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 »  Home  »  Endodontic Articles 3  »  An in vitro comparison of pH changes in root dentine following canal dressing with calcium hydroxide points and a conventional calcium hydroxide paste
An in vitro comparison of pH changes in root dentine following canal dressing with calcium hydroxide points and a conventional calcium hydroxide paste
Results - Discussion - References.



Results.

Dentine thickness.
The mean thickness between the floor of the apical cavity and the root canal was 0.90 mm (SD 0.07) and the mean thickness in the cervical cavity was 1.51 mm (SD 0.15). There was no significant difference in dentine thickness between the experimental groups either apically ( P = 0.617) or cervically ( P = 0.812).

pH values.
Tables 1 and 2 show the mean pH values in the apical and cervical sites for the three groups. There were no significant differences in the baseline pH either apically ( P = 0.84) or cervically ( P = 0.62).
In group A, the highest mean pH value was 10.38 at the apical site after 3 weeks and 10.63 at the cervical site after 2 weeks. In group B, the highest mean pH value was 11.24 at the apical site after 3 weeks and 11.57 cervically after 2 weeks. In group C, the highest mean pH values were at baseline for both cervical (pH 7.61) and apical (pH 7.62) sites. The lowest mean pH in this group was 6.68 apically after 1 week and 6.49 at the cervical site after 2 weeks.
There was a significant difference in pH between all pairs of groups at the apical site ( P < 0.001) (Table 1) with the mean values for group B being greater than those for group A which, in turn, were greater than those for group C.
There was a significant difference between the mean pH values at the apical and cervical sites, for each tooth, with lower pH values for the apical sites ( P < 0.001).
A sudden rise in pH was recorded within the first 3 days in group B at the cervical site, reaching approximately pH 11.4 and then levelling to over pH 11 for the remainder of the time (Table 2). Group A also demonstrated a rise in pH but to a level of pH 10.5 and this took 1 week to achieve. Group C dropped to pH 6.7 over the first week.
There was a significant difference between all pairs of groups at the cervical site ( P < 0.001) (Table 2) and this reflected the differences recorded for the apical mean pH values (Table 1) with the mean pH values for group B being greater than those for group A which were, in turn, greater than those for the control group.

Discussion.
This study was intended to investigate the diffusion dynamics of hydroxyl ions through root dentine with time by measuring the rapidity, magnitude and duration of pH change on the external aspect of the root at apical and cervical levels in roots dressed with calcium hydroxide points and paste. It was found that the pH increased after dressing with both preparations, concurring with the findings of Tronstad et al. (1981), who examined histological sections of monkey teeth with experimentally induced root resorption, 1 month after placement of a calcium hydroxide root canal dressing. Using pH indicator solutions, they noted that there was a pH gradient with high values around the canal decreasing toward the dentine on the periphery. When cementum was present, the pH remained unchanged, but in areas of resorption in which the cementum was not present, the pH of the dentine root surface increased. This was attributed to the outward diffusion of hydroxyl ions via the dentinal tubules. Wang & Hume (1988) also measured hydroxyl ion diffusion across dentine between an occlusal cavity containing calcium hydroxide and a saline-filled pulp chamber, using a pH meter and noted that there was a pH gradient from the cavity floor decreasing toward the middle and pulpal layers.
In our study, the greatest change was recorded cervically, a strategic area of tooth also considered by Kehoe (1987), who investigated the action of calcium hydroxide in cases of cervical root resorption. Calcium hydroxide was placed in the cervical part of root canals previously filled with bleaching agents. Using pH electrodes and alkacid test papers, Kehoe recorded a reversal from a slightly acid environment to one which was slightly alkaline.
In teeth dressed with calcium hydroxide points, the initial pH rise was more rapid apically in the initial period. This may have been due to a closer approximation of the point to the canal wall. The overall pH rise at apical and cervical sites was significantly greater in the paste group compared with the point group. The finding that the pH was lower in both points and paste groups of teeth at the apical aspect may be attributed either to the size and orientation of the dentinal tubules or to the fact that there was closer contact of the material with the root dentine coronally. The use of a point one size smaller than that of the canal preparation size may have been influential in this respect. This finding may be of significance in teeth bearing narrow canals when use of a calcium hydroxide impregnated point could facilitate controlled placement at, and removal of the medicament from the desired site.
Certain aspects of our experimental model may have had a minor effect on the outcome. For example, a chelating agent was not used, because it was possible that use of such a material may have affected the pH dynamics. Radiographs were not taken to check placement of the calcium hydroxide paste material for teeth in group B, following a pilot study in which all canals were shaped to a uniform size which easily accommodated placement of the delivery needle. A further consideration is related to the experimental environment. Dissociation of calcium hydroxide is dependent on the constitution, quantity and buffering environment of the surrounding medium. In the in vitro situation, there could be large variations between these factors in different teeth. In our experimental model, a controlled environment was established in order that other variables could be meaningfully tested.

References.

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