Humans have a long growth period of active stretching from birth to 20 years of age. During this period, the child’s overall growth includes physical growth, which manifests as a change in the proportions of body parts and mental, psychological, and compositional growth. Various organs grow at different times, differing in quantity and intensity. Hence, it would be unwise to consider a child as a miniature version of an adult. Changes in the physical proportions of a child are perhaps the most dramatic events during active skeletal growth periods.

At birth, a child’s head is relatively large compared with the rest of the body, occupying approximately 30% of the total body volume. With the continued growth of the skeleton, the head assumes a relatively smaller proportion of the body, occupying only about 10% of the total volume ( Fig. 13.2 ).

Schematic representation of body proportions at different ages.

Initially, the head occupies a relatively large proportion of total body length. As the child grows, the body occupies an increasingly larger proportion of total body volume.

The relative size follows the opposite of the rest of the body. With growth, the volume of the lower limbs increases from 15% at birth to 30% in adults, while that of the trunk increases from 45% to 50%. This phenomenon is called the cephalocaudal gradient of growth, which implies differential growth of various body parts in such a way that parts farthest away from the head grow at a faster rate than parts closer.

The large size of a child’s head also makes the child’s upper half of the body heavy with a higher centre of resistance. This, coupled with a lack of proprioceptive development and balance, may contribute to children falling on their heads more often than adults. The head circumference reaches closer to adult size by 6 years of age. The skeleton starts to mature from the head downwards, with the skull showing maturity before the trunk, which is ahead of the limbs. However, proportion-wise, the limbs usually grow faster than the trunk, which, in turn, grows faster than the head.

The body shows changes not only in physical proportions but also in composition. Proportion-wise, the muscle mass, adipose tissue and skeleton all show an increase, while the percentage of the neuronal mass decreases ( Table 13.1 ). This reduction is not due to regression of the nervous system but seems so because of a relative increase in the mass of the remaining systems. Additionally, elemental changes also occur, leading to a 17% reduction in total body water, a 40% increase in fat and protein and a 250% increase in minerals.

The pre-pubertal spurt is also called the mid-childhood growth spurt. It is a small and inconsistent spurt seen in both sexes at around 6–7 years of age. The mid-childhood growth spurt is associated with adrenarche, an endocrine event related to the release of androgenic hormones. The secretion of adrenal androgens causes a transient spurt in height, accelerated bone maturation, redistribution of body fat and appearance of pubic and axillary hair. Interestingly, this phenomenon is unique to humans and a few animals like the chimpanzee.

The pubertal spurt is the more predictable growth spurt and occurs earlier in females than males. It is linked to increased secretion of sex steroids (oestrogen in females and aromatisation of testosterone to oestrogen in males ) in conjunction with growth hormone secretion.

Just before the adolescent growth spurt, height gain enters a quieter period followed by sudden and rapid increases in height, which makes its onset. This phase of the growth spurt can be divided into two stages :

• Stage I is the period of accelerated skeletal growth, which corresponds to the upswing phase, as seen on a growth curve. It is associated with the rapid increase in standing height in both sexes, most of which is contributed by the increase in the length of the trunk. This stage starts around 10½–11 years in females and around 13 years in males, the difference being 2 years on average. ^{, ,} It lasts 2–3 years in both sexes (11–13 years in females and 13–15 years in males). There is an average gain of about 15 cm in females and about 16.5 cm in males. Peak height velocity (PHV) during this stage may reach 9.8 cm/year for males (at around 14 years of age) and in females around 8.1 cm/year (at 12–13 years of age).

• Stage II corresponds to the phase when growth decelerates. It lasts about 3 years (13–16 years in females and 15–18 years in males). During this phase, both sexes gain about 6 cm in height, most of which is contributed by the growth of the lower limbs. Following the conclusion of the growth spurt, rapid reduction in height velocity occurs, and females attain 98% of their final height by about 16 years, while males reach the same by around 18 years. In females, menarche occurs 1 year after PHV. ^, Little skeletal growth occurs after the onset of menarche.

Although the growth rate is rapid during the spurt, it is not consistent during the whole period. Growth velocity is very high to begin with and reaches a maximum at PHV, followed by a slow yet steady decrease in the rate of height gain until adulthood.

As with other growth characteristics, significant differences in growth spurts are seen among individuals and between various ethnic groups and populations for timings, duration (length), age of onset of menarche, total amount of height gain and other variables.

One of the hallmarks of growth is the extreme variability in the timing, amount and direction of growth. Growth not only varies between seasons or months but also on a day-to-day basis. Every day, periods of exaggerated growth may be interspersed with times of little or no activity. These are called mini-growth spurts.

Growth cycles have been found on a weekly and daily basis corresponding to rhythmic changes in the levels of circulating hormones. A person may be slightly taller when they get up in the morning and, by evening, be shorter by up to 1–2 cm due to the effect of gravity compressing the inter-vertebral discs. On a weekly basis, a small but rapid burst of growth may be seen interspersed with times of very little activity ( Fig. 13.4 ). This has given credence to the dual effector hypothesis.

Mini growth spurts.

Growth velocity data for lower-leg length (knee height) of an 8–9-year-old boy, measured once weekly. Mini growth spurts occur from week to week; a longer-term cycle of increase and decrease in the size of spurts is also apparent.

Source: Reproduced from Ulijaszek SJ, Johnston FE, Preece MA. The Cambridge encyclopedia of human growth and development. Cambridge: Cambridge University Press; 1998; Data from Hermanussen M, et al., Periodical changes of short term growth velocity (mini growth spurts) in human growth. Ann Hum Biol. 1998;15(2):103–9.

The dual effector hypothesis states that the growth of any organ occurs in two stages:

• I.

  Differentiation stage : A stage during which specific types of cells differentiate themselves from stem cells. This is a stage of relative quiescence.

• II.

  Expansion stage : A stage of rapid proliferation of differentiated cells, which causes physically measurable saltatory growth.

Essentially, the skull-to-face proportions at birth manifest as a large head and a smaller face. As the child grows, the postnatal period witnesses larger growth of the face, which then stands out from the cranium ( Fig. 13.6 ). The head of a newborn is about 55%–60% of adult head breadth, 40%–50% of adult height and 30%–35% of adult depth. The cranium-to-face ratio in a newborn is 8:1. With continued development, especially of the lower face, the ratio changes to 1:2 in adulthood.

Changes in skull growth and face-braincase proportions from infancy to adult. Column 1 shows growth of human skull and in a sequential change at early infancy, late infancy, child, puberty and adult. Column 2 shows a comparison of face–braincase proportions in the child and adult.

Source: White TD, Folkens PA. Skull. In: The human bone manual. Academic Press; 2005:75–126. https://doi.org/10.1016/B978-0-12-088467-4.50010-7

Cranial vault

At birth, the sutures of the cranial bones do not inter-digitate; they are separated from each other by areas of interposed connective tissue. These areas are called fontanelles ( Fig. 13.7 i). There are six fontanelles at the time of birth: two unpaired and two paired. The unpaired fontanelles include the anterior and the posterior fontanelles. The anterior fontanelle is large and diamond in shape, while the posterior fontanelle is smaller and triangular in shape. The paired fontanelles include the sphenoidal and mastoid fontanelles, both of which lie on the lateral sides of the skull. All the fontanelles are occluded with fibrous connective tissue except the mastoid fontanelle, which is occluded by cartilage (also known as synchondrosis).

Fontanelles in a newborn and their closure patterns with age.

(i) Fontanelles in a young skull. At birth, the sutures are wide and the skull is relatively softer than that of an adult.

Fontanelles allow deformation of the head and thus help the large head of the foetus pass through the birth canal. They also help in accommodating the rapidly enlarging brain in early childhood. They close at different times after birth ( Table 13.3 ). The first to close is the posterior fontanelle at 3 months, and the last is the anterior at 18–24 months ( Fig. 13.7 ii). With the fusion of the fontanelles, the remaining growth and remodelling of the cranial vault occur mainly at the sutures and, hence, the neural growth curve. An increase in the size of the brain creates tension at the sutures, which leads to new bone deposition in the area. Remodelling of the outer and inner surfaces of cranial bones also occurs to allow contour changes with growth.

TABLE 13.3

Cranial fontanelles and their characteristics

Fontanelle	Type	Adjacent bone anlagen	Time of fusion (after birth)
Anterior	Unpaired	Both the frontal and the parietal	Median age of anterior fontanelle closure is 14 to 16 months, with 90% to 96% closing by 24 months of life
Posterior	Unpaired	Both the parietal and the occipital	Third month
Sphenoidal	Paired	Frontal, parietal and sphenoid	Sixth month
Mastoid	Paired	Sphenoid, temporal and occipital	Eighteenth month

Shows order of closure of fontanelles from beginning at 3 months to 18 months. The closure occurs from posterior to anterior with posterior fontanelle at 3 months to form lambda, sphenoidal at 6 months to form pterion, mastoid at 12–18 months to form asterion and anterior fontanelle at 18–24 months to form bregma.

The cranial cavity achieves 87% of its adult size by the age of 2 years, 90% by 5 years and 98% by 15 years of age. Between 15 years and adulthood, additional growth changes occur secondary to pneumatisation of the frontal sinuses and thickening of the anterior part of the frontal bone. The cranial vault and base also grow by surface remodelling. Inside the cranium, elevated bony partitions and depressions partially segment the cranial fossa. The elevated partitions are depository, and the depression portions are resorptive. Remodelling of the cranial fossa causes resorption on the inside and deposition on the outside surface, leading to a cortical drift of the fossa.

Cranial base

The cranial base is the most stable structure among the facial structures, and its growth is affected least by functional matrices. Cranial base synchondroses are important growth centres of the craniofacial skeleton and the last sites in the cranium to terminate growth. ^, The growth of the cranial base is multi-dimensional and, therefore, can alter the structure, line angles and placement/cause displacement of various facial parts attached ( Fig. 13.8 A).

The cranial base expands in a three-dimensional format due to angulation of the sutures and synchondrosis at the cranial base.

Growth of the cranial base occurs at the synchondroses and by surface remodelling. A synchondrosis is similar to a two-sided epiphyseal plate with proliferating cartilage cells in the centre, where mature cartilage cells and ossification occur in both directions away from the centre. Early in embryonic life, centres of ossification develop within cranial base cartilage. The remaining primary cartilages between the centres of ossification form synchondroses after birth.

There are five major synchondroses in the cranial base: intra-ethmoidal, intra-sphenoidal, intra-occipital, spheno-occipital and spheno-ethmoidal ( Fig. 13.8 B):

• •

  The intra-ethmoidal and intra-sphenoidal synchondroses close before birth.

• •

  The intra-occipital synchondrosis closes before 5 years.

• •

  The spheno-ethmoidal synchondrosis closes around 6 years of age.

• •

  The spheno-occipital synchondrosis closes by 13–15 years of age.

Synchondrosis at the base of skull.

Major growth of the anterior cranial base is complete by 5 years of age with the fusion of the spheno-ethmoidal synchondrosis.

The spheno-occipital synchondrosis contributes most to the growth of the posterior cranial base as it is the last cranial base suture to ossify. Growth at the spheno-occipital synchondrosis causes elongation of the middle portion of the cranial base as a result of primary displacement, while growth at the posterior part leads to flexion in the cranial base ^, since the posterior part of spheno-occipital synchondrosis has a greater amount of bone formation in its inferior part than its superior part.

The nasomaxillary complex consists of the bones and cartilages of the nose and maxilla. Growth of the nasomaxillary complex occurs by primary growth, secondary displacement and surface remodelling ( Fig. 13.9 ). Condylar cartilage is secondary cartilage covered with fibrous connective tissue. The principal sites of nasomaxillary growth are now discussed.

Composite growth and direction of displacement of maxilla.

The maxilla displaces downwards and forwards due to sutural growth at its posterior margins, while surface resorptive changes lead to deepening of its facial surface. The secondary displacement of the maxilla occurs due to the growth of the base of the skull.

The maxillary complex is attached to the cranium by zygomaticomaxillary sutures, frontomaxillary sutures, zygomaticotemporal sutures and pterygopalatine sutures. Growth at these sutures leads to anterior and vertical descent of the maxilla. Growth at the median palatine suture enhances the transverse dimensions of the maxilla. Following the cessation of cranial base development at 6–7 years, growth at the sutures and nasal septal cartilage are the primary contributors to further growth of the maxilla.

Nasal septal cartilage plays a significant role in maxillary growth. Growth of the cartilaginous part of the vomer and the perpendicular plate of the ethmoid contribute to the downward and forward growth of the maxilla. This growth also creates space in the area of a maxillary tuberosity for the eruption of the permanent molars. Nasal cartilage has innate growth potential and serves as a primary growth centre, in contrast to the mandibular condyle. Experiments have shown that early loss of septal cartilage is associated with midface deficiency. ^,

Deposition at the posterior end of the maxilla at tuberosity causes an increase in anteroposterior dimensions the arch ( Fig. 13.10 ), while surface resorption at the facial surface gives the maxilla its characteristic contour as a result of its functional needs. Bone deposition on the palatal surface and resorption at the nasal surface of the palatal process lead to downward drift of the palate, which increases the size of the nasal cavity. At the same time, the growth of the alveolar process contributes to enhancing the depth of the palate. Surface remodelling also contributes to an increase in the width of the maxilla and expansion of the nasal airway ( Fig. 13.11 A–C). Deposition on the buccal aspect of the alveolar process, along with growth across the mid-palatine suture, contribute to an increase in maxillary width.

Only gold members can continue reading. Log In or Register to continue

Share this:

• Click to share on Twitter (Opens in new window)
• Click to share on Facebook (Opens in new window)

Related

Related posts:

1. Psychological implications of malocclusion and orthodontic treatment
2. Epidemiology of malocclusion and orthodontic treatment needs
3. Classification and methods of recording malocclusion
4. Downs’ analysis
5. Digital and computerised cephalometrics
6. Clinical and functional evaluation

Stay updated, free dental videos. Join our Telegram channel

Join