Class II- Undercured Composites Sensitivity

Contents:

• Post-operative Sensitivity: The Contribution of Undercured Composites
• The Polymerization of Light-cured Composites 
• Undercured Composites and Post-operative Sensitivity
• Restorative Issues and Post-operative Sensitivity
• Curing Light Variables
• Curing Light Beam Characteristics
• Curing Light Tip Positioning
• Curing Time
• Clinical Technique Variables
• Technique Errors
• Potential Solutions to Avoid Undercured Composites
• Avoid Post-operative Sensitivity with Help from Dentsply Sirona

Post-operative Sensitivity: The Contribution of Undercured Composites

Post-operative sensitivity following the placement of direct composite restorations is a significant issue for patients and clinicians.^{1, 2} This condition is particularly common after placement of Class II restorations – making it essential to understand and avoid this condition, given that 50% of all direct restorations are Class IIs.³ Here, we’ll take a close look at the role of undercured composites in post-operative sensitivity. Let’s begin with the polymerization process for light-cured composites.   

The Polymerization of Light-cured Composites

All light-cured composites contain photoinitiators that initiate polymerization – the process by which monomers join to form polymers. Composite polymerization begins when photoinitiators are exposed to the energy emitted from the curing light and typically react with a coinitiator to form free radicals, thereby connecting the monomers in the composite to polymers through the crosslinking of double bonds. This produces a network of polymer chains containing the composite’s filler particles.⁴ For each composite, there is a critical amount of energy (i.e. time of exposure with a sufficiently strong beam of light) that must be delivered to form enough radicals also in the deeper part of the restoration so that sufficient cure is reached.  The percentage of monomers in the composite converted into polymers during polymerization is referred to as the degree of conversion.⁴ As more energy is delivered from the curing light, more free radicals can be formed and contribute to the formation of the polymer network until the maximum degree of conversion is achieved.

Restorative Issues and Post-operative Sensitivity

Issues that can result in post-operative sensitivity include:^1,5,6,7

• Marginal gaps and increased potential for microleakage.
• Composite degradation.
• Open margins and fracture of the restoration if the composite layer is adequately cured superficially but undercured in its deeper areas.
• Wash out of undercured material.
• Pulpal irritation caused by the presence of excess amounts of residual monomer (due to an inadequate degree of conversion).

Any restorative process that results in open dentinal tubules inherently predisposes the tooth for post-operative sensitivity. Dentinal sensitivity occurs when a stimulus causes movement of fluid within the dentinal tubules which results in local changes in pressure that stimulate mechanoreceptors near the odontoblast processes. This leads to neural transmission to the brain that we interpret as pain.^1,2 Local changes in pressure and fluid movement within the dentinal tubules may also result from undercured composite resin flexing significantly more than enamel when subjected to masticatory forces (chewing).⁷  

Curing Light Variables

Characteristics that influence the polymerization of light-cured composites include the light source and the composite’s formulation. The most important variable is the light source. Adequate light curing relies on using a suitable curing light and technique. The curing light must sufficiently cure all areas of the composite exposed to the energy emitted by it, and sufficient energy must reach the full depth of the composite increment/layer, including deep in the proximal box of Class II restorations. Let’s now look more closely at the variables. 

Curing Light Beam Characteristics

The beam of light reaching the clinical site is influenced by beam collimation and beam uniformity. A well-collimated beam has close-to-parallel rays which means less dispersion of the light and better delivery of energy at a distance.⁴ Secondly, while a wide-diameter beam may appear to capture a greater area of the composite and evenly cure it, if the beam of light is uneven this can cause some areas of composite to be undercured while other areas are not. 

Curing Time

Reducing the curing time and using a higher-intensity light may seem to be a good idea. However, it increases the risk of undercuring composite – increasing  the risk of post-operative sensitivity – and magnifies the effect of transient tip positioning errors since their duration becomes a larger percentage of the total curing time.⁸ Furthermore, the ability to absorb a high amount of energy in a short time depends on the composite formulation. Therefore, the composite manufacturer’s recommended curing time should be followed.

Clinical Technique Variables

The notion that light curing is the easiest step in the provision of direct composites is refuted by studies where more than 37% of composites were inadequately light-cured.⁹ Class II composite restorations are at particular risk of undercuring, especially at the floor of the proximal box which is often as much as 8 mm away or more from the tip of the curing light.¹⁰ An appropriate clinical technique is key – among operators participating in a study on curing lights, a tenfold difference in the amount of energy delivered to simulated composite restorations was found.¹¹

Technique Errors

Potential technique errors when using curing lights, including the following:

• Inadvertently selecting a curing cycle with the wrong parameters.
• Angling the tip to improve intraoral access – this results in shadowing and uneven illumination of the composite being cured.
• Slight movement of the tip due to hand fatigue during longer procedures or exposure times or looking away from the blue light to help protect the eyes when not using proper eye protection.
  
• Debris is not removed from the tip – blocking the beam and reducing the curing light’s output.
• Using higher irradiance for a shorter time than described in the IFU of the composite manufacturer.

Potential Solutions to Avoid Undercured Composites

The list below contains potential solutions to meet the challenges associated with the curing of composite resins.

• Use a light curing unit with intuitive settings and a limited number of settings/cycles.
• Use a lightweight, low profile, pen-style ergonomic curing light that improves intraoral access, makes it possible to keep the tip close to and parallel to the occlusal surface of Class IIs, and may help avoid inadvertent tip movement.
• Make sure the curing light is free of defects and debris before using it and know how well your curing light performs over distance.
• Reposition the patient for access to the clinical site.
• Use proper eye protection and observe the correct positioning of the light.
• Check the light regularly for sufficient radiance

It’s important to follow the composite resin manufacturer’s written instructions for use, including the recommended light exposure times and increment thickness, considering the light curing unit being used. For eye protection, "blue blocking" (orange colored) protective eyewear or shields should be worn when operating light curing units. Finally, place barrier protection over the curing light tip and handpiece area prior to use and follow the curing light manufacturer’s written instructions for decontamination.

In summary, using a reliable and effective curing light, an appropriate technique and a suitable composite are crucial factors in achieving adequate polymerization and successful clinical outcomes. 

Dentsply Sirona’s SDR^® flow+ Bulk Fill Flowable is formulated to optimize its properties for the reliable creation of high-quality restorations even in deep posterior cavities. This low-viscosity, self-leveling bulk fill flowable composite offers excellent flowability enabling placement of gap-free restorations with a 4mm depth of cure. Thanks to the patented SDR^™ Technology that includes a patented urethane dimethacrylate structure (UDMA) and a polymerization modulator, energy is effectively dissipated during polymerization and a more relaxed polymer network is produced. This results in minimized polymerization stress, even with a 4 mm bulk placement. Other features include: 

• Easy and controlled delivery with a precise application tip for access to the site, accurate and void-free placement.
• Fast bulk fill placement of up to 4 mm in depth, resulting in fewer steps and up to 40% reduced placement time.¹¹

SDR^® flow+ Bulk Fill Flowable material, used for the bulk fill technique, is proven to be safe, effective and clinically durable compared to conventional layering techniques.¹²

Here at Dentsply Sirona we want to support you further with our entire online dental academy complete with webinars, how-to videos, and real-world examples on how to create streamlined solutions with efficient procedures and even greater patient satisfaction. Contact us now and let’s get started!