Use of variable torque brackets to enhance treatment outcomes

Transcription

1 Use of variable torque brackets to enhance treatment outcomes Ralph Nicassio DDS Many clinicians performing Orthodontics for their patients are missing an opportunity to get better results because they are using the same standard Roth prescription on the incisor brackets on every case. One example of the limitations using standard Roth brackets is simple alignment of a blocked-out tooth. Evidence that the root has not adequately moved forward can be seen when the clinical crown is shorter than the contra-lateral tooth. (Fig. 1, 2) Fig. 1 Fig. 2 For most patients impeccable resolution of this problem is their chief complaint regardless of other issues in the case. Resourceful clinicians Fig. 3

2 typically attempt to solve this with strategies including bonding brackets upside down or arbitrarily angling placement to enhance the labial root torque. (Thomas, 09) (Fig.3) While possibly effective, other compensations are typically required later and it can be challenging to remember which cases these changes were made on. Advances in manufacturing technology have produced super-elastic rectangular nitie wires that can easily and efficiently apply root torque. One such wire is a Super Elastic NiTi Braid 8,.021 x.025 (Ortho Organizers, Carlsbad, CA, USA), that has approximately the same flexibility as.016n wire. (Fig. 4, 5) Fig. 4 Fig. 5

3 In McLaughlin-Bennett-Trevisi, the author reviews Andrews six keys to normal occlusion. Key 3 is refers to crown angulation and labiolingual or buccolingual inclination (torque) describing it as follows: Torque is expressed in plus or minus degrees, representing the angle formed by a line which bears 90 degrees to the occlusal plane and a line that is tangent to the middle of the labial or buccal long axis of the clinical crown. A plus reading is given if the gingival portion of the tangent line is lingual to the incisal portion. A minus reading is recorded when the gingival portion of the tangent line is labial to the incisal portion. (Fortini, Lupoli, 89) Fig. 6 A more elegant approach is to select bracket torque prescription designed to best align the teeth and/or prevent unwanted tooth movements. Torque is affected only when 2 edges of rectangular wire touch the walls of the bracket slot. But there cannot be excessive binding such that arch wires are not permitted to move easily for alignment and to allow sliding mechanics. (Andrews, 1972)(Fig. 6) To balance this dilemma manufactures machine up to 20 degrees of wire spin when.019 x.025 ss wire is engaged into a.022 slot bracket and 6 degrees on a.021 x.025 ss wire. (Archambault, et al., 2010) The range of this bracket spin has both A-P and vertical consequences on clinical outcomes. (Fig. 7) The ramifications of this are very clinically significant. This is a central dilemma of bracket design: friction is the enemy of some tooth movements such as alignment and sliding mechanics while it is our best friend for other tooth movements like application of torque. For most patients upper incisor inclination would have the upper incisor long-axis pointing right behind the orbit. In most cases the treatment objective is to finish with the upper incisors-sn line to approximate 103 degrees. (Fig. 8) Fig. 7

4 Fig. 8 But when retraction forces are applied to upper incisors this quickly results in these teeth moving to the retraction limit of the bracket prescription being used. If standard Roth prescription brackets are being used the negative A-P and vertical consequences to the upper incisors include: a) de-torqueing (Fig. 9) Fig 9

5 b) anterior deep bite (Fig. 10) Fig. 10 c) increase in gingival display Fig. 11 And while it is possible to recover from these undesirable results, re-establishing incisor torque is typically very slow and inefficient. The smarter approach is to prevent the problems before they occur! Many clinicians have learned to make skillful compensations to prevent these unwanted tooth movements. These include adding torque to arch wires or using reverse curve wires. Even these may not adequately eliminate the retraction limits when using standard Roth brackets. But simply employing variable torque prescription to the appliance design can prevent the unwanted tooth movements including de-torqueing of the incisors. There are significant efficiency and esthetic advantages in cases requiring upper incisor retraction to select upper incisor brackets with a higher torque prescription. The range of bracket torque still has approximately 20 degrees of wire spin (depending on the manufacture). This is a surprise to many as even rectangular wire essentially acts like a round wire in diameter until a tooth either proclines or retroclines enough for the edges to bind into the rectangular bracket slot. (Fig. 12)

6 This play or slop is needed to permit sliding mechanics but the retraction limit using these brackets is the ideal upper 1-MP=103 degrees. Positive torque prescriptions move incisor roots lingually. Negative torque prescriptions move incisor roots facially. (Ortho Organizers, Carlsbad, CA) (Fig. 12) Fig. 12 As a clinician it is important to remember that using these brackets often will initially result in the upper incisors proclining MORE than you are accustomed to seeing during leveling when using a Standard Roth bracket prescription. But the reward is that the upper incisors will finish with more ideal A-P and vertical inclination as retraction mechanics completes. This translates into more ideal results and shorter treatment time as less recovery of unwanted tooth movements is required. (It must be emphasized that light forces must also be used during mechanics. Excessive force

7 could overpower the designed customized torque prescription selected. Orthodontics remains an art form that requires patience.) Variable torque prescription is also very important for the lower arch. For example, if there is crowding in the lower arch and the case is being treated non-extraction the typical result is advancement of the lower incisors and increased proclination. (Fig. 13) Fig. 13 To prevent this selecting lower incisor brackets with more negative torque can be effective in minimizing the advancement. (Fig. 14) Fig. 14

8 Non-extraction Class II cases planning to use Class II elastic mechanics also could benefit from using Negative torque prescription to prevent excessive proclination lower incisors. This can result in more stability and a better periodontal prognosis. (Fig. 15) Fig. 15 However, in Class I or Class II cases where lower bicuspids are removed the ideal lower incisor bracket prescription changes dramatically!!! The typical problem when lower bicuspids are removed is that extraction space closure using lower intra-arch mechanics often are too much at the expense of the lower anterior teeth retracting. The results of this can be miserable including deep bite, increase in gingival display, clockwise change in occlusal plane, and Class II finishes. (Fig. 16) Fig. 16 Much of these complications can be prevented by using lower anterior brackets with more positive torque prescription. The effect of this is to increase the lower anterior anchorage to assist closing the lower extraction spaces by bringing the lower

9 posterior teeth forward more than by retracting the lower anterior teeth. (Fig. 15) Note: if excessive lower retraction is a concern it often additionally is better to extract lower 2 nd bicuspids rather than lower 1 st bicuspids. Ideally in non-extraction Class III cases where upper incisors start out being proclined as a dental compensation for skeletal Class III it is helpful to use upper incisor brackets with more negative bracket torque prescription(move the roots labially) to finish with more esthetically pleasing upper incisors that do not procline the upper incisors further. (Fig. 17) Fig. 17 Unfortunately manufactures have resisted providing this prescription due to inadequate demand from clinicians. It is the author s contention that far too many cases currently are being treated nonextraction. But when this is done open bite is a common finishing complication of the upper and lower incisor advancement. Custom appliance design using incisor brackets with negative torque prescription could greatly prevent open bite complications. Until bracket suppliers provide upper incisor brackets with negative root torque that could prevent incisor advancement, excessive upper incisor inclination, and open bite complications, other strategies may need to be employed. (Fig. 18)

10 Fig. 18 The problem when deciding which variable torque brackets should be selected is that many cases have conflicting treatment objectives. For example if the decision has been made to extract upper teeth ONLY in a Class II case positive torque brackets would normally be used on the upper incisors. But if there are also blocked-out lateral

11 incisors, negative torque would best move the roots labially of these laterals while the upper centrals would get more positively torqued prescription. The first priority in any case must be to impeccably straighten the teeth and bracket torque prescription should be selected paramount to achieve this treatment objective. Secondly, anticipation of any unwanted tooth movements during mechanics should be considered. Thirdly the goal is to select upper torque prescription that creates the most ideal esthetics and lower torque prescription that enables dental compensations when there is skeletal discrepancy limitations (skeletal Cl II or Cl III). The most common situations and recommended bracket prescriptions include: Upper incisors Negative bracket torque prescription (If they become available) A) advancement of upper crowding in non-extraction cases B) open bite prevention C) advancement of upper incisors in non-extraction cases needing Cl III elastics Positive bracket torque prescription A) non-extraction cases where the upper incisor start out being retroclined B) Class II cases where the upper arch is extracting and the upper incisor will be retracted C) Cases where there are gingival display concerns Lower Incisors Negative bracket torque prescription A) advancement of lower crowding in non-extraction cases B) advancement of lower incisors in non-extraction cases needing Class II elastics C) Class III non-extraction cases to minimize the lower incisor advancement Positive bracket torque prescription A) Class I cases where lower bicuspids are extracted to add lower anterior anchorage B) Class II cases where lower bicuspids are extracted to add lower anterior anchorage

12 Finally it is important to consider that each stage or orthodontic treatment has specific treatment objectives: Stage Level and Alignment Mechanics Finishing Objective to straighten the teeth to effect bodily tooth movements to detail esthetics and finalize the occlusion Conclusion: Perhaps the most elegant Orthodontics would include selecting specific bracket torque prescriptions that would most efficiently produce superior results and reduce the need to recover from unwanted tooth movements. The most complex Orthodontic cases might best be treated by changing bracket prescriptions at each stage if necessary to optimize results. For much of the tooth movement 19 x 25 wire and a 22 slot appliance essentially act like a round wire. Using variable torque brackets creates wire spin limits more favorable to upper aesthetics and lower tooth compensation. One of the most sought after topics in Orthodontics is case finishing. Many cases require excessive time and energy as the clinician struggles to correct unwanted tooth movements during the treatment. Better case diagnosis and the use of variable torque brackets in many cases improves outcomes, greatly reduces treatment time, produces more stable results, enables more intra-arch mechanics, reduces the need for patient compliance, increases profitability, and increases overall satisfaction of performing Orthodontics. BLIBIOGRAPHY Archambault, A., Badawi, H., Carey, J., Flores-Mir, C., Lacoursiere, R., Major, P. W. Torque expression in stainless steel orthodontic brackets. Angel Orthodontist. 2010;80: Andrews, L. F., The six keys to normal occlusion. American Journal of Orthodontics. 1972;62:3: Fortini, A., Lupoli, M. Orthodontic treatment conceptions according to McLaughlin- Bennet-Trevisi. Virtual Journal of Orthodontics. 1998;2.3. Retrieved from

13 Thomas, W. W. Variable torque for optimal inclination. Clinical Impression, 2009;17:1 Retrieved from