Key points

  • Provides information on the extension of the indication for placing a sealant.

  • Highlights the CPI instrument as an easy to use measuring instrument in the decision to seal or to restore.

  • Further supports the concept of minimal intervention dentistry.

Introduction

Current management of dental caries is guided by the minimal intervention (MI) concept.1 The concept includes maintaining healthy, functional teeth through sealing high-caries risk pits and fissures systems that may contain enamel carious lesions. MI also deals with minimally invasive operative interventions for treating cavitated dentine carious lesions. In the past, such interventions were based on Black's principles of cavity design, removing sound and remineralisable tooth tissues in the process unnecessarily. In conjunction with adhesive restorative materials, MI based interventions have the potential for keeping cavitated dentine carious lesions relatively small, which maintains a high level of tooth integrity and increases the life of a restored tooth.

The stage at which a dentine carious lesion should be intervened invasively has shifted gradually from cavitation that is clearly visible to ambiguous micro-cavitation, with a very small opening.2,3 Instead of being restored, micro-cavities with a diameter of the orifice of < 0.9 mm were sealed.4,5 By sealing over the micro-cavity opening, plaque is prevented from penetrating the cavity and this stops the caries process from functioning, provided the sealant is well placed. This argument is accepted from a cariological point of view,6 but intervention success is also dependent on the mechanical properties of the sealant material used and level of oral hygiene of the patient.

According to an in vitro study, small cavitated dentine carious lesions in pits and fissures showed a higher level of microleakage and insufficient penetration of resin sealant material into the cavity, compared to sound pits and fissures.7 Furthermore, it is known that the retention of sealants deteriorates over time, which may lead to the re-exposure of the micro-cavity and may ignite the caries process again. However, it is also possible that the small cavity opening stays blocked with remnants of the sealant material, as shown for glass-ionomer cement.8,9

Few studies have reported the effectiveness of sealing micro-cavities in pits and fissures systems. The present secondary analysis, using data from a sealant trial in China,10 contributes to the understanding of the potential for sealing micro-cavities with a high-viscosity glass-ionomer (HVGIC) placed according to the ART method, a glass-carbomer and a resin composite sealant. The hypothesis tested was that dentine carious lesion progression is higher in sealed micro-cavitated pits and fissures than in sealed pits and fissures with no or enamel carious lesions at baseline over a period of four years.

Materials and methods

The main trial study was approved by the research ethics committee of Wuhan University, Reference No. 200,704, and was registered at the Dutch Trial Registration Centre, with Reference No. 1411. Children's parents or guardians received and signed individual informed consent forms that contained information about the aim of the study and the treatment procedures. Children whose parents declined to sign the consent form were excluded from the study. The methodology of the main trial, including the CONSORT diagram, has been published previously.10,11 Therefore, only a summary is presented in this article.

Study population and treatment allocation

The study was conducted in Wuhan, China in 2008. Prior to the study, an oral health epidemiological survey of grade two children attending five primary schools was conducted using the caries criteria described in Table 1. A follow-up survey was performed four years later. The inclusion criteria for the main trial enrolment were: a fully erupted first permanent molar, no dentine carious lesion in pits and fissures of these molars, deep and/or intermediate pits or fissures,12 and a mean dmft ≥2. However, at the four year data analyses, it was discovered that 102 occlusal surfaces had been sealed, against protocol, that contained a small dentine lesion with a cavity opening that the CPI probe (diameter of 0.5 mm) could not penetrate (caries code 2), at baseline.11

The main trial was randomised controlled. Per school, the principal investigator randomly allocated each child to one of the four sealant groups, using a list obtained after block-randomisation (12 children per block for three operators) that was prepared by a statistician who did not do the analyses. A four-week laboratory and field training programme in a primary school was carried out before the trial began as the sealant procedures were new to the three operating dentists and the two dental ancillaries who assisted them.

The sealants were placed in first permanent molars on the school premises using portable equipment over two months. Children received instructions about good oral health behaviour and how to clean their teeth. The operators provided emergency treatment at baseline. Teeth with failed sealants, dentine carious lesion in re-exposed pits and fissures with a cavity opening that the CPI probe could penetrate (caries code 3), were restored. Lost sealant material was not replaced.

Sealant procedures

HVGIC/ART group

The high-viscosity glass-ionomer Ketac Molar Easymix (3MESPE, Seefeld, Germany) was used. Sealant application followed the atraumatic restorative treatment (ART) sealant procedure.5

Thermo-cured HVGIC/ART group

The Ketac Molar Easymix was thermo-cured using the LED high-intensity curing light, Elipar Freelight 2 (3MESPE, Seefeld, Germany), producing 850 mW/cm2. The sealant application described for the HVGIC/ART group was followed, except that the sealant was cured for 60 seconds after burnishing.

Glass-carbomer group

A glass-ionomer-based material containing fluorapatite and powder particles reduced to nano size, Glass Carbomer (First Scientific Dental, Elmshorn, Germany), was used. Surface cleaning was done under cotton wool isolation as described for the HVGIC/ART group, followed by applying Glass Carbomer Tooth Cleaner over the tooth surface for 20 seconds and washing and drying the surface with two wet and dry cotton pellets respectively. The Glass Carbomer capsule was mixed for 15 seconds in Rotomix (3MESPE, Seefeld, Germany), extruded onto the tooth surface, spread into a thin film, covered with Glass Carbomer Surface Gloss (First Scientific Dental, Elmshorn, Germany) and held under finger pressure for 5-10 seconds. After bite adjustment, the material was light-cured for 75 seconds with the same LED lamp as used in the thermo-cured HVGIC/ART group.

Resin C Group

A resin composite, Clinpro (3MESPE, Minneapolis, USA), was used. The pits and fissures were cleaned with a rotating brush, Prophy Angle (3MESPE, Wuhan, China), and a no. 6 explorer, acid-etched with Scotchbond etchant (3MESPE, St. Pauls, Minneapolis, USA) for 20 seconds, and rinsed and dried using a portable suction machine. The sealant material was placed in the pits and fissures, manipulated with an explorer to free potential air bubbles and cured for 20 seconds with the LED curing light 1 mm above the surface. Carbon paper and rotary instruments were used in bite adjustment.

Evaluation

The coverage of the pits and fissures with sealant material was recorded at baseline. A dentine carious lesion was recorded clinically if the enamel surface appeared cavitated and the carious lesion judged to have involved the dentine (codes 2, 3, 4). The CPI probe was used as an aid for determining codes 2 and 3 (Table 1). Before examination, the sealed tooth surface was dried with a piece of cotton tightly attached to the end of a stick. The examination site was well illuminated by an intraoral light with attached disposable mirrors (Mirrorlight, Kudos, Hong Kong).

Table 1 (ART caries assessment criteria) Dental caries diagnostic index used in the present study
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Four independent evaluators (dentists) were trained and calibrated by a senior epidemiologist (two at years 0.5, 1, and 2, and two at years 3 and 4). Training and calibration was performed by first explaining the evaluation criteria through the use of a PowerPoint presentation. Examining children by the two evaluators and the epidemiologist together at the school compound followed this. Thereafter, evaluators examined batches of three children independently. Assessment scores were compared after each batch and differences discussed until a consensus was reached. This process continued until evaluators were truly calibrated. Before and during the morning of the first day of each evaluation year, evaluators were recalibrated by examining the first arriving children twice. In the presence of the senior epidemiologist, differences in scores were discussed and consensus was reached. Final year dental students trained in recording data assisted the evaluators.

The children's caries status was reassessed one and a half years after sealants had been placed according to the caries assessment criteria used at baseline by two examiners, one of whom participated in the oral health epidemiological survey at baseline, and after three and a half years by other examiners, all trained and calibrated by the senior epidemiologist. The kappa-coefficient for inter-evaluator consistency for assessing caries lesions on tooth sections for evaluation years 0.5, 1, and 2, combined and evaluation years three and four combined were 0.63 and 0.86 respectively.

Statistical analyses

Data were analysed by a biostatistician (JM) using SAS software (version 9.2). All tests were carried out using a proportional hazard model with frailty correction (PHREG). The independent variables were 'baseline caries code' (0, 1, 2) and 'sealant procedure' (HVGIC/ART, thermo-cured HVGIC/ART, glass-carbomer, resin C). Background variables were gender, age and caries status in the primary dentition at baseline. Failure over four years (dependent variable) was defined as caries code ≥ 2 for baseline caries codes 0 and 1, and caries code 3 or 4 for baseline caries code 2. In this analysis, baseline caries codes 0 and 1 were tested against baseline caries code 2. A secondary analysis was performed in which caries code ≥2 for all three baseline caries codes was considered a failure. The difference between baseline caries codes 0 and 1 was ascertained using all data and all four sealant procedures in the model. Differences between D2MFS and D3MFS counts at baseline and four years for the four sealant procedures were tested using ANOVA. Statistical significance level was set at p = 0.05.

Results

Disposition of subjects

A total of 405 children, 215 boys and 190 girls, with an average age of 8.0 years (range 7.0-9.1 years) participated in the trial. In total, 1,344 first permanent molars were sealed divided over HVGIC/ART (312), thermo-cured HVGIC/ART (351), glass-carbomer (324) and resin C (357) groups. The trial number of children and sealants that dropped out over the four years was 12.3% and 15.4% respectively.

The mean d2mft (± SD) scores at baseline were 6.2 (± 2.8) for HVGIC/ART, 6.3 (± 2.9) for thermo-cured HVGIC/ART, 6.3 (± 2.8) for glass-carbomer and 6.4 (± 2.7) for resin C. The mean D2MFS and D3MFS scores and standard deviations by sealant group after four years are presented in Table 2.11 No difference in caries experience in the permanent dentition was observed between the four groups at baseline (D2MFS: p = 0.62; D3MFS: p = 0.59) and at the four-year evaluation (D2MFS: p = 0.45; D3MFS: p = 0.39).

Table 2 2N = number of children Mean DMFS and D3MFS scores and standard deviation of each sealant group obtained from the follow-up epidemiological examination after four years.
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There was a gender effect (p = 0.03) observed. Proportionally more cavitated dentine carious lesions were observed in girls than in boys. No age (p = 0.71), mean d2mft (p = 0.11) and mean d3mft (p = 0.17) effect on cavitated dentine carious lesion development in sealed occlusal surfaces of first permanent molars was observed at baseline.

Progression of dentine carious lesions over four years

The number of failed sealants (expressed as caries codes 3 and 4 = frank cavitation) for baseline caries code 2 over four years was: two (HVGIC/ART), one (Thermo-cured HVGIC/ART), 0 (glass-carbomer) and one (resin C). Progression of carious lesions was determined for baseline caries code 0 + 1 as the development of caries code ≥2 (failure); for baseline caries code 2 it was caries codes 3 and 4. The progression of carious lesions over the 4 years in the group baseline caries code 0 + 1 combined was not statistically significantly different from that in the group of baseline caries code 2 (p = 0.29). The hazard ratio was 0.57 (SE: 0.99).

Presence of cavitated dentine carious lesion by sealant procedure over four years

The number of survived and failed sealants over four years by sealant procedure and baseline caries score is presented in Table 3. A total of 47 sealed occlusal surfaces in first permanent molars (including eight sealants with baseline caries code 2) developed a cavitated dentine carious lesion over the four-year period. Using the PHREG model for determining the survival percentages of sealants with caries code ≥2 as failure, and baseline caries codes 0, 1 and 2 and sealant procedures as independent variables, showed no statistically significant difference between baseline caries codes 0 and 1 (p = 0.07). This outcome allowed combining the data of both baseline caries codes. Further analyses (PHREG) with the baseline caries code (0 + 1 and 2) and sealant procedure showed no statistically significant difference for the sealant procedure (p = 0.38). However, an effect of the baseline caries code (0 + 1) and baseline caries code 2 was observed (p = 0.002). The chance of developing a cavitated dentine carious lesion in the group baseline caries code (0 + 1) was 3% and in the group baseline caries code 2 it was 10%. The hazard ratio between the two groups of baseline caries codes was 0.276 (SE: 1.047), meaning that the risk for developing a cavitated dentine carious lesion (failure) over four years in occlusal surfaces of first permanent molars was about three times higher for the group baseline caries code 2 than for the group baseline caries code (0 + 1).

Table 3 Total number of sealed pits and fissures in first permanent molars with (F) and without progression of the original caries status of the surface into a dentine carious lesion development (S) after four years by baseline caries codes and by sealant procedure
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Discussion

The hypothesis was rejected. No significant difference in dentine carious lesion progression was found between sealed micro-cavitated pits and fissures at baseline and sealed pits and fissures with no or enamel carious lesions at baseline over a period of four years. The fact that only four of the 79 sealed micro-cavitated dentine carious lesions progressed from a small dentine carious lesion to frank cavitation over a four-year period supports the view that such dentine carious lesions do not necessarily need to be restored, as has been advocated.13 The type of sealant material did not influence the study finding. Progression of enamel/dentine carious lesions depends very much on the caries risk of the individual. In the present trial, caries experience of the, on average, 12-year-olds (four years after baseline epidemiological survey) was very low, showing that this child population had moved from a high-caries risk status at baseline to a low-caries risk status after four years. Carious lesion preventive instructions only were presented to the school children at the start of the trial and during each of the evaluation exercises. The schools had not instigated collective toothbrushing programmes. We are not aware of the toothbrushing pattern of the children nor the composition of their diet.

The number of studies that have investigated the effectiveness of sealing over micro-cavitated dentine carious lesions appears to be low. Comparing the findings of the present study with those of other studies is difficult because of differences in subject age, caries risk level, maximum opening of the orifice of the cavity, type of dentition and materials used, some of which are currently considered outdated.4,5,14,15 Compared to a failure rate of 12.6% after three years4 and 31.8% after five years5 of sealed over cavities with a diameter of the orifice of <0.9 mm in permanent molars, the result of the present study (5% of the micro-cavities sealed over progressed into a frank cavity after four years) is low. A major difference between these studies is the size of the orifice of the cavity, which was lowest in the present study. Further studies should investigate the effect of size of the cavity opening.

The present study also showed that the risk for developing a cavitated dentine carious lesion over four years in occlusal surfaces of first permanent molars is about three times (10% vs 3%) higher in occlusal surfaces with a cavitated dentine carious lesion at baseline than in those with no or an enamel carious lesion at baseline. This finding should be considered obvious, as a failed cavitated dentine carious lesion sealed over will re-expose such a dentine carious lesion in the occlusal surface. But it also implies that many of the cavitated dentine carious lesions sealed over remained unchanged with respect to its caries lesion level over four years. It means that the sealant intervention has contained the progression of cavitated dentine carious lesions (code 2) and made a more invasive restoration unnecessary. However, it is not known if the cavitated dentine carious lesions diagnosed are the same as those sealed over or whether they have been developed on the same surface but at a different spot. The present analysis did not distinguish the actual site of carious lesions, whether in enamel or in dentine and whether they were cavitated or non-cavitated. Therefore, in future studies colour photographs should accompany the clinical carious lesion assessment of occlusal surfaces.16,17,18

In the present study, no significant difference was observed in cavitated dentine carious lesion development over the four-year period between sealants with no and those with enamel carious lesions in occlusal surfaces sealed over at baseline. This finding corroborates the conclusion of a systematic review on this topic19 and implies that cutting away the signs of enamel carious lesions (enameloplasty) appears to be unnecessary20 and is considered overtreatment.21 The latter consideration has received support from a three-year long study among initially six- to seven-year-old high-caries risk children who had their high-caries risk occlusal surfaces either sealed with a resin composite or with a high-viscosity glass-ionomer according to the ART method in comparison with supervised toothbrushing during school time. The behavioural management of the occlusal surfaces by the child was as good as sealing these in preventing the development of cavitated dentine carious lesions.22

Conclusions

It is concluded that, in this child population, which moved from a high- to a low-caries risk status, the progression of micro-cavities sealed over with a high-viscosity glass-ionomer cement according to the ART method, a glass-carbomer or a resin composite, over a four-year period was low. It shows that sealants placed over micro-cavities have the ability to stop carious lesion progression. The type of sealant material appears less relevant.