Diastema Closure and Long-Term Stability · forces of occlusion pass through and near the ... necessary to do something that many orthodon-tists dread. I can assure you, ... increases

560 JCO/OCTOBER 2003

Long experience has shown that there arenumerous areas of instability following ortho-

dontic treatment. The tendency for lower anteriorteeth to develop crowding after treatment iswidely known. Maxillary transverse changesduring treatment frequently have a tendencytoward later relapse, as does lower cuspid expan-sion. None of this excludes relapses due simplyto poor treatment. Teeth are often placed in posi-tions that are not in equilibrium with their func-tional environment and are therefore destined torelapse. On the other hand, even teeth that havebeen placed in a reasonably stable environmentmay show relapse tendencies due to environmen-tal changes over a period of time.

Diastemas1-3 constitute a dilemma that hastraditionally required frenectomies,4 circumfer-ential fiberotomies, and/or permanent retention.Do we as orthodontists simply decide that per-manent retention is the best solution to our prob-lems of instability—or is it possible that we canfirst ask why our present “solutions” are notalways successful? Although it is not unusual inorthodontic treatment to look for devices to over-come or prevent undesirable tooth movements,perhaps a greater effort to understand cause-and-effect relationships involved in relapse can leadto better solutions for instability, as well as over-coming the undesirable side effects we so oftenobserve during treatment.5 Orthodontists mustnot depend entirely on devices to resolve ortho-dontic problems, but must also make an effort tobetter understand the nature of these problems.

“Lifetime” Retention

It is a concern of orthodontists and patientsalike that diastemas be eliminated withoutdepending on lifetime retention. Even with surgi-cal procedures,6 diastemas often tend to recur andrequire some form of retention as a result.Obviously, retention with removable appliances

will result in back-and-forth movement, sinceretainers are not worn for 24 hours every day—not to mention that no patient wants to wear aremovable appliance for a lifetime. I have neverseen an adult treated as a youngster, 10 to 20years earlier, who was still wearing a removableretainer. A bonded retainer has the potential toloosen, usually at the most inopportune time,while at the same time not completely relievingthe orthodontist from legal responsibilities aslong as it remains in the mouth. It is not uncom-mon for a patient to believe that if a retainer islost after having been worn for a considerableperiod of time, the teeth will no longer move. Ofcourse, we know this is not the case, but as longas the patient thinks so, there will be disappoint-

© 2003 JCO, Inc.

Diastema Closure andLong-Term StabilityTHOMAS F. MULLIGAN, DDS, MSD

Fig. 1 A. Patient with typical diastema. B. Power-chain elastics used to close space rapidly.

B

A

ment in the treatment or in simply accepting thediastema as a fact of life.

Figure 1A shows a patient with a typicaldiastema. Power-chain elastics can rapidly closethe space (Fig. 1B), which is usually impressiveto the patient. The orthodontist hopes that uponfull eruption of the permanent cuspids, there willbe sufficient tooth contact to maintain the spaceclosure. But we know this does not always occur,even when there is no evidence of a frenum prob-lem.

Archwire Removal

It has been my strong opinion that the mostreliable means of testing for post-treatment sta-bility is to remove all archwires for a minimumof six weeks at some point during treatment.7

This does not mean that archwires must be re-moved following each procedure; many changes,including crossbites, overbites, open bites,diastemas,8 and rotations, may be checked forstability—or instability—at the same time.

Even in cases where the orthodontist knowswith confidence that certain areas will be unsta-ble, it is advantageous to point out the degree ofinstability to the parents and patients duringtreatment. When it is obvious that instability isunavoidable—as frequently occurs when consid-ering facial profiles—the orthodontist can thenallow the parents and patients to observe thesechanges rather than discovering them followingtreatment, when only “perfection” has beenexperienced. We all know the tendency for par-ents and patients to interpret explanations of laterrelapse as simply defensive postures on the partof orthodontists. This provides an opportunity totell them of the importance of absolutely follow-ing post-treatment instructions regarding reten-tion requirements. When they have seen andobserved the problem during treatment, ratherthan following appliance removal, much greater

cooperation and understanding are likely tooccur. The orthodontist also has the opportunityto observe any changes that occur and to incor-porate the patient’s functional environment intotooth-positioning decisions.

The Gedanken Experiment

This is a German expression that essential-ly refers to an experiment conducted in one’smind, as was frequently done by Albert Ein-stein.9 The outcome is determined by consideringknown facts without actually performing theexperiment. In this article, the Gedanken experi-ment will be applied to the discussion ofdiastemas.

The first question to be asked is, “Are thereany analogous situations in orthodontics wheremaintaining space closure presents a retentionproblem?” The answer is, clearly, “Yes.” Weknow from experience that space closure afterbicuspid extractions in adults is often difficult tomaintain. Let’s suppose that instead of parallel-ing the roots following space closure, we weresimply to tip the crowns together. Obviously, thiswould present periodontal problems, but as youwill see, this analogy is only being made to pre-determine the outcome of altering root inclina-tions following diastema closure. The question tobe asked about tipping the crowns together in anadult case is, “Would this assist in maintainingspace closure?” The answer, without performingthe experiment, is, “Yes.”

Now we will look into the reason behindthis prediction. When roots are parallel, verticalforces of occlusion pass through and near thecenters of resistance of the teeth. However, whenthe teeth are tipped, the vertical forces will pro-duce “functional moments”. Since we know thatmoments are simply a result of forces acting per-pendicular to the center of resistance, it can read-ily be seen that when teeth are tipped, the per-

VOLUME XXXVII NUMBER 10 561

Dr. Mulligan is in the private practice of orthodontics at 6843 N. Eighth Ave.,Phoenix, AZ 85013. His website is at www.commonsensemechanics.com.This article is adapted from a chapter in Dr. Mulligan’s book, CommonSense Mechanics in Everyday Orthodontics, CSM, Phoenix, 1998.

pendicular distances—not the forces—are in-creased, thereby resulting in larger moments.These moments are referred to as “functionalmoments” because they are produced as a resultof forces occurring during function—unlikemoments produced by archwires.

Without having performed the experiment,but having concluded what effect the tipping ofteeth will have on stability, we can now considerthe diastema. When we tip the crowns togetherfor space closure, instability is frequently recog-nized. Once the space is closed, we can’t tip thecrowns any more, but we can diverge the roots,thereby creating the change in inclination thathas already been shown to produce higher func-tional moments (Fig. 2). It can be seen that whenthe roots are convergent, simply uprighting theroots results in increasing the moments. As wewill see, further divergence of the roots willafford larger functional moments.

Only by removing the archwire will wedetermine the point of stability, which makes itnecessary to do something that many orthodon-tists dread. I can assure you, however, thatremoving archwires on every patient, regardlessof the degree of malocclusion, has been thegreatest learning experience of my 41 years inpractice. If all orthodontists did so, I think ithighly likely that intra-arch mechanics wouldbecome much more routine in daily practice thanthe interarch mechanics so commonly usedtoday. Midline elastics, Class II elastics, and thelike result in tooth displacements leading toinstability that will be quickly recognized whenarchwires are routinely removed.

Initial Patient Samples

To test the Gedanken experiment, I gath-ered patients whose parents were willing to havetreatment initiated early, informing them that thiswas an attempt to discover the legitimacy ofseeking stability for diastema space closure. Theparents knew beforehand that this attempt couldresult in success or failure, but having trusted thepractice as part of their families for a consider-able period of time, they were most cooperative.

It was important to evaluate the x-raysclosely, as some patients were beginning thisexperiment prior to the eruption of permanentcuspids, which would provide contact adjacent tothe four incisors, and other patients had missinglaterals, offering the opportunity to move thecentral incisors together with no lateral contact.Obviously, if stability could be achieved in thesecases, further eruption of teeth would only add tothe existing stability. Orthodontists would nolonger have to pay special attention to the x-rays,as such treatment could simply be incorporatedinto normal treatment planning. Again, successcould not be determined without archwireremoval.

Producing the Moments

In Figure 3A, it can be seen that the use ofan .016" anterior segment with no bends results

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Fig. 2 When incisor roots converge, uprightingincreases functional moments.

in equal and opposite moments, as a result of thewire/bracket relationship formed by the maloc-clusion.10 This particular relationship producesthe same moments as a center bend, and is char-acterized by equal and opposite moments when-ever there are equal and opposite angles betweenthe wire and brackets.

As the roots upright, the bracket slots then

become aligned, and a center bend is placed inthe archwire (Fig. 3B). This is done intraorallywith a Tweed loop plier and produces a 45° anglein the wire.

Next, the roots diverge as a result of thecenter bend, and the anterior segment is removed(Fig. 3C). If the space remains closed for a min-imum of six weeks, the closure can be deemedstable. If it reopens, the same wire with the sameoriginal bend is placed in the bracket slots, andthe root is permitted to undergo additional diver-gence.

Finally, the incisal edges can be reshapedusing a diamond disk (Figs. 3D, 4). It is critical-ly important not to reshape these incisors if thearchwire has not been previously removed.Otherwise, any later relapse would result in anundesirable cant to the incisal edges.

Factors Regarding Inclination

The orthodontist will discover that thetreatment time and amount of root movementrequired will vary from patient to patient, usual-ly depending on the inclination of the incisors.Small diastemas will often exhibit a convergenceof the roots (divergence of the crowns). There-fore, the original archwire will automaticallyproduce moments at the brackets, and when thebracket slots become level and a center bend isplaced, this will create the moments necessaryfor further divergence. In other cases, the tooth


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Fig. 3 A. Equal and opposite angles between .016"anterior segment and incisor brackets, producingequal and opposite moments. B. Center bendplaced in archwire after roots have been uprightedand bracket slots aligned. C. After roots divergedue to center bend, anterior segment is removedfor evaluation of stability. D. Incisal edges recon-toured with diamond disk.

Fig. 4 Recontouring of incisal edges with dia-mond disk.

A

B

C

D

inclinations may be parallel from the beginning,thus requiring less movement than previouslydescribed. And finally, some of the largerdiastemas, following rapid space closure, have ahead start on root divergence (crown conver-gence) and, surprisingly, will often require lesstime to achieve stability than some smallerdiastemas.

Applying the Moments

The patient in Case 1 had an obviousdiastema, but closer evaluation showed thediastema to involve root inclinations that werenearly parallel (Fig. 5). After removal of thearchwire for six weeks, the space remainedclosed, so the archwire was reinserted and a dia-mond disk was used to contour the incisal edges(Fig. 6). With no further need for the archwire, itwas removed, and the patient was placed on

observation for several months while waiting forthe permanent cuspids to erupt (Fig. 7). Twomonths later, additional cuspid eruption could beseen, but there was no recurrence of the diaste-ma, despite the lack of tooth contact to maintainspace closure (Fig. 8). This is a sure indication

Fig. 5 Case 1. Close-up evaluation of diastemashows nearly parallel central incisor root inclina-tions.

Fig. 6 Case 1. After confirmation of stability byarchwire removal, archwire is reinserted and dia-mond disk used to contour incisal edges.

Fig. 7 Case 1. Cuspids beginning to erupt twomonths after archwire removal.

Fig. 8 Case 1. Further cuspid eruption two monthslater, with no recurrence of diastema.


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that upon full eruption of the cuspids, the stabil-ity of the closure will be further enhanced.

Missing Lateral Incisors

The next patient also exhibited parallel rootinclinations, but had missing lateral incisors (Fig.9). This was an excellent opportunity to discoverwhether root divergence could permit stablespace closure. Initially, an .016" anterior segmentwith a center bend was placed to provide theequal and opposite moments (Fig. 10). Power-chain elastics provided rapid space closure.Crown movement always precedes root move-ment, but once the space is closed, the crownscan no longer move and the roots move in theopposite direction. Anything that prevents crownmovement in one direction results in root move-ment in the opposite direction.

Bracket angulations are not estheticallypleasing after root divergence, but it is importantnot to reposition these brackets until stability hasbeen obtained, because any evidence of instabil-ity will require reinserting the same archwiresegment. Once stability has been confirmed, ifthe patient is ready to resume full treatment,brackets can be placed ideally. In Case 2,improper bracket placement initially resulted in aslight vertical discrepancy between the two

incisors (Fig. 11A). By sliding the wire slightlyto the patient’s left, a long section and a shortsection were created (Fig. 11B). The long sectionalways points in the direction of the force pro-duced at the bracket engaged by the long section.These forces are produced by definition to main-tain equilibrium whenever moments are notequal and opposite.

Fig. 9 Case 2. Patient with parallel central incisorroot inclinations and missing lateral incisors.

Fig. 10 Case 2. .016" anterior segment with centerbend placed to produce equal and oppositemoments.

Fig. 11 Case 2 A. Slight vertical discrepancy be-tween central incisors created by improper initialbracket placement. B. Equilibrium restored bysliding wire segment to patient’s left.

A

B


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Nine months later, the cuspids were erupt-ing, but there was no space opening whatsoeverbetween the central incisors (Fig. 12). If spaceclosure can be maintained without the presenceof lateral incisors in contact with the distal sur-faces of the central incisors, then stability willonly increase with further treatment.

Root Divergence

In Case 3, the diastema was obvious to anyobserver, and a closer view showed an inclina-tion that was predominantly parallel (Fig. 13).Six years later, the patient could smile with pride,having had no retention of any kind (Fig. 14).The root inclinations were divergent, but theexact amount of divergence required for stabilitycannot be known unless archwires are removedduring treatment.

The next patient, Case 4, revealed adiastema similar to that of her sister in Case 3(Fig. 15). Both sisters were treated at the sametime, yet in one case the archwire was removedonly once to determine stability, whereas the sib-ling required several archwire removals beforestability was established. Keep in mind that sim-ilar diastemas do not necessarily require thesame amount of treatment time or root move-ment. This is determined solely by archwireremoval. Six years later, the patient had a beauti-ful smile without retention of any kind (Fig. 16).The root divergence was similar to that of her sis-ter. Slight differences in inclination can make thedifference between stability and instability.

Fig. 12 Case 2. Cuspid eruption nine months later,with no recurrence of diastema.

Fig. 14 Case 3. Patient six years later, showingstability of diastema closure without retention.

Fig. 13 Case 3. Close-up view of diastema showsrelatively parallel central incisor root inclinations.


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Root Convergence

Case 5 shows a patient with a smallerdiastema than any seen thus far (Fig. 17). Whentaking a closer look, however, it can readily beseen that the root inclinations were convergent,although not in equal amounts. The initial arch-wire leveled the bracket slots, followed by place-ment of the center bend (Fig. 18). More than ayear and a half later, while waiting for cuspideruption, the space closure remained stable (Fig.19). Another several months later, the cuspids

Fig. 16 Case 4. Patient six years later, showingstable results with root divergence similar to sis-ter’s.

Fig. 15 Case 4. Sister of patient in Case 3, show-ing similar diastema.

Fig. 17 Case 5. Patient with small diastema andconvergent central incisor root inclinations.

Fig. 18 Case 5. Center bend placed after initial lev-eling of central incisor bracket slots.


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were about to erupt, but the space closureremained stable with no tooth contact distal tothe lateral incisors (Fig. 20). This assures stabili-ty following completion of treatment.

The next young lady also displayed a con-vergence of incisor roots (Fig. 21). After leveling

of the bracket slots, a center bend was placed toproduce further root divergence (Fig. 22). Threemonths later, there was only minor additionalmovement (Fig. 23), but archwire removal short-

Fig. 19 Case 5. Stability of diastema closure morethan 18 months later, while awaiting cuspid erup-tion.

Fig. 20 Case 5. Stability of closure another fewmonths later, with cuspids about to erupt.

Fig. 21 Case 6. Patient with convergent centralincisor root inclinations.

Fig. 22 Case 6. Center bend placed after initial lev-eling of central incisor bracket slots.

Fig. 23 Case 6. Minor tooth movement threemonths later.


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ly thereafter indicated stability, and treatmentwas concluded with no retention (Fig. 24).

Another root convergence is evident inCase 7, but this time in combination with a rota-tion of the upper right central incisor (Fig. 25).Rather than remove an archwire for each individ-ual problem, it only makes sense to diverge theroots, over-rotate the central incisor, and thenremove the archwire so stability can be checkedfor both conditions at the same time (Fig. 26). Inthis case, stability was demonstrated after arch-wire removal (Fig. 27).

Minor Cosmetic Adjustments

If the contact area between the centralincisors is a little greater than normal, very slightmovements can be obtained with the center bendto produce some cosmetic improvement. In Case8, the patient required only a minor amount oftooth movement (Fig. 28), so a center bend wasplaced as shown (Fig. 29). Although the move-ment was small, the patient’s appearanceimproved (Fig. 30).

Producing Pure Momentson Four Incisors

A continuous archwire with esthetic bendsis incapable of producing pure moments on all ofthe incisors without vertical forces. These can beavoided by placing two separate anterior seg-ments11 (Fig. 31). The segment connecting thetwo central incisors is an .016" stainless steel

Fig. 24 Case 6. Stability of diastema closure con-firmed after archwire removal, with no retention.

Fig. 25 Case 7. Patient with convergent centralincisor root inclinations and rotated upper rightcentral incisor.

Fig. 26 Case 7. After divergence of central incisorroots and correction of incisor rotation.

Fig. 27 Case 7. Stability confirmed after archwireremoval (photos taken 18 months apart).


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wire, while the segment connecting the lateralincisors is .019" × .025". The latter segment isrectangular simply to prevent any twisting of thewire in the slot. Each segment is activated 45°degrees as shown (Fig. 32). This activation isstandard for all the wire bends discussed here.

Fig. 28 Case 8. Patient with small diastema.

Fig. 29 Case 8. Center bend placed to produceminor tooth movement.

Fig. 30 Case 8. Improvement in patient’s finalappearance.

Fig. 32 Each wire segment activated 45°.

Fig. 31 Pure moments produced on all fourincisors by using two segments: .016" stainlesssteel wire connecting central incisors and .019" ×.025" rectangular wire connecting lateral incisors.


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Generalized Spacing in Deep Overbites

The young lady in Case 9 had not only adiastema, but a deep overbite (Fig. 33). Theincisor roots can be diverged during overbite cor-rection, but the archwire should not be removeduntil the overbite is corrected. Obviously, duringoverbite correction (Fig. 34), the anterior mesio-distal dimensions between the cuspids arereduced, so stability cannot be properly evaluat-ed until the incisors are placed within thesedimensions. In this case, the spaces were closedand remained so without retention (Fig. 35). Avery slight space remained between the centralincisors, but both the patient—a young adult—and her parents were unaware of it.

(continued on next page)Fig. 33 Case 9. Patient with diastema and deepoverbite.

Fig. 34 Case 9. Anterior mesiodistal dimensions between cuspids reduced during overbite correction.

Fig. 35 Case 9. Patient after diastema closure and confirmation of stability, with only slight space remaining.


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Problems of Morphology

Sometimes a patient will complain about alittle space between the front teeth, when theproblem is actually not a diastema, but rathercrowns that taper toward the incisal edges (Fig.36). A center bend can be placed to move thecontact area incisally, thus reducing or eliminat-ing the “space” that concerns the patient. Insteadof referring the patient to the family dentist for asolution, a center bend can usually resolve theproblem orthodontically.

Long-Term Rewards

The young man in Case 10 was treated inthe original experimental group described above(Fig. 37). Seven years later, when he was drivinghis younger sister to the office for treatment, achairside visit brought up a discussion of neverhaving worn a retainer. He is now a handsomeyoung man with a beautiful smile (Fig. 38), andhe also has the satisfaction of knowing thediastema is not destined to reopen.

Contrast this with the case of a despondentyoung adult woman who visited the office won-dering if anything could possibly be done for herfront teeth (Fig. 39). She had been told to “leavethem alone” and that she would be better off nothaving orthodontic treatment. She certainly had aneed for cosmetic treatment, if nothing else.

The spaces were closed, but the incisorsshowed no root divergence (Fig. 40). The origi-nal space was simply consolidated into spacesbetween the lateral incisors and the cuspids. Withno center bends having been placed or archwiresremoved to evaluate stability, we had no choicebut to deliver a removable retainer, with its labi-al bow passing through the residual spaces. Thepatient was instructed to begin wearing theretainer at night only, which meant there wouldbe continued movement of the teeth.

The patient’s stains were removed, and thefinal facial pictures showed a beautiful andhappy adult. Although she stopped by the officeperiodically for about two years just to saythanks, she is no longer in the area. Is it possible

Fig. 36 Appearance of diastema caused by centralincisor crowns tapering toward incisal edges.Center bend can be placed to move contact areaincisally.

Fig. 37 Case 10. Patient with diastema beforetreatment.

Fig. 38 Case 10. Patient seven years later, show-ing stability of space closure.


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Fig. 39 Case 11. Adult patient with diastema and need for cosmetic treatment (note stained teeth in occlusalview).

Fig. 40 Case 11. Diastema closed without root divergence, requiring retention. Original space was consoli-dated into spaces between lateral incisors and cuspids.


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she might no longer be wearing her retainer? Is itpossible the retainer was lost and treatment notreinstituted? If she is still wearing the retainerand still looks as beautiful as ever, is it possiblethat continued movement of the teeth might haveresulted in some damage to the tissue? None ofthese questions would have to be asked if I hadused center bends and archwire removal as a rou-tine part of diastema treatment at that time.

The Black Triangle

Root divergence in the treatment ofdiastemas results in a greater mesiodistal widthoccupied by the incisors. With normal tooth-mass proportions, this divergence creates someoverjet. By performing interproximal reductionwith an .003" disk, however, the overjet can bereduced while minimizing or eliminating the“black triangle”. Keeping this in mind, even inthe absence of diastemas, root divergence of thecentral incisors—or of all four incisors—pre-sents the opportunity to eliminate generalizedspacing in cases where tooth mass is deficient, aswell as in situations where there is no tooth-massdeficiency, but a “black triangle”.

Conclusion

An approach to treating diastemas has beenpresented that requires no additional expense, butmay even reduce costs as a result of eliminatingretainers that would normally be required tomaintain the space closure. It has been my expe-rience that 90-95% of diastemas treated in thismanner will not require retention. The orthodon-

tist might decide on retainers for reasons otherthan treatment of the diastema, but should findthis procedure to be highly successful in themajority of cases.

As difficult as some may find it to be, youcan be assured that removing archwires in allorthodontic malocclusions—even those youknow beforehand will not be stable—will be anextremely rewarding and educational experience.Greater respect will be gained for the normalfunctional and environmental positions of teethand the need to avoid many of the interarchapproaches to orthodontic mechanics that areprevalent today. Being able to let the patientobserve the degree of stability or instability priorto termination of treatment is rewarding in itself.

REFERENCES

1. West, E.E.: Diastema, a cause for concern, Dent. Clin. N. Am.8:86-95, 1968.

2. Baum, A.T.: The midline diastema, J. Oral Med. 21:30-39,1966.

3. Bishara, S.E.: Management of diastemas in orthodontics, Am.J. Orthod. 61:55-63, 1972.

4. Edwards, J.G.: The diastema, the frenum, the frenectomy: Aclinical study, Am. J. Orthod. 71:489-507, 1977.

5. Edwards, J.G.: Diastema relapse, Dent. Clin. N. Am. 37:212-225, 1993.

6. Bell, W.H.: Surgical-orthodontic treatment of interincisaldiastemas, Am. J. Orthod. 57:158-163, 1970.

7. Mulligan, T.F.: Common Sense Mechanics in Everyday Ortho-dontics, CSM, Phoenix, 1998, p. 106.

8. Campbell, P.M.; Moore, J.W.; and Matthew, J.L.: Orthodontic-ally corrected midline diastemas, Am. J. Orthod. 67:139-158,1975.

9. Hey, T. and Walters, P.: Einstein’s Mirror, CambridgeUniversity Press, Cambridge, England, 1997, p. 271.




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Diastema Closure and Long-Term Stability · forces of occlusion pass through and near the ... necessary to do something that many orthodon-tists dread. I can assure you, ... increases

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