Suwanchai A, Theerapiboon U, Chattipakorn N, Chattipakorn SC. Na(V) 1.8, but not Na(V) 1.9, is upregulated in the inflamed dental pulp tissue of human primary teeth. International Endodontic Journal, 45, 372-378, 2012. ABSTRACT: Aim  To investigate alterations in Na(V) 1.8 and Na(V) 1.9 expression within inflamed dental pulp tissue of human primary teeth. Methodology  Dental pulp tissue obtained from both normal and inflamed pulps in primary teeth as well as pulps from normal and inflamed permanent teeth was used. The quantity of Na(V) 1.8 and Na(V) 1.9 expression in the dental pulp tissue was investigated using Western blot analysis. General neuron marker (PGP9.5) was used to quantify for neural density, and an increase in metalloproteinase-9 was used to indicate pulpal inflammation in inflamed teeth. Statistically significant differences for each determined parameter between normal and inflamed teeth of both primary and permanent teeth were tested using the Mann-Whitney rank sum test. Results  There was no significant difference in neural density of normal and inflamed dental pulp tissue, although degrees of inflammation were increased in the inflamed dental pulp of both permanent and primary teeth (P < 0.05). Na(V) 1.8 and Na(V) 1.9 expression in inflamed pulps of permanent teeth increased significantly compared with normal permanent teeth (P < 0.05). However, only Na(V) 1.8 expression was increased significantly in the inflamed dental pulp of primary teeth (P < 0.05). Conclusions  Na(V) 1.8 alone may be the therapeutic target for treatment of painful pulpitis in primary teeth.