1. Introduction

Oral diseases appear to be a global problem that should be addressed as a matter of global health concern. Oral health issues include various behavioral and social features such as habits, oral health knowledge, practices, availability, modifiable risk factors, and accessibility to oral health treatments [1]. Health is considered as a significant factor in making life valuable [2]. In general, lifestyles and behavioral patterns are continuously changing, making people more susceptible to oral disorders. Common preventable risk factors for oral diseases include consuming great amounts of sugary food and alcohol and smoking excessively [3]. Back in 2015, untreated oral disorders crippled over half of the world’s population (age-standardized prevalence: 48.0 percent), affecting 3.5 million individuals worldwide ^[4][5][4,5].

Oral and orofacial problems can affect children and adolescents, affecting physical functioning and psychosocial well-being [6]. One of the scientific theories used to influence human health-related behaviors is the knowledge, attitude, and practices (KAP) theory. According to the KAP theory, healthy knowledge is the foundation for developing an optimistic and healthy lifestyle, attitudes are the motivating factor behind changing behavior, and the goal is to promote oral health [7]. This is why oral health professionals play a critical role in disease prevention and diagnosis through screening and raising awareness [8]. Recently, a shift of focus in health care has been noticed, signaling a transition from biological to a more complete and broader biopsychosocial concept of health [9].

Rationale: The most critical risk factor associated with the onset of various gingival and periodontal diseases is tobacco smoking. It reduces the quality of life of patients and poses a risk to oral health. It has been demonstrated that oral health among smokers is compromised in comparison to nonsmokers. Thus, this study is aimed at reviewing the literature to evaluate the effect of smoking on oral health.

Objectives: In this systematic review, we aim to examine the effects of cigarette smoking on oral health, present the major oral diseases caused by cigarette smoking, and determine if there is any possibility of bacterial or fungal infections among smokers.

2. Analysis on Study Results

2.1. Study Selection Results

A total of 3696 studies were retrieved from the PubMed, Scopus (2271), WOS (1822), and MDPI (711) according to the inclusion/exclusion criteria as listed in Table 12. Data were extracted from 19 studies that purely met the eligibility criteria. Figure 12 and Figure 23 shows the results of the total studies evaluated. Initially, a total of 3696 articles were screened from PubMed, 711 from MDPI and 4093 form other databases (Scopus and WOS) as per the search criteria described in Table 21. After identifying duplicate articles, 972 were excluded from PubMed, 657 from Scopus, 507 from WOS, and 120 from MDPI. After removal of duplicates, the remaining 3315 articles were screened by reading the title and abstracts, after which 2929 articles were excluded. The remaining 47 articles were then fully read and assessed for the inclusion/exclusion criteria and quality assessment. After reading the full text, 28 studies were excluded due to reasons including cigarette cessation studies with no oral effects, prevalence of cigarette smoking among different population reporting no oral effects, questionnaire-based studies, and studies with chewable tobacco or other oral tobacco products. The finally selected articles were finalized to proceed further for data extraction. Based on the quality assessment of the research studies, these 19 articles were screened for the present study. A meta-analysis of the studies included in this study was not performed due to the methodological heterogeneity of the findings.

Table 1. Criteria for inclusion and exclusion of research studies.

Characteristics	Inclusion Criteria	Exclusion Criteria

Serial #	Keywords	PubMed	Scopus	WOS	MDPI
Study design	Clinical studies including trials and randomized clinical trials, evaluation studies, original research articles	Review articles, narrative reviews, short communication, case report, editorials, letters, unpublished articles, abstracts, systematic reviews, and meta-analyses
Study period	Last 10 years	Articles before 2011.
Publication language	English	Other than English
Interventions	Articles examining the impact of cigarette smoking on oral health initiatives. Individual and community-based studies reported with context, effects, disease outcome of smoking and the process	Articles that only have the observational data.
Publication status	Published	Not published yet

Table 2. Search strategy for study-related articles.

1	Smoking and oral health	184	910	777	36
2	Smoking effects on oral health	134	223	140	05
3	Cigarette smoking	1186	460	508	421
4	Smoking and tobacco use	2192	678	397	249
Total articles retrieved		3696	2271	1822	711
Removal of duplicate articles		972	657	507	120

 

Figure 12. Flowchart of articles retrieved from different Web sources.

Figure 23. Articles included in the current study (MDPI and PubMed).

From the total retrieved articles (MDPI, PubMed, Scopus, and Web of Sciences), only MDPI and PubMed articles were further included in this study.

2.2. Study Features

A total of 19 studies were included in this systematic review. The studies were conducted in different countries; many researchers cited different time durations. The number of citations for each of the study was observed from Google Scholar. Each of the included studies was published in reputed and indexed journals. Table 3 summarizes the sample type, total sample size, adopted methodology, results, and the conclusion of each study. Different types of samples were collected from the patients to observe the effects of smoking on oral health, including biopsies, blood, buckle cells, teeth, saliva, etc. In the included studies, a total of 26,236 samples were observed.

Table 3. Methodology, outcomes, and conclusion of articles included in the current study.

Authors	Study Design	Duration of Study	Sample Obtained From	Sample Size	Methodology	Study Outcomes	Author Conclusion
Yuki D et al., 2013 [10]	Quasirandomized cross-over	4 days	Blood, Saliva	16	After smoking one cigarette, the analysis of plasma and saliva nicotine and cotinine.	The concentration profiles of saliva cotinine were identical to those of plasma cotinine, and all of the computed cotinine pharmacokinetic characteristics were the same in both plasma and saliva.	Saliva cotinine, which reflects plasma cotinine content and kinetics, might be a suitable and less intrusive cigarette smoke exposure measurement.
Al-Bayaty et al., 2013 [11]	Comparative cross-sectional	Not mentioned	Blood and teeth	197	BOP, PI, and the levels of serum haptoglobin, cotinine, and alpha 1-antitrypsin were tested.	BOP levels were determined to be low, while plaque indices were modest. Smokers had considerably greater levels of serum haptoglobin, cotinine, and alpha 1-antitrypsin than nonsmokers.	A study found that smoking for a longer period, but not for a higher number of cigarettes per day, was linked to less gingival bleeding in smokers.
Medina Solis CE et al., 2014 [12]	Cross-sectional	Not mentioned	Questionnaire	22,229	Questionnaires base study to evaluate risk factors.	The prevalence of oral or dental diseases was 25.7%.	Tobacco users were more likely to report oral and dental issues.
Haswell et al., 2014 [13]	Cross-sectional	28 days	Urine, Saliva, Blood	263	The levels of biomarkers in 143 smokers, 61 never-smokers, and 61 ex-smokers were compared. A total of 27 potential biomarkers were evaluated.	14 biomarkers were substantially different between smokers and never-smokers, and 12 of these 14 biomarkers could differentiate between smokers and former smokers, indicating the possibility of reversibility.	Twelve of the twenty-seven BOBE are potentially valuable instruments for future product evaluation.
Du D et al., 2014 [14]	RCT	Pre-/postintervention data	Teeth	322	A 0–100 mm visual analog scale was used to measure baseline cravings. Craving assessments were taken at 50 s, 3, 5, 7, 15, 20, 25, and 30 min after the medication was given.	Both treatments demonstrated equal maximal effects on desire alleviation and decreased cue-induced craving. At 50 s, 3 min, and 5 min after treatment, the 2.5 mg nicotine film alleviated cue-induced desire to a larger extent than the 2 mg nicotine lozenge.	While both had equal maximal effects, the 2.5 mg nicotine film alleviated cue-provoked cravings substantially faster than the 2 mg nicotine lozenge. For low-dependence smokers, nicotine film might be effective for providing fast desire relief.
Lee CP et al., 2015 [15]	Case control	5 year	Blood	507	Single-nucleotide polymorphisms (SNPs) in DNA repair genes (CHAF1A and CHAF1B) and a chromosomal segregation gene (AURKA) were discovered using a genotyping assay and gene–environment interaction analysis.	AURKA’s Phe31Ile polymorphism (rs2273535, T91A) was shown a linkage of an increased risk of oral cancer. The 91A allele’s gene dosage was likewise linked to greater risk of mouth cancer. Furthermore, by high usage of cigarettes, the AURKA 91AA homozygote can be modify resulting to a high risk of oral cancer.	The functional Phe31Ile polymorphism of AURKA gene may be a strong susceptibility gene in the incidence of oral cancer.
De Carvalho LD et al., 2014 [16]	RCT	One year	Physical check-up	26	G1: etch-and-rinse in nonsmokers. G2: selective enamel etching in nonsmokers. G3: etch-and-rinse in smokers. G4: selective enamel etching in smokers. One operator applied a nanofilled resin composite to each group and light-cured it sequentially.	Only minor discoloration revealed a statistically significant difference between groups 1, 3, and 4 after 12 months when compared to baseline in the evaluations.	The clinical efficacy of resin composite cervical restorations was unaffected by cigarette smoking.
Abduljabbar T et al., 2017 [17]	RCT	3 months	Oral BBL swab	22	The presence of oral erythematous lesions and the position of the denture in jaws were examined by a clinical oral examination. Exfoliative cytology was used to confirm the appearance of fungal hyphae.	Fungal CFU/mL levels were statistically substantially greater in smokers than nonsmokers at the 3-month follow-up.	In both smokers and nonsmokers, aPDT is effective at inactivating oral fungus colonization.
Javed F et al., 2017 [18]	RCT	12 weeks	Questionnaire/Teeth	54	At baseline and during a 12-week follow-up, periodontal parameters were measured. Group A: mechanical curettage (MC) with adjunct antimicrobial photodynamic therapy (aPDT) Group B: mechanical curettage (MC) only.	Patients in groups A and B had significantly lower PI and PD at 12-week follow-up as compared to their baseline levels. At the 12-week follow-up, patients in Group B had substantially greater PI and PD than those in Group A.	When compared to MC alone, MC with aPDT is more successful in treating peri-implant mucositis in cigarette smokers.
Rodriguez-Rabassa M et al., 2018 [19]	Cross-sectional	Not mentioned	Saliva	34	To evaluate the response from the host, cytokine and chemokine expression analyses were performed.	Some bacterial species connected with the smokers group have associations with hormones and cytokines found to be statistically different between smokers and nonsmokers. Inflammation and carcinogenesis in the oral cavity have been linked to these variables.	The findings might help researchers figure out how the salivary microbiome, host inflammatory responses, and metabolism interacts in smokers.
Blasi PR et al., 2018 [20]	Secondary analysis	2015–2017	Questionnaire	718	Between the baseline and the 6-month follow-up survey, professional dental treatment was received.	The findings provide light on variables that may encourage or discourage low-income smokers from seeking professional dental treatment.	This study provides enough material regarding smoking effects on oral health and motivates the public to visit the dental clinics.
AlAhmari et al., 2019 [21]	RCT	3 months	Teeth	83	The periodontal parameters were examined at baseline, 1 month, and 3 months follow-up.	Probing pocket depth (PD), plaque index (PI), and the clinical AL were all increased in smokers than nonsmokers after 1 and 3 months of follow-up.	For treatment of CP among the cigarette smokers, the results of SRP with and without aPDT are compromised.
Angst PDM et al., 2019 [22]	RCT	2 year	Teeth	62	PD, BOP and CAL.	The test group’s mean PPD was higher at the start than the control groups, but the two groups were similar after two years. Significant decreases in PPD and BOP, as well as an increase in CAL, were found with time, with no significant differences between groups.	During the two years of SPT, oral prophylaxis with oral hygiene instructions alone or in conjunction with subgingival instrumentation was able to preserve the previously achieved periodontal state to a comparable level.
AlDeeb M et al., 2013 [23]	RCT	12 weeks	Peri-implant sulcular fluid, radiography	25	The baseline (before therapy) and the 12-week follow-up (after therapy). The ultrasonic scaler and profuse irrigation were used to provide full-mouth disinfection (FMD). A diode laser was used to perform the photodynamic treatment (PDT).	All groups showed statistically significant reductions in PI and PD markers at the baseline examination and after 12 weeks of follow-up. At 12 weeks, BOP among smokers had increased significantly.	In cigarette smokers, PDT with additional mechanical debridement decreased plaque index and probing depth while increasing probing bleeding and lowering proinflammatory indicators.
Julkunen -Iivari A et al., 2020 [24]	Cohort	1985–2015	Teeth	1080	Associations between tobacco products, periodontal health parameters, education level, and death ages.	Tobacco products, as well as a low level of education, are linked to poor periodontal health. Tobacco users who had a lower level of education had greater PI, calculus, and GI scores than nonusers. When compared to nonusers, missing teeth and a lower education level were associated with a significantly greater frequency of deep periodontal pockets.	Tobacco products were found to be hazardous to periodontal health.
Javed F et al., 2020 [25]	Cohort	Not mentioned	Saliva	46	Full-mouth PI, BOP, PD and AL, marginal bone loss (MBL), and missing teeth. Levels of IL-17A and IL-23 in saliva were measured.	Marijuana users, cigarette smokers, and nonsmokers with periodontitis had poorer clinic-radiographic characteristics than periodontally healthy nonsmokers.	The whole salivary immune-inflammatory response may be somewhat poorer in marijuana users compared to heavy cigarette smokers and nonsmokers with periodontitis.
Nettore IC et al., 2020 [26]	Cross-sectional	Oct 2014-Feb 2019	Flavor recognition	348	Oral administration of aqueous aromatic solutions was used to detect 21 distinct chemicals in the test. The total of the correctly detected tastes was used to determine the flavor score (FS).	Cigarette smoking seemed not to influence flavor recognition.	Smoking was not significantly associated with the flavor identification.
Varghese J et al., 2020 [27]	RCT	3 months	Saliva	40	Periodontal parameters were assessed. Saliva samples were collected before start and after the end of treatment to determine the levels of salivary 8-hydroxyguanosine (8-OHdG) using the ELISA method. CPs: Chronic periodontitis in smokers. CPns: CP nonsmokers (CPns). CHS: Clinically healthy subjects in smokers. CHns: CH nonsmokers.	At baseline, the PI, GI, PD, and clinical AL values in the CPs and CPns groups were substantially greater than those in the CHns and CHs groups. The CPs group had considerably greater baseline salivary levels of 8-OHdG than others. CP group showed improvement by the third-month recall interval; however, the CPs still had a greater level of 8-OHdG values than the CPns.	According to this study for detecting periodontal tissue degradation the salivary 8-OHdG levels might be recognized as an oxidative biomarker, which reveals an ongoing periodontal destructive condition in smokers.
Wychowanski P et al., 2021 [28]	Case series	2012–2015	Bone	164	In the maxilla, immediate implants were placed. Implants were placed in the palatal alveolus in the posterior area. Insertion Torque Value (ITV) and two types of equipment were used to assess implant stability: Periotest (PT) and Osstell (ISQ). Cone beam computed tomography images were used to assess minor bone loss.	Smokers had greater PT values at 6 months post-implantation in an aesthetic region compared to those of nonsmokers. At six months after implantation, smokers’ ISQ scores were considerably lower than nonsmokers’ scores. Smokers had greater PT values in the posterior area than nonsmokers on the day of implantation, 6 months after surgery, and 24 months after surgery. On the day of implantation, as well as 6 months later, smokers had lower ISQ levels than nonsmokers. In the aesthetic and posterior areas, smokers had lower ITV measures than nonsmokers.	According to this study, smoking has a deleterious impact on the durability of immediate implants in the maxilla.

Methodology, outcomes, and conclusion of articles included in the current study.

2.3. Quality Assessment of Research Articles

All of the articles were shortlisted and screened based on the inclusion and exclusion criteria, titles, and abstract. Full texts were read one by one after the screening process and assessed for the quality of material using the CHPPHF recommendations. CHPPHF assessed articles for internal and external validity and rated the criteria for allocation biases, selection biases, intervention integrity, blinding, withdrawals and dropouts, confounding, data collection methods, and statistical analysis. No statistical assessment of publishing bias was carried out for the included studies as there were limited experimental techniques. A total of eight RCTs were included in the present systematic review.

Bias assessment was conducted according to the Cochrane tool of bias risk assessment. Overall, four included RCTs were at higher risk of bias, four were at lower risk of bias, and many items according to Cochrane tool of bias risk assessment were unclear in eight included RCTs. Selection bias was observed in two of the eight included RCTs, as was performance bias in two studies, detection bias in one study, attrition bias in one study, reporting bias in two studies, and other concerns in one study (Figure 34).

Figure 34. Risk of bias summary: review authors judgment about each risk of bias item for each included RCT.