Conventional sculptable composites work well when access to a cavity is not a problem, but a material with more flow definitely comes in handy when that access is limited. However, while the original idea behind these products was that they would indeed possess adequate flow, this current generation would probably be better termed "low viscosity" or better yet, "lower viscosity", since some of them have very little flow at all.
Due to these differences in viscosity, many of these products cannot be easily used in all applications. For example, some with more flow are better suited for the gingival wall of Class II preparations, where you want the material to flow against the matrix band, filling in all the irregularities. On the other hand, those with less flow will allow you to restore Class V lesions more expeditiously.
Another fact about these products and one that is readily apparent when you glance at their names is that the majority are merely offshoots of sculptable composites. As such, they are designed to be used in conjunction with these siblings instead of by themselves. This is especially important when repairs of their sculptable brethren are necessary, since the shade matching should be automatic. So repairs may be the only reason that you purchase one of these products.
Is Their Lower Modulus Of Elasticity Advantageous?
Used to restore abfraction lesions, flowables are supposed to "bend with the tooth" due to their presumably more elastic character. This elastic property supposedly should lead to better retention. However, this theory that the restoration will flex with the tooth and lead to better retention is just that -- a theory. There is no clinical evidence that these materials are better retained than any other type of material in Class V lesions. Therefore, if you are planning to use a flowable composite for restoring a Class V lesion just because it is more elastic or has a low modulus, you may want to reconsider. In other words, don't just use a flowable due to its presumed elasticity property.
A flowable composite is a good choice as the first increment to be placed on the gingival wall of a proximal box in a Class II preparation. Due to the numerous nooks and crannies in a proximal box, a flowable can more readily adapt to the margins compared to a more sculptable material. However, since the gingival wall can be quite a distance from the tip of the light, this increment may require extended curing times. We measured the hardness of the flowable in a simulated Class II preparation with the depth of the gingival wall 6mm from the tip of the light. The gingival increment was placed no thicker than 2mm and was cured either for 20 or 40 seconds with a curing light emitting >800mW/cm2. This test will tell you if the increment of flowable placed on the gingival wall has achieved the benchmark 80% hardness value of the occlusal surface.
Finishing and Polishing
Restorations were polished with three standardized instruments for 30 seconds and then were compared to a natural extracted tooth with a typical enamel glossy surface.
One of the main purposes of a flowable material is that it actually flows into all the nooks and crannies of the cavity. However, too much flow may not be what you need for a specific restoration. To quantify the flow, we place a premeasured volume of material on a mixing pad and turn it vertical for 30 seconds. The flow of the material is then measured on a calibrated scale ranging from 0-5, with 0 being maximum flow (very runny) and 5 being virtually no flow.
NOTE: Different shades of the same product can have different flow characteristics. Our sampling of shades has revealed a disturbing lack of quality control almost across the board when it comes to flow. Even different syringes of the same lot number have exhibited different flow rates. This means that even the scores we have posted in this section may not be applicable to the product you receive. Please keep this lack of consistency in mind when you are ordering flowable -- you may not actually get what you expect.
Many venues use black light for its special effects. If a restorative material does not exhibit fluorescence similar to tooth structure, it could create an embarrassing situation for a patient. This test shows how the material appears in vivo under black light. Veneers are fabricated 1mm thick, placed on the maxillary right central incisor of a human model, and viewed/photographed with the model's head (still attached to her body!) placed in a custom-made, black light box. You cannot test fluorescence on a tabletop or on extracted teeth, the latter of which fluoresce at a different level than vital teeth. Materials exhibiting fluorescence that do not match that of natural teeth would not be a good choice in the mouth of patients with high esthetic needs.
Note that, even though we use a veneer for this test, we are not suggesting these materials are suitable for this type of restoration.
When you are close to finishing and polishing a restoration, the last thing you need is to find small voids in the surface. These voids will collect everything from lipstick to coffee and will basically doom the success of your work of art. And repairing them is a real nuisance and not easily accomplished. While the way we handle a material can certainly cause some of these voids, many of them are caused by incomplete air extraction by the manufacturer during the fabrication of the material.
This test shows how well the material has been vacuum mixed by the manufacturer to remove air from the final product. Discs of composite are fabricated and then transilluminated on a light box. The discs are then photographed using a special Nikon camera attached to a stereomicroscope. The images are imported into a graphical software program and the porosity is quantified. The higher the percentage of porosity, the higher the probability you will have voids present on the surface when the restoration is finished and polished.
Some dentists prefer to use restorative materials with a high level of radiopacity, while others just want it to match that of tooth structure. To test this property, we took radiographs with these products on the gingival wall of the Class II preparation as the first increment under a packable or universal composite. These radiographs can be seen in the commentary under each product.
If the material comes with a shade guide, we compared the A2 tab to the actual material and to the Vita A2.
Shade Shift after Curing
This test shows how much 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.
Closely related to flow, we actually restore a standard Class V preparation in an extracted tooth mounted in a manner to simulate a maxillary anterior tooth in a patient in a typically reclining position in a dental chair. After restoring the preparation to slightly more than full contour (as you would clinically to allow for contouring and finishing procedures), we allow the material to remain undisturbed for 30 seconds. It is then light cured and photographed. This will give you immediate visual feedback on how you could expect the material to behave in a similar situation.
When you select a shade, you are typically using some type of shade guide based on Vita shades. These shade tabs allow you to determine which hue or basic color you should use to match the tooth to be restored as closely as possible. However, the contrast ratio, better known as the translucency or opacity of the material, may place an equally important role as the hue. If you choose a material that has too much translucency, the restoration may appear gray or dark (low in value). Conversely, a material that is very opaque may appear too light (high in value).
To test materials for their relative translucency/opacity, we fabricate discs of selected enamel, body, and opaque shades in 1.0mm thicknesses and incisal shades in 0.5mm thicknesses. These discs are placed in a digital spectrophotometer, which measures this property on a scale from 0-100, with 0 being totally clear and 100 being totally opaque. Based on our clinical comparisons, here is a rough guide to the relative scores:
Note that translucency/opacity is sometimes confused with the so-called "chameleon effect", which is that elusive quality of a material that presumably allows it to blend into tooth structure, taking up the color of its surroundings. This characteristic is virtually impossible to quantify and may depend as much on the refractive properties of the restorative material as it does on any other factor, such as the translucency/opacity.
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 (30.0in/76.2cm) from the preparation.
Here are some of the uses of flowable composites, which we have found to be particularly valuable:
Blocking Out Small Undercuts
Instead of unnecessarily removing healthy tooth structure in the preparation of a tooth for an indirect restoration, blocking out small undercuts is simple and fast using these materials.
Class V Defects
Notwithstanding the flexibility issue, flowable composites can facilitate the restoration of abfraction lesions since filling up the defect is fast and easy. With some practice, you can reduce finishing and polishing time compared to the time spent when a sculptable composite is used.
Gingival Wall of Class II Restorations
Our own research suggests that using a flowable material on the gingival wall of a proximal box may reduce leakage at this margin. The surprising findings show that the least leakage was recorded in the light-cured groups compared to the dual or self-cure groups, regardless of whether the gingival margin is coronal to, equal to, or apical to the CEJ.
Minimal Class I Restorations
Improperly designated as preventive resin restorations (aren't all restorations preventive in that they are designed to help prevent recurrent caries?), flowable composites could be viewed as heavily filled, thick sealants. Even though there is a lack of research showing that these materials are wear-resistant enough to use on occlusal surfaces, we expect most flowable composites to hold up if there is no direct occlusal contact on them. Preparations made with air abrasion seem to be especially well suited to be restored with a flowable composite.