Improving fixed retainers: Is it time for titanium?

As we all know, retention remains a ‘problem in orthodontia’, with the need for fixed retention increasingly accepted. However, there are unresolved issues: fixed retainers can fail and become active, posing an impediment to cleaning. 

Given these shortcomings, novel fixed retainer materials and configurations have increasingly been considered in recent years. Many studies evaluating these new designs and products demonstrate comparability with more established retainer designs. While stainless-steel variants are the most popular type of fixed retainer, titanium grade 5 (Ti5) has been trialled due to its strength and corrosion resistance. Preliminary lab-based research has also been promising. By using CAD/CAM approaches, fabrication is also made more accessible. 

The authors therefore aimed to test the clinical effectiveness of CAD-CAM Ti5 fixed retainers comparing these to established 8-stranded stainless steel fixed retainers over a 6-month period. This study was carried out in Egypt and published in Clinical Oral Investigations. 

What did they do? 

They performed a two-group randomised controlled trial with a 1:1 allocation (18 participants per group) as follows. They performed a sample size calculation, although they based this on the change in inter-canine width (rather than the primary outcome). 

Participants: 

Patients with adequate oral hygiene and no obvious enamel defects in the lower inter-canine region were included. 

Interventions:

The intervention group were fitted with a 0.013 × 0.027-in customized Ti5 CAD/CAM retainer and while the control had a 0.011 × 0.027-in dead soft ribbon shaped 8-strand braided stainless-steel fixed retainer (Bond.A.Braid, Reliance, Inc., USA). Scaling was done prior to retainer fit. Intra-oral scans were obtained before debonding. The Ti5 retainer was designed 0.3 mm think with rectangular cross-section and sited at the upper region of the middle third of the lingual sur­faces. Subtractive manufacturing using a CNC machine was undertaken to mill the Ti5 retainer from a blank. The fretainer surfaces were polished with a wheel brush and burs on all but the fitting surface. 

In group II, the multistranded SS wire retainer was bent chairside and placed directly. All patients in both groups underwent the same bonding protocol, which included prophylaxis, conventional etch and bond, and the use of flowable composite. Scans were taken after placement of the fixed retainer (T0), after 3 months (T3) and at 6-month (T6) follow-up.

Outcomes

These included the cumulative irregularity score in the lower inter-canine region (Little’s Irregularity Index), inter-canine width, tooth movement using digital superimposition and a battery of standard periodontal outcomes at baseline, 3 and 6 months.

What did they find?

All 36 participants completed the study. Changes in both the inter-canine width and Little’s Index scores were marginal in both groups, with no more than 0.2mm of cumulative irregularity observed at 6 months in either group. Unsurprisingly, there was no statistical difference between the two groups in respect of either outcome.

The authors did undertake a within-group assessment – I felt that this was unnecessary and may confuse or indeed mislead the reader. Similarly, no difference in linear, vertical or angular changes were noted between the groups over the 6 months. In terms of periodontal outcomes, the results with the CAD/CAM retainers were positive. However, it is notable that the baseline plaque scores were considerably higher in the SS retainer group. This was not accounted for in the analysis.

What did I think? 

I think that this was an interesting study. It is great to see translational research with early clinical testing of a novel material. It would appear reasonable to conclude that Ti5 CAD/CAM retainers may offer comparable levels of effectiveness and a similar impact on periodontal health as conventional multistranded SS retainers. 

There are some limitations in terms of conduct and reporting. Studies concerning fixed retention often yield unflattering results. I think that this usually relates to the (lack of) experience of student operators. In the present study, it does not appear that any of the retainers failed over the study period. It is therefore unsurprising to observe low levels of post-treatment change. This is not unrepresentative.

However, considerably longer follow-up periods (2 years or more) are required to appreciate the impact of these varying designs. These effects may include not only the occurrence of failure but also, crucially, the activation of fixed retainers. We know that the latter can be particularly problematic (and is a reason why I do not use multistranded SS wires). It would be important to appreciate how this new design fares in this respect.

This short follow-up period is compounded by the small sample size (18 per group). These low numbers reduce the study’s power and also limit the authors’ ability to account for the impact of important confounding factors (e.g., baseline hygiene on periodontal outcomes or pre-treatment level of irregularity on post-treatment scores) within the analysis.

I also noted that the statistical analysis involves a large number of tests on a small sample, potentially risking false positive outcomes (which risk being over-emphasised). Again, this problem is aggravated by the use of within-group testing. In a comparative study (evaluating how retainer type might affect alignment and periodontal outcomes), the statistical tests should ideally reflect this. Nevertheless, we can learn a little more about a relatively novel retainer material and design.

What can we conclude?

Based on this small, short-term study, CAD/CAM Ti5 fixed retainers may offer a viable alternative to trusty stainless-steel alternatives. I expect to see these designs being championed at trade stalls at a conference soon. However, while the time for titanium may come, I do think that further primary research would help us to inform any decision to throw out the tried and tested. 

Key points of this post

• Study Purpose and Design: The study was a randomised controlled trial comparing the clinical effectiveness of CAD/CAM Ti5 fixed retainers to traditional stainless-steel retainers over six months, involving 36 participants.
• Interventions Compared: Participants received either a customised Ti5 CAD/CAM retainer or a conventional stainless steel retainer, with assessments conducted at baseline, 3 months, and 6 months.
• Main Findings: Both types of retainers showed minimal changes in inter-canine width and irregularity scores, with no significant differences between the groups over the study period.
• Study Limitations and Observations: Limitations include short follow-up, small sample size, and potential confounding factors, highlighting the need for longer studies to fully assess retainer performance and failure rates.
• Conclusions and Implications: The study suggests CAD/CAM Ti5 retainers may be a comparable and promising alternative to stainless steel, but further research is necessary to confirm long-term effectiveness.