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Objectives: To evaluate the relationship between gingival phenotype, classified using a steel periodontal probe (TRAN method), and soft tissue dimensions measured clinically and histologically.

Materials and methods: Forty-five healthy volunteers were categorized into thin or thick phenotype groups based on gingival transparency at one maxillary central incisor. Clinical thickness measurements of the gingiva and mucosa were taken with an ultrasonic device, while histological assessments were conducted on tissue samples from the same region. The keratinized tissue width (KTW) was also recorded.

Results: Twenty-four participants were classified as thick phenotype and twenty-one as thin. Phenotype showed a significant moderate correlation with clinical gingival thickness (r = 0.682, p < 0.001), a weaker positive correlation with KTW (r = 0.290, p = 0.023). The optimal threshold for distinguishing thin and thick phenotypes was 1.065 mm, with the TRAN method showing good predictive accuracy (AUC = 0.912). Both clinical and histological measurements revealed a gradual thinning of soft tissues from the midpoint of the keratinized tissue to the MGJ and beyond. Ultrasonography demonstrated good repeatability for gingival thickness (ICC = 0.744) but underestimated mucosal thickness compared to histology (p < 0.001).

Conclusions: The TRAN method moderately correlates with clinical gingival thickness at the midpoint of KTW and with KTW. Soft tissue thickness decreases towards the MGJ. Clinical relevance: Probe concealment correlates with a gingival thickness of 1.065 mm at the midpoint of the KTW. Ultrasonography is reliable for gingival, but not mucosal, thickness assessment.