• 대한치과보철학회지
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• 제32권4호
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• pp.484-514
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• 1994

Cantilever bridge is widely used by mny clinicians, but its worst mechanical character, so called Class I lever system, makes dentists hesitate to restore the missing tooth with it. Therefore it is important to study stress of the cantilever bridge. In this study, two models of cantilever bridges that restores the missing mandibular second molar with two abutment teeth were constructed. One model was a type of cantilever bridge supported by a normal alveolar bone, the other one was supported by an alveolar bone resorbed to its 1/3 of root length. Maximum bite force(550N) and funtional maximum bite force(300N) were vertically applied to the distal end of the pontic, distal 1/3, and distal half of the pontic. And each force was also applied to centric occlusal contacts as a distributed force. Total 16 loading cases were compared and analyzed with 3-dimensional finite element method. The results were as follows: 1. The stress was concentrated on the joint of the pontic and the retainer, grooves, and distal cervical margin of the posterior retainer. 2. In case of maximum bite force(550N) at the end of the pontic, the risk of fracture at the joint of the pontic and the retainer was high. 3. In case of distributed force in centric occlusion and functional maximum bite force(300N), the stresses were less than the yield strength of the type VI gold for any loading cases. 4. In case of alveolar bone resorption, the occlusal force to the cantilever pontic caused more stress on the root apex and less stress on the alveolar crest region of the distal surface of the posterior abutment. 5. In case of alveolar bone resorption, the displacement was larger than that of normal alveolar bone in all loading cases.

• Journal of Periodontal and Implant Science
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• 제46권6호
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• pp.362-371
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• 2016

Purpose: The increasing demand for esthetically pleasing results has contributed to the use of ceramics for dental implant abutments. The aim of this study was to compare the biological response of epithelial tissue cultivated on lithium disilicate ($LS_2$) and zirconium oxide ($ZrO_2$) ceramics. Understanding the relevant physicochemical and mechanical properties of these ceramics will help identify the optimal material for facilitating gingival wound closure. Methods: Both biomaterials were prepared with 2 different surface treatments: raw and polished. Their physicochemical characteristics were analyzed by contact angle measurements, scanning white-light interferometry, and scanning electron microscopy. An organotypic culture was then performed using a chicken epithelium model to simulate peri-implant soft tissue. We measured the contact angle, hydrophobicity, and roughness of the materials as well as the tissue behavior at their surfaces (cell migration and cell adhesion). Results: The best cell migration was observed on $ZrO_2$ ceramic. Cell adhesion was also drastically lower on the polished $ZrO_2$ ceramic than on both the raw and polished $LS_2$. Evaluating various surface topographies of $LS_2$ showed that increasing surface roughness improved cell adhesion, leading to an increase of up to 13%. Conclusions: Our results demonstrate that a biomaterial, here $LS_2$, can be modified using simple surface changes in order to finely modulate soft tissue adhesion. Strong adhesion at the abutment associated with weak migration assists in gingival wound healing. On the same material, polishing can reduce cell adhesion without drastically modifying cell migration. A comparison of $LS_2$ and $ZrO_2$ ceramic showed that $LS_2$ was more conducive to creating varying tissue reactions. Our results can help dental surgeons to choose, especially for esthetic implant abutments, the most appropriate biomaterial as well as the most appropriate surface treatment to use in accordance with specific clinical dental applications.

• 대한치과보철학회지
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• 제51권4호
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• pp.245-251
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• 2013

연구 목적: 본 연구는 생체 내 티타늄과 지르코니아 표면에 치면세균막의 형성 정도를 비교하기 위함이다. 연구 재료 및 방법: 티타늄과 지르코니아의 구강 내 치면세균막의 형성을 위해 구강 내 장치를 아크릴릭 레진과 교정용 와이어를 이용하여 9명의 실험대상자에 맞추어 제작한 후 티타늄과 지르코니아 봉을 일정 크기의 시편 ($6mm{\times}6mm{\times}2mm$)으로 만들어 장치에 고정하여 실험 대상자 구강 내에 24시간, 72시간 유지시켰다. 2쌍으로 만들어 장치한 시편을 실험 대상자는 치약 등의 구강세정제를 사용하지 않고 잇솔질만으로 구강위생을 유지하였다. 24시간, 72시간 경과 후 시편을 제거하여 SEM (주사전자 현미경)으로 치면세균막을 관찰하였다. 결과: 주사전자현미경의 결과 치면세균막의 형성 정도는 개인의 특성에 따라 큰 편차를 보였고, 24시간 후 치면세균막의 비교했을 때 지르코니아 표면에서 치면세균막의 형성 정도가 티타늄의 표면에 비해 적었다. 72시간 후 치면세균막의 형성 정도는 티타늄 표면보다 지르코니아 표면에서 적은 경향을 보였다. 결론: 구강 내에서 치면세균막의 초기 형성은 지대주 소재의 차이에 의해 영향을 받을 것으로 생각된다.

• 대한치과보철학회지
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• 제38권2호
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• pp.242-254
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• 2000

Accurate impression is very important to achieve desirable prosthesis and there are many factors in taking a good impression. For example, types of impression material, types of impression tray, impression taking methods and so on. Recently individual tooth tray technique is accepted as obtaining good impression that can be applied to multiple abutment impression, heavy salivated patient, to minimize the effect of natural teeth s undercuts and to reduce pain during cord packing procedures. The purpose of this study was to compare the accuracy according to materials and forms of the individual tooth tray which is clinically applied nowadays. Used materials in experiment were divided into 3 types (acrylic resin. $Futar^{(R)}$ occlusion. $Blu-mousse^{(R)}$) and forms were divided into 2 types (forming occlusal vent hole or not and forming marginal vent space or not). Stone master model from impression body and metal master model were measured by $X-PLAN360d^{(R)}$ to compare occlusal surface discrepancy and marginal discrepancy. The results were as follows: 1. In comparison of occlusal surface discrepancy and marginal discrepancy according to materials, groups with three materials showed no statistical difference 2. In comparison of occlusal surface discrepancy and marginal discrepancy according to occlusal vent hole, groups with occlusal vent hole showed significantly less marginal discrepancy than groups with no occlusal vent hole(p<0.05). 3. In comparison of occlusal surface discrepancy and marginal discrepancy according to 0.5mm-marginal-vent-space, groups with no 0.5mm-marginal-vent-space showed significantly less marginal discrepancy than groups with 0.5mm-marginal-vent-space (p<0.05). In summary these results suggest that individual tooth tray made of 3 types of materials with occlusal vent hole and individual tooth tray made of acrylic resin with no marginal vent space showed good accuracy of impression. In addition, individual tooth tray which is made of bite registration materials may be more useful because of advantage in facility and timesaving aspect of fabrication.

• 대한치과기공학회지
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• 제41권1호
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• pp.21-27
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• 2019

Purpose: To evaluate 2D and 3D of occulsal, mesial-occlusal and mesial-occlusal-distal cavity of composite resin inlay. Methods: Abutment tooth 16, 36 of FDI system was selected for the study. Inlay prostheses classified as occlusal cavity (OC group), mesial-occlusal (MOC) and mesial-occlusal-distal cavity (MODC) were prepared using composite resin. Composite resin was injected with composite resin in prepared tooth cavity and then photopolymerized with UV light. Additional thermal polymerization was performed. Marginal gap of composite resin inlays were measured by digital microscope(x160) with silicone replica technique. The data was analyzed from statistical software for Kruskal-Wallis test (${\alpha}=0.05$). 3-dimensional analysis was analyzed through superimposition method. Results: The smallest 2D marginal fit measure of the three groups was $47.0{\pm}21.6{\mu}m$ in the MOC group. The largest 2D marginal was $69.1{\pm}33.8{\mu}m$ in the MODC group. In the trueness of the three groups, the most accurate figure was $14.4{\pm}2.3{\mu}m$ for the MODC group. In Precision, the most accurate figure was $14.5{\pm}4.3{\mu}m$ for the MODC group. Conclusion : In this study, 2D marginal fit of OC, MOC, and MODC cavities fabricated with composite resin was applicable to all clinical applications. In the 3D inner surface accuracy evaluation, the MODC group showed the accuracy results.

• 대한치과보철학회지
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• 제36권1호
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• pp.26-49
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• 1998

The purpose of this study was to confirm the formation of hybrid layer and resin tags in dentin tissue and the possibility of bonding between luting cements used for the prosthesis and the resinous surface coated with resin bonding agents to prevent the dentin hypersensitivity after abutment preparation. Some resin bonding agents, which may have the possibility of bonding with polyacrylic acid as a liquid ingredient of polycarboxylate and glass ionomer cements, were selected. All-Blond desensitizer containing NTG-GMA and BPDM, Scotch-Bond Multipurpose plus containing HEMA, and XR-bond containing organophosphate were selected as a coating agent. Dental cements were zinc phosphate, polycarboxylate, and glass ionomer cement. After the exposed dentin surface of premolars was ethced with 10% phosphoric acid and coated with resin bonding agents, the morphology of treated surfaces and the resin tags and hybrid layers on sectioned surfaces were observed by SEM. Shear bond strength between the resin bonding agents and 3 kinds of cements was measured 24 hours after bonding. On the debonded surfaces of the shear bond strength tested specimens, the cement tags and the bonding sites between the resin materials and cements were examined by SEM. Following conclusions were drawn : 1. Coating of dentin with resin bonding agents had no effect on the shear bond strength of zinc phosphate cement. 2. Both of polycarboxylate and glass ionomer cements showed the increased shear bond strength by the dentinal coating with Scotch-Bond Multipurpose plus containing HEMA. However, in the case of dentinal coating with some agents containing NTG-GMA and BPDM or organophosphate, polycarboxylate cement exhibited the lowered shear bond strength, and glass ionomer cement showed the unchanged shear bond strength. 3. Complete obstructions of dentinal tubules were observed on the dentin coated with All-Bond desensitizer or XR-bond, but distinct shape of the orifices of dentinal tubules was observed consistently on the dentin coated with Scotch-Bond Multipurpose plus. 4. The hybrid layer was thickest on the dentin coated with All-Bond desensitizer, and the length of resin tags was longest on the dentin coated with Scotch-Bond Multipurpose plus. 3. On the debonded specimens which had been bonded with polycarboxylate cement or glass ionomer cement after coating with Scotch-Bond Multipurpose plus, the cement tags and the bonding sites between the resinous surface and the cements could be examined.

• 구강회복응용과학지
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• 제17권4호
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• pp.257-274
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• 2001

To properly prepare teeth, dentists require a direct view of the working area and are often placed in a difficult position, moreover, a high proportion of dentists suffer from headache and back pain. Dentists who make use of the dental mirror and position their patients carefully to gain a proper view report less headache, pain and discomfort in the shoulders. It is recommended that dentists learn the "Home Position(H.P.)" which among the various "Random Position(R.P.)" methods, enables dentists to approach their patients in a stable posture. The purpose of this study was to compare tooth preparation in the H.P. and the R.P., and evaluate the clinical efficacy of the H.P.. Tooth preparation for a full cast crown was performed on the maxillary left 1st molar using the H.P. and the R.P., and the shapes of the prepared tooth surfaces at the two different operating positions were compared. The amount of occlusal reduction, marginal width, height, and axial taper were measured and analyzed. A T-test was performed separately to compare the results of the H.P. and the R.P. with respect to the accuracy of the corresponding tooth reduction. The results were as follows. ; 1. The amount of occlusal reduction was excessive on the mesiobuccal cusp(P<0.05), and deficient on the lingual cusp in the H.P.(P<0.01). In the R.P., this was excessive on the buccal cusp and deficient on the fossa and distolingual cusp(P<0.01). 2. The amounts of marginal width were excessive in all areas except on the lingual and mesial surfaces in the H.P. and lingual surface in the R.P.(P<0.01). 3. The marginal heights were achieved more accurately in the R.P. than the H.P.(P<0.01). 4. Axial surface taper was excessive in all areas in the H.P.(P<0.01). But the axial taper of measured areas was even, and tooth is more like to retain its original axis after reduction. In the R.P., axial surface taper was excessive on the mesial and buccal area, and deficient on the distolingual area(P<0.01), and therefore, the axis of the prepared teeth was tipped in the distolingual direction. 5. The times needed for preparation were 12 minutes and 49 seconds in the H.P., and 11 minutes and 35 seconds in the R.P., and the R.P. was statistically faster(P<0.01). The tooth preparation in the H.P. achieved its goal, in that it enabled the operator to make even tooth reduction. In conclusion, the H.P. system offers an improved method that can be used in clinic after specific training.

• 대한치과기공학회지
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• 제31권1호
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• pp.55-61
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• 2009

Passive fitting of meso-structure and super-structures is a predominant requirement for the longevity and clinical success of osseointegrated dental implants. However, precision and passive fitting has been unpredictable with conventional methods of casting as well as for corrective techniques. Alternative to conventional techniques, electro discharge machining(EDM) is an advanced method introduced to dental technology to improve the passive fitting of implant prosthesis. In this technique material is removed by melting and vaporization in electric sparks. Regarding the efficacy of EDM, the application of this technique induces severe surface morphological and elemental alterations due to the high temperatures developed during machining, which vary between $10,000{\sim}20,000^{\circ}C$. The aim of this study was to investigate the morphological and elemental alterations induced by EDM process of casting dental gold alloy and non-precious alloy used for the production of implant-supported prosthesis. A conventional clinical dental casting alloys were used for experimental specimens patterns, which were divided in three groups, high fineness gold alloy(Au 75%, HG group), low fineness gold alloy(Au 55%, LG group) and nonprecious metal alloy(Ni-Cr, NP group). The UCLA type plastic abutment patterns were invested with conventional investment material and were cast in a centrifugal casting machine. Castings were sandblasted with $50{\mu}m\;Al_2O_3$. One casting specimen of each group was polished by conventional finishing(HGCON, LGCON, NPCON) and one specimen of each group was subjected to EDM in a system using Cu electrodes, kerosene as dielectric fluid in 10 min for gold alloy and 20 min for Ni-Cr alloy(HGEDM. LGEDM, NOEDM). The surface morphology of all specimens was studied under an energy dispersive X-ray spectrometer (EDS). The quantitative results from EDS analysis are presented on the HGEDM and LGEDM specimens a significant increase in C and Cu concentrations was found after EDM finishing. The different result was documented for C on the NPEDM with a significant uptake of O after EDM finishing, whereas Al, Si showed a significant decrease in their concentrations. EDS analysis showed a serious uptake of C and Cu after the EDM procedure in the alloys studied. The C uptake after the EDM process is a common finding and it is attributed to the decomposition of the dielectric fluid in the plasma column, probably due to the development of extremely high temperatures. The Cu uptake is readily explained from the decomposition of Cu electrodes, something which is also a common finding after the EDM procedure. However, all the aforementioned mechanisms require further research. The clinical implication of these findings is related with the biological and corrosion resistance of surfaces prepared by the EDM process.

• 대한치과보철학회지
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• 제37권5호
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• pp.658-671
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• 1999

The major influencing factors on the strength of all-ceramic crowns are types of dental ceramics, fabrication techniques, methods of abutment preparation and cementation modes of all-ceramic restorations. Zinc phosphate cement and glass-ionomer cement were used as an early lot-ing media for all-ceramic crowns. Recently many studies have reported that resin cements have more advantages in increasing the fracture strength of restorations comparing with zincphosphate cement and glass-ionomer cement. The purpose of this study is to investigate the effect of etching, silane treatment, sandblasting and dentin bonding agents on fracture strengths of dental ceramics. 40 flat dentin specimens and 40 ceramic discs of 1.5mm thickness and 8mm diameter were fabricated, and divided into 4 groups according to surface treatments. Surface treatments before cementation were as follows Group I : (ceramic) : HF etching - silane treatment - application of bonding resin (dentin) : application of dentin bonding agent Group II : (ceramic) : sandblasting - application of bonding resin (dentin) : application of dentin bonding agent Group III : (ceramic) : application of bonding resin (dentin) : application of dentin bonding agent Group IV : (ceramic) : HF etching - silane treatment - application of bonding resin (dentin) : no dentin bonding procedure Dentin specimens and ceramic discs were cemented with dual cure resin cement, and went through thermocycling. Compressive stress es were loaded on the centers of ceramic discs with Instron test-ing machine, and fracture strengths resistance for catastrophic fracture were measured The results were as follows. 1. The group I showed the highest fracture resistance. The next was group II And group III, IV followed. 2. There was a significant difference in the mean value of fracture strengths between group I and group III (p<0.05), but no significant differences between group I and group II, and group II and group III (p>0.05). 3. There was a significant difference in the mean value of fracture strengths between group I and group IV (p<0.05).

• 대한치과보철학회지
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• 제35권4호
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• pp.742-766
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• 1997

The purpose of this study was to determine the effect of finish line design, amount of incisal reduction, and loading condition on the stress distribution in anterior all-ceramic crowns. Three-dimensional finite element models of an incisor all-ceramic crown with 3 different finish line designs : 1) shoulder with sharp line angle 2) shoulder with rounded line angle 3) chamfer : and 2 different incisal reductions : 2mm and 4mm were developed. 300 N force with the direction of 45 degree to the long axis of the tooth was applied at 3 different positions : A) incisal 1/3, B) incisal edge, C) cervical 1/5. Stresses developed in ceramic and cement were analyzed using three-dimensional finite element method. The results were as follows : 1. Stresses were concentrated in the margin region, which were primarily compressive in the labial and tensile in the lingual. 2. Stresses were larger in the area near line angle than on the crown surface of the margin region. In case of shoulder with sharp line angle, stresses were highly concentrated in the porcelain near line angle. 3. At the interface between porcelain and cement and at the porcelain above the margin on crown surface, stresses were the highest in chamfer, and decreased in shoulder with sharp line angle and shoulder with rounded line angle, respectively. 4. At the interface between cement and abutment on crown surface, stresses were the highest in shoulder with sharp line angle, and decreased in shoulder with rounded line angle and chamfer, respectively. 5. The amount of incisal reduction had little influence on the stress distribution in all-ceramic crowns. 6. When load was applied at the incisal edge, higher stresses were developed in the margin region and the incisal edge than under the other loading conditions. 7. When load was applied at the cervical 1/5, stresses were very low as a whole.