M.M.A. Vrijhoef

Four bonding systems for resin-retained cast metal prostheses

Abstract The aim of this study was to test and evaluate 4 resin-metal bonding systems for tensile bond strength. The resin-metal bonds were established between pairs of similar, and simultaneously treated Co−Cr and Ni−Cr cylinders. Before testing, the bonds were stored for 1 h dry at room temperature or in water 37°C for 1 week. The systems tested were: (1) silicoating (Micropont), (2) sandblasting (Panavia Ex), (3) electroplating (Panavia Ex) and (4) etching (Clearfil F). Highest bond strength values were found for silicoated and sandblasted Co−Cr samples whereas lowest bond strength values were found for etched Ni−Cr samples.

Controlled clinical study of amalgam restorations: survival, failures, and causes of failure

The survival and modes of failure of amalgam restorations were investigated retrospectively. 2660 Class I or II lesions were restored and evaluated yearly or half-yearly for failures during the 30- to 84-month follow-up. Restorations with unacceptable margins were not counted as failures if no traces of secondary caries could be seen. 8% of the restorations were lost because of patient drop-out. Of the remaining restorations, 1% was replaced due to primary caries. Of the remaining number (2431), 9% failed because of all other reasons. The leading mode of failure was bulk fracture (4.6%), followed by tooth fracture (1.9%), and marginal ridge fracture (1.3%). For all other reasons, 0.8% of the restorations failed. Only two restorations were replaced because of secondary caries. The alloy selection in both conventional and high-copper categories significantly influenced the survival of the restorations for reasons directly related to the restoration.

Intraoral humidity during operative procedures

Results of dentine adhesion studies are influenced by many factors such as intrinsic and extrinsic dentine wetness. Relative air humidity and temperature are extrinsic environmental factors whose influence on dentine bonding capability is not precisely known. It was the aim of this study to gain an understanding of these factors as present in the mouths of patients and as influenced by several variables. In six different experiments the influence of application of a rubber dam, high and low relative humidity in the dental surgery, nose and mouth breathing and tooth drying was investigated. The results show that without application of a rubber dam there was no statistically significant difference in temperature for the variables nose and mouth breathing and tooth drying (mean 27.7 +/- 1.5 degrees C). Only the difference in relative air humidity of the dental surgery was statistically significant. With the application of a rubber dam the relative air humidity and temperature were essentially the same as the dental surgery conditions. It is concluded that without rubber dam the intraoral environment in which bonding procedures are to be performed is comparable with a high humidity climate such as that of Central Africa or the South Pacific.

Facial injuries sustained during sports and games

This study is an investigation into the number and type of facial injuries due to sports and games, because no detailed information on these dental misfortunes could be found in the literature. The group investigated consisted of 319 patients, treated at the Department of Oral and Maxillo-Facial Surgery, Nijmegen in the period January 1, 1971-December 31, 1978. Facial injuries were classified into different types of fractures according to site as also were further series of associated injuries. Males were shown to be more prone to facial injuries than females (2.4:1). In the age group 15-40 years, males proved to be more prone to such injuries than the age group under 15 years. The major part of the injuries is due to fractures of the alveolar process and/or luxation of teeth (59.6%), the zygomatic bone and arch (24.2%) and the mandible (15.3%). Fractures of the maxilla and the nose were rarely seen.

A clinical comparison of three types of resin-retained cast metal prostheses

A preliminary clinical trial comparing three types of resin-retained cast metal FPDs was conducted. Micromechanical retainers were found to be more retentive than macromechanical retainers. The retention values in this investigation were in agreement with similar studies, but longitudinal studies are still desirable.

Metallurgical Aspects of High-palladium Alloys

Nine commercial high-Pd alloys were investigated. Microstructure and phase composition were screened by x-ray diffraction, light microscopy, and an electron microprobe. After being etched, some high-Pd alloys revealed dendritic structures. The others showed a more homogeneous structure with distinct grain boundaries. Etching was necessary to reveal distinct structures, though the overall etching effect turned out to be limited. On unetched specimens, only a slight chemical heterogeneity could be determined. Except for one alloy, the systems turned out to have complex multi-phase structures. The main face-centered-cubic (fcc) phase was Pd-based. As secondary phases, body-centered-cubic (bcc) and/or simple cubic ones were detected. The latter phases were similar to a Cu3Ga and PdGa intermetallic compound, respectively. Face-centered-tetragonal (fct) structures reported by other investigators were not found.

Loss of substance of dental composite restorations

Abstract A method for the direct in vivo measuring of loss of substance of Class I and II restorations was tested. On models of the teeth involved, silver caps were made. The occlusal surface was relieved by a piece of tinfoil. With the silver cap, silicone impressions were made for baseline registration and also at 3 recall periods, 6, 12 and 18 months after baseline registration respectively. The average thickness of the loss of substance was computed by the weight, the density and the thickness of both the enclosed impression material and the piece of tinfoil. The results show the in vivo repeatability of the test method to be in good agreement with data obtained in a previous in vitro study. The error of the test method accounts only for a relatively small part of the total experimental variance (7, 9 and 12%). The wear values show that the method registers, with adequate accuracy, wear rates of approximately 20 μm/year. Because of its simplicity, inexpensiveness and accuracy, the method is highly productive and suitable for clinical screening tests of the wear behaviour of restorations, especially for the registration of losses of substance of posterior composites.

Axial strengths of foil, all-ceramic and PFM molar crowns

Abstract The axial strength of crowns on master dies, made of 3 foil systems (Flexobond; Plati-deck; Ceplatec), has been evaluated. A conventional porcelain-fused-to-metal (PFM) crown, a castable ceramic system (Dicor) as well as an injection molded all-ceramic crown system (Cerestore) were used as a reference. The PFM crowns turn out to have significantly higher failure loads. Cerestore and Flexobond have corrected failure loads which are approximately 60% of the PFM fracture load. Ceplatec follows at approximately 40% of the PFM fracture load, while the fracture loads of Plati-deck and Dicor turn out to be approximately 30% of the PFM value. Plati-deck can be improved by a better metal/porcelain bond. Similarly, but to a lesser extent, it might be possible to improve Ceplatec (Renaissance) and Flexobond. The Dicor strength was restricted by the presence of gross porosities present at the inner side of the crown.

The corrosion behavior of palladium-silver-ceramic alloys.

Five commercial Pd-Ag alloys were investigated. Their electrochemical behavior was tested with standard potentiodynamic techniques in 0.9% saline solution and an artificial saliva and compared with high-Pd systems. Corrosion characteristics of the Pd-Ag alloys were quite similar regardless of microstructural and compositional differences. In the area of oral interest, all alloys showed a sufficient corrosion resistance. The alloys were, unlike their high-Pd counterparts, adversely affected by a high Cl- content under more extreme conditions, and a visible film formed.

A mechanical investigation of the functioning of mouthguards

Mouthguards may play an important role in the prevention of injuries to the teeth and the related tissues of people participating in various branches of sport. Several publications provide statistical data concerning the effect of mouthguards in protecting the head and neck region, including the teeth of e.g. American football players (Ref. 1, 2, 3).Also, much information is available on the mechanical properties of potential mouthguard materials (Ref. 4, 5, 6). However, basic investigations to the mechanics of teeth protection by mouthguards have only scarcely been done (Ref. 7). It was the aim of this study to investigate the functioning of mouthguards, the attenuation of impact forces, non-destructively in terms of both local attenuation in the contact area and distribution of impact forces over adjacent teeth.