The Journal of Prosthetic Dentistry

217October 2009

Ucar et alUcar et al

Clinical ImplicationsThere should be no clinical concern about biocompatibility when using any of the 5 noble cast-to components evaluated with noble casting alloys for screw-retained implant-supported prostheses.

Statement of problem. Cast-to components are commonly used in screw-retained implant-supported restorations to produce precise fit. There is little information in the literature about the compositions and microstructures of com-mercially available products.

Purpose. The purpose of this study was to characterize as-received cast-to components from 5 manufacturers (Dent-sply Friadent CeraMed, Lifecore Biomedical, Inc, Nobel Biocare AB, Institut Straumann AG, and Zimmer Dental).

Material and methods. Two components from each manufacturer were mounted in metallographic resin, sectioned into quarters, remounted, wet polished with alumina abrasives, cleaned by ultrasonic agitation in distilled water, etched with aqua regia solutions, and carbon coated for scanning electron microscope (SEM) observation. Secondary (SE) and backscattered electron (BSE) images were collected to investigate the variations in surface topography and composition, respectively. Elemental analyses (EDS) were performed using an energy-dispersive x-ray spectrometer coupled to the SEM. Overall Vickers hardness (500-g load) and Vickers hardness of the 2 primary microstructural constituents (10-g load) were measured. Mean values and standard deviations were determined for the composition and Vickers hardness data.

Results. All implant components were composed of 2 distinctive parallel-band constituents containing gold, pal-ladium, and platinum. Trace concentrations of iridium were also found. Elemental compositions of the darker bands observed by BSE differed by up to 20% for Au and Pt in the 5 products, whereas there was a minimal difference in Pd content. The lighter bands observed by BSE had nearly the same compositions in all 5 products, and contained much more Au and much less Pt than the darker bands. The gold-rich bands in each product were found to have much lower Vickers hardness. At high magnifications, each of the 2 bands appeared to contain 2 phases.

Conclusions. The elemental compositions, microstructures, and Vickers hardness of the 5 as-received cast-to implant components were similar. Because both microstructural bands principally contain gold, palladium, and platinum, these noble cast-to implant components should be metallurgically compatible with noble metal casting alloys. (J Prosthet Dent 2009;102:216-223)

Characterization of cast-to implant components from five manufacturers

Yurdanur Ucar, DDS, MS, PhD,a William A. Brantley, PhD,b Sreenivas N. Bhattiprolu, PhD,c William M. Johnston, PhD,d and Edwin A. McGlumphy, DDS, MSe

Cukurova University, Balcali Adana, Turkey; The Ohio State University, Columbus, Ohio

Support for this research was provided by a grant from the National Institutes of Health (grant number DE10147).

aAssistant Professor, Department of Prosthodontics, Cukurova University; former graduate student, Dental Materials Science and Oral Biology, College of Dentistry, The Ohio State University. bProfessor and Director of the Graduate Program, Dental Materials Science, Division of Restorative and Prosthetic Dentistry, Col-lege of Dentistry, The Ohio State University.cApplications Specialist, Oxford Instruments, Inc, Concord, Mass; former Senior Electron Microscopist, Microscopic and Chemical Analysis Research Center (MARC), Department of Geological Sciences, The Ohio State University. dProfessor, Division of Restorative and Prosthetic Dentistry, College of Dentistry, The Ohio State University.eAssociate Professor and Director of Implant Prosthdontics, Division of Restorative and Prosthetic Dentistry, College of Dentistry, The Ohio State University.

Endosteal implants have been commonly used in dental treatment for more than 40 years1,2 and cur-rently have high clinical success rates exceeding 95%.3-5 Long-term success is impacted by many factors, one of which is precision of fit.1,6 Precise fit of multiunit connections prevents the occurrence of deleterious ten-sile and compressive stresses, as well as excessive bending moments, on the implant-supported restorations during functional loading. Excessive stresses and bending moments may cause loosening of the prosthesis or abutment screws,7 as well as distor-tion or breakage of the restoration, microfractures around the bone sur-rounding the implant, or fracture of the implant body.6 Besides providing appropriate stress transfer, precise fit between the implant and implant-supported prosthesis results in favor-able biologic response of periimplant host tissues and avoids mechanical complications in the prosthodontic rehabilitation.8

Conventionally, both the implant and the abutment are prefabricated. Thus, misfit of these 2 components is generally not a problem for dental implant applications.9 Nevertheless, establishing a clinically acceptable fit between the abutment and the super-structure is important and a challenge to the dentist. It has been proposed that the gap between an abutment and its superstructure should be less than 30 μm.10 However, the gap can-not be easily measured intraorally, and it has been reported that the definitive implant restoration can undergo clinically significant distor-tion and deformation when the gap is more than 30 μm.6

To obtain clinically precise fits be-tween implants and their superstruc-tures, prefabricated cast-to (or cast-on) components are recommended for screw-retained implant restora-tions,2 and are known by different names, depending on the manufac-turer. The cast-to component is some-times referred to as a gold cylinder, coping, or attachment element,2 al-

though alternative terminology, such as casting and waxing sleeve or im-plant cylinder, is sometimes used. The cast-to component is designed for standard screw-retained restorations, and a wide range of cast-to structures can be used with most implant sys-tems. Once casting is completed, the cast-to component is integrated with the definitive restoration.11

Castable abutments are based upon the same concepts as other cast-to components. This type of abut-ment, advocated by Lewis et al12,13 as the UCLA abutment, is widely used for single tooth restorations.8 It al-lows fabrication of the restoration di-rectly to the implant,13 and there is no need to use a transmucosal abutment cylinder. Castable abutments are commonly preferred for patients with limited interocclusal and/or inter-proximal distances.13 They also may provide better soft tissue response.13 Placement of the restoration subgin-givally allows improved esthetics to be established easily using a castable component.12

Gilson et al14 observed that when an alloy was cast to a wrought com-ponent, an excellent fit was found between the superstructure and the implant body. Nevertheless, when premanufactured metal cylinders are used, the metal framework will be composed of 2 different alloy struc-tures: the gold alloy cylinder and the casting alloy. Metallurgical compat-ibility of the gold alloy coping or the castable abutment with the casting alloy is necessary to obtain good me-chanical performance of an implant-supported fixed restoration.9 Metal cylinders composed of gold alloys are most frequently used for the cast-to process, because they are highly com-patible with the high-noble casting al-loys used for the superstructure.9,15,16

There is limited information in the prosthodontic literature about metal-lurgy of the cast-to components. Even though Carr and Brantley16 presented microstructures, elemental analysis, interface analysis, and hardness val-ues for popular cast-to systems in-

volving noble metal cylinders from 3 manufacturers and 2 cast noble alloys (high gold and high palladium), fur-ther research is needed to understand their metallurgical structures. Carr and Brantley16 observed that noble metal implant cylinders are highly compatible with noble casting alloys, whereas a titanium alloy (Ti-6Al-4V) cylinder was not compatible.15 To ad-dress the scientific reasons for both the metallurgical compatibility and incompatibility of different alloys with premanufactured cast-to com-ponents, a thorough investigation of these as-received components is nec-essary. Both previous studies of cast-to interfaces by Carr and Brantley15,16 found that noble metal implant cyl-inders from different manufacturers had a distinctive wrought microstruc-ture consisting of 2 different alternat-ing bands that were parallel to the cylinder axis and that both bands were primarily composed of gold, platinum, and palladium. This obser-vation is in accordance with the pub-lished ternary phase diagram for gold-platinum-palladium alloys. Although the previous studies9,15,16 investigated the cast-to interface with different casting alloys, a thorough character-ization of the as-received cast-to com-ponent is necessary to understand the metallurgy of the interfacial region.

The objective of this study was to determine the microstructure, com-position, and Vickers hardness of the alloys used by 5 manufacturers for as-received noble prefabricated implant components commonly used in den-tal practice. This study is the first step of a future comprehensive investiga-tion of the interfaces between several representative casting alloys and the castable abutments.

MATERIAL AND METHODS

Two prefabricated implant com-ponents were obtained from 5 differ-ent manufacturers (Dentsply Friadent CeraMed, Lifecore Biomedical, Inc, Nobel Biocare AB, Institut Straumann AG, and Zimmer Dental). Manufac-

The Journal of Prosthetic Dentistry

217October 2009

Ucar et alUcar et al

Clinical ImplicationsThere should be no clinical concern about biocompatibility when using any of the 5 noble cast-to components evaluated with noble casting alloys for screw-retained implant-supported prostheses.

Statement of problem. Cast-to components are commonly used in screw-retained implant-supported restorations to produce precise fit. There is little information in the literature about the compositions and microstructures of com-mercially available products.

Purpose. The purpose of this study was to characterize as-received cast-to components from 5 manufacturers (Dent-sply Friadent CeraMed, Lifecore Biomedical, Inc, Nobel Biocare AB, Institut Straumann AG, and Zimmer Dental).

Material and methods. Two components from each manufacturer were mounted in metallographic resin, sectioned into quarters, remounted, wet polished with alumina abrasives, cleaned by ultrasonic agitation in distilled water, etched with aqua regia solutions, and carbon coated for scanning electron microscope (SEM) observation. Secondary (SE) and backscattered electron (BSE) images were collected to investigate the variations in surface topography and composition, respectively. Elemental analyses (EDS) were performed using an energy-dispersive x-ray spectrometer coupled to the SEM. Overall Vickers hardness (500-g load) and Vickers hardness of the 2 primary microstructural constituents (10-g load) were measured. Mean values and standard deviations were determined for the composition and Vickers hardness data.

Results. All implant components were composed of 2 distinctive parallel-band constituents containing gold, pal-ladium, and platinum. Trace concentrations of iridium were also found. Elemental compositions of the darker bands observed by BSE differed by up to 20% for Au and Pt in the 5 products, whereas there was a minimal difference in Pd content. The lighter bands observed by BSE had nearly the same compositions in all 5 products, and contained much more Au and much less Pt than the darker bands. The gold-rich bands in each product were found to have much lower Vickers hardness. At high magnifications, each of the 2 bands appeared to contain 2 phases.

Conclusions. The elemental compositions, microstructures, and Vickers hardness of the 5 as-received cast-to implant components were similar. Because both microstructural bands principally contain gold, palladium, and platinum, these noble cast-to implant components should be metallurgically compatible with noble metal casting alloys. (J Prosthet Dent 2009;102:216-223)

Characterization of cast-to implant components from five manufacturers

Yurdanur Ucar, DDS, MS, PhD,a William A. Brantley, PhD,b Sreenivas N. Bhattiprolu, PhD,c William M. Johnston, PhD,d and Edwin A. McGlumphy, DDS, MSe

Cukurova University, Balcali Adana, Turkey; The Ohio State University, Columbus, Ohio

Support for this research was provided by a grant from the National Institutes of Health (grant number DE10147).

aAssistant Professor, Department of Prosthodontics, Cukurova University; former graduate student, Dental Materials Science and Oral Biology, College of Dentistry, The Ohio State University. bProfessor and Director of the Graduate Program, Dental Materials Science, Division of Restorative and Prosthetic Dentistry, Col-lege of Dentistry, The Ohio State University.cApplications Specialist, Oxford Instruments, Inc, Concord, Mass; former Senior Electron Microscopist, Microscopic and Chemical Analysis Research Center (MARC), Department of Geological Sciences, The Ohio State University. dProfessor, Division of Restorative and Prosthetic Dentistry, College of Dentistry, The Ohio State University.eAssociate Professor and Director of Implant Prosthdontics, Division of Restorative and Prosthetic Dentistry, College of Dentistry, The Ohio State University.

Endosteal implants have been commonly used in dental treatment for more than 40 years1,2 and cur-rently have high clinical success rates exceeding 95%.3-5 Long-term success is impacted by many factors, one of which is precision of fit.1,6 Precise fit of multiunit connections prevents the occurrence of deleterious ten-sile and compressive stresses, as well as excessive bending moments, on the implant-supported restorations during functional loading. Excessive stresses and bending moments may cause loosening of the prosthesis or abutment screws,7 as well as distor-tion or breakage of the restoration, microfractures around the bone sur-rounding the implant, or fracture of the implant body.6 Besides providing appropriate stress transfer, precise fit between the implant and implant-supported prosthesis results in favor-able biologic response of periimplant host tissues and avoids mechanical complications in the prosthodontic rehabilitation.8

Conventionally, both the implant and the abutment are prefabricated. Thus, misfit of these 2 components is generally not a problem for dental implant applications.9 Nevertheless, establishing a clinically acceptable fit between the abutment and the super-structure is important and a challenge to the dentist. It has been proposed that the gap between an abutment and its superstructure should be less than 30 μm.10 However, the gap can-not be easily measured intraorally, and it has been reported that the definitive implant restoration can undergo clinically significant distor-tion and deformation when the gap is more than 30 μm.6

To obtain clinically precise fits be-tween implants and their superstruc-tures, prefabricated cast-to (or cast-on) components are recommended for screw-retained implant restora-tions,2 and are known by different names, depending on the manufac-turer. The cast-to component is some-times referred to as a gold cylinder, coping, or attachment element,2 al-

though alternative terminology, such as casting and waxing sleeve or im-plant cylinder, is sometimes used. The cast-to component is designed for standard screw-retained restorations, and a wide range of cast-to structures can be used with most implant sys-tems. Once casting is completed, the cast-to component is integrated with the definitive restoration.11

Castable abutments are based upon the same concepts as other cast-to components. This type of abut-ment, advocated by Lewis et al12,13 as the UCLA abutment, is widely used for single tooth restorations.8 It al-lows fabrication of the restoration di-rectly to the implant,13 and there is no need to use a transmucosal abutment cylinder. Castable abutments are commonly preferred for patients with limited interocclusal and/or inter-proximal distances.13 They also may provide better soft tissue response.13 Placement of the restoration subgin-givally allows improved esthetics to be established easily using a castable component.12

Gilson et al14 observed that when an alloy was cast to a wrought com-ponent, an excellent fit was found between the superstructure and the implant body. Nevertheless, when premanufactured metal cylinders are used, the metal framework will be composed of 2 different alloy struc-tures: the gold alloy cylinder and the casting alloy. Metallurgical compat-ibility of the gold alloy coping or the castable abutment with the casting alloy is necessary to obtain good me-chanical performance of an implant-supported fixed restoration.9 Metal cylinders composed of gold alloys are most frequently used for the cast-to process, because they are highly com-patible with the high-noble casting al-loys used for the superstructure.9,15,16

There is limited information in the prosthodontic literature about metal-lurgy of the cast-to components. Even though Carr and Brantley16 presented microstructures, elemental analysis, interface analysis, and hardness val-ues for popular cast-to systems in-

volving noble metal cylinders from 3 manufacturers and 2 cast noble alloys (high gold and high palladium), fur-ther research is needed to understand their metallurgical structures. Carr and Brantley16 observed that noble metal implant cylinders are highly compatible with noble casting alloys, whereas a titanium alloy (Ti-6Al-4V) cylinder was not compatible.15 To ad-dress the scientific reasons for both the metallurgical compatibility and incompatibility of different alloys with premanufactured cast-to com-ponents, a thorough investigation of these as-received components is nec-essary. Both previous studies of cast-to interfaces by Carr and Brantley15,16 found that noble metal implant cyl-inders from different manufacturers had a distinctive wrought microstruc-ture consisting of 2 different alternat-ing bands that were parallel to the cylinder axis and that both bands were primarily composed of gold, platinum, and palladium. This obser-vation is in accordance with the pub-lished ternary phase diagram for gold-platinum-palladium alloys. Although the previous studies9,15,16 investigated the cast-to interface with different casting alloys, a thorough character-ization of the as-received cast-to com-ponent is necessary to understand the metallurgy of the interfacial region.

The objective of this study was to determine the microstructure, com-position, and Vickers hardness of the alloys used by 5 manufacturers for as-received noble prefabricated implant components commonly used in den-tal practice. This study is the first step of a future comprehensive investiga-tion of the interfaces between several representative casting alloys and the castable abutments.

MATERIAL AND METHODS

Two prefabricated implant com-ponents were obtained from 5 differ-ent manufacturers (Dentsply Friadent CeraMed, Lifecore Biomedical, Inc, Nobel Biocare AB, Institut Straumann AG, and Zimmer Dental). Manufac-

218 Volume 102 Issue 4

The Journal of Prosthetic Dentistry

219October 2009

Ucar et alUcar et al

Table I. Implant component products used in study and their manufac-turers. General nominal composition reported by manufacturers for these products is 60% Au, 20% Pd, 19% Pt

turer information and product names of these components are listed in Ta-ble I. All components were evaluated in the as-received condition.

Components were mounted in-dividually in metallographic resin (LECO Corp, St. Joseph, Mich) and sectioned longitudinally, twice, using a slow-speed, water-cooled diamond saw (LECO Corp). Thus, each compo-nent yielded 4 quarters for study, cor-responding to the separate longitudi-nal sections. After removal from the original metallographic resin, each quarter was then remounted in the resin. Mounted specimens were first wet ground with a series of alumi-num oxide (alumina) abrasive papers (LECO Corp) of 800-, 1000-, 1200-, 2400-, and 4000-grit size. Then, the mounted specimens were polished with a sequence of slurries using 15-, 5-, 1-, 0.3-, and 0.05-μm alumina abrasive powders (LECO Corp). Spec-imens were agitated ultrasonically for 15 minutes in distilled water after each grinding and intermediate pol-ishing step, and for 30 minutes in dis-tilled water after final polishing with the 0.05-μm slurry.

Polished specimens were etched with aqua regia (3HCl:1HNO3) solu-tions that were prepared with a dilu-tion that had been determined previ-ously17 to yield optimum results. After etching, each specimen was again agi-tated ultrasonically in distilled water for 30 minutes.

For scanning electron microscope (SEM) examination (JEOL JSM-820; JEOL Ltd, Tokyo, Japan), the etched specimens were carbon coated (SPI Module; SPI Supplies, West Chester, Pa). The general nature of the micro-structures of the as-received implant components was first observed at low magnification. Secondary (SE) and backscattered electron (BSE) im-ages were then collected at different higher magnifications that showed18 variations in surface topography and composition, respectively. Energy-dis-persive x-ray spectrometric analyses (EDS) were also performed with the SEM on the carbon-coated specimens

to determine elemental compositions (INCA software; Oxford Instruments America, Inc, Concord, Mass). There were 15 raster scans (5 scans for each of the 2 types of bands and 5 scans of the overall microstructure) at selected representative sites on each specimen, and mean values and standard devia-tions were obtained for the elemental composition data.

Following the procedure previ-ously described in the study by Carr and Brantley,16 the overall Vickers hardness of each as-received compo-nent product was determined using a 500-g load and 10-second dwell time. Mean values and standard deviations for overall hardness were obtained from 5 indentations on each speci-men in each group.

Etched specimens were used for hardness measurements to observe the 2 types of alternating bands for placement of the indenter. The hard-ness of each of these 2 microstruc-tural constituents was determined us-ing a lighter 10-g load with 10-second dwell time, following a procedure that had been previously used to probe microstructural constituents in high-palladium alloys.19 Ten indentations were made on each test specimen to measure the hardness of the 2 bands, with 5 measurements of each type of band. Mean values and standard de-viations were obtained for the Vickers hardness of each band in the 5 as-re-ceived components.

RESULTS

Scanning electron microscopy exami-nation of specimens

The BSE images clearly showed differences in mean atomic number for the 2 groups of bands (Fig. 1). The darker bands in the BSE images had a lower mean atomic number,18 com-pared to the lighter bands. The BSE images also revealed that the centers of the darker bands were darker in ap-pearance compared to the peripheries of these bands, indicative of compo-sitional variation that originated dur-ing solidification of the component alloy.18 The SE images provided mi-crostructural details of the longitu-dinal bands in each product (Figs. 2 and 3). Generally, one type of band in the SE images (except for the Lifecore product shown in Fig. 3) had evident grains and grain boundaries, whereas the other type of band had an inter-nal structure containing fine-scale particles. These bands varied in thick-ness for the different products, and the thinnest bands were found in the Lifecore component (Fig. 3). Com-parison of the corresponding images for each product showed that the darker bands in the BSE images had a lighter appearance in the SE images.

Elemental analysis of cast-to compo-nents

Large-area raster scans for the 5

FRIADENT AuroBase

UCLA Gold/Plastic Combo Sleeve

GoldAdapt Non-Engaging

synOcta Abutment

AdVent Gold Abutment

Dentsply Friadent CeraMed, Lakewood, Colo

Lifecore Biomedical, Inc, Chaska, Minn

Nobel Biocare AB, Göteborg, Sweden

Institut Straumann AG, Basel, Switzerland

Zimmer Dental, Carlsbad, Calif

ManufacturerProduct

implant products tested provided the overall compositions summarized in Table II, where it can be seen that the cast-to components have similar com-positions and are primarily composed of the 3 noble metals commonly used for noble dental casting alloys: gold, palladium, and platinum. Within the limitations of the EDS analyses, all cast-to components appeared to con-tain approximately 1% iridium. While the overall palladium content for the 5 implant component products was found to be nearly identical, the over-all gold content was slightly higher for the Lifecore and Dentsply prod-ucts, and slightly lower for the Zim-mer product, compared to the Nobel Biocare and Straumann products. The differences in overall platinum content for the 5 implant component

products had an inverse relationship to the differences in overall gold con-tent.

The results of EDS analyses and the mean weight percentages for the compositions of the 2 different types of bands in the microstructure of each product are shown in Tables III and IV. The darker bands in the BSE images contained less gold, more platinum, and approximately the same amount of palladium, compared to the lighter bands. For the darker BSE bands (Ta-ble III), the gold content was highest for the Lifecore product, with nearly the same intermediate values for the Zimmer and Dentsply products, and had similar lower values for the No-bel Biocare and Straumann products. The palladium contents were nearly the same for the darker BSE bands

in all 5 products. Consequently, the platinum contents in these bands had the inverse trend found for the gold content: highest for the Straumann and Nobel Biocare products, inter-mediate for the Dentsply and Zimmer products, and lowest for the Lifecore product. For the lighter bands ob-served with the BSE images (Table IV), the gold, palladium, and plati-num contents for all 5 products were similar.

Vickers hardness measurements

The Vickers hardness results for the as-received cast-to components were consistent with the elemental composition and the microstructure results. Table V shows the mean hard-ness values along with the standard

1 Microstructure (BSE) image of Straumann cast-to component, showing 2 types of bands. Internal structure of dark bands cannot be distinguished at this magnification. Bar = 50 μm (x600 original magnification).

2 Microstructure (SE image) of Nobel Biocare cast-to component, showing details of 2 types of bands. Bar = 5 μm (x5000 original magnification).

3 Microstructure (SE image) of Lifecore cast-to compo-nent, showing details of alternating bands, which are nar-rower than bands of other 4 products. Bar = 5 μm (x3500 original magnification).

218 Volume 102 Issue 4

The Journal of Prosthetic Dentistry

219October 2009

Ucar et alUcar et al

Table I. Implant component products used in study and their manufac-turers. General nominal composition reported by manufacturers for these products is 60% Au, 20% Pd, 19% Pt

turer information and product names of these components are listed in Ta-ble I. All components were evaluated in the as-received condition.

Components were mounted in-dividually in metallographic resin (LECO Corp, St. Joseph, Mich) and sectioned longitudinally, twice, using a slow-speed, water-cooled diamond saw (LECO Corp). Thus, each compo-nent yielded 4 quarters for study, cor-responding to the separate longitudi-nal sections. After removal from the original metallographic resin, each quarter was then remounted in the resin. Mounted specimens were first wet ground with a series of alumi-num oxide (alumina) abrasive papers (LECO Corp) of 800-, 1000-, 1200-, 2400-, and 4000-grit size. Then, the mounted specimens were polished with a sequence of slurries using 15-, 5-, 1-, 0.3-, and 0.05-μm alumina abrasive powders (LECO Corp). Spec-imens were agitated ultrasonically for 15 minutes in distilled water after each grinding and intermediate pol-ishing step, and for 30 minutes in dis-tilled water after final polishing with the 0.05-μm slurry.

Polished specimens were etched with aqua regia (3HCl:1HNO3) solu-tions that were prepared with a dilu-tion that had been determined previ-ously17 to yield optimum results. After etching, each specimen was again agi-tated ultrasonically in distilled water for 30 minutes.

For scanning electron microscope (SEM) examination (JEOL JSM-820; JEOL Ltd, Tokyo, Japan), the etched specimens were carbon coated (SPI Module; SPI Supplies, West Chester, Pa). The general nature of the micro-structures of the as-received implant components was first observed at low magnification. Secondary (SE) and backscattered electron (BSE) im-ages were then collected at different higher magnifications that showed18 variations in surface topography and composition, respectively. Energy-dis-persive x-ray spectrometric analyses (EDS) were also performed with the SEM on the carbon-coated specimens

to determine elemental compositions (INCA software; Oxford Instruments America, Inc, Concord, Mass). There were 15 raster scans (5 scans for each of the 2 types of bands and 5 scans of the overall microstructure) at selected representative sites on each specimen, and mean values and standard devia-tions were obtained for the elemental composition data.

Following the procedure previ-ously described in the study by Carr and Brantley,16 the overall Vickers hardness of each as-received compo-nent product was determined using a 500-g load and 10-second dwell time. Mean values and standard deviations for overall hardness were obtained from 5 indentations on each speci-men in each group.

Etched specimens were used for hardness measurements to observe the 2 types of alternating bands for placement of the indenter. The hard-ness of each of these 2 microstruc-tural constituents was determined us-ing a lighter 10-g load with 10-second dwell time, following a procedure that had been previously used to probe microstructural constituents in high-palladium alloys.19 Ten indentations were made on each test specimen to measure the hardness of the 2 bands, with 5 measurements of each type of band. Mean values and standard de-viations were obtained for the Vickers hardness of each band in the 5 as-re-ceived components.

RESULTS

Scanning electron microscopy exami-nation of specimens

The BSE images clearly showed differences in mean atomic number for the 2 groups of bands (Fig. 1). The darker bands in the BSE images had a lower mean atomic number,18 com-pared to the lighter bands. The BSE images also revealed that the centers of the darker bands were darker in ap-pearance compared to the peripheries of these bands, indicative of compo-sitional variation that originated dur-ing solidification of the component alloy.18 The SE images provided mi-crostructural details of the longitu-dinal bands in each product (Figs. 2 and 3). Generally, one type of band in the SE images (except for the Lifecore product shown in Fig. 3) had evident grains and grain boundaries, whereas the other type of band had an inter-nal structure containing fine-scale particles. These bands varied in thick-ness for the different products, and the thinnest bands were found in the Lifecore component (Fig. 3). Com-parison of the corresponding images for each product showed that the darker bands in the BSE images had a lighter appearance in the SE images.

Elemental analysis of cast-to compo-nents

Large-area raster scans for the 5

FRIADENT AuroBase

UCLA Gold/Plastic Combo Sleeve

GoldAdapt Non-Engaging

synOcta Abutment

AdVent Gold Abutment

Dentsply Friadent CeraMed, Lakewood, Colo

Lifecore Biomedical, Inc, Chaska, Minn

Nobel Biocare AB, Göteborg, Sweden

Institut Straumann AG, Basel, Switzerland

Zimmer Dental, Carlsbad, Calif

ManufacturerProduct

implant products tested provided the overall compositions summarized in Table II, where it can be seen that the cast-to components have similar com-positions and are primarily composed of the 3 noble metals commonly used for noble dental casting alloys: gold, palladium, and platinum. Within the limitations of the EDS analyses, all cast-to components appeared to con-tain approximately 1% iridium. While the overall palladium content for the 5 implant component products was found to be nearly identical, the over-all gold content was slightly higher for the Lifecore and Dentsply prod-ucts, and slightly lower for the Zim-mer product, compared to the Nobel Biocare and Straumann products. The differences in overall platinum content for the 5 implant component

products had an inverse relationship to the differences in overall gold con-tent.

The results of EDS analyses and the mean weight percentages for the compositions of the 2 different types of bands in the microstructure of each product are shown in Tables III and IV. The darker bands in the BSE images contained less gold, more platinum, and approximately the same amount of palladium, compared to the lighter bands. For the darker BSE bands (Ta-ble III), the gold content was highest for the Lifecore product, with nearly the same intermediate values for the Zimmer and Dentsply products, and had similar lower values for the No-bel Biocare and Straumann products. The palladium contents were nearly the same for the darker BSE bands

in all 5 products. Consequently, the platinum contents in these bands had the inverse trend found for the gold content: highest for the Straumann and Nobel Biocare products, inter-mediate for the Dentsply and Zimmer products, and lowest for the Lifecore product. For the lighter bands ob-served with the BSE images (Table IV), the gold, palladium, and plati-num contents for all 5 products were similar.

Vickers hardness measurements

The Vickers hardness results for the as-received cast-to components were consistent with the elemental composition and the microstructure results. Table V shows the mean hard-ness values along with the standard

1 Microstructure (BSE) image of Straumann cast-to component, showing 2 types of bands. Internal structure of dark bands cannot be distinguished at this magnification. Bar = 50 μm (x600 original magnification).

2 Microstructure (SE image) of Nobel Biocare cast-to component, showing details of 2 types of bands. Bar = 5 μm (x5000 original magnification).

3 Microstructure (SE image) of Lifecore cast-to compo-nent, showing details of alternating bands, which are nar-rower than bands of other 4 products. Bar = 5 μm (x3500 original magnification).

220 Volume 102 Issue 4

The Journal of Prosthetic Dentistry

221October 2009

Ucar et alUcar et al

Table II. Overall compositions of cast-to components (wt%) deter-mined by EDS (mean (SD)). There were 5 analysis sites on each specimen

Table III. Compositions (wt%) of darker bands in etched microstructures of cast-to components, determined by EDS (mean (SD)). Five analysis sites were selected on darker bands for each specimen

Table IV. Compositions (wt%) of lighter bands in etched microstructures of cast-to components, determined by EDS (mean (SD)). Five analysis sites were selected on lighter bands for each specimen

Table V. Vickers microhardness comparisons of cast-to components from 5 manufacturers (mean (SD)). For overall hardness, 5 indentations (500-g load) were placed on each test speci-men. For darker and lighter bands, 5 indentations (10-g load) were placed on each type of band for each test specimen of each component (except for single case noted)

Dentsply

Lifecore

Nobel Biocare

Straumann

Zimmer

57.9 (0.9)

59.4 (1.2)

55.5 (1.6)

55.2 (2.9)

52.7 (0.1)

Gold

23.6 (1.0)

22.3 (1.6)

25.9 (1.5)

26.2 (3.2)

28.8 (0.1)

Platinum

18.6 (0.1)

18.3 (0.4)

18.6 (0.1)

18.6 (0.3)

18.5 (0.1)

PalladiumCompany

Dentsply

Lifecore

Nobel Biocare

Straumann

Zimmer

44.8 (2.6)

56.5 (7.3)

38.7 (3.4)

35.9 (0.4)

47.0 (2.0)

Gold

37.3 (3.2)

25.4 (8.1)

43.6 (4.0)

46.9 (0.6)

34.8 (2.0)

Platinum

18.0 (0.5)

18.1 (0.8)

17.7 (0.5)

17.2 (0.2)

18.2 (0.0)

PalladiumCompany

Dentsply

Lifecore

Nobel Biocare

Straumann

Zimmer

61.9 (0.6)

62.2 (1.2)

61.6 (0.3)

61.3 (0.2)

60.0 (2.0)

Gold

19.3 (0.6)

19.3 (1.1)

19.2 (0.1)

20.0 (0.0)

21.4 (1.9)

Platinum

18.8 (0.0)

18.5 (0.1)

19.2 (0.4)

18.7 (0.2)

18.6 (0.1)

PalladiumCompany

Dentsply

Lifecore

Nobel Biocare

Straumann

Zimmer

*Measured from only 1 specimen

273 (9)

229 (11)

257 (6)

277 (1)

256 (4)

Hardness

227 (7)

200 (10)

223 (5)

229 (8)

218 (6)

Bands (BSE)

177 (1)

155*

167 (7)

179 (5)

174 (1)

Bands (BSE)Overall Darker Lighter

Company

deviations of the darker and lighter bands in the BSE images for all 5 products. The hardness of the darker band was always considerably high-er than for the lighter band in each product, which was consistent with its lower gold and higher platinum contents (Tables III and IV). It was also found, with the light 10-g indent-ing load, that the center of the darker bands had higher hardness than the periphery of these bands.

The hardness of the darker bands for all products was similar, differing by only about 15% for Straumann, Dentsply, and Nobel Biocare (highest values), compared to Lifecore (low-est value). The hardness of the light-er bands likewise was similar for all products, differing by approximately only 15% between Straumann, Dent-sply, and Zimmer (highest values), compared to Lifecore (lowest value). The most striking result was that the overall hardness of each implant com-ponent was much higher than that of the harder dark microstructural band in the component.

DISCUSSION

The ability to withstand repeti-tive functional and parafunctional loading over time in the dynamic oral environment is the primary clinical requirement of implant framework prostheses.16 The precise fit between components of an implant is impor-tant for the restoration to endure these loads.1,6 Premachined cast-to com-ponents, commonly used in screw-retained implant systems, should fit with high precision to implant (to the abutment if implant cylinders are used) and dental restorations. Prefab-ricated implant components subject-ed to elevated temperatures during the casting procedure should not un-dergo clinically excessive dimensional changes. Precise fit between these structures should also be maintained after porcelain firing cycles, as well.20

The interface between the cast-to implant component and the cast al-loy for the implant superstructure is

critical for clinical success. Character-istics of an ideal interface have been described by Carr and Brantley16: (1) microstructures of the implant com-ponent and the cast alloy should be maintained up to the interface; (2) interfacial reaction regions and po-rosity should be absent; and (3) there must be sufficient interfacial bonding between the 2 alloys to withstand an-ticipated loads.

As a first study in a series of in-vestigations that subsequently will include casting of noble alloys, the compositions, microstructures, and Vickers hardness were investigated for as-received noble cast-to com-ponents from 5 implant companies (Table I). One component was an implant cylinder (Straumann), while the other 4 components were specifi-cally designed by the manufacturers as castable abutments. The present SEM observations and EDS analyses revealed that all 5 premanufactured noble components have similar com-positions (Tables II-IV) and micro-structures (Figs. 1-3). In agreement with the findings of Carr and Brant-ley,15,16 all components were primarily composed of gold, platinum, and pal-ladium, with only small differences in their proportions. Iridium was detect-ed as a trace element in the amount of approximately 1 wt%, but accurate determinations of the iridium concen-trations in the different products were not possible with the EDS analyses.

Gold is the most noble metal,21 and dental castings containing at least 50% gold should not present an adverse galvanic response when con-nected to titanium.13 Palladium, plati-num, and iridium have higher melting temperatures compared to gold, and addition of these metals will increase the melting temperature and strength of the resulting alloy.21 Palladium and platinum also contribute to tarnish and corrosion resistance of the com-ponent alloy.21 Iridium is commonly used for grain refinement of gold al-loys, and an alloy with finer grains has improved mechanical properties.21 To maintain precise fit of the cast-

to component with other implant components, its melting tempera-ture must be higher than the melting temperature of the casting alloy and firing temperature for opaque porce-lain to avoid distortions of the cast-to component that might occur during alloy casting or porcelain firing.20

As purported by the manufactur-ers, the nominal composition of the Ceramicor alloy used for the Dentsply castable abutment is 60% Au, 20% Pd, 19% Pt, and 1% Ir, and the Straumann and Lifecore components are also composed of the same alloy. Small dif-ferences in the nominal compositions of these 3 products and the composi-tions determined by EDS in the pres-ent study for the overall components (Table II) are attributed to: (1) differ-ences in the proprietary manufactur-ing processes by the implant compa-nies; (2) the area selection process for raster scanning during the EDS analyses; (3) their nonuniform micro-structures because of the 2 alternat-ing bands (accounting for the stan-dard deviations in Table II); and (4) the need for precise EDS standards for the ternary alloy specimens (which are not available and would also have inhomogeneous microstructures). It is expected that there would be mini-mal motivation for the manufacturers to change the compositions of these cast-to implant products.

Machining of the implant compo-nents by the manufacturer introduces residual stresses,22 which can poten-tially affect dimensional stability and corrosion resistance, although the magnitudes of these effects have not been investigated. The directionality of the microstructure for the compo-nents is the result of the thermome-chanical steps (mechanical deforma-tion followed by annealing) during wrought processing by the manufac-turer. This microstructure with the 2 types of bands, observed for all 5 components, is in agreement with the gold-palladium-platinum ternary phase diagram. Differences in the widths of the bands are attributed to proprietary thermomechanical pro-

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Ucar et alUcar et al

Table II. Overall compositions of cast-to components (wt%) deter-mined by EDS (mean (SD)). There were 5 analysis sites on each specimen

Table III. Compositions (wt%) of darker bands in etched microstructures of cast-to components, determined by EDS (mean (SD)). Five analysis sites were selected on darker bands for each specimen

Table IV. Compositions (wt%) of lighter bands in etched microstructures of cast-to components, determined by EDS (mean (SD)). Five analysis sites were selected on lighter bands for each specimen

Table V. Vickers microhardness comparisons of cast-to components from 5 manufacturers (mean (SD)). For overall hardness, 5 indentations (500-g load) were placed on each test speci-men. For darker and lighter bands, 5 indentations (10-g load) were placed on each type of band for each test specimen of each component (except for single case noted)

Dentsply

Lifecore

Nobel Biocare

Straumann

Zimmer

57.9 (0.9)

59.4 (1.2)

55.5 (1.6)

55.2 (2.9)

52.7 (0.1)

Gold

23.6 (1.0)

22.3 (1.6)

25.9 (1.5)

26.2 (3.2)

28.8 (0.1)

Platinum

18.6 (0.1)

18.3 (0.4)

18.6 (0.1)

18.6 (0.3)

18.5 (0.1)

PalladiumCompany

Dentsply

Lifecore

Nobel Biocare

Straumann

Zimmer

44.8 (2.6)

56.5 (7.3)

38.7 (3.4)

35.9 (0.4)

47.0 (2.0)

Gold

37.3 (3.2)

25.4 (8.1)

43.6 (4.0)

46.9 (0.6)

34.8 (2.0)

Platinum

18.0 (0.5)

18.1 (0.8)

17.7 (0.5)

17.2 (0.2)

18.2 (0.0)

PalladiumCompany

Dentsply

Lifecore

Nobel Biocare

Straumann

Zimmer

61.9 (0.6)

62.2 (1.2)

61.6 (0.3)

61.3 (0.2)

60.0 (2.0)

Gold

19.3 (0.6)

19.3 (1.1)

19.2 (0.1)

20.0 (0.0)

21.4 (1.9)

Platinum

18.8 (0.0)

18.5 (0.1)

19.2 (0.4)

18.7 (0.2)

18.6 (0.1)

PalladiumCompany

Dentsply

Lifecore

Nobel Biocare

Straumann

Zimmer

*Measured from only 1 specimen

273 (9)

229 (11)

257 (6)

277 (1)

256 (4)

Hardness

227 (7)

200 (10)

223 (5)

229 (8)

218 (6)

Bands (BSE)

177 (1)

155*

167 (7)

179 (5)

174 (1)

Bands (BSE)Overall Darker Lighter

Company

deviations of the darker and lighter bands in the BSE images for all 5 products. The hardness of the darker band was always considerably high-er than for the lighter band in each product, which was consistent with its lower gold and higher platinum contents (Tables III and IV). It was also found, with the light 10-g indent-ing load, that the center of the darker bands had higher hardness than the periphery of these bands.

The hardness of the darker bands for all products was similar, differing by only about 15% for Straumann, Dentsply, and Nobel Biocare (highest values), compared to Lifecore (low-est value). The hardness of the light-er bands likewise was similar for all products, differing by approximately only 15% between Straumann, Dent-sply, and Zimmer (highest values), compared to Lifecore (lowest value). The most striking result was that the overall hardness of each implant com-ponent was much higher than that of the harder dark microstructural band in the component.

DISCUSSION

The ability to withstand repeti-tive functional and parafunctional loading over time in the dynamic oral environment is the primary clinical requirement of implant framework prostheses.16 The precise fit between components of an implant is impor-tant for the restoration to endure these loads.1,6 Premachined cast-to com-ponents, commonly used in screw-retained implant systems, should fit with high precision to implant (to the abutment if implant cylinders are used) and dental restorations. Prefab-ricated implant components subject-ed to elevated temperatures during the casting procedure should not un-dergo clinically excessive dimensional changes. Precise fit between these structures should also be maintained after porcelain firing cycles, as well.20

The interface between the cast-to implant component and the cast al-loy for the implant superstructure is

critical for clinical success. Character-istics of an ideal interface have been described by Carr and Brantley16: (1) microstructures of the implant com-ponent and the cast alloy should be maintained up to the interface; (2) interfacial reaction regions and po-rosity should be absent; and (3) there must be sufficient interfacial bonding between the 2 alloys to withstand an-ticipated loads.

As a first study in a series of in-vestigations that subsequently will include casting of noble alloys, the compositions, microstructures, and Vickers hardness were investigated for as-received noble cast-to com-ponents from 5 implant companies (Table I). One component was an implant cylinder (Straumann), while the other 4 components were specifi-cally designed by the manufacturers as castable abutments. The present SEM observations and EDS analyses revealed that all 5 premanufactured noble components have similar com-positions (Tables II-IV) and micro-structures (Figs. 1-3). In agreement with the findings of Carr and Brant-ley,15,16 all components were primarily composed of gold, platinum, and pal-ladium, with only small differences in their proportions. Iridium was detect-ed as a trace element in the amount of approximately 1 wt%, but accurate determinations of the iridium concen-trations in the different products were not possible with the EDS analyses.

Gold is the most noble metal,21 and dental castings containing at least 50% gold should not present an adverse galvanic response when con-nected to titanium.13 Palladium, plati-num, and iridium have higher melting temperatures compared to gold, and addition of these metals will increase the melting temperature and strength of the resulting alloy.21 Palladium and platinum also contribute to tarnish and corrosion resistance of the com-ponent alloy.21 Iridium is commonly used for grain refinement of gold al-loys, and an alloy with finer grains has improved mechanical properties.21 To maintain precise fit of the cast-

to component with other implant components, its melting tempera-ture must be higher than the melting temperature of the casting alloy and firing temperature for opaque porce-lain to avoid distortions of the cast-to component that might occur during alloy casting or porcelain firing.20

As purported by the manufactur-ers, the nominal composition of the Ceramicor alloy used for the Dentsply castable abutment is 60% Au, 20% Pd, 19% Pt, and 1% Ir, and the Straumann and Lifecore components are also composed of the same alloy. Small dif-ferences in the nominal compositions of these 3 products and the composi-tions determined by EDS in the pres-ent study for the overall components (Table II) are attributed to: (1) differ-ences in the proprietary manufactur-ing processes by the implant compa-nies; (2) the area selection process for raster scanning during the EDS analyses; (3) their nonuniform micro-structures because of the 2 alternat-ing bands (accounting for the stan-dard deviations in Table II); and (4) the need for precise EDS standards for the ternary alloy specimens (which are not available and would also have inhomogeneous microstructures). It is expected that there would be mini-mal motivation for the manufacturers to change the compositions of these cast-to implant products.

Machining of the implant compo-nents by the manufacturer introduces residual stresses,22 which can poten-tially affect dimensional stability and corrosion resistance, although the magnitudes of these effects have not been investigated. The directionality of the microstructure for the compo-nents is the result of the thermome-chanical steps (mechanical deforma-tion followed by annealing) during wrought processing by the manufac-turer. This microstructure with the 2 types of bands, observed for all 5 components, is in agreement with the gold-palladium-platinum ternary phase diagram. Differences in the widths of the bands are attributed to proprietary thermomechanical pro-

222 Volume 102 Issue 4

The Journal of Prosthetic Dentistry

223October 2009

Ucar et al Ucar et al

cessing procedures and to small dif-ferences in alloy compositions (such as the percentage of iridium). Be-cause both types of bands contain gold, palladium, and platinum, the cast-to components should be mi-crostructurally compatible with the noble metal casting alloys that also contain these elements.15,16,21

At the high magnifications used for SE imaging (Figs. 2 and 3), it was found that 1 type of band appeared to contain 2 phases: (1) a gray-ap-pearing matrix phase that had the same appearance as the phase found in the other type of band; and (2) a fine-scale, heavily etched second phase with a light appearance in the SE images. Careful examination of the SE images suggests the presence of occasional larger precipitate par-ticles, which are more evident in the dark-appearing bands (which are the lighter bands in the BSE images). The number of phases in these microstruc-tures and their lattice parameters will be investigated in a future study using micro-x-ray diffraction.23

Measurement of Vickers micro-hardness can provide information about yield strength for an alloy sys-tem22 and can thus serve as a probe of relative differences in strength for individual microstructural constitu-ents. As previously noted, the higher values of Vickers hardness shown in Table V for the darker bands in the BSE images are consistent with their lower gold and higher platinum con-tent compared to the lighter bands in the BSE images, shown in Tables III and IV, and might suggest that these bands contain 2 phases. Table V also shows that the overall Vickers hard-ness of each implant component, which was measured with a 500-g load, exceeds the hardness of the indi-vidual dark bands in the component, which was measured with a 10-g load. This is due to the strengthening effect of the 2-constituent microstructure,22 which impedes dislocation movement in the implant component alloy.

Since the current work was de-signed as a descriptive study to pro-

vide the means and standard de-viations for elemental compositions and hardness values of as-received cast-to components from the 5 dif-ferent manufacturers, no statistical comparisons were made. The use of 2 specimens (as-received implant com-ponents) for each group was deemed sufficient to provide the desired com-parisons for elemental compositions and hardness for the 5 cast-to prod-ucts. While the small sample size in this study limited the management of an experimental design and testing of a null hypothesis, a larger sample size would not have altered the primary results; namely, that all 5 products have similar noble metal composi-tions, microstructures, and Vickers hardness values. While differences among the compositions and proper-ties of the products are of metallurgi-cal interest, they are not expected to have clinical significance.

The clinical implication of the cur-rent work is that these noble cast-to implant components should be com-patible with noble metal casting al-loys, because both microstructural bands contain the noble elements gold, palladium, and platinum found in the casting alloys. While design differences among the products may affect the bond with casting alloys, metallurgical differences are relatively minor. Characterization of the 5 im-plant components is the first step of a comprehensive investigation of the interfaces between representative casting alloys and these components.

CONCLUSIONS

Evaluation of cast-to compo-nents from 5 implant manufacturers revealed that all products were com-posed of the same primary elements (gold, palladium, and platinum) with only small differences in concentra-tions. Microstructures of these im-plant components were also similar. However, substantial differences were found in the gold and platinum con-tents of the darker group of bands observed by backscattered electron

imaging with the SEM, although a minimal compositional difference was found for the light microstruc-tural bands observed by BSE. Vickers hardness results were in agreement with the compositions and the mi-crostructures. The bands with higher gold and lower platinum content had lower Vickers hardness and were less affected by the etchant.

REFERENCES

1. Adell R, Lekholm U, Rockler B, Brånemark PI. A 15-year study of osseointegrated implants in the treatment of the edentulous jaw. Int J Oral Surg 1981;10:387-416.

2. Fonseca RJ, Davis WH. Reconstructive preprosthetic oral and maxillofacial surgery. 2nd ed. Philadelphia: Saunders; 1995. p. 259-72, 282-3.

3. Jeffcoat MK, McGlumphy EA, Reddy MS, Geurs NC, Proskin HM. A comparison of hydroxyapatite (HA) -coated threaded, HA-coated cylindric, and titanium threaded endosseous dental implants. Int J Oral Maxillofac Implants 2003;18:406-10.

4. McGlumphy EA, Peterson LJ, Larsen PE, Jeffcoat MK. Prospective study of 429 hydroxyapatite-coated cylindric omniloc implants placed in 121 patients. Int J Oral Maxillofac Implants 2003;18:82-92.

5. Comfort MB, Chu FC, Chai J, Wat PY, Chow TW. A 5-year prospective study on small diameter screw-shaped oral implants. J Oral Rehabil 2005;32:341-5.

6. Watanabe F, Uno I, Hata Y, Neuendorff G, Kirsch A. Analysis of stress distribution in a screw-retained implant prosthesis. Int J Oral Maxillofac Implants 2000;15:209-18.

7. McGlumphy EA, Mendel DA, Holloway JA. Implant screw mechanics. Dent Clin North Am 1998;42:71-89.

8. Vigolo P, Majzoub Z, Cordioli G. Measure-ment of the dimensions and abutment rotational freedom of gold-machined 3i UCLA-type abutments in the as-received condition, after casting with a noble metal alloy and porcelain firing. J Prosthet Dent 2000;84:548-53.

9. Carotenuto G, Palumbo M, Zarone F, Nicolais L. Characterization of the interface between prefabricated gold copings and cast dental alloy in implant restorations. Clin Oral Implants Res 1999;10:131-8.

10.Klineberg IJ, Murray GM. Design of su-perstructures for osseointegrated fixtures. Swed Dent J Suppl 1985;28:63-9.

11.Larsen PE, McGlumphy EA. Contemporary implant dentistry. In: Hupp JR, Tucker MR, Ellis E III. Contemporary oral and maxillofa-cial surgery. 5th ed. St. Louis: Mosby; 2008. p. 253-87.

12.Lewis SG, Beumer J 3rd, Perri GR, Horn-burg WP. Single tooth implant supported restorations. Int J Oral Maxillofac Implants 1988;3:25-30.

13.Lewis SG, Llamas D, Avera S. The UCLA abutment: a four-year review. J Prosthet Dent 1992;67:509-15.

14.Gilson TD, Asgar K, Peyton FA. The quality of the union formed in casting gold to em-bedded attachment metals. J Prosthet Dent 1965;15:464-73.

15.Carr AB, Brantley WA.Titanium alloy cylinders in implant framework fabrication: a study of the cylinder-alloy interface. J Prosthet Dent 1993;69:391-7.

16.Carr AB, Brantley WA. Characterization of noble metal implant cylinders: as-received cylinders and cast interfaces with noble metal alloys. J Prosthet Dent 1996;75:77-85.

17.Farne JF, Nealey ET. The effects of etching on the margins of cast gold restorations. J Prosthet Dent 1976;35:273-8.

18.Goldstein J, Newbury D, Joy D, Lyman C, Echlin P, Lifshin E, et al. Scanning electron microscopy and x-ray microanalysis. 3rd ed. New York: Kluwer Academic Publishers; 2002. p. 404-5, 613-4.

19.Wu Q, Brantley WA, Mitchell JC, Vermilyea SG, Xiao J, Guo W. Heat-treatment behav-ior of high-palladium dental alloys. Cells Mater 1997;7:161-74.

20.Byrne D, Houston F, Cleary R, Claffey N. The fit of cast and premachined implant abutments. J Prosthet Dent 1998;80:184-92.

21.Anusavice KJ. Phillips’ science of dental materials. 11th ed. St. Louis: Elsevier; 2003. p. 56-70, 633, 636.

22.Dieter GE. Mechanical metallurgy. 3rd ed. New York: McGraw-Hill; 1986. p. 208-12, 329-32, 557-9.

23.Iijima M, Ohno H, Kawashima I, Endo K, Brantley WA, Mizoguchi I. Micro X-ray diffraction study of superelastic nickel-titanium orthodontic wires at different temperatures and stresses. Biomaterials 2002;23:1769-74.

Corresponding author:Dr William A. BrantleyDivision of Restorative and Prosthetic DentistryCollege of Dentistry, The Ohio State UniversityPostle Hall, Rm 3005-L305 W 12th AveColumbus, OH 43218-2357Fax: 614-292-9422E-mail: brantley.1@osu.edu and wbrantle@columbus.rr.com

AcknowledgementsThe authors thank Tridib Dasgupta, Direc-tor of Materials Research at Ivoclar Vivadent (US), for providing the Straumann specimens; Dentsply Friadent CeraMed, LifeCore Medical, Inc, Nobel Biocare AB, and Zimmer Dental for providing the other implant component specimens used in this study; and Dr Dae Kyu Chang (KoDent, Inc, Anaheim, Calif ), who holds the patent for Ceramicor, for providing information about this alloy.

Copyright © 2009 by the Editorial Council for The Journal of Prosthetic Dentistry.

Noteworthy Abstracts of the Current Literature

Effect of implant support on distal-extension removable partial dentures: In vivo assessment

Ohkubo C, Kobayashi M, Suzuki Y, Hosoi T.Int J Oral Maxillofac Implants 2008;23:1095-101.

Purpose: The use of a limited number of implants for support of a removable partial denture (RPD) changes a Ken-nedy Class I or II situation to that of a Class III. This in vivo pilot study evaluated implant-supported distal-extension removable partial dentures (RPD) in 5 partially edentulous patients.

Materials and Methods: Two implants (Brånemark TU MK III, Nobel Biocare) were placed in a mandibular Kennedy Class I arch. To fabricate an implant-supported RPD (ISRPD), a conventional RPD base was fitted to the healing abut-ment with autopolymerizing acrylic resin (Uni-fast II, GC) to support the posterior aspect of the RPD. By changing the healing abutment to a healing cap, there was no connection between the denture base and implant, and the ISRPD became a conventional RPD (CRPD). Using a crossover study design, the masticatory movements (mandibular move-ments during mastication) of both dentures were measured using a commercially available tracking device (BioPACK, Bioresearch, Japan). The occlusal force and contact area were also measured using pressure-sensitive sheets and an image scanner (T-scan system). Using a visual analog scale (VAS), the 4 criteria of comfort, chewing, retention, and stability were evaluated. All the data obtained were analyzed using Wilcoxon signed rank tests (α= .05).

Results: There were no significant differences (P > .05) in masticatory movements between the ISRPD and the CRPD (5 patients: 4 women, 1 man). However, the ISRPD had significantly greater force and greater area than the CRPD (P = .043). The center of occlusal force of the ISRPD tended to move more distally compared to the CRPD. All the patients preferred the ISRPD for comfort, chewing, retention, and stability.

Conclusions: One implant per edentulous area and a simple attachment technique yielded a stable distal extension RPD.

Reprinted with permission of Quintessence Publishing.

222 Volume 102 Issue 4

The Journal of Prosthetic Dentistry

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Ucar et al Ucar et al

cessing procedures and to small dif-ferences in alloy compositions (such as the percentage of iridium). Be-cause both types of bands contain gold, palladium, and platinum, the cast-to components should be mi-crostructurally compatible with the noble metal casting alloys that also contain these elements.15,16,21

At the high magnifications used for SE imaging (Figs. 2 and 3), it was found that 1 type of band appeared to contain 2 phases: (1) a gray-ap-pearing matrix phase that had the same appearance as the phase found in the other type of band; and (2) a fine-scale, heavily etched second phase with a light appearance in the SE images. Careful examination of the SE images suggests the presence of occasional larger precipitate par-ticles, which are more evident in the dark-appearing bands (which are the lighter bands in the BSE images). The number of phases in these microstruc-tures and their lattice parameters will be investigated in a future study using micro-x-ray diffraction.23

Measurement of Vickers micro-hardness can provide information about yield strength for an alloy sys-tem22 and can thus serve as a probe of relative differences in strength for individual microstructural constitu-ents. As previously noted, the higher values of Vickers hardness shown in Table V for the darker bands in the BSE images are consistent with their lower gold and higher platinum con-tent compared to the lighter bands in the BSE images, shown in Tables III and IV, and might suggest that these bands contain 2 phases. Table V also shows that the overall Vickers hard-ness of each implant component, which was measured with a 500-g load, exceeds the hardness of the indi-vidual dark bands in the component, which was measured with a 10-g load. This is due to the strengthening effect of the 2-constituent microstructure,22 which impedes dislocation movement in the implant component alloy.

Since the current work was de-signed as a descriptive study to pro-

vide the means and standard de-viations for elemental compositions and hardness values of as-received cast-to components from the 5 dif-ferent manufacturers, no statistical comparisons were made. The use of 2 specimens (as-received implant com-ponents) for each group was deemed sufficient to provide the desired com-parisons for elemental compositions and hardness for the 5 cast-to prod-ucts. While the small sample size in this study limited the management of an experimental design and testing of a null hypothesis, a larger sample size would not have altered the primary results; namely, that all 5 products have similar noble metal composi-tions, microstructures, and Vickers hardness values. While differences among the compositions and proper-ties of the products are of metallurgi-cal interest, they are not expected to have clinical significance.

The clinical implication of the cur-rent work is that these noble cast-to implant components should be com-patible with noble metal casting al-loys, because both microstructural bands contain the noble elements gold, palladium, and platinum found in the casting alloys. While design differences among the products may affect the bond with casting alloys, metallurgical differences are relatively minor. Characterization of the 5 im-plant components is the first step of a comprehensive investigation of the interfaces between representative casting alloys and these components.

CONCLUSIONS

Evaluation of cast-to compo-nents from 5 implant manufacturers revealed that all products were com-posed of the same primary elements (gold, palladium, and platinum) with only small differences in concentra-tions. Microstructures of these im-plant components were also similar. However, substantial differences were found in the gold and platinum con-tents of the darker group of bands observed by backscattered electron

imaging with the SEM, although a minimal compositional difference was found for the light microstruc-tural bands observed by BSE. Vickers hardness results were in agreement with the compositions and the mi-crostructures. The bands with higher gold and lower platinum content had lower Vickers hardness and were less affected by the etchant.

REFERENCES

1. Adell R, Lekholm U, Rockler B, Brånemark PI. A 15-year study of osseointegrated implants in the treatment of the edentulous jaw. Int J Oral Surg 1981;10:387-416.

2. Fonseca RJ, Davis WH. Reconstructive preprosthetic oral and maxillofacial surgery. 2nd ed. Philadelphia: Saunders; 1995. p. 259-72, 282-3.

3. Jeffcoat MK, McGlumphy EA, Reddy MS, Geurs NC, Proskin HM. A comparison of hydroxyapatite (HA) -coated threaded, HA-coated cylindric, and titanium threaded endosseous dental implants. Int J Oral Maxillofac Implants 2003;18:406-10.

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Corresponding author:Dr William A. BrantleyDivision of Restorative and Prosthetic DentistryCollege of Dentistry, The Ohio State UniversityPostle Hall, Rm 3005-L305 W 12th AveColumbus, OH 43218-2357Fax: 614-292-9422E-mail: brantley.1@osu.edu and wbrantle@columbus.rr.com

AcknowledgementsThe authors thank Tridib Dasgupta, Direc-tor of Materials Research at Ivoclar Vivadent (US), for providing the Straumann specimens; Dentsply Friadent CeraMed, LifeCore Medical, Inc, Nobel Biocare AB, and Zimmer Dental for providing the other implant component specimens used in this study; and Dr Dae Kyu Chang (KoDent, Inc, Anaheim, Calif ), who holds the patent for Ceramicor, for providing information about this alloy.

Copyright © 2009 by the Editorial Council for The Journal of Prosthetic Dentistry.

Noteworthy Abstracts of the Current Literature

Effect of implant support on distal-extension removable partial dentures: In vivo assessment

Ohkubo C, Kobayashi M, Suzuki Y, Hosoi T.Int J Oral Maxillofac Implants 2008;23:1095-101.

Purpose: The use of a limited number of implants for support of a removable partial denture (RPD) changes a Ken-nedy Class I or II situation to that of a Class III. This in vivo pilot study evaluated implant-supported distal-extension removable partial dentures (RPD) in 5 partially edentulous patients.

Materials and Methods: Two implants (Brånemark TU MK III, Nobel Biocare) were placed in a mandibular Kennedy Class I arch. To fabricate an implant-supported RPD (ISRPD), a conventional RPD base was fitted to the healing abut-ment with autopolymerizing acrylic resin (Uni-fast II, GC) to support the posterior aspect of the RPD. By changing the healing abutment to a healing cap, there was no connection between the denture base and implant, and the ISRPD became a conventional RPD (CRPD). Using a crossover study design, the masticatory movements (mandibular move-ments during mastication) of both dentures were measured using a commercially available tracking device (BioPACK, Bioresearch, Japan). The occlusal force and contact area were also measured using pressure-sensitive sheets and an image scanner (T-scan system). Using a visual analog scale (VAS), the 4 criteria of comfort, chewing, retention, and stability were evaluated. All the data obtained were analyzed using Wilcoxon signed rank tests (α= .05).

Results: There were no significant differences (P > .05) in masticatory movements between the ISRPD and the CRPD (5 patients: 4 women, 1 man). However, the ISRPD had significantly greater force and greater area than the CRPD (P = .043). The center of occlusal force of the ISRPD tended to move more distally compared to the CRPD. All the patients preferred the ISRPD for comfort, chewing, retention, and stability.

Conclusions: One implant per edentulous area and a simple attachment technique yielded a stable distal extension RPD.

Reprinted with permission of Quintessence Publishing.