Background: Probe visibility is the clinical gold standard to discriminate thick from thin biotype but is prone to subjective interpretation. The primary objective of this study is to determine at what objective gingival thickness the probe becomes invisible through the tissue. A secondary objective is to compare mean buccal plate thickness between thick and thin biotypes as determined by probe visibility.
Methods: Maxillary anterior teeth (n = 306) were studied in 56 human patients. Biotype was determined by probe visibility through the tissue. Gingival thickness was measured via transgingival sounding. Buccal plate thickness was measured (n = 66 teeth) by cone beam computed tomography. For the primary objective, the gingival thickness that best corresponded with probe invisibility was selected using the receiver operating characteristic and area under the curve (AUC) with the highest combination of sensitivity and specificity. For the secondary objective, mean buccal plate thickness was compared between sites in which the probe was visible and when it was not (Student t test, α= 0.05).
Results: The gingival thickness that most closely corresponded with probe invisibility was >0.8 mm (0.666 AUC, 67.7% sensitivity, 65.4% specificity). When the probe was visible, mean gingival thickness was 0.17 mm less (P <0.001) compared to the "thick" counterparts. When the probe was visible, mean buccal plate thickness tended to be smaller by 0.212 mm (P = 0.08), but the difference was not statistically significant.
Conclusions: The study failed to identify a gingival thickness threshold that can discriminate reliably between sites in which the probe was visible (i.e., thin biotype) and those in which it was not (i.e., thick biotype). Probe visibility was associated with thinner measurements of gingival thickness and showed a tendency to be associated with a thinner buccal plate.
Keywords: Bone and bones; cone-beam computed tomography; gingiva; phenotype..