The development of the periodontium--a largely ectomesenchymally derived unit

Response of immortalized murine cementoblasts/periodontal ligament cells to parathyroid hormone and parathyroid hormone-related protein in vitro

Cementum is an essential component of the periodontium, but the mechanisms involved in regulating the activity of this tissue are poorly understood. As one approach to better defining the cellular and molecular properties of cementum and the associated ligament, immortalized murine cell populations expressing gene markers associated with both cementoblasts (CM) and periodontal ligament cells (PDL), termed CM/PDL cells, were established. To further characterize these cells, their responsiveness to parathyroid hormone (PTH) and parathyroid hormone-related protein (PTHrP) was examined. CM/PDL cells were tested for the presence of steady state PTH-1 receptor mRNA using Northern blot analysis. In addition, the ability of PTH and PTHrP to stimulate cAMP production and c-fos mRNA expression in CM/PDL cells was determined, using a cAMP-binding assay and northern blot hybridization, respectively. Rat osteosarcoma cells (ROS 17/2.8) were used as a positive control and human periodontal ligament cells as a negative control. Northern blot analysis demonstrated that cells within the CM/PDL cell population expressed PTH-1 receptor mRNA. Both PTH (1-34) and PTHrP (1-34) increased cAMP and c-fos mRNA in CM/PDL cells. Furthermore, PTHrP treatment for either 24 or 48 h downregulated expression of transcripts for bone sialoprotein, osteocalcin and PTH-1 receptor by CM/PDL cells and abolished CM/PDL cell-mediated mineralization in vitro. These results indicate that cells within the CM/PDL population are targets for PTH and PTHrP action and that PTHrP may play an important part in regulating the biomineralization of cementum.

Epithelial Dlx-2 homeogene expression and cementogenesis

The Dlx-2 (distal-less gene) homeoprotein transcription factor controls early tooth development but has not been studied during the late stages of biomineralization. Transgenic mice containing a Dlx-2/LacZ reporter construct were used to map the Dlx-2 expression pattern in cementoblasts, the dental cells most closely related to bone cells and therefore suggested to be uniquely positioned osteoblasts. During initial root formation, marked expression of Dlx-2 was evident in molar and incisor root epithelium, whereas dental papilla and follicle were negative. Dlx-2 was expressed in this epithelium from the apical loop to the area of its disruption. During acellular cementum formation in both incisors and molars, Dlx-2 expression was observed in the majority of differentiated cementoblasts from the apical region to the erupting zones. During cellular cementum formation, the presence of which characterizes growth-limited molars, Dlx-2 expression was restricted to the innermost cementoblasts and entrapped cementocytes. These data further support the hypothesis of a complex origin and fate of cementum-forming cells, as previously suggested by the expression patterns of a set of mesenchymal and epithelial markers, notably ameloblastin as shown here. Dlx-2 expression might constitute a landmark of cementoblast subpopulations of epithelial origin. (J Histochem Cytochem 48:277-283, 2000)

Dental root resorption

This article presents a review of physiologic mechanisms involved in various types of root resorption that may be encountered clinically. Included is a brief overview of suggested homeostatic mechanisms of the periodontal ligament and the role of the intermediate cementum in inhibiting root resorption. Root resorption (surface, inflammatory, and replacement) associated with traumatic injuries is discussed, with emphasis on etiology and the ability to provide treatment. The final discussion relates to other types of resorption, based on a classification of internal, cervical, and external resorption associated with periradicular pathosis and resulting from pressure in the periodontal ligament.

Response of periradicular tissues to growth factors introduced into the surgical site in the root-end filling material

AIM

The objective of this study was to evaluate the healing of the periradicular tissues when exogenous growth factors were delivered to the respected root-end. The healing response was compared with that when Diaket was used as a control.

METHODOLOGY

Non-surgical root canal treatment was performed on mandibular teeth in mongrel dogs. Surgical treatment followed and included root-end resection and root-end cavity preparation. Insulin-like growth factor in combination with platelet-derived growth factor, or fibroblast growth factor alone, were then placed in the root-end preparations on a polylactic acid carrier (Atrisorb) with or without the incorporation of the carrier tetracalcium phosphate. The healing was evaluated at 60 days with regard to presence of inflammatory response, bone regeneration, periodontal ligament formation and cementum formation.

RESULTS

Osseous regeneration in the excisional would and periodontal formation were significantly greater when Diaket was used as the root-end filling material. Likewise, cementum deposition occurred significantly more frequently in the Diaket group (P < 0.05). The polylactic carrier Atrisorb remained in the surgical sites for the duration of the study.

CONCLUSIONS

The use of specific growth factors, FGF and a combination of IGF/PDGF, delivered to the prepared root end in a collagen carrier did not initiate the desired periradicular tissue response of regeneration. Diaket, as used in this study, did stimulate a periradicular tissue response compatible with regeneration.