INSIDE DENTISTRY SEPTEMBER 200!

OptlONSA review from the experts

Advantages and Disadvantages ofTreatment Options for CongenitallyMissing Lateral IncisorsThomas E. Dudney, DMD

The treatment 0/congenitally miss-ing maxillary lateral incisors presentsunique challenges to the dental professionand often requires a coordinated inter-disciplinary approach involving ortho-dontists, oral surgeons, periodontists, andrestorative dentists to achieve optimalesthetic and functional results. Carefuldiagnosis and information gathering aswell as communication with the patient—and often, depending on age, their par-ents—is necessary to formulate a treat-ment plan that will accomplish the desiredresults and satisfy patient expectations.There are many factors that affect treat-ment options, such as occlusion; align-ment of teeth; patient age; available space;alveolar bone thickness; facial profile;shape, color, and size of the canines; lipposition; gingival display; and conditionof adjacent teeth.'"4 An ideal treatmentplan should take into account all of thesefactors to achieve the esthetic and func-tional goals with the least-invasive optionavailable.5 This article will not recommenda particular treatment modality, but iden-

tify the available options and discuss theiradvantages and disadvantages.

SPACE CLOSURE WITHCANINE SUBSTITUTIONThe two main treatment options includeeither space opening with prosthetic re-placement or space closure with caninesubstitution.1'4 In ideal situations wherepatients have a balanced or slightly con-vex facial profile; an angle class II mal-occlusion with no mandibular crowd-ing or an angle class I malocclusion withmandibular crowding necessitating extrac-tions; and small canines that are lighterin color, space closure may be a viablealternative.6 The advantages of caninesubstitution are that natural teeth are bio-compatible and preferable long term andthe finished result is permanent, negat-ing the need for future prosthetic replace-ment.1'2 Furthermore, even though canine-protected occlusion is not possible, long-term studies have shown that space clo-sure using a premolar is equally soundocclusally and preferable periodontally

Figure 1A Unilateral congenitaily missing later-

al incisor with canine substitution (tooth No. 11

moved into site No. 10).

Figure IB The canine was reshaped and the

smile was restored with porcelain veneers.

Figure 2A Bilateral congenitaily missing lateral Figure 2B Fiber-reinforced resin-bonded

bridges with ceramic veneers on the pontics at

site Nos. 7 and 10.

to space opening. The disadvantages ofcanine substitution are the need for certainconditions to exist as previously stated,adverse effects on dentoalveolar and facialesthetics as a result of the canine promi-nence being moved mesially, the tenden-cy for space to sometimes reopen, andvery large or dark canines that are difficultto reshape or bleach to an acceptable shadeand may require a restoration (ie, porce-lain veneer) to achieve the desired esthet-ic result (Figure 1A and Figure IB).

SPACE OPENING WITHPROSTHETIC REPLACEMENTHistorically, options for space openingwith prosthetic replacement were lim-ited to removable partial dentures andconventional fixed bridges. Neither optionwas very appealing and in the past madespace closure with canine substitution amore attractive alternative. The only ad-vantage of removable partial dentureswas that they were far more conservativethan fixed bridges. However, their disad-vantages included their bulky and cum-bersome design, which made it difficultto achieve esthetic results, and the fact thatpatients disliked wearing them.

Although conventional fixed bridgeswere more comfortable and esthetic thanremovable partial dentures, they requiredgross reduction of healthy tooth struc-ture, which is generally contraindicatedin young patients. With today's materi-als, fixed bridges offer excellent resultsfrom esthetic and functional perspectives,but because they still require an amountof tooth reduction their use should belimited to situations where a conven-tional bridge already exists or the condi-tion of the abutment teeth (ie, wear,caries, fracture, etc) would dictate a moreaggressive preparation.

The first attempt at a conservative fixedrestorative option was the Marylandbridge, which had metal wings that bond-ed to the lingual surface of the centraland canine. The advantage of a Marylandbridge was that it was minimally invasive,but the disadvantages included compro-

Thomas E. Dudney, DMD

Private Practice

Aesthetic, General, and

Restorative Dentistry

Alabaster, Alabama

showing through translucent enamel anthe inability of the rigid metal wings to fkwith the slight mobility of the antericteeth, often leading to debonding.7 Irecent years two more options for pro;thetic replacement have gained favoOne is the fiber-reinforced resin-bondebridge and the other is the single-tootimplant. Both options offer a conserv;live approach with acceptable esthetiiand, although each option has certaiadvantages, each also has disadvantage;

THE FIBER-REINFORCEDRESIN-BONDED BRIDGEThe fiber-reinforced resin-bonded bridgsometimes referred to as the Enco:bridge,7 is based on the same principas the Maryland bridge. Instead of metwings, this type of bridge incorporatlaboratory-processed composite resin wifiber reinforcement in the form of a linguframework with a ceramic veneer bond<to the facial of the pontic. This design eisures long-term esthetics and vitalitythe restoration.7 Unlike metal, the fibereinforced resin framework readily bomto enamel and dentin and has the strengand elasticity to resist fracture ardebonding, even in the presence of sligmobility of the anterior teeth.

Furthermore, because the materialtooth-colored, the problem of disccoration and graying of enamel causedmetal show-through is eliminated (Figu2A and Figure 2B). In cases where patierdesire a more comprehensive smile ehancement procedure in addition to iplacing the congenitaily missing lateiincisors, this technique works well becauporcelain veneers can be placed on tnatural teeth as well as the pontics oftresin frameworks, thus giving the restortive team control of the size, shape, po.1tion, and color of the restorations in t

INSIDE DENTISTRY SEPTEMBER 2008

Fiber-reinforced resin-bonded bridgeswith ceramic overlays on the pontics canbe an excellent treatment option, but thereare some disadvantages of this procedureas well. While they are much less invasivethan conventional three-unit or even two-unit canine cantilevered fixed bridges,these bridges do require some tooth prepa-ration on the lingual and interproximalsurfaces of the abutment teeth. Also,because of their high failure rate whensubjected to excessive lateral forces, thesebridges are not recommended for pa-tients with a deep overbite relationship.5Although different preparation designsexist, the one that incorporates as muchof the lingual surface as possible (a depthof about 1 mm) and has a horizontal cen-tral groove for strength and a proximalbox design for increased thickness andfiber concentration in the connector sitesseems to achieve the best long-termresults,7 but also requires the most prepa-ration of healthy tooth structure. Fur-thermore, this type of fixed restorativeoption likely would have to be remadeseveral times over the lifetime of a youngpatient, and the possibility of connec-tor site fractures, material delamination,or debonding still exists. However, in caseswhere canine substitution or single-toothimplant replacement are contraindicatedor the patient chooses not to go throughthe necessary protocol for implant place-ment, the fiber-reinforced resin-bondedbridge maybe the best restorative option.7

THE SINGLE-TOOTH IMPLANTA more recent option for treating con-genitally missing lateral incisors, and onethat currently is recommended often, isthe single-tooth implant. Over the pastseveral years, the predictability and long-term success rates of implants have madethem an obvious restorative choice,5 espe-cially when teeth adjacent to the spaceare healthy, of normal size and shape, andunrestored.8'9 Furthermore, placementof an implant may provide a functionalstimulus to help preserve bone and preventresorption.10 However, when choosing thesingle-tooth implant as a restorative op-tion, several factors must be taken into ac-count such as growth considerations, spacerequirements, and site development.3

Because an implant acts essentially likean ankylosed tooth, any vertical alveolargrowth and eruption of teeth would causea discrepancy between the gingival mar-gin of the natural tooth and the implant.

Therefore, implant placement shouldoccur only after growth has been com-pleted,2"4 and it has been suggested thatneither chronological age nor hand-wristradiographs are reliable enough to makethat determination.3 Instead it would bebest to compare superimposed cephalo-metric radiographs taken at 1-year in-tervals until no growth changes are de-tected.3'9 Also, the amount of space be-tween the roots is critical to successfulimplant placement, and orthodontic inter-vention usually is necessary to achievenot only the amount of interradicularspace needed, but also the proper rootarigulation.2'3 Because orthodontic treat-ment usually occurs at an early age, sev-eral years of maintenance therapy maybe required until the appropriate age forimplant placement. It is also importantto maintain proper spacing for idealtooth proportions of the final restoration.

In addition to the tooth width require-ments for mesiodistal spacing, the alve-olar width in a buccolingual directionmust be adequate for implant placement.Often an additional surgical appointmentis necessary to graft or augment the alve-olar ridge before an implant can be placed.It has been suggested in the literature thatby allowing or guiding the eruption of thecanines into the lateral position and orth-odontically moving them to their naturalposition, the necessary amount of buc-colingual alveolar thickness for implantplacement can be achieved naturally, with-out the need to perform any ridge aug-mentation.2'4'7 Although not completelyunderstood, it has been shown that verylittle, if any, resorptive change in alveolarbone width is observed when space isopened orthodontically compared withthe decrease in alveolar ridge width afterextraction of maxillary anterior teeth.However, a disadvantage of orthodon-tic canine distalization for implant sitedevelopment is the potential for loss ofarch length when the canines are allowedto erupt mesially.3

While single-tooth implants as a pros-thetic replacement for congenitally missinglateral incisors can conservatively satisfythe esthetic, functional, and biologic goalsof treatment, they are not without disad-vantages and often require very carefulcase selection and a diligent and well-coordinated interdisciplinary approach.In addition to site development, spacerequirements, and age restrictions becauseof the necessity for growth completion

as conditions that must be met for suc-cessful treatment, implants as a restora-tive option have the potential for estheticfailure as a result of gingival darkening,exposure at the margin from gingivalrecession, incisal edge and gingival dis-crepancies from long-term facial growthand vertical movement of teeth,1' andthe difficulty of matching natural toothcolor and translucency with an implantcrown. When restoring congenitally miss-ing lateral incisors with implants, or anytype of restorative option, the patientshould be committed to a lifetime ofwearing a prosthesis in the area of themouth where esthetics are critical and notalways easy to control.11

CONCLUSIONThe treatment of congenitally missingmaxillary lateral incisors is challengingand complex, requiring very careful treat-ment planning, communication with thepatient, and often the coordinated inter-disciplinary efforts of the orthodontist,periodontist, surgeon, and restorativedentist. The two categories of treatmentoptions include space closure with caninesubstitution and space opening withprosthetic replacement. At the presenttime, the two most recommended proce-dures for prosthetic replacement are thesingle-tooth implant and the fiber-rein-forced resin-bonded bridge with a ceram-ic overlay. Although this article did notrecommend a particular treatment mod-ality or extol the virtues of one choiceover another, it identified the availableoptions and discussed the advantages anddisadvantages of each one. There is prob-ably not one treatment choice for thisparticular clinical situation that is clearlythe best option for each individual case.It is only after weighing all of the optionsavailable, analyzing the conditions thatexist, and consulting with the patient andother specialists that a method of treatmentshould be chosen.

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Figure 3A Bilateral congenitally missing lateral

incisors with a removable partial denture in place.

Figure 3B Facial view with the removable par-

tial denture out of the mouth.

Figure 3C Fiber-reinforced resin-bonded bridges

and ceramic veneers on the pontics (site Nos. 7

and 10) and natural teeth restored with veneers

(site Nos. 4,5,6,8,9,11,12, and 13).