Table 2.

Objectives of the included studies and patient details.

Author/Year	Study Design	Objective	n	Age	Gender	Smokers
				Mean/Range	Male/Female
Pozzi et al., 2014 [26]	RCT (split-mouth)	Compare clinical and radiological outcomes of two implant designs with different prosthetic interfaces and neck configurations in a randomized, controlled, split-mouth clinical trial.	34	52.20/39–59	NR	4 patients smoke less than 10 cigarettes/day
Doornewaard et al., 2021 [27]	RCT (split-mouth)	They assessed the effect of implant neck (microthreaded vs. non-microthreaded) and the type of abutment connection (internal conical vs. external flat-to-flat) on peri-implant bone stability and peri-implant health after at least 36 months.	27	62/42–83	M:15 F:12	Limited to patients smoking less than 10 cigarettes/day
Pessoa et al., 2017 [28]	RCT (split-mouth)	To evaluate clinical, radiographic, microbiologic, and biomechanical parameters related to bone remodeling around implants with external hexagon (EH) and Morse taper (MT) connections.	12	63/18–75	M:3 F:9	0
Glibert et al., 2018 [29]	RCT	This RCT assesses whether a coronal microthreaded design and an internal abutment connection affect crestal bone loss up to one year of function.	21	65/44–66	M:12 F:9	Limited to patients smoking less than 10 cigarettes/day
Cooper et al., 2016 [30]	PS	Over 3 years, compare the proximal marginal bone responses at external hex interface (EXI) versus internal conus interface (ICI) implants.	36	53.1/18–75	M:13 F:23	14 previous smokers
Peñarrocha-Diago et al., 2013 [31]	PS	To conduct a comparative study of two implants with different neck features and prostheses platform connection (machined with external connection and rough-surfaced with switching platform) upon peri-implant marginal bone loss, before and after functional loading.	15	56.9/44–77	M:4 F:11	3 smoking patients, less than 10 cigarettes/day

PS: prospective study; RCT: randomized controlled trial; vs.: versus; NR: not reported.