One of the common challenges dentists face, especially during colder months, is the handling of composite resins. Dental composites such as 3M composite materials can become stiff and difficult to manipulate in low temperatures, leading to poor adaptation and handling difficulties. To overcome this issue, many clinicians have adopted the technique of preheating dental materials, which has shown significant improvements in both handling and clinical performance.
This article explores the science, benefits, and practical considerations of heating and preheating different dental restorative materials including composites, resin cements, and glass ionomer cements (GICs).
Why Preheating Dental Composites Matters
When dental composites are stored or used in cold environments, their viscosity increases, making them difficult to dispense, manipulate, and adapt to cavity walls. Preheating offers several advantages:
- Reduces viscosity, making the material easier to handle.
- Improves adaptation to cavity walls.
- Increases the degree of conversion during polymerization.
- Decreases polymerization shrinkage.
- Enhances marginal adaptation, reducing the risk of microleakage.
Clinically, a preheated composite can perform similarly to flowable composites in terms of handling but maintains the superior mechanical properties of conventional restorative materials.
Preheating Resin Cement
For indirect restorations such as inlays, onlays, and veneers, preheating resin cement provides additional benefits:
- Improved bond strength to dentin.
- Enhanced adhesion to restorative materials.
- Higher degree of conversion, leading to stronger and more durable restorations.
Interestingly, some studies suggest that preheated composite resin may even outperform resin cement at restoration margins due to higher filler loading and better long-term color stability.
Preheating Glass Ionomer Cement (GIC)
Unlike composites and resin cements, glass ionomer cements behave differently when preheated:
- Viscosity increases upon heating.
- Preheating can accelerate the setting reaction.
- It can also improve adaptation and reduce long-term solubility.
Additionally, exposing GIC to light curing during mixing can further enhance setting properties.
How to Preheat Dental Materials
There are multiple ways to preheat composites and cements:
- Composite heaters (specialized devices).
- Water bath.
- Digital wax heaters.
Optimal Preheating Temperature
Research dating back to the 1980s indicates that the ideal preheating temperature for composites ranges between 54°C and 68°C.
- Above 68°C, negative outcomes may occur.
- Dentists must be cautious since an increase in pulp chamber temperature of more than 5.5°C can cause irreversible pulp damage.
- Dentin thickness plays a crucial role as a thermal barrier to protect the pulp.
Compared to the heat generated from light curing, preheating composites is generally considered safer.
Practical Considerations
- Time in the heater: Studies suggest anywhere between 40 seconds and 24 hours, depending on material type. However, 11–15 minutes is typically sufficient.
- Loss of heat: Once removed from the heater, composites lose about 50% of their temperature within 2 minutes, and 90% within 5 minutes. This means dentists must work quickly for maximum benefits.
- Storage tip: If composites are kept in a refrigerator, they should be left at room temperature for at least 11 minutes before use.
- Mechanical properties: Preheating does not negatively affect flexural strength, but repeated reheating cycles may lead to color changes.
When used correctly—with the right temperature, timing, and caution to avoid pulp damage—preheating can be a valuable tool in daily dental practice.
Reference
- Heating and preheating of dental restorative materials: A systematic review, 2020.