A joint restorative-orthodontic approach for missing lateral incisors
Shivani Patel presents three case studies highlighting the necessity of treatment planning with a multidisciplinary team for orthodontic treatment involving restorative elements.
Missing teeth – or hypodontia – is a term used to describe the developmental absence of one or more primary or secondary teeth, excluding third molar teeth (Goodman et al, 1994).
The prevalence of missing primary teeth is low (0.3-0.9%), however, this does mean that the likelihood of missing permanent successor teeth increases.
The prevalence of hypodontia in the permanent dentition is 3.5-6.5% (Polder et al, 2004). There is also a usual ethnic and gender variation – found higher in Asians and females.
Dentists often encounter patients with missing or malformed teeth.
The maxillary lateral incisor is the most common congenitally absent tooth after third molar teeth (20-25% of the population).
The incidence of missing lateral incisors is 2% (Lamour et al, 2005).
Hypodontia can be classified according to its severity (Hobkirk et al, 1995):
- Mild (one to two missing teeth)
- Moderate (three to five missing teeth)
- Severe (more than six missing teeth).
The main aetiology for missing lateral incisor teeth is genetics (Cobourne, 2007). Often, there will be a family history for both peg and missing lateral incisor teeth. There can also be an environmental factor such as in cleft palate where the cleft can lead to the localised disruption of the development.
In today’s world, the management of any hypodontia involves a multidisciplinary team approach, involving the restorative dentist/prosthodontist, orthodontist, and sometimes the oral surgeon.
This interdisciplinary approach determines the final outcome, as sometimes a single discipline may only provide suboptimal care and result alone.
If detected early then it is advisable to maintain the deciduous lateral incisors for as long as possible. This in turn preserves the alveolar bone for any future planning.
However, if bilateral lateral incisor teeth are missing and the deciduous lateral incisor teeth are lost or of poor prognosis, then this will allow for the canines to erupt in a more mesial position.
There are a number of treatment options that exist for replacing missing lateral incisors (Savarrio and McIntyre, 2005), including:
- Do nothing and accept. This is seldom the case unless appliance therapy is contraindicated due to poor oral hygiene and high caries rate
- Camouflaging the deciduous lateral incisor teeth restoratively. This may not need any active treatment. However, it’s not always ideal as the deciduous teeth are not designed to last for very long and once lost the space would be too small to ideally restore
- Closing the space with a canine substitution
- Opening the space and replacing it with a tooth-supported restoration, or a single-tooth implant.
A trial diagnostic (Kesling) set-up, using duplicate study models, can aid the team in deciding the final aesthetic and occlusal outcome.
Selecting the appropriate option depends on:
- Specific space requirements
- Tooth-size relationship
- Size and shape of the canine
- Patient opinion and cooperation
- Commitment to medium/long-term treatment
- The ideal treatment is the most conservative option.
Closing the lateral incisor space with the canine
Space closure is preferred to space opening (Robertsson and Mohlin, 2000). You would consider this option if the patient did not have very large canine teeth, the teeth were not too yellow or of poor anatomy. This option is ideal in patients with a slightly increased overjet where space closure would aid in reducing this. The major advantage of this option is that there is no need for a prosthesis and further dental treatment involving lifelong maintenance. The anterior teeth can be modified with minimally invasive restorations such as bondings or veneers and tooth contouring to camouflage the appearance.
In order to achieve this, the dentist can extract the deciduous lateral incisor teeth early to allow mesial drift of the permanent canine tooth. It will require fixed appliance therapy to detail the occlusion. Bracket placement is crucial.
Can we place upper two brackets on upper threes? It is not ideal, because:
- The bracket is too thick
- The base contour is incorrect
- There is insufficient labial root torque.
- A canine bracket should be placed on a canine tooth
- Invert an Andrews bracket to reduce the labial root torque from +7 degrees to -7 degrees
- Use the gingival margin as guidance to place the bracket, not the cusp tip. This will cause extrusion of the canine and in turn over time the orthodontist can reduce this tip to prevent any occlusal interference but also start camouflaging the canine (Nordquist and McNeil, 1975). This will establish group function
- Also consider reducing the width of the canine tooth with sessional interproximal reduction
- Add further palatal torque to the canine to reduce the canine eminence (Rossa and Zachrisson, 2001)
- The upper first premolar teeth will be taking place of the canine teeth. These can be intruded so that the gingival margin was lifted like a canine (the cuspal tip will need bonding) and the tooth should be rotated mesiobuccally to increase its width along with the palatal cusp reduction over time to prevent any occlusal interferences
- Finally, tooth whitening to aid in the camouflage process and final bondings on the canine teeth to lateralise them (Figures 10 and 11).
It has been a common belief that the canine to central incisor tooth arrangement would lead to the reduction in the upper arch width and also deny the patient canine guided occlusion and this, in turn, would lead to TMJD. However, recent studies have shown that this is not the case.
Long-term periodontal studies have suggested that space closure is preferable to space opening. This is because prostheses of any kind tend to accumulate more plaque.
Opening the space for the replacement of the missing lateral tooth/teeth
This is usually considered if:
- The patient already has a contralateral incisor tooth of good shape and size
- The patient has a class III malocclusion and we want to keep the upper labial segments forwards to maintain a positive overjet and overbite and soft tissue support
- The patient has a good class I interdigitated occlusion that doesn’t need to be disrupted
- It would improve aesthetics; if the patient has aesthetically poor canines where canine substitution would be undesirable (Asher and Lewis, 1986)
- It is advantageous both functionally and occlusally, favouring good intercuspation in the buccal segments.
Fixed appliances are usually necessary to create the appropriate space for the prosthetic replacement, which can be either fixed or removable. Fixed appliances are ideal as they can control bodily movement and in particular root apices.
Guidance for space can be determined by:
- Contra-lateral tooth width. If this is diminutive, then the clinician would need to decide whether to build up this tooth first and then to use it as a guide or match the reduced width (which may prevent later implant placement and compromise aesthetics)
- The ‘golden proportion’ states that the width of the lateral incisor tooth should be two thirds that of the central incisor. However, there is some research suggesting that that this may not be the ideal aesthetic standard
- Use Bolton (1958) analysis.
Following removal of the appliances, if the spaces are closed then consider bonded retainers coupled with pressure from removable retainers. Ensure that the space opening is further minimised by good occlusal finishing.
If space opening, then while the gingivae is returning to good health you may consider a pressure-formed retainer with a prosthetic tooth or a Hawley retainer incorporating mesial and distal stops against the central incisor and canine tooth and a prosthetic tooth/teeth is advisable.
This usually takes place once the gingival margins have stabilised and, in the case for implants, the alveolar bone growth has been completed.
The most commonly used options to replace missing lateral incisor teeth are resin-retained adhesive bridges and implant-retained crowns.
Planning for resin-retained bridges
Even though the survival rates are lower than for fixed bridgework, resin-retained bridges (RBB) are a simple and conservative option for medium- to long-term management of the spaces(s).
Survival rate of RBB has been found to be affected by area available for bonding, rigidity of the framework and the design of the retentive elements (Djemal et al, 1999). The prognosis of the prothesis can be improved with a cantilever design, upright central incisor teeth, minimal overbite (Creugers et al, 1997). The survival rate is more than 80% over six years.
Patient satisfaction can be affected if there is display of greying caused by metal shine through, loss of translucency, staining of the resin at the margins and the difficulty of matching pontics with young natural teeth (Wyatt, 2007).
Tooth movements associated with space opening are prone to relapse. Patients should be aware that RBB can debond and space can be lost. It would be advisable to reinforce retention with a pressure-formed retainers.
Planning for implants
Implants are the long-term choice and systematic reviews have shown the survival rate to be between 90% and 95%. It has been suggested, to prevent alveolar bond atrophy, implants should not be placed in young patients. If this option is being considered then it is important to always ensure that the costs and lifelong maintenance are outlined from the outset.
The clinician has to bear in mind both the inter-coronal and inter-radicular space creation. Even if the tooth is initially supported by a prothesis, it is essential that there is root parallelism of the central incisor and canine tooth. This allows the patient to consider future implant placement without further fixed appliance therapy.
Measurement to bear in mind
The minimal interocclusal space from the head of the implant to the occlusal plane is 5mm. The recommended intercoronal space is 6.5mm and inter-radicular space if 5.7mm. The traditional width of an implant is 3.5mm and the platform width is 4mm. These measurements are really important as there should be at least 1mm space between the implant and adjacent teeth. This space allows adequate papilla healing.
Prior to removing the fixed appliances, it is prudent the restorative dentist sees the patient to assess the space created with periapical X-rays to ensure he is satisfied with the root divergence, inter-radicular and inter-occlusal spacing.
Note: there is often tertiary growth, especially in females (downwards and forwards), so do not place the implants too early – ideally after the age of 21.
Any orthodontic treatment involving restorative element must be meticulously planned with a multidisciplinary team. Advances in technology and also restorative materials ensures that long term success and predictability leads to patient satisfaction.
For a list of references please email [email protected].
This article was first commissioned for Clinical Dentistry magazine. To sign up and receive a print version of the magazine, visit www.fmc.co.uk/shop/clinical-dentistry.