• The Journal of Advanced Prosthodontics
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• v.15 no.3
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• pp.155-170
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• 2023

PURPOSE. This study aims to clinically compare the fitness and trueness of zirconia crowns fabricated by different combinations of open CAD-CAM systems. MATERIALS AND METHODS. Total of 40 patients were enrolled in this study, and 9 different zirconia crowns were prepared per patient. Each crown was made through the cross-application of 3 different design software (EZIS VR, 3Shape Dental System, Exocad) with 3 different processing devices (Aegis HM, Trione Z, Motion 2). The marginal gap, absolute marginal discrepancy, internal gap(axial, line angle, occlusal) by a silicone replica technique were measured to compare the fit of the crown. The scanned inner and outer surfaces of the crowns were compared to CAD data using 3D metrology software to evaluate trueness. RESULTS. There were significant differences in the marginal gap, absolute marginal discrepancy, axial and line angle internal gap among the groups (P < .05) in the comparison of fit. There was no statistically significant difference among the groups in terms of occlusal internal gap. The trueness ranged from 36.19 to 43.78 ㎛ but there was no statistically significant difference within the groups (P > .05). CONCLUSION. All 9 groups showed clinically acceptable level of marginal gaps ranging from 74.26 to 112.20 ㎛ in terms of fit comparison. In the comparison of trueness, no significant difference within each group was spotted. Within the limitation of this study, open CAD-CAM systems used in this study can be assembled properly to fabricate zirconia crown.

• Journal of Technologic Dentistry
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• v.22 no.1
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• pp.5-12
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• 2000

The gaps between the die margin worked and the casting body were measured with an optical microscope and compared after making crown prosthetic materials using three kinds of die material - dental stone, extra hard stone, epoxy resin - used in crown prosthesis. The results are as follows : 1. All the gaps between the cast cervical margin and the casting bodies were relatively good regardless of die materials used with the gaps under $50{\mu}m$, the allowable limit. 2. The cervical margin suitability of epoxy resin die was the highest among the three kinds of die material with the suitability value of $30.28{\pm}12.67$. 3. Among the four surfaces(buccal, lingual, mesial, distal) of all the casting bodies, buccal surface was the highest in the cervical margin suitability with the value of $25.93{\pm}15.51$.

• Journal of Technologic Dentistry
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• v.33 no.4
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• pp.283-289
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• 2011

Purpose: The purpose of this study was to evaluate flexural strength of full zirconia crown using block after clinical work. Methods: The three point bending test was used to measure the flexural strength of zirconia block. Statistical analysis was done using the Statistical Package for Social Sciences version 19.0 for Windows. As for the analysis methods, the study used analysis of variance, Tukey's test. Results: The ave Rage value of flexural strengths of WIELAND, Zirkonzahn, Hass, D-MAX were 516.2 MPa, 612.6MPa, 566.2MPa, 744.6MPa. The ave Rage value of Surface Roughness of WIELAND, Zirkonzahn, Hass, D-MAX were 0.39Ra, 0.33Ra, 0.33Ra, 0.47Ra. Conclusion: Flexural strength of zirconia block decreased after clinical work. Flexural strength of zirconia block is equal to or higher than flexural strength of dental metal, so zirconia block can be used as dental material.

• Journal of Technologic Dentistry
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• v.38 no.3
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• pp.151-156
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• 2016

Purpose: The dental implant should be enough to endure chewing load and it's required to have efficient design and use of implant to disperse the stress into bones properly. This study was to evaluate the stress distribution on a supporting bone by lengths and diameters of the implant fixture. Methods: The modeling and analysis of stress distribution was used for the simple molar porcelain crown model by Solidworks as FEM program. It was designed on applying with tightening torque of 20 Ncm of a abutment screw between a cement retained crown abutment and a fixture. The fixtures of experimental model used 10, 13mm by length and 4, 5mm by diameter. A external vertical loading on the two buccal cusps of crown and performed finite element analysis by 100 N. Results: The maximum von Mises stress(VMS) of all supporting bone models by fixture length and diameter were concentrated on the upper side of supporting compact bone. The maximum stress of each model under vertical load were 164.9 MPa of M410 model, and 141.2 MPa of M413 model, 54.3 MPa of M510 model, 53.6 MPa of M513 model. Conclusion: The stress reduction was increase of fixture's diameter than it's length. So it's effective to use the wider fixture as possible to the conditions of supporting bone.

• The Journal of the Korean dental association
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• v.11 no.12
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• pp.787-799
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• 1973

Surveying the calcification degree of permanent tooth crown in 719 Korean children (Male 387, female 332) from 2 to 10 years old by orthopantomograph, the author got the following results. 1. Female was earlier than male in calcification of permanent teeth. 2. The results of the complete calcification of the permanent tooth crown were as follows. 3. The completion of calcification in the mandibular crown was seen earlier than that of the maxilla. 4. The order of calcification in permanent tooth crowns was as follows : 1 st molar, central incisor, lateral incisor, canine, 1st premolar, 2nd premolar, and 2nd molar. 5. The completion of calcification of the permanent crowns in Korean children was slightly retarded comparing with the Japanese and the American children.

• Proceedings of the KACD Conference
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• 2003.11a
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• pp.581-581
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• 2003

The purpose of this study was to search non-invasive and reproductive pulp test. Temperature of the crown surface was measured using the infrared thermography, and the pulp test was investigated with difference of crown temperature of the vital and the non-vital tooth in vitro and in vivo. Twenty extracted human maxillary central incisors were used in this study. Two sample teeth after access cavity preparation were arranged setting with one pair. Then, the each tooth wes estimated as the vital and the non-vital tooth.(중략)

• The Journal of Advanced Prosthodontics
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• v.13 no.2
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• pp.89-99
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• 2021

PURPOSE. This study aimed to compare the accuracy (trueness and precision) of interim crowns fabricated using DLP (digital light processing) according to post-curing time. MATERIALS AND METHODS. A virtual stone study die of the upper right first molar was created using a dental laboratory scanner. After designing interim crowns on the virtual study die and saving them as Standard Triangulated Language files, 30 interim crowns were fabricated using a DLP-type 3D printer. Additively manufactured interim crowns were post-cured using three different time conditions-10-minute post-curing interim crown (10-MPCI), 20-minute post-curing interim crown (20-MPCI), and 30-minute post-curing interim crown (30-MPCI) (n = 10 per group). The scan data of the external and intaglio surfaces were overlapped with reference crown data, and trueness was measured using the best-fit alignment method. In the external and intaglio surface groups (n = 45 per group), precision was measured using a combination formula exclusive to scan data (10C2). Significant differences in accuracy (trueness and precision) data were analyzed using the Kruskal-Wallis H test, and post hoc analysis was performed using the Mann-Whitney U test with Bonferroni correction (α=.05). RESULTS. In the 10-MPCI, 20-MPCI, and 30-MPCI groups, there was a statistically significant difference in the accuracy of the external and intaglio surfaces (P<.05). On the external and intaglio surfaces, the root mean square (RMS) values of trueness and precision were the lowest in the 10-MPCI group. CONCLUSION. Interim crowns with 10-minute post-curing showed high accuracy.

• The Journal of Advanced Prosthodontics
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• v.13 no.2
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• pp.79-88
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• 2021

Purpose. To assess peri-implant stress distribution using finite element analysis in implant supported fixed partial denture with occlusal schemes of cuspally loaded occlusion and implant protected occlusion. Materials and methods. A 3-D finite element model of mandible with D2 bone with partially edentulism with unilateral distal extension was made. Two Ti alloy identical implants with 4.2 mm diameter and 10 mm length were placed in the mandibular second premolar and the mandibular second molar region and prosthesis was given with the mandibular first molar pontic. Vertical load of 100 N and and oblique load of 70 N was applied on occlusal surface of prosthesis. Group 1 was cuspally loaded occlusion with total 8 contact points and Group 2 was implant protected occlusion with 3 contact points. Results. In Group 1 for vertical load, maximum stress was generated over implant having 14.3552 Mpa. While for oblique load, overall stress generated was 28.0732 Mpa. In Group 2 for vertical load, maximum stress was generated over crown and overall stress was 16.7682 Mpa. But for oblique load, crown stress and overall stress was maximum 22.7561 Mpa. When Group 1 is compared to Group 2, harmful oblique load caused maximum overall stress 28.0732 Mpa in Group 1. Conclusion. In Group 1, vertical load generated high implant stress, and oblique load generated high overall stresses, cortical stresses and crown stresses compared to vertical load. In Group 2, oblique load generated more overall stresses, cortical stresses, and crown stresses compared to vertical load. Implant protected occlusion generated lesser harmful oblique implant, crown, bone and overall stresses compared to cuspally loaded occlusion.

• The Journal of Advanced Prosthodontics
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• v.5 no.3
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• pp.326-332
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• 2013

PURPOSE. The purpose of this study was to compare stress distributions of implant-supported crown placed in fibula bone model with those in intact mandible model using three-dimensional finite element analysis. MATERIALS AND METHODS. Two three-dimensional finite element models were created to analyze biomechanical behaviors of implant-supported crowns placed in intact mandible and fibula model. The finite element models were generated from patient's computed tomography data. The model for grafted fibula was composed of fibula block, dental implant system, and implant-supported crown. In the mandible model, same components with identical geometries with the fibula model were used except that the mandible replaced the fibula. Vertical and oblique loadings were applied on the crowns. The highest von Mises stresses were investigated and stress distributions of the two models were analyzed. RESULTS. Overall stress distributions in the two models were similar. The highest von Mises stress values were higher in the mandible model than in the fibula model. In the individual prosthodontic components there was no prominent difference between models. The stress concentrations occurred in cortical bones in both models and the effect of bicortical anchorage could be found in the fibula model. CONCLUSION. Using finite element analysis it was shown that the implant-supported crown placed in free fibula graft might function successfully in terms of biomechanical behavior.

• Journal of Technologic Dentistry
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• v.37 no.2
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• pp.69-76
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• 2015

Purpose: In this study, the marginal fitness of ceramic Co-Cr metal crown made by precision casting, milling, and selective laser melting method were compared. Methods: The ceramic Co-Cr metal crown manufactured by precision casting used the lost wax(LC specimen) method. The abutment were scanned and then made by milling(CM specimen), selective laser melting(CS specimen) method. The specimen were cut bucco-lingual and mesio-distal, and absolute marginal discrepancy and marginal gap were measured using a digital microscope. The surface roughness of the crown was also observed. Results: On the bucco-lingual axial, absolute marginal discrepancy was the LC specimen $31.72({\pm}4.58){\mu}m$, the CM specimen $78.29({\pm}3.28){\mu}m$ and the CS specimen $143.13({\pm}3.83){\mu}m$, respectively. On the bucco-lingual axial, marginal gap was the LC specimen $22.70({\pm}1.46){\mu}m$, the CM specimen $22.70({\pm}1.49){\mu}m$ and CS specimen $99.60({\pm}1.57){\mu}m$, respectively. Conclusion: For ceramic Co-Cr metal crowns, LC specimen was superior for absolute marginal discrepancy and marginal gap. The surface of metal crowns by selective laser melting were the roughest.