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Space supervision and guidance of eruption in management of lower transitional crowding: A non-extraction approach

  • Ronald A. Bell
    Correspondence
    Address correspondence to Ronald A. Bell, DDS, MEd, Department of Pediatric Dentistry and OrthodonticsJames B. Edwards College of Dental Medicine, Medical University of South Carolina, 30 Bee St MSC126, Charleston, SC 29425.
    Affiliations
    Department of Pediatric Dentistry and Orthodontics, James B. Edwards College of Dental Medicine, Medical University of South Carolina, Charleston, SC
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  • Andrew Sonis
    Affiliations
    Children's Hospital Boston, Boston, MA

    Department of Developmental Biology, Harvard School of Dental Medicine, Boston, MA
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Published:December 26, 2013DOI:https://doi.org/10.1053/j.sodo.2013.12.003
      Mandibular incisor crowding in the mixed dentition is one of the most common problems presenting to the orthodontist. Asymmetry of alignment, premature loss of primary canine(s), and disruption in arch integrity are all early benchmarks of a tooth size/arch length discrepancy in the transitional dentition that can occur independent of any skeletal discrepancy. Space supervision and guidance of eruption refer to treatment interventions during the early to mid-mixed dentition periods that influence the eruption patterns and positioning of the permanent teeth during their transition. Generally considered applicable to individuals with adequate overall arch dimensions to accommodate a normal complement of permanent teeth with an acceptable esthetic and functioning occlusion, guidance of eruption involves the implementation of directed interventions to optimize the eruption and alignment patterns of the permanent teeth as part of a non-extraction protocol.
      The concept of an early phase of treatment intervention with guidance of eruption procedures to correct mandibular incisor crowding is not a new one. Space supervision, guidance of eruption, pre-orthodontic guidance, and interceptive orthodontics are all terms that have been used to refer to the treatment of crowding discrepancies presenting during the early to mid-mixed dentition (Nance, 1947
      • Nance H.N.
      The limitations of orthodontic treatment. I. Mixed dentition diagnosis and treatment.
      ; Popovich, 1962
      • Popovich F.
      Preventive and interceptive orthodontics.
      ; Hotz, 1970
      • Hotz R.
      Guidance of eruption versus serial extraction.
      ; Ackerman and Proffit, 1980
      • Ackerman J.L.
      • Proffit W.R.
      Preventive and interceptive orthodontics—a strong theory proves weak in practice.
      ; Moyer, 1988
      ). While considerable debate has ensued as to the proper terminology, the definitions are far less important than the concepts of intervention. The authors have elected to utilize Hotz’s
      • Hotz R.
      Guidance of eruption versus serial extraction.
      term guidance of eruption in referring to “treatment procedures that influence the eruption patterns and positioning of the permanent teeth during the transition from the primary dentition through the mixed dentition.” The effectiveness of preserving “leeway space” with a lingual arch to resolve mandibular crowding was reported by Nance
      • Nance H.N.
      The limitations of orthodontic treatment. I. Mixed dentition diagnosis and treatment.
      in a presentation to the Southern Society of Orthodontics in 1946 and in an article in the American Journal of Orthodontics in 1947. Nance describes a series of cases dating back to 1934 that were successfully treated with passive lingual arches in the mixed dentition. A similar approach to preserving arch length was described by Hotz
      • Hotz R.
      Guidance of eruption versus serial extraction.
      in 1970 and later by Singer
      • Singer J.
      The effect of the passive lingual arch on the lower denture.
      in 1974. These opinion articles and case series were later substantiated in clinical studies by Wagers,
      • Wagers L.E.
      Pre-orthodontic guidance and the corrective mixed-dentition treatment concept.
      Arnold,
      • Arnold S.
      Gianelly,
      • Gianelly A.A.
      Crowding: timing of treatment.
      DeBaets and Chiarini,
      • DeBaets J.
      • Chiarini M.
      The pseudo Class I: a newly defined type of malocclusion.
      Dugoni et al.,
      • Dugoni S.A.
      • Lee J.S.
      • Varela J.
      • Dugoni A.A.
      Early mixed dentition treatment—post-retention evaluation of stability and relapse.
      Gianelly,
      • Gianelly A.A.
      One-phase versus two-phase treatment.
      • Gianelly A.A.
      Leeway space & resolution of crowding in the mixed dentition.
      Rebellato et al.,
      • Rebellato J.
      • Lindauer S.J.
      • Rubenstein L.K.
      • Issacson R.J.
      • Davidovitch M.
      • Vroom K.
      Lower arch perimeter preservation using the lingual arch.
      Brennan and Gianelly,
      • Brennan M.M.
      • Gianelly A.A.
      The use of the lingual arch in the mixed dentition to resolve incisor crowding.
      Villalobos,
      • Villalobos F.J.
      • Sinha P.L.
      • Nanda R.S.
      Longitudinal assessment of vertical and sagittal control in the mandibular arch by the mandibular fixed lingual arch.
      Gianelly,
      • Gianelly A.A.
      Treatment of crowding in the mixed dentition, International Symposium on Early Orthodontic Treatment (2002).
      and Bell.
      • Bell R.A.
      Eruptive driftodontics of canines and premolars.
      Despite these positive reports, opponents of early intervention have argued that a second phase of therapy is frequently necessary, resulting in both increased length of treatment time and cost. While this opinion is frequently mentioned in the literature, there is scant research to substantiate such a conclusion. Wagers
      • Wagers L.E.
      Pre-orthodontic guidance and the corrective mixed-dentition treatment concept.
      reported in a survey of 100 patients undergoing mixed dentition treatment a 0.2-month difference in treatment time over those patients treated in the permanent dentition (21.6 months vs. 21.4 months). Popowich et al.
      • Popowich K.
      • Nebbe B.
      • Heo G.
      • Glover K.E.
      • Major P.W.
      Predictors for Class II treatment duration.
      reported very similar results of patients treated in the mixed dentition with average treatment durations of 20.25 months in non-extraction Class I cases.
      The short-term and long-term dental health benefits of early mandibular incisor alignment also remain unclear and unsubstantiated. Empirically, one would think that well-aligned teeth are easier to clean and thus less prone to plaque-mediated dental disease, namely caries and periodontal disease. Yet clinical studies fail to consistently demonstrate a causal relationship. A 2007 review by Burden
      • Burden D.
      Oral health-related benefits of orthodontic treatment.
      entitled “Oral Health-Related Benefits of Orthodontic Treatment” in this same publication concluded that “orthodontists today could not claim to prevent caries by orthodontic intervention” and that “orthodontic treatment confers neither harm nor benefit in terms of long-term periodontal health.” A more recent systematic review of the literature by Hafez et al.
      • Hafez H.S.
      • Shaarawy S.M.
      • Al-Sakiti A.A.
      • Mostafa Y.A.
      Dental crowding as a caries risk factor: a systematic review.
      arrived at this same conclusion.
      If not for overall dental health benefits and with questions regarding multiple-phase efficiency, then why treats crowding in the mixed dentition? Proponents of early treatment argue long-term lower incisor positional stability is better in patients treated during this period. The study by Dugoni et al.
      • Dugoni S.A.
      • Lee J.S.
      • Varela J.
      • Dugoni A.A.
      Early mixed dentition treatment—post-retention evaluation of stability and relapse.
      is often cited as evidence supporting such early guidance intervention. However, while the abstract of this study shows impressive results with 19 of 25 (76%) patients showing clinically satisfactory lower anterior alignment 10 years post-retention, a close review of the study suggests the reader may be misled by the abstract. Although it is unclear as to how patients were selected for the study and while no patients were stated to receive lower Edgewise treatment, it is clear the patients received more than just a passive lingual arch to maintain leeway space. Quoting the article, “In most cases the lingual arch was removed and a lower fixed canine-to-canine retainer was placed” for a period of time. In addition, 16 (64%) patients had circumferential fiberotomies and 18 (72%) had interproximal enamel stripping. In contrast, while the classic 10-year post-retention follow-up study of first premolar extraction cases by Little et al.
      • Little R.M.
      • Wallen T.R.
      • Reidel R.A.
      Stability and relapse of mandibular anterior alignment—first premolar extraction cases treated by traditional Edgewise orthodontics.
      found satisfactory incisor alignment to be less than 30%, no circumferential fiberotomies were performed on any of the patients, and presumably none had interproximal enamel stripping. Consequently, to suggest that incisor alignment exhibited better long-term stability in the Dugoni et al.
      • Dugoni S.A.
      • Lee J.S.
      • Varela J.
      • Dugoni A.A.
      Early mixed dentition treatment—post-retention evaluation of stability and relapse.
      study compared to the first premolar extraction cases reported by Little et al.
      • Little R.M.
      • Wallen T.R.
      • Reidel R.A.
      Stability and relapse of mandibular anterior alignment—first premolar extraction cases treated by traditional Edgewise orthodontics.
      may be somewhat misleading. Unfortunately, in another study by Little et al.
      • Little R.M.
      • Reidel R.A.
      • Stein A.
      Mandibular arch length increase during the mixed dentition—post-retention evaluation of stability and relapse.
      that examined post-retention stability in non-extraction cases treated in the mixed dentition that involved an increase in lower arch length, patients treated with leeway space preservation were specifically excluded from the study. The study results involving mixed dentition arch dimensional expansion did demonstrate an instability and high relapse potential even when small amounts of expansion were utilized to resolve incisor crowding. Consequently, it is unclear whether one can conclude resolution of lower crowding via leeway space preservation is any more stable than either premolar extractions or mixed dentition arch expansion. In addition to “relapse” of incisor alignment, some of the recurrence in crowding is likely related to normal physiologic changes as those observed in untreated individuals. The results of the Belfast longitudinal studies
      • Richardson M.E.
      Late lower arch crowding in relation to skeletal and dental morphology and growth changes.
      • Richardson M.E.
      A review of changes in lower arch alignment from seven to fifty years.
      showed a mean decrease in crowding of about 1 mm between 7 and 11 years of age; the crowding increased an average of 2.3 mm from 13 to 18 years.
      Given the information available suggesting post-treatment lower incisor stability is likely comparable with any of these approaches, the clinician might again ask—why bother with early treatment? In an essay entitled “Timing of early treatment: An overview,” Proffit
      • Proffit W.R.
      The timing of early treatment: an overview.
      suggested the indications for considering early treatment basically involve two issues—the effectiveness and the efficiency of treatment. The authors of the present article would argue that two “guidance of eruption” concepts meet these effectiveness and efficiency requirements: the utilization of E-space just prior to exfoliation of the mandibular second primary molar and the sequential utilization of leeway space for the relief of mixed dentition lower incisor crowding. An understanding of normative eruption patterns and arch dimensional changes in relation to the primary to mixed dentition transitional stages is imperative in understanding the rationale for the various treatment approaches that will be discussed under the general concept of “guidance of eruption.”

      Normative transitional dimensional changes and anticipatory guidance

      Recognition of an impending tooth size–arch length discrepancy is often first evident in the primary dentition. The significance of spacing in the primary dentition (both generalized and primate spaces) and its relationship to potential crowding of the permanent incisors is well illustrated by the longitudinal study by Leighton,

      Leighton BC. Early recognition of normal occlusion. In: McNamara JA Jr, ed. The Biology of Occlusion Development, Monograph #7, Craniofacial Growth Series; 1977:147-168.

      the work of Baume,
      • Baume L.J.
      Physiological tooth migration and its significance for the development of occlusion: I. The biogenetic course of the deciduous dentition.
      • Baume L.J.
      Physiological tooth migration and its significance for the development of occlusion. II. The biogenesis of the accessional dentition.
      • Baume L.J.
      Physiological tooth migration and its significance for the development of occlusion: III. The biogenesis of the successional dentition.
      and the work of Moorees and co-workers.
      • Moorees C.F.A.
      • Moorees C.F.A.
      • Chadha J.M.
      Available space for the incisors during dental development: a growth study based on physiologic age.
      • Moorees C.F.A.
      • Reed R.R.
      Changes in dental arch dimensions expressed on the basis of tooth eruption as a measure of biologic age.
      • Moorees C.F.A.
      • Gron A.M.
      • Lebret L.M.L.
      • Yen P.K.J.
      • Fronlich F.J.
      Growth studies of the dentition—a review.
      Observing 200 children during the transition from full primary dentition to permanent dentition, Leighton

      Leighton BC. Early recognition of normal occlusion. In: McNamara JA Jr, ed. The Biology of Occlusion Development, Monograph #7, Craniofacial Growth Series; 1977:147-168.

      noted a direct relationship between the amount of spacing in the primary dentition and subsequent crowding of the permanent incisors. Specifically, those children having 6 mm or more of spacing in the primary dentition had well-aligned permanent incisors, while approximately two-thirds of those with no spacing experienced significant crowding of the permanent incisors. Baume
      • Baume L.J.
      Physiological tooth migration and its significance for the development of occlusion. II. The biogenesis of the accessional dentition.
      also observed a similar relationship, where 44% of subjects lacking interdental spacing in the primary dentition exhibited significant crowding in the permanent dentition while those with generalized primary spacing transitioned into normally aligned lower permanent incisors. The retrospective assessment of adolescents with well-aligned permanent dentitions by Moorees and Chadha
      • Moorees C.F.A.
      • Chadha J.M.
      Available space for the incisors during dental development: a growth study based on physiologic age.
      showed that the individuals expressed generalized spacing in the primary dentition at 5 years of age. There is also some historical evidence that impending malalignment of permanent incisors may be seen radiographically well prior to their eruption.
      • Schwartz M.
      • Lewis S.J.
      • Lehman I.A.
      A quantitative study of the relation between certain factors in the development of the dental arches and the occlusion of the teeth.
      Thus, the clinician seeing children in the primary dentition can inform parents of potential crowding concerns based on clinical observations supported by timely radiographs.
      On eruption of the lower lateral permanent incisors, there is a normative increase in lower intercanine arch width of 2–3 mm, with a range from 0 to 5 mm.
      • Baume L.J.
      Physiological tooth migration and its significance for the development of occlusion. II. The biogenesis of the accessional dentition.
      • Moorees C.F.A.
      • Chadha J.M.
      Available space for the incisors during dental development: a growth study based on physiologic age.
      After lower permanent incisor transition is complete by 8 years of age, the normative amount of lower incisor crowding in the mid-mixed dentition approximates an incisor liability of about 1.5–2 mm, with a standard deviation of ±1 mm.
      • Hagberg C.
      The alignment of permanent mandibular incisors in children—a longitudinal study.
      • Lindsten R.
      • Ogaard R.B.
      • Larsson E.
      Anterior space relations and lower incisor alignment in 9-year-old children born in the 1960s and 1980s.
      These dimensional parameters indicating lower incisor crowding of 1–4 mm are expressed in the vast majority of children at 8–9 years of age after permanent lower incisor eruption is complete. Studies of transitional arch dimensional changes further document that no future increase in lower intercanine width will occur after the incisor eruption is complete.
      • Baume L.J.
      Physiological tooth migration and its significance for the development of occlusion. II. The biogenesis of the accessional dentition.
      • Moorees C.F.A.
      • Chadha J.M.
      Available space for the incisors during dental development: a growth study based on physiologic age.
      • Bishara S.E.
      • Jakobsen J.R.
      • Treder J.
      • Nowak A.
      Arch width changes from 6 weeks to 45 years of age.
      • Bishara S.E.
      • Khadavi P.
      • Jakobsen J.R.
      Changes in tooth size–arch length relationships from the deciduous to the permanent dentition—a longitudinal study.
      These findings suggest that normative transverse arch dimensional changes do not compensate for the relief of any malalignment that might be present in the mid-mixed dentition as the intercanine width is established by 8 years of age (Fig. 1). Relative to arch length changes, studies assessing dimensional changes occurring over the course of the transitional dentition show arch length decreases on average of about 2–3 mm per lower quadrant.
      • Rebellato J.
      • Lindauer S.J.
      • Rubenstein L.K.
      • Issacson R.J.
      • Davidovitch M.
      • Vroom K.
      Lower arch perimeter preservation using the lingual arch.
      • Moorees C.F.A.
      • Reed R.R.
      Changes in dental arch dimensions expressed on the basis of tooth eruption as a measure of biologic age.
      • Moorees C.F.A.
      • Gron A.M.
      • Lebret L.M.L.
      • Yen P.K.J.
      • Fronlich F.J.
      Growth studies of the dentition—a review.
      • Bishara S.E.
      • Khadavi P.
      • Jakobsen J.R.
      Changes in tooth size–arch length relationships from the deciduous to the permanent dentition—a longitudinal study.
      • Bishara S.E.
      • Jakobsen J.R.
      • Treder J.
      • Nowak A.
      Arch length changes from 6 weeks to 45 years.
      A slight decrease of about 1 mm, as the first permanent molars erupt and close any available posterior primary dentition spaces (i.e., early mesial shift), is mostly offset by more forward incisor positioning during the incisor transition. The arch length is generally stable over the course of the mid- to late-mixed dentition, but shows a significant average decrease of 2–3 mm as the final buccal segment transition occurs with the exfoliation of the second primary molar and late mesial shift of the permanent first molars (Fig. 2). Concurrently with the late transition period and subsequently into the adolescent years, an additional decrease in arch length may be associated with uprighting of the lower incisors as the overbite and overjet are defined.
      • Rebellato J.
      • Lindauer S.J.
      • Rubenstein L.K.
      • Issacson R.J.
      • Davidovitch M.
      • Vroom K.
      Lower arch perimeter preservation using the lingual arch.
      The lack of width increase in the lower anterior segment after lower lateral incisors have erupted and the decrease in arch length concurrent with buccal segment transition and incisor uprighting combine to result in a notable decrease in mandibular arch perimeter as the mixed dentition transitions into the young permanent occlusion. This arch perimeter decrease is on the order of 4–6 mm in the lower arch during this period and helps explain why mixed dentition incisor crowding either remains the same or typically worsens more during the transition to the full permanent dentition. As noted, the majority of lower arch perimeter reduction occurs as the second primary molars exfoliate, and the residual space secondary to the size differential between this tooth and the succedaneous second premolar (i.e., “E-space”) is eliminated due to “late” mesial shift adjustments of the first molars. Prior to this, minimal arch length change and the increase in arch width during incisor eruption actually produce an increased arch perimeter through the majority of the mid-mixed dentition. The arch perimeter changes in the mixed to adolescent dentition period are illustrated in Fig. 3
      Figure thumbnail gr1
      Figure 1Dimensional 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 lateral incisors have fully erupted by 8 years of age. The normative finding is a resulting average lower incisor crowding of 1.5 mm, with a SD of ±1 mm. Thus, lower crowding in the range of 1–4 mm should be expected in the majority of mixed dentition children at 8–9 years of age.
      Figure thumbnail gr2
      Figure 2Lower arch length decreases significantly on exfoliation of the lower second primary molar as the permanent first molars shifts forward toward the available “E-space.” The decrease of 2–3 mm in each lower quadrant translates to an arch perimeter decrease of 4–6 mm during this late “mesial shift” transition period.
      Figure thumbnail gr3
      Figure 3An increase in lower arch perimeter during the 2-year incisor eruption period (Inc—age 6–8 years) is related to increase in intercanine width associated with incisor transition and counter-balanced arch length adjustments. A stable period of arch dimensions follows during the mid-mixed dentition (8–11 years) until a dramatic decrease in arch length of 2–3 mm per side is associated with turnover of the buccal dentition, specifically second primary molar exfoliation. The resultant decrease in arch perimeter associated with the late mesial shift period (LMS—11–12 years of age) is on the order of 4–5 mm.
      After the lower permanent incisors have erupted and intercanine width changes have been realized in terms of anterior space dimensions, any crowding of the incisors should be considered an established dimensional reality with no “self-improvement” anticipated through future growth changes.
      • Sampson W.S.
      • Richards L.C.
      Prediction of mandibular incisor and canine crowding changes in the mixed dentition.
      Since arch circumference decreases anterior to the first permanent molars during normal development and with “space loss” often complicating alignment when arch integrity has been disrupted by premature loss of primary molars,
      • Northway W.M.
      • Wainwright R.L.
      • Demirjian A.
      Effects of premature loss of deciduous molars.
      it is often desirable to supervise the eruption sequence and positioning of the permanent teeth during the transitional occlusion. The review of normative arch dimensional changes revealed that extra space is actually available within the overall arch prior to the transition of the buccal dentition as represented by the size difference between the primary canines and molars vs. the permanent canines and premolars.
      • Nance H.N.
      The limitations of orthodontic treatment. I. Mixed dentition diagnosis and treatment.
      This “leeway space” represents a +1.7-mm space on average in each lower quadrant (overall +3.4 mm) and provides some potential for the relief of lower incisor crowding. Gianelly,
      • Gianelly A.A.
      Crowding: timing of treatment.
      in a study of 100 mixed dentition children presenting for orthodontic needs, reported that 85 patients showed lower incisor crowding on an average of 4.4 mm, a level of crowding notably greater than the normative average of about 2 mm. Gianelly
      • Gianelly A.A.
      Crowding: timing of treatment.
      calculated via space analysis that leeway space would provide adequate room to accommodate an aligned dentition in 72% of the cases presenting with incisor crowding. It is important to note that leeway space is most directly related to the size difference between second primary molars and the successor second premolars. This “E-space” approximates to 2–3 mm in comparative widths, and these are the last teeth to normally transition in the lower buccal segment eruption sequence.
      • Cooper J.D.
      • Bell R.A.
      The value of E-space.
      Thus, the control of leeway/E-space through space supervision and guidance of eruption techniques offers potential opportunities for the clinician to significantly improve tooth size–arch size adjustments for the relief of typical levels of dental arch crowding that present in the mixed dentition age child. Given this potential, diagnostic procedures to evaluate the overall space should be instituted to determine treatment alternatives whenever lower incisor alignment is disrupted by a lack of lower anterior space. Perhaps the most widely accepted diagnostic procedure used to evaluate available space is the use of a mixed dentition space analysis. While numerous mixed dentition analyses have been reported in the literature, studies by Luu et al.
      • Luu N.S.
      • Mandich M.A.
      • Tieu L.D.
      • Kaipatur N.
      • Flores-Mir C.
      The validity and reliability of mixed-dentition analysis methods: a systematic review.
      and Irwin et al.
      • Irwin R.D.
      • Herold J.S.
      • Richardson A.
      Mixed dentition analysis: a review of methods and their accuracy.
      would suggest that little clinically significant differences exist between the different methods. If a selected space analysis indicates the overall arch perimeter could accommodate or be within 2–3 mm of relieving the presented incisor crowding, the clinician should consider several options to facilitate dentition adjustments through a sequenced and staged guidance of eruption plan with the timely use of available posterior leeway space.

      Stage 1—Eruption guidance in the mandibular incisor segment (6–9 years of age)

      Disking of primary canines

      The first option considered when lower incisor crowding is in the range of 2–4 mm is disking of the primary canines to reduce their mesiodistal diameter in providing additional space to improve the position of the adjacent permanent incisors. The technique of reducing the width of primary canines to provide space for incisor alignment was likely first introduced in 1851 by Linderer

      Linderer J. Die Zahnheilkunde Nach Ihrem Neuesten Standpunkte. J.J. Palm und E. Enke; 1851.

      and re-introduced by Hotz
      • Hotz R.
      Guidance of eruption versus serial extraction.
      in the 1960s. Other clinicians have subsequently presented the concepts of disking both mesial and distal surfaces of the primary canines to enhance the space dimensions for lower incisor alignment.
      • Gellin M.E.
      • Haley J.V.
      Managing cases of over-retention of mandibular primary incisors where the permanent successors erupt lingually.
      • Gellin M.E.
      Conservative treatment for malaligned permanent mandibular incisors in the early mixed dentition.
      • Rosa M.
      • Cozzani M.
      • Cozzani G.
      Sequential slicing of lower deciduous teeth to resolve incisor crowding.
      • Foley T.F.
      • Wright G.Z.
      • Weinberger S.J.
      Management of lower incisor crowding in the early mixed dentition.
      • Bell R.A.
      Lower incisor crowding & guidance of eruption.
      The disking procedures work best when the malpositioned permanent incisors are displaced lingual to the anterior arch form (Fig. 4). The disking of the mesiolingual corner of the primary canines provides a “sluiceway” for the lingually positioned incisors to slide forward under the muscular pressure of the tongue. Bilateral disking of the mesiolingual aspect of the primary canines readily provides space of 1 mm and up to 2 mm per side for incisor “unraveling” (2–4 mm overall). With proper slicing of the mesiolingual corner of the primary canine at the gingival contact area with the lateral incisor, there is the potential for no measurable encroachment on the overall leeway space in the quadrant. Labial movement of the lingual displaced incisors may actually increase the midline arch length and overall arch circumference as the arch form is rounded out in a forward direction by the action of the tongue.
      • Bell R.A.
      Lower incisor crowding & guidance of eruption.
      Figure thumbnail gr4
      Figure 4Disking the mesiolingual angle of lower primary canines provides additional space for an improved alignment of the permanent incisors without overly encroaching on leeway space. Two examples of primary canine mesiolingual 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 two sequential disking procedures—first at initial presentation and second at the child's 6-month recall visit.
      While some clinicians disk the distal surfaces of the primary canines as well as mesial surfaces to allow more displacement of the intercanine distance, this tends to result in encroachment on the leeway space as a long-term consideration. In the case of labial malpositioned incisors, while disking may provide additional room for incisor alignment, the lips are a more significant factor in the balance between muscular forces such that the result is a lingual flattening of the anterior segment rather than improved incisor positioning and an associated decrease in overall arch space. In addition to lingual displacement of the incisors and crowding in the range of 2–4 mm as indicators for a favorable disking outcome, the general guidelines and recommended procedures for successful disking of primary canines are as follows:
      • 1.
        Local anesthesia (block, infiltration, or topical anesthetic compound) may be required as the canine must be sliced subgingivally to completely free the contact area. Disking just the crown is not adequate as the contact area is subgingival. Placement of a wedge is sometimes necessary to protect the lateral incisor and access the contact area. Thirdly, dentin exposure is usually necessary to reduce the primary canine width adequately—another indicator for local anesthesia or nitrous oxide support. Coordinating with restorative work requiring anesthesia in the area may be beneficial in treatment planning.
      • 2.
        A tapered fissured bur (#699 or #169) to allow effective tooth reduction and access without injury to adjacent permanent teeth is recommended. Re-approximating diamond disks or strips at this stage of development is not recommended due to risk of soft tissue injury. Emphasis on the mesiolingual corner of the primary canine rather than the straight mesial surface is facilitated with tapered fissure burs.
      • 3.
        Timing is critical to allow ease of access and optimal tooth positioning response. Given the normative intercanine width increases during lateral incisor eruption, disking should be delayed until “wedging” effects of erupting incisors and arch width increases are realized. Disking is best around 7 ½ to 8 ½ years of age in proximity to the completion of lateral incisor eruption. The primary canine roots should be relatively intact without ectopic resorption changes from the erupting lateral incisors or due to the eruption timing of the lower 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 the incisor segment, early “ectopic” loss of a single lower primary canine or even bilateral canine loss through displaced eruption of permanent lateral incisors is a significant indicator for a thorough orthodontic evaluation (Fig. 5). The ectopic loss of a lower primary canine unilaterally is frequently followed by lingual and distal movement of the incisor segment with shifting of the dental midline toward the side of the premature primary canine tooth loss. The disruption in arch integrity further compounds normal space use for eruption of the permanent canines and premolars in subsequent development. The early bilateral loss of both lower primary canines may allow maintenance of midline and arch symmetry, but ultimately results in significant lingual retroclination of permanent incisors, deepening of overbite, increased overjet, and bilateral loss of arch length over time.
      • Taylor G.S.
      • Hamilton M.C.
      Ectopic eruption of lower lateral incisors.
      • Shapira Y.
      • Kuftinec M.
      The ectopically erupted mandibular lateral incisor.
      • Hollander C.S.
      • Full C.A.
      Midline correction by extraction of the remaining mandibular canine-myth or reality.
      Figure thumbnail gr5
      Figure 5Unilateral ectopic loss of a lower primary canine typically results in an asymmetric space loss as the incisors shift toward the side of loss and move lingually (A and B). Bilateral ectopic loss of lower primary canines (C and D) allows maintenance of arch symmetry, but results in significant lingual retroclination and supraeruption of the lower incisors, increased overjet, deepened overbite, and reduction in overall lower arch dimensions.
      If one primary canine is lost ectopically during incisor eruption, it is usually desirable to extract the contralateral primary canine to maintain arch symmetry.
      • Taylor G.S.
      • Hamilton M.C.
      Ectopic eruption of lower lateral incisors.
      • Shapira Y.
      • Kuftinec M.
      The ectopically erupted mandibular lateral incisor.
      • Hollander C.S.
      • Full C.A.
      Midline correction by extraction of the remaining mandibular canine-myth or reality.
      • Atkinson C.D.
      The case against early extraction of mandibular primary canines.
      • Sayin M.O.
      • Turkkaharaman H.
      Effects of lower primary canine extraction on the mandibular dentition.
      While extraction of the contralateral primary canine may improve incisor alignment and midline integrity otherwise distorted by the asymmetric anterior space, the early loss of both primary canines will mimic the response seen when bilateral primary canines are ectopically lost. The result will be lingual retroclination of the permanent incisors, deepening of the overbite, increased overjet, and bilateral loss of arch length. In either scenario of unilateral or bilateral loss, alignment problems producing ectopic loss of primary canines are strong indicators of a significant incisor liability and arch length deficiency that will likely become grossly evident upon permanent canine and premolar eruption. Much more frequent than ectopic loss of lower primary canines, the canines most often remain in the mixed dentition arrangement with the permanent incisors erupted with a crowded malposition. While disking of the primary canines as described is the procedure of first choice, elective extraction of the primary canines in an attempt to maintain arch symmetry, coincident midlines, and incisor positional integrity can be considered under certain circumstances. Such intervention becomes more viable when the incisor crowding and liability is greater than 4 mm or when the eruptive alignment and dental midline is significantly skewed toward one side with a totally blocked incisor from the arch form (Fig. 6). The objective of lower primary canine extraction is to provide space in the arch for an improved incisor alignment and to maintain midline symmetry with the thought that negative effects on the occlusion (i.e., lingual inclination of incisors, deepened overbite, increased overjet, and additional space loss) can be overcome through later orthodontic tooth movement.
      • Foley T.F.
      • Wright G.Z.
      • Weinberger S.J.
      Management of lower incisor crowding in the early mixed dentition.
      • Hollander C.S.
      • Full C.A.
      Midline correction by extraction of the remaining mandibular canine-myth or reality.
      • Sayin M.O.
      • Turkkaharaman H.
      Effects of lower primary canine extraction on the mandibular dentition.
      • Sjogren A.
      • Arnrup K.
      • Lennartsson B.
      • Huggare J.
      Mandibular incisor alignment and dental arch changes 1 year after extraction of deciduous canines.
      This same concept is followed if a primary canine is lost unilaterally during incisor eruption and the contralateral primary canine is removed in an effort to maintain midline symmetry.
      • Shapira Y.
      • Kuftinec M.
      The ectopically erupted mandibular lateral incisor.
      • Hollander C.S.
      • Full C.A.
      Midline correction by extraction of the remaining mandibular canine-myth or reality.
      The clinician must remember that early extraction of lower primary canines will mimic what happens with bilateral ectopic loss and will likely result in notable lower anterior arch collapse.
      • Atkinson C.D.
      The case against early extraction of mandibular primary canines.
      • Sayin M.O.
      • Turkkaharaman H.
      Effects of lower primary canine extraction on the mandibular dentition.
      • Sjogren A.
      • Arnrup K.
      • Lennartsson B.
      • Huggare J.
      Mandibular incisor alignment and dental arch changes 1 year after extraction of deciduous canines.
      Therefore, the extraction of primary canines should not be undertaken without parental understanding of the consequences and ideally, orthodontic consideration of the long-term implications to the occlusion. Some clinicians recommend the use of a lingual holding arch to control the incisor positioning and prevent encroachment on permanent canine positions when lower primary canines are lost prematurely (Fig. 7). However, the displacement of the incisors attendant with ectopic loss or early extraction of lower primary canines typically contradicts the passive placement of a lingual holding arch at this stage without first aligning the incisors with active appliance therapy. Early selective extraction of primary canines goes beyond a simple first step in guidance of eruption and actually represents the start of either a phased early treatment protocol with arch expansion or a serial extraction program. In the context of a non-extraction treatment plan as part of first-phase arch development, a 2 × 4 Edgewise setup to decompensate displacements and position the lower incisors forward into the proper arch form may be indicated. The goal of such 2 × 4 treatment in Phase 1 is to establish coincident midlines, normative overjet and overbite with the maxillary incisors, and increase arch dimensions for eruption of the buccal segment dentition to optimize the potential for a long-term non-extraction treatment plan. After the incisor alignment has achieved the proper anterior positioning with the first-phase mechanics, a lingual holding arch can be placed as a “retainer” for the achieved incisor antero-posterior (A-P) positioning (Fig. 8).
      Figure thumbnail gr6
      Figure 6Extraction 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 incisor alignment achieved at expense of arch length and perimeter through lingual and distal movement of the incisors.
      Figure thumbnail gr7
      Figure 7Loss of primary canines—what about a lingual holding arch? Usually not that simple as incisors tend to align along LHA wire shaped to the most lingual position, i.e., loss of arch length as incisors drift distal and lingual along lingual wire into the canine space.
      Figure thumbnail gr8
      Figure 8Phase 1 2 × 4 arch development—pre-treatment (upper left): arch changes associated with bilateral ectopic loss of lower primary canines and narrowed maxillary arch form. Upper 2 × 4 arch development supported by E-spyder expander to emphasize fan-like anterior expansion of maxillary arch (upper right). Tieback of NiTi archwires restrained upper incisors and resulted in some retraction. Lower 2 × 4 arch development using AW lock stopped sequential archwires (0.016 NiTi, 0.020 NiTi, and 0.020 SS) to advance lower incisors, correct midline discrepancy, and increase arch perimeter to accommodate leeway space adjustments (at 4 months). Active appliances removed at 7-month treatment time (lower left). Retention with upper transpalatal bar and lower lingual holding arch at 18 months post-treatment maintained achieved arch width and arch length changes. Note facial profile changes influenced by correcting initial excessive overjet and lip interpositioning.

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

      In patients aged 10–11 years, panoramic evaluation of the exfoliation and eruption patterns of the posterior segment provides a particular site of assessment for timely mandibular guidance of eruption procedures. The clinician should take note of resorption patterns in the premolar area as well as desired molar adjustments and leeway space usage needed to achieve optimal alignment while maintaining stable occlusal relationships. In the usual eruption sequencing, the lower canine and first premolar frequently erupt at approximately the same time frame of 10–11 years of age. Since most of the leeway space is located in the size difference between the second primary molar and second premolar area, the canine and first premolar are forced toward a mesial eruption path.
      • DeBaets J.
      • Chiarini M.
      The pseudo Class I: a newly defined type of malocclusion.
      • Sampson W.S.
      • Richards L.C.
      Prediction of mandibular incisor and canine crowding changes in the mixed dentition.
      The resultant alignment finds the permanent lower canines positioned labial to the contact area of the lateral incisors with exacerbation of any anterior malalignment. To allow distal placement and to minimize malpositioning of the canine labial to the lateral incisor, extraction of the primary first molar (and primary canine if exfoliating improperly) is considered around this time. Disking of the mesial surface of the second primary molar may provide additional space for distal positioning of the erupting canine and first premolar. One can utilize up to 2–3 mm of “E-space” with coordinated disking of the primary canines, selective extraction of primary canines and first primary molars, and disking of the mesial surface of the second primary molars (Fig. 9). This second stage of intervention continues the guidance concept of unraveling lower anterior crowding toward the available posterior “E-space.” As long as the second primary molars are maintained in position as abutments against the fully erupted first permanent molars during lower canine and first premolar eruption, no measurable arch length changes should occur through mesial movement of the first permanent molars.
      • Moorees C.F.A.
      • Reed R.R.
      Changes in dental arch dimensions expressed on the basis of tooth eruption as a measure of biologic age.
      • Moorees C.F.A.
      • Gron A.M.
      • Lebret L.M.L.
      • Yen P.K.J.
      • Fronlich F.J.
      Growth studies of the dentition—a review.
      As discussed, the major decrease in lower arch length occurs concurrent with exfoliation of the second primary molar as the first molar shifts forward (i.e., “late” mesial shift) into the available “E-space.” This forward shift of the molars upon loss of the second primary molars typically results in a decrease in lower arch length of 2–3 mm per mandibular quadrant. Particularly under the impact of erupting second permanent molars, the arch length decrease occurs rapidly from back to front before more anterior teeth can distalize into the available “leeway” space.
      Figure thumbnail gr9
      Figure 9Removal of primary first molars concurrent with disking the mesial surfaces of second primary molars enhances distal eruptive positioning of the permanent 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 premolars erupted. This continued the guidance concept of unraveling anterior crowding toward available leeway/E-space.

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

      Hopefully, the eruption sequence has followed a normal canine-first premolar-second premolar pattern so the clinician has had the opportunity to perform the suggested Stage 1 and Stage 2 guidance procedures with guided canine and first premolar distal positioning along with relief of incisor malpositioning. The next critical timing sequence in a staged guidance program occurs around 11–12 years of age in association with the projected exfoliation of the second primary molars. The second premolars frequently take a path of eruption along the distal root of the second primary molar and eruption transition problems may occur. Occasionally, extraction of the second primary molar is indicated to allow normal eruption of the second premolar if such atypical patterns are noted. In addition to assessing the transitional patterns of the second premolars, consideration should be given to the placement of a lingual holding arch or a lip bumper concurrent with removal of the second primary molars (Fig. 10). If the available buccal segment space is tight, if the optimal use of leeway/E-space for crowding is desirable, and/or if the second permanent molars are erupting before the second premolars, a lingual arch or lip bumper may be a critical element in controlling lower arch dimensions at this point. In the Gianelly article
      • Gianelly A.A.
      Crowding: timing of treatment.
      on the value of leeway space as to treatment timing, lower crowding with an average discrepancy of 4.4 mm could be theoretically accommodated in 72% of the cases that presented with incisor crowding when the leeway space was calculated into a space analysis. Subsequent to that article, treatment-based articles have documented dramatic and positive alignment effects in the timely use of passive lingual holding arches (LHA) for control of lower leeway space in the late-mixed dentition.
      • DeBaets J.
      • Chiarini M.
      The pseudo Class I: a newly defined type of malocclusion.
      • Dugoni S.A.
      • Lee J.S.
      • Varela J.
      • Dugoni A.A.
      Early mixed dentition treatment—post-retention evaluation of stability and relapse.
      • Rebellato J.
      • Lindauer S.J.
      • Rubenstein L.K.
      • Issacson R.J.
      • Davidovitch M.
      • Vroom K.
      Lower arch perimeter preservation using the lingual arch.
      • Brennan M.M.
      • Gianelly A.A.
      The use of the lingual arch in the mixed dentition to resolve incisor crowding.
      • Villalobos F.J.
      • Sinha P.L.
      • Nanda R.S.
      Longitudinal assessment of vertical and sagittal control in the mandibular arch by the mandibular fixed lingual arch.
      These LHA studies, individually reviewed and presented chronologically, consistently show that a passive lingual holding arch placed in conjunction with selected removal of second primary molars will stabilize permanent first molars from forward mesial drift, minimize lingual movement of lower incisors, and allow canines and premolars to erupt distally as much as 1–2 mm into the held leeway space. Such leeway space control has been shown to result in reductions of up to 2–4 mm in lower incisor irregularity as a consistent finding.
      Figure thumbnail gr10
      Figure 10Control of late lower arch length decrease using lingual holding arches and selected extraction of second primary molars allows alignment of crowded lower 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.
      DeBaets and Chiarini
      • DeBaets J.
      • Chiarini M.
      The pseudo Class I: a newly defined type of malocclusion.
      reported on arch changes in 39 mixed dentition cases with lower anterior crowding treated with passive lingual arch therapy and selected removal of primary molars. Changes over a 4-year period were compared to a matched group of 60 untreated children with similar crowding who received no space supervision. In untreated subjects, lower canine and premolar mesial displacement occurred upon eruption with resulting overlap of the already crowded lower incisors that worsened the anterior displacement. In lingual arch subjects, lower anterior crowding decreased an average of 3–4 mm through the period of second permanent molar eruption. Lower arch length decreased less than 1 mm in children with lingual arches while permanent canines and premolars erupted an average of 1.5 mm (up to 3.5 mm) more distally per side than controls. In sum, the control of molar shifting and sustained arch length using lingual arches allowed spontaneous alignment of crowded lower incisors as the dentition distalized into the maintained leeway space.
      Dugoni et al.
      • Dugoni S.A.
      • Lee J.S.
      • Varela J.
      • Dugoni A.A.
      Early mixed dentition treatment—post-retention evaluation of stability and relapse.
      published similar findings from 25 mixed dentition patients with reductions in lower incisor crowding greater than 3 mm demonstrated after placement of passive lingual arches and selected primary molar extractions. After an average long-term post-retention period of 10 years, 19 of the 25 patients continued to show clinically satisfactory lower anterior alignment. Compared to 10-year follow-up of orthodontically aligned patients, these results show reductions in lower incisor crowding and long-term stability of the alignment with lingual arch therapy that was greater than or at least equal in effectiveness to active orthodontic treatments.
      Rebellato et al.,
      • Rebellato J.
      • Lindauer S.J.
      • Rubenstein L.K.
      • Issacson R.J.
      • Davidovitch M.
      • Vroom K.
      Lower arch perimeter preservation using the lingual arch.
      assessing cephalograms, study models, and tomograms of the mandibular body, reported on arch dimensional changes in 30 mixed dentition patients presenting with incisor crowding of 3 mm or more. In 14 patients treated with passive lingual arches, the arch length did not measurably change over the course of the eruption of the succedaneous teeth while an average arch length decrease of −2.5 mm per side was demonstrated in 16 untreated children used as controls. The arch length changes were related to first molars moving forward +1.7 mm in the control group compared to only +0.3 mm in the lingual arch group. Concurrently, incisors tipped forward slightly in the lingual arch group (+0.4 mm), while lingual uprighting of incisors in the controls reduced arch length by 0.65 mm. In sum, the action of the lingual arch was to reduce mesial molar migration and incisor lingual movement in controlling the quadrant arch length of 2.49 mm per side compared to non-LHA controls. The additional bilaterally sustained arch length resulted in concurrent relief of 3–4 mm of lower incisor crowding in treatment subjects.
      Brennan and Gianelly
      • Brennan M.M.
      • Gianelly A.A.
      The use of the lingual arch in the mixed dentition to resolve incisor crowding.
      quantified the arch dimensional changes in 107 consecutive mixed dentition patients treated with passive lingual arches through eruption of all succedaneous teeth. Occasional extraction of second primary molars to facilitate eruption of premolars and canines was the only other intervention. Arch length decreased an average of 0.4 mm in the lingual arch patients while arch width increased slightly. The patients presented an average +4.4 mm of total available lower leeway space, which resulted in an average decrease in lower incisor crowding from a pre-treatment level of −4.8 mm to +0.2 mm of space post-treatment. The space adjustments were enough to resolve incisor crowding completely in 65 of the lower crowding subjects (roughly 60%). An additional 16 subjects (one in six) had a final discrepancy of less than 1.0 mm and 13 subjects (one in 10) had a final discrepancy of less than 2 mm. Only 14 patients (13%) had crowding greater than 2 mm after the full buccal segment eruption was complete. Of note, the majority of patients with higher levels of post-treatment crowding presented with initial ectopic loss of the lower primary canines. In sum, a passive lingual arch with selected removal of primary teeth provided adequate space and eruption guidance to relieve significant lower incisor crowding in 105 of the 107 subjects.
      Villalobos et al.
      • Villalobos F.J.
      • Sinha P.L.
      • Nanda R.S.
      Longitudinal assessment of vertical and sagittal control in the mandibular arch by the mandibular fixed lingual arch.
      reported on 23 patients treated with lingual arches between 10 and 12 years of age compared to 24 matched untreated subjects. Molar and incisor movements were restricted to about a one-half millimeter arch length decrease for the 18 months of lingual arch wear while untreated subjects had a decrease of 2 mm in arch length. The lingual arch also limited first molar extrusion by about 2 mm compared to non-LHA patients. The study concluded that the lingual arch was effective for preservation of arch length and control of vertical eruptive movements of banded molars. The cited consecutive and chronologic LHA studies consistently confirm that arch length remains relatively constant or decreases minimally in patients treated with a passive lingual arch in the late transitional mixed dentition period. Forward movement of the lower first molars and lower incisor lingual movement is reduced notably in accounting for the relative stability of arch length which in turn contributed to approximately 4–5 mm greater arch perimeter than would have been available after normative arch dimensional adjustments in the late transitional dentition. The additional buccal segment space allowed distal eruptive positioning of the lower canines and premolars with a positive influence on relief of incisor crowding in the range of 3–4 mm. Thus, the timely use of lingual holding arches and selected extraction of primary molars in the manner described utilizes the leeway space for the relief of typical lower crowding amounts that present in the mixed dentition for about two-thirds to three-fourths of patients. These numbers are in line with the percentages predicted by Gianelly in his original work
      • Schwartz M.
      • Lewis S.J.
      • Lehman I.A.
      A quantitative study of the relation between certain factors in the development of the dental arches and the occlusion of the teeth.
      and are confirmed in the clinical studies reviewed.
      • DeBaets J.
      • Chiarini M.
      The pseudo Class I: a newly defined type of malocclusion.
      • Dugoni S.A.
      • Lee J.S.
      • Varela J.
      • Dugoni A.A.
      Early mixed dentition treatment—post-retention evaluation of stability and relapse.
      • Gianelly A.A.
      One-phase versus two-phase treatment.
      • Gianelly A.A.
      Leeway space & resolution of crowding in the mixed dentition.
      • Rebellato J.
      • Lindauer S.J.
      • Rubenstein L.K.
      • Issacson R.J.
      • Davidovitch M.
      • Vroom K.
      Lower arch perimeter preservation using the lingual arch.
      • Brennan M.M.
      • Gianelly A.A.
      The use of the lingual arch in the mixed dentition to resolve incisor crowding.
      • Villalobos F.J.
      • Sinha P.L.
      • Nanda R.S.
      Longitudinal assessment of vertical and sagittal control in the mandibular arch by the mandibular fixed lingual arch.
      Similar to lingual holding arches for the preservation of lower leeway/E-space, Woods
      • Woods M.G.
      Mandibular arch dimensional and positional changes in late mixed dentition Class I and Class II treatment.
      reported on the treatment of 182 late-mixed dentition patients using segmented 2 × 4 appliances to manage leeway space supervision. All 182 patients were started in treatment while second primary molars remained and possessed potential available E-space for relief of crowding. In all cases, upper and lower 2 × 4 appliances using segmental tip-back archwires were applied to control molar adjustments and incisor alignment. Buccal segments were bracketed and aligned to include second molars upon eruption with an average total treatment time of 28 months. The actual bilateral E-space measured directly from models represented a mean of 4.2 mm, with a range of ±1.6 mm. The actual mandibular space requirements 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 for about 10%, the crowding was greater than 8 mm. The 2 × 4 setup followed by sequential full appliances controlled arch dimensions such that the mean change in arch depth was −1.4 mm after treatment was completed. Molars were held back and the lower incisors tipped forward less than 1 mm on average. Canine arch width increased a mean of 0.9 mm. The greater the initial crowding was, the greater the dimensional changes. In most patients with approximately 4–6 mm of crowding, the control of E-space and the anterior Edgewise changes accommodated dentitional alignment. Thus, starting treatment in the late-mixed dentition using a sequenced 2 × 4 setup allowed the use of E-space and minimal anterior expansion needs to provide about 4–6 mm of space for aligning the mandibular dentition. Weinberg and Sadowsky
      • Weinberg M.
      • Sadowsky C.
      Resolution of mandibular arch crowding in growing patients with Class I malocclusions treated non-extraction.
      reported that similar amounts of arch dimensional changes were found in 30 Class I comprehensive orthodontic patients started in the mixed dentition for the resolution of mandibular arch crowding. The phased Edgewise treatment results represent similar dimensional values as reported with the use of lower lingual holding arches for molar and incisor control.
      An alternative to lingual holding arches for E-space preservation is the use of a lip bumper or lip shield in the late transitional dentition to enhance the forward positioning of the incisors, hold the first molar positioning, and allow some arch development as the buccal segments transition into the adolescent dentition (Figure 11, Figure 12).
      • Bell R.A.
      Lip bumpers for lower arch development.
      • Bergersen E.O.
      A cephalometric study—clinical use of the mandibular labial bumper.
      • Nevant C.T.
      • Buschang P.H.
      • Alexander R.G.
      • Steffen J.M.
      Lip bumper therapy for gaining arch length.
      • Osborn W.S.
      • Nanda R.S.
      • Currier G.F.
      Mandibular arch perimeter changes with lip bumper treatment.
      • Werner S.P.
      • Shivapuja P.K.
      • Harris E.F.
      Skeletodental changes in the adolescent accruing from use of the lip bumper.
      • Grossen J.
      • Ingervall B.
      The effect of lip bumper on lower arch dimensions and tooth positions.
      • Davidovitch M.
      • McInnis D.
      • Lindauer S.J.
      Effects of lip bumper therapy in the mixed dentition.
      • Hodge J.J.
      • Nanda R.S.
      • Ghosh J.
      • Smith D.
      Forces produced by lip bumpers on mandibular molars.
      • O'Donnell S.
      • Nanda R.S.
      • Ghosh J.
      Perioral forces and dental changes resulting from mandibular lip bumper treatment.
      • Murphy C.
      • Magness W.B.
      • English J.D.
      • Frazier-Bowers S.A.
      • Salas A.M.
      A longitudinal study of incremental expansion using a lip bumper.
      • Solomon M.
      • et al.
      Long-term stability of lip bumper therapy.
      Primarily acting through incisor proclination (about +2 mm on average) as a result of altered muscle equilibrium between the lip and tongue, the lip bumper approach also provides distalization or holding forces against the banded molars to hold leeway space. The molar effects are primarily a result of distal crown tipping and not through a true molar bodily distalization. Approximately 1 year of lower lip bumper wear appears to be necessary to gain 2–3 mm of arch length beyond the available leeway space. Additionally, evaluation of lip bumper wear over the transition time of canine and premolar eruption indicates that transverse arch width increases of about 1–3 mm at the canines and 4–5 mm at the molars are possible. Such increases in arch dimension along with modifications in muscle function are in turn associated with improved anterior alignment and more laterally developed arches during the active phase of lip bumper treatment. The application of lip bumpers in the late-mixed dentition offers an arch development technique when forward movement of the incisors can be tolerated, when distal uprighting and/or anchorage stabilization of the molars would enhance overall arch length, and when an increase in arch circumference might be significant in relieving moderately crowded incisor levels that are beyond simple leeway space preservation with lingual holding arches. Given the reported record of mandibular expansion approaches with an almost inherent tendency to return toward pre-treatment levels, the realization of long-term stability without a structured retention program seems questionable, though the altered functional environment does offer some advantages over more direct “mechanical” lower expansion approaches (e.g., Schwarz plates).
      • Solomon M.
      • et al.
      Long-term stability of lip bumper therapy.
      Figure thumbnail gr11
      Figure 11Case example—Removable lip bumper. Lip bumper placed as lower second primary molars exfoliated at age 11 years and 6 months. Bumper placement low in vestibule provided holding force on molars while allowing lip to contour over the bumper to lessen incisor labial movement. After 8 months of bumper wear (age 12 years and 2 months), a significant relief of anterior crowding resulted. Edgewise appliances aligned the dentition into the established arch form.
      Figure thumbnail gr12
      Figure 12Case example—Soldered lip bumper placed before second primary molars exfoliated. Bumper positioned at cervical margins provided holding force on molars, reduced lip contact on incisors to enhance labial movement. At 6 months (12 years and 5 months), lower crowding reduced through distal movement of canines and premolars toward E-space, with some arch expansion. Edgewise appliances aligned dentition with retraction of buccal segments and establishment of a broader arch form.
      The complications of conventional fixed appliance therapy rarely manifest themselves in the limited appliance approaches of mixed dentition guidance of eruption treatment mechanics. However, preservation of the “E-space” is not a totally benign intervention. By preventing the late mesial shift of the lower first permanent molars, less posterior arch length is available for the erupting mandibular second permanent molar with a resulting increase in second molar eruption problems. A study by Sonis and Ackerman,
      • Sonis A.
      • Ackerman M.
      E-space preservation—is there a relationship to mandibular second molar impaction?.
      in examining 200 patients having undergone E-space preservation with a passive lingual arch for second molar eruption problems, reported that 29 patients had at least one impacted second molar—a four- to five-fold increase over normative population reports of impacted lower second molars. A significant relationship was found between the mandibular first permanent molar and permanent second molar angulation patterns and likelihood of impaction. An intermolar angulation created by the long axis of the first and second molar of 24° or greater resulted in a positive predictive value of 1, indicating a high risk of impaction. A similar study by Rubin et al.
      • Rubin R.L.
      • Bacetti T.
      • McNamara J.A.
      Mandibular second molar eruption difficulties related to the maintenance of arch perimeter in the mixed dentition.
      found that those patients treated with a fixed lingual arch for E-space preservation had a 4.7% impaction rate of second molars, which was associated with an increased intermolar angulation and reduced space distal to the first molar. Consequently, the prudent clinician observing this relationship will inform the patient of a likely increased length of treatment.

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

      The control of leeway/“E-space” adjustments in terms of influencing arch dimensional changes through various space supervision, and guidance of eruption techniques offers opportunities to significantly improve lower tooth size–arch size discrepancies in the mixed dentition. The relief of typical levels of lower arch mixed dentition crowding (i.e., less than 3–4 mm in the mandibular arch) involves a timely, age-appropriate, sequenced, and staged protocol involving the following:
      • (1)
        Preservation of inherent arch dimensions through a comprehensive preventive, restorative, and space maintenance oversight program to optimize the integrity of the primary and the mixed dentitions throughout the transitional periods.
      • (2)
        After incisor eruption is complete, the average lower alignment shows crowding of 1.5 ± 1.0 mm. No subsequent “growth” changes will increase lower anterior canine-to-canine arch dimensions. The preferred approach during active incisor transition is to allow any “wedging” effect of eruption to influence arch dimensions. After lateral incisor eruption is complete at 8 years of age, what you see is what you get! NOW is the time for Stage 1 decision as to no intervention necessary, accept as is, disking of the primary canines, extraction of primary canines, or Phase 1 arch development.
      • (3)
        Selected disking of primary canines to enhance incisor positions when crowding is in the range of 2–4 mm and the lower incisors are lingually malpositioned to the arch form is the first choice of intervention, especially in deepbite/brachyfacial occlusion patterns. If intercanine space can be “fine-tuned” with disking, tongue pressures will tend to position the lingually displaced incisors forward into an enhanced arch form alignment. Intercanine space of 1–2 mm per side for incisor alignment can be achieved by disking the mesiolingual corner of the primary canines to provide “sluiceway” for incisor alignment once the lateral incisors are erupted (usually around 7 ½ to 8 ½ years of age).
      • (4)
        Decompensation of severe lower incisor malpositioning, midline asymmetry associated with ectopic eruption patterns, and lower incisor crowding at a level where removal of lower primary canines is required to allow proper incisor alignment integrity (greater than 3–4 mm of liability). Clinicians must understand and relate to the parent that the necessity of early primary canine extraction indicates a significant tooth size–arch size problems. It is frequently step one of a serial extraction program, particularly in vertically sensitive dolichofacial patterns. The negative effects with lingual collapse of incisors, arch length loss, deepening of bite, and increased overjet all are significant detriments in brachyfacial cases.
        Such levels of tooth size–arch size discrepancy may indicate the need for an early Phase 1 intervention using Edgewise 2 × 4 mechanics to position incisors and molars toward favorable Class I relationships, with incisor integrity, midline coincidence, and normal overbite and overjet. Crowding and incisor positioning discrepancies requiring canine extraction or extensive arch expansion to relieve incisor crowding and offset negative effects of space loss are candidates for early 2 × 4 intervention, and it generally implies a long-range non-extraction protocol as compared to a situation where the extraction of the primary canines is the first step in a serial extraction plan. The amount of crowding discrepancy and facial type are critical factors in the decision-making process as to long-term extraction vs. non-extraction plan. Brachyfacial deepbite patients lead to a prioritized arch development with arch expansion to enhance facial balance. Dolichofacial openbite patients tend to be directed toward a serial extraction protocol that is much more likely to offset vertical facial imbalance.
      • (5)
        Consideration of selective disking of the mesial surface of the second primary molars to enhance more distal eruptive positioning of the permanent canines and first premolars.
      • (6)
        Timely use of passive lingual holding arches, lip bumpers, and/or late-staged Edgewise setups along with selected extraction of second primary molars to provide space for relief of typical lower crowding amounts (2–4 mm). The space control allows canines and premolars to erupt in more distal positions than under normal transitional patterns. This “driftodontics” of the buccal segments will in turn result in more intercanine distance for relief of incisor malpositioning in about two-thirds to three-fourths of patients. In keeping with the idea of supervising space changes in the late transitional dentition, patients should be evaluated before the transition of the buccal teeth in each arch. A good clinical guide for timing is upon the clinical emergence of the lower canines and first premolars around 10–11 years of age. These teeth erupt about 1 year ahead of the final buccal segment transition, leaving adequate time to assess dimensional needs and plan treatment interventions for the relief of crowding.
      The dimensional parameters presented through optimal use of available leeway space in the transitional dentition provide the developmental potential for a non-extraction protocol as an achievable priority in the majority of children. It is likely that most clinicians would prefer a non-extraction approach whenever possible provided other outcome objectives are able to be met. It is even more likely that patients and parents would prefer not to have healthy teeth removed whenever possible. These comments should not imply that orthodontic extraction of permanent teeth leads toward a negative result as a general rule. This is not the case, as a significant proportion of patients present malocclusion factors and dentofacial patterns in which an extraction protocol is consistent with the achievement of overall esthetic and functional objectives. As a conceptual model however, a non-extraction approach for the majority of patients that possess the developmental potential for a full complement of teeth provides a sound foundation as a starting point for orthodontic diagnosis and treatment in the mixed dentition age patient.

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