Expert article: jaw
Edge-to-edge bite and crossbiteWhy the lower jaw is guided by muscles
Your front teeth meet edge to edge, or the lower ones sit outside? Here you will learn what edge-to-edge bites and crossbites are, why muscles and tongue guide the lower jaw and how training and braces fit together.
Does this sound familiar?
How do your teeth meet?
What applies to you?
Tap whatever applies to you.
If two or more points apply, it is worth taking a closer look at your bite and at what guides it. In our view, this is usually not the bone alone, but the musculature with the tongue at its centre.
What edge-to-edge bite and crossbite areWhy the lower jaw is guidedThe key points at a glance
- In an edge-to-edge bite, the incisal edges meet. In a crossbite, lower teeth sit outside the upper ones, at the front or at the side, on one or both sides.
- The lower jaw hangs from two joints and in muscles. In our view, where it sits is usually determined by the musculature, and the tongue centres it from within.
- Braces and surgery change the shape, not the pattern. In our view, surgery is therefore not a good first choice, and whether braces hold is decided by the function. It is best to train it in parallel.
Video
Overbite, edge-to-edge bite, crossbite: understanding jaw misalignments
Das Video lädt erst nach dem Klick. Dann werden Daten an YouTube (Google) übertragen.
The terms
Edge-to-edge bite and crossbite: what is meant
In a normal bite, the upper front teeth overlap the lower ones slightly, and at the sides the upper back teeth reach over the outside of the lower ones.
In an edge-to-edge bite, the front teeth meet edge to edge instead of overlapping. In a crossbite, the rows of teeth cross, and lower teeth sit outside the upper ones. If this is at the front, it is called an anterior crossbite. If it is at the back teeth, it is called a posterior crossbite, on one side or both sides.
Normal bite
The upper front teeth overlap the lower ones slightly; at the sides, the upper back teeth reach over the outside of the lower ones.
Edge-to-edge bite
The incisal edges meet. Often the back teeth then lack contact, or contact only occurs when the lower jaw deviates.
Anterior crossbite
Some or all of the lower front teeth sit in front of the upper ones. If the whole lower jaw is forward, this is called mandibular prognathism or a tendency towards it.
Posterior crossbite
At the back teeth, the lower ones bite outside the upper ones. If only one side is affected, the midline of the lower jaw often shifts towards that side.
Bilateral crossbite
On both sides the lower back teeth sit outside, and the upper jaw appears narrow by comparison.
of children and adolescents in Europe and America respectively have a posterior crossbite, according to a Cochrane review1
A crossbite can be due to the jaws having grown to different widths, teeth being tilted or the lower jaw deviating when biting. The same finding can therefore have different stories behind it. If the front teeth do not meet at all, it is an open bite; see Open bite and tongue thrust.
Signs
Crossbite and edge-to-edge bite: symptoms you notice
Many people notice a crossbite or edge-to-edge bite not in the teeth themselves, but in what happens around them.
Cheek biting on one side
You repeatedly bite the same cheek. Often the lower jaw is then shifted towards the opposite side.
Shifted midline
The midline of the lower front teeth lies beside the midline of the upper ones.
Chewing on one side
One side feels more secure when chewing, and you avoid the other.
Worn edges
In an edge-to-edge bite, the incisal edges rub against each other and wear visibly. Biting off food is difficult.
The lips join in
If the back teeth lack contact when swallowing, the lips and chin compensate with pressure.
The jaw joint is making itself felt
Clicking, pressure in front of the ear or tense chewing muscles, often on one side. More in the article on craniomandibular dysfunction (TMD).
A unilateral crossbite often also shows in the face. If the lower jaw sits off centre for years, muscles and soft tissues adapt. How position and shape differ in this is described in the article Facial asymmetry and crooked jaw.
The core
The lower jaw is guided by muscles
The upper jaw is firmly attached to the skull. The lower jaw is a separate, movable bone, and this is exactly where it is decided how a bite comes about.
The lower jaw hangs from the skull via two jaw joints. It is carried and moved by muscles: the masseter and temporalis close the mouth, the floor-of-mouth muscles open it, and the pterygoid muscles push it forwards and to the side. Without these muscles it would simply drop.
In our view, where the lower jaw sits and where the teeth meet is therefore usually determined not by the bone alone, but by the interplay of these muscles. If they work in balance on both sides, the lower jaw sits in the middle.
Try it out: tilt your head to one side and tap your back teeth together lightly, then to the other side, then with your head forward. What do you notice?
opened and closed their mouths rhythmically in a study from Umeå. The head moved along throughout, and its movement usually began before that of the lower jaw2
of 36 children with an anterior crossbite whose lower jaw slid forwards when biting had no family history, and three out of four had normally interlocking back teeth in their habitual bite position3
Orthodontics calls such forward sliding pseudo-prognathism. The lower jaw is not too large. It slides forwards on closing because the front teeth would otherwise meet edge to edge, and ends up in a reverse bite. In this way an edge-to-edge bite can become an anterior crossbite. The position arises in movement, not in the bone.
The lower jaw has no fixed place. It is guided.The teeth show where the guidance takes it. That is why the training targets the guidance and not the teeth.
We also view the label “hereditary” critically. Families pass on not only genes but also patterns such as mouth breathing, swallowing habits and dummies. In many cases, we consider it a false conclusion to infer an unchangeable bone from a family pattern alone.
The tongue
The tongue centres the lower jaw
The chewing muscles pull from the outside. From the inside, the tongue gives the lower jaw its centre.
In the tongue reference position, the tip of the tongue rests on a small ridge behind the upper front teeth, with the body of the tongue broad against the palate. Seen from above, the tongue fills the dental arch and its tip points exactly to the middle.
This contact is light, but it provides orientation, and the lower jaw aligns itself to it. If, on the other hand, the tongue lies at the bottom of the mouth, the inner centre is missing and the lower jaw slides wherever the stronger muscles pull.
Like the keel of a sailing boat
A sailing boat with a keel holds its course even when the wind pushes from the side. Without a keel it drifts off. That is how we see the tongue: it is the keel in the middle of the mouth. If it is missing, a slightly stronger side of the muscles is enough for the lower jaw to drift forwards or to the side.
were compared in a study from Ljubljana. In a prognathic bite the tongue lay considerably lower than in a normal bite, the upper jaw was narrower at the canines and the lower dental arch wider at the back4
Such a comparison cannot reliably show the direction of the relationship. It does, however, fit our model: if the tongue lies low and forward, the upper jaw lacks the pressure from within, which the lower jaw receives instead. The upper dental arch stays narrow, the lower one becomes wide, and the bite moves forwards or crosses.
The picture shows the other side of the balance: the lips, cheeks and chin pull from the outside towards the midline. If the tongue and the ring of muscles work in balance, the lower jaw is centred. It is exactly this balance that the training targets, not an individual muscle.
Causes
How a bite moves off centre
In our view, a crossbite or edge-to-edge bite does not usually develop overnight. It is the result of a pattern that becomes ingrained over years.
Low or forward-thrusting tongue
If the tongue lies low or pushes forwards when swallowing, the upper jaw lacks support from within, and the lower jaw is guided forwards.
Mouth breathing
If you breathe through your mouth, you have to lower your tongue. In children with signs of a blocked nose, an analysis from Jerusalem found a posterior crossbite in 49 per cent, compared with 26 per cent in nasal breathers5.
One-sided chewing and swallowing
Favouring one side for years loads the muscles unevenly. The imbalance becomes the lower jaw’s habitual path.
Habits
Dummy, thumb, lip biting, resting the chin in the hand. In our view, an expression of a missing function, which they reinforce at the same time because they exert forces for hours.
Head balance
If the head hangs forwards or to the side, the frame of reference in which the lower jaw is guided shifts.
A research group in Amsterdam measured with fine electrodes that both sides work in every chewing cycle, the side with the food just more strongly6. People who favour one side also often choose the one on which the teeth fit together better. The preference follows the imbalance and ingrains it further.
with milk teeth and a unilateral crossbite chewed more often in the reverse direction on the crossbite side than children with a normal bite7
were examined in Ljubljana at the ages of three, four and five, and one in five had a posterior crossbite at the end. In these children, deviant swallowing increased, while in the others it decreased. Mouth breathing and dummies were more common in the crossbite group8
The pattern deviates
Mouth breathing, a low-lying tongue or habits alter the interplay of tongue, lips and chewing muscles early on.
The body compensates
The lower jaw deviates to where the teeth find contact most easily. The nervous system stores this path as the habitual bite.
Form follows
In many of those affected, the dental arches, joints and bones adapt to the guided position during growth.
Complaints appear
Worn teeth, a jaw joint loaded on one side, tension extending into the neck or an uneven face can be the end result.
Treatments
Braces and surgery change the shape, the function remains
Orthodontics and oral and maxillofacial surgery do technically precise work. The question is what they change and what they do not.
For children, it is well established that devices for expanding the upper jaw correct a posterior crossbite. The Cochrane review analysed 31 randomised trials and found with high certainty for seven- to eleven-year-olds that a quad helix or an expansion plate corrects better than waiting1.
after palatal expansion, 14 children with a posterior crossbite chewed as quickly as their peers. The reversed form of their chewing movement, however, remained unchanged9
is the success rate reported in studies for treating a unilateral crossbite in childhood10
This is the point that matters to us. Teeth and bones can be moved, but the stored movement pattern keeps running. In our view, this explains why a bite can drift back after braces or surgery: the function that shifted it is still there.
In our view, surgery is therefore not a good first choice for an edge-to-edge bite or crossbite, because it changes the shape and not the pattern that shifted the bite. Braces also reposition teeth and jaws. In our view, whether the result holds usually depends on whether the function goes along with it.
A brace moves the teeth. Where they go afterwards is decided by function.Why teeth have to be held in place after treatment is described in the article Retainer and relapse. What surgery can and cannot do is covered under Jaw surgery and BiMax.
Children
Crossbite in children: treatment and prevention
In the milk and mixed dentition, the jaw is still growing. What muscles and tongue impose on it can be reflected in its shape, in both directions.
A posterior crossbite in the milk teeth only rarely corrects itself. In a long-term observation in Stockholm, this happened by the age of nine in 17 per cent of untreated four-year-olds, and in 50 per cent after early grinding of interfering tooth contacts11. Unequal halves of the lower jaw largely evened out after early treatment12.
of dummy use marked the threshold in a study from Ljubljana beyond which a posterior crossbite became more likely. The authors attribute this to the low tongue posture13
met the criteria of a systematic review on so-called orthodontic dummies. For posterior crossbite, none showed a difference from conventional dummies14
In our view, there is no such thing as a physiological dummy, even if manufacturers promise it. A teat holds the tongue down and forward, whatever its shape. We see thumb sucking and lip biting as oral habits, as the result of a missing function. Breaking the habit works most reliably when the child learns the correct function.
Have a crossbite in a child checked early by a dentist or orthodontist. For children aged 2 to 10, the FaceFormer ZERO is recommended; more under FaceFormer for children.
Training
Training for edge-to-edge bite and crossbite
Whatever the type of bite: the musculature is harmonised, the tongue is positioned and centred, and breathing, swallowing and head balance run together in one sequence.
A pattern does not change through insight; it is displaced by precise, frequent repetition. In the basic exercise, the FaceFormer sits in the oral vestibule. The lips press the lip wedge, the tip of the tongue rests at the reference point, the back teeth bite down briefly, and then you swallow. In this way the lower jaw aligns itself to the centre with every swallow.
For an edge-to-edge bite, an anterior crossbite and a forward-positioned lower jaw, the downward pull exercise is used from about week 3 instead of the forward pull exercise. The upward pull exercise is intended for a retruded lower jaw and is not suitable for mandibular prognathism.
For a posterior crossbite, the pull exercise in varying directions may be an option; it practises centring the lower jaw during swallowing. It is best to determine the direction with a practice.
- From day 1
Basic exercise
A few minutes three times a day with the FaceFormer ZERO; you increase the repetitions week by week.
- From around week 3
Direction of pull by bite type
Instead of the forward pull exercise, the appropriate direction is added. At night you wear the ZERO as a supplement.
- After a few weeks
Switching to the ONE
During the day you train with the ONE, the same size as the ZERO, just made of firmer material. Children up to about ten years stay with the ZERO.
- Every four weeks
Compare photos
From the very start, photograph your bite with lips parted, from the front and from the side. That way you can see changes that go unnoticed in the mirror.
- Over months
The pattern runs by itself
The exercise manual allows six to twelve months until the new sequences run without thinking.
The free FaceFormer app guides you through the basic exercises; all the modules are on the exercise pages. If you are not making progress on your own, a practice is good support. If you have pain in the jaw joint, stop the training.
Together
Braces and training in parallel
Training does not move teeth, and braces do not train function. That is why the two complement each other.
Training is also possible with fixed braces; with brackets, dental wax helps. Do not end ongoing orthodontic treatment on your own initiative. If you train with a practice, coordinate the process together with the orthodontist.
In our view, this phase in particular is favourable. While the brace changes the shape, the musculature learns to support the new position instead of continuing to pull towards the old one.
What the brace does
It moves teeth and can widen the upper jaw during growth.
What the training addresses
It positions the tongue and trains lip closure, swallowing, nasal breathing and head balance, the forces that guide the lower jaw in everyday life.
What remains open
Whether training reduces relapse after crossbite treatment has not been studied, and there is no FaceFormer study on edge-to-edge bite or crossbite.
In adults, growth is complete, and for an edge-to-edge bite, braces, a splint or surgery are often recommended. In our view, function should come before any of these decisions. If you train the lower jaw for six to twelve months and photograph your bite, you will see how much of the alignment is position and how much is bone.
A bite splint imposes a position on the lower jaw from the outside and takes load off the teeth. It cannot guide it: you bite down, in our view the masticatory muscles tend to be triggered rather than retrained, and the pattern that pulls the lower jaw off centre remains. That is why, for us, it is a support, not an answer to why the bite has moved off centre. Whether and when it can be discontinued is something you discuss with the practice that fitted it.
The training does not replace an orthodontic examination, and a particular result cannot be promised. More under FaceFormer and other treatments.
Everyday life
What you can do for your bite in everyday life
Teeth apart
Except when chewing and swallowing, the teeth do not touch. If you catch yourself clenching, release them and place the tip of your tongue on the palate.
Chew on both sides
Consciously distribute mouthfuls to both sides, even if one feels unfamiliar.
Nose instead of mouth
Nasal breathing keeps the tongue up and the mouth closed. More on this under Mouth breathing and nasal breathing.
Chin out of your hand
Do not rest your head in your hand on one side, and change the side you sleep on from time to time.
Do not push forwards
Do not push your lower jaw forwards to bring your front teeth together. Doing so tends to train the path forwards.
No show of strength
Do not press your tongue against the palate with force. The reason is explained in the article on Mewing.
Questions
Frequently asked
What is an edge-to-edge bite?
In an edge-to-edge bite, the incisal edges of the upper and lower front teeth meet instead of overlapping. Often the back teeth then lack contact. In our view, this is usually a matter of the muscular guidance of the lower jaw.
What is a crossbite?
In a crossbite, lower teeth sit outside the upper ones. At the front it is called an anterior crossbite, at the back teeth a posterior crossbite, on one side or both sides. In a unilateral crossbite, the lower jaw is often shifted to one side.
What are the symptoms of a crossbite?
Typical signs are a shifted midline of the front teeth, cheek biting and chewing on one side, a jaw joint that clicks on one side and a face that looks uneven. With an edge-to-edge bite, worn incisal edges and difficulty biting off food are added.
Treating an edge-to-edge bite as an adult: is it possible without surgery?
That depends on how much of the alignment is position and how much is bone. If the lower jaw deviates forwards mainly through muscular guidance, function plays a major role in our view; if the bone has grown markedly differently, orthodontics and oral and maxillofacial surgery come into question. We advise training for months beforehand and documenting the bite with photos. A result cannot be promised.
When should a crossbite be treated in a child?
It is best to have it checked early, already in the milk teeth. A posterior crossbite only rarely corrects itself. At the same time, it is worth looking at mouth breathing, dummy, thumb and swallowing pattern. For children aged 2 to 10, the FaceFormer ZERO is recommended.
Can a unilateral crossbite change the face?
That is possible. If the lower jaw is shifted to one side for years, muscles, soft tissues and, during growth, the bone as well adapt. Often the difference lies more in the position of the lower jaw than in its shape.
Why does a crossbite come back after braces?
A brace changes teeth and jaws, but not the stored movement pattern by itself. In one study, the children’s reversed chewing movement persisted after palatal expansion. In our view, the function that shifted the bite continues to act. That is why it should be trained in parallel.
Which pull exercise suits an edge-to-edge bite or mandibular prognathism?
For an edge-to-edge bite, anterior crossbite and forward-positioned lower jaw, the downward pull exercise; for a posterior crossbite, the pull exercise in varying directions, each from about week 3. The upward pull exercise is not suitable for mandibular prognathism. It is best to determine the direction with a practice.
More articles from the knowledge section
Where to go next
Sources
- Ugolini A, Agostino P, Silvestrini-Biavati A, Harrison JE, Batista KB (2021). Orthodontic treatment for posterior crossbites. Cochrane Database of Systematic Reviews 12:CD000979. PMID 34951927. Source
- Eriksson PO, Häggman-Henrikson B, Nordh E, Zafar H (2000). Co-ordinated mandibular and head-neck movements during rhythmic jaw activities in man. Journal of Dental Research 79(6):1378-1384. PMID 10890716. Source
- Rabie AB, Gu Y (2000). Diagnostic criteria for pseudo-Class III malocclusion. American Journal of Orthodontics and Dentofacial Orthopedics 117(1):1-9. PMID 10629513. Source
- Primozic J, Farcnik F, Perinetti G, Richmond S, Ovsenik M (2013). The association of tongue posture with the dentoalveolar maxillary and mandibular morphology in Class III malocclusion: a controlled study. European Journal of Orthodontics 35(3):388-393. PMID 22467568. Source
- Harari D, Redlich M, Miri S, Hamud T, Gross M (2010). The effect of mouth breathing versus nasal breathing on dentofacial and craniofacial development in orthodontic patients. The Laryngoscope 120(10):2089-2093. PMID 20824738. Source
- Blanksma NG, van Eijden TM (1995). Electromyographic heterogeneity in the human temporalis and masseter muscles during static biting, open/close excursions, and chewing. Journal of Dental Research 74(6):1318-1327. PMID 7629340. Source
- Sever E, Marion L, Ovsenik M (2011). Relationship between masticatory cycle morphology and unilateral crossbite in the primary dentition. European Journal of Orthodontics 33(6):620-627. PMID 21118909. Source
- Ovsenik M (2009). Incorrect orofacial functions until 5 years of age and their association with posterior crossbite. American Journal of Orthodontics and Dentofacial Orthopedics 136(3):375-381. PMID 19732672. Source
- Throckmorton GS, Buschang PH, Hayasaki H, Pinto AS (2001). Changes in the masticatory cycle following treatment of posterior unilateral crossbite in children. American Journal of Orthodontics and Dentofacial Orthopedics 120(5):521-529. PMID 11709671. Source
- Thilander B, Lennartsson B (2002). A study of children with unilateral posterior crossbite, treated and untreated, in the deciduous dentition: occlusal and skeletal characteristics of significance in predicting the long-term outcome. Journal of Orofacial Orthopedics 63(5):371-383. PMID 12297966. Source
- Lindner A (1989). Longitudinal study on the effect of early interceptive treatment in 4-year-old children with unilateral cross-bite. Scandinavian Journal of Dental Research 97(5):432-438. PMID 2617141. Source
- Pinto AS, Buschang PH, Throckmorton GS, Chen P (2001). Morphological and positional asymmetries of young children with functional unilateral posterior crossbite. American Journal of Orthodontics and Dentofacial Orthopedics 120(5):513-520. PMID 11709670. Source
- Melink S, Vagner MV, Hocevar-Boltezar I, Ovsenik M (2010). Posterior crossbite in the deciduous dentition period, its relation with sucking habits, irregular orofacial functions, and otolaryngological findings. American Journal of Orthodontics and Dentofacial Orthopedics 138(1):32-40. PMID 20620831. Source
- Medeiros R, Ximenes M, Massignan C, Flores-Mir C, Vieira R, Porporatti AL, De Luca Canto G (2018). Malocclusion prevention through the usage of an orthodontic pacifier compared to a conventional pacifier: a systematic review. European Archives of Paediatric Dentistry 19(5):287-295. PMID 30054865. Source
Get started
Ready for the training?
The free FaceFormer app guides you through the basic exercises, counts along and reminds you of your sessions. If you wish, a practice from the practitioner directory can support you.
FaceFormer ZERO + ONE
Both material hardnesses for getting started, day and night. The set for adults.
FaceFormer ZERO
The softer FaceFormer for getting started, for children and for the night.
FaceFormer ZERO Children’s Set
ZERO with hygiene box, plush bag and success book with stamp.
FaceFormer training aims to restore the physiological setting of the basic functions of breathing, swallowing and head balance, with lip closure and the tongue reference position, thereby creating the conditions under which symptoms can improve. It does not replace a medical assessment. You can find practitioners near you in the practitioner directory.
