This category has basically been replaced by bulk-fill composites. However, since these products are still being sold, we decided to leave this category posted for the time being. It includes packable composites as well as other types that are best suited for posterior use. Packable composites, in particular, are essentially stiff microhybrids that were created to give dentists switching from amalgam a material with similar handling characteristics. They are definitely, as a class, more packable than universal composites, but they are not condensable in the same manner as amalgam.
Main Criteria for Choosing a Posterior Composite as an Amalgam Replacement
When you do an amalgam, you do not place a layer, wait for it to harden, and continue to place additional layers in a similar manner. You fill up your carrier, insert the increment, pack it into the nooks and crannies of the cavity, and repeat the process until the preparation is filled. Posterior composites aspire to allow you to do the same procedure, with one material having included an amalgam carrier in its box in the past. The main problem with inserting composites in bulk is depth of cure. If you cannot cure deeply due to the nature of the composite, bulk placement will be a risky proposition at best. Please see how we determine depth of cure under Tests. Our results, however, suggest that these materials do not cure as deeply as their promotional literature states. Please see the commentary for each product for this information.
Even if you were able to cure these materials in thicknesses up to 5mm, the bulk of material may lead to excessive polymerization shrinkage. To allow bulk placement, several new products have been introduced with very low shrinkage and/or shrinkage stress. However, depth of cure is still an issue. Therefore, it seems incremental placement is still the key as long as the increments do not exceed the depth of cure of the specific materials. Please see the Bulk-fill category for additional information.
With amalgam, just about any matrix band will work when it comes to creating tight contacts. To be sure, you still need to wedge aggressively, but when you pack amalgam into a cavity, the material itself has enough body to hold the matrix tightly against adjacent teeth. Universal composites, on the other hand, do not have this property. To create tight contacts with composite, we recommend contoured, sectional matrices that are retained with ring-type devices that generate a squeezing-like pressure at the line angles, keeping these bands in close approximation to the adjoining tooth surfaces. Even though it is not difficult to learn how to use these sectional-type matrices, a conventional, Tofflemire-type is still commonly used. Please see MATRICES for more information.
While posterior composites do typically have more body than universal composites, you still need to wedge and burnish the matrix aggressively. Even then, do not expect the composite to hold the matrix against the adjacent tooth as securely as amalgam.
The occlusal contours of an amalgam can usually be completely created with hand instruments, due to its unique carvability. This carving can be done all through its hardening stage. Composites, on the other hand, must be shaped prior to polymerization. Since composites are light-cured, there is no intermediate stage like amalgam. Even though you can sculpt posterior composites with relative ease, it is a stretch to call that carvability. There is still a need to finish any composite with a rotary instrument.
Conventional shade matching is typically not really relevant with posterior composites since you are primarily trying to blend in with the occlusal surface. Therefore, we prepared a Class I preparation in an extracted natural tooth in which the main shade was roughly equivalent to B2. The corresponding B2 or equivalent shade of each material was used to restore this preparation and the ability of the material to blend into the tooth was assessed. Our results plus the photos of the restored teeth are presented in each product commentary. Notwithstanding this test, shade matching for Class I and II restorations is usually not critical for most patients.
Discs of A2 or equivalent and occlusal shades (if any) in 1.0mm thicknesses were measured for relative degrees of translucency/opacity in a spectrophotometer. The scale was 0-100, with 0 being totally clear and 100 being totally opaque. Our findings are in each product commentary. For those critical shade matching cases, using a dentin-like shade (70-80) to replace the lost dentin followed by an enamel-like shade (50-60) on the surface will typically give you the most esthetic result.
If the material comes with a shade guide, we compared the A2 tab to the actual material and to the Vita A2. If A2 was not available, we used an alternate shade of the material and its matching Vita shade tab.
Shade Shift after Curing
This test shows how much the color change there is after light curing the material. This is only important if you want to do a shade check without bothering to light cure the mockup. If the material does not have a shade shift, you could do a mockup without light curing. However, removing uncured material from a tooth can be messy, so light curing is a good idea in any event. This shift, if any, was measured using the spectrophotometer.
Depth of Cure (mm)
This test will tell you the maximum thickness of each increment of restorative material you can place, using hardness measurements in 1.0mm increments from the occlusal surface in the proximal box. The depth of cure limit is reached when the hardness value in the proximal box falls below the benchmark 80% of the occlusal surface hardness. This 80% hardness value is generally recognized as the standard to judge whether a composite has been adequately cured, although we are unaware of any clinical correlation with this value. Nevertheless, it is indisputable that the physical properties of a restorative material will not be maximized if a restoration is undercured. The test was done in a simulated Class II preparation with the depth of the gingival wall 6mm from the tip of the light.
Curing Time for Gingival Wall Increment
This test will tell you if the increment of restorative material you place on the gingival wall of the proximal box has achieved the benchmark 80% hardness value of the occlusal surface. The test is done in simulated Class II preparations with the depth of the gingival wall 6mm from the tip of the light. The gingival increment is placed no thicker than 2mm.
Working Time under Dental Unit Light
This test will tell you when the material will start to cure under the dental unit light, if the light is at high power and positioned at a typical working distance (30in/76.2cm) from the preparation.
Conventional wisdom hypothesizes that low shrinkage materials should put less stress on the bond to tooth, which in turn means restorations should leak less and be more resistant to secondary caries, although this has never been demonstrated clinically. Measurements were made using a computerized imaging device and software developed by Bisco called AccuVol. These shrinkage measurements were recorded after 5 and 10 seconds to ascertain how much of the total shrinkage occurred in the initial stages of curing and then at five minutes, after each specimen had been cured for 40 seconds.
Finishing and Polishing
Restorations were polished with three of our top-rated polishing brushes, which are particularly effective on occlusal surfaces. These instruments were used for 30 seconds and then compared to the gloss of the occlusal surface of a natural molar and scored as matching the gloss, coming close to the gloss, or not being even close.
This test shows how well the material has been vacuum mixed by the manufacturer to remove air from the final product. The higher the percentage of porosity, the higher the probability you will have voids present on the surface when you finish and polish the material. These voids are an annoyance and repairing them can be time-consuming as well as being an esthetic challenge.
While these materials are not being marketed for veneers, they could be used as support for high stress anterior restorations, such as Class IV. In addition, they could also be used to rebuild an esthetically prominent premolar. This test shows how the material appears as a veneer in vivo under black light. Materials exhibiting fluorescence that does not match that of natural teeth would not be a good choice in the mouth of patients such as models, actors, etc.
Should You Switch?
Only you can decide if you prefer a posterior composite over a universal type. The decision is greatly influenced by the type of matrix band you typically use. If you have mastered using one of the contoured, sectional-type bands with its accompanying retaining ring, a more syringeable type of composite may still be the best choice. But, if you are changing from amalgam and want to continue using conventional Tofflemire-like bands, a thicker posterior version may make your life easier.