Risky Business: Is Root Resorption More Likely with Fixed or Removable Appliances? The Latest Evidence Might Surprise You. . .

Root resorption after 12 months in fixed appliances. In the current study, the risk of such resorption was no different with fixed vs. removable appliances.

BY SYLVIA  A. FRAZIER-BOWERS , DDS, PhD

STUDY SYNOPSIS
The authors of Orthodontically-induced external apical root resorption in patients treated with fixed appliances vs. removable aligners, present a thoughtful and relevant clinical study that investigates the relationship of orthodontically induced external root resorption (OIERR) with the use of two different orthodontic treatment modalities (fixed appliances versus Invisalign®).
 
The objective of this case-control study was to determine if an association exists between OIEARR, appliance type, radiographic, clinical, and genetic factors using a backward stepwise conditional logistic regression analysis. OIEARR Cases and controls were selected in a non-random fashion from a private practice and a university clinic. OIEARR was defined as >2mm resorption of at least one incisor after completion of treatment, as judged using panoramic and lateral radiographs.
 
For each of the 372 participants, 12 clinical variables were assessed as well as polymorphisms in 3 genes, Interleukin 1B (IL1B), Interleukin 1 receptor agonist gene (IL1RN), and the osteopontin gene (SPP1).
 
The findings were as follows: of the 12 factors, two were associated with an increase of OIEARR, when controlling for the influence of all of the clinical and genetic factors recorded: 1) clinical case complexity (ABO discrepancy index) and 2) extent of incisor displacement in the sagittal plane.  The results also showed that when subjects were homozygous for the T allele of the IL1RN gene (rs419598) they were 3 times as likely (or 2 times more likely) to experience root resorption.
 
Perhaps more importantly, the predisposition for OIEARR was similar whether using removable or fixed appliances. The odds ratio of 1.66 for predisposition of OIEARR in fixed versus removable appliances, in fact, indicates a modest but not statistically-confirmed increase in OIEARR associated with the use of removable versus fixed appliances.

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WHAT THE PROFESSOR THINKS
The development of root resorption is a topic of growing interest to orthodontists; based on a nationwide survey conducted by the AAO, root resorption was considered a very important clinical issue by 60% of participating orthodontists. Accordingly, the study is timely and presents a unique view of an interesting question: Is root resorption more likely in a cohort with specific genetic factors and treatment modalities?
 
The authors, therefore, conduct a study that may translate into the clinical/practical orthodontic setting as follows:
“Would I advise my patients that one appliance type carries less risk than another in the development of root resorption?”
 
Based on the authors’ analyses, it is clear that the patients studied developed OIEARR at comparable rates with fixed or removable appliances. This finding is quite illuminating since anecdotally the assumption is that removable appliances may be gentler in terms of orthodontic tooth movement and lead to less root resorption.
 
This study ranks modestly in the hierarchy of study effectiveness. Given the retrospective design, systematic (non-random) factors may have determined treatment choice with removable versus fixed appliances.  Also, the analysis considers a high number of variables that may be inter-correlated. In other words, it is likely that several of these factors actually cluster together and they are not independent, which could possibly change the relationship of clinical outcome and etiology.
 
The bottom line is that this study provides an important contribution to our ever-changing understanding of the relationship between specific clinical, genetic, and treatment factors on adverse treatment outcomes, such as root resorption (see the Figure above).  
 
The take-home message when you go into the office on Monday morning is that orthodontically-induced root resorption happens more often than we may imagine, regardless of appliance type.
 
The simple notion that changing orthodontic treatment modality may decrease the risk of root resorption is not supported, based on the evidence here. Given advances in genomic studies, we can speculate that a combination of factors lead to the development of root resorption, with the problem being a defect in the repair mechanism of those who develop moderate or severe root resorption.  The promise of more refined genotype-phenotype correlations that provide a practical tool to predict the risk of root resorption is foreseeable.

Article Reviewed: Iglesias-Linares et al. Orthodontically induced external apical root resorption in patients treated with fixed appliances vs removable aligners. The Angle Orthodontist. January 2017.