Title	Fifteen-degree Angulated Zirconia Abutments Are Comparable to Zero-degree Angulated Zirconia Abutments in Fracture Resistance
Clinical Question	For a patient with an anterior zirconia implant abutment, would a proclined implant abutment as compared to a vertically positioned implant abutment be as effective at fracture resistance?
Clinical Bottom Line	Fifteen-degree angulated zirconia abutments are comparable to zero-degree angulated zirconia abutments in fracture resistance. For patients with a zirconia implant abutment, there’s a chance that an angulated zirconia abutment will have a similar or better fracture resistance to a straight angulated zirconia abutment. This is supported by two in vitro studies by Katsavochristou and Saker. Katsavochristou’s study investigated fracture resistance of zirconia abutments with different angulations and the abutments with 15 and 25 degrees outperformed the zero-degree abutments. Saker’s study evaluated zirconia abutments with zero- and 15-degree angulations with varying implant platform sizes and concluded that the straight and angulated abutments had similar fracture resistances.
Best Evidence
PubMed ID Author / Year Patient Group Study type (level of evidence) 31746068 Katsavochristou/2019 N/A Laboratory study Key results Zero-degree angulated zirconia abutments had statistically significant (p<0.0001) lower fracture resistance compared to 15- or 25-degree angulated zirconia abutments. 32645732 Saker/2020 N/A Laboratory study Key results Zero-degree angulated zirconia abutments had no significant difference in fracture resistance compared to 15-degree angulated zirconia abutments with implant diameters 3.0mm and 3.5mm.
Evidence Search	(zirconia) AND ((implant) OR (abutment)) AND (fracture) AND ((angulation) OR (angle))
Comments on The Evidence	As these studies are in vitro lab studies, the validity of these studies is low and we cannot assume to observe these same results clinically. Katsavochristou’s study lacks evaluation of thermal cycling and its relation to fatigue of the zirconia abutments, which cannot be ignored in a live patient. In addition, neither of the studies evaluated laterally applied forces, which is a crucial factor for understanding fracture resistance during chewing motion and bruxism especially for a tooth in the anterior region. Additionally, the two studies differ in the type of zirconia abutment. Katsavochristou’s study used a custom zirconia abutment and Saker’s study used a prefabricated zirconia abutment so this should be taken into consideration. Lastly, studies with loading of more than 1,000,000 cycles (which is equivalent to a year of normal function) is needed to understand if there is a difference in fracture resistance among the different angulated abutments with increased cycling. These would be assessed if these studies were done clinically.
Applicability	These studies have been designed to understand the fracture resistance of a zirconia abutment with varying angulations mimicking an implant restored in the anterior region which are commonly angulated. As most material studies, the results of these studies should be applied clinically with a degree of caution. Although these studies show similar fracture resistance between straight and angulated implant abutments, it is known for zirconia abutments to fracture when they are angulated beyond certain amount. According to these studies, use of a zirconia abutment on implants with greater than 30 degrees angulation and 3.5-mm diameters is contraindicated.
Specialty	(General Dentistry) (Oral Surgery) (Periodontics) (Prosthodontics)
Keywords	Zirconia; Fracture; Implant; Angulation
ID#	3480
Date of submission	11/30/2021
E-mail	haah@uthscsa.edu
Author	Aaron Haah, DDS
Co-author(s)	Vrinda Gupta, BDS, MDS
Co-author(s) e-mail	Guptav1@uthscsa.edu
Faculty mentor	Panagiotis Gakis, DDS, MS, FACP
Faculty mentor e-mail	gakis@uthscsa.edu
Basic Science Rationale (Mechanisms that may account for and/or explain the clinical question, i.e. is the answer to the clinical question consistent with basic biological, physical and/or behavioral science principles, laws and research?) None available
Comments and Evidence-Based Updates on the CAT (FOR PRACTICING DENTISTS', FACULTY, RESIDENTS and/or STUDENTS COMMENTS ON PUBLISHED CATs) None available