Table 3.

Results of risk of bias assessment by AMSTAR tool

Author (year), country of origin, funding(Y/N/?)-Conflict of interest(Y/N/?) [JCR]	Research question or objectives	Primary outcome(s)	Number and designs of included studies (number of patients and implants)	Control group	SR/SR and M	Databases searched (search date)	Follow-up	Quality assessment tools	Implant loading (immediate/late)	Type of edentulism (total/partial)	Main findings	Main conclusion
Wang et al. (2015) [49], China and Spain, (Y-N) [Q1; 1,96]	To assess the predictability of oral rehabilitation by four zygomatic implants with no anterior support in regard to implant survival, technical and biologic complications	The survival rate of the zygomatic implants	3 human clinical trials (2 prospective and 1 retrospective) (49 patients, 196 ZIs)	None	SR and M	(from September 2000 to November 2013)	30–363 (mo)	None	Immediate loading	Fully edentulous	- Zygomatic implant survival rate weighted mean (WM) was 96.7% (range, 95.8 to 99.9%), with a 95% confidence interval (CI) of 92.5 to 98.5%. - Limited number of surgical complications and prosthetic complications	Maxillary rehabilitation by four zygomatic implants with no anterior support is a reliable approach
Tuminelli et al. (2017) [44], USA, (NR-NR) [2.39]	To systematically review the outcome of immediate loaded zygomatic implants	Immediate load survival, complications	38 articles	None	SR	PubMed (from 1990 until June 2016)	At least 12 months follow-up (according to text follow-ups ranged between 1 and 10 (y))	None	Immediate loading	Both totally or partially edentulous maxilla	- The success of implants and prostheses ranged from 96 to 100%. - The complication rates are relatively few, rarely catastrophic, and easily managed	Immediately loading zygomatic implants for the restoration of the severely atrophic maxilla presents a viable alternative for treatment of the atrophic maxilla and is recommended for the restoration of the severely atrophic maxilla with or without anterior conventional implants
Molinero-Mourel et al. (2016) [47], Spain, (NR-N) [1.07]	To analyze and describe the most frequent surgical complications associated with the use of zygomatic implants	Complications	13 articles (1 SR, 5 pros, 5 retros, 1 pros and retros, 1 cohort) (3240 ZIs)	None	SR	PubMed (up to December 2015)	1–12 (y)	None	All studies were immediate loading	Both totally or partially edentulous maxilla	- Out of the most frequent surgical complications, sinusitis (3.9%) and failure in osseointegration (2.44%) are highlighted	Rehabilitation using zygomatic implants is a consolidated therapeutic option although it does not lack in possible complications; therefore, it should be reserved only to professional clinicians with vast surgical experience
Goiato et al. (2014) [46], Brazil (N-N) [1.52]	To evaluate clinical studies on the follow-up survival of implants inserted in the zygomatic bone for maxillary rehabilitation.	Survival of implants	25 articles (design NR) (748 ZIs)	None	SR	PubMed/MEDLINE, Embase, and Cochrane Library databases (from 2000 to July 2012)	Mean follow-up: 42.2 (mo) (range 0–144)	None	Fifteen studies conducted late loading (prosthesis insertion at 4–6 months after initial implant loading), whereas 10 studies reported immediate loading	Both totally or partially edentulous maxilla	- These studies reported the insertion of a total of 1541 zygomatic implants and 33 implant failures -After a 36-month follow-up, the survival rate was 97.86%	- The survival of osseointegrated implants may also be related to the use of suitable presurgical examinations and the parameters used during the surgical procedures - Zygomatic implants appear to be an effective alternative for the treatment of an atrophic maxilla.
Chrcanovic et al. (2013) [45], Sweden (NR,N) [1.66]	“What is the survival rate of zygomatic implants (ZIs)?” and “What are the most common complications related to surgery of zygomatic implants?”	Survival rate, complication	42 article, 1145 patients and 2402 ZIs	None	SR	PubMed (Up to March 2012)	Range: 6–120 (mo)	None	Between 42 studies, 12 evaluated the use of ZIs applied with immediate function protocols	Both totally or partially edentulous maxilla	- 12 evaluated the use of ZIs applied immediate protocol and 3 after maxillary resections for tumor ablations (showed lower success.). - Of 2402 ZIs, 56 ZIs were reported as failures - The CSR over a 12-year period was 96.7%.	- ZI placement needs very experienced surgeons since delicate anatomic structures such as the orbita and brain may be involved - Despite the high survival rate observed, there is an impending need for further investigations
Chrcanovic et al. (2016) [15], Sweden (NR-N) [1.66]	To assess the survival rate of zygomatic implants (ZIs) and the prevalence of complications based on previously published studies	Complications	Sixty-eight studies were included one randomized clinical trial,16 prospective studies, and 51 retrospective analyses, comprising 4556 ZIs in 2161	Conventional implants	SR	PubMed/Medline, Web of Science, and the Cochrane Oral Health Group Trials Register (up to December 2015)	Range: 1–144 (mo)	None	26 studies immediate loading and studies 34 studies evaluating delayed loading protocols	Both totally or partially edentulous maxilla	Immediate loading showed a statistically lower ZI failure rate than other studies (P = .003). - Studies evaluating ZIs for the rehabilitation of patients after maxillary resections presented lower survival rates. - Postoperative complications: sinusitis, 2.4% soft tissue infection, 2.0%, paresthesia, 1.0% and oroantral fistulas, 0.4%	- ZIs present a high 12-year CSR, with most failures occurring at the early stages postoperatively. - Main complication was sinusitis, which can appear several years after placement
Aboul-Hosn Centenero et al. (2018) [48], Spain (Y-N) [1.15]	To compare the survival rates (SRs) of oral rehabilitations performed with 2 zygomatic implants (ZIs) combined with regular implants (RIs) versus 4 ZIs	Survival rates	6 articles (4 prospective and 2 retrospective case series) A total of 130 ZIs and 186 conventional implants were placed in 64 patients.	4 ZIs (case) versus2 ZIs combined with regular implants RIs (control)	SR and M	MEDLINE/PubMed, Cochrane Central register of Controlled trials Cochrane Oral Health group Trials Register, and EMBASE between 2007, and June 30, 2015	Range: 12–82 (mo)	The criteria were modified according to the PRISMA 2009 checklist statement [17]	Immediate loading	Fully edentulous	- ZIs SR weighted mean was 98.0%, CI [96.7 to 99.8%]. For the control group (2 ZIs + 2 RIs) and the test group (4 ZIs), the implant SR was 98.6% and 97.4%, respectively - No statistically significant differences in terms of SRs were obtained between both groups, P = 0.286.	- No statistical differences in 2 groups in terms of survival and failure rates. The reduction on treatment time and morbidity related to regenerative approaches may be its main advantage. - The zygoma quad seems to be the treatment of choice for the severely atrophic maxilla.

Legends: Y yes, N no, ZIs zygomatic implants, SR systematic review, M meta-analysis, Mo month(s), Yr year(s)