November 10, 2020
by Naheed Janmohamed, DMD
Aesthetic dilemmas created by congenitally missing teeth in the maxillary anterior segment pose a challenge for dentists not only in achieving harmony between hard and soft tissues but also in producing a conservative and functional result. Maxillary lateral incisors and first premolars are among the most common congenitally missing teeth.1,2
The first step in selecting a suitable treatment option is the correct diagnosis of congenitally missing lateral incisors, also known as lateral incisor agenesis. This is usually made in childhood by the general dentist, who will coordinate initial treatment options with an orthodontist.3 As the case progresses, other specialists including periodontists, oral surgeons and prosthodontists may be involved in producing an optimal treatment outcome. Selecting a path of treatment depends on the age of the patient, presenting malocclusion, space requirements, the size and shape of neighbouring teeth and patient preference.4
There are three traditionally accepted options for treating maxillary lateral incisor agenesis that each rely on careful case selection and coordinated interdisciplinary management. The first treatment option is canine substitution, whereby space closure is obtained by orthodontic mesialization of the canines and premolars according to a set of parameters that would allow for further restorative treatment. The second and third treatment options, tooth supported restoration and single implant restoration, involve space opening by orthodontic distalization of the canines and premolars to create an ideal space for restorative or prosthetic tooth addition at the lateral incisor position.
A 40-year-old female patient presented to our clinic with a desire to improve her smile. In addition to her concerns regarding misshapen and discoloured teeth, her chief concern was regarding the bilateral spacing between her premolars and canine teeth. The patient advised us that she had completed two previous rounds of orthodontic clear aligner therapy in an attempt to close these spaces and further restorative treatment to reshape the canine teeth. The patient’s goal was for straighter, whiter teeth with no gaps and without the need for further orthodontic repositioning.
Upon examination, she presented with a Class II Division II malocclusion with a slightly retruded and canted position of her central incisors. (Figs. 1-4) There was no indication of clinical or radiographic decay and all anterior teeth tested were vital. Her canine teeth had already been restoratively reshaped, however, they appeared much larger and more prominent in comparison to the already narrow and retruded central incisors. Her canine teeth also appeared much more saturated in colour than what would be expected of lateral incisors. Lastly, due to the orthodontic movement of the canine teeth mesially into the lateral incisor position, the gingival levels of her canines did not match those expected of lateral incisor gingival levels. Similarly, her first premolar gingival levels did not match those expected of canine gingival levels. (Fig. 1) Fortunately, she had a low lip line, obscuring these gingival levels from view during smiling. Her presenting condition and previous treatment history were consistent with canine substitution. For completeness, we reviewed the three previously described treatment options for lateral incisor agenesis with the patient for her consideration. As the patient had previously opted for the canine substitution pathway, she was not interested in further orthodontic movement. The decision was made to proceed with restorative treatment of the maxillary anterior six teeth. Further considerations were discussed with the patient including in-office tooth whitening, referral to a periodontist for aesthetic crown lengthening and gingival sculpting and the use of ceramic veneers to address tooth shape, colour and spacing.
A wax-up of teeth 14, 13, 11, 21, 23 and 24 was fabricated on mounted models according to the parameters necessary to achieve ideal tooth proportions and to correct the left-sided canting. The central incisors and first premolars were widened mesio-distally and lengthened in an apical direction to improve gingival levels. The canine teeth were slimmed down both in antero-posterior thickness and in a mesio-distal direction. As the treatment was mostly additive, an intra-oral mockup was fabricated to evaluate aesthetic parameters including tooth colour, position, size, shape and tissue support. (Figs. 5,6,7) A duplicate cast of the wax-up was sent to the periodontist for guidance on tissue levels. After aesthetic crown lengthening and gingival sculpting was completed, the tissue was allowed to heal for six weeks (Figs. 8,9) prior to in-office whitening and the start of the restorative treatment.
A clear essix retainer was fabricated from the the duplicate cast for use as a reduction guide during the preparation appointment. After anesthesia, tooth preparations on teeth 14, 13, 11, 21, 23 and 24 were made to accommodate lithium disilicate veneers in shade BL3 according to the proportions set out in the wax-up and mockup. Single 00 size cord with a hemostatic agent was gently packed into the sulcus for tissue retraction and an impression was recorded with heavy and light body polyvinyl siloxane (PVS) in a rigid tray. An apposing record was captured in alginate and bilateral bite registrations were taken in PVS. One-piece provisional veneers were constructed using spot-etch, spot-bond and dual cure LuxaTempTM bis-acryl shade B1 in a PVS putty matrix. The provisional veneers were polished, flash removed and interproximal clearance over the papillae was achieved to allow for ease of hygiene. Occlusion was assessed in maximum intercuspation (MIP) and in excursive movements and adjusted to allow anterior group function. It was noted at this point that a slight difference in gingival levels was present on the patient’s right side. Given her low lip line, our patient was content not to revise the gingival levels and chose to proceed to cementation. A final alginate impression of the maxillary teeth was captured to allow for ease of communication with the dental ceramist. Cementation of the final ceramic veneers was carried out two weeks after preparation using the MultilinkTM dual cure resin cement protocol. (Figs. 10,11) After finishing and polishing was completed, occlusion was again assessed in MIP and excursive movements and adjusted accordingly. Although the patient did not have any marked parafunctional habits, a night guard was fabricated to protect the veneers from inadvertent chipping or debonding during sleep. Final photo records (Figs. 12-15) were captured two weeks after insertion.
Although lateral incisor agenesis presents a significant clinical challenge, canine substitution, tooth supported restoration and single implant restoration are all reasonable treatment options depending on patient anatomy, age and preference. At an early stage in treatment planning, it is important to consider the patient’s occlusal scheme. For instance, canine substitution can only be predictably achieved in an Angle Class II malocclusion with no crowding in the mandibular arch or in an Angle Class I malocclusion with enough crowding to necessitate mandibular extractions.4 In our patient’s case, she presented in a stable Class II position with bilateral equal contacts in MIP and with no crowding in the mandibular arch. At this stage, a diagnostic wax-up of the proposed final occlusion is also important to allow the restorative dentist to determine how much canine reduction would actually be necessary. The more the canine is reduced to appear like the lateral incisor, the higher the likelihood of the underlying darker dentin shining through thin enamel causing shifts in colour and occasionally heightened sensitivity.5 As our patient’s canine teeth were already re-shaped, managing the colour and proportion of these teeth was much more predictable. Idealizing these cases with bleaching and restorative measures such as bonding or ceramic veneers in a stable anterior group function guided occlusion can provide a great aesthetic outcome.6 This option, however, is one of the least conservative. Another consideration with canine substitution is understanding and planning for the resultant difference in gingival levels between neighbouring teeth. Typically, the lateral incisor gingival zenith should reside approximately 1mm coronal to neighbouring central incisor and canine tooth.7 This can usually be addressed with aesthetic crown lengthening guided by the diagnostic wax-up. This is especially imperative when the patient has high lip mobility as the gingival levels will be seen more easily.
Tooth replacement by way of tooth supported restoration can be more conservative than canine substitution if considering a resin bonded bridge or a maryland bridge. A conventional fixed partial denture, however, requires full coverage preparation of neighbouring teeth and, therefore, is the least conservative option.
With advances in surgical techniques and soft and hard tissue procedures, single implant restoration has become an attractive and conservative option for treating lateral incisor agenesis. For instance, if this condition is diagnosed prior to the eruption of the permanent canine, the canine tooth can be orthodontically guided upon eruption into the lateral incisor position, thereby developing the alveolus.8 The canine is then subsequently moved distal, leaving behind a well-developed site for implant placement without the buccal alveolar depression noted in lateral incisor positions when this technique is not employed. In the latter case, buccal bone and gum augmentation is usually performed at the time of implant placement to produce a similar outcome. In both cases however, clinicians will have to wait several years before implants can be placed due to the need for completion of facial growth. As such, restorative tooth addition including resin bonded bridges or maryland bridges then becomes more of a transitional tool in lieu of implant therapy.
We have observed from the presentation of maxillary lateral incisor agenesis that several aesthetic and functional challenges exist. Balancing conservative dentistry with the patient’s desires and goals is an important consideration and must be addressed early in treatment planning. Once a treatment pathway is selected, interdisciplinary collaboration becomes imperative and can lead to excellent treatment outcomes. Even though many variables can be accounted for in the treatment planning phase, it is important to set realistic expectations with patients given the complexity of these cases. While not the most conservative option, we proceeded with the restorative and surgical enhancement of our patient’s teeth and periodontium as the last step in the canine substitution pathway. The final result addressed her chief concerns of spacing, colour and alignment and achieved our treatment goal of creating an aesthetically balanced and functional smile.
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