Jaw surgery jargon, in plain language.
Every term below is one a surgeon may reasonably use in a first orthognathic consultation. Each is paired with the thing patients actually want to know: what it does to a face. Clinics are welcome to link or hand this to patients.
Written from the patient side, for the reason described in why this exists. General education, not clinical advice about any individual case.
The operations
Orthognathic surgery
also called: jaw surgery, corrective jaw surgery
Surgery that cuts and repositions the jaw bones themselves, rather than moving teeth through bone. Usually done alongside orthodontics, which prepares the bite for the new skeletal position.
On the face: Changes the underlying facial skeleton, so it changes facial proportions in a way braces alone cannot.
Le Fort I osteotomy
also called: maxillary osteotomy, upper jaw surgery
A horizontal cut across the maxilla above the tooth roots, freeing the whole upper jaw so it can be moved as one block.
On the face: Moving it forward fills out the midface and supports the upper lip and nose base. Moving it up (impaction) shortens a long midface and lets the chin rotate forward automatically.
BSSO
also called: bilateral sagittal split osteotomy, lower jaw surgery
A lengthwise split of the mandible on both sides, letting the tooth-bearing part of the lower jaw slide forward or back while the joints stay put.
On the face: Advancement brings the chin and jawline forward and tightens the area under the chin. Setback does the reverse for a protruding lower jaw.
Bimaxillary surgery
also called: bimax, double jaw surgery
A Le Fort I and a BSSO in the same operation, moving both jaws.
On the face: Allows the whole bite to move together, which is what makes larger advancements and occlusal plane changes possible.
Genioplasty
also called: chin osteotomy, sliding genioplasty, mentoplasty
A separate cut through the chin point, below the tooth roots, moving only the chin. It is not the same operation as a BSSO, though the two are often combined.
On the face: Adjusts chin projection, height and left/right position independently of the jaw and bite.
SARPE
also called: surgically assisted rapid palatal expansion, maxillary disjunction
A surgical release of the maxilla combined with an expander, widening a narrow upper jaw. Usually a separate, earlier operation with several months of bone consolidation afterwards.
On the face: Widens the upper dental arch and the smile; the facial change is modest compared with advancement.
MMA
also called: maxillomandibular advancement
Bimaxillary surgery performed specifically to enlarge the upper airway, most often for obstructive sleep apnoea.
On the face: Same facial change as any bimaxillary advancement. The goal is functional, and the appearance change comes with it.
The movements
Advancement / setback
also called: A-P movement, anteroposterior
Moving a jaw forward (advancement) or back (setback) in the front-to-back direction.
On the face: The single biggest driver of profile change. Most visible from the side.
Impaction / down-graft
also called: vertical maxillary movement
Moving the upper jaw up into the face, or down away from it.
On the face: Impaction shortens the midface and reduces gummy smiles; it also lets the mandible rotate closed and forward, bringing the chin with it.
Occlusal plane rotation
also called: occlusal plane pitch, clockwise / counter-clockwise rotation
Tilting the whole bite as a unit around a chosen pivot, rather than sliding it forward. Direction is named as seen from the patient's right.
On the face: Counter-clockwise rotation swings the chin up and forward while moving the upper front teeth much less. It can change a profile more than straight advancement, and often flattens the angle under the chin.
Pivot point
also called: hinge point, centre of rotation
The point the bite rotates around during an occlusal plane change: commonly the jaw joint, the upper front teeth, or the back teeth.
On the face: Same rotation, very different result. Rotating about the front teeth keeps the incisors where they are and moves the chin a lot.
Occlusal cant
also called: roll, tilted bite plane
One side of the bite sitting higher than the other.
On the face: Shows as a tilted smile line from the front. Correcting it levels the mouth.
Yaw / midline deviation
also called: asymmetry, midline shift
The jaw or chin sitting off to one side of the facial midline.
On the face: Visible from the front as an off-centre chin or mismatched dental midlines.
The diagnosis
Skeletal Class II
also called: retrognathia, overjet
The lower jaw sits behind the upper one relative to the skull base.
On the face: Typically a receding chin, a deep fold between lip and chin, and a poorly defined jawline. Often associated with a narrowed airway.
Skeletal Class III
also called: prognathism, underbite
The lower jaw sits ahead of the upper one, or the upper jaw is deficient.
On the face: A prominent chin and flat midface.
Maxillary transverse deficiency
also called: narrow upper jaw, maxillary atresia
An upper jaw too narrow for the lower one, usually with a crossbite where the upper back teeth bite inside the lower.
On the face: A narrow smile with dark corners, and often a high, vaulted palate.
Dentoalveolar compensation
also called: compensation, decompensation
Teeth that have tipped over years to disguise a skeletal mismatch. Orthodontic decompensation deliberately undoes this before surgery.
On the face: Decompensation temporarily makes the bite and profile look worse, because it exposes the true size of the skeletal discrepancy.
Lip incompetence
also called: incompetent lips, lips apart at rest
Lips that do not meet when the face is relaxed, usually because the jaws sit too far apart or too far out of line for the mouth to close without effort. Forcing them shut strains the chin muscle (mentalis).
On the face: Parted lips and a puckered chin in every relaxed photo. When surgery brings the jaws together, the lips can often seal at rest - one of the most visible soft-tissue changes, and the reason an honest before photo may show the mouth slightly open.
Reading a profile
Nasolabial angle
The angle between the base of the nose and the upper lip.
On the face: Maxillary advancement tends to open the upper lip forward and rotate the nasal tip up, changing this angle.
Labiomental fold
also called: mentolabial sulcus
The crease between the lower lip and the chin.
On the face: Deep in Class II patients; advancement and genioplasty typically soften it.
Cervicomental angle
also called: submental angle, neck-chin angle
The angle between the underside of the chin and the neck.
On the face: One of the most noticeable changes in mandibular advancement: the area under the chin tightens and the jawline separates from the neck.
Pogonion, A-point, B-point
also called: cephalometric landmarks
Fixed reference points on the chin, upper jaw and lower jaw used to measure movements on an X-ray.
On the face: These are how millimetres get quoted. They are bone landmarks, so a millimetre of bone movement is not a millimetre of skin movement.
Soft-tissue response ratio
How far the overlying skin and lip move for a given movement of bone. It varies by region, by direction and between people.
On the face: The reason no photo preview can be exact, and the reason JawSim is explicit about being illustrative.
The technology
CBCT
also called: cone beam CT
A 3D X-ray of the facial skeleton, taken as part of the surgical workup.
On the face: The basis of accurate planning. Not usually available at a first consultation.
VSP
also called: virtual surgical planning, 3D planning
Planning the exact osteotomies and movements on the CBCT data, often producing printed splints or cutting guides.
On the face: This is where precise soft-tissue simulation happens, typically late in the process and after the patient has committed.
Cephalometric analysis
also called: ceph, tracing
Measuring standardised angles and distances on a side-view skull X-ray.
On the face: How the plan is quantified and communicated between orthodontist and surgeon.
General information, not medical advice. Which movements apply to a given patient, and in what magnitude, is a clinical judgement made by their surgeon on the basis of a full workup. JawSim visualizes a plan illustratively; it never decides or predicts one.
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Why I built this
JawSim puts these movements on your patient's own photographs during the consultation. 14-day trial, no card.