Bite - In

This update of Step by Step give you a very lucid and detailed, clinically oriented presentation on restoring cervical lesions with tooth colored restorative materials. Dr.V.S.Mohan explains all the steps with vivid photographs to explain the same.

THE CERVICAL RESTORATION

It is estimated that nearly 20% of all permanent teeth have cervical lesions either due to abrasion, erosion, abfraction or due to caries. As it is, with any restoration there are always certain objectives for carrying out the restoration, viz alleviate pain, hypersensitivity, to prevent food lodgement and to facilitate partial denture construction. Today we have various materials, which could be used to carry out these restorations viz. GI, COMPOSITES, COMPOMERS AND ALSO COMBINATION OF GI AND COMPOSITES.( SANDWICH TECH ).

STEP ONE - ANALYSIS

The cervical lesion on a lower canine. Even though it may sound very elementary, the first step in a cervical restoration is the which is more often than not missed out. It is a very common practice on the part of the clinician to consider restoring cervical lesions as childs play and hence no focus is put into analysing the kind of lesion. The clinician has to evaluate multiple points so as to ensure that perfect esthetics and an adequate margianl seal is achieved. Always check for the following points.

a) Absence of enamel in the cervical area
b) Lesion depth and Size - from biological depth and also from the point of material to be used
c) The margin of the lesion vis a vis the periodontium i.e. supra or sub gingival
It will be prudent to check the occlusion after making the patient sit upright on the chair and in case, there is a premature contact it will have to be relieved before one embarks on the restorative procedure.

STEP TWO - ANAESTHESIA

The use of an anaesthetic is both operator dependent and patient dependent. If the operator is more comfortable working on an anaesthetized patient, LA can be given. Some patient are more senstive to dental tissue manipulation in relation to others. It is possible to get away only with a topical anaesthetic for inserting the retraction cord. The ultimate parameter is patient comfort.

STEP THREE - SHADE SELECTION

Shade selection has to be done under proper illumination. Day light is normally the ideal. In case sufficient natural light is not available shade matching lights can be used (like the Efos esthelite shade matching light). It is mandatory that oral prophylaxis be carried out prior to the restoration since any bleeding dut to gingival inflammation will hamper the restoration. Secondly by polishing the tooth prior to the restorative procedure, we are eliminating the external stains and the natural color of the tooth is visible to facilitate color selection. Involve the patient and the clinical staff. Make sure that the shade selection is carried out prior to application of the rubber dam. Isolating with a rubber dam may lead to dessication of the tooth and hence will appear one shade lighter.

When comparing the shade of the tooth with the shade guide make sure that the tooth surface as well as the shade guide is moist. This will ensure a more closer match. It would be better if one could make a personal shade guide with the actual restorative material, since the shade guide supplied by the manufacturers are in plastic and not in composite. The enamel shade should be taken from the incisal third of the tooth and the dentine shade from the middle and cervical portion of the tooth. It is important to note that the tooth is polychromatic and not monochromatic. Hence the shade should be observed as closely as possible and not just merely take a single shade for the entire restoration for maximum esthetics.

STEP FOUR - REMOVAL OF CARIES

As we do not have to follow the principles of cavity preparation, preparation of the site is limited to removal of caries. Caries should be removed with excavators or round steel burs. If in doubt, use of caries indicators is very useful in cervical restorations. Caries indicators are essentially dies which stain the carious sections of the tooth. There is no definite guideline for cavity preparation unlike amalgam restorations, like outline form, retention form/resistance form. In the presence of caries I generally prefer to use the caries indicator from ultradent so that I am sure that I have just removed the lesion and not sound tooth structure. After the application of caries indicator and washing it, the carious area gets stained. It is preferable to use rotary instruments rather than excavators. Small round steel burs are ideal in removing the carious part and not cut the tooth structure, thereby keeping up with the principles of conservation of tooth structure.

STEP FIVE - ISOLATION

The next step is to isolate the tooth for which the restoration has to be carried out. On a case to case basis isolation may be carried out using either rubber dams, cheek retractor & cotton rolls, retraction cords or transparent mylar strips. A retraction cord is more or less a must in all cervical restorations. The options are between using a rubber dam, cotton rolls or a mylar strip. If the patient is co-operative, cotton rolls with a cheek retractor tends to be sufficient isolation. Transparent mylar strips can also be shaped as hoods around the gingival margin for further isolation. It is assumed that a suction is available, since it is almost impossible to do any kind of composite restoration without a suction.

STEP SIX - BEVEL AND GROOVE PREPARATION

It is beneficial to place a bevel towards the incisal area. As far as possible the enamel on the gingival/cervical area should be preserved. The bevel will help in blending the composite to the tooth and masks the union line. Never try and place a bevel on the cervical area as the enamel thickness will be less and it is wise to conserve any remaining enamel. It is preferable to place the bevel with the help of a small tapered fissure bur, holding it at an angle of about 45 degrees to the long axis of the tooth. Bevels should be placed on the cervical area of the cavity only when the lesion is more towards the middle third of the tooth. The retentive groove (0.5mm) is placed directed gingivally on the cervical area with the help of a small round bur and it provides extra retention .

The cleaned, etched and prepared cavity.

STEP SEVEN - CLEANSING AND ETCHING

The enamel should be conditioned before the etchant is applied. It should be thoroughly cleaned with pumice and water to ensure complete removal of the salivary pellicle. The cavity should be washed with an antibacterial (chlorhexidene). The total etch technique is carried out using 37% phosphoric acid gel. The etching time is about 20 seconds. The etch has to be thoroughly washed off and dried. Be carefull not to dessicate the restoration since it can be as harmful as wet enamel.

STEP EIGHT - PRIMING, BONDING

The primary guideline for this procedure is to follow the manufacturers instructions. Since this step entirely depends on the bonding system being used, it is beyond the scope of this article to go into each and every available system. In my practice I use the SYNTAC system from Vivadent. This system is supplied with a self-etching primer that contains maleic acid and TEG-DMA acetone. Hence a dentine conditioner is not used. After application and drying of the primer, two adhesive resins are applied. The first, referred to in the system as Adhesive contains glutaraldhehyde and polyethylene glycol dimethacrylate in water. Following air drying of the adhesive , Heliobond ( BIS GMA & TEG DMA) is applied and light cured. For a thorough understanding of the resin reinforced layer /hybrid layer and the action of the primer etc refer to the faqs

STEP NINE - COMPOSITE PLACEMENT & CURING

Composite placement will depend on the size of the cavity and also whether all the margins are in enamel and if enamel is absent in the cervical area. In case, the cavity is shallow and only enamel has to be replaced, then a single layer of microfilled composite would suffice. In case it is a deep cavity, a combination of an initial hybrid layer and then a microfilled layer would be needed. During placement and curing of the material, take into account the fact that the bond strength of the composite resin and enamel is stronger as compared to the bond strength of composite resin and dentin.

Hence, in cervical restorations where cervical enamel is absent the material should be initially placed away from the existing enamel and then cured. Subsequently, a second increment should be placed and cured. Finally, the microfilled material should be placed and the composite cured. Since the superficial layer is not cured due to the oxygen present in the atmosphere, De-Ox, an oxygen inhibiting agent, should be applied on the surface and final curing carried out.

The placement of the composite material is carried out with the help of a teflon coated instrument and also involving the least possible surface area of the instrument. The instrument should not be dipped in the bonding agent it would only increase the polymerisation shrinkage. Always use a clean instrument which is dedicated for composite work .

I would like add at this stage that some clinicians prefer initially curing from the palatal aspect or the lingual aspect of the cavity so that the polymerisation vector will be directed towards the light and hence the material will shrink towards the tooth, but I would say that this depends on the thickness of the tooth and for which one needs to see that the material thickness should be less than the normally accepted 2mm, because the light has to travel for a longer distance through the tooth.

The completed restoration.

STEP TEN - FINISHING & POLISHING

Any excess material should be removed with the help of finishing bur/blade. The margin (cervical ) should be checked so that no excess remains which in turn would irritate the periodontium. Polishing is carried out after 24 hours. Points and/or discs could be used and a good polish is advisable as any roughness would lead to irritation to the gums. The reason for delaying polishing is that the material is known to show hygroscopic expansion and it is probably a wishfull thinking that the hygroscopic expansion would in some way compensate for the polymerisation shrinkage. I prefer to use cosmodent discs to carry out the polishing procedure. You have the color coded discs from coarse to superfine and finally I use the buff. As a final step I use the polising paste from caulk to get the final polish.

It is mandatory to call the patient for a regular checkup every six months so that the marginal seal and ditching can be spotted and corrective measures can be adopted early.