Neuronal and Bacterial Driven Inflammation of the Dental Pulp in Molar Hypomineralization

Project Summary Molar hypomineralization (MH) is a prevalent enamel defect affecting 15% of children worldwide and is characterized by soft and porous demarcated opacities on the enamel surfaces of primary and permanent dentition. These soft spots on enamel have elevated protein content, hindering restorative success. This

defective enamel's unique structure and composition facilitate the continuous transmission of oral stimuli to the dentin-pulp complex underneath the enamel. Therefore, children with MH suffer greatly from longstanding hypersensitivity associated with an underlying pulpal inflammation called pulpitis. However, the mechanisms of

bacterial-induced pulpitis fail to explain the MH-associated pulpitis, hindering effective diagnosis and treatment. This project aims to dissect the role of sensory neuron-driven and bacterial-driven activation of pulpitis in MH using in vivo and ex vivo approaches by studying the innate immune responses of the dentin-pulp complex.

Finally, we aim to test the effect of enamel remineralization on bacterial colonization and bacterial-driven immune response of the dental pulp organ. We hypothesize that continuous activation of the sensory neurons and bacterial infection contribute to the development of pulpitis in MH in tandem, and treatment of the soft enamel

will reduce the pulpal response. Two specific aims are proposed to test this hypothesis: Aim1) The role of sensory neuron activation in pulpal inflammation will be examined using a hypomineralized KLK4-KO mouse model and WT mice. Sensory afferents will be activated with repetitive noxious stimuli, and the innate immune responses

in dental pulp tissue will be assessed by flow cytometry, cytokine analysis, and immunofluorescence imaging. Aim 2.1) The role of bacterial infection in MH-associated pulpal inflammation will be investigated by quantifying bacterial colonization and activity on enamel surfaces and assessing the therapeutic impact of silver diamine

fluoride. Aim 2.2) The bacteria-induced pulpal immune response will be assessed. Topical SDF application will aim to remineralize the soft enamel, reduce bacterial colonization on the surface, and improve the barrier function of enamel against bacterial infection, ultimately reducing inflammatory responses. This research project will shed

light on the mechanistic components of pulpitis in MH patients and facilitate the researcher's transition towards an independent clinician-scientist career track. During this 5-year K08 Mentored Career Development Award (PA-20-203), Dr. Karaaslan will receive training and test the proposed two aims under a multidisciplinary team

of mentors and experts in hard tissue biology, microbiology, immunology, and pulp biology. Ultimately, the results of this study will guide translational and clinical studies to develop targeted therapeutics to prevent and treat pulpitis in MH patients and the general population.