Dental occlusion (Angle classifications)

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The mouth is made up of two key bones: the mandible, which is the bone beneath the bottom row of teeth; and the maxilla, which is the bone above the top row of teeth.
The bones are lined by the gums and have an alveolus, or socket, for each tooth. Since the mouth is symmetrically divided down the middle, let’s look at one side of a mouth containing the permanent, or adult, teeth.
The teeth that pair up vertically have the same names. Starting in the center, first, there are the central incisors and then the lateral incisors.
And incisors are used for cutting into something like a juicy peach. Next, are the canines, which get their name from being the same teeth that are extra long and sharp in dogs.
They’re also called the cuspids, which comes from the word cusp, meaning point. These are used for gripping and tearing into food like a piece of meat.
Then, there are the first and second premolars or bicuspids which have two cusps each. Next comes the first permanent molars and the second permanent molars.
Molars usually have four to five cusps, and are great for crushing and grinding food. Lastly, there are the third permanent molars, or wisdom teeth, which, in some people, never erupt at all.
All together, that makes 32 permanent teeth.The front teeth from canine to canine are called anterior teeth. The rest are called the posterior teeth.
Each tooth has five surfaces that are named based on their location and function. Each tooth has one chewing surface.
The chewing surface of posterior teeth are called occlusal surfaces, and the cutting edges of anterior teeth are called incisal edges.
Each tooth has two proximal surfaces which are surfaces that face adjacent teeth. Proximal surfaces are mesial when they are closer to the midline of the mouth and distal when they are away from the midline.
Tooth surfaces next to the face, the ones resting next to cheek or lips, on the upper and lower teeth are called facial surfaces.
Facial surfaces of posterior teeth are sometimes called buccal surfaces.The facial surfaces of anterior teeth that face the lip are called Labial surfaces.Surfaces that face the tongue on lower teeth are called lingual surfaces and the surfaces that face the palate on the upper teeth are called palatal surfaces.
Each anterior tooth, including the central and lateral incisors and the canines, has a cingulum, which is the name of the little hump about one-third of the way from the gums toward the occlusal surface of the tooth.
The occlusal surface of the molars and premolars, have a central fossa and ridges - like a mountain ridge - that arise from cusps.
The marginal ridges connect the buccal and lingual or palatal cusps, and the triangular ridges start at cusp tip and terminate in the central groove.
Transverse ridges connect facial and lingual cusps through the center of the tooth and oblique ridges, which are only seen in upper molars, connect the distobuccal cusp to mesiopalatal cusp.
The intersection of two ridges forms a groove and the intersection of three or four ridges forms a pit. There are also multiple grooves or valleys that run between cusps and each one is named for its location.
For example, the valley running across the length of the tooth is called the central groove, and the one running outward from the center in the section of the tooth where the mesial and buccal sides collide is called the mesiobuccal groove.
Now, the point or plane where a tooth touches an adjacent tooth to the side of it is called a proximal contact. Embrasures are the V-shaped spaces that occur between teeth, right next to where side-by-side teeth make contact with each other.
Finally, there’s the incline, which refers to the steep planes of teeth, including the canines, that lead up to the cusp or point of the tooth, kind of like the side of a mountain leading up to the peak.
Dental occlusion refers to the way in which the teeth line up with each other as the jaw goes from open to closed. So malocclusion is when the teeth don’t line up properly, and Angle’s classification of malocclusion is a system used to categorize that.
The system bases everything on the position of the maxillary first permanent molar. And it was designed this way because its creator, Edward Angle, believed that the maxillary first molar reliably stayed where it was after eruption while the other teeth tended to have a bit more movement.
In people who don’t have maxillary first molars, he based the system on the location of the canines instead. In those who have maxillary first molars, Angle’s classification states that the mesiobuccal cusp, which is the cusp at the intersection of the mesial and buccal sides of the tooth, normally lines up with the buccal side of the mandibular first molar’s groove, rather than right in the middle of the valley.
In the canine system, the maxillary canine slides right down in between the mandibular canine and the mandibular premolar so that it sits half on the distal part of the mandibular canine and half on the mesial part of the mandibular premolar.
In general, the teeth align on an imaginary arch called the line of occlusion. For the maxillary teeth, it runs through the central fossa of each posterior tooth and through the cingulum of each anterior tooth.
As for the mandibular row, it runs through each buccal cusp of the posterior teeth and the sharp, incisional edges on the anterior teeth.
This produces a normal small overbite, which refers to the vertical distance that the maxillary central incisors hang over the mandibular central incisors.
It also produces a normal small overjet, which refers to the horizontal distance that the maxillary central incisors extend forward in front of the mandibular central incisors.
Angle’s classifications of malocclusion are broken down into classes. In the molar system, class I malocclusion is characterized by a mesiobuccal cusp of the maxillary first permanent molar aligning with the mesiobuccal groove of the mandibular first molar.
In the canine system, class I is characterized by the maxillary canine’s mesial incline landing on the distal incline of the mandibular canine and, similarly, the distal incline of the maxillary canine colliding with the mandibular first premolar’s mesial incline.
Angle’s class I is very common, but it can be complicated by other tooth or jaw abnormalities which can result in overcrowding and alignment irregularities.
This results in a normal, mesognathic, straight facial appearance from the side. In the molar system, in class II malocclusion, also called distocclusion, the mandibular teeth are distal to the maxillary teeth so that the mesiobuccal cusp of the mandibular first molar is aligned with the buccal groove of the maxillary first molar.
In the canine system, class II is characterized by the maxillary canine’s mesial incline landing on the anterior portion of the distal incline of the mandibular canine, and the distal surface of the mandibular canine sitting at least one premolar’s width posterior to the maxillary canine’s mesial surface.
This arrangement can be caused by many different irregularities including overcrowding of teeth resulting from a mandible that’s relatively small for the mouth.
This results in a retrognathic, or convex facial appearance from the side. Class II malocclusion also has subtypes.
Class II, division 1 is characterized by proclined maxillary front teeth, meaning the bottoms of the teeth incline forward, which gives them a protruding appearance.
This results in an overjet of these teeth, often in the setting of an undersized mandible and chin. The upper arch is said to resemble a V-shape.
Class II, division 2 represents the opposite situation, where the central incisors are retroclined, or angle inwards toward the mouth, and the lateral incisors can either have a normal incline or can be proclined.
The upper arch is typically wide, and affected individuals have a deep overbite, usually the setting of a normally-sized mandible.
There’s also class II sub-division, which is where one side of the mouth has a class II occlusion, and the other side has a class I occlusion.
In the molar system, class III malocclusion, also called mesioocclusion, is characterized by a mesiobuccal cusp of the maxillary first permanent molar that aligns posterior to the mandibular first permanent molar’s mesiobuccal groove or in the embrasure between mandibular first and second molar.
In the canine system, class III is characterized by the distal surfaces of the mandibular canines shifting, so that they are anterior to the mesial surface of the maxillary canines by the width of at least one premolar.
The mandibular incisors are also in a crossbite, meaning the mandibular canines have crossed under the midline of the maxillary molars and have become the more lingual of the two teeth.
This can be caused by various irregularities including overcrowding of teeth.This results in a prognathic, or concave facial appearance from the side.
Class III has subtypes as well. True class III malocclusion, also called the skeletal subtype, is a genetic condition resulting in either a relatively small maxilla or a relatively large mandible.
Pseudo-class III malocclusion, also called the postural or false subtype, is a result of an anterior shift in the mandible.
This can result if the canines or incisors collide too early as the permanent teeth erupt and settle into their closure positions.
This can also occur if the posterior deciduous, or baby, teeth are lost too early in life. Lastly, there’s the class III sub-division, where a class III malocclusion occurs on one side of the mouth while the other side of the mouth has a class I occlusion.
All right, as a quick recap... Class 1 malocclusion has essentially the same molar relationship as normal occlusion and results in a straight facial profile.
Class 2, or distocclusion, results in an overjet and has two divisions where division one has proclined central incisors and division two has retroclined central incisors.
It results in a retrognathic or convex facial profile. Lastly, class 3, or mesioocclusion, results in a negative overjet and has two divisions with a skeletal class determined by genetics, and a pseudo class caused by an anterior shift in the mandible.
It results in a prognathic, or concave facial profile.