Extractions

Premolar Extractions Controversy

There is probably no facet of orthodontic treatment that has caused as much controversy as the decision to extract, or not to extract, permanent teeth: and more specifically, whether to extract four premolars or to “develop” room for non-extraction treatment.

Besides the obvious reasons of avoiding the trauma and expense of surgery, and the desire to preserve permanent teeth; other alleged negative sequela, such as TMD problems, flattened facial profiles, and “dark buccal corridors” have contributed to the premolar extraction controversy. Like a pendulum, the popularity of premolar extractions has swung back and forth, between the extremes of non-extraction at any cost and “routine” extractions to achieve arbitrary cephalometric norms.

Some of the factors we consider are:

When dealing with a fairly “normal” orthodontic problem (no gross asymmetries) the decision to extract four premolars is straightforward although often not easy. It is impossible to extract less than a whole tooth, and usually the extraction of a tooth on the left requires an extraction on the right to balance the midline. Likewise, lower extractions usually require upper extractions (and visa versa) to prevent excessive overjet or underbite. These parameters normally lead to extraction of four first premolars or to treat as a non-extraction case. There are times when upper premolars only, a single lower incisor extraction, molar extraction, or interproximal enamel reduction (IPR) are appropriate but, in general, the decision for extractions is often framed around “4-bi’s”.

Given the usual all or nothing nature of the premolar extraction decision, it is no surprise that different orthodontists often appear to have conflicting treatment plans for the same patient. The reason is not that they see very different problems or have radically different philosophies of treatment, but rather that each doctor has a different line in the gray area between extractions and nonextraction. Two treatment plans that appear very different can both be based on a similar analysis of the patient’s problem, but end up with very different treatments due to the black and white nature of the decision making process.

It is important to understand that in borderline cases there are no correct or right answers. Both treatments performed by competent orthodontists would produce a good result, but neither is perfect. Each option would have pros and cons, and orthodontists and dentists could (and do!) spend endless amounts of time debating which option is “right”.

We try to avoid extractions as much as possible, but extractions should be considered when esthetics and stability call for it. Truthfully, almost any patient can be treated without extractions and, often, this is technically the easier way. This is the reason that the weekend orthodontic courses aimed at general dentists almost always stress nonextraction treatment.

Where there is a conflict between facial esthetics and dental stability, it is our judgment to favor esthetics. This is not to say that patients with flat facial profiles and extreme crowding should be treated without extractions, nor that patients with full profiles and large tongues should have teeth extracted, but rather that esthetics should be the primary determinant of treatment in any borderline situation. In these cases it is very important that the patient understands the necessity of long-term retention

Contrary to the beliefs of many nonextraction proponents, good scientific studies (evidenced based) done on TMD and orthodontic treatment fail to show any correlation between the development of TMD type problems and the extraction (or nonextraction) of teeth. All dentists can remember patients who develop TMD problems after extraction treatment and, if you feel there is a correlation, you will fixate on these patients. Statistically, you are just as likely to find TMD problems in patients treated nonextraction or, for that matter, patients who never received orthodontic treatment at all.

Scientific studies have also shown that well treated extraction cases do not adversely affect facial profiles. Again, it is easy to visualize patients with flat profiles who have had premolar extractions. Assuming a good treatment decision, these patients would have had a flat profile even if they never had treatment (and an extremely unstable dental alignment if they had been treated without extractions). The truth is: tight facial structures (flat faces) lead to crowding, which leads to extraction rather than extractions cause flat faces. As a matter of fact, the most dished in and flattened faces often belong to those patients whom we have treated without any extractions. Like the TMD controversy, negative esthetic effects attributed to extractions fall into our favorite logical fallacy “post hoc ergo propter hoc” (after this therefore because of this). Other studies have also shown that dark buccal corridors and a narrow smile are not “caused” by premolar extractions.

A good selling point for premolar extractions can be a patient with moderate crowding and well-formed and positioned third molars. Treated without premolar extractions this patient usually needs third molars removed. Extract premolars, close some of the space by mesial movement of the posterior teeth, and hopefully the thirds can erupt and be kept—an exchange of four small, easily removed teeth for four molars that would be difficult to extract. Unfortunately no guarantee can be made that the thirds will always come in with enough room.

There seems to be a great deal of confusion about early expansion treatment (AKA arch development or growth modification). There is a important difference between expanding a constricted upper arch to match a normal lower arch (OK) and significantly expanding both arches in a patient whose arches may be narrow, but are in a normal transverse occlusal relationship to each other (not OK). Although it is possible to upright lingually verted lower posterior arches (which may have collapsed in, to compensate for a narrow maxillary arch), it is not possible to expand the mandibular basal bone, as there is no suture to distract as in the maxilla. Of all the inviolate “facts” of orthodontics, one of the most established is the stability of the lower inter-canine width. Expansion beyond the original width is almost a guarantee of collapse and recrowding.

Every decade or so a new “magic bullet” comes along promising the ability to create space and avoid extractions or unstable expansion. The latest iteration of this is the Damon™ orthodontic bracket with its manufacturer’s promise of extremely light forces that “grow” more room than regular braces. As usual, no good science backs up these claims!

In an attempt to avoid first premolar extractions, various alternatives can be considered:

o Expanding the arch, especially in a flat-faced individual, is often preferable to extractions, with the understanding this is an unstable correction and perpetual detention will be needed.

o For patients with a good posterior occlusion, a good upper arch with relatively small upper incisors, moderately severe lower crowding, and minimal overbite, the extraction of a lower incisor can be considered. Extraction of an incisor should be evaluated very carefully, for it can result in an untreatable problem with excessive overjet/overbite in the wrong individual.

o Interproximal enamel reduction (IPR) can provide a moderate amount of room but should be reserved for older patients. Excessive IPR as an initial treatment complicates the orthodontist’s ability to correct minor relapses in the future.

o Consider extraction of second premolars rather than first premolars. Theoretically, this reduces the amount of anterior retraction when only some space is needed for crowding and the facial profile is acceptable. This works best when the second premolars resemble the first, but large, molar-like second premolars may provide too much room and small, canine-like first premolars may not work against first molars.

o Distilization of full arches is very difficult so extraction of third molars or even second molars to provide anterior room has never been shown to provide significant space. With the advent of temporary anchorage devises (TAD’s) this may become a “new” way to treat nonextraction…. we’re already trying it!

Bottom line: Extractions are just a tool, not good or bad in themselves. Used right, they improve the quality of treatment, used wrong they may create a poor result.