Compomer, a term evidently created by Dentsply and adopted by the rest of the industry, is a polyacid-modified composite that incorporates some of the attributes of resin ionomer, such as being relatively self-adhesive and having fluoride release. The self-adhesive property of both resin ionomers and compomers is presumably due to their both undergoing an acid-base reaction. This reaction requires the presence of water, which is present in the resin ionomer liquid. As soon as the powder and liquid are mixed, resin ionomers undergo the acid-base reaction. But being anhydrous, compomers need external moisture to initiate their acid-base reaction. This occurs after a compomer is light-cured and exposed to moisture in the mouth. This acid-base reaction presumably allows compomers to bond to tooth structure without etching.
Etching vs. No Etching REALITY RESEARCH LAB (RRL) results found significantly higher bond strengths to etched enamel compared to unetched enamel. We did not find a significant difference in bond strength between etched and unetched dentin. When this information is coupled with our clinical experience that shows better enamel margins with etching, we continue to advise using a bonding agent (etch & rinse or self-etch) when compomers are placed as definitive restorations or core build-ups in primary and permanent teeth.
ADVANTAGES/DISADVANTAGES COMPARED TO COMPOSITES
+ More fluoride release than fluoride-releasing composites
- Less shades and worse surface finish
- Not as strong
ADVANTAGES/DISADVANTAGES COMPARED TO RESIN IONOMERS
+ Superior esthetics
+ No-mix formula
+ Better handling
+ More polishable
- Cannot alter consistency by mixing thinner or thicker
- Light-cured-only, while resin ionomers are dual-cure (for the most part)
- Does not release as much fluoride
+ Class V lesions, especially carious
+ Blocking out undercuts in inlay/onlay/crown preparations
+ All types of restorations in primary teeth
- Highly visible restorations
- High stress areas
Translucency/Opacity Discs of several body shades in 1.0mm thicknesses and incisal shades (if available) in 0.5mm thicknesses were measured in a spectrophotometer. The scale was 0 - 100, with 0 being totally clear and 100 being totally opaque. Our findings are in each product's commentary.
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.
Porosity 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.
Fluorescence 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. 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.
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 the products marketed for posterior use placed 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.
Hardness (Knoop) Class I or II preparation was restored with the material, cured for 40 seconds, and tested for hardness. This test is mainly for comparative purposes to known standards.
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.
Volumetric Shrinkage 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. Measurements are made using a computerized imaging device and soft ware developed by Bisco called AccuVol.
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.
Radiopacity We took a digital x-ray with the flowable product in the proximal box of the Class II preparation. This x-ray can be seen in its commentary.