Dental enamel is the hardest tissue in the body and cannot be replaced or repaired, because the enamel secreting cells are lost at tooth eruption. X-linked amelogenesis imperfecta (MIM 301200), a phenotypically diverse hereditary disorder affecting enamel development, is caused by deletions or point mutations in the human Xchromosomal amelogenin gene. Although the precise functions of the amelogenin proteins in enamel formation are not well defined, these proteins constitute 90% of the enamel organic matrix. We have disrupted the amelogenin locus to generate amelogenin null mice, which display distinctly abnormal teeth as early as 2 weeks of age with chalky-white discoloration. Microradiography revealed broken tips of incisors and molars and scanning electron microscopy analysis indicated disorganized hypoplastic enamel. The amelogenin null phenotype reveals that the amelogenins are apparently not required for initiation of mineral crystal formation but rather for the organization of crystal pattern and regulation of enamel thickness. These null mice will be useful for understanding the functions of amelogenin proteins during enamel formation and for developing therapeutic approaches for treating this developmental defect that affects the enamel.

Dentin sialophosphoprotein (Dspp) is mainly expressed in teeth by the odontoblasts and preameloblasts. The Dspp mRNA is translated into a single protein, Dspp, and cleaved into two peptides, dentin sialoprotein and dentin phosphoprotein, that are localized within the dentin matrix. Recently, mutations in this gene were identified in human dentinogenesis imperfecta II (Online Mendelian Inheritance in Man (OMIM) accession number 125490) and in dentin dysplasia II (OMIM accession number 125420) syndromes. Herein, we report the generation of Dspp-null mice that develop tooth defects similar to human dentinogenesis imperfecta III with enlarged pulp chambers, increased width of predentin zone, hypomineralization, and pulp exposure. Electron microscopy revealed an irregular mineralization front and a lack of calcospherites coalescence in the dentin. Interestingly, the levels of biglycan and decorin, small leucine-rich proteoglycans, were increased in the widened predentin zone and in void spaces among the calcospherites in the dentin of null teeth. These enhanced levels correlate well with the defective regions in mineralization and further indicate that these molecules may adversely affect the dentin mineralization process by interfering with coalescence of calcospherites. Overall, our results identify a crucial role for Dspp in orchestrating the events essential during dentin mineralization, including potential regulation of proteoglycan levels.

Available evidence suggests that sealants are effective and safe to prevent or arrest the progression of noncavitated carious lesions compared with a control without sealants or fluoride varnishes. Further research is needed to provide information about the relative merits of the different types of sealant materials.

Amelogenins, major components of developing enamel, are predominantly involved in the formation of tooth enamel. Although amelogenins are also implicated in cementogenesis, their precise spatial expression pattern and molecular role are not clearly understood. Here, we report for the first time the expression of two alternate splice forms of amelogenins, M180 and the leucine-rich amelogenin peptide (LRAP), in the periodontal region of mouse tooth roots. Lack of M180 and LRAP mRNA expression correlated with cementum defects observed in the amelogenin-null mice. The cementum defects were characterized by an increased presence of multinucleated cells, osteoclasts, and cementicles. These defects were associated with an increased expression of the receptor activator of the nuclear factor-B ligand (RANKL), a critical regulator of osteoclastogenesis. These findings indicate that the amelogenin splice variants, M180 and LRAP, are critical in preventing abnormal resorption of cementum.Ameloblasts synthesize and secrete amelogenins into the dental enamel matrix that undergo systematic proteolysis during enamel mineralization. Numerous mutations were found in the amelogenin coding sequences in patients with the most common genetic disorder affecting enamel, amelogenesis imperfecta (1-5). The targeted disruption of the amelogenin gene locus in mice also showed a hypoplastic enamel phenotype similar to amelogenesis imperfecta, confirming an important role of amelogenins in enamel formation (6).In addition to their role in enamel formation, amelogenins are also believed to play a key role in the formation of root cementum, a mineralized layer on the surface of root dentin (7,8). During cementogenesis, Hertwig's epithelial root sheath dissociates to form cell aggregates (epithelial rests of Malassez) that are located between the alveolar bone and the tooth root. The mesenchyme-derived cementoblasts secrete cementum matrix onto the root surface to form cementum. The presence of amelogenins was detected on the tooth root surface close to the site of acellular cementum (9) and in the epithelial remnants of the root sheath in rat molars (10), indicating their potential role during cementogenesis. Interestingly, amelogenins were also detected in Hertwig's epithelial root sheath cells and the epithelial rests of Malassez (11-13). Therapeutic application of an enamel matrix derivative (EMDOGAIN®, Biora AB, Malmö, Sweden) rich in amelogenins resulted in regeneration of cementum, the surrounding alveolar bone, and periodontal ligament (PDL) 1 in the experimental treatment of periodontitis (14 -17). However, it is not clear from these studies whether the amelogenin or non-amelogenin components of an enamel matrix derivative regulate regeneration of cementum and periodontal tissues.The present study was undertaken to investigate the expression of various alternate splice forms of amelogenins in tooth roots and correlate their expression with the cementum defects observed in amelogenin-null mice teeth. Herein, we report the expression of ...

These recommendations are designed to inform practitioners during the clinical decision-making process in relation to the prevention of occlusal carious lesions in children and adolescents. Clinicians are encouraged to discuss the information in this guideline with patients or the parents of patients. The authors recommend that clinicians reorient their efforts toward increasing the use of sealants on the occlusal surfaces of primary and permanent molars in children and adolescents.

Cystic fibrosis (CF) is a hereditary condition that affects cAMP-regulated chloride channels in epithelial tissues due to a defect in the cystic fibrosis transmembrane conductance regulator (CFTR) gene. Recently, a transgenic CF mouse model was developed at UNC that exhibits no CFTR expression. Interestingly, the CF mouse demonstrates abnormal incisor enamel. Therefore, the purpose of this investigation was to characterize the enamel in this CF mouse model. Incisors from CF and normal mice were evaluated by light microscopy (LM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The enamel proteins were examined by amino acid analysis, SDS-PAGE, and Western blot. Gross examination showed that 100% of CF mice had soft, chalky white incisor enamel, while the enamel of normal mice was hard and yellow-brown. LM indicated that the ameloblasts in the CF mice underwent premature degeneration shortly after completion of the secretory phase. The CF mouse enamel appeared to be of relatively normal thickness and showed a prism structure similar to that of normal mouse enamel. However, the CF mouse enamel crystallites appeared to have a rough granular surface compared with normal enamel. SDS-PAGE indicated that mature CF enamel retained low-molecular-weight material (approximately 20 kDa), whereas normal mature enamel did not. This low-molecular-weight material cross-reacted with anti-amelogenin antibodies in Western blot analysis. This investigation shows that abnormal CFTR expression in the mouse results in developmental abnormalities in the incisor enamel. Although further investigation is required to determine the mechanism leading to abnormal enamel formation, the CF mouse provides a potentially useful animal model for investigating aberrant enamel development.

Transforming growth factor (TGF)-␤1 is expressed in developing tooth from the initiation stage through adulthood. Odontoblast-specific expression of TGF-␤1 in the tooth continues throughout life; however, the precise biological functions of this growth factor in the odontoblasts are not clearly understood. Herein, we describe the generation of transgenic mice that overexpress active TGF-␤1 predominantly in the odontoblasts. Teeth of these mice show a significant reduction in the tooth mineralization, defective dentin formation, and a relatively high branching of dentinal tubules. Dentin extracellular matrix components such as type I and III collagens are increased and deposited abnormally in the dental pulp, similar to the hereditary human tooth disorders such as dentin dysplasia and dentinogenesis imperfecta. Calcium, one of the crucial inorganic components of mineralization, is also apparently increased in the transgenic mouse teeth. Most importantly, the expression of dentin sialophosphoprotein (dspp), a candidate gene implicated in dentinogenesis imperfecta II (MIM 125420), is significantly down-regulated in the transgenic teeth. Our results provide in vivo evidence suggesting that TGF-␤1 mediated expression of dspp is crucial for dentin mineralization. These findings also provide for the first time a direct experimental evidence indicating that decreased dspp gene expression along with the other cellular changes in odontoblasts may result in human hereditary dental disorders like dentinogenesis imperfecta II (MIM 125420) and dentin dysplasia (MIM 125400 and 125420).Mammalian development is a complex and highly orchestrated process that involves intricate cross-talk between growth factors and other regulatory molecules. These molecules interact with each other to induce specific molecular and cellular changes leading to organogenesis. Interactions between epithelium and mesenchyme are particularly crucial during the initiation of development of key organs such as teeth, skin, hair, mammary gland, and prostate (1). Tooth development is initiated by epithelial-mesenchymal interactions in the first branchial arch, and several transcription factors and growth factors are known to be expressed by dentin extracellular matrix (DECM)-producing 1 odontoblasts and enamel-producing ameloblasts during tooth development (2-5). Transforming growth factor-␤1 (TGF-␤1), a prototype of the TGF-␤ superfamily, is a multi-functional growth factor expressed in a wide variety of developing tissues from the early stages. The regulation of cell proliferation, differentiation, embryonic development, and apoptosis by TGF-␤1 is well established (6 -8). During mouse tooth development, TGF-␤1 is expressed initially in the oral epithelium at embryonic day 13, and later its expression extends into the mesenchymal compartment and then gets restricted to the ectomesenchymal layer (odontoblasts). The odontoblast-restricted expression of TGF-␤1 persists throughout life in the mice (9). Odontoblasts produce DECM from embryonic day 16 and subseq...

Introduction-Although human dental pulp stem cells isolated from healthy teeth have been extensively characterized, it is unknown whether stem cells also exist in clinically compromised teeth with irreversible pulpitis. Here we explored whether cells retrieved from clinically compromised dental pulp have stem cell-like properties.