READERS’ FORUM

Letters to the editor*

Unexpected complicationsIt is always satisfying when one’s strongly held beliefs

are validated. Such was the case with “Unexpected compli-cations of bonded mandibular lingual retainers” (Katsaros C,Livas C, Renkema AM. Am J Orthod Dentofacial Orthop2007;132:838-41). For the reasons the authors cited, I havelong held that the introduction of the flexible spiral wire wasone of the more ill-advised retaining devices to be imposed onthe specialty (my opinion, not theirs). Purportedly, one of thechief reasons for its use was the physiologic stimulation theflexible wire afforded the periodontium. But this claim has nobasis in fact when one considers the long-term health ofmultiple splinted prosthetic units.

Additionally, I have never been an advocate of bondingall incisors, particularly when these teeth were never irregu-lar. Not only can this compromise hygiene, but also there isgreater risk of individual bond failure. Granted, bonding onlythe canines might still result in some future incisor irregular-ity, but this problem can be minimized by light strippingbefore and during the retention period.

The authors’ choice of a rectangular wire is a good one,particularly if the torque is harmonized with the lingualinclination of the incisors. My personal choice is Markleythreaded wire (Almore International, Inc, Beaverton, Ohio). Iwas introduced to this by Dr Roger Wise of Swampscott,Mass, a dual specialist (orthodontics and periodontics) and aninternational lecturer, who has successfully used this systemfor over 25 years. The threaded wire enhances compositeadhesion, much like the irregular surface of the flexible spiralwire, but without its inherent disadvantages. Furthermore, thestiffness of Almore’s wire allows the option of bonding onlyto the canines (and select incisors if you choose), withoutcompromising the wire’s stability. My preference is .032inch, but all dimensions are available.

One last word: occasionally a patient comes to our clinicwith a request from the dentist to remove the lingual wirebecause of excessive tartar accumulation. Invariably, thisresults from a wire placed too far gingivally. It just makesgood sense to place these retainers as incisally as estheticallypossible.

Morton SpeckBelmont, Mass

Am J Orthod Dentofacial Orthop 2008;133:4840889-5406/$34.00Copyright © 2008 by the American Association of Orthodontists.doi:10.1016/j.ajodo.2008.02.002

*The viewpoints expressed are solely those of the author(s) and do not reflect

those of the editor(s), publisher(s), or Association.

484

Authors’ responseWe thank Dr Speck for his interest in our article and the

important points he raises. In our article, we dealt only withpatients with unexpected complications during retention witha mandibular 3-strand twist flex retainer, and not with theeffectiveness of 3-strand twist-flex retainers in general. In anupcoming article, we examine the long-term effectiveness ofthis type of retainer in a large number of patients followed for5 years posttreatment. This new study shows that, in mostpatients without complications, twist-flex retainers are effi-cient in preventing relapse of the mandibular anterior teeth.1

Despite the effectiveness of these retainers in most cases, wedo not use them anymore, because undetected complicationsusually led to retreatment, which we want to avoid.

We agree that often a thick retainer bonded only to themandibular canines is efficient in maintaining acceptablealignment of the mandibular anterior teeth.2 However, whenperfect retention of incisor alignment is desired, a rectangularstainless steel retainer bonded on all anterior teeth is, for us,the method of choice.3 Whether another type of wire is moresuitable for this purpose has still to be investigated.

Christos KatsarosChristos Livas

Anne-Marie RenkemaNijmegen, the Netherlands, and Athens, Greece

Am J Orthod Dentofacial Orthop 2008;133:4840889-5406/$34.00Copyright © 2008 by the American Association of Orthodontists.doi:10.1016/j.ajodo.2008.02.003

REFERENCES

1. Renkema AM, Renkema AAP, Bronkhorst EM, Katsaros C.Long-term effectiveness of canine-to-canine bonded lingual re-tainers. Am J Orthod Dentofacial Orthop 2008 (submitted forpublication).

2. Renkema AM, Al-Assad S, Bronkhorst EM, Weindel S, KatsarosC, Lisson JA. Effectiveness of 3-3 bonded lingual retainers inpreventing relapse of the mandibular incisors. Am J OrthodDentofacial Orthop 2008 (in press).

3. Katsaros C, Livas C, Renkema AM. Unexpected complications ofbonded mandibular lingual retainers. Am J Orthod DentofacialOrthop 2007;132:838-41.

Friction and anchorage loadingThe article on friction and anchorage loading, “Friction

does not increase anchorage loading” (Southard TE, MarshallSD, Grosland NM. Am J Orthod Dentofacial Orthop 2007;131:412-4), seems to have produced considerable interest inthe orthodontic community, as it was followed by 3 letters tothe editor and 2 author replies. I believe that a few morethoughts are warranted.

First, the scientific question. To simplify the system

American Journal of Orthodontics and Dentofacial OrthopedicsVolume 133, Number 4

Readers’ forum 485

under discussion as much as possible, but without loss ofgenerality, I assume we have 2 identical teeth, instead of acanine and a molar, one acting as the anchor unit and the otheras the retraction unit. We need to differentiate between 2cases: the first when the wire is a sectional piece joining justthese 2 teeth, and the other when the wire continues as a fullarchwire engaging other teeth.

Case A (sectional wire): In his letter, Dr Burrow (Am JOrthod Dentofacial Orthop 2007;132:725-6) considered dif-ferent width brackets and concluded that frictional forces willbe different at the 2 teeth, at least part of the time. Thisimplies that the teeth will not move equal distances justbecause the bracket widths are unequal, when all other factorsare identical. This does not seem valid, and it does not agreewith classical mechanics. I do not contend that frictionalforces will be equal. However, if 1 frictional force is greaterthan the other, then the wire does not need to slide at bothsides; it will slide on the side of less friction, and the systemwill be equivalent to a tooth with a rigidly attached extensionwire going through the other tooth’s bracket slot. It is evidentthat such a system will produce equal forces at both roots. DrSouthard et al are right in their conclusion, which followsinevitably from the principles of static equilibrium. In fact, noextended explanations or full-length articles are needed; theargument fits into 1 (albeit long) sentence: the whole system(bone, teeth, wire, elastic) is in static equilibrium, and noexternal forces are present, so the total force acting on thealveolar bone must be zero, and since this comes only fromthe roots of the 2 teeth, each root must apply the samemagnitude of force (in opposite directions). This is alwaystrue, irrespective of friction or binding at the brackets.

Case B (full archwire): A full archwire might havefriction or binding at other teeth. Let’s consider the extremesituation when complete binding of the archwire occurs at theincisors and the retraction tooth (canine). Then, the incisorsand the canine act as a single unit, so the force will bedistributed over a larger root surface area, and the caninemight move less, whereas the anchor unit continues to “feel”the same force and will probably move more. Therefore, DrSouthard et al’s tenet does not hold in cases of a full archwire,where relative movement depends on relative friction at eachof the 2 teeth. For a more extreme example, additionallyassume that the incisors are ankylosed; there will be zeromovement of the canine and complete loss of anchorage.

In my initial letter (Am J Orthod Dentofacial Orthop2007;131:699), I expressed disappointment that the originalarticle needed to be published. It analyzed one of the simplestbiomechanical cases possible: 2 teeth connected by a rigid,passive piece of straight wire. There is no rocket science here.It is not a matter of opinion, and it is not a matter ofexperimental evidence. It is just judicious application of verybasic principles of classical mechanics. Yet, the obviousconclusion was considered an important insight warrantingpublication, and it was then debated by university professors,no less. Our specialty is more than 100 years old. Shouldn’t

this biomechanics question be a first-semester postgraduate

student exercise, at most? What does this tell us about oureducational system? Isn’t disappointment justified?

Demetrios J. HalazonetisKifissia, Greece

Am J Orthod Dentofacial Orthop 2008;133:484-50889-5406/$34.00Copyright © 2008 by the American Association of Orthodontists.doi:10.1016/j.ajodo.2008.02.008

Authors’ responseWe proposed a basic tenet of sliding friction that keeps

getting lost in letters to the editor. We examined the effect offriction during sliding mechanics from the viewpoint of thearchwire. Frictional loading during canine sliding retraction(canine and molar are free to slide along archwire) occurs onlyif the archwire between the canine and the molar is undercompression. This compressive force decreases the retractionload on the canine but, at the same time, decreases the protrac-tion (anchorage) load on the molar by an equal amount.

If sliding friction is present when pitting severalanterior teeth (being retracted) against several posterioranchorage teeth (being protracted), the archwire will stillbe compressed by the frictional force, the anterior retrac-tion load will be reduced by the amount of the frictionalforce, and the posterior protraction load will be reduced byan equal amount.

Tom SouthardSteve Marshall

Iowa City, IowaAm J Orthod Dentofacial Orthop 2008;133:4850889-5406/$34.00Copyright © 2008 by the American Association of Orthodontists.doi:10.1016/j.ajodo.2008.02.009

Realities of mandating 3-yearprograms

Steve Lindauer should be congratulated for his conciseyet comprehensive editorial regarding the true realities asso-ciated with the current movement toward increasing orth-odontic postgraduate programs to 3 years (“Is the time reallyright for mandatory 3-year orthodontic residency programs?”Am J Orthod Dentofacial Orthop 2008;133:2-3). There isindeed far more to the issue than just the argument thatresidents can complete more of the cases they start and thususe them when they go for their boards. Dr Lindauer pointedout many issues and problems, but one issue was notdiscussed. It is one that I believe that we as a specialty needto take heed of.

Although much of my writing can be interpreted asanti-ABO, nothing could be further from the truth. As the firstthird-generation boarded orthodontist in the world, I believethat completing a meaningful process that results in boardcertification should be what every practitioner aspires toachieve. However, I disagree with the process that the ABOhas adopted over the past few years to increase the number of

board-certified practitioners. I fully agree with the goal; but I