Introduction

Alveolar arch crowding is the most common manifestation of dental malocclusion. Correction of dental malocclusions has been shown to improve periodontal health and psychosocial status (Rusanen et al., 2010). The conventional orthodontic approach for the resolution of dental crowding involves either extraction of selected teeth (often bicuspids) or alternative mechanics like expansion, interproximal stripping, and/or angulation modifications using nonsurgical orthodontic treatment alone. In most cases, mild to moderate crowding can be managed without teeth extraction; conversely, moderate to severe cases are usually best treated with dental extractions. Adult orthodontics is becoming very popular, and an increasing number of adults have undergone orthodontic treatment in recent years. Duration and costs remain the biggest challenges for the orthodontic field in the current era relative to treatment of adults. Typically, orthodontic treatment ranges from 1 to 2 years; it requires continuous compliance and expense from the patient’s perspective for a considerable period. The duration and management of comprehensive orthodontic treatment for adults are significantly longer compared to adolescents (Vig et al., 1990). Thus, many potential orthodontic patients often decline or discontinue the treatment due to a change in their social and financial situations.

In the last decades, many clinicians and researchers have focused on decreasing the time for tooth movement (TM). Investigators have recommended many unique treatment modifications to reduce the overall treatment time. The introduction of newer minimally invasive, predictable surgical techniques (e.g., distraction osteogenesis and alveolar bone corticotomies) has been the main focus of many clinicians for the past century (Frost, 1983, 1989a, b). This chapter will discuss the surgical technique of 1‐selective alveolar decortication or corticotomy (SAD) or single flap corticomy (SFC) 2‐tunnel regenerative corticotomy (TURC) and the differences between the two techniques.

SAD is a relatively new technique in the dental literature. However, documentation of the original concept in the orthopedics literature dates back to the early 19th century. SAD refers to the intentional surgical disruption of alveolar cortical bone that aims to reduce the resistance that native bone offers to orthodontic dental movement, thereby making orthodontic treatment more rapid. Many modifications of this basic technique have evolved in the field of dentistry over the last few years with and without the addition of a regenerative material and different authors have changed the terminology as per their preferences (e.g., corticotomy, periodontally accelerated osteogenic orthodontics [PAOO], corticotomy‐facilitated orthodontics, accelerated osteogenic orthodontics [AOO], and Piezocision^®).

In the orthodontic literature, “corticotomy” is vaguely defined and often confused with “osteotomy.” The corticotomy procedure refers to a surgical technique in which a cut is made into the buccal and/or lingual cortical plates that surround the tooth without completely going through both cortices; as a result, the teeth will be present in an alveolar bone segment connected to other adjacent teeth and structures only through the medullary bone. In contrast, an osteotomy is defined as complete cuts through the entire thicknesses of both buccal and lingual cortical plates and the interposed medullary bone, potentially creating a mobilized segment of bone and teeth. Osteotomies theoretically may have a higher incidence of complications such as ischemic necrosis of the bone segment, wound dehiscences at the osteotomy site, and devitalization of the teeth adjacent to the osteotomy sites.

When adding a regenerative technique to the decortication of the bone, the procedure is named PAOO^® or regenerative corticotomy (RC).

Historical Background

The technique to accelerate TM (alveolar corticotomy) was first introduced by Köle, in 1959. It was believed that by creating blocks of bone with vertical buccal and lingual corticotomies and apical horizontal osteotomy connecting cut segments of bone with embedded teeth could be moved rapidly. However, due to the invasive nature of Kole’s technique, it was never widely accepted. In the early 1990s, Suya (1991) revised Kole’s technique with the “substitution of subapical horizontal corticotomy cuts in place of the horizontal osteotomy cut beyond the apices of the teeth.” It published a clinical study that showed promising results. “Another orthopedist introduced regional acceleratory phenomenon” (RAP), Dr. Henry Frost (1983) proposed that intentional injury to the cortical bone results in a modification of the bone metabolism, leading to a transient state of osteopenia, described as RAP. The RAP mechanism potentiating tissue healing was shown to occur in the mandible as well as in long bones (Yaffee et al., 1994).

It was not until the Wilcko brothers in 2000 reintroduced and later perfected this combined surgical‐orthodontic therapy with an innovative technique of combining corticotomy surgery with alveolar grafting. They initially termed their technique as AOO and more recently changed the terminology to PAOO^® (Wilcko et al., 2001). This technique entails comprehensive fixed orthodontic appliances in conjunction with full‐thickness flaps and labial and lingual corticotomies around teeth to be moved. In addition, a particulate bone graft is also applied directly over the bone cuts, and the flap is sutured in place. TM is initiated at least 1 week before the surgery and every 2 weeks thereafter by activation of the orthodontic appliance. The Wilcko were the first to demonstrate that the movement does not result from repositioning of tooth–bone blocks but rather from a cascade of transient localized reactions in the bony alveolar housing leading to bone healing. The earlier concept of rapid TM was based on bony block movement in corticotomy techniques, including buccal and lingual vertical and subapical horizontal cuts circumscribing the roots of the teeth. Current research has proven that the rapid TM after corticotomy is facilitated by RAP described as accelerated bone turnover and decreased regional bone density (Wilcko et al., 2001).

Biophysiologic Considerations

An injury of any type initiates healing by perturbing some of the surviving local cells, sensitizing them so that they can respond better to specific local and systemic messengers and stimuli. Injury also releases local biochemical and biophysical messengers that make cells respond and help to determine how they should respond. The bone remodeling basic multicellular unit (BMU) first produces osteoclasts that remove preexisting hard tissue and then produce osteoblasts that replace it with well‐oriented lamellar bone in the stereotypical activation–resorption–formation sequence. Bone resorption and bone formation occur in tandem with the remodeling process. This coupling mechanism has been postulated as a means by which bone is neither lost nor gained during repair. When the stimulus to RAP resolves at the end of healing, the BMU activation declines to normal, remodeling spaces fill back with new bone, and osteopenia disappears.

The initial response of bone to a traumatic injury is by a biological state called “regional acceleratory phenomenon,” characterized by a transient increase in bone turnover and a decrease in trabecular bone density (Frost, 1983). This localized burst of tissue remodeling is also witnessed after a surgical osteotomy or a fracture (Shih and Norrdin, 1985). Alveolar corticotomy is a surgical intervention limited to the cortical bone that is incorporated into the orthodontic treatment plan to facilitate the treatment of complex occlusal problems (Kole, 1959). It generates the localized RAP phenomenon at the injury site (Wilcko et al., 2001) due to which bone regenerates faster than the normal regional regeneration process. This faster regeneration is due to the enhanced stages of bone healing, which could be as fast as 2–10 times the normal physiologic healing (Frost, 1983). A localized and reversible decrease in mineral bone density or osteopenia that begins with the initial stage of RAP and diminishes with the end of RAP is responsible for the faster TM. Locally induced osteopenia weakens the trabeculae of the alveolar bone, and this less resistance subsequently leads to the rapid movement of teeth (Sebaoun et al., 2008). Once, orthodontic TM is completed, an environment is created that favors alveolar remineralization. The effect of RAP begins within 2–3 days of injury and peaks at 1–2 months. This effect usually lasts 4 months but may take 6–24 months to subside completely (Wilcko et al., 2003).

Indications for SAD or Corticotomy Alone

1. Decreasing the duration of orthodontic treatment in patients who are undergoing conventional, nonsurgical orthodontic therapy (treatment of dental malocclusions with orthodontics alone) (cf. Chapters 4, 5, and 6) and decreasing the duration of preoperative 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. Facilitating treatment of impacted teeth (cf. Chapter 6).

If a regenerative material is added (ODO):

1. 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 in the long term (cf. Chapter 7).
2. Expanding the alveolar basis, therefore, reducing the needs for premolar extractions and strengthens the periodontium.
3. A powerful tool in multidisciplinary treatment, including managing of partial edentulism in adult and growing patients (cf. Chapter 8).
4. Modifying the lower third of the face (cf. Chapters 6 and 7).
5. Alternative to orthognathic surgery for combined surgical‐orthodontic management of select dento‐skeletal malocclusions in borderline cases.
6. “Salvage technique” for the management of post orthognathic, occlusion‐related complications.
7. To safeguard periodontal tissue during decompensation and expansion in orthognathic cases.

Contraindications

Contraindications are similar to those for any minor oral surgery or periodontal surgery procedures, especially when related to conditions affecting systemic health and illness (cardiac, endocrine, musculoskeletal, etc.). Additionally, SAD may be contraindicated in certain local disease states, such as active periodontitis or systemic conditions (e.g., uncontrolled osteoporosis). It may also have an increased complication rate in patients with a history of using some medications (e.g., nonsteroidal anti‐inflammatory drugs [NSAIDs], immunosuppressive medications, steroids, and bisphosphonates) and radiation therapy to the maxillofacial region.

Advantages

1. Minimally invasive surgery
   1. Decreased postoperative discomfort (compared to orthognathic surgery such as SARPE)
   2. Minimal complications
2. Eliminates the need for dental extractions in many patients
3. Improved postsurgical outcomes
   1. Less root resorption during active orthodontic movement due to decreased resistance of cortical bone
   2. Improved quantity and quality of periodontium
      1. More bone support due to the addition of bone graft
4. Decreased duration of treatment
   1. Orthodontic treatment
   2. Total treatment time
   3. decrease of length‐related side effects of orthodontics due to plaque accumulation, such as decay and periodontal disease
5. Ability to perform surgery in an office setting
   1. Improved efficiency
   2. Decreased costs
   3. No requirement for hospitalization

Surgical Technique

Flap Reflection and Exposure

The elevation of a full‐thickness mucoperiosteal flap is carried out next. The sharp end of a periosteal elevator is inserted underneath the papilla in the area of the incision. It is turned laterally to reflect the papilla away from the underlying bone. This technique is utilized for the remainder of the flap, extending laterally. Care should be exercised not to damage any neurovascular bundles exiting the bone and stay subperiosteal so as not to invade deeper muscle attachments. After this initial reflection of the free edge of the flap, the broad end of the periosteal is then used to reflect the entire mucoperiosteal flap and this exposes the alveolar housing and bone plates (Figure 3.2). This technique assures an atraumatic, hemostatic reflection of the mucoperiosteal flap.

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