Failure probability, stress distribution and fracture analysis of experimental screw for micro conical abutment

Abstract The aim of this study was to evaluate the failure probability of two types of abutment screws after compressive load and to analyze the stress distribution with finite element method. Sixty (60) single-tooth implant restorations were assembled on titanium implants (e-fix, A.S. Technology - Titanium Fix). The groups were divided into Conventional screw (Screw neck 1.5 ø mm) and Experimental screw (Screw neck constricted with 1.2 ø mm). Specimens were subjected to single load to failure with compressive test according ISO 14801. The fractured specimens were subjected to stereomicroscopy for measurement of remaining screws inside the implant and characterization of fracture origin. Representative specimens were analyzed by scanning electronic microscopy. For finite element method (FEM), an identical 3D model of the two in vitro test groups were used with similar conditions (30º, 100 N load). The stress in the abutment screw was analyzed by von-Mises criteria. The results of strength means were 4132.5 ± 76 MPa and 4528.2 ± 127.2 for conventional and experimental groups, respectively. During microscopy, the mean (mm) of the remaining screw piece inside the implants were 0.97 ± 0.23 and 1.32 ± 0.12 for conventional and experimental groups, respectively. In FEM, the conventional group showed stress concentered in an unfavorable region (peak of 39.23 MPa), while the experimental group showed more stress areas but less concentration than the conventional group (36.6 MPa). In using the tested experimental geometry, the abutment screw can have its strength improved, and the origin of failure can be more favorable to clinical resolution.

Resumo O objetivo deste estudo foi avaliar a probabilidade de falha de dois tipos de parafusos para pilar protético após a compressão e analisar a distribuição da tensão com o método dos elementos finitos. Sessenta (60) restaurações unitárias foram montadas em implantes de titânio (e-fix, A.S. Technology - Titanium Fix). Os grupos foram divididos em parafusos convencionais (parafuso de pescoço 1,5 ø mm) e parafuso experimental (parafuso de pescoço estreitado com 1,2 ø mm). As amostras foram sujeitas ao teste de compressão de acordo com ISO 14801. Os espécimes fraturados foram submetidos a estereomicroscopia para a mensuração dos parafusos restantes dentro do implante e caracterização da origem da fratura. Os espécimes representativos foram analisados ​​por microscopia eletrônica de varredura. Para o método de elementos finitos (FEM), utilizou-se um modelo 3D idêntico dos dois grupos de teste in vitro com condições semelhantes (30º, 100 N). A tensão no parafuso do pilar foi analisada pelo critério de von-Mises. Os resultados de resistência a compressão foram 4132,5 ± 76 MPa e 4528,2 ± 127,2 para grupos convencionais e experimentais, respectivamente. Durante a microscopia, a média do remanescente do parafuso restante dentro dos implantes foi de 0,97 ± 0,23 e 1,32 ± 0,12 mm para os grupos convencionais e experimentais, respectivamente. Em FEM, o grupo convencional mostrou tensão concentrada em uma região desfavorável (pico de 39,23 MPa), enquanto o grupo experimental apresentou mais áreas de tensão, porém menor concentração do que o grupo convencional (36,6 MPa). Ao usar a geometria experimental testada, o parafuso do pilar pode ter sua resistência melhorada e a origem da falha pode ser mais favorável à resolução clínica.

Repairment of abutment and abutment screw fracture in implant prosthesis: A case report / 대한치과보철학회지

Dental implants are an effective and predictable treatment for restoration of missing teeth. However, as the use of implants increases, complications are also increasing. The mechanical complications are not only highly frequent, but also increasing as life span of an implant increases, thus, solutions should be prepared. In this report, we will present a case dealing with abutment fracture and abutment screw fracture which are the most common mechanical complication of the implant, focusing on preserving and reusing existing components by reconstructing only the damaged parts.

Finite element analysis of the effect of novel Lock Screw system preventing abutment screw loosening

PURPOSE: The purpose of this finite element analysis study is to introduce the novel Lock screw system and analyze its mechanical property to see if it can prevent abutment screw loosening. MATERIALS AND METHODS: The Lock screw is a component tightened on the inside of the implant abutment which applies compressive force to the abutment screw head. To investigate the effect, modeling was done using CAD program and it was analyzed by finite element analysis under various load conditions. First, the preload was measured according to the tightening torque of the abutment screw then it was compared with the theoretical value to verify the analytical model. The validated analytical model was then divided into those with no external load and those with 178 N, and the tightening torque of the lock screw was changed to 10, 20, 30 Ncm respectively to examine the property of stress distribution on the implant components. RESULTS: Using Lock screw under various loading conditions did not produce equivalent stresses beyond the yield strength of the implant components. In addition, the axial load was increased at the abutment-abutment screw interface. CONCLUSION: The use of Lock screw does not exert excessive stress on the implant components and may increase the frictional force between the abutment-abutment screw interface, thus it is considered to prevent loosening of the abutment screw.

The effect of heat to remove cement on implant titanium abutment and screw / 대한치과보철학회지

PURPOSE: The purpose of this study was to investigate the effect of heat applied to disintegrate cement on the removal torque value and fracture strength of titanium abutment and abutment screw. MATERIALS AND METHODS: Implants, titanium abutments and abutment screws were prepared for each 20 piece. Implant abutments and screws were classified as the control group in which no heat was applied and the experimental group was heated in a vacuum furnace to 450℃ for 8 minutes and cooled in air. The abutments and screws were connected to the implants with 30 Ncm tightening torque at interval 10 minutes and the removal torque value was measured 15 minutes later. And the fracture strength of abutment screw was measured using universal testing machine. RESULTS: The mean removal torque value was 27.84 ± 1.07 Ncm in the control group and 26.55 ± 1.56 Ncm in the experimental group and showed statistically significant difference (P .05). CONCLUSION: The heat applied for cement disintegration significantly reduced the removal torque value of the abutment screw and did not significantly affect fracture strength of the abutment screw. Therefore, in the case of applying heat to disintegrate cement it is necessary to separate the abutment screw or pay attention to the reuse of the heated screw. However further studies are needed to evaluate the clinical reuse of the heated screw.

Removal torque of a two-piece zirconia abutment with a novel titanium component in an internal connection implant system after dynamic cyclic loading / 대한치과보철학회지

PURPOSE: The aim of this study was to evaluate screw removal torque of the two-piece zirconia abutment with the novel titanium component compared to the conventional onepiece titanium abutment in the internal connection implant before and after dynamic cyclic loading. MATERIALS AND METHODS: Two types of the abutment assemblies with internal connection were prepared and divided into the groups; titanium abutment-titanium abutment screw assemblies as control, and zirconia abutment-titanium socket-titanium abutment screw assemblies as experimental group. A total of 12 abutments and implants were used of six assemblies each group. Each assembly was tightened to 30 Ncm. A cyclic load of 300 N at an angle of 30 degrees in reference to the loading axis was applied until one million cycles or failure. The removal torque values (RTVs) of the abutment screws were measured with a digital torque gauge before and after cyclic loading. The RTVs of the pre load and post load were analyzed with t-test, and P-values .05). CONCLUSION: Within the limitation of this study, the two-piece zirconia abutment with the titanium component did not show a significant RTV difference of the abutment screw compared to the titanium abutment after dynamic cyclic loading.

Evaluation of removal torque values for titanium screws of prosthetic abutments after different torque application techniques: in vitro study / Avaliação dos valores de torque de remoção para parafusos de titânio de abutments protéticos após aplicação de diferentes técnicas de torque: estudo in vitro

Objetivo: Avaliar os valores de torque de remoção em abutments parafusados após aplicação de diferentes técnicas de torque. Materiais e Métodos: Trinta espécimes de implante hexágono externo, abutment pré-fabricado e parafuso de titânio foram distribuídos randomicamente em três grupos. No grupo 1, os parafusos receberam um torque de 30 N.cm; no grupo 2 receberam um torque de 30N.cm e um segundo torque após 10 min, de acordocom a técnica proposta por Brending et al. e Dixon et al.; no grupo 3, um torque de 30 N.cm foi aplicado e mantido por 20 s, de acordo com a técnica recomendada por Sella et al. Os espécimes foram inseridos na máquina de teste universal e uma chave digital foi acoplada a célula de carga para controlar o valor de torque e a velocidade de 1N.cm/s. O torque de remoção foi realizado 10 min após o torque de aplicação. Os valores foramestatisticamente analisados usando 1-way ANOVA e Tukey HSD test (α = 0,05). Resultados: As médias e desvio padrão (±SD) dos valores de torque deremoção encontrados foram 27,95 ± 0,99N.cm para o grupo 1; 28,32 ± 0,68N.cm para o grupo 2 e 26,89 ± 1,03 N.cm para o grupo 3. Os grupos 1e 2 exibiram valores estatisticamente mais altos de torque quando comparados ao grupo 3 (p < 0,05).Conclusão: A técnica recomendada por Breeding et al. e Dixon et al. pareceu ser a melhor opção quando considerado os valores do torque de remoção de implantes hexágono externo.

Objective: To evaluate the removal torque values on abutment screws after different torque application techniques. Materials and Methods: Thirty specimens of an external hexagon implant, a prefabricated abutment and a titanium screw were distributed randomly in three groups. In group 1, the screws received a torque of 30N.cm; group 2 received a torque of 30N.cm and a second torque after 10 min, in accordance with the technique proposed by Brending et al. and Dixon et al.; in group 3, a torque of 30 N.cm was applied and maintained for 20 s, in accordance with the technique recommended by Sella et al. The specimens were attached to a universaltesting machine and a digital key was coupled to the load cell in order to control the torque value at a velocity of 1 N.cm/s. Removal torque was performed 10 minutes after torque application. Values were statistically analysed using one-way ANOVA and Tukey’s HSD test (α = 0.05). Results:The mean and standard deviations (±SD) of removal torque values found were 27.95 ± 0.99N.cm for group 1, 28.32 ± 0.68N.cm for group 2 and 26.89±1.03N.cm for group 3. Groups 1 and 2 exhibited statistically higher values of torque than group 3 (p < 0.05). Conclusion: The techniquerecommended by Breeding et al. and Dixon et al. seemed to be the best option when considering the removal torque values of external hexagonimplants

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.

Efeito de diferentes níveis de torques na resistência ao destorque do parafuso e dos pilares de duas peças em junções cone-morse. Estudo in vitro / The effect of different torque levels on detorque resistance of a two-piece, cone Morse abutment and screw. An in vitro study

Objetivos: determinar se a quantidade da pré-carga influencia a resistência ao destorque do parafuso e pilar de duas peças com junção cone-morse indexada. Material e métodos: foram utilizados 60 análogos de implantes conexão tipo cone-morse de 11,5° com indexador hexagonal e 60 munhões universal cone-morse parafuso passante (4,5 mm de diâmetro, 2,5 mm de altura cinta de transmucoso e 4 mm de altura, não indexados), divididos em três grupos segundo o torque aplicado: 15 Ncm (G1); 20 Ncm (G2) e 25 Ncm (G3). A análise de variância fator único (Anova) e o teste LSD foram usados para as comparações entre os grupos (nível de significância 5%). Imagens em MEV foram realizadas na cabeça do parafuso e na chave de aplicação de torque. Resultados: os valores médios para os destorques dos parafusos foram: G1=17,48 Ncm, G2=21,16 Ncm e G3=26,42 Ncm, com diferencas estatisticamente significativas (p < 0,001) entre todos os grupos. Os valores médios para os destorques nos pilares foram: G1=15,17 Ncm, G2=19,58 Ncm e G3=21,64 Ncm, sendo (G1 e G2) e (G1 e G3) (p < 0,001); e G2 e G3 (p=0,02). Conclusão: 1) o aumento do torque no parafuso gerou valor médio aumentado do destorque em todos os grupos; 2) o aumento do torque gerou valor médio de destorque equivalente ao torque inicial dado para o G1 e G2, sendo este aumento menor no G3; 3) torques maiores do que os indicados pelo fabricante foram capazes de promover a deformação plástica na cabeça do parafuso após apertos repetidos

Objectives: to determine whether the applied preload influences on detorque resistance of abutment and abutment screw of a two-piece, indexed cone-morse taper connection. Material and methods: Sixty implant analogs (cone-morse taper=11,5 degrees) with internal hexagonal indexing and sixty cone morse universal abutments (4.5 mm diameter, 2.5 mm collar height, and 4 mm in height, non-indexed), were divided into three groups according to applied torques: 15 Ncm (G1); 20 Ncm (G2), and 25 Ncm (G3). The one-way Anova and LSD tests were used for comparisons among groups (at 5% level). Representative SEM images were obtained from screw heads and key drivers. Results: mean detorque abutment screw values were as follows: G1=17.48 Ncm, G2=21.16 Ncm, and G3=26.42 Ncm, with statistically significant differences (p < 0,001) among all tested groups. Also, the mean detorque abutment levels were: G1=15.17 Ncm, G2=19.58 Ncm, and G3=21.64 Ncm, being (G1 and G2); (G1 and G3) (p < 0.001); and G2 and G3 (p=0.02). Conclusion: 1) an increase on abutment screw torque level also increases detorque values for all groups; 2) an increase on abutment torque level provided detorque values proportional to that found in G1 and G2, being this lower for G3; 3) torque values higher than those preconized by the manufacturer lead to plastic deformation at screw heads after repeated tightening sequences

Comparison of removal torque between prefabricated and customized abutment screw / 대한치과보철학회지

PURPOSE: The purpose of this study is to compare the removal torque between prefabricated and customized implant abutment screw. MATERIALS AND METHODS: Three types of implant system (Osstem, Astra, Zimmer) were used. For each system, prefabricated abutment screw (control group) and customized abutment screw (test group) were used to connect the fixture and the abutment (n = 6). Digital torque gauze was used to control the tightening torque and the screws were tightened under each manufacturer's recommendation. 10 minutes after the connection the same tightening torque was applied, and 5 minutes after the second connection, the removal torque was measured. This procedure was repeated 10 times. In the cyclic loading test, 10 minutes after the first connection to the 6 groups (n = 3), the same tightening torque was applied, and a total of 1,000,000 time loading was applied at 30 degree angle to long axis with 50 N load. Repeated measures of ANOVA test (alpha=.05) was used as statistics to evaluate the effect of repeated loading number on the removal torque. Independent t-test was used to evaluate the difference in removal torque after cyclic loading. RESULTS: The removal torque significantly decreased as the number of loading repetition increased (P<.05). In the 10 time repetition test, there was no significant difference between the prefabricated and customized implant abutment screw of the 3 implant system (P<.05). Also in the cyclic loading test, there was no significant difference between the prefabricated and customized implant abutment screw of the 3 implant system (P<.05). CONCLUSION: Within the limitation of this study, there was no significant difference in the removal torque between the prefabricated abutment screw and customized abutment screws.

Evaluation of the stress distribution in the external hexagon implant system with different hexagon height by FEM-3D / 대한치과보철학회지

PURPOSE: To analyze the stress distribution of the implant and its supporting structures through 3D finite elements analysis for implants with different hexagon heights and to make the assessment of the mechanical stability and the effect of the elements. MATERIALS AND METHODS: Infinite elements modeling with CAD data was designed. The modeling was done as follows; an external connection type Phi 4.0 mm x11.5 mm Osste(R) USII (Osstem Co., Pusan, Korea) implant system was used, the implant was planted in the mandibular first molar region with appropriate prosthetic restoration, the hexagon (implant fixture's external connection) height of 0.0, 0.7, 1.2, and 1.5 mm were applied. ABAQUS 6.4 (ABAQUS, Inc., Providence, USA) was used to calculate the stress value. The force distribution via color distribution on each experimental group's implant fixture and titanium screw was studied based on the equivalent stress (von Mises stress). The maximum stress level of each element (crown, implant screw, implant fixture, cortical bone and cancellous bone) was compared. RESULTS: The hexagonal height of the implant with external connection had an influence on the stress distribution of the fixture, screw and upper prosthesis and the surrounding supporting bone. As the hexagon height increased, the stress was well distributed and there was a decrease in the maximum stress value. If the height of the hexagon reached over 1.2 mm, there was no significant influence on the stress distribution. CONCLUSION: For implants with external connections, a hexagon is vital for stress distribution. As the height of the hexagon increased, the more effective stress distribution was observed.

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.

Removal torque of zirconia abutment screws under dry and wet conditions

The aim of this study was to verify whether screw abutment lubrication can generate higher preload values compared to non-lubricated screws, a titanium abutment was screwed onto an implant analog and scanned with the Procera System to generate 20 zirconia abutments. MKIII Brånemark implants were clamped to a precision torque device, and the abutments were distributed in dry and wet groups with 10 specimens each. In the wet groups, the inner threads of the implants were filled with artificial saliva. All abutments were fastened with a Torqtite screw under 32 Ncm. Ten detorque measurements were performed per group pushing the reverse button of the Torque controller soon after screw tightening with values registered. The mean detorque values were calculated and compared by a Student's t test (?=0.05). The wet condition presented significantly higher mean detorque than the dry condition (31.5 ± 1.2 versus 27.5 ± 1.5 Ncm, respectively; p=0.0000024). In conclusion, there was always a loss in the initial torque values when the removal torque was measured under both conditions. The wet condition presented higher mean torque than the dry condition. Better preload values were established in the wet group, suggesting that the abutment screw must be lubricated in saliva to avoid further loosening.

A fim de verificar se a lubrificação do parafuso do pilar pode gerar valores maiores de pré-carga do que nos parafusos não lubrificados, um pilar de titânio foi parafusado no análogo do implante e escaneado pelo Sistema Procera para gerar 20 pilares de zircônia. Depois, os implantes MKIII Brånemark foram presos num dispositivo de torque. Os pilares foram distribuídos em grupos seco e úmido com 10 amostras cada. No grupo úmido, as roscas internas dos implantes foram preenchidas com saliva artificial. Então, todos os pilares foram apertados com parafuso Torqtite a 32 Ncm. Dez medidas de destorque foram realizadas por grupo apertando-se o botão reverso do Torque Controller logo depois do parafusamento, e os valores foram registrados. As medias de destorque foram calculadas e comparadas pelo teste t de Student (?=0,05). Os valores médios obtidos nas condições seca e úmida foram 27,5 ± 1,5 Ncm e 31,7 ± 1,2 Ncm, respectivamente. Diferenças estatisticamente significantes foram observadas (p=0,0000024). Observou-se sempre existir uma perda do torque inicial quando o torque de remoção é mensurado em ambas as condições. A condição úmida demonstrou um valor médio maior de torque do que a condição seca. Valores melhores de pré-carga podem ser estabelecidos no grupo úmido, sugerindo que o parafuso do pilar deve ser lubrificado em saliva para evitar seu afrouxamento.

Abrasion of abutment screw coated with TiN

STATEMENT OF PROBLEM: Screw loosening has been a common complication and still reported frequently. PURPOSE: The purpose of this study was to evaluate abrasion of the implant fixture and TiN coated abutment screw after repeated delivery and removal with universal measuring microscope. MATERIAL AND METHODS: Implant systems used for this study were Osstem and 3i. Seven pairs of implant fixtures, abutments and abutment screws for each system were selected and all the fixtures were perpendicularly mounted in liquid unsaturated polyesther with dental surveyor. After 20 times of repeated closing and opening test, the evaluation for the change of inner surface of implant and TiN-coated abutment screw, and weight loss were measured. Mann-Whitney test with SPSS statistical software for Window was applied to analyze the measurement of weight loss. RESULTS: TiN-coated abutment screws of Osstem and 3i showed lesser loss of weight than non-coated those of Osstem and 3i (P < .05, Mann-Whitney test). CONCLUSION: Conclusively, TiN coating of abutment screw showed better resistance to abrasion than titanium abutment screw. It was concluded that TiN coating of abutment screw would reduce the loss of preload with good abrasion resistance and low coefficient of friction, and help to maintain screw joint stability.

Influence of Tightening Torque on Implant-Abutment Screw Joint Stability / 대한치과보철학회지

STATEMENT OF PROBLEM: Within the elastic limit of the screw, the greater the preload, the tighter and more secure the screw joint. However, additional tensile forces can incur plastic deformation of the abutment screw when functional loads are superimposed on preload stresses, and they can elicit the loosening or fracture of the abutment screw. Therefore, it is necessary to find the optimum preload that will maximize fatigue life and simultaneously offer a reasonable degree of protection against loosening. Another critical factor in addition to the applied torque which can affect the amount of preload is the joint connection type between implant and abutment. PURPOSE: The purpose of this study was to evaluate the influence of tightening torque on the implant-abutment screw joint stability. MATERIAL AND METHODS: Respectively, three different amount of tightening torque (20, 30, and 40 Ncm) were applied to implant systems with three different joint connections, one external butt joint and two internal cones. The initial removal torque value and the postload (cyclic loading up to 100,000 cycles) removal torque value of the abutment screw were measured with digital torque gauge. Then rate of the initial and the postload removal torque loss were calculated for the comparison of the effect of tightening torques and joint connection types between implant and abutment on the joint stability. Results and CONCLUSION: 1. Increase in tightening torque value resulted in significant increase in initial and postload removal torque value in all implant systems (P .05), however GS II and US II systems exhibited significantly lower loss rates with 40 Ncm torque value than with 20 Ncm (P .05).

Detorque force and surface change of coated abutment screw after repeated closing and opening / 대한치과보철학회지

STATEMENT OF PROBLEM: Recently researches about WC/C (Tungsten Carbide/Carbon) or TiN (Titanium Nitride) coating on abutment screws are going on. It decreases friction coefficient, resistance against corrosion and withdrawal of physical fragility when the coating is applied to the metal surfaces. It is reported that coated abutment screws improved abrasion, adaptability and detorque force. PURPOSE: This study is about the effects of coated abutment screws on loosening of screw and for the purpose of solving the loosening phenomenon of abutment screws which is clinical problem. MATERIAL AND METHODS: Detorque force and surface changes are compared when 10 times of repeated closing and opening are applied to both uncoated titanium abutment screws (Group A) and coated abutment screws with WC/C (Group B) and TiN (Group C). Each group was made up of 10 abutment screws. RESULTS: 1. Before repeated closing and opening, Somewhat rough surface with regular direction was observed in Group A. Coated granules were observed in group B and group C and overall coated layer appeared in regular and smooth form. 2. Before repeated closing and opening, The coated surface showed bigger and thicker size of coated granules in Group C than Group B. 3. After repeated closing and opening, abrasion and deformation of abutment screw surface was observed in Group A and Group B. Exfoliation phenomenon was observed in Group B. 4. Group A showed biggest range of decrease when the weight changes of abutment screws were measured before and after repeated closing and opening. Group C showed less weight changes than Group B but there was no statistical difference between two groups. 5. Group B and Group C showed higher average detorque force than Group A and there was statistical difference. 6. Group A showed more prominent decrease tendency of average detorque force than Group B and Group C. CONCLUSION: Coated abutment screws with WC/C or TiN did not show prominent surface changes than uncoated titanium abutment screws even though they were repeatedly used. And they showed excellent resistance against friction and high detorque force. Thus it is considered that adaptation of WC/C or TiN coating on abutment screws will improve the screw loosening problem.

Detorque force of TiN-coated abutment screw with various coating thickness after repeated closing and opening / 대한치과보철학회지

STATEMENT OF PROBLEM: When TiN coating is applied to the abutment screw, occurrence of greater preload and prevention of the screw loosening could be expected due to decrease of frictional resistance. However, the proper thickness of TiN coating on abutment screw has not been yet reported. PURPOSE: The purpose of this study is to find out the appropriate TiN coating thickness by evaluating the detorque force and the surface change of titanium abutment screw with various TiN coating thickness. MATERIAL AND METHODS: 1. Material Thirty five non-coated abutment screws were prepared for TiN coating. TiN coatings were prepared by Arc ion plating method. Depending on the coating deposition time(CDT), experimental groups were divided into 6 groups(CDT 30min, 60min, 90min, 120min, 150min, 180min) and those of 1 group was not coated as a control group. Each group was made up of 5 abutment screws. 2. Methods FE-SEM(Field Emission Scanning Electron Microscoper) and EDX(Energy Dispersive X-ray Spectroscopy) were used to observe the surface of the abutment screw. Electric scales was used to measure the weight of the abutment screw after the repeated closing and opening of 10 trials. Detorque force was measured with digital torque gauge, at each trial. RESULTS: 1. As the coating deposition time increased, the surface became more consistent and smooth. 2. As for the abutment screws that were TiN coated for more than 60 minutes, no surface change was found after the repeated closing and opening. 3. The TiN coated abutment screws showed less weight change than the non-coated abutment screws. 4. The TiN coated abutment screws showed higher mean detorque force than the noncoated abutment screws. 5. The abutment screw coated for 60 minutes showed the highest mean detorque force. CONCLUSION: The coating layer of proper thickness is demanded to obtain consistent and smooth coating surface, resistance to wear, and increased detorque force of the abutment screw. In conclusion, the coating deposition time of 60 minutes indicated improved mechanical property, when TiN coating was conducted on titanium abutment screw.

Effect of TiN coating of abutment screw on detorque force / 대한치과보철학회지

PURPOSE: The aim of this study is to evaluate the effect of TiN coating of abutment screw on the unscrewing torque. MATERIAL AND METHODS: Titanium and Gold-Tite abutment screws were classified into two groups, Group A and C respectively, as control groups. Titanium abutment screws with TiN coatings were also classified into two groups, Group B and D, as experimental ones. Group A and B were tightened to 20 Ncm input torque, and Group C and D were tightened to 32 Ncm torque. Detorque values were measured with digital torque gauge during repeated closing and opening experiment. RESULTS: Abutment screws with TiN coating (Group B and D) showed statistically significant higher mean detorque values than those of Group A and C. DISSCUSION: Physical properties of TiN coating, such as low friction coefficient, high hardness and wear resistance, might contribute to higher detorque values. CONCLUSION: It is suggested that TiN coating of abutment screw help to reduce the risk of screw loosening and improve the stability of screw joint.

A study of the effect of an anti-rotational inner post screw systems on abutment screw loosening for single implant : Part 1 / 대한치과보철학회지

STATEMENT OF PROBLEM: Implant abutment screw joints tend to loosen under clinical conditions. Abutment screw loosening results in loss of preload in function. PURPOSE: Anti-rotational inner post screw (ARIPS) systems were compared with conventional abutment screws to reduce screw loosening. Reverse torque values were evaluated. MATERIAL AND METHODS: 32 implant assemblies (Warentec, Co, Ltd, Seoul, Korea) were organized as the 30-Ncm-torque conventional groups and 30-Ncm-torque ARIPS groups in external and internal system. The specimens were tested to 10(6) cycles at a load of 200N. Preload reverse torque, postload reverse torque, and the ratio of postload reverse torque to preload reverse torque were evaluated. The data were analyzed with unpaired t-test in external and internal systems. RESULTS: In the ratio of postload reverse torque to preload reverse torque, the ARIPS groups showed significant differences than the conventional screw group in both external and internal system. CONCLUSION: Within the limitations of this study, abutment screw loosening was effectively reduced using ARIPS system.

Influence of tungsten carbide/carbon coating on the preload of implant abutment screws / 대한치과보철학회지

STATEMENT OF PROBLEM: In order to increase preload with reducing the friction coefficient, abutment screws coated with pure gold and Teflon as dry lubricant coatings have been introduced. But the reported data indicate that if screw repeated tightening and loosening cycle, an efficiency of increasing preload was decreased by screw surface wearing off. PURPOSE: This study was to evaluate the influence of tungsten carbide/carbon coating, which has superior hardness and frictional wear resistance, on the preload of abutment screws and the stability of coating surface after repeated closures. MATERIAL AND METHOD: The rotational values of abutment screws and the compressive forces between abutment and fixture were measured in implant systems with three different joint connections, one external butt joint and two internal cones. Moreover, the stability and the alteration of coating surface were examined by comparison of the compressive force and the removable torque values during 10 consecutive trials, observation with scanning electron microscope and analyzed the elemental composition with energy dispersive x-ray spectroscopy. RESULTS AND CONCLUSION: 1. Application of coating resulted in significant increase of compressive force in all implant systems(P.05). 3. Removable torque values were greater with non-coated screw than that with coated screw (P.05). 5. After repeated trials, the surface layer of coated screw was maintained relatively well. However, surface wearing and irregular titanium fragments were found in non-coated screw.

The influence of abutment screw length and repeated tightening on screw loosening in dental implant / 대한치과보철학회지

Statement of problem: One of common problems associated with dental implant is the loosening of abutment screws that retain the implants. Purpose: This study was performed to investigate the influence of abutment screw length and repeated tightening on screw loosening in dental implant. Material and method: Forty nine Hexplants (13mm length, 4.3mm diameter, Ti grade IV, Warantec. Co. Ltd. Seongnam, Korea) and cementation type abutments(straight abutment) and abutment screws (0.4mm/pitch) were divided into 7 groups, depending on abutment screw length. Each implant and abutment was tightened to 30Ncm by torque controller(MGT50, MARK-10 Inc., USA) and the removal torque values were measured during 10 consecutive closure/opening trials Results and Conclusion: The results of comparing the removal torque value are as follows: 1. There is no significant difference in the removal torque value between groups in 10 consecutive closure/opening trials(p=0.97). 2. If the fractured abutment screw is engaged in longer than 2.425 thread length, there is no significant difference in the preload between the fractured abutment screw and the new abutment screw when both are equally tightened to 30 Ncm 3. The removal torque value in the 1st trial(24.510 Ncm) was lower than that in the 2nd,3rd,4th,5th,6th,7th trials and the removal torque value in the 2nd trials(25.551 Ncm) was maximum and was decreased in following trials. The removal torque value in the 1st trial was significantly lower than that in the 2nd,3rd,4th trials and was significantly higher than that in the 8th,9th,10th trials(p<0.05). 4. In the 2nd,3rd,4th,5th,6th,7th trials, the abutment screw was mainly influenced by settling effect and the higher preload was obtained. In the 8th,9th,10th trials, the abutment screw was mainly influenced by adhesive wear and the progressively lower preload was obtained.