## 4 Discussion
\begin{table}
\begin{tabular}{c c c c} \hline  & **Univariate** & **Multivariate** \\  & **Variables** & _Regression Coefficient (95\% CI)_ & _Regression Coefficient (95\% CI)_ \\ \cline{3-4}  & & **2 nd Primary Mesial Decay** \\ \hline \multirow{4}{*}{**2 nd Primary Mesial Sound**} & 1 st Primary Distal Decay & 0.61 (0.59–0.68) * & 0.61 (0.58–0.69) * \\ \cline{2-4}  & \multicolumn{2}{c}{Gender (female)} & 0.00 (\(-\)0.15–0.16) & 0.02 (\(-\)0.08–0.21) \\ \cline{2-4}  & \multicolumn{2}{c}{Age} & \(-\)0.04 (\(-\)0.07–0.01) & 0.06 (0.01–0.08) * \\ \cline{2-4}  & \multicolumn{2}{c}{Nationality (Saudi)} & 0.05 (\(-\)0.35–0.03) & \(-\)0.02 (\(-\)0.25–0.11) \\ \cline{2-4}  & \multicolumn{2}{c}{Medical History (healthy)} & \(-\)0.04 (\(-\)0.48–0.07) & \(-\)0.05 (\(-\)0.53–0.00) \\ \cline{2-4}  & \multicolumn{2}{c}{Patient Cooperation (non-cooperative)} & 0.09 (0.07–0.52) * & 0.1 (0.16–0.53) * \\ \cline{2-4}  & \multicolumn{2}{c}{**2 nd Primary Mesial Sound**} \\ \hline \multirow{4}{*}{**2 nd Primary Mesial Filled**} & 1 st Primary Distal Sound & 0.62 (0.62–0.72) * & 0.60 (0.61–0.72)* \\ \cline{2-4}  & \multicolumn{2}{c}{Gender (female)} & 0.00 (\(-\)0.16–0.17) & \(-\)0.02 (\(-\)0.20–0.09) \\ \cline{2-4}  & \multicolumn{2}{c}{Age} & \(-\)0.07 (\(-\)0.9—0.01) * & \(-\)0.05 (\(-\)0.08–0.00) \\ \cline{2-4}  & \multicolumn{2}{c}{Nationality (Saudi)} & 0.03 (\(-\)0.9–0.31) & 0.02 (\(-\)0.1–0.27) \\ \cline{2-4}  & \multicolumn{2}{c}{Medical History (healthy)} & 0.07 (0.05–0.62) * & \(-\)0.04 (\(-\)0.47–0.07) \\ \cline{2-4}  & \multicolumn{2}{c}{Patient Cooperation (non-cooperative)} & \(-\)0.07 (\(-\)0.48—0.02) * & \(-\)0.09 (\(-\)0.52—0.15) * \\ \hline \multicolumn{4}{c}{**2 nd Primary Mesial Filled**} \\ \hline \multirow{4}{*}{**3 rd Primary Mesial Filled**} & 1 st Primary Distal Filled & 0.61 (\(-\)0.05–0.10) & 0.61 (0.55–0.66) * \\ \cline{2-4}  & \multicolumn{2}{c}{Gender (female)} & 0.001 (\(-\)0.06–0.06) & 0.00 (\(-\)0.06–0.06) \\ \cline{2-4}  & \multicolumn{2}{c}{Age} & 0.03 (\(-\)0.01–0.02) & 0.01 (\(-\)0.01–0.02) \\ \cline{2-4}  & \multicolumn{2}{c}{Nationality (Saudi)} & 0.01 (\(-\)0.06–0.09) & 0.00 (\(-\)0.06–0.07) \\ \cline{2-4}  & \multicolumn{2}{c}{Medical History (healthy)} & 0.00 (\(-\)0.10–0.11) & 0.02 (\(-\)0.07–0.14) \\ \cline{2-4}  & \multicolumn{2}{c}{Patient Cooperation (non-cooperative)} & 0.01 (\(-\)0.08–0.11) & 0.01 (\(-\)0.05–0.09) \\ \hline \multicolumn{4}{c}{* Statistically significant at \(p=0.05\).} \\ \end{tabular}
\end{table} 
Table 3: Linear regression models showing the influence of patients’ behaviors on the associations between the sound, carious, and filled 1 st and 2 nd primary molars, adjusted for demographical variables (\(n=888\)). with the first primary molars once the second primary molars erupt into the oral cavity, which results in increased susceptibility to caries. On the other hand, our findings showed that the mean of the sound mesh surfaces of the second primary molars was higher than the distal surfaces of the first primary molars. This result is logically explained by the fact that the spread of caries to the mesial surfaces of the second primary molars is a result of caries in the distal surfaces of the first primary molars. [PERSON] et al. highlighted how dental caries could spread to the proximal surfaces of teeth adjacent to a cautious proximal surface of another tooth [24]. In addition, the second primary molars erupt later than the first primary molars, and their susceptibility to caries and exposure to cariogenic bacteria in the oral cavity starts after the earlier erupted first primary molars [16]. Therefore, the second primary molars have a higher mean of sound mesial surfaces than the first primary molars. Consequently, it is critical to provide early treatment for the first primary molars before caries spreads to the adjacent surfaces of the second primary molars. The mean of filled surfaces of the first primary and second primary molars in our study was found to be similar (0.171 and 0.173, respectively).