Shimizu et al.

Int Chin J Dent 2004; 4: 67-71.

Mold filling of titanium castings using a 45° marginal edge
angle
Hiroshi Shimizu, DDS, PhD,a Kouichi Watanabe, PhD,b Toru Okabe, PhDc, andYutaka Takahashi, DDS, PhDa
aDivision of Removable Prosthodontics, Department of Oral Rehabilitation, Fukuoka Dental
bCollege, Fukuoka, Japan, Division of Dental Biomaterials Science, Department of Oral HealthScience, Course for Oral Science, Niigata University Graduate School of Medical and DentalcSciences, Niigata, Japan, and Department of Biomaterials Science, Baylor College of Dentistry,Texas A&M University System Health Science Center, Dallas, TX, USA
Purpose: The objective of the present study was to investigate the mold filling of pure titanium andtitanium alloys using a wedge-shaped mold with a marginal edge angle of 45°.
Materials and Methods: The metals tested were commercially pure Ti, Ti-6Al-7Nb, and Ti-6Al-4V; they
were cast using an Ar-arc centrifugal casting machine. The castings were cut into four pieces parallel to thetriangular surface. An optical microscope was used to evaluate mold filling as the distance between the tipof the cast wedge and the theoretical tip of the triangle. The data gathered for the 45° marginal edge angle
in this study and for the 30° angle in a previous study were compared.
Results: The mold filling of the 45° angle was superior to that of the 30° angle for all three cast titanium
metals.
Conclusion: Proper mold filling of titanium metals can be achieved with the 45° marginal edge angle
compared with the 30° angle. (Int Chin J Dent 2004; 4: 67-71.)
Clinical Significance: Wide marginal edge angles are strongly recommended when titanium is used tofabricate dental appliances.
Key Words: casting, margin, mold filling, titanium.

Introduction
Pure titanium and titanium alloys could be excellent candidates for the production of dental appliances
because of characteristics that are similar to those of dental gold alloys, i.e., outstanding biocompatibility,1high corrosion resistance,2,3 good mechanical properties,4 and good machinability.5,6 However, several
problems associated with titanium casting prevent it from being widely used. One of the requirements of adental alloy is a superior capacity to fill a mold completely.7-12 The results in our previous study11 showedthat the mold filling of the marginal edges of the titanium alloy castings having a 30° wedge angle waswithin the acceptable level for dental appliances, but these values were significantly inferior to those forconventional gold alloy.
It is hypothesized that increasing the edge angle should improve the mold filling. Therefore, in thisstudy, we used a wider wedge angle (45°) to attempt to obtain more acceptable mold filling for titanium
and titanium alloys. The purpose of the present study was to investigate the mold filling of pure titanium
and titanium alloy castings made with a marginal edge angle of 45º.

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Materials and Methods
The three metals tested in this study were commercially pure (CP) titanium (ASTM Grade 2, Titanium
Industries, Grand Prairie, TX, USA) and two commercial titanium alloys (Ti-6Al-7Nb, 5.5-6.5% Al,
6.5-7.5 Nb, T Alloy Tough, GC Corp., Tokyo, Japan; Ti-6Al-4V, 6.10% Al, 3.97% V, Titanium Industries,Grand Prairie, TX, USA).
A wedge-shaped pattern with an edge angle of 45° was prepared using an acrylic plate. The shape anddimensions of the pattern are given in Fig. 1. Every edge of the pattern was examined with an optical
microscope (Zeiss H-PI, Oberkochen, Germany) to select good patterns with high-quality edges. Threepatterns were attached to the sprue former using a wax sprue. A sprue rod (about 3 mm diameter and 8 mmlong) was connected to the flat bottom end of the smaller cross section of the wedge pattern. The open endof the sprue was attached directly onto the sprue former. The three patterns were placed horizontally at
equal intervals. The patterns were vacuum-invested in a mold ring with a magnesia-based investment
material (Selevest CB, Selec Inc., Osaka, Japan). The distance from the top of the pattern to the top rim of
the casting ring was approximately 30 mm.

The invested mold was allowed to bench-set at room

temperature for 120 minutes. After the investment had set, the molds were burned out in a furnace(Accu-Therm III 6000, Jelenko, Armonk, NY, USA) in accordance with the manufacturer’s instructions.

4 mm45˚10 mm

dFig. 1. Shape and dimensions of the pattern used.

Fig. 2. Definition of mold-filling index (µm).

The three titanium metals were then cast using an arc-melting centrifugal casting machine (Ticast SuperR, Selec Inc.). The mold temperature at casting was approximately 200°C. After the sprue rod was cut,each cast wedge specimen was embedded in self-curing resin (Orthodontic Resin, Caulk/Dentsply, Milford,DE, USA) such that the triangular surface appeared on one of the flat surfaces. The embedded specimenwas sliced using a diamond wheel (Alpha Resources Inc., Stevensville, MI, USA) into four pieces to makethree sectioned surfaces perpendicular to the triangular surface. Each sectioned surface was polished under
running water using up to 800 grit silicon carbide paper. Each edge on the polished cross section wasphotographed using a microscope (Zeiss H-PI) at 68X magnification.

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Int Chin J Dent 2004; 4: 67-71.

The amount of mold filling was evaluated by determining the missing length (µm) of the partially filled
tip of the triangle (mold-filling index) using these photographs (Fig. 2). Fifteen measurements for eachtitanium metal (three sliced surfaces of each of five castings) and the data for the 30° angle obtained in ourprevious study11 were statistically analyzed using two-way analysis of variance (ANOVA). The variables
were edge angle and metal.

Duncan’s new multiple range test was applied when appropriate at asignificance level of α=0.05.

Results
Two-way ANOVA and Duncan’s new multiple range test revealed that there were significant differences(p<0.05) in the mold-filling indexes between the two edge angles. The mold-filling index of each metal forthe 45° angle was significantly (p<0.05) lower than for the 30° angle. However, there were no significant
differences in the indexes due to the metals and their interaction (p>0.05).

The mean and standard

deviations with statistical categories for each metal for the two wedge angles are summarized in Table 1.
Table 1. Mold filling indexes for each metal.
Material

Edge angle (˚)

Mold filling Index (µm)

SDDuncan grouping

CP Ti
CP Ti

453034.7
135.511.0
27.0

aTi-6Al-7Nb
Ti-6Al-7Nb

45
30

32.7
138.2

23.3
46.4

aTi-6Al-4V
Ti-6Al-4V

4530

32.9
143.9

26.4
41.8

abbb

The data presented here for the 30° wedge angle were obtained from the reference 11. Identical letters indicate that thevalues are not statistically different (p>0.05).

Discussion
The main purpose of the present study was to evaluate the effect of marginal edge angle on mold fillingof titanium metals. This investigation using wedge-shaped patterns with two different marginal angles of45° and 30° provided a mold-filling index range for the titanium metals examined.
Since Brockhurst et al.7 reported on a castability standard for dental alloys in restorative dentistry, mostresearchers have used the 30° angle for their molds, including a simulated cylindrical single crown mold,regardless of the dental metal used; titanium casting studies are no exception. However, no information isavailable about mold filling with angles wider than 30°. The 45° marginal angle used in the present study
is the widest angle used in any study of this type.
When a 30° wedge angle was used, the mold filling of the marginal edges of the titanium alloy castings
was significantly inferior to that of the conventional gold alloy.11 However, titanium is still an attractive
metal for dental use because it offers many advantages, as described above. The shortcomings of any
casting material should be improved if at all possible. The goal of the present study was for titanium to fill69

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Int Chin J Dent 2004; 4: 67-71.

a mold as well as conventional gold alloy does.
The results of this study revealed that the three titanium metals tested filled the 45° marginal angle better
than the 30° angle. The mold-filling values of the three metals in the 45° marginal angle were at asatisfactory level for dental casting. It should be noted that contrast evaluation revealed that they were evenbetter than that of the gold alloy in the 30° marginal edge angle (71.2±18.5 µm).11
A 45° marginal angle is clinically acceptable when abutment teeth are prepared using a torpedo-shaped
diamond point or tungsten bur because the appropriate marginal finish for a full veneer crown preparation
is what is termed a "135° chamfer".13 When the 135° chamfer is prepared using the bur parallel to the longaxis of the abutment tooth, the marginal edge angle of the wax pattern should be 45° or more. The reason
for this configuration is that the profile of the crown of a human tooth is generally convex, since the heightof convexity is located closer to the cervix, approximately one-third or one-half of the distance from thecervical line to the marginal ridge. Then, the angle of the prepared surfaces vs. the unprepared surfaces isnearly 28°.14
The mold-filling indexes of the three titanium metals used in this study showed no statistical differences
at both wedge angles (p>0.05). The reason for this finding may be the similar solidification behavior of thethree metals. The estimate from the published equilibrium phase diagrams for Ti-Al-Nb and Ti-Al-V
alloys15 at the present alloy chemical compositions suggests that the temperature differences of the liquidus
and solidus lines in these two alloys are minimal, indeed almost identical in melting behavior.11 Even at a15° wedge angle, the mold-filling indexes of the three metals were statistically same (p>0.05),11 so it is not
surprising that no statistical differences were found in marginal filling at a wider angle.
The clinical significance drawn from the present study is that the marginal finish for a full veneer crown
preparation should be a 135° chamfer or more, and the marginal finish of the wax pattern should be 45° or
more for titanium casting. The standard deviations of mold-filling values of the three metals in the 45°
marginal angle were all smaller than those in the 30° angle. This fact indicates that this technique is highly
reliable and that there will be less irregularity of the marginal line.

Conclusion
Proper mold filling of titanium metals can be achieved with the 45° marginal edge angle compared withthe 30° angle.
Acknowledgment
This study was partially funded through NIH/NIDCR grant R01 DE11787. The authors gratefully acknowledge theeditorial assistance of Mrs. Jeanne Santa Cruz.

References
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11. Shimizu H, Habu T, Takada Y, Watanabe K, Okuno O, Okabe T. Mold filling of titanium alloys in two different
wedge-shaped molds. Biomater 2002; 23: 2275-81.
12. Sato H, Komatsu M, Miller B, Shimizu H, Fujii H, Okabe T. Mold filling and microhardness of 1% Fe titanium alloys.
Dent Mater J 2004; 23: 211-7.
13. Grundy JR. A colour atlas of conservative dentistry. Rome: Wolfe Medical Publications Ltd; 1980. p. 68-75.
14. Kokubo S. Studies on marginal castability of cast crown. J Med Dent Sci 1992; 59: 33-47.
15. Murray JL, Ed. Phase diagram of binary titanium alloys. Metals Park, OH: ASM International; 1987.

Reprint request to:
Dr. Hiroshi Shimizu
Division of Removable Prosthodontics, Department of Oral Rehabilitation, Fukuoka Dental College
2-15-1, Tamura, Sawaraku, Fukuoka 814-0193, Japan
FAX: +81-92-801-0513 E-mail: simizuh1@college.fdcnet.ac.jp
Received August 17, 2004. Revised August 19, 2004. Accepted August 19, 2004.
Copyright ©2004 by the Editorial Council of the International Chinese Journal of Dentistry.

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