Clinical performance of zirconia crowns Tartaglia GM et al. for a substantial reduction in core thickness.4 Cyclical stresses are also well tolerated by this extremely biocompa- tible material.2-4,9 Exposure to moisture for an extended period of time, even at the low temperatures found in the mouth, can have a detrimental effect on the properties of zirconia.13 Therefore, zirconia crowns should be covered by ceramics to increase their resistance towards the conditions of the oral cavity.3,13 Coloring salt solutions can be added to zirconia without altering its microstructure, color, flexural strength, or aging resistance.13 A shaded zirconia core, which has a more natural appearance with an opaque, yellow dentin over- laid by translucent enamel, provides greater aesthetic results.10,13 Zirconia-based prostheses can be used for both single- and multiple-unit crowns that are anchored on either implants or teeth.1,7,8,10-12,14-16 However, there have not been a significant amount of data published regarding a comparison of long-term clinical results from the use of different kinds of zirconia-based crowns, particularly for patients who have attended private dental practices. Indeed, most published studies have been laboratory-controlled investigations,1,17,18 and the majority of these clinical evaluations have reported data on small numbers of patients.7,8,11,12,19 An extensive review of the relevant literature was recently performed by Denry and Kelly,2 who reported that the largest published comprehensive series included 68 patients who were rehabilitated with 81 total prostheses and were followed for four-five years. Only the studies from Ortorp et al.16 and Encke et al.15 followed a larger number of patients, but they analyzed only single crowns fixed on teeth. Schley et al.5 reviewed studies on tooth-supported fixed prostheses and analyzed 330 zirconia- based fixed prostheses over a minimum follow-up period of three years. From this review, only one study was conducted in a private practice, and the other nine were performed at universities. Two types of problems have been reported in the literature: biological and technical. Among the biological issues, many studies have reported caries and loss of tooth vitality, whereas the loss of retention and the chipping or fracturing of veneers have been the most frequently reported as technical complications.5,7,12,16 Additionally, marginal degrees of adaptation together with mediocre or inadequate periodontal conditions have been observed.8,15 The aim of the current clinical follow-up study was to evaluate the three-year clinical results of a large number of zirconia-core crowns that had been installed at a general dental private practice. Both single crown and multiple crown units, supported by either teeth or implants, were followed-up with for this study. MATERIALS AND METHODS Patient selection This study consisted of a clinical follow-up examination of 142 patients who had been given single- or multiple-unit zirconia crowns at a general private practice in Italy. One hundred and forty two patients (69 men, 73 women), who were between 28 and 82 years of age (mean age 49.2 years, SD 13.4) and had received zirconia crowns between January 2005 and January 2006, were recalled to be evaluated during the follow-up between January 2009 and August 2009 by 2064 CLINICS 2011;66(12):2063-2070 two independent evaluators (GMT, ES). Four patients were lost to follow up for various reasons (deceased, no contact, or moved). The inclusion criteria consisted of having received a zirconia crown from the same private practice during the aforementioned time span. Clinical procedures for zirconia crowns All patients had indications for one or more, one to three- six unit fixed dentures supported by either implants or teeth. All of the patients were examined for oral hygiene by a dental hygienist and were found to have moderate or good oral hygiene with less than 25% marginal plaque. These patients also had low or moderate caries activity, with less than five new restorations during the preceding five-year period. Good general health without severe medical or psychological conditions was generally self-reported by patients. Preliminary dental treatment was performed to obtain the aforementioned inclusion criteria. All subjects provided informed consent for the clinical procedures, as required by current Italian law. For tooth-supported prostheses, preliminary clinical examinations found that the bone level of the supporting teeth was at least half the root length and was without signs of active bone resorption, furcation involvement, mobility, or periapical pathology. Furthermore, the residual coronal tooth structure was shown to have a tooth restorability index value equal to or less than 2.20 All teeth were root-canal treated or non-surgical re-root canal-treated and received prefabricated posts. A core was built using a composite material (LuxaCore, DMG Hamburg Germany) if the occlusal space had more than 2 mm of centric occlusion. All of the tooth preparations were made in a standardized manner. The occlusal reduction was 2 mm, and the axial reduction was 1.5 to 2 mm. There was also a 10-degree taper made that followed the scalloping of the free gingival margins. For aesthetic reasons and for a sound tooth structure, the facial side taper was located 0.5 mm deep subgingivally with a supragingival lingual side. Each of the multiple three-six units had a total gap that was equal to but did not exceed the crown-root surface area of the abutment teeth compared to the teeth to be restored. Moreover, these had at least 3 mm of occlusogingival height from the col of the interproximal papilla to the marginal ridge of the prospective abutments adjacent to the space to be restored.19 For implant-supported prostheses, all of the implants (Titanmed, Milde Implants, Bergamo, Italy) displayed good osseous integration in both the clinical and radiographic tests. Implant abutments (titanium) were prepared accord- ing to the principles outlined for teeth. In terms of crown thickness, the core generally supports a uniform thickness of veneering ceramic, and there should be a maximum of 2 mm of unsupported porcelain. Polyether (Impregum/Permadyne, 3M ESPE AG, Seefeld, Germany) was used for the impressions in a customized tray (Apex trays, Megadenta Dentalprodukte Radeberg, Germany). Individualized, provisional resin crowns (Takilon BB, Salmoiraghi srl, Melegnano, Lodi, Italia) were cemented using a temporary zinc oxide-eugenol (ZOE) cement (Temp Bond, Kerr Italia, Scafati, Salerno, Italia). A plaster model (Esthetic-base gold, Dentona AG, Dormund, Germany) was obtained and used to create an anatomical contour wax-up.