This article briefly reviews the history of the concept of critical pH for enamel demineralization, and its theoretical background with some comments on enamel acid erosion. It is known that the critical pH is dependent on not only the acidic pH but also calcium and phosphate ion concentrations in the acidic medium. Moreover, the critical pH is influenced by the solubility of enamel; i. e., the thermodynamic solubility product. This study estimated the critical pH values at different Ca²⁺ and phosphate concentrations using calculation formulas for degree of saturation (DS) of acidic mediums regarding enamel and pure hydroxyapatite minerals, where mathematical algorithms were employed including dissociation constants of relevant chemical reactions, electrical neutrality, mass balance of the ions such as calcium and phosphate, and so on. Representative calculations based on calcium and phosphate concentrations measured in plaque fluid found the critical pH value to be around 5.15. Similarly this calculation found quite a wide range of critical pH value for different enamel solubility products, with 5.02 for the least soluble and 5.81 for the most soluble enamel minerals, respectively. The calculated critical pH values are discussed in relation to the actual demineralizing plaque in vivo, where ionizable calcium and phosphate substances are present in plaque. These substances will be ionized when acid is produced and increase Ca²⁺ and phosphate ion concentrations, resulting in lower critical pH than the theoretically calculated pH. Moreover, the actual rate of enamel dissolution in vivo at the critical pH would be substantially very low due to the inherent nature of the solubility product of apatite.

View full abstract

 Purpose: Enamel matrix derivative (EMD) has been applied clinically as well as for periodontal regeneration therapy and root coverage therapy. However, there have been few reports on new attachment formation after root coverage therapy with EMD. This study examined the formation of new attachment at the ultrastructural level following application of EMD.
 Methods: Buccal dehiscense defects were surgically created on both sides of the maxilla in the first and second premolars of two monkeys. EMD was applied on the denuded root surface of the left side but not on the right, and the monkeys were sacrificed at 8 weeks. The biopsies, including teeth, gingiva and bone, were comparatively examined with light and transmission electron microscopes.
 Results: Numerous active cells had accumulated adjacent to the dentin surface treated with EMD, and a large amount of collagen fibrils had formed between the dentin surface treated with EMD and neighboring cells. Artifacts were observed along the dense granular layer (dgl) between the root surface and new cementum in the control group, but were not seen in the experimental group.
 Conclusion: It is suggested that EMD has the potential to promote new attachment formation, and so could be effective for root coverage therapy.

View full abstract

 Purpose: Enamel matrix derivative (EMD) extracted from the tooth germ of young pigs has been clinically used as a convenient material for periodontal tissue regeneration. However, EMD might be rejected by patients, because it is animal-derived material and may carry unknown pathogenic organisms. Development of a new synthetic oligopeptide with the same function as EMD is desirable. The present study examined the differences between enamel matrix derivative and a new synthetic oligopeptide on the effects of human periodontal ligament cells that play an important role in periodontal tissue.
 Methods: Human periodontal ligament cells were obtained from healthy adult human mandibular third molars. The effects of the new synthetic oligopeptide on the human periodontal ligament cells were examined by hard tissue differentiation and screening of the gene expression for TGF-beta. In each group incubated for 2 or 3 weeks, the gene expression of human periodontal ligament cells and the production of osetocalcin in culture supernatants stimulated with 10 μg/ml of EMD or 100 ng/ml of the oligopeptide were measured.
 Results: Significant differences were found by real-time PCR array after 3 weeks of incubation, and platelet-derived growth factor beta polypeptide increased. The production of osteocalcin did not show any significant difference between the EMD stimulated group and the oligopeptide stimulated group after 2 weeks, but production in the EMD stimulated group was significantly higher than in the oligopeptide stimulated group after 3 weeks.
 Conclusion: These results suggest that the oligopeptide produced from EMD's previous study promoted hard tissue differentiation at the same level as EMD in the process of periodontal tissue regeneration.

View full abstract

 Purpose: The purpose of this study was to evaluate the effect of dentin conditioning by various ethylenediaminetetraacetic acid (EDTA) conditioners of various pHs on dentin surfaces.
 Methods: EDTA conditioners at 0.5 mol/l with pH 8.0, pH 10.0, and pH 12.0 were used to remove the dentin smear layer on the surface of extracted human molar dentin. E-Lize Conditioner with pH 7.4 was used as a control. The change in the micro Vickers hardness of the dentin caused by conditioning was measured with a universal testing machine. The wall-to-wall polymerization contraction gap of the resin composite was examined with a light microscope. After conditioning, the dentin surface was observed with a scanning electron microscope (SEM, ×5,000).
 Results: No significant differences were observed in the micro Vickers hardness of the dentin between the conditioners at all pHs. In the contraction gap measurements, complete marginal adaptation was observed for the pH 7.4 and 8.0 EDTA conditioners. The SEM observations showed that the removal of the dental smear layer was caused by the change in pH; thus, more of the surface of the dentin smear layer remained as the EDTA pH increased.
 Conclusion: The optimum pH for 0.5 mol/l EDTA conditioner is pH 7.4-8.0, which results in complete marginal adaptation.

View full abstract

 Purpose: To observe the tooth structure after bleaching by using experimental swept-source optical coherence tomography (SS-OCT, Yoshida Dental).
 Methods: This study was approved by the Showa University Institutional Review Board (Approval number 2011-035). Fourteen extracted intact human incisors were used. Commercial in-office bleaching gel containing 35% hydrogen peroxide (Shofu Hi-Lite, Shofu) was applied to the labial enamel surface according to the manufacturer's instructions. The bleaching gel was applied to the surface for 3 min once a week for 4 weeks, and the 4-week bleaching regimen was repeated three times. Before and after bleaching, the tooth structure was observed by SS-OCT, which constructs images by ultrahigh-speed scanning of the converted wavelength of a near-infrared laser and allows rapid noninvasive construction of tomographic images of teeth.
 Results: In the SS-OCT images, light reflection from the enamel surface became strong after bleaching. The light reflection intensity deep in the tooth tended to be lower than that at the enamel surface. The light reflection intensity in the SS-OCT images of the control before and after storage in water at 37℃ either decreased or remained the same. The tooth appeared whiter after bleaching to the naked eye. The value of luminosity (L^*) increased, and the values of color parameters (a^* and b^*) decreased. Significant differences in the color difference (ΔE^*ab) before and after bleaching were found by Student's t-test (p＜0.05).
 Conclusion: The light reflection intensity in the SS-OCT images increased for the enamel surface bleached with 35% hydrogen peroxide, indicating that small structural changes may occur that are not visible by SEM. SS-OCT can be used to provide patients with information in a clinical setting and may be a promising new tool for tooth bleaching.

View full abstract

 Purpose: Gram-negative bacteria is a periodontal pathogen. Although the proportion of gram-negative bacteria increases markedly in gingival microflora with increasing severity of periodontitis, gram-positive bacteria is dominant in healthy gingival sulcus. Therefore, it is important to investigate the influence of gram-positive bacteria on the onset of periodontitis. In our previous study, we used heat-treated and sonicated Staphylococcus aureus as gram-positive bacteria, or Aggregatibacter actinomycetemcomitans as gram-negative bacteria, and both bacteria induced strong periodontal destruction in rats, so it was not clear which bacteria has a stronger influence in periodontal destruction. In the present study, we used a lower concentration of bacterial suspension than in the previous study, and histopathologically examined the influences of both bacteria homogenates on periodontal tissue.
 Methods: Rats previously immunized with heat-treated and sonicated S. aureus or A. actinomycetemcomitans were used as immunized groups. The non-immunized groups intraperitoneally received only sterile phosphate-buffered saline. In each animal, 12.5 μg/μl S. aureus or A. actinomycetemcomitans suspension was applied topically to the palatal gingival sulcus of first molars every 24 hours for 10 days. The first molar regions were resected and observed histopathologically. The control group did not receive the topical application.
 Results: The loss of attachment and decreases in alveolar bone level in the A. actinomycetemcomitans immunized group were significantly greater than in the control group. However, a statistically significant difference was not observed in the S. aureus immunized group or the A. actinomycetemcomitans non-immunized group. C1qB, which indicates the existence of immune complexes, was observed in the junctional epithelium in the A. actinomycetemcomitans immunized groups.
 Conclusion: Our results suggest that A. actinomycetemcomitans as gram-negative bacteria has a stronger influence on periodontal destruction than S. aureus as gram-positive bacteria. The presence of C1qB suggests that the formation of immune complexes is involved in periodontal destruction.

View full abstract

 Purpose: Recently, bulk-fill resin composites, which enable increments up to 4 mm thick to be cured in one step, have been developed. This study was conducted to evaluate the mechanical properties of bulk-fill resin composites.
 Methods: Five resin composites were used in this study (Bulk-fill: Tetric N-Ceram Bulk Fill (Ivoclar Vivadent) and SDR (Dentsply DeTrey); Universal: Tetric N-Ceram (Ivoclar Vivadent) and Esthet・X HD (Dentsply DeTrey); Flowable: Tetric N-Flow (Ivoclar Vivadent) ). Depth of cure, inorganic filler content, flexural properties and polymerization shrinkage were measured. SEM observation of the cured resin composites was also conducted.
 Results: The depth of cure of the bulk-fill resin composites ranged from 3.42 to 4.27 mm, which is significantly greater than that of conventional resin composites. The inorganic filler contents of the employed resin composites ranged from 60.3 to 77.5 wt% and those of the universal resin composites were significantly higher than those of the flowable resin composites. The flexural strength and elastic modulus of bulk-fill resin composites ranged from 123.3 to 127.5 MPa and from 7.0 to 8.0 GPa, respectively. The polymerization shrinkage of bulk-fill resin composites after 180 sec of irradiation ranged from 2.12 to 2.23 vol%; these values are the same or lower than those of conventional resin composites.
 Conclusions: Based on the results of this study, the depth of cure of bulk-fill resin composites was higher than that of conventional resin composites. In addition, the mechanical properties of bulk-fill resin composites were similar to or better than those of conventional resin composites. Therefore, bulk-fill resin composites have good potential for the development of resin composites.

View full abstract

 Purpose: We have established a potential cell therapy for pulp regeneration in a canine pulpitis model harnessing autologous dental pulp stem cells (DPSCs). Complete disinfection is essential for complete pulp regeneration in periapical disease. Our previous study suggested that medicaments could be delivered deeply into the dental tubules using nanobubbles together with ultrasound leading to rapid disinfection of the intracanal space. Thus, this study was performed in a canine periapical disease model to examine complete disinfection of the root canal system and complete pulp regeneration by the same cell therapy as in a pulpitis model.
 Methods: The most suitable conditions for ultrasound and nanobubbles of less than 1 μm in diameter were examined to deliver medicaments deeper into the dentinal tubules of root canals. The canine root canal was kept open for 14 days to construct a periapical disease model. Vibramycin was applied in the root canal with or without ultrasound and nanobubble treatment every week, and the change in the number of bacterial colonies was examined during the root canal treatment. The transplantation of autologous DPSCs and a migration factor in the root canal was performed after four times of treatment, followed by morphological examination 2 weeks after transplantation.
 Results: The most suitable condition of the ultrasound was a voltage 32 V, 1.12 MHz and for 120 seconds to deliver medicaments to the depth of over 1,000 μm from the dentinal wall. Two times of medication using ultrasound with nanobubbles decreased the number of bacterial colonies under the limit of detection in the canine periapical disease model, demonstrating a significant difference compared to the root canal dressing only. A significantly higher volume of regenerated pulp and periapical tissue was demonstrated two weeks after cell transplantation in the ultrasound treated teeth compare to that in untreated teeth and there was no inflammatory cell infiltration.
 Conclusion: It is suggested that enhanced delivery of medicaments using ultrasound with nanobubbles has potential utility for pulp regeneration and root canal treatment.

View full abstract

 Purpose: In the super-aging society of Japan today, although a growing percentage of elderly people aged 65 and over still have at least 20 of their own natural teeth, there are serious problems of increased risk of periodontal disease and root caries.
 It has been considered that degradation of the oral environmental arises from xerostomia via hyposalivation. A main symptomatic treatment for xerostomia is management of mucosal pain and discomfort by using artificial saliva and moisturizing agents for retaining the moisture of the mucous. In this study, we evaluated variations in the quantity of salivation and after oral myofunctional therapy in elderly periodontal patients.
 Methods: This study included 20 patients aged 65 and over with at least 20 of their own natural teeth who were diagnosed as moderate to severe chronic periodontitis and under supportive periodontal therapy (SPT) at Outpatient Clinic of Periodontology, Matsumoto Dental University Hospital. The patients received lip-closing force by using an oral rehabilitation apparatus, Patakara (Patakara) for oral myofunctional therapy. The lip-closing training was performed once for 3 minutes per day for four weeks.
 Lip-closing force was measured by a multidirectional lip-closing force measurement system (Patents JP-4487132, JP-4554630). The unstimulated saliva flow rate was measured by the spitting method, while the stimulated saliva flow rate was measured by the Saxon test. Oral mucosa wettability on the tongue and buccal mucosa was measured by a moisture checker Mucas (Life).
 Results: The subjects included 6 males and 14 females. The average age of the subjects was 71.6±5.7 years old. The number of present teeth was 23.6±5.6. The average PD was 2.5±0.5 mm, CAL was 3.2±1.5 mm, and BOP was 10.1±12.4%. The lip-closing training was continued for four weeks, and the unstimulated saliva and stimulated saliva flow rates were significantly higher than at the start of the experiment. Furthermore, oral mucosa wettability on the tongue and buccal mucosa were also significantly increased compared to the start of the experiment.
 Conclusion: The lip-closing training increased both the unstimulated and stimulated saliva flow rates. In addition, the improvement of the wettability in oral cavity will have a possibility of the decrease of the number of the oral bacteria due to xerostomia by improvement of lip-closing force.

View full abstract

 Purpose: The use of cone-beam computed tomography (CBCT) in the diagnosis of complex endodontic cases has been well documented in recent literatures. In this case report, we present a successful case of treatment of acute apical periodontitis by CBCT for detecting the root canals.
 Case Description: The patient was a 79-year-old male manifesting strong spontaneous pain and occlusal pain in the upper left premolars. From the clinical finding and dental X-ray images, we diagnosed the first premolar as flare-up of a chronic apical abscess with partial pulp necrosis, and the second premolar as acute apical periodontitis. Although we tried drainage via root canals to ease the acute pain, it was difficult to access root canals because of the thickly formed dentin made of secondary and tertiary dentin. Sectional images obtained by CBCT enabled us to remove thickly formed dentin safely and to access the root canals, thus leading to successful treatment of infected root canals.
 Conclusion: CBCT scanning was extremely effective for the detection of root canals covered by thickly formed dentin.

View full abstract