GROWTH OF mandible
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CONTENTS • • • • • • •
Introduction Pre-natal growth of the mandible Post-natal growth of the mandible Mandibular condylar cartilage Growth rotation of mandible Clinical considerations Conclusion www.indiandentalacademy.com
INTRODUCTION The craniofacial bony skeleton is a composite structure which supports and protects a series of vital functions. The mandible, the most highly mobile of the cranial bones, is singularly important, for it is involved in the functions of mastication, maintenance of the airway, speech and facial expression. The mandible is the largest and strongest bone of the face. It is the second bone (next to clavicle) to ossify in the body. www.indiandentalacademy.com
PRE-NATAL GROWTH OF MANDIBLE
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Origin of the Mandible • The mandible has its origin in the mandibular processes of the first branchial arches around the 40th day of intrauterine life. • It begins to form lateral to Meckel’s cartilage and then develops inward, medial to the dental and incisive nerves. • With these as centers of ossification are formed the angle, coronoid process, inner alveolar wall and alveolar borders. www.indiandentalacademy.com
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• By the 42nd day the ramus and alveolar process may be distinguished. • At 55 days, the beginning of the coronoid process and condyles is seen. • By the middle of the 3rd month the mandible reaches its characteristic shape.
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Ossification of the Mandible • Centers of ossification can be seen in the mandible on the 39th day. • During the 6th week of intrauterine life, a center of ossification appears at the angle. • Bone formation spreads rapidly beginning with the 7th week and continues forward towards the midline and backwards. • Meckel’s cartilage supports the mandibular processes prior to ossification and union of the two sides of the mandibular bone. www.indiandentalacademy.com
• At 4 ½ months I.U. the adult form of the mandible can be recognized. • Mandibular Symphysis : the mandible is originally formed in two halves which are joined at the mental symphysis by fibrocartilage at about the 6th month of intrauterine life. • Condyle : the condylar cartilage grows downward and forward into the ramus. At 4 ½ months I.U., the cartilage begins to ossify and the condylar process joins the ramus. www.indiandentalacademy.com
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POST-NATAL GROWTH OF THE HUMAN MANDIBLE
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The overall process of mandibular growth was first described almost 200 years ago by the English anatomist, John Hunter. He realized that that the mandible actually grows in a predominantly posterior direction, toward the base of the skull, rather than by an elongation of the chin. This concept was experimentally confirmed by Humphrey in 1864, who inserted metal rings on both the anterior and posterior margins of the mandibular ramus in the growing pig. Rings implanted on the growing posterior surface became more deeply embedded, but the rings secured on the resorptive anterior surface were www.indiandentalacademy.com released following continued growth.
These concepts were verified once again in 1924 by Brash, who used the method of vital staining with madder (alizarin) to study the growth process. Charles (1925) and Brodie (1941) added another milestone to the understanding of mandibular growth. They recognized that the mandibular condyle represents an important growth center and that it brings about the forward and downward growth of the mandible at a rate that is proportional to cortical increases at the posterior border of the ramus and to the growth of alveolar bone on the mandibular body. www.indiandentalacademy.com
Mandibular Growth from Infancy to Adolescence • A thin line of fibrocartilage and connective tissue exists at midline to separate the right and left mandibular bodies. Between 4 months and 1 yr. this symphyseal cartilage is replaced by bone. • Birth – 6 months symmetric broadening downward and mainly forward. • During the 1st yr. of life, appositional growth is active at the alveolar border, distal and superior surfaces of ramus, condyle, lower border of mandible and lateral surface of the mandible. www.indiandentalacademy.com
• 6 months – 4 years symmetric broaddening posteriorly, downward and forward. • 4 – 8 years broadening at condyles, downward and forward. • 8 years onwards downward and forward.
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• Till 4 years of age, there is rapid growth in all three dimensions. After 4 years, transverse growth occurs only in the posterior segment and it slows by 8 years. • Vertical and postero-anterior growth continues till 20 years of age. • Overall, mandibular growth continues at a steady rate before puberty. On average, ramus height increases 1 – 2mm/yr. and body length increases 2 – 3mm/yr. www.indiandentalacademy.com
Basic remodeling processes The basic principles of structural remodeling involved in the growth of the human mandible are: • Area relocation. • Activity at surfaces determined by regional directions of growth. • Principle of the V. Structural remodeling is a companion process to growth and serves to maintain the constant shape of the mandible as it continues to increase in size.www.indiandentalacademy.com
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While the mandible appears in the adult as a single bone, it is developmentally and functionally divisible into several skeletal subunits. Scott divided the mandible into: 1. Basal portion – a tube like central foundation running from condyle to condyle. 2. Muscular portion – has the gonial angle and coronoid process under the influence of masseter, medial pterygoid and temporalis muscles. 3. Alveolar bone – holds the teeth and is gradually resorbed in the event of tooth loss. www.indiandentalacademy.com
• 1. 2. 3. 4. 5. 6.
Moss describes the mandible as a group of microskeletal units: Coronoid process Condylar process Alveolar process Angular / gonial process Body Chin
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Enlow and Harris (AJO 1964) studied 25 wellpreserved human mandibles ranging from 4 to 12 years of age, and mapped the distribution of the various types of endosteal and periosteal bone deposits throughout all areas of the mandible, and gave a detailed analysis of local directions of growth in each part of the mandible.
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The Condylar Neck • The condyle contributes to the overall size of the mandible through a process of endochondral replacement of proliferating condylar cartilage by bone tissue. • As the mandible grows in a generally posterior direction, the condyle grows in a posterior and cephalic direction. • The bone formerly located in the condyle comes to occupy a position in the enlarging condylar neck. www.indiandentalacademy.com
• The diameter of the condylar neck is reduced by the formation of endosteal bone as the cortical plates on both sides grow in an inward direction towards each other. • At the same time, the funnel- or V-shaped neck moves in a progressive direction behind the condyle in a cephalic and posterior course. • The posterior side of the base of the neck grades into the posterior face of the ramus. Here, an outward or periosteal reversal takes place. A zone of periosteal bone is formed in a superimposed position over the older endosteal bone formed during the condylar reduction. www.indiandentalacademy.com
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This reversal continues down the length of the ramus and brings about the posterior growth of the ramus. • An outward reversal also occurs on the anterior side of the neck, and the older endosteal bone is covered by a zone of periosteal bone. This deposition occurs selectively on the lingual side. On the buccal side, this newly formed periosteal bone is abruptly resorbed. • This situation continues into the upper part of the ramus along the sigmoid notch and the coronoid process. It results in a drift of the anterior base of the neck in a lingual and cephalic direction, thus increasing the height of www.indiandentalacademy.com the ramus.
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Bjork (1963) used metallic implants to determine the direction of condylar growth between 5 to 19 years in a male sample. This study showed that: a) On an average, the condyle grew upward and backward. b) It can vary between a sagittal and vertical direction. This variation influences mandibular growth direction at pogonion. www.indiandentalacademy.com
Katsavrias and Halazonetis (AJO DO 2005) studied the shapes of the condyle and glenoid fossa in patients with Class II division 1, Class II division 2 and Class III patients. • They concluded that shape variability of the condyle was mainly related to inclination of the eminence and fossa height.
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• Condylar and fossa shapes were found to be different between the groups : - The Class III group had a more elongated and anteriorly inclined condylar head and a wider and shallower fossa. The condyle was closer to the roof of the fossa. - The condyle was situated more anteriorly in the fossa in the Class II division 1 group, than in the Class II division 2 group. www.indiandentalacademy.com
The Coronoid Process •
The lingual surface of the coronoid process faces three general directions: cephalic, posterior and medial. • This arrangement produces three corresponding results as the mandible grows in overall size: 1. Periosteal deposition occurs in the cephalic direction on the lingual side of the coronoid process. Corresponding periosteal resorption occurs on the buccal side. 2. An accumulation of endosteal bone deposits on the lingual www.indiandentalacademy.com side of the process,
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with corresponding removal from the buccal side, produces continued growth in a posterior and cephalic direction. The anterior edge of the coronoid process undergoes progressive periosteal resorption. 3. Since the coronoid process grows by addition of periosteal bone onto its lingual surface with contralateral periosteal resorption and production of endosteal bone on its buccal side, the base of the process is thereby shifted in a medial or lingual direction, while the apex grows in a lateral direction and the entire process increases in overall size. www.indiandentalacademy.com
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The Ramus • On the buccal surface of the ramus, as the condylar neck grades into the ramus, a reversal in direction of growth is seen. The endosteal cortex produced earlier during condylar reduction is replaced by periosteal deposits. • The buccal side of the ramus (except the coronoid process and neck) has a predominantly periosteal direction of growth. This side is oriented in a posterior direction, and with deposits on the posterior edge of the ramus, continued growth and relocation of the ramus in this direction occurs. www.indiandentalacademy.com
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• On the anterior buccal side of the ramus, the periosteal deposits continue directly onto the trihedral eminence of the mandibular body. • The part of the lingual surface of the ramus located anterior and superior to the lingual ridge of the neck is composed of periosteal bone and it grows in a posterior and superior direction. This periosteal growth continues into the lingual tuberosity above the mylohyoid line. www.indiandentalacademy.com
• As the bone of the posterior-moving ramus becomes relocated as the newly lengthened body, the cortex of the anterior edge of the ramus undergoes simultaneous resorption. This relocation is accomplished by the lingual shift of the ramus through periosteal deposits on the lingual side. www.indiandentalacademy.com
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In the region below the mandibular neck and the mylohyoid line, growth occurs in the buccal direction. So, the contralateral lingual surface here undergoes resorption. A zone of periosteal bone is present around the posterior border of the ramus and onto the lingual surface. This contributes to the posterior movement of the entire ramus. The mandibular foramen maintains its relative position in the ramus by “drifting” in a posterior direction through resorption in the postlingular fossa and periosteal addition on the lingula. www.indiandentalacademy.com
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• Vertical lengthening of the ramus continues after horizontal ramus growth ceases or slows. • This is to match the continued vertical growth of the midface. www.indiandentalacademy.com
The Mandibular Body • The zone of periosteal bone which covers the angle of the ramus continues along the base of the ramus to the premassetric incisure. At this point, growth reversal takes place – endosteal deposition and periosteal resorption occurs. • The endosteal growth continues anteriorly along the basal surface of the premassetric incisure. At the level of the last molar, a periosteal reversal occurs the body proceeds to grow in a downward direction by periosteal deposits www.indiandentalacademy.com on its basal margin.
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• Basal to the lingual tuberosity, the fossa undergoes endosteal growth. This erodes the periosteal growth of the lingual tuberosity. This growth pattern serves to increase the height of the mandibular body and contributes to an increase in its overall size towards the buccal side, leading to formation of a trihedral eminence on the buccal side of the posterior mandibular body. www.indiandentalacademy.com
• The entire mandibular body, along with its dental arch, lies on an axis which is positioned towards the midline from the ramus. Thus, the successive relocation of the old ramus into the elongating body involves a medial (lingual) shift in order to bring the body into symmetrical line with the axis of the dental arch.
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Gonial Angle • The angle between the ramus and corpus of the mandible is known as the Gonial angle. • The gonial angle closes with growth in order to prevent change in the occlusal relationship between the upper and lower arches. • Thus, the gonial angle which is obtuse (140° or more) in infants changes to about 110° in adults.
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• To achieve this, condylar growth becomes vertically directed deposition occurs along the anterior border and resorption along the posterior border in upper part of coronoid process. • This results in a more upright alignment and a longer vertical dimension of ramus without material increase in breadth.
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Antegonial Notch • When the growth of the mandibular condyle fails to contribute to the lowering of the mandible, the masseter and medial pterygoid, by their continued growth, cause the bone in the region of the angle to grow downward, producing Antegonial notching. • There is pronounced apposition beneath the angle with excessive resorption under the symphysis. The resultant upward curving of the inferior border of the mandible anterior to the angular processwww.indiandentalacademy.com is known as Antegonial notch.
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• Thus, a single field of resorption is present on the inferior edge of the mandible at the ramuscorpus junction. This forms the antegonial notch by remodeling from the ramus behind it as the ramus relocates posteriorly. • The gonial region is anatomically variable in the pattern of growth. Depending on the presence of inwardly or outwardly directed gonial flares, the buccal side can be either depository or resorptive, with the lingual side having the converse type of growth. www.indiandentalacademy.com
• The size of the antegonial notch is determined by the ramus-corpus angle (gonial angle) and by the extent of bone deposition on the inferior margin of the corpus just posterior or anterior to the notch. • Antegonial notch is less prominent when gonial angle becomes closed. More prominent when gonial angle becomes opened. www.indiandentalacademy.com
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Singer and Hunter (AJO 1987), in a study to evaluate depth of antegonial notch as an indicator of mandibular growth potential, concluded that: a) Clinical presence of deep notch is indicative of diminished mandibular growth potential. b) It also indicates a vertically directed mandibular growth pattern. c) Deep notch patients required a longer duration of orthodontic treatment than shallow notch patients. www.indiandentalacademy.com
Tariq, Tandon, Sharma and Kapoor (JIOS 2005) studied the correlation between antegonial notching and craniofacial morphology. They concluded that : • Subjects with shallow antegonial notches ( < 1mm.) had a more horizontal mandibular plane, shorter anterior facial heights and smaller gonial angles than deep notch subjects. • Moderate antegonial notch (1.5 – 2.5 mm.) subjects exhibited a morphology between shallow and deep notch subjects. www.indiandentalacademy.com
• Deep notch ( > 3mm.) subjects had a more retrusive mandible with shorter corpus length, less ramus height and greater gonial angle than shallow notch subjects. • The mandibular growth in deep notch subjects was more vertically directed than in shallow notch subjects. • Deep notch subjects had longer total facial height than shallow notch subjects.
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The Chin • The chin is a unique anatomic structure characteristic of Homo sapiens. • It is associated with cortical recession on the labial region of the mandibular body, between the right and left canine teeth. • This process involves endosteal cortical growth, with or without periosteal deposition at localized surfaces on the apex of the protruding chin, or covering the alveolar ridges of teeth. • On the lingual side of the mandible opposite the chin, massive periosteal deposition occurs. www.indiandentalacademy.com
â&#x20AC;˘ Growth changes at the glenoid fossa determine the forward growth of the chin. If the area of temporal bone to which the mandible is attached moves forward relative to the cranial base during growth, this will translate the mandible forward, thus moving the chin forward. However, this rarely happens. More often, the attachment point moves straight down or posteriorly, thus subtracting from rather than augmenting the forward projection of the chin. www.indiandentalacademy.com
Alveolar Process • Formation of the alveolar process is controlled by dental eruption and it resorbs when teeth are exfoliated or extracted. • It serves as a “buffer zone” helps to maintain occlusal relationships during differential mandibular and midface growth. • Vertical alveolar growth persists even after corpus growth is over, to compensate for the occlusal surfaces wear of teeth. This helps to maintain the occlusal height in adulthood. • Adaptive remodeling of the alveolar process makes orthodontic too movements possible. www.indiandentalacademy.com
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Timing of growth in width, length and height. For the three planes of space, there is a definite sequence in which mandibular growth is completed : Growth in width length height â&#x20AC;˘ Growth in width, including width of dental arches, is completed before the adolescent growth spurt and is affected minimally by adolescent growth changes. Both molar and bicondylar widths show small increases until the end of growth in length. Anterior width dimensions stabilize earlier. â&#x20AC;˘ Growth in length and height continue through the period of puberty. www.indiandentalacademy.com
A study by Konno, Sato et al (AJO DO 2005) investigated the relationship between muscle conduction velocity (MCV) and direction of mandibular growth. â&#x20AC;˘ The results showed that MCV was significantly correlated with the vertical facial height at the postpubertal period and the direction of mandibular condylar growth. â&#x20AC;˘ MCV of the masseter muscle was low in a long face, when lower facial height is long, than in a short face. www.indiandentalacademy.com
Late Mandibular Growth • As a result of the cephalocaudal gradient of growth, the mandible undergoes more growth in the late teens than the maxilla. • When the mandible grows forward relative to the maxilla, the mandibular incisor teeth tend to be displaced lingually. • If a tight anterior occlusion is present when the mandible grows ahead of the maxilla, the contact relationship between lower and upper incisors changes. www.indiandentalacademy.com
â&#x20AC;˘ One of 3 events may occur : 1. The mandible is displaced distally, accompanied by a distortion of mandibular joint function and displacement of the articular disc. 2. The upper incisors flare forward, opening space between the teeth. 3. The lower incisors displace distally and become crowded. Of these, distal displacement of lower incisors, with concomitant crowding and a decrease in the lower intercanine width, is the most likely response. The more the mandible grows after other growth has essentially stopped, the greater the chances of lower incisor crowding. www.indiandentalacademy.com
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MANDIBULAR CONDYLAR CARTILAGE
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• The mandibular condylar cartilage is derived from cells of periosteal origin. • It develops adjacent to the intramembranous bone of the mandible, distinct from Meckel’s cartilage. • Since its morphogenesis occurs late in prenatal development, the condylar cartilage has been designated as a secondary cartilage.
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Histology of mandibular condylar cartilage. â&#x20AC;˘ The mandibular condylar cartilage differs primarily in its superficial layers, which comprise a perichondrium in which undifferentiated (prechondroblastic) cells secrete a matrix rich in type I collagen. â&#x20AC;˘ It is these undifferentiated cells that proliferate and mature to effect growth at the condylar cartilage. â&#x20AC;˘ The perichondrium that caps the condylar cartilage is continuous with the periosteum www.indiandentalacademy.com covering the bone of the ramus.
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Phenotypic expression of the cells of the cartilage. • The dividing cells of the condylar cartilage exhibit a dual potential for a chondrogenic or an osteogenic phenotype, with the phenotypic expression dependent on the functional environment of the jaw. • For example, restriction of jaw movement by intermaxillary fixation results in significant reduction of condylar thickness and some transformation of cartilage into bone in the condyle. • Similarly, transplantation of the condylar cartilage to a nonarticular location causes transformation of the cartilage to bone within days. www.indiandentalacademy.com
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• The mandibular condylar cartilage was initially considered a growth center with an intrinsic capacity for growth. • For many years, it was considered the primary “growth center” of the mandible, controlling and pacing its entire growth. • However, later studies showed that in the absence of condyles, the mandibles continued to function adequately and were positioned normally. • This led to the conclusion that soft tissue development carries the mandible downward and forward while condylar growth fills in the resultant space to maintain contact with the basicranium. www.indiandentalacademy.com
â&#x20AC;˘ It is currently understood that mandibular condylar cartilage growth is highly adaptive, and responsive to growth in the adjacent regions of the head, particularly the maxilla. â&#x20AC;˘ Transplantation experiments with the condyles and adjacent tissues show that when the condyle is transplanted alone, it does not grow; but when it is transplanted with adjacent bones, it does. www.indiandentalacademy.com
ROTATION OF MANDIBLE DURING GROWTH
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The rotation that occurs in each jaw is of two types: 1. Internal Rotation â&#x20AC;&#x201C; which occurs in the core of each jaw. 2. External Rotation â&#x20AC;&#x201C; which is produced by the surface changes and alterations in the rate of tooth eruption that mask the internal rotation. The overall changes in the orientation of the mandible, as determined by the mandibular plane, results from a combination of internal and external rotation. www.indiandentalacademy.com
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The core of the mandible is the bone surrounding the inferior alveolar nerve.
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The rest of the mandible consists of several functional processes: 1. Alveolar process – bone supporting teeth and providing for mastication. 2. Muscular process – bone to which the muscles of mastication attach. 3. Condylar process – provides articulation of the jaws to the skull. www.indiandentalacademy.com
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â&#x20AC;˘ Implants placed in the areas of stable bone away from the functional processes show that the core of the mandible rotates during growth in a way that tends to decrease the mandibular plane angle (i.e. up anteriorly and down posteriorly)
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Bjork and Skieller (EJO 1983) stated that total rotation (or internal rotation) of the mandible had two components : 1. Matrix rotation â&#x20AC;&#x201C; rotation around the condyle. 2. Intramatrix rotation â&#x20AC;&#x201C; rotation centered within the body of the mandible. The internal rotation of the mandible varies from 10 to 15 degrees between individuals. For an average individual, there is a -15 degree internal rotation from age 4 to adult life. Of this, 25% results from matrix rotation and 75% from www.indiandentalacademy.com intramatrix rotation.
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• The pattern of vertical facial development is strongly related to the rotation of both jaws. • Individuals of the short face type, characterized by short anterior lower facial height, have excessive forward rotation the mandible during growth, resulting from an increase in internal rotation and decrease in external compensation. • This results in a “square jaw”, with a low mandibular plane angle and a square gonial angle. • A deep bite malocclusion and crowded incisors are seen in this case. www.indiandentalacademy.com
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â&#x20AC;˘ In long face individuals, characterized by excessive lower anterior facial height, the mandible shows a backward rotation, with increase in the mandibular plane angle. â&#x20AC;˘ The mandibular changes result from lack of normal forward internal rotation or from a backward internal rotation, both of which are a matrix rotation. â&#x20AC;˘ This is associated with anterior open bite malocclusion and mandibular deficiency. www.indiandentalacademy.com
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CLINICAL CONSIDERATIONS
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G - Axis â&#x20AC;˘ The G - axis was suggested as a growth vector for mandible by Stanley Braum (Angle Orthod. 2004). â&#x20AC;˘ The net result in growth of the mandible is a downward and forward displacement of the mandible. This was previously quantified to a degree through description of the Y-axis. However, the usefulness of Y-axis has been questioned due to extensive remodeling of the www.indiandentalacademy.com external symphyseal area.
• G – Point point representing center of largest circle that is tangent to internal, inferior, anterior and posterior surfaces of mandibular symphyseal region as seen on a lateral cephalogram. • G – Axis
line drawn from sella to G – point.
• G – Axis vector defined by the angle α (alpha) which the G – axis establishes relative to the S-N plane. www.indiandentalacademy.com
• α values : In females : At age 6 yrs. At age 19 yrs.
67.16° ± 3.03° 66.87° ± 3.03°
In males: At age 6 yrs. At age 19 yrs.
66.12° ± 4° 67.93° ± 4°
G – axis allows for quantification of complex mandibular growth processes in cephalometric forms relative to various craniofacial structures in sagittal plane.www.indiandentalacademy.com
Effect of Functional and Orthopedic Appliances â&#x20AC;˘ Areas of muscle attachment and the alveolar process are most adaptive region in mandible. â&#x20AC;˘ Functional appliances take advantage of this. They change the way that muscle contractions shape the areas of attachment and guide the eruption of teeth and hence shape of alveolar process. www.indiandentalacademy.com
â&#x20AC;˘ In addition, the appliances reposition the mandible and bring about the changes in amount and direction of growth in condylar cartilage. â&#x20AC;˘ A new pattern of function is dictated by the appliance and leads to development of a corresponding new morphologic pattern.
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â&#x20AC;˘ Orthopedic appliances utilize the teeth as handles to transmit forces to adjacent skeletal structures, modify the growth pattern and produce desired skeletal change.
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• A study by de Almeida, Henriques et.al (Angle Orthod. 2005) evaluated the dentoalveolar and skeletal cephalometric changes produced by the Herbst appliance during treatment of mixed dentition patients with Class II division I malocclusion. The results of the investigation indicated that the treatment effects produced were primarily dentoalveolar. • Mandibular incisors were tipped labially, maxillary incisors were retruded. • Increase in mandibular posterior dentoalveolar height. www.indiandentalacademy.com • Significant increase in total mandibular length.
Nalbantgil et al (Angle Orthod. 2005) evaluated the skeletal, dental and soft tissue changes in late adolescent patients treated with Jasper Jumper applied with sectional arches. The sample consisted of 30 subjects with skeletal and dental Class II malocclusion. The results showed that: â&#x20AC;˘ There were no significant changes in the vertical skeletal parameters. â&#x20AC;˘ There was a significant decrease in the SNB www.indiandentalacademy.com angle.
• Mandibular incisors were protruded and intruded; maxillary incisors were retruded and extruded. • Overbite and overjet were improved. • Soft-tissue profile improved significantly.
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A study by Palomo, Hunt et al (AJO DO 2005) compared longitudnal changes in the shape and size of craniofacial structures between 16 untreated Class II division I girls and 16 untreated Class I Bolton girls. â&#x20AC;˘
The results showed that the craniofacial complex underwent continuous shape change from ages 6 to 15 in both groups.
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â&#x20AC;˘ Compared to class I sample, the Class II sample had: a)A longer facial pattern b)Smallest mandibular shape difference at age 6 and largest at age 15 c) More protrusive maxillary landmarks at all ages compared with the Class I sample.
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Gill and Lee (AJO DO 2005) compared the dentoskeletal effects of a conventional and modified Twin-block (TB) appliance. The conventional TB appliance was constructed with a large, single-step advancement. The modified appliance, termed Mini-block (MB) was incrementally advanced, incorporated a maxillary incisor torquing spring, and had a reduced bite-block height. www.indiandentalacademy.com
The results showed that: â&#x20AC;˘ Progressive mandibular advancement is not associated with greater mandibular growth compared with a large, single-step advancement with the TB appliance. â&#x20AC;˘ There was great variability in the mandibular growth response to both appliances.
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CONCLUSION A thorough background in craniofacial growth and development is necessary for every orthodontist to distinguish normal variations from effects of abnormal or pathologic processes. Since orthodontists are heavily involved in the development of not just the dentition but the entire dentofacial complex, a conscientious practitioner may be able to manipulate facial growth for the benefit of the patient. This is not possible to accomplish without a thorough understanding of the pattern of normal growth and the www.indiandentalacademy.com mechanisms that underlie it.
REFERENCES • Enlow DH, Harris DB. A study of the postnatal growth of the human mandible. Am J Orthod 1964; 50 (1) : 25-50. • Enlow DH. Handbook of facial growth. 2nd Ed.,1982, W. B. Saunders Company. • Moyers RE. Handbook of orthodontics. 4th Ed., 1988, Year Book Medical Publishers. www.indiandentalacademy.com
• Proffit WR. Contemporary orthodontics. 3rd Ed., 2000, Mosby, Inc. • Salzmann JA. Practice of orthodontics vol.1. 2 nd Ed., 1966, J. B. Lippincott Co. • Sadler TW. Langman’s medical embryology. 9th Ed., 2004, Lippincott, Williams & Wilkins. • Bjork A. Normal and abnormal growth of the mandible – a synthesis of longitudnal implant studies over a period of 25 years. Eur J Orthod www.indiandentalacademy.com 1983 (5): 1-46.
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