Cranial bone remodeling in adults
Unlike the rapid expansion during childhood driven by brain growth, adult cranial changes are the result of a lifelong process called bone remodeling. This dynamic process, which occurs across the entire skeleton, involves the resorption of old bone tissue by osteoclasts and the formation of new bone by osteoblasts. While the skull's main vault is relatively stable after the cranial sutures fuse around age 20-25, the facial skeleton experiences more pronounced shifts.
The changing facial skeleton
The most noticeable age-related changes occur in the facial bones, contributing to the hallmarks of an aging appearance. This includes:
- Expansion of the eye sockets (orbits).
- Bone loss in the upper jaw (maxilla), causing it to move downward and backward.
- Remodeling of the lower jaw (mandible), affecting its angles and projection. Bone loss here can reduce jawline definition.
- Widening of the opening for the nasal passages (piriform aperture), contributing to the nose's lengthening and drooping appearance.
Cranial vault changes
While less dramatic, the skull's vault also changes with age. The outer skull can expand in areas, while the forehead may flatten. The inner layer of the frontal skull bone can thicken, especially in older women.
Perceived vs. actual changes
It's important to distinguish between actual bone changes and perceived shifts in head shape, which can be influenced by factors unrelated to skeletal remodeling.
The role of soft tissue
Soft tissue changes play a significant role in how the head appears to change shape. This involves:
- Fat distribution: Facial fat compartments shift and atrophy with age, contributing to a sunken or sagging look.
- Skin and muscle laxity: Loss of collagen and elastin, along with muscle movements, leads to wrinkles and changes in facial contour.
- Cartilage growth: Cartilage in the ears and nose continues to grow, making them appear larger and longer in older age.
Other contributing factors
Other factors can influence the perceived head shape:
- Hair loss or thinning.
- Significant weight fluctuations.
- Hormonal shifts affecting facial structure, fluid retention, and fat distribution.
Comparison of Skull vs. Soft Tissue Changes with Age
Feature | Bony Skull Changes | Soft Tissue Changes |
---|---|---|
Mechanism | Continuous bone resorption (osteoclasts) and deposition (osteoblasts). | Shifting/atrophy of fat pads, loss of collagen/elastin. |
Effect on orbits | Increases in size, particularly inferolateral and superomedial margins. | Causes eyes to appear more deep-set or hollow. |
Effect on midface | Maxilla retracts, losing vertical projection. | Fat pads descend, skin sags, leading to deeper nasolabial folds. |
Effect on mandible | Angle widens, leading to loss of jawline definition. | Skin sags over the jawline, creating jowls. |
Effect on nose | Piriform aperture widens and retracts. | Cartilage weakens and stretches, causing the nose to appear longer and droop. |
Effect on forehead | Outer portion may recede slightly, inner table may thicken. | Muscle and skin laxity can lead to forehead creases. |
Medical conditions affecting skull shape
Certain medical conditions can cause more significant or rapid changes in skull shape than normal aging:
- Acromegaly: Excess growth hormone can thicken skull bones, especially the jaw and brow ridge.
- Paget's disease: This bone disorder can cause skull bones to enlarge and become misshapen.
- Hyperostosis frontalis interna (HFI): Thickening of the inner frontal bone, common in older women.
The interplay of all these changes
The visible signs of an aging face are a result of the combined effects of bony remodeling, shifting fat pads, and soft tissue laxity. Loss of skeletal support, particularly in the midface and jawline, exacerbates the effects of sagging skin and migrating fat. Understanding this complex interplay is crucial for approaches like cosmetic procedures.
Conclusion
Your head can change shape as you get older due to continuous bone remodeling. While changes are subtle and gradual, they are most noticeable in the facial skeleton and combine with soft tissue changes to create the appearance of aging. While these changes are normal, medical conditions can cause more pronounced alterations. Resources like the National Institutes of Health offer further information.