The gingival biotype revisited: transparency of the periodontal probe through the gingival margin as a method to discriminate thin from thick gingiva

AIM: To detect groups of subjects in a sample of 100 periodontally healthy volunteers with different combinations of morphometric data related to central maxillary incisors and surrounding soft tissues. MATERIAL AND METHODS: Four clinical parameters were included in a cluster analysis: crown width/crown length ratio (CW/CL), gingival width (GW), papilla height (PH) and gingival thickness (GT). The latter was based on the transparency of the periodontal probe through the gingival margin while probing the buccal sulcus. Every first volunteer out of 10 was re-examined to evaluate intra-examiner repeatability for all variables. RESULTS: High agreement between duplicate recordings was found for all parameters, in particular for GT, pointing to 85% (kappa=0.70; p=0.002). The partitioning method identified three clusters with specific features. Cluster A1 (nine males, 28 females) displayed a slender tooth form (CW/CL=0.79), a GW of 4.92 mm, a PH of 4.29 mm and a thin gingiva (probe visible on one or both incisors in 100% of the subjects). Cluster A2 (29 males, five females) presented similar features (CW/CL=0.77; GW=5.2 mm; PH=4.54 mm), except for GT. These subjects showed a clear thick gingiva (probe concealed on both incisors in 97% of the subjects). The third group (cluster B: 12 males, 17 females) differed substantially from the other clusters in many parameters. These subjects showed a more quadratic tooth form (CW/CL=0.88), a broad zone of keratinized tissue (GW=5.84 mm), low papillae (PH=2.84 mm) and a thick gingiva (probe concealed on both incisors in 83% of the subjects). CONCLUSIONS: The present analysis, using a simple and reproducible method for GT assessment, confirmed the existence of gingival biotypes. A clear thin gingiva was found in about one-third of the sample in mainly female subjects with slender teeth, a narrow zone of keratinized tissue and a highly scalloped gingival margin corresponding to the features of the previously introduced "thin-scalloped biotype" (cluster A1). A clear thick gingiva was found in about two-thirds of the sample in mainly male subjects. About half of them showed quadratic teeth, a broad zone of keratinized tissue and a flat gingival margin corresponding to the features of the previously introduced "thick-flat biotype" (cluster B). The other half could not be classified as such. These subjects showed a clear thick gingiva with slender teeth, a narrow zone of keratinized tissue and a high gingival scallop (cluster A2)