The influence of intentional mobilization of implant fixtures before osseointegration / 대한치과보철학회지

PURPOSE: The purpose of this study was to investigate the influence of mobilization on bone-implant interface prior to osseointegration of fixtures. MATERIALS AND METHODS: The experimental implants (3.75 mm in diameter, 4.0 mm in length) were made of commercially pure (Grade IV) titanium, and were treated with RBM (MegaGen(R): Ca-P). The 80 implants (two in each tibia) were inserted into the monocortical tibias of 20 rabbits which each weighed more than 3.5 kg (Female, New Zealand White). According to the removal torque interval, the groups were divided into 10 groups, Group I (6 wks), Group II (4 days + 6 wks), Group III (4 days + 1 wk + 6 wks), Group IV (1 wk + 6 wks), Group V (1 wk + 1 wk + 6 wks), Group VI (2 wks + 6 wks), Group VII (2 wks+ 1 wk + 6 wk), Group VIII (3 wks + 6 wks), Group IX (3 wks + 1 wk + 6 wks) and Group X (10 wks). The control groups were Group I and X, the removal torque was measured at 6 wks and 10 wks with a digital torque gauge (Mark-10, USA). In the experimental groups, the removal torque was given once or twice before the final removal torque and the value was measured each time. After which, the implants were put back where they had been except the control groups. All the experimental groups were given a final healing time (6 wks) before the final removal torque test, in which values were compared with the control groups and the 1st and/or 2nd removal torque values in each experimental group. RESULTS: In the final removal torque tests, the removal torque value of Group X (10 wks) was higher than that of Group I (6 wks) in the control groups but not statistically different. There were no significant differences between the experimental groups and control groups (P>.05). In the first removal torque comparison, the experimental groups (4 days or 1 wk) values were significantly lower than the other experimental groups (2 wks or 3 wks). In the comparison of each experimental group according to healing time, the final removal torque value was significantly higher than the 1st torque test value. CONCLUSION: Once or twice mobilization of fixture prior to osseointegration did not deter the final bone to implant osseointegration, if sufficient healing time was given.

Erratum: The influence of intentional mobilization of implant fixtures before osseointegration / 대한치과보철학회지

The author list should be corrected as follows. Jin-Hyun Cho, Kwang-Heon Jo, Kyu-Bok Lee, Cheong-Hee Lee.

Effect of thread design on the marginal bone stresses around dental implant / 대한치과보철학회지

PURPOSE: The purpose of this study was to investigate the effect of different thread designs on the marginal bone stresses around dental implant. MATERIALS AND METHODS: Standard ITI implant(ITI Dental Implant System; Straumann AG, Waldenburg, Switzerland), 4.1 mm in diameter and 10 mm in length, was selected as control. Test implants of four different thread patterns were created based on control implant, i.e. maintaining all geometrical design of control implant except thread pattern. Four thread designs used in test implants include (1) small V-shape screw (model A), (2) large V-shape screw (model B), (3) buttress screw (model C), and (4) trapezoid screw (model D). Surface area for unit length of implant was 14.4 mm2 (control), 21.7 (small V-shape screw), 20.6 (large V-shape screw), 17.0 (buttress screw) and 28.7 mm2 (trapezoid screw). Finite element models of implant/bone complex were created using an axisymmetric scheme with the use of NISA II/DISPLAY III (Engineering Mechanics Research Corporation, Troy, MI, USA). A load of 100 N applied to the central node on the crown top either in parallel direction or at 30 degree to the implant axis (in order to apply non-axial load to the implant NKTP type 34 element was employed). Quantification and comparison of the peak stress in the marginal bone of each implant model was made using a series of regression analyses based on the stress data calculated at the 5 reference points which were set at 0.2, 0.4, 0.6, 0.8 and 1.0 mm from implant wall on the marginal bone surface. RESULTS: Results showed that although severe stress concentration on the marginal bone cannot be avoided a substantial reduction in the peak stress is achievable using different thread design. The peak marginal bone stresses under vertical loading condition were 7.84, 6.45, 5.96, 6.85, 5.39 MPa for control and model A, B, C and D, respectively. And 29.18, 26.45, 25.12, 27.37, 23.58 MPa when subject to inclined loading. CONCLUSION: It was concluded that the thread design is an important influential factor to the marginal bone stresses.

Influence of microthread design on marginal cortical bone strain developement: A finite element analysis / 대한치과보철학회지

PURPOSE: The present study was aimed to evaluate the level of cortical bone strain during the placement of an implant. The primary concern was to investigate if the extent of overloading area near the marginal bone could be affected by microthread fabricated at the cervical 1/3 of an implant. MATERIALS AND METHODS: Three dimensional finite element analysis was used to simulate the insertion of 3 implants. Control model was 4.1 x 10 mm implant (Submerged model, Dentis Co,, Daegu, Korea) equipped with a main thread only. Type I was with main thread and microthread, and Type II had similar thread pattern but was of tapered body. A PC-based finite element software (DEFORM 3D ver 5, SFTC, Columbus, OH, USA) was used to calculate a total of 3,600 steps of analysis, which simulated the whole insertion. RESULTS: Results showed that the strain field in the marginal bone within 1 mm of the implant wall was higher than 4,000 micro-strain in the control model. The size of bone overloading was 1-1.5 mm in Type I, and greater than 2 mm in Type II implants. CONCLUSION: These results indicate that the marginal bone may be at the risk of resorption on receiving the implant for all 3 implant models studied. Yet, the risk was greater for Type I and Type II implants, which had microthread at the cervical 1/3.

Influence of crestal module design on marginal bone stress around dental implant / 대한치과보철학회지

PURPOSE: This study was to investigate how the crestal module design could affect the level of marginal bone stress around dental implant. MATERIALS AND METHODS: A submerged implant of 4.1 mm in diameter and 10 mm in length was selected as baseline model (Dentis Co., Daegu,Korea).A total of 5 experimental implants of different crestal modules were designed (Type I model : with microthread at the cervical 3 mm, Type II model : the same thread pattern as Type I but with a trans-gingival module, Type III model: the same thread pattern as the control model but with a trans-gingival module, Type IV model: one piece system with concave transgingival part, Type V model: equipped with beveled platform). Stress analysis was conducted with the use of axisy mmetric finite element modeling scheme. A force of 100 N was applied at 30 degrees from the implant axis. RESULTS: Stress analysis has shown no stress concentration around the marginal bone for the control model. As compared to the control model, the stress levels of 0.2 mm areas away from the recorded implant were slightly lower in Type I and Type IV models, but higher in Type II, Type III and Type V models. As compared to 15.09 MPa around for the control model, the stress levels were 14.78 MPa, 18.39 MPa, 21.11 MPa, 14.63 MPa, 17.88 MPa in the cases of Type I, II, III, IV and V models. CONCLUSION: From these results, the conclusion was drawn that the microthread and the concavity with either crestal or trans-gingival modules maybe used in standard size dental implants to reduce marginal bone stress.

Cervical design effect of dental implant on stress distribution in crestal cortical bone studied by finite element analysis / 대한치과보철학회지

STATEMENT OF PROBLEM: High stress concentration on the crestal cortical bone has been regraded as a major etiologic factor jeopardizing long term stability of endosseous implants. PURPOSE: To investigate if the design characteristics of crestal module, i.e. internal type, external type, and submerged type, affect stress distribution on the crestal cortical bone. MATERIAL AND METHODS: A cylindrical shaped implant, 4.3 mm in diameter and 10 mm in length, with 3 different crestal modules, i.e. internal type, external type, and submerged type, were analysed. An axisymmetric scheme was used for finite elment formulation. A vertical load of 50 N and an oblique load of 50 N acting at 45degrees with the implant's long axis was applied. The peak crestal bone stress acting at the intersection of implant and crestal bone was compared. RESULTS: Under vertical load, the crestal bone stress was high in the order of internal, external, and submerged types. Under the oblique loading condition, it was in the order of internal, submerged, and external types. CONCLUSION: Crestal module design was found to affect the level of the crestal bone stresses although the actual amount was not significant.

Finite element analysis of peri-implant bone stress influenced by cervical module configuration of endosseous implant / 대한치과보철학회지

STATEMENT OF PROBLEM: Crestal bone loss, a common problem associated with dental implant, has been attributed to excessive bone stresses. Design of implant's transgingival (TG) part may affect the crestal bone stresses. PURPOSE: To investigate if concavely designed geometry at a dental implant's TG part reduces peri-implant bone stresses. MATERIAL AND METHODS: A total of five differently configured TG parts were compared. Base model was the ITI one piece implant (Straumann, Waldenburg, Switzerland) characterized by straight TG part. Other 4 experimental models, i.e. Model-1 to Model-4, were designed to have concave TG part. Finite element analyses were carried out using an axisymmetric assumption. A vertical load of 50 N or an oblique load of 50 N acting at 30degrees with the implant's long axis was applied. For a systematic stress comparison, a total of 19 reference points were defined on nodal points around the implant. The peak crestal bone stress acting at the intersection of implant and crestal bone was estimated using regression analysis from the stress results obtained at 5 reference points defined along the mid plane of the crestal bone. RESULTS: Base Model with straight configuration at the transgingival part created highest stresses on the crestal bone. Stress level was reduced when concavity was imposed. The greater the concavity and the closer the concavity to the crestal bone level, the less the crestal stresses. CONCLUSION: The transgingival part of dental implant affect the crestal bone stress. And that concavely designed one may be used to reduce bone stress.

Quantitative Ultrastructural Analysis of Periodontal Afferent Terminals in the Trigeminal Motor Nucleus / 대한해부학회지

Little is known about processing mechanism of sensory input from the periodontal ligaments to the trigeminal motor nucleus for the control of chewing force and modulation of chewing pattern. Low threshold mechanoreceptive periodontal afferent was labeled with horseradish peroxidase by use of intra-axonal injection technique and investigated with electron microscopy. Quantitative ultrastructural analysis was performed on the 39 serially reconstructed labeled boutons in the trigeminal motor nucleus in cat. Labeled bouton contained clear spherical vesicles and one or two large dense cored vesicles. Most of labeled boutons were dome or round shape. All the analysed labeled boutons were presynaptic to dendritic shaft or distal dendrite and those presynaptic to soma or proximal dendrite were not observed. A large number of labeled boutons (46.2%) were postsynaptic to one or two presynaptic pleomorphic vesicle containing endings. Synaptic triad, in that a presynaptic ending which is presynaptic to the labeled bouton, in turn, is presynaptic to dendrite that is postsynaptic to the labeled bouton, was observed in 10.3% of the labeled boutons. Most of the labeled boutons showed simple synaptic organization, in that 64.1% of the labeled boutons made synaptic contacts with one or two neuronal profiles. One (2.6%) of the 39 analyzed labeled boutons showed synaptic contacts with 5 or more neuronal profiles. Labeled bouton volume, mitochondrial volume, apposed surface area and active zone area showed wide variation. These ultrastructural parameters were positively correlated with bouton volume. The values for apposed surface area and active zone area with presynaptic p-endings, in contrast to those with postsynaptic dendrites, showed narrow range and had little correlation with bouton volume. The present study revealed characteristic features on ultrastructural parameters of labeled boutons from periodontal afferent which is involved in periodontal masseteric reflex, and that influence on the postsynaptic trigeminal motoneurons showed wide variability.