mandibular incisor extraction therapy

American Journal of ORTHODONTICS and DENTOFACIAL ORTHOPEDICS

Founded in 1915 Volume 105 Number 2 February 1994

Copyright © 1994 by the American Association of Orthodontists

CLINICIANS' CORNER

Mandibular incisor extraction therapy

Joseph R. Valinoti, DDS* New York, N.Y.

Extracting a mandibular incisor has been stigmatized as an expedient that may adversely affect the occlusion. However, when properly used, the extraction is only one aspect of the total correction of the malocclusion. Failure to observe this will fulfill the negative predictions. Articulating six maxillary with five mandibular anterior teeth necessitates a visualization of the posttreatment occlusion, and therefore specific criteria for case selection are essential. Treatment trends oscillate between nonextraction and four premolar extractions, with perhaps insufficient attention currently given to alternatives. This middle of the road approach is indicated in carefully selected cases, especially where space requirements and facial esthetics do not call for greater dental movements. (AM J ORTHOD DENTOFAC ORTHOP 1994;105:107-16.)

S e v e r a l approaches for crowded mandibular anterior teeth are currently employed: distal movement of posterior teeth, lateral movement of canines, labial movement of incisors, interproximal enamel reduction, removal of premolars, removal of one or two incisors, and various combinations of the above. Selecting the best treatment is often difficult, and all guidelines do not apply to every case.

Even more vexing to the clinician is that no one of these treatment plans can predict ultimate stability with even reasonable certainty. Studies show a natural long- term unpredictable tendency for mandibular intercanine width to decrease in treated and untreated dentitions, for bites to deepen, and for posterior teeth to move forward for many years with recrowding of anterior teeth. '~ These findings are at variance with some of the previously mentioned treatment plans for crowding. It does seem reasonable, however, to ask: "Are retainers forever?"

REVIEW OF THE LITERATURE

No reports are available on the frequency of a mandibular incisor extraction, perhaps indicating its infre- quency, or its infrequent reporting. However, there are

*Clinical Professor, New York University College of Dentistry, New York, and Consultant. Catholic Medical Center of Brooklyn and Queens, New York. Copyright © 1994 by the American Association of Orthodontists. 0889-5406194151.00 + 0.10 8/4/41184

references to it, often as c a s e reports, 6m or as one of many possible approaches for crowding. ,-16 Others ad- vise it for cases of anterior tooth size discrepancies, ",17'~8 or to harmonize with an absent maxillary lateral incisor.tg"2° Gingival hypertrophy in this area may be another indication. 21

The prevailing opinion is to reserve the procedure for the atypical, compromise, or relapse case, and even then caveats are voiced regarding overjet increase, space opening, and a compromised contour of the pa- pillae. Increase in anterior overbite is the most frequent warning. ~o.~o.2z

Tuverson is more optimistic. "Occasionally the orthodontic treatment plan indicates extraction of a lower incisor or space closure when a lower incisor is missing. Because of the excellent results frequently ob- tained, these are no longer considered 'closet cases.' Although once looked upon as a 'dastardly act,' pro- voking negative feelings similar to those encountered when premolars were first extracted, the extraction of one or even two lower incisors is becoming more com- mon in orthodontic treatment and case presentations. ''t9 In conjunction with the extraction, he advises "accurate mesiodistal enamel reduction of maxillary central incisors" where indicated.

SELECTION OF SUITABLE CASES

There are malocclusions with crowding of mandibular anterior teeth that may be candidates for one incisor

107

108 Valinoti American Journal of Orthodontics and Dentofacial Orthopedics February 1994

Fig. 1. Case 1. Pretreatment facial and oral views (top and center). Completion of first phase (bottom).

extraction. As with every malocclusion, a visualized treatment objective (VTO) is necessary, but in addition, these cases require visualizing the atypical articulation of six maxillary anterior teeth with five mandibular anterior teeth. Certain criteria will aid in the selection of suitable cases:

1. Treatment strategy will begin with accurate mea- surements of required arch length and available arch length in the entire mandibular arch, or tooth-size-arch- length-discrepancy (TSALD). 4 A calculation will indicate whether removal of an incisor produces harmony between the two, or excess space or deficiency.

An assessment of available space will also include both a consideration of the depth of the curve of Spee, and the inclination of the lower incisors. Leveling the curve of Spee and incisor uprighting, will require additional space if these are indicated. 23

2. An additional consideration is the intercanine width, and the effect of an incisor extraction on it. Unless these teeth were originally ectopic, function and future stability are best served if the width is maintained, 1,2 and a future natural decrease anticipated. 3,s

3. With six maxillary anterior teeth now articulating with five mandibular anterior teeth, the overbite must be maintained or, if deep, reduced. Overjet is likewise maintained or reduced to produce centric oc- clusal contacts. Maxillary and mandibular canines will finish in ideal Class I relations, or the distoincisal inclines of maxillary canines may occlude with the me- sioocclusal inclines of mandibular first premolars.

Reference to the Neff Coefficient or the similar Bol- ton Index and other guides will aid in determining max- ilIary to mandibular tooth size discrepancies and asym- metries. 11.17.24

These, in conjunction with TSALD, will indicate whether the removal of the larger lateral incisor or the smaller central incisor is indicated. Usually, removal of the smaller central incisor is advisable. However, it is our observation that the decision to remove a partic- ular incisor because it exhibits dehiscence of its labial gingiva is usually contraindicated, since the defect may remain. A surgical repair is first performed and then the decision made whether to remove the incisor with the repaired gingiva, or another. The decision to remove

American Journal of Orthodontics and Dentofacial Orthopedics Valinoti 1 0 9 Volume 105, No. 2

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an incisor in the presence of bony defects in this area must be carefully evaluated.

A diagnostic set-up of both arches is informative if performed with extreme accuracy, and often suggests minor interproximal reduction of maxillary anteriors to allow their retraction, alignment and maxillary to mandibular arch coordination. 8,t2'l~'~9'24,z~ However, Sheri- dan warns that "stripping is an irreversible procedure and should be initiated with this in mind. ''26

4. As with all ideal treatment, an objective will be canine rise or posterior group function on the working side, and an absence of cuspal interferences on the nonworking side. The protrusive excursion will result in posterior disclusion.

5. Dental esthetics will require proper positioning in the sagittal plane of maxillary and mandibular anterior teeth, relative to the commonly used reference lines. An interincisal angle in the normal range is a major contributor to esthetics. However, standards for-

mulated for four mandibular incisors may not be applicable when only three are present.

Facial esthetics will require a reasonably accurate prediction of the effects of growth and dental movements. Two maxillary or four premolar extractions, or nonextraction therapy, may affect the facial profile. A lower incisor extraction in itself will not.

6. This modification of the anterior occlusion re- quires consideration of the reciprocal reactions that may occur in the posterior occlusion, and whether they are desirable. There are instances where after alignment and positioning of the three lower incisors, part of the extraction space remains. This may be advantageously used to mesialize posterior teeth in cases where one or both buccal segments are in full or partial Class II relation. If space exists where canines are in Class I relationship, their slight additional mesial movement for space closure will place maxillary canines in partial occlusion with mandibular first premolars. This may be

110 Valinoti American Journal of Orthod;mtics and Dentofacial Orlh~gedics Februao' 1994

Fig. 3. Case 1. Posttreatment facial and oral views.

Fig. 4. Case 2. Pretreatment ,acial and orai views.

American Journal of Orthodontics and Dentofacial Orthopedics Valinoti 111 Volume 105, No. 2

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preferable to esthetic bonding, which we have not found necessary.

If these criteria are to be satisfied, orthodontic treatment will rarely be in the mandibular arch only. If they can be satisfied, the case may be a candidate for mandibular incisor extraction therapy.

7. The decision to extract is best postponed until the early permanent dentition, when fewer dental and skeletal variables are present. The concept of early premolar removal is not applicable to mandibular incisor removal. In addition, mechanotherapy is improved with a full complement of teeth.

DISCUSSION

Treatment of the total malocclusion is primary, and the removal of a lower incisor is only part of it. Yet the "stigma" attached to this therapy has been notedfl a and the references cited are predominantly negative, arising perhaps from unfavorable experiences. These may be the result of faulty case selection, faulty me-

chanics, or mechanics suitable for other extractions, but not for a mandibular incisor. The ease and rapidity of the extraction space closure and resulting alignment may distract attention from the total requirements of the malocclusion. The caveats regarding increase in overbite are well taken if control of the vertical di- mension is inadequate. However, in our experience, a deep anterior overbite does not in itself contraindicate this therapy.

The maxillary midline will overlie the remaining central incisor. We do not believe that this absence of a mandibular dental midline affects occlusion, esthetics, periodontal health, or stability, the principal requirements of orthodontic therapy.

Treatment options in the mandible are more limited than in the maxilla, because of the predominantly cortical bone, the mentalis muscle, and the absence of sutures. In addition, facial and orbicularis muscles, to- gether with the buccinator and the superior constrictor of the pharynx, combine to form a continuous func-

1 12 Valinoti American Journal of Orthodontics and Dentofacial Orthopedics February 1994


tioning envelope which limits anterior, lateral, and posterior movements. 27 If achieved, instability may fol- low. 2"2s'29 Periodontal integrity, 29"3° and facial esthetics "-9 may also be negatively affected by expansion of anterior teeth.

Interproximal enamel reduction (stripping), another treatment alternative, has been advised by Peck and Peck 3t "as an essential orthodontic treatment ingredient," and has gained popularity in recent years with air rotor stripping. 26 Questions have been raised concerning the thinness o f lower incisor enameP 2"33 possible damage to it, 34 and the need for its protection in a plaque prone area. 3s Others have voiced concerns about re- sorbing crestal bone and reducing space for the interproximal papillaef1.34.36,37

Do mandibular incisor extraction cases exhibit less recrowding after long-term retention? It is our clinical impression that they do. This may be due to the main- tenance o f teeth nearer their original positions where muscle pressures are less likely to introduce instability. Another possibility is the minimum stress on adjacent anchorage during space closure, leaving all or most o f

the acquired space for the anterior correction. Riedel has suggested that incisor extraction may give greater stability in this area in the absence of permanent retention. 2° His most recent investigation confirms this. 38 Today's concern with stability indicates the need for further research.

Four premolar extractions will continue to be the optimum treatment for many malocclusions having greater space requirements and the need for improved facial esthetics. However, with careful selection and management, there are cases that can be successfully treated with a mandibular incisor extraction. This approach will be a valuable addition to our armamen- tarium.

CASE REPORTS Case 1

The patient was 9 years old at the start of appliance therapy. Oral and model analysis showed a Class II, Division 1 malocclusion in the mixed dentition, with a 9 mm overjet, a 50% overbite (Fig. 1), and a tooth-size-arch-length-discrepancy (TSALD) of - 8 . 0 mm. The ANB angle was 5 °, mandibular incisor to mandibular plane was 88 ° , and the

American Journal of Orthodontics and Dentofacial OrthopedicsVolume 105, No. 2

Valinoti 113

Fig. 7. Case 3. Pretreatment facial and oral views.

maxillary central incisor was 11 mm anterior to line Na-Po.Lips were protrusive relative to the nose-chin ("E") line (Fig.2).

The first phase treatment was designed to reduce overjetand overbite and open spaces for permanent mandibular ca-nines, where deciduous canines had exfoliated. Edgewise at-tachments (0.022 x 0.028) were placed on all permanentmolars and incisors, and a progression of round stainless steelAustralian arch wires were placed. Light Class II elasticsretracted maxillary incisors. Earlier, cooperation with an ac-tivator was inadequate, and therefore extraoral force was notused in either phase. Overjet was reduced, and to test stabilityof the spaces gained for mandibular canines no retention wasplaced, and the spaces rapidly decreased (Fig. 1). The firstphase treatment was 12 months, followed by observationwithout appliances.

The second phase treatment was begun when all teethother than second and third molars had erupted. All teeth,except the lower right central incisor, which was extracted,received edgewise attachments. Immediate closure of the ex-traction space was begun before the natural resorption of thelabial and lingual cortical plates, which occurs rapidly in thisarea and hinders closure. Simultaneously, maxillary and man-dibular incisors were intruded, rotations corrected, and pos-

terior corrections made with light Class II elastics. Six max-illary anterior teeth were interproximally reduced a total of3.5 mm. Rectangular finishing arch wires (0.019 x 0.025)were placed for maxillary incisor lingual root torque, and formandibular incisor lingual root-labial crown torque, with con-tinuation of Class II elastics. Vertical elastics for canine seat-ing were used for the final 4 months.

The second phase active treatment was 18 months. Re-tainers are a maxillary Hawley appliance and a mandibularbonded lateral to lateral incisor wire. Facial and intraoralphotographs were taken during retention (Fig. 3).

Case 2

The patient was 13 years 11 months old at the start ofappliance therapy. Dental analysis showed a Class II, Division2 malocclusion, with buccal segments between Class I andClass II, supraocclusion of both anterior segments producinga deep overbite, and a mandibular TSALD of — 8.0 mm (Fig.4). Cephalometric values were within acceptable parameters,with the exception of the mandibular incisor to the mandibularplane (75°), and the interincisal angle (165°). Lips wereslightly retrusive relative to the "E" line (Fig. 5).

The treatment plan was overbite correction by intrusionof maxillary and mandibular incisors, rotation corrections


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Fig. 8. Case 3. Pretreatment and posttreatment superimposition on S-Na (left). Pretreatment and posttreatment superimpositions; the maxilla on ANS-PNS, and the mandible on the symphysis and mandibular plane (right).

with space gained by 3.5 mm of upper anterior interproximal reduction and the extraction of a mandibular left central incisor, and slight mesialization of mandibular buccal segments to improve molar relations. Lingual root-labial crown torque to maxillary and mandibular incisors was indicated.

These goals were achieved with full edgewise (0.022 x 0.028) appliances, a progression of nitinol and round stainless steel arch wires, and rectangular finishing arch wires (0.021 × 0.025 maxillary and 0.019 x 0.025 mandibular). No extraoral forces or Class II elastics were used. Vertical elastics for canine seating were used for the final 3 months.

The active treatment time was 29 months. Retainers are a maxillary Hawley appliance and a mandibular bonded lateral to lateral incisor wire. Facial and intraoral photographs were taken during retention (Fig. 6).

C a s e 3

The patient was 13 years 2 months old. Dental analysis showed a Class I malocclusion with 50% overbite, a 6 mm

overjet, and a mandibular TSALD of - 6 . 4 mm (Fig. 7). Large maxillary central incisors partially compensated for small maxillary lateral incisors. Significant cephalometrie de- viations were an ANB angle of 6 °, a mandibular incisor to mandibular plane angle of 100 °, and the maxillary central incisor 13 mm anterior to the Na-Po line. Lips were slightly protrusive relative to the "E" line (Fig. 8).

The treatment plan was intrusion of maxillary central incisors, their retraction aided by their interproximal reduction and the reduction of the mesial surfaces of maxillary canines of 3.5 mm, mandibular arch length deficiency correction by the extraction of the mandibular left central incisor, and intrusion of the five mandibular anterior teeth. Lingual root torque to maxillary central incisors was indicated, as was minor lingual root-labial crown torque to mandibular incisors, to maintain their existing positions.

Edgewise attachments were placed on all teeth, including mandibular second molars; maxillary second molars and third molars were not attached. This was followed by a progression of nitinol, round stainless steel and rectangular finishing

American Journal of Orthodontics and Dentofacial Orthopedics Valinoti 115 Volume 105, No. 2

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arches. Class 1I elastics were used in conjunction with the maxillary torque force, and vertical elastics to maxillary canines for cusp seating near completion.

The active treatment time was 26 months. Retainers are a maxillary Hawley appliance and a mandibular bonded lateral to lateral incisor wire. Facial and intraoral photographs were taken during retention (Fig. 9).

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AM J OR'nIoD 1972;61:374-83. 2. Riedel RA. A post-retention evaluation. Angle Orthod

1974;44:194-212. 3. Little RM, Wallen TR, Riedel RA. Stability and relapse of man-

dibular anterior alignment--first premolar extraction cases treated by traditional edgewise orthodontics. AM J ORTItOD 1981;80:349-65.

4. Bishara SE, Jakobsen JR, Treder JE, Stasi MJ. Changes in the maxillary and mandibular tooth size-arch length relationship from early adolescence to early adulthood. AM J OaTHOD DEtzroFAc ORTHOP 1989;95:46-59.

5. Sinclair PM, Little RM. Maturation of untreated normal occlusions. Ar~l J OR'rHOD 1983;83:114-23.

6. Reid PV. Differences in concept. AM J ORIHOD 1965;51:490- 509.

7. Rosenstein SW, Jacobson BN. A case report. Angle Orthod 1980;50:28-33.

8. Kokich VG, Shapiro PA. Lower incisor extraction in orthodontic treatment; four clinical reports. Angle Orthod 1984;54:139-53.

9. Hinkle F. Incisor extraction case report. A.,,t J OR'rHOD DEm'OrAC ORnto~' 1987;92:94-7.

10. WintnerMS. Surgically assisted palatalexpansion. AM JORTI.tOD DENIOFAC ORTtIOP 1991 ;99:85-90.

11. Neff CW. The size relationship between the maxillary and mandibular anterior segments. Angle Orthod 1957;27:! 38-47.

12. Swain BF. Case analysis and treatment planning in Class I1 Division 1 cases. Angle Orthod 1952;22:187-204.

13. Berger H. The extraction index. AM J ORTIIOD 1956;42:307-9. 14. Reid PV. Extractions in the problem case. AM J OR'roOD

1959;45: ! 2-31. 15. Levin S. An indication for the three incisor case. Angle Orthod

1964;34:16-22. 16. Buchner HJ. Treatment of cases with three lower incisors. Angle

Orthod 1964;34:108-14. 17. Ballard ME A fifth column within normal dental occlusions.

AM J OR'ntOD 1956;42:116-24. 18. Joondeph DR, Riedel RA. Retention. In: Graber TM, Swain BF,

eds. Orthodontics, current principles and techniques. St. Louis: CV Mosby, 1985:872-3.

19. Tuverson DL. Anterior interocclusal relations. Part I1. At~I J OR'rHOD 1980;78:371-93.

20. Riedel RA. Retention. In: Graber TM, ed. Current orthodontic concepts and techniques. Philadelphia: WB Saunders, 1969.

21. Carranza FA. Glickman's clinical periodontol~y. Philadelphia: WB Saunders, 1978:1032-4.


22. Salzmarm JA. Orthodontics in daily practice. Philadelphia: JB Lippincott, 1974:256.

23. Tweed foundation manual. Tucson, Arizona: Tweed Foundation 1987:43-8.

24. Bolton WA. The clinical application of a tooth size analysis. AM J OR'rHOD 1962;48:5134-29.

25. Sheridan JJ, Hastings J. Air rotor stripping and lower incisor extraction treatment. J Clin Orthod 1992;26:18-22.

26. Sheridan JJ. Air rotor stripping. J Clin Orthod 1985;19:58-63. 27. Strang RHW, Thompson WM. A text book of orthodontia. Phil-

adelphia: Lea & Febiger, 1958:69-71. 28. Weinstein S, Haack DC, Morris LY, Snyder BB, Attaway HE.

On an equilibrium theory of tooth position. Angle Orthod 1963;33:1-26.

29. Proffit WR, Ackerman JL. Diagnosis and treatment planning in orthodontics. In: Graber TM, Swain BF, eds. Orthodontics, current principles and techniques. St. Louis: CV Mosby, 1985: 90-1.

30. Schluger S, Youdelis RA. Periodontal disease. Philadelphia: Lea & Febiger, 1977:615.

31. Peck S, Peck H. Reproximation (enamel straipping) as an essential orthodontic treatment ingredient. Transactions of the 3rd international orthodontic congress. London: Staples, 1975:513- 23.

32. Gillings B, Buonocore M. Enamel thickness of lower incisors. J Dent Res 1961;40:105-18.

33. Hudson AL. A study of the effects of mesiodistal reduction of mandibular anterior teeth. AM J OR'I'HOD 1956;42:615-24.

34. Radlanski R.I, Jager A, Schwestka R, Bertzbach F. Plaque ac- cumulations caused by interdental stripping. AM J OR'n~OD DEN- TOFA¢ ORTHOP 1988;94:416-20.

35. Rogers GA, Wagner MJ. Protection of stripped enamel surfaces with topical fluoride applications. AM J ORTHOD 1969;56: 551-9.

36. Zachrisson BU. Iatrogenie damage in orthodontic treatment. J Clin Orthod 1978;12:113.

37. Cox PR. Changes in the periodontium resulting from reproxi- marion of the mandibular incisors. Abstract. AM J ORTIIOD DEN- 'rOFAC ORTHOP 1990;98:86-7.

38. Riedel RA, Little RM, Bui TD. Mandibular incisor extraction-- postretention evaluation of stability and relapse. Angle Orthod 1992;62:103-16.

Reprint requests to" Dr.Joseph R. Valinoti 66 Park Ave. Manhasset, NY 11030

AAO MEETING CALENDAR

1994--Orlando, Fla., April 30 to May 4, Orange County Convention and Civic Center 1995--San Francisco, Calif., May 13 to 18, Moscone Convention Center

(International Orthodontic Congress) 1996--Denver, Colo., May 11 to 15, Colorado Convention Center 1997--Philadelphia, Pa., May 3 to 7, Philadelphia Convention Center 1998--Dallas, Texas, May 16 to 20, Dallas Convention Center 1999--San Diego, Calif., May 15 to 19, San Diego Convention Center

mandibular incisor extraction therapy

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