Dental Restoration – Fissure sealing
Sealing of susceptible pits and fissures is carried out as soon after eruption as possible. First, second, and third permanent molars are obvious candidates, but all molars are not automatically fissure sealed. Where plaque control is good (and this should be checked with disclosing solution) and where no lesion is visible, a sealant is not needed. However, caries or missing teeth which have been extracted because of caries in a child’s mouth indicate caries risk and will favour the use of sealants. Similarly, if a young adult requires restoration of one second molar, fissure sealing the remaining second molars seems to be a logical preventive measure. Fissure morphology is also relevant. A fissure pattern of shallow rounded grooves is unlikely to decay, but a deep fissure pattern is more susceptible since it is difficult to clean. Where the dentist believes that the patient’s diet contains frequent sugar intakes or when poor oral hygiene cannot be improved – for example where patients are mentally or physically disabled – fissures should be sealed. Children with significant medical conditions which put them at risk from the consequences of dental disease should also be offered sealant treatment. These medical conditions include cardiac problems, immunosuppression, bleeding disorders, blood dyscrasias, and metabolic and endocrine problems. Finally, the tooth to be fissure sealed must be capable of being isolated from salivary contamination since contamination while placing the sealant is the most common cause of failure. At best, salivary contamination will result in the sealant falling off, with no permanent harm. At worst, however, the sealant will be partly retained but leak, so that caries can progress beneath it, safe from salivary protection, fluoride ions, and detection by the dentist. Therefore good isolation from saliva is an essential part of the clinical technique, with a rubber dam being the preferred method.
Clinical technique for resin sealers
Anaesthesia and isolation
If necessary, a little local anaesthetic is infiltrated or topical anaesthetic is applied to avoid discomfort from the rubber dam clamp.
The tooth surface to be etched and sealed may be cleaned with a bristle brush in a handpiece and a pumice and water slurry. Oil-based polishing pastes or those containing fluoride should not be used, as these may interfere with etching. The pumice is washed away using the three-in-one syringe. Some dentists clean the fissure with a high-pressure spray of sodium hydrogen carbonate; this is known as ‘air polishing’. This is similar to ‘air abrasion’ as already described in earlier posts. In this format a high-velocity air stream contains soft sodium bicarbonate powder (baking soda), shrouded by water, and has little cutting effect on intact enamel. The powder is water-soluble and is easily removed after cleaning.
The tooth is now etched with phosphoric acid (30–50 per cent). The acid etchant is supplied by the manufacturer in the form of a coloured gel. The etchant is applied over the whole occlusal surface extending onto the lingual or buccal surface where grooves require sealing. Etching the entire occlusal surface avoids the danger of covering an unetched surface with sealant and thus inviting leakage. The acid can be applied with a brush, or alternatively the gel can be placed accurately with a disposable syringe and blunt needle. As soon as the complete area to be etched is covered with acid, the time is noted and the enamel is etched for 15–20 seconds.
After 20 seconds the acid is washed away. Initially a water jet from the three-in-one syringe is used to remove most of the acid. If a rubber dam is not in place, careful aspiration is important to avoid damage to soft tissue by the acid. After approximately 5 seconds of water, the air button is also pressed, forming a strong water–air spray which should be played over the etched surface for 20–30 seconds. With coloured gels, it is tempting to stop washing when the colour has gone. However, the purpose is not just to remove the surplus acid, but to flush the precipitates out of the newly formed etch pits, and this takes a full 20–30 seconds.
Many fissure sealants are still based on hydrophobic resins and so a careful drying regime is required. It is good practice to check that the airline is not contaminated by water or oil by blowing it at a clean glass or paper surface. The tooth surface is now thoroughly dried with air from the three-in-one syringe. This drying is most important since any moisture on the etched surface will stop penetration of the hydrophobic resin into the enamel. A minimum of 15 seconds drying is recommended. At this stage the etched area should appear matt, white, and frosty. With a rubber dam, there should be no danger of salivary contamination of the etched surface. If this does occur, however, it is essential to re-etch the enamel because adherent organic material in saliva will block the pores and it cannot be removed completely, even by vigorous washing.
Applying the sealant
Fissure sealants are supplied both as light-curing and chemically-curing materials. A light-cured resin does not require mixing but a chemically-cured resin has two components which are gently mixed together with a brush.
A sealant is applied to the etched surface using a small disposable brush or applicator supplied by the manufacturer.
The sealant is applied to the etched pits and fissures and up the etched cuspal slopes. If a light-cured material has been chosen, the light should be placed directly over the sealant but should not touch it. With a molar tooth, if the light source is of a smaller diameter than the tooth it should be directed at the distal part of the occlusal surface for the full curing time recommended by the manufacturer of the resin and then moved mesially for a similar period. Any buccal or palatal groove or pit should be similarly cured with the light source directly over it. Since the polymerizing lights are potentially damaging to the operator’s eyes, special eye-protective glasses should be used or the dental nurse should hold a special filter screen in the operator’s line of vision. Some lights Fissure sealing 123have protective cups which can be placed over the end of the light guide. Most chemically-cured sealants polymerize in 1–3 minutes and the manufacturer’s instructions should be followed. The outer surface layer of any sealant will not polymerize due to the inhibiting effect of oxygen in the atmosphere. The sealant will therefore always appear to have a greasy film after polymerization. Finally, a fluoride-containing varnish may be applied to the etched enamel at the periphery of the restoration where it has not been covered with sealant.
Checking the occlusion
The rubber dam is now removed and the occlusion checked with articulating paper. Whilst it is considered acceptable to allow any high spots to be abraded away when unfilled resin fissure sealants are used, with the lightly-filled materials it is wiser to reduce high spots by grinding with a small round diamond stone in a low-speed handpiece.
Clinical technique for glass ionomer cement sealers
The authors would rarely choose a glass ionomer cement for fissure sealing because the scientific evidence on retention and caries prevention has shown these not to be as effective as resin sealants. It is possible that the fluoride in the material may exert a cariostatic effect. However, they are the material of choice on an erupting tooth, where oral hygiene is poor, caries risk is high, and good moisture control is difficult. They should be considered a temporary measure in these circumstances. The tooth to be sealed is isolated and the fissure is cleaned with 10 per cent polyacrylic acid-conditioning agent, supplied by the manufacturer, for 20 seconds. It is then washed and dried, and the glass ionomer material, mixed to a flowable consistency, is applied along the fissure and firmly burnished into position. Excess material is easily removed with the burnisher. Although glass ionomer will almost certainly be less well retained than a resin-based system, the material may have a protective effect for high-risk fissures whilst the tooth is at its most vulnerable: in this situation a resin sealant would not work because the tooth may be impossible to isolate satisfactorily.
The sealant restoration (or preventive resin restoration)
The sealant restoration was born out of the use of pit and fissure sealants. It is a natural extension of the technique where pit and fissure decay is confined to one area in the fissure system. The technique restores the carious area and seals the rest of the fissures. The restoration is indicated where a cavity is present (either a microcavity in the enamel, or a cavity with dentine at its base). The lesion will usually be visible on a bitewing radiograph as an area of radiolucency in the dentine.
Occlusal contacts should be marked with articulating paper prior to preparation so that the dentist can remember where these contacts are. A local anaesthetic is given. A rubber dam is applied and the tooth is thoroughly cleaned as before (Fig. 7.3a). A small, pear-shaped tungsten carbide bur (Jet 330) is used in the air turbine to widen slightly and deepen the fissure and to gain access to caries in dentine. The air turbine is also used to remove the minimum amount of enamel necessary to gain access to caries. A small round bur is now used in the low-speed handpiece to remove soft, demineralized dentine, which is often stained, from the enamel–dentine junction. During this process the access cavity may require further enlargement to allow access to caries on the enamel-dentine junction. Thus high- and low-speed handpieces are used alternately so that the cavity is kept as small as possible commensurate with removing the soft dentine from the enamel–dentine junction so that it feels hard when a sharp probe is run along it. Finally, any soft caries overlying the pulp is removed with either a slowly rotating round bur in the slow-speed handpiece or a sharp excavator.
Lining and etching
If the cavity is much larger than expected, the deep dentine directly overlying the pulp may be covered with a calcium hydroxide-containing cement. A second layer of resin-modified glass ionomer may be placed in a deep cavity to act as a dentine replacement. The polyacrylic acid conditioning liquid supplied by the manufacturer should be applied to any exposed dentine with a brush. After 10 seconds the cavity is washed and dried and the glass ionomer cement placed. Once this material has set, any glass ionomer material on the enamel walls should be removed with a bur. The enamel walls of the cavity and the occlusal surface of the tooth are now etched with acid. After 20 seconds this is washed and dried as before.
Filling the cavity
A composite, designed for use in posterior teeth, is selected. It is supplied with a bonding resin which should be painted on the etched enamel walls and occlusal surface and blown with dry air to form a thin layer, avoiding puddles of material in the cavity. The resin is polymerized with light as before. The cavity is now filled with the posterior composite. These light-cured materials will not cure reliably in depths exceeding 2 mm. Thus, if the cavity is deeper than this (a graduated pocket-measuring probe can be used to check depth), the material must be placed in increments. Each increment is then cured before the next is placed, taking care not to dispense more than is needed because normal light in the surgery will polymerize the unused material. An increment of composite is placed or syringed directly into the cavity and gently nudged into position using a small ‘non-stick’ instrument. Care should be taken not to trap air under the material. When the final increment is placed an instrument is used to shape the occlusal surface, restoring cuspal inclines in the larger cavity before light-curing the material. Alternatively, the glass ionomer material is brought up to the enamel–dentine junction to replace all the missing dentine so that only one increment of composite, the thickness of the enamel, is required. An alternative to the glass ionomer/composite layered technique is to bond the composite filling materials directly to the etched dentine and enamel. This is called the all-etch technique. The enamel and dentine of the cavity and the enamel of the occlusal surface are etched for 15 seconds and then washed and gently dried. The dentine in particular should not be over-dried. Now a dentine bonding agent is applied following the exact descriptions of the manufacturer. The bonding agent is polymerized and then the composite is built up in increments as described previously.
Whether the layered technique or the all-etch technique have been used, the remaining fissure system has already been covered by the bonding resin. A layer of fissure sealant is now painted over the entire occlusal surface and polymerized. Alternatively, composite can be gently agitated with a plastic instrument into the adjacent pits and fissures, and light-cured to act as a heavily-filled pit and fissure sealant.
Finishing the restoration
Excess resin is carefully removed with 12-bladed tungsten carbide finishing burs or with fine diamond composite finishing burs. Once the rubber dam has been removed, the occlusal contacts should be checked with thin articulating paper. This is placed between the dried teeth and the patient is asked to move the teeth over each other as if eating. Any ‘high’ spot on the restoration will be located by a mark and can be reduced; the aim is to have the restoration in harmonious occlusion. The restoration can finally be smoothed with aluminium-impregnated rubber points.
Larger posterior composites
It is not uncommon for occlusal caries to undermine the occlusal enamel widely. In the past such restorations have often been restored with amalgam after all the overhanging enamel has been cut away. With posterior composite materials and glass ionomer cements, it is now possible to use these adhesive materials to restore the missing tooth tissue and support the remaining enamel without needing to remove so much of it. Therefore once soft demineralized dentine has been removed, decisions have to be made about the strength of the remaining tooth tissue. Figure c shows a large occlusal cavity with a considerable amount of overhanging enamel. This cavity was restored with a calcium hydroxide lining over the deepest pulpal part of the cavity used as an indirect pulp cap followed by a layer of glass ionomer cement to replace much of the missing dentine. Finally, the enamel walls were acid-etched and the remainder of the tooth restored with a posterior composite which was built up in increments as described previously. The same restoration is shown after 5, 9, and 14 years in Figs. In these large restorations as much sound tissue should be preserved as possible. Undermined and overhanging enamel can be supported with adhesive posterior composite materials and glass ionomer cements. Where mastication pressure is obvious, a minimum thickness of 2 mm of composite material is required. Where the outline of the preparation is placed beyond the occlusal surface, perhaps because a cusp has fractured or been completely undermined by extensive caries, a bevel should be prepared to optimize the adaptation of the composite to the enamel.