Purpose: The purpose of this study was to assess the pull-out bond strength (PBS) of endodontically treated anterior teeth that had been restored with monolithic zirconia endocrowns using different extension depths (EDs) and post-and-core crowns after chewing simulation.

Methods: Thirty-six maxillary central teeth were used (n = 12). Group I: Glass fiber post-and-core crown, Group II: Endocrown with 3-mm EDs, Group III: Endocrown with 5-mm EDs. Restorations were fabricated from monolithic zirconia blocks using a CAM (computer-aided manufacturing) device. For cementation, conventional resin luting agent (Multilink N) was used. All samples were aged with a chewing simulator and PBS tests were conducted at a speed of 1 mm/min using an electromechanical servo universal testing machine. The values were recorded in MPa by dividing the failure load by the bonding area. One-way ANOVA and the post-hoc Tukey test were used for statistical analysis (P = 0.05).

Results: Group III demonstrated significantly greater PBS values than Groups I and II (P = 0.001). No significant difference was found between Groups I and II (P = 0.072).

Conclusion: Increasing the ED of an endocrown influences the PBS of endodontically treated anterior teeth restored with monolithic zirconia endocrowns.

Purpose: To identify secular trends in the use of radiotherapy prostheses in the Clinic for Maxillofacial Prosthetics at Tokyo Medical and Dental University Hospital and to ascertain patient characteristics and future needs.

Methods: The study included all patients who visited the clinic between January 1, 2000, and December 31, 2019. Data on numbers of cases, gender and age, numbers and types of radiotherapy prostheses, primary cancer site, and time required for prosthesis fabrication during the study period were collected from medical records and retrospectively analyzed.

Results: During the 20-year study period, 1,066 prostheses were fabricated for 1,135 cases. In most years, at least 60% of cases were male. The mean age increased from 60.6 to 67.1 years during the study period, and the number of cases older than 70 years increased over time. The most common cancer site was the tongue, and the most common type of radiotherapy prosthesis was a spacer. The mean time for spacer fabrication was 11 days.

Conclusion: During a recent 20-year period, mean age and the proportion of elderly patients requiring savers increased. When treating elderly patients, prosthodontists responsible for fabricating radiotherapy prostheses must collaborate effectively with radiation oncologists.

Purpose: To evaluate the effect of three concentrations of bismuth trioxide (Bi₂O₃) on the biological and physicochemical properties of an experimental mineral trioxide aggregate-type (MTA-type) cement at different time points.

Methods: Three experimental groups with white Portland cement containing 15, 20, or 25 wt% of Bi₂O₃ were assessed. Cellular proliferation in human periodontal ligament fibroblasts was evaluated with an MTT assay. Radiopacity, dimensional stability, pH, and compressive strength were evaluated at different time points.

Results: Bismuth trioxide induced cell proliferation in the Bi15 and Bi25 groups in a time-dependent manner; pH was similar in all groups. Compressive strength was associated with time and bismuth concentration. Bi25 had significantly contracted at day 7 and expanded at day 14 (ANOVA P < 0.05, post hoc Tukey test P < 0.05).

Conclusion: A higher Bi₂O₃ concentration had a negative effect on the physical properties of the cement at all time points.

Purpose: Rapid sintering technology has become one of the most direct methods for shortening the manufacturing time of zirconia restorations. This study aimed to explore the aging resistance of rapid-sintered 5 mol% yttria-partially-stabilized zirconia (5Y-PSZ).

Methods: Specimens were made from two types of 5Y-PSZ material and subjected to rapid sintering (RS) and conventional sintering (CS). After in vitro aging for 5 h, morphology observation, grain size measurement, and phase composition analysis were performed. The mechanical properties were evaluated by biaxial, three-point flexural tests, and the Vickers microhardness test. Results were analyzed by 3-way ANOVA.

Results: Both the RS group and the CS group had a dense microstructure. The tested zirconia ceramics had different grain sizes, which were affected by the interaction between the sintering method and aging. Both groups revealed the same characteristic peaks of the cubic phase after aging. Regardless of the sintering method used, there was no significant difference in the mechanical properties of the tested zirconia before and after aging.

Conclusion: The rapid-sintered 5Y-PSZ materials had a microstructure, phase composition and mechanical properties similar to those of conventional sintered materials. The characteristics of the materials prepared using the two sintering methods did not change significantly after aging.

Purpose: To investigate the mineral density and lesion depth of artificial caries lesions on aprismatic enamel and prismatic enamel created by lactic acid and acetic acid buffers.

Methods: Forty bovine enamel blocks were allocated to: aprismatic enamel (Group A) and prismatic enamel (Group C) in acetic acid buffer for 192 h and aprismatic enamel (Group B) and prismatic enamel (Group D) in lactic acid buffer for 96 h. The mineral loss and lesion depth were measured using micro-computed tomography.

Results: A significant difference (P = 0.01) was observed in the mineral loss (%) in the lesions on aprismatic enamel and prismatic enamel treated with lactic acid buffer while no significant difference (P = 0.51) was observed in the mineral loss (%) in the lesions on aprismatic enamel and prismatic enamel treated with acetic acid buffer. No significant difference was noted in the mean lesion depth of lesions on aprismatic enamel and prismatic enamel treated with acetic acid and lactic acid buffers (P > 0.05).

Conclusion: Aprismatic enamel and prismatic enamel have similar mineral loss in acetic acid while prismatic enamel showed more mineral loss compared to aprismatic enamel in lactic acid.

Purpose: To examine the use of liquid-based exfoliative cytology to determine the presence of genomic instability and cell death in the oral mucosa of patients with orthodontic appliances.

Methods: Fifty-four oral mucosa samples were collected from 18 patients and divided into three stages: T0, before fixation of orthodontic appliances; T1, 25 days after appliance fixation; T2, 90 days after appliance fixation. All samples were Papanicolaou-stained and observed by microscopy (1,000 cells/sample) to ascertain the frequency of micronucleated cells (MN) and nuclear abnormalities (nuclear buds (NB), binucleated (BN), condensed chromatin (CC), karyorrhexis (KR), and karyolysis (KL)). Differences were analyzed statistically using the Mann-Whitney, Wilcoxon, Kruskal-Wallis and chi-squared tests.

Results: After placement of orthodontic appliances, significant differences were observed for genomic instability biomarkers (MN and NB) and cell death (CC, KR and KL) (P < 0.05). Female patients and older patients exhibited a higher frequency of MN.

Conclusion: Liquid-based cytology has revealed that orthodontic appliances induce genomic instability and cell death in epithelial tissue of the oral mucosa, facilitating sample preservation and yielding more than one preparation per sample. Future studies should investigate whether such cell damage can be reversed through cell repair or whether cell alterations evolve and lead to disease.

Purpose: The study aimed to examine the association of self-rated chewing function, the number of teeth and periodontal status with metabolic syndrome.

Methods: The participants were 11,119 adults aged 40-74 years who underwent specific health checkups, including an oral health examination, in 2018 in Japan. This study used the standard questions of the specific health checkups to obtain information on self-rated chewing function. A multinomial logistic regression analysis was performed with metabolic syndrome status as the dependent variable, and age, sex, lifestyle questions, self-rated chewing function, number of teeth, and periodontal status as the independent variables.

Results: Number of teeth and periodontal status were significantly associated with metabolic syndrome after adjusting for confounding variables. Self-rated chewing function was significantly associated with metabolic syndrome in the crude analysis, but not after adjustment for confounding variables. Both number of teeth and periodontal status were significantly associated with self-rated chewing function.

Conclusion: There was no significant direct association between self-rated chewing function and metabolic syndrome. Self-rated chewing function may be an indicator of poor oral condition that links to metabolic syndrome.

Purpose: To assess root temperature during filling techniques and quantify the volume of endodontic filling materials using infrared thermography (IT) and micro-computed tomography (micro-CT).

Methods: Ninety premolars were divided into three groups: lateral condensation (LC), single cone (SC) and thermomechanical compaction (TMC). For thermal analysis, 45 teeth were assessed using a FLIR T650sc IT camera during filling techniques and 45 teeth were scanned using a Nikon micro-CT to assess gutta-percha, cement, and void volumes. Descriptive and inferential statistical analyses were performed (non-parametric Mann-Whitney test, Kruskal-Wallis test, and Friedman test with Tukey’s bidirectional analysis of variance).

Results: TMC showed the highest temperature increase at 15 s after the procedure and a significant temperature decrease at 45 s after its completion. TMC showed the largest volume of gutta-percha and LC the highest void volume.

Conclusion: The temperature increase generated by gutta-percha endodontic filling techniques is within acceptable limits. A greater volume of endodontic cement was observed for the SL and LC filling techniques.

Purpose: The dual imaging plate (DIP) method, which synthesizes intraoral radiographs from a front imaging plate (FIP) and a back imaging plate (BIP), produces adequate image quality and allows the radiation dose to be reduced. However, there are slight errors in superimposition and alignment between the FIP and BIP. The aim of this study was to establish positional correction in the DIP method and evaluate the effect.

Methods: Six sets of two imaging plates were used for imaging a mesh plate and a porcine mandible phantom. Subtraction images between FIP and BIP images were synthesized in four steps: correcting horizontal and vertical direction, rotation, enlargement ratio, and enlargement ratio into 12 blocks. Variance of the pixel value on the subtraction images at each step was compared to evaluate the alignment of FIP and BIP images.

Results: The variance of the pixel values in the subtraction images was gradually and significantly decreased by each step of image processing (P < 0.01), indicating that the degree of alignment of FIP and BIP images improved during the image processing.

Conclusion: The present study revealed that it is possible to synthesize more precise DIP images using an additional four-step image processing technique.

Purpose: Overtime work is associated with a risk of developing various diseases, including oral diseases. Oral Health-Related Quality of Life (OHRQoL) is a more comprehensive assessment than those of individual diseases and can be affected by longer working hours.

Methods: This cross-sectional study examined the association of overtime work duration with OHRQoL. Data were obtained from an online survey of Japanese workers in February 2016. OHRQoL was assessed using the Oral Health Impact Profile-49 (OHIP-49). Poisson regression with robust variance was used to estimate the ratio of means and 95% confidence intervals (CI) of overtime work duration for OHIP-49 scores after adjusting for sociodemographic and health behavior covariates.

Results: Of 2,764 (2,178 male and 586 female) workers (mean age, 44.6 ± 10.0 years), those with longer duration of overtime work tended to exhibit poorer OHRQoL. The mean OHIP-49 scores of those who did not work overtime and worked for ≥5 h overtime were 27.93 ± 28.53 and 40.97 ± 38.86, respectively. After adjusting for covariates, compared to those who did not work overtime, the mean OHIP-49 score was 1.41 times higher (95% CI 1.38-1.44) for those who worked for ≥5 h overtime.

Conclusion: Longer overtime work duration was associated with poor OHRQoL.

Purpose: To investigate the bactericidal and biofilm removal effect of super reducing water (SRW) on Streptococcus mutans (S. mutans) adhered to orthodontic brackets, in vitro.

Methods: Three types of brackets were bonded to aluminum disks. After the formation of S. mutans biofilms on the surfaces, the brackets were divided into three groups (n = 44 each) based on their exposure to SRW: group 1, no treatment; group 2, treated for 5 min; and group 3, treated for 10 min. Total viable counts, adenosine triphosphate measurements, crystal violet assay, and scanning electron microscopy were used to evaluate the effect of SRW.

Results: The bacterial counts in groups 2 and 3 were significantly lower than those in group 1 (P < 0.001); however, no significant differences were observed between groups 2 and 3. Marked decreases in the number of bacterial colonies and extent of biofilm formation were observed in groups 2 and 3 compared to group 1. No significant differences in the number of bacterial colonies and amount of biofilm were observed among the three types of brackets in each group.

Conclusion: These findings indicate the bactericidal and biofilm removal effect of SRW treatment on S. mutans adhered to orthodontic brackets.

Purpose: The purpose of this study was to investigate the reaction products formed by application of three tooth etchants to hydroxyapatite.

Methods: Tooth etchants with three different compositions, designed for application to teeth before dental adhesive – “ K-etchant GEL” (containing phosphoric acid), “Enamel Conditioner” (containing organic acids), and “Multi Etchant” (containing acidic monomer) – were applied to hydroxyapatite plates.

Results: Atomic force microscopy measurements revealed that Multi Etchant formed nano-sized particles on the hydroxyapatite. X-ray diffraction and Fourier transform infrared spectrometer analyses of the powdered hydroxyapatite indicated that Enamel Conditioner produced calcium tartrate whereas K-etchant GEL generated monetite. These results indicated that each etchant reacted with hydroxyapatite in a different way.

Conclusion: Not only differences among the etching ability of etchants, but also differences in the reaction compounds they produce may influence bonding performance in clinical practice.

Purpose: The aim of this study was to evaluate the effects of apical backfilling depth on the apical sealing of different root canal filling qualities and morphologies.

Methods: 3D-printed root canals (A: round, B: oval, C: long oval, D: flat) were used and divided into subgroups by root canal filling quality (a: good, b: poor, c: nonfilling) and backfilling depth (3 mm, 5 mm). A glucose microleakage device was used to measure leakage.

Results: (1) 3-mm iRoot BP Plus was filled at the apex, and no obvious leakage occurred in the good root canal filling group, which was significantly smaller than that in the poor/nonfilling groups (P < 0.05). Under good root canal filling conditions in groups A, B, C, and D, no obvious leakage was observed. Under poor/nonfilling root canal filling conditions, there was significant leakage; A and B (P > 0.05) and C and D were compared (P < 0.05). (2) Apical backfilling with 5-mm iRoot BP Plus showed no significant leakage in the poor root canal filling groups with the four morphologies.

Conclusion: 3-mm iRoot BP Plus was filled at the apex, root canal filling was poor, apical sealing was poor, and root canal morphology affected apical sealing. Apical backfilling with 5-mm iRoot BP Plus improved apical sealing under poor root canal filling conditions, and apical sealing was unaffected by root canal morphology.

This study aimed to clarify the usefulness of automatic cleaning in analysis of occlusal force. The maximum occlusal force was calculated in 151 healthy adults before cleaning (B), after manual cleaning (M), and after automatic cleaning (A) and compared among the three conditions. The absolute value of the error rate of A, based on M, was calculated. The occlusal forces in M and A were similar and significantly smaller than the occlusal force in B. The absolute error rate of A was 2.4%. These results suggest that automatic cleaning has a similar effect to manual cleaning and can be applied clinically.

Definitive radiotherapy is an effective treatment for early-stage lip cancer. The goal of radiotherapy is to irradiate the cancer site effectively while protecting healthy surrounding tissue from the adverse effects of radiation. To this end, radiotherapy prostheses have been widely and effectively used. A maxillofacial prosthodontist working in collaboration with a radiation oncologist can create a custom-made radiotherapy prosthesis that minimizes adverse effects. This report demonstrates the successful use of spacers in external beam radiotherapy and brachytherapy in consideration of the patient’s radiation therapy treatment plan and wearing conditions, ensuring adequate availability and preventing radiation-related complications.

Superficial angiomyxomas are myxoid mesenchymal tumors, and intraoral superficial angiomyxoma is extremely rare. This paper reports a novel case of a 41-year-old Japanese male patient with a 32 × 22 mm superficial angiomyxoma in the right soft palate. Tumor resection was performed and a polyglycolic acid sheet was attached. Over a 28-month follow-up, there was no evidence of disease recurrence. This paper also reviewed 11 cases of intraoral superficial angiomyxomas reported in previous literature. The condition was more common among middle-aged men. Surgical resection was the most common treatment, and local recurrence was observed in only one case.