The effects of loading locations and direct retainers on the movements of the abutment tooth and denture base of removable partial dentures

The purpose of this study was to evaluate the degree and amount of movement of the abutment tooth and denture base influenced by the direct retainer of distal extension removable partial denture and the location of functional loading, then to suggest direct retainer design with minimal adverse effect and with optimum functional loading location for residual tissue. The displacement of the abutment tooth and inclination of the denture base were determined, with 30 N as work load utilizing simulation model and strain gauge system, about two types of direct retainers with mesial or distal rest and nine loading points on denture base. Displacement and inclination was determined with the one-way analysis of variance and Scheffe's multiple test was performed. The results revealed that type of direct retainer influenced on the magnitude rather than direction of the abutment tooth displacement. The distal displacement of abutment tooth was significantly less in Type M clasp (with mesial rest and connection) than in Type D clasp (with distal rest and connection) (p<0.05). The location of loading points influenced both of the magnitude and direction of the abutment tooth and denture base movement. Posterior and lingual loading resulted in significantly distal displacement of abutment tooth (p < 0.05).     

In vitro evaluation of the antimicrobial activity of a new resin-based endodontic sealer against endodontic pathogens

The purpose of this study was to compare the antimicrobial activities of a new resin-based SuperBond (SB) Sealer and five other sealers/cements against endodontic pathogens. The antimicrobial activities of SB Sealer, Sealapex, AH plus, Roeko Seal Automix, Canals N, and ProRoot mineral trioxide aggregate (MTA) were examined using a double-layered method. The microorganisms Staphylococcus aureus, Enterococcus faecalis, Candida albicans, Streptococcus mutans, and Streptococcus sanguinis were used. Live microorganisms were stained using triphenyltetrazolium chloride, and the zones of inhibition of microorganism growth were measured. The antimicrobial activity of SB Sealer was significantly lower than that of the other sealers, except for Pro Root MTA, against S. aureus, C. albicans, S. mutans, and S. sanguinis, but no activity against E. faecalis was detected. On the other hand, AH plus exhibited the highest antimicrobial activity. Pro Root MTA showed no antimicrobial activity against any of the microorganisms tested. SB Sealer offered no antimicrobial advantage over the other sealers tested except for Pro Root MTA. (J. Oral Sci. 50, 309-313, 2008).     

Influence of mechanical properties of two resin cements on durability of bond strength to dentin after cyclic loading

The purpose of this study was to evaluate how the different mechanical properties of two luting agents (acrylic resin cement and resin composite cement) influenced their bond strength to dentin, after cyclic loading that simulated chewing. Stainless steel rods were bonded to the flattened dentin surfaces with each luting agent. After immersion in water for 24 hours, half the specimens of each group were tested for tensile bond strength and the remaining half were subjected to a vertical load (75.6 N, 1.2 Hz) using an acrylic stylus--which upon contact with the specimen would rotate counterclockwise and then counter-rotate. Bond strength of the resin composite cement with self-etching was found to be significantly lower than the other adhesive systems. After 100,000 cycles, the bond strength of resin composite cement was significantly decreased while acrylic resin cement showed no decrease in bond strength.     

Possible involvement of extracellular signal-regulated kinases 1/2 in mitogenic response of periodontal ligament cells to enamel matrix derivative

The efficacy of enamel matrix derivative (EMD) as an adjunct to periodontal regenerative therapy has been demonstrated in recent clinical studies, however, little is known about its molecular mechanism (s). We examined the mitogenic response of cultured periodontal ligament (PDL) cells to EMD and characterized associated changes in proliferation-related intracellular signaling molecules, including mitogen-activated protein kinases (MAPK) and Akt kinases/protein kinase B (Akt/PKB) kinases. The DNA synthesis of PDL cells increased following treatment with EMD at concentrations higher than 1 microg ml(-1). This mitogenic response to EMD was associated with the selective activation of extracellular signal-regulated kinase (ERK) 1/2. No other MAPKs, or Akt/PKB kinases, responded to EMD stimulation. The EMD induction of DNA synthesis and activation of ERK 1/2 were diminished by pretreatment with suramin, an inhibitor of receptor tyrosine kinases (RTK). The signaling pathway induced by EMD from RTK to ERK 1/2 was similar to that activated by epidermal growth factor (EGF), although the specific binding of 125I-EGF to PDL cells was not affected by pretreatment or concomitant treatment with EMD. These findings suggest that EMD elicits its mitogenic signal through an EMD-specific RTK towards ERK 1/2.     

Impact of <Emphasis Type="Italic">Streptococcus mutans</Emphasis> on the generation of fluorescence from artificially induced enamel and dentin carious lesions in vitro

The purpose of this study was to examine whether Streptococcus mutans is implicated in the generation of fluorescence detected in carious lesions. Enamel surfaces and dentin cavities of extracted human teeth were subjected to artificial caries generation by exposing them either to a culture medium containing S. mutans or to a lactic acid buffer for 2 weeks. Fluorescence from the lesions was detected with confocal laser scanning microscopy or fluorescence microscopy at various excitation wavelengths, and maximum fluorescence radiance was computed using imageanalyzing software. Culture media of S. mutans were also examined for fluorescence generation. The results demonstrated that S. mutans-induced enamel and dentin lesions exhibited increased fluorescence in the red and green spectral regions, with the signal stronger in the red region. In the blue region, however, fluorescence signals in the corresponding area were below the background level. Significantly weaker or virtually no fluorescence was detected in lactic acid-demineralized lesions at all excitation wavelengths. Neither bacterial cells nor culture media generated any fluorescence. These results indicate that, although the presence of S. mutans may be a prerequisite for the emission of fluorescence from carious lesions, some interaction of S. mutans with exposed tooth matrix elements may also be required for the generation or unmasking of fluorophores.     

Calcification of degenerating tissues in the periodontal ligament during tooth movement

OBJECTIVE: Calcification of degenerating tissues in the periodontal ligament (PDL) during tooth movement was investigated longitudinally. MATERIALS AND METHODS: Upper first molars of male Wistar rats were moved lingually for 1, 7 and 21 d, following which unfixed undecalcified sections of the lingual PDL (in the pressure zone) were examined histologically, histochemically (autoradiography and electron probe microanalysis). RESULTS: On d 1 of tooth movement, degenerating tissues, together with some calcified particles, were visible in the pressure zone of the lingual PDL. On d 7, substantial calcified aggregations were seen in the degenerating tissues, predominantly situated between the bone and root. This was confirmed by the 45Ca autoradiography. On d 21 of tooth movement, large calcified aggregations were still clearly evident between the bone and root. CONCLUSIONS: This calcification of the degenerating tissues is a self-defense response of the living body to prevent direct contact between alveolar bone and the tooth root during compression of the PDL, so preventing friction between them and the development of ankylosis.     

Effects of plaque control on the patency of dentinal tubules: an in vivo study in beagle dogs

BACKGROUND: The aim of this in vivo study was to evaluate the effects of plaque control on the patency of dentinal tubules using vital teeth of beagle dogs. METHODS: Class V cavities were prepared on the cervical areas of the mandibular and maxillary molars in each dog with a diamond point. To simulate the state of dentinal hypersensitivity, the teeth were etched with 50% citric acid for 2 minutes to obtain patent dentinal tubules. Plaque control was achieved by brushing the left-side teeth every day, whereas no plaque control was performed for the right-side teeth. A dentin biopsy was performed after 1, 2, and 3 weeks using the cylindrical diamond point to obtain dentin specimens. RESULTS: In the plaque control group, some of the dentinal tubules were occluded with precipitate (Ca/P=1.49), and the diameter of the dentinal tubules decreased from 2.42+/-0.33 microm (mean+/-SD) to 1.11+/-0.51 microm after 7 days, although most of the dentinal tubules remained open. In contrast, no precipitate was observed in the dentinal tubules of the non-plaque control group. Also, the diameter of the dentinal tubules increased from 2.42+/-0.33 to 2.9+/-0.49 microm, due to the demineralization of the peritubular and intertubular dentin. CONCLUSION: Plaque control plays a key role in reducing the patency of dentinal tubules and, therefore, might promote the natural repair of dentinal hypersensitivity.