TBU #049: 5 Ways to Reduce C-Factor In Biomimetic Restorations

New Issue of The Biomimetic Uprising

Read Time: 3 min  

 C- Factor in dentistry is one of the concepts that can be hard to understand and visualize but is one of the most important concepts for clinical success. 

The "C-factor" refers to the cavity configuration factor. It is a numerical value that represents the ratio between the bonded and unbonded surfaces in a dental restoration. The C-factor is used to evaluate the polymerization shrinkage stress that occurs during the placement of composite resin restorations.

When a composite resin material is used to fill a cavity, it undergoes a polymerization process in which it hardens and shrinks. This shrinkage can generate stress within the material and at the adhesive interface between the tooth structure and the restoration. The C-factor helps to determine the magnitude of this stress.

The C-factor is calculated by dividing the bonded surface area by the unbounded surface area. The bonded surface refers to the surfaces of the restoration that are in direct contact with the tooth structure, while the unbounded surface represents the surfaces of the restoration that are not in contact with the tooth structure or are in contact with a cavity wall.

A higher C-factor indicates a higher ratio of bonded to unbounded surfaces, which leads to a higher polymerization shrinkage stress. This increased stress can potentially result in problems such as marginal gaps, post-operative sensitivity, or even restoration failure.

Dentists consider the C-factor when planning and performing dental restorations. They may modify the cavity design, use incremental layering techniques, or employ other strategies to minimize the negative effects of polymerization shrinkage stress associated with a high C-factor.

As a Biomimetic Dentist, we can employ several techniques to reduce the C-factor and minimize the negative effects of polymerization shrinkage stress during dental restorations. Here are some commonly used methods:

1. Incremental Layering: Instead of placing the entire composite resin restoration in one bulk, layer the material incrementally. This involves placing and curing the composite resin in multiple smaller increments, reducing the overall volume of material being polymerized at once. By layering the restoration, each increment has a lower C-factor, resulting in reduced shrinkage stress.

2. Cavity Design: Modifying the cavity design can help to lower the C-factor. Dentists can create conservative preparations that minimize the number of bonded surfaces. For example, using bevels or chamfers can alter the cavity configuration, reducing the bonded surface area, flared preparations, etc. When a high C- Factor preparation is expected, it can beneficial to modify a prep to an onlay/inlay.

3. Matrix Systems: Matrix systems, such as sectional matrices or matrix bands, provide support and stability during the placement of composite resin restorations. They help to create proper contact and contour with adjacent teeth. The use of matrix systems can help to limit the size of the restoration and reduce the C-factor. However, in this case, depending on how they are employed, they can help build the foundation for an indirect restoration. Such as the DME band from Garrison. Indirect restorations are the most stress reduced dental restoration.

4. Soft Start Polymerization: Some dental curing lights have a feature called "soft start" or "ramp-up" mode. This mode initiates the polymerization process at a lower intensity and gradually increases the light output over time. Soft start polymerization allows for better adaptation of the composite resin to the cavity walls, reducing shrinkage stress and improving the overall integrity of the restoration.

5. Use of Low-Shrinkage Composite Resins: Dental manufacturers have developed composite resin materials with reduced polymerization shrinkage. These low-shrinkage composites typically incorporate modified resin formulations or filler particles with special properties. By using these materials, dentists can reduce the overall shrinkage stress associated with the C-factor. One of my favorites is Clearfil Ap-x by Kuraray. Its properties match very well to the natural tooth.

It's important to note that the choice of technique may depend on the specific clinical situation, the size and location of the restoration, and the preferences and expertise of the dentist. Evaluate each case individually to determine the most appropriate approach to minimize the effects of the C-factor and optimize the longevity and success of dental restorations.

Whenever you're ready, here are the ways I can help you:

1.  If you're looking for better application in your practice, take a look at our online courses and guides 
   1. The Foundations Of Biomimetic Dentistry
   2. How To Do Biomimetic Posterior Direct Composites.
   3. Get our 53 page biomimetic protocols guide for posterior direct restorations.