Advances in Composite Restorative Materials Support Conservative Dentistry
Rena Vakay, DDS
Composite restorations were introduced in the mid-1950s.1 Their evolution has primarily revolved around filler type and size.2 While, overall, composite material has good clinical performance, the potential for failure certainly exists. Annual failure rates of composite in posterior teeth are 1% to 3%, and in anterior teeth failure rates are 1% to 5%.3 Clinically, failure is defined mainly by recurrent caries or fracture of the restoration.4 Causes of these failures are multifactorial. Volumetric shrinkage and microleakage are inherent in the material itself, and lack of structural strength may be an issue in larger restorations. Factors such as the armamentarium used, operator training and technique, curing-light ergonomics, patient habits and caries risk, location in the oral cavity, and particle size are some of the variables that determine long-term success.
This article will explore contemporary ways to reduce these risks and increase efficiency with composite restorations.
Composite Technique
The technique used to place a composite material is fundamentally critical. Because each composite material possesses different physical and chemical properties, it is important that clinicians adhere to the manufacturer's recommendations. Staying within the same resin system when placing restorations is also highly recommended as best practice.
To be mechanically retentive, traditional cavity preparations require increased sacrifice of tooth structure. Composite preparation lends itself toward more conservative, minimally invasive preparations and the use of additive techniques. Conventional bonding technique has entailed placement of composite in incremental layers, which is time- and labor-intensive. The layering of composite is vulnerable to the creation of voids, seams, volumetric shrinkage, and cuspal flexure. These issues can contribute to failure of the restoration.
To reduce failures caused by the layering of composite, the bulk-fill technique was introduced and recently has become more dominant in private practice,5 for good reason. Efficiency is increased with the ability to place composite in 4 mm to 5 mm depths.6 Bulk-fill composite has shown equal or improved qualities in comparison to conventional technique, including less shrinkage, cusp deflection, polymerization stress, and marginal gap, increased degree of conversion, and improved flexural and fracture strength.7
One of the most recent significant alterations in technique is the preheating of composite prior to placement. Preheating the material may increase the degree of monomer conversion and reduce polymerization shrinkage force.7 This creates a stronger composite and results in less polymerization stress. Preheating allows for a more intimate adaptation of the composite into the preparation and allows easier restoration of interproximal areas, which are traditionally difficult to properly restore.
Many excellent bulk-fill composites have been studied in the literature and are available on the market. Some of these include Tetric EvoCeram® Bulk Fill (Ivoclar Vivadent, ivoclarvivadent.com), SonicFill™ (Kerr, kerrdental.com), and Filtek™ Universal (3M Oral Care, 3m.com). Recently a technique has been refined that incorporates bulk-fill composite placement with a preheating technique to increase quality and efficiency.8 This approach solves the ledging problem that can occur in interproximal areas and decreases time of placement of the composite.
Other advances aimed at simplifying the direct restorative process have involved composite technology that allows the clinician to limit color choices without compromising esthetics (eg, Omnichroma, Tokuyama, tokuyama-us.com; Beautifil II Enamel Shades, Shofu, shofu.com; Admira Fusion x-tra, Voco, vocoamerica.com). Universal composites that are designed to match virtually any tooth shade can reduce chairside time for shade selection and also help dental practices reduce inventory and thus overhead costs, because fewer color shades of composite need to be stocked.9
Matrix Systems
When attempting to re-establish tooth form, a clinician is heavily reliant on an effective matrix system. The Tofflemire matrix system was introduced in 1946 and has been a popular system for both amalgam and composite restorations for many years.10 This system employs a screw-type retainer and thin stainless-steel bands that are used with various sized wedges to separate teeth interproximally. This method allows for a tight contact area in the finished restoration.
Assorted matrices subsequently have evolved that offer easier placement of the matrix, better light-curing ergonomics, decreased chairtime, and the ability to create enhanced contours of the restoration. Three types of matrices may be used: a matrix for interproximal surfaces, an occlusal surface matrix, and a cervical matrix.
Posterior interproximal matrix systemsare moving away from the traditional stainless-steel Tofflemire-style bands and retainers. The newer posterior retainers are clamp-like and can support either a clear or a very thin metal band. Palodent® BiTine ring (Dentsply Sirona, dentsplysirona.com) was one of the first of this kind, featuring a spring action that gently separates teeth to provide the space needed to achieve proper contours. Garrison Dental Solutions (garrisondental.com) was soon to follow with the Composi-Tight® sectional matrix system that comprises a naturally contoured band and operator-friendly retaining system. The company now offers several ring systems and sectional matrices. A more recent entry, the Waterpik® ClearView (Water Pik, Inc., waterpik.com), features an hourglass matrix system designed to increase visibility and access.
One of the newest matrix systems has clear interproximal matrices for both anterior and posterior restorations (Bioclear, bioclearmatrix.com). The anterior matrices are ideal for closing "black triangles" that may manifest after orthodontic treatment or certain periodontal surgeries. Along with the preheating of both flowable and paste composite, these matrices use injection molding to prevent interproximal ledges that can occur with the use of straight mylar strips.11
An occlusal matrix or stamp made from clear polyvinyl can serve to record the occlusal surface of the tooth prior to preparation.12This matrix is used near the end of completion of a bulk-fill restoration to help decrease procedure time and increase efficiency. A cervical matrix could be constructed in the same fashion and used to restore the cervical portion of the tooth.
Curing
Perhaps the most crucial step in the long-term success of a composite restoration-and maybe the one that clinicians most take for granted-is proper polymerization. Just as it is crucial to follow the manufacturer's instructions with the handling of the composite, so it is with respect to light curing.
The characteristics of the composite material affect the time needed for complete cure. Particle size, opacity due to color, photoinitiators, and depth of preparation all influence the rate of cure. The performance of the light also is dependent on the maintenance of the light. The light tip must be kept clean of debris, and the clinician should routinely validate the performance of the light. One study found that when both the performance of the curing light and the effects of operator technique were considered, 30% of the curing light/composite combinations could not deliver even half of the energy dose required by the resin composite.13
To ensure that the light is in proper working order, it must be evaluated periodically. Curing lights cannot be accurately measured by radiometers, as radiometers provide only relative information.14 A spectrometer is the recommended instrument to precisely measure the output of a light source.15 This instrument can be quite expensive, and a cost-effective alternative for clinicians is to use a device such as a checkUP™ (BlueLight Analytics, bluelightanalytics.com). Via an app and a small device connected to a smartphone, a report is constructed with information about light intensity and the specific materials being used.16
Proper ergonomics are needed to thoroughly cure the composite. The restoration must directly receive the light emission for the correct amount of time based on the manufacturer's recommendation.
Conclusion
Clinicians can take simple steps to increase the success of composite restorations, such as knowing and following the manufacturer's recommendations for the composite material and making the right light selection and proper choice of matrix. Perhaps most important is ensuring that the curing light is properly maintained and calibrated for the appropriate output. These newer techniques and products highlighted in this article are compatible with the goals of conserving tooth structure, increasing efficiency, and delivering superior results to patients.
About the Author
Rena Vakay, DDS
Clinical Instructor, Kois Center, Seattle, Washington; Member, American Academy of Restorative Dentistry; Accredited Member, American Academy of Cosmetic Dentistry; Section Editor, Restorative, Compendium of Continuing Education in Dentistry; Private Practice, Centreville, Virginia
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