Introduction

The last half of the 20th century witnessed countless improvements in the orthodontic specialty, and those of the last 10–15 years have been particularly profound. Improvements in appliance aesthetics, self‐ligating bracket systems, clear aligners, computerized imaging systems, implant‐like anchorage screws, and many other developments have elevated the expectations of clinician’s and patient’s alike. These recent advances offer convenience and esthetic advantages that make orthodontic therapy more acceptable, especially to adults. Despite all these innovative changes, the length of the orthodontic treatment still haunts the specialty as a major deterrent for many patients. So, in the last two decades, enterprising periodontists have resurrected and refined century‐old methods of accelerating orthodontic therapy.

The procedures in general are referred to as “surgically facilitated orthodontic therapy” (SFOT) and in this book defined as orthodontically driven osteogenesis (ODO). Originally, two basic procedures were performed but are now generally eschewed by periodontists because of their excessive morbidity. These traditional surgeries included crude segmental osteotomies luxated with chisels and mallets and rudimentary corticotomies that were undisciplined in their applications. Popularized largely by the intrepid studies of one clinical professor of periodontology¹, the rudimentary methods have been refined to discrete and minor out‐patient procedures using selective alveolar decortication (SAD). Today, a growing consortium of visionary clinicians worldwide are refining and developing new incarnations (Figure 4.1) of SAD which continues this global renaissance into a new generation of periodontists and orthodontic specialists.

Most recently, even these manipulations have been enhanced with sophisticated grafting. Interestingly, these innovations – (regenerative corticotomy (RC), periodontally accelerated osteogenic orthodontics^TM, PAOO), ODO (Figure 4.2) – have been enthusiastically received by patients. But, they are attracted to them neither for scientific reasons nor the minimal morbidity they enjoy. Rather patients prefer them because they reduce total treatment time.

However, the surprisingly high degree of patient acceptance of such tissue engineering, – singularly reducing treatment times by 200–400% – should not eclipse other professional advantages. These include but are not limited to, less infection, fewer caries, and less gingival damage (Waldrop, 2008), or attachment loss (Zachrisson and Alnaes, 1974).

Traditional side effects such as root resorption and decalcifications (Levander and Malmgren, 1988; Geiger et al., 1992; Segal et al., 2004; Fox, 2005; Bishara and Ostby, 2008; Pandis et al., 2008) and compromised patient compliance (Royko et al., 1999) and a wider spectrum of other therapeutic changes also may be a thing of the past when SAD and its regenerative variants are employed.

In our fast‐paced world, there have been many other attempts to shorten the orthodontic treatment time, such as rapid distraction of the canines (Liou and Huang, 1998), local application of prostaglandin (Spielmann et al., 1989), pulsed electromagnetic fields (Showkatbakhsh et al., 2010) mechanical vibration (Nishimura et al., 2008), low‐intensity laser (Cruz et al., 2004, Yamaguchi et al., 2010) minor perforation (perturbation) of the adjacent alveolus bone (Murphy, 2006; Murphy et al. 2012) and the derivatives, corticision (Kim et al., 2009), piezocision (Dibart et al., 2009), and piezopuncture (Kim et al., 2013).

However, these pale in comparison to the profound structural changes which are evoked by the salient incarnations of decortication‐facilitated orthodontics (Bell and Levy, 1972; Anholm et al., 1986; Gantes et al., 1990; Suya, 1991; Wilcko et al., 2001, 2003) PAOO^TM or and ODO in particular. In a very recent study, Long et al. (2012) conducted a systematic review of interventions for accelerating tooth movement (TM). They compared low‐level laser therapy, corticotomy, electrical current, pulsed electromagnetic fields, and dentoalveolar or periodontal distraction. They concluded that among these five interventions, the decortication procedure was safest and clearly able to accelerate orthodontic TM.

The Basic Concepts

SAD², as it has evolved into the 21st century, employs an intentional but minor, superficial “injury” to the cortical bone. Its origin lies in less discrete procedures first described in the late 19th century as an expedient way of surgically treating malocclusion and found its way into American literature in the mid‐20th century (Kole, 1959). At the cell level, mechanical microfractures of the osteon will induce remodeling that adapts the bone to novel mechanical stimuli, and SAD is the macroscopic, clinic‐level analog. At the turn of the 21st century, Wilcko et al. (2001) added the alveolar augmentation (bone grafting) to SAD protocol and termed the innovation PAOO^TM (Wilcko et al., 2001, 2003). This technique, combining alveolar decortication with bone grafting with DFDBA or Xenograft to expand alveolar volume, exploits both the SAD‐induced opportunity for rapid TM and the enlargement of alveolus bone volume to accommodate dental arch expansion.

To explain the startling results of this pioneering work, the designers called upon established histophysiologic mechanisms of decalcification and recalcification of the alveolus bone, which is commonly encountered after periodontal osseous surgery. This posited mechanism is supported by the medical orthopedic literature (Bogoch et al., 1993) wherever it is applied to SAD. Therefore, a decalcification–recalcification description of the alveolus bone response is a direct and legitimate extrapolation of histophysiology seen in long bone fractures. The concept was extended further into 21st‐century tissue engineering with the addition of mesenchymal stem cells (MSCs) (Murphy et al., 2012).

Since the validity of SAD procedures has been scientifically validated by independent replication, and the scientific justification is sound, the next developmental challenge is determining how predictable and realistic goals may be achieved with this nascent science: oral tissue engineering. Thus, the aim of this chapter is to explain how various alveolar decortication procedures can play a significant role in orthodontic treatment.

Orthodontic Implications of Bone Injury: The RAP

When bone is traumatized in any way, a very specific and dynamic healing process occurs at the site of the bone “injury,” which is proportional to the extent of the insult. This is best described by Frost in the orthopedic literature as a regional acceleratory phenomenon (RAP) (Shin and Norrdin, 1985; Frost, 1989a, b). The term “regional” refers to the demineralization of both the trauma site and histological reaction in the adjacent bone. The term “acceleratory” refers to an exaggerated or intensified metabolic response nearby that extends slightly into the marrow (spongiosa). This metabolic burst is a manifestation of normal remodeling which speeds up healing.

For SAD the demineralization is later followed by subperiosteal appositional osteogenesis. There is a localized surge of coordinated osteoclastic and osteoblastic activity which, in the early phases, manifests a decrease in bone density with an increased bone turnover. The RAP begins within a few days of the surgery and becomes amenable to practical orthodontic TM after 14 days. Then, depending on the degree of decortication, the demineralization peaks after 2–4 months – in the absence of orthodontically induced strain – and diminishes as remineralization sets in.

As alveolar decortication became popular various animal experiments were conducted to explain its effects on the alveolar bone and orthodontic TM potential. Sebaoun et al. (2008) evaluated the effects of decortication per se in the absence of TM in a split‐mouth rat model. They found that at 3 weeks, the catabolic activity (osteoclast count) and anabolic activity (apposition rate) were threefold greater in decortication sites. Calcified spongiosa decreased by two‐fold, and periodontal ligament (PDL) surface increased by twofold. Surgical injury to the alveolus which induced a significant increase in tissue turnover by week 3 dissipated to a steady state by postoperative week 11, and the impact of the injury was localized to the area immediately adjacent to the decortication. These data confirmed that alveolar decortication induced a RAP response in the alveolus like that in long bones, but Sebaoun et al. did not integrate the study with actual TM.

In 2008, Lee investigated the effects of corticotomy‐facilitated orthodontic therapy with micro CT. Later Baloul et al. (2011) compared the effects of alveolar decortication with and without TM. In an award‐winning²* experiment, the researchers studied three groups: decortication only, TM only, and a “combined group” (TM and decortication). They used morphologic analysis, quantitative MicroCT for structural analysis, and q‐PCR to analyze mRNA gene expression associated with both osteoclasts and osteoblasts. Their data conclusively established that alveolar decortication enhances the rate of TM during the initial tooth displacement phase with a “coupled” mechanism of bone cell activation adding to the natural histologic phenomena of orthodontic treatment.

The term “coupling” refers to the fact that resorption and apposition are not strictly sequential or independent events; they are simultaneous and functionally connected with each other, overlapping in their effects (King and Keeling, 1995; Proff and Romer, 2009) and vary by location, intensity, and duration.

From Corticotomy to Grafting with Decortication

Increased alveolar mass and increased distances through which teeth are moved may be greater gifts from PAOO than the mere acceleration of TM rate. The ultimate spatial limits of treatment prior to the introduction of the Wilcko research were dictated by perceptions that the “alveolar housing” of the dentition was immutable. This is not true. Alveolus bone by its very histological and ontological nature is malleable. However, this malleability, a kind of single‐generation “phenotypic plasticity,” occurs only under specific conditions in healthy tissue. The functional matrix hypothesis of Moss (1997a–d) tells us that the roots are the supporting framework or matrix of alveolar bone. That is, the osteogenic framework and “container” of bone mass dictates the functional development of alveolar phenotype.

When the alveolus periosteum is supported further from a given point by more tooth eruption, a longer root, or periosteum elevated by a bone graft, a potential space is realized. Since bone is a reactive tissue. So, analogous to water, bone tends to “fill the container” in which it is placed. So the bone graft, besides providing bone morphogenetic protein (BMP) or viable allografts to induce osteogenesis, also serves as a volumetric scaffold within which endogenous stem cells can replicate and differentiate into functional osteoblasts. This is the developmental basis of the alveolus form that justifies safe TM and augmentation of periodontal‐alveolar mass.

The limits of orthodontic TM are thus defined by the “walls” of the alveolus, viz. the periosteum and the periodontal ligament. Wherever these “walls” are built, within a reasonable phenotypic range, the bone will develop within them. So, orthodontists are wise to define “available space” not by a projection of an aligned and uprighted dentition but rather by the labial limits of the marginal gingiva and bony walls of the alveolus.

Without PAOO orthodontic treatment of teeth beyond the limits of the labial or lingual, alveolar plate can lead to dehiscence formation (McComb, 1994; Wennstrom, 1996; Zachrisson, 1996; Melsen and Allais, 2005; Joss‐Vassalli et al., 2010) and predispose the patient to recession (Zachrisson, 1996; Melsen and Allais, 2005), especially where chronic infection inhibits adaptive fibroplasia (Aleo et al., 1974) (Figure 4.3).

In a case, where there is already alveolar dehiscence formation before the orthodontic treatment, TM may be contraindicated. But in some cases, the alternative – premolar extraction – can lead to a flattened profile, premature aging, and a generally unaesthetic, “dished‐in” appearance to the lower face. PAOO and periodontal stem cell therapy (PSCT) solve this dilemma by grafting the defective areas at the beginning of orthodontic treatment to help prevent further destruction and allow movement through a greater distance.

This saving grace was demonstrated by Ahn et al. (2012) and Kim et al. (2011) independently. They reported the use of alveolar decortication and bone augmentation in decompensation of the mandibular teeth in Class III patients. Both reports concluded that alveolar decortication with bone augmentation reduced complications such as gingival recession, alveolar bone dehiscence, and bone loss in the mandibular anterior region in the treatment of Class III patients undergoing orthognathic surgery.

Since bone grafting increases both alveolar volumes and increases the dimensions through which teeth can be moved, it follows that more severely crowded cases can now be treated without tooth extraction. Indeed, Ferguson et al. (2006) reported that the limits of orthodontic TM, posited by Sarver and Profitt in adult patients (2005) can be expanded two‐ to threefolds in all dimensions (except retraction) if PAOO is incorporated into orthodontic therapy.

Wilcko et al. reported non‐extraction treatment of crowding with PAOO™ where maxillary intercanine distance was increased, (by tipping) more than 7 mm using bone augmentation and at the reentry 15 months later, noted an increase in the post‐treatment buccolingual thickness of the overlying buccal bone (Figure 4.4) (Wilcko et al., 2001). It appears that this thickness is significant because it may relate to treatment stability. Rothe et al. (2006) evaluated mandibular incisor relapse and found that patients with thinner mandibular cortices are at increased risk for dental relapse.

This observation suggests that bone augmentation during PAOO may increase stability of orthodontic outcomes due to the increased alveolar mass (Ferguson et al., 2006). An incidentally positive effect of bone augmentation during alveolar decortication is that it improves the patient’s lower facial profile. By grafting the mandibular anterior region one may provide lip support, morph an unpleasing profile, and reduce an unaesthetic labiomental fold (Figure 4.5). The same can be done in the maxilla (Figure 4.6). The ability of ODO to modify the lower third of the face is a very promising field of application of ODO in the future.

In recent studies, it has shown what Wilko anticipated long before. Only when bone grafting was added did the procedure have osteogenic abilities. More recently, several systematic reviews (Kamal et al., 2019; Kao et al., 2020; Gao et al., 2021; Alsino et al., 2022) confirmed the ability of PAOO (R) or ODO to improve thickness of alveolar soft tissues and bone during orthodontic treatment in what it is also described as phenotype modification therapy (PhMT) (Kao et al., 2020).

Practical Applications and Indications

These findings are directly applicable to any clinical setting because they suggest accelerating the rate of TM treatment and engineering RAP can impact orthodontic treatment planning in two major ways. First, manipulating the consequent osteopenia with SAD enhances the relative degree of orthodontic anchorage (corticotomy only). Second, to increase the mass of the alveolus and expand the envelope of possible TM treatment necessitates a kind of concentrated or focused biomechanical protocol during an osteopenic window of opportunity (corticotomy plus bone graft or ODO).

Indications of SAD or corticotomy alone

1. Decrease the duration of orthodontic treatment in patients who are undergoing conventional, nonsurgical orthodontic therapy (treatment of dental malocclusions with orthodontics alone) (cf. Chapters 4551,79, 5 and 6), and decrease duration of pre‐operative orthodontic treatment in patients undergoing conventional, combined surgical‐orthodontic therapy (treatment of skeletal malocclusions with orthognathic surgery).
2. Selectively alter the differential anchorage among groups of teeth, hasting and facilitating the movements of teeth that have to be moved and diminishing the counter effect in the teeth that should not be moved (cf. Chapters 6, 7 and 8).
3. Facilitate treatment of impacted teeth (cf. Chapter 6).

When regenerative material is added (ODO)

4. Augmentation of periodontal tissues (both hard and soft tissue components) and therefore Stretching the limits of safe orthodontic treatment, lowering the risk for periodontal damage during and after treatment (long term) (cf. Chapter 7).
5. Expand the alveolar basis, therefore reducing the need for premolar extractions and strengthen the periodontium.
6. Powerful tool in multidisciplinary treatment, including managing of partial edentulism in adult and growing patients (cf. Chapter 8).
7. Modify the lower third of the face (cf. Chapters 6 and 7).
8. Alternative to orthognathic surgery for combined surgical‐orthodontic management of select dento‐skeletal malocclusions in borderline cases (cf. Chapter 9).
9. Salvage technique for the management of post orthognathic, occlusion‐related complications.
10. In conjunction with orthognathic cases to protect periodontal tissue in decompensation and expansion (cf. Chapter 10).

Enhancing Relative Anchorage

The practice of orthodontics is largely dependent on the availability of anchorage. Anchorage, by definition, is a body’s resistance to displacement. Newton’s third law suggests that for every force there is an equal and opposite reactive force. This explains differential rates of movement of two opposing objects which, practically speaking, is inversely related to the mass of the moved objects or resistance the force encounters. Thus, orthodontic treatments are designed with this law in mind, the goal being to resist unwanted TM. According to Profitt, in treatment planning,

… it is simply not possible to consider only the teeth whose movement is desired. Reciprocal effects throughout the dental arches must be carefully analyzed, evaluated, and controlled. An important aspect of treatment is maximizing the tooth movement that is desired, while minimizing undesirable side effects

(Profitt, 2000).

In orthodontic movement, segments of teeth that resist movement are often ligated together, with thin stainless steel wire or elastic chain, to serve as “anchors” and used to pull or push against other segments to be moved. Usually, the anchor segment will contain more teeth or teeth with greater “root enface”³ (Murphy et al., 1982) than the segment of teeth that are to be moved. This concept of differential anchorage is important in most orthodontic treatment, especially in cases of severe arch length deficiencies (ALD) i.e., “crowding” or skeletal dysplasias. In fact, treatment of certain malocclusions is often defined by the available anchorage, e.g., “a maximum anchorage case.”

There are numerous ways in which orthodontics has tried to augment anchorage, including auxiliary devices such as headgear, transpalatal arches, palatal acrylic pads

(Nance appliances), and mini‐implants of various designs. Many of these appliances are uncomfortable for patients or lead to “anchorage loss (slippage)” an untoward movement of dental anchorage units. Also, lower levels of patient compliance are common where extraoral traction or intraoral elastics interfere with patients’ psycho‐social imperatives. Thus, treatment outcomes can become compromised.

When movement of anchor teeth is not important the term “minimal anchorage” is employed. For example, if an extraction space needs closing by the mesial movement of posterior teeth in addition to the posterior movement of anterior teeth, the term “minimal anchorage” is appropriate. Where very little posterior TM is desired, as anterior teeth are pulled against them the term “maximum anchorage” is used. However, “maximum anchorage” is often more of a wish than a reality because even in this ideal scheme some posterior TM may occur.

Recently, titanium screws used as temporary anchorage devices(TAD), TAD have been shown to provide excellent absolute anchorage where no posterior anchor movement whatsoever can be demonstrated. Because titanium screws do not have a reactive periodontal ligament the titanium anchors are as perfectly stable as ankylosed teeth. So TADs have, over the last two decades, emerged as very acceptable anchorage adjuncts to orthodontic treatment. But due to a number of limitations, such as patient disdain and premature exfoliation, they may be as unreliable as extraoral traction.

Tissue resistance to TM must also be considered in assessing anchorage potential by estimating volume and density of the alveolar bone in addition to the cross‐sectional area of the roots perpendicular to TM vector sum This osseous tissue that must be resorbed for a tooth to move thus contributes greater or lesser “anchorage value” (Roberts, 2005). That is, where there is less bone and less dense bone in the trajectory, there is less anchorage value. So, rendering a given volume of bone less dense through SAD increases the relative resistance of the opposing biomechanical anchorage units. This is why SAD, PAOO, PSCT, or trans‐mucosal perturbations (TMP) should not be used within 4–6 mm of ligated molars or TADs.

In addition to these histological assets, the shrewd use of “relative anchorage” provided by SAD allows orthodontists to avoid notoriously unpredictable anchorage paraphernalia such as intraoral elastics and extraoral traction (headgear), which rely on capricious adolescent compliance.

Maximizing the Window of Opportunity

Following the reactive demineralization after SAD, there is a 3–4 month clinical “window of opportunity” to move teeth rapidly through demineralized bone before it remineralizes (33).

The “classical” Wilcko PAOO approach involved a full mouth surgery at Time 0. Considering the effect of the decortication can diminish with time the orthodontist was forced to complete the major TMs in the first months of the treatment. This can translate to combining different mechanics and, therefore, make the procedure more complicated. With the segmental and/or sequential approach (orthodontically driven RC concept), small surgeries can be designed when these major movements are planned. 3D digital planning with Clincheck^®, it is an extremely useful tool to plan the timing of the surgeries (cf. Chapter 9).

Contraindications

SAD and PAOO, PSCT, and TMP are all limited by the same criteria that any oral surgery would suggest. These include – but are not limited to – bone pathoses, that could reduce treatment quality, efficiency, or comfort. However, periodontal infection is not one of them. Indeed, periodontal surgery to eliminate infection and regenerate supporting alveolar bone has been combined with PSCT with impunity (Murphy et al., 2012). However, where all infectious elements cannot be removed any bone graft is limited in its healing potential. That is axiomatic.

Despite these advances, publication of successful movement of implants or ankylosed teeth has not been available to date. Theoretically, a “bony block” movement could reposition such teeth but these are SFOT procedures that reassemble bony parts and incur significantly more risk than a merely superficial re‐engineering the alveolus physiology to new forms.

Because of the inhibitory action of the immune system and osteoclastic potential, long‐term use of immunosuppressants such as corticosteroids or bisphosphonates, respectively, may contraindicate decortication procedures categorically. There is no absolute age limit for decortication procedures because the physiologic mechanism of action is merely an acceleration of normal physiological bone healing. So, treatment in the mixed or deciduous dentitions is contraindicated only relative to other factors such as compliance and the availability of less invasive alternatives.

Applications

Decortication Procedures with Clear Aligners

As long as a particular style of orthodontic TM respects the basic physiology of decortication‐enhanced orthodontic TM then the particular brand or design of appliance is largely irrelevant. As the population is getting more esthetically conscious the demand for clear orthodontic aligners and lingual braces has been increasing. Therefore, it is not surprising that the combination of decortication with clear aligner biomechanics would be attempted.

Such a combination was first reported in 2001 by Owen (2001). After undergoing PAOO he used Invisalign^® to treat his own personal malocclusion. He reported very satisfactory results in correcting a Class I ALD in about 8 weeks and provided unique first‐person reportage. In such cases, decortication can be performed within 1 week of commencing treatment with aligners which can be changed every 5 days instead of every 2 weeks. This protocol can be applied in cases where there are 30 aligners or less. If the number of aligners required to correct the malocclusion exceeds this number, a surgical revision or employment of TMP may be necessary to “reboot” (rejuvenate) the RAP.

Interprofessional Communication

It is obvious that clear and unequivocal communication between the orthodontist and the periodontist is crucial during the treatment planning. But due to the insular development of specialty protocols, a body of jargon in each realm sometimes makes communication a Tower of Babel. And, even ideal collaboration can be impaired by jargon or other semantic impediments. So each collaborator should understand universal terms of the others’ databases. Moreover, patient should be explicitly informed,