A dental laboratory survey of clinical failure rates in zirconia and conventional restorations over six years

Clinical data comparing the failure rates of zirconia restorations with those of conventional restorations-such as lithium disilicate and metal-ceramic restorations-remain limited. In particular, the clinical performance of monolithic restorations fabricated from translucent zirconia (5 mol% yttria-stabilized zirconia, 5YSZ) has not been previously reported. The purpose of the present study was to evaluate the clinical failure rates of zirconia restorations, including both single and multi-unit fixed dental prostheses in comparison with lithium disilicate and metal-ceramic restorations and to compare clinical failure rates of porcelain-veneered restorations fabricated from 3 mol% yttria-stabilized zirconia (3YSZ) and monolithic restorations fabricated from 5YSZ. Data from 2016 to 2021 were collected from a dental laboratory in Sweden. Extracted variables included restoration material (zirconia, lithium disilicate, or metal-ceramic), site of placement (anterior, posterior, or mixed), placement date, return date, restoration type (single or multi-unit), and whether the restoration was porcelain-veneered or monolithic. Restorations returned to the laboratory during or after the warranty period were classified as clinical failures. Thus, all types of clinical failures, such as fracture, poor fit, loss of retention, and loss of supporting tissue, were included. Factors associated with clinical failure rates were analyzed using logistic regression (α=.05). A total of 31 379 restorations were analyzed: 11 245 zirconia restorations, 6453 lithium disilicate restorations, 13 171 metal-ceramic restorations with cobalt chromium (Co-Cr) frameworks, and 510 metal-ceramic restorations with titanium (Ti) frameworks. Clinical failure rates were 3.7% for zirconia, 4.0% for lithium disilicate, 2.5% for Co-Cr metal-ceramic, and 4.3% for Ti metal-ceramic. The differences between zirconia and lithium disilicate (P=.023), between zirconia and Co-Cr metal-ceramic (P<.001), and between lithium disilicate and Co-Cr metal-ceramic (P<.001) were statistically significant. Of 3608 zirconia restorations, 109 failed, corresponding to an overall failure rate of 3.0%. Porcelain-veneered 3YSZ restorations showed a failure rate of 4.0%, whereas monolithic 5YSZ restorations demonstrated a failure rate of 2.5%. The failure rates of the 2 groups were statistically similar (P=.071). Zirconia restorations exhibited slightly higher clinical failure rates than Co-Cr metal-ceramic restorations but lower rates than lithium disilicate and Ti metal-ceramic restorations. Furthermore, despite their lower flexural strength, monolithic 5YSZ restorations demonstrated clinical performance comparable with that of porcelain-veneered 3YSZ restorations.