Impact of 2D:4D Ratio on Oral Hygiene and Gingival Health

NCT07147998 | Completed

• 1 other identifier: 2023/165-01
• Study Type: observational
• Target: 126
• Locations: 1 country
• Sites: 1

Brief Summary

The second-to-fourth digit ratio (2D:4D)-the ratio of the length of the index finger to that of the ring finger-has gained increasing attention as a non-invasive, stable biomarker of prenatal sex hormone exposure. The 2D:4D ratio is believed to reflect the balance of prenatal androgens (especially testosterone) and estrogens. Lower ratios (more masculinized) indicate higher prenatal testosterone exposure, whereas higher ratios (more feminized) are associated with lower testosterone and higher estrogen levels. Research has linked variations in 2D:4D to a broad spectrum of behavioral traits, cognitive abilities, and health outcomes. 2D:4D has been shown to have strong associations with motor performance, especially skills that require fine motor coordination. However, while many studies have examined the role of 2D:4D in sports and cognition, its relationship to health-related behaviors involving motor skills remains underexplored. One such domain is oral hygiene, which requires sustained fine motor coordination-particularly in actions like tooth brushing and flossing. Despite the clear motor demands of such behaviors, the potential connection between 2D:4D and oral hygiene has not yet been systematically investigated. This study aims to fill this gap by exploring the association between the 2D:4D digit ratio and oral hygiene practices.

Conditions

Oral Hygiene; Gingivitis

Outcome Measures

Primary Outcomes (2)

• Mean Quigley-Hein Plaque Index Score (Turesky Modification)

  Dental plaque will be scored on buccal and lingual surfaces of all teeth except third molars using the Turesky Modification of the Quigley-Hein Plaque Index (scale 0-5; 0 = no plaque, 5 = plaque covering ≥ two-thirds of crown). Scores per tooth will be averaged per participant.

  Baseline (Day 0) and 1 week after oral hygiene instruction.

• Mean Löe-Silness Gingival Index Score

  Gingival inflammation will be assessed on buccal and lingual surfaces at mesial, mid-buccal, and distal sites using the Löe-Silness Gingival Index (scale 0-3; 0 = healthy, 3 = severe inflammation with spontaneous bleeding). Scores will be averaged per participant.

  Baseline (Day 0) and 1 week after oral hygiene instruction.

Secondary Outcomes (2)

• Right-hand 2D:4D Digit Ratio

  Baseline (Day 0)

• Self-reported Tooth Brushing Frequency

  Baseline (Day 0)

Interventions

Oral hygiene instruction OTHER

Oral hygiene and gingival health of all patients were assessed using the Turesky Modification of the Quigley-Hein Plaque Index and the Gingival Index. Tooth brushing frequency was recorded. The 2D:4D ratio was calculated by dividing the second digit length by the fourth, with three measurements taken per finger to ensure reliability. A cut-off value of 1 was used to evaluate prenatal androgen influence, and participants were grouped by 2D:4D ratio (≥1 or \<1). All participants received standardized oral hygiene instructions from the same instructor, including Modified Bass brushing and interdental cleaning. A second clinical exam was performed one week later by the same examiner, and both indices were re-scored.

Eligibility Criteria

• Age: 18 Years+
• Sex: all
• Healthy Volunteers: Yes
• Age Groups: Adult (18-64), Older Adult (65+)
• Sampling Method: Non-Probability Sample

Study Population

Adults over 18 years of age, systemically healthy, without psychological or neurological disorders, able to cooperate during examinations and procedures, university students or graduates, with at least 28 natural teeth, non-smokers, with no fixed orthodontic appliances or crown prostheses, no prior oral hygiene education from a dental professional, and a clinical diagnosis of gingivitis.

You may qualify if:

• Systemically healthy University graduates or currently enrolled in a university program Presence of 28 natural teeth No orthodontic appliances or crown restorations in the oral cavity Non-smokers No previous oral hygiene instruction from a dental professional Clinical diagnosis of gingivitis

You may not qualify if:

• Presence of any systemic disease or condition that may affect periodontal health Not a university graduate and not currently enrolled in a university program Fewer than 28 natural teeth Orthodontic appliances or crown restorations present in the oral cavity Current smokers Previous oral hygiene instruction from a dental professional Clinical diagnosis of periodontitis

Sponsors & Collaborators

• Okan University: lead

Study Sites (1)

İstanbul Okan University, Faculty of Dentistry

Istanbul, 34947, Turkey (Türkiye)

Location

MeSH Terms

Conditions

Gingivitis

Condition Hierarchy (Ancestors)

Infections; Gingival Diseases; Periodontal Diseases; Mouth Diseases; Stomatognathic Diseases

Study Officials

• Ekin Beşiroğlu Turgut

  Okan University

  STUDY DIRECTOR

Study Design

• Study Type: observational
• Observational Model: OTHER
• Time Perspective: CROSS SECTIONAL
• Target Duration: 1 Week
• Sponsor Type: OTHER
• Responsible Party: PRINCIPAL INVESTIGATOR
• PI Title: Assist. Prof.

Study Record Dates

• First Submitted: August 8, 2025
• First Posted: August 29, 2025
• Study Start: September 1, 2023
• Primary Completion: May 1, 2024
• Study Completion: August 1, 2025
• Last Updated: August 29, 2025

Record last verified: 2025-08

Locations

TU (1)