Consultant in Oral and Maxillofacial Surgery, Department of Orthodontics and Oral and Maxillofacial Surgery, Gloucester Royal and Cheltenham General Hospitals, Gloucester, UK
Scissorbite correction of posterior teeth can often be challenging. For adolescent patients, they may occur due to late eruption of the second permanent molar teeth after appliances are removed, or due to operator preference not to include them on the appliance. This case report describes a 17-year-old patient who had previously been treated with fixed appliances but did not originally have second permanent molars bonded. Complete correction of the scissorbite on the UR7 was effectively achieved in 14 weeks using a minimal system comprising only a palatal mini-screw, molar band and elastomeric chain.
CPD/Clinical Relevance: Mini-screws placed in a palatal position can provide an effective way to correct posterior scissorbites.
Article
Jason Matharu
Second permanent molars can often be problematic if they are not bonded and included on a fixed orthodontic appliance. This can occur following appliance removal when there is late eruption of the second permanent molars, or when operators simply do not consider the need to bond them or check their occlusal relationship. If the occlusion is not checked before appliances are removed, or indeed retained in a suitable fashion, it can lead to a number of significant problems.
The following article describes a case in a 17-year-old adolescent patient where the upper right second permanent molar (UR7) was left in scissorbite after treatment with a fixed appliance, and the patient had noticed that both its position and the occlusion had substantially worsened since eruption of the upper right third molar (UR8). Figure 1 shows the patient at presentation, showing the UR7 in scissorbite. The patient was understandably not keen to wear further fixed appliances, so a plan was made to place a mini-screw between the palatal roots of the UR7 and UR6 to provide traction to align the UR7 and then extract the UR8 to provide the necessary space.
Figure 1.
(a–e) Pre-treatment views – patient at initial presentation.
Temporary anchorage devices (TADs), or mini-screws, are titanium screws that are mostly used for short periods of time as an adjunct during orthodontic treatment to help with treatment mechanics. The first fully osseointegrated dental implants were first described in 1969 by Brånemark et al1 but, as documented by Kanomi,2 it was not until some two decades later that documentation of titanium mini-screws being used for orthodontic anchorage is seen. In general, mini-screws can be used for a wide variety of applications in orthodontic treatment, and a growing amount of evidence is available regarding optimal mini-screw design, placement technique, ideal time of loading, stability and success versus failure rates.
For the inexperienced operator, placing a mini-screw can initially seem a daunting prospect. Indeed, Cho et al3 found that, in 21% of cases, inexperienced users were more likely to contact the roots of adjacent teeth during placement, compared to just 13% for experienced users. Placement of mini-screws in the palate, such as in between palatal roots of upper molar teeth, have the advantage of there being more interradicular bone and space, as described by Baumgaertel4 and some studies, such as the one by Mannchen and Schatzle,5 have shown the success rates of mini-screws when placed in this area to be as high as 92%. In our case, it was decided to use a single mini-screw with carefully applied force vectors from an elastomeric chain to a band cemented on the UR7 to achieve the desired tooth movement. Indeed, it was deemed that traction from a temporary anchorage device placed in the palate would, by itself, provide an optimal method of providing orthodontic traction to the UR7, without needing to use any other orthodontic appliance or system.
Case report
Upper and lower alginate impressions were taken to construct both study and working models. Pre-treatment periapical views of the UR7 region were taken to establish the root morphology regarding divergence of the palatal roots of the UR7 and UR6, which is not usually as critical for mini-screw placement as it would be buccally due to the increased interdental bone and space present on the palatal aspect. One of the potential hurdles in placing a mini-screw in the palate can, however, be access and achieving the correct orientation for optimal placement without damaging the adjacent structures. This applies particularly for the less experienced operator. In our case, a customized lab-made stent was made to act as an initial guide for the path of insertion and to help locate correct placement of the mini-screw.
Soft tissue analgesia was achieved by application of topical lidocaine anaesthetic gel and 0.2 ml palatal infiltration with 1:80,000 2% lidocaine/epinephrine. Figure 2 shows immediate placement of the self-drilling mini-screw (VectorTAS™, Ormco). This self-drilling mini-screw has the added advantage that no pilot hole was required, with some studies, such as the one by Kim et al,6 demonstrating that this can achieve better primary stability. Figure 3 illustrates movement of the UR7 into a palatal position after 6 weeks of initial traction. Figure 4 demonstrates full alignment of the UR7 and correction of the associated scissorbite at 14 weeks with good stability of the palatal mini-screw. Following removal of the band on the UR7, an upper alginate impression was taken for construction of an upper removable retainer (1.0 mm Essix ACE), which the patient was instructed to wear for retention at night-time.
Figure 2. Palatal mini-screw in situ.Figure 3. Following 6 weeks of orthodontic traction.Figure 4. 14 weeks post insertion of mini-screw showing full alignment and resolution of the scissorbite associated with the UR7.
Conclusion
This case report has described a simple, yet effective technique to provide orthodontic traction to a tooth without the use of a full conventional fixed or removable appliance, resulting in full resolution and correction of the scissorbite (Figure 5). It is an effective technique to consider using for patients who do not wish to have fixed appliances placed. Without the use of a mini-screw, achieving the above treatment mechanics and getting the desired end result in such a short treatment duration would have been challenging.
