A feasibility study for the analysis of reparative dentinogenesis in pOBCol3.6GFPtpz transgenic mice

To examine the feasibility of using the pOBCol3.6GFPtpz [3.6-green fluorescent protein (GFP)] transgenic mice as an in vivo model for studying the biological sequence of events during pulp healing and reparative dentinogenesis.

Pulp exposures were created in the first maxillary molar of 12-16-week-old 3.6-GFP transgenic mice with CD1 and C57/Bl6 genetic background. Direct pulp capping on exposed teeth was performed using mineral trioxide aggregate followed by restoration with a light-cured adhesive system (AS) and composite resin. In control teeth, the AS was placed in direct contact with the pulp. Animals were euthanized at various time points after pulp exposure and capping. The maxillary arch was isolated, fixed and processed for histological and epifluorescence analysis to examine reparative dentinogenesis.

Analysis of teeth immediately after pulp exposure revealed absence of odontoblasts expressing 3.6-GFP at the injury site. Evidence of reparative dentinogenesis was apparent at 4 weeks in 3.6-GFP mice in CD1 background and at 8 weeks in 3.6-GFP mice with C57/Bl6 background. The reparative dentine with both groups contained newly formed atubular-mineralized tissue resembling a dentine bridge and/or osteodentine that was lined by cells expressing 3.6-GFP as well as 3.6-GFP expressing cells embedded within the atubular matrix.

This study was conducted in a few animals and did not allow statistical analysis. The results revealed that the 3.6-GFP transgenic animals provide a unique model for direct analysis of cellular and molecular mechanisms of pulp repair and tertiary dentinogenesis in vivo. The study also shows the effects of the capping material and the genetic background of the mice in the sequence and timing of reparative dentinogenesis.