ASSESSING COMPOSITE SHRINKAGE IN TEETH WITH µCT

Diana Zeiger, Jirun Sun, Gary Schumacher, Sheng Lin-Gibson

            Establishing the shrinkage of dental restorative materials upon polymerization is of particular importance for the following reasons:  firstly, as the material contracts, mechanical stresses are placed on the tooth; and secondly, shrinkage creates gaps between tooth and restoration that allow for ingress of oral fluids and bacteria.  X-ray microcomputed tomography (µCT) is a useful, non-destructive method to determine the polymerization shrinkage of materials, as it provides a three-dimensional image of the object with spatial resolution.    Previous work1 examined the shrinkage of composites of various compositions by µCT and found the technique provided precise measurements of the volumetric changes that occurred during polymerization.  The composites used in these experiments required the addition of radiopaque filler (similar to the filler in commercially available restorative materials), and were conducted using a prepared polypropylene platform.  The ultimate objective of this project is to determine the extent of polymerization shrinkage in the context of an actual tooth; however, as the composite and tooth enamel are both highly scattering materials, it is vital to establish the threshold that resolves the two materials with a high degree of accuracy.  In this study, three-dimensional reconstructions of the raw data gathered during µCT scans of human teeth with composite restorations (before and after light-curing) were performed using thresholds of different values.  Dentin is lower-scattering than either enamel or composite, and so was easily resolved.  The contrast between enamel and composite is small, however, and therefore, the threshold was more difficult to establish.  Reconstructions were performed on either composite or enamel with composite, varying the thresholds until minimal losses of composite volume were obtained.  By this method, it was found that a higher threshold value was necessary to distinguish the composite, but the two materials can be separated with sufficient confidence.  Based on these findings, our initial efforts will focus on determining polymerization shrinkage in a surrounding environment of dentin, which permits the composite to be more easily isolated from the background.

(1)        Sun, J.; Lin-Gibson, S. Dent Mater 2008, 24, 228-234.

Author information:

Name: Diana Zeiger

Mentor’s Name: Sheng Lin-Gibson

Division: Polymers

Laboratory: MSEL

Address:  Building 224/Room A111

Mail Stop: 8543

Phone: x6803

Fax: x4977

E-mail: diana.zeiger@nist.gov

Sigma Xi Members: No

Category: Materials