Updates on periodontally accelerated osteogenic orthodontics

ABSTRACT

Purpose:

The objective of this review was to investigate the recent reports on periodontally accelerated osteogenic orthodontics (PAOO) in major orthodontic journals in order to summarize the relevant updates and clinical findings.

Materials and methods:

The PubMed database was searched for PAOO-related articles published in The American Journal of Orthodontics and Dentofacial Orthopaedics (AJO-DO), The Angle Orthodontists (AO), The European Journal of Orthodontics (EJO), The International Journal of Oral and Maxillofacial Surgery (IJOMS), The Australian Orthodontic Journal (AOJ) and other major orthodontic journals. Keywords used for searching were corticotomy, PAOO, piezocision and micro-osteoperforations (MOPs). Based on the information from the titles and abstracts, relevant articles on PAOO were selected and analysed.

Results:

As an alternative surgical method, the PAOO technique can accelerate adult patients’ tooth movement and shorten the treatment time. Compared with conventional orthodontic treatment, the PAOO technique shows advantages in terms of treatment cycle and treatment effect. Currently, scholars tend to believe that the PAOO technique does not increase the risk of root resorption, periodontium injury, and alveolar bone defect.

Conclusions:

Long-term efficacy of PAOO lacks randomized controlled clinical trials. However, with the deepening of research, PAOO – a relatively mature means of accelerating tooth movement – is likely to be more attractive in orthodontic treatment.

KEYWORDS:

• Corticotomy
• PAOO
• piezocision
• MOPs
• periodontal hygiene

Development review

Corticotomy

Since the nineteenth century, there have been attempts to use surgical methods to assist orthodontic treatment. Corticotomy-facilitated tooth movement was first described by L.C. Bryan in 1893 [1]. After that, in 1959, Köle [2] first reported the corticotomy technique, describing it as a method to enable rapid tooth movement. Köle suggested that the disruption of the continuity of the bone cortex would reduce the resistance to tooth movement during orthodontic treatment so that orthodontic treatment could be completed in a shorter cycle. Köle’s surgical method consists of three main procedures: a vertical buccal cortical incision, a vertical lingual incision, and a subapical horizontal osteotomy; this allows the target tooth to form a complete ‘bony block’ and speed up the target tooth’s movement. However, this method was not popularized in practice because of its large trauma and poor patient acceptance.

Modified corticotomy

In 1975, Düker [3] studied Köle’s surgical method; using a beagle dog experiment, Düker showed that if the vertical incisions on the buccal and lingual sides of Köle’s method were made and the alveolar crest was avoided, better periodontal attachment and soft tissue morphologies could be obtained after surgery. Thus, he changed the buccal and lingual vertical incisions design to the buccal vertical incisions from 2 to 3 mm below the alveolar crest to 2 mm below the apex. After that, the corticotomy technique underwent several minor modifications in clinical practices. What is called the corticotomy now usually tends to indicate the modified corticotomy, with a large flap to fully expose the alveolar bone and cuts between the teeth but lighter force to move teeth [4]. Relative adverse effects such as root resorption and periodontal injury were not found in recent study (Table 1) [5].

Table 1. Features of surgically assisted orthodontics

	Corticotomy	PAOO	Piezocision	MOPs/Piezopuncture
Flap	Flap elevation [2]	Flap elevation [7]	Flapless [13]	Flapless [16,17]
Bone grafting	Without bone grafting [4]	With bone grafting [4]	With limited bone grafting [13]	Without bone grafting [16,17]
Cortical incision manner	Cut [4]	Cut and perforation [4]	Cut with piezo-knife [13]	Perforation with ultrasonic-assisted device [16,17]
Tooth movement	Accelerated [5]	Accelerated [5,8,9,12]	Accelerated [14,15]	Unclear [14,18]
Root resorption	Seems no effects [5]	Seems no effects [5,9,12]	Little or no effects [14,15]	Seems no effects [14]
Periodontal health	Unaffected [5]	Improved [5,8,9,12]	Unaffected [14,15]	Unaffected [14]

Periodontally accelerated osteogenic orthodontics

In the early twenty-first century, Wilcko et al. [6] proposed accelerated osteogenic orthodontics (AOO) and periodontally accelerated osteogenic orthodontics (PAOO) based on the research of Köle and Düker. The main characteristics of the PAOO technique include placing of bone graft material after corticotomy and receiving bone augmentation during orthodontic treatment. This technique has the benefit of decreasing the duration of treatment and also provides a way for orthodontists to address bone defects during orthodontic treatment. In 2009, Wilcko et al. [7] reported a modified PAOO technique, which acclaimed the reduction of orthodontic treatment time to one third to one fourth of the conventional treatment cycle. Other studies [5,8–12] tend to show that the PAOO technique can reduce root resorption, shorten the duration of orthodontic treatment, increase bone thickness, and in some cases reduce the need for orthognathic surgery (Table 1).

Piezocision

In 2009, Dibart et al. [13] proposed a new surgical-assisted method. This method does not require flaps; rather, only a vertical incision is made at the attached gingiva, and an ultrasonic osteotomy knife is inserted along the vertical incision to cut the bony cortex. This procedure is called piezocision. If the patient requires intraoperative bone grafting, blunt dissection can be performed between vertical incisions to form a subperiosteal tunnel for bone grafting. This procedure has the advantages of less trauma and bone augmentation. Available literature tends to show no increased root resorption or periodontal injury compared with conventional orthodontics (Table 1) [14,15].

Advanced surgical methods

In 2013, by Kim et al. explored another ultrasonic-assisted method, piezopuncture, to directly perforate the bony cortex through the attached gingiva in the target area with the aid of ultrasonic surgical instruments. In Kim et al.’s animal research [16], piezopuncture significantly accelerated the tooth movements at all observation times, and the acceleration was the greatest during the first 2 weeks for the maxilla and during the second week for the mandible. To evaluate the effect of micro-osteoperforations (MOPs) on the rate of tooth movement, Alikhani [17] conducted a clinical study and concluded that MOPs increased the rate of tooth movement by 2.3 times. However, several conflicting systematic reviews [14,18] indicated that no accelerated tooth movement was found in the MOPs group and insufficient evidence to support the single use of MOPs could accelerate tooth movement. Furthermore, rare adverse effects on gingival recession and root resorption were found in recent researches (Table 1) [14,18].

In 2015, Cassetta et al. [19] described an innovative, flapless procedure combining piezoelectric surgical cortical micro-incisions with the use of a 3D-printed CAD/CAM surgical guide. Two years later, Cassetta [20] performed a clinical pilot study to estimate the accuracy of computer-guided piezocision. In that study, the planned piezocisions were compared to the actual piezocisions. The mean deviation at the entry point was 0.67 mm (range, 0.06–1.44 mm; standard deviation, 0.31) and the mean depth deviation was 0.54 mm (range, 0.17–0.80 mm; standard deviation, 0.21), confirming the clinical applicability of the innovative technique.

Biological basis

Köle originally believed that corticotomy accelerated tooth movement due to the block movement theory. In the early twenty-first century, Wilcko et al. studied X-ray images of two patients who underwent corticotomy [6]. They found that bone turnover was promoted after cortical incision. Wilcko later insisted that the regional-acceleratory-phenomenon (RAP) after selective alveolar decortication caused the acceleration of tooth movement. Surgical trauma stimulates the reconstruction of the surrounding tissues, which leads to frequent demineralization and remineralization of bone tissues, thus accelerating tooth movement [7].

In 1983, RAP was first reported by Frost, who believed that RAP was the response of tissues to local stimuli [21]. RAP often occurs after arthrodesis, fractures, osteotomy or bone grafts and involves the aggregation and activation of precursor cells during locally stimulated bone healing [21]. The principle of PAOO is to stimulate the alveolar bone by cutting the bony cortex so that the local reaction of the alveolar bone is accelerated; thus, the operative area enters the state of temporary reversible osteopenia, and the bone resorption appears immediately. During this process, bone density decreases and orthodontic force is applied to move the bone matrix and soft tissue matrix around the root. During subsequent remineralization, new bone is deposited, and the osteoid matrix is remineralized [22].

RAP generally begins a few days after the cortical incisions, reaches a peak within 1–2 months, lasts for 4 months, and subsides after 6–24 months. However, as long as the teeth remain moving, the RAP phenomenon is prolonged. When the orthodontic movement of the tooth is complete, the supporting alveolar bone is remineralized. RAP disappears, osteopenia disappears and normal cancellous bone reappears on radiographic images [23,24].

At present, there are many studies on the molecular mechanism of PAOO involved in the acceleration of tooth movement. Some scholars believe that cortical incisions affect the production of RANKL, M-CSF and OPG in periodontal tissue mainly through two pathways, which in turn affects the differentiation of osteoclasts. On the one hand, surgery changes the blood flow in the periodontal tissue, and the periodontal tissue is in anoxic microenvironment, which promotes the expression of VEGF and other cytokines in osteoblasts, acting on RANKL, M-CSF and OPG. On the other hand, surgery causes local tissue trauma, which in turn causes inflammation, and the release of local pro-inflammatory factors is increased, which also acts on the above three factors. Finally, RANKL, M-CSF and OPG jointly regulate osteoclast differentiation and accelerate tooth movement [25,26].

Surgical technique

The PAOO technique proposed by Wilcko et al. was performed on the buccal and lingual sides of the target tooth, and bone graft material was placed in the surgical area as needed, including the following steps [1,4,27].

Flap design

The idea is mainly to expose enough areas of the alveolar bone surface and effectively cover the bone graft material. The basic flap design is a combination of a full-thickness flap in the most coronal aspect of the flap with a split-thickness dissection performed in the apical portions. The flap should be extended beyond the corticotomy sites mesially and distally so that vertical releasing incisions are not required. During the operation, the gingival papilla should be protected from unnecessary damage to the gingival morphology. For the sake of aesthetics, the interdental papilla of the maxillary incisor should be kept on the labial side. The base of the gingival flap should be slightly larger than the gingival margin to ensure blood supply.

Decortication

Decortication should be just enough to initiate the RAP response, and it should not create movable bone segments. After flap elevation, corticotomy is made between 2 mm below the alveolar crest and 2 mm below the apex by using low-speed round burs under local anaesthesia. Decortication is performed at clinical sites without entering the cancellous bone, thus avoiding the risk of damage to the underlying structures, such as maxillary sinus and mandibular canal.

Particulate grafting

Before bone grafting, the incision range and the thickness of alveolar bone should be evaluated first. The volume of the graft material used is dictated by the direction and amount of tooth movement predicted, the pretreatment thickness of the alveolar bone and the need for labial support by the alveolar bone. A typical volume used is between 0.25 and 0.5 mL of graft material per tooth. The materials most commonly used for grafting after decortication are deproteinized bovine bone, autogenous bone, decalcified freeze-dried bone allograft or their combination.

Closure

The flap should be closed using nonresorbable interrupted sutures without creating excessive tension. The middle part of the soft tissue should be sutured to ensure that the gingival papilla is aligned in the correct position. The stitches should be removed after 1–2 weeks.

In recent years, PAOO technology has continuously improved, with decreasingly invasive procedures. These modified procedures can accelerate tooth movement; furthermore, they can also reduce postoperative reactions. In clinical work, the type of malocclusion and the needs of patients should be considered comprehensively to select the appropriate surgical methods.

Time of applying orthodontic treatment

The placement of the orthodontic brackets and the activation of the arch wires are usually performed one week before the surgical procedure. In all cases, the initiation of orthodontic force should not be delayed more than 2 weeks after surgery because prolonged delay in orthodontic force application would not make full use of the stage of RAP occurrence. Orthodontists need to complete accelerated tooth movement within 4–6 months. After 4–6 months, the tooth movement rate returns to normal [22]. Given this limited ‘window’ of rapid movement, orthodontists need to advance arch wire sizes rapidly, initially engaging the largest arch wire possible. A case report of double corticotomy showed that the tooth movement speed was maintained in an accelerated state for another period of time after the second surgery; however, there was no significant difference in treatment cycle between once and twice corticotomy [28].

Clinical applications

PAOO technique as a surgically assisted method could significantly shorten the treatment duration, especially suitable for patients with moderate-to-severe dental crowding or with the requirement of bone augmentation. Reviewing the literature, we find that the PAOO technique has been applied in the following situations [27,29–33]:

1. need to resolve crowding, especially moderate-to-severe crowding, in the short term;

2. the canines need to be retracted quickly;

3. impacted teeth open windows to help eruption;

4. facilitation of maxillary arch expansion;

5. orthognathic patients desiring a reduced treatment time.

Outcome evaluation

Root resorption

There have been a few case reports of increased root resorption in the practice of the PAOO technique [34]. However, recent studies [5,9,12] have not found increased root resorption with the PAOO technique compared with conventional orthodontics. We could assume that after cortical bone incision, the bone resistance, the burden on the root and the duration of treatment are reduced, so the root resorption may eventually be reduced. However, long-term randomized clinical trials and studies of mechanisms are still needed.

Periodontal health

Some studies explored whether the periodontal health of patients with periodontitis was affected after PAOO treatment. The study performed by Kamal et al. [8] taking the pocket depth and bone density as the periodontal health indexes found that the PAOO technique was beneficial to periodontal health. Patients showed improvements in periodontal condition, i.e., periodontal pocket depth decreased and bone density increased during the treatment. Systematic reviews [35,36] tend to show that PAOO is a safe procedure without significant effects on probing depth or on attachment level and an almost beneficial surgical procedure without any adverse effect [5,8,9,12] on the periodontal health.

Treatment duration

There is no doubt that PAOO shows a significant reduction in orthodontic treatment duration [33,37–40]. When Wilcko applied PAOO in the treatment of non-tooth extraction patients, the treatment period was shortened to 4–6 months, which was 1/3–1/4 of the period of traditional orthodontic treatment. In Shoreibah’s research [37] on patients with tooth extraction, the duration of conventional treatment was approximately 31 months. However, the total duration of treatment was reduced to one half of that of conventional treatment after corticotomy, and the time required to close the tooth extraction gap was also significantly reduced. Indeed, shorter orthodontic treatment time has always been the main advantage of the PAOO technique.

Postoperative stability

Retention is an important research direction for orthodontists, and many scholars have been studying the stability of postoperative PAOO. Several reports indicated that patients undergoing PAOO treatment maintained higher postoperative stability. Makki et al. [41] found that the stability of the corticotomy group was higher after 10 years of follow-up, which provided favourable evidence for the clinical application of PAOO. Bahammam et al. [39] evaluated the relapse rate; after 9 months, these patients did not experience any regression. As for the reasons for the increased stability after surgery, Binderman et al. suggested that flap dissects most of the gingival fibres from the root and crown, changes the memory of the physiological position of the dentition, and is not easy to relapse [42]. Other scholars believe that bone augmentation is a major contributor to the difficulty of relapse. Further experimental studies are needed to confirm specific mechanisms.

Complications and side effects

Although the PAOO technology has undergone several modifications since its introduction by Wilcko, there are still complications related to surgical invasion or improper manipulation [43]:

1. when the location of the surgical incision is close to the marginal gingiva or the root of the adjacent teeth, alveolar crest atrophy and bone loss are likely to occur;

2. improper suture of gingival flap or improper placement of bone graft material is likely to cause bone graft failure and graft material resorption;

3. systemic diseases may occur, for instance, oral pathogenic bacteria entering through the surgical wound may spread into the blood, causing bacteraemia;

1. subcutaneous haematoma on the face or neck can develop.

Advantages and disadvantages of PAOO

Advantages of the PAOO technique [41,44]

1) PAOO technology can shorten the orthodontic cycle and reduce the attachment time of plaque biofilm on the orthodontic appliance, which is beneficial to oral health.

2) The stability of PAOO after surgery is better than that of conventional orthodontic treatment.

3) The open area of the bony cortex has little resistance to tooth movement, while the area without cortex incision is less affected. The use of this difference can reduce the use of anchorage devices.

4) Bone grafting increases the amount of alveolar bone and makes the periodontal tissue more stable. By bone grafting, the periodontal soft tissue can also be supported, and the gingival morphology can be improved.

5) Root resorption is reduced. Some scholars believe that PAOO reduces the resistance of tooth movement, and the pressure suffered during tooth movement is reduced, and the application time of orthodontic force is shortened due to the shortening of orthodontic cycle.

Disadvantages of the PAOO technique [43]

Disadvantages of the PAOO technique include the following aspects:

1) increased operating costs;

2) frequent return visits with longer time for each return visit;

3) possible occurrences of postoperative complications, such as pain, swelling and infection;

4) long-term stability of PAOO needs to be further studied and confirmed.

Conclusions

In orthodontic treatment, shortening the treatment time is beneficial to the periodontal health. Shorter treatment time can also improve the patient’s orthodontic treatment compliance. PAOO is an alternative surgical procedure that can accelerate adult tooth movement, shorten orthodontic treatment time and provide more complete periodontal tissue. However, to confirm the long-term efficacy of PAOO, further studies are needed. With the deepening of research, PAOO, as a relatively mature means of accelerating tooth movement, will likely become more attractive in orthodontic treatment.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This project was supported by the National Programme for Multidisciplinary Cooperative Treatment of Major Diseases (Grant No. PKUSSNMP-202013 to X.-D.W.), Beijing Municipal Science & Technology Commission (Grant No. Z171100001017128 to X.-D.W.) and National Natural Science Foundation (China No. 81671015 to X.-D.W.)