Teeth represent a crucial component of the human skeleton. Among all bones, teeth are the most chemically and physically resilient and well-preserved structures. The mineral composition of teeth allows for the long-term preservation and analysis of DNA, which is a significant advantage in solving crimes that occurred a long time ago. The use of strong acids to destroy bodies is one of the methods employed by criminals. To investigate this issue, the most durable structures, namely tooth samples, were chosen. The parameters affecting the destruction of tooth samples by acids include the duration of exposure and the strength of the acids. As the duration and strength of the acid increase, the extent of dissolution also increases. Studies on teeth exposed to strong acids have concluded that DNA analysis cannot be performed conclusively when the teeth are completely dissolved [7,8,9].

To observe the DNA amount recoverable from teeth without exposure to any chemicals, molar and incisor teeth were selected. DNA amounts of 7.74 ng/µl were obtained from the molar, which is significantly higher compared to 1.72 ng/µl from the incisor. The analysis of both acid-exposed and reference samples demonstrated that the highest DNA recovery was achieved predominantly from molars, whereas the lowest recovery was observed in incisors. Notably, acid-exposed molars yielded DNA quantities comparable to those recovered from incisors. Despite this, the DNA recovered from molars was sufficient for identification, whereas none of the incisors provided adequate DNA for identification purposes (Tables 1 and 2, and 3). These results further highlight the superior efficiency of molars in DNA recovery.

The effect of nitric acid on tooth samples increases with exposure time, leading to more effective dissolution with prolonged exposure. The color of the acidic solution and the morphological changes in the teeth reflect the dental material’s reaction to the acid. Changes in solution color indirectly indicate the degree of dissolution.

Among the DNA isolation results, the group exposed for 8 h was more successful in terms of DNA yield compared to the 24-hour group, as anticipated. For the 8-hour exposure group, DNA amounts ranging from 0.194 ng/µl to 16.3 ng/µl were obtained. In the 24-hour group, most of the tooth morphology had been lost, which suggests that the acid had largely destroyed the parts of the tooth that preserved DNA. However, a DNA yield of 0.0302 ng/µl was achieved from a completely dissolved liquid sample in nitric acid. The DNA amounts obtained from the 24-hour group ranged from 0.244 ng/µl to 0.0260 ng/µl.

The sample exposed to nitric acid for 8 h, which yielded 4.5 ng/µl DNA, was subjected to identification. The results showed alleles from full STR profile (24 STR), achieving a 100% success rate.

The sample exposed to nitric acid for 24 h, which yielded 0.244 ng/µl DNA, was subjected to identification. The results showed alleles from 17 out of 24 STR loci, achieving a 70.83% success rate. Although not all alleles from the 24 STR loci were obtained and the profile was fragmented in 24 h, previous generation identification kits that used 16 STR loci were known to provide a 99.999% identification rate [10]. Thus, it is concluded that the DNA profile with alleles from 17 STR loci can be used to identify the individual. This result indicates that identification is feasible with molar tooth samples exposed to nitric acid for up to 24 h.

The effects of hydrochloric acid on dental materials increase in proportion to the duration of exposure. The color of the acidic solution changes in relation to the degree of dissolution of the teeth, with more extensive dissolution resulting in a lighter color. Even when the dental sample is completely dissolved, residues on the outer surface continue to persist.

In the DNA isolation process, 8-hour-exposed samples yielded more successful DNA amounts compared to 24-hour-exposed samples. For the 8-hour exposure, DNA quantities ranged from 0.0426 ng/µl to 7.92 ng/µl. In the 24-hour samples, DNA quantities ranged from 0.0301 ng/µl to 0.171 ng/µl, with one sample failing to yield any detectable DNA. Despite incomplete dissolution of blood and tissue residues on the tooth surfaces in the 24-hour samples, one sample that underwent significant morphological changes became completely liquid. Even from this liquid sample, 0.0398 ng/µl of DNA was recovered.

For identification purposes, a DNA sample with a concentration of 3.15 ng/µl, treated with hydrochloric acid for 8 h, was analyzed. The resulting data yielded alleles from a complete STR profile (24 STR loci), achieving a 100% success rate. Additionally, a DNA sample (Sample 1) with a concentration of 0.171 ng/µl, treated with hydrochloric acid for 24 h, resulted in successful allele recovery from 18 out of 24 STR loci, yielding a 75% success rate. A second DNA sample (Sample 2) with a concentration of 0.154 ng/µl, also treated with hydrochloric acid for 24 h, produced alleles from 13 out of 24 STR loci, resulting in a 54.16% success rate. These findings demonstrate that allele recovery decreases as DNA concentration diminishes. Nevertheless, identification was still achievable in the sample treated with hydrochloric acid for 24 h. Although not all alleles from the 24 STR loci were recovered and the profile was fragmented after 24 h, prior studies using identification kits based on 16 STR loci have reported a 99.999% identification success rate [10]. Therefore, it is concluded that a DNA profile with alleles from 18 STR loci can be utilized for individual identification. This outcome suggests that identification remains feasible for molar tooth samples exposed to hydrochloric acid for up to 24 h.

In samples exposed to sulfuric acid, no morphological changes were observed after 8 h, while 24-hour samples showed slight erosion and a darker solution color. In 120-hour samples, blood and tissue residues were completely dissolved, resulting in a dark, opaque solution. White residues were noted on the tooth surfaces at each stage, indicating a general interaction effect.

In the DNA isolation process, 8-hour-exposed samples provided more successful DNA amounts compared to 24-hour and 120-hour samples. DNA quantities ranged from 0.0233 ng/µl to 7.65 ng/µl in the 8-hour samples, from 0.0210 ng/µl to 0.255 ng/µl in the 24-hour samples, and from 0.0318 ng/µl to 0.0456 ng/µl in the 120-hour samples. Average DNA recoveries were 1.870 ng/µl for 8-hour samples, 0.0828 ng/µl for 24-hour samples, and 0.0387 ng/µl for 120-hour samples.

For identification purposes, DNA samples with concentrations of 7.65 ng/µl, 0.255 and 0.160 ng/µl, treated with sulfuric acid for 8 h and 24 h respectively, were analyzed. From the sample with a concentration of 7.65 ng/µl treated for 8 h was subjected to identification. The results showed alleles from full STR profile (24 STR), achieving a 100% success rate. Additionally, a DNA sample (Sample 1) with a concentration of 0.160 ng/µl, treated with sulfuric acid for 24 h, produced alleles from 12 out of 24 STR loci, resulting in a 50% success rate. A second DNA sample (Sample 2) with a concentration of 0.255 ng/µl, also treated with sulfuric acid for 24 h, resulted in successful allele recovery from 20 out of 24 STR loci, yielding an 83.3% success rate. Finally, although not enough DNA for identification, a DNA sample with a concentration of 0.0456 ng/µl treated with sulfuric acid for 120 h produced alleles from 8 of the 24 STR loci, resulting in a 30% success rate as a partial profile.

Among the acids evaluated, both nitric acid and hydrochloric acid induced the most significant morphological changes in dental samples. Of the two, nitric acid was found to be the most effective in eliminating residues from tooth surfaces. Although sulfuric acid caused fewer morphological changes, it resulted in the lowest DNA recovery across all groups. Notwithstanding the greater damage caused by sulfuric acid, allele recovery was more successful in samples treated with this acid.

When similar studies in the literature are examined: In a study by Raj et al. the morphological changes induced by nitric acid, hydrochloric acid, and sulfuric acid in dental samples were examined. Like our study, the acids were used at the same concentrations7. In their study, complete dissolution of the teeth occurred after 8 h of exposure to 37% hydrochloric acid. In contrast, our study did not observe complete dissolution after 8 h of exposure. In experiments with 65% nitric acid, the dissolution process was completed within 8 h, which does not align with the results of our study. For experiments conducted with 96% sulfuric acid, a whitish appearance and dissolution in the enamel layer were observed after 3 h, but the tooth morphology remained largely intact even after 8 h. This finding is consistent with our results, where sulfuric acid did not cause significant changes to the tooth surface after 8 h, but over time, it led to the formation of a whitish tissue on the surface, causing dissolution in the enamel [9].

In a study conducted by Turner et al., morphological changes were examined in human teeth soaked in acid. The commercial acids used included 37% hydrochloric acid (HCl), 65% nitric acid (HNO3), and 96% sulfuric acid (H2SO4). This study utilized six anterior canine human teeth, each individually immersed in separate beakers containing one of the acids and observed at various intervals. The findings revealed that the teeth were completely dissolved in 37% hydrochloric acid and 65% nitric acid within 48 h. In contrast, teeth immersed in 96% sulfuric acid did not dissolve completely but instead formed a white precipitate [11]. In the present study, sulfuric acid was determined to be less effective at tooth dissolution. However, due to the inclusion of DNA analysis, it was determined that although sulfuric acid has a lower dissolution capacity, it causes significant DNA damage and DNA quantities are very low, but despite this, identification can be made from samples exposed to sulfuric acid for up to 24 h, and only a partial profile can be obtained from samples exposed for 120 h.

In a study conducted by Snedeker et al., the effect of immersing partial human remains (including whole heads, forearms, and hands) in five different household products—bleach, Rid-X® septic treatment, lye drains opener, sulfuric acid drain opener, and muriatic acid (hydrochloric acid) pool cleaner—were investigated. The researchers assessed the impact of each chemical on visual changes, DNA recovery, and the potential for successful human identification through traditional STR or mitochondrial DNA analyses. Human remains exposed to bleach, Rid-X®, and lye generated full STR profiles after 4 weeks of exposure. Sulfuric acid shortened this timeframe to 3 weeks, while hydrochloric acid, the most damaging chemical, restricted full STR profile recovery to just the first 3 days of exposure. In sulfuric acid, tooth samples remained intact until the 5th day, after which they dissolved completely. On day 5, DNA recovery was determined to be 0.2 ng/µl, and identification was considered possible; however, DNA extraction became impossible after this point. Similarly, tooth samples exposed to hydrochloric acid remained intact until day 1, after which they dissolved completely. On day 1, DNA recovery was 2 ng/µl, and identification was deemed possible; however, DNA extraction was not possible after this day [12]. Consistent with these findings, our study demonstrated that DNA profiles could be obtained, and identification was possible from samples exposed to hydrochloric and sulfuric acid for up to 24 h.

Robino et al. conducted DNA typing to identify soft (muscle) and hard (bone and teeth) tissues from pig samples immersed in strong acids (hydrochloric, nitric, and sulfuric acids) or acid mixtures (aqua regia). The samples were subjected to various immersion times, ranging from 2 to 6 h for soft tissues and 2 to 28 days for hard tissues. Soft tissue samples (n = 4 per acid) consisted of pork meat specimens (600–800 g) including skin, muscle, fascia, and connective tissue. For hard tissues, sections of adult pig femurs (n = 4 per acid) were used, obtained by cross sectioning each bone at the mid-diaphysis. DNA recovery results indicated that compact bone tissue samples could be processed for DNA extraction regardless of immersion time or acid type (e.g., after 2, 7, and 28 days for sulfuric acid; 2 and 7 days for nitric acid; and 2 days for hydrochloric acid and aqua regia). DNA yields were generally high, with 30.6 ng/µl recovered from bone samples treated with sulfuric acid, 4.5 ng/µl from samples treated with nitric acid, and 0.9 ng/µl from samples treated with hydrochloric acid. Complete DNA profiles were obtained for all bone samples using DNA extraction by spin-column methods following pulverization, along with a kit containing 12 pig-specific STR panels [13]. In the present study, DNA recovery reached concentrations of up to 16 ng, consistent with the findings of Robino et al. However, in parallel to Robino et al. using porcine femur bone exposed to acids for up to 2 days and obtaining a complete profile at 13 STRs in pigs, this study focused on human teeth exposed to acids for up to 24–120 h. The results showed that successful DNA isolation and full profile recovery can be achieved from teeth exposed to strong acids for up to 24 h. It is important to note that the femur samples used by Robino et al. were immersed in acid in large sections, likely minimizing degradation compared to the single, isolated teeth used in this study.

In a study by Damascena et al., the effects of various chemical agents on dental samples were evaluated in terms of identification and the impact of acids on DNA. The dental samples were exposed to 37% hydrochloric acid, 10% formaldehyde, and 2.5% sodium hypochlorite for 4 days. Complete dissolution of the teeth was observed because of hydrochloric acid exposure. This complete dissolution rendered DNA recovery impossible, indicating that hydrochloric acid effectively dissolved dental tissue and caused DNA degradation. In our study, the maximum exposure time was 24 h, with only two samples exposed to sulfuric acid for up to 120 h. Therefore, complete dissolution was not observed in all samples. However, like the findings of the study, there were two samples that completely turned into liquid after 24 h of exposure to hydrochloric acid and DNA could be recovered from them [14].