Periodontal phenotype: the limitations of conventional assessment methods

Accurate characterization of the periodontal phenotype — including gingival thickness (GT) and keratinized tissue width — is an essential prerequisite in implant and periodontal surgery. A thin phenotype (≤ 1 mm) significantly increases the risk of tissue recession in the face of inflammation or trauma. However, current clinical tools, such as visual inspection or periodontal probing, lack precision, while transgingival probing (TGP) under local anesthesia can induce measurement bias through volume increase. Although ultrasonography (UGTM) allows for non-invasive measurement of total thickness, it does not allow for differentiation of the structural components of the gingiva, particularly the epithelium.

Objectives and hypotheses of the combined OCT/Ultrasound approach

This cross-sectional pilot study aims to evaluate a new tissue analysis method combining optical coherence tomography (OCT) and biometric ultrasound (Pirop® device). The challenge is to determine the feasibility of using these technologies jointly to measure horizontal mucosal thickness in 13 healthy patients. The authors test the exploratory hypothesis of a correlation between epithelial thickness and the overall gingival phenotype. A central aspect of this work is to validate an image analysis protocol that can be performed directly by the clinician, without the intervention of a computer specialist, in order to guarantee a concrete application in the practice for surgical planning and donor site evaluation.

Methodology: multimodal imaging put to the test

This cross-sectional pilot study recruited 13 periodontally healthy patients (7 women, 6 men) aged 30 to 65 years. Inclusion criteria excluded any systemic pathology, medication interfering with periodontal health, or surgical history in the maxillary area of interest.

The evaluation of the attached gingiva utilized two non-invasive technologies on a standardized 6x6 mm examination frame:

• Ultrasonic biometry (Pirop®): Measurements were performed in A-scan mode. The device generates 10 pulses per point to define an average thickness. Systematic repetition was performed if the standard deviation exceeded 0.05 mm, ensuring rigorous metric precision.
• Optical Coherence Tomography (OCT): This 3D imaging system allowed for a fine volumetric reconstruction of the tissues. The objective was to discriminate the thickness of the epithelium relative to the total gingival thickness.

The reliability of the Pirop® device was verified by an initial calibration via transgingival probing (TGP), using an endodontic instrument with a silicone stop. Data analysis, performed independently by several clinicians, integrated Kruskal-Wallis (ANOVA) and Mann-Whitney U statistical tests to evaluate the impact of demographic variables on the gingival phenotype.

Morphometric analysis: the epithelium under the OCT eye

This pilot study, conducted on 13 healthy patients (7 women, 6 men), allowed for the quantification of tissue structures with micrometric precision. Combined measurements from the Pirop® ultrasound and the 3D-OCT camera reveal a stable gingival architecture within the sample, without influence from demographic variables.

Quantitative data and correlations

The main results highlight the following average values for the maxillary central incisor site (tooth 11):

Statistical analysis (Kruskal–Wallis and Mann–Whitney U tests) shows an absence of significant correlation between epithelial thickness and total gingival thickness. The data also highlight independence regarding the patient profile:

• Age and Sex: No statistically significant influence was observed on GT or epithelial thickness (p > 0.05).
• Significance: All inter-group comparisons showed a p > 0.05. The authors state that these exploratory results, although imprecise due to the sample size, provide a solid methodological basis.

Qualitative observations and imaging

OCT imaging enabled the generation of 128 slices (B-scans) per patient, spaced 47 μm apart, allowing for a complete 3D reconstruction of the gingiva. Unlike ultrasound imaging, which measures the overall distance to the bone surface, OCT allows for the specific distinction of the epithelial layer. This in situ visualization, performed without anesthesia or biopsy, confirms the potential of OCT for real-time virtual histological analysis.

Conclusion

Optical coherence tomography (OCT) effectively complements ultrasonographic measurement by isolating the epithelial component of the gingival phenotype.

Discussion: Towards infra-millimetric tissue mapping

The results of this pilot study highlight a major biological distinction: the absence of statistical correlation between epithelial thickness (mean 0.33 mm) and total gingival thickness (mean 1.31 mm). For the clinician, this means that a thick gingival phenotype is not systematically synonymous with a denser epithelium. This data is crucial when planning connective tissue grafts or muco-gingival surgeries, where the management of tissue layers conditions aesthetic success and long-term stability.

The major contribution of this protocol lies in the technological complementarity. While the Pirop® Echo-son device allows for precise ultrasonographic measurement of the total thickness (GT), OCT (optical coherence tomography) offers a quasi-histological in situ vision without biopsy. Unlike traditional periodontal probing or the transgingival probing (TGP) method — which remains invasive and subject to pressure variations — this non-invasive duo allows for the evaluation of the donor site with an axial resolution of 0.01 mm.

However, the scope of these observations remains limited by the small sample size (n=13). The absence of significant differences according to age or sex (p > 0.05) must be interpreted with caution and deserves to be confirmed by larger-scale studies. Nevertheless, the study demonstrates the feasibility of a multimodal analysis directly at the practice, performed by clinicians without the intervention of computer scientists, paving the way for a more objective pre-implant evaluation of the aesthetic zone.

Gingival thickness: what 3D imaging teaches us

This pilot study conducted on 13 patients reveals a mean gingival thickness (GT) of 1.31 mm for an epithelial thickness of 0.33 mm. The results demonstrate the absence of statistical correlation between these two measurements: epithelial thickness does not predict total GT. Furthermore, these biometric parameters appear to be independent of the patients' age and sex.

In concrete terms, for the practitioner:

• Reliability of your measurements: Prioritize non-invasive methods (ultrasound, OCT) over transgingival probing under anesthesia, as the injection of local solution artificially increases tissue volume and distorts your phenotype assessment.
• Target the harvest: OCT allows the isolation of epithelium measurement, data that is invisible to standard ultrasound. It is a major asset for planning your connective tissue grafts by precisely evaluating the donor site.
• Do not prejudge the phenotype: A globally thick tissue does not guarantee a thick epithelium. In periodontal plastic surgery, treat each tissue layer as a distinct biological entity when preparing your flaps.

Technical lexicon of the study

Gingival thickness (GT): Horizontal dimension of the mucosa measured perpendicularly to the bone or tooth surface, allowing the categorization of the periodontal phenotype as "thin" (≤ 1 mm) or "thick" (> 1 mm).

Epithelial thickness: Selective measurement of the superficial stratum of the keratinized stratified squamous epithelium, distinguished from the connective tissue by OCT imaging for in situ histological analysis.

Periodontal phenotype: A global clinical entity encompassing the bone morphotype (thickness of the buccal bone plate) and the gingival phenotype, defined by gingival thickness (GT) and keratinized tissue width (KTW).

Optical Coherence Tomography (OCT): Non-invasive 3D digital imaging technology using an 840 nm wavelength to visualize the different layers of gingival tissues in real time without the need for biopsy.

Ultrasonic biometer: Diagnostic device (Pirop® type) calculating the total thickness of soft tissues by measuring the return time of a wave reflected from the bone or dental surface.

Transgingival probing (TGP): Invasive measurement method by puncture, using an endodontic instrument equipped with a silicone stop to determine the physical depth of the tissues until bone contact.

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