• Journal of Korean Dental Science
• /
• v.12 no.1
• /
• pp.13-19
• /
• 2019

Purpose: The aim of this study was to compare the flexural strength of provisional fixed dental prostheses which was three-dimensional (3D) printed by several build directions. Materials and Methods: A metal jig with two abutment teeth and pontic space in the middle was fabricated. This jig was scanned with a desktop scanner and provisional restoration was designed on dental computer-aided design program. On the preprocessing software, the build angles of the restorations were arranged at $0^{\circ}$, $30^{\circ}$, $45^{\circ}$, $60^{\circ}$, and $90^{\circ}$ and support was added and resultant structure was sliced to a thickness of $100{\mu}m$. Processed restorations were printed with digital light processing type 3D printer using poly methyl meta acrylate-based resin. After washing and post-curing, compressive loading was applied at a speed of 1 mm/min on a metal jig fixed to a universal testing machine. The maximum pressure at which fracture occurred was measured. For the statistical analysis, build direction was set as the independent variable and fracture strength as the dependent variable. One-way analysis of variance and Tukey's post hoc analysis was conducted to compare fracture strength among groups (${\alpha}=0.05$). Result: The mean flexural strength of provisional restoration 3D printed with the build direction of $0^{\circ}$ was $1,053{\pm}168N$; it was $1,183{\pm}188N$ at $30^{\circ}$, $1,178{\pm}81N$ at $45^{\circ}$, $1,166{\pm}133N$ at $60^{\circ}$, and $949{\pm}170N$ at $90^{\circ}$. The group with a build direction of $90^{\circ}$ showed significantly lower flexural strength than other groups (P<0.05). The flexural strength was significantly higher when the build direction was $30^{\circ}$ than when it was $90^{\circ}$ (P<0.01). Conclusion: Among the build directions $0^{\circ}$, $30^{\circ}$, $45^{\circ}$, $60^{\circ}$, and $90^{\circ}$ set for 3D printing of fixed dental prosthesis, an orientation of $30^{\circ}$ is recommended as an effective build direction for 3D printing.

• Journal of Dental Rehabilitation and Applied Science
• /
• v.37 no.4
• /
• pp.281-293
• /
• 2021

Patients who went through maxillectomy can have severely impaired swallowing, mastication, and pronunciation functions because of palatal defects. Leakage occurs through the nasal cavity while eating, chewing becomes difficult due to the loss of teeth and alveolar ridges, and oral and nasal passages are not separated, leading to hyper-nasal sound, and significantly reducing the quality of life. To prosthetically reconstruct the defect, the weight of the obturator should be reduced as much as possible to minimize dropout because of gravity, and the bulb of the obturator should be properly extended into the defect to get additional retention and stability. In this case of a partially edentulous patient who underwent additional maxillary resection because of tumor recurrence, a metal framework was designed by applying the basic design principles of removable partial dentures. An obturator with improved retention, stability, and support was fabricated through functional impressions. The patient was satisfied with the improved facial expression, mastication, swallowing, and pronunciation, and showed stable occlusion and oral hygiene management during the follow-up period.

• Journal of Chest Surgery
• /
• v.31 no.10
• /
• pp.919-923
• /
• 1998

Background: Calcific degeneration is unavoidable in either homo- or heterografts implanted in the human body. We have developed a calcification-resistant cardiovascular tissue patch using a novel technique of anticalcification. Materials and methods: Fresh bovine pericardium was harvested at the slaughter house and transfered to the laboratory in Hank's solution. After trimming and fixing the pericardium, it was embedded in 4$^{\circ}C$ 0.65% glutaraldehyde for a week and then washed by phosphate-buffered saline(PBS) of pH 7.4. This prepared pericardium was then stored in 2.5% sulphonated polyethyleneoxide(PEO-SO3) solution for 2 days at room temperature and reversed by 4$^{\circ}C$ NaBH4 solution for 16 hours. To evaluate the calcification-resistance of surface modified bovine pericardium with PEO-SO3, either glutaraldehyde- treated(GA group, n=4) or PEO-SO3-treated pericardial patch(PEO-SO3 group, n=4) was implanted into adult mongrel dog to reconstruct the main pulmonary artery and the descending aorta using a partial clamp technique. After 1 month follow-up, the implanted patches were retrieved to evaluate the pathologic findings and the content of calcium and phosphorous. Results: The PEO-SO3 group showed substantially less retraction and significantly less calcium deposition than the GA group in both aortic(7.10$\pm$1.05 vs. 13.81$\pm$2.33 mg/g of dried tissue) and pulmonary positions(1.55$\pm$0.29 vs. 6.72$\pm$0.70 mg/g)(p<0.01). Phosphorous contents were also less in the PEO-SO3 group than the GA group significantly, 8.11$\pm$1.07 mg/g vs. 19.33$\pm$4.31 mg/g in the aortic and 2.58$\pm$0.40 vs. 12.60$\pm$3.40 mg/g in thepulmonary position(p<0.01). Conclusions: These findings suggest that PEO-SO3 modified bovine pericardium is highly calcification-resistant but further study is needed to evaluate the long-term biological safety and compatibility of the prosthesis.

• Journal of Technologic Dentistry
• /
• v.24 no.1
• /
• pp.51-63
• /
• 2002

The purpose of this study was to be of use for getting rid of job stress from dental technicians, by examining how much they were stressed out at work place as one of the professional medical personnels. The subjects in this study were 255 selected dental technicians who were working in the region of Taegu. The one-on-one interview was conducted from March 1 to 30, 2001, with structured questionnaire. The questionnaire sued in this study included 19 question items about the general characteristics and 29 items regarding job stress. The job stress was categorized into seven subareas based on earlier studies and considering the job situations of dental technicians: heavy workload, job conflicts, improper treatment, role and job knowledge, human relations, physical environment and personal matters. The job stress extent was measured on five-point Likert scale that is widely used in social science: one point for no stress, two for little stress, three for so-so, four for a little stress, and five for severe stress. Therefore, a higher point means a severer job stress. The reliability of the questionnaire turned out very good with Cronbach a = 0.9272. The findings of this study were as follows: 1. The general characteristics of the dental technicians investigated could be described as below: (1) By gender, 80.4% of the dental technicians were male, and 50.2%, the largest percentage, were in their 20s, followed by those in their 30s, those in their 40s, and those in their 50s in the order named. (2) The most common work place was dental technician shop(92.5%), followed by dental technology room in dental hospital or clinic and in general hospital in the order named. The primary duties were coating materials work(30.6%), followed by sculpture, grinding, partial and full denture and orthodontics in the order named. 2. The most larges (1) The most largest motivation to be a dental technician was its being a professional(33.7%), followed by the advice from others, their own aptitude, and good economic treatment in the order named. 3. Their job stress could be explained as below: (1) Their collective job stress average was 3.96$^{\circ}{\ae}$0.50 on the basis of 5 point, which showed that they were exposed to a fairly severe job stress. (2) By area, they were most stressed out from heavy workload (4.12), and they also were severely stressed from role and job knowledge(4.02) and personal matters(4.00). (3) By situation, they were most stressed when the disagreement of prosthesis that results from a specific error is unconditionally attributed to them(4.43). And they were also stressed a lot when their workload increases due to the rework(4.38), when a dentist asks something difficult for them to resolve(4.20), when heavy workload makes their working hours irregular and it's impossible to lead a personal life or have leisure time(4.16), and when they are o work for an excessively short time(4.16). This fact indicated that most of the dental technicians were exposed to a lot of stress in conjunction with job performance. 4. The main duties they took charge of didn't make any significant difference to their job stress, but yielded a significant difference to the extent of job stress in individual areas and the order of the most stressful one. Those who were engaged in grinding were most stressed from their own matters, whereas heavy workload was most stressful for those who were engaged in the other types of works. 5. As a result of seeing if their personal characteristics yielded any differences to job stress, the personal characteristics that made their job stress vary significantly were working hours, motivation of being a dental technician, job satisfaction and willingness to continue doing dental technology works. There was a tendency that longer working hours led to severer job stress, and those who chose to be a dental technician according to their own aptitude were less stressed than the others who became a dental technician because of economic reason or advices from others. And the people who were satisfied with their job were exposed to less job stress than the others who weren't, and those who had an intention to keep that job as much as possible were less stressed, compared to the others who hadn't.

• Journal of Dental Rehabilitation and Applied Science
• /
• v.27 no.2
• /
• pp.149-159
• /
• 2011

Restoring and replacing teeth with fixed prostheses commonly used in dental practice. Because of improper oral hygiene care and inaccurate laboratory procedure, complication of fixed prostheses was found in the mouth of patient. Although many efforts have been continually made to obtain the data of long term prognosis of fixed prostheses, it was difficult to do it. The purpose of this study was to evaluate the clinical status of fixed prostheses to improve the quality of dental care. In order to assess the clinical status of fixed prostheses, a total of 154 individuals (aged 22-82, 88 women and 66 men loaded with 578 unit of fixed prostheses, and 423 abutments) who visited the Department of Prosthodontics, Pusan National University Hospital, between January 2009 to December 2009 and removed old fixed prostheses were examined. The results of this study were as follows: 1. Length of service of fixed prostheses was $10.3{\pm}05.5$ years (mean), 10.0 years (median). 2. Location of fixed prostheses was found to have statistically significant influence on longevity of fixed prostheses (P<.05). The longevity of fixed prostheses was high in anterior-posterior combination region (mean:13.1, median:13.5) than anterior and posterior region. 3. Longevity of fixed prostheses made of metal was longest (mean:13.3, median:12.3). 4. Number of units in fixed prostheses was found to have no statistically significant influence on longevity of fixed prostheses (P>.05). 5. Condition of opposing dentition was found to have statistically significant influence on longevity of fixed prostheses (P>.05). The fixed prostheses lasted longest when opposed by complete denture (mean:17.1, median:19.7), removable partial denture, fixed prosthesis and natural dentition trailing behind (P<.05) 6. Periodontal disease (37.5%), dental caries (19.0%), defective margin (18.4%) were frequent complications. In 33.1% of the cases, abutment state after removing fixed prostheses was needed to be extracted.

• The Journal of Korean Academy of Prosthodontics
• /
• v.46 no.4
• /
• pp.381-395
• /
• 2008

Purpoose: For decades dental implants have been used widely in the field of prosthetic dentistry. However there is confusion when establishing treatment plans in cases where some teeth are remained but an insufficient number of implants can be used due to limited anatomical status and ecomomical problems. Many clinicians have tried to connect natural teeth and implants, and it still has controversy. But, there have been few studies on mechanical analysis of connecting natural teeth and implants with konus telescopic removable partial dentures. The purpose of this study was to analyze the stress distribution of prosthesis, abutment and alveolar bone when teeth and implants were connected with the konus telescopic denture, by means of 3-dimensional finite element analysis. Material and methods: The assumption of this study was that there were 2 mandibular canine (11 mm in length, 4 mm in diameter) and 2 implants(10 mm in length, 4 mm in diameter) which are located in the second premolar region. The mandible, teeth, implants, abutments, and connectors are modeled, and analyzed with the commercial software, ANSYS Version 8.1(Swanson, Inc., USA). The control group used implants instead of natural teeth. 21038 elements, 23544 nodes were used in experimental group and 107595 elements, 21963 nodes were used in control group, Stress distribution was evaluated under 150 N vertical load on 3 experimental conditions - between teeth and implants (Load case 1), posterior to implants (Load case 2), between natural teeth (Load case 3). Results: 1. In all load cases, higher von mises stress value was observed in the experimental group. 2. Maximum von miss stress observed in all load cases and all locations were as follows ; a. 929.44 Mpa in the experimental group, 640.044 Mpa in the control group in outer crown and connector - The experimental group showed 1.45 times high value compared with the control group. b. 145,051 Mpa in the experimental group, 142.338 Mpa in the control group in abutment - The experimental group showed 1.02times high value compared with the control group. c. 32.489 Mpa in the experimental group, 25.765 Mpa in the control group in alveolar bone - The experimental group showed 1.26times higher value compared with the control group. 3. All maximum von mises stress was observed in load case 2, and maxim von mises stress in alveolar bone was 32.489 Mpa at which implant failure cannot occur. 4. If maximum von mises stress is compared between two groups, the value of the experimental group is 1.02 times higher than the control group in abutment, 1.26 times higher than the control group in alveolar bone. Conclusion: If natural teeth and implants are connected with the konus telescopic denture, maximum stress will be similar in abutment, 1.26 times higher in alveolar bone than the control group. With this result, there may be possible to make to avoid konus telescopic dentures where natural teeth and implants exist together.