To compare the surface wear of aligner attachments fabricated using different composite resins

Litt, Rebecca Jane (2025). To compare the surface wear of aligner attachments fabricated using different composite resins. University of Birmingham. M.Sc.

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Abstract

Aims: To evaluate the difference in surface wear between various composite materials
when utilised as clear aligner attachments.
Materials and Method: A custom-made experimental apparatus was utilised, in
combination with an MTS Criterion Model 42 machine (Model 42, MTS Criterion® Series
40 Electromechanical universal test systems, MTS systems corporation, Minnesota, USA),
to replicate the clinical technique of aligner removal. Rectangular composite attachments
were placed onto a first permanent molar within a typodont. Four commercially available
nanohybrid composite resins were evaluated. These included two conventional
composites, Venus Pearl (Heraeus-Kulzer, GmbH) and Tetric EvoCeram (Ivoclar Vivadent,
Liechtenstein), one flowable composite Wave (SDI Limited, Bayswater, Victoria,
Australia) and BracePaste an orthodontic adhesive (American Orthodontics, Sheboygan,
CA, USA). A baseline 3D surface scan was taken and a second scan re-taken after a 250
and 500 aligner insertion and removal cycle. Following scan superimposition the median
surface wear was assessed for each composite.
Results: Using the current model, wear occurs only on the gingival aspect of composite
attachments, with the greatest wear being found on the distal corner of the gingival
aspect. The median value of wear in the distal corner of the gingival aspect after 500 cycles
was 0.06mm for Tetric EvoCeram (ranging from 0.05mm-0.06mm), 0.04mm for Venus
Pearl (ranging from 0.03-0.05mm), 0.08mm for Wave (ranging from 0.05-0.08mm) and
0.06mm for BracePaste (ranging from 0.05-0.06mm). The amount of wear found was
progressive from 250 to 500 cycles. There was a statistically significant difference in wear
at the distal corner of the gingival aspect of the attachments, across the four composite
resins tested (p-value = 0.013 and p = 0.024 for 250 and 500 cycles respectively). PostIII
hoc pairwise comparisons of the four composite resins showed that there was statistically
significantly more wear of Wave composite compared to Venus Pearl (p-value = 0.006 and
p = 0.016 for 250 and 500 cycles respectively after Bonferroni correction).
Conclusion: Based on the current in vitro model of aligner insertion and removal the
distal gingival surface of the attachments showed the greatest wear. The wear of Wave
was statistically significantly (p < 0.05) greater than Venus Pearl. Clinically, the amount
of wear would probably not be significant.