Purpose: We studied the abrasive effect of a dentifrice that included mastic-essential-oil: MEO paste type and MEO gel type on the dental enamel surface over a long period.
 Methods: The testing surface of each polished specimen of bovine incisor was subjected to the toothbrush abrasion test. The test was performed in an automatic brushing machine in conditions of 10,000 cycles and 150 g as brushing pressure. The mean surface roughness values (Ra) of each specimen were measured using a surface roughness and profile analyzing system. In addition, SEM observation of each specimen surface was carried out.
 Results: The Ra values of both MEO paste and gel type decreased significantly as compared with those of positive control specimens (p<0.01). SEM findings confirmed those phenomena.
 Conclusion: The results of this study suggested the dentifrice that included mastic essential oil might have a slight abrasive affect on the dental enamel surface even though it is used for a long period.

View full abstract

 Purpose: The maxillary lateral incisor is regarded as a type of tooth that is difficult to treat because it has poor diagnosis after root canal filling despite the fact that it is an anterior tooth with a single root canal. Recently, μ-CT has been introduced, by which it is possible to observe a specimen from a three-dimensional viewpoint without destroying it, and it is frequently used for the study of internal structure. In the present study, by using μ-CT, we have carried out observation and analysis on a maxillary lateral incisor that has a complicated root canal morphology and is difficult to heal by treatment.
 Materials and methods: On 50 pieces of human extracted maxillary lateral incisors with no dental caries, tomography was performed continuously by using μ-CT. From the images obtained by a three-dimensional study on the curvature and oblateness of the root canal, observations and studies were carried out on accessory root canals, and morphological abnormalities were examined. Regarding the root canal oblateness, these cases were compared with the results of a study on 50 pieces of human extracted maxillary central incisor with no dental caries.
 Results: Root canal curvature in a distal direction was studied in 46 teeth, and root canal curvature in a lingual direction was seen in 35 teeth, and cases of dual or triple curving have been confirmed. The curvature of the root canal was mostly seen in 1/4 of the apical side. Dens invaginatus was found in 5 teeth, and a radicular groove was observed in 3 teeth. In one of these teeth, the root canal showed a rather complicated shape under the influence of a radicular groove. Oblateness of the root canal at a position of 2 to 6 mm from the apex in the maxillary lateral incisor was more severely compressed than the maxillary central incisor. Apical ramification was found in 26 teeth, a lateral canal was seen in 7 teeth, and the form of apical ramification was diverse.
 Conclusion: The results of the present experiment revealed anatomical complexities and difficulties in the treatment of maxillary lateral incisors. In particular, curvature, bending, and oblateness of the root canal on the apical side and branching of the root canal were the factors that make it difficult to control files, and these results suggest difficulties in the treatment of the maxillary lateral incisor. Maxillary lateral incisor root canals are full of variations. Accordingly, it seems that sufficient anatomical knowledge and experience are required to accomplish endodontic treatment in a more efficient manner.

View full abstract

 Purpose: This study examined how different methods of root canal preparation affected the development of postoperative pain after endodontic treatment.
 Materials and Methods: The study examined 105 patients with chronic apical periodontitis who visited the Kyushu Dental University Hospital; 8 dentists performed either the conventional method (root canal preparation to save the apex) on 53 patients or the intentional preparation method (root canal preparation to enlarge the apex) on 52 patients. We analyzed the difference of rate of postoperative pain episodes between the two methods, and the factors involved in episodes of postoperative pain after root canal treatment.
 Results: The incidence rate of postoperative pain between the two methods showed no difference in 13 patients (25%) in both groups. By age, postoperative pain occurred in 15 patients (42%) under 50 years old, and in 11 (16%) aged 50 years or older. The incidence rate of postoperative pain due to the presence or absence of root canal filling material preoperatively was 20 patients (42%) with material present and 6 patients (11%) without material. Furthermore, a t-test for differences in average treatment times between the two groups showed significantly increased treatment times in the intentional preparation method group compared with the conventional preparation method group. The results of logistic regression analysis of the factors involved in episodes of postoperative pain suggested that less than 50 years and the presence of root canal filling material preoperatively were associated with episodes of postoperative pain.
 Conclusion: In this study, the intentional preparation method group showed significantly increased number of treatments compared with the conventional preparation method group. There was no statistically significant difference associated with the occurrence of postoperative pain and the different preparation methods. However, it is suggested that 1) patients less than 50 years old, and 2) presence of root canal filling material preoperatively, are associated with the occurrence of postoperative pain. Thus, the two results may be used as indexes for predicting postoperative pain preoperatively.

View full abstract

 Purpose: The removal of oral biofilm to prevent dental diseases and systemic conditions has been investigated in recent years. In environments where oral cleaning is difficult, such as during a disaster, biofilm increases susceptibility to pneumonia and infections, requiring a simpler and more effective means of oral care. The present study used polymicrobial biofilms from saliva to investigate the antibacterial effects of surface pre-reacted glass-ionomer (S-PRG) filler eluate on biofilm. The eluate contained fluoride and other ions (BO₃^3-, Na⁺, Sr²⁺, SiO₃^2-, and Al³⁺).
 Methods: S-PRG filler was suspended in distilled water, and the clear supernatant was used as the S-PRG eluate (110.5 ppmF). Buffered McBain 2005 culture medium prepared with this eluate was used for group S. Thereafter, buffered McBain 2005 was used to adjust 2-fold and 10-fold diluted culture containing S-PRG filler eluate (0.5S and 0.1S samples). For group F, NaF solutions with the same concentration of fluorides as that of S-PRG filler eluate, culture medium containing 2-fold and 10-fold diluted NaF (0.5F and 0.1F samples), were similarly created. These six solutions were used as test media. Buffered McBain 2005 medium was used as a standard medium for the control sample (Cont). A polymicrobial biofilm model was cultivated on glass plates in buffered McBain 2005 medium with stimulation saliva of one healthy subject and by continuous anaerobic culture for 24 h at 37°C. The media were refreshed at 10 h. Thereafter, anaerobic culture was performed using the test media from 24 hours until 48 hours following commencement of the experiment, to investigate the impact of S-PRG eluates. These media were refreshed at 34 h. In each sample, pH values were measured after 24, 34, and 48 h. The CFU count of each group was measured after 48 h. The data of pH and CFU were statistically analyzed (One-way ANOVA, Games-Howell test, p<0.05).
 Results: The pH value of S after 34 h was 6.8, and that of 0.5S was 6.4. After 48 h, the pH of S was 6.8, a significantly higher value than those of the other samples. CFU counts (CFU/ml) after 48 h were: S: 1.7×10⁷, 0.5S: 1.2×10⁸, F: 8.6×10⁷, and 0.5F: 2.3×10⁸. These values were significantly lower than that of Cont (5.8×10⁸). Group S showed significantly lower values compared to group F.
 Conclusion: Various kinds of ion contained in the S-PRG eluate affect biofilm, indicating the possibility that they can reduce live bacterial counts.

View full abstract

 Purpose: It has been reported that some epithelial cells of Malassez undergo apoptosis in the periodontal ligament. However, their exact function in cell proliferation and apoptosis in the epithelial cells of Malassez during cementum formation is still unknown. We reported that the epithelial-mesenchymal interactions promote the induction of enamel matrix proteases that facilitates the degradation of enamel matrix proteins. The aim of the present study was to investigate cell proliferation and apoptosis in the epithelial cells of Malassez concerning interactions between the epithelial cells of Malassez and periodontal ligament fibroblasts.
 Methods: Explants of human periodontal ligament tissues produced outgrowths containing both the epithelial cells of Malassez and periodontal ligament fibroblasts after incubation in a modified serum-free medium. Both the epithelial cells and fibroblasts were co-cultured in the same dish. The distribution and expression of the Bcl-2 family proteins, Bax and Bcl-2, were evaluated using immunohistochemistry and RT-PCR analysis. Furthermore, cell proliferation and apoptosis were evaluated by nuclear incorporation of BrdU (5-bromo-2'-deoxy-uridine) and the TUNEL (Terminal deoxynucleotidyl Transferase-mediated dUTP Nick End Labeling) method.
 Results: Immunohistochemical analysis revealed that the epithelial cells of Malassez strongly expressed Bax in co-cultured cells, whereas Bcl-2 was detected weakly both in the epithelial cells of Malassez and fibroblasts of co-cultured cells. RT-PCR analysis confirmed significant mRNA expression of Bax in co-cultured cells compared with control cells. There were more BrdU-positive cells in the epithelial cells of Malassez than in fibroblasts of co-cultured cells. Also, some apoptotic cells were detected by TUNEL staining in the epithelial cells of Malassez.
 Conclusion: These results suggest that the epithelial-mesenchymal interactions enhance cell proliferation and apoptosis in the epithelial cells of the rests of Malassez to maintain the periodontal ligament by performing tissue repair and regeneration.

View full abstract

 Purpose: The cervical region is one of the well-known predilection sites of dental diseases, such as dental caries and abrasion lesions. Recently, flowable resin composites have been widely applied to cervical restoration as an easy-to-handle aesthetic restorative, instead of universal resin composite. The purpose of this study was to examine the difference in adhesion between flowable and universal resin composites applied to cervical restoration under thermo-mechanical cyclic stress condition simulating the intra-oral environment.
 Methods: Prior to this study, suitable experimental conditions, i. e., the number of thermo-mechanical stress cycles and type of resin adhesive system, had been investigated. A standardized V-shaped cavity was prepared in the bucco-cervical region of 30 extracted human mandibular premolars. The cavities were pretreated by an etch-and-rinse adhesive system, Adper Single Bond Plus (3M ESPE), according to the manufacturer's instructions. A flowable resin composite, Filtek Supreme Ultra Flowable Restrative (F; 3M ESPE), or a universal resin composite, Filtek Supreme Ultra Universal Restrative (U; 3M ESPE), was filled into the cavities and then light-cured. Restored specimens were subjected to a combination stress simulating the intra-oral environment: thermal cycling (5°C/55°C×200 sets) and simultaneous repeated load (118 N×10⁴ times). Two slabs 1.0 mm thick were obtained from each specimen, and were trimmed and shaped into a standardized dumbbell-form specimen having a bonded area onto the gingival dentin wall of the restored cavity. Micro-tensile bond strengths (μ-TBS) of the dumbbell-form specimens were measured. The data of μ-TBS (n=30) were examined using the t-test and Weibull analysis.
 Results: Mean μ-TBS in MPa/Weibull modulus value (Wm) of the dumbbell-form specimens were F: 30.1/2.9, U: 24.4/1.2. There was no significant difference between the μ-TBS of F and that of U. However, Wm of F was significantly greater than that of U at p<0.01. The μ-TBS of F (15.4 MPa) at 10% probability of failure was statistically greater than that of U (4.5 MPa) at p<0.01. The μ-TBS of F (45.1 MPa) at 90% probability of failure was statistically similar to that of U (56.3 MPa).
 Conclusion: The adhesion of F applied to cervical restoration was significantly superior in the bonding reliability to that of U-restoration. Especially at the 10% probability of failure, which was considered to be a clinically significant condition, cervical restoration using F might require greater external stress to cause debonding compared with U-restoration.

View full abstract

 Purpose: Plasmin, a serine protease, is involved in degradation of the extracellular matrix either directly, or indirectly through activation of metalloproteases and other zymogens. Plasmin plays an important role in several physiological and pathological phenomena such as fibrinolysis, inflammation, and tissue remodeling. Recently, plasmin has been demonstrated to activate cell signaling, suggesting that it may also participate in the inflammatory response. In this study, we demonstrated that plasmin participates in cyclooxygenase-2 (COX-2) expression and prostaglandin E₂ (PGE₂) secretion in cultured human dental pulp cells through calcineurin activation.
 Methods: Human dental pulp cells were cultured in 10% fetal calf serum (FCS) -supplemented alpha-minimal essential medium (α-MEM). When the cells were confluent, they were incubated in α-MEM containing 1% FCS for 24 h, and then stimulated with 100 nmol/l plasmin. The expression of COX-2 mRNA was determined by reverse transcription-polymerase chain reaction (RT-PCR). COX-2 protein expression and nuclear translocation of NFAT were detected by Western blotting, and the PGE₂ concentration in the culture medium was measured using an enzyme immunoassay kit.
 Results: When the cells were stimulated by plasmin, PGE₂ release was clearly increased in a time-dependent manner. COX-2 mRNA and protein expression, and NFATc1 nuclear translocation were markedly enhanced by plasmin. However, in the presence of the calcineurin antagonist FK506, these effects were suppressed. Stimulation of the cells with the PAR-1 agonist SFLLRN yielded similar results as observed with plasmin treatment.
 Conclusion: Plasmin is involved in COX-2 production and PGE₂ secretion via calcineurin activation, suggesting that it is involved in inflammation in the human dental pulp.

View full abstract

 Purpose: Er:YAG lasers are clinically applied to specific cases in which laser use is preferable. However, the energy irradiated to dentin is converted to heat in the irradiation area, causing a degradation layer to develop on the dentin surface, and this is considered to decrease the bond strength of adhesive restorations. Details of the degradation layer have not been sufficiently clarified, and so the irradiation conditions and a protocol for manual techniques need to be clarified for the clinical application to adhesive restorative treatment. Therefore, in this study, we evaluated the influence of the irradiation conditions of Er:YAG laser on the bond strength of the dentin surface to resin.
 Materials and Methods: Fresh extracted human molars were cut vertically or horizontally to the tooth axis, and adjusted dentin specimens were used. The influence of the irradiation output of the Er:YAG laser and energy density varying with the tip diameter on the evaporation depth, thickness, and hardness of the degradation layer, and temperature at the dentin irradiation surface was evaluated. Furthermore, we applied the composite resin bonding system to the adhesion of resin to the degradation layer formed under each laser irradiation condition, and evaluated the relationship between the thickness of the degradation layer and bond strength. We also performed prior treatment (chemical treatment) of the degradation surface, and evaluated the conditions that resulted in improved adhesion properties.
 Results: The evaporation depth and thickness of the degradation layer significantly increased when the energy density was high and irradiation was performed in the direction of the orifice of the dentinal tubules. When the energy density was high, the temperature of the dentin surface significantly increased, and the indentation hardness of the dentin surface significantly decreased. Furthermore, the bond strength increased when the energy density was low, and the degradation layer was treated with sodium hypochlorite, a reducing agent, and a mild acid.
 Discussion and Conclusion: The irradiation energy density of the Er:YAG laser and course of the dentinal tubules influenced the evaporation depth, thickness, and hardness of the degradation layer. Furthermore, it was suggested that, in cases of adhesive composite resin restoration, the selection of low energy density and chemical treatment of the degradation layer with sodium hypochlorite and a reducing agent can achieve the same bond strength as dentin cut with rotary cutting instruments.

View full abstract

 Purpose: The purpose of this study was to investigate changes in Streptococcus mutans and Streptococcus sobrinus levels in saliva using TaqMan real-time PCR, once when the subjects were aged 12-13 years, and again 3 years later when the subjects were aged 15-16 years, in order to gain insights into caries prevention during adolescence.
 Methods: The subjects were 88 Japanese adolescents (46 boys and 42 girls) in their first year of Tsurumi Junior High School in 2010, and in their first year of high school in 2013. Stimulated saliva was collected, and salivary S. mutans and S. sobrinus levels were obtained by real-time PCR. DMFT scores were also examined.
 Results: Neither S. mutans nor S. sobrinus had formed colonies in 32 students (36.4%) at age 12-13 years, and remained undetected (<10³ cells/ml) in 24 of these students (75%) 3 years later. These results suggested that individuals in whom S. mutans and S. sobrinus have not formed colonies by age 12-13 remained non-carriers (<10³) for 3 years. In 9.1% of students, bacteria were detected in 2013 only, possibly due to horizontal transmission. In 5.7% of students, S. mutans and S. sobrinus were only detected in 2010, suggesting that transient flora had been detected. In 57.9% of students, bacteria were detected at both time points, indicating possible colonization. DMFT scores in S. mutans and S. sobrinus carriers tended to be higher than in non-carriers.
 Conclusion: This study demonstrated the importance of inhibiting S. mutans and S. sobrinus colonization to prevent dental caries. As two or more bacterial tests must be conducted in order to determine S. mutans and S. sobrinus colonization, it is recommended that such bacterial tests be conducted at a dental clinic or during school health check-ups.

View full abstract