Development of a graduated alumina polymer composite as a potential orthodontic bracket material

Abstract

Objective: To create an orthodontic bracket material combining the favourable properties of
ceramic and polymer while minimising their adverse properties.
Design, Materials and Methods: Unidirectional gelation – freeze casting was used to produce
graded porous ceramic scaffolds, following which the pores were infiltrated with polymer for
microstructural evaluation. The first phase of the research investigated the effect of
sedimentation at three time points: 0, 8 and 24 hours. The initial ceramic solid loading and
gelatine concentration were kept at 20 vol% and 2.5 wt% respectively. In the second phase of
the research, the focus was on the effect of three ceramic loadings: 15, 20, and 25 vol% with
2.5 wt% gelatine concentration and a sedimentation time of 8 hours. All ceramic scaffolds were
infiltrated with epoxy for optical evaluation and 20 vol% ceramic scaffolds at 8 hours
sedimentation (20-8) were infiltrated with UDMA/TEGDMA to test for compressive strength,
modulus of elasticity and fracture toughness.
Results: Graded ceramic structures of varying pore architecture were produced. Most of the
ceramic scaffolds displayed porosity gradients across the samples ranging between 9.86 to
63.84 vol%, except for those with 25 vol% ceramic solid loading at 8 hours sedimentation. Al2O3
–UDMA/TEGDMA composites had compressive strengths of 60.25 to 120.92 MPa, modulus of
elasticity of 19.84 to 35.29 GPa, and fracture toughness of 0.78 to 1.78 MPa·m1/2
, midway
between those of dense ceramic and pure polymer.
Conclusion: Ceramic – polymer gradient structures fabricated using gelation – freeze casting,
particularly those with 20 vol% ceramic solid loading at 8 hours sedimentation, show great
potential as orthodontic bracket materials.

Date of Award	23 Jan 2024
Original language	English
Awarding Institution	University of Bristol
Supervisor	Julie C Williams (Supervisor)