• Wasan Vatanasak, D.D.S.
• Kamolporn Wattanasirmkit, D.D.S., MSc Prosthodontics, Ph.D.

Background: Low temperature degradation, also known as ageing, is the major challenge we cannot
avoid in zirconia restorations. Changes in temperature, pressure, mechanical force and moisture are
few of the factors which contribute to ageing which eventually leads to failure of zirconia restorations.

Objectives: To compare the phase transformation, surface roughness and grain morphology as

indications of low temperature degradation that might occur in translucent monolithic zirconia after
try in procedure which finished the restoration by chairside polishing or annealing technique.

Materials and methods: A total of 10 single implant crowns would be milled from the one Vita HT
(VITA-Zahnfabrik, Germany) monolithic zirconia block. Before delivery, all the crowns would be
examined under X-ray diffractometry, scanning electron microscope, and contact profilometry to serve
as base line information regarding crystalline phase, surface roughness, and surface morphology. After
proximal contact and occlusal surface adjustment, 5 of 10 polished specimens would be selected to
undergo annealing at 1000°C for 15 minutes. Both polished and annealed groups would then be
re-examined following the same methods as control. The data would be analysed by means of paired
sample t-test.

Results: On the occlusal surface, the percentage of tetragonal and rhombohedral phases as well as the
surface roughness showed significant difference (p-value < 0.05) between before delivery in both the
polished and annealed zirconia crowns. Data obtained from the buccal surface showed significant
difference between before and after delivery in percentage of te-tragonal and monoclinic phases in the
both annealed and polished groups (p-value < 0.05). As for the proximal surface, significant difference
between before and after delivery was seen in percentage of tetragonal phase in the annealed and
polished groups, monoclinic phase in the annealed group, and the surface roughness for both groups
(p-value < 0.05).

Conclusion: Within the limitations of this study, it was shown that finishing and polishing does affect
the surface morphology of zirconia restoration, crystalline phase of zirconia, and surface roughness of
zirconia. Annealing at 1000°C for 15 minutes did show an increase in tetragonal phase content.

(CU Dent J. 2019;42:23-38)