5-Management of Space Problems

1330 JADA, Vol. 130, September 1999

CLINICAL

PRACTICE

Crowding and irregularity are the most preva-lent components of a malocclusion in dentalpatients. Surveys conducted by the U.S. PublicHealth Service in the 1960s1,2 found in a sample of8,000 that 40 percent of children (aged 6 to 11years) and 85 percent of youths (aged 12 to 17years) have crowding problems. The data from theThird National Health and Nutrition Examina-tion Survey, or NHANES III,3 which was con-ducted by the National Center for Health Statis-tics from 1988 to 1991, also indicate thatcrowding and irregularity remain a consistentproblem for children and adults.

Space management is an area of major interac-tion between primary dental care providers andspecialists. A recent survey of general dentists in

Ohio4 found that 77 percent performed spacemaintenance and 32 percent incorporated someform of interceptive orthodontics into their prac-tice. On the other hand, a survey of the orthodon-tists in the same state found that only 63 percentfelt that general dentists were referring patientsto their offices at the appropriate age for evalua-tion.4 The remaining 37 percent felt that patientswere referred too late.

Diagnosing space problems and treating casesof mild, moderate and severe crowding requiresan understanding of the etiology of crowding andof the development of the dentition. This articleattempts to update clinicians on the currentknowledge of space management. Proper spacemanagement in the primary and mixed dentitions

MANAGEMENT OF SPACE PROBLEMS IN THE PRIMARY AND MIXED DENTITIONSPETER NGAN, D.M.D.; RANDY G. ALKIRE, D.D.S., M.S.; HENRY FIELDS JR., D.D.S., M.S., M.S.D.

A B S T R A C T

Background. According to the ThirdNational Health and Nutrition Examination Survey,crowding and irregularity remain a consistentproblem for children. Management of space problemscontinues to play an important role in a dental prac-tice. It also represents an area of major interactionbetween the primary provider and the specialists.This article attempts to update clinicians on the cur-rent knowledge of space management.Description of Condition. Propermanagement of space in the primary and mixed den-titions can prevent unnecessary loss in arch length.Diagnosing and treating space problems requires anunderstanding of the etiology of crowding and thedevelopment of the dentition to render treatment forthe mild, moderate and severe crowding cases. Mostcrowding problems with less than 4.5 millimeters canbe resolved through preservation of the leeway space,

regaining space or limited expansion in the latemixed dentition. In cases with 5 to 9 mm of crowding,some can be approached with expansion after thor-ough diagnosis and treatment planning. Most ofthese cases will require extraction of permanentteeth to preserve facial esthetics and the integrity ofthe supporting soft tissue. Serial extraction or guid-ance of eruption is reserved for treatment of severetooth-size/arch-size discrepancies. Due to variationsin the timing and extraction sequence depending onthe diagnosis, serial extraction should be reserved forthose who can complete the treatment successfully.Clinical Implications. The recom-mended timing of referring patients with moderatecrowding to specialists for treatment is in the latemixed-dentition stage of development. Patients withsevere crowding will require earlier evaluation forserial extraction.

Copyright ©1998-2001 American Dental Association. All rights reserved.

JADA, Vol. 130, September 1999 1331

CLINICAL PRACTICE

can prevent unnecessary loss inarch length.

CROWDING: DEFINITIONAND ETIOLOGY

Definition. The problem ofcrowding has been broken downinto two categories: simple andcomplex.5 Simple crowding isdefined as “disharmonybetween the size of the teethand the space available in thealveolus with no skeletal, mus-cular, or occlusal functional fea-tures. It is most frequentlyassociated with a Class I maloc-clusion, although it may befound with Class II malocclu-sions with maxillary dental pro-trusion and a normal skeletalpattern.”5 Complex crowding isdefined as “crowding caused byskeletal imbalance, abnormallip and tongue functioning,and/or occlusal dysfunction aswell as disharmony between thesizes of the teeth and the avail-able space.”5 Fields6 categorizedcrowding as an alignmentproblem based on the amount ofcrowding.

Etiology. The exact cause ofcrowding or malocclusion ingeneral is unknown. Severalresearchers have suggested thatthe problem is hereditary and isassociated with the evolu-tionary development of modernhumans.7 These investigatorsattributed the main cause ofcrowding to a progressive reduc-tion in the jaw size as comparedwith tooth size. Another author8

believed there are true signs ofhereditary and environmentallyinduced tooth-size/jaw-size dis-crepancy—as indicated in theboxes “Signs of a True Heredi-tary Tooth-Size/Jaw-Size Dis-crepancy” and “EnvironmentalFactors Causing Crowding.”Given the size of these lists, theetiology of crowding must be

considered multifactorial.

DEVELOPMENT OF THEDENTITION

Primary dentition. In a

classic article, Baume9 foundthat the primary dentition canbe either spaced or closed. “Pri-mary spacing,” according toBaume, occurs in the maxilla in

SIGNS OF A TRUE HEREDITARY TOOTH-SIZE/JAW-SIZE DISCREPANCY.*dMaxillary mandibular alveolodental protrusion

without interproximal spacing

dCrowded mandibular incisor teeth

dA midline displacement of the permanent mandibular incisors, resulting in the premature exfoliation of the primary canine on the crowded side

dA midline displacement of the permanent mandibular incisors with the lateral incisors on the crowded side blocked out, usually lingually but occasionallylabially

dA crescent area of external resorption on the mesial aspect of the roots of the primary canines, causedby crowded permanent lateral incisors

dBilateral primary mandibular canine exfoliation,resulting in an uprighting of the permanentmandibular incisors; this, in turn, increases the overjet, the overbite or both

dA splaying out of the permanent maxillary or mandibular incisor teeth due to the crowdedposition of the unerupted canines

dGingival recession on the labial surface of theprominent mandibular incisor

dEctopic eruption of the permanent maxillary firstmolars, which indicates a lack of development inthe tuberosity area and results in the prematureexfoliation of the primary second molars

dA vertical palisading of the permanent maxillary first, second and third molars in the tuberosity area

* Based on information in Dale.8

ENVIRONMENTAL FACTORS CAUSING CROWDING.*dAn aberration in the eruptive pattern and sequence

of the permanent teeth

dTransposition of teeth

dUneven resorption of primary teeth

dPremature loss of primary teeth, resulting in thereduction of arch length due to subsequent driftingof permanent teeth

dReduction of arch length due to interproximal cariesin the primary teeth

dProlonged retention of primary teeth

* Based on information in Dale.8


70 percent of children and inthe mandible in 63 percent ofchildren. The intercanine dis-tance is 1.7 millimeters and 1.5mm more in “spaced” dentitionsthan in “closed” dentitions,respectively in the maxillas andmandibles. A primary dentitionwithout spacing is followed bycrowding in approximately 40percent of cases.

Contrary to a widely heldmisconception, arch length isreduced after the prematureloss of the primary incisor.9 Thisis particularly true if the incisoris lost very early. It is also trueif there is no primary spacing inthe dentition, if there is a ten-dency toward a Class II molarrelationship, or if the incisorshave a deep overbite relation-ship. Overbite is related to thegrowth of the jaws and to therate of eruption of the incisorteeth. It decreases from the pri-mary to the permanent denti-tion in only 10 percent of cases;it remains unchanged in 43 per-cent of cases and increases in 47percent of cases.10 The archdimension anterior to the first


CLINICAL PRACTICE

permanent molars does notchange appreciably during theprimary-dentition period.

Mixed dentition. In a longi-tudinal study, Moorrees andReed11 found that arch lengthdecreases 2 to 3 mm betweenthe ages of 10 and 14 years,when primary molars arereplaced by permanent premo-lars. These authors also found areduction in arch circumferenceof approximately 3.5 mm in themandible in boys and 4.5 mm ingirls during the mixed-dentitionperiod. If crowding is evident inthe early mixed-dentition years,it will not improve with furthergrowth and development.

Mesial shift. In patients witha spaced primary dentition anda flush or straight terminalplane, the eruption of the per-manent mandibular first molarsat approximately 6 years of agecloses the space distal to theprimary canines (primatespace) and transforms themolar relationship into a ClassI relationship. This has beenreferred to as “early mesialshift.”9 In patients with a closedprimary dentition (no primatespace) and a straight terminalplane, the transformation into aClass I molar relationship maynot occur until the exfoliation ofthe primary molars. At approxi-mately 11 years of age, the per-manent first molars migrateforward to close up the excessleeway space provided by thedifference in size between theprimary molars and the suc-cedaneous premolars (Figure 1).This has been called “latemesial shift.”9

The transformation into aClass I molar relationshipdepends on a number of dentaland facial skeletal changes,both genetic and environ-mental, that interact to achieve

(or not achieve) a normal occlu-sion. Several factors may pre-vent the establishment of anormal posterior occlusion.Extensive interproximal cariesor ectopic eruption of the maxil-lary first molars may result inpremature loss of primarysecond molars and a subsequentloss of arch length. Periapicalpathology of primary teeth mayhasten the eruption of their per-manent successors. Tumors andsupernumerary teeth mayimpede the course of eruption.Prolonged retention of primaryteeth may disturb the eruptionsequence.

Leeway space. The differencein size between the primarymolars and the succedaneouspremolars is termed “leewayspace.” This varies greatly fromperson to person, according to alongitudinal study by Bisharaand colleagues.12 The averageleeway space in that study was2.2 mm (1.1 mm per side) in themaxilla and 4.8 mm (2.4 mm perside) in the mandible. The dif-ferences in the leeway spacesbetween the maxillary andmandibular arches were 1.3 mmfor male subjects and 1.1 mm forfemale subjects. The range inthe amount of leeway spacebetween people is quite remark-able and can exceed the aboveamounts.

Incisor liability. The size dif-ferential between the primaryand permanent incisors is called“incisor liability.” In the ante-rior segment, the four perma-nent maxillary incisor teeth are,on average, 7.6 mm larger thanthe primary incisors. In themandibular arch, the perma-nent incisors are 6.0 mm largerthan the corresponding primaryteeth.13 Incisor liability variesgreatly from person to person.The spacing of the primary

Figure 1. Late mesial shift: thepermanent first molars migrateforward and close up the excessleeway space. Leeway space isthe difference in the mesiodistaldimension of the teeth in themolar area from the primary tothe permanent dentition.


anterior teeth; lateral and evenpossibly distal shifting of theprimary canines; and facial posi-tioning of the incisors all con-tribute to the incisor liability.All of these factors will increasethe arch perimeter and help themouth accommodate the largerpermanent teeth.

Eruption sequence. In a studyby Lo and Moyers,14 the mostfavorable sequence of eruption toobtain a normal molar relation-ship was as follows: first molar,central incisor, lateral incisor,first premolar, second premolar,canine, second molar in the max-illa and first molar, centralincisor, lateral incisor, canine,first premolar, second premolar,second molar in the mandible.The most unfavorable sequencein the maxilla was that in whichsecond molar erupted earlierthan either the premolars. Themost unfavorable sequence inthe mandible was that in whichthe canines erupted later thanthe premolars.

DIAGNOSIS OFCROWDING PROBLEMS

Diagnosis of crowding problemsshould take into account any jawdiscrepancies, muscle imbalanceand the environmental influ-ences listed in the Box, “Envi-ronmental Factors CausingCrowding.” The amount of intra-arch crowding can be calculatedin part by performing one of sev-eral space analyses.

Conventional space anal-ysis. The conventional orcanine space analysis was firstproposed by Nance in 1947.15

This analysis consists of com-paring the amount of spaceavailable for the alignment ofthe teeth to the amount of spacerequired for proper alignment.dThe space available is esti-mated by measuring the arch


CLINICAL PRACTICE

Figure 2. Pretreatment photographs of a 4-year-old patient with prema-ture loss of primary maxillary incisors and unrestorable teeth nos. B, I, Land S. A. Anterior view. B. Maxillary occlusal view. C. Mandibularocclusal view.

C

B

A


perimeter from the mesial con-tact of the permanent firstmolar from one side of thedental arch to the mesial con-tact of the permanent firstmolar on the opposite side ofthe dental arch. This can beaccomplished either by sepa-rating the dental arch into seg-ments that can be measured asstraight-line approximations ofthe arch or by contouring apiece of wire to the line of occlu-sion and then straightening outthe wire for measurement.dThe space required is thesummation of the mesiodistalwidths of the erupted mandib-ular permanent incisors and theestimated mesiodistal widths ofthe unerupted permanentcanines and premolars. The sizeof the unerupted permanentteeth can be estimated usingone of the following methods:measuring the teeth on a radio-graph and adjusting for themagnification by use of a simpleproportional relationship16; esti-mating the size of the unerup-ted teeth from a predictiontable; or using a combination ofboth methods.

Tanaka and Johnstonanalysis. The Tanaka andJohnston method17 is recom-mendable as a predictive tech-nique because it has reasonableaccuracy, does not requireradiographs, requires no predic-tion tables and predicts thesizes of the unerupted perma-nent canines and premolars inmaxillary and mandibularteeth. The Tanaka and John-ston analysis is completed bytaking one-half of the mesio-distal widths of the four lowerincisors and adding 10.5 mm,which is equal to the estimatedwidth of the mandibularcanines and premolars in onequadrant. Also, one-half of the


CLINICAL PRACTICE

Figure 3. Posttreatment photographs of the same patient shown inFigure 2. Teeth nos. B, I, L and S were extracted. Maxillary Nance appli-ance with prosthesis and mandibular band and loop appliances withocclusal rest on the canines were used for space maintenance. A. Ante-rior view. B. Maxillary occlusal view. C. Mandibular occlusal view.

C

B

A


nance is not necessary unlessesthetic concerns warrant thereplacement. If one or more pri-mary anterior teeth are lostprematurely, the teeth can bereplaced using either a remov-able or fixed partial denture.The fixed partial denture actu-ally is a lingual arch with pros-thetic teeth attached (Figures 2and 3).

Premature loss of primarycanines. Premature loss of pri-mary canines in the mandibulararch usually is a result of largesuccedaneous permanentincisors and ectopic eruption. Alateral shift of the incisor teethusually accompanies the loss ofthe primary canine, resulting ina midline discrepancy. A fixedlingual holding arch with sol-dered spurs can be used tomaintain arch integrity andprevent lingual tipping of themandibular incisors.

Early loss of primary firstmolars. Early loss of primaryfirst molars can cause distaldrifting of the primary canine ifthe loss occurs during the active

eruption of the permanent lat-eral incisors. Early loss of pri-mary second molars is a problembecause these teeth serve as aguide for the erupting perma-nent first molars. Early loss of aprimary second molar, especiallyin the maxillary arch, results inarch length reduction due tomesial migration of permanentmolars.21,22 If the first permanentmolar has fully erupted, then aband and loop can be placed oneither the first permanent molarrunning mesial to the primaryfirst molar or on the primaryfirst molar running distal to themesial aspect of the first perma-nent molar.

A distal shoe applianceshould be used if the primarysecond molar is lost before thepermanent first molar erupts(Figure 4). There are, however,some drawbacks to the use ofthis appliance.23 These compli-cations include difficulty in theaccurate construction of theappliance, the presence of a con-stant foreign body in a sensitivearea in the mouth, and a pos-


CLINICAL PRACTICE

mesiodistal width of the fourlower incisors plus 11.0 mmequals the estimated width ofthe maxillary canine and pre-molar in one quadrant. How-ever, one must be cautionedthat neither conventional spaceanalysis nor the Tanaka andJohnston method takes intoaccount the axial inclination ofthe mandibular anterior teeth,the effects of the curve of Spee,innate prediction bias, ethnicgroup biases or facial profile, allof which can affect the amountof crowding and space requiredin the analyses.

The total space analysis devel-oped by Merrifield18 took intoaccount the tooth measurement,cephalometric correction and soft-tissue modification. This methodalso indicated the exact area(anterior, middle or posterior)where the crowding occurred.

The severity of space problemscan be categorized into mildcrowding (space shortage of lessthan 2 mm), moderate crowding(space shortage of 2 to 4 mm),severe crowding (space shortageof 5 to 9 mm) and extremelysevere crowding (space shortageof 10 mm or more).

MANAGEMENT OF MILDCROWDING PROBLEMS

Space maintenance. Earlyloss of primary teeth is mostcommonly attributable tocaries.19,20 Caries, if left un-treated, will lead to loss in archlength. Space maintenance isindicated when there is a loss ofone or more primary teeth,there is no loss in arch perim-eter and there is a favorableprediction from the space anal-ysis if it can be completed. Earlyloss of a primary incisor as aresult of caries or trauma usu-ally results in very little changein the dentition. Space mainte-

Figure 4. A distal shoe space maintenance appliance for early loss of asecond primary molar before the eruption of the permanent first molar.A stainless steel crown is fitted on the primary first molar. A stainlesssteel extension is soldered to the crown and extended to the formerdistal contact of the primary second molar to guide the eruption of thepermanent first molar.


sible route of infection betweenintraoral and submucosal areas.If multiple primary posteriorteeth are missing, the distalshoe should be incorporated in aremovable partial denture.

Ectopically erupted perma-nent first molars. The perma-nent maxillary first molars mayerupt ectopically underneaththe distal surface of the primarysecond molars, causing patho-logical resorption of the roots.24

This path of ectopic eruptionleads to loss of arch length andshould be monitored for majorarch length deficiency or betreated as needed. Spontaneousself-correction of the impactedfirst permanent molar occurs in66 percent of cases. In thesecases, the second primary molar

exhibits resorption of the disto-buccal root. In most instances,these primary molars can lastuntil normal exfoliation. Forectopic molars that are not self-correcting, some type of inter-vention is warranted. When theimpacted molar is clinicallyaccessible, some type of separa-tion can be used for disim-paction.25,26 With reciprocalanchorage, either a brass wire,a spring-type deimpactor or anelastic separator can be used.

When the degree ofimpaction or inaccessibility ofthe first permanent molar pre-vents separation, active appli-ance therapy can be used to dis-impact the tooth.27 Theappliance consists of a bandcemented to the second primarymolar with an active spring orarm soldered to the band. Thearm extends distally and bondsto the occlusal surface of thepermanent first molar (Figure5). The arm is activated everythree or four weeks using athree-prong plier or optical plieruntil the ectopically eruptedmolar has cleared the distalsurface of the primary secondmolar, as seen in radiographs.Alternatively, a wire extensioncan be soldered to the primarymolar band and an elastomericchain is used for distal tractionto disimpact the permanentfirst molar.

When the resorption on thedistal surface of the primarymolar is extensive, the amount ofentrapment of the first perma-nent molar may approach one-half of the clinical crown. Resorp-tion may extend into the pulp ofthe primary molar, and the toothmay be mobile. In these cases,the tooth should be extracted anda plan for regaining space shouldbe formulated.

Use of leeway space to

resolve transient crowding.There are situations in which,on arch length analysis, there isno space deficiency but the per-manent incisors are crowded,sometimes to an extent greaterthan 2 mm. This is usually theresult of large permanentincisors and primary molars incombination with small premo-lars. Moorrees and colleagues,28

Moorrees and Chadha29 andBaume30 found that up to 2 mmof incisor crowding may resolvespontaneously with no treat-ment required. In childrenwhose succedaneous premolarsare smaller than the primarymolars they replace, the leewayspace can be used to unravelanterior crowding by main-taining the arch length. A studyby Gianelly31 showed thatcrowding of 4.5 mm could beresolved without active treat-ment in 77 percent of cases ifleeway space was used.

Methods such as disking ofthe primary incisors or extract-ing the primary canines arereserved for situations in whichthe permanent mandibularincisors are severely crowded. Ifeither of these methods is usedfor crowded arches and theleeway space is used to relievethe crowding, adjustment of themolar relationships may requiresubsequent use of headgear orinterarch elastics.

MANAGEMENT OFMODERATE CROWDINGPROBLEMS

Moderate crowding problemsusually are the result of aninherent lack of space or a lossof space. In the maxillary arch,early space loss usually is mani-fested as mesial tipping ormesial-lingual rotation32 of thepermanent first molars. Spacecan be regained or expanded by


CLINICAL PRACTICE

Figure 5. Active appliance therapyto disimpact ectopically eruptedpermanent first molar. Anorthodontic band is cemented onthe primary second molar and anactive arm soldered to the band.The arm extends distally andbonds to the occlusal surface ofthe permanent first molar. Athree-prong plier is used to acti-vate the arm until the ectopicallyerupted molar clears the distalsurface of the primary molar.



CLINICAL PRACTICE

distal tipping or bodily distaliza-tion of the permanent firstmolars. Regaining space iseasier in the maxillary archbecause of the increasedanchorage afforded by thepalate. A transpalatal arch canbe used to correct molar rota-tions and a certain degree ofdistal molar movement. Cetlinand Ten Hoeve33 showed a highdegree of success in regainingspace using a removable appli-ance in combination with head-gear. In the late mixed dentitionafter the upper premolars haveerupted, a Nance appliance maybe banded or bonded to the pre-molars as anchorage. Maxillarymolars can be distalized usingseveral appliances such as thependulum appliance,34 Jones Jig(American Orthodontics Corp.)35

or nickel-titanium, open-coilsprings.36 Most of these appli-ances are supported by a Nance-type lingual arch to obtainpalatal anchorage (Figure 6).

Space can be regained orexpanded in the mandibulararch using a lip bumper if thespace loss is bilateral.37 Thisappliance functions by tipping

the lower molars distally whileat the same time removing lippressure from the lower incisors.It provides forward movement ofthe lower incisors due toincreased tongue pressure. Uni-lateral space loss may be cor-rected by using a removable lin-gual holding arch. The lingualarch has a loop that, if opened,places a distal force on the lowerfirst molars. Alternatively, a lin-gual arch that supports a seg-mental arch wire and a coilspring to the mesially driftedpermanent molar (a variant ofthe maxillary segmental appli-ance supported by a Nance arch)can be used. A Schwarz appli-ance may be used if crowding isup to 3 mm in the lower anteriorregion and there is a significantamount of lingual tipping of theposterior molars.38

MANAGEMENT OFSEVERE CROWDINGPROBLEMS

The decision whether to regainspace or resign oneself toextraction is a difficult one.When crowding problems aresevere, expansion of maxillary

and mandibular arches orextraction of primary and, ulti-mately, permanent teeth maybe the only possible method ofreducing the discrepancybetween tooth mass and archlength. Maxillary expansioncould be orthodontic or ortho-pedic in nature. Orthodonticexpansion involves lateralmovement of teeth in alveolarbone. Orthopedic expansioninvolves the movement of basalbone such as the palatal halvesof the maxilla. One study showsthat every millimeter oftranspalatal width increase inthe premolar region, createdwith the use of a rapid palatalexpansion appliance, produces a0.7-mm increase in availablearch perimeter.39 However, theability of this treatmentmodality to reduce the need forextraction of permanent teethremains controversial. Onereason is the lack of well-designed long-term studies ofthe stability of maxillary expan-sion. Most of the publishedlong-term studies are casereports lacking comparison withcontrol groups.40-42

The possibility of expansionin the mandibular arch also islimited because of the lack of amidline suture and the need forsurgical intervention. Spacesupervision may be an alterna-tive method of guiding the erup-tion of permanent teeth in acrowded situation. However, thegoal of space supervision is inkeeping with Stemm’s43 recom-mendation of “timely extrac-tions,” a sequence of extractingprimary teeth but not perma-nent teeth. The goal of thisapproach is to squeeze all per-manent teeth into minimalspace. The indications, timingand sequence for timed extrac-tions are presented in an article

Figure 6. Molar distalization in the maxillary arch using a Nance appli-ance as anchorage and a segmental arch wire with a nickel-titaniumcoil spring.


by Musselman and Chadha.44

MANAGEMENT OFEXTREMELY SEVERECROWDING PROBLEMS

In the case of space shortages of10 mm or more, there is nodoubt that the size of the perma-nent teeth when compared withthe amount of space availableindicates a deficiency significantenough to warrant extraction ofpermanent teeth. “Serial extrac-tion”45 or “guidance of eruption”46

involves the sequential removalof primary and, ultimately, per-manent teeth to resolve tooth-size/arch-length problems. Inserial extraction, a sequence ofextractions begun in the earlymixed dentition eventually cul-minates in the extraction of thepermanent first premolars, withthe goal of the distal movementof the canine and general allevi-ation of tooth-size/arch-lengthdiscrepancy. The decision toextract maxillary and mandib-ular first or second premolars ismade early, depending on thetype of malocclusion.

Many articles have beenwritten about serial extractionsince its inception in the 1930sin Europe.47-52 Dale8 provided adetailed discussion on the sub-ject of serial extraction for bothClass I and Class II occlusions.The timing of extractions shouldbe based on the stage of develop-ment of the erupting permanenttooth and should coincide withits phase of active eruption. Fan-ning49 found that the rate of for-mation of the permanent pre-molar did not change after theextraction of its primary pre-cursor. However, an immediateeruption spurt occurred fol-lowing extraction of the primarymolar regardless of its stage ofdevelopment and the age of thechild.52 The findings of

Fanning49—coupled with those ofGron,50 who found that premo-lars emerge when one-half tothree-quarters of their roots areformed—provided good guide-lines for the timing of toothremoval during serial extraction.

The ideal guidelines forserial extractions are as follows:dabsence of skeletal discrepan-cies;dlarge (greater than 10 mm)arch-length deficiency;dnormal overbite;d(usually) Class I malocclu-sion;da commitment on the practi-tioner’s part to finishing thecase.

Ideally, the extractionsequence begins with removal ofthe primary canines as the per-manent lateral incisors erupt.Then, the primary first molarsare extracted to speed the erup-tion of the first premolars.Next, the permanent first pre-molars are removed to allow thepermanent canines to erupt inthe first premolar space. Asmentioned earlier, there arevariations in the timing andsequence of extractions,depending on the diagnosis.Mayne51 stated that diagnosis inthe mixed dentition is the clini-cian’s most challenging taskand that serial extractionshould be practiced only bythose who could complete thetreatment successfully.

TIMING OF TREATMENTTO RESOLVE CROWDING

Gianelly31 examined 100 patientsin the mixed-dentition stage ofdevelopment to determine theincidence and quantity of incisorcrowding. He found that 77 per-cent of the patients would haveadequate space to accommodatean aligned dentition if leewayspace was preserved; 84 percent


CLINICAL PRACTICE

would have adequate space if alip bumper was used to move themandibular first molars 1 mmdistally. Even if extraction treat-ment is necessary at that time,the permanent first premolarsare available for extraction.Gianelly concluded that latemixed-dentition stage of develop-ment is a favorable time to starttreatment to resolve crowding.

It is recommended, therefore,that patients with moderatecrowding be referred to special-ists for treatment if they are ina later stage of developmentthan the late mixed-dentitionstage. Patients with severecrowding will require earlierevaluation to determine if serialextraction is an appropriatetreatment.

CONCLUSIONS

Management of space problemscontinues to play an importantrole in a dental practice. Anunderstanding of the dentaldevelopment in the primary andmixed dentitions can help indeciding when and how to inter-cept the malocclusion ifcrowding is detected. Spacemaintenance in the developingdentition can prevent unneces-sary loss in arch length. Most ofthe crowding problems causedby a space shortage of less than4.5 mm can be resolved startingin the late mixed-dentition stageby preserving the leeway space,regaining space or accom-plishing limited expansion. Incases with 5 to 9 mm of spaceshortage, maxillary expansioncan be attempted after thoroughdiagnosis and treatment plan-ning. Most of these cases willrequire extraction of permanentteeth to preserve facial estheticsand the integrity of the sup-porting soft tissue. Serial extrac-tion or guidance of eruption is



CLINICAL PRACTICE

reserved for treatment of severetooth-size/arch-size discrepancy.Due to the variations in thetiming and extraction sequencedepending on the diagnosis,serial extraction should be prac-ticed only by those who can com-plete the treatment successfully.The recommended timing ofreferring patients with crowdingto the specialists for treatment isin the late mixed-dentition stageof development. ■

Dr. Ngan is professor and chair, West Vir-ginia University, School of Dentistry, Depart-ment of Orthodontics, Health Science CenterNorth, P.O. Box 9480, Morgantown, W.V.26506. Address reprint requests to Dr. Ngan.

Dr. Alkire is in private practice in Albu-querque, N.M.

Dr. Fields is professor and dean, The OhioState University, College of Dentistry,Columbus.

1. Kelly JE, Sauchey M, VanKirk LE. Anassessment of the occlusion of teeth of chil-dren. Washington, D.C.: National Center forHealth Statistics; 1973. Department ofHealth Education and Welfare publicationnumber (HRA) 74-1612.

2. Kelly JE, Harvey C. An assessment of theteeth of youths 12-17 years. Washington,D.C.: National Center for Health Statistics;1977. Department of Health Education andWelfare publication (HRA) 77-1644.

3. Brunelle JA, Bhat M, Lipton JA. Preva-lence and distribution of selected occlusalcharacteristics in the U.S. population, 1988-91. J Dent Res 1996;75(special issue):706-13.

4. Ngan P, Amini H. Self-confidence of gen-eral dentists in diagnosing malocclusion andreferring patients to orthodontists. J ClinOrthod 1998;32(4):241-5.

5. Moyers RE. Handbook of orthodontics.4th ed. Chicago:Mosby-Year Book MedicalPublishers; 1988:442-3.

6. Fields HW. Treatment of nonskeletalproblems in preadolescent children. In: ProffitWR, ed. Contemporary orthodontics. 2nd ed.St. Louis: Mosby-Year Book; 1993:376-99.

7. Wolpoff MH. Paleoanthropology. NewYork: Knopf; 1980.

8. Dale JG. Guidance of occlusion: serialextraction. In: Graber TM, Swain BF, eds.Orthodontics: Current principles and tech-niques. St. Louis: Mosby; 1985:259-366.

9. Baume LJ. Physiological tooth migrationand its significance for the development ofocclusion. I. The biogenetic course of thedeciduous teeth. J Dent Res 1950;29:123-32.

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5-Management of Space Problems