TITLE:

Surface Composition and Structure of Titanium Polished with Aqueous Slurry of Ferric Oxide

LANGUAGE:

ENGLISH

AUTHORS:

Akhter,R., Okawa,S.*, Nakano,S.*, Kobayashi,M.** and Miykawa,O.*

INSTITUTE:

Chemistry of Dental Materials, Dhaka Dental College and Hospital,
* Dental Materials and Technology, Faculty of Dentistry, Niigata University,
** EMX Laboratory, Niigata University.

JOURNAL:

Dental Materials Journal 19(1): 10-21, 2000

KEY WORDS:

Titanium, Polishing, Surface composition

ABSTRACT:
Cast plates were prepared from commercial titanium. The plates were polished with a slurry of fine ferric oxide powder. The surface composition and structure were investigated by electron probe microanalysis (EPMA) and X-ray photoelectron spectroscopy (XPS). In the high pressure-polished surface, iron was non-uniformly distributed but oxygen was mostly uniformly distributed, while in a light pressure-polished surface, iron and oxygen were uniformly distributed though at lower and higher concentrations, respectively. EPMA state analysis and XPS suggested that the iron might exist as Fe²⁺ in the outermost surface, while it might be in a metallic state in the inner surface layer. 

http://www.ncbi.nlm.nih.gov:80/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=11219087&dopt=Abstract

TITLE:

Long-term Changes of Hydroxyapatite-Coated Dental Implants.

LANGUAGE:

ENGLISH

AUTHORS:

Baltog,I., Watanabe,K., Kusakari,H., Tagucho,N., Miyakawa,O.*, Kobayashi,M.**, and Ito,N.

INSTITUTE:

Department of Fixed Prosthodontics, *Department of Dental Materials and Technology, and **EMX Laboratory, Niigata University School of Dentistry

JOURNAL:

Journal of Biomedical Materials Research. (Appl Biomater) 53: 76-85, 2000.

KEY WORDS:

hydroxyapatite, retrieved implant, X-ray diffraction, FTIR, electron probe microanalysis

ABSTRACT:
There are many controversies about the long-term prognosis of hydroxyapatite (HA)-coated implants. Failure may be related to compositional and structure changes of the coating occurring during implantation. Two retrieved and two unused HA-coated blade-type implants were examined by stereomciroscopy, secondary electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction, and electron probe microanalysis. The objective was to investigate the HA morphology, composition and structure, and to characterize the change that occurred in the retrieved implant coatings. Retrieved implants presented partial loss of the coating, especially at the apical and mesiodistal edges. Remaining HA was thick and flattened in the cervical and central area and gradually thinner and rougher towards the apical and mesiodistal edges. Increase or Cl and Mg, decrease of OH, and X-ray diffraction peak broadening were found in the retrieved implant coatings, in comparison with the unused implants. Morphological changes of the retrieved implants seem to depend on stress values in the surrounding bone and on implant mobility. Compositional changes and increased amount of lattice perfections appeared in the retrieved implant coatings, as a result of ion substitutions in the apatite lattice. However, the present study could not confirm the influence of these changes on implant failure.

http://www.ncbi.nlm.nih.gov:80/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=10634956&dopt=Abstract

TITLE:

Guide to Access to Web Database of the Literature of Dental Materials and Devices on the Internet

LANGUAGE:

in JAPANESE with English Abstract

AUTHORS

Database and Homepage Committee Japanese Society for Dental Materials and Devices

Tajima,K. and Miyakawa,O.¹

INSTITUTE:

Department of Materials Science, Kyushu Dental College and ¹Dental Materials and Technology, Faculty of Dentistry, Niigata University

JOURNAL:

The Journal of the Japanese Society for Dental Materials and Device , 19: 491-494, 2000

KEYWORDS:

Computer, Database, Information retrieval, Internet, Web database

ABSTRACTS:
The Japanese Society for Dental Materials and Devices (JSDMD) has started to provide Internet access to the database of literature on dental materials and devices (DENTMATE). The DENTMATE has been developed by the JSDMD with the cooperation of the members from 1986. For this new project, the retrieval system by Japanese Web database was constructed on the Internet, and is available free through our homepage site. This paper describes the guide to the retrieval system on the Japanese Web site. This retrieval system on the Web allows many users to obtain important biographical information on dental materials and devices.

TITLE:

Influence of Prosthesis Material on Stress Distribution in Bone and Implant: A 3-Dimensional Finite Element Analysis

LANGUAGE:

ENGLISH

AUTHORS:

Stegaroiu,R., Kusakari,H., Nishiyama,S., and Miyakawa,O.*

INSTITUTE:

Department of Fixed Prosthodontics and Department of *Dental Materials and Technology, Niigata University School of Dentistry

JOURNAL:

The International Journal of Oral & Maxillofacial Implants, 13(6) 781-790, 1998

KEY WORDS:

dental implants, fixed partial prostheses, prosthesis material, 3-dimensional finite emenet analysis

ABSTRACT:
A 3-dimensional finite element analysis was conducted to asses stress distribution in bone, implant, and abutment when gold alloy, porcelain, or resin (acrylic or composite) was used for 3-unit prosthesis. A unit force was applied axially and then buccolingually to the center of the pontic. For gold and porcelain, similar maximum equivalent stress was found in each part of the models. In almost all cases, stress in the model with the resin prostheses was similar to or higher than that in the models with the other 2 prosthesis materials. The highest increase in stress with the resins was found in the implant-abutment unit under axial load. The protective role of resin for the implant-bone interface could not be demonstrated under the conditions of this analysis.

http://www.ncbi.nlm.nih.gov:80/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=9857588&dopt=Abstract

TITLE:

Reactivity of Titanium with Abrasive Materials and Its Polishing

LANGUAGE:

in JAPANESE with English Abstract

AUTHORS:

Miykawa,O.

INSTITUTE:

Dental Materials and Technology, Niigata University School of Dentistry

JOURNAL:

The Journal of the Japan Prosthodontic Society, 42(2), 540-546, 1998

KEY WORDS:

Titanium, Polishing, Abrasive material, Chemical wear

ABSTRACT:
Titanium is a difficult-to-machine metal, due to its high reactivity with abrasives. The cutting rate of alumina is significantly low. In contrast, at higher rotational speed and heavier grinding force, the cutting rate of carborundum is much greater, but accompanied by violent loss of the tool. Since titanium has a low thermal conductivity, the grinding temperature influencing titanium-abrasive reactions should be kept from rising. Relatively low rotational speed and light force are recommended. In addition, the tool should not be depressed against the work during grinding but moved over the work, otherwise unfavorable results are yielded: abrasive attrition, chip loading and oxidation of the surface, or grinding burn. Since polishing is also a procedure of cutting by abrasives, inhibition of titanium-abrasive reactions is an important key to efficient polishing. Recently, two finishing techniques were successfully applied in dentistry; electro-chemical buffing and mechanical buffing with colloidal silica as abrasive. When the reaction-inhibition mechanism is clarified in these techniques, a new development will be possible.

TITLE:

Surface Contamination of Titanium by Abrading Treatment

LANGUAGE:

ENGLISH

AUTHORS:

Miykawa,O., Okawa,S., Kobayashi,M.* and Kazuyoshi Uematsu,K.**

INSTITUTE:

Dental Materials and Technology, Niigata University School of Dentistry, *EMX Laboratory, Niigata University, and **Faculty of Engineering, Niigata University

JOURNAL:

Dentistry in Japan, 34(1), 90-96, 1998

KEY WORDS:

Titanium, Abrasion, Surface, In-vivo corrsoion, X-ray photoelectron spectroscopy

ABSTRACT:
Titanium was abraded with a lapping film of 9 micron a-Al₂O₃ grits. The composition and structure of the abraded surface was examined by EPMA and XPS. The abrasion increased the content of oxygen with a non-uniform distribution in the abraded surface. The surface was contaminated also by aluminum with a non-uniform distribution. The oxygen existed in O^2- state as a major component. With one exception, where Al₂O₃ grits were observed in a spotty pattern, embedded within and exposed at the surface, the majority of alumina was found as a hydroxide, which tended to concentrate at the upper surface rather than at the lower surface. The abrading process was suggested to consist not only in embedding of Al₂O₃ grits within the surface, but also in the breakdown, re-formation and growth of the passive oxide film, accompanied by a change of Al₂O₃ to a hydroxide. The passive oxide film could be resistant to in-vivo corrosion, if it had a uniform thickness. How the aluminum combination in the abraded surface influences in-vivo corrosion resistance and tissue reaction with titanium should be investigated.

TITLE:

Influence of Restoration Type on Stress Distribution in Bone Around Implants: A Three-Dimensional Finite Element Analysis

LANGUAGE:

ENGLISH

AUTHORS:

Stegaroiu,R., Sato,T., Kusakari,H., and Miykawa,O.*

INSTITUTE:

Department of Fixed Prosthodontics and Department of *Dental Materials and Technology, Niigata University School of Dentistry

JOURNAL:

The International Journal of Oral & Maxillofacial Implants, 13(1), 82-90, 1998 (in English)

KEY WORDS:

Bone stress, Dental implants, Fixed partial prosthesis, Three-dimensional finite element analysis

ABSTRACT:
The three-dimensional finite element analysis was used to assess stress in bone around titanium implants using three treatment designs for a partially edentulous mandible, under axial (AX), buccolingual (BL), or mesiodistal (MD) loads. For each of these loads, highest stress was calculated in the model with a cantilever prosthesis supported by two implants (M2). Less stress was found in the model with a conventional fixed partial denture on two implants (M3), and lowest stress was calculated in the model with three connected crowns supported by three implants (M1). When BL load was applied to M3, cortical bone stress was high, comparable to that calculated for M2 under the same load. When AX or MD load was applied to M3, the cortical bone stress was low, similar to that found in M1 under each of these loads.

http://www.ncbi.nlm.nih.gov:80/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=9509784&dopt=Abstract

TITLE:

Surface Contamination of Titanium by Abrading Treatment

LANGUAGE:

ENGLISH

AUTHORS:

Miykawa,O., Watanabe,K., Okawa,S., Nakano,S. and Kobayashi,M.*

INSTITUTE:

Dental Materials and Technology, Niigata University School of Dentistry and *EMX Laboratory, Niigata University

JOURNAL:

Dental Materials Journal, 15(1), 11-21, 1996

KEY WORDS:

Titanium, Abrasive, Surface Contamination

ABSTRACT:
This study investigated the contamination of abraded titanium surfaces. Using a polishing machine, specimens were abraded with waterproof silicon carbide grit papers under water cooling. The abraded surfaces were examined using element analysis, X-ray diffraction, and hardness tests. Contaminant deposits with dimensions reaching about 30 micron were observed throughout the surface. In these deposits, titanium was apparently reduced by about 10 % and replaced by silicon and oxygen. The chemical bond state of the silicon was similar to that of silicon carbide or a titanium silicide. The oxygen was solute in titanium, which increased the surface hardness. The contaminant deposits were amorphous or very thin. The contamination of titanium, the extent of which was related to hardness, resulted from a reaction with abrasives.

http://www.ncbi.nlm.nih.gov:80/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=8940534&dopt=Abstract

TITLE:

Three Dimensional Finite Element Analysis of Bone around Dental Implants in Posterior Mandibular Region --Biomechanics of Implant Connections --

LANGUAGE:

in JAPANESE with English Abstract

AUTHORS:

Sato,T., Kusakari,H., and Miyakawa,O.

INSTITUTE:

JOURNAL:

The Journal of the Japan Prosthodontic Society 40:682-694, 1996

ABSTRACT:
The effect of superstructure connection on bone stress around implants was investigated by three-dimensional finite element analysis. Three models (M1-M3) of a mandibular segment with a premolar and two distal implants were constructed from CT-scans. In M1, tooth and implants were not connected, in M2, only implants were connected, and in M 3, tooth and implants were connected.
In M2, maximum equivalent stress was 60-65% of that in M1 under mesial loads and 1-point buccal load. Under vertical loads, stress in M2 and M1 were similar and concentrated around the loaded implant. Under mesial loads, stress concentrated mesially and distally around each implant of Ml, but in M2 and M3, bone stress between implants was low. In M3, under vertical and buccal loads, high stress concentrated mesial to the mesial implant. Under buccal loading of the tooth in M3 and of the mesial implant in M2, similar stress was calculated. 'Thus lateral guidance on a tooth connected to implants should be avoided.
Regardless of the model, stress in cortical bone was much higher than that in cancellous bone. Therefore, increasing implant diameter (i.e., contact area of cortical bone) may be more meaningful than increasing.
These results may be useful during treatment planning of implant placement and superstructure design.
Key words: implant, connection, three-dimensional model, finite element analysis, bone stress

TITLE:

Dental Soldering of Titanium with 16 Karat Gold Solder

LANGUAGE:

in JAPANESE with English Abstract

AUTHORS:

Sakano,T.

INSTITUTE:

JOURNAL:

The Journal of the Japan Prosthodontic Society 4:185-194, 1996

ABSTRACT:
From the point of view that soldering of titanium with gold solder is necessary for its application to partial dentures, the purpose of this study was to establish a technique of dental soldering with 16 karat gold solder.
Success or failure of titanium soldering depends on the level of oxidation control. Therefore, a technique for vacuum furnace soldering was introduced. The influences of the vacuum degree and holding time on the soldering strength were investigated separately, and the best condition for each was considered.
The technique was compared with the conventional technique of infrared soldering in an atmosphere of argon gas, and the possibility of applying it in the dental clinic was considered.
The results were as follows:
1. The lowest vacuum degree for successful soldering was 7.5 x 10^-3 torr and a soldering strength of about 37 kg/mm² was obtained.
2. Holding is unnecessary, because the soldering strength tends to decrease with increase of holding time.
3. Good soldering strength could not be obtained by the present infrared soldering technique because of insufficient oxidation control.
Key words: titanium, gold solder, soldering strength, vacuum degree, holding time

TITLE:

The Study of the Porosity of Cast Titanium Crowns

LANGUAGE:

in JAPANESE with English Abstract

AUTHORS:

Ozaki,Y., Kusakari,H. and Miyakawa,O.

INSTITUTE:

JOURNAL:

The Journal of the Japan Prosthodontic Society 40:738-748, 1996

ABSTRACT:
The purpose of this study was to investigate the influence of sprue size, casting method, and investment material on the porosity of titanium castings, approximating the form of dental crowns by density and X-ray transparent methods. The results were as follows.
1. The X-ray transparent method used in this study allowed the inspection of both occlusal and axial parts of the crown.
2. The X-ray investigation revealed a higher degree of porosity in the occlusal part than in the axial one. Furthermore, higher porosity was observed near the sprue.
3. When a 2 chambers type casting machine was used, porosity of crowns invested with high permeability investment material decreased with increase of sprue diameter. When an investment material of low permeability was used, crowns of defective form were obtained.
4. In the case of a 1 chamber type casting machine, number and size of crown porosities invested with high permeability investment material increased remarkably. Large porosities of irregular form were distributed throughout the casting. Whereas, in the case of low permeability investment materials, few porosities were detected using a thin sprue (1.5 mm).
Key words . casting porosity, X-ray transparent method, sprue size, permeability of investment material, casting machine

TITLE:

A Study on the Fit of Unalloyed Titanium Cast Crowns

LANGUAGE:

in JAPANESE with English Abstract

AUTHORS:

Hoshino,H., Kusakari,H. and Miyakawa,O.

INSTITUTE:

JOURNAL:

The Journal of the Japan Prosthodontic Society 4:796-805, 1996

ABSTRACT:
Standardized forms cast in titanium and 2 types (shoulder and chamfer) of titanium crowns were fabricated, and their fit was evaluated. Chamfer type Ag Pd alloy crowns were also fabricated and their fit was compared with that of the titanium crowns. In addition, the castability was investigated using wedge-shaped casts of gold alloy and titanium. In the latter, 2 different spruing methods were used. The results obtained were considered as a baseline during the examination of titanium crowns. The titanium samples were fabricated using a casting machine (pressure difference type) and Al2O3/MgO based investment. The results were as follows.
1. Accuracy of the standardized forms depended on heating conditions of the mold.
2. The fit of titanium crowns surpassed that of the Ag-Pd alloy crowns.
3. The fit of the shoulder type crowns was superior to that of the chamfer type crowns.
4. The spruing method influenced the accuracy of the edge in the titanium wedges.
The marginal fit of titanium crowns is influenced by titanium castability. The heating condition and spruing method should be chosen carefully and crown margins should be given an appropriate thickness to improve marginal fit.
Key words . titanium, crown casting, fit, castability

TITLE:

Retention and failure mode after cyclic loading in two post and core systems

LANGUAGE:

ENGLISH

AUTHORS:

Stegaroiu,R., Yamada,H., Kusakari,., and Miyakawa,O.*

INSTITUTE:

Fixed Prosthodontics and *Dental Materials and Technology, Niigata University School of Dentistry

JOURNAL:

Journal of Prosthetic Dentistry, 75(5), 506-511, 1996

KEY WORDS:

ABSTRACT:
Retention of a prefabricated post and composite resin core system was compared with that of a cast post and core restoration in anterior maxillary teeth on which root canal preparations, enlarged in the coronal part, were performed. The effect of cyclic loading on restoration retention was also investigated. Retention of restorations not subjected to cyclic loading was not influenced by post type, but loaded prefabricated post restorations showed lower retention than both loaded cast post and core restorations and nonloaded prefabricated post restorations. After dislodgement, the failure mode was also determined. The results of this study suggest that if a canal requires extensive preparation, a well-adapted cast post and core restoration may be more retentive than a prefabricated post restoration that does not match the canal shape.

http://www.ncbi.nlm.nih.gov:80/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=8709015&dopt=Abstract

TITLE:

Reaction Layers of Titanium Cast into Molds Containing Spinel

LANGUAGE:

in JAPANESE with English Abstract

AUTHORS:

Miykawa,O., Watanabe,K., Okawa,S., Nakano,S. and Kobayashi,M.*

INSTITUTE:

Dental Materials and Technology, Niigata University School of Dentistry and *EMX Laboratory, Niigata University

JOURNAL:

The Journal of the Japanese Society for Dental Materials and Device, 14(5), 560-568, 1995

KEY WORDS:

Titanium casting, Reaction layers, Spinel

ABSTRACT:
Reaction layer structures of titanium cast in three molds containing spinel (MgO-Al₂O₃) were investigated and compared by microstructure observation, electron probe microanalysis and measuring hardness. The molds were made from a spinel powder and two commercial investments, in which alumina and magnesia were involved and reacted to form spinel by heating. For the spinel mold, the reaction zone consisted of a baked product layer and the alpha case which was divided into two layers. Whereas the outside was stabilized and hardened by solid solution of aluminum, the inside was not so much hardened without a solid solution of aluminum. For the phosphate bonded investment, aluminum diffused deeply into the casting, the phosphorus-rich phase with a net-like structure extended more deeply, but the aluminum-stabilized alpha case was not formed. For the investment mixed with magnesium acetate solution, the aluminum-stabilized alpha case with higher hardness value formed on limited surfaces. On most surfaces, however, the acicular crystal structure was exposed without such a hard casing. For these investments, components other than spinel influenced the reaction layer structure.

TITLE:

IN SEARCH OF SUITABLE DENTURE MARKER

LANGUAGE:

ENGLISH

AUTHORS:

Thomas,CJ., Mori,T., Miyakawa.O.,* and Chung,HG.

INSTITUTE:

School of Dental Studies, University of Sydney, Australia and * Dental Materials and Technology, Niigata University School of Dentistry

JOURNAL:

The Journal of Forensic Odonto-Stomatology, 14(5), 560-568, 1995

KEY WORDS:

Denture marker, metal strip, radiolucency

ABSTRACT:
The ID-Band (SDI AB, Sweden) has become the standard, internationally and FDI accepted denture marking system. In Australia however the strip is not easily obtainable and is expensive. Two other materials have been trialled as possible alternatives: (1) Titanium foil (9 micron) and (2) Ho Band (matrix) (3 micron) (Lorvic Corp, USA). All three bands were tested for tensile strength and elongation at temperatures: RT, 700 and 900 C. As the ID- and Ho Bands are both 18-8 stainless steel their performance was similar.
The 18-8 was stronger, had a higher percentage break point and a higher elongation. The latter meant that it was softer and could be more easily inscribed and was therefore more suitable for denture marking. Ti is becoming increasingly used in dentistry but in spite of its abundance it is not likely to replace stainless steel for denture marking at present. On the other hand the Ho band is cheaper, more readily available and it could replace ID-Band for use in Australia. An alternative paper based marking system is also presented together with the rationale for its use.

http://www.ncbi.nlm.nih.gov:80/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=9227068&dopt=Abstract

TITLE:

Skin Holes of Titanium Casting

LANGUAGE:

ENGLISH

AUTHORS:

Miykawa,O., Watanabe,K., Okawa,S., Nakano,S., Honma,H., Kobayashi,M.* and Shiokawa,N.

INSTITUTE:

Dental Materials and Technology, Niigata University School of Dentistry and *EMX Laboratory, Niigata University

JOURNAL:

Dental Materials Journal, 12(2), 171-181, 1993

KEY WORDS:

Titanium casting, Skin hole, Investment

ABSTRACT:
The present study describes refractories which contribute to formation of skin holes of titanium casting. Plates consisting of quartz (Qu) and cristobalite (Cr) powders and Qu- and Cr-MgO mixtures were fired at high temperatures and used as phosphate-free molds. The cross-section of the castings was investigated using an optical microscope and an electron probe microanalyzer. Whereas the castings into the Qu molds were almost complete, those into the Cr molds were incomplete. The surface reaction zone of the Qu molds formed a typical layered structure with fewer skin holes. That of the latter extended deeply into the interior with a net-shaped titanium-silicon phase, cracks, and holes. Addition of magnesia to Cr effectively improved the castability and changed the reaction zone to the typical layered structure. However, slender holes occurred along the mold wall. The overall area around the holes was contaminated by silicon and magnesium. Probably, this resulted from a reaction of forsterite with titanium. The reactivity difference between Qu and Cr was not related to the fired strength of mold.

http://www.ncbi.nlm.nih.gov:80/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=8004911&dopt=Abstract

TITLE:

Skin Holes of Titanium Castings into Silica Investment Molds

LANGUAGE:

in JAPANESE with English Abstract

AUTHORS:

Miykawa,O., Watanabe,K., Okawa,S., Nakano,S., Honma,H., Kobayashi,M.* and Shiokawa,N.

INSTITUTE:

Dental Materials and Technology, Niigata University School of Dentistry and *EMX Laboratory, Niigata University

JOURNAL:

The Journal of the Japanese Society for Dental Materials and Device, 12(6), 734-742, 1993

KEY WORDS:

Titanium casting, Skin hole, Magnesium phosphate, Silica, Forsterite

ABSTRACT:
We examined the formation mechanism of skin holes in titanium castings in silica investment molds. Possibly, phosphorus in the typical reaction zone came from magnesium orthophosphate, but magnesium was not detected in this zone. If reduction reactions produce metallic magnesium, it will vaporize rather than dissolve in molten titanium, because of its very low boiling point. Skin holes contaminated by magnesium, however, occurred in the vicinity of the area where magnesium orthophosphate was locally concentrated. The higher the mold temperature was, the greater the tendency became. The reaction of silica with titanium also caused the formation of skin holes. The inner surface was contaminated by silicon and oxygen, and a silicon-rich phase was observed. When phosphate-bonded and ethyl silicate-bonded investments were heated at temperatures above 1,000 C, forsterite formed between the silica and magnesia. The reaction of forsterite with titanium caused the formation of slender holes along the mold wall. The area around them was contaminated by silicon and magnesium. Even if forsterite did not form in the burnout, it is likely that magnesia reacted easily with titanium under co-existence of silica, which caused the formation of skin holes.

TITLE:

Study on the Deformation and Fracture Mechanism of Titanium by Means of Acoustic Emission Analysis. Part 2 Roles of the Surface Layered Structure of Titanium Cast into a Phosphate-bonded Silica Alumina Investment Mold

LANGUAGE:

in JAPANESE with English Abstract

AUTHORS:

Miykawa,O., Watanabe,K., Okawa,S., Nakano,S., Honma,H., Shiokawa,N., Kobayashi,M.* and Tamura,H.**

INSTITUTE:

Dental Materials and Technology, Niigata University School of Dentistry, *EMX Laboratory, Niigata University and **Department of Machinery System Engineering, Faculty of Engineering, Niigata University

JOURNAL:

The Journal of the Japanese Society for Dental Materials and Device, 11(4), 559-569, 1992

KEY WORDS:

Titanium casting, Acoustic emission, Phosphate-bonded silica investment, Crack, Reacted Layers

ABSTRACT:
The deformation and fracture mechanism of titanium cast into a phosphate-bonded silica alumina investment mold was examined by means of 3-point bending test, acoustic (AE) analysis, and metallographic examination.
The alpha case formed on the casting increased the elastic limit and the maximum load, and so the removal of the surface by pickling deceased them. For the as-cast, sharp cracks propagated through the silicon, phosphorus-rich layer into the acicular structure in the elastic deformation stage and then opened in the plastic deformation stage.
As with the room°temperature mold casting, low-amplitude AEs were generated at a constant rate throughout the entire deformation process, in which crack formation, propagation, and opening occurred in the tension-side surface ranging from the center to both the end supports.
As with the 800 C mold casting, low-amplitude but high-energy AEs of a continuous type were generated during the elastic deformation, and they suggested simultaneous propagation of the primary crack. In the later half stage of plastic deformation, the load and the AE rate were remarkably reduced. This is because of a few main cracks near the center propagated continuously within the internal structure which possesses little resistance to the crack propagation.
As with the pickled casting, AEs were generated not in the elastic deformation stage but in the plastic deformation stage, thus releasing high energy. The cause of such high-amplitude AEs is obscure.

TITLE:

Study on the Deformation and Fracture Mechanism of Titanium by Means of Acoustic Emission Analysis. Part 1 Roles of the Oxygen-stabilized alpha Case and the Acicular Structure Formed by Heating in Air

LANGUAGE:

in JAPANESE with English Abstract

AUTHORS:

Miykawa,O., Watanabe,K., Okawa,S., Nakano,S., Honma,H., Shiokawa,N., Kobayashi,M.* and Tamura,H. **

INSTITUTE:

Dental Materials and Technology, Niigata University School of Dentistry, *EMX Laboratory, Niigata University and **Department of Machinery System Engineering, Faculty of Engineering, Niigata University

JOURNAL:

The Journal of the Japanese Society for Dental Materials and Device, 11(3), 503-514, 1992

KEY WORDS:

Rolled titanium, Acoustic emission, Crack, Twin formation, Oxygen-stabilized alpha case, Acicular structure

ABSTRACT:
A preliminary study was conducted to elucidate the influence of the surface reacted layers of titanium casting on the deformation and fracture mechanism. The testpiece cut from a rolled plate was heated in air or vacuum and thereafter subjected to 3-point bending. The real time measured acoustic emission (AE) was analyzed and metallographic examination was performed.
Heating above the transformation point in vacuum decreased the elastic limit (EL) and the maximum load. During the plastic deformation, high-amplitude AEs with very large energy were frequently detected. They suggested a large twin deformation. The EL reduction and the twin deformation are caused by the grain growth due to heating.
Heating in air tended to increase the EL, but caused a continuous generation of low-amplitude AEs before reaching the EL; secondary cracks were probably formed and primary and secondary cracks propagated within the tension-side alpha case.
Heating above 1,000 C in air and furnace-cooling resulted in a step-wise reduction of the load before or during transfer to the stage of plastic deformation, which was accompanied by generation of high-amplitude AEs with very large energy. This suggests a step-by-step propagation of main cracks within the acicular structure which possesses a high resistance to the crack propagation.

TITLE:

Internal Defects in Titanium Casting Caused by Investment Inclusions

LANGUAGE:

in JAPANESE with English Abstract

AUTHORS:

Miykawa,O., Watanabe,K., Okawa,S., Nakano,S., Shiokawa,N., Kobayashi,M.*, and Tamura,H. **

INSTITUTE:

Dental Materials and Technology, Niigata University School of Dentistry, *EMX Laboratory, Niigata University and **Department of Machinery System Engineering, Faculty of Engineering, Niigata University

JOURNAL:

The Journal of the Japanese Society for Dental Materials and Device, 10(3), 393-403, 1991

KEY WORDS:

Titanium casting, Internal defect, Investment inclusion, Silica, Alumina

ABSTRACT:
This paper reports the micro structure and the elemental maps of some internal defects in the titanium casting, formed by reactions with the investment inclusion.
The defect, without a hole or with an irregular or a circular hole, accompanied the oxygen-stabilized alpha phase and the acicular structure corresponding to the oxygen content distribution. Silicon and aluminium, occasionally phosphorus and magnesium, existed in and around the defect; the microstructure was similar to the layered structure of the casting surface.
The defect, especially the oxygen-stabilized alpha phase, played an important role in the source of crack initiation. Probably, some of the observed cracks were formed through the plastic bending deformation of the casting, and the others, through the cooling process of the casting.

TITLE:

Grinding of Titanium

Part 2 Commercial Vitrified Wheels Made of Alumina Abrasives

LANGUAGE:

in JAPANESE with English Abstract

AUTHORS:

Miykawa,O., Watanabe,K., Okawa,S., Nakano,S., Shiokawa,N., Kobayashi,M.*, and Tamura,H. **

INSTITUTE:

Dental Materials and Technology, Niigata University School of Dentistry, *EMX Laboratory, Niigata University and **Department of Machinery System Engineering, Faculty of Engineering, Niigata University

JOURNAL:

The Journal of the Japanese Society for Dental Materials and Device, 9(1), 42-52, 1990

KEY WORDS:

Titanium, Grinding performance, Alumina, Vitrified, Grinding burn, Chemical attrition

ABSTRACT:
Cast titanium was ground with commercial vitrified wheels made of alumina abrasives, and their grinding performance was investigated. For cutting, the appropriate circumferential speed of the alumina wheels was about 700 m/min. A speed lower or higher than this yielded unfavorable grinding results, which were attributed to wheel loading or chemical attrition of the abrasive, respectively. The hard wheel made of the A abrasive was suitable for grinding of titanium, and moreover, the wheel of the WA abrasive was more suitable than that made of the A abrasive. Generally, the cutting rate of the alumina wheels was inferior to that of the silicon carbide ones investigated previously. Depression of the wheel against the work yielded unfavorable grinding results; the manner in which the wheel was moved over the work during grinding was very important, compared with the silicon carbide wheels. Although the wheel was moved over the work, the high circumferential speed of the wheel resulted in chemical attrition of the abrasive and discoloration of the work surface, or grinding burn. The grinding burn layer mainly consisted of a few micrometer-thick titanium oxide.

http://www.ncbi.nlm.nih.gov:80/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=2134812&dopt=Abstract

TITLE:

Grinding of Titanium

Part 1 Commercial and Experimental Wheels Made of Silicon Carbide Abrasives

LANGUAGE:

in JAPANESE with English Abstract

AUTHORS:

Miykawa,O., Watanabe,K., Okawa,S., Nakano,S., Shiokawa,N., Kobayashi,M.*, and Tamura,H. **

INSTITUTE:

Dental Materials and Technology, Niigata University School of Dentistry, *EMX Laboratory, Niigata University and **Department of Machinery System Engineering, Faculty of Engineering, Niigata University

JOURNAL:

The Journal of the Japanese Society for Dental Materials and Device, 9(1), 30-41, 1990

KEY WORDS:

Titanium, Grinding performance, Silicon Carbide, Vitrified, Grinding burn, Chemical attrition

ABSTRACT:
Cast titanium was ground with commercial and experimental wheels made of silicon carbide abrasives, and their grinding performance was investigated. With the vitrified wheels made of the GC abrasive, at a higher the wheel circumferential speed and heavier the grinding pressure, the cutting rate was greater, accompanied by violent wear of the wheel. Being independent of the wheel speed, the grinding ratio reached about 1 under pressure heavier than 100 gf. The MgO-MgCl₂-bonded wheels of the C abrasive exhibited a similar tendency. The manner in which the wheel was moved over the work during grinding proved to be very important, compared with the nickel-chromium alloy as reported previously. Only depression of the wheel against the work resulted in chemical attrition of the abrasive and discoloration of the work surface, or grinding burn, due to oxidation of titanium. Even when the wheel was moved over the work, chip-formation process of the cutting edge was far from ideal, and the work surface was contaminated due to reaction of titanium with the abrasive. At a higher wheel circumferential speed, more chips were loaded or built-up in the wheel and strongly rubbed the work surface, resulting in violent wear of the wheel; loading and dislodging of such chips were repeated.

http://www.ncbi.nlm.nih.gov:80/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=2134811&dopt=Abstract

TITLE:

Layered Structure of Cast Titanium Surface

LANGUAGE:

ENGLISH

AUTHORS:

Miykawa,O., Watanabe,K., Okawa,S., Nakano,S., Kobayashi,M.* and Shiokawa,N.

INSTITUTE:

Dental Materials and Technology, Niigata University School of Dentistry and *EMX Laboratory, Niigata University

JOURNAL:

Dental Materials Journal, 8(2), 175-185, 1989

KEY WORDS:

Titanium casting, Interface reaction, Phosphate-bonded investment

ABSTRACT:
The present study concerns the surface layered structure of the cast titanium. A commercial titanium was cast into a mold which was made of a phosphate-bonded alumina/silica investment. Elemental analyses of the interfacial zone of the casting were made under an electron probe microanalyzer. The interfacial zone was composed of four layers: the outermost reaction or casting burn layer, the second layer of an oxygen- and aluminum-stabilized alpha case, the third layer in which silicon, phosphorus, oxygen, and carbon were inhomogeneously concentrated, and the fourth layer which consisted of acicular or plate-like crystals. It was observed that the larger the cast volume and the higher the mold temperature, the thicker became each layer and the coarser became the acicular grains. Probably, the layered structure was formed through decomposition of reducible species in the burnout investment and diffusion of the resulting elements into the casting.

http://www.ncbi.nlm.nih.gov:80/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=2490591&dopt=Abstract

Study on grinding of base metal alloys. 5. Constant pressure grinding of a Ni-Cr alloy with electro-deposited wheels.

Miyakawa O, Watanabe K, Okawa S, Nakano S, Shiokawa N, Kobayashi M, Tamura H.

Shika Zairyo Kikai 1989 Sep;8(5):662-6

The grinding techniques and electro-deposited wheels suitable for a 13% Cr-Ni dental casting alloy were determined. The lever-type grinding test machine modified in the previous study was used to investigate the grinding performance of experimental wheels of CBN- and diamond-particles. Depression of the diamond wheel against the work yielded unfavorable grinding results. Not only depression of the wheel against it but also moving the wheel over it with a heavier pressure is desired for higher grinding efficiency and its durability. Probably, the undurability of this wheel is associated with abrasive attrition due to oxidation or some chemical reaction with the work. The CBN wheel had not been suitable for the Co-Cr alloy tested in the third paper, but it exhibited very excellent performance for grinding of the Ni-Cr alloy, even without being moved over the work. Although being high in cost, the CBN wheel may pay for the very high performance and its durability.

http://www.ncbi.nlm.nih.gov:80/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=2490210&dopt=Abstract

Miyakawa O, Watanabe K, Okawa S, Nakano S, Shiokawa N, Kobayashi M, Tamura H.

Shika Zairyo Kikai 1989 Sep;8(5):653-61

The grinding techniques and the constituent element of vitrified wheels suitable for a 13% Cr-Ni dental casting alloy were determined. The lever-type grinding test machine used in the previous study was modified so that a work might be ground under a constant pressure as it moved reciprocally within a short stroke along the tangential direction of a rotating wheel. The grinding performance of two marketed wheels and eleven experimental wheels with different constituent elements was tested. Abrasive grains on the working surface of alumina wheel wore extremely due to abrasive attrition. Carborundum wheels proved to be more suitable for grinding of the comparatively soft Ni-Cr alloy. Not only depressing a wheel against a work but also moving the wheel over it with heavier pressure should be desired for the maximal grinding efficiency. The experimental carborundum wheels exhibited much the same performance as the marketed carborundum wheel under a less grinding pressure that 100 gf. Only the wheel of grain size #150 bonded with 19% binder wore obviously under the pressure of 150 or 200 gf and provided about two times the performance of the marketed wheel.

http://www.ncbi.nlm.nih.gov:80/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=2490209&dopt=Abstract

TITLE:

Study on Grinding of Base Metals Alloys. Part 3. Grinding of a Co-Cr Alloy under Constant Force

LANGUAGE:

in JAPANESE with English Abstract

AUTHORS:

Miyakawa,O., Watanabe,K., Okawa,S., Nakano,S., Shiokawa,N., Kobayashi,M. and Tamura,H.

INSTITUTE:

JOURNAL:

The Journal of the Japanese Society for Dental Materials and Device 7:1-12, 1988

ABSTRACT:
Keyword: Grinding performance, Base metals alloy, Vitrified wheel, Alumina, Electroless plating,
A lever-type testing apparatus was devised to evaluate the grinding performance of tools. Grinding of a Co-Cr alloy for three successive hours was performed under dry conditions to investigate the performance life of three vitrified bond wheels on the market and experimental electrodeposited wheels of CBN and diamond. The grinding behavior was determined by analyses of workpiece- and handpiece-vibrations and mandrel whirling, and observations of grinding chips, wheel loading and wear. Alumina wheels tended to stop grinding suddenly at a wheel rotation speed of 24,000 rpm or gradually at 12,000 rpm, which produced grooves due to attrition of abrasive grains on some localized areas of the wheel surface. When the height of the workpiece was high at 12,000 rpm or even low at 24,000rpm, the vitrified bond wheels tended to strike against the workpiece at short intervals, causing self dressing of cutting edges. Under high grinding force and at high rotation speed, the diamond wheel exhibited very remarkably high performance at the initial stage of grinding, however, the grinding rate decreased extremely with time. The loss of performance was attributed to a change of plated Ni-P alloy sustaining grains. On the other hand, the performance of the CBN wheel was relatively high. The grinding rate showed little change after three hours of grinding.

TITLE:

Study on Grinding of Base Metals Alloys (2)

LANGUAGE:

in JAPANESE with English Abstract

AUTHORS:

Miyakawa,O., Wtanabe,K., Okawa,S., Nakano,S., Shiokawa,N., Kobayashi,M. and Tamuna,H

INSTITUTE:

JOURNAL:

The Journal of the Japanese Society for Dental Materials and Device 6:674-684, 1986

ABSTRACT:
Keyword: Grinding performance, Base metals alloys, Cubic boron nitride, Electrodeposition, Acoustic emission, Run out
Using a Co-Cr alloy we investigated the grinding performance of three vitrified bond wheels on the market and two experimental wheels containing electrodeposited CBN and diamond. Acoustic emission, mandrel whirling, and handpiece and vice vibrations were analyzed to clarify the various phenomena observed in the grinding process. Stock removal per unit time increases linearly with the work feed speed. The slopes of the regression lines for the electrodeposited wheels were steep, indicating that high feed speed increases the grinding efficiency. Run away of the vitrified bond wheels from the work was greater at lower rotational speeds and higher feed speeds; with higher feed speed, the difference in the grinding efficiency becomes more remarkable between the vitrified bond and the electrodeposited wheels. Performances of alumina wheels vary markedly with their constituent elements.
Periodical undulations corresponding to the rotational speed and feed speed were produced on the ground surfaces, which was caused by beat vibration of the handpiece. Run out of wheel causes intermittent grinding with a period corresponding to the rotational speed. When a wheel was set with a large amount of run out, the actual interval of grinding action became short, thus decreasing the actual depth of the cut.

TITLE:

Study on Grinding of Base Metals Alloys (l) A Testing Apparatus and Results for a Few Dental Grinding Wheels

LANGUAGE:

in JAPANESE with English Abstract

AUTHORS:

Miyakawa,O., Wtanabe,K., Okawa,S., Nakano,S., Shiokawa,N., Kobayashi,M. and Tamuna,H.

INSTITUTE:

JOURNAL:

The Journal of the Japanese Society for Dental Materials and Device 4:645-656, 1985

ABSTRACT:
Keyword: Grinding performance, Base metals alloy, Cubic boron nitride, Electrodeposition
A testing apparatus was devised to evaluate the grinding performance of tools; the tool engagement was set, and the depth of cuts were measured throughout successive strokes of the work at constant speeds. Using a 13% Cr-Ni alloy, the performance of a CBN-electrodeposited wheel was compared with that of two vitrified-bond alumina wheels on the market.
Because of the run-out effect of the wheels, there were some differences in grinding action between rotational speed of 22,000 rpm and speeds below 18,000 rpm. At the high speed the ground surface was very wavy, and the final depth of cut exceeded the engagement. At lower speeds the surface was relatively even, but the engagement tended not to be entirely removed. Also at high speeds of work, the grinding had to be repeated many times for a certain depth of cut, and a lot remained uncut.
In consideration of run-out, the CBN-electrodeposited wheel was tested at only 12,000 rpm. Nevertheless, it exhibited high performance even at the high speed of work.

TITLE:

A NEW METHOD FOR FINITE ELEMENT SIMULATION OF ORTHODONTIC APPLIANCE-TEETH-PERIODONTIUM-ALVEOLUS SYSTEM

LANGUAGE:

ENGLISH

AUTHORS:

Miykawa,O., Shiokawa,N., Matsuura,T.,* and Hanada,K.*

INSTITUTE:

Dental Materials and Teclogy and *Orthodontics, Niigata University School of Dentistry

JOURNAL:

Journal of Biomechanics, 18(4), 277-284, 1985

ABSTRACT:
This paper describes a new simulation method to analyze the initial behavior of the total system comprising orthodontic appliance, teeth, and their supporting structure. It is based on a finite element method which additionally takes account of a rotational degree of freedom. Beam and rod elements are used for finite element idealization of orthodontic appliance. Through spring elements it is connected with the teeth supported by the alveolar structures. The technique of 'initial strain' is introduced so as to analyze the effects of a gable bend and activation on the force system which is delivered by the orthodontic appliance. As compared with the photo-elastic technique hitherto used, this method serves to investigate systematically and quantitatively the initial aspect of orthodontic tooth movement.

http://www.ncbi.nlm.nih.gov:80/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=4019526&dopt=Abstract

Suzuki H, Iguchi S, Miyakawa O, Irie M.

Nippon Kyosei Shika Gakkai Zasshi 1984 Dec;43(4):497-506

http://www.ncbi.nlm.nih.gov:80/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=6597837&dopt=Abstract

Iguchi S, Suzuki H, Irie M, Miyakawa O.

Nippon Kyosei Shika Gakkai Zasshi 1984 Jun;43(2):245-56

http://www.ncbi.nlm.nih.gov:80/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=6590706&dopt=Abstract

Irie M, Iguchi S, Suzuki H, Nishijima K, Miyakawa O.

Nippon Kyosei Shika Gakkai Zasshi 1983 Jun;42(2):186-200

http://www.ncbi.nlm.nih.gov:80/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=6577103&dopt=Abstract

Suzuki H, Iguchi S, Nishijima K, Irie M, Miyakawa O.

Nippon Kyosei Shika Gakkai Zasshi 1982 Jun;41(2):302-13

http://www.ncbi.nlm.nih.gov:80/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=6957493&dopt=Abstract

Miyakawa O.

Journal of the Japan Society for Dental Apparatus and Materials 1976 Nov;17(40):269-77 1976 Nov;17(40):287-96

http://www.ncbi.nlm.nih.gov:80/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=794426&dopt=Abstract

Forces and moment transmitted to the abutment teeth were numerically analyzed using a model for a posterior bridge. Three cases were chosen to investigate the influence of loading condition; a vertical (A) and a mesially inclined (B) load at the center of pontic and a vertical load at the abutment (C). The results obtained are as follows: Under the condition (A), as reported previously, both moment and force increase as bridge flexural rigidity is less or bridge span longer. When the load shifts to the abutment tooth, the moment slightly increases as flexural rigidity is greater or bridge span shorter, but horizontal force is scarcely transmitted to the abutment teeth. Maximum moment under the condition (C), however, is not so great as that under the condition (A) and the difference decreases among the moment values calculated from the present model and two theories of general-beam and rigid-beam model. Consequently, special attention should be given to the more flexible pontic which might very possibly cause injury to the abutment teeth under the first two conditions. Even though the resultant force is not very great, its supporting tissues with smaller surface area tend to be subject to higher stress.

Miyakawa O.

Journal of the Japan Society for Dental Apparatus and Materials 1976 Nov;17(40):269-77 1976 Nov;17(40):278-86

http://www.ncbi.nlm.nih.gov:80/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=794425&dopt=Abstract

The biomechanical behavior of bridge support was studied by the finite element method. An idealized bridge model was constructed by using the previously reported tooth model as the two-sided abutment teeth. Under a vertical load at the center of pontic the stress distributions were shown in the constituent elements. Forces transmitted to the abutment teeth were calculated from these distributions. The results obtained were compared with theoretical models based on the beam theory in engineering. 1) For the finite element model, moment M and horizontal force H are given by (see article) wherein P is load, B is flexural rigidity of pontic, L is bridge span length, and KM and KH are spring constants of the supports with respect to moment and horizontal force, respectively. 2) If it is assumed that a dental bridge is a rigid body, the moment is underestimated and the horizontal force is neglected. 3) According to the fixed-ended-beam model which allows neither movement nor deformation of the supports, the moment is overestimated in many cases. 4) According to the general-beam model which allows the vertical movement and rotation of the supports, the moment is underestimated because of the assumption that no forces are acting in the longitudinal direction of beam.

Miyakawa O.

Journal of the Japan Society for Dental Apparatus and Materials 1976 Nov;17(40):269-77

http://www.ncbi.nlm.nih.gov:80/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=794424&dopt=Abstract

Biomechanical considerations are very important to design a prosthetic appliance; however, there have been no satisfactory quantitative studies of such problems, mainly because theoretical and experimental models are unable to represent exactly the natural conditions in the mouth. The finite element method has been successfully applied in each field of applied mechanics and found to be effective for the structural analysis of the biological systems, for it has the advantage of greater versatility for modelling. Accordingly, this analytical, computer-aided method was applied to the dental bridges to evaluate the loads transmitted to the abutment tooth and the stress distributions in the supporting tissues. As the preliminary study a two-dimensional model was constructed to simulate the tooth subject to a vertical and a horizontal load and a moment at the coronal portion. The stress distributions in the tooth and the periodontal membrane and the force distributions on the socket wall were calculated for three load conditions. The tooth mobility and the center-of-rotation position were compared with actual data available in some literatures and the characteristics of tooth support were discussed in terms of three spring constants.

TITLE:

An Investigation on the Aging Behavior and Precipitate in 17-7 PH stainless Steel

LANGUAGE:

in JAPANESE with English Abstract

AUTHORS:

Furukawa,T. and Miyakawa,O.

INSTITUTE:

JOURNAL:

Journal of the Japan Inst.itute of Metals 30:1167-1172-1966

ABSTRACT:
It is generally believed that the age hardening in 17-7 PH stainless steel is accomplished by the precipitation of an ordered Ni-Al compound. However, the details are unknown, mainly because the microstructure is complex and the precipitate cannot be detected or identified with certainty. As a fundamental study of the age hardening mechanism in this steel, it was investigated whether or not the ordered Ni-Al compound was precipitated by aging. The results obtained are summarized as follows: (1) The decrease in dilatation diagram was observed at 440° and 570 °C on heating 17-7 PH stainless steel in martensite matrix. Whereas, in the case of 17 Cr-7 Ni stainless steel (no Al), the decrease at about 440 °C was not observed. The former seems to be caused by the reaction due to the presence of Al, the latter by the transformation of martensite to austenite. (2) The changes in dilatation diagram, specific electrical resistance, B-H diagram, lattice constant, and electron micrograph, all suggest that precipitation take place on aging. One of the precipitates in the overaged specimens turned out to be a CsCl type structure with a lattice constant of 2.88A, viz. NiAl, from X-ray and electron diffraction measurements and chemical analysis.