Maxilla Anatomy and Its Role in Facial and Craniofacial Development

The maxilla is the central bone of the midface, and its development shapes everything from how your teeth align to how wide your airway is and how your face looks in profile. Often called the “upper jaw,” the maxilla is actually far more than a tooth-bearing structure. It forms the floor of each eye socket, the lateral walls of the nasal cavity, most of the hard palate, and a significant portion of the cheek. Because it sits at the intersection of so many functional systems, even small disruptions in maxillary growth during fetal life or childhood can ripple outward into breathing problems, dental crowding, and visible facial asymmetry.

How the Maxilla Forms Before Birth

The maxilla begins its existence not as bone but as a stream of migrating cells. During early embryonic development, neural crest cells peel away from the developing brain and spinal cord and travel along specific routes into the face, populating the structures that will become the jaws, palate, and surrounding tissues.¹ These cells are remarkably versatile. Once they arrive in the facial region, they differentiate into the bone-forming cells that will construct the maxilla through a process called intramembranous ossification, meaning the bone forms directly within sheets of connective tissue rather than from a cartilage template.

Microscopic studies of human embryos have captured this process in detail. Mesenchymal cells first cluster together, then produce tiny spicules of bone that gradually fuse into thin plates called trabeculae. The outer surfaces of these trabeculae are lined by osteoblasts (the cells that lay down new bone), while osteocytes become embedded within the bone matrix itself. At this stage, the bone is rough and disorganized, with collagen fibers running in random directions rather than the orderly layers seen in mature bone.² Gradually, the spaces between these trabeculae fill with blood vessels and connective tissue, and the bone matures into a more structured form.

The signaling molecules that guide this process are tightly regulated. One protein, Jagged1, plays a particularly important role in osteoblast development within the maxilla. Animal studies in which Jagged1 was knocked out specifically in cranial neural crest cells showed pronounced maxillary underdevelopment, with altered collagen deposition, delayed bone formation, and measurable differences in bone density.³ The resulting condition, maxillary hypoplasia, leads to problems with tooth alignment, restricted airways, and cosmetic deformities, illustrating how a single molecular signal can have broad consequences for facial form.

What the Adult Maxilla Looks Like

The mature maxilla is not a solid block of bone. It is a complex, partially hollow structure organized around several key features. The largest internal space is the maxillary sinus, a pyramid-shaped cavity that sits just below the eye socket and alongside the nasal cavity. This sinus is already present at birth, though tiny, and it keeps expanding until around age 18. Its most dramatic growth happens in the first eight years of life, with nearly all its final dimensions reached by age 16. Gender-related differences in sinus size become apparent after about age eight.⁴

Running through the floor of the eye socket is the infraorbital canal, a bony tube that carries the infraorbital nerve and blood vessels from the back of the orbit to the face. This canal is better developed in postnatal life than before birth, with thicker walls and more complex branching patterns as a child grows.⁵ In adults, the canal averages about 24 millimeters in length, and in most people it sits embedded within the roof of the maxillary sinus.⁶ Surgeons and dentists care about this anatomy because the infraorbital nerve provides sensation to the cheek, upper lip, and side of the nose, and damage to it during surgery or trauma can cause numbness in those areas.

The orbital floor itself, which the maxilla partially forms, is the thinnest and weakest wall of the bony eye socket, measuring only about 35 to 40 millimeters across.⁷ This weakness is why “blowout” fractures of the orbital floor are so common after blunt trauma to the eye. The thin maxillary bone cracks under pressure, potentially trapping the muscles that move the eyeball and causing double vision. In some cases, surgeons can harvest bone from the front wall of the maxilla itself to reconstruct the damaged orbital floor, since this wall is thicker and more easily accessible.⁸

How the Maxilla Grows After Birth

Postnatal growth of the maxilla is driven by two complementary processes: bone remodeling on its surfaces and growth at the sutures that connect it to surrounding bones. Bone remodeling involves selectively adding bone in some areas and removing it in others. Detailed studies of bone surfaces in human skulls have revealed a characteristic pattern. In the front of the face, the outer surface of the maxilla undergoes resorption (bone removal), while bone is deposited on its inner surfaces. This combination produces a net downward and slightly backward shift of the front of the face.⁹ The mandible simultaneously displaces forward and downward to keep pace, maintaining the relationship between the upper and lower teeth.

Growth at the sutures, particularly the circummaxillary sutures that ring the maxilla where it meets the surrounding skull bones, adds new bone along the edges, effectively pushing the maxilla forward and downward as well. This sutural growth is what orthodontists attempt to harness during treatments that pull the midface forward in growing patients, and research has confirmed that tensile forces applied across these sutures do stimulate new bone deposition.¹⁰

The adolescent growth spurt in the maxilla generally follows a similar timeline to the mandible, with both starting their accelerated growth phase at roughly the same age and reaching peak growth velocity around the same time. Both the maxilla and mandible begin their growth spurt earlier, peak later, and stop growing later than the cranial base.¹¹ This synchrony matters because a mismatch in timing or magnitude between upper and lower jaw growth is one of the main causes of malocclusion, where the teeth do not meet properly when the mouth closes.

How the Maxilla Handles Chewing Forces

Every time you bite down, the forces generated by your jaw muscles travel through your teeth, into the alveolar bone that holds them, and then through the body of the maxilla toward the skull base. The traditional clinical model describes this force transfer as happening along vertical “pillars” or “buttresses,” with horizontal reinforcements bracing them. A computational analysis of how chewing forces actually distribute through the midface found that occlusal loads travel along roughly five vertical and two horizontal pathways, and that cortical bone (the dense outer shell) carries most of the load in the front of the maxilla, while both cortical and spongy trabecular bone share the load more equally toward the back.¹²

A separate study using a validated computational model of the skull under maximum bite force found that the lateral maxilla is the main vertical load-bearing structure, with the naso-maxillary region contributing far less than textbooks typically suggest. The study also found no evidence that the pterygomaxillary junction, long described as a major buttress, functions as one at all.¹³ This challenges a model that has been taught in surgical training for decades. And a broader review of in-vivo bone strain studies and material property data went even further, concluding that available evidence does not support the existence of distinct pillars and buttresses in the human facial skeleton at all.¹⁴ The real picture appears to be less neatly organized than the classic teaching implies, with forces spreading diffusely through a structure that behaves more like a complex shell than a building with load-bearing columns.

This biomechanical understanding has direct consequences for dental implants. The posterior maxilla, where the bone is more spongy and less dense, shows lower stress concentration during implant insertion and loading compared to other jaw regions.¹⁵ That lower density means implants placed there may have less initial stability, which is why augmentation procedures like sinus lifts are sometimes needed before placing posterior maxillary implants.

The Maxilla, the Airway, and Breathing

Because the maxilla forms the lateral walls and floor of the nasal cavity and shapes the roof of the mouth, its width has a direct effect on how easily air flows through the nose. A narrow maxilla constricts the nasal passages and increases airway resistance. This relationship has been demonstrated clearly in patients with Marfan syndrome, where marked constriction of the maxillary arch correlated significantly with increased nasal resistance and with the severity of sleep apnea.¹⁶

The relationship works the other way, too. Children who are habitual mouth breathers develop measurably narrower maxillary arches compared to nasal breathers, along with reduced airway volumes and cross-sectional areas in both the area behind the nose and the area behind the soft palate.¹⁷ Whether the narrow maxilla causes the mouth breathing or the mouth breathing causes the narrow maxilla remains debated, but the association is consistent enough that orthodontists sometimes recommend maxillary expansion as part of managing pediatric airway problems. The maxilla is also functionally tied to the jaw muscles through the teeth it holds. When force is applied to a tooth, receptors in the ligament that anchors each tooth to the maxillary bone fire signals that reflexively inhibit the jaw-closing muscles within about 12 milliseconds.¹⁸ This feedback loop protects both the teeth and the bone from excessive force, and it is part of why losing teeth (and the receptors that came with them) changes how much bite force a person can control.

When Maxillary Development Goes Wrong

The most familiar developmental failure of the maxilla is cleft palate. The palate forms when shelves of tissue grow inward from the maxillary prominences on either side, elevate above the tongue, and fuse at the midline. This fusion requires an intricate sequence of signaling between the surface epithelium and the underlying tissue, involving growth factors that control cell proliferation, programmed cell death at the fusion seam, and even a temporary “teflon coat” of periderm cells that prevents the palatal shelves from sticking to the wrong surfaces before the time is right.¹⁹ Disruption at any stage, whether the shelves fail to grow enough, fail to elevate, or fail to fuse, can produce a cleft.²⁰ The final fusion step requires both programmed cell death and a transformation of epithelial cells into mesenchyme, processes regulated by overlapping signaling pathways.²¹

Syndromic conditions that affect craniofacial sutures can also produce severe maxillary underdevelopment. In Apert syndrome, premature fusion of skull sutures leads to a dramatically underdeveloped midface. A case study of a nine-year-old with Apert syndrome found that retarded growth of the anterior cranial base produced a cascade of downstream effects, including a hypoplastic nasal septum, retruded cheekbones, and stunted maxillary and palatal growth, even years after corrective skull surgery.²² For years, the conventional explanation was that the midface hypoplasia in syndromes like Apert, Crouzon, and Pfeiffer was entirely secondary to premature closure of the cranial base sutures, which tethered the maxilla and prevented it from growing forward. But research comparing the sutures around the maxilla in these patients to those in unaffected children has found that the facial sutures themselves also fuse prematurely, suggesting the problem is not just the skull base dragging the midface back but also intrinsic failure of maxillary sutural growth.²³

A less dramatic but extremely common clinical problem is maxillary canine impaction, where the permanent canine tooth fails to descend into its normal position and instead becomes trapped within the maxillary bone. When this happens, the impacted tooth can press against the roots of neighboring teeth and cause resorption, essentially dissolving parts of them. Physical proximity of less than one millimeter between the impacted canine and an adjacent root is the strongest predictor of this damage.²⁴ The thickness of the alveolar bone around the lateral incisor also matters: thinner bone is associated with greater risk of resorption, particularly when the impacted canine sits on the palatal side.²⁵

Orthodontic Expansion and Surgical Repositioning

Rapid maxillary expansion (RME) is one of the most common orthodontic interventions involving the maxilla. It works by applying lateral force to the midpalatal suture, the fibrous joint running down the center of the hard palate, to physically widen the upper jaw. A systematic review of the evidence found that actual sutural opening accounts for roughly 12 to 53 percent of the total screw expansion (the rest comes from bending of the bone and tipping of the teeth), and that the suture recalcifies after treatment, making the expansion stable.²⁶ Age is a major factor. As patients get older, the midpalatal suture becomes more ossified and resistant to separation. Animal research has confirmed that increased age correlates with less sutural opening and less new bone formation in response to expansion forces. Heavier forces can overcome some of this resistance and produce more separation in the short term, but they also trigger more bone resorption, potentially weakening the surrounding bone.²⁷ Experimental work has explored whether low-power laser therapy applied to the expanding suture can accelerate bone regeneration. In animal models, laser treatment significantly increased new bone formation between two and four weeks after expansion.²⁸

When growth is complete and the suture has fused, orthodontic expansion alone is no longer sufficient to widen a narrow maxilla. Adults with severe midface deficiency often require Le Fort I osteotomy, a surgical procedure in which the maxilla is cut free from the rest of the skull along a horizontal line and physically repositioned forward, downward, or sideways. The freed maxilla is then fixed in its new position with titanium plates and screws. Biomechanical modeling consistently shows that four-plate fixation distributes stress more evenly than two-plate fixation, particularly when the maxilla has been moved both forward and downward.²⁹ As the amount of advancement increases, stress on both the plates and the surrounding bone rises, with the plates behind the molars bearing the greatest load in larger movements.³⁰ Different fixation configurations also matter when the surgical plan involves rotating the occlusal plane, where some plate arrangements can exceed the yield strength of titanium and risk hardware failure.³¹

The Maxilla in Evolutionary Perspective

The human face is strikingly flat compared to those of our closest evolutionary relatives, and the maxilla is a major reason why. A study comparing bone remodeling patterns in Neanderthal and early hominin sub-adults to those of modern humans found a fundamental difference that appears by about five years of age. In Neanderthal and Sima de los Huesos children, the front of the maxilla showed extensive bone deposition, building the face forward into a projecting, prognathic form. In modern human children, the same surfaces showed extensive bone resorption, actively removing material and pulling the face inward.³² The retracted face of modern humans is not simply a scaled-down version of an ancestral face. It is the product of a fundamentally different growth program at the cellular level.

Diet has also left its mark on maxillary form. A large-scale analysis of human skull shape across the agricultural transition found modest but consistent directional differences between foraging and farming populations, with changes most pronounced in dairy-consuming groups. The pattern is consistent with the mechanical effects of softer diets: less chewing force, less functional stimulus to the jaws, and a tendency toward smaller, more gracile facial bones.³³ This finding fuels ongoing debates about whether modern rates of dental crowding and malocclusion are partly a consequence of the mismatch between our jaws, shaped by a softer dietary environment, and our teeth, which have not changed as rapidly in size. The maxilla sits at the center of that mismatch, being both the structure most responsive to mechanical loading during growth and the one that most visibly defines the shape of the human face.