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INDIAN DENTAL ACADEMY Leader in continuing dental education


• Arne Bjork- The Man and his work. • Method and application of use of metallic implants. • Three dimensional growth of the maxilla • Growth of the Mandible and Growth Rotations • Growth Rotation of the Frontal Bone. • Study of RME using metallic implants.

Arne Bjork- The Man and his Work. • Arne Bjork is internationally known for his contributions to the understanding of craniofacial growth. • His early publication, The Face in Profile, 1947, made him known all over the world. • Bjork practiced as a clinician in Sweden for 14 years before moving to Denmark in 1951, where he chaired the Dept of Orthodontics,Royal Dental College, Copenhagen.

• There, Bjork combined the methods of metallic implantation and serial cephalometric roentgenography to unravel the secrets of facial growth. • His sample consisted of children attending the Department of Orthodontics, who were willing to take part in the study. • Around 100 persons of each sex were included in this study, having different types of malocclusions, and ranging from 4-25 years of age.

• The implant method was used and annual radiographs were obtained from childhood to adulthood. • The systematic superimposition of these serial radiographs with the help of implants form the basis of Bjork’s studies. • The results of these studies have been published in the major American and European journals since the 1950s and have become classics on the subject of facial growth.

Method and application of the use of metallic implants. • Small pins of hard tantalum are hammered into bone under local analgesia with a special pencilshaped instrument in which the implant is placed.

• The tantalum pins are more radiopaque than chrome cobalt alloy and retain their position in bone well. • These measure 1.5mm in length and 0.5mm in diameter. • A smaller pin has also been designed, measuring 1.2 x 0.37 mm. • The instrument is made of stainless steel and has a hard, replaceable tip, into which the pin fits.


The instrument is pressed through the periosteum to secure a firm basis before the pin is hammered in.

Sites for Implant placement The mandible: Before the pins are inserted, the form of the mandible and position of the dental germs are studied on the profile radiographs. Usually, 5 or 6 pins are inserted in 4 regions.

• Region 1: One pin is placed on the anterior aspect of the symphysis, as low down as possible in the midline beneath the germs or root tips. This pin has proved to be highly stable, but may be exposed by resorption, if placed too high in the supramental region. • Region2: Two pins are inserted on the right side of the basal part of the mandible, under the 1st premolar and 2nd premolar (or 1st molar), beneath their germs or root apices. • Region 3: One pin is placed on the external aspect of the right ramus, on a level with occlusal surfaces of the molars. This may be gradually exposed by resorption and a new one needed. • Region 4: One or two pins are also inserted in the mandibular base on the left side, under the 2nd premolar or 1st molar.( By using small pins on the right side and larger ones on the left, they can be recognized easily.)

The Maxilla • There are 4 regions in which implants are unlikely to be disturbed. • It is usual to use six implants, preferably small ones on the right side. • Region 1: Before eruption of permanent incisors, pins are inserted, one on each side of the hard palate, behind the deciduous canines, near the median plane of the face.(Their stability depends on the extent to which the nasal floor is lowered by resorption process.)

• Region 2: After eruption of the permanent central incisors, an implant is placed on each side of the median suture, below the anterior nasal spine • Useful for analyzing sutural growth of upper face in sagittal plane as well as transverse growth of maxilla. Region 3: Even at an early age, 2 implants can be placed in the zygomatic processes of the maxilla on each side of the head.

• In order not to be disturbed by erupting teeth, these must be placed lateral to the alveolar process. • Occasionally when there is a thin bone wall and maxillary sinus increases greatly during growth, one implant may be lost through the nose.)

•These implants are particularly useful for measuring growth in the width of the in the median suture.

• Region 4: Implants have also been placed with good results at the border of the hard palate and the alveolar process, medially to the 1st molar. • It is standard technique to insert pins in both jaws as described.

Radiographic Method: • Reproducibility of head positioning in the cephalostat is very necessary in implant studies. • Any discrepancies in this procedure from year to year will result in differences in projection, causing large and unacceptable errors. • Bjork used a specially designed X-ray cephalostat with a built-in 5” image intensifier which would enable the position of the head to be monitored by television.

•The setting of the head in the cephalostat is carried out by traditional 3 point contact, (two ear rods and a nose rest), and in addition, a vertical and horizontal beam of light, delineating the median plane and the level of the ear rods. •Setting by means of ear rods is not rigid. Fine adjustment is monitored by television.

Evaluation of facial growth using serial radiographs: • In order to avoid the errors associated with the tracing procedure, a printer called the Log-Etronic printer combined with an enlarger is used.

• By copying superimposed films by the Log-Etronic technique, a picture of the growth of the face or of a single jaw is obtained in a lateral view. • These pictures are obtained by superimposing the positive films of the radiographs to be compared and making a negative Log-Etronic film of the superimposed films.

Method of Superimposition: • Evaluation of facial growth is based on superimposition of film from various stages of development, on the anterior cranial base. • The films are superimposed so as to obtain the closest coincidence for the maximum number of structures in the anterior cranial fossa.: cribriform plate, medial border of orbital roof, trabecular system, anterior walls of median fossae,and anterior contours of pterygopalatine fossae. These are used to obtain a negative composite Log-Etronic film. • This orientation shows remodeling of the sella from late juvenile to adult age, as well as forward movement of nasion. • This is called the structural method of superimposition


• In execution of the growth tracing, positive LogEtronic film is made and traced for each of the radiographs in the series, and the positives are superimposed as described. • The Nasion –Sella line can be used in growth analysis only after adjustments have been made for forward displacement of Nasion and remodeling of Sella. • The practical method consists in placing a sheet of cellophane, with printed cross-lines on the top of the first film of a series, passing through the nasion with the center of the cross-lines at the Sella point

. • The tracings are superimposed according to the negative composite Log Etronic film, from which the position of the implants is transferred to the tracings. • Only the principal implants are marked, using a point. • The orientated cross-lines from the first film are also transferred to these tracings.

Evaluation of jaw growth • The original radiographs are placed and projected on a tracing table, and with the help of an enlarger , the tracing of the mandible is enlarged by a factor of three. • These negative Log Etronic copies are superimposed and oriented by means of implants in the mandible, and are copied together in the Log Etronic printer to give a composite negative film. • With the help of the composite film, the tracings are oriented correctly in relation to one another. • Similarly, one may obtain a radiographic growth tracing of the maxilla, oriented with respect to the implants in this jaw. • On the basis of these tracings, the paths of eruption of the teeth in each jaw may be analyzed in relation to the implants, by means of eruption diagrams.

Superimpositions of mandibular tracings made at 5yrs 8 mos and 10y 8 mo Superimposition of maxillary tracings at ages 7y 5 mo and 18y 5mo.

Evaluation of dental arch development • The eruptive movements of the teeth in the occlusal view are studied in the two jaws by means of tracings of the respective dental casts. • The dental casts from the different stages of development are inserted in the enlarger and drawn in three fold magnification. • The enlarged tracing of the cast is transferred to the enlarged radiographic growth tracing and oriented with respect to the corresponding teeth. • A composite tracing will show the movements of the teeth in relation to the implants. Study of mandibular dental arch development

Arch development of the maxilla

3 dimensional growth of the maxilla as revealed by the implant method. • In an article published in BJO 1977, by Arne Bjork and V. Skieller, they described the growth of the maxilla studied by the implant method with the help of lateral and PA cephalograms, in nine 4 year old boys with normal primary occlusion who were followed annually up to the age of 21 years. • The implant method used was as described earlier. • The pins inserted in the zygomatic process of the maxilla at 4 years of age were referred to as the lateral implants. • The increase in distance between these measured on a PA cephalogram indicated the increase in width of median suture at level of 1st molars.

• The implants placed in the anterior aspect of the maxilla after full eruption of permanent incisors (10-11yrs) were referred to as anterior implants. • The increase in distance between these implants measured on the frontal film indicates the growth in width of the median suture anteriorly, at level of incisors. • A line drawn from one of the anterior implants to the midpoint between the lateral implants on one side, on a lateral cephalogram, was referred to as the implant line.

• A change in inclination of implant line at different ages in relation to Nasion-Sella line indicates vertical rotation of the maxilla in relation to the cranial base. • Also, superimposition of various radiographs on implant line is used to analyse remodeling of maxilla.

Growth of Maxilla analysed by means of Lateral Implants from age of 4 years. Maxillary height: • Earlier implant studies by Bjork have shown that increase in maxillary height takes place by sutural growth at its frontal and zygomatic processes, and by apposition on the lower aspect of alveolar process, in relation to eruption of teeth. • There is also apposition at the floor of the orbits, with resorptive remodeling of the lower surface. • Simultaneously, the nasal floor is lowered by resorption and apposition takes place at the hard palate. • In their study in 1977, Bjork and Skieller clarified the mean magnitudes of these growth changes from 4 years of age to adulthood.

• Using the lateral implants as fixed reference points , vertical growth of the maxilla was calculated at right angles to the Nasion-Sella line. • Sutural lowering of the maxilla was found on average to be 11.2 mm (range 9-13.5mm). • Orbits do not increase in height from childhood to adolescence to the same extent as the nasal cavity, and apposition at the floor of the orbit is on average, 6.4 mm ( range 5-8 mm) • The height of the nasal cavity increased up through puberty as result of resorptive lowering of nasal floor of the order of 4.6 mm ( range 1.5-7.5 mm). This was about one-third of the increase in sutural height of nasal cavity . • Appositional growth in the height of the alveolar process was about 14.6 mm, which was one third greater than the increase in alveolar process height as a result of resorption of nasal floor. Mean growth changes from 4 yrs to adulthood.

Maxillary width: • There was considerable controversy regarding the role of the median palatal suture in maxillary growth, which was resolved by the histological studies of Melsen and the implant studies of Bjork. • Bjork showed that growth in the suture continues until puberty. • By measuring the distance of separation between the lateral implants on the frontal cephalogram over time, it was shown that sutural growth was the most important factor in the development of the width of the maxilla. • The mean transverse growth in the median suture, measured between the lateral implants, from childhood to adulthood was 6.9mm. • The curves for cumulative growth in the width of the median suture from year to year followed the same pattern as the curves for growth in body height.

• The curves also showed that the time of the pubertal growth spurt and sutural growth coincided, but that sutural growth terminated earlier than growth in body height. • The pubertal growth spurt in the median suture however coincided exactly with growth maximum in the facial sutures in the sagittal plane.

Bimolar width: • A question of clinical interest is “ How far is the increase in the width of the dental arch of upper jaw related to growth in the median suture?” • Bjork’s implant studies show that though growth in the median suture from eruption of 1st permanent molars to adulthood is 4.8 mm, increase in arch width during this period was on average, 3.1 mm.

• The reason for this difference in growth in width is related to transverse rotation of the maxillae.

Bicanine width: • The development in width of the dental arches between the canines was different from that of molar region. Though there was an overall increase of 3.1 mm in intercanine width from 4 years to adulthood, most of this increase occurred early, with only 1.1 mm increase from age 6 years to adulthood.

Co-ordinated 3 dimensional growth of maxilla analyzed by means of anterior and lateral implants from age of 10-11 years. • Maxillary length: • Growth in length of the maxilla occurs by sutural growth toward the palatine bone and by apposition at the tuberosities. • Bjork’s implant studies show that the anterior surface of the maxilla is stable sagittally, with the anterior surface of the maxilla retaining its close relation to the anterior implants. • The anterior surface of the maxilla may be described as an area “ under continuous remodeling in connection with resorptive lowering of the nasal floor.”

Transverse mutual rotation of the two maxillae: • Comparison of increase in width between the anterior and the lateral implants showed that increase in width between the lateral implants was on average, 3.5 times greater than that between the anterior implants.(3 mm and 0.9 mm respectively). • This indicates that the two maxillae rotate in relation to one another in the transverse plane, which results in decreased length of the maxilla in the mid sagittal plane.

• Mutual transverse rotation of maxillae also results in greater separation of lateral segments of dental arch posteriorly,than anteriorly. • There is thus, greater increase in intermolar width than intercanine width, and also a corresponding decrease in arch length. • Thus, shortening of arch length is related to transverse growth of the maxilla.

Changes in maxillary arch form between ages of 10 and 21.

Vertical rotation of the maxillary complex • Early studies by Brodie (1941) suggested that maxilla is lowered without rotation in the vertical plane. • The implant studies of Bjork and Skieller (1972) however have shown that downward and forward displacement of the maxilla during growth is associated with varying degrees of forward rotation. • The inclination of the nasal floor to the anterior cranial base is however maintained as a result of compensatory differenciated resorption.

• Forward rotation of the maxilla is associated with greater resorption of the nasal floor anteriorly than posteriorly, and vice versa. • Because of this differential remodeling of the nasal floor, it cannot be used as a reference structure in analysis of the growth of the maxilla. • Forward rotation of the face occurs because of greater facial growth posteriorly than anteriorly, associated with development in height of the cranial base.

The Zygomatic process • Orientation of successive lateral films on the implant line clearly showed that no striking remodeling of the anterior surface of the zygomatic process takes place in the antero posterior direction.

• The posterior surface however is appositional, with the greatest apposition downwards. • The infrazygomatic crest is also appositional, being displaced downward and backward on the maxillary corpus. • Thus, the anterior contour of the zygomatic process is strikingly stable and should be regarded as a natural reference structure in the growth of the maxilla. • These findings are in contrast to those of Enlow and Bang (1965) who stated that the anterior surface was resorptive in nature

The Growth of the Mandible as studied by the implant method • In two classic articles, by Bjork (AJO 1969) and Bjork and Skieller (AJO 1972) respectively, the growth of the mandible as well as the nature of mandibular growth rotations were described. • This was done on the basis of superimposition of follow up radiographs from the original implant sample. • Growth of the mandible was assessed by orienting the serial tracings according to the implant line drawn through two principal implants in mandible.

• The position of articulare point was marked with a cross in the serial tracings. • These points were used to calculate the direction of condylar growth. • The findings showed that in a majority of cases there was a forward (negative) rotation of the mandible, while in only two cases there was a backward (positive) rotation of the jaws. • There was strong correlation for the rotation of the maxilla and the mandible, but mandibular rotation was more than thrice as great, with a mean of - 6° • Thus, forward rotation seems to be a general trend of facial growth.

• Study of growth rotation by conventional cephalometry without the aid of implants is complicated by compensatory remodeling at the lower border. • Using the mandibular line as reference showed a rotation of only –3.4°, masking upto half the growth rotation. Nature of compensatory remodeling: • In forward rotation, there is marked apposition below the symphysis and anterior part of lower mandibular border, and resorption below the angle. • In backward rotation, there is only slight apposition below symphysis and anterior lower border, and marked apposition below the angle.

• Ramus growth: • The inclination of the ramus in relation to the Nasion-Sella line was practically unchanged over the observation period (mean change -1°) • Also there was no significant correlation with mandibular rotation. • This constancy is ascribed to remodeling of the ramus to maintain its functional relation to neck muscles and spinal column. • This compensatory remodeling at posterior border of ramus is on average -5°

Posterior remodeling of the ramus depends on • Condylar growth direction • Degree of appositional growth behind the angle. Gonial angle decreases by apposition at posterior border of the ramus and increases by resorption at lower border of mandible. Resorption at anterior border of ramus is generally small, with development of arch length being more dependent on increase in height against the slope of the ramus.

Condylar growth • The condyles are the center of greatest growth in the craniofacial complex during the pubertal period. • Growth in length of the mandible in man occurs essentially at the condyles. • The growth in the condyle in most cases follows a curved path (forward) through an average angle of -8°(range 22°). • In a small number of cases there may be backward(positive) curvature of mandibular growth. • There is also a strong correlation between condylar curavature and the rotation of the mandible. • There is a correlation also between condylar growth direction and maxillary rotation, but it is weaker.

Prediction of Mandibular Growth Rotation: • Mandible may be regarded as an unconstrained bone, which may change its inclination in several ways. • A critical factor is the site of rotation which may be located at posterior or anterior end or somewhere in between. • Forward rotation as studied by the implant method may occur in one of three ways:

Type I Forward Rotation: • Forward rotation takes place about centers in the joints. • Gives rise to deep bite in which the lower dental arch is pressed into the upper. • Leads to under development of anterior facial height. • Cause: Occlusal imbalance due to loss of teeth , or powerful musculature. • May occur at any age.

Type II Forward Rotation: • Occurs about a center located at the incisal edges of lower anterior teeth. • Cause: Combination of marked development of posterior face height and normal increase in anterior height. • The increase in the posterior face height occurs due to lowering of middle cranial fossa and increase in height of ramus. • Mandible is lowered more than it is carried forward.

Type III Forward Rotation: • Occurs in case of anomalous occlusion of anterior teeth e.g. large overjet. • Center of rotation lies at level of premolars. • Anterior face height becomes under-developed and posterior face height increases. • Dental arches are pressed into one another and basal deep bite develops.

Influence of jaw rotation on inclination of teeth: • Position of lower incisors is functionally related to the upper incisors. • Incisors in their eruption are guided forward with an increase in alveolar prognathism. • Jaw rotation also displaces the path of eruption of all teeth in a mesial direction, tending to create crowding anteriorly. • Forward growth rotation causes the lower posterior teeth to be more upright in relation to the posteriors, with an increase in inter molar and inter premolar angles.

Backward Rotation Type I: • Center of rotation lies in the TMJ’s. • Occurs when the bite is raised by orthodontic means. • Results in increase in anterior face height. • May also be associated with cranial base growth in case of a flat cranial base (where posterior cranial base is raised ) and mandible is also raised. • Leads to over development of anterior facial height and possible anterior open bite.

Backward Rotation Type II Occurs about a center situated at the most distal occluding molars. Occurs in connection with growth in the sagittal direction at condyles, which is curved backwards. The symphysis swings backwards and the chin is drawn back below the face. Lower incisors become retroclined, crowding may develop. Inter premolar angles and inter molar angles are small: the lower molars and premolars are inclined forward more with respect to the uppers.

Both forward and backward rotation may be divided into three components Total rotation : Rotation of the mandibular corpus (implant line or reference line) relative to the anterior cranial base. Matrix rotation: Rotation of the soft-tissue matrix of the mandible (tangential line to lower mandibular border) relative to the anterior cranial base. Intramatrix rotation: Rotation of the mandibular corpus within its soft-tissue matrix (or the difference between reference lines), expressing the amount of remodeling at the lower border of the mandible.

Total rotation, which is the sum of matrix and intramatrix rotation, generally shows a steady increase with age, forward or backward, dependent on the case. Matrix rotation, on the contrary, displays a pendulum movement, forward or backward, in the same person during development. Intramatrix rotation, like the total rotation, increases steadily during growth, but with fluctuations counteracting the pendulum movements of the matrix.

Bjork’s structural signs of growth rotation Seven structural signs of mandibular rotation were given by Bjork: 1. 2. 3. 4. 5. 6. 7.

Inclination of condylar head. Curvature of mandibular canal Shape of lower border of mandible Inclination of symphysis Inter incisal angle Inter premolar or inter molar angles. Anterior lower face height.

Clinical relevance of growth rotation: • More extreme the growth rotation of mandible, greater the clinical problems it presents. • Extreme rotation, whether forward or backwards, influences strongly the paths of eruption of the teeth. • Serious risk of extreme migrations following extractions, which calls for secure anchorage. • Crowding in the mandible results from both directions of growth rotation. • In pronounced forward rotation there is risk of development of deep bite, while backward rotators are at greater risk of developing anterior open bite.

Intra Matrix rotation of the frontal bone • Bjork, Sarnas and Rune (EJO 1995) studied the growth and dvelopment of the frontal bone using metallic implants in 5 patients at the Center for Craniofacial Anomalies, Sweden. • They were able to detect rotations of the corpus inside the periosteal matrix from 1 to 9.5 degrees in the mid sagittal plane. • However the applicability of this study to patients without congenital anomalies could not be elucidated.

Long term effects of RME studied with metallic implants. • A study by Sarnas, Bjork and Rune (EJO 1992) was carried out using metallic implants inserted in the maxillary bone of a girl who underwent RME for a narrow maxillary arch. • A ten year follow up revealed extensive relapse in maxillary rotations as well as translations, and a limited effect in the long term. • The cause for relapse was ascribed to resistance from circum maxillary sutures as well as soft tissues, and also inadequate healing of bone. • This led them to seriously question the rationale for RME traement.

Conclusion • The longitudinal implant studies of Arne Bjork, with their ingenious method, painstaking attention to detail, and meticulous follow up, have created a body of literature that has revolutionized the way orthodontists understand and visualize facial growth. • The findings of the implant studies have helped to solve age old mysteries concerning the pattern of facial growth and rotations of the jaw bones, which have important clinical implications.

References: • Björk A: The use of metallic implants in the study of facial growth in children: method and application. Am J Phys Anthropol 1968. 29: 243254. • Bjork A, Skieller V. Growth of the Maxilla in three Dimensions as revealed radiographically by the implant method. BJO 1977: 53-64. • Björk A: Prediction of mandibular growth rotation. Am J Orthod 1969; 55: 585-599. • Bjork A, Skiller V. Facial development and tooth eruption: An implant study at the age of puberty.Am J Orthod 1972; 62(4): 339-383.

• Skieller V, Bjork A. Prediction of mandibular growth rotationevaluated from a longitudinal implant sample.AJO 1984. 86; 5:359-370. • Bjork A, Sarnas K, Rune B. Intramatrix rotationthe frontal bone. EJO 1995;17:3-7. • Long term effect of rapid maxillary expansion studied in one patient with the help of metallic implants and roentgen stereometry. EJO 1992;14: 427-432. Leader in continuing dental education

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