In cases of permanent tooth avulsion, it is widely accepted that some necrosis always occurs after avulsion injury. If the pulp tissue does not revascularize or if endodontic therapy is not performed, the pulp space can become infected. Platelet rich fibrin (PRF) is a second generation platelet concentrate that allows the clinician to obtain fibrin membranes enriched with platelets and growth factors from an anticoagulant-free blood harvest. Clinical relevance of PRF and revascularization has been demonstrated in several case studies of avulsion. To date no human clinical trials have been performed evaluating the effectiveness of PRF on pulpal revascularization after reimplantation and its benefits in limiting inflammation. The following study consists of two phases: Phase 1: An in vitro model evaluating the effects of PRF in limiting inflammatory response of pdl cell cultures in the presence of an inflammatory mediators. Phase 2: An in vivo model utilizing mature teeth previously treatment planned for extraction, treating with PRF, reimplanting teeth and following for three to four months before extracting and performing histological analysis. If PRF is capable of promoting revascularization in mature teeth the potential benefits extend to limiting the need for endodontic therapy following mature tooth avulsion, potential for mature tooth transplantation in situations of congenitally missing teeth, and utilization of PRF in endodontic revascularization therapy.

When a tooth is avulsed, it is separated from its socket causing damage to the attachment apparatus. The periodontal ligament (pdl) is a group of specialized connective tissue fibers that attaches the cementum of the root (outer layer) to the alveolar bone. Avulsion can cause damage to the pdl and possible cemental tears. If the periodontal ligament is left attached to the root and minimal time lapse occurs damage to the tissues is usually limited. In these cases, reimplantation is a widely accepted treatment; however the long term success of an avulsed tooth is dependent on various factors. When excessive drying occurs prior to re-implantation, a severe inflammatory response is elicited directly on the root surface which may result in osseous replacement or replacement resorption. Some necrosis always occurs after avulsion injury, and while the necrotic pulp is of little consequence, this necrotic tissue is at high risk for bacterial contamination. If the pulp tissue does not revascularize or if endodontic therapy is not performed, the pulp space can become infected. It has been suggested that treatment strategies should attempt to limit peri-radicular inflammation therefore promoting favorable cemental healing and limiting unfavorable osseous replacement.

Platelet rich fibrin (PRF) is a second generation platelet concentrate that allows the clinician to obtain fibrin membranes enriched with platelets and growth factors from an anticoagulant-free blood harvest and without the addition of artificial biochemical modification. PRF has demonstrated clinical relevance through its ability to stimulate cell proliferation of osteoblasts, gingival fibroblasts, and periodontal ligament (PDL) cells. In addition, PRF has been shown to limit epithelial cell growth therefore promoting connective tissue and alveolar bone regeneration and inhibiting epithelial proliferation. These properties make it a favorable product for surgical procedures requiring micro vascularization.

In vitro studies with PRF and canine dental pulp cells demonstrate PRF's ability to promote chemotaxis and proliferation of the pulp cells and contributed to pulp repair. When PRF was combined with human dental pulp cells derived from extracted third molars it did not interfere with vitality and stimulated proliferation and differentiation. Additionally it upregulated the expression of osteoprotegerin and alkaline phosphatase.

Animal models evaluated PRF granules combined with human pdl stem cells and placed them on the root surface of freshly extracted canine teeth. The teeth were then reimplanted and evaluated histologically after a healing phase. A regeneration of the PDL-like tissue and reduction in ankylosis and inflammation were noted in animals with the PRF granules.

Clinical relevance of PRF and revascularization has been demonstrated in several case studies of avulsion. These case studies utilized a general protocol of minimally instrumenting the avulsed tooth. One study performed a 3 mm resection of the root apex followed by minimal instrumentation of the canal. Blood is then drawn from the patient and PRF is prepared via Choukroun's method. The PRF is then placed on the root surface and condensed into the canal. The tooth was then reimplanted, splinted, and the patient followed for up to 24 months. The tooth tested vital to thermal and percussion testing and radiographically did not show signs of replacement resorption or inflammation.

To date no human studies have been performed evaluating the effectiveness of PRF on pulpal revascularization after reimplantation and its benefits in limiting inflammation. Additionally, only histological evidence of the benefits of PRF has been demonstrated in animal models. If PRF is capable of promoting revascularization in mature teeth the potential benefits extend to limiting the need for endodontic therapy following mature tooth avulsion, potential for mature tooth transplantation in situations of congenitally missing teeth, and utilization of PRF in endodontic revascularization therapy.

The following research would consist of two phases: Phase 1. An in vitro model evaluating the effects of PRF in limiting inflammatory response of pulp and pdl cell cultures in the presence of an inflammatory mediators. Phase 2. An in vivo model utilizing mature teeth previously treatment planned for extraction, treating in accordance to the procedure documented by one group, reimplanting teeth and following for three to four months before extracting and performing histological analysis.

Inclusion Criteria:

• any adult with single rooted vital teeth previously treatment planned for extraction to meet their prosthetic or orthodontic needs.

Exclusion Criteria:

• exclusion criteria will include: individuals with systemic illnesses that could compromise vascularity or healing,
• patients who are pregnant,
• or bisphosphonates.

Half of the subjects teeth will have PRF endodontic revascularization therapy and the other teeth will be reimplanted alone.

Initiation of study to termination of study (11 months total)

Limitations of study include bias in patient reporting of sensation for vitality testing, lack of control of possible contributing factors including bruxism, and finally differing values for time out of mouth for control vs experimental groups.

Participant and Operating Surgeon were masked to tooth designation. Principal investigator/outcomes assessor aware of designation.