The Class IV Malocclusion

I had written about how teeth are supposed to fit together on February 10th, 2020. You can read the post here. The three classifications dentists use are classes I, II, and III. My colleague Dr. Kevin Boyd has proposed adding a class IV classification. I will get into what that is later—first, a primer on Classes I, II, and III. The classifications only consider how the teeth mesh together or occlude. Where the arches fit in your skull is another matter. We call the skeletal structures and the related soft tissues the craniofacial complex, which goes from the base of the skull down to the larynx.

Class I

 The illustration above shows a Class I (ideal) occlusion. Notice how the point of the upper canine lines up just behind the lower canine. Also, notice how the upper teeth cover the lower teeth, which is the norm. 

Class II

A Class II bite occurs when the upper teeth are forward of the normal position. The red line in the illustration below marks the normal position. Notice how the front teeth are positioned anterior to the ideal position.

Class III

Finally, a class III bite is when the lower teeth are forward to the normal position. The front teeth are in an underbite, also called an anterior cross-bite. Again, the red line is where the canine tip should line up.

Arch Width

Another essential component of a good bite is the arch shape and size. The form of the arches should be U-shaped or close to it, and the distance between the first molars should be at least 40 to 45 millimeters, ensuring adequate space for the tongue. When the arches are wide enough, they provide more space for proper breathing. The position of the arches within our skull, or craniofacial respiratory complex, matters more. The upper and lower arches must match in size; otherwise, the teeth will not mesh well. When the arch sizes are at issue, orthodontists refer to the problem as a skeletal one. Treatment options for younger patients include arch expansion appliances, while surgeries in combination with conventional orthodontics to move the jaws are the norm for adults.

Sagittal Problems 

Orthodontists, airway-focused dentists, and anyone familiar with the craniofacial respiratory complex use lateral radiographs (X-rays) to measure the arches from front to back, otherwise known as the sagittal plane. Previously, a class II malocclusion was considered an overgrowth of the upper arch because the teeth have a buck-toothed appearance. Conversely, when the lower jaw juts too far forward in a class III relationship, the assumption is that the lower jaw is too big.

The Cephalometric Analysis

The lateral x-ray can be taken traditionally or constructed from a 3-D image known as a cone beam, CBCT, or just a CAT scan for short. First, an analysis of the lateral view of the craniofacial bones and soft tissue is done by plotting points. Lines are then connected to specific points, and angular analyses are performed. Finally, from the data, a determination is made of the relative positions of both jaws to other landmarks, showing whether one or both are in the correct positions and are fully developed.

Kevin Boyd and the Class IV Malocclusion

As I have described in this post, our jaws are smaller than they should be due to various factors, soft food being a prominent contributor. In addition, many cephalometric analyses show that classes I, II, and III bites result from inadequate growth of BOTH jaws, particularly in the sagittal (front to back) plane. Therefore, Dr. Boyd has proposed this condition as a class IV malocclusion. The upper jaw is generally the real problem because the lower jaw is trapped behind it. So if the upper jaw is not large enough, the lower jaw is held back, resulting in a smaller airway-one where the tongue can block breathing, especially when we sleep. This situation is a risk factor for sleep apnea. Until this classification is adopted, many orthodontic treatments will not address the airway. This will result in lower quality of life for many.

The Correction

https://www.researchgate.net/publication/262672055_Comparison_between_cavum_and_lateral_cephalometric_radiographs_for_the_evaluation_of_the_nasopharynx_and_adenoids_by_otorhinolaryngologists/figures

Early intervention is crucial, as growth deficiencies do not self-correct. Unfortunately, we grow tall, but our facial bones do not appreciably grow much past ten. At birth, our head size is already 60% formed. By 1-3, it is 74%; by 6-10, it is 91%, and by 10-17, it is 100%. Thankfully, sagittal growth is achieved by early correction of the arch width. In the diagram above, the width of AD1 and AD2 (blue and green) usually increase with only the expansion of the arches. They represent the width of the airway.

Early intervention typically includes a special physical therapy called myofunctional therapy to ensure that the tongue and other muscles are not impeding growth. Additionally, removable myofunctional trainers like the one pictured above can be worn by very young children. Pacifiers and thumb habits, which interfere with proper development, are removed via these appliances as well. Fixed and removable expanders can be done; finally, extra-oral appliances can be used with older children to achieve proper sagittal growth.

Treating adults is trickier but is routinely done. Arch expansion can be done using traditional orthodontics. Additionally, surgeries to advance one, or both jaws are commonly done. They are called maxillomandibular advancements, MMA, or orthognathic surgery. If you want to have an evaluation by a qualified professional, the American Academy of Physiological Medicine and Dentistry, AAPMD can help. Click on this link for a list of practitioners near you.