A study on the responses of osteoblasts to various surface-treated titanium / 대한치과보철학회지

STATEMENT OF PROBLEM: The long-term success of implants is the development of a stable direct connection between bone and implant surface, which must be structural and functional. To improve a direct implant fixation to the bone, various strategies have been developed focusing on the surface of materials. Among them, altering the surface properties can modify cellular responses such as cell adhesion, cell motility and bone deposition. PURPOSE: This study was to evaluate the cellular behaviors on the surface-modified titanium by morphological observation, cellular proliferation and differentiation. MATERIAL AND METHODS: Specimens were divided into five groups, depending on their surface treatment: electropolishing(EP) anodizing(AN), machining(MA), blasting with hydroxyapatite particle(RBM) and electrical discharge machining(EDM). Physicochemical properties and microstructures of the specimens were examined and the responses of osteoblast-like cells were investigated. The microtopography of specimens was observed by scanning electron microscopy(SEM). Surface roughness was measured by a three-dimensional roughness measuring system. The microstructure was analyzed by X-ray diffractometer(XRD) and scanning auger electron microscopy(AES). To evaluate cellular responses to modified titanium surfaces, osteoblasts isolated from neonatal rat were cultured. The cellular morphology and total protein amounts of osteoblast-like cell were taken as the marker for cellular proliferation, while the expression of alkaline phosphatase was used as the early differentiation marker for osteoblast. In addition, the type I collagen production was determined to be a reliable indicator of bone matrix synthesis. RESULTS: 1. Each prepared specimen showed specific microtopography at SEM examination. The RBM group had a rough and irregular pattern with reticulated appearance. The EDM-treated surface had evident cracks and was heterogeneous consisting of broad sheet or plate with smooth edges and clusters of small grains, deep pores or craters. 2. Surface roughness values were, from the lowest to the highest, electropolished group, anodized group, machined group, RBM group and EDM group. 3. All groups showed amorphous structures. Especially anodized group was found to have increased surface oxide thickness and EDM group had titaniumcarbide(TiC) structure. 4. Cells on electropolished, anodized and machined surfaces developed flattened cell shape and cells on RBM appeared spherical and EDM showed both. After 14 days, the cells cultured from all groups were formed to be confluent and exhibited multilayer proliferation, often overlapped or stratified. 5. Total protein amounts were formed to be quite similar among all the group at 48 hours. At 14 days, the electropolished group and the anodized group induced more total protein amount than the RBM group(P<.05). 6. There was no significant difference among five groups for alkaline phosphatase(ALP) activity at 48 hours. The AN group showed significantly higher ALP activity than any other groups at 14 days(P<.05). 7. All the groups showed similar collagen synthesis except the EDM group. The amount of collagen on the electropolished and anodized surfaces were higher than that on the EDM surface(P<.05).

The effect of abutment height on screw loosening in single implant-supported prostheses after dynamic cyclic loading / 대한치과보철학회지

STATEMENT OF PROBLEM: One of the common problems of dental implant prosthesis is the loosening of the screw that connects each component, and this problem is more common in single implant-supported prostheses with external connection. PURPOSE: The purpose of this study was to examine the changes of detorque values of abutment screws with external connection in different abutment heights. MATERIALS AND METHODS: After cyclic loading on three different abutment heights, detorque values were measured. Abutments were retained with titanium abutment screws tightened to 30 Ncm (30.5 kgmm) with digital torque gauge as recommended by the manufacturer. Replacing abutments, implants and titanium abutment screws with new ones at every measurement, initial detorque values were measured six times. In measuring detorque values after cyclic loading, Avana Cemented Abutments of 4.0 mm collar, 7.0 mm height (Osstem Co., Ltd., Seoul, Korea) were used with three different lengths of 5.0, 8.0, 11.0 mm. Shorter abutments were made by milling of 11.0 mm abutment to have the same force-exercised area of 4.5 mm diameter. Sine curve force (20N-320N, 14Hz) was applied, and detorque values were measured after cyclic loading of 2 million times by loading machine. Detorque values of initial and after-loading were measured by digital torque gauge. One-way ANOVA was employed to see if there was any influence from different abutment heights. RESULTS: The results were as follows : 1. The initial detorque value was 27.8+/-0.93 kgmm, and the ratio of the initial detorque value to the tightening torque was 0.91(27.8/30.5). 2. Measured detorque values after cyclic loading were declined as the height of the abutment increased, that was, 5.0 mm; 22.3+/-0.82 kgmm, 8.0 mm; 21.8+/-0.93 kgmm, and 11.0 mm; 21.3+/-0.94 kgmm. 3. One-way ANOVA showed no statistically significant differences among these (p> 0.05). 4. Noticeable mobility at the implant-abutment interface was not observed in any case after cyclic loading at all.

Bone response of three different surface implants: histomorphometric and resonance frequency analysis in dogs / 대한치과보철학회지

STATEMENT OF PROBLEM: Reducing treatment time in implant dentistry is a matter of main concern. There are so many factors affecting the success rate of immediate or early loaded implant for the initial bone response. The especially microscopic properties of implant surfaces play a major role in the osseous healing of dental implant. PURPOSE: The aims of this study were to perform a histologic and histomorphometric comparison of the healing characteristics anodically roughened surface, HA coated surface and RBM surface implant, and to compare of ISQ values measured by Osstell(TM) for resonance frequency analysis in dogs mandible during 2 weeks. MATERIAL AND METHOD: Bone blocks from 2 dogs were caught after covered healing for 0 day(2h); Group I, 1 week; Group II and 2 weeks; Group III. One longitudinal section was obtained for each implant and stained with hematoxylin and eosin. Histomorphometric analysis was done with Kappa Imagebase system to calculate bone-to-implant contact and bone volumes inside the threads. ISQ values were measured in every time of surgery schedule. CONCLUSION: The experiment revealed that : 1. The percentages of bone-to-implant contact on the fixture in each group were not significantly different(P > 0.05). 2. The percentages of bone area inside the threads on the fixture in each group were not significantly different(P > 0.05). 3. The ISQ level showed clinical stability of each fixture during 2 weeks(all ISQ level >_71).

The effect of growth factors in platelet-rich plasma on the activity of osteoblast cell line / 대한치과보철학회지

STATEMENT OF PROBLEM: Platelet-rich plasma(PRP) is well known to be very effective method to stimulate and accelerate the healing of bone and soft tissue. However, there are few reports which deal with the mechanisms of the PRP on the activation of the osteoblasts. PURPOSE: This study was aimed to investigate the effect of growth factors in PRP on the activity of osteoblasts. MATERIAL AND METHOD: To evaluate the effect on human, human osteoblast cell line was cultured. PRP was extracted from the blood of a healthy volunteer. Using the recombinant growth factors of PDGF, TGF-beta, IGF-1, bFGF which are mainly found at bone matrix and their neutralizing antibody, the effect of PRP on the attachment and proliferation of osteoblasts was evaluated. To evaluate the autocrine and paracrine effects, conditioned media(CM) of PRP was made and compared with PRP. By the western blot analysis, the expression of growth factors in PRP, CM was examined. Cell morphology was compared by the light microscope. RESULTS: 1) The effects of CM on osteoblast were similar to the effects of PRP. 2) PRP, CM, recombinant TGF-beta, bFGF, IGF-1 showed significantly higher cellular attachment than control(P<0.05) in the cell attachment assay. In the cell proliferation assay, PRP, CM, recombinant TGF-beta, IGF-1, bFGF, PDGF increased significantly cell proliferation(P<0.01). Among the recombinant growth factors, IGF-1 showed the highest cellular attachment and proliferation. 3) In the western blot assay, bFGF, IGF-1, PDGF were equally expressed in PRP and CM. 4) The attachment of osteoblast cell decreased significantly after the addition of neutralizing antibody against TGF-beta, IGF-1(P<0.05). In the cell proliferation assay, the addition of neutralizing antibody against TGF-beta, bFGF, PDGF, IGF-1 decreased significantly the cellular proliferation(P<0.05). The amount of decreasing in the cell attachment and proliferation is the highest in ab-IGF-1. 5) The cells in control group were flattened and elongated with a few cellular processes in the a light microscope. But, the cells appeared as spherical, plump cells with well developed cellular processes in experimental groups. The cells in PRP and CM had more prominent developed features than recombinant growth factor groups. CONCLUSIONS: These findings imply that PRP maximize the cellular activity in early healing period using the synergistic effect, autocrine, paracrine effects of growth factors and increase the rate and degree of bone formation.

Functional reconstruction of dento-palatal and maxillary defect using staged operation of prefabricated scapular free flap and dental implants

The flap considered at first for the reconstruction of large maxillary defect, especially mid-face defect, is scapular free flap, because it provides ample composite tissue which can be designed 3-dimensionally for orbital, facial and oral reconstruction. In case of maxillary defect involving hard palate, however, this flap has some limitations. First, its bulk prevents oral function and physio-anatomic reconstruction of nasal and oral cavity. Second, mobility and thickness of cutaneous paddle covering the alveolar area reduce retention of tissue-supported denture and give rise to peri-implantitis when implant is installed. Third, lateral border of scapula that is to reconstruct maxillary arch and hold implants is straight, not U-shaped maxillary arch form. To overcome these problems, new concept of step prefabrication technique was provided to a 27-year-old male patient who had been suffering from a complete hard palate and maxillary alveolar ridge defect. In the first stage, scapular osteomuscular flap was elevated, tailored to fit the maxillary defect, particulated autologous bone was placed subperiosteally to simulate U-shaped alveolar process, and then wrapped up with split thickness skin graft(STSG, 0.3mm thickness). Two months later, thus prefabricated new flap was elevated and microtransferred to the palato-maxillary defect. After 6 months, 10 implant fixtures were installed along the reconstructed maxillary alveolus, with following final prosthetic rehabilitation. The procedure was very successful and patient is enjoying normal rigid diet and speech.

An experimental study of newly designed implant with RBM surface in the rabbit tibia: resonance frequency analysis and removal torque study / 대한치과보철학회지

STATEMENT OF PROBLEM: The importance of fixture design and surface treatment. PURPOSE: The clinical success of dental implants is affected by many factors such like as degree of osseointegration, the effective load dispersion for the prostheses, and a lot of attempts have been made to overcome the difficulties. In this study, efforts were made to find the possibility of clinical acceptance of the dental implants of newly designed surface and resorbable blast media surcace. MATERIALS AND METHODS: In this study, two groups of custom-made, screw-shaped implants were prepared. Tthe first with the consisting of Branemark clone design and the other with the new design. These implants were divided into four groups according to the kinds of surface treatment. Four implants(AVANA., Osstem, Busan, Korea) of each group were installed in twenty rabbits. Group A was consisted of Branemark clone implant left as machined, Group B with Branemark clone implants with RBM(Resorbable blast media) surface, Group C with newly designed implants left as machined and Group D with newly designed implants with RBM surface. One of the twenty rabbits died from inflammation and the observation was made for six weeks. Specimens from four groups were observed using scanning electron microscopy with 40, 100, 1000 magnification power and microsurface structures were measured by white-light scanning interferometry for three dimensional surface roughness measurements(Accura 2000., Intek-Plus, Korea.). Removal torque was measured in 17 rabbits using digital torque gauge(MGT 12R, Mark-10 corp., NY, U.S.A.) immediately after the sacrifice and two rabbits were used for the histologic preparation(EXAKT 310., Heraeus Kulzer, Wehrheim, Germany) of specimens and observed under light microscope. Resonance frequency measurement(Osstell(R)) was taken with the 19 rabbits at the beginning of the implant fixation and immediately after the sacrifice. RESULTS: Following results were taken from the experiment. 1. The surface of the RBM implants as seen with SEM had rough and irregular pattern with reticular formation compared to that of turned specimens showing different surface topographies. 2. The newly designed implant with RBM surface had high removal torque value among four groups with no statistical significance. The average removal torque was 49.95+/-6.70Ncm in Group A, 51.15+/-4.40Ncm in Group B, 50.78+/-9.37Ncm in Group C, 51.09+/-4.69Ncm in Group D. 3. The RFA values were 70.8+/-4.3Hz in Group A, 71.8+/-3.1Hz in Group B, 70.9+/-2.5Hz, 72.7+/-2.5Hz in Group D. Higher values were noted in the groups which had surface treatment compared to the untreated groups with no statistical significance. 4. The results from the histomorphometric evaluation showed a mean percentage of bone-toimplant contact of 45+/-0.5% in Group A, 55+/-3% in Group B, 49.5+/-0.5% in Group C, and 55+/-3% in Group D. Quite amount of newly formed bone were observed at the surface RBM-treated implants in bone marrow space.

A study on the adhesion of a soft liner containing 4-META to the base metal alloy and its viscoelastic property / 대한치과보철학회지

STATEMENT OF PROBLEM: Soft lining materials, also referred to as tissue conditioning materials, tissue treating materials, relining materials, soft liners or tissue conditioners, were first introduced to dentistry by a plastic manufacturer in 1959. Since the introduction of the materials to the dental field, their material properties have been continually improved through the effort of many researchers. Soft lining materials have become widely accepted, particularly by prosthodontists, because of their numerous clinical advantages and ease of manipulation. Unfortunately, few reports have been issued upon the topic of increasing the bond strength between the base metal alloy used in cast denture bases and PMMA soft liner modified with 4-META, nor upon the pattern of debonding and material change in wet environment like a intra oral situation. PURPOSE: The purposes of this study were comparing the bond strength between base metal alloy used for the cast denture bases and PMMA soft liner modified with 4-META, and describing the pattern of debonding and material property change in wet environment like the intraoral situation. MATERIAL AND METHODS: This study consisted of four experiments: 1. The in vitro measurement of shear bond strength of the adhesive soft liner. 2. The in vitro measurement of shear bond strength of the adhesive soft liner after 2 weeks of aging. 3. A comparison of debonding patterns. 4. An evaluation the gelation time of modified soft liner. The soft liner used in this study was commercially available as Coe-soft (GC America.IL., USA), which is provided in forms of powder and liquid. This is a PMMA soft liner commonly used in dental clinics. The metal primer used in this study was 4-META containing primer packed in Meta fast denture base resin (Sun Medical Co., Osaka, Japan). The specimens were formed in a single lap joint design, which is useful for evaluating the apparent shear bond strength of adhesively bonded metal plate by tensile loading. Using the 20x20mm transparent grid, percent area of adhesive soft liner remaining on the shear area was calculated to classify the debonding patterns. To evaluate the change of the initial flow of the modified adhesive soft liner, the gelation time was measured with an oscillating rheometer (Haake RS150W/TC50, Haake Co., Germany). It was a stress control and parallel plate type with the diameter of 35mm. CONCLUSION. Within the conditions and limitations of this study, the following conclusions were drawn as follows. 1. There was significant increase of bond strength in the 5% 4-META, 10% 4-META containing groups and in the primer coated groups versus the control group(P<0.05). 2. After 2 weeks of aging, no significant increase in bond strength was found except for the group containing 10% 4-META (P<0.05). 3. The gelation times of the modified soft liner were 9.3 minutes for the 5% 4-META containing liner and 11.5 minutes for the 10% 4-META liner. 4. The debonding patterns of the 4-META containing group after 2 weeks of aging were similar to those of immediaely after preparation, but the debonding pattern of the primer group showed more adhesive failure after 2 weeks of aging.

A study of screw loosening after dynamic continous fatigue test of several abutment screw / 대한치과보철학회지

STATEMENT OF PROBLEM: Chronic implant screw loosening remains a problem in restorative practices. Some implant manufactureres have introduced abutment screws with treated material, surfaces and macrostructures in an effort to reduce potential loosening. PURPOSE: This study evaluated the materials and loading cycles on detorque value after dynamic continous fatigue test in the sinulated conditions of posterior single restoration. MATERIAL AND METHOD: Fourteen of each of the following abutment screws - titanium alloy, gold alloy, gold-tite, and titanium alloy modified - were used in test. SEM is used to verify macrostructures of each screws. ZrO2/Al2O3 composite abutment was tightened on 4x10.0mm titanium external implant at 30 Ncm. Cyclic loading machine delivered dynamic loading forces between 20 and 320N for 100,000, 200,000, 300,000, 500,000, and 1,000,000 cycles at frequencies 14Hz. Torque and detorque value after loading was measured. RESULTS: All measued screws had different screw length and thread form. Titanium modified screw had greater detorque value than others before and after cyclic loadings(p<0.05). All abutment screws had no significant change in mean percentage of detorque value after loading to initial value after less than 500,000 cyclic loadings, but significant lower value after 1,000,000 cycles(p<0.05). CONCLUSION: Within limintations of this study, all abutment screws may be loosend after about1 year use. Annual check-up is nessasary to prevent screw loosening.

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.

A study on osteoblast-like cell responses to surface-modified titanium / 대한치과보철학회지

STATEMENT OF PROBLEM: The success of implants depends on intimate and direct contact of implant material on bone tissue and on functional relationship with soft tissue contact. Creation and maintenance of osseointegration depend on the understanding of the tissue's healing, repairing, and remodeling capacity and these capacities rely on cellular behavior. Altering the surface properties can modify cellular responses such as cell adhesion, cell motility, bone deposition. Therefore, various implant surface treatment methods are being developed for the improved bone cell responses. PURPOSE: The purpose of this study was to evaluate the responses of osteoblast-like cells to surface- modified titanium. MATERIALS AND METHODS: The experiment was composed of four groups. Group 1 represented the electropolished surface. Group 2 surfaces were machined surface. Group 3 and Group 4 were anodized surfaces. Group 3 had low roughness and Group 4 had high roughness. Physicochemical properties and microstructures of the d iscs were examined and the responses of osteoblast-like cells to the discs were investigated. The microtopography was observed by SEM. The roughness was measured by three-dimension roughness measuring system. The microstructure was analyzed by XRD, AES. To evaluate cell responses to modified titanium surfaces, osteoblasts isolated from calvaria of neonatal rat were cultured. Cell count, morphology, total protein measurement and alkaline phosphatase activities of the cultures were examined. RESULTS AND CONCLUSION: The results were as follows 1. The four groups showed specific microtopography respectively. Anodized group showed grain structure with micropores. 2. Surface roughness values were, from the lowest to the highest, electropolished group, machined group, low roughness anodized group, and high roughness anodized group. 3. Highly roughened anodized group was found to have increased surface oxide thickness and surface crystallinity. 4. The morphology of cells, flattened or spherical, were different from ach other. In the electropolished group and machined group, the cells were almost flattened. In two anodized groups, some cells were spherical and other cells were flattened. And the 14 day culture cells of all of the groups were nearly flattened due to confluency. 5. The number of attached cells was highest in low roughness anodized group. And the machined group had significantly lower cell count than any other groups(P<.05). 6. Total protein contents showed no difference among groups. 7. The level of alkaline phosphatase activities was higher in the anodized groups than electropolished and machined groups(P<.05).

The effect of the bioresorbable collagen membrane on the regeneration of bone defect by using the mixture of autograft and xenograft bone / 대한치과보철학회지

STATEMENT OF PROBLEM: In cases where bony defects were present, guided bone regenerations have been performed to aid the placement of implants. Nowadays, the accepted concept is to isolate bone from soft tissue by using barrier membranes to allow room for generation of new bone. Nonresorbable membranes have been used extensively since the 1980's. However, this material has exhibited major shortcomings. To overcome these faults, efforts were made to develop resorbable membranes. Guided bone regenerations utilizing resorbable membranes were tried by a number of clinicians. Bio-Gide. is such a bioresorbable collagen that is easy to use and has shown fine clinical results. PURPOSE: The aim of this study was to evaluate the histological results of guided bone regenerations performed using resorbable collagen membrane(Bio-Gide.) with autogenous bone, bovine drived xenograft and combination of the two. Surface morphology and chemical composition was analyzed to understand the physical and chemical characteristics of bioresorbable collagen membrane and their effects on guided bone regeneration. MATERIAL AND METHODS: Bioresorbable collagen membrane (Bio-Gide.), Xenograft Bone(Bio-Oss), Two healthy, adult mongrel dogs were used. RESULTS: 1. Bioresorbable collagen membrane is pure collagen containing large amounts of Glysine, Alanine, Proline and Hydroxyproline. 2. Bioresorbable collagen membrane is a membrane with collagen fibers arranged more loosely and porously compared to the inner surface of canine mucosa : This allows for easier attachment by bone-forming cells. Blood can seep into these spaces between fibers and form clots that help stabilize the membrane. The result is improved healing. 3. Bioresorbable collagen membrane has a bilayered structure : The side to come in contact with soft tissue is smooth and compact. This prevents soft tissue penetration into bony defects. As the side in contact with bone is rough and porous, it serves as a stabilizing structure for bone regeneration by allowing attachment of bone-forming cells. 4. Regardless of whether a membrane had been used or not, the group with autogenous bone and Bio-Oss. filling showed the greatest amount of bone fill inside a hole, followed by the group with autogenous bone filling, the group with blood and the group with Bio-Oss. Filling in order. 5. When a membrane was inserted, regardless of the type of bone substitute used, a lesser amount of resorption occurred compared to when a membrane was not inserted. 6. The border between bone substitute and surrounding bone was the most indistinct with the group with autogenous bone filling, followed by the group with autogenous bone and Bio-Oss. filling, the group with blood, and the group with Bio-Oss. filling. 7. Three months after surgery, Bio-Gide. and Bio-Oss. were distinguishable. CONCLUSION: The best results were obtained with the group with autogenous bone and Bio-Oss. filling used in conjunction with a membrane.

The level of residual monomer in injection molded denture base materials / 대한치과보철학회지

STATEMENT OF PROBLEM: The residual monomer of denture base materials causes hypersensitivity on oral mucosa and intereferes with the mechanical properties of the cured resin. The amount of residual monomer is influenced by materials, curing cycle, processing method, and etc. PURPOSE: The aim of this study was to investigate the residual methyl methacrylate(MMA) content of injection molded denture base polymer, and to compare this with the self-cured resin and the conventional compression molded heat-cured resin. MATERIALS AND METHODS: Disc shaped test specimens (50mm in diameter and 3mm thick) were prepared in a conventional flasking technique with gypsum molding. One autopolymerized denture base resins (Vertex SC. Dentimex. Netherlands) and two heat-cured denture base resins (Vertex RS. Dentimex. Netherlands, Ivocap. Ivoclar Vivadent, USA) were used. The three types of specimens were processed according to the manufacturer's instruction. After polymerization, all specimens were stored in the dark at room emperature for 7 days. There were 10 specimens in each of the test groups. 3-mm twist drills were used to obtain the resin samples and 650mg of the drilled sample were collected for each estimation. Gas chromatography (Agillent 6890 Plus Gas Chromatograph, Agillent Co, USA) was used to determine the residual MMA content of 10 test specimens of each three types of polymer. RESULTS: The residual monomer content of injection molded denture base resins was 1.057+/- 0.141%. The residual monomer content of injection molded denture base resins was higher than that of compression molded heat cured resin (0.867+/-0.169%). However, there was no statistical significant difference between two groups (p > 0.01). The level of residual monomer in self cured resin(3.675+/-0.791) was higher than those of injection molded and compression molded heat cured resins (p<0.01). CONCLUSION: With respect to ISO specification pass/fail test (2.2% mass fraction) of residual monomer, injection molding technique(1.057+/-0.141%) is a clinicaly useful and safe technique in terms of residual monomer.

Strain changes of acrylic resin specimens cured by three curing cycles / 대한치과보철학회지

The acrylic resin was first introduced as denture base materials in 1937 and it is commonly used for denture base fabrication nowadays. Three different curing cycles (Conventional curing cycle, short curing cycle and long curing cycle) and three commercially available heat-activated acrylic resins (Vertex RS, Lucitone 199 and ProBase Hot) were investigated to find the curing cycle and ma-terial that showed the minimum shrinkage of the resin during polymerization process. A brass master mold was fabricated and duplicated by additional silicone impression material. Stone molds were made by pouring of type III dental stone (SILKY-ROCK YELLOW, Whip-Mix, Louisville, Kentucky). It was embedded in the flask. Strain gauge and thermocouple were embedded in the specimen. Strain gauge and thermocouple were connected to signal conditioning amplifier and data was recorded by pre-programmed software. The parameters ESmax (Maximum ex-pansion strain), Sb (Strain measured just before deflasking procedure), Sa (Strain measured just af-ter deflasking procedure) and Sf (Strain measured at the end of the experiment) were measured delta S was calculated from Sb and Sa (delta S=Sb-Sa). In the experiment concerned about materials, the pa-rameters 90-ESmax (Maximum expansion strain measured during early 90 minutes of curing procedure), 180-ESmax (Maximum expansion strain measured from 90 minutes to 180 minutes), Sb, Sa, delta S and Sf were measured and the following conclusions were made. 1. The ESmax value of conventional curing cycle showed the largest value and the 180-ESmax val-ue of Lucitone 199 showed the smallest value. 90-ESmax values showed no significant difference (p<0.05). 2. delta S values of conventional curing cycle showed the positive values. delta S values of short curing cycle and long curing cycle showed the negative values. All three materials cured by conventional curing cycle showed the positive values. 3. The Sf values of long curing cycle and ProBase Hot (cured by conventional curing cycle)showed the smallest values.

Effect of the surface modifications and the use of washer on the reverse torque of the implant prosthetic gold retaining screw / 대한치과보철학회지

The screw loosening is one of the complications that happen frequently in dental implant prostheses. The purpose of this study was to evaluate the changes of reverse/loosening (opening) torque of the screw according to the surface modifications by sandblasting and 24K gold electroplating as well as to determine the possibility of the clinical use of a washer in dental implant. The reverse torque of 4 experimental conditions(control, sandblasted, use of washers, electroplasted) was measured by digital torque gauge (Model MGT50Z, Mark-10 Corp., 458 West John Street Hicksville, NY 11801 USA). Electronic torque controller (Nobel Biocare DEA 020) was used in fastening the gold screws into abutment replicas. Mixed Linear Model Analysis method was used for statistical analysis. To examine the changes of screw thread surface, microphotographs were taken by Olympus PME-3 metallurgic microscope (Olympus Optical Co. Ltd., Tokyo, Japan). Within the limitations of this study, the following results were drawn: 1. The surface modifications of the gold screws and the use of a washer have significantly affected the reverse torque value compared to the control group (p<0.01). 2. Sandblasting and electroplating treatments demonstrated significantly higher reverse torque val-ue than that of control group. 3. The use of a washer may be one of the useful clinical methods that prevent the screw loosening. However, further studies are necessary for the material selection and design of the washer.

A Study On The Temperature Changes Of Bone Tissues During Implant Site Preparation / 대한치과보철학회지

The purpose of this study is to examine the possibility of thermal injury to bone tissues during an implant site preparation under the same condition as a typical clinical practice of Branemark implant system.All the burs for Branemark implant system were studied except the round bur.The experiments involved 880 drilling cases:50 cases for each of the 5 steps of NP, 5 steps of RP,and 7 steps of WP,all including srew tap,and 30 cases of 2mm twist drill. For precision drilling,a precision handpiece restraining system was developed(Eungyong Machinery Co.,Korea).The system kept the drill parallel to the drilling path and allowed horizontal adjustment of the drill with as little as 1 mu m increment.The thermocouple insertion hole.that is 0.9mm in diameter and 8mm in depth,was prepared 0.2mm away from the tapping bur,the last drilling step.The temperatures due to countersink,pilot drill,and other drills were measured at the surface of the bone,at the depths of 4mm and 8mm respectively. Countersink drilling temperature was measured by attaching the tip of a thermocouple at the rim of the countersink.To assure temperature measurement at the desired depths,''bent-thermocouples'' with their tips of 4 and 8mm bent at 120 were used.The profiles of temperature variation were recorded continuously at one second interval using a thermometer with memory function (Fluke Co.,U.S.A.)and 0.7mm thermocouples (Omega Co.,U.S.A.). To simulate typical clinical conditions,35mm square samples of bovine scapular bone were utilized.The samples were approximately 20mm thick with the cortical thickness on the drilling side ranging from 1 to 2mm.A sample was placed in a container of saline solution so that its lower half is submerged into the solution and the upper half exposed to the room air,which averaged 24.9 degrees C.The temperature of the saline solution was maintained at 36.5 degrees C using an electric heater (J.O Tech Co.,Korea).This experimental condition was similar to that ofa patient's opened mouth. The study revealed that a 2mm twist drill required greatest attention.As a guide drill, a twist drill is required to bore through a '' virgin bone,''rather than merely enlarging an already drilled hole as is the case with other drills.This typically generates greater amount of heat.Furthermore,one tends to apply a greater pressure to overcome drilling difficulty, thus producing even greater amount heat. 150 experiments were conducted for 2mm twist drill.For 140 cases,drill pressure of 750g was sufficient,and 10 cases required additional 500 or 100g of drilling pressure.In case of the former,3 of the 140 cases produced the temperature greater than 47 degrees C,the threshold temperature of degeneration of bone tissue (1983.Eriksson et al.5))which is also the reference temperature in this study.In each of the 10 cases requiring extra pressure,the temperature exceeded the reference temperature.More significantly,a surge of heat was observed in each of these cases.This observations led to addtional 20 drilling experiments on dense bones.For 10 of these cases,the pressure of 1,250g was applied.For the other 10,1,750g were applied.In each of these cases,it was also observed that the temperature rose abruptly far above the thresh-old temperature of 47 degrees C,sometimes even to 70 or 80 degrees C.It was also observed that the increased drilling pressure influenced the shortening of drilling time more than the rise of drilling temperature.This suggests the desirability of clinically reconsidering application of extra pressures to prevent possible injury to bone tissues. An analysis of these two extra pressure groups of 1,250g and 1,750g revealed that the t-statistics for reduced amount of drilling time due to extra pressure and increased peak temperature due to the same were 10.80 and 2.08 respectively suggesting that drilling time was more influenced than temperature. All the subsequent drillings after the drilling with a 2mm twist drill did not produce excessive heat, i.e.the heat generation is at the same or below the body temperature level. Some of screw tap,pilot,and countersink showed negative correlation coefficients between the generated heat and the drilling time,indicating the more the drilling time,the lower the temperature. The study also revealed that the drilling time was increased as a function of frequency of the use of the drill.Under the drilling pressure of 750g, it was revealed that the drilling time for an old twist drill that has already drilled 40 times was 4.5 times longer than a new drill. The measurement was taken for the first 10 drilings of a new drill and 10 drillings of an old drill that has already been used for 40 drillings. ''Test Statistics''of small samples t-test was 3.49,confirming that the used twist drills require longer drilling time than new ones.On the other hand,it was revealed that there was no significant difference in drilling temperature between the new drill and the old twist drill. Finally,the following conclusions were reached from this study: 1.Used drilling bur causes almost no change in drilling temperature but increase in drilling time through 50 drillings under the manufacturer-recommended cooling conditions and the drilling pressure of 750g. 2.The heat that is generated through drilling mattered only in the case of 2mm twist drills,the first drill to be used in bone drilling process;for all the other drills there is no significant problem. 3.If the drilling pressure is increased when a 2mm twist drill reaches a dense bone, the temperature rises abruptly even under the manufacturer-recommended cooling conditions. 4.Drilling heat was the highest at the final moment of the drilling process.

THE EFFECT OF AUTOLOGOUS PLATELET-RICH PLASMA (PRP) ON BONE FORMATION AROUND DENTAL IMPLANT IN THE RABBIT : A HISTOMORPHOMETRIC AND REMOVAL TORQUE STUDY / 대한치과보철학회지

Platelet-rich plasma (PRP) has been known to increase the rate and degree of bone formation by virtue of growth factors in concentrated platelets. Although its great healing effect on bone defect or pre-implantation site preparation in conjunction with bone substitute has been reported, the effect associated with implant is unknown. The purpose of this study was to investigate the effect of PRP on rapid osseointegration of endosseous dental implants in the rabbit tibiae. Twenty two adult female New Zealand white rabbits, weighing approximately 2.7-3.3kg, were used for this study. Twelve of the 22 animals were used for histomorphometric analysis and ten of the 22 were for removal torque test. Each animal received two implants in each tibia (two treated with PRP and two as control) and was given fluorochrome intramuscularly. For histomorphometric analysis, rabbits were divided into four groups according to the healing period. At 1 week, 2 weeks, 4 weeks and 8 weeks postoperatively, each three animals were sacrificed serially and the amount and rate of bone formation around dental implant were examined on the undecalcified sections under fluorescent microscope, polarized microscope and light microscope connected to a personal computer equipped with image analysis system. For removal torque test, rabbits were divided into two groups and removal torque tests were performed at 4 weeks, 10 weeks after implant placement. In total, 88 screw shaped, commercially pure titanium implants (Neoplant, Neobiotech, Seoul, Korea) were used in this study. Labeling pattern reflected differences of two groups in bone formation rate at each period. Histomorphometrically, PRP group showed significantly higher bone volume within threads compared to control group at 2 weeks (70.30+/-4.96% vs. 50.68+/-6.33%; P.05). These findings imply that PRP could induce rapid, more bone formation around implant during early healing period and get faster secondary stability for reducing healing period, though it has not induced bone maturation enough to resist functional loading.

STRAIN AND TEMPERATURE CHANGES DURING THE POLYMERIZATION OF AUTOPOLYMERIZING ACRYLIC RESINS / 대한치과보철학회지

The aims of this experiment were to investigate the strain and temperature changes simultaneously within autopolymerizing acrylic resin specimens. A computerized data acquisition system with an electrical resistance strain gauge and a thermocouple was used over time periods up to 180 minutes. The overall strain kinetics, the effects of stress relaxation and additional heat supply during the polymerization were evaluated. Stone mold replicas with an inner butt-joint rectangular cavity (40.0x25.0mm, 5.0mm in depth) were duplicated from a brass master mold. A strain gauge (AE-11-S50N-120-EC, CAS Inc., Korea) and a thermocouple were installed within the cavity, which had been connected to a personal computer and a precision signal conditioning amplifier (DA 1600 Dynamic Strain Amplifier, CAS Inc., Korea) so that real-time recordings of both polymerization-induced strain and temperature changes were performed. After each of fresh resin mixture was poured into the mold replica, data recording was done up to 180 minutes with three-second interval. Each of two poly (methyl methacrylate) products (Duralay, Vertex) and a vinyl ethyl methacrylate product (Snap) was examined repeatedly ten times. Additionally, removal procedures were done after 15, 30 and 60 minutes from the start of mixing to evaluate the effect of stress relaxation after deflasking. Six specimens for each of nine conditions were examined. After removal from the mold, the specimen continued benchcuring up to 180 minutes. Using a waterbath (Hanau Junior Curing Unit, Model No.76-0, Teledyne Hanau, New York, U.S.A.) with its temperature control maintained at 50degrees C, heat-soaking procedures with two different durations (15 and 45 minutes) were done to evaluate the effect of additional heat supply on the strain and temperature changes within the specimen during the polymerization. Five specimens for each of six conditions were examined. Within the parameters of this study the following results were drawn : 1. The mean shrinkage strains reached -3095mu epsilon, -1796mu epsilon and -2959mu epsilon for Duralay, Snap and Vertex, respectively. The mean maximum temperature rise reached 56.7degrees C, 41.3degrees C and 56.1degrees C for Duralay, Snap, and Vertex, respectively. A vinyl ethyl methacrylate product (Snap) showed significantly less polymerization shrinkage strain (p0.05).

THREE DIMENSIONAL FINITE ELEMENT ANALYSIS OF BRANEMARK NOVUM(R)IMMEDIATE IMPLANT PROSTHODONTIC PROTOCOL / 대한치과보철학회지

Since the treatment of edentulous patients with osseointegrated implant was first introduced more than 30 years ago, implant therapy has become one of the most important dental treatment modalities today. Based on the previous experience and knowledge. Branemark Novum(R) protocol was introduced with the concept of simplifying surgical and prosthetic technique and reducing healing time recently. This protocol recommends the installation of three 5mm wide diameter fixtures in anterior mandible and the prefabricated titanium bars for superstructure fabrication. This study was designed to analyze the stress distribution at fixture and superstructure area according to changes of fixture number, diameter and superstructure materials. Four 3-dimensional finite element models were fabricated. Model 1 - 5 standard fixtures (13mm long and 3.75mm in diameter) & superstructure consisted of type IV gold alloy and resin Model 2 - 3 wide diameter fixtures (13mm long and 5.0mm in diameter) )& superstructure consisted of type IV gold alloy and resin Model 3 - 3 wide diameter fixtures (13mm long and 5.0mm in diameter) )& superstructure consisted of titanium and resin Model 4 - 3 wide diameter fixtures (13mm long and 5.0mm in diameter)& superstructure consisted of titanium and porcelain A 150N occlusal force was applied on the 1st molar of each model in 3 directions-vertical(90degree)horizontal(0degree)and oblique (120degree). After analyzing the stress and displacements, following results were obtained. 1. There were no significant difference in stress distribution among experimental models. 2. Model 2,3,4 showed less amount of compressive stress than that of model 1. However, tensile stress was similar. 3. Veneer material with a high modulus of elasticity demonstrated less stress accumulation in the superstructure. Within the limits of this study.Branemark Novum(R) protocol demonstrated comparable biomechanical properties to conventional protocol.

EFFECTS OF CHOPPED GLASS FIBER ON THE STRENGTH OF HEAT-CURED PMMA RESIN / 대한치과보철학회지

The fracture of acrylic resin dentures remains an unsolved problem. Therefore, many investigations have been performed and various approaches to strengthening acrylic resin, for example, the reinforcement of heat-cured PMMA resin using glass fibers, have been suggested over the years. The aim of the present study was to investigate the effect of short glass fibers treated with silane coupling agent on the transverse strength of heat-polymerized PMMA denture base resin. To avoid fiber bunching and achieve even fiber distribution, glass fiber bundles were mixed with PMMA powder in conventional mixer whose blade was modified to be blunt. Composite of glass fiber (11micrometer diameter, 3mm & 6mm length, silane treated) and PMMA resin was made. Transverse strength and Young's modulus were estimated. Glass fibers were incorporated with 1%, 3%, 6% and 9% by weight. Plasticity and workability of dough was evaluated. Fracture surface of specimens was investigated by SEM. The results of this study were as follows 1. 6% and 9% incorporation of 3mm glass fibers in the PMMA resin enhanced the transverse strength of the test specimens (p<0.05). 2. 6% incorporation of 6mm glass fibers in the PMMA resin increased transverse strength, but 9% incorporation of it decreased transverse strength (p<0.05). 3. When more than 3% of 3mm glass fibers and more than 6% of 6mm glass fibers were incorporated. Young's modulus increased significantly (p<0.05). 4. Workability decreased gradually as the percentage of the fibers increased. 5. Workability decreased gradually as the length of the fibers increased. 6. In SEM and LM, there was no bunching of fibers and no shortening of fibers.

ANALYSIS OF THE FIT IN THE IMPLANT PROSTHESIS USING LASER DISPLACEMENT METER AND THREE-DIMENSIONAL FINITE ELEMENT METHOD / 대한치과보철학회지

A precise fit of the implant prosthesis is one of the most important factors in preventing mechanical complications. To analyze the degree of the misfit of implant prosthesis, a modal testing experiment was accomplished. And to interpret the modal testing analysis mathematically, three-dimensional finite element models were established. In the experimental modal testing analysis, with a laser displacement meter, FFT analyzer, impact hammer, etc., natural frequencies of the models with various degree of prosthesis fit were determined after the frequency response function were calculated. In the finite element analysis, the natural frequencies and mode shapes of the models which simulated those of experimental modal testing were computed. The results were as follows : 1. Natural frequencies of the prosthesis-abutment were related to the contact state between components. 2. In the modal testing experiment, the natural frequencies increased from 50micrometer to 200micrometer gap and reached a plateau. 3. In the finite element analysis, the natural frequencies decreased gradually according to the increase of the gap size. 4. In the finite element analysis, the mode shapes of model 1 with misfitting prosthesis showed different patterns from those without misfitting prosthesis. 5. The devices including a laser displacement meter used in this study were useful for measuring the natural frequencies of an implant prosthesis which had various degrees of fit.