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Ortho Tribune Middle East & Africa No.6, 2017

E4 ◊Page E3 ORTHO TRIBUNE Dental Tribune Middle East & Africa Edition | 6/2017 in the size and shape of the maxil- lary and mandibular alveolar bone observed in adolescent, adult and children treated with a passive self- ligating, continuousarch appliance and Damon low-friction/low-force treatment protocols. Specifi cally, the increase in the transverse di- mension of the alveolus appears to be the result of lateral translation of the buccal and lingual cortical plates induced by the biomechanical load applied to the teeth and transmitted to the alveolar bone. These cases pro- vide additional clinical evidence for the ability of the alveolar bone to un- dergo biomechanical loadinduced modeling. As Frankel had done previously with his Function Regulator appliance, Damon has proposed a mechanism of action for the dentoalveolar re- sponse to his treatment regimen. Based on clinical observations and analysis of photographs, plaster study model measurements and medical CT surveys36 of treated cases, he suggests that the light, continu- ous force delivered by his treatment approach disrupts the equilibrium of the tooth positions maintained by the inner and outer oral musculature acting on the alveolus and dentition. When the anterior component of the force acting along the continuous archwire is kept low, it is mitigated by the resting pressure of the lip38 in patients with adequate circumoral muscle tonus. The posterior compo- nent of force is likewise resisted by multi-rooted molars along with the ascending ramus in the mandible and the tuberosity in the maxilla. A resultant lateral component of force is expressed and transmitted from the teeth to the alveolar bone, induc- ing bone modeling or posterior arch adaptation as he describes it. The OSIM fi ndings of Badawi sup- port Damon’s proposed mechanism of action, specifi cally the assertion of a lower anterior vector of force delivered with a passive self-ligating appliance compared with an elasto- meric-ligated appliance applied to the same simulated malocclusion. In addition, there is a cellular mecha- nism of action that supports alveolar bone modeling induced by tooth dis- placement. Figure 8 from Graber de- scribes bone modeling occurring in the periodontal ligament and on the periosteal surfaces resulting from net apposition of bone in the direc- tion of the line of applied force and net resorption of bone away from the direction of force. Furthermore, this ability to move bone with a light, continuous load applied to the teeth has been corroborated in the sagittal dimension by Melsen39,40 and Allais.41 Despite the evidence presented in this article, there remains consider- able debate regarding the immuta- bility of the alveolar bone and the treatment response to low-friction/ low-force passive self-ligating appli- ances. Rigorous investigation should be undertaken to validate and un- derstand these clinical observations. Future clinical investigations should incorporate case selection criteria that include subjects with adequate circumoral muscle tonus as well as close adherence to the established treatment protocols as described in the case reports above. In addition, future CBCT analysis should consider the voxel size and resolution of the machines used in making alveolar bone determina- tions as well as the time period in which the posttreatment assess- ments are undertaken to allow ad- equate time for completion of sec- ondary mineralization. Conclusions This article presents case reports demonstrating a change in the size and shape of the alveolar bone in child, adolescent and adult patients treated by a continuous-arch, self- ligating appliance. These cases, along with a growing body of evidence, challenge the immutability of the alveolar bone and the axiom of treat- ing to the existing arch form. It is the authors’ considered opinion that Melvin Moss’s Functional Matrix Theory is correct and the change in alveolar form induced by this low- friction, low-force treatment ap- proach provides an opportunity to recapture the full genetic potential of the patient’s alveolus. Furthermore, alveolar bone mode- ling is a practical treatment objective ÿPage E5 CASE STUDY 2 PERIADOLESCENT ALVEOLAR MODELING: Pretreatment Diagnosis An 11.5-year-old female patient pre- sented with a Class I jaw relationship and severe tooth size/arch length discrepancies with 9 mm of crowd- ing in the maxillary arch and 15 mm of crowding in the mandibular arch. Her mandibular incisors were up- right at 89° to the mandibular plane and she exhibited normal circu- moral muscle tonus and competent lips. Her parents wanted to attempt a nonextraction treatment plan. In- formed consent was obtained and a therapeutic diagnosis was initi- ated with a reassessment planned for approximately 6 to 9 months to determine if the nonextraction attempt could continue or if extrac- tion would be required. Treatment Summary Damon protocols were employed with initial .013” Copper Ni-Ti wires and NiTi open-coil springs activated one-half-of-a-bracket width to begin to create space for the unbracketed, blocked-out teeth. Eyelet attach- ments were placed on the lingually blocked-out teeth and lightly ligated to the coil springs with enough force to minimally defl ect the archwire. Since the alignment at the 10-week appointment was deemed insuf- fi cient to engage a larger wire and comfortably close the bracket door, the initial wires were inspected for deformation and replaced. The springs were then reactivated, the blocked teeth religated and the pa- tient reappointed for 8 weeks. Although in signifi cantly crowded cases the transitional wire is typically a .018” Copper Ni-Ti wire engaged in preparation for a .014” x .025” Copper Ni-Ti wire, at the 18th week bracket alignment was again deemed insuffi cient for rectangular wire engagement so a .014” Copper Ni-Ti wire was placed, the springs were reactivated and the blocked-out teeth religated. At subsequent appointments as space was created, initially blocked-out teeth were bracketed and engaged with .014” Copper Ni-Ti wires. At 8.5 months, the decision was made to continue with the nonextraction treatment plan. This severely crowd- ed case did not progress beyond the .018” Copper Ni-Ti wires until 12 months into treatment. Results The fi nal result was obtained after 23 months of treatment. Retention included bonded lingual wire retain- ers and clear, vacuum-formed Essex- style removable retainers to be worn while sleeping. Sizecorrected lower occlusal photographs taken at initial bonding and debonding illustrate the change in the size and shape of the mandibular alveolus induced by passive self-ligation treatment. By the three-year posttreatment follow up appointment, teeth #8 and #9 had been crowned and the bonded maxillary lingual wire had been re- moved. The patient reported infre- quent removable retainer wear and the alveolar modeling obtained had remained remarkably stable. PERIADOLESCENT ALVEOLAR MODELING: Pre-/Posttreatment Comparison Demonstrates Alveolar Modeling PERIADOLESCENT ALVEOLAR MODELING: Results PRETREATMENT POSTTREATMENT 3 YEARS POSTTREATMENT

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