This study aims to investigate the effect of periodontal treatment on olfactory function in patients with periodontitis by comparing pre- and post-treatment periodontal indices, Winkel tongue coating scores, and Sniffin' Sticks TDI components.

Periodontitis is a multifactorial chronic inflammatory disease caused by dental plaque, characterized by connective tissue destruction, periodontal pocket formation, and alveolar bone loss. Pathogenic bacteria associated with periodontitis and the host inflammatory response contribute not only to periodontal tissue breakdown but also to oral malodor (halitosis) and disruption of the oral microbiota. Progressive periodontal inflammation promotes the formation of a dense biofilm on the dorsum of the tongue, containing bacterial products, keratinized epithelium, and protein residues. This leads to increased tongue coating, which serves as a primary source of volatile sulfur compounds (VSCs) strongly associated with halitosis.

The Winkel Tongue Coating Index (WTCI) is commonly used to assess tongue coating and is an important clinical indicator for both halitosis and periodontal status. The bacterial load on the tongue also acts as a reservoir, contributing to dysbiosis of the oral microbiota in periodontitis patients.

Recent studies have also highlighted a potential relationship between periodontitis and olfactory function. Proinflammatory cytokines released during periodontal inflammation, such as IL-1β, TNF-α, and IL-6, may negatively affect the olfactory epithelium, leading to impaired odor threshold, discrimination, and identification abilities. Olfactory function is commonly evaluated using the Sniffin' Sticks test, which includes three subtests: odor threshold, odor discrimination, and odor identification. The sum of these tests, known as the TDI score, reflects overall olfactory capacity.

Previous studies have shown that periodontal treatment can improve tongue coating and halitosis. However, studies simultaneously evaluating pre- and post-treatment tongue coating indices, periodontal indices, and olfactory function (TDI scores) are limited. The aim of this study is to compare these parameters before and after periodontal treatment in patients with periodontitis and to investigate the effect of periodontal therapy on olfactory function.

This study was approved by the Batman University Interventional Clinical Research Ethics Committee (Approval No: 2024/08-04). All procedures and data collection were conducted in accordance with the Declaration of Helsinki, and all participants provided written informed consent.

Participant Selection and Exclusion Criteria

A total of 108 non-smoking volunteers with periodontitis were included. Inclusion required the presence of at least two teeth with probing pocket depth (PPD) ≥ 5 mm and alveolar bone loss visible on full-mouth radiographs. Exclusion criteria were: current smokers, participants who received periodontal treatment in the last 6 months, pregnant or breastfeeding women, individuals who had received antibiotics in the last 3 months, or those with systemic conditions potentially affecting olfactory function.

Radiographic Periodontal Assessment

Full-mouth orthopantomographic radiographs were obtained to confirm the periodontal diagnosis and assess alveolar bone status for all participants.

Olfactory Function Assessment

Before periodontal treatment (Phase 1), olfactory function was objectively evaluated in all 108 participants using the Sniffin' Sticks test (Burghart Messtechnik, Holm, Germany). This psychophysical test assesses odor threshold, odor discrimination, and odor identification, each scored on a scale from 0 to 16. The sum of these subtests provided the TDI score, reflecting overall olfactory capacity. A second assessment was performed 3 days after the final periodontal treatment session.

Periodontal Measurements

Clinical periodontal parameters-including Plaque Index (PI), Gingival Bleeding Index (GBI), Probing Pocket Depth (PPD), and Clinical Attachment Loss (CAL)-were recorded for all teeth except third molars using a Williams periodontal probe (Hu-Friedy, Chicago, IL, USA). Four sites per tooth (mesial, distal, buccal, lingual) were measured. All measurements were performed by a calibrated periodontist (GGT), and post-treatment measurements were repeated 3 days after the final session. Intra-examiner reliability was assessed using the weighted Kappa test, yielding satisfactory values (e.g., 0.82 for PPD).

Tongue Coating Assessment

Digital photographs of the tongue dorsum were taken at a standardized distance of 60 cm, ensuring patient privacy. Images were analyzed at 1680 × 1050 pixels resolution using Adobe Photoshop. The Winkel Tongue Coating Index (WTCI) was applied, dividing the dorsum into six areas (three anterior, three posterior). Each region was scored as: 0.5 - no coating, 1.5 - mild coating, 2.5 - severe coating. Scores from all six areas were summed (range 0-12) to obtain the final tongue coating score. Two calibrated observers (GGT, VE) independently scored all images, and the average was used as the final score for each participant. Inter-rater reliability and reproducibility were confirmed.

Inclusion Criteria:

1. Adults with a clinical diagnosis of periodontitis
2. At least two teeth with probing pocket depth (PPD) ≥ 5 mm
3. Alveolar bone loss visible on full-mouth radiographs
4. Non-smokers
5. Ability to provide written informed consent

Exclusion Criteria:

1. Current smokers
2. Periodontal treatment within the past 6 months
3. Pregnancy or breastfeeding
4. Antibiotic use within the past 3 months
5. Systemic diseases or conditions known to affect olfactory function

Individual participant data (IPD) from this study will not be shared due to ethical and privacy considerations, including protection of participant confidentiality and informed consent restrictions.

No parties are masked in this study; it is an open-label trial.