Retrospective study on survival and complication rates of posterior single implant according to the implant diameters, lengths and position / 대한치과보철학회지

Purpose@#. This retrospective study was to investigate the survival and complication rates of posterior single implant according to the implant diameters, lengths and position. @*Materials and methods@#. Patients who had been restored single implant prosthesis in the posterior area by the three prosthodontists in the department of prosthodontics, Daejeon dental hospital of Wonkwang university, in the period from February 2014 to May 2018 were selected for the study. A total of 505 patients with 697 implants were observed. The survival and complications of implants were investigated using electronic medical records and radiographs. Fixture diameters, lengths, position, patient’s sex and age were assessed as possible factor affecting the survival and complications of implants. @*Results@#. 3-year cumulative survival rates of posterior single implants were 98.5% and 5-year cumulative survival rates were 94.4%. 5-year cumulative survival rates were higher in implants with diameter > 4.0 mm (97.0%) than implants with diameter ≤ 4.0 mm (89.5%), and in females (98.8%) than males (92.4%). There were statistically significant differences (P 4.0 mm than implants with diameter ≤ 4.0 mm and in females than males. Abutment screw loosening which was the most commonly occurring complication occurred more frequently in the lower molar region, in males than females, and in patients aged < 65 years than patients aged ≥ 65 years. There were statistically significant differences.

Comparison of shear bond strength between various temporary prostheses resin blocks fabricated by subtractive and additive manufacturing methods bonded to self-curing reline resin / 대한치과보철학회지

Purpose@#This study aimed to compare and evaluate the shear bond strength between various temporary prostheses resin blocks fabricated by subtractive and additive manufacturing methods bonded to self-curing reline resin. @*Materials and methods@#The experimental groups were divided into 4 groups according to the manufacturing methods of the resin block specimens and each specimen was fabricated by subtractive manufacturing (SM), additive manufacturing stereolithography apparatus manufacturing (AMS), additive manufacturing digital light processing manufacturing (AMD) and conventional self-curing (CON). To bond the resin block specimens and self-curing resin, the reline resin was injected and polymerized into the same location of each resin block using a silicone mold. The shear bond strength was measured using a universal testing machine, and the surface of the adhesive interface was examined by scanning electron microscopy. To compare between groups, one-way ANOVA was done followed by Tukey post hoc test (α = 0.05). @*Results@#The shear bond strength showed higher values in the order of CON, SM, AMS, and AMD group. There were significant differences between CON and AMS groups, as well as between CON and AMD groups. but there were no significant differences between CON and SM groups (P > .05). There were significant differences between SM and AMD groups, but there were no significant differences between SM and AMS groups. The AMS group was significantly different from the AMD group (P < .001). The most frequent failure mode was mixed failures in CON and AMS groups, and adhesive failures in SM and AMD groups. @*Conclusion@#The shear bond strength of SM group showed lower but not significant bond strength compared to the CON group. The additive manufacturing method groups (AMS and AMD) showed significantly lower bond strength than the CON group, with the AMD group the lowest. There was also a significant difference between the AMD and SM group.

The survey on foreign body ingestion and aspiration during the dental prosthetic treatment

Purpose@#This study was to investigate the dentists’ experience and awareness of foreign body ingestion and aspiration during dental prosthetic treatment. @*Materials and Methods@#A survey of 157 dentists working at 108 dental institutions in Daejeon and Chungcheong provinces was carried out and frequency analysis was conducted. Chi-square test was conducted to find out the difference between the sociodemographic data and experience of foreign body ingestion and aspiration of patients and independent sample t-test was conducted to find out the difference in awareness depending on whether receiving related education. @*Results@#The percentage of dentists experiencing dropping foreign body into patients’ oral cavity was 99.4% and the percentage of dentists experiencing foreign body ingestion and aspiration of patients was 53.5%. There were more dentists who experienced foreign body ingestion and aspiration of patients in male than female, longer working career, and general practitioners than specialists (P < .05). 50.3% of the respondents received related education. When they receive related education, they had low degree of concern, high confidence in coping with situations, and low willingness to receive education in the future (P < .05). @*Conclusion@#The percentage of foreign body dropping was 16% higher in prosthetic treatment than general treatment. The percentage of dentists with experience of foreign body ingestion and aspiration of patients was 53.5%. Among them, 92.9% experienced foreign body ingestion of patients and 7.1% of them experienced foreign body aspiration of patients.

Pattern of Malocclusion Among Orthodontic Patients in East Coast of Sabah (Corak Maloklusi di Kalangan Pesakit Ortodontik di Pantai Timur Sabah) / Jurnal Sains Kesihatan Malaysia

@#This study reviewed the pattern of malocclusion among orthodontic patients in East Coast of Sabah and the type of treatment indicated for the patients. A total of 138 pre-treatment orthodontic records of patients who attended the orthodontic consultation clinic in year 2018 were included in this cross-sectional retrospective study. Data taken were demographic data, source of referral, BSI (British Standards Institutes) incisor classification, skeletal pattern, and type of treatment. All data were analysed descriptively using Stata 15. Based on the results, mean age of the patients was 16.89 ± 0.37 years. More females sought orthodontic treatment (n=101, 73.19%) than males. Majority of the patients were Chinese (n=68, 49.28%) and Bumiputera Sabah (n=55, 39.86%). Main source of referral was from dental officers (n=128, 92.75%). The distribution of malocclusion showed high percentage of Class II Division 1 (n=56, 40.58%), followed by Class III (n=45, 32.61%), Class I (n=34, 24.64%) and Class II Division 2 (n=3, 2.17%). For skeletal pattern, more patients presented with Class II (n=54, 39.13%), while the number of patients presented with Class I and Class III were equal (n=42, 30.43%). Class III malocclusion (n=29, 42.65%) and Class III skeletal pattern (n=29, 42.65%) were more common in Chinese patients. Treatment indicated was mostly fixed orthodontic appliance (n=120, 86.96%). In conclusion, Class II Division 1 malocclusion and Class II skeletal pattern were most common among the patients. Class III malocclusion and Class III skeletal pattern were typical features among the Chinese patients. Fixed orthodontic appliance was the most common treatment method.

Infection control of dental implant hand drivers using ethanol solution

Purpose@#The purpose of this study was to study the effects of the utilization of ethanol solution in infection control of dental implant hand drivers, a common practice in dental prosthodontic clinics. @*Materials and Methods@#Infection control methods were divided into two groups. One swabbed with 83% ethanol gauze and the other immersed in 83% ethanol solution for 30, 60, 90, 120, 150, 180 and 300 second intervals after inoculation of the dental implant hand drivers with Staphylococcus aureus. After measuring the number of colony forming units and analyzing the optical density, the effects of infection control in the experimental group were compared with the positive control group without infection control after inoculation with bacteria and the negative control group without inoculation with bacteria after sterilization. @*Results@#The number of colony forming units and optical density analysis showed a statistically significant difference compared to the positive control. On the other hand, there was no statistically significant difference between the negative control and the group immersed in the 83% ethanol solution for more than 150 seconds. @*Conclusion@#It is recommended to use the ethanol solution as a pre-cleaning process before sterilization, since the intermediatelevel disinfection method using ethanol solution alone for the infection control of the dental implant hand driver cannot clinically secure the sterility.

Infection control of dental implant hand drivers using ethanol solution

Purpose@#The purpose of this study was to study the effects of the utilization of ethanol solution in infection control of dental implant hand drivers, a common practice in dental prosthodontic clinics. @*Materials and Methods@#Infection control methods were divided into two groups. One swabbed with 83% ethanol gauze and the other immersed in 83% ethanol solution for 30, 60, 90, 120, 150, 180 and 300 second intervals after inoculation of the dental implant hand drivers with Staphylococcus aureus. After measuring the number of colony forming units and analyzing the optical density, the effects of infection control in the experimental group were compared with the positive control group without infection control after inoculation with bacteria and the negative control group without inoculation with bacteria after sterilization. @*Results@#The number of colony forming units and optical density analysis showed a statistically significant difference compared to the positive control. On the other hand, there was no statistically significant difference between the negative control and the group immersed in the 83% ethanol solution for more than 150 seconds. @*Conclusion@#It is recommended to use the ethanol solution as a pre-cleaning process before sterilization, since the intermediatelevel disinfection method using ethanol solution alone for the infection control of the dental implant hand driver cannot clinically secure the sterility.

Electroencephalographic Changes Induced by a Neurofeedback Training : A Preliminary Study in Primary Insomniac Patients / 수면정신생리

OBJECTIVES: Insomnia is one of the most prevalent sleep disorders. Recent studies suggest that cognitive and physical arousal play an important role in the generation of primary insomnia. Studies have also shown that information processing disorders due to cortical hyperactivity might interfere with normal sleep onset and sleep continuity. Therefore, focusing on central nervous system arousal and normalizing the information process have become current topics of interest. It has been well known that neurofeedback can reduce the brain hyperarousal by modulating patients' brain waves during a sequence of behavior therapy. The purpose of this study was to investigate effects of neurofeedback therapy on electroencephalography (EEG) characteristics in patients with primary insomnia. METHODS: Thirteen subjects who met the criteria for an insomnia diagnosis and 14 control subjects who were matched on sex and age were included. Neurofeedback and sham treatments were performed in a random order for 30 minutes, respectively. EEG spectral power analyses were performed to quantify effects of the neurofeedback therapy on brain wave forms. RESULTS: In patients with primary insomnia, relative spectral theta and sigma power during a therapeutic neurofeedback session were significantly lower than during a sham session (13.9 ± 2.6 vs. 12.2 ± 3.8 and 3.6 ± 0.9 vs. 3.2 ± 1.0 in %, respectively; p < 0.05). There were no statistically significant changes in other EEG spectral bands. CONCLUSION: For the first time in Korea, EEG spectral power in the theta band was found to increase when a neurofeedback session was applied to patients with insomnia. This outcome might provide some insight into new interventions for improving sleep onset. However, the treatment response of insomniacs was not precisely evaluated due to limitations of the current pilot study, which requires follow-up studies with larger samples in the future.

The Effectiveness of Two Manual Slim Bristles Toothbrushes among Fixed Orthodontic Appliance Patients / Jurnal Sains Kesihatan Malaysia

@#This research aimed to evaluate the oral hygiene status in fixed orthodontic appliance patients when using two different slim bristles toothbrushes and to assess patients’ toothbrush perception. Twenty six fixed orthodontic appliance patients participated in the six weeks prospective, crossover clinical trial. All patients used two different slim bristles toothbrushes (Toothbrush A and Toothbrush B) for two weeks each with a washout period in between. Gingival health and plaque value were assessed based on Lӧe & Silness Gingival Index and Silness & Lӧe Plaque Index at baseline, week 2, week 4 (washout) and week 6. At the end of the trial, patients’ toothbrush perception was assessed through questionnaire. All data were analysed using SPSS version 22. The mean age of the patients was 21.5 ± 4.3 years, with female predominant (n= 17, 65.4%). More than half were Malay (n= 15, 57.7%) and had tertiary education (n=14, 53.8%). Patients could achieve good oral hygiene when using Toothbrush A (65.4%) and Toothbrush B (69.2%). However, the occurrence of gingivitis was significantly higher when using Toothbrush A (OR=1.889, 95% CI=1.207-2.957, p value < 0.05). Toothbrush B was felt to clean better (n= 14, 53.8%) while Toothbrush A was perceived to be easier to use (n=14, 53.8%). Both toothbrushes maintained patients’ oral hygiene status. However, when using Toothbrush B, oral health status was better as it significantly reduced gingivitis occurrence compared to Toothbrush A. As for the toothbrush perception, most patients preferred Toothbrush A to be taken home.

The survey on the infection control of noncritical instruments used in dental treatment

PURPOSE: The aims of this study were to evaluate the dentist's awareness and the actual status of infection control of noncritical dental instruments. MATERIALS AND METHODS: 40 dental clinics in Daejeon, South Chungcheong, North Chungcheong and North Jeolla provinces were surveyed. The questionnaire was delivered to the dentists belonging to those clinics, and the awareness and the practice of infection control were examined. The microbial contamination on the surface of five noncritical instruments (impression gun, light curing unit, 3-way syringe, shade guide, and dental floss dispenser) used by them was measured with an ATP luminometer. Correlation analysis between the awareness and the actual state of infection control was conducted. RESULTS: Awareness and frequency of infection control was highest in the 3-way syringe. Surface disinfection using disinfectant was most frequent in all instruments. 3-way syringes and shade guides were less contaminated than impression guns, light curing units, and dental floss dispensers. CONCLUSION: 3-way syringes had a significant correlation between user awareness of infection control and surface contamination, and the higher awareness, the lower the contamination measurement was shown.

Prevention and management of foreign body ingestion and aspiration during the dental treatment

Prosthetic restorations through implants were popularized, and they became routine treatments. Small accessories used in the implant prosthodontic procedure are more likely to slip or fall off the dentist's hands. If the dental appliance or material passes into the upper gastrointestinal tract, there is a high possibility of excretion to the outside of the body without complications, but serious complications may occur depending on the type of foreign body. If the foreign body is passed to the airway, it is an emergency situation, and if it is not done properly, it can be fatal. The purpose of this review report is to investigate the process of foreign body ingestion or aspiration during dental treatment, and the method of prevention and treatment.

Retrospective study on marginal bone resorption around immediately loaded implants / 대한치과보철학회지

PURPOSE: Patients who treated implant immediate loading within a week after implant placement at Wonkwang University Dental Hospital Implant Center were evaluated marginal bone resorption. These retrospective analyses are intended to reinforce the clinical evidence for the implant immediate loading. MATERIALS AND METHODS: Medical history and radiographic data were investigated, which were the patients' who treated implant immediate loading and restoration with provisional prostheses between January 2005 and June 2016, at Wonkwang University Dental Hospital Implant Center. Total number of implants was 70, marginal bone resorption was measured according to implant length, diameter and connection type. To measure marginal bone resorption, periapical radiographs were taken when the implants were placed and after 6 month. Statistical analysis was done in Mann-whitney U test and Kruskal-wallis test with SPSS 22.0 software (P < .05). RESULTS: Mean marginal bone resorption around immediately loaded implants according to implant connection type was shown 1.24 ± 0.72 mm in internal hexagon connection type and 1.73 ± 1.27 mm in external hexagon connection type. There was no statically significant difference in marginal bone resorption with implant length and diameter. CONCLUSION: Implants with immediated loading in internal hexagon connection type showed less marginal bone resorption significantly than in external hexagon connection type.

Effect of abutment screw length and cyclic loading on removal torque in external and internal hex implants

PURPOSE: The purpose of this study was to evaluate the effects of abutment screw length and cyclic loading on the removal torque (RTV) in external hex (EH) and internal hex (IH) implants. MATERIALS AND METHODS: Forty screw-retained single crowns were connected to external and internal hex implants. The prepared titanium abutment screws were classified into 8 groups based on the number of threads (n = 5 per group): EH 12.5, 6.5, 3.5, 2.5 and IH 6.5, 5, 3.5, 2.5 threads. The abutment screws were tightened with 20 Ncm torque twice with 10-minute intervals. After 5 minutes, the initial RTVs of the abutment screws were measured with a digital torque gauge (MGT12). A customized jig was constructed to apply a load along the implant long axis at the central fossa of the maxillary first molar. The post-loading RTVs were measured after 16,000 cycles of mechanical loading with 50 N at a 1-Hz frequency. Statistical analysis included one-way analysis of variance and paired t-tests. RESULTS: The post-loading RTVs were significantly lower than the initial RTVs in the EH 2.5 thread and IH 2.5 thread groups (P<.05). The initial RTVs exhibited no significant differences among the 8 groups, whereas the post-loading RTVs of the EH 6.5 and EH 3.5 thread groups were higher than those of the IH 3.5 thread group (P<.05). CONCLUSION: Within the limitations of this study, the external hex implants with short screw lengths were more advantageous than internal hex implants with short screw lengths in torque maintenance after cyclic loading.

Management of osteoporosis patients for prosthetic restoration

The average life expectancy has been increased, so the proportion of elderly patients that visit to the dental clinic for prosthetic restoration has increased. Elderly patients have various chronic diseases. Recent trends show an increase of osteoporosis in elderly patients, and thus, the number of osteoporosis patients is expected to escalate. Currently, the most widely used drug for osteoporosis is bisphosphonate. However, osteonecrosis of the jaw has been reported as a side effect derived from long-term oral administration or injection treatment of the drug. Surgical dental treatment was the main cause of medication related osteonecrosis of the jaw (MRONJ). As MRONJ is very difficult to cure, it is important to take preventive measures. Surgical operation may be needed for the mouth preparation before prosthetic restoration. For successful treatment, the dentist should have a full understanding of osteoporosis and show a continued interest toward this disease for careful management.

Three dimensional accuracy analysis of dental stone casts fabricated using irreversible hydrocolloid impressions

PURPOSE: The objects of this study was to evaluate the accuracy of the dental stone casts made from alginate impressions according to storage condition and stone pouring time. MATERIALS AND METHODS: Each of upper and lower impressions of dental model was taken. The dental stone models were made immediately, 10, 30, 60, 180, 360 minutes after the impressions were taken at each storage condition. 3D models were constructed by scanning the stone model using 3D laser scanner. With Reference points, positioned on digital models, linear measurements of the dimensional change were compared by 3D metrology software, 3D average models were made and superimposition to identify the specific site of dimensional change and to measure surface deviation (mm). RESULTS: Dental stone models which were made immediately after taking the impression showed the smallest linear dimensional change. As the stone pouring time was prolonged, the linear dimensional change was increased. More than 180 minutes after impression taking, linear dimensional change and surface distortion increased in the posterior molar region, regardless of the storage condition. CONCLUSION: For the optimum accuracy of the dental stone casts, alginate impression should be poured as soon as possible. If there were a need for storing, a humidor with 100% relative humidity must be used and be stored less than 180 minutes to fabricate the accurate dental model.

The study of awareness and practice of infection control on dental practitioners during the prosthodontic treatment / 대한치과보철학회지

PURPOSE: The aim of this study was to assess the degree of awareness and actual practice of dental practitioners regarding infection control during prosthodontic treatment. MATERIALS AND METHODS: Study participants were composed of dentists, dental hygienists, dental technicians working at dental university hospital, general hospital, dental hospital and dental clinics in Daejeon, Korea (n=126). The questionnaires included the data on general characteristics, education, awareness and practice of infection control procedures during prosthodontic treatment through personal self-administration survey. Awareness and practice were measured by Likert scale ranging from 1 to 5. Statistical analysis was done by one-way ANOVA. Influence of awareness on practice was estimated by regression analysis. RESULTS: 27.7% of the respondents answered that the infection control education regarding prosthodontic treatment is insufficient. The mean value of awareness and practice of infection control during the prosthodontic treatment were 2.72 +/- 0.80, 1.58 +/- 0.88, respectively. The mean value of practice who answered that had education curriculum at college was 1.62 +/- 0.9, and 1.31 +/- 0.49 who did not. The mean value of awareness who equipped guideline was 3.01 +/- 0.9, and 2.56 +/- 0.70 who did not. CONCLUSION: 1. The respondents who received the infection control education by college curriculum showed higher degree of practice than the respondents who did not. 2. The respondents who have appropriate infection control guidebook in their workplace showed higher degree of awareness than the respondents who did not. 3. There was a correlation between the awareness and practice of infection control during prosthodontic treatment; the degree of awareness becomes higher, so does the degree of practice. 4. During the prosthodontic treatment, the degree of practice was lower than the degree of awareness on infection control.

Clinical study on the food impaction between implant prostheses and adjacent teeth / 대한치과보철학회지

PURPOSE: The purpose of this study was to investigate the food impaction between implant prostheses and adjacent natural teeth. MATERIALS AND METHODS: For this study, 51 patients with food impaction were selected and investigated mobility, tightness of contact area, gingival index, plaque index, attachment loss, alveolar bone level, proximal caries, marginal ridge distance and occlusal relationships. RESULTS: Food impaction was found in the upper teeth (60.7%) more than the lower teeth (39.2%). Food impaction was occurred on mesial side of implant prostheses (86.2%) more than distal side (13.7%). Food impaction was mostly found in loose or open contact area (94.2%). Food impaction was frequent on stepped relationship between implant and adjacent teeth. CONCLUSION: Treatment plan should include proper adjacent and antagonistic occlusal plane and occlusal surface, to prevent food impaction, and the plan should include less adjacent tooth mobility with proper tightness between implant prostheses and adjacent teeth.

A study on accuracy and application of the implant torque controller used in dental clinic / 대한치과보철학회지

PURPOSE: This study was to evaluate the accuracy of the implant torque controller used in dental clinics and to investigate whether it was applied appropriately. MATERIALS AND METHODS: Fifty dentists who work in dental clinics were enrolled in this study. Dental (implant) practice career, experience frequency of implant screw loosening and fracture, education of implant torque controller application and infection control methods were included in the survey. 25 Ncm and 30 Ncm of the tightening torque applied to the implant screw were measured by 50 clinicians. After measuring the torque value by using the torque controller, the torque mean according to where education about the implant torque controller was received was analyzed with independent t-test at the significance level of 0.05. RESULTS: The torque controller used in private dental clinics showed 4.78% error ratio. When 50 dentists applied 25 Ncm to the implant screw was 29.0 +/- 8.4 Ncm, and that in 30 Ncm was 34.3 +/- 9.1 Ncm. Statistical significance was found between the group that was educated about implant torque application and the group that was not educated. CONCLUSION: During the prosthodontic treatment with implant, there was difference between actual applied torsion force and the amount torque controller indicated. Clinicians have to not only be well-informed about the accurate usage method of the torque controller, but also keep and manage the torque controller so as to maintain continuous and accurate torque values. Through this, it is considered to achieve clinical results to minimize problems of screw loosening or fracture.

A Study on the Fitness of Adjustable Dental Impression Trays on the Chinese and Japanese / 대한치과보철학회지

PURPOSE: This study was designed to investigate the fitness of adjustable dental impression trays on the Chinese and the Japanese. MATERIAL AND METHODS: Initial design of the adjustable dental trays was developed from the results of the dental arch size of Korean adults. This design was applied to the CAD-CAM process in order to create tray model samples. Simple silicon-base molds were then replicated based on these sample models. Polyurethane injection into the silicon-base molds completed the process of creating a large number of test products. 60 Chinese dental students (male:30, female:30) from the Shanghai Second Medical University and 60 Japanese alumni from the Kumamoto high school (male:30, female:30) were selected for taking irreversible hydrocolloid impression with these trays. The width and length of the impression body were measured on several measuring points by Vernier caliper. The results were analyzed statistically to evaluate the fitness of the trays. RESULTS: 1. Uniform impression material thickness was achieved on the Chinese and Japanese by controlling the width of the tray using stops and beveled guides. The material thickness was generally within the range of 3 mm to 6 mm. 2. In the maxillary tray of the Chinese, average thickness of the impression material of the labial vestibule of the incisal teeth was 6.2 mm, the canine was 5.9 mm and the midpalatal part 10.5 mm and the posterior palatal part 9.7 mm. These were relatively large values. 3. In the mandibular tray of the Chinese, average length of the impression material of the lingual vestibule of first, second premolar contact point was 8.9 mm, the incisal teeth was 7.8 mm and thickness of the labial part of canine was 6.8 mm and premolars 7.0 mm. These were relatively large values. 4. In the maxillary tray of the Japanese, average thickness of the impression material of the labial vestibule of the incisal teeth was 7.4 mm, the canine was 7.7 mm and the midpalatal part 9.1 mm. These were relatively large values. 5. In the mandibular tray of the Japanese, average thickness of the impression material of the labial vestibule of first, second premolar contact point was 8.4 mm, and thickness of the labial part of canine was 7.4 mm. These were relatively large values. CONCLUSION: This adjustable dental tray shows good accuracy to Korean because it was designed by the analysis of the dental arch size of Korean adult model. With this result, it can be applied to Chinese and Japanese, we can take more easy and accurate dental impressions.

Fracture strength of the IPS empress crown: The effect of occlusal using depth and axial inclination on lower first molar / 대한치과보철학회지

The purpose of this study was to compare the fracture strength of the IPS Empress ceramic crown according to the occlusal depth (1.5mm, 2.0mm, 2.5mm) and axial inclination (4degree, 8degree, 12degree) of the lower First Molar. After 10 metal dies were made for each group, the IPS Empress ceramic crowns were fabricated and cemented with resin cement(Bistite resin cement, Tokuyama Soda Co. LTD., Japan). The cemented crowns were mounted on the testing jig with inclination of 30 degrees and the universal testing machine(Zwick Z020, Zwick, Germany)was used to measure the fracture strength. The results of this study were as follows : 1. The fracture strength of the ceramic crown with 2.5mm depth and 12degree inclination was the highest (1789 N). Crowns of 1.5 mm depth and 4degree inclination had the lowest strength (1091 N). 2. There were no significant differences in the fracture strength by axial inclination of the same occlusal depth group. 3. Most fracture lines began at the loading area and extended through proximal surface perpendicular to the margin, irrespective of occlusal depth. Size of fragment was affected by the amount of occlusal reduction.

The fracture resistance and stress distribution of all ceramic crowns with two types of finish line on maxillary central incisor / 대한치과보철학회지

PURPOSE: The purpose of this sudy was to compare the fracture resistance of the IPS Empress ceramic crown with 1.0mm width rounded shoulder, which is usually recommended in all ceramic crown, and 0.5mm width chamfer finish lines on the maxillary central incisor. MATERIAL AND METHOD: After 15 metal dies were made for each group, the IPS Empress all ceramic crowns were fabricated and cemented with resin cement(Bistite resin cement, Tokuyama Soda Co. LTD., Japan) on the metal die. The cemented crowns were mounted on the positioning jig and the universal testing machine(Zwick Z020, Zwick Co, Germany)was used to measure the fracture strength, with loading on the incisal edge. And also, three-dimensional finite element stress analysis was used to measure the stress distribution with the various types of the finish lines(1.0mm width rounded shoulder, 0.5mm width chamfer), the loading site(incisal edge, incisal 1/3), and the type of loading(concentration loading, distribution loading). RESULTS AND CONCLUSION: 1. In the fracture resistance experiment according to the finish line, the mean fracture strength of rounded shoulder(876N) and the mean fracture strength of chamfer(882N) did not show any significant difference between each other(p<0.05). 2. The stress distribution of all ceramic crown in three dimensional finite element analysis showed concentration aspect at loading point and cervical area of labial surface. 3. In metal die, there were no differences in stress distribution between finish lines, but in natural teeth model, chamfer finish line showed higher stress than rounded shoulder finish line. 4. When force was loaded on the incisal edge, the stress was concentrated on the incisal edge and the cervical area of labial surface. When force was loaded on the incisal 1/3, the stress concentrated on the cervical area of labial surface and the cingulum area. 5. Generally, natural teeth model showed higher and various stress than the metal die.