Experimental Investigation on Diamond Band Saw Processing of Resin Mineral Composites.

Resin mineral composite (RMC) is a new material with several times the damping properties of gray cast iron and great corrosion resistance. Due to its overall brittleness, sawing with a diamond band saw would be a suitable method. In this research, sawing experiments are carried out to study the sawing force characteristics of the material and its surface morphology during the processing. The results show that the feed force level is in the range of 3.5~5.5 N and the tangential force level is relatively low. The distribution of resin mineral components does not have a significant impact on the average sawing force but increases the fluctuation of the lateral force signal. The maximum fluctuation volume is 94.86% higher than other areas. Uneven lateral force, generated when diamond particles pass through the resin-mineral interface, is one of the causes of fluctuations. The machined surface of RMC has uniform strip scratches and a small number of pits. Maintaining a constant ratio of sawing speed to feed speed can result in approximately the same machined surface. A step structure with a height of about 10 µm appears at the interface of resin minerals. As a processing defect, it may affect the performance of RMC components in some aspects, which need a further precision machining processing.

Hybrid surface implants: Influence of residual stress on mechanical behavior, evaluated by finite element analysis and validation by fatigue tests.

OBJECTIVES: To determine the influence of different surface roughness and residual stress of hybrid surface implants on their behavior and mechanical failure. METHODS: Three types of implants with different surface roughness were used as specimens: smooth, rough, and hybrid. A diffractometer was used to determine the residual stress of the implants according to their different surface treatment. These results were used as an independent variable in a finite element analysis that compared the three specimens to determine the von Mises stress transferred to the implants and supporting bone and the resulting microdeformations. Flexural strength and fatigue behavior tests were performed to compare the results of the three types of implants. RESULTS: Higher residual stress values were found for rough surfaces (p < 0.05, Student's t-test) compared to smooth surfaces, and both types of stress were different for the two types of hybrid implant surfaces. Finite element analysis found different von Mises stress and microdeformation results, both at the level of the implant and the bone, for the three types of implants under study. These results were correlated with the different flexural strength behaviors (lower resistance for hybrids and higher for rough surfaces, p < 0.05) and fatigue behavior (the rough implant had the longest fatigue life, while the hybrid implant exhibited the worst fatigue behavior). SIGNIFICANCE: The results show a trend toward a less favorable mechanical behavior of the hybrid implants related to the retention of different residual stresses caused by the surface treatment.

Comparison of Surface Morphology and Tool Wear in the Machining of Ti-6Al-4V Alloys with Uncoated and TiAlN Tools under Dry, Minimum Quantity Lubrication, Flood Cooling, and Low-Temperature Spray Jet Cooling Conditions.

TiAlN-coated carbide tools have been used to machine Ti-6Al-4V alloys in aviation workshops. However, the effect of TiAlN coating on surface morphology and tool wear in the processing of Ti-6Al-4V alloys under various cooling conditions has not been reported in the public published literature. In our current research, turning experiments of Ti-6Al-4V with uncoated and TiAlN tools under dry, MQL, flood cooling, and cryogenic spray jet cooling conditions were carried out. The machined surface roughness and tool life were selected as the two main quantitative indexes for estimating the effects of TiAlN coating on the cutting performance of Ti-6Al-4V under various cooling conditions. The results showed that TiAlN coating makes it hard to improve the machined surface roughness and tool wear of a cutting titanium alloy at a low speed of 75 m/min compared to that achieved by uncoated tools. The TiAlN tools presented excellent tool life in turning Ti-6Al-4V at a high speed of 150 m/min compared to that achieved by uncoated tools. From the perspective of obtaining finished surface roughness and superior tool life in high-speed turning Ti-6Al-4V, the selection of TiAlN tools is feasible and reasonable under the cryogenic spray jet cooling condition. The dedicative results and conclusions of this research could guide the optimized selection of cutting tools in machining Ti-6Al-4V for the aviation industry.

Effect of Coating Thickness on Abrasion and Cutting Performance of NCD-Coated Ball Endmills on Graphite Machining.

Nano-crystalline diamond (NCD) coating to improve the performance of cutting tools, as the coating thickness varies, the cutting performance and lifespan of the tool varies because the radius of its cutting edge and coating surface roughness are altered. Therefore, an in-depth analysis on the impact of the variations in coating thickness on the cutting tool abrasion and quality of machined surface is necessary. In this study, two NCD ball endmills were coated with 8 and 12 µm thicknesses, and the tool abrasion and roughness of the machined plane were observed after milling. Furthermore, the morphology of the coated surface and abrased cutting edge were observed using a 3D confocal microscope. Consequently, we observed that individual nodules were formed on the continuous aggregates as the coating thickness increased, which increased the coated surface roughness. The two damage modes of the aggregation determined the dominant abrasion that occurred on the cutting edges of both types of coating thicknesses. Delamination and crater wear caused a sharp increase in the roughness of the machined surface. In summary, the increase in coating thickness delayed the delamination of the coating but increased the roughness of the cutting edge, which reduced the machined surface roughness.

Effect of Pre-Existing Micro-Defects on Cutting Force and Machined Surface Quality Involved in the Ball-End Milling Repairing of Flawed KDP Crystal Surfaces.

When serving in extremely high-power laser conditions, KH2PO4 (KDP) surfaces are susceptible to incur laser damage points (also known as defects). Using micro-ball end milling cutters to repair and remove the pre-existing damage points on the flawed KDP crystal surface is the most effective method to control the growth of laser damage points on KDP crystal surfaces and prolong their service life. However, there are various forms of micro-defects (such as pits, scratches and brittle fractures) around the laser damage points on KDP crystal surfaces which possess remarkable effects on the micro-milling repair process and consequently deteriorate the repair quality. In this work, combined with nano-indentation experiments, elastic-plastic mechanics and fracture mechanics theory, a constitutive model considering the anisotropic property of KDP crystals and a three-dimensional (3D) finite element model (FEM) were established to simulate the cutting force and surface topography involved in the ball-end milling repairing of flawed KDP crystal surfaces. Besides, the micro-milling experiments were conducted to evaluate the change of cutting force and machined surface quality in the presence of micro-defects with various feed rates. The results show that micro-defects would induce the fluctuation of cutting force and a change of the undeformed cutting thickness (UCT) in the process of repairing the damage points on the crystal surface, which would lead to the brittle-ductile transition (BDT) and affect the machined surface quality. The machined surface quality was found to be deteriorated by the pre-existing micro-defects when the UCT was small (the UCT was less than 375 nm). On the contrary, brittle mode cutting in the local area can be transformed into ductile mode cutting, resulting in an improvement of repaired surface quality that is exhibited by the cutting force and microtopography. This work has great theoretical significance and engineering practical value for the promotion and application of micro-milling repairing technology in the practical manufacturing and operation of KDP optics applied to high-power laser systems.

Extraction and Reconstruction of Arbitrary 3D Frequency Features from the Potassium Dihydrogen Phosphate Surfaces Machined by Different Cutting Parameters.

To comprehensively analyze the effect of cutting parameters on the 3D surface topography of machined potassium dihydrogen phosphate crystals, 2D power spectrum density and continuous wavelet transform are used to extract and reconstruct the arbitrary actual 3D frequency features of machined potassium dihydrogen phosphate crystal surfaces. The 2D power spectrum density method is used to quantitatively describe the 3D surface topography of machined potassium dihydrogen phosphate crystals. The continuous wavelet transform method is applied to extract and reconstruct 3D topographies of arbitrary actual spatial frequency features in machined surfaces. The main spatial frequency features fx of the machined surfaces are 0.0056 µm-1, 0.0112 µm-1, and 0.0277 µm-1 with the cutting depth from 3 µm to 9 µm. With the feed rate changing from 8µm/r to 18 µm/r, the main spatial frequency features fx are 0.0056 µm-1-0.0277 µm-1. With the spindle speed from 1300 r/min to 1500 r/min, the main spatial frequency features fx are same as the main spatial frequency features of the cutting depths. The results indicate that the variation of cutting parameters affects the main spatial frequency features on the 3D surface topography. The amplitudes of the spatial middle-frequency features are increased with the increasing of cutting depth and spindle speed. The spatial low-frequency features are mainly affected via the feed rate. The spatial high-frequency features are related to the measurement noise and material properties of potassium dihydrogen phosphate. The distributional directions of the frequency features in the reconstructed 3D surface topography are consistent with the distribution directions of actual frequency features in the original surface topography. The reconstructed topographies of the spatial frequency features with maximum power spectrum density are the most similar to the original 3D surfaces. In this machining, the best 3D surface topography of the machined KDP crystals is obtained with a cutting depth ap = 3 µm, feed rate f = 8 µm/r and a spindle speed n = 1400 r/min.

Tool Wear Monitoring in Milling Based on Fine-Grained Image Classification of Machined Surface Images.

Cutting tool wear state assessment during the manufacturing process is extremely significant. The primary purpose of this study is to monitor tool wear to ensure timely tool change and avoid excessive tool wear or sudden tool breakage, which causes workpiece waste and could even damage the machine. Therefore, an intelligent system, that is efficient and precise, needs to be designed for addressing these problems. In our study, an end-to-end improved fine-grained image classification method is employed for workpiece surface-based tool wear monitoring, which is named efficient channel attention destruction and construction learning (ECADCL). The proposed method uses a feature extraction module to extract features from the input image and its corrupted images, and adversarial learning is used to avoid learning noise from corrupted images while extracting semantic features by reconstructing the corrupted images. Finally, a decision module predicts the label based on the learned features. Moreover, the feature extraction module combines a local cross-channel interaction attention mechanism without dimensionality reduction to characterize representative information. A milling dataset is conducted based on the machined surface images for monitoring tool wear conditions. The experimental results indicated that the proposed system can effectively assess the wear state of the tool.

Characterization of Machined Surface Topography Based on the Normal Declination Angle of Microfacets.

It is important to characterize surface topography in order to study machined surface characteristics. Due to the features of periodicity and randomness of machined surface topography, the existing topographical parameters may not describe its features accurately. A novel characterization method called the normal declination angle of microfacet-based surface topography is thus proposed for this task. The topography of machined surfaces is measured and the data on the normal declination angle are obtained. Then, surface topography is analyzed via the distribution of the normal declination angle. The lognormal distribution characterization model of machined surface topography is established, and the accuracy of the model is verified by error analysis. The results show that the calculated results of the present characterization model are generally consistent with the distribution of the normal declination angle, where the maximal root mean square errors (RMSE) is 4.5%. Therefore, this study may serve as an effective and novel way to describe the characteristics of the machined surface topography.

Evaluation of decontamination methods of oral biofilms formed on screw-shaped, rough and machined surface implants: an ex vivo study.

BACKGROUND: To evaluate the effect of several representative decontamination methods of oral biofilms on different implant surfaces. MATERIAL AND METHODS: Eleven participants wore a hard resin splint carrying 6 rough (GC Aadva® implant; 3.3-mm diameter, 8-mm length) or machined (not commercially available) surface implants for 4 days to accumulate dental plaque naturally on the titanium surfaces of the implants. Apart from surface roughness, the morphology of all implants was identical. After detaching the implants from the splints, the ability of the following decontamination methods-gauze soaked in saline (G), ultrasonic scaler (US), air abrasive (Air), rotary stainless steel instrument (Rot), and Er:YAG laser (Las)-to cleanse the contaminated implant surface for 1 min extra-orally was tested. The control (Cont) group did not receive any decontamination. Scanning electron microscopic (SEM) investigation of one participant's samples was employed to examine the post-instrumented implant surface for qualitative analysis, and bacterial culture of the remaining 10 participants' samples was performed to count the number of colony-forming units (CFU) for quantitative analysis. The experimental sequence was initially performed for the rough surface implants and then similarly repeated for the machined surface implants. Bacterial CFU counts among the six groups were analyzed using the Steel-Dwass test, and differences between rough and machined surface implants were determined using the Mann-Whitney U test. RESULTS: G and Rot eliminated most biofilms on machined surface implants according to SEM analysis. G, Air, and Rot removed significantly more of the biofilms on rough and machined surface implants compared with US according to CFU counts. Moreover, G significantly reduced more biofilms than Las on machined surface implants. The analysis between rough and machined surface implants showed that Cont, G, and US were better able to cleanse biofilms on machined surface implants compared with rough surface implants. CONCLUSIONS: Gauze soaked in saline and rotary stainless steel instruments may be advantageous for cleansing contaminated implant surfaces based on the qualitative and quantitative analyses. In contrast, air abrasives were not shown to be preferable in the qualitative analyses. Additionally, apart from the Er:YAG laser, the reduction of biofilms assessed in both qualitative and quantitative analyses demonstrated that all decontamination methods were better at cleansing machined surface implants compared with rough surface implants.

Research on the Relationship between Cutting Force and Machined Surface Quality in Micro Ball End-Milling of Potassium Dihydrogen Phosphate Crystal.

Potassium dihydrogen phosphate (KDP or KH2PO4) crystal is widely used as terminal frequency converters in inertial confinement fusion (ICF). However, KDP crystal is a typical difficult-to-cut optical crystal with the characteristic of soft-brittle. In this work, the relationship between cutting force and processed surface quality in micro ball end-milling of KDP crystal with various depth of cut and spindle speed is studied by carried out the micro-milling experiments. Fast Fourier Transform (FFT) algorithm is used to diagnose the recorded cutting force. The periodic change of cutting force and the cutting force after filtering noises can be got through FFT analysis. Through calculating the correlation coefficients between the static component of thrust force and roughness value Ra of machined grooves, as well as the peak-valley (P-V) value of thrust force and dimensional error of machined grooves, the roughness value Ra and dimensional error of machined grooves would be predicted by monitoring the static component and P-V value of the thrust force, respectively. The relatively large spindle speed helps to reduce the roughness value Ra. The spindle speed with moderate value is recommended to reduce the dimensional error of machined groove because the dimensional error of machined groove will increase when the spindle speed is small enough (causing brittle cutting) or large enough (reducing cutting stability).

Plaque accumulation on titanium disks with different surface treatments: an in vivo investigation.

Implants with rough surfaces are today widely used. It has been speculated that rough surfaces (Ra > 0.2 µm) provide a better "substrate" for retention and accumulation of plaque in terms of area, thickness and colony-forming unit that can eventually lead to peri mucositis and/or peri-implantitis. The aim of this investigation was to evaluate in vivo the plaque accumulation after 48 h on three implant surfaces with different treatments. For this investigation, we used 21 sterilized titanium disks, with a diameter of 8mm and a thickness of 3 mm, provided by the manufacturer: 7 with machined surface, as smooth control, 7 with HA grit sandblasted RBM surface and 7 with Ca++ incorporated in titanium Xpeed surface. One disk for each surface treatment was characterized at time 0 by SEM and AFM to study, respectively, the surface morphology and roughness. The other 18 disks were mounted randomly on three upper acrylic bites in a buccal lateral position, worn for 48 h by three volunteer students for plaque accumulation. After 48 h each disk was removed and analyzed qualitatively and quantitatively by an independent operator, not involved into the study, in order to avoid bias. Data collected were statistically analyzed by one-way ANOVA. The qualitative analysis showed no differences in terms of total plaque accumulation between the surfaces. Data from quantitative analysis using Anova Test showed no significance between all groups. In this in vivo investigation all the surfaces studied promoted plaque formation. The degree of surface roughness seems not to be a critical factor for plaque accumulation.

Experimental Investigation on Cutting Characteristics in Nanometric Plunge-Cutting of BK7 and Fused Silica Glasses.

Ductile cutting are most widely used in fabricating high-quality optical glass components to achieve crack-free surfaces. For ultra-precision machining of brittle glass materials, critical undeformed chip thickness (CUCT) commonly plays a pivotal role in determining the transition point from ductile cutting to brittle cutting. In this research, cutting characteristics in nanometric cutting of BK7 and fused silica glasses, including machined surface morphology, surface roughness, cutting force and specific cutting energy, were investigated with nanometric plunge-cutting experiments. The same cutting speed of 300 mm/min was used in the experiments with single-crystal diamond tool. CUCT was determined according to the mentioned cutting characteristics. The results revealed that 320 nm was found as the CUCT in BK7 cutting and 50 nm was determined as the size effect of undeformed chip thickness. A high-quality machined surface could be obtained with the undeformed chip thickness between 50 and 320 nm at ductile cutting stage. Moreover, no CUCT was identified in fused silica cutting with the current cutting conditions, and brittle-fracture mechanism was confirmed as the predominant chip-separation mode throughout the nanometric cutting operation.

A 7-year prospective radiographic evaluation of marginal bone level around two different implant systems: a randomized clinical trial.

OBJECTIVE: The aim of this study was to evaluate the change in marginal bone level radiographically around two different implant systems after 7 years of use. MATERIAL AND METHODS: Twenty fully edentulous patients were included in the study and randomly assigned to two treatment groups of machined surface implants (Brånemark, n = 40) and rough-surface implants (Xive, n = 40). The implants were early loaded with individual bar-retained overdentures. All patients were treated by the same surgeon and the same prosthodontist. Clinical and radiographic examinations were conducted at the time of implant loading (baseline) and annually for up to 7 years of use. Measurements to the nearest 0.1 mm were taken at the mesial and distal site, and the average values were calculated for each implant. A three-level mixed-effect analysis of covariance (ANOVA) was used to test the significance of the mean marginal bone change in the two implant groups. RESULTS: The study population consisted of 15 women (75%) and five men (25%) with an average age of 61.6 years. A total of 79 of 80 implants integrated successfully. n = 1 Brånemark implant failed after 3 weeks. There was a significant difference (P < 0.001) between the two implant systems at the baseline measurements (0.14 mm Brånemark vs. 0.39 mm Xive) and a highly significant difference for the annual bone loss (0.07 mm [Brånemark] vs. 0.18 mm [Xive], P < 0.001). CONCLUSION: Both the implant systems are clinically satisfying. Nevertheless, the Brånemark group showed a better radiological performance than the Xive group.

Influence of implant neck design and implant-abutment connection type on peri-implant health. Radiological study.

OBJECTIVE: To carry out a comparative study of two implants with different neck features and prostheses platform connection (machined with external connection and rough-surfaced with switching platform) upon peri-implant marginal bone loss, before and after functional loading. MATERIAL AND METHODS: A randomized, prospective radiological study was made. Eighteen totally edentulous patients were selected. Subjects were divided into two groups according to the type of implant neck used: (a) Osseous(®), with machined surface, without microthreads, external connection, and without platform switching; and (b) Inhex(®), with treated surface, microthreads, internal connection, and platform switching. Mesial and distal marginal bone loss was measured. Implant success was assessed according to the criteria of Buser. Control timepoints were as follows: (a) at implant placement; (b) at prosthesis placement; (c) 6 months after loading; (d) 12 months after loading. RESULTS: Fifteen patients that received 120 dental implants were included: 47% Osseous(®) group and 53% Inhex(®) group. Global mean marginal bone loss with Osseous(®) was 0.27 ± 0.43 mm and 0.38 ± 0.51 mm as determined 6 and 12 months after prosthetic loading, respectively, whereas in the case of Inhex(®) was 0.07 ± 0.13 and 0.12 ± 0.17 mm. These differences were statistically significant (P = 0.047). Difference between Osseous(®) and Inhex(®) in maxilla (P = 0.272) and mandibular (P = 0.462) bone loss were not statistically significant. CONCLUSIONS: Bone loss after 6 and 12 months proved statistically significant between two groups, with comparatively greater loss in the case of Osseous(®) implants vs. Inhex(®) implants. Regardless the heterogeneity of the two groups (neck shape, microthreads, surface texture), the implant-abutment connection appears to be a significant factor on peri-implant crestal bone levels. Anyway, in both groups, the values obtained were within normal ranges described in the literature.

Histomorphometric study of machined titanium implants and calcium phosphate coated titanium implants / 대한치과보철학회지

PURPOSE: The objective of this study was to investigate the effects of calcium phosphate coated titanium implant surface on bone response and implant stability at early stage of healing period of 3 weeks and later healing period of 6 weeks. MATERIAL AND METHODS: A total of 24 machined, screw-shaped implants (Dentium Co., Ltd., Seoul, Korea) which dimensions were 3.3 mm in diameter and 5.0 mm in length, were used in this research. All implants (n = 24), made of commercially pure (grade IV) titanium, were divided into 2 groups. Twelve implants (n = 12) were machined without any surface modification (control). The test implants (n = 12) were anodized and coated with thin film (150 nm) of calcium phosphate by electron-beam deposition. The implants were placed on the proximal surface of the rabbit tibiae. The bone to implant contact (BIC) ratios was evaluated after 3 and 6 weeks of implant insertion. RESULTS: The BIC percentage of calcium phosphate coated implants (70.8 +/- 18.9%) was significantly higher than that of machined implants (44.1 +/- 16.5%) 3 weeks after implant insertion (P = 0.0264). However, there was no significant difference between the groups after 6 weeks of healing (P > .05). CONCLUSION: The histomorphometric evaluation of implant surface revealed that: 1. After 3 weeks early healing period, bone to implant contact (BIC) percentage of calcium phosphate coated implants (70.8%) was much greater than that of surface untreated machined implants (44.1%) with P = 0.0264. 2. After 6 weeks healing period, however, BIC percentage of calcium phosphate coated implants group (79.0%) was similar to the machined only implant group (78.6%). There was no statistical difference between two groups (P = 0.8074). 3. We found the significant deference between the control group and experimental group during the early healing period of 3 weeks. But no statistical difference was found between two groups during the later of 6 weeks.

Evidencia de cambios clínicos y radiográficos en implantes oseointegrados de superficie maquinada y modificada, 3-12 meses de seguimiento / Evidence of clinical and radiographic changes in machined and modified surface osseointegrated implants. 3 to 12 months follow up

En este estudio se realizó una evaluación clínica y radiográfica entre un grupo de pacientes con implantes de superficie maquinada y otro grupo con superficie modificada para determinar si existe alguna diferencia significativa que justifique la utilización de una u otra superficie; para ello se trabajó con dos tipos de implantes de la casa comercial Lifecore®, un grupo con 30 implantes de superficie maquinada o lisa (SuperCAT®) y 30 implantes de superficie modificada o rugosa (RBM®), de conexión externa, tipo tornillo, para la restauración de diente único. El procedimiento quirúrgico se realizó de acuerdo con las recomendaciones del fabricante y a los seis meses se realizó la cirugía de destape y se colocó una restauración temporal. Se siguieron los parámetros de Roos y colaboradores (1997) para la evaluación clínica y radiográfica. Se obtuvo el 100% de oseointegración de los implantes para ambos grupos. La pérdida ósea promedio fue de 0,78 mm. No se encontraron diferencias estadísticamente significativas en la evaluación clínica y radiográfica entre los dos grupos de implantes de superficie maquinada o modificada para la restauración de diente único.

The aim of this study is to undertake a clinical and radiographic evaluation between two different patient groups: machined versus modified surface, to find out if there is statistically significant difference that support the use of implants with different surface properties. Sixty screw, external hex connection implants were examined: one group with 30 machined surface implants (SuperCAT®), and a second group with 30 implants with modified surface (RBM®), for restoring a single tooth. The surgical procedure was performed according with the manufacturer’s protocol. After six months the second phase surgery was performed and the temporary restoration was placed. At this point, the first radiographic evaluation was made. The Roos et al (1997) parameters were followed for the clinical and radiographic evaluation. A 100% of osseointegration was accomplished in both groups. The average marginal bone loss was 0.78 mm, without significant differences between the groups. All implants were reported as success grade 1, with no complications. There are not significant differences between the two groups of machined and modified implant surfaces for single tooth restoration.

Comparision of Osseointegration Depending on Surface Treatment / 대한치주과학회지

The present study was performed to evaluate histomorphological difference in various surface-treated implants in beagle. Implants(Implantium(R), Dentium Co. Korea) with pure titanium machined surface, acid treated surface, and Al2O3(50~100micrometer)blasted with acid treated surface were used in this study. All mandibular premolars of 1.5~2 year old male beagle dogs were extracted. At 3 months after extraction, the implants(phi 4mm, l6mm) were installed. The beagle were sacrificed at 1, 3 months after installation and then tissues including implants were prepared for non-decalcified specimens. These specimens were analyzed comparatively under light microscope. The results of this study were as follow 1. Higher rate of osseointegration were showed in the Al2O3(50~100micrometer)blasted with acid-treated surface. 2. Increased osseointegration were showed in the Al2O3(50~100micrometer)blasted with acidtreated surface with time. 3. Higher maturation of integration were showed in the Al2O3(50~100micrometer)blasted with acid-treated surface. In conclusion, surface treatment of Al2O3blasted with acid might be considered to shorten healing time and improve success rate as increasing contact of implant and bone.

A study on the change of implant stability using resonance frequency analysis / 대한치과보철학회지

STATEMENT OF PROBLEM: Resonance frequency analysis (RFA) has been increasingly served as a non-invasive and objective method for clinical monitoring of implant stability. Many clinical studies must be required for standardized baseline data using RFA. PURPOSE: This study was performed to evaluate RFA value changes in two stage surgery group and one stage surgery group in patients. MATERIAL AND METHOD: Forty-seven mandibles in consecutively implant installed patients were selected for this study and 141 fixtures were installed. Ninety-three fixtures were double threaded, machined surface design (Bra.nemark. MK III, Nobel Biocare AB, Go teborg, Sweden) and 48 fixtures were root form, threaded, HA-coated surface one (Replace(TM), Steri-Oss/Nobel Biocare AB, USA). Among those, each 10 fixture was installed in one stage group patients. ISQ values were measured using Osstell(TM) (Integration Diagnostics Ltd. Sweden) during fixture installation, at healing abutment connection and in the loading period for two stage surgery group patients and during at each 4, 6, 8, 10, 12 week and in the loading phase for one stage surgery group patients and evaluated the changes according to the time and fixture type. RESULTS: In two stage surgery group, mean and SD of ISQ values of machined surface implants were 76.85 +/- 3.74, 75.76 +/- 5.04, 75.73 +/- 4.41 and those of HA-coated surface implant were 75.05 +/- 6.23, 77.58 +/- 5.23, 78.32 +/- 4.29 during fixtures installation, at healing abutment connection and in the loading period, respectively. In one-stage surgery group, the ISQ values of machined surface and HA-coated surface implants decreased until 4 or 6 week and maintained at plateau for 1-3 week and increased to the loading period. CONCLUSIONS: Machined and HA-coated surface implants showed minimal ISQ changes with time if they were installed at the sites showing at least intact cortical plate and good bone qualities. And HA-coated implants had a tendency to show somewhat increased ISQ values with time.