The XRD studies of Ramachandran et al. (1968), Belli et al., (1994-1996) and Kramer et al., (1999-2000) and NMR studies of Fullerton et al. (2006) and Cameron et al. (2007) demonstrated that most proteins are surrounded by bound water, especially collagen. Objective: As little work has been done on bound water in dentin, the purpose of this work was to estimate the fractional volume percent of tightly bound, loosely bound and bulk water in demineralized dentin. Methods: Dentin beams 2 x 1 x 6 mm were completely demineralized and a wet weight taken. Beams were dried to achieve absolutely dry dentin, defined as having <0.02 g H2O/g dry mass. This dentin was slowly rehydrated by water vapor (32% RH). Rehydration was followed gravimetrically on a microbalance. The first layer of bound water was complete when the water content reached 0.0606 g H2O/g dry mass; the second layer was complete when the water content reached 0.166 g H2O/g dry mass. Results: The final water content was 1.88 g H2O/g dry mass.
| “Wet” Weight | “Bone dry” | 1st layer water (5 hrs) | 2nd layer water (7 days) | “Unbound” water |
Raw data (mg) | 12.91 ± 1.00 | 4.49 ± 0.40 | 4.78 ± 0.43 | 5.23 ± 0.46 | 7.69 ± 0.68 |
g water / g dry mass | 1.88 ± 0.13 | 0.02 ± 0.01 | 0.064 ± 0.011 | 0.094 ± 0.010 | 1.716 (theoretical) |
% | 100% | 0% | 6.36% ± 1.07% | 9.43% ± 0.97% | 84.21% ± 0.20% |
Conclusions: Bound water represents about 15% of the total water of demineralized dentin. It cannot be removed by acetone or ethanol, while up to 23% of bulk water can be removed by acetone in 1 min. Residual water remains a critical barrier to creation of perfect resin-dentin bonds. Supported, in part, by R01DE015306 from the NIH/NIDCR to DHP (PI).