Introduction:

 

 This course is designed to introduce the dental student into the scope of orthodontic part of the dental science with simple way. So, its logic to cover the following points:  

-      Introduction to normal growth and development of the face and teeth are included.

-      Development of the occlusion.

-      Etiology and classification of malocclusion.

-      Preventive and interceptive orthodontic treatment.

 

References:

       (Moyers, 1972, Graber, 1972, and proffitt, 1985).

 

Essential Definition

 

Orthodontics:

It is the dental Science which is concerned with the study of the growth, development and infinite variations of the face, jaws, and teeth and particularly with the treatment of dentofacial abnormalities within the limits sets by certain biological factors. The prefix Ortho means correct or upright while suffix tics indicates arts or sciences. The Greek odonto means a tooth.

 

Normal occlusion:

           It is an occlusion within the accepted deviation of the ideal.

 

Malocclusion:

             It is an irregularity in the occlusion beyond the accepted range of normal.

 

Scope and Aims of Orthodontic Treatment:

 

1- Improvement of facial and dental aesthetics.

2- Alignment of the teeth to eliminate stagnation areas around teeth

3- Elimination of premature contacts which gives rise to mandibular displacements and may cause late muscle or joint pain or facial asymmetry.

4- The elimination of traumatic irregularities of the teeth to keep healthy periodontal tissues.

5- The alignment of protruded teeth which are liable to be damaged by trauma.

6- The alignment of irregular teeth prior to bridge work, crowns or partial dentures.

7- Correction of some speech defects where part of its cases are dental factors.

  

Timing of Orthodontic Treatment:

 

 The Deciduous Dentition:

Treatment at this age is hardly ever indicated. Only, exceptionally, where a malpositioned tooth gives rise to mandibular displacement.

 

The early mixed dentition:

At this stage, treatment would be confined to planned balanced extractions, serial extractions, instancing incisors, etc.

 

The late mixed and early permanent dentition:

         At this stage, the greater part of orthodontic treatment is carried out because of :

1- Eruption of most permanent teeth.

2- Little further growth in arch width, therefore, crowding can reliably be estimated.

3- Children in this age group are often more willing to wear appliances than are adults.

4- The late permanent dentition:

Although treatment can be undertaken at any age, adults are often unwilling to wear appliances over a prolonged period.

 

 

GROWTH AND DEVELOPMENT

 OF FACIAL SKELETON

 

1. GROWTH AND DEVELOPMENT OF CRANIO – FACIAL STRUCTURES AND SOFT TISSUES:

Growth: refers to an increase in size or number which is liked to change in anatomic form. It is a physiochemical                         process.

 Development: increasing degree of organization, or specialization of an organ i.e. physiologic change.

 

Methods of studying physical growth:

1.  Craniometrist (measurements of skulls found among human skeletal remains).

2.  Anthropometry (measurements of skeletal dimensions on living individuals).

3.  Cephalomertric radiography.

4.  Implant radiography. (Metal pins).

  

TYPES OF BONE FORMATION

 There are two types:

1.     Endochondral bone. It formed by calcification of the hypertrophied cartilaginous matrix.

2.     Intramembranous bone. It formed by activation of the osteoblast cells in one layer of connective   tissue.

 

NOTE

The bone of the cranial vault, the face, and the clavicles are intramembranous in origin, while, all other bones in the body are formed from cartilage.

 

Sites of skill growth

A-Suture growth.

B-Surface apposition and remodeling resorption includes alveolar bone formation.

C-Growth of the contained organs as the brain, the eye ball and the tongue.

 

GROWTH OF THE HEAD

 The head composed of:

A-Cranium

  1-Cranial vault

  2-Cranial base

B-Face

  1-Upper face

  2-Lower face

 

A-Growth of the cranium

 1-The Cranial Vault:   

The cranial vault is made up of a number of flat bones. From the time that ossification begins at a number of centers, periosteal activity at the surface of the bone is responsible for growth.

 

At birth, the flat bones of the skull are rather widely separated by relatively loose connective tissues. These open spaces, the fontanelles allow a considerable amount of deformation of the skull at birth. After birth, apposition of bone along the edges of the fontanelles eliminates these open spaces fairly quickly, but the bones remain separated by a thin periosteum line sutures for May years, eventually fusing in adult life.

 

Apposition of new bone at these sutures is the major mechanism for growth of the cranial vault. Also, remodeling in the cranial vault takes place to allow for changes in the contour growth.

 

2-Cranial Base:

In contrast to the cranial vault, the bones of the base of the skull are formed initially in cartilage and are later transformed by endochondral ossification to bone.

 

The cranial base consists of basic – occipit, basi – sphenoid and the ethmoid. At birth, they are separated by cartilage, the most important of which is the synchondrosis connecting the basi – sphenoid to the basi – occipit (Fig. 2). The direction of growth in these sutures is forward and upward carrying the anterior cranial base and upper face bodily upwards and forwards. Ceasation of active growth at the spheno-occiptal synchondrosis occurs about 17-20 years of age while the spheno-occipital synchondrosis remains active until about 10 years of age.

 

B-Growth of the face

 

1-Upper face (Nasomaxillary Complex):

  The nasomaxillary complex is connected to the cranial base by means of six pairs of sutures (the growth sites)

 

 These sutures are:

1-Fronto-maxillary.

2-Fronto-nasal.

3-Zygomatico-frontal.

4-Zygomatico-temporal.

5-Ptergo-palatine

6-Zygomatico-maxillary.

 

The maxilla enlarges in all dimensions mainly by surface apposition of bone. Its vertical height increases with the building up of alveolar bone supporting the teeth. It's buttressed against the neighboring bones (frontal, zygomatic and sphenoid) joined to them by sutures containing connective tissue. In the early years of life, activity at these suture sites with new bone formation at their margins makes an early contribution to the downward and forward project of the maxilla. As the maxilla increases in size, the antrum becomes established by internal resorption and it reaches half adult size by 7 years. The palate descends with the downward growth of the maxilla. The palatal vault deeps as the alveolar process develop (Fig.3).

 

2-Lower face (Mandible):

Theories show that active growth site on each side of the mandible is an area of cartilage beneath the fibrous covering of the condoyle. Interstitial and appositional growth of the cartilage at this site propels the body of the mandible downwards and forwards. The increase in height of the so – called mandibular body is mainly due to alveolar growth as the vertical height between jaw increases; the chin become more prominent as the mandible elongates. Remodelling the anterior of the ramus and the rising level of the alveolus meeting with the sloping ramus, provide space for the eruption of teeth. The contour of the gonial region does not change.

 

  Generalized surface apposition on the outer surface of the mandible is responsible for the increase in its thickness. The mental foramen is situated during the early years of life under the mesial cusp of the first deciduous molar, whereas in adults it is situated below and between the roots of the first and second premolars. This change in position is attributed to the backward and outward inclination of the canal, so by surface apposition of bone this foramen is carried backwards. The path of eruption and the inclination of the mandibular permanent teeth are upwards and forwards leaving the mental foramen behind. The inferior dental canal increases in length by the addition of bone to its posterior end.

 

Theories of Growth Control:

 A.  Suture theory

          Facial growth depends on the proliferation of the connective tissue in the sutures or spaces between the bones. As these bones are forced apart, apposition of bone occurs on the surface to close the sutures. Because many of the sutures are parallel to each other, the resultant vector of bone growth of the face is downward and forward.

 

B.   Cartilaginous theory:

         It is believed that the initial growth begins at the cartilaginous areas of the condoyle, sphenoid – ethmoidal synchondrosis and the nasal septum. According to this theory, the sutures separate but only secondary to the growth of the cartilage. Bone apposition on the surfaces of the opposing bones then closes the sutures as in the previous theory.

 

 C.  Functional matrix theory:

        It states that both growths of the suture and cartilage sites occur but secondary to the original stimulus and the genetic predetermination of the size of various facial activities. Proponents of this theory have performed condylectomies of animal mandibles, yet the bone grew normally.

 

GROWTH OF THE SOFT TISSUE:

 Principles of muscular Growth:

              Muscle growth usually follows the general curve. The peak of the muscle growth velocity is somewhat later than the height growth velocity. Apart form remodeling response in the bone tissue, further adaptation between muscle tissue skeletal frameworks can take place through changes in the origin of the muscle and their insertion.

 

Growth of the Soft Tissue Profile:

            Generally speaking, in the soft tissue profile with age follow the growth in the underlying hard tissue but changes in the soft tissues are not directly correlated with those in the underlying hard tissues. There is a marked sex difference in the development of the frontal sinuses, nasal growth, and mandible and muscle growth. The boys being more pronounced.

 

          The convexity of the face increases with age as nasal growth mainly occurs downwards or forwards (average increase in nose length of about 1.5 mm annually). The ridge of the nose also straightens; therefore, the nose not only increases in size but also in shape.

 

          The tip profile change partly due to growth and partly due to changes in dentition. Children often exhibit incomplete lip closure, decreasing with age as growth in the upper and the lower lip height exceeds that in the lower face, also alteration in the pattern of swallowing and respiration often lead to further improvement.

 

GROWTH OF THE NASO – PHARYNX TONGUE AND ORAL CAVITY:

 

1- The nasopharynx increases greatly in height during growth of the cranium until adolescence.

2- A continues increase in depth from increase in depth from posterior nasal spine to posterior pharyngeal wall, has been also demonstrated.

3- The size of the naso – pharyngeal cavity is influenced by the size of the tonsil and adenoids which are present during birth and grow very rapidly during childhood and atrophies during puberty.

4- Mouth breathing can thus be explained by the size of the naso – pharynx and adenoids.

5- The tongue reaches its maximum size at about 8 years of age which go parallel to the general body curve.

  

REFERENCES:

 

1.

Baume, L. J.

Physiologic tooth migration and its significance for the development of occlusion: the biogenesis of the accessional dentition. J. Dent. Res: 29: 331, 1954 .

2.

Clinch, L.

Variations in the mutual relationships of the upper and lower gum pads in the newborn child, Brit. Soc. Study of orthodontics. Tr. pp 91 – 107, 1932.

3.

Moorress, C.F.

A. and chadha: available space for incisors during dental development.A growth study based on physiologic age. Angle orthodont 35: 12 – 22 (1965).

4.

Proffit, W.

Contemporary orthodontics; Textbook 1986, the C.V. mosby Co.

5.

Sillman, J.H.

Relationship of maxillary and mandibular gum pads in the newborn infant. Am.J. orthodont. 24: 409, 1983.

6.

Thilander, B.

Introduction to orthodontics Tandlakarforlaget, Stockholm, 1985.

  

2- DEVELOPMENT OF OCCLUSION

Studies involving growth and development are of two types:

 

 A.    Cross sectional study:

         A cross section of males or females of both is selected at random from different groups of population from an area or city.

 

       This type of study can be done quickly with fewer expenses. But since it is mixed population with different racial, ethnic, socio – economic, nutritional and other factors, there is more variation which may lead to inaccuracies in the results.

 

B.   Longitudinal study:

It is of two types: pure longitudinal and mixed longitudinal. In pure longitudinal study, males and females from a selected population are studied from birth to adulthood. A period spanning over 18 to 21 years old. The same children are studied so any variation observed is in relation to the same children.

 

This type of study is more accurate and valuable but takes very long time. In order to decrease the period, the children are selected in different age group and studied for a shorter period of time. For example, a fixed number of children are studies from birth to 5 years; at the same another group is studied from 6 – 12 years and so on. Because the study takes a very long time, few people have studied occlusion on a longitudinal basis.

  

       Sillman and Clinch have described 4 phases of normal development of occlusion:

 

Phase I

Period from birth 2 ½ years (completion of deciduous dentition )

Phase  II

2 ½ years – 6 years (completion of deciduous dentition to eruption of first permanent molars).

Phase III

6 – 12 years mixed dentition (from eruption of first permanent molars to complete shedding of deciduous teeth).

Phase IV

12 years onwards – adult dentition all permanent teeth

       

 

A.  GUM PADS :

          At birth no teeth are present. The arches are called “GUM Pads”. Upper arch is sallow and has a saucer – shaped palate. Alveolar part is separated from palate by a groove called “dental groove”. The alveolar part is divided into 10 oblique segments by transverse grooves. Each segment indicates the position of a deciduous tooth. The transverse groove distal to the position of canine is called the lateral sulcus.

 

         The lower gum pad is U – shaped. A continuous groove runs on lingual aspect. The alveolar part is divided into 10 segments.

 

At birth there is no definite relation of the gum pads. The upper gum pad is bigger and overlaps the lower gum pad around. It is very much anterior to lower (3 – 4 mm). Interiorly, the upper and lower gum pads are separated by an open space through which the large tongue protrudes. Posteriorly, the gum pads may be in contact in the tuberosity and heel region. Upper lip is short. The mandible shows mainly anteroposterior movement and no lateral movement. The anterior space is provided so that the deciduous incisors erupt without impinging on the opposite pad.

 

           At birth the gums pads are not big enough to accommodate the developing teeth which lie crowded and rotated in their crypts. The gum pads grow in size first laterally and later antero-posteriorly to accommodate all the teeth.

 

B.  DECIDUOUS DENTITION:

           Between 2nd and 3rd month of intra – uterine life, the facial processes fuse and the dental laming appears. The sequence of initial calcification of primary teeth is a   follows:

 

Central incisor……………

14

Weeks

First molar …………

-15

½   Weeks

Lateral incisor……………

16

Weeks

Canine ………………

17

Weeks

Second molar……………

18

Weeks

 

           At birth about ½ to Ύ or more of the crown is formed. The sequence of eruption of deciduous teeth is as follows.

 

            A   B          D  C      E

       A               B  D     C E

 

Sequence of eruption is more important than the time of eruption. The time of eruption shows great variation.

 

Central incisor……………………

   2 months

First molar ………………

   2 months

Lateral incisor ……………………

year

   3 months

Canine ……………………

mos.

   3 months

Second molar ……………………

 yrs.

   6 months

       

By 2 ½ years all the deciduous teeth are fully erupted and by 3 years root formation of these teeth is completed. The central incisors may erupt slightly crowed but later on they line up. The overbite is deep and the over-jet may be reduced. The second molars end in a flush terminal plane relationship.

 

          The teeth may show inter-dental spacing between 3 – 5 years of age. There are known as developmental spaces: or “Growth spaces” specific spaces distal to maxillary lateral incisor and mesial to canine and distal to mandibular canine and mesial to molar are called “semian space” or “primate space” which are seen in the large apes (primates or semians) for example Gorilla, chimpanzee Gibbon and Orang utan. The spaces are meant for the large tusk like cnaine to occlude. These teeth are so large and strong that they may knock of other teeth if they occlude with them or cause injury to soft tissues, so they are provided space in which to occlud .

           

On an average 3 –4 mm of inter-dental space develop. Nature provides this space for accommodating the developing permanent teeth which are larger than deciduous teeth.  Lack of inter-dental spacing may cause crowding of permanent teeth.

 

        First phase shows the greatest increase in all the dimensions of the dental arches and jaws. The position of maxillary deciduous canine in relation to the lower teeth is very stable. Any deviation from normal relationship indicates a specific type of developing malocclusion.

 

PHASE II:    2 ½ TO 6 YEARS  

         The deep incisor bite is slowly reduced. All the deciduous teeth being to show attrition of occlusal and incisal surfaces due to change in diet from semisolid to food, increased chewing function and greater development of masticatory muscles and jaws.

 

         By the age of 6 years, practically half the incisal edges and occlusal surfaces are worn, which frees the dental arches from interlocking allowing the mandible to grow more forward. If occlusal wear does not take places, the mandible remains distal. The incisors show edge relationship. The second deciduous molars no longer show a flush terminal plane but the lower molar ½ mm mesial to the to the upper. The roots of deciduous teeth begin resorption by 3 ½ to 4 years. During this phase growth takes place at a steady slow rate.

 

PHASE III:      6 – 12 YEARS (MIXED DENTITION) 

          

1.

Time of eruption of permanent teeth

2.

Path of eruption of 6

3.

Path of eruption of 1

4.

Ugly duckling stage of Broadbent

5.

Incisor Liability

6.

Leeway space of Nance and change of Occlusion of 6 from Cusp to Groove.

    

First molars 

years

9 months

Central incisors

years

9 months

Lateral incisors 

years

9 months

Mandibular canines

years

9 months

Mandibular 1st & 2nd premolars 

years

9 months

Maxillary 1st premolars

years

9 months

Maxillary canine & 2nd premolars

years

9 months

Second molars

years

9 months

Third molars

years

To    21 years

 

2.  PATH OF ERUPTION OF FIRST MOLARS:

   MAXILLA:

The crown of the first permanent molar is directed distally and buccally before eruption. As the maxilla moves forward during growth space is created posteriorly permitting the maxillary tuberosity to grow.

 

The crown of the first molar then changes its direction and moves distally at first and later lingually, occlusally and mesially. It is guided into its position by the distal surfaces of the deciduous second molar.

 

MANDIBLE:

The crown faces mesially and lingually. As the resorption occurs on the anterior border of the ramus with simultaneous deposition on its posterior border, space is created distally and the molar occlusally and bucally (not completely) and is guided into position by second deciduous molar.

 

The first permanent molars erupt in an end to end or cusp to cusp occlusion. With the eruption of the first permanent molars growth spurt occurs specially in the mandible causing it to move downward and forward.

 

3. PATH OF ERUPTION OF INCISORS: 

The permanent incisors develop lingual to the deciduous incisors. During eruption they move labially resorbing the roots of their deciduous predecessors. Then they move occlusally.

 

The maxillary central incisors erupt more labially with a marked labial inclination about 2 mm forwards to the position of the deciduous incisors. The mandibular incisors erupt more lingually. Much time they get lingually locked if the central incisors do not erupt with labial inclination or when there is a deep bite in the incisor region.

 

    4. UGLY DUCKLING STAGE (BROADBENT) PATH OF ERUPTION OF CANINES: 

Broadbent described this stage which is seen during the period when the maxillary incisors erupt (8 years), 7 + gets self corrected when permanent canine erupt during 12 years. The maxillary central incisors erupt more labially; a diastema appears between these teeth. The face is thin and long (less broad). The lips are short and the incisor appears protruded with large median diastema. The large developing crown of the cupids press on the roots of the lateral incisors (due to lack of space) causing the roots to tilt mesially and the crown distally. The central and lateral incisors fan distally from the midline giving a rising sun appearance. The face of the child looks ugly at this stage with a large labial fermium.

 

          As the maxilla grows, space is created inside the bone and the canine slides along the root of lateral incisor. As the canine approaches the gum. The crown tilts distally then push between the lateral incisor and deciduous first molars (wedging) occupying the primate space and pushing the crown of the lateral incisor mesially and its root distally correcting the distal axial inclination to normal. The crown of the lateral incisor transmits the mesial force to crown of the central incisors which upright, closing the diastema. With the eruption of maxillary lateral incisors, there is a maxillary growth spurt. The dimension of the face increase and face becomes broader restoring the ugly appearance of the child to a more pleasing appearance of the adolescent.

 

          The upper canines develop close to the floor of the orbit and the lower canines develop close to the lower borders. They have to travel a great distance through bone before they erupt and by the time they their destination, there may not be sufficient space causing impaction of the canines or the canines displace the lateral incisor by pressure on their roots.

 

5. INCISOR LIABILLITY:

          There is an inverse size difference between deciduous and permanent incisors. The permanent incisors are larger by 7.6 mm in the maxillary arch and 6.0 mm in the mandibular arch. This size difference is called “incisor liability” this incisor liability is met by:

   A. interdentally spacing (developmental spaces). Maxillary arch average 4.0 mm and mandibular arch 3.0 mm.

             b. More labial inclination of the permanent incisors on eruption. About 2.0 mm.

   c. Inter-canine arch width growth. About 3.0 mm.