Table 2.

Strengths and limitations of included studies according to the STROBE checklist

Reference	Strengths	Limitations	Scores
Ast et al., 1961 [12]	• Clear objectives • Ascertainment of outcome and reliability of examiners were described • Extraction and non-extraction groups were matched for age	• Cross-sectional study with convenience sample • The study design was not mentioned • The sample size and power of the sample was not calculated • The study setting was not clear • Retrospective study • Age at time of extraction was not mentioned • Potential confounders and participant characteristics were not described • Weak methodology (method of assessment of molar relationship was not uniform or acceptable)	5*
Oliver et al., 1988 [15]	• The objectives were clear • The sample was stratified; however, the eligibility criteria for participant selection was not clear • Age of participants at time of extraction and evaluation of consequences were clear • Examination was carried out by one examiner • Intraexaminer reproducibility was established • Numbers of participants used for each examination was mentioned with reasons for withdrawal	• The study design was not mentioned • There was no sample size power calculation • Potential confounders were not addressed	9**
Telli and Aytan, 1989 [7]	• The objectives were clear • Age of participants at time of extraction and evaluation of consequences were clear • Split-mouth (extraction and non-extraction sides in the same patient) • Method used to assess variables was powerful (superimposition of cephalometric radiographs)	• The study design was not mentioned • There was no sample size power calculation • The location from which the sample was recruited was not clear • Reason for “non-participants” was not mentioned	10**
Ay et al., 2006 [13]	• The objectives were clear • The age was clear both at the time of extraction and evaluation of consequences • The setting was clear (Department of Oral and Maxillofacial Surgery of Cumhuriyet University, Sivas, Turkey) • Participant characteristics were mentioned • The same investigator undertook all measurements, and the reproducibility of the method was tested	• The study design was not mentioned • Retrospective • The number of extracted teeth was not clear • No sample size power calculation was performed	9**
Yavuz et al., 2006 [19]	• The objectives were clear • The location of participant recruitment was clear • The age was clear both at the time of extraction and evaluation of consequences • Reliability testing was done • Extraction and non-extraction sides were in the same patient • All assessments were performed by one examiner • Intraexaminer reproducibility was established	• The study design, method for selecting the sample, and period of recruitment were not mentioned • No sample size power calculation • A retrospective study design • Potential confounders were not addressed • Follow-up duration was not clear	11**
Jälevik and Möller, 2007 [14]	• The objectives were clear • The setting and location of patient recruitment were clear • The age of participants at time of extraction and time of evaluation of consequences were clear • Methods used to assess variables were powerful (panoramic X-rays, bitewings, casts and photographs)	• The study design was not mentioned • Period of recruitment was not mentioned • A cross-sectional study design • No sample size power calculation was performed	11**
Rãducanu et al., 2009 [16]	• The objectives were clear • The study design was clear • The location and duration of participant recruitment were clear • Intraexaminer and interexaminer reliability tests were performed	• No sample size power calculation was performed • The age at extraction and at evaluation of consequences was not clear • Numbers of each category were not mentioned, only percentages. • Convenience sample • Retrospective study • Potential confounders were not addressed • Small sample size	13**
Normando and Cavacami, 2010 [20]	• The objectives were clear • Cases and controls were matched for age, gender, and location	• The study design was not mentioned • The sample size power was not calculated • The setting in which the study was performed was not mentioned • Age at extraction time was not mentioned • Retrospective study from records • Follow-up time was not clear	13**
Teo et al., 2013 [18]	• The objectives were clear • The location and duration of participant recruitment were clear • All assessments were undertaken by one examiner • Intraexaminer repeatability was done	• The study design was not mentioned • No sample size power calculation was performed • Retrospective study from records	11**
Rahhal, 2014 [21]	• The objectives were clear • The setting was clear (Arab-American University Clinic, Jenin, Palestine) • Confirmed eligible sample	• Study design was not mentioned • The sample size power was not calculated • Age at evaluation of consequences was not mentioned • Study only performed at the upper arch • No controls • Follow-up duration was not clear	6*
Teo et al., 2015 [17]	• The objectives were clear • The setting was clear (Dental Hospital, London, UK) • The age was clear both at the time of extraction and evaluation of consequences • Intraexaminer reliability was done	• The study design was not mentioned • No sample size power calculation was performed • Retrospective study design	14**

Notes: *Scores from 1 to 7 (weak strength); **scores from 8 to 15 (moderate strength)

Abbreviation: STROBE Strengthening the Reporting of Observational Studies in Epidemiology