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International Poster Journal of Dentistry and Oral Medicine
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Int Poster J Dent Oral Med 10 (2008), No. 4     15. Dec. 2008

Int Poster J Dent Oral Med 2008, Vol 10 No 04, Poster 426

Dental Alloys structural analyses of welded frameworks

Language: English
 

Authors:
Prof. Dr. Cristina Maria Bortun, Lecturer. Dr. Liliana Sandu, Assist. Sorin Porojan,
"Victor Babeş" University of Medicine and Pharmacy Timişoara, University School of Dentistry, Specialization of Dental Technology
Prof. Dr. Eng. PhD, Livius Miloş,
Politehnica University Timişoara, Faculty of Mechanical Engineering, Welding Equipment and Technology Department
Lecturer. Dr. Brandusa Ghiban,
Politehnica University Bucharest, Faculty of Materials Science and Engineering

Date/Event/Venue:
Sept 26th -29th, 2007
42nd annual meeting of IADR-Continental European and Israeli Divisions,
Thessaloniki, Greece
 

Introduction

Dental alloys structural analyses are important in order to obtain quality prosthetic pieces. The defects appeared in removable partial dentures metallic compounds are in connection with the casting, processing and welding.
 

Objectives

The aim of study was to detect casting, processing and welding optimal parameters for some long lasting prosthetic pieces.
 

Material and Methods

CoCrMo alloys were used: "C" alloy (Vaskut Kohàszati Kft - Budapest, Hungary), WIRONIT (Bego - Bremen, Germany) and HERAENIUM CE (Heraeus Kulzer, Hanau, Germany). They were analyzed both as metallic frameworks of removable partial dentures and as metallic cast plates (dimensions: 10x20mm and thickness of 0,4mm - 1mm). The welds were made in butt joint configuration with or without filling material. As filling material a special 0.5 mm diameter Co-Cr Finalloy - Fino, Bad Bocklet, Germany wire was used. Equipments like: Nd:YAG lasers - HL 124P LCU TRUMPF (TRUMPF GmbH Ditzingen Germany) and Welder (Schütz Dental, Rosbach, Germany) were used for welding.

Fig. 1a: Welding equipments: Nd:YAG laser - HL 124P LCU TRUMPF
 
Fig. 1b: Welding equipments: microimpulse Welder.
 
Radiographic, metallographic and microhardness analyses were made in order to certify welding quality, casting alloys structural defects, to stand out possible the cracks within the base material. The welding parameters used for laser welding were: P med(W): max.120; Pp(KW) max. 5; tp(ms) 0,3-20; f max (Hz) 600; Ep (J) 0,1-50 and for microimpulse were: power - level 4, overlapping more than ½, time delay 40 milliseconds, one side welding.

Fig. 1c: Welding equipments: Nd:YAG laser - HL 124P LCU TRUMPF Fig. 1d: Welding equipments: microimpulse Welder.
Fig. 2a: Different welding types: Cast plates Fig. 2b: Different welding types: Laser welding
Fig. 2c: Different welding types: Microimpulse welding Fig. 3a: Heat treatments for dental alloys: Preparing for heat treatment
Fig. 3b: Heat treatments for dental alloys: Alloy heating Fig. 4a: Welding of RPD framework: Details of clasp welding
Fig. 4b: Welding of RPD framework: Welded Mc Cracken clasp Fig. 4c: Welding of RPD framework: Crack of circumferential clasp
Fig. 4d: Welding of RPD framework: Preparing for welding
 
Fig. 4e: Welding of RPD framework: Detail of welded clasp
 

Results

Noninvasive analyses methods point out casting alloys structural defects, distinguish the cracks within the base material. The cracks appear mostly in base material, being caused by casting, non-adequat processing and rapid cooling of weld. Structural analyses present dendritic structure specific for cast alloys, non-metallic inclusions and some temporary particles. Intergranular pellicular precipitations and spherical shape compounds placed inside the crystalline grains appear on some welding. Welded area alloys chemical composition discreetly differs from the base material.

WIRONIT alloy -FIROFINE (BEGO) investment material
HV5 hardness
Nr. zone HT and welding without HT and welding
850°C / 1h 950°C / 1h 1050°C / 1h
1 BM1 401 367 362 367
2 HAZ 460 423 407 386
3 WM 502 454 412 418
4 HAZ 460 412 381 376
5 BM 401 371 371 345
"C" alloy -FIROFINE (BEGO) investment material
HV5 hardness
Nr. zone HT and welding without HT and welding
850°C / 1h 950°C / 1h 1050°C / 1h
1 BM1 412 423 371 367
2 HAZ 418 391 412 435
3 WM 418 371 381 429
4 HAZ 423 441 429 376
5 BM 412 401 391 362
HERAENIUM CE alloy -FIROFINE (BEGO) investment material
HV5 hardness
Nr. zone HT+ welding without HT and welding
850°C / 1h 950°C / 1h 1050°C / 1h
1 BM1 367 336 371 336
2 HAZ 435 412 412 381
3 WM 460 429 391 412
4 HAZ 412 376 381 376
5 BM 441 366 332 329
Tab. 1: Microhardness values of welded joints
 
Fig. 5a: Non invasive procedures to analyse the welded zone: X-rays Fig. 5b: Non invasive procedures to analyse the welded zone: pseudo chromatisation
Fig. 6a: Metallographic aspects: discontinuous precipitation in metallic matrix Fig. 6b: Metallographic aspects: non-uniform dendritic structure with interdendritic microporosities
Fig. 6c: Metallographic aspects: interdendritic cracks in a structure with fine lace eutectic Fig. 6d: Metallographic aspects: welded areas
Fig. 6e: Metallographic aspects: welded areas Fig. 6f: Metallographic aspects: welded areas
Fig. 6g: Metallographic aspects: Heat affected zone Fig. 6h: Metallographic aspects: Heat affected zone
Fig. 6i: Metallographic aspects: Base metal Fig. 6j: Metallographic aspects: Base metal
Fig. 7a: Numeric analyses of welding: Welding type no.1 Fig. 7b: Numeric analyses of welding: Welding type no.2
Fig. 7c: Numeric analyses of welding: Stress distribution in alloy Fig. 7d: Numeric analyses of welding: Stress distribution 2

Conclusions

Dental alloys structural analyses are important for structural defects knowledge. The cracks appear mostly on base material, being caused by casting, non-adequate processing and rapid cooling of the weld.
 

Literature

  1. Bertrand, C., Le Petitcorps, Y., Albingre, L. - Dupuis V.: Optimization of operator and physical parameters for laser welding of dental materials. BDJ 2004, 196, 413.
  2. Borţun Cristina, Mitelea, I., Miloş, L., Bîrdeanu, V., Sandu Liliana - Analysis of laser welded joints on "C" alloy used in removable partial dentures technology, European Cells and Materials vol.10, 2005, Suppl.I: 31.
  3. Dobberstein, H., Orlick, H., Fisher, P., Zhurt, R. - Experimental studies of the laser welding of Cr-Co alloys using a pulse laser Nd:Yag. Zahn, Mund, Und Kieferheilkunde Mit Zentralblatt 1989; 77:578-579.
  4. Ghiban, B., Bortun, C., Sandu, L.: Structural features in cobalt based alloys for dental applications, Bull. Transilvania Univ. Brasov, 2007, vol.II, 80-86.
  5. Hoffman, J. - Dental laser welding technique. Procedural report.1.2.Quality, expense, and risks of innovative bonding technique. Dental labor Munch 1992 Jul;40(7):1221-4.
  6. Matsuda, S, Veyama, T. - Solidification crack susceptibility of laser weld metal in 0.2C-Ni-Cr-Co steels: effects of bead configuration and S and P contents. Welding International 1993, 7:686-92.
  7. Wang, R., R Chang C T. - Thermal modeling of laser welding for titanium dental restorations. J. Prosthetic. Dent. Mar; 1998, 79(3):335-41.
     

Acknowledgements: This study was supported by the CNCSIS Grant, no. 744/2006, from the Ministry of Education and Research of Romania
 

This Poster was submitted by Prof. Dr. Cristina Maria Bortun.
 

Correspondence address:
Prof. Dr. Cristina Maria Bortun
"Victor Babeş" University of Medicine and Pharmacy Timişoara
University School of Dentistry, Specialization of Dental Technology
Blv. Revolutiei 1989, no 9
300041, Timisoara
Romania