Microstructural Observations of Laser-Sintered Specimens for Prosthodontic Applications

Objective: Laser sintering is a recently introduced technology that has been used to prepare dental restorations from a biocompatible Co-Cr base metal alloy (Ucar et al, 2009). Two promising areas for this technology are preparation of frameworks for dental implant applications, which presently requires a time-consuming milling procedure, and waxing/casting copings for metal-ceramic restorations which can be problematic for Co-Cr alloys. While recent articles have described dental applications of laser sintering, also using titanium and titanium alloys, detailed study of laser-sintered microstructures has not been reported. The objective of this study was to examine extensively the microstructures of representative laser-sintered Co-Cr restorations to gain fundamental insight into predicted clinical performance. 

Method: Representative implant framework and maxillary coping specimens were prepared from STL files by a commercial laser sintering apparatus (PHENIX SYSTEMS), using the dedicated Co-Cr alloy. A compatible dental porcelain was bonded to the coping specimen (North Shore Dental Labs, Lynn, MA). Specimens were sectioned with a slow-speed diamond saw, prepared for metallographic examination by resin-mounting and polishing with a series of abrasives, and observed with a scanning electron microscope at a range of magnifications. 

Result: The dimensions of the laser-sintered specimens were in excellent agreement with the original STL files, and the porcelain-metal bonding was judged to be clinically acceptable. The laser-sintered Co-Cr alloy had a fine-grained microstructure, characteristic of this technique, which should yield excellent mechanical properties. 

Conclusion: Further study of these Co-Cr alloy microstructures is recommended, using a nanoindentation technique to investigate local variations in mechanical properties. Additional research should be performed to determine if laser-sintered Co-Cr restorations are suitable for widespread replacement of restorations from other alloys prepared by traditional dental laboratory methods. Extension of the present laser sintering work on prosthodontic applications to titanium alloys will require the availability of very small starting powder particles.