Dental hygiene and dental students' motivations for future work: a cross-sectional study of first-year students at a dental hygiene school and a dental school in Japan.

BACKGROUND: It is important to understand the career motivations and perceptions of students who intend to become dental health professionals. Both dental and dental hygiene students may have different opinions about the profession and future work prospects. To our knowledge, no study has compared the career motivations and career perceptions of Japanese dental and dental hygiene students after admission to dental or dental hygiene school. This cross-sectional study examined the motivations of dental and dental hygiene students for their future career perceptions.  METHODS: First-year students of dental and dental hygiene schools in the academic years 2021 and 2022 participated in the study. Group 1 comprised 104 female dental hygiene students, Group 2-1 comprised 55 female dental students, and Group 2-2 comprised 61 male dental students. A self-administered questionnaire survey was conducted on opinions of the work and prospects of future work with four-point Likert scales ranging from "strongly agree" to "strongly disagree," according to the items. RESULTS: Dental hygiene students consider that they would like to work as professionals and would also like to earn efficiently. Specifically, female dental students prioritized contributing to society by working long-term in a fulfilling environment rather than earning an income, whereas male dental students would like to work as a professional while also effectively earning income. CONCLUSIONS: Small but significant differences were found in opinions of the dental hygienist/dentist profession in terms of attractiveness and credibility. Small but significant differences were found for income and working hours when considering future job prospects. The results of this study revealed differences in the first year students between dental and dental hygiene school in their attitudes toward career motivation and prospects for future work.

The relationship of tooth crown dimensions between first molar and central incisor in maxilla.

The purpose of this study was to investigate a correlation between the cusp dimensions of the first molar and mesiodistal crown diameters of the central incisors in the maxilla. The study materials were composed of dental casts from 29 modern Japanese female subjects with a mean age of 20 years and 8 months. The mesiodistal crown diameters of the maxillary central incisors were measured. The mesiodistal and bucco-lingual crown diameters and the cusp diameters of the maxillary first molars, such as the paracone, metacone, protocone, and hypocone, were also measured. The crown areas and indices of the first molars were calculated. The Spearman's single rank correlation coefficients between the mean values for the crown dimensions of the first molars and the mesiodistal crown diameters of the central incisors were calculated. The hypocone cusp diameter and the hypocone index were the largest compared to those of the paracone, protocone, and metacone cusps. The bucco-lingual diameter and hypocone cusp diameter of the first molars positively correlated with the mesiodistal crown diameters of the central incisors on the same sides. There were positive correlations between the hypocone index of the first molars and the mesiodistal crown diameters of the central incisors. Based on the results, if a large hypocone is observed in eruption of the maxillary first molars, it will be predictable that of the mesiodistal crown diameter of the maxillary central incisor large.

Relationship between index of orthodontic treatment need dental health component (IOTN-DHC) and caries prevalence in school-age children.

OBJECTIVES: The objectives of the study were to investigate the relationship between caries prevalence and the Index of Orthodontic Treatment Need Dental Health Component (IOTN-DHC) in school-age children who live in the dentistless area and to consider the effective way to reduce the potential progression of malocclusion with the growth through the dental survey in Arbulag district, Khövsgöl province, Mongolia. MATERIALS AND METHODS: The 95 school-age children (49 males, 46 females) who participated in the study were born in and were residents of Arbulag district, Khövsgöl province, Mongolia. The mean ages of the participants were 8.3 years (y) ± 1.7 y for males and 8.8 y ± 1.7 y for females. The Mann-Whitney U test was performed to determine the sex difference for the dmf/DMF index. The relationship between the IOTON-DHC and the dmf/DMF index was statistically examined using Spearman's rank correlation coefficient. RESULTS: Regarding the dmf/DMF index, no sex difference was observed. There were significant, fair positive correlations between the IOTON-DHC grade and F; between the IOTON-DHC grade and DMF index in males. There were significant, fair positive correlations between the IOTON-DHC grade and M; between the IOTON-DHC grade and DMF index in females. CONCLUSIONS: Significant, fair positive correlations were found between the caries prevalence and the grade of malocclusion. Thus, prevention and early treatment of dental caries in a mixed dentition may be effective to reduce the potential progression of malocclusions in dentistless area.

Student Potential for Self-assessment in a Clinical Dentistry Practical Training Course on Communication Skills.

This study aimed to investigate student potential for self-assessment in a clinical dentistry practical training course focused on communication skills. Participants were 124 fourth-year students (70 males, 54 females; all Japanese) in 2017 and 2018 at the Nippon Dental University, School of Life Dentistry at Niigata. Participating students belonged to different cohorts in 2017 and 2018. Participants were asked to complete a self-evaluation sheet at the end of each unit of the course. Their self-evaluation scores and the faculty evaluation scores for each student for Units 1-1, 1-2, and 1-3 were statistically analyzed. The results showed that females tended to rate themselves significantly higher than males. Furthermore, there were significant differences in evaluation scores between students and faculty for nine of 11 evaluation items for male students and 10 of 11 items for female students in Unit 1-3. Faculty expectations increased from Unit 1-1 to Unit 1-3, although students were satisfied with their performance and had a sense of achievement. However, students' actual performance was below faculty expectations, suggesting faculty evaluations were stricter than students' self-evaluation. Self-assessment may enhance students' ability for self-directed learning and may also inform how faculty can effectively educate dental students. Dental educators should support students to increase their levels of self-efficacy, which will enhance their self-evaluation skills.

Effects of contact compressive force on bracket bond strength and adhesive thickness : Study using orthodontic resins with different viscosities.

PURPOSE: To assess the effect of the contact compressive force to seat orthodontic brackets on shear bond strength (SBS) and adhesive thickness using adhesive resins with different viscosities. METHODS: A total of 184 premolars were divided equally into eight groups of 23. Transbond XT and Beauty Ortho Bond paste viscous self-etching adhesive systems were used with contact compressive forces of 0.5, 1, 2, and 3 N (groups 1-4 and groups 5-8, respectively) via a push-pull tension gauge. SBS and adhesive thickness were measured in each adhesive system for each contact compressive force. RESULTS: Significant differences existed in the SBSs between the adhesive systems for each contact compressive force and the SBSs were significantly higher in groups 1 (17 MPa) and 2 (16 MPa) than in groups 3 (14 MPa) and 4 (13 MPa). Significant differences existed for the adhesive thickness between the adhesive systems for the three contact compressive forces less than 3 N. The adhesive in group 1 (0.184 mm) was significantly thicker than that in groups 2-4 (from 0.098 to 0.129 mm). In groups 2 (0.129 mm) and 3 (0.121 mm) it was thicker than in group 4 (0.098 mm), and in group 5 (0.119 mm) it was thicker than in groups 6-8 (from 0.087 to 0.088 mm). CONCLUSIONS: The high-viscosity adhesive Transbond XT exhibited higher SBSs than the low-viscosity Beauty Ortho Bond paste. For the adhesive Transbond XT, lower contact compressive forces produced greater adhesive thicknesses and higher SBSs. For the Beauty Ortho Bond paste, no significant changes in the adhesive thickness or SBS values were observed for contact compressive forces greater than 0.5 N.

The relationship between the incisor position and lingual surface morphology in normal occlusion.

This study aimed to investigate the relationship between the morphological characteristics of maxillary incisors and the anterior occlusion. The study materials comprised dental casts and lateral cephalograms of 26 modern Mongolian females with Angle Class I normal occlusion (mean age, 21 years 5 months). Computed tomography (CT) images of the dental casts were taken with an X-ray micro-CT system (SMX-100CT, Shimadzu, Kyoto Japan). The thickness of the marginal ridges and incisal edges, and the overjet and overbite, was measured on the three-dimensional images of the dental casts. On the lateral cephalogram, maxillary incisor to sella-nasion plane angle (U1 to SN angle), maxillary incisor to nasion-point A plane distance (U1 to NA distance), mandibular incisor to nasion-point B plane distance (L1 to NB distance), incisor mandibular plane angle, and interincisal angle were measured by tracing the left incisors of the maxilla and mandible. Spearman's single rank correlation coefficients were used to investigate any correlation between measurement items for each maxillary incisor. The thickness of the marginal ridges and incisal edges was positively correlated with the overbite. The thickness of the incisal edges was positively correlated with the irregularity index of the maxilla. There were significant negative correlations between overbite and U1 to SN angle, U1 to NA distance, and L1 to NB distance. Significant positive correlations were noted between the overbite and the overjet. In conclusion, there was no strong relationship between the morphological characteristics of maxillary incisors and the anterior occlusion.

Emotional intelligence score and performance of dental undergraduates.

The purpose of this study was to investigate the relationship between emotional intelligence (EI) and undergraduate dental students' ability to deal with different situations of communication in a clinical dentistry practical training course of communication skills. Fourth-year students in 2012 and in 2013 at the Nippon Dental University School of Life Dentistry at Niigata participated in the survey. The total number of participating students was 129 (88 males and 41 females). The students were asked to complete the Japanese version of the Mayer-Salovey-Caruso Emotional Intelligence Test in communication skills. Female students tended to have significantly higher EI score than males. The EI score in the group with high-grade academic performers was higher than in the low-grade group. The influence of EI on academic performance appeared to be mainly due to the students' ability to accurately perceiving emotions and to their ability to understand emotional issues. The importance of EI may also lie in its ability to parse out personality factors from more changeable aspects of a person's behavior. Although further studies are required, we believe that dental educators need to assume the responsibility to help students develop their emotional competencies that they will need to prosper in their chosen careers. In our conclusion, dental educators should support low achievers to increase their levels of self-confidence instead of concentrating mainly on improving their technical skill and academic performance. This may lead to upgrading their skills for managing emotions and to changing their learning approach.

Comparison of mesiodistal tooth crown diameters and arch dimensions between modern Mongolians and Japanese.

The purposes of this study were to establish normative data for mesiodistal tooth crown diameters and arch dimensions in Mongolian adults and to compare them with those of Japanese adults. The study materials comprised dental casts of 100 modern Mongolian and 100 Japanese subjects (50 males, 50 females for each) with Angle Class I normal occlusion. The mean ages were 20 years 8 months for the Mongolian subjects and 20 years 0 months for the Japanese subjects. On the dental casts, the mesiodistal tooth crown diameters (excluding wisdom teeth) and dental arch dimensions were measured. The following arch dimensions were measured: inter-canine lingual, inter-premolar lingual, inter-molar lingual, inter-molar central, coronal arch length, basal arch length, and basal arch width. In the Mongolian samples, significant sex differences were noted, and most of the items were significantly larger in males than in females. Significant differences between the Mongolian and Japanese samples were mainly noted in the premolar and molar regions, rather than in the anterior region, and were significantly smaller in the Mongolian samples. In the Mongolian samples, the molar section widths and basal arch width and length were significantly larger in males and females compared with the Japanese samples. These results suggest that the tooth crown size and arch dimensions in the Mongolian samples differed from those in the Japanese samples, and that establishment of the clinical norm for Mongolian adults might be helpful in formulating treatment plans for Mongolian patients, given that these parameters are the basic tools for diagnosis.

Repeated bonding of fixed retainer increases the risk of enamel fracture.

The aim of this study was to investigate the influences of repeated bonding, using 2 different orthodontic adhesive systems, on the shear bond strength (SBS) and the enamel surface morphology. Sixty premolars were divided into 2 groups (n = 30), and either Transbond XT (T group) or Fuji Ortho LC (F group) adhesives were used. SBS was measured 24 h after bonding, using a universal testing machine. Then, the enamel surfaces were investigated and the mode of failure was described using adhesive remnant index (ARI) scores. After each debonding, 10 teeth from each group were examined by scanning electron microscopy to determine the penetration of adhesives, the length of resin tags, and the state of the enamel surface. The other teeth were subjected to two more bonding/debonding procedures. In T group, the second debonding sequences had significantly higher bond strengths than the other sequences. The length of resin tags was greatest in the second debonding sequence, although there was no significant difference. In F group, the SBS increased with further rebonding and the failure mode tended towards cohesive failure. In both groups, the ARI scores increased with rebonding. Enamel loss could have occurred with both adhesives, although the surfaces appeared unchanged to the naked eye. From this study, we suggest that enamel damage caused by repeated bonding is of concern. To prevent bond failure, we should pay attention to the adhesion method used for bondable retainers.

Influence of third molar space on angulation and dental arch crowding.

The influence of the third molars on mandibular incisor crowding has been extensively studied but remains controversial. The purpose of this study was to ascertain whether, in Mongolian subjects, the lower third molar can affect anterior crowding and/or the inclination of teeth in the lower lateral segments. Panoramic radiographs, 45° oblique cephalograms, and dental casts were taken from Mongolian subjects (age range 18.3-24.1 years, mean 21.0 years) exhibiting impaction of all four third molars and an Angle Class I molar relationship. The Ganss ratio was calculated using panoramic radiographs, whereas the gonial angle and angulation of lower canines, premolars and molars were measured using 45° oblique cephalograms. Little's index of irregularity was calculated using dental casts. Significant relationships between the angulation of the third and second molars and between the first molars and second premolars were found. Conversely, there was no significant correlation between the angulation of third molars, first premolars and canines. The Ganss ratio calculations showed that the lower first and second molars and the second premolars inclined mesially if there was insufficient space for the lower third molars. However, there was no significant correlation between Little's index of irregularity and third molar angulation. Furthermore, although the third molar influences the lateral segments, no obvious relationship between the third molar and anterior crowding was observed. Therefore, the angulation of the third molar appears not to cause anterior crowding.

Trehalase-2 protein contributes to trehalase activity enhanced by diapause hormone in developing ovaries of the silkworm, Bombyx mori.

Diapause hormone (DH) targets developing ovaries in female pupae to induce embryonic diapause immediately after completion of mesoderm segregation of the silkworm, Bombyx mori. At the same time, DH enhances trehalase activity on the oolemma, which leads to higher concentrations of glycogen in oocytes through the stimulated incorporation of hemolymph trehalose. In B. mori, the treh-1 and -2 genes encoding soluble trehalase (68 kDa) and integral-membrane trehalase (74kDa) have been isolated. DH stimulates mRNA expression of both of these genes. In this study, we aimed to clarify whether ovarian trehalase originates from Treh-1 or Treh-2. Western blotting of the developing ovaries showed positive bands in the membrane-bound fraction, containing trehalase activity, only with antibodies against Treh-1&2 and Treh-2, but not Treh-1, irrespective of nondiapause or diapause egg-producers. The intensities of the positively stained 74 kDa bands were increased approximately 4-fold in ovaries from pupae with intact subesophageal ganglion (SG, a unique DH-biosynthesizing organ), and from pupae that were injected with DH at the middle pupal stage after their SGs were removed on the day of pupation. Furthermore, quantitative real-time PCR data showed that in developing ovaries, copy number of treh-2 mRNA per one copy of rp49 mRNA was approximately 1000-fold higher than that of treh-1 mRNA. These results demonstrate that trehalase activities enhanced by DH originate mainly from treh-2 protein regulated at the transcriptional level.

Study of delayed development of the upper first molars.

The present study was undertaken to analyze the status of formation of the upper first molar in individuals suspected as having delayed eruption of the upper first molar. The subjects of this study were 51 patients presenting to orthodontic specialists with delayed eruption of the upper first molars. The 95 teeth of these 51 patients were observed. The investigation of the tooth development status included evaluation of the tooth development stage on panoramic radiographs according to the method of Moorrees et al. The upper first molars that showed delayed development were at the stage of initial cleft formation, reflecting a delay by 2.09 years in boys and 2.84 years in girls. In most cases, the delayed eruption was bilateral, and the development stage of the subject teeth did not differ between right and left sides. The plot of the developmental stage of the subject teeth (Y-axis) against the calendar age of the subjects (X-axis) showing delayed upper first molar development was fitted to the logistic curve. The tooth development was at the stage of initial cleft formation was delayed 2.5 years or more, according to these curves.

Influence of shovel-shaped incisors on the dental arch crowding in Mongolian females.

The aim of this study was to investigate the influences of shovel-shaped incisors on the dental arch crowding in the samples of modern young female adult Mongolians (belonging to the Khalkha-Mogol grouping) ranged between 18.5 and 25.0 years, with a mean age of 20.7 years. Materials in this study comprised of 33 dental casts. Plaster replicas of the A.S.U. system plaques were used to facilitate standardization in scoring and classify shoveling regarding both upper central and lateral incisors. Dimensions of the dental arch namely, overjet, overbite, arch depth, arch width and irregularity index were measured. The correlation between the shovel shape of the central incisor and the lateral incisor was highly significant. Significantly relations were found between the grades of shoveling and the mesiodistal diameters of upper first molars and lower incisors. Positive correlation was admitted between the shoveling and upper arch depth anterior, and upper arch depth. It may be considered that the grades of shoveling are indirectly related with upper and/or lower anterior crowding. Although crowding is looks like an expression of disharmony between teeth and alveolar arch, it may be caused by multiple etiologic factors interacted directly and/or indirectly.