The lower right bridge is sectioned between the pontic of 2nd molar and the retainer of the posterior abutment.  The anterior segment of the bridge falls out.  The anterior abutment is nonsalvageable due to severe 2nd caries (Fig.3 (5) part of panaramic X-ray). The yellow lines denote the inferior alveolar nerve.  In brief, the apex of the affected tooth is most likely closely associated with the mental loop. 

Loop

Xin Wei, DDS, PhD, MS 1st edition 09/05/2013, last revision 01/01/2014