Bite classes are a classification that describes where the upper and lower first molars sit relative to each other, front to back, when the teeth are closed, and they are the most commonly used language in orthodontics. In Class I, the molars are in the correct relationship; if there are problems such as crowding or gaps, they relate to alignment. In Class II, the lower molars sit behind where they should be; in Class III, they sit in front. This classification alone is not a diagnosis; however, determining your class at the examination, together with the question of how much of the problem comes from the teeth and how much from the jaws, forms the backbone of the treatment plan.
How is the bite class determined?
The classification is based on the Angle classification, first described at the beginning of the 20th century and still in use today. The reference point is the outward-facing front cusp of the upper first molar and the groove on the outer surface of the lower first molar. The following are also assessed at the examination:
- The relationship of the canines: If the molars are missing or have shifted, the canines can be a more reliable indicator.
- The right and left sides separately: The two sides can be in different classes. This is usually seen together with a midline shift; for details, see our midline shift page.
- Horizontal and vertical overlap of the front teeth: How far the upper front teeth sit in front of the lower teeth (overjet) and how far they sit over them (overbite) is measured.
- The position of the jaws: On a cephalometric X-ray taken from the side, the position of the jaws relative to the skull base and to each other is calculated with angles.
Why does the difference between a dental class and a skeletal class matter?
The Angle classification describes the relationship of the teeth; it does not describe the relationship of the jaws. For example, a Class II bite can result from the lower jaw being set back, or from the upper teeth having drifted forward while the jaws are in harmony. In the first case there is a skeletal problem, in the second a dental problem, and the treatment approach differs. Dental problems can usually be corrected with braces or clear aligners. With skeletal problems, appliances that guide the jaws are considered during the growth years, while camouflage or jaw surgery is considered for those whose growth is complete. For general information on jaw structure, see our article on jaw deformities.
What does the classification not show?
The Angle classification describes only the front-to-back relationship. Yet the bite is three-dimensional. Vertical problems (open bite, deep bite) and transverse problems (narrow jaw, crossbite) do not show up in the classification; for this reason, treatment for two patients in the same class can be very different. In addition, the classification does not include other information that affects the treatment decision, such as how the teeth harmonize with the face and lips, the condition of the gums or the jaw joint. That is why the orthodontist interprets the class not on its own but together with facial analysis and X-ray findings. Saying 'Class II' at the examination is a starting point; the treatment plan is made after all three dimensions have been assessed.
Why are bite problems treated?
Bite problems are not only about appearance. A misaligned bite can lead to overloading and wear on some teeth, a risk of protruding teeth breaking from a knock, gum recession on teeth in a reverse bite, and an increased risk of cavities and gum disease because of hard-to-clean areas. Some people also have difficulty chewing and speaking. On the other hand, not every class difference requires treatment; minor differences can be monitored if they do not impair function and do not bother the person. The decision is guided by assessing the findings and expectations together.
How is treatment planned for a Class I bite?
In Class I, the jaws are in harmony front to back. This does not mean the bite is free of problems; crowding, gaps between teeth, open bite, deep bite or crossbite can also occur within Class I. Treatment targets these problems and is carried out while maintaining the molar relationship. Class I cases are the group in which clear aligner treatment is most often used; mild to moderate crowding or spacing problems can be planned with the Invisalign system in suitable cases. Related pages: clear aligners for crowding and clear aligners for deep bite.
How is treatment planned for a Class II bite?
Class II is divided into two subgroups, and this distinction affects treatment:
- Division 1: The upper front teeth are tilted forward, with a noticeable distance between them and the lower teeth. The lips may close with difficulty; protruding teeth are more easily damaged in falls and knocks.
- Division 2: The upper central incisors are tilted inward, the lateral incisors may stick out, and the bite is often deep. Viewed from the outside, the teeth may not look protruding.
Treatment options vary depending on age and the source of the problem:
- Growing children and teenagers: If the lower jaw is set back, functional appliances or aligners that position the lower jaw forward; if the upper jaw has grown too far forward, headgear in some cases.
- Adults with dental Class II: Moving the upper molars back, Class II elastics or, if necessary, camouflage with extractions in the upper jaw. These movements can be done with fixed braces or, in suitable cases, with clear aligners.
- Adults with marked skeletal Class II: Orthodontics combined with jaw surgery.
For detailed information, see our retruded lower jaw treatment and clear aligners for protruding teeth pages, and for general information on protruding upper teeth, our article on protruding upper teeth.
How is treatment planned for a Class III bite?
In Class III, the lower molars sit forward; in most cases there is a reverse bite or edge-to-edge bite at the front teeth. In this class, the first question is whether the problem stems from an overgrown lower jaw, an underdeveloped upper jaw, or the lower jaw sliding forward when closing (pseudo-Class III).
- In children: Pseudo-Class III is often resolved by correcting the teeth. For an underdeveloped upper jaw, expansion and a face mask are used; these treatments respond better at a young age.
- In adults with mild cases: Camouflage by moving the lower teeth back and the upper teeth forward; in suitable cases, with clear aligners.
- In marked skeletal cases: Because lower jaw growth finishes late, surgery is planned together with orthodontics after it is confirmed that growth has ended.
For details, see our underbite (forward lower jaw) treatment page.
How does the bite class affect suitability for clear aligners?
Clear aligners move teeth; they do not change the size of the jawbones. For this reason, suitability depends less on the class itself than on the source and size of the problem:
- Class I cases: Usually suitable for aligner treatment.
- Dental and mild to moderate Class II or III: Aligner treatment is possible with elastics, mini-screws when needed, and planned tooth movements.
- Marked skeletal cases: Aligners alone are not enough; they can be used together with appliances during the growth years or with surgery in adults.
If class correction is needed with aligner treatment, the order of movements and the period in which elastics will be used can be seen in advance in the ClinCheck plan. Wearing the elastics as directed by the orthodontist affects the outcome as much as wearing the aligners 20–22 hours a day; if elastic wear lapses, the molar relationship may not be corrected as planned. Other criteria for aligner suitability are explained on our who are clear aligners for page.
What should you ask about your class at the examination?
- Which class is my bite in, and are both sides the same?
- Is the problem dental, skeletal or both?
- How does my stage of growth affect the treatment options?
- Will the recommended treatment change my profile, or will it only correct the bite?
- What is the risk of relapse after treatment, and how long will I need to wear a retainer?
For more thorough preparation, you can use our orthodontic checkup question list page. You can find all types of treatment on our orthodontic treatments page.