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Ortho Tribune Middle East & Africa No.3, 2017

Dental Tribune Middle East & Africa Edition | 3/2017 ORTHO TRIBUNE E3 A Practical Treatment Objective: Alveolar Bone Modeling with a Fixed, Continuous-Arch Appliance Figure 1. Alveolar Process Figure 2. Typical transverse alveolar modeling observed in response to treatment with the Frankel Function Regulator. Pretreatment study model shown on the left and post- treatment on the right, size-corrected and marked for transverse development. By Thomas W. Barron & Frank Bog- dan, USA Bone is a dynamic tissue that is con- tinuously adapting its structure via the processes of remodeling and modeling. Remodeling is the cou- pled sequence of resorption and formation involved in physiologic turnover. It is necessary to adjust internal architecture in response to mechanical needs, repair microda- mages in the bone matrix, and to maintain plasma calcium homeosta- sis. Remodeling can only be observed histologically or by chemical assay of biomarkers. Modeling is a change in the size and shape of a bone that can be observed and measured ra- diographically. It is the net gross ana- tomic result of bone resorption and formation on a given bone surface in response to growth and develop- ment or mechanical load. These pro- cesses are well-accepted phenomena in the field of physiology. In the orthodontic literature, it is widely held that the alveolar bones of the maxilla and mandible are im- mutable—that once formed, their size and shape cannot be changed significantly with tooth-borne, continuous-arch orthodontic appli- ances. Attempts to do so have been associated with root and cortical plate resorption, loss of periodontal attachment and unstable tipping of teeth.1-4 Under this paradigm, ortho- dontic treatment must maintain the existing size and shape of the alveo- lar bone. In many cases, this can only be accomplished with surgery, tooth extraction, or separation of the mid- palatal suture. In recent years, there has been a growing body of clinical evidence bolstered by studies that challenge the immutability of the alveolar bone and the mandate to treat to the existing dentoalveolar arch form. The purpose of this article is to pre- sent a review of the literature chal- lenging alveolar bone immutability along with clinical cases treated with passive self-ligating orthodontic brackets and low-friction/low-force protocols that demonstrate alveolar bone modeling. Challenging Alveolar Bone Immutability The alveolar process is defined as that part of the maxilla and mandi- ble that forms and supports the sock- ets of the teeth (Fig. 1). It includes the thin lamella of bone that surrounds the root of the tooth and gives attachment to the prin- cipal fibers of the periodontal liga- ment. It also includes the supporting inner and outer cortical plates of compact bone along with the spongy bone between the cortical plates.5 Though anatomically, no distinct boundary exists between the body of the max- illa or the mandible and their respec- tive alveolar processes, the bone sur- rounding the teeth from root apex to the crest of the socket is considered to be the alveolar bone.6 By means of the teeth, alveolar bone can be loaded with biomechanical force. The cellular response of the PDL to orthodontic force has been well characterized on both the pres- sure and tension sides of the bony socket surrounding the root as the tooth and its periodontal ligament are translated through the trough of bone confined by the buccal and lin- gual cortical plates.7-10 Until recently, modeling—or changing the size and shape of the developed alveolus by translating the cortical plate—was not deemed possible with fixed orthodontic appliances, and conse- quently, has not undergone rigor- ous study. The critical questions that must be answered to challenge alve- olar bone immutability and foster an acceptance of treatment modalities that are not confined to the existing size and shape of the alveolus are: 1. Is the alveolus, confined by the buc- cal and lingual cortical plates, immu- table or is there evidence that it can undergo modeling? 2. If it can undergo modeling, under what conditions can it occur? 3. Can fixed, continuous-arch ortho- dontic appliances induce alveolar bone modeling? 4. Is there a cellular mechanism of ac- tion that can explain orthodonticin- duced alveolar bone modeling? Myo-Periosteal Induction of Alveolar Bone Modeling Dr. Rolf Frankel described the trans- verse alveolar modeling observed in periadolescent patients treated with his Function Regulator Appli- ance (Fig. 2).11-13 He reported that the increase in the transverse dimen- sion observed in these patients is achieved primarily through the ac- tion of the buccal shields on the ap- pliance. The acrylic shields disrupt the equilibrium of forces acting on the dentoalveolus by removing the Figure 3. From Kokich, G., Kokich, V.: Congenitally missing mandibular second premolars: clinical options Am. J. Orthod. 130:437, 2006. Figure 4. Alveolar bone modeling with the low load, constant force Passive/Active Dissociation Appliance described by Fontenelle. From Fontenelle, A: Challenging The Boundaries of Orthodontic Tooth Movement in Orthodontics for the Next Millennium, ed., R. Sachdeva, H.P. Bantleon, L. White, J. Johnson, ORMCO Glendora 1997, pp. 248-267 Figure 5a-c. From Williams, M.O., Murphy, N.C., Beyond the ligament: a whole bone periodontal view of dentofacial orthopedics and falsification of universal alveolar immutability, Semin Orthod 14:246, 2008. pressure of the buccal musculature and allowing the light continuous force of the tongue to dominate. Ac- cording to Frankel, when the forces of the cheeks are eliminated, the teeth tip laterally in the direction of least resistance. The alveolar walls in the radicular area are likewise de- formed in a buccal direction. Furthermore, the acrylic shields ex- tending into the vestibule exert a constant outward pull on the con- nective tissue fibers and muscle attachments that is transmitted to the alveolar bone by the fibers of the periosteum. Apposition of buc- cal bone aids in the lateral move- ment of the dentoalveolus. The abil- ity of periosteal tension to induce apposition of bone on the lateral alveolus has been demonstrated in the animal studies of Altmann14-16 and Harvold.17,18 In addition, a study by Breiden, et al.,19 utilizing metallic implants placed in the maxillae of patients treated with the Frankel ap- pliance demonstrated that widening of the maxilla was due to deposition of new bone along the lateral border of the alveolus rather than increased growth at the midpalatal suture. This phenomenon of alveolar mod- eling, specifically lateral translation of the alveolus, achieved by disrupt- ing the equilibrium of the inner and outer oral musculature and peri- osteal tension is consistent with the Functional Matrix Theory of Moss.20- 22 While granting the innate growth potential of cartilage and bone, his theory holds that growth of the face occurs as a response to functional needs and neuromuscular influenc- es and is mediated by the soft tissue in which the jaws are embedded. The theory, simply stated, is that bones do not grow but are grown, emphasizing the ontogenetic pri- macy of function over form. The Frankel appliance achieves a change Figure 6a-b. Routine hematoxylin and eosin histological section at buccal aspect of tooth #5, labial to Max 2000 palatal alveolus development appliance. Note absence of a “lamellar” pattern that is characteristic of mature bone (a). A polarized light section of specimen. Note “woven bone” pattern characteristic of immature bone (b). From Williams, M.O., Murphy, N.C.: Beyond the ligament: a whole bone periodontal view of dentofacial orthopedics and falsification of universal alveolar immutability, Semin. Or- thod. 14:246, 2008. Elastomeric Ligation vs. Damon Passive Self Ligation RED = 50+ Grams of Force Arrows Indicate Magnitude and Direction of Force Elastomeric Ligation Damon Passive Self Ligation Figure 7. A malocclusion simulating bilaterally high canines leveled and aligned on an .014” Copper Ni-Ti wire with elastomeric ligation and Damon passive self ligation. Elas- tomeric ligation demonstrated labial force vectors with higher forces compared with Damon passive self-ligation appliances. Data reprinted by permission from Dr. Hisham Badawi. in form by changing the function of the matrix tissues of the orofacial musculature. Load-Induced Alveolar Bone Modeling It is commonly observed in the field of dental medicine that the continu- ous load of a growing odontogenic cyst can significantly model the alveolar bone of the maxilla and mandible, causing remarkable dis- placement of the cortical bone.23 This pathologic process is well established and has been extensively document- ed in case reports and textbooks. The interstitial pressure of various odon- togenic cysts have been measured24 and found to exert an ultra-low force load on the alveolar bone. This phenomenon clearly demonstrates that the developed alveolus can be modeled via pathologic induction with light, continuous force. Another commonly observed example of ÿPage E4

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