FISSURE SEALING-Introduction, Definition, Clinical technique, Advantages, Disadvantages

Introduction

Fissure sealants cannot be discussed in isolation from caries diagnosis or treatment of pit and fissure caries. The authors discuss use of these materials both preventively and therapeutically.

Toothbrush bristles cannot access the pit and fissure system because the dimensions of the fissures are too small. As a result micro-organisms remain undisturbed within the fissure system. The tooth is most susceptible to plaque stagnation during eruption, that is, a period of between 12 and 18 months. During this time, children need extra parental help in maintaining their oral hygiene. Lesion formation takes place in the plaque stagnation area at the entrance to the fissure and commences with subsurface demineralization. Demineralized enamel is more porous than sound enamel. The more demineralized and porous the affected enamel, the more it shows up both clinically and on radiographs.
Before and after fissure sealing


Key Point
To detect the earliest white spots the tooth must be dried to render them more obvious.

Once the initial lesion has developed, caries may spread laterally such that a small surface lesion may hide a much greater area of destruction below the surface.

Remineralization of occlusal lesions is much more difficult to achieve. Fissure sealing, 6 monthly 2.26% fluoride varnish application with oral hygiene instruction, and a weekly 0.2% sodium fluoride rinse, have all been found to help stabilize the disease and retard the progress of occlusal caries, but the fissure sealing group exhibited the best effectiveness. Many studies have shown that generally as the caries rates decline, the proportion of caries that affects pits and fissures of molar teeth increases, and also that the caries appears to be concentrated in a smaller cohort of children¾most of the decay occurs in 25% of the child population. This predilection has meant that correct use of fissure sealants should have a maximal effect.

There is no dispute that when correctly applied and monitored, fissure sealants are highly effective at preventing dental caries in pits and fissures, but interpretation of the correct application and monitoring requires scrutiny.
 
Key Point
Fissure sealants reduce caries incidence but must be carefully monitored and maintained.

Hidden caries ¾ although the occlusal surface looks mostly intact it hides extensive caries.

Caries has been removed. The size of the cavity emphasizes the extent of the lesion.

Who will benefit?
Not every fissure will become carious if it is not sealed. Therefore, each tooth for each child must be assessed on its own merits. The clinician must assess the risk factors for that tooth developing pit or fissure caries. As a general guide to who will benefit, review the British Society for Paediatric Dentistry Policy Document (Nunn et al., 2000).

The main beneficiaries are:

1. Children and young people with medical, intellectual, physical, and sensory impairments, such that their general health would be jeopardized by either the development of oral disease or the need for dental treatment. In such children all susceptible sites in both the primary and permanent dentitions should receive consideration.

2. All susceptible sites on permanent teeth should be sealed in children and young people with caries in their primary teeth (dmfs = 2 or more).

3. Where occlusal caries affects one permanent molar, the operator should seal the occlusal surfaces of all the other molars.

4. If the anatomy of the tooth is such that surfaces are deeply fissured, then these should be sealed.

5. Where potential risk factors, such as dietary factors or oral hygiene factors, indicate a high risk of caries, then all sites at risk should be sealed.

6. Where there is a doubt about the caries status of a fissure or it is known to have caries confined to the enamel, fissure sealants may be used therapeutically. After application, it is essential to monitor the surface both clinically and radiologically.

Sealant use must be based on personal, tooth, and surface risk, and the clinician must assess these risks since it might change at any time in the life of the patient. So whereas it was traditionally stated that dentists should complete sealant application up to a year or two after eruption, he or she should assess the potential risk factors regularly, and place the sealant, when indicated irrespective of age. Failure rates are higher when sealants are placed on newly erupted teeth and in mouths with higher previous caries experience. Monitoring the integrity of sealant is vital in those circumstances and any deficiencies in a sealant should be corrected.
Fig. 9.6  This tooth which is too early to seal with resin, should be painted with fluoride varnish or if the caries risk is very high should be sealed with glass ionomer until further eruption has taken place.
Fig. 9.7  This molar is just at the correct stage to apply fissure sealant. The very small operculum of gingival tissue can be held away from the tooth gently with a flat plastic.

Fissure sealing technique
Clinical technique
Pretreatment prior to sealant application
Tooth preparation with pumice and a rotary brush results in a good clinical retention rate. Dry brushing achieves similar results. Air polishing, using a 'Prophy-Jet', an early air abrasion system that uses sodium bicarbonate particles as the abrasive medium, provides good bond strength and sealant penetration but has not received general acceptance, probably, because most dental surgeries do not possess this equipment.

Some researchers have advocated the use of 'Enameloplasty', a more aggressive intervention into the tooth, that is, mechanical enlargement of the fissures with a bur or with air abrasion, to improve sealant penetration and reduce micro-leakage. Although some studies have confirmed these claims, the authors feel that this is an unnecessary extra procedure to subject the child to, and do not recommend it.

Etching
All the methods of cleaning the tooth, discussed above, should be accompanied with etching of the enamel surface. Etching for just 20 s with a range of concentrations of acid but most often, 35-37.5% phosphoric acid is the tried and tested method. Its one drawback is the susceptibility of the etched surface to saliva or moisture contamination, which reduces the bond strength. Salivary contamination results in significantly reduced bond strengths unless removed by thorough washing. Re-etching of the surface is usually necessary if salivary contamination has occurred.

Bonding agents
Bonding agents used as an additional layer under a resin sealant yield bond strengths significantly greater than the bond strength obtained when using sealant alone. Initial results of clinical trials also show increased retention of the sealant when an intermediate bond is used. New bonding techniques are proving to be less technique sensitive, with respect to moisture control than erstwhile procedures.

The use of a bonding agent under a sealant on wet contaminated surfaces yields bond strengths equivalent to the bond strength obtained when sealant is bonded directly to clean etched enamel without contamination. Most of the data on the subject of using a bonding agent as part of the sealant procedure supports its use. Use of a bonding agent would tend to increase the time and cost of the sealant application but in cases where maintaining a dry surface is difficult or where there are areas of hypomineralization on the surface, it would have many advantages.

Logically, combination of these technologies to achieve better penetration with less steps in the application sequence would be beneficial and there is some evidence already in the use of self-etching primer-adhesive systems. As yet, there has only been a 2-year follow-up but the early results are promising in relation to retention. Other studies have shown that there are concerns about micro-leakage compared with conventional acid etching. The big bonus of the self-etching primer-adhesive system is the speed with which the operator can apply it. In the application procedure for the Prompt-L-Pop system, the operator brushes the self-etching adhesive on to the surface; air thins it, and follows this by immediate placement of the sealant and polymerization. In the study, the average time operators took for the procedure was 1.8 min compared with 3.1 min for conventional technique. Such time saving is very useful in young fidgety children. At present, therefore, there are conflicting views on these systems but with technology moving ever onwards it does seem likely that in the future it should be possible to achieve good etching and bonding with a simpler application method.

Most clinicians will employ a resin-based sealant, because they have a good track record. Many clinical trials have demonstrated the effectiveness of resin sealants and there are several long-term studies, which show the benefits. Fifteen years after a single application, resin sealants have shown 28% complete retention of sealants and 35% partial retention on first permanent molars. Where researchers re-applied sealant to those surfaces that had deficient sealant as determined by yearly exams, 65% complete retention was obtained and only 13% of the surfaces had caries or restorations after 20 years.

Retreatment
Sealants placed in the first permanent molars in children of ages 6, 7, and 8 and in second permanent molars in children of ages 11 and 12 required more re-application than those placed in older teeth. If the clinician places fissure sealant in newly erupted teeth it is more likely to fail, but should still be placed as early as possible, because the teeth are more vulnerable to caries at this time.

Modifying the resin to incorporate fluoride is a logical rationale. However, fluoride release occurs only for a very short time and at a very low level. Many studies over 2-3-year periods have reported good retention but with a similar caries incidence to conventional sealant. Since the addition of fluoride to sealant resin does not have any detrimental effect it could certainly be used, but until the chemistry can be adapted to readily unlock the fluoride, the anti-cariogenicity cannot be attributed to the fluoride.

Greater release of fluoride can be achieved using glass ionomer (poly-alkenoate). Such cements have high levels of fluoride available for release but they suffer from the drawback of poor retention. Even with the very poor retention rates, sealing with glass ionomer does seem to infer some caries protective effect. This may be due to both the fluoride released by the glass ionomer and residual material retained in the bottom of the fissure, invisible to the naked eye.

Hence, glass ionomers, used as sealants can be classed as a fissure sealant but more realistically as a fluoride depot material. They can be usefully employed to seal partially erupted molars in high risk children since eruption of the molars takes 12-18 months and during this time they are often very difficult to clean. Once the teeth are sufficiently erupted the operator may place a resin sealant. They are also useful in children where there are difficulties with the level of co-operation, as the technique does not depend on absolute moisture control.

Logically, improvement in glass ionomer technology has occurred and both resin-modified glass ionomers (RMGI) and compomers have been used as sealants. As yet, studies of these materials used as fissure sealants while available, show no improvement over resin-based sealants and so there is nothing to recommend them in preference to resins.

Filled or unfilled resins?
Retention is better for unfilled resins probably because it penetrates into the fissures more completely. It also does not need occlusal adjustment as it abrades very rapidly. If a filled resin is not adjusted there is a perceptible occlusal change, possible discomfort, and wear of the opposing antagonist tooth.

Coloured or clear material?
Opaque sealants have the advantage of high visibility at recall. It has been found that identification error for opaque resin was only 1% while for clear resin the corresponding figure was 23% with the most common error being false identification of the presence of clear resin on an untreated tooth. The disadvantage of opaque sealant is that the dentist cannot examine the fissure visually at future recalls. The choice of an opaque versus a clear sealant is usually one of personal choice.

Safety issues
There has only been one report of an allergy to the resin used for pit and fissure sealing and concern has been raised about the oestrogenicity of resin-based composites. The proposed culprit, bis-phenol A (BPA), is not a direct ingredient of fissure sealants, but is a chemical that appears in the final product when the raw materials fail to fully react. The amount released orally is undetectable in the systemic circulation and concerns about potential oestrogenicity are probably unfounded.

Sealant bulk in relation to application
It is important to remember that the sealant must be kept to a minimum, consistent with the coverage of the complete fissure system including buccal and lingual pits. Overfilling can lead to reduction in retention and increased micro-leakage.

Sealant monitoring
Once the sealant has been placed the operator must monitor it at recall appointments and repair or replenish as necessary. Teeth lose is between 5% and 10% of sealant volume per year. Partial loss of resin sealant allows ingress of bacteria into the fissure system. This leaves that surface equally at risk from caries compared to an unsealed surface.

Cost-effectiveness
Cost-effectiveness will depend on the caries rate for the children in the population. Where there is a higher caries rate, generalized sealing will protect more surfaces that would have become carious in the future. However, if the caries rate is very high, then the risk of developing interproximal lesions is also higher and may lead to a two surface restoration even when the fissure sealed surfaces remain caries free. In low caries areas, the cost-effectiveness of sealant application en masse is questionable and the dentist should assess each child's individual risk factors. In contrast to this general concept, one study has shown that it is 1.6 times as costly to restore the carious lesions in the first permanent molars in an unsealed group of 5-10-year-old children living in a fluoridated area than it is to prevent them with a single application of pit and fissure sealant. This study also revealed a greater number of lesions if sealant was not utilized.

Sealing over caries
Once caries has been diagnosed it is important to determine its extent. If there is clear unequivocal evidence that the lesion does not extend beyond the enamel, then the surface may be sealed and monitored both clinically and radiologically. If the lesion extends into the dentine, the dentist would normally place either a preventive resin restoration (PRR), or if in an area of occlusal load, a conventional restoration. However, several authors have shown that dentinal carious lesions do not progress under intact sealants. Nevertheless, if the sealant were to fail immediately or shortly after application, then the lesion would have 4-6 months to progress before the next review. We do not advocate sealing over caries except in very exceptional circumstances, that is, very nervous children who cannot cope with even minimal intervention dentistry.


White fissure sealants can easily be check at recall, they are also visible to show the patient and parent to help them understand the procedure.


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Clear fissure sealant is less easy to see though its presence can be checked, if an area is giving cause for concern, by etching.0

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