Association of Cadaveric Factors with the Degree and Region of Discoloration on Pink Teeth: An Approach to Serial Cases

Abstract

The pink teeth phenomenon has been observed in cases of hanging and drowning, but the relationship of this phenomenon with cause of death has not been positively affirmed. To date, teeth with a pinkish tone have been simply regarded as pink teeth. However, we speculated that classification and evaluation of the degree and region of discoloration with reference to how color is classified in prosthodontic dentistry may produce novel findings regarding the pink teeth phenomenon. Therefore, we classified the degree and region of discoloration on teeth into three grades and attempted to evaluate the relationship of grade with various cadaveric factors in 68 cases of pink teeth. The degree and region scores of discoloration did not show significant differences in terms of sex, age, cause of death, and place of discovery, but the degree of discoloration in terms of time after death showed a significant increase at 6 months (p < 0.01) and a significant decrease after 7 months (p < 0.05), while the region score also showed a significant decrease after 7 months. Furthermore, in 18 cases of drowning, the degree of discoloration significantly increased with time after death (p < 0.01). Thus, it was clarified that time after death was most strongly related to the pink teeth phenomenon, suggesting cadaveric decomposition may affect the occurrence of pink teeth. Further investigation in cases of early postmortem changes would be required to determine whether pink teeth in putrefactive cadavers have utility in medico–legal assessments.

1. Introduction

The pink teeth phenomenon was first reported in victims of hanging and drowning by Bell in 1829 [1]. Since then, many other reports have been published [2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22]. Pink teeth have been observed in corpses in various conditions, without limitation to any specific cause of death. It has been suggested that wet or moist environments and a prone position might be factors in the pink teeth phenomenon [3,6,8,10,12,13,14,15,16,18,19,20,21,22], and so far, no evidence has been reported that could support an association between pink teeth and cause of death [5,8,10,11,12,13,14,15,16,18,20,22]. We also previously reviewed 68 cases of pink teeth among 324 dental autopsies of unidentified cadavers and investigated the association between pink teeth and cadaveric information such as sex, age, place of recovery, time after death, and cause of death in all 324 cases [23]. The results showed that pink teeth tended to occur more frequently in the anterior teeth and in relatively young decedents. However, we could not find novel evidence for an association with cause of death, suggesting that the pink teeth phenomenon might be a nonspecific finding.

However, because there are no published criteria for classifying the color of pink teeth, any teeth with a pinkish tone that can be discriminated from teeth with a normal color have been simply regarded as pink teeth. In prosthodontics dentistry, shade guides have been used to determine teeth color, such as VITA-classic, which comprises four-letter groups (A–D), and as a general principle, the coloration of a given tooth differs according to the region, namely the incisal, middle, and cervical regions, which have different color densities and translucencies [24,25,26]. Therefore, visual color matching must consider both shade and region. However, as mentioned above, most previous reports have evaluated the pink teeth phenomenon without considering the degree and region of discoloration. Although it has been reported that discoloration is generally more pronounced around the region of the cementoenamel junction [10,11,14,15,16,21], pink teeth have also been reported in a wide range of crowns. Thus, although both the degree and region of discoloration vary, no previous study has objectively scored discoloration on pink teeth. We speculated that classification and evaluation of the degree and region of discoloration with reference to how color is classified in prosthodontic dentistry may produce novel findings regarding the association of the pink teeth phenomenon with various cadaveric factors such as age, sex, time after death, cause of death, and place of discovery.

In the present study, we created three grade classifications for the degree and region of discoloration, which we call the “Score of Pink Teeth Color” (SPTC) and the “Score of Pink Teeth Region” (SPTR), respectively (Figure 1 and Figure 2). We then used these measures to assign scores for every tooth of 68 pink teeth cases and attempted to determine the association of pink teeth with various cadaveric factors.

2. Materials and Methods

2.1. Subjects

Subjects were 68 cases of pink teeth among 324 unidentified cadavers autopsied during 2015–2021 [26]. Oral photographs obtained at the dental autopsy were used for the present analysis. The photographs were obtained according to the guidelines from the American Board of Forensic Odontology. The sex was male in 46 cases (67.6%), female in 20 cases (29.4%), and unidentified in 2 cases (2.9%). The age range was <20 years in 1 case (1.5%), 20–39 years in 9 cases (13.2%), 40–59 years in 20 cases (29.4%), 60–79 years in 15 cases (22.1%), 80–99 years in 6 cases (8.8%), and unidentified in 17 cases (25.0%).

2.2. Cadaveric Information

The time after death was ≤1 week in 10 cases (14.7%), between 2 weeks and 1 month in 27 cases (39.7%), 2–6 months in 18 cases (26.5%), and 7 months ≤ in 13 cases (19.1%). The cause of death was determined in 31 of the 68 cases, including hanging in 3 cases (9.7%), drowning in 18 cases (58.0%), CO poisoning in 4 cases (12.9%), and other (e.g., barbiturate poisoning, upper gastrointestinal bleeding, natural death, intracranial hemorrhage, and hypothermia) in 6 cases (19.4%). The places where the cadavers were recovered were indoors in 36 cases (52.9%), outdoors in 11 cases (16.2%), and water in 21 cases (30.9%). These data are summarized from the report by Minegishi et al. [26] and are shown in

Table 1. Sixty-eight cases of pink teeth classified according to sex, age, time after death, cause of death, and place of recovery.

Sex	Cases	Age	Cases	Time after Death	Cases	Cause of Death	Cases	Recovery	Cases
Male	46 (67.6%)	<20	1 (1.5%)	≤1 week	10 (14.7%)	Hanging	3 (9.7%)	Indoors	36 (52.9%)
Female	20 (29.4%)	20–39	9 (13.2%)	2 weeks to 1 month	27 (39.7%)	Drowning	18 (58.0%)	Outdoors	11 (16.2%)
Unidentified	2 (2.9%)	40–59	20 (29.4%)	2–6 months	18 (26.5%)	CO poisoning	4 (12.9%)	Water	21 (30.9%)
	68	60–79	15 (22.1%)	≥7 months	13 (19.1%)	Other	6 (19.4%)		68
		80–99	6 (8.8%)		68		31
		Unidentified	17 (25.0%)
			68

Created by the authors based on data from Minegishi et al. [23].

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2.3. Method for Evaluating Pink Teeth

The degree of discoloration of a given tooth was visually classified into 3 grades as follows: faint pink, 1.0; pink, 2.0; and dark pink, 3.0. The numerical value was used as the SPTC (Figure 1). When multiple pink teeth were present in one oral cavity, the average SPTC was used.

The region of the tooth where the discoloration occurred was also visually classified into 3 grades as follows: the root just below the cervical region, 1.0; the cervical half of the crown, 2.0; and the incisal half of the crown, 3.0. The numerical value was used as the SPTR (Figure 2). When multiple pink teeth were present in one oral cavity, the average SPTR was used.

Because the photographs were obtained under different conditions, the scores were assessed visually by the authors without using analytical equipment.

2.4. Association of the Degree and Region of Pink Teeth with Cadaveric Factors

After SPTC and SPTR values were assessed in all 68 cases of pink teeth, the association with sex, age, time after death, cause of death, and place of discovery was analyzed. Statistical analysis was performed using one-way analysis of variance with Tukey–Kramer post-hoc testing. The level of statistical significance was set at 1%.

3. Results

3.1. Association of SPTC with Cadaveric Factors

The associations of SPTC with sex and age were examined. As shown in Figure 3a (51 cases, n = 2–16), the value of SPTC was 2.18 ± 0.59 for males and 2.47 ± 0.42 for females <39 years old; 2.47 ± 0.55 and 2.38 ± 0.75 for those 40–59 years old; 2.23 ± 0.47 and 2.50 ± 0.87 for those 60–79 years old; and 2.38 ± 0.53 and 2.25 ± 0.50 for those 80–99 years. There were no significant differences in sex and age.

The association of SPTC with time after death was examined. As shown in Figure 4a (68 cases, n = 11–36), the value of SPTC was 1.87 ± 0.62 for ≤1 week, 2.30 ± 0.39 between 2 weeks and 1 month, 2.63 ± 0.53 for 2–6 months, and 2.06 ± 0.54 after 7 months. The SPTC for 2–6 months showed a significant increase compared with that for ≤1 week (p < 0.01) and after 7 months showed a significant decrease compared with 2–6 months (p < 0.05).

The association of SPTC with cause of death was examined. As shown in Figure 5a (31 cases, n = 3–18), the value of SPTC was 2.15 ± 0.30 for hanging, 2.21 ± 0.64 for drowning, 2.50 ± 0.58 for CO poisoning, and 2.58 ± 0.49 for other. There were no significant differences in the cause of death.

The association of SPTC with place of recovery was examined. As shown in Figure 6a (68 cases, n = 11–36), the value of SPTC was 2.38 ± 0.53 for indoors, 2.26 ± 0.58 for outdoors, and 2.13 ± 0.61 for water. There were no significant differences in the place of recovery.

3.2. Association of SPTR with Cadaveric Factors

The association of SPTR with sex and age were examined. As shown in Figure 3b (51 cases, n = 2–16), the value of SPTR was 2.17 ± 0.75 for males and 2.25 ± 0.96 for females <39 years old; 1.88 ± 0.81 and 1.75 ± 0.96 for those 40–59 years old; 1.50 ± 0.71 and 2.60 ± 0.89 for those 60–79 years old; and 2.00 ± 1.41 and 1.50 ± 0.58 for those 80–99 years old. There were no significant differences in sex and age.

The association of SPTR with time after death was examined. As shown in Figure 4b (68 cases, n = 11–36), the value of SPTR was 2.33 ± 0.78 for ≤1 week, 1.83 ± 0.76 between 2 weeks and 1 month, 2.00 ± 0.84 for 2–6 months, and 1.36 ± 0.81 after 7 months. The SPTR after 7 months showed a significant decrease compared with ≤1 week (p < 0.05).

The association of SPTR with cause of death was examined. As shown in Figure 5b (31 cases, n = 3–18), the value of SPTR was 1.33 ± 0.58 for hanging, 1.94 ± 0.73 for drowning, 2.20 ± 0.84 for CO poisoning, and 1.80 ± 0.45 for other. There were no significant differences in the cause of death.

The association of SPTR with place of recovery was examined. As shown in Figure 6b (68 cases, n = 11–36), the value of SPTR was 1.92 ± 0.84 for indoors, 1.82 ± 0.98 for outdoors, and 1.90 ± 0.77 for water. There were no significant differences in the place of recovery.

3.3. SPTC and SPTR of Time after Death in 18 Drowning Cases

The associations of SPTC and SPTR with time after death were examined in 18 drowning cases. As shown in Figure 7 (18 cases, n= 2–10), the value of SPTC was 1.55 ± 0.53 for ≤1 week, 2.44 ± 0.37 between 2 weeks and 1 month, and 3.00 ± 0.00 for 2–6 months (Figure 7a). The SPTC between 2 weeks and 1 month and 2–6 months showed a significant increase compared with ≤1 week (p < 0.01). The value of SPTR was 2.33 ± 0.82 for ≤1 week, 1.80 ± 0.63 between 2 weeks and 1 month, and 1.50 ± 0.71 for 2–6 months (Figure 7b). Although there were no significant differences, SPTR tended to decrease with time after death (Figure 7b).

4. Discussion

It was previously speculated that the pink teeth phenomenon might occur due to asphyxia such as in cases of drowning, hanging, and strangulation [5,6,10,12,13,16,22]. It has also been speculated that the discoloration might be caused by hemoglobin, carbon monoxide, or the effect of bacteria that produce red pigment [2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22]. However, the precise mechanism has yet to be established. In particular, the relationship with the cause of death, if any, remains insufficiently explained. In our previous study [26] of 324 unidentified cadavers, we confirmed that pink teeth tended to occur more frequently in the anterior teeth and in relatively young victims, findings that were consistent with other reports [5,10,12,19,20,21]. Thus, our findings did not produce novel evidence for an association with cause of death. In many reports to date, teeth with a pinkish tone that can be discriminated from the color of normal teeth have been simply regarded as pink teeth without consideration for the degree and region of discoloration. Moreover, no studies have objectively scored discoloration on pink teeth. Therefore, we speculated that classification and evaluation of the degree and region of discoloration with reference to color criteria similar to that used in the field of prosthodontic dentistry might produce novel findings for clarifying the pink teeth phenomenon.

We visually scored the degree and region of discoloration by using SPTC and SPTR, respectively, and analyzed the associations of these scores with various cadaveric factors in 68 cases of pink teeth (Table 1). In our sample, pink teeth were present in approximately twice as many male cadavers (67.6%) as female cadavers (29.4%), and were most common in those 40–59 years of age (29.4%). We examined the associations of SPTC and SPTR with sex and with age. As shown in Figure 3, there were no significant differences. In our previous study on 324 unidentified cadavers including 68 cases of pink teeth, we confirmed that pink teeth were more likely to be seen in younger people than in older people, possibly because the dentinal tubules become narrower and the volume of the pulp chamber decreases in secondary dentine with advancing age [10,12,19,20,21], but there was no significant difference in age among the cases with pink teeth. In time after death, the value of SPTC for 2–6 months showed a significant increase compared with ≤1 week (Figure 4a). This result might be due to the decomposition process. The value of SPTC after 7 months showed a significant decrease compared with 2–6 months and that of SPTR after 7 months showed a significant decrease compared with ≤1 week, which might have been affected by fading in the coloration (Figure 4), especially considering that cases after 7 months had begun to skeletonize or mummify. In the cause of death, there were no significant differences between SPTC and SPTR (Figure 6). However, when the time after death was investigated among 18 drowning cases, the value of SPTC ≤1 week showed a significant increase compared with 2 weeks and 1 month and for 2–6 months (Figure 6a), suggesting a strong association with cadaveric decomposition. Although the value of SPTR did not show a significant difference, it seemed to decrease over time (Figure 6b). The discoloration was most pronounced at the root just below the cervical region (Grade 1) with time, as shown in the results of Figure 4 and Figure 6, and also the coloration tended to remain at the cervical region as fading occurred elsewhere. These results would seem to be consistent with the report by Ortmann et al. [11] that “the pink discoloration was most pronounced at the neck of the teeth”. In the place of recovery, neither SPTC nor SPTR showed a significant difference among indoors, outdoors, and water (Figure 7).

In this study, it was confirmed that the time after death was most strongly associated with the pink teeth phenomenon among the various cadaveric factors examined. Furthermore, it was more clearly shown that cadaveric decomposition greatly affected the pink teeth phenomenon, indicating that pink teeth of putrefactive cadavers cannot contribute to medico–legal assessment. Because we investigated cases of pink teeth in unidentified cadavers in this study, all the subjects have since decomposed. Although pink teeth may rarely be seen in cadavers as early postmortem changes, further investigation is warranted to clarify the relationship with the cause of death. As it stands, the pink teeth phenomenon is not a valuable finding in cadavers with late postmortem changes and must not be misinterpreted in medico–legal investigations.

5. Conclusions

We confirmed that time after death was associated with the pink teeth phenomenon by classifying and evaluating the degree and region of discoloration into three grades with reference to a method for classifying color as used in the field of prosthodontic dentistry. However, we recognize that this preliminary study did not include sufficient validation of the method and that sample distributions might be insufficient for statistical analysis. The scores were also assessed visually without using analytical equipment because the autopsy photographs were obtained under various conditions. Therefore, before we perform further investigations of cases involving early postmortem changes, we need to develop a more standardized methodology. In conclusion, it was suggested that cadaveric decomposition might affect the occurrence of pink teeth, indicating that the phenomenon must not be misinterpreted in medico–legal investigations.