Monolithic Zirconia Single Crowns Supported by Narrow or Standard Diameter Titanium-zirconium Implants in Posterior Sites: One-year Results of a Randomized Controlled Trial.

Abstract

The replacement of missing teeth with implant-supported prostheses has become a standard treatment option with reliable long-term outcomes in various clinical indications.1-6 The 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.5,6 A 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.9 Yet, 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.11 Zirconia-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.16,17 These implants were thought to offer potential advantages in terms of costeffectiveness and surgical morbidity.18,19 The 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.22-26 The 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.