Clinical performance of monolithic zirconia crowns on titanium-zirconium reduced-diameter implants in the molar area: Interim data at three years of a randomized controlled trial.

AIM: The aim of the present study was (i) to evaluate the clinical performance of reduced-diameter implants placed in the molar area and (ii) to test whether monolithic zirconia implant-supported crowns lead to similar clinical outcomes compared to porcelain-fused-to-metal crowns. MATERIALS AND METHODS: A total of 76 patients needing a single implant crown in the posterior region were recruited. All patients received a titanium-zirconium reduced-diameter implant (Straumann Roxolid, Tissue Level, Standard Plus, diameter 3.3 mm, regular neck) randomly allocated to receive either a (1) monolithic zirconia crown (test) or (2) porcelain-fused-to-metal crown (control). Implant survival, prosthetic outcomes, and patient-reported outcomes were assessed at crown delivery and after 3 years of follow-up. Marginal bone levels (MBL) as well as clinical parameters including probing depth (PD), bleeding on probing (BOP), and plaque levels (PCR) were also recorded. RESULTS: A total of 59 patients were available at the 3-year follow-up; 32 patients with a monolithic zirconia crown (TEST) and 27 patients with a porcelain-fused-to-metal crown (CONTROL). 14 implants (11 implant fractures/3 aseptic losses) were lost leading to an estimated implant survival rate of 80% ± 5.1% (95% CI 70.8%-90.8%). Prosthetic complications were limited to the control group and involved minor chippings. CONCLUSIONS: This type of reduced-diameter implant to support single implant molar crowns in the molar area cannot be recommended. Monolithic zirconia crowns appear to be a viable option in the posterior region showing similar prosthetic outcomes to porcelain-fused-to-metal crowns.

Time efficiency and efficacy of a centralized computer-aided-design/computer-aided-manufacturing workflow for implant crown fabrication: A prospective controlled clinical study.

OBJECTIVE: To assess time efficiency and the efficacy of the prosthetic manufacturing for implant crown fabrication in a centralized workflow applying computer aided design and computer aided manufacturing (CAD-CAM). MATERIAL AND METHODS: Fifty-nine patients with one posterior implant each, were randomly allocated to either a centralized digital workflow (c-DW, test) or a laboratory digital workflow (l-DW, control). Patients were excluded from efficiency and efficacy analyses, if any additional restoration than this single implant crown had to be fabricated. A customized titanium abutment and a monolithic zirconia crown were fabricated in the c-DW. In the l-DW, models were digitalized for CAD-CAM fabrication of a monolithic zirconia crown using a standardized titanium base abutment. Time for impression, laboratory operating and delivery time were recorded. The efficacy of the prosthetic manufacturing was evaluated at try-in and at delivery. Data was analyzed descriptively. Statistical analyses using student's unpaired t- and paired Wilcoxon were performed (p < 0.05). RESULTS: At impression taking, 12 patients (c-DW) and 19 patients (l-DW) were included. The impression time was 9.4±3.5 min (c-DW) and 15.1 ± 4.6 min (l-DW) (p < 0.05). The laboratory operating time was 130 ± 31 min (c-DW) and 218.0±8 min (l-DW) (p < 0.05). The delivery time was significantly longer in the c-DW (5.9 ± 3.5 1 days) as compared to the l-DW (0.5±0.05 days). At try-in and at delivery, efficacy of prosthetic manufacturing was similar high in both workflows. CLINICAL RELEVANCE: The c-DW was more time efficient compared to the lab-DW and rendered a similar efficacy of prosthetic manufacturing.

Load-bearing capacity of CAD/CAM 3D-printed zirconia, CAD/CAM milled zirconia, and heat-pressed lithium disilicate ultra-thin occlusal veneers on molars.

OBJECTIVES: The load-bearing capacity of ultra-thin occlusal veneers made of 3D-printed zirconia were compared to the ones obtained by fabricating these reconstructions by CAD/CAM milling zirconia or heat-pressing lithium-disilicate. METHODS: On 60 extracted human molars, the occlusal enamel was removed and extended into dentin. Occlusal veneers of 0.5 mm thickness were digitally designed. The specimens were divided into 3 groups (n = 20 each) differing in the restorative material and the fabrication technique of the occlusal veneer. (1) 3DP: 3D-printed zirconia (Lithoz); (2): CAM: milled zirconia (Ceramill Zolid FX); (3) HPR: heat-pressed lithium disilicate (IPS e.max Press). After conditioning procedures, the restorations were adhesively bonded onto the conditioned tooth. Thereafter, all specimens were aged in a chewing simulator by exposure to cyclic fatigue and temperature variations. Subsequently the specimens were statically loaded and the load which was necessary to decrease the maximum load by 20% and initiate a crack (Finitial) and the load which was needed to fracture the specimen (Fmax) were measured. Differences between the groups were compared applying the Kruskal-Wallis (KW) test and the Wilcoxon-Mann-Whitney-Test (WMW: p < 0.05). RESULTS: The median Finitial values for the groups 3DP, CAM and HPR were 1'650 N, 1'250 N and 500 N. The differences between all three groups were statistically significant (KW: p < 0.0001). The median Fmax values amounted to 2'026 N for the group 3DP, 1'500 N for the group CAM and 1'555 N for the group HPR. Significant differences were found between 3DP and CAM (WMW: p = 0.0238). SIGNIFICANCE: Regarding their load-bearing capacity, 3D-printed or milled zirconia as well as heat-pressed lithium disilicate can be recommended as restorative material for ultra-thin occlusal veneers to prosthetically compensate for occlusal tooth wear. Despite statistically significant differences between the restoration materials, all load-bearing capacities exceeded the clinically expected normal bite forces.