Orthodontic Root Resorption Versus Orthodontic Apical Root Shortening

I would like to begin this editorial guest essay with an apology:

In the publication named “The highly cited orthodontic articles from 2000 to 2015” ¹ that appeared in the January 2018 issue of The American Journal of Orthodontics and Dentofacial Orthopedics, 2 articles—“Orthodontically induced inflammatory root resorption part I and part II”,^{2, 3} written by my colleague Atalia Wasserstein and me—were listed in places 22 and 75, respectively. This gave us great honor; however…

Only in very rare situations scientists disclose that they were wrong. This time it is us. Therefore, I want to apologize to all the readers of this journal by saying that only lately we came to the understanding that we were part of the misunderstanding related to the process of root resorption and, further, that the profession needs to rout its way differently, as the path it took for the past 110 years, studying and researching the subject of orthodontic root resorption (ORR), did not give any real scientific evidence of the unquestionable factors that are responsible for orthodontic apical root shortening (OARS). It requires special energies to admit, following the abovementioned overwhelming success, that for years we were wrong; however, it is never too late.

We all have to clarify that ORR is a very wide term and has several meanings. For example, when I say to a colleague of mine that one of my patients experienced ORR, he or she will immediately understand that one or several roots of this patient’s teeth became noticeably shorter following the treatment. Here is the basic mistake that brought us, in the past, to believe, for example, that using heavier forces will cause more severe OARS than lighter forces will. Additionally, the unfortunate outcome of this perception or concept is heard, time after time, in law suits against orthodontists (“Due to the heavy forces the defendant had used during the orthodontic treatment, the upper incisors’ roots of the plaintiff became shorter!”). This direct relation between the level of the forces and the amount of OARS was never proven by any randomized control trial. I am sure that many of you are amazed, or even skeptical, but this and many other factors that are written in the long list of those that cause OARS were in fact never truly investigated.

In order to prove it, we have to differentiate between 2 kinds of resorptions: (1) ORR and (2) OARS. Every orthodontic force application changes the homeostasis in the involved periodontal ligament (PDL) and develops local aseptic inflammation. The severity of this inflammation is different in different persons (genetics) and is further dependent on many parameters like the force level, its direction, the root’s morphology of the periodontal construction, the local blood flow and many others. There cannot be tooth movement without this inflammation. As a part of the inflammation, we can detect some root’s surface resorption in different areas of the root—apical, central, and cervical. This resorption is a part of the way the root defends itself from the local environmental changes it experiences and is the initial phase of a remodeling cycle that usually ends with a full recovery, namely the resorbed cementum is rebuilt and there are almost no traces seen on the roots’ surfaces (the cycle is Activation, Resorption, Reversal, Apposition, and Rest). It was found, in numerous short-term in vivo studies, that in the same person, the heavier the applied force is, the more severe inflammation is present (not OARS), and therefore, more resorption is detected, namely more ORR (the number of resorption loci and local resorption depth); however, almost all of those zones are being fully recovered. This process is the normal ORR. There is not even one short-term in vivo study that connected between the amount of this ORR detected during the short-term study period and the long-term OARS seen at the end of the treatment. OARS is a completely different ball game. This happens only in the apical zone. How many times you could detect teeth that following orthodontic treatment became narrower due to resorption? I believe that the answer is never! Shorter yes, but thinner, probably never.

The apical zone is a completely different area than the rest of the tooth surface. (I want to exclude the cervical zone from this paper.) For example, the apical zone includes the bundle of blood vessels that nourish, and the nerve that innervates, this tooth. There is no PDL tissue around this bundle that can defend it. It is obvious that this bundle is stretched along with the movement of the apex, especially in apical anterior–posterior incisal torque movements. It might be that this stretching has to do something with the OARS. There might be some other reasons why the apex is more sensitive to be lost but those are beyond the scope of this paper.

In the next editorial guest essay, I will try to convince the readers that OARS is a social problem rather than an orthodontic problem.