1. Barcol hardness tester. (Hardness tester GYZJ 935 mounted in custom press with X-Y sample positioning stage.)
2. curing light
3. composite resin
4. composite resin instrument
5. microscope slides (75mm X 25mm)
6. lint free tissue (Kimwipes)
7. photocopier
8. sample molds (2mm thick stainless steel with 5mm diameter hole)
9. vinyl gloves (powder free)
10. small "butterfly" clamps
11. isopropyl alcohol
12. sample punch (handle of dental instrument, <5mm diameter)
13. KY jelly
14. mylar matrix material, 0.05mm thick (Mylar Roll 3/8" X 45FT., jr RAND Corporation)
15. small nylon brushes
16. mixing pads
17. scissors
18. calculator
19. flat block (Bakelite block measuring 9mm wide by 6mm thick by 51mm long)

1. Using scissors, cut mylar into 10mm lengths.

Backing Paper:

1. sample molds
2. Kimwipes
3. microscope slides
4. composite resin
5. mixing pad
6. composite resin instrument
7. vinyl gloves
8. KY jelly
9. clamps
10. small brushes
11. mylar
12. curing light
13. backing paper
14. flat block

1. Barcol hardness tester in custom press

2. Kimwipes

3. sample punch

4. small brushes

5. record sheet & pen

For this test, Barcol hardness values are used to determine degree of cure. Resin is considered cured when it has a hardness value greater than or equal to 90% of the surface hardness value.

1. Lubricate mold by applying KY jelly with a brush, then wipe well with Kimwipe to remove excess, leaving just a thin layer.

2. Make sample mold by placing microscope slide on black backing paper, then place stainless steel mold on top of slide. Clamp the three pieces together with a clamp on either side of hole. See diagram #2.

3. Dispense resin onto mixing pad.

4. Pack resin into sample mold with condensing instrument. To prevent air bubbles around edge, add resin to center of mold & carefully work resin towards sides. To prevent incorporating air bubbles, avoid folding resin over itself & keep interfaces between additional layers smooth. Slightly overfill mold. Always keep presure from instrument slightly towards sides of mold to prevent pulling resin away from walls & creating voids.

5. Trim away excess resin using flat side (knife edge) of instrument. Place knife edge across resin close to the middle, & draw instrument towards near side. Repeat in 3 - 4 locations around sample. Resin surface should be left flat with a slight mound in the center. See diagram #3.

6. Place mylar strip over resin & press flat with flat block. Excess resin should form a fine flashing around lip of mold. Resin in mold under mylar should have a smooth, uniform appearance. Repeat sample if any voids are present.

7. Position light guide over resin & press flat against mylar (0.0mm gap between resin & light guide tip).

8. Cure resin for 5 seconds.

1. On record sheet, record date, Barcol hardness reading from calibration disk, & initials of researchers performing work.

2. Remove clamps, microscope slide, & mylar.

3. Place mold in sample positioning equipment with the top surface facing up.

4. Measure and record Barcol hardness at the center of the resin, and at two additional sites located 1 mm from the center along the same diameter. Record the three measurements as T1, T2, & T3. See diagram #4.

5. Turn mold over so bottom resin surface is facing up.

6. Measure and record Barcol hardness at the same three locations on bottom surface of resin, record as B1, B2, & B3. As Barcol hardness is measured, do not count obviously erroneous readings due to voids or surface imperfections, instead, move the indenter to the side and take an additional reading.

7. Label top surface with run number.

8. Remove resin from mold using sample punch if necessary.

9. Clean sample mold and microscope slide as necessary using Kimwipes and alcohol.

10. Calculate the average hardness value of the top and bottom surfaces, record as T_ave and B_ave.

11. Ratio B_ave to T_ave & record as % (percentage): % = 100 ´ B_ave / T_ave.

12. If % is greater than or equal to 90%, then resin is considered cured. Reduce cure time by 1 second (one time interval) for next sample. Continue reducing cure time for subsequent samples until % is less than 90%. The shortest time used which results in cure is the minimum cure time (to the nearest second). This process is illustrated in the following example record sheet which shows a single sequence.

13. If % is less than 90%, then resin is considered uncured. Increase cure time by 5 seconds (one time interval) for next sample. Continue increasing cure time for subsequent samples until % ³ 90%. The time which results in cure is the minimum cure time (to the nearest 5 seconds). This process is illustrated in the following example record sheet which shows a single sequence.

Repeat the test for two or more additional sequences of samples. It is not always necessary to start with a 5 second exposure time. For example, if a previous sequence indicates that the cure time is 40 seconds, then subsequent sequences may consist of only two samples, using 35 and 40 second exposure times, showing that the resin is uncured after 35 seconds, but does cure after 40. No matter what exposure times are used in a sequence, the final minimum cure time determined must always be proven as such by a sample exposed for one time interval less which results in uncured resin.

Calculate the average cure time from the 3 or more tests and round up to the nearest time interval.

Minimum cure time can be found to any desired accuracy. As outlined, cure time is found to the nearest second for times less than 5 seconds, & to the nearest 5 seconds for times greater than 5 seconds. Greater accuracy could be achieved by reducing the time interval to 0.5 or 0.1 seconds, however, as the interval is made smaller the influence of other variables increases.