Abstract
Dental sealants have been utilized for over 50 years in different parts of the world with varying degrees of success.1 Dentists, dental hygienists, dental assistants and even patients have spent much effort in either providing dental sealants or receiving them on their own teeth. Still, international information sadly reports that occlusal caries is present and even increasing in certain age groups.2 A review of literature provides an explanation for this poor performance; however, newer studies, materials and findings may provide hope for the future.3,4,5
Early sealant materials were resin based and were light or chemical cured. The sealants that were chemical cured were usually two liquids, one a base and one a catalyst in liquid form. Usually one drop of one and one drop of the other were dispensed, mixed and applied to teeth. The operator than had to wait for a certain period of time for the chemical reaction to occur and set. This at times was difficult when the patient was a wiggling six year old.
The next version of sealant materials was the light cured resins that allowed demand cure and faster setting. These replaced most chemical cured resin sealants and became market leaders. Unfortunately, most of these chemical and light cured sealants required etching, rinsing and then complete drying of the tooth before application. In order to provide complete isolation, most manufactures recommended that a rubber dam be used. This may be possible for fully erupted teeth but can be quite difficult for partially erupted teeth. Because of these various issues, sealants have not been as effective as hoped.6
Another group of dental biomaterials, glass ionomers, has been used for sometime mostly outside the USA and Canada as a temporary or in some cases a permanent restorative material. Recently, this material has been reformulated as a sealant material that has properties different from and in most cases is better suited as a sealant material (Product example: Triage). Maybe glass ionomer will be the material that can make occlusal caries a thing of the past.
THE PARTIALLY ERUPTED PERMANENT FIRST MOLAR:
WHY ISIT DIFFERENT AND SO IMPORTANT?
The first permanent molar is a critical tooth for obvious reasons. It is the primary chewing tooth and if lost has detrimental effects on one’s chewing efficiency and arch integrity. If lost at an early age, arch alignment is changed, bone is reabsorbed and the masticatory system is compromised.
What makes the first molar difficult to keep caries free is the fact that it is unique by needing between 12 and 18 months to fully erupt into occlusion with other teeth in the arch.7 Where bicuspids require only 3-6 months to reach occlusal height, the first molar takes its time to reach occlusal height. This is not good, since during this time in most cases, its occlusal surface is probably not being brushed due to the toothbrushes’ inability to contact its occlusal surface. This happens because the bristles are being held up by the height of the deciduous teeth mesial to it (Fig. 1).
This issue translates into the occlusal surface of the first permanent molar not being brushed and in most cases being covered with plaque, food particles and a low pH environment. This tooth then becomes carious on the occlusal surface by the time it fully erupts. This is now too late for the brush, which now can reach the occlusal, to do its duty. Obviously, brushing alone has not been shown to totally prevent occlusal caries. Bristles are too large to reach the narrow fissures in the enamel so caries can be produced.
Fluoride can assist in caries prevention, however, we all know fluorides are beneficial mostly on smooth surfaces of teeth.8 This leads us to dental sealants that have been advocated for many years, but unfortunately, until recently, they have been resin based, which means hydrophobic. Thus they are not the best chemistry to be used on permanent first molars since these teeth are most of the time not fully erupted when they really need the sealants and necessary isolation is not practical. It has been shown that improperly placed sealants can have a negative effect by leaking and allowing caries to develop and in some cases be unnoticed under the leaking sealant.9 Also, resin sealants “cover” the under mineralized, early, enamel surface preventing oral fluids, at times containing fluoride from tooth pastes, topical professional applications and even chewing gums with fluoride or calcium/apatite chemistries from contacting the immature enamel surface. Enamel requires almost three years to become ideally mineralized and during this time the enamel is incompletely formed and susceptible to early low pH attack.10
From this brief scenario, we can see that given the reality of the permanent first molar: slow eruption sequence, delayed time of total mineralization, tooth brush inaccessibility, and the limitations of resin sealant chemistries, and difficulty in proper isolation, there are reasons why people continue to experience occlusal caries! What can be done?
WHY GLASS IONOMER?
Glass ionomer has been available to the dental profession for many years. Until recently, it has been used mostly outside the USA, however, it is now being advocated more as its benefits are being recognized and taught in dental schools. Is it a beneficial material for dental sealants? If we look at its properties, it seems to be a better choice for the challenge of sealing teeth, especially, partially erupted ones.
1. Hydrophilic: Whereas resin sealants are hydrophobic, glass ionomers can bond in an aqueous environment, in fact in their “directions for use’, tooth structure should not be dry in order for its chemistries to reach their full effect.11 This property blends itself to an environment where perfect isolation is difficult and possible saliva contamination could be possible.
2. Contains and Releases fluoride: Unlike resin sealants that only seal enamel, glass ionomers seal enamel, but additionally, contain fluoride and can recharge the fluoride via dentifrices and any topical source of fluoride. Given the limitation of immature enamel to be highly mineralized immediately after eruption, the presence of fluoride on the enamel surface has a benefit. The fluoride in the glass ionomer can assist in mineralization and even remineralization of the enamel. On the other hand, resin sealants are solid materials, seal the tooth and thus are not able to provide fluoride to the enamel. Glass ionomers are porous and have spaces large enough for saliva containing calcium and fluoride to diffuse through the glass ionomer and assist the enamel in the hardening process.12
3. Easy to place: Glass ionomers do not require acid etching, rinsing and drying of the enamel. Their ‘Directions for Use’ recommends the application of a conditioning agent and then placement of the sealant.13 This is faster than resin sealant application and therefore, when a rubber dam cannot be utilized, there is less risk of saliva contamination.
4. Flow deeper into enamel fissures than resin sealants: In a study of the ability of resin sealants and glass ionomer sealants to penetrate into enamel fissures, it was found that GI sealants were able to penetrate deeper and also flow into more convoluted fissures14 (Figs. 2 & 3). This study showed that due to the deeper penetration, sometimes the GI sealant was not visible during clinical examination, however, after sectioning the teeth, the fissures were in many cases, sealed below the level previously visible from the occlusal.
Some studies have reported GI sealant as missing but the GI sealed teeth did not become occlusally carious.15,16. This result could most likely be that GI sealant particles were still sealing the deeper areas of
the fissures. Clinicians should be aware that even though the GI sealants may look missing, they might still be sealing the deeper portion of the fissure.
POSSIBLE GOALS FOR THE PROGFESSION
One of the primary goals of the dental profession has been to provide knowledge, materials, and techniques that will lead to the prevention of dental disease. To this purpose, the longevity of survival of the permanent first molar is critical. If the profession could find the resources to accomplish this via practical and effective pit and fissure sealants, a major breakthrough in the status of oral health would be realized. It appears that glass ionomer sealant material may be the material of choice. To accomplish this goal, sufficient resources would need to be created to support providers, i.e., dentists, dental hygienists, dental assistants, as children are having their first permanent first molars sealed. It is not enough to just have these teeth sealed, these teeth need to be sealed as soon as possible after they are visible in the mouth. This means sealing during early eruption and not waiting until the teeth are fully erupted (Fig. 4). To wait until the teeth are fully erupted in most cases is too long which can lead to the teeth developing occlusal caries.
SUMMARY
Dental patients have always wanted to avoid going to a dentist, however, human nature being as it is, caries for many reasons continues to occur and patients still need treatment. Maybe this trend can change and patients may experience fewer occlusal caries. With the new information concerning glass ionomer sealants, this may be a possible solution at least for partially erupted molars. Glass ionomers are easily placed, contain fluoride, allow immature enamel a chance for mineralization, and are hydrophilic. Research provides support for their use and dental health care providers are finding them easy to apply. OH
Donald E. Antonson, DDS, M. Ed, Associate Dean for Academic Affairs and Professor, Department of Restorative Dentistry, School of Dental Medicine, University at Buffalo, The State University of New York. Oral Health welcomes this original article.
REFERENCES
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