• Journal of Dental Rehabilitation and Applied Science
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• v.26 no.3
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• pp.221-239
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• 2010

Bone loss may occur depending on the loading conditions. careful treatment planning and prosthetic procedures are very important factors for the proper distribution of stress. Evaluate the stress distributions according to numbers and location of implants in three-unit fixed partial dentures. A mandible missing the right second premolar, first molar and second molar was modeled. Using the CT data. we modeled a mandible with a width of 15mm, a height of 20mm and a length of 30mm, 2mm-thickness cortical bone covering cancellous bone mallow. An internal type implant and A solid type abutment was used. A model with 3 implants placed in a straight line, offset 1.5 mm buccally, offset 1.5 mm lingually and another model with 3 implants offset in the opposite way were prepared. And models with 2 implants were both end support models, a mesial cantilever model and a distal cantilever model. Three types of loading was applied; a case where 155 N was applied solely on the second premolar, a case where 206 N was applied solely on the second molar and a case where 155 N was applied on the first premolar and 206 N was applied on the first and second molar. For all the cases, inclined loads of 30 degrees were applied on the buccal cusps and vertical loads were applied on the central fossas of the teeth. Finite element analysis was carried out for each case to find out the stress distribution on bones and implants. This study has shown that prostheses with more implants caused lower stress on bones and implants, no matter what kind of load was applied. Furthermore, it was found out that inclined loads applied on implants had worse effects than vertical loads. Therefore, it is believed that these results should be considered when placing implants in the future.

• The Journal of Korean Academy of Prosthodontics
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• v.51 no.3
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• pp.160-166
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• 2013

Purpose: The purpose of this study was to compare the fracture strength of traditional metal-ceramic crowns and full zirconia crowns according to the occlusal thickness. Materials and methods: A mandibular first molar resin tooth was prepared with 1.5 mm occlusal reduction, 1.0 mm rounded shoulder margin and $6^{\circ}$ taperness in the axial wall. Duplicating the resin tooth, 64 metal dies were fabricated. 48 full zirconia crowns were fabricated using Prettau zirconia blanks by ZIRKONZAHN CAD/CAM and classified into six groups according to the occlusal thickness (0.5 mm, 0.6 mm, 0.7 mm, 0.8 mm, 0.9 mm, 1.0 mm). 16 metal-ceramic crowns were fabricated and classified into two groups according to the occlusal porcelain thickness (1.0 mm, 1.5 mm). All crowns were cemented on each metal die and mounted in a universal testing machine. The load was directed at the functional cusp of each specimen until catastrophic failure occurred. One-way ANOVA, Tukey multiple comparison test (${\alpha}=.05$) and t-test (${\alpha}=.05$) were used. Results: The results were as follows. 1. The test 1 group (646.48 N) showed the lowest fracture strength (P<.05), and the value of the test 2.3.4.5 groups (866.40 N, 978.82 N, 1196.82 N, 1222.41 N) increased as thickness increased, but no significant difference were found with the groups (P>.05). The value of test 6 group (1781.24 N) was significantly higher than those of the other groups (P<.05). 2. There were no significant differences of the fracture strength of metal ceramic crowns according to occlusal porcelain thickness 1.0 mm (2515.71 N) and 1.5 mm (3473.31 N) (P<.05). Conclusion: Full zirconia crown needs to be 1.0 mm or over in occlusal thickness for the posterior area to have higher fracture strength than maximum bite force.

• The Journal of Korean Academy of Prosthodontics
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• v.51 no.3
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• pp.147-152
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• 2013

Purpose: The aim of this study was to propose the position of maxillary anterior teeth and intercanine width measurements based on the incisive papilla in accordance with the cephalic type and gender of dentate Korean adult with normal teeth alignment. Materials and methods: 42 students with Class I normal occlusion, without crowding or spacing, were selected from the Chonnam National University School of Dentistry. The lateral skull radiographs of the subjects were taken and were classified as different cephalic types, based on their PFH / AFH ratios. 42 casts of their maxilla were prepared and both the distance between the upper central incisors and the middle of the incisor papilla was measured with a vernier caliper (A) and the distance between the maxillary canine cusp tips (B) were measured. Statistical analysis was performed using SPSS version 15 and their significance was investigated. Results: For dolichocephalic group, the mean values for A and B were 8.43 (SD: 0.61) and 36.73 (SD: 2.17), respectively. The mean value for A was 8.51 (SD: 1.27) for the mesocephalic group and 8.76 (SD 1.03) for the brachycephalic group. The mean value for B was 35.91 (SD: 1.86) for the mesocephalic group and 37.34 (SD: 2.23) for the brachycephalic group. For the male group, the mean A value was 8.86 (SD: 1.04) and the mean B value was 37.60 (SD: 0.24). For the female group, the mean A value was 8.41 (SD: 0.93) and the mean B value was 36.18 (SD: 2.01). The difference between male and female group in A values were not statistically significant (P>.05). The B values of the male subjects were greater than those of the female subjects and was statistically significant (P<.05). Conclusion: 42 students with normal dentition and occlusion in korea, the distance from the incisive papilla and the incisal edge of maxillary central incisors had no difference in cephalic type or gender. However, the distance between the cusp tip of both canines had significant difference in gender where the male showed higher values than the female, while having no difference in cephalic types.

• Journal of Dental Rehabilitation and Applied Science
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• v.35 no.4
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• pp.214-219
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• 2019

Purpose: The aim of this study was to evaluate the correlation between inter-condylar width and inter-maxillary first molar width to present the criteria for prosthetic reconstruction of dental arch width in maxillary and mandibular fully edentulous patients. Materials and Methods: 120 Koreans (60 males and 60 females) who underwent the cone beam computerized tomography (Cone-beam CT) were selected. The Cone-beam CT images were analysed using Invivo 5.1. After reorientation of axis, inter-maxillary first molar width was measured by clicking both mesio-buccal cusp tip of maxillary first molar. And inter-condylar width was measured by clicking both middle points of condyles. The collected data were analysed with SPSS Version 20.0 and statistical significance of the correlation between inter-condylar width and inter-maxillary first molar width was verified by Pearson's correlation analysis. Results: The mean inter-condylar width of Korean was 105.9 mm, and that of male (108.3 mm) was statistically significantly wider than the female (103.4 mm). The inter-maxillary first molar width of Korean was 57.1 mm, and that of male (57.9 mm) was statistically significantly wider than the female (56.2 mm). Pearson's correlation analysis between inter-condylar width and inter-maxillary first molar width showed a Pearson correlation coefficient of 0.614 and statistically significantly positive correlation. Conclusion: Intercondylar width and inter-maxillary first molar width showed positive correlation and the average ratio of inter-condylar with and inter-maxillary first molar width was 1:0.54. Based on the results of this limited study, inter-condylar width can be used as a guide for setting up dental arch width in fully edentulous patient.

• Journal of Dental Rehabilitation and Applied Science
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• v.37 no.3
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• pp.130-137
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• 2021

Purpose: The various suture techniques can be utilized in order to maximize the keratinized tissue healing around dental implants. The aim of this study is to compare the soft tissue healing pattern between two different suture techniques after implant placement. Materials and Methods: 15 patients with 18 implants were enrolled in this study. Simple implant placement without any additional bone graft was performed. Two different suture techniques were used to tug in the mobilized flap near the healing abutment after paramarginal flap design. Digital intraoral scan was performed at baseline, post-operation, stitch out, and 3 months after operation. The scan data were aligned using multiple points such as cusp, fossa of adjacent teeth, and/or healing abutment. After subtracting scan data at baseline with other time-point results, closed space indicating volume increment of peri-implant mucosa was selected. The volume of the close space was measured in mm³. The volume between two suture techniques at three time-points was compared using nonparametric rank-based analysis. Results: Healing was uneventful in both groups. Both suture technique groups showed increased soft tissue volume immediately after surgery. The amount of volume increment significantly decreased after 3 months (P < 0.001). Flap folding suture group showed higher median of volume increment than interrupted suture group after 3 months without any statistical significance (P > 0.05). Conclusion: After paramarginal flap reflection, the raised flaps stabilized by flap folding suture showed relatively higher volume maintenance after 3-month healing period. However, further studies are warranted.

• Journal of Dental Rehabilitation and Applied Science
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• v.36 no.4
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• pp.254-261
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• 2020

Purpose: The purpose of this study was to assess the marginal and internal fit of interim crowns fabricated by two different manufacturing method (subtractive manufacturing technology and additive manufacturing technology). Materials and Methods: Forty study models were fabricated with plasters by making an impression of a master model of the maxillary right first molar for ceramic crown. On each study model, interim crowns (n = 40) were fabricated using three types of 3D printers (Meg-printer 2; Megagen, Zenith U; Dentis, and Zenith D; Dentis) and one type milling machine (imes-icore 450i; imes-icore GmbH). The internal of the interim crowns were filled with silicon and fitted to the study model. Internal scan data was obtained using an intraoral scanner. The fit of interim crowns were evaluated in the margin, absolute margin, axial, cusp, and occlusal area by using the superimposition of 3D scan data (Geomagic control X; 3D Systems). The Kruskal-wallis test, Mann-Whitney U test and Bonferroni correction method were used to compare the results among groups (α = 0.05). Results: There was no significant difference in the absolute marginal discrepancy of the temporary crown manufactured by three 3D printers and one milling machine (P = 0.812). There was a significant difference between the milling machine and the 3D printer in the axial and occlusal area (P < 0.001). The temporary crown with the milling machine showed smaller axial gap and higher occlusal gap than 3D printer. Conclusion: Since the marginal fit of the temporary crown produced by three types of 3D printers were all with in clinically acceptable range (< 120 ㎛), it can be sufficiently used for the fabrication of the temporary crown.

• Journal of Oral Medicine and Pain
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• v.33 no.3
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• pp.279-294
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• 2008

This study aimed to make an analysis of the occlusion in the state of muscle fatigue produced by excessive mouth opening and clenching during the dental treatment to control the dental pain and to evaluate the sensory nerve in the muscle pain state. Most of the reasons why patients visit the dental office result in pain-either conceivably the dental origin pain or the non-dental origin pain. The dental offices have many therapeutic actions to produce the masticatory muscle fatigue for the treatment. Dental treatment with long minutes of mouth opening can cause some headaches, masticatory muscle pain and mouth opening difficulties. Patients with mastication problems who visits a dental office to alleviate pain run against another unexpected pain with other aspects. This study uses T-scan II system(Tekscan Co., USA) for the evaluation on the occlusal pattern in the experimental muscle fatigue after clenching, opening the mouth excessively and chewing gum. The occlusal contact pattern is analyzed by the contact timing, namely first, intercuspal, maximum and end point of contact. This inspection was performed at frequencies of 2000Hz, 250 Hz and 5 Hz before and after each experimental muscle pain was produced to 24 subjects who had normal occlusion without the orthodontic treatment or a wide range of the prosthesis by using $neurometer^{\circledR}$ CPT/C(Neurotron, Inc. Baltimore, Maryland, USA). The measuring sites were mandibular nerve experimental muscle fatigue respectively. This study could obtain the following results after the assessment of occlusion and sensory nerve of the experimental muscle fatigue. 1. There were the fastest expression after the excessive mouth opening in muscle fatigue and after tooth clenching in muscle pain. In the visual analog scale that records the subjective level, there was the highest scale after the clenching in the muscle fatigue in jumping off the point of pain. 2. Tooth contact time, contact force, relative contact force on the point of the first contact had no difference, and there were decreases in the contact force after the excessive mouth opening on intercuspal position point, after the excessive mouth opening and the gum chewing on the point of the maximum, and in the contact time after all the experimental muscle fatigue state on the point of the end contact. 3. There was no statistic significance in the current perception threshold before and after the experimental muscle fatigue. 4. There was no significant difference in the contact number, the maximal contact number on the point of the first contact, and the contact number after the mouth opening and gum chewing on the point of the intercuspal position and the contact number after the experimental muscle fatigue on the maximum point, and showed significant decreases. In conclusion, it was found that the occlusal pattern can cause the changes on the case of the clinical muscle weakness by intra-external oral events. It was important that the sedulous attention to details is required during dental treatment in case of excessive mouth opening, mastication and clenching.

• The Journal of Korean Academy of Prosthodontics
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• v.49 no.1
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• pp.38-48
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• 2011

Purpose: Dentists suffer back, neck and shoulder pain during their careers due to bad operating posture. If dentists have a good operating posture ergonomically, there would be less pain and discomfort in the shoulder and back. Therefore, dentists should learn the Home position which enables dentists to approach a stable posture ergonomically. This study was to compare tooth preparation in the Home position and the Random position, and evaluate the clinical efficacy of the Home position. Materials and methods: Tooth preparation for fixed partial denture was performed on the maxillary left 2nd premolar and maxillary left 2nd molar at the two different operating positions were compared. The amount of occlusal reduction, marginal width, subgingival margin depth, and convergence angle were measured. A T-test was performed separately to compare the results of the Random position and the Home position. Results: 1. The amounts of average thickness of occlusal reduction on fossa were deficient to the ordered ones in the Random position and the Home position (P > .05). 2. The average subgingival margin depth of prepared margin on maxillary left 2nd premolar, maxillary left 2nd molar were excessive in the Random position than in the Home position. On the maxillary left 2nd premolar, there was no statistical difference in the Random position and the Home position except Distal midline, DL line angle, Lingual midline, ML line angle (P< .05). On the maxillary left 2nd molar, there was no statistical difference in the Random position and the Home position (P < .05). 3. Average convergence angle in the Random position and the Home position were excessive compared to the ordered angle. There was no statistical difference in the Random position and the Home position (P > .05). 4. Analysis of pearson correlation : In the Random position, the amounts of average thickness of occlusal reduction, the average subgingival margin depth of prepared margin, convergence angle were significantly associated with each other (P < .05). But in the Home position, they were not significantly associated with each other (P < .05). 5. The time needed for preparation in the Home position was faster or equal than that of the Random position as time went on. Conclusion: In conclusion, there were no significant differences between Home position and Random position in measures of occlusal reduction, marginal width, marginal depth, convergence angle. However, preparation time and incidence of damaging adjacent teeth were less in Home position than in Random position. Therefore, if trained properly, Home position which is more ergonomically stable can be adopted for clinical use.

• The Journal of Korean Academy of Prosthodontics
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• v.47 no.4
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• pp.365-375
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• 2009

Statement of problems: Stress analysis on implant components of the combined screw- and cement-retained implant prosthesis has not investigated yet. Purpose: The purpose of this study was to assess the load distribution characteristics of implant prostheses with the different prosthodontic retention types, such as cement-type, screw-type and combined type by using 3-dimensional finite element analysis. Material and methods: A 3-dimensional finite element model was created in which two SS II implants (Osstem Co. Ltd.) were placed in the areas of the first premolar and the first molar in the mandible, and three-unit fixed partial dentures with four different retention types were fabricated on the two SS II implants. Model 1 was a cement-retained implant restoration made on two cement-retained type abutments (Comocta abutment; Osstem Co. Ltd.), and Model 2 was a screw-retained implant restoration made on the screw-retained type abutments (Octa abutment; Osstem Co. Ltd.). Model 3 was a combined type implant restoration made on the cement-retained type abutment (Comocta abutment) for the first molar and the screw-retained type abutment (Octa abutment) for the first premolar. Lastly, Model 4 was a combined type implant restoration made on the screw-retained type abutment (Octa abutment) for the first molar and the cement-retained type abutment (Comocta abutment) for the first premolar. Average masticatory force was applied on the central fossa in a vertical direction, and on the buccal cusp in a vertical and oblique direction for each model. Von-Mises stress patterns on alveolar bone, implant body, abutment, abutment screw, and prosthetic screw around implant prostheses were evaluated through 3-dimensional finite element analysis. Results: Model 2 showed the lowest von Mises stress. In all models, the von Mises stress distribution of cortical bone, cancellous bone and implant body showed the similar pattern. Regardless of loading conditions and type of abutment system, the stress of bone was concentrated on the cortical bone. The von-Mises stress on abutment, abutment screw, and prosthetic screw showed the lower values for the screw-retained type abutment than for the cement-retained type abutment regardless of the model type. There was little reciprocal effect of the abutment system between the molar and the premolar position. For all models, buccal cusp oblique loading caused the largest stress, followed by buccal cusp vertical loading and center vertical loading. Conclusion: Within the limitation of the FEA study, the combined type implant prosthesis did not demonstrate more stress around implant components than the cement type implant prosthesis. Under the assumption of ideal passive fit, the screw-type implant prosthesis showed the east stress around implant components.