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Altering the Extraction Decision with Mini-screws – Part 1 S. Jay Bowman, DMD, MSD

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The Endless Enigma of Extractions and Expansions
The most divisive and persistent argument throughout the history of orthodontics has been whether to extract teeth.1,2 For patients that present with some degree of crowding or protrusion, the question is not whether to extract, but when and which teeth (even if only third molars). The instability of expansive treatments to avoid extraction has been repeatedly examined and reaffirmed,3,4 yet we continue to (re-)introduce "new" ways of squeezing all teeth into dental arches, encroaching upon the enveloping muscular and periodontal equilibrium and "filling" the face and smiles with teeth to o'erflowing. All this kvetching – in the hopes of avoiding the extraction of premolars – often ensures the removal of third molars and the utilization of "permanent" retention, permanently. So, what's this Pecksniffian exchange actually worth?

The contemporary meme of expanding younger patients (with jackscrew appliances)4,5 or older ones (with "slippery" braces and wider wires)6-9 is not an insurance policy for better stability, function or aesthetics (e.g., smiles, buccal corridors or profiles). We seem easily enticed to buy into concepts featuring braces that are said to have unique attributes, concepts of "truly lighter forces"7 and wide-body arch wires, or ancient appliances1 resurrected with arcane claims of bone development6,10 (e.g., bony "adaptation" or "tissue engineering" expanders5); all with the promise of better treatment results through the avoidance of extraction.5,6,8,9,10 The hype is usually novel, but the patient's intrinsic biology hasn't changed.11

The Extraction Decision
Appropriately applied extraction treatment does not produce routine adverse effects on profiles (lack of "fullness") or smiles (narrow dental arches with dark buccal corridors).12-22 But what typically determines our decision to extract? When diagnosis is carried out by typical evaluation of patients' photographs, radiographs and model analysis, it appears from statistical analysis that an orthodontist's decision to extract has been primarily based on the following factors: 1) how "flared" are the upper incisors? (e.g., upper incisor to S-Na angle); 2) how "flared" are the lower incisors? (e.g., lower incisor to S-Nb angle); 3) upper arch length discrepancy; 4) lower arch length discrepancy; 5) how "scrambled" are the lower incisors? (e.g., Irregularity Index); and 6) protrusiveness of the profile (e.g., "full" E-plane or Z-angle).23 There seems little mystery inherent to these factors influencing this "life-and-death" decision for teeth. Yet, there are modernists who believe that defending the extraction strategy is nothing more than oikophobic exercises from hoary academia and exodontia fanatics.

Full-face or Bald-face Orthodontics?
Some within our specialty profess there is a tacit understanding that "expansion" of some contrivance is required to correct nearly any angle classification of malocclusion. Some would have patients believe that the avoidance of extraction (nee, expansion) is the only treatment that will produce the preferred "full faces" and Hollywood smiles.6,8,9 Yet, if we take a moment to evaluate the desired "look" within the faces of those who populate the runways and red carpets, we find that they might occasionally reveal "full lips," but they also manifest "flatter" profiles – without any contribution from extraction orthodontics (e.g., Angelina Jolie, Brad Pitt, Paris Hilton, Gisele Bündchen, Milla Jovovich, Katie Holmes, Jennifer Garner, Nick Lachey, Jessica Simpson, Salma Hayak, Prince William, Halle Berry, Anna Nicole Smith, Charlize Theron, Hilary Duff, Jackie Kennedy Onassis, Sarah Palin, Bollywood's Aishwarya Rai (Miss World 1994), Princess Grace, Drew Barrymore and George Clooney). Bimaxillary protrusions certainly seem to travel in the minority within the circles stalked by paparazzi (Hilary Swank, Rosanna Arquette, Chelsea Clinton, Olivia and Maryam d'Abo, Jason Biggs, Bill Clinton's paramour Paula Jones). In fact, those with the most popular "wide, Hollywood" smiles (Cameron Diaz, Brad Pitt, Angelina Jolie, Farrah Fawcett, Michelle Pfeiffer, Prince William, Justin Timberlake, Ellen DeGeneres, CNN anchorwoman Robin Meade, Gossip Girl's Leighton Meester, Rachel McAdams, Mary Tyler Moore, President Barack Obama, Azra Akin (Miss World 2002), George Clooney, and above all, Julia Roberts) also display the largest "negative spaces."18 It would then seem all the more questionable to promote non-extraction treatments, especially unstable expansive ones,3,4,24 with the intent of preventing "dark corridors."15,17,22,25,26 This holds especially true when smile aesthetics for extraction and non-extraction treatments have been clearly shown to be equivalent12,13,17,22 and also when the common folk (the "end-users" of orthodontic services) are not particularly discerning or afraid of the "dark."25,26

Challenges to orthodontic treatment approaches have left the arena of scientific discourse and landed squarely in the court of opinion. In other words, those who boast the loudest or are engendered with the most financial backing appear to prevail. The fact of the matter is that data and dollars are often at odds in our profession, especially since the range of treatment alternatives apparently offer no health-altering consequences. Besides, a few folks have apparently either benefitted from extractions or were at least not crippled by that dental decision: actors Meryl Streep, Richard Chamberlin, Catherine Zeta-Jones, Renée Zellweger, Jada Pinkett Smith, Heather Locklear, Shia LeBeouf, Meg Ryan, Kristin Davis, Angela Little, Chris Rock, Miss U.K. Globe Hannah McCuaig, Miss Teen USA 2005 Chelsea Cooley, Miss America 2002 Katie Harman, Miss Universe 2004 Jennifer Hawkins, TV personality Kelly Ripa, CNN reporter Richelle Carey, Meredith Viera, John Edward's mistress Rielle Hunter, quarterback Brett Favre, Olympic runner Sanya Richards, Metallica drummer Lars Ulrich, Guns 'n Roses drummer Steven Adler, comedian Rita Rudner, French pop singer Julie Zenatti, Australian pop singer Kylie Minogue, a trio of 90210 TV stars: Shenae Grimes, Jessica Stroup and Jessica Lowndes, along with supermodels Heidi Klum and Molly Sims... just to name a few. As might be assumed, it is an exceedingly difficult exercise to find photographs of celebs with wide-enough smiles and sharp-enough resolution to "count teeth." It is also, perhaps, just simply ludicrous at this point to serve-up celeb anecdotes as proof 8,9 in any scientific discourse.

Mini-screws Enter the Fray
Orthodontists have contemplated concerns for predictable anchorage control for more than a century. The recent introduction of skeletal anchorage, specifically with mini-screws, has provided relatively simple methods for creating innovative biomechanical constructs and, consequently, more predictable orthodontic results. Mini-screws are applicable when designing treatment solutions for a wide range of orthodontic malocclusions.27 The point of the present discussion is to determine if the advent of mini-screws offers any attributes that might, in fact, alter the extraction decision. Please note the caveat that "extraction" is not a diagnosis, but rather, merely a part of a specific treatment plan.

Maximum Retraction
Patients exhibiting severe crowding or protrusion would appear to be the most obvious benefactors for TAD-supported differential forces (in either or both arches) to improve the predictability of biomechanics (Figs. 1 & 2).27-31 These types of treatment plans most often require absolute anchorage and maximum retraction to resolve patients' chief complaints. Occasionally, crowding is resolved with traditional orthodontic mechanics, but anchorage might be lost prior to any significant reduction in protrusion. For example, consider a half-step Class II, crowded patient (treated with extractions) where the dental discrepancy is resolved, but the upper molars remain uncorrected or inadvertently migrate into full-step Class II before overjet is even addressed. All manner of anchorage support has been attempted in these scenarios (e.g., headgear, tip back bends, "setting" anchorage, lingual and palatal arches, Nance holding arches, etc.), but suffer inclusively from limited predictability.


Figs. 1: An adult female with lip incompetency selected a treatment plan involving the extraction of maxillary premolars. Using miniscrews for direct anchorage support of anterior retraction permits the choice of either first or second premolars for extraction and allows for en masse retraction of all anterior teeth, rather than first retracting canines. Retraction with screws is predictable and effective; consequently, anterior torque control is critical. Note: Improvement in facial profile, although additional lingual root torque for the incisors might have been beneficial.


Figs. 2: Young male was embarrassed by his bimaxillary protrusion and lip incompetency. Maxillary anteriors were retracted using sliding mechanics with direct anchorage from miniscrews. Favorable "full face" esthetics achieved with extraction of first premolars.

In contrast, molar positions can be maintained (or enhanced) by direct or indirect support from mini-screws (Figs. 2). In this manner, dental anchorage might not be stressed and maximum anterior retraction or complete utilization of extraction space for the resolution of severe crowding or protrusion is achievable.27-30 As an added benefit, the vertical dimension can be simultaneously controlled by "multi-tasking" with the same mini-screws.30,31

Maintaining Incisor/Lip Position
Sometimes substantial space is required to resolve dental crowding, but no change in incisor angulation or anteroposterior position of the anterior teeth is desired. This situation has been historically problematic as a non-extraction approach could yield "flaring" of the incisors, unstable inter-canine expansion, and possibly untoward lip incompetence. As a more predictable alternative, mini-screws can provide anchorage to retract teeth "just enough" to eliminate the arch-length discrepancy.3,27,32-35 In extraction scenarios, screws can support subsequent protraction of the posterior teeth to close any residual spaces that remain after the resolution of crowding without disturbing lip support.27 Unfortunately, many extraction detractors have conveniently forgotten that orthodontists can move teeth in both directions, especially with mini-screw anchorage (Figs. 3).


Figs. 3: A single miniscrew was used to simultaneously: 1), push the mandibular dentition to the left to correct the midline discrepancy, and also 2) pull molars into the site of a congenitally-missing second premolar ("Pushmi-Pullyu" mechanics).

Mini-screws can also be quite useful in situations where there are already missing teeth (e.g., mutilation or congenital absence) to assist with more predictable closure or opening of edentulous spaces.36 For instance, direct anchorage from miniscrews can facilitate molar protraction to close space where there was agenesis of a premolar.27 Elaborate mechanisms have been devised to avoid the unintended lingual movement of anterior teeth and associated adverse increase in overjet. Using mini-screws for direct or indirect anchorage support can effectively preclude those attendant side effects, while also enabling simplified and efficient biomechanics (Figs. 4).




Figs. 4: An adolescent male with congenitally missing mandibular second premolars. The mandibular molars were protracted using Niti coil springs supported by miniscrews placed in the buccal alveolus. The archwire was inserted through the eyelet of a superelastic coil spring that was then, in turn, hooked onto the lingual cleat of the molar. A stainless steel ligature also was placed through the eyelet and was used to stretch the coil spring mesially. Then the ligature was tied to the head of the screw to maintain the spring activation and provide counter-rotational force. In this manner, no lingual miniscrew was required, yet there was balanced buccal and lingual protraction produced from a single screw.

When spaces are to be opened for the prosthetic replacement of congenitally missing maxillary lateral incisors, there has occasionally been an associated mesial drift of posterior teeth into a partial Class II relationship. Therefore, simply attempting to push "open" sufficient space for an implant might produce an increased overjet. Distal en masse retraction with mini-screws helps to control the space-opening procedure, reduce undesired incisor flaring, preclude extraction of premolar( s), and might also direct movement of posterior teeth into Class I (Figs. 5).27


Figs. 5: An adolescent female with a Class II malocclusion, a congenitally-missing maxillary left lateral incisor, and significant maxillary midline deviation (ala Tom Cruise, Michael Jordan, Princess Stephanie, and Rob Lowe) was treated with Class II distal en masse movement supported by direct anchorage from miniscrews. A space-closer elastic module, elastic chain, and eventually a miniscrew supported Jones jig were used to produce a Class I molar and canine relationship on the left side. Opening of adequate space for future prosthetic replacement of the missing left lateral incisor and a Class I occlusion were produced.

Extract which Teeth?
Can the advent of TAD-based mechanics make a difference in the actual choice of specific teeth for extraction? Occasionally, compromises are required when teeth are selected for extraction. For instance, viable, "virgin" first premolars have often been sacrificed in deference to "root canaled/cored/crowned" second premolars, especially in situations requiring maximum anchorage like those with severe arch length constraints. In addition, "bombed-out" first molars have been maintained while freshly erupted premolars were removed (Figs. 6). Also, second premolars have been occasionally extracted with the intent to limit anterior retraction (the average effect is said to be about 1mm less incisor retraction than that produced by first premolar extraction)19,20 or to facilitate protraction of molars. Although the lip response to retraction in any extraction strategy is not especially predictable,21,37 all of these decisions might need to be re-thought in a world with mini-screw anchorage and efficiently applied directional forces.27,28

Figs. 6: Mandibular first molars required extraction. Protraction of the second molars, while maintaining the incisor and lip position, was completed in 12 months using anchorage from miniscrews placed between first and second premolars. Care was taken to prevent mesial rotation and tipping. Molar uprighting arms were placed into the auxiliary tubes on the first molars to reduce molar tipping. Note: Biomechanics would have been more ideal if the screws had been placed at the mucogingival junction.

There should be no fear to extract premolars if properly designed biomechanics are employed. If, however, retraction mechanics are initiated with no real objective or goal in mind, the consequences of efficient TAD-based mechanics might produce unintended results. It would seem that the use of the visual treatment object (VTO)38 or something similar should enjoy a renaissance in the age of the mini-screw as predictions of tooth movement might now be reasonably accurate. The bottom line: The advent of mini-screw anchorage should finally eliminate the age-old (real or conjured) concerns of adverse facial changes from extraction, as spaces can be closed predictably, while maintaining or even enhancing specific incisor and lip position: moving them either anteriorly or posteriorly as the situation warrants.

Borderline Extraction
Proof has been nugatory for any "better" alternatives for producing the amount of space that the extraction of premolars provides for patients with clear-cut situations that demand them: those with crowding or protrusion.13,18 But, what of the "borderline" extraction case?12,19,20 Can the extraction decision for these patients be altered with mini-screws? Mini-screw-supported molar distalization (e.g., Horseshoe Jet, AOA Orthodontic Laboratory, Sturtevant, Wisconsin) has been demonstrated to be an alternate to maxillary premolar extractions for the resolution of overjet and mild to moderate crowding (Figs. 7).32 Some degree of distal en masse movement (i.e., bodily retraction) of both the maxillary and mandibular dentition has also been reported (Figs. 8).27,32-35 Taken one step beyond, could minor crowding (3-4mm) be resolved by simple TAD-based retraction without questionable two-phase bimaxillary expansion, drastic interproximal reduction or extractions of premolars? At a minimum, perhaps the extraction of a mandibular incisor could be avoided in some instances with this type of mass retraction. Certainly, the limitations of available posterior arch length (e.g., third molar space), the efficiency/ predictability of this type of retraction, and the long-term stability of these "backward-pulling mechanics" are yet to be explored (Figs. 9 & 10). As a result, TAD-based "bimaxillary retraction" as a non-extraction alternative should be approached with cautious optimism.


Figs. 7: A 15-year old female full-step Class II with anterior crossbite, midline deviation, and crowding. Rather than extract maxillary premolars, a miniscrew supported Horseshoe Jet molar distalizer was used to push molars to Class I. Lower leveling and alignment with fixed appliances were achieved concurrent with distalization. No upper brackets were added until necessary for a more esthetic and hygienic appliance during the first 1/3 of treatment. Premolars moved back initially due to forces from transeptal fibers. At the conclusion of distalization, the Horseshoe Jet was "locked" in place and used as indirect support for subsequent retraction of the remaining upper teeth. The Horseshoe Jet is unique to distalizing appliances in that anchorage is derived purely from skeletal support. Although miniscrews may be placed in any number of locations with this device (e.g., anterior or posterior palate; mesial or distal to the horseshoe wire), a favored insertion location is between the first molar and second premolar as this has the largest interradicular space and the premolar will migrate past the screw due to the typical buccal angulation of these teeth.

Some distal tipping of the entire dentition might be anticipated when pulling back all teeth in a dental arch (as might also be expected to accompany bimaxillary retraction with dual J-hook headgear); therefore, full-size arch wires and torque control would be required to limit this effect. Only long-term evaluation of finished results will determine if encroachment on third molar space and this type of posterior "uprighting" is as stable as traditional extraction treatments; however, it certainly appears this might be a more appealing alternative for some patients compared to aggressive, early expansion schemes or relying upon pious hopes for stability of "bone-growing" appliances. 3-6 Although we continue to consistently revisit or resurrect many of these "expansive" dead zones in the evolution of our specialty; proof of efficacy still eludes us.3,4,39,40 This is especially disconcerting as there is the potential for enormous sample pools of patients that should seemingly be easy to tap from practices of those who tout such unique extraction alternatives.


Figs. 8: An adult female with a Class II Division 1 Subdivision Left with midline discrepancy transferred for completion of treatment. In the absence of growth modification, distal en masse movement of the maxillary dentition is required for a non-extraction correction. Direct anchorage from a single miniscrew was combined with intermaxillary elastics to achieve a favorable posterior occlusion and improvement in midline.


Figs. 9: A 13-year old male transferred after Phase I treatment. Bimaxillary en masse "retraction" with miniscrews was initiated to reduce the protrusion and lip incompetency. Progress after 1 year of comprehensive treatment demonstrated significant improvement in profile. Miniscrews maintained the position of the dentition as normal facial growth progressed, resulting in favorable change in Ricketts' E-plan and lip posture.


Figs. 10: Mild bimaxillary protrusion treated with en masse "retraction" using direct anchorage from miniscrews and improvement in protrusion and profile was achieved.

ACKNOWLEDGEMENT
A portion of this paper was originally published in Bowman, S.J.: Thinking Outside the Box with Mini-screws, In: Microimplants as Temporary Orthodontic Anchorage, ed. McNamara, Jr., Craniofacial Growth Series, Ann Arbor, Vol. 45:327-390, 2008.
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  37. Ramos, A.L.; Sakima, M.L.; Pinto A.S.; Bowman, S.J.: Upper lip changes correlated to maxillary incisor retraction—a metallic implant study." Angle Orthod 2005;75:499-505.
  38. Ricketts, R.M.; Roth, R.H.; Chaconas, S.J.; Schulhof, R.J.; Engel, G.A.: Orthodontic Diagnosis and Planning. Denver, Colo: Rocky Mountain Orthodontics 1982:151–269.
  39. Paventy, A.M.: Nonextraction treatment using the Damon System: A CBCT Evaluation. Book of Abstracts. 109th Annual Session of the American Association of Orthodontists, 2009.
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Author’s Bio
Dr. Bowman is a diplomate of the American Board of Orthodontics, a member of the Edward H. Angle Society of Orthodontists, a fellow of both the International and the American College of Dentists, and a fellow of the Pierre Fauchard Academy International Honor Organization. He developed and teaches the Straightwire course at the University of Michigan, is an adjunct associate professor at Saint Louis University and an assistant clinical professor at Case Western Reserve University.

Bowman is a contributing editor for the American Journal of Orthodontics and Dentofacial Orthopedics, Journal of Clinical Orthodontics, Orthodontics:The Art and Science of Dentofacial Enhancement, Hellenic Orthodontic Journal, among several other journals. He was also co-author/editor of the book: Mini-Implants in Orthodontics: Innovative Anchorage Concepts.
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