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The use of fibre-reinforced composite for the creation of anchor units in sectional orthodontic appliances Ian Hutchinson Aidan McKeever Dental Update 2024 7:1, 707-709.
Authors
IanHutchinson
BDS, FDS RCS(Ed), MOrth, MSc
Specialist Orthodontist, Whitetree Specialist Centre, 1–3 North View, Westbury Park, Bristol BS6 7PU, UK
The benefits of fibre-reinforced composite (FRC), such as strength, excellent bonding characteristics and aesthetics, are widely appreciated in restorative dentistry. These properties are well suited to the creation of orthodontic anchorage units in full-arch or sectional appliances. In this article, two clinical cases are presented where FRC has been used to create anchorage units in adult orthodontic patients with high aesthetic demands. Anchorage units created in this way are immediate, aesthetic, comfortable and require minimal unwanted tooth movement.
Clinical Relevance: The article describes techniques that may be of interest to clinical orthodontists by describing a novel use for a material not commonly used in orthodontics.
Article
Fibre-reinforced composites (FRC) have many applications in prosthetic dentistry and periodontology, where their use has been described in fixed partial dentures, endodontic posts, and periodontal/post-traumatic splinting.1,2,3 In all of these applications, FRC has been used as an alternative to traditional cast metal structures as a result of its several advantages:
Flexural durability;
High bond strength;
Superior aesthetics.
The improved aesthetics and ‘bondability’ of FRC, compared with metal,4,5 means that it's a natural choice for use in permanent bonded lingual retainers in orthodontics. Further novel uses for FRC in orthodontics have been described,6 such as space maintenance and framework construction for temporary pontics in cases of hypodontia or avulsion.7 The bond strength of FRC used to splint teeth into groups has been demonstrated (in vitro) to be stronger than that of metal attachments,8 and the flexural strength of FRC used to link adjacent teeth has been shown to be of sufficient strength to withstand chewing forces over a long period.9,10,11 For these reasons, an ideal use for FRC is in the creation of orthodontic anchorage units, particularly in the event of:
High aesthetic demands; and
Sectional tooth movement.
Anchorage can be defined as the resistance to unwanted tooth movement. For example, preventing undesirable mesial movement of the buccal segments requires anchorage when retracting the upper labial segment to reduce an overjet in extraction cases. However, anchorage must be thought of as a three-dimensional problem, with vertical and transverse components, and not only in the sagittal plane. Anchorage is reinforced by increasing the root surface area of the anchor unit, which may be done by:
Using teeth with larger root surface areas; or
Increasing the cumulative root surface area by increasing the number of teeth in the anchor unit.
Conventionally, anchor units of multiple teeth are created by the rigid ligation of adjacent units along the archwire, or by employing cross-arch anchorage devices such as trans-palatal and lingual arches. This usually requires the placement of a multi-bracket appliance and orthodontic levelling and alignment, which may not be necessary or desirable in cases of sectional movement. Further to both this and the obvious aesthetic compromise, a significant concern for both the patient and clinician may be the delay in commencing correction of the presenting complaint while anchor units are being prepared.
Fibre-reinforced composite presents an alternative means of preparing multi-unit anchorage that is immediate, aesthetic, reliable and comfortable.12 The handling characteristics of these materials make them relatively easy to adapt to the anchor tooth surfaces, thereby supporting either direct chairside or indirect laboratory fabrication. Two examples of cases where FRC has been used to create anchorage in adult patients are presented below.
Case 1
A 38-year-old female was referred to the practice for orthodontic correction of the overerupted and periodontally compromised upper right central incisor tooth (Figure 1). Although her periodontal disease was stable following successful treatment, her periodontist had requested that full fixed orthodontic appliances be avoided. The patient was also reluctant to wear a removable appliance. To intrude the incisor, vertical anchorage was required, which was achieved by using adjacent teeth secured with ‘Stick’ FRC (Stick Tech; Turku, Finland) as an anchor unit. A three-unit FRC anchorage appliance was created indirectly on the patient's study casts, to which a lingual orthodontic bracket was then attached (Figure 2). The appliance was then bonded into the patient's mouth and a lingual bracket placed onto the over-erupted central incisor (Figure 3). Sixteen weeks later, the amount of intrusion can be seen (Figure 4). Periodontal health was maintained and the patient was pleased with the result.
Figure 1. Case 1: Anterior view, pre-treatment.Figure 2. Case 1: FRC anchorage appliance on working model.Figure 3. Case 1: Occlusal view, FRC and orthodontic appliance in situ.Figure 4. Case 1: Anterior view, post-treatment.
Case 2
A 63-year-old female presented to the practice complaining about the appearance of her upper front teeth (Figures 5 and 6). The patient reported having a two-wing, resin-retained bridge, to replace the missing upper right central incisor, placed many years ago. Recently, the bridge failed and she returned to her general dental practitioner (GDP) for re-cementation. At the time, she complained about the appearance of a gap between the pontic and the upper left central incisor, which had slowly increased in size over the years.
Figure 5. Case 2: Anterior view, pre-treatment.Figure 6. Case 2: Occlusal view, pre-treatment.
The GDP re-cemented the bridge. The space was a result of the wing on the upper left central incisor failing some time ago and the tooth drifting distally, possibly exacerbated by occlusal forces transferred from the bridge via the now debonded wing. The suggested restorative solution to the problem was a new bridge or implant, however, this would have required either the new prosthetic tooth to have an increased mesio-distal width and therefore a poor aesthetic result, or more destructive preparation of the adjacent teeth to accommodate a combination of bridge and veneers to restore anterior symmetry.
An orthodontic solution was proposed which was to move the upper left central incisor back to its original position, and retain the adhesive bridge as a single wing cantilever. The patient refused to wear a conventional labial fixed appliance. The treatment comprised the removal of the wing bonded to the upper left central incisor, and the creation of an anchor unit by joining the upper left lateral incisor, canine and premolar with ‘Stick’ fibre re-enforced composite resin. The active component was created from two 2D orthodontic lingual brackets (Forestadent) bonded to the upper left lateral and central incisor, and a 0.012” nickel titanium wire was used (Figure 7).
Figure 7. Case 2: Occlusal view, FRC and orthodontic appliance in situ.
Eight weeks later, the upper left central incisor had aligned (Figures 8 and 9). The patient was delighted with the result, and the appliance was left in situ for six months for retention.
Figure 8. Case 2: Anterior view, post-treatment.Figure 9. Case 2: Occlusal view, post-treatment.
Conclusion
Fibre-reinforced composites enable the clinician to create an anchorage unit for orthodontic treatment without the need for conventional brackets. The technique is aesthethic, comfortable to the patient, and enables tooth movement to commence immediately when compared to the conventional method of levelling and aligning with fixed appliances prior to placement of a rigid anchorage archwire. The two examples described above demonstrate how the use of this technique can offer clinically efficient and conservative solutions to otherwise complicated presenting complaints.
