Bulk fill best practices

Your patients have expectations for dental restorations. When trusting you with restorative dentistry, patients not only want to return their teeth to the best possible condition and function, but they also want their restorative dental work to look good. Composite resin is a popular material for meeting patient expectations with direct restorations, and in some cases, bulk-fill composite resins are the type of composite you should reach for to meet them.

Composite resin has additional benefits to patient outcomes, too. It does not include mercury, and fillings made with it look better than previous materials (i.e., amalgam). Another significant benefit of using composite for direct restorations is its ability to bond with healthy tooth structure, which also means you do not need to create retentive features in the prep.

However, composite materials as a whole are much more technique sensitive than the materials that came before them. They require excellent isolation during placement, something that is not true with materials such as amalgam. The layer and curing process is essential to perform perfectly to reduce the effects of polymerization shrinkage inherent in the chemical makeup of the materials. Moreover, many resin composites can be time-consuming to place 2mm at a time in a preparation, particularly in deep preparations that can often occur in the posterior teeth.

In response to the growing popularity of composite resin for direct restorations, manufacturers responded by developing bulk-fill resins with different features than other types of composite. Bulk fills, as the name implies, can be layered in preparations thicker than traditional composite. This method is possible because the depth of cure for bulk fill materials is four to five millimeters. Furthermore, the materials retain many of the benefits of composite materials over other restoratives, including the ability to have a conservative restoration, better adaptation to preparations, and improved esthetics over other restorative materials.

Having fewer layers in preparations has many benefits. First, fewer layers mean less time spent curing the materials, which adds up to a faster placement process. Also, fewer layers mean fewer chances for voids and marginal leakage, which leads to complications for the restoration. Finally, having a predictable outcome is another reason many clinicians reach for bulk fills.

Many times, clinicians use bulk fills for posterior restorations and there are a few reasons why. Often, the preps are deep in the posterior, so the material can be an excellent way to “fill the hole.” Also, to get the 4-5mm depth of cure, bulk-fill material has a higher translucency, which makes it easy to cure but sometimes hard on the eyes. Therefore, some dentists prefer to use bulk fills in the back only where they are not in the limelight of the patient’s smile. Furthermore, some of the materials labeled as bulk fills are intended to be liners for the prep and then finished on the top with a thin layer of conventional composite for the occlusal surface, so clinicians grab them to streamline the placement process. 

However, bulk-fill materials have drawbacks, too. For example, when the material is packed in, there might not be voids underneath, but there could be some internally, which can lead to problems in the outcome. Also, because the material is only cured once and at the same time, significant polymerization shrinkage can have a more pronounced shrinkage effect that interferes with the interfacial relationship between the material and the teeth. Polymerization in a deep prep could still be adequate, regardless of what the label says the depth of cure is for the materials, as Gordon J. Christensen’s Clinician’s Report pointed out several years ago.[i] (In fact, Clinician’s Report did not recommend the use of bulk-fill over incremental composite materials available at the time.)

However, as the materials improve, manufacturers of bulk fill composite resins have improved esthetics and handling, ostensibly to address these issues and expand their uses. The tooth can be restored up to the occlusal surface with some bulk fills, unlike generations past.

So, what are some of the best practices for bulk fills? Here’s what our research turned up:

Know your material’s strengths-and its limitations

Bulk Fill composite materials are always improving in many areas, from handling, to shade matching, to the reduction of polymerization shrinkage during curing. These improvements are not unilateral. In other words, all bulk fill composites are not created equal, nor were they meant to be. Individual formulations were meant to serve specific restorations well, and in their specific way. Therefore, it’s essential that you read the manufacturer’s instructions and follow them closely. Also knowing your chosen products’ strengths and limitations will drive what cases they can be used for with the most success.

Set yourself up for success with shade matching

There are many factors involved in getting the correct shade for the material. Many manufacturers have addressed shade matching in various ways. Many are reducing the amount of shades from specific shade-to-shade clouds, which allows for a wider range of patients to be served by one material. Other manufacturers are changing how the chemistry of the composite material itself reflects light to create shade. However, with most shade matching, there are other ways to achieve success other than materials. For example, the Dental Academy of Continuing Education (DACE) suggests that environmental light (such as overhead fluorescent lighting) can affect the outcome of the match. The DACE indicates that natural daylight (at noon whenever possible) is the best possible light. Then, a second match should be completed with a secondary light source to ensure the same shade matches. However, operatory lights are not recommended for shade matching. Also, it’s best to remove other distractions-such as lipstick shades or clothing colors-from the equation by removing the makeup or putting a bib on over the colors. Furthermore, shade match early in the appointment, before the tooth desiccates and alters the appearance of shade. Also, check the shade against surrounding dentition, too.[ii]

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Achieve standardized placement for the entire mass of the bulk fill material in the prep area

Like with all resin composite materials, the placement technique is essential for success. Bulk fills are placed all at one time, which prevents voids between layers but doesn’t necessarily protect against voids in the thickness of the bulk fill itself. To achieve a consistent placement with bulk fill requires careful addition of the material. Also, it is essential with less-viscous bulk-fill materials (Like flowables, for example) to keep the tip in the mass when you extrude the material.[iii] Furthermore, the application tip can be used to push the resin into the nooks and crannies of a prep.[iv]

Know when to go with the flow

The Journal of Adhesive Dentistry’s 2017 literature review suggested that different viscosities were better for different preparations.[v] Their research indicated that flowable bulk fill materials are best for narrow cavities with a depth greater than four millimeters.[vi]  Anything more substantial than that could handle a full-bodied composite. Thicker body bulk fill materials improve contact points and exhibited better mechanical properties, the JAD stated.[vii]

Sectional Matrices can facilitate robust contact areas in posterior Class II restorations with composite resin

The pre-wedging the matrix provides will provide a separation between the patient’s teeth that eschew the matrix deformation when inserting it, according to the British Dental Journal.[viii]   

Curing light functionality is essential for adequate curing

The depth of cure is much higher in bulk fill resins, but the deeper cure needs the full light energy on the unit. Clinician’s Report recommends verifying the light’s performance by curing resin stretched in a line of up to 7mm from end to end, using the cure time indicated on the manufacturer’s instructions.[ix] After curing, scrape away the uncured portion of the material to see the depth of light penetration your material and light are producing. It is important to mention that this is an approximate depth of light penetration and that proper polymerization is not the same depth. However, Clinician’s Report advises that to increase the depth of cure, the cure time of the material should be increased as well.[x]

When curing time is increased to provide adequate light penetration, manage the heat to protect the tooth

Increasing cure times is an excellent way to ensure proper depth of cure for the restoration. However, using high intensity curing lights can heat the pulp and other tissues of the patient’s tooth too much. Be sure to train the team on how to dissipate the heat of the light with air stream onto the tooth surface when curing.[xi]

Keep trying new materials

Knowing your bulk-fill material is crucial, but we would also caution you not to get too comfortable with a material as they are always improving. Ignoring new developments in the materials science means you could miss out on some excellent patient outcomes.

References

[i] “Advantages and Challenges of Bulk-Fill Resins.” www.cliniciansreport.org. January 2012, Volume 5 Issue 1. Accessed via web. 13 February 2020. < https://www.cliniciansreport.org/uploads/files/19/201201.pdf>.

[ii] Lowe, DDS. FAGD, FICD, FADI, FACD DIADFE, Robert A. “Composite Restorations: Subtleties in Shade and Technique.” Web. PennWell. dentalacademyofce.com. October 2010. Web. 2 January 2019. https://www.dentalacademyofce.com/courses/1972/PDF/1011cei_nuance_web2.pdf.

[iii] “Advantages and Challenges of Bulk-Fill Resins.” www.cliniciansreport.org. January 2012, Volume 5 Issue 1. Accessed via web. 13 February 2020. < https://www.cliniciansreport.org/uploads/files/19/201201.pdf>.

[iv] Ibid.

[v] Van Ende, Annelies & De Munck, Jan & Lise, Diogo & Meerbeek, Bart. (2017). Bulk-Fill Composites: A Review of the Current Literature. The journal of adhesive dentistry. 19. 10.3290/j.jad.a38141. From Web: https://www.researchgate.net/publication/316524305_Bulk-Fill_Composites_A_Review_of_the_Current_Literature

[vi] Ibid.

[vii] Ibid.

[viii] Peña, Victor & García, R. & García, R. (2016). Sectional matrix: Step-by-step directions for their clinical use. BDJ. 220. 11-14. 10.1038/sj.bdj.2016.18.

[ix] Advantages and Challenges of Bulk-Fill Resins.” www.cliniciansreport.org. January 2012, Volume 5 Issue 1. Accessed via web. 13 February 2020. < https://www.cliniciansreport.org/uploads/files/19/201201.pdf>.

[x] Ibid.

[xi] Ibid.