Smoking Cessation and Outcome of Non‐Surgical Periodontal Therapy: A Retrospective Analysis

ABSTRACT

Objective

The aim of this retrospective analysis was to investigate how smoking cessation impacts the results of non‐surgical periodontal therapy in patients diagnosed with periodontitis. Additionally, the analysis sought to determine the percentage of patients who quit smoking after receiving cessation counselling before undergoing non‐surgical periodontal therapy.

Materials and Method

This retrospective analysis looked into potential links between smoking cessation and treatment outcomes, as well as the impact of gender and age. For the analysis, data from the periodontal charts of smoking patients who were referred to the Clinic for Periodontology Utrecht for moderate to severe periodontitis between 2019 and 2022 were utilised. Demographic and clinical information was collected from both intake and evaluation appointments, and the percentage of patients who stopped smoking was assessed. For each patient, the total number of teeth (excluding implants), the percentage of teeth and sites with a pocket probing depth (PPD) > 5 mm, and the percentage of sites with bleeding upon probing (BOP) were identified.

Results

The current retrospective analysis included a total of 143 patients, out of which 24 patients (17%) quit smoking after receiving cessation counselling before non‐surgical periodontal therapy. However, no significant difference was observed for percentage teeth and sites with PPD > 5 mm and percentage BOP between patients who quit smoking and those who continued smoking at the evaluation stage. This indicates that smoking cessation did not significantly impact the outcome of non‐surgical periodontal therapy. Sub‐analysis showed no relation between age and the effect of smoking cessation on the results of non‐surgical periodontal therapy. However, for patients over the age of 50, the number of teeth at evaluation was lower than those ≤ 50 years (24.7 vs. 26.5, respectively, p < 0.001). Sub‐analysis on gender showed that male quitters had a significantly lower number of pack‐years than those who continued smoking (10.4 vs. 20.4, respectively, p = 0.04). Comparison of males and females showed no significant differences.

Conclusion

In this retrospective analysis, overall, no significant effect of smoking cessation on the outcome of non‐surgical periodontal therapy at the evaluation appointment has been found. Sub‐analysis showed that neither age nor gender had a significant effect on the results of non‐surgical periodontal therapy. For male gender, the number of pack‐years seems to impact on the intention to quit smoking.

1. Introduction

Tobacco smoking, both in general and specifically smoking products, is a well known preventable risk factor in the initiation and progression of periodontal diseases, as it increases periodontal bone loss and impairs periodontal healing, as evidenced by epidemiological studies [1]. Smoking is associated with a higher incidence and progression of periodontitis [2]. Cigarette smokers were found to have a statistically significant higher risk of severe periodontitis than non‐tobacco users [3]. Long‐term supportive periodontal treatment in smokers is also associated with deeper periodontal pockets and higher bleeding on probing scores than non‐smokers [4, 5, 6]. Furthermore, smokers have a higher risk of recurrence of periodontitis, which decreases significantly after smoking cessation [7]. A significant dose–response relationship was observed between to the number of cigarettes consumed and the effect of non‐surgical periodontal therapy [8] as well as between pack‐years of smoking and the recurrence of periodontitis [7]. Additionally, a substantial decrease in the risk of recurrence was evident as the duration of smoking cessation increased [7].

The exact mechanisms through which smoking negatively impacts the immune‐inflammatory system and the reparative healing response in periodontal disease remain unclear. However, in vitro studies suggest that compounds found in tobacco smoke have deleterious effects on various oral cells, including epithelial cells, immune cells, bone cells, gingival cells and periodontal ligament fibroblasts [9]. Histo‐pathologically, smokers showed a decreased blood vessel density and inflammatory cells [10, 11]. Heavy smokers presented significantly lower levels of gingival inflammation, as reflected by both GI and GBI, than both light and moderate smokers, despite their having increased amounts of plaque and calculus [12].

Additionally, smoking promotes the destruction of connective tissue and bone through a proinflammatory stimulus [2, 13]. Smokers exhibit dysbiosis of the periodontal microflora irrespective of periodontal condition and remain significant only in smokers even after the reduction of clinical signs of periodontitis with non‐surgical periodontal treatment [14]. Following periodontal therapy, the microbial response of former smokers is comparable to that of nonsmokers; therefore, smoking cessation may restore the normal periodontal healing response and be beneficial for promoting a health‐compatible subgingival microbial community [14, 15].

As smoking is a major risk factor for poor response to initial treatment, the importance of smoking cessation in periodontal therapy is emphasised [16]. Quitting smoking cannot undo the previous effects of smoking, but the rate at which bone and attachment loss occurs decreases once patients stop smoking [17, 18]. Few studies have evaluated the effect of smoking cessation on the outcome of periodontal therapy [19]. However, smoking cessation has been found to lead to favourable alterations in the subgingival microbiome, increases the host's immune‐inflammatory response and promotes periodontal healing [2, 14, 20]. Smoking cessation also has a positive influence on periodontitis occurrence, periodontal healing and the risk of tooth loss, particularly after 10–20 years [19, 21, 22, 23].

Combining smoking cessation with non‐surgical periodontal therapy appears to have a positive effect on the outcome of periodontitis treatment, particularly for younger and older adults [21]. However, conclusive evidence on the effect of smoking cessation on the outcome of non‐surgical periodontal therapy is limited due to small sample sizes, high loss to follow‐up, short follow‐up periods and low rates of smoking cessation [22, 24, 25, 26]. Therefore, in this retrospective analysis, the aim was to evaluate the effect of smoking cessation on the outcome of non‐surgical periodontal therapy in patients referred for periodontitis, as well as to assess the percentage of patients who successfully quit smoking after cessation counselling prior to non‐surgical periodontal therapy.

2. Materials and Method

The analysis presented adheres to the STROBE and RECORD guidelines, which outline the essential elements to include in observational studies and those using routinely collected observational data [27, 28]. The data for this retrospective analysis were obtained from digital treatment records of patients at the Clinic for Periodontology Utrecht, The Netherlands, which exclusively deals with patients with periodontitis. Before their first visit to the Clinic for Periodontology Utrecht, each new patient was asked for consent to use their anonymised clinical data for retrospective analysis. The Institutional Review Board of the Academic Centre for Dentistry Amsterdam (ACTA) approved this retrospective analysis under number 2021‐65719.

2.1. Population

Data on demographics and clinical characteristics were gathered from patients with moderate to severe periodontitis who were smokers at the time of their intake appointment at the Clinic for Periodontology Utrecht in 2019 and 2020. Every patient who reported smoking at the time they made their appointment was given a brochure outlining the unfavourable effects of smoking on oral health as distributed by the Dutch Society of Periodontology (NVvP) (https://www.nvvp.org/diensten/webshop/folders/18836). This was sent to them by mail before their intake appointment.

2.2. Clinical Parameters

Patient treatment records were used to obtain clinical data from the intake appointment and the evaluation following non‐surgical periodontal therapy. The clinical periodontal assessment was described in detail by Van der Weijden et al. (2019) [5]. In short, at the intake appointment, patients completed a medical history questionnaire, which was reviewed and discussed. A full‐mouth periodontal chart was used to collect clinical parameters, including periodontal pocket depth (PPD), bleeding on probing (BOP) and furcation involvement. PPD and BOP were recorded at six sites around each tooth, namely mesio‐buccal, buccal, disto‐buccal, mesio‐lingual, lingual and disto‐lingual, with measurements being rounded off to the nearest millimetre marking.

2.3. Procedure

At the intake appointment, patients who smoked were urged to quit smoking using motivational interviewing methods, which were reinforced at subsequent visits. The non‐surgical periodontal therapy began after the intake appointment and was conducted by dental hygienists, consisting of two to four sessions of professional scaling and root planing with professional oral hygiene instructions. Based on individual patient needs, the treating periodontist could prescribe a combination of systemic amoxicillin (375 mg) and metronidazole (250 mg) three times a day for seven consecutive days as a supplement to non‐surgical periodontal therapy. An interim assessment was performed about 6 weeks after the last non‐surgical periodontal therapy session, followed by an evaluation of the non‐surgical periodontal therapy 3 months later by the same periodontist. PPD, BOP and furcation involvement were assessed again as described above. At this appointment, patients were asked if they had successfully quit smoking during or after the periodontal therapy.

2.4. Data Extraction and Statistical Analysis

The electronic patient records were used to extract data on various clinical parameters of periodontal patients at the intake appointment and the evaluation appointment following non‐surgical periodontal therapy. These parameters included the total number of teeth (excluding implants), mean percentage of sites with BOP, mean percentage of teeth and sites with PPD > 5 mm (along with their standard deviations) [5, 29]. Additionally, the patient's gender, age at intake and the time between the intake and evaluation appointments were noted. A custom‐designed data extraction form was used to collect patient data, and before analysis, all identifiable information was removed to ensure anonymity. Mean values, percentages and standard deviation values were calculated in Microsoft Excel, and the statistical analysis was performed using R software [30] and Jamovi software [31]. Differences in change scores between smokers and quitters were tested using Wilcoxon rank‐sum tests. Rank‐biserial correlations were calculated, which provide a transparent approach to presenting the observed trends without overinterpreting non‐significant results [32], where values of 0.1, 0.3, and 0.5 are commonly interpreted as small, medium and large effects, respectively [33, 34]. A sub‐analysis was conducted on the variables of gender and age, and a retrospective power analysis was performed to calculate the statistical power and the required sample size. p values of ≤ 0.05 were considered as statistically significant.

3. Results

During the period of January 2019 to December 2022, a total of 274 patients who were smokers and had periodontitis attended an intake appointment at the Clinic for Periodontology. After excluding 131 patients for the reasons outlined in Table 1, the treatment records of 143 patients were deemed suitable for inclusion in this retrospective analysis.

TABLE 1.

Number of included and excluded patients and the reasons for exclusion.

Study population	Number
Periodontitis patients who were smokers at intake between January 2019 and December 2020	274
Excluded patients	131
Reasons for exclusion
Patients with no pockets deeper than 5 mm	77
Patients with an intake appointment for a retreatment	11
Patients who discontinued non‐surgical periodontal therapy	5
Patients who did not return for follow‐up treatment after the intake appointment	24
Patients smoking e‐cigarettes.	3
Patients with no information about smoking years and or the number of cigarettes	11
Included patients	143

Of the 143 periodontitis patients who were included in this retrospective analysis, 67 (47%) were male and 76 (53%) were female. The average age of the participants during the intake appointment was 49, ranging from 20 to 70 years. Among the patients, 119 (83%) continued smoking after the intake appointment, while 24 (17%) reported quitting smoking before undergoing non‐surgical periodontal therapy. The average period between the intake and evaluation appointments was 8.8 (SD = 2.8) months. The mean number of pack‐years was 17 (SD = 13.6). Figure 1 shows a Violin Plot depicting the distribution of pack years per smoking status, which was not statistically different (Table 2).

FIGURE 1.

Violin Plot showing pack years per smoking status (0 = quitter, 1 = continued smoker).

TABLE 2.

Demographics at the intake appointment (n = 143).

Characteristics
Included patients	143
Gender
Male (%)	67 (47%)
Female (%)	76 (53%)
Age (years)
Mean (SD)	49.0 (10.8)
Smoking status at follow‐up
Smokers (%)	119 (83%)
Quitters (%)	24 (17%)
Mean number of months from intake to evaluation	8.8 (2.8)
Pack‐years	17.0 (13.6)

3.1. Overall Analysis

At intake, no significant differences were found between smokers that were continuing smoking and those that were going to quit. There was a statistically significant, albeit weak, association between the cumulative exposure to smoking (measured in pack‐years) and the percentage of teeth and sites with PPD > 5 mm at evaluation (r = 0.19).

At the evaluation appointment, both smokers and quitters showed a significant reduction in the various clinical parameters compared to the intake (baseline) (p < 0.001), as shown in Table 3. Although quitters had numerically lower clinical outcomes than smokers in mean percentage of teeth with PPD > 5 mm and mean percentage of sites with a PPD greater than 5 mm, there was no significant difference found between quitters and smokers in any of these clinical parameters at the evaluation (Table 3).

TABLE 3.

Baseline and evaluation data of continued smokers (n = 119) and quitters (n = 24) in relation to the mean (SD) of various clinical parameters.

	Smokers at baseline (intake) (n = 119)	Quitters at baseline (intake) (n = 24)	p value baseline	Smokers at evaluation (n = 119)	Quitters at evaluation (n = 24)	p value smokers vs. quitters at evaluation	Effect size
Mean number of teeth (SD)	26.3 (2.9)	27.0 (1.9)	0.40 a	25.5 (3.4)	26.1 (2.2)	0.76 a	0.011 b
Mean percentage of BOP (SD)	65% (19)	61% (23)	0.64 a	22% (15)	24% (15)	0.32 a	0.152 b
Mean percentage of teeth with PPD > 5 mm (SD)	48% (24)	41% (27)	0.09 a	16% (16)	11% (13)	0.09 a	0.092 b
Mean percentage of sites with PPD > 5 mm (SD)	20% (14)	18% (16)	0.26 a	5% (5)	3% (4)	0.14 a	0.08 b
Pack‐years	17.5 (13.7)	14.3 (13.3)	0.19 a

Note: Results from the Wilcoxon Signed‐Rank Test showed significant differences between baseline and evaluation for both smokers and quitters across all measures. Specifically, comparisons for the number of teeth for quitters yielded a significance level of p < 0.008, while all other measures were significant at p < 0.001.

^a Mann–Whitney U test.

^b Rank‐Biserial correlation.

3.2. Sub‐Analysis by Gender

Figure 2 shows the number of smokers separated by gender at intake and those that quit or remained smoking at evaluation.

FIGURE 2.

Change in smoking status after intake separated by gender.

To examine any gender‐related differences between smokers and quitters, a sub‐analysis was carried out on male participants who were either smokers (n = 58) or quitters (n = 9) at the evaluation appointment. The results showed that male quitters had a significantly lower number of pack‐years than male smokers at the evaluation (10.4 vs. 20.4 respectively, p = 0.04) (Table 4).

TABLE 4.

Analysis of various clinical parameters by gender (male, n = 67) at evaluation.

	Male smokers at baseline (intake) (n = 58)	Male quitters at baseline (intake) (n = 9)	Male smokers at evaluation (n = 58)	Male quitters at evaluation (n = 9)	p value male smokers vs. male quitters at evaluation	Effect size
Mean number of teeth (SD)	26.2 (2.9)	27.2 (1.5)	25.5 (3.7)	25.8 (1.6)	0.80 a	0.154 b
Mean percentage of BOP (SD)	67% (20)	76% (20)	23% (14)	33% (18)	0.08 a	0.026 b
Mean percentage of teeth with PPD > 5 mm (SD)	50% (26)	50% (32)	18% (19)	11% (11)	0.33 a	0.049 b
Mean percentage of sites with PPD > 5 mm (SD)	20% (15)	23% (20)	5% (6)	3% (3)	0.31 a	0.044 b
Pack‐years	20.4 (15.9)	10.4 (8.4)	0.04 a

Note: The fact that they are presented as bold is that they are smaller or equal to 0.05 which is considered significant as stated in Material and Methods.

^a Mann–Whitney U test.

^b Rank‐Biserial correlation.

A sub‐analysis was conducted to determine if there were any differences between female smokers (n = 61) and female quitters (n = 15) at the evaluation stage. Although female quitters at evaluation showed numerically lower clinical outcomes for percentage BOP and mean percentage of teeth with PPD > 5 mm, no significant difference was found between female smokers and female quitters at evaluation (Table 5).

TABLE 5.

Analysis of various clinical parameters by gender (female, n = 76) at evaluation.

	Female smokers at baseline (intake) (n = 61)	Female quitters at baseline (intake) (n = 15)	Female smokers at evaluation (n = 61)	Female quitters at evaluation (n = 15)	p value female smokers vs. female quitters at evaluation	Effect size
Mean number of teeth (SD)	26.4 (2.9)	26.9 (2.1)	25.0 (3.0)	26.3 (2.6)	0.55 a	0.113 b
Mean percentage of BOP (SD)	64% (19)	52% (21)	20% (15)	19% (10)	0.73 a	0.236 a
Mean percentage of teeth with PPD > 5 mm (SD)	47% (23)	36% (22)	14% (12)	11% (15)	0.16 a	0.195 b
Mean percentage of sites with PPD > 5 mm (SD)	19% (12)	15% (12)	4% (4)	4% (5)	0.29 a	0.193 b
Pack‐years	14.8 (10.6)	16.7 (15.3)	0.97 a

^a Mann–Whitney U test.

^b Rank‐Biserial correlation.

A sub‐analysis was conducted to investigate whether there were any differences between male quitters at evaluation (n = 10) and female quitters at evaluation (n = 13). There was no significant difference found between male quitters at evaluation and female quitters at evaluation with for any of the clinical parameters, with the exception of those males and females that continued smoking with respect to the percentage of BOP (23% vs. 20% respectively) (Table 6).

TABLE 6.

Analysis of various clinical parameters between male (n = 67) and female (n = 76) at evaluation.

	Male smokers at evaluation (n = 58)	Female smokers at evaluation (n = 61)	p value a male vs. female smoker at evaluation	Male quitters at evaluation (n = 9)	Female quitters at evaluation (n = 15)	p value a male quitters vs. female quitters at evaluation
Mean number of teeth (SD)	25.5 (3.7)	25.4 (3.3)	0.83 a	25.8 (1.6)	26.3 (2.6)	0.58 a
Mean percentage of BOP (SD)	23% (14)	20% (15)	0.05 a	33% (18)	20% (10)	0.07 a
Mean percentage of teeth with PPD > 5 mm (SD)	18% (19)	14% (12)	0.31 a	11% (11)	11.4 (14.7)	0.46 a
Mean percentage of sites with PPD > 5 mm (SD)	5% (6)	4% (4)	0.51 a	3% (3)	4% (5)	0.57 a
Pack‐years	20.4 (15.9)	14.8 (10.6)	0.07 a	10.4 (8.4)	16.7 (15.3)	0.46 a

Note: The fact that they are presented as bold is that they are smaller or equal to 0.05 which is considered significant as stated in Material and Methods.

^a Mann–Whitney U test.

3.3. Sub‐Analysis by Age

No significant association was observed between the age of smokers or quitters and the clinical outcome of non‐surgical periodontal therapy. A sub‐analysis based on age was conducted using a cut off point of 50 years, which is the median age of the population in this retrospective analysis. The aim was to compare the clinical parameters of patients who were 50 years or younger at evaluation (n = 72) and those who were 51 years or older at evaluation (n = 71). No significant difference was observed between the two groups in terms of any of the clinical parameters PPD and BOP (Table 7). However, for patients over the age of 50, the number of teeth at evaluation was lower than those ≤ 50 years (24.7 vs. 26.5 respectively, p < 0.001). Also, the number of pack‐years (22.0 vs. 12.1 respectively, p < 0.001).

TABLE 7.

Analysis of various clinical parameters by age at evaluation.

	Patients ≤ 50 years at evaluation (n = 72)	Patients > 50 years at evaluation (n = 71)	p value patients ≤ 50 years vs. patients > 50 years at evaluation
Mean number of teeth (SD)	26.5 (3.0)	24.7 (3.4)	< 0.001 a
Mean percentage of BOP (SD)	24% (17)	20% (12)	0.32 a
Mean percentage of teeth with PPD > 5 mm (SD)	15% (15)	15% (16)	0.92 a
Mean percentage of sites with PPD > 5 mm (SD)	4% (5)	4% (6)	0.96 a
Pack‐years	12.1 (8.5)	22.0 (15.9)	< 0.001 a

Note: The fact that they are presented as bold is that they are smaller or equal to 0.05 which is considered significant as stated in Material and Methods.

^a Mann–Whitney U test.

3.4. Mixed‐Effects Regression Models Analysis

To account for the longitudinal nature of the data and relevant confounders, such as age, gender and diabetes, mixed‐effects regression model analysis was performed, including parameters BOP, % teeth and % sites with PPD > 5 mm, number of teeth and the time lapse between intake and evaluation. The outcome showed that smoking cessation did not significantly influence periodontal outcomes in our cohort compared to continued smoking.

3.5. ‘Post Hoc’ Statistical Power Analysis

A statistical power analysis was conducted retrospectively using the pwr package [33, 34] in R.

The findings from the analysis revealed an achieved power of 0.1 [31]. Therefore, additionally, Rank‐biserial correlations were calculated as non‐parametric effect sizes to quantify group differences. Table 3 shows that overall, the highest rank‐biserial correlation was 0.152 for bleeding scores, indicating a negligible to small effect size in favour of the quitters.

4. Discussion

The purpose of this retrospective analysis was to assess how smoking cessation affects the outcome of non‐surgical periodontal therapy in patients referred for periodontitis, as well as to analyse the effects of gender and age. A total of 17% of patients included in the analysis quit smoking after cessation counselling prior to therapy. Both quitters and smokers at evaluation showed a significant decrease in all clinical parameters compared to intake values. Overall, no significant association was found between smoking cessation and the clinical outcome of non‐surgical periodontal therapy in this analysis.

4.1. Smoking Cessation

A recent study by reported successful quit rates of 37.2%, 12.8% and 11.4% after 30‐day, 6‐month and 1‐year follow‐ups, respectively, for participants who were ready to quit after 1 year of counselling [35]. Participants who were ambivalent about quitting received an additional 4 weeks of motivational interviewing prior to the 1 year of counselling and subsequently demonstrated successful quit rates of 33.7%, 15.2% and 11.2% after a 30‐day, 6‐month and 1‐year follow‐up, respectively. The study suggests that motivational interviewing may be more effective in smoking cessation than counselling alone. The quit rates for smokers with chronic periodontitis who received cessation counselling prior to non‐surgical periodontal therapy were investigated [36]. The study found that 41%, 33%, 29% and 25% of the participating patients quit smoking after 1 month, 3 months, 6 months and 12 months, respectively. In the present analysis, approximately 9 months after intake, 24 (17%) out of 143 participants self‐reported quitting smoking after cessation counselling prior to non‐surgical periodontal therapy, which appears to be relatively in line with the above‐mentioned studies. The information was based on self‐reporting and limited to whether the smoking patient had quit in the context of their periodontal treatment. Many patients who attempt to quit smoking will relapse, which is the reason why generally many attempts are required to quit smoking. Relapse is a natural part of the quitting process [37]. The rate of relapse for quitters is highest within the first year after quitting, ranging from 54% to 67% [38]. Considering the average period of 8.8 months between intake and evaluation in the present retrospective analysis, relapse in the population of quitters may, in the future, also be expected.

4.2. There Is a Role for the Dental Care Professional

To assess the risk of disease progression and anticipate the effectiveness of periodontal therapy, dental care professionals ought to inquire about their patients' smoking habits. They play a vital role in enhancing the oral and systemic well‐being of smokers by offering tailored and effective tobacco‐cessation counselling [19, 39, 40]. They should also educate patients about the possibility of experiencing temporary increases in gingival bleeding and pocket depth when they quit smoking. By providing this advice, dentists can help alleviate any concerns that might lead patients to resume smoking [41].

The success rates of smoking cessation, when smoking cessation advice was included as part of periodontal treatment, exceeded national quit rates achieved in specialised smoking cessation clinics [36]. This highlights the potential importance of smoking cessation support provided by dental professionals in improving both periodontal health and the outcome of periodontal treatment [42]. While many dentists hold positive attitudes towards encouraging patients to quit smoking, not all stakeholders share the belief that the dental team should actively engage in delivering smoking cessation interventions. Factors such as time constraints, reimbursement issues, the need for additional training and poor coordination between dental and smoking cessation services contribute to the reasons why some dentists do not provide smoking cessation support [43, 44].

To address these concerns and provide guidance, Davis et al. (2014) published Guidelines for Motivating and Assisting Patients With Smoking Cessation in Dental Settings [45]. These guidelines outline the characteristics of patients and factors that contribute to successful smoking cessation, offering practical examples and information that can be utilised in the dental office to assist patients in their journey to quit smoking. To offer well informed patient recommendations, dental professionals must possess a comprehensive understanding of the overall health and oral implications linked to a diverse array of tobacco and nicotine products [46].

Findings from the study conducted by Lung et al. (2005) illustrate the limited understanding among patients regarding the association between smoking and periodontal diseases [47]. The results indicate that a mere 6% of respondents were aware of the connection between tobacco use and periodontal diseases. Periodontitis is one of the first signs of smoking and, as such, provides a unique opportunity to identify smokers who are particularly susceptible to the consequences of smoking [48]. Smoking status represents a key parameter to assess the periodontal risk of an individual subject and therefore to make evidence‐based clinical decisions [17]. Dental care professionals are in an advantageous position to assess the smoking status of their young patients and play a significant role in delivering smoking cessation advice, particularly in relation to periodontal health. By doing so, the dental profession can contribute significantly to the overall health and well‐being of young individuals and future generations [49, 50, 51].

4.3. Clinical Parameters

The clinical parameters of periodontitis in smokers and quitters were significantly improved at evaluation compared to intake values. This confirms previous findings that non‐surgical periodontal therapy has a positive impact on these parameters [52, 53, 54]. However, smoking has been associated with a reduced response to non‐surgical periodontal therapy, as indicated by smaller reductions in pocket depth in smokers compared to non‐smokers [55]. While a recent study found that smokers had less clinical attachment level gain than non‐smokers following non‐surgical periodontal therapy, the effect of smoking on clinical outcomes was modest [56].

Evidence regarding the additional benefit of antibiotic therapy in smokers with chronic periodontitis is insufficient and inconclusive [57]. One study showed that individuals who smoke exhibit a diminished response to SRP treatment, irrespective of whether systemic or locally administered adjunctive metronidazole is utilised [58].

While some studies have reported a negative effect of smoking on the clinical outcome of non‐surgical periodontal therapy, others have not found such an effect [59, 60, 61]. Smoking cessation has been shown to have a positive effect on the clinical outcome of periodontal therapy [7, 23, 62]. In the present retrospective analysis, overall no significant difference was found in clinical parameters between smokers and quitters. However, it is possible that the follow‐up period after smoking cessation in this analysis was too short to observe the full beneficial effect of quitting. Previous studies have suggested that a follow‐up period of at least 12 to 24 months is necessary to observe the effect of smoking cessation on clinical parameters [7, 22]. While these long‐term positive impacts of smoking cessation on oral health are widely recognised, it should be noted that short‐term smoking cessation can result in temporary increases in pocket probing depth and gingival bleeding [41]. In former smokers, the risk of tooth loss attributed to periodontitis was found to be comparable to that of never smokers [63]. However, a retrospective analysis revealed that it took nearly 15 years of smoking cessation for the risk among former smokers to equal that of individuals who had never smoked [64].

4.4. Gender

In this analysis of periodontitis patients, 53% were female and 47% were male. The literature does not provide a clear indication of whether gender is significantly associated with periodontitis. Some studies suggest that females are more prone to periodontal disease than males, while others found no significant correlation between gender and the disease [65, 66]. One study on the effectiveness of non‐surgical periodontal therapy in a large Chinese population with chronic periodontitis reported that males had a significantly higher reduction in pocket depth than females [67]. However, few studies have investigated the relationship between gender and smoking cessation [68, 69]. One study observed that male gender, lower carbon monoxide levels at baseline, no coexistence with another smoker, and lower cigarette dependence were associated with a 24‐month smoking abstinence, while another study found that females had fewer sites with a pocket depth reduction of more than 1 mm than males [25, 70]. In the present patient population, there was no significant difference in any of the clinical parameters at the evaluation between male and female quitters. Sub‐analysis of male quitters only showed that they had a significantly lower number of pack‐years than male smokers at the evaluation.

4.5. Age

In the retrospective analysis conducted, no significant association was observed between the age of smokers or quitters and the clinical outcome of non‐surgical periodontal therapy. For patients over the age of 50, the number of teeth at evaluation was lower than those ≤ 50 years (24.7 vs. 26.5 respectively, see Table 7). An obvious finding was the difference in the number of pack‐years (22.0 vs. 12.1 respectively, p < 0.001). There have been limited studies that have explored the correlation between patient age and the effectiveness of periodontal treatment, and these have suggested that age does not influence the outcome of non‐surgical periodontal therapy [71, 72]. Moreover, it has been proposed that periodontal disease is not necessarily a consequence of the aging process [69]. Although a few studies have examined the relationship between smoking cessation and the clinical outcome of non‐surgical periodontal therapy, none have focused on the interplay between age and the effectiveness of non‐surgical periodontal therapy after smoking cessation. Future research in this area may consider investigating these factors.

4.6. Limitations

A potential limitation of our study is the reliance on self‐reported smoking status, and it was not verified through clinical examination. This may be subject to recall bias and social desirability bias, potentially leading to underestimation of smoking exposure.

Furthermore, we could not stratify participants based on smoking intensity, which may have diluted the potential impact of heavy smoking on treatment outcomes. Future studies incorporating biochemical validation methods, such as cotinine measurements, and distinguishing between light and heavy smokers could provide a more precise assessment of smoking's influence on periodontal therapy.

Another limitation of our study is the variability in follow‐up time after non‐surgical therapy, which was accounted for as a continuous covariate in our mixed‐effects models. However, differences in follow‐up duration may still introduce bias, potentially diluting the observed effects of smoking cessation. This variability makes it challenging to fully capture long‐term changes that may only become evident after a prolonged cessation period. Future studies with standardised follow‐up intervals could provide a clearer understanding of the temporal effects of smoking cessation on periodontal outcomes. Also, the duration of the smoking cessation period was not determined in this retrospective analysis, and it is likely to have varied among patients.

The retrospective analysis encompassed a cohort of 143 patients, and subsequent power analysis revealed an increased susceptibility to Type II errors. The limited statistical power implies that interpretations of non‐significant findings should be approached with caution, as the study may lack the capability to detect subtle effects. Consequently, future investigations should prioritise larger sample sizes to enhance statistical power and provide more robust insights.

4.7. Future Research

To minimise potential bias in future studies investigating the effect of smoking cessation on the outcome of non‐surgical periodontal therapy, objective methods for assessing smoking exposure, such as carbon monoxide and salivary nicotine metabolite measurements, should be used instead of self‐reported patient information. It is also recommended that future studies include patients who have abstained from smoking for at least 12 months and that follow‐up evaluations occur to at least 24 months after smoking cessation, as these follow‐up periods have shown significant differences between smokers and quitters in previous studies [22, 23]. Since gender and age have been minimally studied in relation to the effect of smoking cessation on non‐surgical periodontal therapy outcomes, further research on this topic is necessary to identify any potential associations.

5. Conclusion

In this retrospective analysis, overall, no significant effect of smoking cessation on the outcome of non‐surgical periodontal therapy at the evaluation appointment has been found. Furthermore, sub‐analysis showed that age had no significant effect on the results of non‐surgical periodontal therapy. For male gender, the number of pack‐years seems to impact on the intention to quit smoking.

Author Contributions

All authors gave their final approval and agreed to be held accountable for all aspects of the work, ensuring integrity and accuracy. Van der Weijden: contributed to conception and design, analysis and interpretation and drafted the manuscript. Valkenburg: contributed to analysis, interpretation and critically revised the manuscript.

Conflicts of Interest

The authors declare that they have no conflicts of interest. Van der Weijden formerly held a minority interest in the Clinic for Periodontology Utrecht in the Netherlands.

Data Availability Statement

The data that support the findings of this study are available from the corresponding author upon reasonable request.