Is it acceptable to repair an existing composite restoration, or should you always replace the entire restoration?

One of the main advantages of composite restorations is the fact that they are repairable, unlike amalgams. It is well documented that composite bonds to itself as well as to dentin and enamel. Therefore, if you are certain there is no decay in any other area of the existing restoration, you can remove the portion of the restoration that you need to repair, and re-bond with flowable or restorative composite in those areas, depending on the size of the area to repair. If you are using a 4^th– or 5^th-generation adhesive, you will need to acid etch with phosphoric acid. If you are using a 6^th– or 7^th-generation adhesive, you can place the adhesive in the preparation, followed by the composite according to manufacturer’s instructions. Flowable composites are not as strong and do not wear as well as restorative composites, but are easier to flow into small spaces. So, my recommendation would be to use flowable composite only if the repaired area is small, as you would a preventive resin. If the preparation is similar to a traditional Class I or II design, you should use a restorative posterior composite.