Dimensional changes of one-piece frameworks cast from titanium, base metal, or noble metal alloys and supported on telescopic crowns.
BACKGROUND
The dimensional accuracy of 1-piece frameworks cast from commercially pure titanium and used to accommodate supporting telescopic crowns has not been demonstrated.


OBJECTIVE
To compare dimensional changes incurred in frameworks cast from commercially pure titanium, a cobalt-chromium alloy, and a noble metal (gold) alloy.


METHODS
This study was based on 2 different models, both prepared to receive telescopic crowns: 1 with 4 dies, designed to measure dimensional changes of the castings in the horizontal plane; and another with 2 dies, designed to measure dimensional changes in the vertical plane. As variables for the 2-die models, the palatal shape (16- and 20-mm radius) as well as the palatal depth (20-mm radius with the smallest palatal depth of 8 mm, 16-mm radius with flat palate and palatal depth of 10 mm, 16-mm radius with greatest palatal depth of 16 mm) were studied. Ten specimens each were fabricated from a commercially pure titanium, a cobalt-chromium alloy, and a gold alloy. All castings were fabricated under standardized conditions. All measurements were taken with a computer-controlled measuring microscope at the margins of the simulated telescopic crowns; these served to calculate the ideal midpoint from which the distances between the telescopic crowns were measured. The positional relation of the telescopic crowns was determined in horizontal and vertical directions. The measurements of the cast models were compared with measurements of the original model. The distances between the dies and the angles of the chosen telescopic crowns were calculated in fractions of millimeters and the angles were measured in degrees. The Kruskal-Wallis test and the Mann-Whitney U test were used for statistical analysis. The level of significance was alpha=5%.


RESULTS
With the following exceptions, none of the 3 alloy types showed significantly different results. With the 4-die model, all 3 alloys showed significant variations from the original model for chosen lengths (P=.001). For those lengths, the dimensional accuracy of the noble metal alloy was approximately 99.9% of the length of the original; for the 2 other alloys, an average value of 99.4% was determined. With the 2-die models the calculated angle was significantly different from the original model for all alloys (P=.001 or.000), independent from the palatal vault and depth. Significant differences from the original model were also found for the distance between the 2 telescopic crowns with all alloys for the 2-die model with a 16-mm depth palatal vault and a 16-mm radius (P=.001,.006, or.009).


CONCLUSIONS
Within the limitations of this study, the significant different dimensional changes both for the 4-die models and the 2-die models did not depend on the type of alloy. The 2-die models demonstrated significant dimensional changes resulting from the palatal geometry of the corresponding test models; the 4-die models demonstrated a tendency to contract toward the geometric center.
Gebelein
Matthias
M
Department of Prosthetic Dentistry, School of Dentistry, Medical Faculty Carl Gustav Carus, Technical University of Dresden, Germany.
Richter
Gert
G
Range
Ursula
U
Reitemeier
Bernd
B
D002858:Chromium Alloys; D003442:Crowns; D003722:Dental Alloys; D003735:Dental Casting Technique; D003799:Dental Stress Analysis; D003779:Denture Design; D003829:Denture, Partial; D006047:Gold Alloys; D006801:Humans; D008422:Materials Testing; D008437:Maxilla; D015203:Reproducibility of Results; D018709:Statistics, Nonparametric; D014025:Titanium
D002858:Chromium Alloys; D003722:Dental Alloys; D006047:Gold Alloys; D014025:Titanium