# Dental Hydrogels with Essential Oils with Potential Activity in Periodontitis
## Materials and Methods
### Gas Chromatography-Mass Spectrometry (GC-MS)  
One of the goals of the current work was to use GS-MS to demonstrate the presence of essential oils (Oregano(r), Thieves(r), and Frankincense(r)) in the gel composition. A volume of 1 \(\mu\)L was fed into the apparatus after the essential oils (3 \(\mu\)L) were diluted in hexane (1 mL). The gel (1 g) was dispersed for two hours in a mixture of hexane and acetone (6 mL each, at a ratio of 2:1), then centrifuged at 4400 rpm for 15 min before being used as a sample for GS-MS. The solvent phase was dried over anhydrous sodium sulfate after centrifugation. By using GC-MS, the extracted essential oils from the gel were evaluated.  
Agilent GC-MS Gas Chromatograph-7890A/5975/2008 was used for the analyses (Agilent Technologies, Inc., Europe, Waldbronn, Germany). The studies were carried out in scan mode on an Agilent DB-5 MS capillary column (30 m \(\times\) 0.25 mm \(\times\) 0.25 m) using high-purity helium as the carrier gas at a flow rate of 1 mL/min. Programming of the temperature included the following: the GS oven temperature for the column set was 40 \({}^{\circ}\)C, 5 \({}^{\circ}\)C/min to 220 \({}^{\circ}\)C (10 min hold), then with 20 \({}^{\circ}\)C up to 280 \({}^{\circ}\)C (5 min hold), injector temperature 250 \({}^{\circ}\)C, injection volume of 1 \(\mu\)L, 100:1 split ratio, MS 70 eV, and mass range u.a.m. 30-400. The NIST library was utilized to locate and confirm the existence  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Ingredients (\%)**} & \multicolumn{6}{c}{**Formulation Code of Experimental Hydrogels**} \\ \cline{2-9}  & **G1** & **G1O** & **G1T** & **G1F** & **G2** & **G2O** & **G2T** & **G2F** \\ \hline Xanthan gum & 0.86 & 0.86 & 0.86 & 0.86 & 0.86 & 0.86 & 0.86 & 0.86 \\ Glycerin & 17.19 & 17.19 & 17.19 & 17.19 & 17.19 & 17.19 & 17.19 & 17.19 \\ Lyophilized Whey & 0.58 & 0.58 & 0.58 & 0.58 & 0.58 & 0.58 & 0.58 & 0.58 \\ Polyvinylpyrrolidone & 0.58 & 0.58 & 0.58 & 0.58 & 0.58 & 0.58 & 0.58 & 0.58 \\ PEG 400 & 0.58 & 0.58 & 0.58 & 0.58 & 0.58 & 0.58 & 0.58 & 0.58 \\ Distilled water & 80.20 & 79.99 & 79.99 & 79.99 & - & - & - & - \\ Kaqun® water & - & - & - & - & 80.20 & 79.99 & 79.99 & 79.99 \\
2-Hydroxyally salicylate & 0.015 & 0.015 & 0.015 & 0.015 & 0.015 & 0.015 & 0.015 & 0.015 \\ \({}^{\star}\) Oregano® & - & 0.21 & - & - & - & 0.21 & - \\ \({}^{\star}\) Thieves® & - & - & 0.21 & - & - & - & 0.21 & - \\ \({}^{\star}\) Frankincense® & - & - & - & 0.21 & - & - & - & 0.21 \\ pH of hydrogels & 6.5 & 6.5 & 6.5 & 6.5 & 6.5 & 6.5 & 7 & 7 \\ \hline \hline \end{tabular} \({}^{\star}\) Young Living Essential Oils (Young Living Europe B.V., Groningen, The Netherlands).  
\end{table}
Table 4: The chemical composition and the pH of the experimental hydrogels based on essential oils.  
of components from essential oils. For the calculation of the linear retention index (LRI), the C8-C20 standard alkanes solution (Alkane Standard Solution C8-C20, Sigma Aldrich, St. Louis, MO, USA) was used. The experimental values matched those reported in the literature for similar chromatographic columns and identical conditions. The compounds identified in the oil samples are presented in Table 2. Each value in Table 2 represents the mean percentage value \(\pm\) standard deviation (SD) of triple analyses. The percentage peak area method was used for the qualitative analysis of the investigated compounds.