How Dentists Assess the Need for Adult Orthodontics

You may know someone who has braces or Invisalign who seemed to have straight teeth before treatment. Indeed, teeth can be in alignment and yet not mesh together well. There are several parameters dentists use to determine whether teeth function together for adequate appearance, speech, breathing, and mastication. Today I am going to talk about some of the things we look at to determine whether orthodontic treatment is required. This post is going to be nothing more than a quick primer. Keep in mind that this post is not intended for you to self-diagnose whether you need orthodontics. If you feel you may have an issue, consult with your dentist.

The way the upper and lower arches fit together is called the occlusion. There are three general classifications of occlusion. There are several methods of classifying occlusion that are beyond the scope of this blog. For the sake of simplicity, I will use the method that employs the third tooth from the midline called the canine or cuspid as a guide.  The illustration below 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. Most patients that have a class I bite do not have ideal occlusion as they may have some crowding, rotations, or other issues. For patients like this, orthodontic movement is for strictly cosmetic reasons if done at all.

Class I (Ideal) Occlusion

Class I (ideal)

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 II Occlusion

Class II

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

Class III Occlusion

Class III

The relationship between the upper and lower front teeth is very important because when the lower jaw moves around during chewing, the lower front teeth slide on the backs of the upper front teeth causing the back teeth to come apart, which protects the back teeth from wear. This is called cuspid or anterior guidance. Additionally, the back teeth can’t tolerate excessive lateral contact, which, when present, can traumatize the nerves and ligaments associated with them, causing pain.

The measure of the horizontal space between the top and bottom front teeth is called the overjet. It usually is 1-3 millimeters, where the upper teeth are covering the lower teeth. When the overjet is excessive, we refer to it as an overbite, which is unfortunate, as overbite refers to something else which I will explain later. In the class III illustration, we see a negative overjet, where the lower front teeth cover the upper teeth when they are together. This situation is commonly referred to as an underbite.

The amount of overlap the front teeth have is referred to as the overbite. Typically, there should be 2-4 millimeters of overbite. When there is an excessive overbite, the upper teeth can obscure the lower teeth when the teeth are in occlusion, which results in wear and breakage over time, pain in the TMJ and muscle soreness. Conversely, there can be no overlap in the front, a condition known as an open bite. Open bites can result in wear and tear on the back teeth, similar to what happens in patients with excessive overjets.

The Dental Arches

Another essential component of an adequate 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 45 millimeters, ensuring adequate space for the tongue. When the arches are wide enough, they provide sufficient space for proper breathing. Both the upper and lower arches must match in size; otherwise, the teeth will not mesh well together. When the arch sizes are at issue, orthodontists refer to the problem as a skeletal one. With skeletal issues, traditional orthodontics alone is not sufficient to correct all problems. 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.

Good Dental Arches. The Black Line Represents the Distance Between The Molars

 Related to arch form is the shape of the palate. A narrow high palate can lead to speech and breathing problems. More and more orthodontists and dentists are practicing airway dentistry, where not only the shape and size of the arches are of concern, their three-dimensional positions are taken into account vis-à-vis the airway space. Three-dimensional imaging facilitates the diagnosis.

The teeth of each arch should touch the neighboring teeth, which leads to a stable situation where the teeth should be able to maintain their positions over time. Additionally, food impaction is much less likely when the teeth maintain contact with each other.

The plane of occlusion is also important. Generally speaking, the back teeth are usually on an even plane, or slightly curved upward as you look further back in the mouth. We call this the curve of spee. Refer to the illustration of the dental arches and note how the back teeth are aligned in a level plane. Sometimes teeth can be below or above the plane, causing interferences when chewing.

Other parameters are rotations of individual teeth, improper angulations, improper positioning of teeth outside of the arch, missing teeth, extra teeth, misshapen teeth, mismatched midlines, and over-retained baby teeth. When a lower tooth is closer to the lips or cheeks than its corresponding upper tooth, it is in cross-bite.

Cross Bite

Malocclusion, which means “bad bite,” is the term dentists use when referring to problems with the bite. The reasons for malocclusions are numerous and complicated. The usual reason is that our jaws are less robust than they used to be due to our less nutrient-dense diets compared to our ancestors, resulting in one or both jaws being too small, too narrow, or too retruded for adequate function.

Other reasons include teeth being misshapen or missing

Teeth can be naturally missing resulting in over-retained baby teeth that don’t have the proper dimensions to occlude well with other teeth. Extractions can result in drifting teeth. Trauma to the teeth can loosen them and change their location. Fractured jaws can heal incorrectly, causing the teeth to become misaligned. Inflammation in the TMJ via trauma or clenching can cause the bite to change. Tooth decay can lead to drifting teeth when extensive enough. Gum disease can loosen teeth and lead to drifting. Oral habits like thumb and pacifier sucking can slowly change the shape of the arch and palate. Excessive tooth wear from grinding or gum chewing can also alter occlusion.

I want you to keep in mind that most people do not have ideal occlusion. In fact, many of my adult patients have several issues with the way their teeth look and fit together but have no problems chewing, have no tooth wear, no problems breathing, and no pain. Do they need orthodontic treatment? My short answer is no. The issues I discussed today are risk factors. Just because you have a rotated tooth does not mean that it will manifest in a problem. On the other hand, if the rotated tooth is causing food impaction, which in turn is leading to gum disease, then orthodontic treatment may be an option. Don’t panic if you identify some of the things I discussed today with your won teeth. If you have any concerns, call your dentist.