NEws Paper ARTICLES
The Journey From the Past to the Future - American Journal of Orthodontics
Your Colleagues at Work in The Community - Twelfth Night by the Ft. Worth Dental Society
Smile Makers: Arlington Orthodontics Practice Makes a Lasting Impression - Ft. Worth Business Press
Orthodontics Practice Marks a Half Century - Star Telegram
Journal of Orthodontics (JCO)
Master Clinician - R. G. "Wick" Alexander, DDS, MSD
JCO Roundtable - The Future of Orthodontics
"Room of Truth"
Published Book Reviews
The Lip Bumper Alternative
Proper Timing with Class 2 Elastics
by R. G. “Wick” Alexander, D.D.S., M.S.D.
As in most things in life, “timing is everything.” Diagnostically, class II malocclusions can be classified as either skeletal or dental. In the Alexander Discipline, treatment of a skeletal class II case begins with headgear wear 8 – 10 hours each night. Almost every such case, however, class two elastics are worn toward the end of treatment to obtain final occlusion. If the case does not need orthopedic correction, this dental class II can be treated only with class two elastics.
Proper timing for elastic wear is critical during orthodontic treatment in the Alexander Discipline. It is very important that the final archwires in both arches, 17×25 stainless steel in an .018 slot, are fully engaged, tied back and have been in the mouth at least one month before class II elastics are initiated. At this point the minus 5 degree torque in the incisor brackets has been established. Also, the minus six degree tip in the lower first molars has uprighted these teeth allowing for additional anchorage. Therefore the posterior force of the class II elastics on the maxillary teeth and the anterior force on the mandibular teeth will not result in unwanted maxillary anterior retraction or mandibular anterior flaring.
It is also important to attach elastics to the appropriate teeth. Ideally, it is beneficial to maximize the horizontal component and minimize the vertical component while wearing these elastics. Most orthodontists attach class 2 elastics from the maxillary cuspids to the mandibular first molars. (Fig. 1) Consider the force vector. The vertical force component is significant. However in our approach, a more horizontal force component is used to achieve the sagital movement. This effect is obtained by attaching class 2 elastics to mandibular second molar brackets and to ball hooks attached to maxillary lateral incisor brackets. (Fig. 2) This more horizontal force vector reduces the bite opening tendencies of traditional Class II mechanics. If elastics attached in this manner are used for only a few months near the end of treatment, when heavier arch wires are in place and mandibular anchorage is preserved, little or no loss of torque or occlusal plane tipping will occur.
In the Alexander Discipline, class 2 elastics are not employed to open the bite. In a case with an extreme deep bite, the overbite will be corrected with reverse curve in the lower archwire and box elastics to the bicuspids. After the lower arch has leveled and the bite has opened, class 2 elastics will then be employed.
Occasionally, second molars are not fully erupted, yet elastics are required. In these instances, the elastics must be attached to the first molars. However, cases are not finished as a rule until the mandibular second molars have erupted and positioned properly.
In addition to skeletal class II correction, class 2 elastics are commonly used to correct the difference between centric occlusion (CO) and centric relation (CR). If early in treatment the patient has worn the extra oral appliance properly and has a good growth response, Class II elastics may not be required. Most often, however during the final stages of treatment, a slight CO/CR discrepancy remains.
There are a number of definitions of CO and CR. One version is as follows: Centric Occlusion- The occlusion of the mandibular and maxillary dentition when the patient bites down normally. Centric Relation- the occlusion created when the mandibular condyle is located in ideal position within the glenoid fossa.
Different clinicians may debate the location of this ideal position. In my thinking, the ideal position has the condyle being superiorly positioned while being centered within the fossa in the A-P dimension.