1: Craniofacial Growth and Development

CHAPTER 1

Craniofacial Growth and Development

Peter H. Buschang

Clinicians require a basic understanding of growth and development in order to properly plan treatments and evaluate treatment outcomes. As determined by the World Health Organization, growth and development provides one of the best measures available of individuals’ health and well-being. Knowledgeable clinicians understand that general somatic growth provides important information about their patients’ overall size, maturity status, and growth patterns. Because the timing of maturity events, such as the initiation of adolescent or attainment of peak growth velocity, is coordinated throughout the body, information derived from stature or weight can be applied to the craniofacial complex. In other words, the timing of peak height velocity (PHV)—a noninvasive and relatively easily obtained measure—can be used to determine the timing of peak mandibular growth velocity. Knowledge of general somatic growth is also useful when evaluating the sizes of patients’ craniofacial dimensions. An individual’s height and weight percentiles provide a measure of overall body size, against which craniofacial measures can be compared. For example, excessively small individuals (i.e., below the 5th percentiles in body size) might also be expected to exhibit a small craniofacial complex. Finally, the reference data available for somatic growth and maturation are based on large representative samples, making them more generally applicable and more precise at the extreme percentiles than available craniofacial reference data.

Postnatal craniofacial growth is a complex, but coordinated, ongoing process. The cranial structures are the most mature and exhibit the smallest relative growth rates, followed by the cranial base, and then the maxillary and mandibular structures, which are the least mature and exhibit the greatest growth potential. Knowledge about a structure’s relative growth is important because it serves, along with heritability, as an indicator of its response potential to treatment and other environmental influences. It is essential that clinicians understand that the maxilla and mandible, the two most important skeletal determinants of malocclusion, follow similar growth patterns. Both are displaced anteriorly and, especially, inferiorly; both tend to rotate forward or anteriorly; both rotate transversely; and both respond to displacement and rotation by characteristic patterns of growth and cortical drift. It is also useful to understand that patients should be expected to adapt skeletally to orthodontic, orthopedic, and surgical interventions and that the adaptations mimic growth patterns exhibited by untreated patients. Perhaps most importantly, clinicians must understand the tremendous therapeutic potential that the eruption and drift of teeth provide. The maxillary molars and incisors, for example, undergo more eruption than inferior displacement of the maxilla, making them ideally suited for controlling vertical and AP growth.

Clinicians also often do not appreciate that adults show many of the same growth patterns exhibited by children and adolescents, simply in less exaggerated forms. It has been well established that craniofacial growth continues though the 20s and 30s, and perhaps beyond. Skeletal growth of adults appears to be predominately vertical in nature, with forward mandible rotation in males and backward rotation in females. The teeth continue to erupt and compensate depending on the individual’s growth patterns. Adults also exhibit important soft tissue changes; the nose grows disproportionately and the lips flatten. Vertical relationships between the incisors and lips should also be expected to change with increasing age.

Finally, malocclusion must be considered as a multifactorial developmental process. Although genes have been linked with the development of Class III and perhaps Class II division 2 malocclusions, the most prevalent forms of malocclusions are largely environmentally determined. Equilibrium theory and the notion of dentoalveolar compensations provide the conceptual basis for understanding how closely linked tooth positions are with the surrounding soft tissues. They also make it possible to predict the type of compensations that should be expected. For example, they explain why the development of malocclusion is associated with various habits, assuming the habits occur regularly and are of long enough duration. In fact, anything that alters mandibular posture might be expected to elicit skeletal and dentoalveolar compensations. This explains why individuals with chronic airway obstructions develop skeletal and dental malocclusions that are phenotypically similar to malocclusions associated with weak craniofacial musculature; both populations of patients posture their mandibles similarly and undergo similar dentoalveolar and skeletal compensations. Based on the foregoing, the following questions are intended to provide a basic—although only partial—understanding of growth and development and its application to clinical practice.

1 At what ages do most children enter adolescence, and when do they attain PHV?

The adolescence growth spurt starts when decelerating childhood growth rates change to accelerating rates. During the first part of the growth spurt, statural growth velocities increase steadily until peak height velocity (PHV) is attained. Longitudinal assessments provide the best indicators of when adolescence is initiated and PHV is attained. Longitudinal studies pertaining to North American and European children< ?xml:namespace prefix = "mbp" />1 show that girls are advanced by approximately 2 years compared with boys in the age of initiation of adolescence and age of PHV. Based on the 26 independent samples of girls and 23 samples of boys, the average ages of PHV are 11.9 and 14.0 years, respectively. Girls and boys initiate adolescence at 9.4 years and 11.2 years, respectively. Maximum adolescent growth velocity in body weight usually occurs 0.3 to 0.5 year after PHV (Fig. 1-1).

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FIG 1-1 Frequency distribution of 26 sample ages of PHV for boys (A) and girls (B).

(From Malina RM, Bouchard C, Beunen G. Ann Rev Anthropol 1988;17:187-219.)

2 What is the mid-growth spurt, and how does it apply to craniofacial growth?

The mid-growth spurt refers to the increase in growth velocity that occurs in some, but not all, children several years before the initiation of the adolescent growth spurt. Mid-growth spurts in stature and weight have been reported to occur between 6.5 and 8.5 years of age; they tend to occur more frequently in boys than girls.2,3 Based on yearly velocities, mid-growth spurts have been demonstrated for a variety of craniofacial dimensions—also between 6.5 and 8.5 years of age—occurring simultaneously or slightly earlier for girls than boys.47 Applying mathematic models to large longitudinal samples, Buschang and colleagues8 reported mid-growth spurts in mandibular growth for subjects with Class I and Class II molar relationships at approximately 7.7 years and 8.7 years of age for girls and boys, respectively.

3 Which skeletal indicators are most closely associated with PHV?

According to Grave and Brown,9 PHV in males and females occurs slightly after the appearance of the ulnar sesamoid and the hooking of the hamate, and slightly before capping of the third middle phalanx, the capping of the first proximal phalanx, and the capping of the radius. According to Fishman’s10 skeletal maturity indicators, capping of the distal phalanx of the 3rd finger occurs less than 1 year before PHV, capping of the middle phalanx of the 3rd finger occurs just after PHV, and capping of the middle phalanx of the 5th finger occurs less than one half year after PHV. Based on the cervical vertebrae, PHV occurs between the development of the concavity on the inferior borders of the 2nd and 3rd vertebrae (CVMS II) and development of a concavity on the inferior borders of the 2nd, 3rd, and 4th vertebrae (CVMS III).11

4 What is the equilibrium theory of tooth position?

Although Brodie12 was among the first to identify the relationship between muscles and tooth position, it was Weinstein and colleagues13 who experimentally established that the teeth are maintained in a state of equilibrium between the soft tissue forces. Based on a series of experiments, they concluded that:

1. The forces (produced naturally or by orthodontic appliances) exerted on the crowns of teeth are sufficient to cause tooth movements
2. Each tooth may have more than one stable state of equilibrium
3. Even small forces (3–7 gm), if applied over a long enough period, can cause tooth movements

Proffit,14 who revisited the equilibrium theory 15 years later, noted that the primary factors involved were:

1. The resting pressures of the lips, cheeks, and tongue
2. The eruptive forces produced by metabolic activity within the periodontal membrane

He further noted that extrinsic pressures, such as habits and orthodontic forces, can alter equilibrium, provided that they are sustained for at least 6 hours each day. Proffit14 also identified head posture and growth displacements/rotations as secondary factors determining equilibrium. As the mandible rotates, the incisors move as dental equilibrium is reestablished. Björk and Skieller,15 for example, have shown an association between changes in lower incisor angulation and true mandibular rotation.

5 What is the prevalence of Class II dental malocclusion among adolescents and young adults living in the United States?

The best direct epidemiologic evidence comes from the National Health Survey,16,17 which evaluated approximately 7400 children between 6 and 11 years of age and over 22,000 youths 12 to 17 years of age. Unilateral and bilateral distoclusion occurs approximately 16.1% and 22.7% of the time among Caucasian children and 7.6% and 6.0% of the time among African-American children, respectively. Comparable incidences among Caucasian youths were 17.8% and 15.8% and 12.0% and 6.0% among African-American youths. Based on overjet provided by the NHANES III, Proffit and associates18 estimated that the prevalence of Class II malocclusion (overjet ≥ 5 mm) decreases from over 15.6% between 12 and 17 years of age to 13.4% for adults. They also showed that Class II malocclusion is more prevalent among African-Americans (16.5%) than Caucasians (14.2%) and Hispanics (9.1%).

6 What is the prevalence of incisor crowding among individuals living in the United States, and how does it change with age?

According to the initial NHANES III data,19 incisor irregularities increase from an average of 1.6 mm for children 8 to 11 years, to 2.5 mm for youths 12 to 17 years, to 2.8 mm for adults 18 to 50 years of age. Although incidences are similar at the youngest age, African-American youths and adults show significantly less crowding than Caucasians and Hispanics. Based on the complete NHANES data set, including 9044 individuals between 15 and 50 years of age, approximately 39.5% of U.S. adults have mandibular incisor irregularities ≥ 4 mm and 16.8% have irregularities ≥ 7.20 Adult males tend to show greater crowding than females; Hispanics show greater crowding than Caucasians, who in turn display greater crowding than African-Americans. Based on the available data for untreated subjects followed longitudinally, rates of crowding increase precipitously between 15 and 50 years of age, especially during the late teens and early 20s (Fig. 1-2).20

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FIG 1-2 Average mandibular alignment scores, U.S. persons, 1988-1991.

(Adapted from Brunelle JA, Bhat M, Lipton JA. J Dental Res 1996;75[special issue]:706-713.)

7 Do the third molars play a role in determining crowding?

Although third molars have been related with crowding,2124 most contemporary studies show little or no relationship. A NIH conference in 1979 came to the consensus that there is little or no justification for extracting third molars solely to minimize present or future crowding of the lower anterior teeth.25 Ades and co-workers26 found no difference in subjects whose third molars were impacted, erupted in function, congenitally absent, or extracted at least 10 years before post-retention records were taken. Sampson and colleagues27 also showed no difference in crowding between subjects whose third molars have erupted completely or partially, remained impacted, or were missing. A randomized controlled trial based on 77 patients followed for 66 months showed a 1.0 mm difference in anterior crowding between patients whose third molars had and had not been removed; the authors concluded that removal of third molars to reduce or prevent late crowding cannot be justified.28 Based on the NHANES data, individuals who had erupted third molars displayed significantly less crowding than those who did not have erupted third molars.20

8 How does horizontal and vertical mandibular growth affect crowding?

Vertical growth makes the maintenance of lower incisor alignment after orthodontic treatment more problematic. Based on the notion that the lower incisors are carried into the lower lip as the mandibula grows anteriorly or rotates downwards, late mandibular growth has been suggested as a major contributor to post-retention crowding.29 Although incisor compensation to backward mandibular rotation has been demonstrated,15 crowding as a result of anterior growth displacements remains to be established. However, changes in lower incisor crowding have been shown to be related to vertical growth. Both treated and untreated patients who undergo greater inferior growth displacements of the mandible and associated greater eruption of the lower incisors show greater crowding than those who undergo less vertical growth and less eruption.30,31 Since vertical mandibular growth continues well beyond the teen years, patients would be well advised to wear their retainers into their early and mid-20s.

9 How much should the mandibular incisors and molars be expected to erupt during adolescence?

Based on natural structure superimpositions of the mandible performed between 10 and 15 years of age, McWhorter32 showed that the mandibular central incisors and first molars erupt approximately 4.3 and 2.5 mm in males and females, respectively. Also using natural structure superimpositions, Watanabe et al.33 demonstrated that the mandibular molars and incisors erupt at rates ranging from 0.4 to 1.2 mm/yr and 0.3 to 0.9 mm/yr, respectively. Rates of eruption were greater in males than females, attaining peak velocities at approximately 12 and 14 years of age for females and males, respectively.

10 How does untreated arch perimeter change between the late primary dentition and the permanent dentition?

Computed based on a centenary curve extending from the mesial of the first molar to mesial of first molar,34 arch perimeter increases during the early mixed dentition and decreases during and after the transition to the permanent dentition. Maxillary perimeter increases 4 to 5 mm between 6 and 11 years of age and decreases 3 to 4 mm between 11 and 16 years. In contrast, mandibular arch perimeter increases approximately 2 to 3 mm initially and then decreases 4 to 7 mm, with greater decreases in females than males (Fig. 1-3).

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FIG 1-3 Maxillary (A) and mandibular (B) arch perimeters between 6 and 16 years of age.

(Adapted from Moyers RE, van der Linden FPGM, Riolo ML, McNamara JA Jr. Standards of human occlusal development. Monograph #5, Craniofacial Growth Series, Center for Human Growth and Development, University of Michigan, Ann Arbor, Michigan, 1976.)

11 How do untreated maxillary and mandibular intermolar widths change during childhood and adolescence?

Bishara and colleagues35 reported that intermolar widths increase 7 to 8 mm between the deciduous dentition (5.0 yrs of age) and the early mixed (8.0 yrs of age) dentitions and an additional 1 to 2 mm between the early mixed and early permanent (12.5 yrs of age) dentitions. Between 6 (first molar fully erupted) and 16 years of age, Moyers and colleagues34 showed greater increases for males than females for both maxillary (4.1 versus 3.7 mm) and mandibular (2.6 versus 1.5 mm) intermolar widths. Based on a sample of 26 subjects followed longitudinally between 12 and 26 years of age, DeKock36 reported no significant change for females and only slight increases (1.4 and 0.9 mm for maxilla and mandible, respectively) in intermolar width for males (Fig 1-4).

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FIG 1-4 Maxillary (A) and mandibular (B) intermolar widths between 6 and 16 years of age.

(Adapted from Moyers RE, van der Linden FPGM, Riolo ML, McNamara JA Jr. Standards of human occlusal development. Monograph #5, Craniofacial Growth Series, Center for Human Growth and Development, University of Michigan, Ann Arbor, Michigan, 1976.)

12 Without treatment, how do maxillary and mandibular arch depths change during childhood and adolescence?

Maxillary and mandibular arch depths, midline distances between a line tangent to the incisors, and a line drawn tangent to the distal crown of the deciduous second molars or their permanent successors show different patterns of growth changes. Maxillary arch depth increases 1.4 and 0.9 mm in males and females, respectively, during the eruption of the permanent incisors.37 Mandibular arch depth shows little change over the same period. With the loss of the deciduous molars, maxillary arch depth decreases 1.5 and 1.9 mm, while mandibular arch depth decreases 1.8 and 1.7 mm in males and females, respectively.37 DeKock36 reported decreases (approximately 3.0 mm) in arch depth between 12 and 26 years of age, />

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Jan 1, 2015 | Posted by in Orthodontics | Comments Off on 1: Craniofacial Growth and Development
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