Bonding of Dental Ceramics to Titanium: Processing and Conditioning Aspects

Abstract

Difficulties related to titanium processing (casting) and the problematic titanium-ceramic bond have been limiting the latter's application in prosthetic dentistry for many years. Recent advances in subtractive and additive CAD/CAM technologies have provided alternative routes for titanium processing. The effect of a processing route on titanium surface characteristics and on the strength of its bond to porcelain need to be assessed, since most paths for enhancing porcelain bonding involve preparation of the titanium surface. Several approaches to bond enhancement have been proposed, some of which are widely accepted (abrasion by airborne-particle and application of a bonding agent), while others have not resulted in a clinical breakthrough. Despite efforts to improve titanium bonding to porcelain and to develop titanium compatible, low-fusing porcelains, many in vitro studies report bond strengths to titanium that are inferior to those for base metals and noble dental alloys. Only a few clinical studies have been reported, revealing that titanium-ceramic restorations are susceptible to mechanical complications (porcelain fractures in 33 % of cases). Current knowledge on titanium-ceramic bonding is here reviewed, focusing on the recent attempts to overcome the limitations of the system and on recent advances in titanium processing. Optimization of the currently available processing and surface conditioning methods seems to be necessary.Although most of the proposed surface preparation methods (surface coating and roughening) appear to show a certain degree of porcelain bond improvement, many of them require application of additional complex procedures. Simplification and improved efficiency therefore appear to be the essentials for implementation of these methods in clinical practice.

Pre-oxidation of selective-laser-melted titanium dental alloy: effects on surface characteristics and porcelain bonding

“…The recorded 10-nm thickness of the oxide is in agreement with that reported for the thickness of the passive oxide scale [28]. This layer is known to be stable and self-limiting, protecting the metal from further oxidation and acting as an effective barrier against metal dissolution and the release of ions [2,28]. At elevated temperatures, however, oxygen diffuses through the originally formed oxide layer and reaches the metal/oxide interface, reacting with the titanium to form titanium oxides.…”

“…Porcelain-fused-to-metal (PFM) fixed dental prostheses (FDPs) are widely used in prosthetic dentistry, providing reliable, long-term clinical outcomes by combining the good mechanical properties of the metal framework and the favorable aesthetics of veneered porcelain [1]. The PFM concept relies on the formation of a strong and durable metal-ceramic bond, which can be a challenging procedure [2]. It has been shown that four mechanisms contribute to the metal-ceramic bonding: chemical bonding, mechanical interlocking, van der Waal's interactions, and the porcelain's exposure to residual compression on cooling from the firing temperatures due to the slightly lower coefficient of thermal expansion (CTE) of the porcelain than that of the metal [3,4].…”

“…Titanium alloys are known for their attractive properties with dental restorations, including good mechanical properties and corrosion resistance, excellent biocompatibility, low allergenic potential, and low cost [2]. Titanium is a highly reactive element that combines readily with oxygen at room temperature, forming a very thin, chemically inert surface layer of titanium oxide [2]. At elevated temperatures, however, titanium tends to oxidize rapidly.…”

“…The microstructure of the framework, on the other hand, is greatly affected by the applied route for metal processing [21]. The recent advances in subtractive and additive Computer Aided Design (CAD) and Computer Aided Manufacture (CAM) technologies have provided alternatives to the traditional casting of titanium [2,21]. Selective laser melting (SLM) is an additive CAM technology that is used to fabricate dental frameworks.…”

The bond strength of dental porcelain to cobalt-chromium alloys fabricated by casting, milling and by selective laser melting: a comparative analysis

“…Surface roughening by abrasion with airborne Al 2 O 3 particles has been widely accepted as a standard operating procedure for bond enhancement in clinical practice. 9,32,33 It promotes mechanical retention between the metal and the ceramics. 9,30,31 Furthermore, airborneparticle abrasion also removes gross surface irregularities and cleans the investment material from the surface of the cast alloys.…”