Ectopic calcification within joints has been reported in humans and rodents exhibiting mutations in genes that regulate the level of extracellular pyrophosphate, e.g., ank and PC-1; however, periodontal effects of these mutations have not previously been examined. These initial studies using ank and PC-1 mutant mice were done to see if such mineral deposition and resulting ankylosis were occurring in the periodontium as well. Surprisingly, results indicated the absence of ankylosis; however, a marked increase in cementum formation on the root surfaces of fully developed teeth of these mutant mice was noted. Examination of ank mutant mice at earlier ages of tooth root formation indicated that this striking observation is apparent from the onset of cementogenesis. These findings suggest that cells within the periodontal region are highly responsive to changes in phosphate metabolism. This information may prove valuable in attempts to design successful therapies for regenerating periodontal tissues.