Composite the ultimate material for minimally invasive dentistry(Hybrid Composites,Micro filled Composites,Nano filled composites)


Educational Objectives

Upon completion of this course, participants should be able to achieve the following:
• Understand what the three classification systems in composite materials and what their indications.
• Learn clinical tips for Class I and Class II direct posterior restorations.
• Learn layering techniques to build in dentinal lobes, incisal edge effects and incisal halos.
• Learn simple polishing techniques to create the appropriate finish and luster.

Introduction
Used in Class I, II and IV restorations in the posterior and anterior regions, composite resins represent an attractive restorative option for patients who desire minimally invasive treatment or cannot afford more costly indirect alternatives. Among the most versatile materials, composites might be used in direct restorations, build-ups, cements, diagnostic mock-ups, gingival stabilization, provisionals and prototypes. Although previous direct composite generations have demonstrated polymerization shrinkage and the potential for marginal leakage resulting in the development of secondary caries, their benefits today outweigh the risks, which can be avoided when proper materials and techniques are utilized. A viable solution to the problems of amalgam, including cusp fractures, increased rates of secondary caries and possible toxicity due to mercury content, has increased the demand for composite resins in recent years.

Composites
Conserving sound tooth structure and with the potential for tooth reinforcement, adhesively bonded composite restorations demonstrate aesthetically acceptable results. The least invasive and predictable restoration of teeth to normal form and function, tooth-colored composites provide patients and dentists with a cost-effective and long-lasting solution for a variety of indications.However, four parameters dictate an ideal composite material outcome:
• Mirror natural tooth structure in color and translucency.
• Strength to withstand function in high stress-bearing areas for the long term.
• Seamless or undetectable margins from restoration to tooth for the long term.
• Appropriate polish and luster that can be maintained throughout the life of the restoration.

Hybrids
Compared by the author to rocks with pebbles loaded between them, hybrids or microhybrids are heavy-loaded materials that display an average 1μ glass particle sizes and .04μ silica in resin.8,9 This class of materials demonstrates high strength and opacity similar to natural dentin and enamel. Less likely to chip, hybrids can provide strength in any of the functional areas and, through layering techniques, can mimic dentin and enamel morphology. A disadvantage, however, is that their polish is not long-lasting.

Microfills
Described as all pebbles and composed of an average 0.1μ glass particles in resin, microfills display high polishability that lasts for the long term.When compared to hybrids, microfills demonstrate a higher resistance to wear and a translucency similar to enamel. These materials also give dentists the ability to replace the color, translucency, polishability, wear resistance and surface texture of natural enamel. However, microfills lack the strength required for many of the functional areas and can be too translucent.

Nanofills (Nanohybrids)
A newer-class of composites, nanofilled materials display 20nm primary particle sizes, consisting of zirconia-silica nanoclusters and silica nanoparticles (0.01μ glass particles in resin). Because this material contains even smaller particles, it has the potential to maintain greater strength and long-term polishability.Therefore, according to the author’s analogy of rocks and pebbles, nanofilled composites would additionally have grains of sand. In this analogy, when wear does occur, only pebbles and grains of sand “pluck out” leading to more favorable mechanical and optical properties. Nanofilled composites also display opacity similar to natural enamel and dentin, with translucency similar to enamel.
Demonstrating high strength, nanofilled composites are less likely to chip in high stress areas.1 The only true disadvantage to nanofilled composites, however, is the lack of in-vivo long-term studies, since the material science is relatively new.When using the different types of composites, it is necessary to understand that both technique and material selection define the outcome. By using the proper composite, tints and opaquers, along with proper layering, customization and polishing, predictable restorative outcomes can be completed and maintained.

Aesthetics
Dentists must realize that there are many different characteristics of the teeth, which are key to understanding aesthetics, that need to be addressed during treatment planning. When recreating tooth shape, the line angle, outline form and profile must be considered, along with tooth proportions, which involves the width-to-length ratio. To develop proper symmetry, the tooth shape must be developed first, followed by the embrasures and contact point.
Another fundamental aspect of aesthetics, age and gender play important roles in the development of highly aesthetic and natural appearing restorations. For example, age should be a major consideration when building the central incisors, and gender should define the lateral incisors. Other aesthetic considerations should include the smile line, cant, tooth size, central dominance, axial inclination, reverse “S and S” line angles and the natural curvature of the dentition. The location and direction of the midline is also crucial to aesthetics and should be evaluated and developed prior to any preparation. Once the dentition is understood and a treatment plan developed, the facial characteristics of the patient and their skin tone must be evaluated. By doing so, harmony between the restorations and the patient’s facial features can be created to develop the best in aesthetics.

Basic Principles for Adhesive Dentistry
A rubber dam should always be used to isolate the preparation and stop contamination from blood and saliva. Rubber dams also provide the added benefit of preventing the patient from swallowing the potentially toxic mercury that is present in amalgam fillings. It is important to note that once removed, amalgam fillings should be disposed of properly. In 2007, the American Dental Association adopted “Best Management Practices for Amalgam Waste,” which include the voluntary use of amalgam separators. Additionally, the Environmental Protection Agency has been reviewing options for regulating the dental industry regarding mercury discharge, as well as for requiring the installation of amalgam separators.The author has an amalgam separator (DRNA ISO Certified BU10 Amalgam Separator, Dental CareWaste Management) in his office and encourages other practitioners to incorporate one in their practices also.

Adhesive Systems
Once rubber dam isolation is achieved, the preparation should be etched, primed and then bonded to provide the most predictable results.Of the adhesive systems available on the market today, total-etch, three-step systems are considered the “gold standard” and are the author’s preference for indirect restorations. These three-step systems come in two bottles and are indicated for use in all indirect and direct restorations. In comparison, a self-etching, two-step system, per the manufacturer, requires pre-etching on uncut enamel, essentially, from a technique standpoint, making a self-etching, two-step system a total-etch, three-step system.

Class-based Preparation and Placement

Class I
To begin preparation of Class I indications, previous restorations and any remaining decay are first removed. Bevels should not be used in these situations, and rounded line angles are required internally. An incremental filling technique must then be used when layering the new composite, being sure not to join the buccal-lingual walls. An example of this type of restorative procedure includes removing the decay and old restorations, then etching the dentin and enamel. The etchant is agitated while on the surface of the tooth and left for 15 to 30 seconds before being rinsed away. The dentin is then wet, followed by priming and bonding using a total-etch, one-bottle system. Multiple coats are placed and agitated before air-drying to remove the necessary contaminants (i.e., solvent).25 To seal the dentin and enamel, the bonding agent is light cured.
To build the restoration, the cuspal inclines are formed using a microhybrid or nanohybrid composite in appropriate shades and tints where desired. Each individual layer is light cured (ramp cured) through the tooth. The cuspal inclines are adjusted as necessary.

Class II
Like in Class I indications, the preparation for Class II restorations begins by removing amalgam or old composite and any remaining decay. Once again, no bevel is used, and rounded line angles are required. The enamel periphery ideally would demonstrate 0.5mm to 1.0mm of enamel in height and width at the gingival floor. Layering is similar to Class I restorations, with incremental filling without joining the buccal-lingual walls. For shading characteristics, 2+ shades of a microhybrid should be used, with incisal/translucent microhybrid or microfill layered over the restoration.
Today’s nanohybrid composites (Venus Diamond, Heraeus, South Bend, Illinois), however, can enable us to achieve such aesthetics with a single-layer composite material. To form the interproximal contact of Class II restorations, several options are available, including pre-wedge before the rubber dam is placed, a sectional matrix with proper wedging, and utilization of special instrumentation.An example of a clinical case involves first cutting out the old amalgam filling. The rubber dam is placed, all previous material and decay is removed, and the matrix is placed. The preparation is then etched for 15 to 30 seconds. After the etchant is rinsed away and the surface partially dried, the total-etch, one-bottle adhesive is applied to the preparation with agitation in multiple coats and, after 30 seconds, thinned with air to blow off the necessary contaminant (i.e., solvent). The adhesive is light cured, after which incremental filling begins, followed by carving to form anatomy. After proper anatomy is achieved and occlusion is checked, the tooth is etched again and glazed. A surface glaze (BisCover LV, BISCO) is then placed on the restoration to lessen micro-leakage and post-operative sensitivity. This incremental-oblique filling technique works well for Class II indications. Different from incremental-horizontal filling, the use of metallic bands with oblique increments lessens the polymerization shrinkage of composites and reduces the chance of microleakage.
In a clinical example of this type of indication and technique, the old filling and decay are removed first. A sectional matrix is then utilized, along with a wedge and oblique filling. Nanofilled composite material (Venus Diamond, Heraeus) is applied to the restoration, with an enamel layer over it.
Fig. 1: Rubber dam isolation of broken-down teeth and restorations on teeth #30 and #31.
Fig. 2: Incremental filling was achieved by developing dentin cuspal inclines on teeth #30 and #31.
Note the sectional matrix and wedge are used to assure proper interproximal contours.
Fig. 3: View of the completed, integrated restorations with appropriate marginal ridge contact and contours.


Class IV
Class IV indications typically require diastema closure or full veneers and can involve no preparation to a full 1+mm of reduction.To help with a seamless restoration, a starburst bevel of 2+mm should be utilized, except on the gingival margin if dentin is exposed.Layering should be completed with at least two shades of a microhybrid material, overlaid with incisal/translucency, or microfill, to create the dentinal lobes, incisal translucency and the incisal halo. However, today we can achieve this with a nanohybrid composite (Venus Diamond).

Undetectable Margins
When margins are in the aesthetic zone, a starburst bevel should be used, followed by etching beyond the bevel.The outer layer of composite should be rolled, while wearing clean gloves, to improve sculptability and prevent voids. The material should then be placed and super-cured, allowing five minutes or more for the material to settle. The margin should then be addressed first, finishing it back between where the etch and the bevel end. Rubber wheels and polishers should not be used on the margins, since the rubber tends to become embedded in this area.
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