We are pleased to participate in this Point/Counterpoint debate regarding corticotomy-facilitated orthodontics, also known as accelerated osteogenic orthodontics or periodontally accelerated osteogenic orthodontics. Drs Wilcko and Wilcko have presented their beliefs in the “Point” article. Our assignment is to present and justify an opposing viewpoint. Actually, there are some statements by Drs Wilcko and Wilcko with which we agree. We disagree with other statements. Finally, some issues regarding this procedure were not discussed, and we will raise these in our “Counterpoint” article. Our goal is to answer the following question for the orthodontic clinician: Is corticotomy-facilitated orthodontics an efficacious, effective, and efficient method of accelerating tooth movement in adult orthodontic patients? Before we begin, let us define these terms. According to accepted definitions, (1) efficacy measures how well treatment works in clinical trials or laboratory studies under ideal conditions; (2) effectiveness measures how well a treatment works in routine clinical practice; and (3) efficiency measures the outcome of a procedure by evaluating the value received relative to the costs in terms of time, money, and morbidity. With this in mind, we will divide this article into a discussion of 7 major questions.
Does alveolar corticotomy result in acceleration of tooth movement?
We agree with Drs Wilcko and Wilcko on the answer to this question; alveolar corticotomy does induce an acceleration of tooth movement. This effect has been documented in rats, dogs, cats, and humans. The best of these experiments were performed using a split-mouth design, with a corticotomy on one side and the opposite side of the dental arch used as the control. A calibrated force is placed on the teeth in both the right and left quadrants, and the rate of tooth movement is calculated by measuring the distance moved over time. The outcomes of these experiments are typically uniform and show that the rate of tooth movement is accelerated on the corticotomy-treated side.
How much acceleration in the rate of tooth movement can be expected? Most animal experiments show that the amount of movement doubled over the time of the experiment. Since most animal experiments extend for 2 to 4 months, and the teeth on the control sides in rats and dogs move about .5 mm per month, the teeth on the corticotomy-treated side would move at the rate of about 1 mm per month.
How does corticotomy produce accelerated tooth movement?
On this topic, we agree partially with Drs Wilcko and Wilcko but would like to differentiate what happens in experimental animal studies and its translation to what is believed to happen in humans. We do agree, and past research has confirmed conclusively, that a corticotomy produces an injury to the alveolar bone that results in an exaggerated response from that organism to send cells to the injured area to facilitate healing. Drs Wilcko and Wilcko have already described this process as the regional acceleratory phenomenon. But how does the regional acceleratory phenomenon facilitate accelerated orthodontic tooth movement?
Drs Wilcko and Wilcko believe that the increase in the rate of tooth movement is due primarily to a demineralization process that occurs in the cancellous bone surrounding the tooth socket and secondarily to alterations within the periodontal ligament. We would propose a different viewpoint.
First, the studies showing demineralization in the interproximal bone surrounding the roots of teeth were performed in rats. Can we translate what happens in rats to humans? Is the extent of the damage inflicted on the alveolus via corticotomy in a rat similar to or perhaps more pronounced than the injury that occurs during corticotomy in a human? Similar studies on the impact of corticotomies in dogs and cats have not reported the demineralization effect seen in rats. Perhaps the demineralization effect is not as pronounced in humans. Although Drs Wilcko and Wilcko stated that a transient localized demineralization-remineralization process can be verified by a surface-computed tomographic scan, we seriously doubt that this type of scan has sufficient resolution to identify accurately the differences in cancellous bone mineralization in humans.
[T]he length of the regional acceleratory phenomenon is probably about 4 months. . . . Therefore, we conclude that corticotomy-facilitated tooth movement is only effective during the 4 months of the regional acceleratory phenomenon. After that, the rate of tooth movement would return to normal.
We must also remember that the tooth root is not moving through the bone. The tooth socket is translating through the bone, and the periodontal ligament facilitates this movement. Animal experiments have clearly shown that an alveolar corticotomy produces a difference in the periodontal ligament during initial tooth movement that results in accelerated tooth movement. Let us explain.
Many studies have documented the histologic and physiologic effects of the initial stages of tooth movement and have shown that compression of the periodontal membrane between the tooth root and the socket wall on the pressure side results in damage and hyalinization of the periodontal ligament. When hyaline forms in the periodontal ligament, bone resorption is inhibited as long as the hyaline is still present. Experiments in dogs have shown that the hyaline is gradually removed from the periodontal ligament by macrophages that differentiate from mesenchymal cells that travel to the area. However, in these experiments, it can take up to 4 weeks for the hyaline to be removed. During this initial period, no tooth movement occurs.
When an alveolar corticotomy is performed near the tooth to be moved, histologic results show that the regional acceleratory phenomenon accelerates the appearance of the macrophages that remove the hyaline as early as 1 week after the initiation of orthodontic force. Earlier removal of the hyaline allows earlier bone resorption, resulting in more rapid tooth movement compared with the noncorticotomy side. So, it is clear that the regional acceleratory phenomenon facilitates the acceleration in the rate of tooth movement.
How does corticotomy produce accelerated tooth movement?
On this topic, we agree partially with Drs Wilcko and Wilcko but would like to differentiate what happens in experimental animal studies and its translation to what is believed to happen in humans. We do agree, and past research has confirmed conclusively, that a corticotomy produces an injury to the alveolar bone that results in an exaggerated response from that organism to send cells to the injured area to facilitate healing. Drs Wilcko and Wilcko have already described this process as the regional acceleratory phenomenon. But how does the regional acceleratory phenomenon facilitate accelerated orthodontic tooth movement?
Drs Wilcko and Wilcko believe that the increase in the rate of tooth movement is due primarily to a demineralization process that occurs in the cancellous bone surrounding the tooth socket and secondarily to alterations within the periodontal ligament. We would propose a different viewpoint.
First, the studies showing demineralization in the interproximal bone surrounding the roots of teeth were performed in rats. Can we translate what happens in rats to humans? Is the extent of the damage inflicted on the alveolus via corticotomy in a rat similar to or perhaps more pronounced than the injury that occurs during corticotomy in a human? Similar studies on the impact of corticotomies in dogs and cats have not reported the demineralization effect seen in rats. Perhaps the demineralization effect is not as pronounced in humans. Although Drs Wilcko and Wilcko stated that a transient localized demineralization-remineralization process can be verified by a surface-computed tomographic scan, we seriously doubt that this type of scan has sufficient resolution to identify accurately the differences in cancellous bone mineralization in humans.
[T]he length of the regional acceleratory phenomenon is probably about 4 months. . . . Therefore, we conclude that corticotomy-facilitated tooth movement is only effective during the 4 months of the regional acceleratory phenomenon. After that, the rate of tooth movement would return to normal.
We must also remember that the tooth root is not moving through the bone. The tooth socket is translating through the bone, and the periodontal ligament facilitates this movement. Animal experiments have clearly shown that an alveolar corticotomy produces a difference in the periodontal ligament during initial tooth movement that results in accelerated tooth movement. Let us explain.
Many studies have documented the histologic and physiologic effects of the initial stages of tooth movement and have shown that compression of the periodontal membrane between the tooth root and the socket wall on the pressure side results in damage and hyalinization of the periodontal ligament. When hyaline forms in the periodontal ligament, bone resorption is inhibited as long as the hyaline is still present. Experiments in dogs have shown that the hyaline is gradually removed from the periodontal ligament by macrophages that differentiate from mesenchymal cells that travel to the area. However, in these experiments, it can take up to 4 weeks for the hyaline to be removed. During this initial period, no tooth movement occurs.
When an alveolar corticotomy is performed near the tooth to be moved, histologic results show that the regional acceleratory phenomenon accelerates the appearance of the macrophages that remove the hyaline as early as 1 week after the initiation of orthodontic force. Earlier removal of the hyaline allows earlier bone resorption, resulting in more rapid tooth movement compared with the noncorticotomy side. So, it is clear that the regional acceleratory phenomenon facilitates the acceleration in the rate of tooth movement.
How long does the regional acceleratory phenomenon persist after the corticotomy?
Drs Wilcko and Wilcko did not discuss the duration of the regional acceleratory phenomenon after corticotomy, but we believe this question is of utmost importance to determine the effectiveness and efficiency of this procedure. Obviously, if the rate of tooth movement were accelerated by the regional acceleratory phenomenon, then it would be important to know how long this effect can be expected to last. Two studies, one in humans and the other in dogs, provide some insight into the duration of the regional acceleratory phenomenon and its influence on the rate of tooth movement.
In a study comparing the rate of tooth movement in foxhounds with a split-mouth design with a corticotomy performed on one side, the authors reported that the rate of tooth movement peaked between 22 and 25 days and then decelerated. During this 3-week period, the corticotomy-facilitated side moved twice as far as the opposite side. The authors then performed a second corticotomy procedure in some animals after 28 days and found that the higher rates of tooth movement could be maintained over a longer period of time with a second surgery.
Similar findings were reported in a sample of 13 adults whose maxillary canines were being retracted after first premolar extractions. Corticotomy was performed on one side, and the other side was not operated. The rate of maxillary canine retraction was then documented over time. During the first 2 months, the rate of tooth movement on the corticotomy side was twice that of the unoperated side. However, during the third month, the rate was 1.6 times greater, and by the fourth month, the rates of tooth movement on both sides were similar.
Based on the results of these 2 studies, it seems that the length of the regional acceleratory phenomenon is probably about 4 months. Perhaps it could be a bit longer, but the regional acceleratory phenomenon does end, and its impact on accelerating tooth movement would also come to an end. Therefore, we conclude that corticotomy-facilitated tooth movement is only effective during the 4 months of the regional acceleratory phenomenon. After that, the rate of tooth movement would return to normal. To determine whether corticotomy is efficient, we need to determine whether its effect produces a decrease in treatment time for adults.
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