Posterior Composites - American Dental Association

ADA Professional Product Review 1 

Posterior Composites: Laboratory Testing Methods 

Volume 1: Issue 1 Summer 2006 (Online) 

www.ada.org/goto/ppr 

Scope 

ADA Professional Product Review 


This protocol for the laboratory testing of posterior composites was developed to provide clinically 

relevant laboratory information that will be used as part of a report on posterior composites in the 

July 2006 issue of the ADA Professional Product Review. When surveyed, the ADA Clinical 

Evaluators (ACE) panel identified wear and shrinkage as important features to be evaluated in the 

laboratory. Also, strength, shade/color stability, polishability, and depth of cure were indicated 

multiple times as areas of interest. The tests described in this protocol should provide the dental 

practitioner with appropriate comparative scientific information to assist in the purchase of 

posterior composites. 

General Information 

All tests were performed with the A3 enamel shade. 

Tests in This Protocol 

A. Depth of Cure 

B. Flexural Strength and Flexural Modulus 

C. Water Sorption and Solubility 

D. Shade Matching and Color Stability After Water Sorption 

E. Radiopacity 

F. Polishability 

G. Shrinkage 

Document posted 2006 

© 2006 American Dental Association





Depth of Cure 

Identifies the depth of cure achieved according to the manufacturer’s recommended curing time 

and offers guidance on the maximum increment-thickness that can be cured under similar 

conditions. Darker shades, lower light intensity, and increased distance between the light tip and 

the composite will decrease the maximum depth of cure. 

Sampling: The test sample shall consist of packages prepared for retail sale from the same 

batch and containing enough material to carry out the specified tests, plus an 

allowance for repeat tests, if necessary (50 g should be sufficient). 

Materials: Stainless steel mold for the preparation of test specimens. Mold should be 

6 mm long × 4 mm in diameter, unless the manufacturer claims a depth of cure in 

excess of 3 mm; in this event, the mold shall be at least 2 mm longer than twice the 

claimed depth of cure. 

Two glass slides/plates, each of sufficient area to cover one side of the mold 

(standard glass microscope slides may be used) 

White filter paper 

Film, transparent to the activating radiation, e.g., polyester, 50 ±30 μm thick 

External energy source (note that the light intensity should be measured according to 

ISO 10650, 3 and the intensity should be above 300 mW/cm 2 ). Include a mylar strip 

between the light and the filters while recording the light intensity. 

Micrometer accurate to 0.01 mm 

Plastic spatula 

Procedure: See 7.10 of ANSI/ADA Spec 27 1 or 7.10 of ISO 4049 2 







Flexural Strength and Flexural Modulus 

Represents the composite’s ability to initially withstand occlusal stress and flex under load, but 

does not predict resistance to wear or fatigue. 





25 ±2 mm × 2 ±0.1 mm × 2 ±0.1 mm (see Figure 7 of ANSI/ADA Spec 271 or ISO 

4049 2 ). 

One metal plate of sufficient area to cover one side of the mold 

Glass microscope slide for use during polymerization 

Small clamp 

Film, transparent to the activating radiation, e.g. polyester, 50 ±30 μm thick 


Water bath capable of being maintained at 37 ±1ºC 

External energy source (Note: the light intensity should be measured according to 




Mechanical test machine appropriately calibrated to provide a constant crosshead 

speed of 0.75 ±0.25 mm/min or a rate of loading of 50 ±16 N/min 

Flexural strength test apparatus, the apparatus consists essentially of two rods (2 mm 

in diameter), mounted parallel with 20 mm between centers, and a third rod (2 mm 

in diameter) centered between, and parallel to, the other two, so that the three rods in 

combination can be used to give a three-point loading to the specimen. 








Water Sorption and Solubility 

Indicates the amount of shrinkage for one hour after polymerization and the rate of stress 

development the adhesive would be subjected to during this time. Theoretically, a lower maximum 

shrinkage stress and a slower rate of stress development would be advantageous to maintain 

marginal integrity, prevent microleakage, and may limit post-operative sensitivity. 




Materials: Mold of internal dimensions 15 ±0.1 mm in diameter and 1.0 ±0.1 mm deep, for the 

preparation of specimen discs. A split ring or “washer” mold is suitable. To aid 

release of the specimen from the mold, the inner surface of the ring can be lubricated 

with a 3% solution of polyvinyl ether wax in hexane. 

Film transparent to the activating radiation, e.g., polyester, 50 ±30 μm thick 

Two metal plates, each of sufficient area to cover one side of the mold 

Two dessicators containing silica gel freshly dried for 5 h at 130ºC. Replace the 

silica gel with freshly dried gel after each weighing sequence. 




Oven capable of being maintained at 37 ±1ºC 

Analytical balance accurate to 0.05 mg. IMPORTANT: unless specified, weight 

measurements should be made at room temperature 23 ±1ºC and humidity 50 ±5%. 


Plastic tweezers. To avoid contamination of the specimens, they should be handled 

at all times with the tweezers. 

Hand dust blower or source of oil-free compressed air with micro-jet nozzle 








Shade Matching and Color Stability After Water Sorption 

Shade matching verifies the color match between the cured composite and the manufacturer’s 

recommended shade guide fore that product. Color stability is a screening test that checks whether 

the color of the material initially will remain stable in a moist environment. . 




Materials: Same as for WATER SORPTION AND SOLUBILITY test above. 








Radiopacity 

Shows how identifiable the composite will be on a radiograph 




Materials: Same as in the WATER SORPTION AND SOLUBILITY test plus the following: 

Single-phase dental x-ray unit with a total filtration of 1.5 mm aluminum and 

capable of operation at 65 ±5 kV, with suitable accessories 

Dental x-ray film of speed group D, developing solution and fixer 

Aluminum step wedge, purity at least 98% (mass fraction) with less than 0.1% 

(mass fraction) copper and less than 1.0% (mass fraction) iron present, 50 mm long 

× 20 mm wide, having a thickness range from 0.5 mm to 5.0 mm in equally spaced 

steps of 0.5 ±0.01 mm. The wedge should be free-standing. 

Sheet of lead not less than 2 mm thick 

Photographic densitometer capable of measuring in the range of 0.5 to 2.5 optical 

density 









Polishability 

Demonstrates the ability to attain maximum surface gloss with a polishing system 





25 ±2 mm × 2 ±0.1 mm × 2 ±0.1 mm (see Figure 7 of ANSI/ADA Spec 27 1 or ISO 

4049 2 ) 

One metal plate of sufficient area to cover one side of the mold 

Glass microscope slide for use during polymerization 

Small clamp 

Film, transparent to the activating radiation, e.g. polyester, 50 ±30 μm thick 


Water bath capable of being maintained at 37 ±1ºC 





Sectioning saw with diamond blade (IsoMet saw, Buehler Ltd.) 

Profilometer (Surtronic 3+, Taylor Hobson Ltd.) 

Polishing discs (Sof-Lex 3M ESPE), medium, fine, and super fine 

Procedure: 1. Cover the metal plate with the filter paper, followed by the polyester film, and 

position the mold on it. 

2. Prepare the material in accordance with the manufacturer’s instructions and fill 

the mold with the material. 







Polishability, cont’d. 

3. Place a second piece of polyester film onto the material in the mold and cover this 

with the glass microscope slide. 

4. Place the exit window of the external energy source at the center of the specimen 

and against the glass plate. 

5. Irradiate that section of the specimen for the recommended exposure time. 

6. Move the exit window to the section next to the center, overlapping the previous 

section by half the diameter of the exit window, and irradiate for the appropriate 

time. Then irradiate the section on the other side of the center in the same way. 

Continue this procedure until the entire length of the specimen has been irradiated 

for the recommended exposure time. 

7. Turn the mold over and repeat the irradiation procedure on the other side of the 

specimen. 

8. Use the sectioning saw with the diamond blade to cut the 25 mm × 2 mm × 2mm 

rectangular specimens into thirds, resulting in three 8 mm × 2 mm × 2mm 

rectangular specimens. A total of six 8 mm × 2 mm × 2mm rectangular specimens 

are required for each product. 

9. For each specimen, designate one of the rectangular, 8 mm × 2 mm surfaces to be 

the top. Then, using a profilometry system, analyze the top of each specimen and 

record its baseline surface roughness (Ra) and the baseline maximum roughness 

(Rz). 

10. For each specimen, polish the side of the specimen that is analyzed by the 

profilometry system (the top side). The polishing procedure shall simulate 

clinical conditions by using a series of medium, fine and super fine polishing 

discs. Polish each specimen for 30 sec with medium, 30 sec with fine, and 

15 sec with super fine polishing discs. 

11. Using a profilometry system, analyze the polished surface of each specimen 

three times and record the surface roughness (Ra) and the maximum roughness 

(Rz) of the polished surface. 

12. Repeat for all six specimens. 

13. For each product, report the average surface roughness (Ra) and the average 

maximum roughness (Rz) of the polished surfaces, along with their standard 

deviations. 







Shrinkage 

(see Shrinkage Testing Method PDF) 

References 

1. American National Standard/American Dental Association Specification No. 27—2005, Resinbased 

Filling Materials. Chicago: American Dental Association. 

www.ada.org/prof/resources/positions/standards/denmat.asp#ansi 

2. International Organization for Standardization. ISO No. 4049:2000, Dentistry—Polymer-Based 

Filling, Restorative and Luting Materials. Geneva: ISO. www.iso.org 

3. International Organization for Standardization. ISO No. 10650-1:2004, Dentistry—Powered 

Polymerization Activators—Part 1: Quartz Tungsten Halogen Lamps. Geneva: ISO. 

www.iso.org 

4. ASTM International. ASTM E399-90 (1997) Standard Test Method for Plane-Strain Fracture 

Toughness of Metallic Materials. West Conshocken, PA: ASTM International. www.astm.org

Posterior Composites - American Dental Association

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