The International Journal of Prosthodontics, 01/1995

Elements that caused cytotoxicity of high-noble, noble, and silver-based dental casting alloys were identified by correlating the release of elements with the cytotoxicities of the alloys. Release of elements was determined by atomic absorption spectroscopy, and the cytotoxic effect was determined by cellular mitochondrial function. The high-noble alloy released low levels of elements that did not increase after 6 hours, whereas the other alloys released higher levels of elements that increased over time. The cytotoxic effects of the alloys were attributed primarily to the release of silver and copper. In some observations, interactions between silver and copper were suspected of having an effect on the cytoxicity.

A quantitative measure of implant stability would be beneficial to decision-making regarding the status of the bone anchorage around an implant. The Periotest device has been reported to provide such a measure, but the in vivo data are incomplete and inconclusive in support of this claim. The purpose of this study was to determine in an in vivo model the relationship between Periotest values (PTV), three different implant biomaterials, and torque to failure. A total of 79 screw-shape implants made of commercially pure titanium, titanium alloy, and HA-coated alloy were evaluated in the posterior maxillary and mandibular quadrants of six female baboons following healing for 3 to 4 months. At uncovering, the implants were tested with the periotest device and torqued to failure using an electronic torque driver. Analysis of the PTV-biomaterial relationship revealed no significant difference among the implants based on the biomaterial (P=.7453). Analysis of PTV-torque revealed a significant relationship (P=.0117), however, the association between PTV and torque was not strong and does not explain 92% of the variation between the parameters (Pearson correlation .2823,, R2=.08).

Patients provided with 24 ball attachment-retained removable partial dentures were followed up to 23.5 years. The prosthetic treatment included fixed partial dentures in 8 arches, and combinations of crowns and splint bars in 16 arches. All ball attachment matrices were supplied with vertical occlusal stops in contact with the patrices. A nonresilient hinged coupling was established between fixed partial dentures and removable partial dentures. Seventeen arches had only two or three remaining teeth. A total of 66 abutments for fixed partial dentures were included, 30 of which were root canal treated and supplied with posts. No technical failures (loss of retention/cement failure, root or tooth fracture, metal framework fracture) with the fixed partial dentures were recorded. With the removable partial dentures, additional retention with clasps was introduced in 2 of the dentures (in addition to 8 originally), 2 had too be remade after fractures, and 4 dentures were relined.

The marginal and internal adaptation of metal ceramic crowns fabricated by electrical discharge machining and conventional metal ceramic alloys were compared. The crowns were cemented using zinc phosphate cement, embedded in epoxy resin, and sectioned in two planes: diagonal and buccolingual. The crowns were then measured at nine sites. The results showed that there were no statistical differences between the external marginal opening of the titanium and the gold-platinum-palladium crowns. The overall marginal discrepancies for the restorations in this study were 61 um (± 34 um) for the titanium metal ceramic crowns and 47 um (± 17) for the gold-platimum-palladium metal ceramic crowns.

Thirty patients with severely resorbed maxillae were treated in a one-stage procedure using bone graft and implant placement. A horseshoe-shaped bone graft was taken from the iliac wing and fixed to the residual maxillary ridge using titanium implants, which supported the prostheses placed after a 6-month healing period. The material constituted two groups: a development group, the first 10 patients; and a routine group, the following 20 patients. At the 3-year follow-up, the implant survial was 87.5% and the prosthesis stability was 100% in the routine group. The probing depth did not change during the follow-up period, while the grafted region decreased in volume during the first postoperative year. The patients reported improved chewing ability and improved life quality. Very few technical and prosthodontic complications occurred.

This study investigated the effect of airborne particle abrasion on the exposed dentin surfaces of 40 extracted teeth. A Siroflow abrasion unit was used to treat four groups of ten specimens that were subjected to 5, 10, 20, and 40 seconds of abrasion respectively. Statistical analysis (Spearman Rank Order) showed a significant difference between all groups (P{.05) but not within groups (P}.05). Scanning electron micrographs showed smear layer removal as an immediate effect of air polishing. Application times of longer than 5 seconds showed obstruction of dentinal tubule openings, possibly a result of abrasive powder residue. It was concluded that airborne particle abrasion removes the smear layer, and the amount of dentin removed corresponded to the time of application.

The color stability of both light-and dual-polymerized samples of three shades of three commercial resin cements was measured using a reflection spectrophotometer after accelerated aging over a period of 179 hours. Porcelite cement was the most color stable, followed by Optec and then 3M. The Optec and Porcelite cements changed color after accelerated aging, but with one exception the changes were not perceptible. Five of six 3M cements had perceptible color changes after accelerated aging, becoming darker and more yellow. The two lighter shades of Optec and 3M changed color more than the darker shade. differences between light-and dual-polymerized samples were significant but none was perceptible.

A method for enhnced retention and function of implant-retained ear epistheses is described. A cast bar containing two encapsulated magnets and a loop is retained on two retroaricular implants. The loop receives a clasp in the prosthesis and prevents its unintentional loss.

This in vitro study determined the fracture toughness of four classes of resin using wet and dry test environments, following 48 hours of wet storage. Two of the resins were light initiated, while the other two were chemically initiated. No significant difference in fracture toughness was detected for the wet and dry test environments using miniature compact tension specimens. The light initiated, urethane dimethacrylate resin demonstrated a significantly higher fracture toughness than the poly(methyl methacrlate) resin.

The bond strength of denture teeth to acrylic resin denture bases was determined by producing tensile test specimens from standardised and anonymously presented partial dentures. Ten dentures were produced by randomly selected commercial dental laboratories and five were produced in a university dental laboratory. The tooth debonding forces exhibited a wide range of variation both within and between dentures. The university produced dentures showed, on average a slightly improved tooth bond strength. This study highlights the need for further investigation of this problem and for the development of a standardised technique to provide satisfactory denture tooth bonding.

Three dimensional finite element analysis and Weibull analysis were used to evaluate the effect of the thickness and the rigidity of the retainers on the risk of failure of an anterior resin-bonded prosthesis. Ratainer thickness ranged from 0.4 to 1.4 mm. The physical properties of metals similar to Ni-Cr and type IV gold alloys were used. A concentrated loan (100 N) was applied to the incisal edge of the finite element analysis modeled pontic, and the data of other loads (150 to 500 N in 50-N increments) were calculated from the data of 100 N. Subsequent Weibull analysis revealed that failure probability diminished when there was an increase in metal thickness at loads of 300 to 350 N, particularly for the retainer made of a type IV gold alloy. The reduction in failure probability caused by increasing the thickness of the metal was greater when type IV gold alloy was used than when Ni-Cr alloy was used. This investigation suggests that the longevity of resin-bonded retainers can be prolonged by thickening the retainers, rather than using more rigid metals.

The masking power of various generic, dry mineral earth, and flocking colorants dispersed in medical-grade silicone was investigated. Reflectance measurements were made by diffuse reflectance spectrophotometry using black and white backings. these data were reduced to optical scattering and absorption coefficients through the use of the Kubelka-Munk reflectance theory. The color difference between a 0.13-cm-thick layer of the colored elastomer placed on an ideal black backing and this layer on an ideal white backing was calculated and established as a translucency parameter. Using analysis of variance and stepwise comparison testing, significant differences were found among the translucency parameters of the colorants. Since these colorants differ substantially in their ability to mask underlying colors and since the translucency of maxillofcial material is an important aspect of color measurement and natural appearance, differences in these colorants go beyond their obvious differences in color.