Restoring conservative class II cavities

Caries that has just progressed past the DEJ can be a challenge to treat. The milder extent of the cavity preparation can be more difficult to manage than large preparations due to the smaller access and higher risk of voids and maladaptation. After preparation, the cavity prep can often appear like in Figure 1.

Class 2 cavity preparation. In shallow caries just into dentine the preparation may be similar to the blue shape. Removal of the orange section may improve visibility and access

This small prep although conservative and in the patient's best interest it may cause a sub standard restoration to be placed. The small access affects placement of etch, prime and bond as well as the placement of restorative material and access for finishing and polishing.

During preparation, the contact may not be broken which will make the placement of a matrix band difficult. You can get around this by using a stiffer band like a Tofflemire and forcing it through the contact or by widening the preparation to clear the contact point. Pre wedging with a wooden wedge when you have identified that it will be a small prep may free the contact and make further steps easier. The wedge needs time to work as the PDL stretches more over time. after about 10 seconds, reapply pressure on the wedge and you should be able to fit it in further. During prep, water should absorb into the wedge and spread the teeth further. It may also act as a lubricant and allow you to fit the wedge in further. 

After the matrix band has been placed, the actual access into the cavity will be reduced and so placement of bonding materials is more difficult. Bonding can be done before placement of the matrix band and this is a much easier method. In cases where the contact is broken, after placement of and before curing of the bond, the matrix band must be placed to avoid the teeth sticking together. Caution must be used as once the wedge is removed, gingival bleeding can occur if rubber dam is not used. If rubber dam hasn't been applied, it may be a better idea to break the contact or to widen the access cavity so that you aren't put in a situation where the wedge is removed after bonding procedures. Ensure you have burnished the band heavily against the adjacent tooth and this will improve the mesiodistal space for restoration as well as assist in gaining a tight contact.

Access to the cavity can also be improved by widening the occlusal aspect (Orange triangle in Figure 1). This is often unsupported enamel anyway and does not have a significant effect on the strength of the tooth. Conversely, the more cervical tooth structure at the base of the box is more likely to have a weakening effect on the tooth if removed.

Placement of restorative material is difficult in these situations and if done in increments may introduce voids to the restoration. If out of the occlusion, a flowable material can be used to restore in one increment or alternatively, a bulk fill composite can be used where strength is required. A concern exists that if the seal of the matrix band is imperfect against the tooth (as it always is) then there will be extrusion of material creating an overhang or excess in the embrasure area. This ism ore of a concern in packable and bulk fill composite as the material has to be compressed into the preparation to avoid voids. Flowable material can be introduced to the base of the prep with a narrow tip and the tip pulled out as material is extruded. To get around this, you must have a tight seal at the base of the box as an overhang will result in gingival inflammation and a poor restoration and is difficult to remove. Embrasure excess can be polished back after the restoration is placed. Tight wedging is difficuly especially as some teeth often have mesial contavities. V3 wave wedges can be used to account for this and must be used with a sectional matrix system. You can place a base of flowable and light cure before bulk filling the cavity and this will improve the seal before material is applied with force. Teflon tape can be packed in the embrasure areas to force the band against the tooth and improve adaptation. Diamond burs or discs can be used in the polishing stage to remove any excess in the embrasure areas.

Conservative cavity preps are challenging but satisfying. Sometimes, compromises have to be made to improve treatment outcomes. The most important step is to provide a well adapted and long lasting restoration which is unlikely to require replacement in the near future. early replacement of these restorations may defeat the purpose of a conservative preparation in the first place