# Comparative Study of the Expansive Behaviour of Different Internal Bleaching Agents
## 4 Discussion  
The present in vitro study shows in an objective and quantifiable way the expansion behaviour that takes place after the interaction of the currently most commonly used internal bleaching agents with the dental tissues inside the pulp chamber. Specifically, measurement and comparison were made of the expansion between four bleaching groups. The experimental model was designed to produce a situation as similar as possible to the conditions of the tooth when internal bleaching is carried out, and consisted of an \begin{table}
\begin{tabular}{l l l l l l l} \hline \hline  & & & & & & \multicolumn{2}{c}{**Confidence Interval 95\%**} \\ \hline
**Group** & **Comparative** & \(\boldsymbol{p}\)**-Value** & **Difference of Means** & **Typical Error** & **Lower Limit** & **Upper Limit** \\ \hline \multirow{3}{*}{CP 37\%} & HP 30\% & 0.022 * & \(-\)136.707 & 45.975 & \(-\)258.72 & \(-\)14.69 \\  & HP 30\% + SP & 0.973 & 15.467 & 36.024 & \(-\)79.84 & 110.77 \\  & SP & \(<\)0.001 * & 190.133 & 26.504 & 117.93 & 262.33 \\ \hline \multirow{3}{*}{HP 30\%} & CP 37\% & 0.022 * & 136.707 & 45.975 & 14.69 & 258.72 \\  & HP 30\% + SP & 0.007 * & 152.173 & 44.810 & 33.07 & 271.28 \\  & SP & \(<\)0.001 * & 326.840 & 37.585 & 224.44 & 429.24 \\ \hline \multirow{3}{*}{HP 30\% + SP} & CP 37\% & 0.973 & \(-\)15.467 & 36.024 & \(-\)110.77 & 79.84 \\  & HP 30\% & 0.007 * & \(-\)152.173 & 44.810 & \(-\)271.28 & \(-\)33.07 \\  & SP & \(<\)0.001 * & 174.667 & 24.428 & 108.12 & 241.21 \\ \hline \multirow{3}{*}{SP} & CP 37\% & \(<\)0.001 * & \(-\)190.133 & 26.504 & \(-\)262.33 & \(-\)117.93 \\  & HP 30\% & \(<\)0.001 * & \(-\)326.840 & 37.585 & \(-\)429.24 & \(-\)224.44 \\ \cline{1-1}  & HP 30\% + SP & \(<\)0.001 * & \(-\)174.667 & 24.428 & \(-\)241.21 & \(-\)108.12 \\ \hline \hline \end{tabular} Data marked with (*) indicate statistical significance: (\(p\)-value \(<\) 0.005).  
\end{table} 
Table 1: Multiple comparison of the expansion results obtained in each bleaching group to assess the significant differences in the expansion behaviour between them. Figure 4: Bar chart with the standard deviations and a box plot with the expansion values after 10 days, in which no outliers are observed. extracted tooth to which a glass tube was affixed in the opening orifice in order to measure the expansion after endodontic treatment for the study. This is the same technique as that used in the study by [PERSON] et al. [23], but with the novelty that, in our study, we also included and compared CP 37%. The bleaching agent with a significantly greater expansion versus the rest was HP 30%, followed by CP 37% and HP 30% + SP, with no significant differences between the latter. In turn, SP showed significantly less expansion with respect to the other groups. All bleaching groups showed greater oil displacement within the first 24 h, with stabilisation over the following days. In the CP 37%, HP 30% and HP 30% + SP groups, oil displacement persisted after 10 days, showing that the reaction that produced expansion continued, although to a much lesser degree than in the first few days. However, in the case of SP, from the fourth day onwards, the oil ceased to displace and even began to decrease from the sixth day onwards. A very different behaviour was therefore observed in the SP group. These results are very similar to those reported in an in vitro study carried out by [PERSON] et al. [28], in which the authors separated the enamel from the dentine to observe the expansive behaviour of the bleaching agents upon both structures separately. The same behaviour was observed as that obtained from mixing the bleaching agents with dentine. This could be due to the fact that in this study, the bleaching agents placed inside the pulp chamber were in direct contact with the dentine and not with the enamel.