• 대한치과교정학회지
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• 제53권4호
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• pp.254-263
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• 2023

Objective: The evidence on the accuracy of bite registration using intraoral scanners is sparse. This study aimed to develop a new method for evaluating bite registration accuracy using intraoral scanners. Methods: Two different types of models were used; 10 stone models and 10 with acrylic resin teeth. A triangular frame with cylindrical posts at each apex (one anterior and two posteriors) was digitally designed and manufactured using three-dimensional (3D) printing. Such a structure was fitted in the lingual space of each maxillary and mandibular model so that, in occlusion, the posts would contact their opposing counterparts, enforcing a small interocclusal gap between the two arches. This ensured no tooth interference and full contact between opposing posts. Bite registration accuracy was evaluated by measuring the distance between opposing posts, with small values indicating high-accuracy. Three intraoral scanners were used: Medit i500, Primescan, and Trios 4. Viewbox software was used to measure the distance between opposing posts and compute roll and pitch. Results: The average maximum error in interocclusal registration exceeded 50 ㎛. Roll and pitch orientation errors ranged above 0.1 degrees, implying an additional interocclusal error of around 40 ㎛ or more. The models with acrylic teeth exhibited higher errors. Conclusions: A method that avoids the need for reference hardware and the imprecision of locating reference points on tooth surfaces, and offers simplicity in the assessment of bite registration with an intraoral scanner, was developed. These results suggest that intraoral scanners may exhibit clinically significant errors in reproducing the interocclusal relationships.

• 대한치과보철학회지
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• 제29권3호
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• pp.121-140
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• 1991

Fifteen dental college students of Chosun University without the abnormal occlusion, the history and symptom of temporomandibular dysfunction(TMD), and who had all permanent teeth except third molar and the fifteen moderate group and the fifteen severe group classified according to Helkimo's dysfunction index among patients on the basis of the symptom of TMD were selected. The occlusal contact, occlusal force and occlusal interference in eccentric movement was studied and analyzed using T-Scan system. The result were as follows : 1. The TLR centering around midsagittal axis was located at $1.42{\pm}0.82mm$ in control group, $3.36{\pm}1.45mm$ in severe group, and as TMD was heavier, occlusal contact was located at the farther point from midsagittal axis. 2. The PLR from the first contact to the fifth contact centering around midsagittal axis was located at $1.73{\pm}1.78mm$ in control group, $3.36{\pm}1.41mm$ in moderate group, and $5.39{\pm}4.32mm$ in severe group, and as TMD was heavier, occlusal contact was located at the farther point from midsgittal axis. 3. The TFB, PFB, RFB and LFB of occlusal contact centering around incisal axis had no significant difference statistically among control group, moderate group, and severe group, and it was located at first molar. 4.The LF and RF was smaller in TMD group than in control group. 5. The LR moment of occlusal force centering around midsagittal axis was located at $178.51{\pm}139.81N.mm$ in control group, $466.25{\pm}296.47N.mm$ in moderate group, and $749.18{\pm}588.18N.mm$ in severe group. And as TMD was heavier, it was located at the farther point from midsagittal axis. 6. The RL and LL of occlusal force centering around incisal axis had not-significance statistically among control group, moderate group, and severe group, and it was at the first molar. 7. The number of occlusal interference of the eccentric movement was increased in the patients of TMD.

• 한국정밀공학회지
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• 제23권9호
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• pp.54-60
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• 2006

Fitting process carried out in automobile transmission assembly line is classified into three classes; heat fitting, press fitting, and their combined fitting. Heat fitting is a method that heats gear to a suitable range under the tempering temperature and squeezes it toward the outer diameter of shaft. Its stress depends on the yield strength of gear. Press fitting is a method that generally squeezes gear toward that of shaft at room temperature by press. Another method heats warmly gear and safely squeezes it toward that of shaft. Warm shrink fitting process for automobile transmission part is now gradually increased, but the parts (shaft/gear) assembled by this process produced dimensional changes of gear profile in both radial and circumferential directions. So that it may cause noise and vibration between gears. In order to solve these problems, we need an analysis of warm shrink fitting process, in which design parameters are involved; contact pressure according to fitting interference between outer diameter of shaft and inner diameter of gear, fitting temperature, and profile tolerance of gear. In this study, an closed form equation to predict contact pressure and fitting load was proposed in order to develop optimization technique of warm shrink fitting process and verified its reliability through the experimental results measured in the field and FEM, that is, thermal-structural coupled field analysis. Actual loads measured in the field have a good agreement with the results obtained by theoretical and finite element analysis and also the expanded amounts of the gear profile in both radial and circumferential directions are within the limit tolerances used in the field.

• 대한치과보철학회지
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• 제56권2호
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• pp.141-153
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• 2018

계속적인 치아의 상실과 마모 및 보철물의 실패로 초래된 생리적이지 못한 교합평면은 비심미성, 저작 효율의 감소 및 교합 간섭와 같은 기능적인 문제을 야기할 수 있다. 따라서, 무치악 환자나 교합 평면이 붕괴된 환자의 보철 치료 시, 저작 기능과 조화로운 교합평면의 설정이 중요하다. 본 증례의 환자는 완전 무치악 상태인 상악을 임플란트 고정성 보철물로 수복하였다. 6년 경과 관찰 시, 기존 임플란트 보철물의 도재 파절, 마모, 나사풀림과 같은 기계적 합병증이 관찰되었고, 대합하는 전치의 마모 및 정출과 일부 구치부 치아의 상실로 인해 교합평면이 붕괴된 상태였다. 진단 과정을 거쳐 무치악 부위의 추가적인 임플란트 식립과 보철물의 재제작 및 모든 잔존 치아의 수복을 통해 전악구강회복을 시행하였다.

• 구강회복응용과학지
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• 제16권2호
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• pp.149-159
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• 2000

Occlusal disease is comparable to periodontitis in that it is generally not reversible. Occlusal disease, however, like periodontitis, often maintainable. It does itself to treatment and when restorative dentistry is utilized it becomes, in that sense, reversible. Moreover, a systematized and integrated approach will lead to a prognosis that is favorable and predictable. This approach facilitates development of optimum oral function, comfort, and esthetics, resulting in a satisfied patient. Such a systematized approach consists of four logical phase : (1) patient evaluation, (2) comprehensive analysis and treatment planning, (3) integrated and systematic reconstruction, and (4) postoperative maintenance. An integrated treatment plan is first developed on one set of diagnostic casts, properly mounted on a semiadjustable articulator using jaw relationship records. This is accomplished by using wax to make reconstructive modifications to the casts. These modified casts become the blueprint for planned occlusal changes and the fabrication of provisional restorations. The treatment goals are : (1) comfortably functioning temporomandibular joints and stomatognathic musculature, (2) adherence to the basic principle of occlusion advocated by Schuyler, (3) anterior guidance that is in harmony with the envelope of function, (4) restorations that will not violate the patient's neutral zone. This report shows the treatment procedures for a patient whose mandibular position has been altered due to posterior bite collapse. Migration of the maxillary anterior teeth had occurred, and the posterior occlusal contacts showed pathologic interference. Precise diagnosis using mounted casts was executed and prosthodontic reconstruction by the aid of an unconventional orthodontic correction on maxillary flaring was planned. An unconventional orthodontic correction can be accomplished by using preexisting natural teeth, which can be modified for use in active tooth movement or splinted together for orthodontic anchorage. This technique has an advantage over conventional fixed appliance orthodontic therapy because it can accomplish tooth movement concurrently with restorative and periodontal therapy. On occasion, minor tooth movement can be necessary to achieve the optimum occlusal scheme, crown form, and tooth position for the forces of occlusion to be displaced down the long axis of the periodontally compromised teeth. Once the occlusion, periodontal health, and crown contours for the provisional splinted restoration are acceptable, the final splinted restoration can be similarly fabricated, and it becomes an excellent orthodontic retainer.

• Maxillofacial Plastic and Reconstructive Surgery
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• 제42권
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• pp.32.1-32.4
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• 2020

Background: Le Fort I osteotomy is a highly effective treatment for skeletal jaw deformities and is commonly performed. High Le Fort I osteotomy is a modified surgical procedure performed for improving the depression of the cheeks by setting the osteotomy higher than the conventional Le Fort I osteotomy. Developments in three-dimensional (3D) technology have popularized the use of 3D printers in various institutions, especially in orthognathic surgeries. In this study, we report a safe and inexpensive method of performing a high Le Fort I osteotomy using a novel 3D device and piezosurgery, which prevent tooth root injury without disturbing the operation field for patients with a short midface and long tooth roots. Results: A 17-year-old woman presented with facial asymmetry, mandibular protrusion, a short midface, and long tooth roots. We planned high Le Fort I osteotomy and bilateral sagittal split ramus osteotomy. Prevention of damage to the roots of the teeth and the infraorbital nerve and accurate determination of the posterior osteotomy line were crucial for clinical success. Le Fort I osteotomy using 3D devices has been reported previously but were particularly large in size for this case. Additionally, setting the fixing screw of the device was difficult, because of the risk of damage to the roots of the teeth. Therefore, a different surgical technique, other than the conventional Le Fort I osteotomy and 3D device, was required. The left and right parts of the 3D device were fabricated separately, to prevent any interference in the surgical field. Further, the 3D device was designed to accurately cover the bone surface from the piriform aperture to the infra-zygomatic crest with two fixation points (the anterior nasal spine and the piriform aperture), which ensured stabilization of the 3D device. The device is thin and does not interfere with the surgical field. Safe and accurate surgical performance is possible using this device and piezosurgery. The roots of the teeth and the infraorbital nerve were unharmed during the surgery. Conclusions: This device is considerably smaller than conventional devices and is a simple, low-cost, and efficient method for performing accurate high Le Fort I osteotomy.

• 대한장애인치과학회지
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• 제9권2호
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• pp.118-121
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• 2013

과잉 소구치는 장애 환자에서 교정적 문제를 일으켜 구강 위생 관리의 어려움을 초래할 수 있는데 발생 시기가 늦고 병리학적 문제의 발생 가능성이 낮으며 재발의 가능성이 높으므로 발거 시기를 전체 영구치열이 완전한 성숙을 이룬 후로 미루어야 하며 매복되어 있어 특이할 만한 합병증이 발견되지 않는 경우, 수술적 위험성을 감수하기보다는 남겨 두는 것을 추천한다.

• 대한치과의사협회지
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• 제58권8호
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• pp.505-512
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• 2020

With the fourth industrial revolution, digitization is accelerating in all healthcare areas. In the field of dentistry, active discussions on digital dental technologies are ongoing, with increasing interest from clinicians daily. Thus far, accuracy and efficiency have primarily been emphasized in digital dentistry, and interest in occlusion has been relatively low. This is because digital dentistry has been predominantly used to restore small numbers of teeth rather than extensive prosthetic reconstruction. However, in the future, most dental treatments will undergo a digital transformation that will require the application of digital technology to more extensive prosthetic rehabilitation, for which discussion of occlusion is essential. In extensive prosthetic reconstruction, occlusion and articulation involve determining the position of the dental arch in relation to the reference plane of the skull or the long axis of the face and the position of the transverse horizontal axis. It also includes determining an occlusal surface with a shape that allows the mandible to move in an eccentric path and masticate most efficiently without any occlusal interference. To better understand how digitization will impact dentistry, this review article summarizes and discusses occlusion and articulation using digital dental technologies. This discussion is divided into several aspects, including facial scan, virtual articulation, augmented reality, and virtual reality.

• 한국소음진동공학회논문집
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• 제20권7호
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• pp.677-684
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• 2010

Backlashes of gears provide gears for good lubrication and for removal of the interference between teeth by the wear and manufacturing errors. The backlash is the strong nonlinear factor to gears. This study deals with nonlinear modeling of helical gears with backlash. Excitation of helical gears comes from torque variation, the tooth surface error, and the periodical change of mesh stiffness. To study the effect of torque fluctuation, equation of motion for the single degree of freedom torsional model of helical gears with the periodical change of mesh stiffness and the backlash was derived. The Newmark beta method and the Newton-Raphson method were used to obtain the nonlinear behaviors of mesh forces of helical gears. All excitation frequencies initially caused the tooth separation and single-sided impacts of the gear pair and eventually led to the normal tooth contact. However, some special excitation frequencies caused the single-sided impacts in the entire time as well as the initial time. Damping increase reduced the duration of single-sided impacts, and the backlash increase caused those in the entire time domain.

• 대한기계학회논문집
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• 제18권3호
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• pp.591-599
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• 1994

A design system for power transmission bevel gears(straight, zerol, and spiral) is developed, in which the strength and durability of bevel gears can be estimated and the size of bevel gears can be minimized by introducing optimal techniques. The size of bevel gear pair as the object function to be minimized is the volume of equivalent spur gear pair at mean normal section, and the design variables to be determined are considered as the number of teeth, face width, diametral pitch, and spiral angle in spiral bevel gear. The strength(bending strength, pitting resistance) according to the AGMA standards, geometrical quantities, and operating characteristics(interference of pinion, contact ratio, etc.) are considered as the constraints in design optimization. The optimization with these constraints becomes nonlinear problem and that is solved with ALM(Augmented Lagrange Multiplier) method. The developed design method is applied to the example designs of straight, zerol, and spiral bevel gears. The design results are acceptable from the viewpoint of strength and durability within the design ranges of all other constraint, and the bevel gears are designed toward minimizing the size of gear pair. This design method is easily applicable to the design of bevel gears used as power transmitting devices in machineries, and is expected to be used for weight minimization of bevel gear unit.