Occlusal Plaque Research Articles

Tooth-Specific Streptococcus mutans Distribution and Associated Microbiome.

Dental caries is multifactorial and polymicrobial in nature and remains one of the most common oral diseases. While caries research has focused on Streptococcus mutans as the main etiological pathogen, its impact at the tooth level is not fully understood. In this cross-sectional study, the levels and distribution of S. mutans in the posterior teeth at different dentition stages were investigated along with the corresponding tooth-specific microbiome. Occlusal plaque samples of 87 individual posterior teeth were collected from thirty children in three dentition stages (primary, mixed, and permanent). The S. mutans levels in the occlusal plaque of individual posterior teeth were quantified with qPCR, and those with preferential colonization were selected for tooth-specific microbiome analysis using 16S rRNA sequencing. Results: Quantification of S. mutans levels in the occlusal plaque confirmed the preferential colonization on the first primary and permanent molars. These teeth were selected for further tooth-specific microbiome sequencing, as they also displayed high caries experience. There were significant differences in the relative abundance of the four most abundant genera: Neisseria, Streptococcus, Rothia, and Veillonella. Furthermore, the tooth-level caries experience was correlated with a reduction in the microbiome diversity. Analyzing the different tooth-associated microbial communities, distinct tooth-specific core microbiomes were identified. Conclusions: Our findings suggest that caries susceptibility at the tooth level, depending on tooth type and dentition stage, is influenced by individual species as well as plaque community.

Visible Occlusal Plaque Index Predicting Caries Lesion Activity

This study was undertaken to appraise the predictive validity of the Visible Occlusal Plaque Index (VOPI) in assessing occlusal caries lesion activity in adolescents. A total of 618 adolescents aged 10 to 15 y were examined at the beginning of the trial and 511 (82.7%) at the 2-y follow-up. Adolescents and parents answered questionnaires about demographics, oral health behavior, and family sociodemographic variables. The VOPI has a 4-point ordinal scale ranging from no plaque to heavy plaque. Molar teeth were assigned to group VOPI 0–1 (no/thin plaque; n = 2,539) and group VOPI 2–3 (thick/heavy plaque; n = 843). At baseline examination, occlusal surfaces at risk of transition (n = 3,382) were either sound (55%), inactive noncavitated lesions (21%), inactive cavitated lesions (1%), active noncavitated lesions (15%), or active cavitated lesions (7%). The relative risk (RR) for caries lesion transition was estimated. Sound occlusal surfaces with no or thin plaque were significantly more likely to remain sound (RR = 1.3; 95% confidence interval [CI]: 1.1–1.4) than those harboring thick or heavy plaque. Inactive noncavitated occlusal lesions presenting no or thin plaque were significantly less likely to progress to active noncavitated lesions (RR = 0.1; CI: 0.0–0.8) than their counterparts with thick or heavy plaque. Active noncavitated lesions harboring thick and heavy plaque had a significantly lowest chance of becoming sound (RR = 0.7; CI: 0.5–0.9) and a highest risk of remaining active (RR = 1.5; CI: 1.1–1.9). Stepwise logistic regression analyses were run according to surface status at baseline and showed that none of the nonclinical predictors were significant for the outcome. The presence of thick and heavy plaque on occlusal surfaces was a predictor for caries lesion development, progression and activity (P < 0.0001). In conclusion, besides being an additional clinical tool for oral hygiene assessment, the VOPI is a predictor for development, progression, and activity of occlusal caries lesion. This is of particular interest for assessment of occlusal lesions undergoing health-promoting transitions.

Correlation between Streptococcus mutans levels in dental plaque and saliva of children.

This study was designed to compare the levels of Streptococcus mutans (S. mutans) in saliva with those in occlusal plaque on posterior teeth at different stages of dentition, and to explore the correlation with caries experience to determine the most suitable source of S. mutans for research. Samples of saliva and occlusal plaque were collected from 83 patients (aged 3-17 years) over three months. S. mutans levels were determined by culture-based selective plating, morphological identification, and S.mutans-specific monoclonal antibody labeling. The mean age of the participants was 8.8 (±3.7) years, and 74.7% of them were Hispanic. Mean caries experience for children with primary, mixed, and permanent dentition was 5.2 (±4.7), 4.0 (±3.3), and 0.8 (±1.3), respectively. Children with primary and mixed dentition had a higher caries experience than children with permanent dentition (P < 0.01), despite having similar S. mutans levels and total bacteria. A positive correlation was observed between S. mutans levels in plaque and those in saliva, but not between S. mutans levels and caries experience. It was noteworthy that plaque samples harbored higher S. mutans levels (>105 CFU/mL) than saliva samples. Both plaque and saliva samples are useful sources for S. mutans isolation. S. mutans levels from both sources were not significantly correlated with caries experience, but occlusal plaque had greater sensitivity for quantification of high S. mutans levels.

Oral colonization of Candida albicans and Streptococcus mutans in children with or without fixed orthodontic appliances: A pilot study

Background/purposeAdolescents undergoing fixed orthodontic therapy have an increased risk of oral diseases due to additional plaque accumulation sites. However, the effect of fixed orthodontics appliances (FOAs) on the colonization of Candida albicans (Ca) and Streptococcus mutans (Sm), two synergistic oral pathogens, is largely unknown and was, therefore, the primary objective of this pilot investigation. Material and methodsSixteen children aged 10–15 years were enrolled, nine in the FOA and seven in the control groups. Saliva and occlusal plaque were collected, and the Ca and Sm levels were quantified with a quantitative real-time polymerase chain reaction (qPCR) assay. ResultsA trend of higher Ca levels was observed in the saliva and occlusal plaque of the FOA group, while the control group contained higher levels of Sm. Furthermore, for Sm levels, a positive correlation between saliva and occlusal plaque was shown in both the FOA and control groups; in contrast, Ca levels were negatively correlated between these samples only in the FOA group. Between Ca and Sm, a positive correlation was observed in saliva and occlusal plaque in the control group; however, this relationship was disrupted in the FOA group. ConclusionOur preliminary study demonstrated that the presence of FOAs disturbs the colonization of Ca and Sm within the oral cavity. This perturbation might increase orthodontic patients’ risk for Ca- and Sm-related diseases.

OCCLUSAL SPLINTS: TYPES, MATERIALS AND PROPERTIES - A LITERATURE REVIEW

ABSTRACT Temporomandibular Disorder (TMD) is considered the major cause of non-dental pain in the orofacial region and the most crucial symptom for which patients seek medical attention, negatively affecting quality of life. The plates have gained prominence as a treatment for TMD but the success or failure of the occlusal plates will depend on their correct selection and indication, materials for making and adjusting, in addition to the cooperation of the patient. The purpose of this study is to highlight the most used types of occlusal plaques, their advantages, disadvantages, indications and contraindications, in addition to identifying and analyzing the materials currently used in their manufacture. A literature review was conducted with searches on articles from the electronic databases PubMed, Virtual Health Library (BVS) and Google Scholar with the descriptors: disfunção, placa occlusal, tratamento, dysfunction, plate, occlusal and treatment. We also use bibliographic information from Okeson (2013). From the data collected in this literature review, it can be concluded that the occlusal plaque is considered a conservative and reversible method and has stood out for its low cost and high success rate. This study demonstrated that the most advantageous material for the manufacture of the plates was the photopolymerizable resin. However, the dentist must be attentive to a correct diagnosis, selection and indication, preparation and adjustment materials, in addition to the patient's cooperation in order to provide the appropriate treatment.

Avaliação funcional após uso de placa oclusal em pacientes com disfuncão temporomandibular

This study aimed to evaluate the amplitude and pattern of mouth opening in patients treated with occlusal plaque (OP) after 1 and 3 months of treatment. The mouth opening pattern was assessed using the metric method and the mouth opening amplitude of 23 patients treated with occlusal plaque (OP; N = 23). All patients were diagnosed with TMD according to axis 1 of the RDC/TMD (Research Diagnostic Criteria for Temporomandibular Disorders). The collected data were evaluated using the SPSS program using the Wilcoxon, Kruskal Wallis, and Fisher’s exact Chi Square tests. The OP showed a satisfactory performance in the opening pattern variable, maintaining the same pattern as the patient throughout the treatment time (P = 0.003). In the variable of maximum opening amplitude, the therapy showed a significant improvement in amplitude gain in the initial time and after one month of therapy (P = 0.002), maintaining the amplitude until the third month, without presenting significant gain. It was concluded that OP has a satisfactory performance for the treatment of TMD when the opening pattern and the mean maximum opening amplitude are analyzed without assistance.

3D distribution of dental plaque on occlusal surface using 2D-fluorescence-image to 3D-surface registration

The accumulation of dental plaque on a tooth surface plays a crucial role in developing dental caries. In this paper, fluorescence imaging modality with structured light-based intraoral 3D scanner were combined to investigate the 3D distribution of dental plaque. The traditional fluorescence imaging method only reveals the 2D spatial distribution of the dental plaque on a tooth surface. To visualize the 3D distribution of the dental plaque on an occlusal surface, mapping a 2D fluorescence image to a 3D occlusal surface was investigated. An iterative closest point (ICP)-based contour registration method was proposed. A fluorescence camera was calibrated to obtain intrinsic parameters. The rotation and translation matrices for projecting the 3D occlusal surface were optimized to match the contours of the 2D fluorescence image and the 3D projected model. The 3D distribution of occlusal plaque reveals that dental plaque accumulation relates to the local and global morphology of the tooth surface. Thus, the depth of the pit-and-fissure is not the only parameter used to determine plaque content. The investigation of the 3D distribution of occlusal plaque using 2D-3D registration paves the path for the quantitative analysis of the tooth surface morphology to perform plaque-guided caries risk assessment.

Metal-ceramic partial fixed dentures: a retrospective study

ABSTRACT Objective Metal-ceramic prosthesis are the treatment of choice in oral rehabilitation because of their high survival rates. However, there are few reports in the scientific literature about factors that lead to fractures of metal-ceramic prostheses. The aim of this study was to evaluate whether prostheses units number, abutment type and number, type of the prostheses, prostheses position in the mouth, bruxism and occlusal plaque influence the incidence of fractures in fixed metal-ceramic prostheses. Methods For this study, 16 patients were selected, totaling 74 metal-ceramic prostheses installed between 2000-2010, with follow up of at least four years. Besides dental history, other information was collected, such as patients’ gender and age, prostheses installation date, and the ceramic system used. In case of prostheses fracture, a questionnaire was applied to identify signs of bruxism. A clinical evaluation was done to evaluate the prostheses integrity and opposing dentition characteristics. Success, failure and survival rates were determined. Results The results showed that the success rate of metal-ceramic prostheses was 87.8% and the survival rate was 89.1%. In addition, the success rate was independent of patient age, prostheses installation time, number of prosthesis, number of prosthesis’ units and abutments. The qualitative variables also did not show significant statistical results between success and failure rates. Conclusion It was concluded that metal-ceramic prostheses have high success and survival rates, what guarantees longevity and indication of this type of prostheses in daily practice.

Do really parents brush their children's teeth better?

Plaque removal from first permanent molar teeth was evaluated when conventional and a new silicone tooth and gum brush was used. Also, the effectiveness of parents' brushing was compared with childrens'. Study design: This crossover clinical study was conducted with 9 children aged 5 to 7 years, with 18 mandibular first permanent molar teeth which were partially erupted. Four appointments were planned at one-week intervals and at every appointment, dental plaque on teeth was disclosed first. At their first appointment, the children were given a conventional toothbrush, and at their second appointment they were given a silicone tooth andgum brush . Then, at the third appointment, parents performed brushing with a conventional toothbrush, and then brushed with a silicone tooth & gum brush at the fourth appointment. Before and after brushing, photographs were taken for baseline and final plaque scores to determine Occlusal Plaque Index with Image Analysis Software Program. Anova was used for comparison of groups with p<0.05 considered to be significant. There was statistically significant difference between baseline and final plaque scores among all of the groups (p<0.05) but, there was not statistically significant difference between the groups (p>0.05). Children under the age of nine are usually believed to lack the developmental skills needed to brush their own teeth, and as a result, the silicone tooth & gum brush might be recommended instead of brushing with parents.

Acupuncture in the treatment of temporomandibular muscle dysfunction

ABSTRACT BACKGROUND AND OBJECTIVES: Temporomandibular dysfunction consists of frequent non-dental pain in the orofacial region of multifactorial origin and interdisciplinary treatment, among them, acupuncture. The treatment of temporomandibular dysfunction acts both in muscle relaxation and pain control, trying to achieve the physical, mental, and emotional balance of the patient, thus reducing anxiety and improving the quality of life. The objective of this study was to evaluate acupuncture as a treatment for temporomandibular dysfunction. METHODS: A total of 34 volunteers screened and selected at the Federal University of Mato Grosso do Sul, diagnosed with muscle dysfunction according to the Research Diagnostic Criteria. They were randomly divided into two equal groups: group 1 treated with occlusal plaque, massage, thermotherapy and self-care guidelines; and group 2 treated with six acupuncture sessions lasting 30 minutes each. The pain was evaluated by the visual analog scale, and an algometer to assess the muscular tension of the temporal and masseter muscles. The limitation of mouth opening was measured with the use of calipers. The Mann-Whitney test was used for the non-normal distribution (visual analog scale and tension threshold) between the two groups (G1 and G2), and the Friedman test to compare the assessment periods (beginning of the treatment, after six weeks and four months) with a significance level of 5%. RESULTS: There was no difference in mouth opening, visual analog scale scores, or muscle tension threshold in relation to the type of treatment used. Both groups improved after six weeks of treatment. There was no statistical difference in the values obtained after six weeks and after four months. CONCLUSION: The statistical results showed that acupuncture increased the muscle tension threshold, improved the mouth opening and reduced pain, being as effective as the most commonly used conventional therapies.

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

ObjectiveThe present study appraises the construct validity of the Visible Occlusal Plaque Index (VOPI) along with its sub-types, convergent and discriminant validity. Methods618 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). ResultsConstruct 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). ConclusionThe 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 significanceThe 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.

Multivariate survival analysis for the identification of factors associated with cavity formation in permanent first molars

This investigation used a multivariate survival model, which allowed for dependent caries data with possible censoring, to analyse the impact of timing of tooth emergence, gender and several reported oral hygiene and dietary habits on the incidence of cavity formation in permanent first molars (PFM) in young children. A 6-yr prospective oral health screening project in Flanders, Belgium, provided clinical and questionnaire data on 4,468 children. The results revealed that PFM in children who reported frequent brushing, who had no visible caries experience in the primary dentition, and who presented without occlusal plaque on the PFM had the best survival estimates. Girls had a higher incidence than boys of cavity formation in mandibular molars. The multiple survival analysis confirmed the major impact of the caries status of the deciduous dentition and self-reported oral hygiene habits on the incidence of cavities in permanent first molars.

Efficacy of occlusal plaque removal in erupting molars: a comparison of an electric toothbrush and the cross-toothbrushing technique

Efficacy of occlusal plaque removal in erupting molars: a comparison of an electric toothbrush and the cross-toothbrushing technique

Efficacy of Occlusal Plaque Removal in Erupting Molars: A Comparison of an Electric Toothbrush and the Cross-Toothbrushing Technique

The aim of this prospective crossover study was to compare the efficacy of two methods of plaque removal on partially erupted occlusal surfaces, which comprise about 80% of the sites affected by caries in schoolchildren. After a baseline examination, 16 children (aged 5–7 years) and their parents were instructed in cleaning the occlusal surface of an erupting molar either with an electric toothbrush or with a manual toothbrush in the cross-brushing technique. After 2 weeks, the proportion of the occlusal surface covered by plaque was measured again using the occlusal plaque index, a new, highly reproducible method (intraclass correlation coefficient >0.90). For the next 2 weeks, they used the other technique. In the multifactorial variance analysis, the individual child and parents were the most important factor for the amount of plaque present. Secondly, both methods resulted in about 50% less plaque on occlusal surfaces compared to baseline (29.2%) with a slightly but significantly smaller mean value for the electric toothbrush (14.7%, manual cross-brushing technique 16.7%; p = 0.025).

Prediction of caries development for molar fissures with semiquantitative mutans streptococci test.

Risk-specific caries prevention requires validated and simple parameters for a caries risk assessment. The aim of the study was to evaluate the validity of a site-specific chair-side mutans streptococci (MS) test for the prediction of caries incidence in fissures. In 230 6- to 7-yr-old children, occlusal plaque samples of teeth 16 and 36 were cultured with Dentocult SM tests at 37 degrees C for 24 hr. Caries (DMFS), initial caries, sealants, and a plaque index (QHI) were recorded and oral hygiene habits were assessed. Not erupted, carious, filled and sealed teeth were excluded from the analysis (n = 154). After 2 yr, the status of the fissures was re-examined, and a fluoride history was recorded with a questionnaire filled out by the children's parents. Sealed teeth were excluded again (n = 54). With a classification of MS score 0 or 1 as low and MS score 2 or 3 as high caries risk, 92% agreement was reached by two independently working examiners. The MS scores and caries incidence correlated significantly. Seventy-eight % of the caries progression in fissures was prognosed correctly. Sensitivity was 50%, specificity 82%, positive predictive value 29%, and negative predictive value 92%. Children with caries progression tended to have lower fluoride scores. Low MS scores were most likely to be associated with low caries incidence, while high mutans streptococci scores seem to be partially compensated by other parameters.

Detection, Diagnosing, Monitoring and Logical Treatment of Occlusal Caries in Relation to Lesion Activity and Severity: An in vivo Examination with Histological Validation

The aims of the present study were to investigate the ability of 3 experienced clinicians to detect occlusal carious lesions, assess their depth, diagnose their activity and define a logical management for each lesion. The material consisted of 35 third molars scheduled for extraction or surgical removal making it possible to validate the accuracy of the clinical recordings histologically. Examinations were carried out at baseline and after 4 months in order to monitor lesion progression. At the first visit a radiograph was taken; the number of filled surfaces was counted and the oral hygiene assessed generally and by disclosing occlusal plaque of the tooth under examination. After cleaning the occlusal surface caries was recorded in a selected investigation site using a visual ranked caries scoring system, as well as an electrical conductance recording (ECM). Apart from counting fillings and taking new radiographs the same procedure was performed at the second visit, which then was followed by extraction of the tooth. After sectioning the tooth lesion depth was recorded, and lesion activity, based on acid production, was assessed using methyl red dye. Lesion activity was also judged by means of polarized light microscopic examinations of the sections. Results showed strong relationships between the visual, ECM and radiographic assessments and both lesion depth and lesion activity. In contrast, all other parameters were poorly related to lesion activity. Changes in visual assessments and in conductance readings from first to second examination were poorly associated with lesion activity. In conclusion, clinicians are able to detect lesions, predict activity and severity and define a logical management of occlusal caries on the basis of a single examination.

Oral health status in Belgian 3- to 5-year-old children.

The aim of this study was to determine the need for oral health care in young Belgian children in the municipality of Leuven, Belgium. The sample consisted of 750 boys and girls (3 years = 200, 4 years = 200 and 5 years = 350). Clinical examination was carried out by one examiner and duplicate recordings were made on 10% of the sample. The clinical examination included recording of: (1) plaque index; (2) gingival index; (3) caries index; and (4) fluorosis index. Plaque and gingival indices were recorded at six sites of smooth surfaces on selected teeth. Occlusal plaque was also registered. Before the clinical examination for caries and fluorosis, the children had their teeth professionally cleaned with toothbrushes and dental floss and dried by means of gauze bandages. In all age groups, the percentage of plaque-free sites was of the order of 60% and sound gingiva was identified at 83% of the recorded sites. The percentages of caries-free children were 69% (3 years), 57% (4 years) and 52% (5 years). The mean deft scores (standard error) were 1.37 (+/- 0.21), 1.76 (+/- 0.21) and 2.03 (+/- 0.17). The corresponding mean defs scores were 2.04 (+/- 0.44), 2.46 (+/- 0.35) and 3.75 (+/- 0.42). Non-cavitated active lesions, included in the defs scores, represented about 50% of all caries lesions. Early signs of dental fluorosis were identified in 19% (3 years), 17% (4 years) and 9% (5 years) of children. The need for oral health care in the population studied is mainly related to non-operative treatment procedures aimed at controlling the progression of disease.

Dental plaque and caries on permanent first molar occlusal surfaces in relation to sagittal occlusion.

This study examines the influence of sagittal occlusion on occlusal plaque formation in permanent first molars (PFM) in 72 7-10-yr-olds before loss of primary second molars. Of a total of 288 PFM, 140 (49%) were sealed and 23 (8%) filled. Occlusal plaque was recorded at two levels of examination: 1) visible plaque on the entire surface and 2) detailed macromorphologic mapping. Enamel caries was recorded after professional tooth cleaning. After 48 h without tooth brushing, plaque examinations were repeated. Stone models were used for 1) identification of interocclusal contact areas and 2) classification of sagittal molar occlusion. The detailed mapping of plaque on unfilled surfaces showed a clear pattern of preferential locations related to the macromorphology of the occlusal surfaces. Active caries was restricted to those anatomic structures where plaque accumulated. 48-h median plaque values on mandibular molars in normal and with one cusp distal occlusion were significantly lower (P < 0.01) compared to surfaces in 1/4, 1/2 and 3/4 distal molar occlusion. Maxillary molars with normal and with 1 cusp distal occlusion had lower median plaque values than other sagittal occlusion categories. In general, however, plaque scores were higher in maxillary teeth because more than 2/3 of these teeth were without occlusal contact in the distal part. Mandibular occlusal surfaces in normal and with one cusp distal occlusion had significantly fewer active lesions than teeth with 1/4, 1/2 and 3/4 cusp distal occlusion.(ABSTRACT TRUNCATED AT 250 WORDS)

Dental Plaque and Caries on Occlusal Surfaces of First Permanent Molars in Relation to Stage of Eruption

The occlusal surfaces of partly and fully erupted first right permanent molars were examined with respect to the occurrence and distribution of plaque and dental caries in a group of 57 six- to eight-year-old children. The children were classified into four groups ranging from one tooth partially erupted to full occlusion. Occlusal plaque was recorded at two levels of examination: (1) visible plaque and (2) detailed mapping by means of a plaque detector system. Dental caries was recorded after professional cleaning. The recording of plaque was repeated after 48 hr without oral hygiene. The findings showed a significant reduction in the easily detectable plaque in fully erupted teeth, compared with the three groups representing partly erupted teeth. The detailed mapping of plaque showed a clear pattern of preferential locations related to the macromorphology of the occlusal surfaces, and revealed reduction in the frequency of thick plaque accumulation in the fully erupted teeth. The proportion of active lesions was reduced in fully erupted teeth, and arrested lesions were mainly observed in the same group. This indicated that erupting teeth are more likely to develop dental caries, due to favorable conditions for plaque accumulation. Functional usage of teeth in addition to improved access for toothbrushing promoted arrestment of lesions initiated during eruption.

The Correlation Between Occlusal Plaque and Dental Caries in Schoolchildren

For the purpose of studying the correlation between the amount of occlusal plaque and the prevalence of dental caries, 829 school-children of Aji Island and Ichinoseki aged 6 to 15 years were examined. The occlusal surfaces of their permanent premolar and molar teeth which had erupted completely and were not decayed nor filled were scored 0 to 3 according to the extent of the area covered with dental plaque. The criteria of scoring were as follows:Score 0-No clinical plaque. Linear staining only of the contents of pits and fissures.1-Less than one-third of the occlual surface covered with stained palaque.2-Less than two-thirds of the occlusal surface covered with stained plaque.3-More than two-thirds of the occlusal surface covered with stained plaque.The mean score per kind of tooth in one individual was called the individual Occlusal Plaque Index (O.P.I.), and the mean of the individual values was called the population O.P.I. of each kind of tooth. The O.P.I. was calculated for the following kinds of teeth; first molars, the second molars, whole molars, premolars, and premolar-and-molars.The values of all kinds of population O.P.I. were already high immediately after complete eruption and declined with age for some years. While the declination was slight in the first molars, it was very marked in premolars. The means of molar O.P.I. were constantly higher in females, but the means of premolars were not so.The coefficients of correlation between the various O.P.I. 's and the numbers of DMFT and DMFS were calculated and investigated statistically. All the correlations seemed to be basically a positive relationship, and statistically significant correlations were frequently found in the several kinds of O.P.I. except for the period just after eruption. High significant correlations were very often present in the O.P.I. of molars but were rarely present in the premolars. The highest coefficients were obtained between the number of DMFS and the O.P.I. of the first molars and whole molars in the 5th and 6th grade elementary schoolchildren because almost all of the children with a high value of the O.P.I. had suffered from more carious lesions than average.From these findings it was concluded that the O.P.I. of the permanent first molars and whole molars had a highly significant correlation with the prevalence of dental caries in schoolchildren.