New regression formula to estimate the prenatal crown formation time of human deciduous central incisors derived from a Roman Imperial sample (Velia, Salerno, Italy, I-II cent. CE)

Abstract

The characterization and quantification of human dental enamel microstructure, in both permanent and deciduous teeth, allows us to document crucial growth parameters and to identify stressful events, thus contributing to the reconstruction of the past life history of an individual. Most studies to date have focused on the more accessible post-natal portion of the deciduous dental enamel, even though the analysis of prenatal enamel is pivotal in understanding fetal growth, and reveals information about the mother's health status during pregnancy. This contribution reports new data describing the prenatal enamel development of 18 central deciduous incisors from the Imperial Roman necropolis of Velia (I-II century CE, Salerno, Italy). Histomorphometrical analysis was performed to collect data on prenatal crown formation times, daily secretion rates and enamel extension rates. Results for the Velia sample allowed us to derive a new regression formula, using a robust statistical approach, that describes the average rates of deciduous enamel formation. This can now be used as a reference for pre-industrial populations. The same regression formula, even when daily incremental markings are difficult to visualize, may provide a clue to predicting the proportion of infants born full term and pre-term in an archaeological series.

Fig 1. Regression of the Velia cross-striations count against the prism length.

The Birch and Dean [27] regression for the central deciduous incisors is also shown.

Fig 2. Boxplot of the DSR variation along the EDJ in the Velia sample.

The boxplot shows the median, the range (lower and upper whisker), the first quartile (lower hinge) and the third quartile (upper hinge).

Fig 3. Variation of the EER along the EDJ in the Velia series.

(A) Scatterplot of the pCFT against EER. (B) Boxplot of the EER variation along the EDJ. The boxplot shows the median, the range (lower and upper whisker), the first quartile (lower hinge), and the third quartile (upper hinge).

Fig 4. Scatterplot and regression line of the EDJ lengths against the pCFT in the Velia series.

The 95% interval of the prediction (dotted lines) is shown together with the 95% confidence interval of the regression (dashed lines).

Fig 5. Individual pCFT variation with reference to the EDJ length in the Velia series.

Each profile was calculated with a locally weighted polynomial regression fit [65]. See methods section for details.

Fig 6. Map of the DSR values across the prenatal portion of the crown of the T.237 individual.

(A) Histological section of the buccal aspect of the T.237 central incisor. (B) Topographic distribution of the DSR values on the prenatal portion of the buccal aspect of the same tooth.

Fig 7. Histogram of the pCFT values in the Velia series.

Fig 8. Scatterplot comparing the individual pCFT from direct counts and from the new regression formula.

The thresholds at 120 days are marked as green lines. Gray dots represent the individuals in which the diagnosis is discordant.

Fig 9. Boxplot of the DSR variability in the Velia series compared with the Birch and Dean [27] figures.

The boxplot shows the median, the range (lower and upper whisker), the first quartile (lower hinge), and the third quartile (upper hinge). A single observation, exceeding the lower interquartile range times 1.5, is marked as an outlier.