Abstract : Purpose : The aim of this study was to compare the cyclic fatigue resistance of two different Ni-Ti files on rotary movement within artificial curved canals at simulated body temperature.

 Methods : Race files (R group) (ISO size : #25, taper : .06, length : 25 mm, n=10) and RaceEVO files (RE group) (ISO size : #25, taper : .06, length : 25 mm, n=10) were tested. All files were tested by rotary movement (600 rpm, 800 rpm) and the testing device was a stainless-steel artificial canal with a radius of curvature of 5 mm and angle of 45°. To simulate the clinical setting, testing was done with up and down motion at 0.5 s/4 mm. All experiments were conducted at 37±1°C. All samples were loaded with rotary movement until fracture.

 The time to fracture and the lengths of broken fragments were recorded. After the cyclic fatigue resistance tests were completed, the fractured surface was inspected by a scanning electron microscope. The data was analyzed using one-way analysis of variance.

 Results : The time to fracture of the RE group was significantly longer than that of the R group (p<0.01). The average length of broken fragments showed no statistically significant difference between the two group. Observation of the fractured cross-section of the heat-treated Ni-Ti rotary file (RE group) with a scanning electron microscope revealed numerous dimples, micro-bubbles and crater-like structures in each.

 Conclusion : The heat-treated Ni-Ti rotary file (RE group) showed higher cyclic fatigue resistance than the conventional Ni-Ti rotary file (R group) with continuous rotary movement in a body temperature environment.

Abstract : Purpose : To assess the root anatomy and canal morphology of maxillary third molars as well as these molars’positional relationships with the floor of the maxillary sinus in a Japanese population using dental cone-beam computed tomography (CBCT).

 Materials and methods : We analyzed the CBCT images of 199 maxillary third molars from 135 patients. The following parameters were observed on CBCT : (1) number of roots and root canals ; (2) Vertucci classifications of the root canal configurations ; (3) root fusion rate ; and (4) the positional relationship between the root apex and the floor of the maxillary sinus.

 Results : Most maxillary third molars had three roots with three root canals (41.2%) and one root with one root canal (31.2%), in which all root canal configurations were type Ⅰ. Additionally, root fusion was found in 70.9% of the maxillary third molars. Regarding the positional relationship between two-four rooted maxillary third molars and the floor of the maxillary sinus, the frequency of the type in which the maxillary sinus floor was located above without touching the root apex was 38.7% and that of the type in which the floor was in contact without apical protrusion into the maxillary sinus was 34.4%.

 Conclusion : This study provided detailed information regarding the root anatomy and root canal morphology of maxillary third molars and these molars’positional relationships with the floor of the maxillary sinus in a Japanese population.

Abstract : Purpose : The aim of this study was to raise awareness about maintaining good oral hygiene, and to deepen understanding of individual oral conditions and the importance of regular dental checkups. We designed a questionnaire survey to investigate public awareness and knowledge of secondary dental caries and endodontic retreatment, and regular dental checkups.

 Materials and Methods : An internet-based nationwide anonymous questionnaire survey was conducted. A total of 200 subjects in four age groups (20s, 30s, 40s, and 50s) were randomly collected, with up to 50 subjects recruited for each age group, from the consumer panels of DO HOUSE Inc., an internet market research company.

 The survey included six questions about dental treatment experience : experience of dental caries, pulpectomy, recognition of which teeth had undergone pulpectomy, secondary caries, endodontic retreatment after pulpectomy, and frequency of oral examinations. A brief profile survey was also included.

 Results and Discussion : Over 80% of the respondents had experienced dental caries treatment. The rate of increment decreased in older age groups. On average, 44% had experienced pulpectomy, with the rate increasing sharply with age after the 40s. Thirty-three percent knew which of their teeth had undergone pulpectomy, however, their knowledge of which teeth had been treated became vague with age. Forty-one percent had experienced secondary caries treatment, with the rate increasing with age. Twenty-one percent had experienced endodontic retreatment, with the rate increasing sharply with age after the 40s. Thirty-two percent did not consult their dentists for regular dental checkups, but did so when remedial treatment was required.

 The occurrence of secondary caries and periapical periodontitis increases with age while the initial onset of caries in adults decreases. As the number of treated teeth increases, keeping dental records may become complicated and bothersome, which could lead to poor oral health maintenance. The increase of secondary caries with age showed a similar trend as that observed for pulpectomy in which the number of missing teeth and prosthetic treatments, and changes in saliva properties, function and secretion volume were considered to be relevant factors. Endodontic retreatment showed a similar trend as pulpectomy and secondary caries treatment. It is considered that less than 50% of pulpectomies or already retreated teeth had developed new problems and repeat endodontic retreatments were required. No specific causes of retreatment were identified, however, inadequate procedures might have caused this post-treatment periapical periodontitis. Tooth restoration, and particularly endodontically treated teeth, should be observed more carefully afterwards by dental professionals. One-third of respondents did not visit their dentist when remedial treatment was not required. Opinions on frequency of checkup were divided into two sides in younger age groups.

 Conclusion : It is suggested that patients should be informed in detail of the location of the tooth and treatment contents, and also of the need for regular dental checkups in writing after dental treatment.