OBJECTIVE: The present study appraises the construct validity of the Visible Occlusal Plaque Index (VOPI) along with its sub-types, convergent and discriminant validity.

METHODS: 618 10-15year old Brazilian adolescents were included. The VOPI has a four-point ordinal scale ranging from no plaque to heavy plaque. VOPI scores and caries status on permanent molars were mapped and recorded at individual anatomical sites of the groove-fossa-system and at surface level. Outcomes were presence of sound site/surface and site/surface with active or inactive caries lesions (non-cavitated or cavitated).

RESULTS: Construct validity was assumed based on qualitative assessment as no plaque (score 0) and thin plaque (score 1) reflected the theoretical knowledge that a regular disorganization of the dental biofilm either maintains the caries process at sub-clinical levels or inactivate it clinically. The VOPI also showed convergent validity since the likelihood that anatomical sites with no or thin plaque had inactive lesions simultaneously with sites with thick plaque (score 2) or heavy plaque (score 3) having active lesions were overall significant (RR=1.0-7.8). At surface level, discriminant validity of the VOPI was evidenced with multivariable analysis (GEE), by its ability to discriminate between the groups of adolescents with different oral hygiene status; negative association between adolescents with thick and heavy plaque and those with sound occlusal surfaces was found (OR=0.3, p<0.001).

CONCLUSION: The VOPI has construct as well as convergent and discriminant validity and is therefore recommended as an additional clinical tool to estimate caries lesions activity and support treatment decisions.

CLINICAL SIGNIFICANCE: The Visible Occlusal Plaque Index is an additional clinical tool to the assessment of oral hygiene and caries lesion activity. The VOPI is recommended to standardize and categorize information on the occlusal biofilm, thus being suitable for direct application in research and clinical settings.