I the 35 years since the concept of osseointegration was first applied to human patients, there have been many advances in the understanding and application of implant dentistry as a method for the replacement of missing teeth. Osseointegration as first defined by Branemark is a scientific milestone that delineates a certain sense of separation of the old from the new in implant dentistry. Osseointegration was a watershed event that has forever changed the way dentists view their options when confronted with a patient requiring tooth replacement. While dental implant therapy was an option for tooth replacement for many years prior to the publication of Branemark’s work, he gave the field a scientific basis and a sense of respectability it had lacked previously. This was particularly true in academic institutions, where dental implants were largely ignored as a viable choice for tooth replacement. Dental implants are now a major focus of didactic and clinical education in 3 dental specialties and soon will likely become mainstream in undergraduate dental school clinics. Osseointegration is the single factor that has most dramatically changed the discipline and specialty of prosthodontics since the introduction of fluoridated water. The evolution and change seen in basic science and the surgical understanding of dental implant therapy have perhaps been more far reaching than parallel advances in knowledge of the restorative aspect of dental implants. As the 20th century draws to a close, it is appropriate to review the significant advances and changes in implant prosthodontics that have occurred over the past 2 decades and, more importantly, describe future directions of investigation that are paramount to the advancement of dental implant therapy as a beneficial treatment modality.

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Implant prosthodontics: current perspective and future directions.

Prosthodontic focus on the restoration of osseointegrated dental implants has evolved dramatically in the last 20 years. Many of the original guiding principles for restoring implants have changed and/or disappeared altogether, and new ideas have taken their place. It is appropriate that this evolution be examined with a 2-fold focus. First, the art and science of prosthodontics as it relates to dental implants today is the result of very real and important lessons learned during the past 2 decades. Second, an appreciation of the history of implant prosthodontics as it relates to osseointegration gives insight into the future direction of research and clinical exploration aimed at continually improving the state of the art and, ultimately, the quality of care provided to patients. This article reviews what the authors consider the most important aspects of the evolution of osseointegrated implants. Pertinent literature was selected for citation, but the discussion does not represent a comprehensive review of the literature.

Twenty years of progress in implant prosthodontics

Joint strength of laser-welded titanium.

This study investigated the effect of laser-beam welding conditions [voltage (V) and spot diameter (mm)] on the penetration depth into dental casting alloys. Castings (3.0 mm x 8.0 mm x 50 mm) were prepared from the metals used in this study: commercially pure titanium (CP Ti), Ti-6Al-4V, Ti-6Al-7Nb, cobalt-chromium alloy (Co-Cr) and Type IV gold alloy. Two cast blocks of each metal were butted against one another at the 8.0 x 50-mm surfaces. They were then welded at their interface under the following conditions: voltage of 160-340 V, spot diameter of 0.4-1.6 mm, and pulse duration of 10 ms. After laser welding, the blocks were separated, and the penetration depth into each alloy was measured. The data were analyzed with the use of ANOVA at the p < 0.05 level of significance. The penetration depths were as follows: CP Ti (0.29-6.45 mm), Ti-6Al-4V (0.32-5.24 mm), Ti-6Al-7Nb (0.34-5.65 mm), Co-Cr (0.24-6.15 mm), and Type IV gold alloy (0.12-5.22 mm). The voltage and spot diameter affected the penetration depth into the metals tested. When the voltage increased and the spot diameter decreased, the penetration depth increased for each metal. Selecting suitable conditions for laser welding to obtain sufficient penetration depth for the optimal thickness of the metal is important when welding prostheses.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/jbm.b.30117

Penetration depth into dental casting alloys by Nd:YAG laser

Purpose: This study investigated the effect of argon gas shielding on the strengths of laser-welded cast Ti and Ti-6Al-7Nb and compared the results to those of two dental casting alloys.



Materials and Methods: Cast plates of Ti, Ti-6Al-7Nb, gold, and Co-Cr alloy were prepared. After polishing the surfaces to be welded, two plates were abutted and welded using Nd:YAG laser at a pulse duration of 10 ms, spot diameter of 1 mm, and voltage of 200 V. Five specimens were prepared for each metal by bilaterally welding them with three or five spots either with or without argon shielding. The failure load and percent elongation were measured at a crosshead speed of 1.0 mm/min.



Results: The factor of argon shielding significantly affected the failure load and elongation of the laser-welded specimens. The failure loads of argon-shielded laser-welded CP Ti and Ti-6Al-7Nb were greater compared with the failure loads of specimens welded without argon shielding for both three- and five-spot welding. Regardless of argon shielding, the failure loads of the laser-welded gold alloy were approximately half that of the control specimens. In contrast, the failure loads of the nonshielded laser-welded Co-Cr alloy were greater. The percent elongations positively correlated with the failure loads.



Conclusions: The use of argon shielding is necessary for effective laser-welding of CP Ti and Ti-6Al-7Nb but not for gold and Co-Cr alloy.

Laser welding of cast titanium and dental alloys using argon shielding.

Statement of the problem. Data on optimal conditions for laser welding commercial pure cast titanium used in dental restorations are sparse and not well established. Purpose. The mechanical properties of laser-welded cast commercially pure titanium under different laser welding conditions were evaluated to find the optimal parameters in terms of duration and voltage (energy level). Material and methods. Fifty-seven cast pure titanium specimens according to ISO specification 6871 were divided into nine experimental groups and one control group. The sectioned titanium bars were laser-welded under different duration (8, 10, and 12 ms) and energy (290, 300, and 310 V) levels and evaluated for ranges of ultimate tensile strength (374 to 562 MPa), 0.2% yield strength (206 to 338 MPa), and percentage elongation (2.49% to 10.58%). Results. Under a suitable laser-welding setting parameter the ultimate tensile strength and 0.2% yield strength of experimental groups were weaker than the unsectioned control specimens (control group ultimate tensile strength 540 ± 11 MPa, 0.2% yield strength 258 ± 49 MPa) or too brittle (control group percentage elongation 12.41% ± 1.83%). Two-way ANOVA, nonparametric tests showed that voltage was the only significant factor for all parameters studied ( p Conclusion. Optimal duration and voltage (energy level) used in laser welding for cast CP grade I titanium bar was superior to or comparable with and produced properties that were superior to or comparable with the unsectioned control specimens. (J Prosthet Dent 1998;79:477-83.)

Chia Kai Chou

Papers

Mechanical properties of laser-welded cast titanium joints under different conditions