Effectiveness of CAD/CAM titanium fixed lingual retainer versus conventional stainless steel fixed retainer (randomized controlled clinical trial)

Abstract

Background: Retention after orthodontic treatment is crucial to maintain aligned teeth and prevent relapse. Traditional fixed retainers, made from multistranded stainless steel wires, are effective but have drawbacks such as operator variability, long chair-time, and risk of biofilm accumulation. Recent advancements in computer-aided design/computer-aided manufacturing (CAD/CAM) technology proposed custom-designed fixed retainers as a modern solution.

The aim of this trial: Primary aim was to evaluate the alignment stability of CAD/CAM grade 5 titanium (Ti5) versus stainless steel lingual fixed retainers. Secondary aim was to assess periodontal health over 6-months.

Methods: A single-center, two-arm, parallel randomized controlled clinical trial with a 1:1 allocation ratio was carried out to address the aims of the study. Participants were randomly allocated into two equal groups: Group I received Ti5 CAD/CAM lingual retainers; Group II received conventional 8-strand braided stainless-steel fixed retainers. Both retainers were bonded directly on the six mandibular anterior teeth. Measurements were performed at 3 time points: immediately after retainer placement (T0), after 3 months (T3) and after 6 months (T6). Intercanine Width, Little’s Irregularity Index and tooth movements in buccolingual, mesiodistal, occluso-gingival and rotational directions were recorded for each tooth by superimposition of digital models. In addition, periodontal parameters (Plaque index, Gingival index, Probing depth and Bleeding on probing) were assessed.

Results: Initially, 54 patients were screened for eligibility. A total of 36 patients were randomly assigned, completed follow-up, and were included in the analysis. The used test for comparison between variance were Chi-square, Welch’s t test and Greenhouse-Geisser test. Inter-canine width showed no statistically significant differences between the two groups at T0, T3, or T6 (p = 0.769, p = 0.440 and p = 0.827 respectively). Little’s Irregularity Index revealed no statistically significant difference between the two retainers at T0 (p = 0.123), T3(p = 0.562) and T6(p = 0.611). No significant changes in tooth positions were observed in the two groups. The mean change of Gingival index showed a significant decrease in CAD/CAM group compared to conventional at (T3 and T6 p = 0.001). The periodontal parameters were significantly better in the CAD/CAM retainers after 6-months.

Conclusions: Ti5 CAD/CAM and conventional retainers are effective in maintaining intercanine width. Ti5 CAD/CAM retainers are capable of maintaining tooth position in three dimensional directions. Ti5 CAD/CAM retainers showed less deterioration of the periodontium in short-term observation.

Keywords: CAD/CAM; Fixed retainers; Intercanine width; Lingual retainer; Tooth irregularity.

Fig. 1

Designing of titanium FR on Meshmixer software; A Retainer design on imported STL file; B Extruded final design of FR from digital model (occlusal); C Intraoral scan of FR immediately after retainer bonding (T0)

Fig. 2

Clinical photos after retainer bonding; A CAD/CAM retainer; B Conventional StSt retainer

Fig. 3

Intercanine Measurement on Medit link design;A ICW in at T0 CAD/CAM group; B ICW at T0 in Conventional group

Fig. 4

Irregualrity Index measurement on Medit link design; A LII at T1 in CAD/CAM group; B LII atT1 in Conventional group

Fig. 5

Digital models superimposition

Fig. 6

Buccolingual and Occluso-gingival movements measurements in proximal view (X-axis)

Fig. 7

Mesiodital and Rotational movement; A Mesiodital measurement of each tooth after digital superimpostion from 3–3; B Difference in mesiodistal direction in a sectioned view; C Rotational angle in occlusal view

Fig. 8

Patient flow diagram during the study