Clinical Implication (Importance ) of Growth and Development

                                                       
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CONTENTS

                           INTRODUCTION

              A thorough background in craniofacial growth and development is necessary for every dentist.Even for those who never work with children, it is difficult to comprehend conditions observed in adults without understanding the developmental processes that produced these problems.For those who do interact professionally with children and almost every dentist does so at least occasionally –it is important to distinguish normal variations from the effects of abnormal or pathologic processes. Since dentists and orthodontists are heavily involved in the development of not just the dentition but the entire dentofacialcomplex, a conscientious practitioner may be able to manipulate facial growth for the benefit of the patient.Obviously,it is not possible to do so without a thorough understanding of both the pattern of normal growth and the mechanisms that underlie it.

Definitions of growth

•      The self-multiplication of living substances-J.S.Huxley

•      Increase in size,change in proportion and progressive complexity-Krogman

•      Entire series of sequential anatomic and physiologic changes taking place from the beginning of prenatal life to senility-Meridith

•      Growth refers to increase in size –Todd

•      Growth refers to an increase in size and number-Proffit

•      Quantitative aspect of biologic development per unit of time-Moyers

•      Change in any morphological parameter which is measurable-Moss

Definition of development

•      Development is progress towards maturity-Todd

•      Development is a maturational process involving progressive differentiation at the cellular and tissue levels-Enlow

•      Development refers to all naturally occurring progressive ,unidirectional ,sequential changes in the life of an individual from its existence as a single cell to its elaboration as a multifactorial unit terminating in death-Moyers

SOME CONCEPTS OF GROWTH

•      CONCEPT OF NORMALITY-normal refers to that which is usually expected, is ordinarily seen or is typical. The concept of normality must not be equated with that of the ideal.

•      Rhythm of growth-There seems to be a rhythm during growth process. This growth is most clearly seen in stature or body height. The first wave of growth is seen in both sexes from birth to fifth or sixth year

GROWTH SPURT

There seems to be periods when a sudden acceleration of growth occurs. This sudden increase in growth is termed growth spurt.

Name of spurt	female	male
infantile/childhood growth spurt	3yrs	3yrs
Mixed dentition/juvenile	6-7yrs	7-9yrs
Prepubertal /adolescent growth spurt	11-12 yrs	14-15yrs

Clinical significance of growth spurt

ü To differentiate whether growth changes are normal or abnormal

ü Treatment of skeletal discrepancies is more advantages if carried out in the mixed dentition period ,especially during the growth spurt

ü Pubertal growth spurt offers the best time for majority of cases in terms of predictability ,treatment direction ,management and treatment time

ü Orthognathic surgery should be carried out after growth ceases

ü Arch expansion is carried out during the maximum growth period

ü There is great deal of individual variation in growth spurts

ü Puberty and adolescent growth spurt occur on an average nearly 2yrs earlier in girls than in boys.

ü Orthodontic treatment must be done earlier in girls than in boys to take the advantage of the adolescent growth spurt. Growth of the jaws usually correlates with the physiologic events of puberty in about the same way as growth in height

ü In significant no of individuals, especiallyamong girls have a “juvenile acceleration in growth that occurs 1to 2 yrs before the adolescent growth spurt. This juvenile acceleration can equal or even exceed the jaw growth that accompanies secondary sexual maturation .In boys if a juvenile growth spurt occurs it is always less intense than the growth acceleration at puberty

ü If orthodontic treatment is delayed too long the opportunity to utilize the growth spurt is missed

ü If most girls are to receive the orthodontic treatment while they are growing rapidly the treatment must begin during the mixed dentition rather than after all succedaneous teeth have been erupted

ü Any growth modification must be done before the adolescent growth spurt ends

Differential growth

•      Human body does not grow at the same rate throughout life.Different organs grow at different rates to different amount and at different times.This is termed as differential growth

Ø Following are the two important aspects of growth which helps as to understand the concepts of differential growth. These are;

  Scammon’s curve of growth

  Cephalo-caudal gradient of growth

Cephalo-caudal gradient of growth

•      There is an axis of increased growth extending from head towards the feet.

•      In fetal life ,about the third month of intrauterine development ,head occupies 50%of the total body length and within the head the cranium is large relative to the face .The trunk and limbs are rudimentary

•      At birth-head-30% of total body length ,legs-1/3^rd of the total body length

•      In adults head-12%of the total body length legs-1/2of the total body length.

•      Therefore with growth trunk and limbs grow faster than the head and face.

Importance of cephalocaudal gradient

v Cephalocaudal gradient strongly affects proportions /leads to changes in proportions with growth

v Cephalo-caudal gradient is more evident at puberty

v More growth occur in the lower extremity than upper ,with in the face more growth takes place in lower jaw than upper .This produces an acceleration in mandibular growth relative to maxilla results in differential growth

Functional matrix theory

•      Theory states that the origin ,form, position ,growth and maintenance of all skeletal tissues and organs are always secondary, compensatory and necessary responses to chronologically and morphologically prior events or processes that occurs in specifically related non skeletal tissues organs and functioning spaces

Clinical implication of functional matrix theory

•      The theory states that growth of the face occurs as response to functional needs /neurotrophic influences mediated by the soft tissues in which jaws are embedded. In this view ,the soft tissues grow both bone and cartilage react

•      Growth of the cranial vault is a direct response to the growth of brain

•      Trauma can result in growth deficiency if there is enough soft tissue injury which lead to to severe scarring as the injury heals

•      Mechanical restriction caused by the scar tissue in the vicinity of TMJ impedes translation of mandible as adjacent soft tissues grow and that is the reason for growth deficiency in some children after condylar fracture

•      Manipulating maxillary growth by influencing growth at sutures has been a major part of orthodontic treatment

•      Maxilla is translated downward and forward as the face grows,and new bone fills the sutures

•      Both surrounding soft tissues and cartilage probably contribute to the forward positioning of maxilla

Growth rotations of jaws

•      Bjork and coworkers first studied about growth rotations

•      Internal rotations-rotation that occurs in the core of the jaw.it is divided into

1. Matrix rotation-rotation around the condyle

2. Intramatrix rotation –rotation centered with in the body of the mandible

·       External rotation –surface changes

Ø The rotation of either jaw is considered forward and given a negative sign if there is more growth posteriorly than anteriorly.The rotation is backward and given a positive sign if it lengthens anterior dimensions more than the posterior ones bringing the chin downward and backward

Ø Internal rotation ranging from upto 10 to 15 degrees

Ø In an average individual with normal vertical facial proportions there is about -15degree,25%results from matrix rotation and75% from intramatrix rotation

Ø External rotation compensates the internal rotation

Ø Total rotation=internal rotation-external rotation

Rotational pattern of growth are quite different in individuals who have short face and long face types of vertical facial development

Ø Short face types

•      They are characterized by short anterior lower face height have excessive forward rotation of the mandible during the growth resulting from both an increase in the normal internal rotation and a decrease in the external compensation

•      The result is a nearly horizontal palatal plane and mandibular morphology of  the square shaped type with a low mandibular plane angle and a square gonial angle

•      A deep bite malocclusion and crowded incisors usually accompany this type of malocclusion

Ø Long face types

•      They have excessive lower anterior facial height ,the palatal plane rotates down posteriorly often creating a negative rather than the normal positive inclination to the true horizontal

•      The mandible shows an opposite backward rotation with an increase in the mandibular plane angle

•      This type of rotation is associated with anterior open bite malocclusion and mandibular deficiency

Growth modification

  Restraint the maxillary growth:The important sites of growth of maxilla are the sutures which separate the middle of the palate and attach the maxilla to zygoma ,pterygoid plate and frontonasal area

•      For modification of excessive maxillary growth the concept of treatment would be to add a force to oppose the natural force that seperates the sutures,preventing the amount of seperation that would have occurred.

•      For deficient growth of maxilla the concept would be to add additional force to the natural force seperating the sutures more than otherwise would have occurred

•      Orthopedic appliances like headgear is used to restrain the maxillary growth

•      Facemask is used to pull the maxilla forward

•      Orthopedic appliances are most effective during mixed dentition period as it takes advantage of the prepubertal growth spurt.

•      However treatment should be maintained till growth is complete as these appliances change only the expression of growth and not the underlying growth pattern

•      There is an increase in the release of growth hormone during the evening and night and associated with the sleep onset.So child is advised to wear the headgear at night

•      To alter the maxillary growth ,the headgear act by compressing the sutures thus restricting the normal downward and forward growth of the maxilla,while at the same time the mandible is allowed to grow normally

•      Facemask works under the principle of pulling the maxillary structures forward with the help of  anchorage from the chin or forehead or usually both

v Effects of orthodontic force on mandible

  Restraint of mandibular growth:chin cup is used to deliberately rotate the mandible down and back redirecting than directly restraining the mandibular growth.This reduces the prominence of chin at the expense of increasing the anterior facial height

  Augmentation of mandibular growth

•      Functional appliances helps in position the mandible forward ,posturing the mandible forward activate the mandibular musculature

•      Bone remodelling changes takes place in the condyle

•      Lengthening of mandible takes place due to the forward displacement of mandible

Functional appliances

•      Functional appliance therapy is done in mixed dentition period.

•      Actively growing individual with favorable growth pattern are good candidate for this therapy.

  Timing of surgery

•      Jaw surgery has an little inhibitory effect on the further growth

•      For this reason orthognathic surgery should be delayed until growth is essentially completed in patients who have problems of excessivegrowth, especially mandibular prognathism

  Importance of growth after orthodontic treatment

•      Relapse after orthodontic treatment has two major causes

1.   continued growth by the patient in an unfavorable pattern

2.   tissue rebound after the release of orthodontic force

•      Control of unfavorable growth

•      Changes resulting from continued growth in a Class II, ClassIII ,deep bite ,or open bite pattern contribute to a return of the original malocclusion ,and so are relapse in that sense

•      For patients with skeletal problems who have undergone orthodontic treatment need active retention

TRANSIENT MALOCCLUSION

•      Transient malocclusion or self correcting anomalies are the anomalies that arise in the child’s developing dentition during the period of transition from that of the gumpad stage to the onset of permanent period and get corrected on their own without any dental treatment

Significance of transient malocclusion

•      Transient malocclusion are part of developing dentition and should not be considered as any developmental or pathological abnormality

•      If there is any apprehension on the part of parents of the child it should be removed promptly and parents should be explained in brief the physiology behind these transitional changes in the dentition

Self correcting anomalies

  Predentate period

•      Retrognathic mandible

•      Anterior open bite

•      Infantile swallowing pattern

  Primary dentition

•      Anterior deep bite

•      Flush terminal plane

•      Spacing

•      Edge to edge

  Mixed dentition period

•      Anterior deep bite

•      Mandible anterior crowding

•      Ugly duckling stage

•      End on relation

  Permanent dentition

•      Overjet and over     

v Retrognathicmandible: Mandible is rudimentary at birth.This retrognathia is corrected by the differential and forward growth of mandible .The chin point moves anteriorly very rapidly during the first three years.The slowdown in anterior maxillary growth during the first year also contribute the correction of retrognathic mandible

v Anterior open bite

•      In predentate period the upper gumpad is both wider and longer than the mandibular gumpad.Thus when the upper and lower gumpads are approximated, there is complete overjet all around.

•      The infantile openbite corrects with eruption of the primary incisors

v Anterior deepbite

•      It may occur in the initial stages of development of primary dentition .Primary teeth are upright.They have an almost vertical inclination with an inter incisal angle of about 150degree between the maxillary and mandibular primary central incisors

•      It is corrected by

Ø Eruption of deciduous molars

Ø Attrition of incisal edges

Ø Forward and downward growth of mandible

v Flush terminal plane

•      When the distal surface of maxillary and mandibular deciduous second molar are in the same vertical plane.Thus the erupting first permanent molars may also be in a flush or end on relationship

Ø correction

•      For the transition of end on molar relation to class 1 molar relation the lower molar has to move forward by about 3-5mm relative to the upper molar

•      This occurs by utilization of the physiologic spaces and leeway spaces in the lower arch and by differential forward growth of the mandible

•      This shift can occur in two ways-the early shift or the late shift

v Physiologic spaces

•      Spaces may be

•      Generalized[development/physiologic]

•      localized(primate spaces)-they exist between the upper lateral incisors and the canines and between lower canines and first deciduous molar

Ø Total space present may vary from 0 to8 mm with an average of 4mm in the maxillary arch and 1 to7mm with an average of 3mm in the mandibular arch

Ø correction

•      Spaces that exist between the primary molars usually close by the time of the first permanent molars whereas those between the primary incisors persist until these teeth are replaced

v Edge to edge relationship of the primary incisors is corrected with the eruption of the permanent incisors

v Anterior deep bite is present in the mixed dentition period.This is  because of larger permanent incisors and shedding of primary molars is usually alleviated following exfoliation of second primary molars

Ø Correction occurs after the eruption of upper and lower first permanent molar

v Mandible anterior crowding

•      Incisal liability along with decreased size of the jaw leads to lower anterior crowding

Ø Correction-tongue pressure leading to widening of the arch

•      Increase in intercanine width by about 3mm in the mandible

v Ugly duckling stage

•      It is a transient or self correcting malocclusion seen in the maxillary incisor region between 8 to 9yrs of age seen during the eruption of the permanent canines

•      The condition usually corrects by itself with the complete eruption of the permanent maxillary canines as the pressure is transferred from the roots to the crown of the incisors

•      UGLY DUCKLING STAGE

v End on relation

•      It is more common for the permanent molars to erupt into an end on relation

•      For the transition of end on molar relation to class 1 molar relation the lower molar has to move forward by about 3 to 5mm

•      This occurs by the utilization of physiologic spaces and leeway space

  Growth changes in adults

•      Facial growth had continued during the adult life

•      The rotation of both jaws continued into adult life ,in concert with the vertical changes and eruption of the teeth

•      Males showed a net rotation of the jaws in a forward direction slightly decreasing the mandibular plane angle,whereas females had a tendency towards backward rotation,with an increase in the mandibular plane angle.

SUMMARY

Why should a dentist or orthodontist be interested in growth &development ?

•      Knowledge of general and facial growth provides a background to the understanding of the etiology and development of malocclusion. Such an understanding is in turn an important part of the diagnosis and treatment planning process 

•      As observers at regular intervals ,of the growing child all dentist should be able to identify abnormal or unusual pattern of skeletal growth and refer as appropriate

•      More particularly, the dentist should be able to identify abnormal occlusal development at an early stage in order to undertake suitable interceptive orthodontic treatment when appropriate. occlusal development is obviously closely linked to facial growth & development

•      Inopportune or poorly timed extraction performed by the dentist during growth may have unfortunate consequences on the developing occlusion

•      Orthodontic treatment may make use of growth spurts &other trends. The timing of treatment in relation to these may be important .Tooth movement is more rapid,when the growth activity is more. For both these reasons an understanding of the kinetics of facial growth is necessary

•      Many malocclusion may be due to skeletal discrepancies between the jaws. Such discrepancies are usually due to the differences in comparative growth of jaws. More severe malocclusion may be related to more distant skeletal discrepancies within the cranial base. Correctly identifying these growth features may be important in deciding upon diagnosis and formulating a treatment plan.

•      Most orthodontic treatment is performed in the actively growing child or adolescent.Some are dependent on favorable growth and these treatments may have an effect on the hard & soft tissues of the area.

•      In some treatment,for example where surgery is being considered,it is important to be able to identify when majority of the growth has been completed

•      Growth effects can have long term effects on the stability of the occlusion after treatment. This needs to be considered when a retention regime is planned.

  References

1.   Contemporary orthodontics-William R.Proffit

2.   Textbook of orthodontics-Gurkeerat Singh

3.   Orthodontics The art and science-Bhalajhi