Please activate JavaScript!
Please install Adobe Flash Player, click here for download

Dental Tribune Middle East & Africa Edition

from dental clinicians throughout the Unit- ed States and eventually eclipsed other use- ful orthodontic appliances such as the Mc- Coy open tube appliance, the Atkinson uni- versal appliance and the Johnson twin wire attachment. Figure 5: Angle’s many iterations of the edgewise bracket Figure 6: Angle’s 447 edgewise bracket, “the latest and best in orthodontic mechanisms.” The universal application and durability of the edgewise bracket confirmed Angle’s immodest claim that it offered the “latest and best in orthodontic mechanisms”.9 In- novators have added minor but practical trimmings such as rotating wings, twin brackets, different dimensions, preadjusted appliances, lingual applications, etc., but the essence has remained edgewise. For any instrument, particularly in the health sciences, to remain virtually unchanged (and almost as useful for close to a centu- ry) approaches unbelievability. In the auto- mobile industry, this would be equivalent to the Model T Ford remaining as the epito- me of motoring sophistication. Other than adding wings and doubling the bracket to make the popular twin edgewise bracket, Angle’s invention has remained basically unchanged. Holdaway10 suggest- ed angulations for brackets to help set an- chorage, parallel roots and artistically posi- tion teeth, while Lee11 had built some ante- rior brackets with the ability to torque inci- sors. But it was Andrews that was to devel- op an appliance that would apply 1st, 2nd and 3rd order movements to the teeth with- out making changes in the wire – hence the Straight Wire Appliance.12 Preadjusted orthodontic appliances have dominated the profession for the past 30 years, and the belief in them shows little sign of abating even though many have questioned the one-size-fits-all idea.13-18 And Back Again The publication of Frankel’s19 work with functional appliances illustrated significant enlargement of dental arches and reawak- ened an interest in nonextraction therapy. Nevertheless, Frankel mechanics required the use of removable appliances, and that didn’t resonate well with many orthodon- tists or their patients. After a brief flurry of interest in the United States, few clinicians continued to use the Frankel appliance on a regular basis. Nevertheless, the successful use of ortho- pedic appliances alerted orthodontists to the possibility of increasing arch widths and arch perimeters with minimum forc- es. Although mandibular canines offer sig- nificant resistance to expansion, mandibu- lar premolars and first molars often dem- onstrate substantial and stable expansion. Brader20 hinted at this with his work on the tri-focal ellipse arch form, but he didn’t fol- low through about how this might give wider and more accommodating arch forms. Low-force titanium coil expanders have shown their ability to develop arches lat- erally,21 and recently Damon22 has suggest- ed that low arch wire forces, coupled with a passive tube and a small wire-to-lumen ratio, enable teeth and their accompany- ing dentoalveoli to expand in all planes of space. Damon feels that using small, low- force wires such as those of Copper Ni-Ti™ (Ormco Corporation, Orange, CA) achieves the ideal biological forces proposed long ago by several investigators.23, 24, 25 Self-ligating brackets that essentially form a tube developed several decades ago with the Ormco Edgelok26 being the first, close- ly followed by the Speed bracket27 . Both of these early self-ligating systems suffered from the fact that the Straight-Wire Appli- ance phenomenon debuted at the approxi- mately the same time, plus a lack of appre- ciation for what the newer titanium wires could achieve. Damon has persisted since 1995 with his version of a self-ligating bracket (Figure 8) and has fundamentally changed the types of arch wires and the sequence in which cli- nicians use them. His experience has shown that with many patients he can often elimi- nate distalisation of molars, extractions (ex- cluding those needed to reduce bimaxillary protrusions) and rapid palatal expansion. He offers compelling clinical evidence of doing this with consistency.22 The Damon bracket is essentially a tube de- signed with the right dimensions to fos- ter sliding mechanics where needed and enough play in the system for torque and rotational control using the larger cross sec- tion wires. Damon starts cases with a large lumen arch wire slot and .014 or smaller di- ameter hi-technology arch wires. Starting cases with a large dimension passive arch wire slot and small diameter wires dimin- ishes the divergence of the angles of the slots. This lowers the applied force and binding friction. (figure 7) Fig 7a: Binding Fig. 7b: Divergence Figure 8: Damon 3 bracket opened and closed The most logical questions readers could propose would be why has Damon shown successful expansion whereas Angle did Dr. Derek Mahony – Specialist Orthodontist 49 Botany Street, Randwick NSW 2031 Australia Contact Information not? The quantity of expansion probably differs little, but the quality of expansion offers a quantum change. Mollenhauer28 has suggested as much with his appeal for light forces. Even though Angle used a rib- bon arch, (which suggests a thin, delicate wire) the actual size of the wire had the di- mension of .036 x .022 inches. Ligating to this wire would overwhelm the periodonti- um and prevent the development of a sup- porting dentoalveolus. Rather than form- ing new bone, the supporting dentoalveo- lus would simply bend and upon comple- tion of treatment quickly return. Astute cli- nicians often see this with molar distaliza- tion from headgear use and over treat such movement in order to compensate for this regressive bone bending. Schwartz25 stated that it takes 20 to 26 g/ cm² of force to collapse the capillaries in the Periodontal Ligament. With RPEs and headgears this force sometimes exceeds 10 pounds! Profitt29 states that that optimal force lev- els for orthodontic tooth movement should be just high enough to stimulate cellular ac- tivity without completely occluding blood vessels in the periodontal ligament. True Biomechanics is staying in the Opti- mal Force Zone i.e. keeping forces below capillary blood pressure. Conventional ties (o-rings and stainless steel ligatures and spring clips) make staying in the Optimal Force Zone nearly impossible due to the in- creased binding and friction. The most important caveat Damon offers clinicians is not to use their ordinary me- chanics with his system, and I could not agree more. When I first began to use the Damon system, I continued to use the reg- ular sequence of arch wires and saw little advantage to these new, more expensive brackets. Nevertheless, as I began to use the brackets according to Dr. Damon’s ad- vice, I started seeing phenomenonal chang- es. The following patient illustrates typical responses to the biomechanics offered by the Damon System: Summary The paradigm shift in our current thought processes is the belief that alveolar bone can be altered and re-shaped with low clin- ical forces. Using low force, low friction or- thodontics, the alveolar bone allows the bodily movement of teeth in all directions. The architecture of alveolar bone appears to improve over time following low force orthodontics so clinicians should be very creative on how to maintain the appro- priate biologic forces during all phases of treatment. Orthodontists are currently witnessing an interest in qualitatively different expansive biomechanics that offer patients the pos- sibility of obviating the use of distalizers, rapid palatal expanders and many needless extractions. The bracket systems that make this possible should command the utmost respect and clinicians should use them as recommended with light forces. I am witnessing shorter treatment in most of my Damon cases with less discomfort to my patients. The playing field seems to be leveled between adults and children. These changes I am seeing are more than enough reasons for me to question my previous force systems. Reference is available upon request. Please contact deyanov@dental-tribune.com Face before Face after Upper before Upper after Frontal before Frontal after 21Dental ortHo triBUneDental tribune Middle East & Africa Edition | March-April 2013