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Rétraction dentaire par segment ou par dent individuelle. Quelle option est la meilleure?

Révision par Dr Michel Champagne, Mai 2017

Cet article, par les Drs. Amy H. Hoch, Gerald Hoch, Analia Veitz-Keenan, Olivier Nicolay, and George J. Cisneros discute des différentes approches de rétraction ainsi que les forces idéales à utiliser.

Il ne semble pas y avoir d’évidence marquée qu’une technique ou une force est supérieure à l’autre mais des situations peuvent se prêter mieux à une approche spécifique. Il reste à savoir si la préférence du clinicien repose davantage sur les besoins d’ancrage, la mécanique nécessaire qui peut-être plus ou moins complexe, l’esthétique ou simplement l’habitude.

Il est démontré que le fait d’inclure les 2es molaires dans les unités d’ancrage, l’utilisation de forces faibles et un système de basse friction aident au contrôle de l’ancrage. Les sites d’extractions contribuent à la perte d’ancrage, donc l’ancrage est plus difficile à établir dans ces cas. Il semble évident que l’usage de mini-vis peut nous aider à maximiser l’ancrage.

Je vous conseille donc de poursuivre cette lecture jusqu’à la fin de l’article afin de faire vos propres conclusions sur les options qui s’offrent à vous.

Abstract: The intent of this article was to review the literature to determine whether canine retraction followed by incisor retraction is more efficient than en masse retraction of the six anterior teeth during extraction space closure. Methods: Specific keyword phrases such as “anchorage loss in orthodontic space closure,” “en masse retraction in orthodontics,” and “two-step retraction in orthodontics” were used to search Google Scholar, PubMed, Embase, and Cochrane Ovid for published articles. No language restrictions were placed when searching for articles. In addition, the authors’ hand-searched related articles as well. Results: Over 41 articles were obtained and reviewed. All articles were categorized according to the following subtitles: anchorage, overjet reduction, duration, adolescents versus adults, mechanics, lingual versus buccal appliances, etc. Within each category, subcategories were created: TADs, NiTi closing coils, power chains, headgear, etc., to further catalog the articles.

Conclusion:

There is no strong evidence supporting one method over the other. Both techniques can be effective along with the use supplemental materials such as TADs, NiTi closing coils, retraction archwires, and more.

Educational aims and objectives

  • Th Closing first premolar extraction spaces usually requires practitioners to select one of the two following strategies: retraction of the canines first, followed by retraction of the incisors thereafter or retraction of the six anterior teeth all at once, otherwise known as en masse retraction. It is yet unclear whether a practitioner’s preference is based on anchorage requirement, orthodontic mechanotherapy, esthetics, or mere habit. Although extraction of premolars may be indicated for cases with crowding, severe overjet, etc., an individual’s parameters will help determine the extent and limits of the dental movements within each dental arch. Clearly, there are multiple factors that contribute to whether clinicians select one technique over another, or whether one is necessarily better than another. Anchorage loss is multi-factorial, making the issue more complex than it appears. The concept of anchorage control is rooted in Newton’s Third Law of Motion: “For every action, there is an equal and opposite reaction.”1 However, with some of the therapeutic advances we have today, different treatment approaches are revisited. Practitioners may prefer to retract the canines first in the belief that retraction of two teeth, then of four teeth may be more effective to maintain anchorage, while others prefer to retract all six anterior teeth at once. All are still trying to achieve the same goal — space closure obtained efficiently with minimal anchorage loss.

There have not been many studies comparing the two aforementioned techniques, but there have been many publications referring to aspects of space closure. Throughout our search of the topic, we found that while canine retraction versus en masse retraction might be a simple question, many factors play a role in its methods.

The most persistent question is, How do we maintain anchorage to use the extraction space for retraction of the anterior teeth? Do we need a transpalatal arch, perhaps with a Nance button to help achieve anchorage? Should we use headgear, mini-implants, tooth-borne anchorage, etc.? As we found more information, more questions surfaced. For instance, what type of retraction devices should we use? For example, there are power chains, nickel-titanium closing coils, retraction archwires with T-loops, retraction archwires with mushroom button loops, etc. When using different methods, there can also be variations between labial appliances and lingual appliances. There can be differences between first premolar extractions and second premolar extractions and much more.

This paper proposes to review the literature and determine whether either two-step retraction is more efficient than en masse retraction or vice versa.

Material and methods

This was a literature review article.

Many articles compared the following materials when it came to efficiency of closing space with Class I mechanics: NiTi closing coils, elastic modules, such as power chains, and power thread.

Results with discussion

Anchorage can be broken into primary anchorage and secondary anchorage. Geron, S., et al. (2003), describe primary anchorage loss factors as crowding and mechanics and secondary anchorage loss factors as extraction sites, age, and overjet. When comparing primary anchorage loss factors, severe crowding was less conducive to anchorage loss than mechanics. When comparing secondary anchorage loss, extraction sites were more critical than age and overjet. However, it was shown that including the second molar in the anchorage system along with low retraction forces and reduced friction-filled mechanics could be considerably more efficient when controlling and establishing absolute anchorage.

Extraction sites can contribute to anchorage loss, e.g., first premolars versus second premolars. Even though some articles refer to second premolar extraction leading to greater anchorage loss than first premolar extraction patterns, this particular study stated that not enough evidence existed to make it statistically significant.3

Growing and non-growing patients demonstrate differences in anchorage loss. Adults experience greater anchorage loss than adolescents, but the difference between the two groups was not statistically significant. Most likely, this is why growth has been considered a secondary factor when it comes to anchorage loss.

Overjet and crowding are also factors of anchorage loss. Studies have shown that the greater the crowding is in the mandibular arch, the more likely anchorage loss will occur, thus making it a primary factor of anchorage loss. Although biomechanically speaking, it requires less anchorage to unravel crowding than to reduce overjet.

Kawakami and co-workers 4 used implants as anchorage with lingual appliances after second premolar extractions and showed that with implant-supported anchorage, little anchorage loss occurred when retracting the six anterior teeth en masse.

Temporary anchorage devices (TADs) and miniscrew implants are now more common in the orthodontic mechanotherapy. Studies have shown that TADs and microscrews offer effective anchorage control in patients that require maximum anchorage.5-15

Even though headgear has been widely used over the years and has been valued as a useful anchorage device, issues like patient compliance and the negative side effects the headgear may have on the patient’s occlusion limits its use.

Thiruvenkatachari, et al.,9 compared the rate of canine retraction with conventional molar anchorage and titanium implant anchorage. In that study, there was a significant difference in retraction with implant anchorage and molar anchorage. They observed approximately 0.35 mm – 0.60 mm more retraction with implants than with conventional molar anchorage. Moreover, Kuroda, et al.,11 conducted a study comparing headgear use and the use of mini-screws to help retract the canines and incisors. Both treatment modalities had acceptable results; however, using mini-screws helped improves the patients’ profiles by providing more effective anchorage.

Force delivery taxes anchorage, and the type of force used during treatment matters. Studies have researched the different types of materials used to achieve this movement. Nickel-titanium (NiTi) closing coils, elastic modules, and closing loop archwires are among some of the most popular approaches in the retraction of the anterior dentition. However, NiTi closing coils seem to be the most efficient and effective modality.16-21

In summary, little difference was found between the two retraction techniques — en masse versus canine retraction — in maintaining molar anchorage and duration of treatment, however, there were variations in the methodology used for retraction of the anterior teeth.22 NiTi coils with 150 grams of force were the most efficient retracting modality with the least amount of unwanted side effects. Moreover, TADs  appear to be the most effective in maximizing anchorage during extraction space closure. Transpalatal arches with a Nance button can also offer effective anchorage as well as headgear; however, headgear is dependent on patient compliance.

Orthodontic practitioners have multiple techniques for treating patients, especially with extractions. Several opinions exist about whether two-step retraction or en masse retraction is the most effective method. This review has found that both techniques will produce similar outcomes. However a few items clinicians consider when treating extraction patients are the type of anchorage used, the materials used to retract the anterior teeth, and the amount of force applied to the teeth.

Conclusion

There is no difference between en masse and two-step retraction. When closing extraction spaces with either method, the most efficient way to retract the anterior segment is with 150-gram NiTi closing coils. In both retraction methods, clinicians should consider additional anchorage devices to reduce anchorage loss.