Orthodontic treatment often evokes questions about third molars, or “wisdom teeth.” Our clinical advisor, Dr. Ken Fischer, has some answers:
“What should be done with the third molars?”
Although frequently congenitally missing, the presence of those teeth, erupted or unerupted, may influence the doctor’s treatment planning. For example, if the second molar needs to be distalized or uprighted, the doctor should be aware of the third molar. If it is present, it will likely interfere with the movement of the second molar. Also, if the doctor is considering the removal of the second molar (due to its condition or position), he or she may want to consider allowing the unerupted third molar to serve as the second molar in lieu of being extracted.
“What is the prognosis for retained unerupted third molars—extract or not?”
One must consider whether removing the retained molars is preventive (to reduce future negative circumstances) or therapeutic (correcting an existing problem).
“When should third molars be removed?”
Every patient is different and assessed individually, however there are some general guidelines that may be followed. One should justify the removal of asystematic teeth, including the wisdom teeth. A third molar can be considered for extraction if:
- it is in decay,
- it is infected,
- there is a pathology associated with it such as a dentigerous cyst, or
- its impacted position is threatening the health of the second molar.
Some dentists believe third molars should be extracted proactively during early adolescence if it is determined that there will be a very low probability there will be enough room for the third to erupt.
Third molar extraction
The most commonly seen scenario for third molar extraction is when the mesially-inclined wisdom tooth is impacted (unable to erupt normally) and placing pressure against the distal surface of the second molar. This condition may cause damage to the second molar and/or a dentigerous cyst may develop around the impacted tooth causing extensive damage to the surrounding bone. Even though impacted, if that tooth is not threatening the health of the adjacent teeth or surrounding bone, there is no requirement for extraction.
Using accepted techniques or experience-based judgement to evaluate the potential for the developing wisdom tooth to not erupt, may lead to a reasoned decision to remove a third molar preventively. If this decision is made, surgically extracting the tooth or teeth before extensive root growth usually results in a less negative abnormality than performing the procedure after full root development occurs.
Treatment plans that include distalizing the second molars should consider the presence and position of the third molar to evaluate if that tooth will limit the distalization. Certain treatment plans may want to replace a missing or defective second molar with the eruption and advancement of the third molar.
Special attention must be given to third molars when clear aligners are used. Even when they have erupted, they rarely display enough of the supra-gingival crown for an aligner to sufficiently cover the crown for optimal adaptation and retention, often causing a poor fit. If the wisdom tooth is erupting during aligner wear, it may interfere with the distogingival margin of the aligner, preventing it from fitting properly.
Many still believe the old adage that eruption of the wisdom teeth causes the lower anterior teeth to crowd. Contemporary research in the literature has convinced many of us that adage should no longer be supported. Late adolescent growth of the mandible forcing the lower anteriors against the lingual of the upper anteriors, causing the lowers to crowd, is a more evidence-based explanation for the observed shifting of the lower incisors.