Adhesive Bond Strength

Clinical Research Associates

Material Science Department

Back to Optilux index

 

Protocol for Adhesive Shear Strength

The test consists of four steps:

1. Construct samples 2. Thermocycle 3. Shear strength test 4. Shear strength results

1. Construct Samples

a. Sample Size - Ten samples for each adhesive/composite combination b. Construct Samples (1.) Selecting Teeth Freshly extracted human molar teeth stored in tap water less than four weeks will be used for the test. The tooth used for each adhesive sample is chosen randomly. (2.) Bonding Steps (See Appendix for steps of the test adhesives listed in alphabetical order.) The composite will be bonded to dentin or enamel of each extracted human molar using a specially designed mold. (See Figure 1.) Figure 1. Mold for Sample Building For Bonding to Dentin:
    1. Embed the teeth up to the CEJ in resin. Store the embedded teeth in tap water.
    2. Grind off the occlusal surface of each tooth using a wet grinder to expose a flat dentin surface. (See Figure 2.) Store teeth in tap water.
    3. Prepare the mold by placing part 1 on a magnetic plate to hold the mold firm.
    4. Remove a thin layer of dentin from the test sample using 600 grit sandpaper to create a fresh surface. Rinse and flash dry the tooth (remove the gross excess of water from the surface but do not dry the surface).
      5.   For Bonding to Enamel:
    5. Same as described above with dentin, except the tooth is mounted with the mesial or distal surface exposed for sanding and sample mounting
      6.   For Both Dentin and Enamel:
    6. Place the embedded tooth sample into Part 2 of the mold.
    7. Apply adhesives per manufacturers’ directions.
    8. Align part 1 and 3 together and press Part 3 of the mold until it rests on the tooth’s occlusal surface that was put into Part 2. Make sure the bonding surface area is just dentin and no enamel is showing through the center hole of Part 3.
    9. Composite - Condense composite in two layers. (Light cure each layer 40 seconds.)
    10. Separate Part 3 of the mold in a lateral direction.
    11. Take bonded tooth out of Part 2.
    12. Check the bonded sample under a stereo microscope. The restorative material sample should be on the flat dentin or enamel surface. Note any flash.
    13. Store the sample in a 37oC water bath for 30 to 60 minutes.
    14. Transfer samples to the thermocycler.

Figure 2. Sample preparation for shear bond test.

2. Thermocycling

The samples will be thermally shocked for 5000 cycles in distilled water at 5° C and 55° C with a dwell time of 15 seconds. The total thermocycling time will be approximately 70 hours. After thermocycling, the samples will be stored in 37° C water immediately prior to strength testing.

3. Shear Strength Testing

The samples will be tested immediately after removal from the thermocycler for shear strength on an MTS 810 using a crosshead speed of 0.5 mm/min. (See Figure 3.) The testing sequence will be the same as that used for sample construction. After the shear strength testing, all the samples will be checked for adhesive or cohesive failure (in composite and/or dentin).

Figure 3. MTS setup for shear bond test

Review of Important Parameters and Settings

Sandpaper Grit: 600, just before applying primer or adhesive.

Step-by-Step Instructions: Follow the adhesive and restorative material directions from the manufacturer.

Sample Size: 10 samples for each resin/adhesive combination.

Mold Size: 3 mm diameter, 4 mm high.

Storage Before Thermocycling: 30 to 60 minutes.

Thermocycle: 5,000 cycles, between 5oC and 55oC.

Shear Blade: Blunt, horizontal.

Crosshead Speed: 0.5 mm/minute.

Calculations: Shear Strength (MPa) = Break force / Bonding surface area.

Observations: Cohesive or Adhesive Fracture.

4. Shear Strength Results

The shear bonding strength of each sample will be calculated using following formula:

Shear Strength (MPa) = Break force / Bonding surface area

The results will be statistically analyzed and reported with consideration of all factors that affect bond.

Bonding results will be analyzed separately for each composite and surface combination.

Observations for each sample bonded will be analyzed to classify the bonding type -Cohesive or Adhesive.

 

Return to top