Methods:
Bovine enamel blocks (n=37, 3x3mm) were prepared and polished to P2500. Specimens were attached to the buccal flange of upper dentures. Panellists were instructed to wear the denture 24h/day, brushing daily with commercial toothpaste. Pellicle mechanical properties were measured on a Hysitron Triboindenter with Berkovich tip. Each sample was indented 25 times: consisting of 11 periods of loading, holding and unloading. The load increased with each loading step up to 2.5mN. The colour of specimens was measured as an average of 5 readings using a Minolta CR241 chromameter with a 0.3mm aperture before and after pellicle formation.
Results:
The in situ generated pellicle seemed to form unevenly, in “globules”. Hysitron data appeared to divide the pellicle into two broad groups: 15 of the 37 specimens consisted of relatively thin deposits, as indicated by force-distance curves, with a high modulus (possibly influenced by the underlying enamel) and the remaining 22 specimens were coated with thicker, softer deposits. Analysis of the modulus of the two groups showed that they were significantly different from one another (p<0.001, Student’s t test). Comparison with the colour data showed that there was no significant difference in ΔL* between the two groups (p>0.05), but there were significant differences in both Δa* and Δb* (p<0.01).
Table: Mean values (standard deviations) of measurements for pellicle films
Film |
Modulus(GPa) |
ΔL* |
Δa* |
Δb* |
In situ overall |
11(9) |
3(2) |
-1.5(0.6) |
3(3) |
In situ “thin” |
19(9) |
3(1) |
-1.1(0.4) |
2(2) |
In situ “thick” |
5(3) |
3(2) |
-1.8(0.6) |
4(3) |
Conclusions:
This method proved suitable for analysing pellicle films. In situ grown pellicle films are variable, but can be divided into 2 groups: thin with a high modulus (which may be influenced by the underlying enamel) or thicker and softer. Thicker films were more highly coloured (greener and yellower).