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Flowable injection technique: How to avoid air bubbles in composite restorations

Depending on the type of composite and technique used, the number of bubble defects in dental restorations may vary, and there are several factors that cause them. (Image: Kuraray Noritake Dental)

Fri. 12. April 2024


LEGNICA, Poland: A composite restoration should be homogeneous in order to ensure the seal of the filling and its durability. However, air bubbles are a common issue either within the composite layers or on their surface, regardless of the material type, the restoration method and the application area. This article discusses their causes and provides a solution from Kuraray Noritake Dental.

The first cause of air bubble formation is the homogeneity of the material itself. Bubbles can be incorporated in the syringe at the manufacturing stage or during use. By opting for premium products, it is possible to ensure that the highest-quality material is supplied and that the syringe’s structure and design allow for proper operation in order to reduce the formation of air bubbles within the material. Flowable composites, while easy to apply, are sensitive to incorrect application.

CLEARFIL MAJESTY ES Flow composite (Kuraray Noritake Dental) is designed to prevent the formation of air bubbles during dispensing. The special design of the syringe and plunger limits the possibility of the dripping and backflow of the material during or after dispensing. A unique safety feature inside the syringe is its special O-ring construction, which prevents the material from flowing after pressure is released and ensures minimal retraction, thereby preventing the plunger from retracting too much.

Another cause of air bubble formation is the incorporation of air into the syringe by deliberately retracting the plunger. If the practitioner or ancillary staff member has a habit of retracting the plunger after administering the composite, he or she may cause air to enter the syringe. During subsequent use, the air will more than likely appear in the restoration as an air void.

In the flowable injection technique, a silicone index is used in which the material is applied to build up the tooth. The index should fit tightly to the tooth and should not move or be moved during injection. If it does, air bubbles may appear. Pressing and then releasing the index will cause a suctioning effect and pull the composite away from the tooth as well as from the index. To avoid defects, constant pressure on the index should be maintained from the moment the material is injected until polymerisation.

Various modifications of the silicone index can be used to limit its mobility and reduce the risk of uncontrolled pressure on the tooth. One example is an index made on the “Treat one, skip one” model, which provides a high degree of stability and working safety.

Another cause of air in the restoration is the width of the injection hole. If the hole is too small, the index can be moved by the application tip during insertion or application. To avoid this problem, the hole could be widened to allow free insertion and manipulation of the tip during injection. A wider opening also allows any air present to escape during dispensing. However, most important is the use of continuous pressure when applying the material and avoidance of the pulling out and reinsertion of the tip into the index. This could result in a non-uniform composite layer.

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