By Dipak Chudasama, BDS, MSC, MORTH, RCS, MBA, and Eric Howard, DMD, PhD
When first asked to write an article about the various finishing archwires or techniques used by orthodontists, or available in the marketplace, it became clear that the archwire alone or an archwire designed to complement a unique bracket prescription is not sufficient to ensure clinical success. Rather, it is the ability to plan care within the context of the anatomical limits of each patient that improves our ability to provide care with increased efficiency and accuracy.
In this article we will present a case for the preprogrammed shape-memory archwire (SMA) alone, or combined with a custom bracket, as the next significant advancement in orthodontic treatment. The development of SMAs—including Nickel Titanium or Copper Nickel Titanium Niti/Cu-Niti archwires—marks important progress in our specialty. Along with prescription orthodontic brackets and techniques to optimize bracket placement, they are used by many of us and have contributed to the successful treatment of our patients. Niti and other SMAs allow us to resolve initial dental crowding by engaging brackets on malaligned teeth. Ideally, the archwire recovers its initial archform while applying light, predictable, constant force to the teeth and supporting bone.1-2 Bendability is an important factor when the clinician sees the need to place corrective bends to more ideally position teeth or provide force to augment mechanics. During the finishing phase and following space closure, for example, archwire properties must include bendability to correct root inclination, torque, and buccal-lingual position. In our finishing protocols, many of us take advantage of lower-force SMAs that can improve intercuspation by allowing dental “settling” to take place.
Figure 1: (a) An SMA is used to engage all teeth in the upper arch, imposing a significant labial-intrusive force on the lateral incisor and the premolars. (b and c) Virtual tooth movement is achieved by a slot-filling archwire in a common bracket prescription.The introduction of the Straight Wire appliance with prescription into the bracket represented a significant advance in orthodontic care, and theoretically allows us to treat to a more ideal finish with stock archwires.3 However, the preadjusted appliance with Straight Wire mechanics has the potential to introduce “difficulties” rather than “solutions” when used by the novice clinician. For example, in Figure 1a, imagine if a SMA was used to engage all teeth in the upper arch. The angle of the upper right canine bracket would impose a significant labial-intrusive force on the lateral incisor and the premolars, which are currently in relatively favorable intercuspation. This state would likely be disrupted.
The drawbacks of the preadjusted appliance are many. The prescription is based on population averages with the notion that “one size fits all, but with the caveat that one could get the tailor to make some minor modifications at the end.” The preadjusted appliance is also placed in tooth positions based on averages, ie, the central incisor is placed at 4.5 mm, the lateral at 4 mm, and so on. In addition, we are aware that the level of the gingiva often compromises ideal placement; and that placement in the lower arch may become problematic as it often introduces occlusal interferences.
In traditional orthodontic cases, both direct and indirect bonding techniques have been utilized to provide a more optimal bracket position based on the clinician’s clinical judgment. However, both have their inherent problems. Due to differing crown anatomy impacting the preadjusted prescription, rarely does the case finish as planned. Hence, an orthodontist has to use various methods that include but are not limited to rectangular twistflex finishing wires, settling elastics, and archwire bends to detail the occlusion. The above-mentioned issues are not new and have been addressed by clinicians to some extent. However, with the advent of newer technologies, we need to rethink our strategies.
A Case for an Individualized Approach
The development of Niti, Cu-Niti, and TMA archwires has significantly impacted our profession. On one hand, they provide improved comfort with light forces that act over a long period of time. This allows for increased treatment intervals and reduces the number of archwire changes. However, it also invites a one-size-fits-all approach to care where a limited number of average archforms are used to treat all patients. Likewise, the marketplace is laden with stock bracket prescriptions based on anatomical averages. Improved ability to image an individual’s anatomical features allows us to test the appropriateness of a given one-size-fits-all approach.
For example, in Figures 1b and 1c, virtual tooth movement is achieved by a slot-filling archwire in a common bracket prescription. This is contrasted with a similar slot-filling wire that was designed to position the tooth roots centered within the alveolus. This is not to say that those of us who use stock prescriptions routinely place roots out of bone. Most do not fully engage the bracket slot. And while the virtual model provides a visual representation of the anatomical boundary, it does not provide the resistance to root movement that intact cortical bone may impose. Nonetheless, our ability to visualize a 3D rendering of our patient and test our prescription of choice brings into question the appropriateness of a standardized approach to treatment.
Examining the Status Quo
Figure 2: (a) A CBCT-generated image of current bracket positions. (b) SureSmile archwires fabricated with detailed bends to detail the occlusion.Many features of SMAs facilitate our treatment. For example, derotation of teeth is easily accomplished with stock, low-force Niti, or Cu-Niti archwire. While many of us were taught in our residency programs that the first stage of treatment is “leveling and aligning” where light, preformed SMAs engage each bracket, this routine often dictates tooth movements that are counterproductive and may, in fact, not be in the best interest of our patient’s oral health or promote treatment efficiency. In addition, unwanted tooth movement is often encountered when a malaligned tooth—for example, the upper right canine in Figure 1a deflects a wire and places unwanted force on neighboring teeth. Likewise, in Figures 1b and 1c, the position of the lateral incisor may be constrained by the position of the labial cortical bone. In each of these cases, a prescription archwire from SureSmile (OraMetrix, Richardson, Tex) or Insignia’s custom-bracket archwire combination (Ormco, Orange, Calif) would provide a better solution with more ideal, controlled tooth movement. Examples of clinical cases/scenarios are depicted in Figures 2 through 4.
Planning with SureSmile Versus Insignia
The archwire for the Insignia appliance system is formed by heat-treating a Niti archwire and placing the wire under pressure to enable it to take a custom shape. By contrast, the SureSmile prescription wire is formed by a robot that heat-treats the wire locally at the point of each bend. The final result is a wire that is bent in three planes of space with first-, second-, and third-order bends. The Insignia wire is formed with the first- and second-order bends but without the third-order bends. A custom base is built into the Insignia bracket that provides patient-specific torque values.
Initiating treatment is significantly different with the two treatment modalities. With Insignia, a PVS impression is taken and used as a starting point for treatment. In the future, this may be replaced with an intraoral 3D scan. A digital model of the tooth crowns and some gingival architecture is used to digitally position the teeth in their final desired position. One of the strengths of the system is the ability to avoid tooth-bracket interference by adjusting custom bracket position and fabricating a straight wire to accommodate the setup and achieve correct tooth position/occlusion at the end of treatment, provided the diagnosis and treatment execution have been thought out well and then implemented.
SureSmile planning can be initiated by scanning a stone model of the patient with an approved 3D scanner (for example, iTero from Cadent). Called a diagnostic scan, each tooth in the 3D model can be manipulated in all planes of space to simulate treatment. Virtual brackets can be placed and checked for interferences. One strength of this system is that it allows the use of nearly any bracket on the market, meaning an orthodontist doesn’t have to change their bracket choice or philosophy. The Insignia brackets are limited to a few Ormco bracket types, and Insignia uses a unique indirect bonding technique to position brackets. Currently, there isn’t an established method to translate virtual bracket position to the patient with SureSmile. However, after brackets are placed, the patient is scanned and the data is used to create the virtual plan. This may be beneficial, however, as the accuracy of the indirect bonding step does not impact the method. The clinical efficiency of SureSmile technology is well documented,4 and planning provides a unique feature. If the patient is scanned with a CBCT, crown, root, and individual bone anatomy are available to plan the final desired tooth position.
Figure 3: (a) Clinical scenario of images seen in Figure 2. (b) Final outcome of clinical result with the detailing wires. SureSmile is comprised of several key components, including the OraScanner, a patented handheld intraoral imaging device that uses white light to capture accurate 3D images of a patient’s dentition. The OraScanner captures the images of teeth at a chairside station, allowing the chairside assistant performing the scan to view the models as they are compiled and displayed. Alternatively, the iTero scanner from Cadent can be used in place of the OraScanner. A practice can also use a SureSmile-certified CBCT scanner at the office or off-site to generate bonded tooth models.
SureSmile 3D software provides visualization tools for more precise diagnosis, treatment simulation, and customized appliance design. Orthodontists can review digital setups with this software and use it to communicate with patients and with the digital lab at OraMetrix. The digital lab in turn provides scan and setup processing to produce precision robotically bent archwires.
Meanwhile, with Insignia, the clinician takes a PVS impression with bite registration that is sent to the Insignia lab. A digital scan is then sent back to the orthodontist to enable them to digitally move teeth into their desired positions. Once the clinician is satisfied with the final digital outcome, Insignia technicians then utilize computer technology to fabricate custom brackets and custom archwires for an individual malocclusion. One of the drawbacks is that midcourse changes in the treatment mechanics or plan cannot be accomplished once the final occlusion/setup is initiated. Still, it gives an orthodontist an ideal upper and an ideal lower arch with the premise that the treatment modality will ensure that occlusal goals are achieved.
Figure 4: Insignia software does not determine patient care. It provides therapeutics as directed by the orthodontist. The best possible results from these processes depend on the application of the orthodontist’s diagnostic and clinical judgement.
One thing to keep in mind is that OraMetrix/Insignia does not determine patient care. They provide therapeutics as directed by you, the orthodontist. The best possible results from these processes depend on the application of your diagnostic and clinical judgment. The software allows you to try out different treatment modalities and decide whether an extraction or nonextraction option is best in a given scenario (to highlight only one variable).
As orthodontists, when we are dealing with “full-mouth reconstruction” in growing and nongrowing individuals, the onus is always on treatment planning. And as prudent orthodontists, we should use available technology to enhance and speed up our delivery of efficient, effective, and healthy functional occlusions. OP
Disclaimer: Opinions presented in this article are purely those of the authors and do not represent those of the companies mentioned in this article.
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Dipak Chudasama, BDS, MSC, MORTH, RCS, MBA, is in private practice in Coppell, Tex. He can be reached at Eric Howard, DMD, PhD, is in private practice in Lancaster, Pa. He can be reached |
References
1. Segner D, Ibe D. Properties of superelastic wires and their relevance to orthodontic treatment. Eur J Orthod. 1995;17:395-402.
2. Jones ML, Richmond S. Initial tooth movement: force application and pain—a relationship? Am J Orthod. 1985;88:111-116.
3. Andrews LF, Andrews WA. The six elements of orofacial harmony. Andrews J. 2000;1:13-22.
4. Alford TJ, Roberts WE, Hartsfield JK Jr, Eckert GJ, Snyder RJ. Clinical outcomes for patients finished with the SureSmile method compared with conventional fixed orthodontic therapy. Angle Orthodontics. 2011;81:383-388.
