Secondary Caries in Teeth

Secondary caries (or recurrent caries) is tooth decay that occurs around the margins of a restoration (seal margin) after a previous restoration has been placed. Although the restoration may appear intact, microleakage (microfluid circulation) at the interface between the restorative material and tooth structure can allow the penetration of bacteria and residual metabolic acids, leading to demineralization at the restoration margins.

Composite resin restorations are often chosen due to their esthetic properties and ease of direct application. However, one major limitation of composite resin is polymerization shrinkage, which refers to the volumetric contraction that occurs during the hardening process after light curing. This shrinkage can generate internal stress (shrinkage stress) and create microgaps that serve as niches for microorganisms, thereby triggering secondary caries.

Relationship Between Polymerization Shrinkage and Secondary Caries

• High shrinkage stress can cause delamination (loss of bonding) between the resin and enamel or dentin.
• These microgaps facilitate the infiltration of bacteria, their byproducts, and oral fluids beneath the restoration.
• The duration and intensity of light curing influence the degree of shrinkage and therefore play a crucial role in the development of secondary caries.

Findings from UGM Research

A study conducted by an FKG UGM student, Nadya Erza Taravinka, under the supervision of drg. Pribadi Santosa, M.S., Sp.KG(K) and drg. Margareta Rinastiti, M.Kes., Sp.KG. Subsp.KR(K)., Ph.D., entitled “Pengaruh Metode Penyinaran Soft-start dan High Intensity Terhadap Pengerutan Polimerisasi Resin Komposit”, concluded that:

• The soft-start curing method produces a lower level of polymerization shrinkage compared to the high-intensity method.
• Nevertheless, the high-intensity method may still be appropriate for composite resins specifically developed to withstand intensive light curing.

With lower shrinkage, the soft-start method has the potential to reduce the formation of microgaps at restoration margins, thereby lowering the risk of secondary caries around restorations.

Strategies to Reduce the Risk of Secondary Caries

Based on the mechanism and research findings, the following clinical strategies can help reduce the incidence of secondary caries in composite resin restorations:

1. Select light-curing methods that minimize shrinkage stress
   • The soft-start method (beginning with low intensity and gradually increasing) can reduce initial stress and allow the resin to adapt before complete hardening.
   • Avoid immediate high-intensity curing unless supported by the specific resin material.
2. Use composite resins formulated for low shrinkage
   • Some modern composites utilize monomer matrices or fillers designed to reduce shrinkage.
   • Materials compatible with curing methods are more resistant to stress development.
3. Layering / incremental fill technique
   • Applying resin in thin layers (incremental build-up) helps control internal shrinkage and minimizes cumulative stress effects.
4. Optimize curing light position and angulation
   • Ensure the curing light is positioned as close as possible to the restoration surface at an optimal angle.
   • Minimize shadows and light obstructions to achieve uniform penetration.
5. Ensure high-quality marginal sealing
   • Proper margin preparation (smooth edges, no undercuts) allows optimal adhesive bonding.
   • Use high-quality adhesive materials and follow correct bonding protocols.
6. Regular maintenance and follow-up examinations
   • Early detection of marginal leakage through clinical or radiographic evaluation.
   • If marginal changes or infiltration are detected, consider restoration repair or replacement.

***

Secondary caries remains a major challenge in composite resin restorations due to polymerization shrinkage that can create microgaps at restoration margins. UGM research indicates that the soft-start curing method is more favorable in reducing shrinkage compared to the high-intensity method, thereby potentially lowering the risk of secondary caries. In clinical practice, appropriate curing methods, suitable composite materials, proper application techniques,

References
NADYA ERZA TARAVINKA, drg. Pribadi Santosa, M.S., Sp.KG(K), drg. Margareta Rinastiti, M.Kes., Sp.KG. Subsp.KR(K)., Ph.D., Pengaruh Metode Penyinaran Soft-start dan High Intensity Terhadap Pengerutan Polimerisasi Resin Komposit, https://etd.repository.ugm.ac.id/penelitian/detail/206890

Author: Rizky B. Hendrawan | Photo: Freepik