When an orthodontist performs an examination, they look at a variety of factors outside and inside the mouth. For instance, we look at jaw gowth and development, tooth eruption sequence, relationships when the patient bites down and many other factors. Orthodontists will categorize the patient’s occlusion into mainly three types of malocclusions.
Angle’s Classification of Malocclusions
In 1890, Dr. Edward Angle, the Father of Orthodontics, published the first classification of malocclusions. He stated that the classification can be based on the mesiobuccal cusp of the maxillary first molar with the buccal grove of the mandibular first molar. We are going to look at the three classifications. The arrows in the above picture show a proper molar relationship.
What is a Proper Occlusion?
A proper occlusion has a Class I molar relationship where the upper molar cusp is in the groove of the lower 1st molar. When this relationship exists, all the teeth will align properly. Other factors for a proper occlusion would included that all the teeth of the upper jaw are slightly over the lower teeth, an overjet. The teeth are in a nice uniform arch and there are no tooth rotations. When we treat a malocclusion, we strive to obtain a Class I molar relationship.
Classification I Malocclusion
Even with a Class I molar relationship, you can still have a malocclusion. A Class I malocclusion will have a proper 1st molar relationship but there will be dental crowding or rotations that classifies it as a malocclusion. A large majority of patients fall into this category.
Classification II Malocclusion
A patient with a Class II malocclusion will have a jaw growth discrepancy where there is a large overjet. Usually the lower jaw is deficient in forward growth causing the overjet. The patient will exhibit a retrusive chin and profile. Most people call an overjet an overbite but the proper term is overjet. A proper overjet is from 1 to 3 mm. Any amount of overjet more than this is not within normal limits. A large group of patients fall into this category.
Classification III Malocclusion
A patient with a Class III malocclusion has an underbite. The patient has a very strong lower forward jaw and their lower front (anterior) incisor teeth are farther forward than their upper incisors, resulting in an anterior crossbite. The lower 1st molar is much farther forward than the upper. Usually a Class III malocclusion is due to the lower jaw growing too far forward. Not very many patients fall into this category. Also, this is the hardest malocclusion to correct. Sometimes orthodontics alone cannot correct a Class III malocclusion and orthognathic surgery is required.
Orthognathic surgery is where an oral surgeon moves the jaws into a proper Class I occlusion through surgery. If a patient with a Class III malocclusion starts treatment at an early age, it lessens the chance of having surgery to correct the bite.
So during the orthodontic examination, you now know the reason an orthodontist asks you to bite down and repeat the bite. It is to classify the type of malocclusion and evaluate other factors of your bite.