From Volume 14, Issue 3, July 2021 | Pages 139-145
This article provides an overview of the management of developmentally missing lateral incisors. When prosthodontic replacement of the missing lateral is required, wherever possible, implant-supported prostheses are considered the preferred definitive replacement option. The developmentally missing lateral incisor presents a unique aesthetic challenge. Developments in dental implant systems have implications in the management of this particular clinical situation.
Hypodontia is the developmental absence of at least one permanent tooth, excluding the third permanent molars. The incidence of missing lateral incisors is reported to be 1–2% in those of European origin,1,2 with a female predilection.3 Missing lateral incisors account for 24% of all developmentally missing teeth, and are more commonly found to be absent bilaterally.4
The missing lateral incisor presents a unique aesthetic challenge for clinicians due to:
Hypodontia involving one or both maxillary lateral incisors affect smile aesthetics and symmetry. The aesthetic issues may involve: spacing; rotations; centreline deviation; microdontia; and overeruption. In unilateral absence cases, achieving an aesthetic result can be more challenging.5,6 This is further complicated by the frequent finding of contralateral diminutive incisors.
Patients often present with retained primary teeth, in the absence of permanent successors.7 In some, the erupting permanent canine resorbs the primary lateral incisor and spontaneously substitutes for the missing lateral incisor, with retention of the primary canine, as shown in Figure 1. Less commonly, the primary lateral is retained when the permanent canine erupts in its normal position. A link between the absence of maxillary lateral incisors and ectopic permanent canines is well documented in the literature.8 Each of these factors results in space loss, which disturbs the symmetry and aesthetics of a smile. A number of studies have found that dental appearance can have a significant impact on an individual's quality of life. 9,10,11
The main treatment options for missing lateral incisors are listed in Table 1. A systematic review found no evidence in favour of one treatment option over another.12 Several factors influence treatment planning, including: patient factors; economical and social factors; skeletal pattern; crowding; buccal segment relationship; and dental factors, such as canine characteristics5 and soft tissue factors.
| Orthodontic space closure |
| Orthodontic space opening and replacement |
The more the canine tooth characteristics deviate from the lateral incisor, the more difficult it is to camouflage.13 The colour discrepancy between the central incisor and the canine has been reported to be the primary cause of dissatisfaction in people who have had space closure.14 A review of patient-centred outcomes suggested that the maxillary canine characteristics need not play such a prominent role in the decision to open or close the lateral incisor space.15 The clinician and patient may not have the same opinion on what is aesthetically pleasing. In the authors' opinion, when planning treatment in challenging cases, where the smile and dental aesthetics are compromised, a greater weighting should be given to the layperson's perspective of aesthetics. This shared decision-making approach highlights the importance of communication and presentation of all diagnostic information to the patient, in the planning phase of treatment.
A thorough assessment involves a full written record of the clinical assessment, as well as study models, photographs and radiographs. These records should then be assessed jointly by an interdisciplinary team. The space requirement for a missing lateral incisor is determined by the aesthetics and the occlusion. The aim is to produce a symmetrical and proportional arrangement of teeth. In unilateral cases, typically, this is based on the contralateral tooth to maintain symmetry. If the contralateral tooth is diminutive, space should be created for its restoration. The space requirements are determined by knowledge of the mean widths and the intended restorative solution. The permanent lateral incisor crown is usually 5.5–6.7 mm wide.16 The golden proportion (1:1.618) states that the width of a lateral incisor should be approximately two-thirds of the central incisor, from a frontal view. However, literature has failed to prove that this ratio commonly exists, or that it is even considered as an ideal aesthetic standard.17 The static and dynamic occlusion should be assessed to determine whether greater interocclusal space prior to restoration, is required.
A diagnostic set-up is useful to evaluate orthodontic tooth movements and the suitability of a type of prosthetic replacement, as well as acting as a visual aid to the patient. A Kesling set-up, involves repositioning the teeth to replicate orthodontic tooth movements. A facebow recording and articulating the wax-ups on an average value articulator can replicate the approximate dynamic occlusion.
Shared decision-making (SDM) is a process in which the clinician and patients work together to make decisions. This is especially important in the case of missing lateral incisors, with a quality of life impact. Each treatment option is preference sensitive with competing risks and benefits. Adolescents with little experience of dentistry, are inexperienced decision-makers and may rely on parents as advocates. The patient and parent need to be counselled on the various treatment options. Emphasis should be placed on life-long maintenance implications and the restorative burden. It is also important to highlight that there may be possible revisions of prosthesis type and design. There are decision aids available to help with this process (Table 2). Patient information, such as the British Orthodontic Society's leaflet on hypodontia, can help communicate information in lay terms.
| Treatment A | Treatment B | |
|---|---|---|
| Discomfort during treatment | No/little discomfort | Moderate discomfort needing painkillers |
| How long treatment takes | 2 months | 3 years |
| Waiting time | 3 years | 1 year |
| Bite after treatment | Teeth and bite feeling the same | Teeth and bite feel much better |
| Appearance after treatment | Small gaps or some teeth might look slightly grey | Teeth are straight without gaps and colour match of teeth is good |
| Which do you like best? | Treatment A | Treatment B |
Generally, it is now accepted that orthodontic space closure is the treatment of choice, wherever possible, to reduce the restorative burden. In studies14,19 and systematic reviews,15,20 the aesthetics of space closure and modification of the canine has been preferred by patients and lay persons over prosthetic replacements. Previously, it was thought that a lack of a canine-protected occlusion would have an adverse effect on the temporomandibular joint (TMJ), and that lateral occlusal forces on the smaller and thinner roots of the first premolars may lead to periodontal breakdown. Studies have shown, however, that orthodontic space closure produces results that are well accepted by patients, does not impair TMJ function and encourages periodontal health in comparison with prosthetic replacements.14
In space closure, a joint orthodontic–restorative approach is required to create an aesthetic arrangement of teeth that has a colour, size and shape within normal limits. This can be an aesthetic challenge, as shown in Figure 2. Restorative and orthodontic techniques to modify the size, shape, colour and gingival margin of canine teeth are detailed in the literature.13,21 Classically, the gingival margins of the central incisors and the canines are level, and the gingival margin of the lateral incisors is slightly lower. It is, therefore, important to assess the gingival tissue show on smiling. Orthodontically, canine brackets can be inverted and placed gingival to produce palatal root torque, extrude the tooth and lower the gingival margins. The tip can then be ground and the width of the canine reduced inter-proximally during orthodontic treatment. Post-treatment, composite can be added, to resemble lateral incisor contour (Figure 3). The darker shade of the canines can be addressed with less invasive options such as bleaching and direct or indirect composite resin restorations. In order for the first premolar to replicate the canine, buccal root torque can be placed in the archwire to mimic a canine eminence, and the bracket can be placed more incisally to intrude the tooth and create a gingival margin level with the central incisor, followed by grinding the palatal cusp. There is, however, often a compromise between the position of the gingival margin and the cusp tip of the premolar. Obtaining an ideal gingival margin often means the cusp tip is left more superior than an optimal position, and further restorative work is required to rectify this. Where there is crowding or an increased overjet, extraction of the contralateral lateral incisor may help preserve symmetry and the dental midline.
Resin-retained bridges (RRBs) are used more commonly to replace missing lateral incisors, than implant-retained prostheses. RRBs provide an aesthetic and conservative option in cases where implant placement is not possible, or desired. They offer a more expedient solution, and have the advantage over implant-retained prostheses that they can be provided in any mesio-distal size, to match the contralateral lateral incisor. Careful case selection, appropriate design and operative procedure are key factors for the longevity of RRBs. A crucial factor for their success is the surface area of enamel for bonding to the retainer wing. Tooth preparation appears to be unnecessary as RRB retainers can be placed high in occlusion, as a Dahl restoration, and can be detrimental with any more extensive preparation than into enamel only.22
Good communication during the planning stages ensures patients have understood the impact that a retainer wing may have, against the associated advantages. Grey shine through of the metal retainer at the translucent incisal edge is reported to be the most common reason for patient dissatisfaction with their RRB,23 as shown in Figure 4. This can be largely eliminated by using opaque cement and avoiding extending the retainer onto translucent enamel. If opaque cements cannot disguise the metal wing, an alternative abutment tooth should be considered.
The dynamic occlusion should be assessed prior to orthodontic debonding, as overbite and guidance in lateral excursions must not be directed onto the pontic. It has been suggested that the central incisors should be more upright and vertical, there should be minimal overbite, with just enough overlap to provide disclusion of the posterior teeth in protrusive function.
Cantilever designs are more successful than fixed–fixed RRBs.24 It has also been suggested that fixed–fixed RRBs can provide a form of orthodontic retention, but retention should be maintained separately from the restorative treatment, with orthodontic retainers.
The aesthetics of RRBs to replace lateral incisors is determined by the retainer wing, the pontic and management of the soft tissues. If the smile line is high, ridge preparation with electrosurgery at the impression or fit stages, along with an ovate pontic, can create the appearance of an emergence profile and interdental papillae. Figure 5 shows an aesthetic outcome of RRBs replacing bilateral missing lateral incisors.
When prosthodontic replacement is required, implant-supported prostheses are considered the preferred definitive replacement option. There are a number of challenges when replacing a maxillary lateral incisor, as listed in Table 3. An implant should only be placed when vertical growth has ceased, otherwise osseo-integration will result in infra-occlusion. It is recommended to maintain the deciduous lateral incisors until growth has ceased, to preserve the alveolar bone.25 Commencing definitive orthodontic treatment later will minimize the potential for relapse, bone atrophy, further growth and will allow a smooth transition from the orthodontic to restorative phases of treatment.
| ▪ Small space |
| ▪ Deficient alveolar ridge, especially bucco-palatally |
| ▪ Adjacent roots could be too close |
| ▪ Gingival levels may be uneven |
The quantity of bone available in the case of a developmentally missing maxillary lateral incisor space is often lacking (Figure 6). A study showed that in only 10% of cases, adequate facial bone wall was present.26 It has been suggested that encouraging the canine tooth to erupt into the lateral incisor position, and then distalizing it with orthodontic treatment, may produce stable bone prior to implant placement. There is controversy in the literature with regards to how stable this appositional bone is.27 Guided bone regeneration (GBR) is nearly always necessary in the aesthetic zone. Contour augmentation with GBR is able to establish and maintain facial bone wall in 95% of patients.28 In light of current evidence, GBR should be more frequently performed for implants replacing developmentally missing maxillary lateral incisors, than orthodontic site development. Radiographic analysis using a CBCT is recommended for selection of the appropriate treatment approach.
The correct inter-coronal and inter-radicular space is also important (Figure 7). It is desirable to obtain a minimum of 1.5 mm at the root–implant interface, to allow adequate post-implant healing, and adequate interdental papilla development.29 If there is limited space crestally, the emergence of an implant crown through a site with little space can compromise gingival health. Depending on the implant system used, there is a minimum diameter of the implant head. This is usually 3.5 mm, which gives an absolute minimum space requirement of 6.5 mm, at the gingival level. If the contra-lateral incisor is less than 6.5 mm, this may lead to a disturbance in symmetry. There are conventional implants now that are 3.0 mm in diameter (Figure 8), which means that, technically, a 6-mm space is required. To ensure adequate room for implant placement and to compensate for any relapse, realistically 6.5 mm should be considered acceptable. This space created for an implant coronally must be available for the full length of the implant. The lateral incisor space should be opened through bodily movement, to ensure the roots are parallel at the end of treatment. It is imperative that an appliance system is used that has the ability to move teeth in three-dimensions and, often, detailing bends in the finishing wire are required to obtain root parallelism. Prior to removal of the fixed appliance, radiographic confirmation should be agreed with the restorative dentist, that the root angulations and amount of space are sufficient for implant placement, as demonstrated in Figures 9 and 10. If there is insufficient space, and the patient presents during the retention phase, then the options include further orthodontic treatment or a RRB. Despite best efforts to torque teeth, sometimes a compromise may be required.
The correct inter-occlusal space is also important to consider, both in static occlusion and in function. Consideration should also be given to intruding the opposing lower canine to provide sufficient inter-occlusal space for the upper restoration, as these are often overerupted. Figure 11 shows an aesthetic outcome of implant-retained crowns replacing bilateral missing maxillary lateral incisors.
Systematic reviews show the 5-year survival rates as 87.7% for RRBs31 and 94.5% for implant-retained single crowns,32 and 90–95% after 5 and 10 years.33 However, technical, biological and aesthetic complications were frequent, as detailed in Table 4. A systematic review comparing the implant survival of narrow and standard diameter implants, and found <3.0 mm diameter implants performed statistically significantly worse. Narrow implants of >3 mm can be used successfully in limited interdental spaces in anterior single-tooth restorations. To prevent biological complications, oral health education should be provided at the treatment planning stage and finalized following completion.
| Implant complications |
|---|
| Surgical complications: implant contact with adjacent roots, dehiscence of the labial plate, or the show through of the implant through thin soft tissues |
| Biological complications: peri-implant mucositis, peri-implantitis and subsequent implant loss |
| Aesthetic complications: infra-occluded implants, inharmonious gingival contours, incorrect implant placement resulting in unnatural emergence profiles. Gingival recession and dark margins, and darkening of the labial gingival due to resorption of labial bone |
| Technical complications: screw-loosening, porcelain fracture and abutment debonds |
| RRB complications |
| Biological complications: caries and periodontal disease |
| Aesthetic complications: ‘greying-out’ of abutment teeth |
| Technical complications: de-bonding, structural damage and shade match deterioration, which can be a result of natural tooth discoloration or porcelain changes |
| Orthodontic relapse of abutment teeth (Figure 12) |
Retention is crucial post-orthodontic treatment, with 11% of patients experiencing enough relapse during the retention phase to prevent implant placement.30 In space opening cases, a Hawley retainer (Figure 13) with a prosthetic tooth, wire stops mesial and distal to the acrylic tooth, can be alternated with a vacuum-formed retainer at night, to allow recovery of the gingivae in the lateral incisor area. The retainer can also conveniently include a flat anterior bite plane to increase the inter-occlusal space and facilitate the provision of the definitive restoration. This type of appliance must be worn fulltime for a minimum of 6 months, allowing dentoalveolar remodelling in the saddle areas prior to restoration. It is also important to use fixed retainers in conjunction with removable retainers on all the anterior teeth to maximize the effectiveness of the retention. In cases where space opening is followed by provision of a RRB, multiple abutments could be considered to prevent relapse; however, fixed–fixed or double-abutment designs of bridgework have a significantly poorer long-term prognosis. Retention should be considered at the planning stage and ideally be maintained separately to restorative treatment.
Interdisciplinary care, involving the orthodontist, restorative dentist and general dental practitioners in treatment of patients with missing lateral incisors is essential. The patient and parent need to be counselled fully on all the treatment options with their associated advantages and disadvantages. Developments in dental implant systems have implications in the management of this particular clinical situation with the historical minimum 7 mm of space required at the end of orthodontic treatment now not necessarily being the case.
