2021 Trends in Restorative Dentistry: Composites, Curing Lights, and Matrix Bands

Universal Shade Composites

Shade-matching anterior composite restorations can be technically challenging for several reasons. First, composite materials do not match standardized VITA shade guides (VITA Zahnfabrik, vita-zahnfabrik.com).¹ Second, they undergo perceptible color changes after light-curing.² And, third, they vary in color based on the lighting source of the room.³ Additionally, shade-matching composites requires the clinician to have an inventory of various shades of composite material available and may be time-consuming if multiple opinions are consulted (ie, dentist, auxiliary, patient, etc). For this reason, several manufacturers now offer multishade universal composites (one shade representing multiple VITA shades, eg, Filtek^™ Universal, 3M Oral Care, 3m.com; TPH Spectra^®, Dentsply Sirona, dentsplysirona.com) and single-shade universal composites (one shade representing all VITA shades, eg, Omnichroma^®, Tokuyama, tokuyama-us.com; SimpliShade^™, Kerr, kerrdental.com; Venus Diamond ONE, Kulzer, kulzer.com; Admira Fusion x-tra, VOCO, vocoamerica.com). These composites are able to blend with surrounding tooth structure based on increased translucency.⁴

Some single-shade universal composites take advantage of structural color, which is the use of filler particles of a certain size (260 nm) to impart a yellowish hue to the composite instead of using pigments.⁵ A laboratory study reported that a single-shade universal composite could more closely blend into Class I preparations of different colored denture teeth (VITA shades A1 through D4) than A2 shades of reference composites.⁴ Another study reported that multishade universal composites could more closely blend into preparations in anterior denture teeth than a single-shade universal composite. In this study, multishade composites were paired with denture teeth of the same shade (A1, A2, and A3), whereas there was only one shade of the single-shade composite.⁶ The increased translucency of single-shade universal composite, however, means it can be affected by a dark substructure (eg, sclerotic dentin, staining, discoloration).⁷ Therefore, an opaque blocker composite may be needed in these clinical situations.

Bioactive Composites

Bioactivity in reference to a dental composite typically implies that it will release ions present in the tooth structure. One benefit of a bioactive composite is that it provides ions at the restoration interface to prevent demineralization of the surrounding tooth structure. A laboratory study demonstrated that a fluoride-releasing resin-modified glass-ionomer material was more effective at preventing demineralization at its restoration borders than a calcium-releasing composite.⁸ Another potential characteristic of ion-releasing bioactive restorative materials is the ability to nucleate hydroxyapatite growth in demineralized dentin (ie, affected dentin) left behind in a cavity preparation.⁹ In this case, the release of calcium and/or phosphate is important as these are the major components of hydroxyapatite.

Going forward, bioactive restorative material science may focus on the interaction of composites with bacteria and biofilm.¹⁰ Strategies include incorporation of charged quaternary ammonium complexes on the surface of these composites, thereby rupturing the cell wall of bacteria or releasing a bacteria-killing or biofilm-inhibiting molecule.¹⁰

Fast-Curing Composites

A new concept in composite efficiency is fast-curing composite, which may be cured in 3 seconds with a 3000 mW/cm² curing light. Aside from increasing efficiency, a faster curing time also reduces the likelihood that the operator holding the curing light will deviate from the correct light tip placement due to waning attention or hand/arm fatigue.

The technology that allows a shorter curing time is the incorporation of the photoinitiator Lucirin-TPO. Unlike camphorquinone, Lucirin-TPO shows an optimal generation of free radicals and degree of conversion after curing for 1 second with a 2000 mW/cm² curing light.^11,12 Despite the rapid curing time, no microgaps were observed at the restoration interface using real-time optical coherence imaging.¹³

A curing light is a medical device that must be tested and approved for use on patients. When purchasing a new curing light, in addition to safety issues such as blue light exposure and ergonomics, clinicians should consider several key parameters.

Irradiance (radiant exitance)- A high irradiance value does not mean that the curing light is powerful. Most lower-budget light-curing units (LCUs) have only a small 6-mm to 7-mm diameter "active" light tip from where useful light is emitted. In contrast, most higher-quality lights have a 9-mm to 11-mm diameter active tip.¹⁴ Because the active area is calculated from the cross-sectional area (πr²) of the tip, any reduction in the active tip diameter will substantially affect the radiant exitance. For example, if the active tip diameter is reduced from 10 mm to 7 mm, the area from where light is emitted is essentially halved from 78.5 mm² to 38.5 mm². This will double the irradiance if the same power is delivered.

Effect of distance- The irradiance delivered to the resin will decline as the distance from the light tip increases,^15,16 but the effect of distance is not the same for all LCUs. Because the bottom of a cavity can easily be 6 mm to 8 mm away from the light tip, when choosing an LCU clinicians should assess the effects of clinically relevant distances up to 10 mm away on the irradiance delivered.

Emission spectrum- Because different LCUs can emit very different wavelengths of light,^17-19 it is important to match the emission spectra from the LCU with the absorption requirements of the resin. Unfortunately, manufacturers do not always divulge the composition of their resin products. To overcome the fact that single-peak LED curing lights deliver very little light below 420 nm, some LED curing lights now include additional LED emitters that produce additional light in the violet range of wavelengths.^15,17 Unless the LCU is carefully designed, however, the addition of several different wavelength LED emitters in the LCU can negatively influence the uniformity of the light beam from the LCU, producing inhomogeneous polymerization of the resin.^20,21

Beam uniformity- To examine the uniformity of light beams a device called a beam profiler is used.¹⁹ Commercial beam-profiling software can produce 2-dimensional and 3-dimensional images of the radiant exitance across the light source's tip and along the light beam.^19,22 A good optical design that can homogenize the light from the light source¹⁹ so that all regions receive a similar irradiance and wavelengths of light is preferable.

Infection control- An LCU can be a source of cross-contamination between patients and dental personnel and must be disinfected properly.^19,23 The areas around the activation buttons or seams are particularly challenging to clean, thus, ideally they should be covered with a disposable barrier. Using plastic barriers or sleeves, however, can reduce the irradiance delivered from the LCU by as much as 40%.¹⁹ The clinician should measure the light output with the barrier over the light tip and, if necessary, increase the exposure time.

Circumferential matrices- Circumferential matrix systems may be indicated when a Class II cavity preparation extends beyond an interproximal-lingual or interproximal-buccal line angle. A traditional circumferential matrix is a band held in a Tofflemire retainer. The advantages of a Tofflemire retainer are that it is reusable and the position of the band may be easily customized within the retainer. Another option is a circumferential matrix system that has the band preloaded in the retainer for even greater efficiency.

Sometimes the location or weight of the retainer can impede the positioning of the matrix band. In this case, a retainerless matrix band may be used. These matrix systems are tightened with matrix tensioning devices. A new concept is a retainerless matrix system that can be hand-tightened. This eliminates the need for a tensioning device; however, in some difficult to access areas, additional instrumentation may be needed to complete the tightening. Regardless of the type of circumferential matrix selected, use of a pre-contoured band will help achieve an optimal contact height and incisal-gingival contact position.

Sectional matrices- Various options are available for sectional matrices based on their contour, hardness, stiffness, and translucency. The original sectional matrices displayed simple incisal-gingival and buccal-lingual contours. Newer matrices have more complex forms with a pronounced curve at the marginal ridge area, a defined bend at the interproximal-lingual and interproximal-buccal line angles, and optional subgingival aprons (eg, Palodent^® Plus, Dentsply Sirona; Composi-Tight^® 3D, Garrison Dental Solutions, ; DualForce^™ Ultra-Wrap^™, Clinician's Choice, clinicianschoice.com.

The material and thickness of the matrix band can affect its stiffness and hardness. Bending of the gingival edge of the matrix during insertion is a common clinical problem. Use of a stiffer matrix can help overcome this issue, however the matrix should be flexible enough to adapt to the tooth without wrinkling and forming voids. Unlike matrices used with amalgam, matrices used with composite should not be burnished in order to prevent bumpy interproximal contours of the restoration. Thus, it is disadvantageous for the matrix to be dead soft. Lastly, translucent mylar matrices or perforated metal matrices allow light to penetrate through the matrix during buccal or lingual curing.¹⁴

Wedges- Wedges may be classified as active wedges (eg, Wizard Wedges®, Waterpik, waterpik.com; WedgeWands®, Garrison Dental Solutions), which provide a significant separation force, and passive wedges (eg, Palodent® Plus, Dentsply Sirona; Diamond Wedge, Bioclear, bioclearmatrix.com; DualForce™ Active-Wedges™, Clinician’s Choice), which do not. Active wedges typically have a solid base, whereas passive wedges have a hollow base. The advantage of an active wedge is that it may provide separation force in cases in which a matrix ring cannot be used. Active wedges, however, typically have only simple triangular geometry, whereas many passive wedges are shaped to apply less pressure to the matrix under the contact point and more pressure buccally and lingually. If the wedge does not adapt the matrix to the tooth, it may be modified by carving it (in the case of wooden wedges) or wrapping it in Teflon.

Nathaniel C. Lawson, DMD, PhD
Associate Professor and Division Director of Biomaterials, Department of Clinical and Community Sciences, University of Alabama at Birmingham School of Dentistry, Birmingham, Alabama

Sridhar Janyavula, DMD, MS
Director of Clinical Affairs and Education,
Geistlich Pharma North America;
Private Practice, Philadelphia, Pennsylvania

Richard B. Price, BDS, DDS, MS, PhD
Professor, Department of Dental Clinical Sciences,
School of Biomedical Engineering Medicine,
Dalhousie University, Halifax, Nova Scotia, Canada