Validation of the Visible Occlusal Plaque Index (VOPI) in estimating caries lesion activity

Abstract

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 10–15 year 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.

Introduction

Based on the understanding that biofilm accumulation on tooth surfaces is a necessary condition for the development of the caries process , assessment of oral hygiene in individuals is of interest in order to control caries initiation and progression. While dental professionals have traditionally been trained in assessing oral hygiene status in relation to periodontal diseases , limited training has been devoted to the assessment of oral hygiene in controlling caries progression. In this context, the assessment and control of dental biofilm on occlusal surfaces have proven a great challenge in daily practice.

Longitudinal studies investigating the role of biological determinants for the development and arrest of occlusal caries in young permanent teeth elucidated that the most influential determinants were biofilm accumulation and stage of tooth eruption whereas the presence of fissure-like structures showed no significant effect . Few plaque indices have been developed in order to assess the occurrence of occlusal biofilm . The Visible Occlusal Plaque Index (VOPI) developed to assess the occurrence and distribution of dental biofilm on the groove-fossa system in relation to caries could be an additional clinical tool in the assessment of oral hygiene and caries lesion activity.

The content validity of the VOPI was established based on experts judgment that this index measured accumulation and distribution of the occlusal biofilm and that the definitions applied measured its different scores rather than the absence/presence of biofilm . Construct validity is the extent to which the measurement corresponds to theoretical concepts concerning the phenomenon under study . Construct validity of the VOPI might be assumed if the criteria reflect the well-established role of the dental biofilm in caries development and arrest , i.e. if plaque scores are casually related to net mineral loss of dental hard tissues which may or not may be detected clinically and/or radiographically and manifest itself either as non-cavitated or cavitated lesions.

Convergent validity is the extent to which two measures of the construct that theoretically should be related are in fact related whereas discriminant validity is the extent to which constructs that should not be associated are in fact not associated. The index might evidence convergent validity if the occlusal plaque scores correlate well with caries lesion activity, a measure related to the construct. Caries lesion activity is determined by surface reflection and texture with chalky and rough lesions, generally covered by plaque, being active in contrast to smooth, shiny and hard lesions being inactive . Likewise, evidence of discriminant validity might be found whether the VOPI scores show ability to discriminate between groups with different exposure to risk factors .

The present study appraises the construct validity of the Visible Occlusal Plaque Index together with its two subtypes, i.e. convergent validity and discriminat validity. The validity of the VOPI would be assumed under the acceptance of the following hypotheses: 1) the likelihood that occlusal plaque scores are associated with no clinical signs of net mineral loss is higher at sites without plaque or harboring thin plaque than at sites harboring thick or heavy plaque; 2) the likelihood that occlusal plaque scores are associated with caries lesion activity is higher at surfaces harboring thick or heavy plaque than at surfaces without plaque or harboring thin plaque and 3) the scores of the VOPI would discriminate between groups of adolescents with different oral hygiene status.

Material and methods

Ethics, study design and sample calculation

The study protocol was approved by the Ethical Committee of the University of Brasília, Brazil (Brazilian register number 1.096.882). Endorsement from the State Educational Division was granted for conducting the research in the only school with secondary schooling located in the Region of Itapoã, Federal District of Brazil. Parents and adolescents were informed about the study and signed a written informed consent before the enrollment of the adolescents. The present study is part of a controlled clinical trial on caries incidence and progression in adolescents with erupting and fully erupted second molars to be followed for 3 years.

The sample size calculation was estimated based on an expected difference in caries incidence of 10% between adolescents with erupting and fully erupted second molars. Given a power of 80% and a confidence interval of 95%, 219 children in each group were required at the end of the study. Considering a dropout rate of 30% after 3 years of the clinical trial, 313 adolescents in each group were foreseen. The sufficiency of the sample size for validating the VOPI as a measure of the association between dental biofilm and caries lesion activity status was considered more than large enough.

Inclusion and exclusion criteria

The adolescents should be attending either the 6th, 7th or 8th grade of the selected school, being willing to participate in the study, accepting to be called for annual control visits in the future and having at least one permanent second molar without sealant, filling or cavitated caries lesions in need for instant restorative treatment. Exclusion criterion was the presence of a serious chronic illness.

Questionnaire and examinations

Adolescents answered a questionnaire about demographic and oral health behavior determinants: age, gender, brushing frequency, use of fluoride toothpaste, use of dental floss, consumption of soft drinks and consumption of sweets. Two mobile dental offices belonging to the University Hospital of Brasília (HUB) were installed at the school for oral health examination and treatment of the adolescents. The clinical and radiographic examinations included assessment of primary as well as permanent teeth. However, only clinical data regarding the permanent dentition were included in the present study and specific recordings were applied for the permanent molars.

Visible Occlusal Plaque Index (VOPI)

In the first dental office, the occurrence and distribution of occlusal biofilm on permanent molars were recorded (HDM).

The VOPI criteria were: 0) no visible plaque identified when carefully running of a dental probe on the groove-fossa-system, 1) thin plaque: hardly detectable plaque which is restricted to the groove-fossa-system and identified by carefully running a dental probe on the groove-fossa-system, 2) thick plaque: easily detectable plaque on the groove-fossa-system identifiable with the naked eye, and 3) heavy plaque: occlusal surfaces partially or totally covered with heavy plaque accumulation identifiable with the naked eye .

Recording at anatomical site level

At individual anatomical sites of the groove-fossa-system occlusal plaque scores were mapped on the individual site of the groove-fossa system of each molar tooth ( Fig. 1 ).

Fig. 1
Detailed mapping of the occlusal surfaces of permanent molars indicating the anatomical sites of the groove-fossa system on which the occurrence and distribution of the occlusal plaque and caries outcomes were registered. Tooth designation: second molars (17,27,37,47) and first molars (16,26,36,46). Anatomical sites: fossae (1–3) and interlobal grooves (4–10).

Recording at surface level

The mean oclusal plaque score of all anatomical sites on each molar tooth was calculated as a continuous variable and classified either as score 0–1 or score 2–3.

Recording at dentition level

The scores of the visible occlusal plaque index determined for all molar teeth in the dentition were established and the highest VOPI score amongst all anatomical sites of each molar tooth was the unit of measurement.

Following the plaque assessment the participants received professional toothbrushing with toothpaste and flossing.

Caries status

In the second office, caries status was assessed for the permanent dentition after air drying by another examiner (JCC). Caries status was recorded as follows.

Recording at anatomical site level

Caries status was assessed at individual anatomical sites of the groove-fossa system of molar teeth. The occlusal site was clinically classified as sound when it showed normal enamel translucency after drying. Active non-cavitated lesion was defined as an opaque enamel area with a dull-whitish aspect. Active cavitated lesion was identified as a cavity in dentine with soft consistency. A lesion was considered inactive, when it showed a shiny appearance of the area with different degrees of brownish discoloration. A dental probe was used to differentiate between soft consistency and hard consistency of cavitated lesions .

Recording at surface level

Caries status was then recorded at surface level according to the following: 1) sound surface, when all anatomical sites of the molar tooth were sound, 2) surface with inactive lesion, when at least one anatomical site of the molar tooth presented inactive lesion while other sites were sound, 3) surface with active non-cavitated lesion, when at least one anatomical site of the molar tooth presented this condition as the most severe status, 4) surface with active cavitated lesion when at least one anatomical site of the molar tooth presented this condition.

The outcomes for anatomical sites of the groove-fossa system and for the occlusal surface were: 1) sound site/surface 2) site/surface with inactive lesion, 3) site/surface with active non-cavitated lesion, 4) site/surface with active cavitated lesion.

Recording at dentition level

Caries status in the whole dentition was determined according to the case status: D 1 MFT/S level (D 1: the decayed component represented both active and inactive non-cavitated as well as cavitated lesions, M = missing due to caries, F: filled, T: tooth, S: surface). A surface/tooth was considered extracted due to caries when clearly indicated at the clinical examination, otherwise it was considered as missing due to reasons other than caries. At adolescent level, the outcomes were no occlusal lesion activity; sound surfaces and surfaces with inactive lesions as the most severe status and occlusal lesion activity; surface with active non-cavitated lesion as the most severe status or surface with active cavitated lesion.

Stage of eruption

Half mouth impressions with silicone were taken for preparation of stones models (NA), used to classify the stage of eruption of molars. Molars were classified according to their stage of eruption as: fully erupted when opposing molars were in functional occlusion, and partially erupted from when the occlusal surface was partially covered by gingival tissue to when the occlusal surface was fully erupted while not yet in functional occlusion . The clinical assessments were electronically encoded in a Personal Digital Assistant for further statistical analysis.

Reliability

Thirty adolescents were re-examined for reliability of occlusal plaque (HDM assessed against JCC, who acted as benchmark) and caries scores (JCC assessed against HDM, who acted as benchmark). Inter-examiner reliability of occlusal plaque and caries scores were 0.74 (95% CI: 0.68–0.80 weighted kappa) and 0.80 (95% CI: 0.74-0.86 non-weighted kappa), respectively. Intra-examiner reliability of stage of eruption was 0.85 (95% CI: 0.81-0.96 non-weighted kappa).

Statistical analysis

The occlusal biofilm was firstly examined as a single determinant for caries outcomes in bivariable analyses. At anatomical site level, occlusal plaque scores and caries outcomes were identified on the same individual site of each molar tooth. The Risk Ratios (RR) and 95% confidence interval (CI) that anatomical sites with no or thin plaque were more likely to be sound than sites with thick or heavy plaque were estimated ( Table 1 ). Also the RR and CI that anatomical sites with no or thin plaque were more likely to present inactive lesions than sites with thick and heavy plaque were calculated ( Table 2 ). These estimations were unadjusted at tooth − and adolescent-level. Filled, sealed or missing surfaces were not included in the analysis.

Secondly, the occlusal biofilm was examined as one of the biological determinants for caries outcomes in the multivariable analysis. A general linear model, fitted using generalized estimation equations (GEE) adjusted at adolescent level, was developed estimating the association between the occlusal biofilm and caries outcomes. The unit of measurement was the surface/tooth, and the adolescent was used as cluster variable. The independent variables were: age (10–12 years; 13–15 years), gender (male; female), brushing frequency (twice daily or more; once daily or less), use of fluoride toothpaste (yes; no) consumption of soft drink (some times; every day), consumption of sweets (some times; every day), dental arch (maxilla; mandible); type of molar (1st molar; 2nd molar), stage of eruption (partially erupted; fully erupted) and D 1 MFS scores without inclusion of the occlusal surface of molars (0–4; ≥5). The mean oclusal plaque score of all anatomical sites on each molar tooth (0–1; 2–3) was added as a continuous, independent variable to the model. The dependent variables were caries outcomes. All adolescents were included in the GEE-analyses. Significance level was set at α = 0.05 ( Table 3 ). Data analyses were carried out using IBM SPSS Statistics (Version 22.0.01, USA). At adolescent level, the highest VOPI score amongst all anatomical sites of each molar tooth was tested for the association with caries outcomes (Fisher exact test, Fig. 2 a-c).

Table 3
Generalized Estimation Equations (GEE) with adolescent as cluster variable for the association between biological determinants and outcomes on occlusal surface of molar teeth (n = 4366).
Outcomes Sound Inactive lesions Active non-cavitated lesions Active cavitated lesions
Determinants n (n = 2283) (n = 1131) (n = 646) (n = 306)
Age 10–12 years 2443 ns 1 ns ns
13–15 years 2057 OR = 1.3
[CI: 1.0–1.6]
p = 0.03
Consumption of soft drink Some times 2687 OR = 1.3
[CI: 1.1–1.6]
p = 0.012
OR = 1.3
[CI: 1.1–1.17]
p = 0.01
ns 1
≥ once per day 1813 1 1 OR = 1.4
[CI: 1.0–1.1.9]
p = 0.04
Dental arch Maxilla 2338 ns 1 1 1
Mandible 2162 OR = 1.2
[CI: 1.1–1.4]
p = 0.003
OR = 1.4
[CI: 1.1–1.6]
p < 0.001
OR = 1.4
[CI: 1.1–1.8]
p < 0.01
Type of molar First 2440 1 OR = 2.6
[CI: 2.1–3.3]
p < 0.001
1 OR = 7.0
[CI: 4.4–11]
p < 0.001
Second 2060 OR = 1.9
[CI: 1.6–2.3]
P < 0.001
1 OR = 16
[CI: 11–25]
P < 0.001
1
Stage of eruption Partially erupted 813 ns 1 OR = 1.8
[CI: 1.3–2.3]
<0.001
1
Fully erupted 3687 OR = 3.9
[CI: 2.5–6.2]
p < 0.001
1 OR = 2.5
[CI: 1.3–4.8]
p < 0.005
Occlusal plaque scores (missing = 6) 0–1 3570 1 1 1 1
2–3 930 OR = 0.4
[CI: 0.3–0.5]
p < 0.001
OR = 1.5
[CI: 1.1–2.0]
p < 0.01
OR = 2.3
[CI: 1.8–2.9]
p < 0.001
OR = 14
[CI: 10–20]
p < 0.001
D 1 MFS scores a (missing = 6) 0–4 3570 1 1 1 1
≥5 930 OR = 0.3
[CI: 0.2–0.4]
p < 0.001
OR = 0.6
[CI: 0.5–0.8]
P < 0.001
OR = 1.6
[CI: 1.2–2.1]
p < 0.003
OR = 3.4
[CI: 2.5–4.7]
p < 0.001
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Jun 17, 2018 | Posted by in General Dentistry | Comments Off on Validation of the Visible Occlusal Plaque Index (VOPI) in estimating caries lesion activity
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