First permanent molars with accentuated line patterns: Assessment of childhood health in an urban complex of the fifth millennium before the present

•Peak frequencies of enamel formation disturbances identified through statistics.•Peak frequencies occur in the sample at c. four, nine, eleven, and twelve months.•These peak frequencies may relate to developmental milestones at population level.•Statistical approaches for future comparative studies, including on peak duration. The objectives are 1) to calculate the position of highly accentuated lines in dental enamel of a group of individuals from Shahr-i-Sokhta, a thriving urban centre in Bronze Age South West Asia; 2) to identify peak frequencies of physiologically stressful periods during early childhood of these individuals; and 3) to relate these peak frequencies to developmental milestones at population level. We analysed highly accentuated lines in the enamel of nine (n = 9) permanent mandibular first molars of nine individuals from the 5th millennium before the present urban and long-distance-trading complex, Shahr-i Sokhta (Iran). Age at death ranged between 4.5 years and 18−20 years. Permanent mandibular first molar enamel begins to mineralise before birth, and is normally completed sometime between 2.1–3.3 years, giving us insight to early childhood physiological stress, the ages at which it occurs, and any peaks in the frequencies in highly accentuated line formation, through histological sections investigated using transmitted light microscopy. Highly accentuated line peak frequencies occur in the sample at c. four, nine, eleven, and twelve months. After 1 year of age, no more peaks occur. The peak frequencies coincide with the timing timing of the type of developmental milestones which may have exposed the individuals to an increased pathogen load, injury, or sub-optimal diet. We note similarity in peak timings in the few published, disparate populations, suggest a potential link with attainment of developmental milestones connected with morbidity, and propose reporting standardised statistics to enable exploration of differences between populations in terms of postnatal health-related stress.