Potassium Nitrate Enhances Occlusion of Dentinal Tubules by Nano-Hydroxyapatite

2265

H.KAWAMATA, K.OHTA, T.SAITO and R.HAYMANSANGI Co., Ltd. Tokyo, Japan

1. Aim of Study

3. SEM Observation: Surface Coating of Dentin and Occlusion of Tubules

Hypersensitivity occurs when exposed dentinal tubules are subject to stimuli such as tooth brushing, heat or cold.
The mechanism is believed to involve hydrodynamic transmission of stimuli to the nerves via fluid in the dentinaltubules.1 We reported at the 85th IADR General Session that nano-hydroxyapatite(n-HAP), administered in a paste,
forms a protective layer on the dentin surface and occludes exposed dentinal tubules.2 Potassium nitrate(KNO3),
used widely in anti-hypersensitivity toothpaste, is known to relieve pain by releasing potassium ions which blockneural transmission.3 But KNO3 has not been associated with tubular occlusion.
To determine whether occlusion of dentinal tubules by n-HAP is (a) dose-dependent, (b) affected by the presence ofKNO3, and (c) an inhibitor of tubular fluid flow rate, we examined the effect on exposed human dentin of test
dentifrice formulations combining KNO3 and n-HAP.
control(untreated)

2. Materials and Methods

low-concentration n-HAP

low-concentration n-HAPwith 5% KNO3

higher concentration n-HAPhigher concentration n-HAPwith 5% KNO3

Fig.2 Effect of test dentifrice formulations on dentin surface

2-1. Dentin Surface Treatment Test
2-1-1. Preparation of specimens
Thin blocks of dentin were prepared by slicing the lower half of sound extracted human teeth parallel to the toothaxis. Each specimen was polished on the cementum side, under running water, using waterproof abrasive papers of
15.3μm, 8.4μm and 5.0μm grain size respectively. After polishing to a width of around 500μm, specimens werecleaned of debris by ultrasound, then masked on their non-polished faces with carbon tape and nail-enamel toprevent penetration from those faces by the test solutions used in the study.
2-1-2. Dipping Treatment
Four dentifrice formulations were used : (1)low-concentration n-HAP, (2)low-concentration n-HAP with 5% KNO3,(3)higher concentration n-HAP, (4)higher concentration n-HAP with 5% KNO3. In each case, 25g of dentifrice wasmixed with distilled water to make 40mL of test solution. Specimens were dipped in one of the solutions for
9 minutes daily at 37℃ for 5 days. Between dippings, specimens were stored in humid conditions at 37℃.

control(untreated)

low-concentration n-HAP

low-concentration n-HAPwith 5% KNO3

higher concentration n-HAPhigher concentration n-HAPwith 5% KNO3

Fig.3 Effect of test dentifrice formulations on dentinal tubules

4. Sensitivity Inhibition: Reduction of Fluid Flow Rate through Dentinal Tubules

2-1-3. Scanning Electron Microscope(SEM) Observation
After 5 days, treated surfaces were examined both directly and in cross section by FE-SEM.

Treatment

2-2. Fluid Flow Rate Test
2-2-1. Preparation of Specimens
Thin disks of dentin were prepared by slicing the crown portion of sound extracted human teeth parallel to the occlusal surface. Specimens were polished on
both sides, under running water, to around 500μm in width, using waterproof abrasive papers of 15.3μm and 8.4μm grain size respectively. Each wasthen cleaned of debris by ultrasound.
2-2-2. Split-chamber device
A split-chamber device for testing fluid flow through dentin was made, according to the method of Pashley.4 Each test disk was placed between the twochambers and held in position by silicon rubber O rings. For flow rate testing, standard Ringer solution(RS, pH5.3) was used. Both chambers were filledwith RS, and RS was then applied to the entry-chamber at a pressure of 17.7cmHg, and the amount emerging through the exit-chamber was measured, bycapturing in a microsyringe.

Flow rate reduction (%)

low-concentration n-HAP

48.6

low-concentration n-HAP with 5% KNO3

66.7

higher concentration n-HAP

90.0higher concentration n-HAP with 5% KNO3

100.0

aluminum lactate(positive control)

51.4

Table.1 Effect of test dentifrice formulations on fluid flow rate through dentinal tubules

5. Results
drain

drain
dentin disk specimen
drain

O rings

5-1. Dentin Surface Treatment
Surface coating and occlusion of dentinal tubules were observed in all specimens, but were greater in specimens
treated with higher concentration n-HAP and formulations containing KNO3. The order of efficacy, by solution, wasdrain

800μm

outflow

entrychamber

exit chamber

inflowhigher conc. n-HAP > higher conc. n-HAP > low-conc. n-HAP > low-conc. n-HAP.
with 5% KNO3
with 5% KNO3

dentin disk specimen

extracted human tooth(showing disc area)

abrasive paper(15.3μm and 8.4μm grain)
cutting device(saw microtome)

polishing device(micro grinding system)

inflow
outflow(measure)MicrosyringeO ring

split-chamber device

Fig.1 Fluid Flow Rate Test: specimen preparation and split-chamber device
2-2-3. Flow Test Procedure
Five tests were carried out according to the method of Nakashima.5 Four used the same test solutions as in 2-1-2 above, and the fifth, as positive control, asolution prepared from commercially available toothpaste containing aluminum lactate, which is known to inhibit dentin permeability.6 For each test: (1) A
dentin disk was fitted to the split-chamber device and both chambers filled with artificial saliva(AS) to simulate conditions in the oral cavity. (2) After
3 minutes, the AS was removed by draining, and RS fluid flow through the disk under hydrostatic pressure was measured. (3) RS was then removed, and after
a further 3 minutes flushing with AS, and removal of AS, entry-chamber was filled with test solution, for treatment, and allowed to rest for 3 minutes. (4) The test
solution was then removed, and RS fluid flow through the disk was again measured. (5) The effect on dentin permeability for each test solution was then calculated
by subtracting the post-treatment RS flow rate from the pre-treatment rate and expressing the result as a percentage of the pre-treatment RS flow rate.

5-2. Fluid Flow Rate
All dentifrice formulations tested inhibited dentinal permeability, in the same order of efficacy as for dentin surface
treatment. All except the low concentration n-HAP formulation without KNO3 were superior in efficacy toaluminum lactate.
Our results showed that dentin surface coating and occlusion of dentinal tubules by nano-hydroxyapatite is bothdose-dependent and enhanced by the presence of potassium nitrate, and reduces dentinal fluid permeability.
This suggests that nano-hydroxyapatite is a promising agent for reduction of dentinal hypersensitivity.
References
・・・・
1. M.Brannstromet al, Caries Res.,1,(4):310-317,1967
2. K.Ohta et al, J. Dent. Res.,86,Special Issue A:1759,2007
3. T.Nagata et al, J. Jpn Periodontol.,34,(2):465-471,1992
4. O.W. Reeder et al, J. Dent. Res.,57,(2):187-193,1978
5. S.Nakashima et al, Japan J. Conserv. Dent.,33,(4):1114-1121,1990
6. E.Maita et al, Japan J. Conserv. Dent.,33,(4):1070-1077,1990

86th General Session & Exhibition of the IADR
July, 2008
contact: kawamata@sangi-j.co.jp