Lingual nerve revisited-A comprehensive review Part II: Surgery and radiology.

The lingual nerve (LN) is a branch of the mandibular division of the fifth cranial nerve, the trigeminal nerve, arising in the infratemporal fossa. It provides sensory fibers to the mucous membranes of the floor of the mouth, the lingual gingiva, and the anterior two-thirds of the tongue. Although the LN should rarely be encountered during routine and basic oral surgical procedures in daily dental practice, its anatomical location occasionally poses the risk of iatrogenic injury. The purpose of this section is to consider this potential LN injury risk and to educate readers about the anatomy of this nerve and how to treat it.

Root canal narrowing patterns of mandibular first premolars on panoramic radiographs according to the number of root canals diagnosed on cone beam computed tomographic images.

Understanding the variations in root canal morphology is important for successful endodontic treatment. Mandibular first premolars have a single root in 98% of cases, and multiple root canals are found in approximately 20% of cases. However, the details of these characteristic findings in panoramic radiography and their diagnostic accuracy are unknown. This study aimed to investigate the characteristic radiographic findings of mandibular first premolars possessing multiple root canals and determine the diagnostic accuracy using panoramic radiography. Four radiologists evaluated 347 mandibular first premolars in 186 patients who underwent panoramic radiography and dental cone beam computed tomography (CBCT). Two radiologists confirmed the existence of single or multiple root canals using CBCT. The remaining two radiologists evaluated the imaging findings of the root canal morphology and classified them into two patterns: gradual narrowing and sudden narrowing. In the case of the sudden narrowing pattern, the location of sudden narrowing was also evaluated. A gradual narrowing pattern was observed in 56% of teeth with a single root canal, and a sudden narrowing pattern was observed in 83% of teeth with multiple root canals. When sudden narrowing between the cervical and apical 1/4 of the root canal was used as the diagnostic criterion for multiple root canal teeth, the highest diagnostic performance was observed (sensitivity, 76.1%; specificity, 73.9%). The sudden narrowing between the cervical level and the apical 1/4 level of the root canal is a practical diagnostic criterion for mandibular first premolar with multiple root canals.

Porphyromonas gingivalis induces the production of interleukin-31 by human mast cells, resulting in dysfunction of the gingival epithelial barrier.

Interleukin (IL)-31 is important for innate immunity in mucosal tissues and skin, and increased IL-31 expression participates in the pathogenesis of chronic inflammatory diseases affecting the skin, airways, lungs, and intestines. We investigated the contribution of mast cells to the induction of IL-31 production following infection with the periodontal pathogen, Porphyromonas gingivalis. We found that oral infection with P. gingivalis increased IL-31 expression in the gingival tissues of wild-type mice but not in those of mast cell-deficient mice. The P. gingivalis-induced IL-31 production by human mast cells occurred through the activation of the JNK and NF-κB signalling pathways and was dependent on the P. gingivalis lysine-specific protease gingipain-K. P. gingivalis infection induced IL-31 receptor α and oncostatin M receptor ß expression in human gingival epithelial cells. Notably, the P. gingivalis-induced IL-31 production by mast cells led to the downregulation of claudin-1, a tight junction molecule, in gingival epithelial cells, resulting in an IL-31-dependent increase in the paracellular permeability of the gingival epithelial barrier. These findings suggest that IL-31 produced by mast cells in response to P. gingivalis infection causes gingival epithelial barrier dysfunction, which may contribute to the chronic inflammation observed in periodontitis.

The effectiveness of an actuator-driven pulsed water jet for the removal of artificial dental calculus: a preliminary study.

BACKGROUND: While hand and ultrasonic scalers are the primary tools used for the removal of dental calculus in periodontal treatment, many studies have shown that they also damage the enamel surface. We have developed a novel actuator-driven pulsed water jet (ADPJ) system, which has the ability to selectively remove materials depending on their stiffness. Considering the different material properties between teeth and dental calculus, it might be possible to develop the ADPJ to remove dental calculus without damage to the tooth's enamel surface using a suitable jet pressure. Therefore, the aim of this study was to assess the effectiveness of the ADPJ in removing dental calculus, and the surface features of the teeth after its use. METHODS: A total of 93 artificial teeth coated with artificial dental calculus were examined in this study. The weights of 90 teeth were measured before and after the use of ADPJ, which had an applied voltage setting of 150, 200, or 240 V. The three remaining teeth were instrumented with a conventional hand scaler, ultrasonic scaler, or ADPJ (set at 240 V). Damage to the artificial tooth surfaces was evaluated using 5% Evans blue dye under an optical microscope. Furthermore, apatite pellets, which are utilized as experimental substitutes for natural teeth, were assessed after the use of ADPJ and both conventional scalers. RESULTS: The ADPJ significantly reduced the amount of artificial calculus, and the removal rate was dependent on the applied voltage. No damage was observed on the surface of the artificial tooth and apatite pellet following the use of ADPJ, in contrast to the conventional scalers. CONCLUSIONS: The results of this study demonstrate the in vitro effectiveness of ADPJ in the removal of dental calculus, without causing damage to tooth surfaces.

Increased interleukin-18 in the gingival tissues evokes chronic periodontitis after bacterial infection.

Periodontal disease is a chronic inflammatory disease that results in the breakdown of the tooth-supporting tissues, and can ultimately lead to resorption of the alveolar bone. Recently, several studies have shown a close relationship between increased interleukin-18 (IL-18) levels and the pathogenesis of chronic periodontitis, a major cause of tooth loss. However, it has yet to be shown whether chronic periodontitis results from or causes an increase in IL-18 after bacterial infection. In the present study, we investigated how IL-18 overexpression relates to periodontal disease using IL-18 transgenic (Tg) mice. IL-18Tg and wild-type mice were inoculated intraorally with Porphyromonas (P.) gingivalis, which has been implicated in the etiology of chronic periodontitis. Seventy days after P. gingivalis infection, alveolar bone loss and gingival cytokine levels were assessed using histo-morphological analysis and enzyme-linked immuno-absorbent assay, respectively. Periodontal bone loss was evoked in IL-18Tg mice, but not in wild-type mice. Interestingly, levels of bone-resorptive cytokines, including IL-1α, IL-1ß, tumor necrosis factor-α, and IL-6, were unchanged in the gingival tissues of IL-18Tg mice infected with P. gingivalis, although levels of interferon γ (a proinflammatory T-helper 1 cytokine) decreased. RT-PCR analysis showed elevated expression of mRNAs for receptor activator of nuclear factor kappa-B ligand (a key stimulator of osteoclast development and activation) and CD40 ligand (a marker of T cell activation) in the gingiva of IL-18Tg mice infected with P. gingivalis. We conclude that increased IL-18 in the gingival tissues evokes chronic periodontitis after bacterial infection, presumably via a T cell-mediated pathway.

Questionnaire survey on the satisfaction of SimEx dental education system.

Background/purpose: The SimEx is dental training system that applies new technology in a computerized dental simulator. The purpose of this study was to understand the usability satisfaction of the SimEx dental education and evaluation system by dental students and dentists at Tohoku University. Materials and methods: In this study, the Tohoku University IRB execution number was 2020-3-33. The number of subjects accepted was 59 at Tohoku University and divided into 4 groups based on years of clinical experience (Group A: 0 years; Group B: 1-2 years; Group C: 2-5 years; Group D: at least 5 years), and a total of 58 usability questionnaires were collected. Subjects completed the SimEx Usability Satisfaction Questionnaire after operating the SimEx (EPED Inc., Kaohsiung, Taiwan) course, which contained 16 questions. Results: Among the 58 questionnaires collected by Tohoku University, there were 19 undergraduate students (4th∼6th grade), 12 post-graduate students, 14 residents, and 13 dentists. Significant differences between Group A and Group B, and between Group A and Group D were found (P < 0.05). The same results were obtained for the "experience satisfaction index". In the items where significant differences were found, longer clinical experience tended to result in lower scores. Conclusion: From these results, we can conclude that the SimEx education and evaluation system facilitates students' self-learning, and this system is very useful for continued study and clinical skill training for dentists, especially for students and junior dentists with high usability satisfaction.

Mapping of dental graduates' career paths in Hong Kong, Japan and mainland China.

Dental graduates have a variety of career-path choices. After graduation, they may join private dental practice, government- or hospital-based dental care services, research groups, academia, business or industry. With globalization and frequent international exchange, dental graduates nowadays can explore careers outside their home country. However, dental education systems and job opportunities vary widely across different regions and countries. Diversity of accreditation in dental education, different licensure requirements, and lack of global competencies in dental care often limit the globalization, operation and survival of dental practice and education worldwide. The requirements for professional education and practice can be quite diverse, and these differences will be barriers to dental graduates seeking career development outside their home home country. Fresh dental graduates have minimal experience in job hunting. More specifically, they are unfamiliar with potential career paths. This paper was based on the 4th trilateral symposium 2022 organized by The University of Hong Kong, Tohoku University, and Fujian Medical University, which offered a lecture to discuss career paths for dental graduates in Hong Kong, Japan, and mainland China. The aim of this paper was to provide dentists, particularly fresh graduated dental students, with practical insight into different career paths in Hong Kong (Special Administrative Region of China, SAR), Japan and mainland China, and factors that may influence their career options. It assists dental students in exploring possibilities in dentistry and preparing for their career development after graduation from dental school.

Effectiveness of an actuator-driven pulsed water jet for removal of softened carious dentin.

The aim of this study was to assess the utility of an actuator-driven pulsed water jet (ADPJ) as a hardness-dependent carious dentin removal device by using different outputs. Thirty-six plane surface dental caries samples were treated with the ADPJ at 150, 200, and 250 voltage (12 teeth each). The Knoop hardness number (KHN) and Ca/P mass ratio were measured at 70 µm from the deepest point of the removing groove. Furthermore, three other teeth samples were manually treated with the ADPJ at the three above mentioned voltages (one tooth each) for 1 min. The KHN and Ca/P mass ratio were measured at 70 µm from the surface of the residual dentin part. In both the KHN and Ca/P mass ratio, higher residual dentin depended on the applied voltage of ADPJ. The ADPJ enabled the removal of softened carious dentin in an applied voltage-dependent manner.

Porphyromonas gingivalis Gingipains-Mediated Degradation of Plasminogen Activator Inhibitor-1 Leads to Delayed Wound Healing Responses in Human Endothelial Cells.

Plasminogen activator inhibitor-1 (PAI-1), a serine protease inhibitor, is constitutively produced by endothelial cells and plays a vital role in maintaining vascular homeostasis. Chronic periodontitis is an inflammatory disease characterized by bleeding of periodontal tissues that support the tooth. In this study, we aimed to determine the role of PAI-1 produced by endothelial cells in response to infections caused by the primary periodontal pathogen Porphyromonas gingivalis. We demonstrated that P. gingivalis infection resulted in significantly reduced PAI-1 levels in human endothelial cells. This reduction in PAI-1 levels could be attributed to the proteolysis of PAI-1 by P. gingivalis proteinases, especially lysine-specific gingipain-K (Kgp). We demonstrated the roles of these degradative enzymes in the endothelial cells using a Kgp-specific inhibitor and P. gingivalis gingipain-null mutants, in which the lack of the proteinases resulted in the absence of PAI-1 degradation. The degradation of PAI-1 by P. gingivalis induced a delayed wound healing response in endothelial cell layers via the low-density lipoprotein receptor-related protein. Our results collectively suggested that the proteolysis of PAI-1 in endothelial cells by gingipains of P. gingivalis might lead to the deregulation of endothelial homeostasis, thereby contributing to the permeabilization and dysfunction of the vascular endothelial barrier.

Effect of exposure parameters and gutta-percha cone size on fracture-like artifacts in endodontically treated teeth on cone-beam computed tomography images.

OBJECTIVES: To ascertain the effects of exposure parameters (tube current and tube voltage) and the gutta-percha cone (GPC) size on root fracture-like artifacts obtained with cone-beam computed tomography (CBCT). METHODS: Fracture-like artifacts appearing on CBCT images of nine extracted human mandibular premolars filled with GPCs of size #50 or #80 were analyzed using six exposure factors: two tube voltages (80 kV and 110 kV); and three tube currents (4 mA, 7 mA, and 10 mA). On axial images, the gray value (GV) was recorded at three points: the mesiobuccal portion (MBP) as the sound dentin, the mesial portion (MP) as the artifact line, and the water area (WA). The rate of decrease in the GV (RDGV) of the artifact line was calculated using the formula: RDGV (%) = (GV of MBP - GV of MP) × 100/(GV of MBP - GV of WA). RESULTS: Comparison of the #80 group and the #50 group with equal tube voltages and tube currents shows that artifact lines in the #80 group were more obvious than those in the #50 group. The artifact lines with 80 kV were markedly more visible than those with 110 kV for each tube current and GPC size. Tube current changes did not affect the artifact line for any tube voltage or GPC size. CONCLUSIONS: For the reduction of artifacts, we recommend selection of higher tube voltages and lower tube currents when taking CBCT images of teeth with each GPC size.

Florid Cemento-Osseous Dysplasia-Associated Simple Bone Cyst Showing Marked Irregular Border and High Apparent Diffusion Coefficient Value.

A simple bone cyst (SBC) is an intrabone cavity without epithelial lining, which occasionally occur with fibrous-osseous lesions. The imaging finding of the scalloped border and conserving the lamina dura, periodontal ligament spaces, or follicular spaces are considered radiographically pathognomonic of SBC. SBC has been reported to occur with fibrous-osseous lesions, including cemento-osseous dysplasia (COD). Computed tomography (CT) imaging findings are sparse, and there are no reports of magnetic resonance imaging (MRI) findings, including apparent diffusion coefficient (ADC) value calculated by diffusion-weighted MRI for the florid COD-associated SBC. We report a case of a 39-year-old woman who was referred to our hospital because a panoramic radiograph of her right mandible showed asymptomatic radiolucency in the apical molar area. CT images showed a low-density lesion in the periapical areas of the right mandible, which accompanied a well-defined, high-density lesion, and a mixed low/high-density lesion with an unusual marked irregular border in the left mandible. The MRI showed cyst-like extremely hyperintense signals on fat-suppressed T2-weighted images at the right mandibular low-density and the left mandibular mixed low/high-density areas. ADC map showed high values (over 2.5 × 10-3 mm2/s) at the cystic areas in the bilateral mandible. We performed incisional biopsies of the bilateral mandibular lesions and resections of the bilateral maxillary lesions. Surgical and histopathological findings established a diagnosis of florid COD in the bilateral mandible and maxilla, simultaneously complicated by multiple SBCs in the bilateral mandible. The ADC value of cystic component is useful for the diagnosis, if the COD-associated SBC exhibits solitary, nonspecific, or rare imaging findings.

Porphyromonas gingivalis Gingipain-Dependently Enhances IL-33 Production in Human Gingival Epithelial Cells.

The cytokine IL-33 is constitutively expressed in epithelial cells and it augments Th2 cytokine-mediated inflammatory responses by regulating innate immune cells. We aimed to determine the role of the periodontal pathogen, Porphyromonas gingivalis, in the enhanced expression of IL-33 in human gingival epithelial cells. We detected IL-33 in inflamed gingival epithelium from patients with chronic periodontitis, and found that P. gingivalis increased IL-33 expression in the cytoplasm of human gingival epithelial cells in vitro. In contrast, lipopolysaccharide, lipopeptide, and fimbriae derived from P. gingivalis did not increase IL-33 expression. Specific inhibitors of P. gingivalis proteases (gingipains) suppressed IL-33 mRNA induction by P. gingivalis and the P. gingivalis gingipain-null mutant KDP136 did not induce IL-33 expression. A small interfering RNA for protease-activated receptor-2 (PAR-2) as well as inhibitors of phospholipase C, p38 and NF-κB inhibited the expression of IL-33 induced by P. gingivalis. These results indicate that the PAR-2/IL-33 axis is promoted by P. gingivalis infection in human gingival epithelial cells through a gingipain-dependent mechanism.

Influence of voxel size and scan field of view on fracture-like artifacts from gutta-percha obturated endodontically treated teeth on cone-beam computed tomography images.

OBJECTIVE: To determine the optimal scan settings (scan mode and position of field of view [FOV]) for cone beam computed tomography to reduce root fracture-like artifacts that are often observed in teeth filled with gutta-percha cones (GPCs). STUDY DESIGN: Fracture-like artifacts that appeared on cone beam computed tomography images of 9 extracted human mandibular premolars filled with GPCs were analyzed using I-mode (FOV, 102 mm; voxel size, 0.2 mm) and D-mode (FOV, 51 mm; voxel size, 0.1 mm) settings. RESULTS: The artificial lines were more obvious in I-mode than in D-mode. Increased distance between the center of the FOV and the GPCs produced stronger artificial lines in both I-mode and D-mode. CONCLUSION: To reduce fracture-like artifacts, it is critical to use a mode with small voxel size and to place the target tooth in the center of the FOV.

Insulin-Like Growth Factor I Inhibits Alveolar Bone Loss Following Tooth Extraction in Rats.

BACKGROUND: Alveolar bone is often lost after tooth extraction. Few studies have assessed the longitudinal changes in bone volume that occur within these extraction sites. PURPOSE: To investigate the longitudinal morphological changes in extraction sockets following sustained continuous subcutaneous infusion of human recombinant insulin-like growth factor I (IGF-I). MATERIALS AND METHODS: Fourteen rats were subjected to right mandibular first molar extraction. Experimental rats (n = 7) received a continuous subcutaneous infusion of human recombinant IGF-I (320 mg/day) for 3 weeks by osmotic minipump. Control animals were treated with saline via the same method (n = 7). All rats were then housed for an additional 3 weeks. Micro-CT scanning was performed immediately after tooth extraction and at 1, 2, 3, and 6 weeks after extraction. RESULTS: New bone formation was markedly higher in the IGF-I-treated group as compared with the control group. The loss in alveolar ridge height in the IGF-I group was significantly lower than that in the control group at each time point after extraction on the buccal side and at 2, 3, and 6 weeks on the lingual side. CONCLUSIONS: IGF-I treatment increases the volume of newly formed bone and reduces the loss in alveolar ridge height following tooth extraction.

Physiological distal drift in rat molars contributes to acellular cementum formation.

Occlusal forces may induce the physiological teeth migration in humans, but there is little direct evidence. Rat molars are known to migrate distally during aging, possibly caused by occlusal forces. The purpose of this study was to determine if a reduction in occlusion would decrease teeth migration and affect associated periodontal structures such as cementum. To reduce occlusal forces, the right upper first molar (M1) in juvenile rats was extracted. The transition of the position of upper second molar (M2) and formation of M2 cementum was followed during aging. From the cephalometric analyses, upper M2 was located more anterior compared with the original position with aging after M1 extraction. Associated with this "slowing-down" of the physiological drift, cementum thickness on distal surface, but not on mesial surface, of M2 root was significantly increased. The accumulation of alizarin red as vital stain indicative of calcification, was observed in the distal cementum of M2 root only on the side of M1 extraction. Extraction of M1 that results in less functional loading, distinctly attenuates the physiological drift only in the upper dentition. The decreased physiological drift appears to activate acellular cementum formation only on distal surface of M2 root, perhaps due to reduced mechanical stress associated with the attenuated distal drift. In conclusion, the physiological distal drift in rat molars appears to be largely driven by the occlusal force and also affects the formation of acellular cementum. These findings provide additional direct evidence for an important role of occlusal forces in tooth migration.

Alendronate inhibits periprosthetic bone loss around uncemented femoral components.

Periprosthetic bone loss can be severe around the femoral component after uncemented arthroplasty. This study investigated the inhibitory effect of alendronate on periprosthetic bone loss. Seventeen patients underwent arthroplasty with an uncemented femoral component. Among them, 8 patients were given alendronate 5 mg once daily for 1 year (ALN group) and 9 patients received no pharmacotherapy (control group). Bone mineral density was measured in six periprosthetic zones by dual-energy X-ray absorptiometry at 1, 6, and 12 months after surgery. The average periprosthetic bone mineral density was 0.674-0.920 g/cm(2) at 1 month after surgery. From 6 months onward, the absolute bone mineral density and the ratio relative to the 1-month value were significantly decreased in the proximal zones of the femur in the control group (the ratio decreased from 0.817 to 0.769; P = 0.0040-0.0353). In the ALN group, however, the absolute and relative bone mineral density of the proximal femur remained unchanged for 12 months. In the other femoral zones, the absolute and relative bone mineral density remained unchanged throughout the study in both groups. We concluded that alendronate significantly inhibited the decrease of periprosthetic bone mineral density in the proximal femur after uncemented arthroplasty.