INTRODUCTION
Treatment planning for missing maxillary lateral incisors is a common clinical predicament encountered by orthodontists, particularly at Holland Bloorview Kids Rehabilitation Hospital where congenital absence of maxillary lateral incisors is a common feature of many of our patients afflicted by syndromal or non-syndromaloligodontia. Three main treatment options exist including: canine substitution; a tooth supported restoration; or a single tooth dental implant. Auto-transplantation and removeable partial dentures are other less common options. Deciding which option is best suited for each individual patient involves careful consideration of multiple clinical variables. An interdisciplinary approach is important throughout treatment planning, and subsequent treatment can involve dental team members such as an orthodontist, oral and maxillofacial surgeon or periodontist and restorative dentist or prosthodontist. The use of a diagnostic set-up is one of the most important aids in clinical decision-making due to the inherent Bolton discrepancy.
This article will discuss considerations involved in deciding which may be the most favoured option for a patient with missing maxillary lateral incisors, following which a case will be presented involving a unique method of substituting canines for lateral incisors using orthodontic temporary skeletal anchorage devices.
CANINE SUBSTITUTION
Canine substitution is the most convenient option for patients already committed to undergoing fixed orthodontic treatment. The final outcome for the missing space can be resolved without having to wait for completion of skeletal growth. It also saves the patient from having additional surgeries or restorative procedures, making it not only a more innocuous but also a more cost effective option.
Canine substitution for missing upper lateral incisors is more easily achieved when the orthodontist is presented with two types of dental malocclusions:
1) A Class II malocclusion with overjet and minimal lower crowding to allow for a final occlusion that finishes with a Class II molar relationship and the upper first premolars substituting for the canines in a Class I position with the lower canines.
2) A Class I malocclusion with sufficient lower crowding to allow for lower premolars to be extracted and a final occlusion that finishes in a Class I molar relationship with the upper first premolars substituting for the canines in a Class I position with the lower canines. Depending on the inter-arch tooth size discrepancy, it may be more ideal for a lower incisor to be extracted. If this is a consideration, a diagnostic set-up should be undertaken to assess the final occlusion, overjet and overbite relationship.
It is desirable that canines substituted for lateral incisors have similar colour as the central incisors. The canine should be no darker than the central incisor or it may need to be individually bleached, bonded or veneered.
It is preferable for the substituted canine to be relatively narrow at the cemento-enamel junction (CEJ) bucco-lingually and mesio-distally and for it to have a relatively flat labial surface and narrow mid-crown width bucco-lingually. The crown width at the CEJ should be evaluated during the treatment planning stages to evaluate the final emergence profile. The narrower the mesio-distal width at the CEJ of the substituted canine, the more likely it will be able to substitute easily for a lateral incisor.
Normally, a canine has a wider and more convex labial surface than a lateral incisor. Recontouring of the labial surface is contraindicated because of the risk of dentinal exposure and sensitivity. Moreover, in patients with a high smile line it becomes desirable to achieve harmonization of the gingival margins as they will be on full display during smiling. Oftentimes, however, harmonization of the gingival margin of a substituted canine with the gingival margins of the adjacent central incisor and first premolar results, because of the normally greater length of the canine crown, in a canine cusp tip that extends coronally below the smile arc. In order to obtain an ideal esthetic relationship, the extending canine cusp tip will have to be amputated, a procedure which likely would result in dentinal exposure, sensitivity and vulnerability to erosion and attrition. In the case of a short canine, where the cusp tip does not extend coronal to the smile arc, it may be sufficient to augment the mesio-incisal and/or disto-incisal edges with composite resin.
When the gingival margin is positioned at the same level or higher than the central incisor gingival margin, or when the canine eminence is prominent, canine substitution is more acceptable in patients with low smile lines.
Canine substitution is usually contraindicated in patients missing a single maxillary lateral incisor due to difficulty in creating restorative symmetry between the substituted canine and the contralateral lateral incisor which often has a smaller mesio-distal width.
Canine substitution is also difficult in patients with a deep overbite, as the bite tends to deepen with space closure. It is also difficult in patients with a minimal overjet, in which case the orthodontist must consider methods to create overjet while closing maxillary anterior space such as interproximal reduction of the lower arch or the extraction of lower premolars or a lower incisor.
If, on balance, substitution of a canine for a missing lateral incisor is deemed ill-advised, the orthodontist can consider a tooth supported restoration or dental implant, in which a Class I molar and canine relationship is typically achieved.
POSITIONING TEETH TO FACILITATE A TOOTH SUPPORTED RESTORATION
An anterior tooth supported restoration is preferable in situations where it is difficult to obtain the proper space for a dental implant intercornally and interradicularly. It is a more cost-effective option for patients but can have a poorer long-term survival rate. It may necessitate sacrifice of usually healthy adjacent tooth structure, but it does not need ridge augmentation in cases where there is not enough bone for a dental implant.
RESIN BONDED BRIDGES
Resin bonded bridges require less preparation of adjacent teeth but have a reduced survivial rate usually as a result of failure due to debonding. The greater the area of coverage of the upper central incisor and canine with a resin-bonded bridge retainer, the greater the retention and likelihood of long-term success.
A resin bonded bridge supported by teeth that are relatively upright with minimal overbitewill have a greater chance of success because they experience more vertical as opposed to lateral forces.
ANTERIOR CONVENTIONAL BRIDGES
This is the least conservative of all options but a consideration if the patient presents with previously endodontically treated anterior teeth, significant restorations, or fractured incisors and canines that require restoration. If failure occurs, it is usually due to fracture or cement washout and caries.
SINGLE-TOOTH DENTAL IMPLANTS
The advantage of using dental implants to replace maxillary lateral incisors lies in excellent success and survival rates, and the lack of need to involve adjacent teeth in a fixed restoration. Dental implants, however, have increased costs and the need for at least one surgery. The quantity and quality of bone must be adequate or the patient may need a separate surgical procedure for ridge augmentation. Typically, there should be a minimum of 10mm of inciso-gingival bone and a minimum of 6.0mm of facial-lingual bone. An aid to assess the height and width of bone is the use of a cone beam CT x-ray. Guiding eruption of the permanent maxillary canine to into the missing lateral incisor position, and then distalizing it orthodontically is a strategy that can often be used to encourage the development of a robu
st alveolar process in the wake of the distalized canine, thus minimizing the need for ridge augmentation surgery prior to dental implant placement.
CASE REPORT
a) 15-year-old patient with congenitally missing upper lateral incisors who refused the option of dental implants as a replacement.
b) Two temporary skeletal anchorage devices placed in the palate and bonded to the upper central incisors to stabilize the their positions. This prevents retroclination of the upper central incisors as the upper space is consolidated to allow for the canines to be substituted as lateral incisors.
c) Following space consolidation. The upper central incisors have not changed position and the patient is still in positive overjet.
d) At day of debonding of orthodontic brackets. The patient is happy with the esthetics of the substituted maxillary canines. A final finish with anterior coupling and a Class II molar relationship. The upper first premolars are substituted for the canines in a Class I relationship to the lower canines. The gingival margin of the substituted canine is located coronally to gingival margin of the central, an important consideration in this patient with a high smile line. Excess gingiva is present between the canine and central incisor, so the need for gingivectomy will be evaluated once it settles.
This Figure is used with permission from: James Noble. Chapter 8. Evidence Based use of Orthodontic TSADs. In Evidence-based clinical orthodontics, edited by Peter G. Miles, Daniel J. Rinchuse, Donald J. Rinchuse. Quintessance, 2012.
CONCLUSION
This article has examined considerations involved in the decision-making process used to evaluate the most favoured option for a patient with missing maxillary lateral incisors. A case was presented that demonstrated the use of a unique method of substituting canines for lateral incisors using orthodontic temporary skeletal anchorage devices.OH
James Noble, Staff Orthodontist, Holland Bloorview Kids Rehabilitation Hospital, Toronto, Ontario. Visiting Lecturer, University of Manitoba, Division of Orthodontics, Winnipeg, Manitoba. Adjunct Professor, University of Seton Hill, Department of Orthodontics, Greensboro, Pennsylvania, Orthodontist, Children’s Aid Society of Toronto, Toronto, Ontario. E-mail: drjamesnoble@gmail.com.
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