September 19, 2022
Dr. Brad Craig, Ph.D.

Bulk Fill composites: Considerations and keys to success

Curing lights, prep depth, material viscosity – do you know all the factors that can impact the success of your bulk fill composite? Learn what to watch for, and how to bring out the best in your bulk fill.

Traditionally, composite resins are placed in multiple layers to minimize shrinkage stress and ensure adequate depth of cure. However, this process is arduous, time consuming and may still result in gaps and microleakage due to shrinkage stress. In fact, placing in multiple layers presents the possibility of increasing voids, gaps, and other imperfections. To help address these issues, bulk fill composites were designed to fulfill this desire for faster, easier placement.

Bulk fill composites present an alternative to incremental placement techniques, as well as an opportunity to achieve strong, esthetic, efficient restorations – but only if the material is used correctly. To help you bring out the best in your bulk fill, we’ve compiled a list of tips designed for achieving esthetic, efficient restorations.

How to bring out the best in your bulk fill composite

 

1. Keep the tip submerged.

Because incremental placement is such a widespread and accepted technique, it can be tempting to remove and reinsert the tip into the material throughout placement. However, this can introduce air pockets and voids into the bulk fill composite. That’s why it’s so important to keep the tip submerged in the material the entire time you’re injecting. Bear in mind that the delivery method, as well as the rheological and handling properties of the material you’re using, can have an impact on the final properties of the finished restoration, even if you use proper technique. For example, 3M recently introduced a new flowable bulk fill with a syringe design that helps eliminate bubbles and material “run-on” during dispensing, while providing more comfortable control. Ideally, the practitioner will choose a material and delivery that not only gives him or her the best control, but also provides the best final material properties for the finished restoration.

2. Understand depth of cure.

Achieving high, uniform depth of cure is critical to the success of any composite restoration, but this is even more important in a bulk filling material. However, the level of light penetration necessary to cure a given material is dependent on a number of factors, including the composite’s composition, color and optical properties, as well as the quality of your curing light and curing technique.

Start by measuring the depth of the preparation to ensure you don’t exceed the limitations of the material – then make sure to place appropriately. Cure with the light as close to the restorative material as possible, and follow the manufacturer’s recommended cure times and procedures, whether in a single layer or multiple, to ensure optimum cure. Keep in mind that curing through occlusal as well as buccal and lingual surfaces may be required for full cure depth and degree of conversion of the composite. Longer exposure times are generally better for most composite materials, taking heat generation as a counterbalance into account, especially when working closer to the pulpal chamber.

3. Know whether you need a capping layer.

While bulk fills in general are intended to fill in fewer layers than conventional composite, some are designed to work solely as liners, or to only fill a portion of the cavity preparation. These materials require an additional “capping layer” of another, stronger, more wear resistant and usually more highly shaded composite to finalize the restoration and achieve adequate esthetics and strength.

However, some bulk fill composites have been engineered for one-step placement, thereby eliminating the need for a capping layer – without compromising physical or cosmetic properties.

4. Check the indications.

Bulk fill composites have come a long way from their earliest formulations. While some legacy bulk fill composites were only indicated for bases or posterior restorations, many modern composites can be used beyond the posterior. That being said, always verify what your bulk fill composite is indicated for before using it for core build-up or in the anterior region – not all bulk fill composites are equally versatile.

On the other hand, before you write off your composite as a posterior-only material, double check the indications – you could be missing out on a great opportunity for a more efficient restorative procedure.

5. Keep an eye on esthetics.

Ideally, restorations should match surrounding dentition as closely as possible – but this is much easier said than done. Many bulk fill materials are highly translucent to enable the curing wavelengths of light to reach the bottom of the cavity and fully cure the composite. But this translucency often translates to grey, unesthetic final restorations, as the translucent material picks up and transmits unwanted color from its surroundings. Particularly for large posterior restorations or those with underlying stains, a low opacity composite can look unnatural or allow underlying stains to show through.

Some manufacturers have developed novel materials that solve this issue, including bulk fill composites that are initially more translucent and increase in opacity during curing, leading to restorations that cure completely and esthetically. This means that dental professionals can take advantage of the benefits of bulk fill composites without worrying about final appearance.

6. Know the flow.

Rheology is an important feature of every dental composite, bulk fills included. The viscosity of the material can have a distinct impact on a number of variables, including adaptation, handling, mechanical strength and shrinkage stress. In addition, how the material thins or thickens during shear and application can impact the adaptation, as well as the composite’s ability to shape and sculpt for final anatomy.

While bulk fill composites come in many different viscosities, they’re generally classified as either low or high viscosity – each with their own set of strengths, weaknesses and ideal preparation techniques. High-viscosity bulk fills tend to be strong, thick and packable or shapeable, but have a reputation of poor adaptation and higher stress. On the other hand, low-viscosity bulk fill (or flowable composites), are more fluid and therefore adapt better, but often at the expense of mechanical and wear properties.
Keep in mind that these pros and cons aren’t hard and fast rules – and certain materials properties can be altered with techniques such as using a composite warmer or selecting a different delivery method.

In fact, some bulk fill materials feature delivery systems that take advantage of the material’s thixotropic, or shear thinning, properties. That is, their viscosity temporarily decreases during the shear induced by extrusion and flows into the cavity preparation, for improved adaptation and fewer voids – without compromising mechanical properties. Depending on the material, this viscosity may increase again relatively rapidly to allow for shaping and sculpting of the material. Make sure your material’s viscosity and delivery method are working together to help give you the best result possible.

7. Know the performance and how to use your curing light.

Curing lights aren’t just another tool in your kit – their performance is extremely important to the final restoration’s quality and durability. In fact, incomplete polymerization can lead to clinical problems like fracture, secondary decay, discoloration or sensitivity.

Regardless of the bulk fill used, your curing light needs to deliver enough energy for enough time to the composite for it to cure completely and to the bottom. Not only does this mean reviewing your technique and the requirements of the material, but also making sure your curing light is performing as expected. Quality notwithstanding, curing lights degrade with use – which can drastically affect output of the light and subsequent cure of the composite material. Beyond selecting a high quality device, make sure you keep your curing light tip clean, test the light regularly and send it in for service as needed. In addition, review your technique – are you placing the light tip as close to the restorative material as possible? And are you angling the light to penetrate deeply into the material to effectively cure it? Finally, are you curing long enough per the manufacturer’s instructions to fully cure the material to the appropriate depth? Remember, no light equals no cure with these materials.

8. Use for restless patients or children.

Because bulk fills can be completed in fewer layers than conventional composite, they can actually make the placement process faster and easier. This, in turn, shortens chair time, which is particularly appreciated by clinicians treating restless or pediatric patients.

9. Pick the right polishing systems.

Finishing and polishing are both important steps in the restorative process, not only to achieve lifelike esthetics, but to minimize plaque accumulation and gingival irritation, and to help maintain overall oral health. And while there are many polishing systems available and every dental professional has their own preferences, it’s important to regularly review your choice of tools. It’s worth investigating new polishing systems – they could help you achieve a long-lasting high gloss in fewer steps.

Conclusion

Restorative success means more than just picking the right bulk fill composite – it means knowing your material inside and out, as well as what tools will help you get to the desired restoration and outcome. The more you control these key contributing factors, the more efficiently you’ll be able to reliably deliver strong, esthetic results – from the bottom of the restoration to the top.

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