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

• Published in: Dental materials 2020-04, Vol.36 (4), p.e109-e116
• Main Authors: Ioannidis, A., Bomze, D., Hämmerle, C.H.F., Hüsler, J., Birrer, O., Mühlemann, S.
• Format: Article
• Language: English
• Subjects: 3D printing; Ceramics; Computer-aided design; Computer-aided manufacturing; Dental porcelain; Dentistry; Fatigue; Lithium-disilicate ceramic; Occlusal dental veneers; Zirconia
• ISSN: 0109-5641; 1879-0097
• DOI: 10.1016/j.dental.2020.01.016

•Occlusal veneers can be reliably produced by 3D-printing with the Lithography-based Ceramic Manufacturing process.•3D-printed zirconia, milled zirconia and heat-pressed lithium disilicate can be recommended as material for ultra-thin occlusal veneers.•These materials exhibit a fracture toughness surpassing the suggested values for posterior restorations if bonded to dentin. 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. 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). 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). 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.