Abstract
Personalised medicine integrates decision making, intervention and products to an individual patient based on their risk of disease or response to treatment. Fully customised labial fixed appliances are a step towards personalised orthodontics and provide a tool to optimise orthodontic outcome in relation to skeletal anatomy, facial aesthetics and occlusion.
Introduction
Computer technology has made computer-aided design and manufacture (CAD/CAM) of patient-specific appliances a clinical and commercial reality. Originally postulated by Craig Andreiko in an interview with Larry White in the Journal of Clinical Orthodontics (Andreiko, 1994); this article described the Ormco Elan system (Brea, CA, USA), which digitised dental and skeletal elements of the patient and used CAD/CAM technology to relate these elements to each other, design an optimised occlusion based on the orthodontist’s treatment plan and then manufacture patient-specific brackets, molar tubes and archwires to deliver that result. Current technology and practice models appliances in silos (labial, lingual and aligners). In the future, digital portals will support hybrid treatments, where combinations of labial, lingual and aligner-type appliances are used in the same course of treatment.
The first commercial patient-specific labial fixed appliance was developed by Rohit Sachdeva and introduced between 2000 and 2001 by SureSmile, a subsidiary of Orametrix (Richardson, TX, USA); but did not become commercially available until 2005 and Orametrix was acquired by Dentsply Sirona (York, PA, USA) in March 2018. SureSmile was followed in 2006 by Ormco’s Insignia appliance, a development of the original Elan system.
Methods of customisation
A patient-specific appliance can customise the appliance to the patient’s skeletal anatomy by positioning the teeth over the mandibular basal bone and then fitting the maxillary teeth around the mandibular archform. The position and shape of the mandibular basal bone is determined by taking a horizontal section through the mandible 3 mm below the scallop of the gingival margins. This plane is called the mandibular trough (ManTrough) and provides a buccal and lingual boundary for the position of the mandibular teeth.
Customisation to optimise facial aesthetics can be achieved by optimal positioning of the upper central incisors in all six degrees of tooth movement. Important considerations are vertical positioning of the incisors, smile arc, torque and anteroposterior position.
Each bracket, tube and archwire is customised to the patient’s occlusal, skeletal and facial characteristics, depending on the sophistication of the product. Patient-specific appliances use four methods to customise bracket and tube prescription to the patient’s treatment needs:
- adjusting the thickness of the composite layer between the enamel surface and the bracket pad (e.g:eXceed Tx);
- customising the bracket slot (this can be technically difficult as a sole method of customisation due to the difference in prominence between posterior and anterior teeth which can result in brackets and tubes that stand off the tooth surface; hence often used in conjunction with some archwire customisation);
- providing customised archwires (e.g SureSmile), which customises archwires, but not brackets, in all six degrees of tooth movement; and
- a combination of all or some of these methods (e.g Ormco Insignia customises the bracket slot in all six degrees of tooth movement and the archwire in the horizontal plane only).
The first method has limited precision and accuracy and is less sophisticated than the methods in the second and fourth bullet points which employ flush bonding. Customisation of the thickness of the composite inter-layer (sometimes called pad-adjusted bonding) is used by eXceed Technologies OÜ (Harju maakond, Republic of Estonia) in eXceed Tx as the sole method of customisation. This may still be used by some systems where the pad and the tooth surface are a poor fit; where this occurs, customised labial systems try to tripodise the bonding pad against the tooth surface and fill in the gaps with composite at bonding. Labial fixed appliances, unlike lingual appliances, do not customise the pad to the tooth surface as the variability of the labial enamel surface is much less than the lingual, where pad customisation is more usual.
The advantages and disadvantages
of customised appliances The potential advantages of customised fixed appliances are:
- the availability of digital diagnostic tools (such as tooth width measurement, estimation of crowding or spacing, measurement of arch widths, indices of severity and outcome);
- customisation of archform (to the shape of the mandibular basal bone); root position within alveolar bone; tooth angulation and vertical position in complex restorative cases (including preparation of implant spaces and incisal edge build-ups; Figure 1); archwires, including nickel titanium alloys by robotic archwire bending; facial aesthetics (optimising the position of the anterior teeth and smile arc);the occlusal fit between the maxillary and mandibular teeth. Collectively, these factors should result in easier finishing, shorter treatment times (and therefore fewer visits) and improved outcomes;
- freedom of the operator to use preferred bracket configurations; a visual representation of the planned outcome (which helps in the patient’s understanding of the purpose and difficulty of treatment); Insignia includes a feature called TruFinishTM, which allows changes in the smile arc and the occlusion to be morphed in the patient’s smiling frontal photograph (Figure 2); is evidence of the aims of treatment and the expected outcome if required in medicolegal proceedings;
- more accurate tube and bracket placement by both orthodontists and therapists;just-in-time stock control;
- a patient preference for a patient-specific appliance; and
- a practice preference for a digital workflow.
Data acquisition
Data acquisition for tooth crown data is by polyvinyl siloxane (PVS) impressions or intraoral scanning. Low-dose cone beam computed tomography (CBCT) scanners allow the acquisition of crown and root data which can be ‘stitched’ to the scanned crown data to represent actual tooth shapes; the CBCT scan requires a voxel size of 0.4 mm or less. The CBCT data shows the proximity of tooth roots to the cortical bone and treatment can be planned so that the final tooth positions keep the tooth roots within the alveolar housing to prevent irreversible damage to the periodontium. This seems a very plausible hypothesis but there is no evidence currently that this results in better treatment outcomes.
Evidence
Published papers on the use of fully customised appliances were initially descriptive, followed by evaluations of gradually increasing sophistication through anecdotal results, retrospective studies and randomised controlled trials. The first descriptive paper on Orametrix SureSmile appeared in 2000 (White and Sachdeva, 2000) and in 2006, Ormco published a white paper entitled ‘Increasing clinical performance with 3D interactive treatment planning and patient-specific appliances’ (Ormco Corporation, 2006). These papers outlined the principles underlying patient-specific appliances and described the methodology and software used to achieve customisation.
Sachdeva et al. (2005) reported on 136 conventional patients and 95 SureSmile class I patients treated on a nonextraction basis. The mean treatment time months/visits/archwires for SureSmile patients was 12.1/13.5/7.9 compared with 23/18.8/10.9 for the conventional patients. No case selection method was described, and the paper is subject to bias.
Saxe et al. (2010) conducted a retrospective study on 62 consecutively treated SureSmile (n = 38) and conventionally treated patients (n = 24). The start of treatment American Board of Orthodontics Discrepancy Index (ABO DI) scores were 9.2 and 11.0, respectively; these were not complex cases. The treatment time was 14.7 ± 4.7 months for SureSmile and 20.0 ± 6.4 months for the conventionally treated patients. The American Board of Orthodontics Orthodontic Grading System (ABO OGS) scores at the end of treatment were 26.3 ± 6.8 for SureSmile and 30.7 ± 8.9 (p < 0.005) for conventional.
Alford et al. (2011) used a convenience sample of 132 consecutively treated SureSmile and conventional treated patients. The SureSmile patients had significantly shorter treatment times than the conventionally treated patients (22.7 ± 1.5 SE versus 32 ± 1.6 SE months p < 0.001) although the outcomes as measured by the American Board of Orthodontics Cast Radiograph Evaluation system were not significantly different (SureSmile 18.5 ± 1.0 SE, conventional 20.8 ± 0.8 SE p = 0.541). From these papers, there is weak evidence that treatment with SureSmile results in shorter treatment times and possibly better outcomes.
In 2013, Weber et al. published a retrospective study on the clinical effectiveness and efficiency of Insignia compared with conventional appliances in patients treated by two orthodontists. Clinical effectiveness was measured using peer assessment rating (PAR) scoring at the start and end of treatment and ABO OGS at the end of treatment. Efficiency was measured by recording the number of debonded/repositioned brackets, finishing bends, scheduled and unscheduled appointments and the treatment time in months. The cases had low initial PAR scores of approximately 10. The treatment time for conventional cases was 22.91 ± 4.35 months and for the Insignia cases 14.23 ± 5.02 months (p ⩽ 0.001); the number of visits for the conventional was approximately seven visits higher than for the Insignia cases. Despite this, the ABO OGS scores for the Insignia group were 21.66 ± 5.87 and for the conventional group 27.09 ± 9.33 (p < 0.03) and the ABO OGS subsection scores were superior in the Insignia group in almost every area, especially alignment/rotations, over-jet (arch coordination), and root angulations. Brown et al.(2015), in a thoughtful retrospective study, investigated whether there was a difference in effectiveness and efficiency between direct and indirect bonding with Damon Q and a fully customised labial appliance. The ages of the patients were in their early teens at the start of treatment and their start of treatment ABO DI scores were in the mid-teens. The treatment times for the direct, indirect bonded and the Insignia cases were significantly different at 21.9 ± 5.0, 16.9 ± 4.1 and 13.8 ± 3.4 months respectively. The Insignia group had 2.5 adjustment visits fewer than the direct bonded group and this was significant. There was a significant difference in the treatment visit intervals between the groups which were 1.4, 1.3 and 1.1 months respectively which may have affected the overall treatment times. This raises the question as to whether reducing treatment intervals is a means of accelerating orthodontic treatment or perhaps what the evidence for a 6-week interval between fixed appliance adjustment visits is? There were no significant differences in the ABO Cast Radiograph Evaluation (ABO CRE) outcome scores at the end of treatment. These two papers provide further weak evidence to support reduced treatment time, reduced number of visits but similar outcomes for fully customised appliances when compared with other appliance systems.
Awad et al. (2018) undertook a retrospective cohort study to compare the outcomes of two clinicians using Incognito (lingual customised appliance) and Insignia (labial customised appliance) and concluded that Incognito was more efficient than Insignia using ABO CRE scores, measures of clinical efficiency (number of appointments, emergencies, overall length of active orthodontic treatment) and the difference between planned and actual treatment outcomes. The study had no power calculation and the patient numbers in each group were small. The start ABO DI scores were surprising low at 5.6 (Insignia) and 5.7 (Incognito); the start PAR scores were 23.8 and 17.8 respectively (p = 0.44).
An equally randomised, parallel-group controlled trial was conducted by Penning et al. (2017) in the Netherlands using two practices to compare outcomes in patients treated with Damon Q and Insignia. Both orthodontists were stated to be equally experienced with the two bracket systems being used. The primary outcome was the treatment duration between Insignia and Damon Q. Secondary outcomes were end PAR scores, the number of treatment visits, loose brackets, complaints and the planning time for the cases. The study was designed to detect a significant difference of four months treatment duration needing 180 patients split between the two orthodontic practices. The trial showed no difference in treatment duration or treatment visits between the Insignia and Damon Q groups. The number of debonded brackets was significantly higher in the Insignia (5.47 ± 4.49) than the Damon Q group (3.58 ± 3.17) and the planning times were 89.22 ± 16.78 and 11.67 ± 11.14 minutes respectively.
Despite the sophisticated randomised control trial design, some questions about this paper arise. What did ‘equally experienced’ mean? The fully customised Insignia appliance was not available until 2010 (prior to this date, variable torque brackets were selected to provide partial customisation). It is unlikely that both orthodontists had done equal number of Insignia and Damon cases as the Damon passive self-ligating appliance was introduced to the market approximately 16years before fully customised Insignia; the two orthodontists may have done equal but different numbers of Damon and Insignia cases. The actual numbers of cases representing the experience of the orthodontists is unreported. The higher number of debonded brackets in the Insignia group would have been affected by the use of 3M Transbond XT which is not appropriate for Insignia as it is too viscous; a flowable composite (3M Transbond LR) is preferred for Insignia. Finally, the planning time for the Insignia cases was high with a range of 53 to 130 minutes; it is assumed this is the time taken to plan the case and excludes any manufacturer processing time. Anecdotally, an Insignia case takes 15–20 minutes to plan and the time quoted in the paper may reflect the fact that the clinicians were inexperienced in using the fully customised Insignia. The authors of the paper comment: ‘The most striking finding of our present trial was that treatment outcome was not related to the appliance system used. Regardless of the system used, the orthodontist was the most important factor in the primary outcome.’ The authors found a difference between the two orthodontists for treatment duration and treatment visits although this was not quantified in the paper. This is not a surprise, as fixed appliance systems have no intrinsic therapeutic capability (whereas, a pharmaceutical product and some orthodontic appliances such as functional appliances and aligners do); their success depends on the ability of the orthodontist to use the technical characteristics of the appliance for the benefit of the patient. Randomised controlled trials of fixed appliances measure the combined effect of an orthodontist’s ability to use the appliance and leverage its technical characteristics. What should be measured is a comparison between an orthodontist’s performance using their usual appliance and a novel appliance after training and acclimatisation. Treatment studies, including randomised control trials, have had little success in evaluating fixed appliance systems since Kattner and Schneider (1993), which compared out-comes of patients treated with the Roth and standard edge-wise appliances and found differences between the practitioners, but not between the appliances. This finding is not confined to orthodontics and Don Berwick’s address ‘Eating Soup with a Fork’ (Berwick, 2007) on evaluating the role of rapid response teams in hospitals is a thoughtful insight into the problems of the evaluation of complex healthcare interventions.
While customised labial fixed appliances represent an advance towards personalised orthodontics, there has been no progress on customising appliances to a patient’s biological characteristics. It is known that:
- cortical bone remodels in response to orthodontic force (Capps et al., 2016) but the rate varies between patients;
- tooth movement occurs at different rates between patients; and
- patients undergo different levels of interdental bone loss during treatment and this is not always directly to oral hygiene status.
In the future, understanding of a patient’s biological status may improve the ability to predict outcome and response.
Conclusions
The ability to customise orthodontic treatment both to the patient’s anatomy, facial aesthetics, occlusion and biological status is a pathway to fully personalised orthodontic treatment which in turn should lead to improved patient outcomes. Patient-specific appliances should be evaluated on their ability to increase the quality, decrease cost, increase morale, decrease treatment time and visits and increase safety for both patients and staff. In the future, biological assessment of an individual patient’s likely response to orthodontic treatment should complement patient-specific appliances. Now however, patient-specific labial appliances move orthodontics towards the goal of better outcomes but depend significantly on clinician training, skill and judgement to maximise their effect.