Ultrastructural changes in the cemento-enamel junction after vital tooth bleaching with fluoride and fluoride-free agents - a pilot study

Abstract

Background: The impact of bleaching on the cemento-enamel junction (CEJ) is not well known. Due to frequent sensitivity of the cervical region of teeth after the vital bleaching, the aim of the present study was to evaluate the morphological features of the CEJ of human teeth after application of fluoridated and fluoride-free bleaching agents, as well as post-bleaching fluoridation treatment, by scanning electron microscopy (SEM) analysis.

Material/methods: Thirty-five extracted permanent human teeth were longitudinally cut, yielding 70 specimens. Thirty specimens were randomly divided into the 3 experimental groups, and 20 specimens, were used as (2) control groups, each: negative (untreated) control group; positive control group treated with 35% hydrogen peroxide; experimental group 1, bleaching with 10% carbamide peroxide (CP); experimental group 2, treatment with a mixture of 10% CP and fluoride; and experimental group 3, treatment with 10% CP and 2% sodium fluoride gel applied 30 minutes after bleaching. Experimental groups were treated 8 h per day for 14 days. The samples were examined by SEM.

Results: The bleaching materials tested caused morphological changes to the surface of the CEJ. There was a statistically significant difference between experimental groups (Kruskal Wallis Test chi-square=11,668; p<0.005). Mean value of experimental group 2 scores showed statistically significant difference from groups 1 and 3.

Conclusions: Bleaching gel with fluorides does not significantly change morphological appearance of the CEJ and represents a better choice than the hard tissue fluoridation process after bleaching.

Figure 1

Negative control group. (A) SEM appearance of the CEJ shows the most frequent type: cementum goes over the enamel surface. (B) “Wave-like” appearance of the CEJ. A gap between enamel and cementum can be observed, of approximate 10 μm in size, partially filled with fragments of inorganic contents. In the upper gap part a structure is observed, which according to its morphological appearance, does not correspond either to the enamel or the cementum, but even with higher magnification, there were not observed dental tubules to confirm that it was dentin.

Figure 2

Positive control group-specimens treated with 35% HP. (A) Notable splitting of enamel from cementum tissue and cementum is involved under the enamel. The enamel edge is ragged at some points and the morphological appearance of enamel surface indicates erosive Type II changes. (B) Very close to the CEJ there may be observed open dentinal tubules. The strip of dentin indicates the possible removing of the intermediate cementum by means of bleaching agent. Other cementum part shows conspicuous irregularity.

Figure 3

Experimental group 1 (Bleaching with 10% fluoride-free carbamide peroxide). (A) Minor lesion of cervical hard dental tissues of lower premolar mesial side. The CEJ is below both the cementum and enamel levels. Enamel surface immediately by the junction indicates “stripping” of prisms parts positioned vertically. There are expressed enamel “caps” along the enamel edge. (B) The CEJ indicates cracks on the enamel margin with insignificantly changed enamel surface and more expressed cement changes which has a pitted appearance with pits of different depths. There may be observed a significant depression of the cementum.

Figure 4

Experimental group 2 (Bleaching with 10% fluoride-added carbamide peroxide). (A) There is a minor depression of the cementum tissue which preserved its morphology. The enamel margin is rounded and CEJ is shown as an edge to edge model. (B) Higher magnification confirms that there is good relationship between marginal structures composing the CEJ. Morphological appearance of the cementum is insignificantly changed.

Figure 5

Experimental group 3 (Bleaching with 10% carbamide peroxide and fluoride application after teeth bleaching). (A) CEJ morphological appearance looks as if masked with structures resembling the fluoride compounds. The junction between the enamel and the cementum is not clearly observable but it is on the same level. Part of cementum has got a pitted appearance. (B) In higher magnification there may be observed cementum irregularity but also the structures which are not the constituent part of the cementum morphology.