Christer Bessing

Clinical results with titanium crowns fabricated with machine duplication and spark erosion

A new method for fabrication of metal crowns has been developed by one of the authors (M.A.). There are two principles involved: machine duplication of models and electric discharge machining. The metal used is pure unalloyed titanium, which is processed as a coping and later covered by a composite resin. In 1986, 205 separate titanium crowns were made on 149 patients. One year later 192 crowns on 137 patients could be examined. Five crowns had been replaced by new ones owing to fracture of the composite resin. In accordance with the CDA quality evaluation system the following results were obtained for the remaining 187 crowns: margin integrity, 186 excellent or satisfactory (99.5%); anatomic form, 185 excellent or satisfactory (98.9%); and surface and color, 181 excellent or satisfactory results (96.8%). The 1-year results are promising, and further follow-up studies will be made.

A 2-year follow-up study of titanium crowns

In 1986, 149 patients were provided with titanium crowns. The method used for fabrication of the titanium copings involved two principles: machine duplication of models and electric discharge machining. For the veneering of the copings, Isosit was used for the first 90% of the crowns in the series, and the Dentacolor-Silicoater technique for the last 10%. Of 205 individual crowns cemented in 1986, 167 could be examined after 2 years. The crowns were rated by four independent examiners using the CDA quality evaluation system. Bleeding Index and Margin Index were also used. The Margin Integrity score was recorded as satisfactory for all crowns examined over the period studied. A vast majority of the margins were rated as excellent. Isosit (n = 145) disclosed shortcomings including fractures and substantial deteriorations of Surface and Color and of Anatomic Form. With Dentacolor as veneering material (n = 18) the results with the factors Surface and Color and Anatomic Form were still rated satisfactory after 2 years, and no fractures of the veneering material were registered. Bleeding Index and Margin Index showed comparatively small changes after 2 years.

A clinical examination of ceramic (Cerec®) inlays

Two hundred and five Cerec ceramic inlays placed by 8 dentists in 72 patients were examined independently by 3 calibrated evaluators 12-24 months after insertion, using the criteria of the California Dental Association (CDA) and also certain periodontal variables. Proximal dental plaque and bleeding on probing were not seen more often on Cerec surfaces than on control homologous surfaces. Ten patients reported postoperative sensitivity after treatment with Cerec inlays. Excellent CDA ratings for Color and Surface were obtained in 57% and 26%, respectively, and for Anatomic Form and Margin Integrity in 55% and 83%, respectively. Obvious differences were seen among the participating dentists with regard to the clinical quality of Cerec inlays. At present, the long-term performance of the Cerec technique cannot be predicted.

An in vivo study of glass ceramic (Dicor®) inlays Preliminary report

For the purpose of evaluating the clinical quality of glass ceramic (Dicor) inlays 15 patients with 37 inlays were examined 1 to 22 months after placement. In addition to certain periodontal variables, the inlays were rated by two independent examiners using the California Dental Association (CDA) quality evaluation system. The results of the present study showed that dental plaque was seen less often on proximal surfaces with inlays than on homologous proximal surfaces. Three patients reported hypersensitivity of the dental pulp. The examination using the CDA criteria showed that 54% of the inlays had a slight color mismatch, and slightly roughened surfaces were occasionally seen (35.5%). In nearly 30% of the inlays there was visible evidence of ditching along the margins. At present, no judgement can be made about the longevity of ceramic inlays.

Evaluation of the castability of four different alternative alloys by measuring the marginal sharpness

The castability of two low-gold and two silver-palladium alloys was evaluated, using a Type III gold alloy as reference. Six castings from each alloy were subjected to a castability test, in which the marginal sharpness of simulated crowns--that is, the edge diameter--was used to assess the castability. The mean crown edge diameters of the silver-palladium alloys were three to four times the corresponding diameters of the gold-based alloys. The differences between these two groups were statistically significant. It is concluded that the castability of the low-gold alloys studied was comparable to that of the Type III alloy, whereas the silver-palladium alloys studied had a castability that may result in technical and clinical problems.

Evaluation of tissue response to dental alloys by subcutaneous implantation

The tissue response of two low-gold alloys (Midas and Rajah), two silver-palladium alloys (Albacast and Alba V), and one type III gold alloy (JSC) was studied after subcutaneous implantation of cylindrical implants in 24 guinea pigs. Casting of each alloy were inserted into polyethylene tubes and implanted by means of a standardized technique. Each animal received five implants representing the five alloys. The implants were left in place for 30 and 90 days. Microscopic evaluation of the implant sites showed that after 30 days the tissue reactions were slight to moderate, with only small differences between the alloys. After 90 days the reactions were slight to extreme. One of the silver-palladium alloys (Alba V) demonstrated several severe and extreme reactions after 90 days. The other silver-palladium alloy (Albacast) demonstrated the least tissue response of the five alloys in the 90-day group.

Metallographic characterization of four alternative alloys intended for fixed prostheses

Four dental casting alloys intended as alternatives for type III gold alloys were studied with regard to their metallographic appearance. The structures of two low-gold and two silver-palladium alloys were evaluated in the as-cast and hardened conditions and in the condition achieved after annealing for 1 h at 100 degrees C below the solidus temperature. The microstructure was studied by light optical microscopy, scanning electron microscopy, electron microprobe analysis, and X-ray diffraction analysis. In addition, the hardness and the grain size of the alloys were determined. The presence of concentration gradients and dissimilar phases is discussed. It was concluded that to obtain the optimum properties of these alloys, strict and detailed instructions about the various heat treatments are needed.

A clinical comparison of alternative alloys

For the purpose of evaluating the clinical performance of 2 alternative dental casting alloys, 17 crowns made from the low-gold alloy Midas and 14 crowns made from the silver-palladium alloy Albacast were inserted at random into 23 patients. In each patient a high-gold type-3 alloy, JS C, served as a reference alloy. The patients were examined after 1 year with regard to tarnishing and certain factors such as plaque index, gingival index, and margin index. In addition, the California Dental Associations quality evaluation of dental care was used by two independent calibrated examiners. The results of the present study showed that the crowns made of the silver-palladium alloy were tarnished and had rough occlusal surfaces more often than crowns made of the low-gold and high-gold alloys.

Five-Year Evaluation of Lifecore Restore® Implants: A Retrospective Comparison with Nobel Biocare MK II® Implants

PURPOSE The purpose of this study was to compare survival rates and marginal bone resorption of the Lifecore (LC) Restore Implant System with the benchmark Nobel Biocare (NB) MK II Implant System. MATERIALS AND METHODS All implants were inserted by the same surgeon and all radiological analyses were performed by the same radiologist. Two hundred ninety LC implants were analyzed radiologically after 1 year and compared with the same number of NB implants serving as a historical reference group. After 5 years, 200 LC implants could be compared with 224 NB implants. Each implant was monitored for exposed threads, as compared with the baseline registrations. RESULTS No significant differences were found between the two implant systems regarding survival rates (LC 100% and NB 99.2%). Considering the findings of this study, the two implant systems compared might be regarded as clones. Nevertheless, because of dissimilar onset of threads, about 1 mm more implant-retaining bone anchorage is gained with the Lifecore Restore Implants as compared with NB MK II Implants. CONCLUSIONS Based on the assumption that >3 exposed NB threads correspond to >4 exposed LC threads, significantly more bone loss (p < .01) could be demonstrated for the NB implants after 5 years. Thus, it may be justified to consider the differences in implant design to have a decisive clinical relevance.

In vivo tarnish of alternative alloys

The in vivo tarnishing of two low-gold alloys, two silver-palladium alloys, and one type-3 alloy in two different structural states was investigated after 4, 8, and 16 weeks. The alloy specimens were placed in 10 mandibular complete dentures by using carriers that enabled removal of the specimens from the dentures to facilitate the evaluation. By means of four different tarnish indices the present study showed that the annealing of the low-gold alloys and the two silver-palladium alloys resulted in a reduction of tarnish, but this was not the case with the high-gold alloy. Least tarnishing was seen in annealed specimens from the silver-palladium alloys and the as-cast specimens of the high-gold alloy.