The replacement of missing teeth with implant-supported prostheses has become a standard
treatment option with reliable long-term outcomes in various clinical indications.1–6The
implant-supported single crowns, in particular, presented the most favorable outcome with a
survival rate of 89.5% to 96% over a 10-year period.5,6A notable prosthetic maintenance
requirement, however, was reported irrespective of the prosthetic material used for the crown
construction.1,7 Metal-ceramic restorations have been considered the gold standard when replacing single
or multiple missing teeth with implant-supported fixed dental prostheses.8 A systematic
review of 4363 metal-ceramic implant-supported single crowns in the anterior and posterior
region reported an impressive survival rate of 98.3% over five years.9Yet, the biologic and
prosthetic complications associated with these restorations were substantial with a rate of
13.5%. In the posterior region, a recent systematic review of short-term randomized
controlled trials10 reported a survival rate of 99.1% for metal-ceramic implant-supported
single crowns. The reported prosthetic complications, mainly ceramic chipping, were also
notable with an incidence rate of 7.6%.mIn recent years, the introduction of high-strength all-ceramic materials
as well as digitaldesign and manufacturing processes, has allowed faster fabrication of more esthetic and
cost effective restorations.11Zirconia-based fixed dental prostheses on teeth and implants are now
increasingly used and show 5-year cumulative survival rates of 89.4 to 100%.12 These
restorations are typically made up of a zirconia framework that is veneered with a layer of
glass ceramic to impart translucency for enhanced esthetics.13 However, chipping of the
ceramic layer has been a lingering issue, shifting the attention toward the use of full anatomic
monolithic zirconia restorations.14,15 Replacement of missing teeth with dental implants in posterior ridges with
limited bone width can be surgically challenging and the notion of narrow diameter implants has been
suggested.16,17These implants were thought to offer potential advantages in terms of costeffectiveness
and surgical morbidity.18,19The literature, however, remains controversial on
treatment outcomes with narrow diameter implants, particularly in posterior sites.19–21
When single tooth replacement with monolithic zirconia implant-supported single
crowns in posterior sites are considered, only short to medium-term outcomes are
available.22–26The survival rates and clinical performances reported in these studies were
variable. Crown survival rates between 84% and 100% were demonstrated over an
observation time of one to three years, while the prosthetic complications were between 0%
to 14%. In three studies,22,23,25 standard diameter titanium implants were used in premolar and
molar sites to support the single crowns. The remaining two studies by Mühlemann et al.
(2020) and Zumstein et al. (2023) reported the one-year and three-year outcomes,
respectively, of the same cohort. In these studies, narrow titanium-zirconium (TiZr) implants
of 3.3 mm diameter were exclusively utilized in molar sites. The implant and crown survival
rates reported at one and three years were 97.4% and 84%, respectively. The lower survival
rate observed in the report of Zumstein et al. (2023) resulted from fracture of five implants
and the subsequent loss of their respective crowns. Aside from these two reports, no other
information on the outcomes of monolithic zirconia single crowns supported by narrow
diameter TiZr implants in posterior sites are available.
The validity of this treatment, therefore, needs further investigation with well-designed
clinical trials. Hence, a randomized controlled trial was undertaken to assess various implant,
prosthetic, and patient-reported outcomes of monolithic zirconia single crowns supported by
either narrow or standard diameter titanium-zirconium (TiZr) implants in posterior sites. The
present report focuses on the one-year prosthetic results.