Joo Cheol Park

FAM83H Mutations in Families with Autosomal-Dominant Hypocalcified Amelogenesis Imperfecta

Amelogenesis imperfecta (AI) is a collection of diverse inherited disorders featuring dental-enamel defects in the absence of significant nondental symptoms. AI phenotypes vary and are categorized as hypoplastic, hypocalcified, and hypomaturation types. Phenotypic specificity to enamel has focused research on genes encoding enamel-matrix proteins. We studied two families with autosomal-dominant hypocalcified AI and have identified nonsense mutations (R325X and Q398X) in the FAM83H gene on chromosome 8q24.3. The mutations perfectly cosegregate with the disease phenotype and demonstrate that FAM83H is required for proper dental-enamel calcification.

Guided Tissue Regeneration of the Mixture of Human Tooth-Ash and Plaster of Paris in Dogs

This study evaluated the efficacy of periodontal tissue regeneration using guided tissue regeneration (GTR) with a mixture of tooth ash and plaster as a bone substitute material in the treatment of class II furcation defects in dogs. GTR was performed at the site of a surgically formed mandibular premolar bifurcation area in dogs. Four adult dogs were used in the animal study. The animals were in a good periodontal state without any systemic disease. A resorbable membrane (Bio-Gide®, Swiss) and bone graft material using a mixture of tooth ash and plaster were used to examine the biological activity. The defect in the control group was filled a Bio-Gide® only. For the experimental group, the defects were filled with a mixture of tooth ash and plaster and covered by a Bio-Gide®. Oral rinsing with 0.12% chlorhexidine was performed twice a day for 2 weeks. In control group, new bone formation was observed adjacent to the preexisting bone. Soft tissue ingrowth was also noted. In experimental group, new lamellar type trabecular bone formation as well as centum and PDL regeneration was observed in the base of the infrabony pocket. More bone regeneration would be expected when GTR is performed using a mixture of human tooth-ash and plaster of Paris as a bone graft material.

Regulation of root patterns in mammalian teeth

Mammalian teeth have diverse pattern of the crown and root. The patterning mechanism of the root position and number is relatively unknown compared to that of the crown. The root number does not always match to the cusp number, which has prevented the complete understanding of root patterning. In the present study, to elucidate the mechanism of root pattern formation, we examined (1) the pattern of cervical tongues, which are tongue-like epithelial processes extending from cervical loops, (2) factors influencing the cervical tongue pattern and (3) the relationship among patterns of cusp, cervical tongue and root in multi-rooted teeth. We found a simple mechanism of cervical tongue formation in which the lateral growth of dental mesenchyme in the cuspal region pushes the cervical loop outward, and the cervical tongue appears in the intercuspal region subsequently. In contrast, when lateral growth was physically inhibited, cervical tongue formation was suppressed. Furthermore, by building simple formulas to predict the maximum number of cervical tongues and roots based on the cusp pattern, we demonstrated a positive relationship among cusp, cervical tongue and root numbers. These results suggest that the cusp pattern and the lateral growth of cusps are important in the regulation of the root pattern.

Bone Formation Effect of HA/β-TCP Composite Powders in Rabbit Calvarial Bone Defects: Histologic Study

This study evaluated the histology results of surgically created bone cavities in the calvaria of rabbits that were subsequently filled with a HA/ß-TCP composite powder developed in Korea (Dentium, Korea). Ten young adult rabbits were used. Four defects were surgically produced in the calvaria of each rabbit. These defects were classified into 4 groups: the control group, no graft materials; experimental group I, normal saline + graft materials; experimental group II, venous blood + graft materials; and experimental group III, graft materials only. The defects were randomly filled with the graft materials. The rabbits were sacrificed with at 1-, 2-, 4-, 6- and 8- weeks after surgery. The histology specimens were prepared using the general method with H & E staining at a 6 ㎛ thickness. Histologically, the degree of new bone formation was similar in all experimental groups. However, for experimental group II, many cells had gathered around the graft materials 1-week after surgery, and new bone formed slightly faster and than in the other groups. No bone formation was observed in the control group. Based on histology findings, the new HA/ß- TCP composite powders appeared to act as a scaffolding material for the regeneration of osseous defects.

Expression and function of OD314, Apin protein during ameloblast differentiation and amelogenesis

1 , Joo-Cheol Park This study was aimed to elucidate the biological function of OD314 (Apin protein), which is related to ameloblast differentiation and amelogenesis. Apin protein, calcifying epithelial odontogenic (pindborg) tumors (CEOTs)-associated amyloid, were isolated from CEOTs, and has similar nucleotide sequences to OD314. We examined expression of the OD314 mRNA using in-situ hybridization during tooth develop- ment in mice. Expression of OD314 and several enamel matrix proteins were examined in the cultured ameloblast cell line up to 28 days by reverse transcription-polymerase chain reaction (RT-PCR) amplifica- tion. After inactivation and over-expression of the OD314 gene in ameloblast cell lines using U6 vector- driven RNA interference and CMV-OD314 construct, RT-PCR were performed to evaluate the effect of the OD314 during amelogenesis. The results were as follows: 1. In in-situ hybridization, OD314 mRNAs were more strongly expressed in ameloblast than odontoblast. 2. When ameloblast cells were cultured in the differentiation and mineralization medium for 28 days, the tuftelin mRNA expression was maintained from the beginning to day 14, and then gradually decreased to day 28. The expressions of amelogenin and enamelin were gradually decreased according to the ameloblast differentiation. 3. Inactivation of OD314 by U6-OD314 siRNA construct down-regulated the expression of OD314, MMP- 20, and tuftelin, whereas over-expression of OD314 by CMV-OD314 construct up-regulated the expression of OD314 and MMP-20 without change in tuftelin. These results suggest that OD314 is considered as an ameloblast-enriched gene and may play the impor- tant roles in ameloblast differentiation and mineralization. ABSTRACT