space for erupting canines10. Ankylosis of primary teeth, most often in 1st and 2nd primary molars,

with adjacent tooth tipping11. Reduction of arch length caused by interproximal caries in the primary

teeth12. Premature loss of primary teeth resulting in a reduction of arch length

from subsequent drifting of permanent teeth13. Altered emergencies sequence14. Exfoliation sequence of primary teeth 15. Prolonged retention of primary teeth

Environmental Crowding

because serial extraction is performed during the mixed dentition

period, careful examination of the transformation from the primary to

the permanent dentition is of utmost importance.

A thorough understanding of the eruption sequence and range of timing

in tooth eruption is critical.

One of the most important daily aspects in mixed dentition patient

evaluation is the observation of the tooth eruption pattern and follow up

on alterations in the patient’s sequence of eruption.

While there are many permutations on normal, intercepting individual,

specific developing problems results in reduced needs for

mechanotherapy.

at present, overwhelming scientific evidence indicates that the posterior teeth move forward throughout life. This tends to reduce arch length.

Moorrees has established that arch length decreases 2 to 3 mm between 10 and 14 years, when the primary molars are being replaced by the permanent premolars.

He also has demonstrated that the arch circumference is reduced about 3.5 mm in the mandible of boys and 4.5 mm in girls during the mixed dentition period.

Dekock measured a 10% decreases in arch length for males and 9% for females over a period of 10 years beyond the period of the mixed dentition, from 12 to 26 years.

Brodie has observed that in newborn infants the tongue tends to fill the oral cavity and often encroaches on the alveolar ridge area.

As a consequence of the more rapid anterior growth of the jaws in the postnatal period, the tongue lags behind and comes to occupy a more posterior position in the oral cavity

This is consistent with the upright positioning of the upright positioning of the incisors that occurs in many adolescent as noted by Enlow, Bjork, Tweed and others.

Dental development in the mixed dentition

First molar

Early Mesial Shift:several situations can exits for the permanent first molars. In patients with a spaced primary dentition and a straight terminal plane relationship of the primary molars, the permanent mandibular 1st molars emerge at about 6 years, move the primary molars mesially, close the space distal to the primary canines, convert the straight terminal plane to a mesial step relationship, reduce arch length in the mandibular dentition, and allow the permanent maxillary molars to emerge into a Class I relationship.

Late Mesial Shift:In patients with a closed primary dentition and a straight terminal plane, the permanent maxillary and mandibular first molars emerge into a cusp to cusp relationship simply because no spaces exist. At about 11 years, the primary mandibular 2nd molars are exfoliated and the permanent mandibular 1st molar migrate mesially into the excess leeway space provided by the differentiated in mesiodistal dimensions of the primary 2nd molars and the permanent 2nd premolar teeth. Again this reduce arch length, converts the straight terminal plane to a mesial step, and provides for a Class I relationship of the permanent 1st molars.

Incisor :

Primary spacing: Ideally the primary spacing of the spaced primary situation

will be sufficient , together with other factors to allow for the accommodation

and favorable alignment of the succedaneous permanent incisors

Secondary spacing: in primary dentitions where there is no interdental

spacing, the permanent mandibular lateral incisors emerge and the primary

mandibular canines are moved laterally, thus a space is created that enables

the permanent maxillary lateral incisors to emerge into a favorable alignment.

.

2 mm of crowding in the incisor segment in the mandible of boys

will recover to no crowding by 8 years on the average.

Girls recover to about 1 mm of crowding

2 to 3 mm of spacing is reduced to 0 during eruption of the

incisors

Incisor liability:

1. The 4 permanent maxillary incisor teeth are on the average, 7.6mm larger than the primary

incisors. the 4 permanent mandibular incisors are 0.6mm larger. the liability varies greatly from

one to another and for this reason the patient’s own tooth measurements should be used in the

analysis. A favorable incisor liability exists when the spacing of the primary anterior teeth is

sufficient to allow for the eruption of the permanent incisors without any crowding.

2. A more precarious incisors liability situation exists when no primary spacing is present in a

closed primary dentition. then the individual must rely on the development of secondary

spacing to create sufficient space for the permanent incisors to emerge without crowding

3. An impossible situation exists when the incisor liability is of such magnitude that growth

and development will never be able to meet the space demands required by the permanent

incisors. Such patients are doomed to severe and irregularity from the outset.

4. in the primary dentition the interdental spacing may range between 0 and 10 mm in

the maxilla, with an average of 4mm, and between 0 to 6 mm in the mandible, with a

range of 3 mm.

5. During the period of permanent incisor eruption, notable amounts of intercanine arch

width development occure in the maxillary and mandibular dentition. In the mandible

the increase occurs between 6 and 9 years for boys and between 6 and 8 years for girls.

In the maxilla it increases longer, to 16 years in boys and 12 years in girls.

6. After 10 years of age little intercanine arch width change is expected in the mandible

of boys or girls. The average increase in the mandibular dentition of boys and girls is

about 3mm, in the maxilla it is about 4.5 mm

7. The permanent incisor teeth erupt slightly labial to the arch position of the primary

incisors and for a time at least are more procumbent

The most frequently occurring sequence of eruption in the maxilla is as follows: Permanent 1st Molar, central incisor, lateral incisor, 1st premolar, 2nd premolar, canine, 2nd molar. The most frequently occurring sequence in the mandible is: permanent 1st molar, central incisor,

lateral incisor, canine, 1st premolar, 2nd premolar, 2nd molar. More girls than boys have a favorable combination. An unfavorable sequence can produce crowding. Maxillary 2nd molars erupt ahead of mandibular molars in 89.11% of Class II patients, whereas in

only 56.5% do maxillary 1st molars erupt ahead of their mandibular counterparts, therefore 2nd molars are more important than 1st molars in development of a Class ii relationship.

Early exfoliation of primary teeth can disrupt the alignment of the dentition, reducing arch length in the maxilla and mandible.

Prolonged retention of primary teeth can cause crowding of the permanent teeth in the maxilla or mandible

Clinically the primary 2nd molars appear to resist mesial migration to some extent, however the permanent mandibular 1st molars are observed to have an exagerated mesial inclination after the premature loss of the primary 2nd molars.

When the primary mandibular 1st molar is lost permanently, the permanent 1st premolar which is scheduled to emerge before the 2nd premolar is not so deeply embedded in bone therefore the tendency for tipping of the primary 2nd molar is not as great.

Canine, Premolars and 2nd molars

Contrary to popular belief, arch length can be reduced and space can be lost after premature exfoliation or extraction of the primary 1st molar

In the maxilla, about 90% of the time the 1st premolar emerge ahead of the canine. This is favorable for serial extraction and maintenance of the overbite because the maxillary incisors are not held forward.

About 10% of the time, the sequence is unfavorable for serial extraction and the overbite.

In the mandible , about 80% of the time the canine emerges ahead of the 1st premolar. This sequence of eruption decreases overbite because it maintains the mandibular incisors in a forward position. However this sequence is not favorable for serial extraction. About 20% of the time the sequence is favorable for serial extraction but not for maintenance of the overbite, that is, the 1st premolars are ahead of the canines.

Serial extraction is beneficial to prevent resorption the roots of the maxillary laterals incisors by impacted canines.