In the present study, GCF samples were taken before treatment and 7 and 21 days after dental restorations with amalgam fillings and SSCs. In the group receiving SSCs, the level of TNF-α was significantly reduced. Moreover, the level of IL-1β cytokine was significantly increased in both groups after 7 days. However, the level of IL-1β cytokine decreased in the group receiving dental amalgam fillings on day 21 post-treatment.
Dental caries is a source of inflammation due to the production of cariogenic microorganisms and other byproducts, as well as the invasion of tooth enamel. In the current study, the level of TNF-α demonstrated a decreasing trend at both time points of 7 and 21 days post-treatment in patients treated with amalgam fillings. Conversely, the level of IL-1β in patients receiving amalgam fillings first increased within 7 days and then decreased significantly on day 21 post-treatment. In a recent short-term controlled prospective study, Stefanović et al. [32] reported that the concentrations of both pro-inflammatory cytokines IL-1β and TNF-α decreased on day 7 and increased on day 30 post-treatment in patients treated with amalgam fillings. Except for TNF-α on day 7, all other results contradicted the current study. This discrepancy could be due to the varying mean age of the participants and the GCF sampling methods. Stefanović et al. used paper strips for GCF sampling, while we used absorbent paper points. Additionally, the mean ages of the participants in the present study and the study by Stefanović et al. were 7.15 ± 0.97 and 31 ± 6.15 years, respectively. Such an evident disparity in the mean age of the participants between the two studies could explain the different levels of hormones and, thus, the different concentrations of inflammatory factors in the GCF.
Recent research has further investigated the levels of inflammatory factors in the dentinal fluid, a plasma-derived fluid containing serum proteins and immunoglobulins [33–35]. Geraldeli et al. [36] reported a greater level of TNF-α and a lower level of IL-1β in dentinal fluid derived from extracted sound molars restored with amalgam fillings than in healthy teeth and teeth with caries. However, in the present study, the levels of TNF-α and IL-1β cytokines were reduced 21 days after restoration with amalgam fillings compared to pre-treatment and control groups with healthy teeth. Due to the absence of clinical or radiological symptoms with restored teeth in the study by Geraldeli et al., we cannot attribute such raised levels to the additional progression of the carious lesion or other inflammatory mechanisms. Again, the different research designs adopted by these two studies may explain the discrepancy in the results. Geraldeli et al. studied extracted third molar teeth and analyzed the extracted and restored teeth separately, providing no data on the post-treatment periodic examination of carious teeth. The authors additionally investigated restored teeth after a long period of decayed teeth treatment, confirming the long-term nature of their study. In contrast, the present study investigated patients only within 7 and 21 days after treatment. In addition, the target population in the present study was children (mean age: 7.14 years), which may lead to different results compared to adult studies.
Subgingival restorations trigger dental biofilm accumulation, thereby provoking the gingival inflammatory response. Such a response may create adverse environmental conditions for gingival health compared to untreated dental surfaces [37–39]. In line with this, some studies have assessed the level of inflammatory factors in the GCF when applying various restorative materials. Saravanakumar et al. [29] studied the level of IL-1β in the GCF of teeth restored with ceramic, metal, and zirconia crowns immediately after crown placement and 45 and 90 days after dental restoration. The inflammatory factor level decreased after 90 days in the groups receiving zirconia and ceramic crowns. In contrast, the inflammatory factor level increased in teeth treated with ceramic crowns.
In a similar study, Sakallioğlu et al. [40] assessed the levels of various inflammatory factors (e.g., IL-1β) in teeth restored with composite, amalgam, and metal-ceramic crowns. In the present study and the study by Geraldeli et al. [36],, the level of IL-1β cytokine decreased in patients receiving dental amalgam fillings compared to controls. However, Sakallioğlu et al. reported that the level of IL-1β cytokine significantly increased in the GCF near restored teeth following dental restoration. The mean ages of the participants in the present study and the study conducted by Sakallioğlu et al. [40] were "6–9" and "35–45," respectively. Such a noticeable discrepancy in the mean age of the participants between the two studies reflects differences in hormone levels and, thus, in the concentrations of inflammatory factors in the GCF. In addition, Sakallioğlu et al. studied only two participants in each group, while 17 participants were included in each group in the present study. Thus, the results reported by Sakallioğlu et al. are slightly questionable due to the small sample size.
During chronic inflammatory conditions caused by restorations, host cells begin to produce and release cytokines such as IL-1β and TNF-α. These cytokines interfere in bone resorption and lead to radicular bone loss [20, 24]. Currently, there is not enough information about the levels of pro-inflammatory cytokines TNF-α and IL1-β in children in the presence of SSCs and amalgam restorations. Several approaches have been used to identify and quantify biological markers in GCF, including bioassay, radioimmunoassay, and ELISA [41]. In the current study, the ELISA method was utilized to analyze the GCF samples. ELISA-based methods are one of the most employed methods in periodontal diagnosis studies to evaluate fluid-based biomarkers [41]. ELISA is the most sensitive, cost-effective, and extensively utilized biochemical diagnostic method in periodontal research. ELISA-based procedures have several advantages, including high throughput and reproducibility, as well as the ability to identify antigens with extremely small samples [31]. In addition, ELISA has been found to be more sensitive than other techniques, such as radioimmunoassay, because it produces results identical to those of radioimmunoassay without the risks associated with radioactive chemicals [42]. Yet, research suggests that analytical approaches with higher sensitivity and linear range may reveal periodontitis-related biomarkers that ELISAs cannot identify [43].
This study had some limitations. First, the use of paper points for GCF sampling could introduce variability, and future studies should consider comparing the precision of paper points with other methods, such as period papers. Moreover, the study only measured TNF-α and IL-1β cytokines; future research should include a broader range of inflammatory markers, such as IL-6, IL-10, and TGF-β, to provide a more comprehensive understanding of the inflammatory response. Additionally, the study focused on children aged 6 to 9, and it would be beneficial to investigate different age groups to determine if the findings are consistent across different developmental stages. Despite these limitations, the study provides valuable insights into the inflammatory response associated with different dental restorative materials in children.