Effect of scaling on the invasion of oral microorganisms into dentinal tubules including the response of pulpal cells—an in vitro study

OBJECTIVES: To investigate how scaling affects the penetration of microorganisms into dentinal tubules, how pulpal cells seeded into the pulp cavity respond to bacterial challenge, and how penetration and inflammatory response may depend on the bacterial composition. MATERIALS AND METHODS: Root canals of 102 extracted human teeth underwent shaping and cleaning. Half of the teeth were subjected to scaling and root planing, the other half remained untreated. Teeth were exposed to either Streptococcus gordonii and Actinomyces oris or S. gordonii and Porphyromonas gingivalis for 10 weeks. Bacterial invasion was assessed in a depth of 1 mm to the root surface. Human pulpal cells were seeded into the cavities to assess the expression of interleukin-8 (IL-8), monocyte chemoattractant protein-1 (MCP-1), and matrix metalloproteinase-3 (MMP-3) by real-time polymerase chain reaction and immunoassay. RESULTS: The percentage of teeth with bacteria detected in dentine was higher when teeth received scaling than when they were untreated: 66.6% versus 44.4% when exposed to A. oris/S. gordonii, and 50% versus 25% when exposed to P. gingivalis/S. gordonii (p = 0.043). Scaling had no impact on IL-8 and MMP-3 expression in pulpal cells. P. gingivalis/S. gordonii caused higher levels of IL-8, MCP-1, and MMP-3 than A. oris/S. gordonii (p = 0.003, p = 0.011, p = 0.037). CONCLUSION: Scaling supports the penetration of bacteria into the dentine of extracted human teeth. P. gingivalis may affect the immune response in pulpal cells. CLINICAL RELEVANCE: Root surface debridement with hand instruments may facilitate bacterial penetration. Other kinds of mechanical instrumentation in this experimental setting should be investigated.