Accelerated Tooth Movement

One of the biological constraints in orthodontics is the amount of time it takes to resolve malocclusion. A reduction in active treatment time would logically mean that teeth would need to move faster. Treatment times for nonextraction and extraction orthodontic treatment strategies, respectively, average 23.8 and 28.1 years, according to Buschang et al. (2012), and corticotomies increase the rates of tooth movement (TM) and decrease treatment duration. Long et al. (2013) evaluated the effectiveness of five interventions on accelerating orthodontic TM including low‐level laser therapy, corticotomy, electrical current, pulsed electromagnetic fields, and dentoalveolar or periodontal distraction; corticotomy was judged as safe and able to accelerate orthodontic TM.

It is well established that TM rate is, in part, a function of alveolar bone density (Verna et al., 2000), and that TM is accelerated under conditions of low bone density. Bone densities change regularly, as bone renews itself. Roberts (2004) contrasted the process of bone renewal for cortical and trabecular bone; cortical bone requires an activation that initiates resorption (cutting cones) followed by formation (filling cones) in a couple of sequences, i.e., remodeling, otherwise known as secondary osteon formation. Trabecular bone is thin which sustains a simpler process, i.e., modeling, wherein stimulus activation can result in either apposition or resorption. The milieu of orthodontic TM is trabecular bone modeling with the exception of the thin cortical lamina dura surrounding each tooth root.

Orthodontic clinicians understand that TM results from alveolar bone resorption and formation, and that application of a biomechanical force results in a shift in cell population dynamics within the periodontal ligament (PDL). Until sufficient osteoclasts and osteoblasts have accumulated within the PDL, TM after initial force application is limited to the width of the PDL space; this 3–5‐weeks “lag” phase dissipates, as PDL cell populations supportive of TM have accumulated and hyalinization has diminished (Von Böhl and Kuijpers‐Jagtman, 2009).

Orthodontic researchers understand “bone turnover” as a phrase describing the dynamics of a living osseous tissue that by nature is compensatory and adaptive. The research methods for the study of bone turnover include histomorphometry, i.e., quantitative analysis of the physical size and shape (form) of bone. “Bone turnover” is a histomorphometric expression that includes anabolic (apposition) and catabolic (resorption) bone changes that occur and an appraisal of the varying degrees and relative amounts of mineral salts, namely, calcium, present or absent.

Alveolar demineralization or decreased alveolar bone density leads to increased TM rate (Verna et al., 2000). Reduction of the availability of calcium metabolite, i.e., calcium manipulation either pharmacologically or through diet, results in greater TM rate and scope (Verna and Melsen, 2003).

Corticotomy

Corticotomy is the intentional cutting of only cortical bone leaving intact the medullary vessels and periosteum and was first cited in the professional dental literature in the late 1800s to correct malocclusion. Alveolar decortication has evolved during the past decade gathering noteworthy attention from orthodontic clinicians and academicians. After lying fallow for the previous half‐century, interest in the corticotomy concept was rekindled by Köle’s journal publication in 1959 describing interproximal corticotomy combined with subapical through‐and‐through osteotomy in the rapid treatment of an open bite patient. Seminal technique changes since Köle include corticotomy‐only (without subapical osteotomy) in the orthodontic treatment of two open bite patients (Generson et al., 1978), and blending augmentation bone grafting with corticotomy‐only in combination with orthodontics treatment (Wilcko et al., 2001).

For 5 years following the Wilcko 2001 publication, only a few corticotomy articles appeared in the professional literature (Chung, 2001; Chung et al., 2001; Hwang and Lee, 2001; Ferguson et al., 2001; Owen III, 2001; Ferguson, 2002; Wilcko et al., 2003; Iseri et al., 2005; Germec et al., 2006; Iino et al., 2006).

Anecdotal accounts of accelerated TM following corticotomy abound in the literature. But it was not until 2007 that evidence based upon controlled experimentation became available describing post corticotomy rapid TM. Corticotomy experiments in laboratory animals prior to 2007 focused on tissue responses (Düker, 1975), but TM rate or magnitude were not studied variables until after 2006.

Since 2007, interest in alveolar decortication as a technique to enhance the rate of TM increased notably (Fischer, 2007; Kanno et al., 2007; Lee et al., 2007, 2008; Moon et al., 2007; Spena et al., 2007; Wilcko et al., 2007, 2008, 2009; Nowzari et al., 2008; Oliveira et al., 2008; Park et al., 2008; Akay et al., 2009; Chung et al., 2009; Dibart et al., 2009, 2010; Ferguson, 2009; Kim et al., 2009a, b, c, 2011; Murphy et al., 2009; Roblee et al., 2009; Wang et al., 2009; Hassan et al., 2010b; Choo et al., 2011; Keser and Dibart, 2011). Moreover, two alveolar corticotomy literature reviews were published in regional journals (AlGhamdi, 2010; Hassan et al., 2010a) and one in an international journal (Long et al., 2013). Ten of the more recent experimental publications have included data on TM as a study variable in human and/or animal subjects with additional information on the biology of alveolar bone change dynamics (Cho et al., 2007; Iino et al., 2007; Kim et al., 2009a; Mostafa et al., 2009; Cohen et al., 2010; Sanjideh et al., 2010; Aboul‐Ela et al., 2011, Baloul et al., 2011; Iglesias‐Linare et al., 2011; Safavi et al., 2012).

Accelerated Tooth Movement in Laboratory Animals

The validity of bone research in laboratory animals depends upon the choice of the animal model (Buschang et al., 2012). Rodgers et al. (1993) pointed out that there are at least three characteristics of an animal model: (i) convenience, (ii) relevance (comparability to the human condition), and (iii) appropriateness (a complex of other factors that make a given species the best for studying a particular phenomenon). As long as the limitations of a specific animal are candidly addressed by the investigator, experimental data can lead to valid understanding of the effects of corticotomy‐induced bone loss on the human skeleton.

It is clear that bone composition in some species more closely resembles human bone composition than others (Jee and Yao, 2001). Aerssens et al. (1998) compared cortical bone composition, density, and quality in bone samples derived from seven vertebrates that are commonly used in bone research: human, dog, pig, cow, sheep, chicken, and rat. Large interspecies differences were observed in all analyses of cortical bone; rat bone was most different, whereas canine bone best resembled human bone. Trabecular bone density and mechanical testing analyses also demonstrated large interspecies variations; human samples showed the lowest bone density and fracture stress values and porcine and canine bone best resembled the human samples. In summary, of all species examined by Aerssens, the bone composition of the dog most resembles that of human bone.

Ten refereed journal articles have been published after 2006 with precision measurement of experimental and control TM following alveolar corticotomy from which amount and rate of TM could be ascertained (Table 2.1).

7 of the 10 investigations used dogs as the laboratory model, two studies used the rat (Baloul et al., 2011; Iglesias‐Linare et al., 2011), and there was one human study (Aboul‐Ela et al., 2011). The type of alveolar cortical bone injury was by surgical bur in all but one project that used a scalpel (Kim et al., 2009a) and was excluded from further consideration. Translation‐type TM following extraction was the prospective design of all studies except three; one was buccal tipping (Iglesias‐Linare et al., 2011) in rats, a second was mesial tipping (Baloul et al., 2011) in rats, and a third was dental distraction (Cohen et al., 2010) in dogs. Dental distraction or distraction osteogenesis articles were not considered.

Accelerated Tooth Movement in the Canine Laboratory Model

Canine Study Description and Design

Given the fact that bone of the canine laboratory animal best resembles the human condition, five dog investigations utilizing bur injury for corticotomy were isolated for further consideration and data pooling (Table 2.2).

Cho et al. (2007) utilized two Beagles in the longitudinal examination of mesial movement of the upper and lower third premolars after extraction of all second premolars followed by 4 weeks of post extraction healing. Corticotomy technique included upper and lower full‐thickness flaps and 12 cortex non‐perforating “dots” with a #2 round bur into the buccal and lingual cortical plates in the right maxillary and mandibular quadrants in a split‐mouth design. The third premolars were protracted into the extraction site with 150‐g nickel–titanium closed coil springs, using adjacent teeth as anchorage; upper third premolars were tipped and lower third premolars were tipped‐translated with a “guide‐wire and slot” device. Measurements were made weekly with a vernier caliper at the cervical–gingival margins of teeth adjacent to the extraction site (Figure 2.1a, b).

Iino et al. (2007) used 12 adult Beagle dogs in the cross‐sectional evaluation of mesial movement of lower third premolars after extraction of the mandibular second premolars and 16 weeks of post extraction healing. Corticotomy technique included lower full‐thickness flaps and #009 fissure bur to make horizontal subapical and vertical interproximal cuts perforating the alveolar cortex buccal and lingual to the lower third premolar in a split‐mouth design. The third premolars were protracted into the extraction site with 0.5 N (51 g) nickel–titanium closed coil springs using adjacent teeth as anchorage; lower third premolars were translated mesially with a fixed band‐and‐tube cemented appliance. Measurements were made at 1, 2, 4, and 8 weeks from radiographs taken, using a standardized format. Radiographs were superimposed on the fourth premolar and measured between the tips of protocone of the third premolar on the tracing; error of method was 0.02 mm (Figure 2.2).

Author	Subjects	Article title	Reference	Injury type	Tooth movement type	Data type
Cho	Dog	The effect of cortical activation on orthodontic tooth movement	Oral Dis, 13, 314–319, 2007	Bur bucling with flap split mouth	Tipping Up3 after ext Up2 Translate Lp3 after ext Lp2	Longitudinal
Iino	Dog	Acceleration of orthodontic tooth movement by alveolar corticotomy in the dog	AJODO, 131, 448e1–448e8, 2007	Bur bucling with flap split mouth	Translate Lp3 after ext Lp2	Cross‐sectional
Mostafa	Dog	Comparison of corticotomy‐facilitated versus standard tooth‐movement techniques in dogs with miniscrews as anchor units	AJODO, 136, 570–577, 2009	Bur buccal with flap split mouth	Tipping Up1 after ext Up2	Cross‐sectional
Kim	Dog	Effects of low‐level laser therapy after corticision on tooth movement and paradental remodeling	Lasers Surg Med, 41, 524–533, 2009	Scalpel bucling no flap split mouth	Translate Up2 after ext Up1	Longitudinal
Sanjideh	Dog	Tooth movements in foxhounds after one or two alveolar corticotomies	EJO, 32, 106–113, 2010	Bur bucling with flap split mouth	Translate Up3 after ext Up2 Translate Lp2 after ext Lp3	Longitudinal
Cohen	Dog	Effects of increased surgical trauma on rates of tooth movement and apical root resorption in foxhound dogs	Orth Craniofac Res, 13, 179–190, 2010	Bur buccal with flap remove labial cortex split mouth	Distract Up2 after ext Up1	Longitudinal
Baloul	Rat	Mechanism of action and morphologic changes in the alveolar bone in response to selective alveolar decortication–facilitated tooth movement	AJODO, 139, S83–S101, 2011	Bur buc‐ling with flap split mouth	Tipping – nonextract	Sross‐sectional
Aboul‐Ela	Human	Miniscrew implant‐supported maxillary canine retraction with and without corticotomy‐facilitated orthodontics	AJODO, 139, 252–259, 2011	Bur buccal with flap split mouth	Translate Up2 after ext Up1	Longitudinal
Iglesias‐Linares	Rat	The use of gene therapy vs. corticotomy surgery in accelerating orthodontic tooth movement	Orth Craniofac Res, 14, 138–148, 2011	Bur buc‐ling with flap split mouth	Tipping – non extract	Cross‐sectional
Safavi	Dog	Effects of flapless bur decortications on movement velocity of dogs’ teeth	Dent Res J, 9, 783–789, 2012	Bur buccal no flap corticotomy monthly split mouth	Translate Up2 after ext Up1	Longitudinal

Author Year	Type dog (sample = n) Data type	Extraction healing TM force	Corticotomy surgery details	Tooth movement type	Anchorage + appl	Measurement Location Frequency
Cho (2007)	Beagle (n = 2) Longitudinal	4 weeks healing Up3 mesial – 150 g Lp3 mesial – 150 g	Flap + non‐perf cortex “dots” 12 holes injury – #2 rd bur Buccal‐lingual	Tipping Up3 after ext Up2 Translate Lp3 after ext Lp2	U canine L canine + slot guide	Digital Vernier caliper Gingival margins Weekly for 8 weeks
Iino (2007)	Beagle (n = 12) Cross sectional	16 weeks healing Lp3 mesial – 51 g	Flap + vert and horizontal cuts 1 mm wide – #009 fissure bur Buccal‐lingual	Translate Lp3 after ext Lp2	L canine Bands + fixed tube	Caliper and radiograph Protocone tip Lp3 Superimposed tracing Weeks 1, 2, 4, 8
Mostafa (2009)	Non purpose‐bred (n = 6) Cross sectional	Immediate Up1 distal – 400g	Flaps + vert and horizontal cuts 8–10 holes – #2 rd bur Extract site buccal cortex	Tipping Lp1 after ext Lp2	Mini‐screw Lp1 cervical lig. tie	Boley gauge Notched cervical crown Weekly for 5 weeks
Sanjideh (2010)	Foxhound (n = 5) Longitudinal	Immediate Up3 mesial – 200 g Lp2 distal – 200 g	Flaps + cuts around root #702 tapered fissure bur Buccal to Up3 Buccal‐lingual to Mn ext site	Translate Up3 after ext Up2 Translate Lp2 after ext Lp3	Teeth Bonds + fixed tube	Digital caliper and radiograph Implant bone markers Lp2 mesial tube to Lc tip Up3 mesial tube to Uc tip Days 10, 14, 28, 42, 56
Safavi (2012)	German (n = 5) Longitudinal	Immediate Up2 mesial – 150 g Lp2 mesial – 150 g	Flapless + holes thru attached Pointed tungsten carbide bur 25 penetrations 2 mm deep Buccal to p2 and extract site	Tipping Up2 after ext Up1 Tipping Lp2 after ext Lp1	Mini‐screw Up2 cervical lig tie Lp2 cervical lig tie	Digital caliper Marks on p2s and canines Months 1, 2, 3

Mostafa et al. (2009) used six dogs that were not purpose‐bred in the cross‐sectional evaluation of distal movement of upper first premolars after extraction of the maxillary second premolars and immediate corticotomy. Corticotomy technique included upper full‐thickness flaps and a #2 round bur to make 2 vertical and 1 subapical cuts, and 8–10 perforations of the buccal alveolar cortex adjacent to the extraction site (not the upper first premolar) in a split‐mouth design. The upper first premolars were tipped into the extraction site with 400‐g nickel–titanium closed coil spring anchored to 1.2 mm diameter miniscrews placed between roots of upper third premolar and first molars. Appliance for lower first premolars consisted of a hook fashioned from a heavy ligature wire secured around the cervical portion of the upper first premolar crown. Direct intraoral measurements were made weekly for 5 weeks from crown notches placed cervically on upper first and third premolars with a Boley gauge to nearest 0.1 mm (Figure 2.3).

Sanjideh et al. (2010) used five Foxhound dogs in the longitudinal appraisal of mesial movement of upper third premolar and distal movement lower second premolars after extraction of the maxillary second and mandibular third premolars and immediate corticotomy. Full‐thickness flaps were made followed by corticotomy cuts with a #703 tapered‐fissure bur buccal‐only to maxillary third premolar and both buccal and lingual surrounding the mandibular second premolar in a split‐mouth design. A 0.045‐in. diameter headgear tube was soldered to bracket bases and an appliance was bonded to lower second and fourth premolars as well as upper third premolar. Premolars were translated along an 0.040‐in. stainless steel round wire using 200‐g nickel–titanium closed coil spring forces calibrated every 2 weeks and stretched from hooks fashioned from heavy ligature wire and secured around the cervical portion of the upper third premolar and canine crowns as well as the lower second premolar and the combined lower first molar and fourth premolar crowns. Direct intraoral measurements were made with a digital caliper on post corticotomy days 10, 14, 28, 42, and 56 from fixed appliance tubes to the canine cusp tips of the respective dental arch. Control data were available only from the lower dental arch. Both maxillary quadrants had initial buccal flaps and corticotomies; one randomly selected quadrant had a second buccal flap surgery and corticotomy after 28 days (Figure 2.4a, b).

Safavi et al. (2012) employed five German dogs in the longitudinal appraisal of mesial movement of upper and lower second premolars after extraction of the first premolars and immediate flapless corticotomy. Corticotomy was performed directly through the attached gingival with a pointed carbide bur in a slow‐speed handpiece; 25 penetrations were made buccal to second premolars and extraction sites in a split‐mouth design. Forces were applied with 200‐g nickel–titanium closed coil springs from hooks fashioned from heavy ligature wire and secured around the cervical portion of the second premolars stretched to miniscrew implants placed mesial to canines. Direct intraoral measurements were made with a digital caliper on post corticotomy months 1, 2, and 3 from 1 mm pointed holes placed in the canine and second premolar crowns. Corticotomies were repeated at the end of months 1 and 2 (Figures 2.5 and 2.6).