The Orthodontics Professors
the latest in contemporary & evidence-based orthodontics
BY TUNG T. NGUYEN
This study, published in the January 2016 issue of the AJODO, followed 43 Class I patients treated with 4 bicuspid extractions for 5 years during retention. The mean age of the subjects was 13.6 +/- 1.4 at the start of treatment and 16.1 +/- 2.0 at the end of treatment. All subjects had maxillary Hawley retainers and mandibular 3-3 fixed retainers. Crowding, spacing, intercanine distance, and incisor angulation, along with multiple dental measurements were made for initial, final, 1-year and 5-year retention records.
30% of the patients had at least one extraction space reopen, with the majority occurring within the first year of retention. Extraction space tended to reopen more in the maxilla (2.5 to 1 ratio) than the mandible and often times only in 1 quadrant. In addition, the reopened extraction space tended to close at the 5-year retention point.
WHAT THE PROFESSOR THINKS
The extraction debate continues to be a source of controversy in our profession. We make decisions between expansion and extraction based on our practice philosophy / training, esthetic preferences, the degree of crowding, and of course, stability. Proponents of extraction will cite the stability of tooth movement as a major advantage. However, it may be the magnitude of tooth movement that has more to do with stability – not simply whether one extracts or expands.
The authors found that the larger degree of incisor retraction and smaller the initial crowding, the more likely premolar extraction space were to reopen; ie: the farther you move teeth, the more likely they are to return to their original anterior-posterior (A-P) position. It is interesting to note that when the initial crowding was at least 11.63mm, none of these subjects showed space opening. When the initial crowding was only 8.39mm, these subjects had 2.6mm of incisor retraction and tended to show space opening. Could 2-3mm of AP movement of the incisor be the threshold for relapse? Unfortunately, the sample size is too small to make that assumption.
The authors should have reported the size of the extraction space opening. 0.25-0.5mm is often clinically insignificant, whereas 1-2mm of space opening is often a source for interdental food impaction.
It is important to note that extraction spaces tended to decrease at the 5-year retention mark. Was that due to late mandibular growth? Bjork’s studies have already hinted at that point, but we need more data.
The Bottom Line: Regardless of whether you extract or not, careful consideration of retention strategy is needed, especially when teeth are moved greater distances. That is true for both growing and non-growing patients.
Article Reviewed:Garib D, Bressane L, Janson G, Gribel B. Stability of extraction space closure. Am J Orthod Dentofacial Orthop 2016;149:24-30.