Polished zirconia crowns better than glazed zirconia in terms of wear and tear: Study

polished zirconia (PZ) and glazed zirconia (GZ) crowns wear substantially with time, with lesser wear observed in PZ crowns, reports a recent study.

The study is published in the Journal of Prosthetic Dentistry.

The purpose of this clinical study was to evaluate and compare the wear over 1 year use of glazed zirconia (GZ) and polished zirconia (PZ) crowns opposing natural enamel and the wear of natural enamel opposing PZ and GZ crowns.

Uvashri Selvaraj and colleagues from the Department of Prosthodontics, Centre for Dental Education and Research, All India Institute of Medical Sciences, New Delhi, India conducted this prospective, split mouth, randomized clinical trial included 14 participants requiring complete coverage crowns on first molars, bilaterally, in a completely dentate mandibular arch.

GZ and PZ crowns were cemented according to a randomization chart. Polyvinyl siloxane impressions were made immediately and 1 year after the cementation of the crowns. The respective casts were scanned by using a 3D scanner and a software program to measure the amount of linear wear of zirconia crowns and opposing natural teeth.

Wear was observed in 8 groups: PZ crowns, GZ crowns, natural enamel opposing natural enamel in the molar and premolar regions (NE-M and NE-PM), natural enamel opposing PZ crowns in the molar region (NE-PZ-M), natural enamel opposing GZ crowns in the molar region (NE-GZ-M), natural enamel opposing PZ crowns in the premolar region (NE-PZ-PM), and natural enamel opposing GZ crowns in the premolar region (NE-GZ-PM).

A descriptive analysis was followed by comparison between groups by using a repeated-measure ANOVA with post hoc adjustments (α=.05).

The study revealed the following findings-

a. The mean wear (μm) observed was as follows (in ascending order): PZ crowns (13 ±3), NE-PM (13 ±1), GZ crowns (27 ±9), NE-M (34 ±3), NE-PZ-PM (44 ±18), NE-PZ-M (63 ±22), NE-GZ-PM (69 ±21), NE-GZ-M (113 ±33).

b. Wear of GZ and PZ crowns was less than wear of NE-M.

c. The difference was statistically significant when comparing PZ with NE-M (P<.001, CI=-17 to -24).

d. Wear of NE-GZ-M and NE-PZ-M was higher than wear of NE-M, with a statistically significant difference (P<.001, CI=-49 to -107 and P =.004, CI=-8 to -49, respectively).

e. Wear of NE-GZ-M was more than that of NE-PZ-M, and the difference was statistically significant (P<.001, CI=-68 to -32).

f. Wear of NE-PZ-PM and NE-GZ-PM was also more than the wear of NE-PM, and the difference was statistically significant (P<.001, CI=-17 to -43 and P<.001, CI=-39 to -70).

Therefore, the authors concluded that "PZ and GZ crowns wear substantially with time, with lesser wear observed in PZ crowns. PZ and GZ crowns also cause more wear in opposing natural enamel than natural enamel antagonists, with the highest wear caused by GZ crowns."