M. Pezzoli

Corrosion under static and dynamic conditions of alloys used for magnetic retention in dentistry

In recent years magnetic retention has gained increasing popularity in dental practice. This investigation compared the corrosion resistance of the palladium-cobalt ferromagnetic alloy (constituent of the keeper cemented on the abutment teeth) coupled with the samarium-cobalt magnets embedded in the removable part of the denture. The behavior of three couples (cobalt-palladium, cobalt-palladium/titanium, and cobalt-palladium/palladium) has been studied. The magnets, because of their poor corrosion resistance, are encapsulated in various materials. To simulate clinical conditions, characterized by the continuous movement of the keeper with respect to the magnet, the experiments were conducted in artificial saliva under intermittent and continuous wear.

Evaluation of load transmission by distal-extension removable partial dentures by using reflection photoelasticity

A technique has been described for fabrication of a surgical template made of soft vinyl mouthguard material. Use of this stent at the time of surgery can be of great value to the oral surgeon and the prosthodontist. The risk of excessive augmentation and migration of the particulate hydroxyapatite to an undesired area will be minimized if the stent is used as a matrix. Uniform results in size and form of the ridge can be obtained from the surgical procedure when the stent is used. The denture-bearing area of the maxillary anterior ridge will improve significantly, enabling the dentist to make a maxillary complete denture.

Metal-porcelain bonding to a magnetizable alloy.

The bond strength of porcelain to a magnetizable Pd-Co alloy was compared with that of a precious and nonprecious ceramic alloy by using the four-point flexure test and a direct shear test. The test procedure consisted of continuous loading until a bond failure occurred. The fractured surfaces were then examined with a scanning electron microscope. A good strength of the magnetizable Pd-Co alloy comparable to that of two specific ceramic alloys and intermediate between precious and nonprecious alloys was observed. Most of the failures of the precious alloy occurred at the oxide-porcelain interface. The preferential fracture paths were observed for the nonprecious alloy between the metal fracture and the oxide layer. The fractures of the magnetizable alloy occurred at the oxide-porcelain interface and in the bulk of the porcelain, clearly pointing out the possibility of using magnetizable Pd-Co alloy for metal ceramic abutment crowns.

Tensile strength of CrCo dental alloys solder joints

Modifications and repairs of removable partial dentures usually involve solder joints. It is important to know the combination of solder and alloy that will provide the strongest junction. The purpose of this work was to investigate the mechanical strengths of different solders commonly used in dental practice. Specimens of three removable partial denture alloys (Dentitan, Crutanium, Wisil) were soldered with various solders having different melting temperatures. The soldered specimens were subjected to tensile testing, and the fracture surfaces were examined by means of scanning electron microscopy. Most of the failures occurred within the soldered joint, which is the weakest portion of a removable partial denture. Excessive use of flux to achieve an adequate flow of solder produced defects in the solder joint. A relationship was found between joint strength and solder fusion temperature for Crutanium and Wisil--the higher the fusion temperature, the higher the joint strength.

Biomechanical Analysis of Coupling Between Mandible and Removable Partial Dentures

The Department of Mechanics and the School of Dentistry of Turin have been involved in research concerning dentistry over the last ten years. The experimental methods used in our work were the reflection photoelasticity and the strain gage technique.