Realigning the National Board Dental Examination with contemporary dental education and practice

Although the National Board Dental Examination (NBDE) was developed for the purpose of supporting the dental licensure process, it can have significant influence on dental school curricula. Efforts to revise and enhance dental curricula, of necessity, must engage stakeholder communities and promote an assessment process that is both valid and relevant to contemporary dental practice. The NBDE uses a systematic and objective process for test development that involves content experts from dental education and practice. This process could be enhanced by reconsidering the types of individuals who should participate in test construction, reconfiguring the groups involved in the process, augmenting training and development of test constructors, and updating the principles and documents that define the competencies and foundational knowledge required for contemporary dental practice. In addition, there is a need for ongoing research and development to explore new testing strategies that stress understanding and the ability to apply information in a problem-solving context. Finally, examinations could be enhanced with a broader array of high-quality supporting case materials through a more structured collaborative arrangement between dental schools and the National Board testing program.

Comparison of 2 clinical techniques for treatment of gingival recession

BACKGROUND

In early case studies, use of a collagen barrier as a guided tissue regeneration (GTR) material has shown particular promise in procedures aimed at root coverage. The similarities between collagen membrane and subepithelial connective tissue graft (SCTG) have made collagen membrane an attractive and a possible alternative material for root coverage. The purpose of this randomized clinical trial was to compare these 2 techniques, SCTG versus a GTR-based procedure (GTRC), for root coverage/recession treatment.

METHODS

Sixteen patients with bilateral Miller's Class I or II (gingival recession > or = 3.0 mm) recession defects were treated either with SCTG or GTRC using a newly designed collagen membrane. Clinical parameters monitored included recession depth (RD), clinical attachment level (CAL), probing depth (PD), width of keratinized gingiva (KG), attached gingiva (AG), and recession width (RW), each measured at the mid-buccal area to the nearest 0.5 mm. Measurements were taken at baseline and 6 months. A standard mucogingival surgical procedure was performed. Data were reported as means +/- SD and were analyzed using the paired t test for univariate analysis and restricted/residual maximal likelihood (REML)-based mixed effect model for multivariate analysis.

RESULTS

No statistically significant differences were observed in RD, CAL, KG, and AG between test and control groups at either time period. However, SCTG showed significantly more residual PD and more RW gain when compared to GTRC at 6 months. Both treatments resulted in a statistically significant (P < 0.05) reduction of recession defects (2.5 mm and 2.8 mm), gain of CAL (2.8 mm and 2.3 mm), reduction of RW (1.9 mm and 2.7 mm), and increase of KG (0.7 mm and 1.1 mm) and AG (0.7 mm and 0.5 mm) for GTRC and SCTG, respectively, when comparing 6-month data to baseline. Mean root coverage of 73% (collagen membrane) and 84% (subepithelial connective tissue graft) was achieved.

CONCLUSIONS

The 2 techniques are clinically comparable. Use of a modified collagen membrane to attain root coverage may alleviate the need for donor site procurement of connective tissue.

Immortalized cementoblasts and periodontal ligament cells in culture

Cementum, a mineralized tissue lining the surface of the tooth root, is required for formation of a functional periodontal ligament attachment during development. Additionally, during regeneration of tissues after disease, cementum is thought to play a critical role in the reparative process. Research efforts aimed toward understanding mechanisms involved in periodontal development and regeneration, and in particular the formation of root cementum, have been hampered by an inability to isolate and culture cells involved in cementum production, i.e., cementoblasts. Using classical techniques for osteoblast isolation, immortalized, heterogeneous cementoblast/periodontal ligament cell (CM/PDL) populations were established from cells lining the tooth root surface of: 1) CD-1 mice, where cells were immortalized using SV40, or 2) H-2KbtsA58 "immorto" mice, where cells containing an immortalizing transgene were removed and cultured. CM/PDL populations were derived from tissues adherent to developing tooth root surfaces, while tissues adherent to the surrounding alveolar bone were specifically excluded from the population. Immortalized CM/PDL cells were characterized to ensure their phenotype reflected that previously demonstrated in situ and in primary, nonimmortalized cultures. Proteins/mRNAs associated with bone/cementum and known to be expressed by root lining cementoblasts, but not by PDL cells, in situ, e.g., bone sialoprotein, osteopontin, and osteocalcin, were expressed by cells within the immortalized populations. Furthermore, CM/PDL cells, in vitro, attached to bone sialoprotein in an arginine-glycineaspartic acid (RGD)-dependent manner, promoted mineral nodule formation and exhibited a PTH/PTHrP-mediated cAMP response. These immortalized heterogeneous populations, containing both CM and PDL cells, provide a unique opportunity to study cells involved in cementogenesis and to enhance our knowledge of the mechanisms controlling development, maintenance, and regeneration of periodontal tissues.

Evaluation of a bioactive glass alloplast in treating periodontal intrabony defects

This study evaluated the use OF bioactive glass (BG) for repairing/regenerating periodontal intrabony defects. Fourteen systemically healthy patients participated. Each patient had 2 contralateral sites with > or = 6 mm clinical probing depth and radiographic evidence of an intrabony defect. One defect was treated with flap debridement plus BG (test) and the other with flap debridement alone (control). Baseline measurements included gingival index (GI), plaque index (PI), position of the free gingival margin (S/FGM), clinical attachment level (CAL), probing depth (PD), and mobility. At the time of surgery and at surgical reentry (9 to 13 months later), hard tissue measurements included: stent to defect base, bone crest to defect base, and defect width at the bone crest. One-way repeated ANOVA was used to analyze the treatment effect. Friedman's test was used to detect any significant changes of GI, PI and mobility at different time periods (baseline, 3 months, 6 months, and reentry). For multivariate analysis, the random coefficients mixed effect model was applied to adjust the intra-correlation effect. Both treatments resulted in decreased PD and gain of CAL. These changes were only significant (P < 0.05) for the BG treated sites (PD reduction = 1.24+/-0.43 mm, CAL gain = 0.87+/-0.38 mm) from baseline. Defect fill was significant for test (1.1+/-0.4 mm) and control (1.4+/-0.4 mm) alike (P < or = 0.01). Although BG treated sites had more PD reduction and CAL gain than debridement only controls, there were no statistically significant differences between groups for any parameter measured. Further studies are required to clarify the beneficial effects, if any, of BG alloplast in treating periodontal intrabony defects.

Expression of type I and XII collagen during development of the periodontal ligament in the mouse

The purpose (of this study) was to determine the temporal and spatial pattern of type XII collagen expression during murine tooth/root development. Using in situ hybridization techniques, expression of type XII collagen was compared with that of type I collagen, the most abundant collagen in periodontal tissues. Mouse first mandibular molars were examined at the following developmental periods: pre-root formation, early root formation, initial alignment of the periodontal ligament (PDL) fibres, and PDL maturation as the tooth erupted and attained occlusal function. Transcripts for type I collagen were identified in bone cells and odontoblasts at all times but not in the dental follicle before root formation. As root formation progressed, type I collagen expression became apparent within cells of the dental follicle and forming PDL. During early stages of tooth development, signal for type XII collagen was not observed in any cells/tissues. Type XII collagen expression was first detected in the dental follicle/PDL region during tooth eruption and increased in the PDL as the molar tooth erupted into the mouth and achieved occlusal contact. These findings suggest that type XII expression is timed with the alignment and organization of PDL fibres and is limited in tooth development to cells within the periodontal ligament.

Guided tissue regeneration. Absorbable barriers

Over the past 15 years, techniques aimed at regeneration of lost periodontal tissue have become widely used and accepted in clinical practice. Among these techniques are those which use the principles of guided tissue regeneration (GTR), wherein barriers (i.e., membranes) are used to control cell and tissue repopulation of the periodontal wound. A variety of non-absorbable and absorbable barriers have been developed and used for this purpose, with a trend in recent years toward increased use of absorbable GTR materials. This article describes the evolution of absorbable barrier materials and overview materials available for clinical use today. In addition, advantages and disadvantages of these materials are discussed, as well as possible new developments in barrier-based GTR therapy.

The effect of an absorbable collagen membrane on the subgingival microflora

The purpose of this study was to determine the effect of use of an absorbable collagen membrane in guided tissue regeneration (GTR) therapy upon the subgingival microflora. The study group consisted of 12 systemically healthy patients with bilateral mandibular furcation defects with attachment loss > or = 6 mm; one site was randomly assigned for GTR treatment while the contralateral site received surgical flap debridement only. Subgingival plaque samples were collected by paper point on the day of surgery and at 2, 4 and 6 months post-surgery. Three sites were sampled in each patient: a collagen membrane site, a control surgical site, and an unoperated control site. Plaque samples were transported in a non-phosphated buffer solution and examined by phase-contrast microscopy. Cocci, rods, spirochetes, fusiforms, curved rods, and total bacteria were recorded per 10 high-power fields. Following statistical analysis utilizing the Bonferroni (Dunn) t test, no differences in total bacterial counts were found among the sites at any of the time intervals examined. Total bacterial counts were found lower at both the collagen membrane and control surgical sites post-surgery as compared to unoperated control sites, but these differences were not statistically significant (P > .05). In addition, no significant differences were detected in bacterial profiles between sites or individual time points. Results from this 6-month limited clinical trial suggest that the placement of an absorbable collagen membrane as part of a standard surgical regimen for GTR therapy does not alter the local microflora.

A morphometric analysis of the furcation region of mandibular molars

This study examined furcation dimensions and morphology in first and second mandibular molar teeth. One hundred thirty-four extracted human mandibular molars with divergent roots were selected. Teeth were viewed at 7X magnification on a dissecting microscope interfaced with a computer equipped with a state-of-the-art histomorphometry software program. Various aspects of furcation anatomy were measured and recorded. Data were examined by using analysis of variance for all paired comparisons. For nonparametric data, the Kruskal Wallis test was used. Results indicated that 61.94% of buccal and 50.75% of lingual molar surfaces presented with cervical enamel projections (CEPs), with the highest frequency noted in second molars. CEPs ranged from 0.98 mm to 1.33 mm, whereas root trunk heights varied between 2.23 mm and 2.93 mm. Generally, lingual molar surfaces had longer root trunks when compared to buccal surfaces. Root separation increased by approximately 0.5 mm at each 1-mm increment apical to the furcal roof. This study provides new information regarding the furcal anatomy of mandibular molar teeth and supplements previous reports that suggest the CEP is a common problem which must be addressed by clinicians when treating molar teeth.

Isolation of murine cementoblasts: unique cells or uniquely-positioned osteoblasts?

While cementoblasts express a number of mineral-related proteins, including bone sialoprotein (BSP), osteopontin (OPN) and osteocalcin (OC), these proteins do not appear to be expressed by cells of the intermediate dental follicle/periodontal ligament (PDL). This information was utilized in an experimental strategy to isolate presumptive cementoblasts from the root surface of day 24 murine mandibular first molars. Using microscopic dissection techniques, molars were carefully extracted from their alveolar crypts and subjected to trypsin-collagenase digestion to remove adherent cells. Primary cultures were established and assayed for expression of proteins known to be expressed by cementoblasts at this timepoint in vivo (i.e. BSP, OPN, OC) and also an odontoblast-specific protein (i.e. DSP) to rule out contamination by pulpal cells. A subgroup of cells were found to express Type I collagen (89% of cells), BSP (46%), OPN (23%) and OC (30%); DSP was not detected within these cultures. We propose that cells within this heterogeneous population, which express this profile of osteogenic proteins, represent cementoblasts. The availability of a cementoblast cell line will make possible rigorous and controlled in vitro analysis of these cells and allow for determination of the unique characteristics of these cells not shared with other cells, particularly osteoblasts.

Development and clinical evaluation of a root coverage procedure using a collagen barrier membrane

The use of guided tissue regeneration (GTR) procedures in the treatment of gingival recession has shown promising results and is gaining clinical acceptance. The purpose of this study was to assess the use of a bioabsorbable collagen membrane as a barrier device in root coverage treatment of gingival recession defects. The study consisted of 10 patients with 10 defects of either Miller Class I or II description and gingival recession > or =2.5 mm. Clinical measurements taken at baseline included plaque index (PI) and gingival index (GI), clinical attachment level (CAL) measured with an automated probe and reference stent, recession depth (RD; mean = 3.19 +/- 0.26 mm), recession width (RW; 3.95 +/- 0.41 mm), probing depth (PD; 2.3 +/- 0.2 mm), and width of keratinized tissue (KT; 2.4 +/- 0.3 mm); measurements were repeated at 1, 2, and 4 weeks and 3 and 6 months post-treatment. During the surgical procedure, a mucoperiosteal flap was elevated and the respective root thoroughly planed. The collagen membrane was cut to cover the defect and surrounding bone, positioned over the root, and secured with 5-0 gut interdental sutures. The flap was coronally positioned to cover the membrane and sutured with 5-0 silk. Data were analyzed using the Student paired t-test to compare pre- and postsurgery measurements. The nonparametric Wilcoxon matched pairs test was used to analyze the significance of PI and GI at different time intervals. A statistically significant (P < 0.01) reduction in RD (-1.66 +/- 0.25 mm) was observed at 6 months, representing 51.6% total attainable root coverage. Clinically, a statistically significant mean gain of 1.34 +/- 0.47 mm CAL and 0.90 +/- 0.32 mm KT was observed at 6 months. No statistical differences were found in PD and RW between baseline and 6 months postoperatively. PI and GI remained low and showed no statistically significant change (P < 0.05) throughout the study period. Results from this study suggest that a collagen membrane can be used successfully as a barrier device in GTR-based root coverage procedures.

Bacterial adherence to guided tissue regeneration barrier membranes exposed to the oral environment

Microbial colonization of barrier materials used in guided tissue regeneration (GTR) is known to adversely affect treatment outcomes. The purpose of this study was to compare the rate at which 11 commonly-occurring oral bacteria species colonize three different barrier materials (collagen, expanded polytetrafluoroethylene, and polylactic acid). The study group consisted of 10 systemically healthy individuals with no history of periodontal disease and absence of antimicrobial therapy within the previous 3 months. In each patient, 4 teeth per quadrant (P1, P2, M1, M2) were selected and 3 teeth were randomly assigned as test teeth while the remaining tooth acted as a control site (i.e., natural colonization of the tooth surface). These teeth were then randomly assigned to receive one of the three barrier types (i.e., each patient received 4 barriers of each type, 1 per quadrant). A 2 x 5 mm piece of barrier material was positioned over the oral surface of the buccal marginal gingiva and secured with an external sling suture. With oral hygiene procedures suspended, one barrier of each type was collected at 1, 3, 7, and 14 days. Slot immunoblot assay demonstrated that all species types (A. actinomycetemcomitans, A. viscosus, B. melaninogenicus, F. nucleatum, P. gingivalis, P. intermedia, S. mutans, S. sanguis, Selenomonas sputigena, T. denticola, and T. vincentii) were present. Semi-quantitative scoring (scale 0 to 3) of slot blot results and analysis by chi-square ratio and Pearson correlation test indicated that while total bacteria adherence increased over time (P < 0.05), the 3 barrier types and the control sites did not differ in numbers or species of colonizing bacteria detected per time point. These results suggest that under these experimental conditions the barrier materials tested do not differ in bacteria adherence or antimicrobial properties.

Expression of bone associated markers by tooth root lining cells, in situ and in vitro

Periodontal disease is marked by inflammation and subsequent loss and/or damage to tooth-supporting tissues including bone, cementum, and periodontal ligament. A key tissue in the initial process of periodontal development as well as regeneration following periodontal disease is cementum. Research efforts aimed toward understanding mechanisms involved in periodontal development and regeneration, and in particular the formation of root cementum, have been hampered by an inability to isolate and culture cells involved in cementum production (i.e., cementoblasts). Much has been learned regarding the processes and mechanisms involved in bone formation and function from experiments using bone cell cultures. Therefore, the purpose of this study was to develop a strategy whereby cementoblasts could be isolated, cultured, and characterized. As a first step, using in situ hybridization, we determined the timed and spatial expression of mineral-associated proteins during first molar root development in CD-1 mice. These proteins included dentin sialoprotein (DSP), osteopontin (OPN), bone sialoprotein (BSP), osteocalcin (OCN), and type I collagen. During root development in mice BSP, OPN, and OCN mRNAs were expressed selectively by cells lining the tooth root surface--cementoblasts--with high levels of expression at day 41. Importantly, at this time point BSP, OPN, and OCN mRNAs were not expressed throughout the periodontal ligament. These findings provided us with markers selective to root-lining cells, or cementoblasts, in situ, and established the time (day 41) for isolating cells for in vitro studies. To isolate cells from tissues adherent to the root surface, enzymatic digestion was used, similar to what are now considered classical techniques for isolation of osteoblasts. To determine whether cells in vitro contained root-lining cells and cementoblasts, cultured cells were analyzed for expression of mineral-associated proteins. Cells within this heterogeneous primary population expressed type I collagen, BSP, OPN, and OCN as determined by in situ hybridization. In contrast, cells within this population did not express dentin sialoprotein, an odontoblast-specific protein. These procedures have provided a means to obtain root-lining cells in vitro that can now be cloned and used for studies directed at determining the properties of root-lining cells, or cementoblasts, in vitro.

Expression of bone sialoprotein mRNA by cells lining the mouse tooth root during cementogenesis

Adhesion molecules are considered to have an active role in controlling cell differentiation, although the mechanisms involved have yet to be determined. The developing tooth provides an excellent model to use for determining the factors/processes regulating cell differentiation. The studies presented here focused specifically on the timed and spatial expression of a bone-associated adhesion molecule, bone sialoprotein, during tooth root development. Mandibular tissues in the first molar region of CD-1 mice, at sequential stages of development, were analysed by in situ hybridization. The results demonstrate distinct expression of bone sialoprotein in surrounding bone at early stages of tooth development. At stages of active cementogenesis, bone sialoprotein transcripts were specific to cells lining the root surface, with limited expression in the surrounding connective tissue (periodontal ligament) region. The strong expression of bone sialoprotein, a mineral-specific protein having the capacity to act as a nucleator of hydroxyapatite in vitro, by cells lining the root surface at early stages of cementogenesis suggests that this molecule is operative in the cell/matrix events that accompany cementum formation.

Utilization of a resorbable collagen membrane in repairing gingival recession defects

Predictable coverage of exposed root surfaces and the corresponding treatment of gingival recession defects remain important objectives of periodontal therapy. A variety of techniques have been developed during the past several decades to address this common clinical challenge. Traditional surgical approaches have been relatively successful in achieving root coverage. Attempts have been made recently to achieve root coverage with surgical techniques based on the principles of guided tissue regeneration, using resorbable and nonresorbable materials. The learning objective of this article is to present case documentations of root coverage, using a resorbable collagen barrier. The results achieved illustrate the potential of this material in the treatment of gingival recession. The biologic properties of collagen as a barrier material, the surgical approach, and the principles of case selection are reviewed.

Agents with periodontal regenerative potential regulate cell-mediated collagen lattice contraction in vitro

A variety of pharmaceutical agents has been proposed for use in periodontal therapy to inhibit loss of alveolar bone and to promote regeneration of tissues lost to disease. The purpose of this study was to determine the effects of such agents on periodontal cell-mediated gel contraction, an in vitro process considered representative of wound contraction and remodeling in vivo. Human gingival fibroblasts were cultured in a type I collagen lattice, and contraction was quantified by means of a computer-assisted video imaging system. Cell-gel combinations were prepared with cells both pre-exposed and non-exposed to agents; non-anchored cell-gels were then incubated with agents for various time periods. Agents tested included Demecolcine (an inhibitor of cytoskeletal contraction), growth factors (i.e., TGF-beta 1, PDGF, and IGF-1), and non-steroidal anti-inflammatory drugs (NSAIDs) (indomethacin, ibuprofen, naproxen, and flurbiprofen). While Demecolcine inhibited gel contraction, TGF-beta 1 (1-20 ng/mL), PDGF (100 ng/ML), IGF-1 (1000 ng/mL), and [PDGF + IGF], all of which have been reported to enhance wound healing in vivo, promoted lattice contraction in this system. In contrast, NSAIDs inhibited cell-gel contraction. Ethanol, used to solubilize two specific NSAIDs, also inhibited cell proliferation and gel contractile ability, even at very low concentrations. These findings indicate that periodontal cells respond differently to various agents in vitro and may be adversely affected by alcohol. Furthermore, the results of this study suggest that the cell-lattice contraction system holds potential as a method for screening agents for positive or negative effects on cell activity.

Localization and expression of osteopontin in mineralized and nonmineralized tissues of the periodontium

To summarize results from various studies focusing on determining the expression/localization of BSP and OPN during tooth root development, there is general agreement that OPN is expressed/localized to the root surface during cementogenesis and is also seen throughout the PDL region. The expression/localization of OPN to odontoblasts and its role in dentinogenesis is less apparent. Recent studies directed at establishing odontoblast cell lines should help to resolve this conflict. Studies on BSP expression during tooth root formation indicate a very precise expression and localization of this molecule during cementogenesis indicating that this molecule may play an important role in the formation of this mineralized tissue. However, as with OPN, the expression of BSP and its role in dentin formation is not clearly defined.

Models for the study of cementogenesis

Cementum is a mineralized tissue that acts to connect the periodontal ligament to the tooth root surface. Its composition is very much like bone, being comprised mainly of type I collagen, inorganic mineral and noncollagenous proteins, however the origin of the cells and factors necessary for cementum formation have yet to be elucidated. Our laboratory has focused on the role that adhesion molecules, and their cell surface receptors, play in the formation of cementum and tooth root. In order to study this, we used a mouse molar as a model system. This system enabled us to study the formation of four distinct mineralized tissues; bone, cementum, dentin and enamel at various stages of their development. For these studies, we initiated experiments to examine potential cementoblast progenitor cells, in vitro. As a first step, we show that dental papilla and dental follicle cells, n vitro, obtained from molar tissues at day 21 of development, induce mineralized nodules, in vitro. In addition, we obtained tissues from mice where defects in root development may exist and determined bone sialoprotein (BSP) protein expression, a mineralized tissue specific adhesion molecule, in such tissues. As discussed here, we found that osteopetrotic (op/op) mice have delayed and/or defective root development and BSP does not localize in the dental tissues, at day 33 of development. In addition, dentin formation was defective and odontoblasts appeared immature, based on morphological examination. In contrast, the day 33 control molars demonstrated positive staining for BSP localized to root cementum, with normal formation of dentin.

Role of two mineral-associated adhesion molecules, osteopontin and bone sialoprotein, during cementogenesis

Adhesion molecules and their cell membrane receptors are known to play important regulatory roles in cell differentiation. Consequently, the following experiments were conducted to determine the role of two adhesion molecules, bone sialoprotein (BSP) and osteopontin (OPN) in tooth root formation. Developing murine molar tooth germs at sequential stages of development (developmental days 21-42) were analyzed using immunohistochemical and in situ hybridization techniques. While BSP was localized to alveolar bone and odontoblasts early in development, BSP was distinctly localized to the cemental root surface at latter periods coincident with the initiation of root formation and cementogenesis. Conversely, OPN was distributed in a nonspecific fashion throughout the PDL and the eruption pathway of the forming tooth. In situ hybridization confirmed that cells lining the root surface express BSP. The fact that BSP is specifically localized to the cemental surface suggests that this protein is involved in cementoblast differentiation and/or early mineralization of the cementum matrix. Localization of OPN to non-mineralized tissues further suggests that OPN functions as an inhibitor of mineralization during periodontal ligament formation. These findings collectively suggest that BSP and OPN are intimately involved in the sequence of cellular and molecular events accompanying cementogenesis.

Evaluation of an absorbable collagen membrane in treating Class II furcation defects

Recent research has focused upon the utilization of an absorbable collagen membrane in guided tissue regeneration (GTR). Concern exists as to whether this type of membrane is beneficial in the treatment of periodontal defects. The purpose of this study was to evaluate the effect of a type I bovine collagen membrane on treatment of Class II furcation defects. Twelve systemically healthy patients (six male and six female, ages 32 to 68) were treated. Each had bilateral mandibular furcation defects with attachment loss > or = 6 mm. Prior to surgery all patients completed initial therapy including scaling and root planing. At the time of the surgery, teeth were randomly assigned to either a control (flap debridement alone) or test (flap debridement plus collagen membrane) group. Data were collected on the day of surgery, and 2, 4, and 6 months post-surgery and at the 12 month re-entry surgery. Clinical measurements included probing depth (PD), clinical attachment level (CAL), gingival recession (GR), stent to base of defect (SB), crestal bone to base of defect (CB), width of defect, and mobility. Statistical analysis was performed utilizing the paired t test. Both control and test groups demonstrated significant (P < 0.05) improvement at 12 months re-entry in PD, CAL, SB, and CB when compared to the presurgery status. While there is no significant difference in PD, CAL, GR, width of defect, and mobility between control and test groups, sites treated with the collagen membrane had significantly higher bone fill (SB and CB) at re-entry.(ABSTRACT TRUNCATED AT 250 WORDS)

Development of the murine periodontium. II. Role of the epithelial root sheath in formation of the periodontal attachment

Experimental manipulation of the developing murine tooth germ has provided evidence that basement membrane components on the forming root surface are involved in early periodontal attachment formation. The purpose of this investigation was to determine the role of epithelial root sheath (ERS) cells in murine cementogenesis and periodontal ligament formation using tissue separation and recombination techniques. Root dentin specimens, with and without root-associated basement membrane components (D + RBM or D - RBM), were recombined with dental sac in the presence or absence of ERS. Recombinations were cultured for 2 weeks, harvested, and examined by light, electron, and immunofluorescence microscopy. Mineralized tissue formed in all tissue recombinations. However, when ERS was included in recombinations between D + RBM and dental sac, 25% of recombinations formed a periodontal ligament with fibrous attachment of the root specimen to adjacent bone. These results support the hypothesis that root and periodontal ligament formation is influenced by epithelio-mesenchymal interactions and further support a key role for ERS in these processes.

Development of the murine periodontium. I. Role of basement membrane in formation of a mineralized tissue on the developing root dentin surface

The presence of basement membrane components on the forming root surface suggests a role for this structure during cementoblast differentiation. The purpose of this study was to investigate the role of root-associated basement membrane (RBM) in murine cementogenesis using tissue separation and recombination techniques. Root dentin specimens, with or without RBM, were combined with dental sac tissue, cultured for 2 weeks, harvested, and examined by light, immunofluorescence, and electron microscopy. Recombinations in which RBM was preserved on the root dentin surface were characterized by formation of an adherent mineralized tissue resembling acellular cementum; recombinations in which RBM was excluded were characterized by formation of mineralized tissue which did not adhere to the root dentin surface. These results suggest that formation of an adherent mineralized tissue on the developing root dentin surface is dependent upon the presence of indigenous basement membrane components.