Table 2.

General description of included studies

Authors, year of publication, country where the study was carried out, and journal where it was published	Objective	Study design	Sample	Exposure diagnosis: periodontitis	Condition outcome: complications and mortality from COVID-19	Association measurement	Confusion covariates	Main findings
1. Marouf et al. 2021 Qatar Journal of Clinical Periodontology	The objective of this case– control study was to investigate the association of periodontitis with COVID-19 complications.	Case–control	568 patients diagnosed with COVID-19 who are part of the national electronic medical records of Hamad Medical Corporation (HMC) of the state of Qatar of which 258 presented periodontitis.	The periodontal status was studied from bitewing and panoramic radiographs (OPG) from the patient records.[28]	Condition of complications and mortality from COVID-19	Association between PD and complications by COVID-19:	Age, sex, smoking, diabetes, co-morbidities, body mass index	Frequency of periodontitis: 45.42% Case group: patients with complications from COVID-19
			Case group: Cases were defined as patients with complications from COVID-19, such as admission to ICU, need for assisted ventilation, or death.	The percentage of bone loss was obtained from the most affected tooth using the criteria of the classification of periodontal and peri-implant diseases.	People with at least one of the following criteria:	Any complication (OR = 3.67, 95% CI 1.46–9.27)		7.04% Control group: COVID-19 patients discharged without major complications 92.957%
			The cases consisted of 40 patients of which 33 had periodontitis and 7 did not present periodontitis.	The patients were classified according to periodontitis stages[29]:	1. Death 2. Admission to ICU 3. Need for assisted ventilation	Mortality (OR = 8.81, 95% CI 1.00–77.7) Admission to ICU (OR = 3.54, 95% CI 1.39–9.05)		The study findings showed a strong association between periodontitis and an increased risk of complications from COVID-19,
			Control group: Controls were defined as COVID-19 patients discharged without major complications.	• Initial periodontitis or periodontally healthy (stages 0-1): bone loss less than the coronal third of the root length (15%) on OPG radiographs, or ≤2 mm on bitewing radiographs.		Need for assisted ventilation (OR = 4.57, 95% CI 1.19–17.4)		including admission to ICU, the need for assisted ventilation, and death after performing adjusted regression models for potential confounding variables.
			The controls consisted of 528 of which 225 presented periodontitis. Women: 258 Males: 310	• Periodontitis (stages 2–4): bone loss greater than the coronal third of the root length (>15%) on OPG, or> 2 mm on bitewing radiographs.
2. Larvin et al. 2020 Reino Unido Frontiers in Medicine	The objective of this study was to quantify the impact of PD on hospital admission and mortality during the COVID-19 pandemic.	Nested case–control	13,502 patients tested for COVID-19 (part of UK Biobank database)	The status of PD was determined by the presence of self-reported oral health indicators such as:	Condition of complications and mortality from COVID-19	Association between PD (gum pain or bleeding) and hospitalization of patients with COVID-19:	Age, sex, ethnicity, family income, body mass index, smoking history, cancer,	Participants with gum pain 365 (2.4%) Participants with bleeding gums
			Case group: Defined as participants with a positive self- reported history of PD.	bleeding gums, painful gums, and loose teeth. These were used as surrogates for PD, since they have demonstrated their validity in the absence of a clinical diagnosis.[30]	People with at least one of the following criteria:	Hospital admission (OR = 0.91, 95% CI 0.12–2.04) Association between PD (gum pain or bleeding) and mortality in patients with COVID-19: Mortality (OR = 1.71, 95% CI 1.05–2.72)	hypertension, angina pectoris, heart attack, diabetes, myocardial infarction,	1,329 (8.7%) Participants with tooth loss 406 (2.7%) Participants without self-report of PD 11,153 (84.1%)
			Control group: Defined as participants with no self-reported history of PD.	Self-reported painful and bleeding gums were associated with mild-to-moderate PD, whereas loose teeth indicated severe PD.	1. Hospital admission 2. Mortality	Association between PD (tooth loss) and hospitalization of patients with COVID-19:	fulminant infarction, peripheral artery disease, heart failure, atrial fibrillation, respiratory disease	Participants with a positive result of COVID-19 1,616 (10.5%)
						Hospital admission (OR = 0.90, 95% CI 0.16–10.63)		Participants with a negative COVID-19 result 11,637
						Association between PD (tooth loss) and mortality in patients with COVID-19: Mortality (OR = 1.85, 95% CI 0.92–2.72)		The study findings showed an increased risk of mortality after COVID-19 infection in people with PD, determined by the presence of oral health indicators. While PD may not increase the risk of COVID-19 infection directly, it can increase the risk of death.