Space supervision and g

uidance of eruption inmanagement of lower transitional crowding: Anon-extraction approachRonald A. Bell, DDS, MEd, and Andrew Sonis, DMD

& 20141073-87http://d

DepartmEdwards CoCarolina, CDepartmentMedicine, B

Addressment of PeCollege of DeBee St MSC

16

Mandibular incisor crowding in themixed dentition is one of themost commonproblems presenting to the orthodontist. Asymmetry of alignment, prematureloss of primary canine(s), and disruption in arch integrity are all earlybenchmarks of a tooth size/arch length discrepancy in the transitional dentitionthat can occur independent of any skeletal discrepancy. Space supervision andguidance of eruption refer to treatment interventions during the early to mid-mixed dentition periods that influence the eruption patterns and positioning ofthe permanent teeth during their transition. Generally considered applicable toindividuals with adequate overall arch dimensions to accommodate a normalcomplement of permanent teeth with an acceptable esthetic and functioningocclusion, guidance of eruption involves the implementation of directedinterventions to optimize the eruption and alignment patterns of thepermanent teeth as part of a non-extraction protocol. (Semin Orthod 2014;20:16–35.) & 2014 Elsevier Inc. All rights reserved.

T he concept of an early phase of treatmentintervention with guidance of eruption

procedures to correct mandibular incisorcrowding is not a new one. Space supervision,guidance of eruption, pre-orthodontic guidance, andinterceptive orthodontics are all terms that have beenused to refer to the treatment of crowding dis-crepancies presenting during the early to mid-mixed dentition (Nance, 19471; Popovich, 19622;Hotz, 19703; Ackerman and Proffit, 19804; Moyer,19885). While considerable debate has ensued asto the proper terminology, the definitions are farless important than the concepts of intervention.The authors have elected to utilize Hotz’s3 termguidance of eruption in referring to “treatmentprocedures that influence the eruption patterns

Elsevier Inc. All rights reserved.46/12/1801-$30.00/0x.doi.org/10.1053/j.sodo.2013.12.003

ent of Pediatric Dentistry and Orthodontics, James B.llege of Dental Medicine, Medical University of Southharleston, SC; Children0s Hospital Boston, Boston, MA;of Developmental Biology, Harvard School of Dentaloston, MA.correspondence to Ronald A. Bell, DDS, MEd, Depart-diatric Dentistry and OrthodonticsJames B. Edwardsntal Medicine, Medical University of South Carolina, 30126, Charleston, SC 29425. E-mail: bellr@musc.edu

Seminars in Orthodontics, Vol 20, N

and positioning of the permanent teeth duringthe transition from the primary dentitionthrough the mixed dentition.” The effective-ness of preserving “leeway space” with a lingualarch to resolve mandibular crowding wasreported by Nance1 in a presentation to theSouthern Society of Orthodontics in 1946 and inan article in the American Journal of Ortho-dontics in 1947. Nance describes a series of casesdating back to 1934 that were successfully treatedwith passive lingual arches in the mixeddentition. A similar approach to preservingarch length was described by Hotz3 in 1970and later by Singer6 in 1974. These opinionarticles and case series were later substantiated inclinical studies by Wagers,7 Arnold,8 Gianelly,9

DeBaets and Chiarini,10 Dugoni et al.,11

Gianelly,12,13 Rebellato et al.,14 Brennan andGianelly,15 Villalobos,16 Gianelly,17 and Bell.18

Despite these positive reports, opponents of earlyintervention have argued that a second phase oftherapy is frequently necessary, resulting in bothincreased length of treatment time and cost.While this opinion is frequently mentioned in theliterature, there is scant research to substantiatesuch a conclusion. Wagers7 reported in a surveyof 100 patients undergoing mixed dentitiontreatment a 0.2-month difference in treatment

o 1 (March), 2014: pp 16–35

Space supervision and guidance of eruption 17

time over those patients treated in the permanentdentition (21.6 months vs. 21.4 months). Popowichet al.19 reported very similar results of patientstreated in the mixed dentition with averagetreatment durations of 20.25 months in non-extraction Class I cases.

The short-term and long-term dental healthbenefits of early mandibular incisor alignmentalso remain unclear and unsubstantiated.Empirically, one would think that well-alignedteeth are easier to clean and thus less prone toplaque-mediated dental disease, namely cariesand periodontal disease. Yet clinical studies failto consistently demonstrate a causal relationship.A 2007 review by Burden20 entitled “Oral Health-Related Benefits of Orthodontic Treatment” inthis same publication concluded that “ortho-dontists today could not claim to prevent caries byorthodontic intervention” and that “orthodontictreatment confers neither harm nor benefit interms of long-term periodontal health.” A morerecent systematic review of the literature by Hafezet al.21 arrived at this same conclusion.

If not for overall dental health benefits andwith questions regarding multiple-phase effi-ciency, then why treats crowding in the mixeddentition? Proponents of early treatment arguelong-term lower incisor positional stability isbetter in patients treated during this period.The study by Dugoni et al.11 is often cited asevidence supporting such early guidanceintervention. However, while the abstract ofthis study shows impressive results with 19 of25 (76%) patients showing clinically satisfactorylower anterior alignment 10 years post-retention,a close review of the study suggests the readermay be misled by the abstract. Although it isunclear as to how patients were selected forthe study and while no patients were stated toreceive lower Edgewise treatment, it is clear thepatients received more than just a passive lingualarch to maintain leeway space. Quoting thearticle, “In most cases the lingual arch wasremoved and a lower fixed canine-to-canineretainer was placed” for a period of time. Inaddition, 16 (64%) patients had circumferentialfiberotomies and 18 (72%) had interproximalenamel stripping. In contrast, while the classic10-year post-retention follow-up study of firstpremolar extraction cases by Little et al.22 foundsatisfactory incisor alignment to be less than30%, no circumferential fiberotomies were per-

formed on any of the patients, and presumablynone had interproximal enamel stripping. Con-sequently, to suggest that incisor alignment exhi-bited better long-term stability in the Dugoniet al.11 study compared to the first premolarextraction cases reported by Little et al.22 may besomewhat misleading. Unfortunately, in anotherstudy by Little et al.23 that examined post-rete-ntion stability in non-extraction cases treated inthe mixed dentition that involved an increase inlower arch length, patients treated with lee-way space preservation were specifically exclu-ded from the study. The study results involvingmixed dentition arch dimensional expansion diddemonstrate an instability and high relapsepotential even when small amounts of expansionwere utilized to resolve incisor crowding. Con-sequently, it is unclear whether one can con-clude resolution of lower crowding via leewayspace preservation is any more stable than eitherpremolar extractions or mixed dentition archexpansion. In addition to “relapse” of incisoralignment, some of the recurrence in crowding islikely related to normal physiologic changes asthose observed in untreated individuals. The resultsof the Belfast longitudinal studies24,25 showed amean decrease in crowding of about 1 mmbetween7 and 11 years of age; the crowding increased anaverage of 2.3 mm from 13 to 18 years.

Given the information available suggestingpost-treatment lower incisor stability is likelycomparable with any of these approaches, theclinician might again ask—why bother with earlytreatment? In an essay entitled “Timing of earlytreatment: An overview,” Proffit26 suggested theindications for considering early treatmentbasically involve two issues—the effectivenessand the efficiency of treatment. The authors ofthe present article would argue that two“guidance of eruption” concepts meet theseeffectiveness and efficiency requirements: theutilization of E-space just prior to exfoliation ofthe mandibular second primary molar and thesequential utilization of leeway space for therelief of mixed dentition lower incisor crowding.An understanding of normative eruption pat-terns and arch dimensional changes in relationto the primary to mixed dentition transitionalstages is imperative in understanding therationale for the various treatment approachesthat will be discussed under the general conceptof “guidance of eruption.”

Bell and Sonis18

Normative transitional dimensionalchanges and anticipatory guidance

Recognition of an impending tooth size–archlength discrepancy is often first evident in theprimary dentition. The significance of spacing inthe primary dentition (both generalized andprimate spaces) and its relationship to potentialcrowding of the permanent incisors is well illus-trated by the longitudinal study by Leighton,27 thework of Baume,28–30 and the work of Moorees andco-workers.31–34 Observing 200 children duringthe transition from full primary dentition topermanent dentition, Leighton27 noted a directrelationship between the amount of spacing inthe primary dentition and subsequent crowdingof the permanent incisors. Specifically, thosechildren having 6 mm or more of spacing inthe primary dentition had well-aligned perma-nent incisors, while approximately two-thirds ofthose with no spacing experienced significantcrowding of the permanent incisors. Baume29

also observed a similar relationship, where 44% ofsubjects lacking interdental spacing in theprimary dentition exhibited significant crowd-ing in the permanent dentition while those withgeneralized primary spacing transitioned intonormally aligned lower permanent incisors.The retrospective assessment of adolescentswith well-aligned permanent dentitions by Moo-rees and Chadha32 showed that the individualsexpressed generalized spacing in the primarydentition at 5 years of age. There is also somehistorical evidence that impending malalignmentof permanent incisors may be seen radiographi-cally well prior to their eruption.35 Thus, theclinician seeing children in the primary dentitioncan inform parents of potential crowding con-cerns based on clinical observations supported bytimely radiographs.

On eruption of the lower lateral permanentincisors, there is a normative increase in lowerintercanine arch width of 2–3 mm, with a rangefrom 0 to 5 mm.29,32 After lower permanentincisor transition is complete by 8 years of age,the normative amount of lower incisor crowdingin the mid-mixed dentition approximates an in-cisor liability of about 1.5–2 mm, with a standarddeviation of �1 mm.37,38 These dimensionalparameters indicating lower incisor crowding of1–4 mm are expressed in the vast majority ofchildren at 8–9 years of age after permanent

lower incisor eruption is complete. Studies oftransitional arch dimensional changes furtherdocument that no future increase in lowerintercanine width will occur after the incisoreruption is complete.29,32,36,39 These findingssuggest that normative transverse arch dimen-sional changes do not compensate for the reliefof any malalignment that might be present in themid-mixed dentition as the intercanine width isestablished by 8 years of age (Fig. 1). Relative toarch length changes, studies assessing dimen-sional changes occurring over the course of thetransitional dentition show arch length decre-ases on average of about 2–3 mm per lowerquadrant.14,33,34,39,40 A slight decrease of about1 mm, as the first permanent molars erupt andclose any available posterior primary dentitionspaces (i.e., early mesial shift), is mostly offset bymore forward incisor positioning during theincisor transition. The arch length is generallystable over the course of the mid- to late-mixeddentition, but shows a significant averagedecrease of 2–3 mm as the final buccal segmenttransition occurs with the exfoliation of thesecond primary molar and late mesial shift of thepermanent first molars (Fig. 2). Concurrentlywith the late transition period and subsequentlyinto the adolescent years, an additional decreasein arch length may be associated with uprightingof the lower incisors as the overbite and overjetare defined.14 The lack of width increase in thelower anterior segment after lower lateralincisors have erupted and the decrease in archlength concurrent with buccal segment transitionand incisor uprighting combine to result in anotable decrease in mandibular arch perimeteras the mixed dentition transitions into the youngpermanent occlusion. This arch perimeterdecrease is on the order of 4–6 mm in thelower arch during this period and helps explainwhy mixed dentition incisor crowding eitherremains the same or typically worsens moreduring the transition to the full permanent den-tition. As noted, the majority of lower arch peri-meter reduction occurs as the second primarymolars exfoliate, and the residual space secon-dary to the size differential between this toothand the succedaneous second premolar (i.e.,“E-space”) is eliminated due to “late” mesial shiftadjustments of the first molars. Prior to this,minimal arch length change and the increase inarch width during incisor eruption actually

Figure 1. Dimensional changes show an average increase in lower intercanine width of 2–3 mm (range of 0–5 mm) during incisor transition, with no other increases in the lower intercanine width noted after the lower lateralincisors have fully erupted by 8 years of age. The normative finding is a resulting average lower incisor crowding of1.5 mm, with a SD of�1 mm. Thus, lower crowding in the range of 1–4 mm should be expected in the majority ofmixed dentition children at 8–9 years of age.

Space supervision and guidance of eruption 19

produce an increased arch perimeter throughthe majority of the mid-mixed dentition. Thearch perimeter changes in the mixed to adoles-cent dentition period are illustrated in Fig. 3

After the lower permanent incisors haveerupted and intercanine width changes havebeen realized in terms of anterior space dimen-sions, any crowding of the incisors should beconsidered an established dimensional realitywith no “self-improvement” anticipated throughfuture growth changes.41 Since arch circumfer-ence decreases anterior to the first permanentmolars during normal development and with“space loss” often complicating alignment whenarch integrity has been disrupted by prematureloss of primary molars,42 it is often desirable tosupervise the eruption sequence and positioningof the permanent teeth during the transitionalocclusion. The review of normative arch dimen-sional changes revealed that extra space is actu-ally available within the overall arch prior tothe transition of the buccal dentition as represen-ted by the size difference between the primary

Figure 2. Lower arch length decreases significantly on epermanent first molars shifts forward toward the availabquadrant translates to an arch perimeter decrease of 4–6

canines and molars vs. the permanent caninesand premolars.1 This “leeway space” represents aþ1.7-mm space on average in each lower qua-drant (overall þ3.4 mm) and provides somepotential for the relief of lower incisorcrowding. Gianelly,9 in a study of 100 mixeddentition children presenting for orthodonticneeds, reported that 85 patients showed lowerincisor crowding on an average of 4.4 mm, a levelof crowding notably greater than the normativeaverage of about 2 mm. Gianelly9 calculated viaspace analysis that leeway space would provideadequate room to accommodate an aligneddentition in 72% of the cases presenting withincisor crowding. It is important to note thatleeway space is most directly related to thesize difference between second primary molarsand the successor second premolars. This“E-space” approximates to 2–3 mm in compara-tive widths, and these are the last teeth to nor-mally transition in the lower buccal segment eru-ption sequence.43 Thus, the control of leeway/E-space through space supervision and guidance

xfoliation of the lower second primary molar as thele “E-space.” The decrease of 2–3 mm in each lowermm during this late “mesial shift” transition period.

Figure 3. An increase in lower arch perimeter during the 2-year incisor eruption period (Inc—age 6–8 years) isrelated to increase in intercanine width associated with incisor transition and counter-balanced arch lengthadjustments. A stable period of arch dimensions follows during the mid-mixed dentition (8–11 years) until adramatic decrease in arch length of 2–3 mm per side is associated with turnover of the buccal dentition, specificallysecond primary molar exfoliation. The resultant decrease in arch perimeter associated with the late mesial shiftperiod (LMS—11–12 years of age) is on the order of 4–5 mm.

Bell and Sonis20

of eruption techniques offers potential oppor-tunities for the clinician to significantly improvetooth size–arch size adjustments for the relief oftypical levels of dental arch crowding that presentin the mixed dentition age child. Given thispotential, diagnostic procedures to evaluate theoverall space should be instituted to determinetreatment alternatives whenever lower incisoralignment is disrupted by a lack of lower anteriorspace. Perhaps the most widely accepteddiagnostic procedure used to evaluate availablespace is the use of a mixed dentition spaceanalysis. While numerous mixed dentition ana-lyses have been reported in the literature, studiesby Luu et al.44 and Irwin et al.45 would suggestthat little clinically significant differences existbetween the different methods. If a selectedspace analysis indicates the overall arch peri-meter could accommodate or be within 2–3 mmof relieving the presented incisor crowding, theclinician should consider several options to faci-litate dentition adjustments through a sequencedand staged guidance of eruption plan with thetimely use of available posterior leeway space.

Stage 1—Eruption guidance in themandibular incisor segment (6–9 yearsof age)

Disking of primary canines

The first option considered when lower incisorcrowding is in the range of 2–4 mm is disking of

the primary canines to reduce their mesiodistaldiameter in providing additional space toimprove the position of the adjacent permanentincisors. The technique of reducing the width ofprimary canines to provide space for incisoralignment was likely first introduced in 1851 byLinderer46 and re-introduced by Hotz3 in the1960s. Other clinicians have subsequentlypresented the concepts of disking both mesialand distal surfaces of the primary canines toenhance the space dimensions for lower incisoralignment.47–51 The disking procedures workbest when the malpositioned permanent incisorsare displaced lingual to the anterior arch form(Fig. 4). The disking of the mesiolingual cornerof the primary canines provides a “sluiceway” forthe lingually positioned incisors to slide forwardunder the muscular pressure of the tongue.Bilateral disking of the mesiolingual aspect of theprimary canines readily provides space of 1 mmand up to 2 mm per side for incisor “unraveling”(2–4 mm overall). With proper slicing of themesiolingual corner of the primary canine at thegingival contact area with the lateral incisor,there is the potential for no measurable encro-achment on the overall leeway space in thequadrant. Labial movement of the lingual dis-placed incisors may actually increase the midlinearch length and overall arch circumference asthe arch form is rounded out in a forwarddirection by the action of the tongue.51

While some clinicians disk the distal surfacesof the primary canines as well as mesial surfaces

Figure 4. Disking the mesiolingual angle of lower primary canines provides additional space for an improvedalignment of the permanent incisors without overly encroaching on leeway space. Two examples of primary caninemesiolingual disking and the favorable response in terms of incisor alignment are shown. Top images shows one-time disking using #169 tapered fissure bur and response at 1-year follow-up. Bottom images represents twosequential disking procedures—first at initial presentation and second at the child0s 6-month recall visit.

Space supervision and guidance of eruption 21

to allow more displacement of the intercaninedistance, this tends to result in encroachment onthe leeway space as a long-term consideration. Inthe case of labial malpositioned incisors, whiledisking may provide additional room for incisoralignment, the lips are a more significant factorin the balance between muscular forces such thatthe result is a lingual flattening of the anteriorsegment rather than improved incisor position-ing and an associated decrease in overall archspace. In addition to lingual displacement of theincisors and crowding in the range of 2–4 mm asindicators for a favorable disking outcome, thegeneral guidelines and recommended proce-dures for successful disking of primary caninesare as follows:

1.

Local anesthesia (block, infiltration, or topicalanesthetic compound) may be required as thecanine must be sliced subgingivally to com-pletely free the contact area. Disking just thecrown is not adequate as the contact area issubgingival. Placement of a wedge is some-times necessary to protect the lateral incisorand access the contact area. Thirdly, dentinexposure is usually necessary to reduce the

primary canine width adequately—anotherindicator for local anesthesia or nitrous oxidesupport. Coordinating with restorative workrequiring anesthesia in the area may bebeneficial in treatment planning.

2.

A tapered fissured bur (#699 or #169) toallow effective tooth reduction and accesswithout injury to adjacent permanent teeth isrecommended. Re-approximating diamonddisks or strips at this stage of development isnot recommended due to risk of soft tissueinjury. Emphasis on the mesiolingual cornerof the primary canine rather than the straightmesial surface is facilitated with taperedfissure burs.

3.

Timing is critical to allow ease of access andoptimal tooth positioning response. Given thenormative intercanine width increases duringlateral incisor eruption, disking should bedelayed until “wedging” effects of eruptingincisors and arch width increases are realized.Disking is best around 7 ½ to 8 ½ years of agein proximity to the completion of lateralincisor eruption. The primary canine rootsshould be relatively intact without ectopicresorption changes from the erupting lateral

Bell and Sonis22

incisors or due to the eruption timing of thelower permanent canines.

Extraction/ectopic loss of primary canines

Most often manifest in a significant tooth size–arch size discrepancy of 4 mm or more in theincisor segment, early “ectopic” loss of a singlelower primary canine or even bilateral canineloss through displaced eruption of permanentlateral incisors is a significant indicator for athorough orthodontic evaluation (Fig. 5). Theectopic loss of a lower primary canine unilaterallyis frequently followed by lingual and distalmovement of the incisor segment with shiftingof the dental midline toward the side of the pre-mature primary canine tooth loss. The disruptionin arch integrity further compounds normalspace use for eruption of the permanent cani-nes and premolars in subsequent development.The early bilateral loss of both lower primarycanines may allow maintenance of midlineand arch symmetry, but ultimately results insignificant lingual retroclination of permanentincisors, deepening of overbite, increased

Figure 5. Unilateral ectopic loss of a lower primary caniincisors shift toward the side of loss and move lingually (A aand D) allows maintenance of arch symmetry, but results inthe lower incisors, increased overjet, deepened overbite,

overjet, and bilateral loss of arch length overtime.52–54

If one primary canine is lost ectopically duringincisor eruption, it is usually desirable to extractthe contralateral primary canine to maintainarch symmetry.52–56 While extraction of thecontralateral primary canine may improve inci-sor alignment and midline integrity otherwisedistorted by the asymmetric anterior space, theearly loss of both primary canines will mimic theresponse seen when bilateral primary canines areectopically lost. The result will be lingual retro-clination of the permanent incisors, deepeningof the overbite, increased overjet, and bilateralloss of arch length. In either scenario of unilat-eral or bilateral loss, alignment problems pro-ducing ectopic loss of primary canines are strongindicators of a significant incisor liability andarch length deficiency that will likely becomegrossly evident upon permanent canine andpremolar eruption. Much more frequent thanectopic loss of lower primary canines, the caninesmost often remain in the mixed dentitionarrangement with the permanent incisorserupted with a crowded malposition. While

ne typically results in an asymmetric space loss as thend B). Bilateral ectopic loss of lower primary canines (Csignificant lingual retroclination and supraeruption ofand reduction in overall lower arch dimensions.

Figure 6. Extraction of lower primary canines. (A) Lingually positioned lateral incisors, dental shift to right,retained left primary lateral. Decision made to extract the primary canines. (B) A year later—symmetry of incisoralignment achieved at expense of arch length and perimeter through lingual and distal movement of the incisors.

Space supervision and guidance of eruption 23

disking of the primary canines as described is theprocedure of first choice, elective extraction ofthe primary canines in an attempt to maintainarch symmetry, coincident midlines, and incisorpositional integrity can be considered under cer-tain circumstances. Such intervention becomesmore viable when the incisor crowding and lia-bility is greater than 4 mm or when the eruptivealignment and dental midline is significantlyskewed toward one side with a totally blockedincisor from the arch form (Fig. 6). The objectiveof lower primary canine extraction is to providespace in the arch for an improved incisor align-ment and to maintain midline symmetry withthe thought that negative effects on the occlusion(i.e., lingual inclination of incisors, deepenedoverbite, increased overjet, and additional spaceloss) can be overcome through later orthodontictooth movement.50,54,56,57 This same concept isfollowed if a primary canine is lost unilaterallyduring incisor eruption and the contralateral

Figure 7. Loss of primary canines—what about a lingual halign along LHA wire shaped to the most lingual position, ialong lingual wire into the canine space.

primary canine is removed in an effort to main-tain midline symmetry.53,54 The clinician mustremember that early extraction of lower primarycanines will mimic what happens with bilateralectopic loss and will likely result in notable loweranterior arch collapse.55–57 Therefore, theextraction of primary canines should not beundertaken without parental understanding ofthe consequences and ideally, orthodontic con-sideration of the long-term implications to theocclusion. Some clinicians recommend the use ofa lingual holding arch to control the incisorpositioning and prevent encroachment on per-manent canine positions when lower primarycanines are lost prematurely (Fig. 7). However,the displacement of the incisors attendant withectopic loss or early extraction of lower primarycanines typically contradicts the passive place-ment of a lingual holding arch at this stagewithout first aligning the incisors with activeappliance therapy. Early selective extraction of

olding arch? Usually not that simple as incisors tend to.e., loss of arch length as incisors drift distal and lingual

Bell and Sonis24

primary canines goes beyond a simple first step inguidance of eruption and actually represents thestart of either a phased early treatment proto-col with arch expansion or a serial extractionprogram. In the context of a non-extractiontreatment plan as part of first-phase arch devel-opment, a 2� 4 Edgewise setup to decompensatedisplacements and position the lower incisorsforward into the proper arch form may be indi-cated. The goal of such 2 � 4 treatment in Phase1 is to establish coincident midlines, normativeoverjet and overbite with the maxillary incisors,and increase arch dimensions for eruption of thebuccal segment dentition to optimize the poten-tial for a long-term non-extraction treatmentplan. After the incisor alignment has achievedthe proper anterior positioning with the first-phase mechanics, a lingual holding arch can beplaced as a “retainer” for the achieved incisorantero-posterior (A-P) positioning (Fig. 8).

Stage 2—Guidance in mandibular canine/first premolar segment (age 10–11 years)

In patients aged 10–11 years, panoramic evalu-ation of the exfoliation and eruption patterns ofthe posterior segment provides a particular site ofassessment for timely mandibular guidance oferuption procedures. The clinician should takenote of resorption patterns in the premolar areaas well as desired molar adjustments and leewayspace usage needed to achieve optimal align-ment while maintaining stable occlusal rela-tionships. In the usual eruption sequencing, thelower canine and first premolar frequently eruptat approximately the same time frame of 10–11years of age. Since most of the leeway space islocated in the size difference between the secondprimary molar and second premolar area, thecanine and first premolar are forced toward amesial eruption path.10,41 The resultant align-ment finds the permanent lower canines posi-tioned labial to the contact area of the lateralincisors with exacerbation of any anterior mala-lignment. To allow distal placement and tominimize malpositioning of the canine labial tothe lateral incisor, extraction of the primary firstmolar (and primary canine if exfoliating impro-perly) is considered around this time. Disking ofthe mesial surface of the second primary molarmay provide additional space for distal position-ing of the erupting canine and first premolar.

One can utilize up to 2–3 mm of “E-space” withcoordinated disking of the primary canines,selective extraction of primary canines and firstprimary molars, and disking of the mesial surfaceof the second primary molars (Fig. 9). Thissecond stage of intervention continuesthe guidance concept of unraveling loweranterior crowding toward the available posterior“E-space.” As long as the second primary molarsare maintained in position as abutments againstthe fully erupted first permanent molars duringlower canine and first premolar eruption, nomeasurable arch length changes should occurthrough mesial movement of the first permanentmolars.33,34 As discussed, the major decrease inlower arch length occurs concurrent with exfo-liation of the second primary molar as the firstmolar shifts forward (i.e., “late” mesial shift) intothe available “E-space.” This forward shift of themolars upon loss of the second primary molarstypically results in a decrease in lower arch lengthof 2–3 mm per mandibular quadrant. Particularlyunder the impact of erupting second permanentmolars, the arch length decrease occurs rapidlyfrom back to front before more anterior teethcan distalize into the available “leeway” space.

Stage 3—Guidance in mandibular secondpremolar/molar segment (age 11–12 years)

Hopefully, the eruption sequence has followed anormal canine-first premolar-second premolarpattern so the clinician has had the opportunityto perform the suggested Stage 1 and Stage 2guidance procedures with guided canine andfirst premolar distal positioning along with reliefof incisor malpositioning. The next critical tim-ing sequence in a staged guidance programoccurs around 11–12 years of age in associationwith the projected exfoliation of the secondprimary molars. The second premolars fre-quently take a path of eruption along the distalroot of the second primary molar and eruptiontransition problems may occur. Occasionally,extraction of the second primary molar is indi-cated to allow normal eruption of the secondpremolar if such atypical patterns are noted. Inaddition to assessing the transitional patterns ofthe second premolars, consideration should begiven to the placement of a lingual holding archor a lip bumper concurrent with removal of thesecond primary molars (Fig. 10). If the available

Figure 8. Phase 1 2 � 4 arch development—pre-treatment (upper left): arch changes associated with bilateralectopic loss of lower primary canines and narrowedmaxillary arch form. Upper 2� 4 arch development supportedby E-spyder expander to emphasize fan-like anterior expansion of maxillary arch (upper right). Tieback of NiTiarchwires restrained upper incisors and resulted in some retraction. Lower 2� 4 arch development using AW lockstopped sequential archwires (0.016 NiTi, 0.020 NiTi, and 0.020 SS) to advance lower incisors, correct midlinediscrepancy, and increase arch perimeter to accommodate leeway space adjustments (at 4 months). Activeappliances removed at 7-month treatment time (lower left). Retention with upper transpalatal bar and lowerlingual holding arch at 18 months post-treatment maintained achieved arch width and arch length changes. Notefacial profile changes influenced by correcting initial excessive overjet and lip interpositioning.

Space supervision and guidance of eruption 25

Figure 9. Removal of primary first molars concurrent with disking the mesial surfaces of second primary molars enhances distal eruptive positioning of thepermanent canine and first premolar as illustrated above on upper left. The case on the lower right had primary canines disked at 8 years and 4 months of age.After exfoliation of primary canines and first primary molars, lower second primary molars were disked at 10 years and 8 months as the canines and first premolarserupted. This continued the guidance concept of unraveling anterior crowding toward available leeway/E-space.

Bell

andSonis

26

Figure 10. Control of late lower arch length decrease using lingual holding arches and selected extraction of second primary molars allows alignment of crowdedlower incisors on the order of 3–4 mm as the buccal dentition (canines and premolars) erupt more distally into the leeway space maintained by the LHA.

Spacesupervision

andguidance

oferuption

27

Bell and Sonis28

buccal segment space is tight, if the optimal useof leeway/E-space for crowding is desirable, and/or if the second permanent molars are eruptingbefore the second premolars, a lingual arch or lipbumper may be a critical element in controllinglower arch dimensions at this point. In theGianelly article9 on the value of leeway spaceas to treatment timing, lower crowding with anaverage discrepancy of 4.4 mm could betheoretically accommodated in 72% of thecases that presented with incisor crowdingwhen the leeway space was calculated into aspace analysis. Subsequent to that article,treatment-based articles have documented dra-matic and positive alignment effects in the timelyuse of passive lingual holding arches (LHA) forcontrol of lower leeway space in the late-mixeddentition.10,11,14–16 These LHA studies, individ-ually reviewed and presented chronologically,consistently show that a passive lingual holdingarch placed in conjunction with selected removalof second primary molars will stabilize perma-nent first molars from forward mesial drift,minimize lingual movement of lower incisors,and allow canines and premolars to erupt distallyas much as 1–2 mm into the held leeway space.Such leeway space control has been shown toresult in reductions of up to 2–4 mm in lowerincisor irregularity as a consistent finding.

DeBaets and Chiarini10 reported on archchanges in 39 mixed dentition cases with loweranterior crowding treated with passive lingualarch therapy and selected removal of primarymolars. Changes over a 4-year period werecompared to a matched group of 60 untreatedchildren with similar crowding who received nospace supervision. In untreated subjects, lowercanine and premolar mesial displacementoccurred upon eruption with resulting overlap ofthe already crowded lower incisors that worsenedthe anterior displacement. In lingual arch sub-jects, lower anterior crowding decreased anaverage of 3–4 mm through the period of secondpermanent molar eruption. Lower arch lengthdecreased less than 1 mm in children with lingualarches while permanent canines and premolarserupted an average of 1.5 mm (up to 3.5 mm)more distally per side than controls. In sum, thecontrol of molar shifting and sustained archlength using lingual arches allowed spontaneousalignment of crowded lower incisors as the den-tition distalized into the maintained leeway space.

Dugoni et al.11 published similar findings from25 mixed dentition patients with reductions inlower incisor crowding greater than 3 mmdemonstrated after placement of passivelingual arches and selected primary molarextractions. After an average long-term post-retention period of 10 years, 19 of the 25 patientscontinued to show clinically satisfactory loweranterior alignment. Compared to 10-year follow-up of orthodontically aligned patients, theseresults show reductions in lower incisor crowdingand long-term stability of the alignment withlingual arch therapy that was greater than or atleast equal in effectiveness to active orthodontictreatments.

Rebellato et al.,14 assessing cephalograms,study models, and tomograms of the mandi-bular body, reported on arch dimensional chan-ges in 30 mixed dentition patients presentingwith incisor crowding of 3 mm or more. In 14patients treated with passive lingual arches, thearch length did not measurably change over thecourse of the eruption of the succedaneous teethwhile an average arch length decrease of�2.5 mm per side was demonstrated in 16untreated children used as controls. The archlength changes were related to first molarsmoving forward þ1.7 mm in the control groupcompared to only þ0.3 mm in the lingual archgroup. Concurrently, incisors tipped forwardslightly in the lingual arch group (þ0.4 mm),while lingual uprighting of incisors in the con-trols reduced arch length by 0.65 mm. In sum,the action of the lingual arch was to reducemesial molar migration and incisor lingual move-ment in controlling the quadrant arch length of2.49 mm per side compared to non-LHA con-trols. The additional bilaterally sustained archlength resulted in concurrent relief of 3–4 mm oflower incisor crowding in treatment subjects.

Brennan and Gianelly15 quantified the archdimensional changes in 107 consecutive mixeddentition patients treated with passive lingualarches through eruption of all succedaneousteeth. Occasional extraction of second primarymolars to facilitate eruption of premolars andcanines was the only other intervention. Archlength decreased an average of 0.4 mm in thelingual arch patients while arch width increasedslightly. The patients presented an averageþ4.4 mm of total available lower leeway space,which resulted in an average decrease in lower

Space supervision and guidance of eruption 29

incisor crowding from a pre-treatment level of�4.8 mm to þ0.2 mm of space post-treatment.The space adjustments were enough to resolveincisor crowding completely in 65 of the lowercrowding subjects (roughly 60%). An additional16 subjects (one in six) had a final discrepancy ofless than 1.0 mm and 13 subjects (one in 10) hada final discrepancy of less than 2 mm. Only 14patients (13%) had crowding greater than 2 mmafter the full buccal segment eruption wascomplete. Of note, the majority of patients withhigher levels of post-treatment crowding pre-sented with initial ectopic loss of the lower pri-mary canines. In sum, a passive lingual arch withselected removal of primary teeth providedadequate space and eruption guidance to relievesignificant lower incisor crowding in 105 of the107 subjects.

Villalobos et al.16 reported on 23 patientstreated with lingual arches between 10 and 12years of age compared to 24 matched untreatedsubjects. Molar and incisor movements wererestricted to about a one-half millimeter archlength decrease for the 18 months of lingual archwear while untreated subjects had a decrease of2 mm in arch length. The lingual arch alsolimited first molar extrusion by about 2 mmcompared to non-LHA patients. The study con-cluded that the lingual arch was effective forpreservation of arch length and control of ver-tical eruptive movements of banded molars. Thecited consecutive and chronologic LHA studiesconsistently confirm that arch length remainsrelatively constant or decreases minimally inpatients treated with a passive lingual arch in thelate transitional mixed dentition period. Forwardmovement of the lower first molars and lowerincisor lingual movement is reduced notably inaccounting for the relative stability of arch lengthwhich in turn contributed to approximately 4–5 mm greater arch perimeter than would havebeen available after normative arch dimensionaladjustments in the late transitional dentition.The additional buccal segment space alloweddistal eruptive positioning of the lower caninesand premolars with a positive influence on reliefof incisor crowding in the range of 3–4 mm.Thus, the timely use of lingual holding archesand selected extraction of primary molars in themanner described utilizes the leeway space forthe relief of typical lower crowding amounts thatpresent in the mixed dentition for about two-

thirds to three-fourths of patients. These num-bers are in line with the percentages predicted byGianelly in his original work35 and are confirmedin the clinical studies reviewed.10–16

Similar to lingual holding arches for the pres-ervation of lower leeway/E-space, Woods58

reported on the treatment of 182 late-mixeddentition patients using segmented 2 � 4 appli-ances to manage leeway space supervision. All 182patients were started in treatment while secondprimary molars remained and possessed potentialavailable E-space for relief of crowding. In allcases, upper and lower 2 � 4 appliances usingsegmental tip-back archwires were applied tocontrol molar adjustments and incisor alignment.Buccal segments were bracketed and aligned toinclude second molars upon eruption with anaverage total treatment time of 28 months. Theactual bilateral E-space measured directly frommodels represented a mean of 4.2 mm, with arange of �1.6 mm. The actual mandibular spacerequirements averaged 2.6 � 3.0 mm. About two-thirds of patients had 4 mm or less of crowding,another 25% had 4–8 mm of crowding, and forabout 10%, the crowding was greater than 8 mm.The 2 � 4 setup followed by sequential fullappliances controlled arch dimensions such thatthe mean change in arch depth was �1.4 mmafter treatment was completed. Molars were heldback and the lower incisors tipped forward lessthan 1 mm on average. Canine arch widthincreased a mean of 0.9 mm. The greater theinitial crowding was, the greater the dimensionalchanges. In most patients with approximately 4–6 mm of crowding, the control of E-space and theanterior Edgewise changes accommodated den-titional alignment. Thus, starting treatment in thelate-mixed dentition using a sequenced 2 � 4setup allowed the use of E-space and minimalanterior expansion needs to provide about 4–6 mm of space for aligning the mandibular den-tition. Weinberg and Sadowsky59 reported thatsimilar amounts of arch dimensional changeswere found in 30 Class I comprehensiveorthodontic patients started in the mixeddentition for the resolution of mandibular archcrowding. The phased Edgewise treatment resultsrepresent similar dimensional values as reportedwith the use of lower lingual holding arches formolar and incisor control.

An alternative to lingual holding arches forE-space preservation is the use of a lip bumper or

Figure 11. Case example—Removable lip bumper. Lip bumper placed as lower second primary molars exfoliatedat age 11 years and 6 months. Bumper placement low in vestibule provided holding force on molars while allowinglip to contour over the bumper to lessen incisor labial movement. After 8 months of bumper wear (age 12 years and2 months), a significant relief of anterior crowding resulted. Edgewise appliances aligned the dentition into theestablished arch form.

Bell and Sonis30

lip shield in the late transitional dentition toenhance the forward positioning of the incisors,hold the first molar positioning, and allow somearch development as the buccal segments tran-sition into the adolescent dentition (Figs. 11 and12).60–70 Primarily acting through incisor pro-clination (about þ2 mm on average) as a resultof altered muscle equilibrium between the lipand tongue, the lip bumper approach also pro-vides distalization or holding forces against the

banded molars to hold leeway space. The molareffects are primarily a result of distal crown tip-ping and not through a true molar bodily dis-talization. Approximately 1 year of lower lipbumper wear appears to be necessary to gain 2–3 mm of arch length beyond the available leewayspace. Additionally, evaluation of lip bumperwear over the transition time of canine andpremolar eruption indicates that transverse archwidth increases of about 1–3 mm at the canines

Figure 12. Case example—Soldered lip bumper placed before second primary molars exfoliated. Bumperpositioned at cervical margins provided holding force on molars, reduced lip contact on incisors to enhance labialmovement. At 6 months (12 years and 5 months), lower crowding reduced through distal movement of caninesand premolars toward E-space, with some arch expansion. Edgewise appliances aligned dentition with retraction ofbuccal segments and establishment of a broader arch form.

Space supervision and guidance of eruption 31

and 4–5 mm at the molars are possible. Suchincreases in arch dimension along with mod-ifications in muscle function are in turn asso-ciated with improved anterior alignment andmore laterally developed arches during the activephase of lip bumper treatment. The applicationof lip bumpers in the late-mixed dentition offersan arch development technique when forwardmovement of the incisors can be tolerated, when

distal uprighting and/or anchorage stabilizationof the molars would enhance overall arch length,and when an increase in arch circumferencemight be significant in relieving moderatelycrowded incisor levels that are beyond simpleleeway space preservation with lingual holdingarches. Given the reported record of mandibularexpansion approaches with an almost inherenttendency to return toward pre-treatment levels,

Bell and Sonis32

the realization of long-term stability without astructured retention program seems ques-tionable, though the altered functional envi-ronment does offer some advantages over moredirect “mechanical” lower expansion approaches(e.g., Schwarz plates).70

The complications of conventional fixedappliance therapy rarely manifest themselves inthe limited appliance approaches of mixed denti-tion guidance of eruption treatment mechanics.However, preservation of the “E-space” is not atotally benign intervention. By preventing thelate mesial shift of the lower first permanentmolars, less posterior arch length is available forthe erupting mandibular second permanentmolar with a resulting increase in second molareruption problems. A study by Sonis andAckerman,71 in examining 200 patients havingundergone E-space preservation with a passivelingual arch for second molar eruption prob-lems, reported that 29 patients had at least oneimpacted second molar—a four- to five-foldincrease over normative population reports ofimpacted lower second molars. A significantrelationship was found between the mandibularfirst permanent molar and permanent secondmolar angulation patterns and likelihood ofimpaction. An intermolar angulation created bythe long axis of the first and second molar of 241or greater resulted in a positive predictive valueof 1, indicating a high risk of impaction. A similarstudy by Rubin et al.72 found that those patientstreated with a fixed lingual arch for E-spacepreservation had a 4.7% impaction rate of sec-ond molars, which was associated with anincreased intermolar angulation and reducedspace distal to the first molar. Consequently, theprudent clinician observing this relationship willinform the patient of a likely increased length oftreatment.

Summary of “age-appropriate” and“staged” guidance of eruption concepts

The control of leeway/“E-space” adjustments interms of influencing arch dimensional changesthrough various space supervision, and guidanceof eruption techniques offers opportunities tosignificantly improve lower tooth size–arch sizediscrepancies in the mixed dentition. The relief oftypical levels of lower arch mixed dentition crowd-ing (i.e., less than 3–4 mm in the mandibular

arch) involves a timely, age-appropriate, sequen-ced, and staged protocol involving the following:

(1)

Preservation of inherent arch dimensionsthrough a comprehensive preventive, restor-ative, and space maintenance oversight pro-gram to optimize the integrity of the primaryand the mixed dentitions throughout thetransitional periods.

(2)

After incisor eruption is complete, the aver-age lower alignment shows crowding of 1.5�1.0 mm. No subsequent “growth” changeswill increase lower anterior canine-to-caninearch dimensions. The preferred approachduring active incisor transition is to allow any“wedging” effect of eruption to influencearch dimensions. After lateral incisor erup-tion is complete at 8 years of age, what you seeis what you get! NOW is the time for Stage 1decision as to no intervention necessary,accept as is, disking of the primary canines,extraction of primary canines, or Phase 1arch development.

(3)

Selected disking of primary canines toenhance incisor positions when crowding isin the range of 2–4 mm and the lowerincisors are lingually malpositioned to thearch form is the first choice of intervention,especially in deepbite/brachyfacial occlusionpatterns. If intercanine space can be “fine-tuned” with disking, tongue pressures willtend to position the lingually displacedincisors forward into an enhanced arch formalignment. Intercanine space of 1–2 mm perside for incisor alignment can be achieved bydisking the mesiolingual corner of theprimary canines to provide “sluiceway” forincisor alignment once the lateral incisorsare erupted (usually around 7 ½ to 8 ½ yearsof age).

(4)

Decompensation of severe lower incisormalpositioning, midline asymmetry associ-ated with ectopic eruption patterns, andlower incisor crowding at a level whereremoval of lower primary canines is requiredto allow proper incisor alignment integrity(greater than 3–4 mm of liability). Cliniciansmust understand and relate to the parentthat the necessity of early primary canineextraction indicates a significant tooth size–arch size problems. It is frequently step oneof a serial extraction program, particularly in

Space supervision and guidance of eruption 33

vertically sensitive dolichofacial patterns.The negative effects with lingual collapseof incisors, arch length loss, deepening ofbite, and increased overjet all are significantdetriments in brachyfacial cases.

Such levels of tooth size–arch size discrep-ancy may indicate the need for an earlyPhase 1 intervention using Edgewise 2 � 4mechanics to position incisors and molarstoward favorable Class I relationships, withincisor integrity, midline coincidence, andnormal overbite and overjet. Crowding andincisor positioning discrepancies requiringcanine extraction or extensive arch expan-sion to relieve incisor crowding and offsetnegative effects of space loss are candidatesfor early 2 � 4 intervention, and it generallyimplies a long-range non-extraction protocolas compared to a situation where theextraction of the primary canines is the firststep in a serial extraction plan. The amountof crowding discrepancy and facial type arecritical factors in the decision-making proc-ess as to long-term extraction vs. non-extrac-tion plan. Brachyfacial deepbite patients leadto a prioritized arch development with archexpansion to enhance facial balance. Doli-chofacial openbite patients tend to bedirected toward a serial extraction protocolthat is much more likely to offset verticalfacial imbalance.

(5)

Consideration of selective disking of themesial surface of the second primary molarsto enhance more distal eruptive position-ing of the permanent canines and firstpremolars.

(6)

Timely use of passive lingual holding arches,lip bumpers, and/or late-staged Edgewisesetups along with selected extraction ofsecond primary molars to provide space forrelief of typical lower crowding amounts (2–4 mm). The space control allows canines andpremolars to erupt in more distal positionsthan under normal transitional patterns.This “driftodontics” of the buccal segmentswill in turn result in more intercaninedistance for relief of incisor malpositioningin about two-thirds to three-fourths ofpatients. In keeping with the idea of super-vising space changes in the late transitionaldentition, patients should be evaluatedbefore the transition of the buccal teeth in

each arch. A good clinical guide for timing isupon the clinical emergence of the lowercanines and first premolars around 10–11years of age. These teeth erupt about 1 yearahead of the final buccal segment transition,leaving adequate time to assess dimensionalneeds and plan treatment interventions forthe relief of crowding.

The dimensional parameters presentedthrough optimal use of available leeway space inthe transitional dentition provide the devel-opmental potential for a non-extraction protocolas an achievable priority in the majority of chil-dren. It is likely that most clinicians would prefer anon-extraction approach whenever possibleprovided other outcome objectives are able to bemet. It is even more likely that patients andparents would prefer not to have healthy teethremoved whenever possible. These commentsshould not imply that orthodontic extraction ofpermanent teeth leads toward a negative result asa general rule. This is not the case, as a significantproportion of patients present malocclusion fac-tors and dentofacial patterns in which anextraction protocol is consistent with the ach-ievement of overall esthetic and functionalobjectives. As a conceptual model however, a non-extraction approach for the majority of patientsthat possess the developmental potential for a fullcomplement of teeth provides a sound founda-tion as a starting point for orthodontic diagnosisand treatment in the mixed dentition age patient.

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