Uncovering system-specific stress signatures in primate teeth with multimodal imaging.

Early life stress can disrupt development and negatively impact long-term health trajectories. Reconstructing histories of early life exposure to external stressors is hampered by the absence of retrospective time-specific biomarkers. Defects in tooth enamel have been used to reconstruct stress but the methods used are subjective and do not identify the specific biological systems impacted by external stressors. Here we show that external physical and social stressors impart biochemical signatures in primate teeth that can be retrieved to objectively reconstruct the timing of early life developmental disruptions. Using teeth from captive macaques, we uncovered elemental imprints specific to disruptions of skeletal growth, including major disruptions in body weight trajectory and moderate to severe illnesses. Discrete increases in heat shock protein-70 expression in dentine coincided with elemental signatures, confirming that elemental signals were associated with activation of stress-related pathways. To overcome limitations of conventional light-microscopic analysis, we used high resolution Raman microspectral imaging to identify structural and compositional alterations in enamel and dentine that coincided with elemental signatures and with detailed medical and behavioural data. Integrating these objective biochemical markers with temporal mapping of teeth enables the retrospective study of early life developmental disruptions and their ensuing health sequelae.

Site-specificity of pain sensitivity to intraoral anesthetic injections in children.

A total of 455 children (242 males and 213 females) aged 5-6 years were investigated for their pain reactions to maxillary and mandibular infiltration anesthesia, middle superior alveolar nerve block, posterior superior alveolar nerve block, greater palatine nerve block, nasopalatine nerve block, and inferior alveolar nerve block, and the responses were quantified using the sound, eye and motor (SEM) scale. Administration of nasopalatine nerve block produced maximum pain (median SEM score: 10) while that of posterior superior alveolar nerve block and inferior alveolar nerve block was accompanied by minimum pain (3 and 4, respectively). There was no significant gender-specific difference in pain reactions (P = 0.39). Administration of local anesthesia in the maxilla was more painful than injections into the mandible (7 versus 5, P < 0.05). Furthermore, infiltration into the anterior and posterior segments of the maxilla produced maximum and minimum pain reactions, respectively (8 versus 3, P < 0.001). It seems that the anatomical location of an injection is one of the most important determinants of pediatric pain reaction, and that mandibular injections are generally less painful. Prioritization of treatment by consideration of site-dependent variability in pain sensitivity may help to achieve optimal behavioral control during dental treatment in young children.

Study of root canal accessibility in human primary molars.

The aim of the present study was to provide a general scheme for pulpectomy of primary molars that may be useful for decision-making about negotiation of root canals and selection of appropriate instruments. A total of 160 vital primary molars in 85 patients (40 males, 45 females) aged 4-6 years were selected. After taking primary radiographs, local anesthesia was induced, and the teeth were isolated using a rubber dam. Canal accessibility index (CAI) and tooth accessibility index (TAI) were calculated according to initial file size. Mandibular first molars had either three canals (79.2%) or four canals (20.8%), and all second molars had four canals. Maxillary first molars had three canals and second molars had either three canals (70.9%) or four canals (29.1%). Lower accessibility of the mandibular first molar distobuccal root accounted for the lower accessibility of these teeth in comparison with mandibular second molars. While three-canal maxillary second molars were more accessible due to the lower accessibility of the distobuccal canal of the maxillary first molar, poor accessibility of the distal canal in four-canal second molars was responsible for the difficult accessibility of these teeth. In conclusion, it seems that the accessibility of a single canal in each tooth determines the difficulty of accessibility for any given tooth. Moreover, while primary second molars are more accessible than first molars, all of them are negotiable.