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EGYPTIAN
DENTAL JOURNAL
Vol. 62, 525:532, January, 2016
* Lecturer, Department of Removable Prosthodontics, Faculty of Dentistry, Mansoura University.
INTRODUCTION
The swing lock is a unique dental prosthesis
that gives good retention and stability as well
as an excellent splinting especially with critical
tooth forms,1-4 critical soft tissue shapes,5 teeth
with questionable prospects.6-8 It can be used in
combination with an implant for partially edentulous
patients9 or for maxillofacial prosthesis.10-12 Also, it
is used for a radiation carrier.13
FIT ACCURACIES OF THE SWING LOCK REMOVABLE PARTIAL
DENTURE FRAMEWORKS CONSTRUCTED WITH TWO DIFFERENT
DOUBLE CASTING TECHNIQUES
Aisha Z. H. Mustafa *
ABSTRACT
Purpose: This article compares the t accuracies of the swing lock metallic frameworks
constructed with two different double casting techniques.
Material and methods: An experimental mandibular acrylic model with the only remaining
6 anterior teeth was constructed. 4 partial metallic frameworks of S/L RPD were constructed using
two methods of the double casting technique. For standardization 4 lingual parts of S/LRPD was
constructed to be used with the 2 groups. The 2 groups differed in the method of construction of the
labial part either with or without reduplication of the master cast. A standard measure scope was
used to measure in micrometer the t of the labial part of each of the S/L RPD metallic framework
to the model. The SPSS program was used for data analysis. Shapiro-Wilk test was used to test the
normality of the data. Paired samples t-test was used to compare the t of the two groups. P was
signicant if < 0.05 at condence interval 95%.
Result: No signicant difference was present between the two different methods for double
casting technique of S/L RPD where P = 0.062.
Conclusion: The two methods for double casting technique results in an accurate casting, but
the one without reduplicating the cast saves time.
Clinical implication: The double casting technique without reduplicating the cast saves the
time.
KEYWORDS: Double casting, Swing lock, RPD.
(526) Aisha. Z. H. MustafaE.D.J. Vol. 62, No. 1
The swing-lock (S/L) removable partial denture
(RPD) incorporates a hinged and locked labial bar
that joins with the lingual part to form a stable and
rigid framework for replacing missing teeth and
gingival tissues.14 The labial bar, with I-bars, likes
vertical bar projections projecting up to the gingival
third of the enclosed teeth, swings from the hinge
and snaps into the latch. When the prosthesis is in the
latched position, all the enclosed teeth are splinted
together and share in retention and stabilization of
the prosthesis.15 The retentive mechanisms of S/L
RPD are rigid so that, they do not lose their retentive
properties with use. Also, it is completely passive
during insertion and removal of the prosthesis.16
One of the reasons that the S/L RPD is rarely
used by clinicians is the sensitivity of the technique,
especially during the hinge and lock, fabrication.17
The laboratory technique, for fabricating the hinge
and latch has two choices. The rst one is the single
casting technique which requires only one refractory
cast, one mold investment, and one casting to create
mutually labial and lingual sections of S/L RPD
metal framework. This technique uses the original
mechanisms, hinge and latch, which are retained
in the wax pattern by means of retentive outlines
of the metal. The second one is the double casting
technique that requires 2 refractory cast, 2 mold
investments, and 2 casting; one to each of labial and
lingual sections of S/L RPD.14 The double-casting
method is more difcult but more precise and
reliable than the conventional single casting method
because it results in minimal errors. In addition to
this, it allows creation of smaller and more accurate
joints than one can achieve with commercial
components.18
Intraoral scanning technology was used
to produce a stereolithographic le that was
successively introduced into a computer-aided
design software program for the digital design of
a partial removable dental prosthesis framework.
After that, computer-aided manufacturing was used
for fabrication of a cast partial removable dental
prosthesis.19
Rapid prototyping (RP) transform the 3D com-
puter data into the custom-made compact models.
RP manufacture technologies include stereolithog-
raphy (SLA), computer numerical controlled (CNC)
milling, fused deposition modeling (FDM), and,
more recently, selective laser sintering (SLS). In
dentistry the RP techniques are used for wax pat-
tern fabrication for dental (facial) prostheses, and
framework fabrication of removable dental prosthe-
ses.20 In the past, a removable partial denture (RPD)
framework plastic pattern was produced using an
RP machine, and then used as a conventional pat-
tern.21, 22,23 However with the introduction of the
selective laser melting (SLM) technique, the metal
frameworks of RPD can be directly constructed,
thus eliminating the casting stage. The new RP tech-
niques in the near future could change traditional
prosthodontic applies.20 Clinical research studies
are necessary to decide the efciency of the CAD/
CAM RPDs treatment modality.24
RPD designs and construction using the CAD/
CAM provide improvement of t, function, and
esthetics.25 But the conventional method for the
RPD construction still used currently.
The accurate t of RPD framework is important
to provide maximum function, aesthetic and stay
biocompatible.26 A careful examination of the gaps or
spaces between the frameworks and casts determine
the accuracy of the tting of the prosthesis before
it is supplied to the patient.27 The accuracy of the
framework constructed by using light-polymerizing
plastic pattern was clinically satisfactory. This
technique decreases the laboratory cost and time
for removable partial denture construction.28
The retentive unit constructed by the light-cured
pattern had a better t than that constructed by the
conventional method.29
The effect of conventional wax or light-
polymerized patterns on the surface roughness
and internal porosity of cobalt–chromium castings
of PRD was revealed no differences between the
two pattern materials.30 Framework t can differ
FIT ACCURACIES OF THE SWING LOCK REMOVABLE PARTIAL DENTURE (527)
according to the construction technique. The t of
the frameworks fabricated of light-cured material
was better than that fabricated with the traditional
technique.31
Several types of research studied the gaps
or spaces between the framework and casts to
determine the amount of the t.32-39 The thickness of
the elastomeric impression material that allowed to
set in gaps was measured.32 The framework and cast
have been accurately maintained by the resin, then
they were sectioned to expose gaps between the
framework and cast.33 Custom made feeler gauges
was used to identify the gap under retentive ends of
the clasps.34 The three main electronic methods for
measuring small gaps are X-rays, Ultrasonic, and
capacitive transducers.27 Also, the digital intraoral
camera was used for imaging the gaps among
the framework and the cast. Then graphic editing
program was used for measuring the gaps on the
images.31 A standard measurescope can be used for
measurement of denture displacement40 in addition
to measuring of the gaps between the denture and
the model.
This article compares the t accuracies of the
S/L RPD metallic frameworks constructed with
two different double casting techniques. The rst
technique is double casting with reduplication of the
master cast. The second technique is double casting
without reduplication of the master cast. The null
hypothesis of this study was that the t accuracies
of the S/L RPD metallic frameworks constructed
with two different double casting techniques were
equivalent.
MATERIAL AND METHODS
Acrylic demonstration model of a mandibular
arch with only 6 anterior teeth were used for
constructing eight metal frameworks of S/L RPD
with double casting techniques using two different
methods. Each group includes 4 frameworks (n=4).
The sample size of four was used as guided by the
research of de Franca, et al.38 For standardization
4 lingual parts of S/LRPD was constructed to be
used with the 2 groups. The lingual section was
casted with cobalt-chromium metal alloy (Biosil-F;
Degussa, Hanau, Germany) then it was repositioned
on the master cast (Fig. 1A) for the casting of the
labial section with one of the two different methods
of double casting technique.
In the rst method of the double casting,
reduplication of the master cast was done with the
lingual section of casting remains on the master
cast and in the duplicating agar (Fig. 1B). Then
the investment material was poured against it. The
refractory cast was hardened without removing the
lingual casting then the labial section was waxed
(Fig. 2) and “cast to” the lingual section. After
casting, an index of the labial surface was made.
In the second method of the double casting,
without reduplication of the master cast, the
separating medium was applied to the labial surface
of the master cast. A light-curing material was
applied as a core for the labial part. Then complete
the wax building of the labial bar component
directly to the lingual section on the master cast.
The waxing of labial part was guided by the index.
After spruing, the lingual casting with waxed labial
part was removed carefully from the master cast for
investing and casting (Fig. 3 A, B).
After casting with either the rst or the second
Fig. (1) A. The casted lingual part of casting is repositioned on
the master cast. B. The lingual part of casting remains
in duplicating agar.
(528) Aisha. Z. H. MustafaE.D.J. Vol. 62, No. 1
method, sprues and ashes on casting that may
cross over or between the labial and lingual aspect
around the hinge and lock attachments were
removed before any attempt to open the prosthesis.
Finish and elector polish were done before freeing
the attachment. An instrument was used for trying
to open the lock-latch combination. the S/L RPD
framework was seated on the master cast and acrylic
demonstration model (Fig. 4 A, B, C).
Measuring the t accuracies
A standard measure scope E0020 (Monocular
measurescope type-10 Nikon- Japan) was used
to measure the t in micrometer of the labial
part of each of the swing-lock removable partial
denture metallic framework to the model (g 5).
The horizontal distance (gaps) between each of
the vertical projections of the labial part and the
abutment tooth of the model was measured. Three
areas to measure the horizontal distance between
a vertical projection and the abutment tooth of the
model. These measurements averaged and treated
as independent variables. These distances represent
the amount of mist.
Fig. (3) A, The labial bar component wax pattern connected to
the casted lingual part on the master cast directly then
sprued. B, The wax pattern with the casted lingual part
removed carefully from the cast for investing.
Fig. (4) A, Metallic framework of S/L RPD in closed position on
master cast and B, on the Acrylic demonstration model
and C, in opened position on the Acrylic demonstration
model.
Fig. (5) The measurescope was used for measuring the gap
between the vertical projection of the labial part and the
teeth of the model.
Fig. (2) Wax pattern of the labial bar component connected to
the casted lingual part after spruing.
FIT ACCURACIES OF THE SWING LOCK REMOVABLE PARTIAL DENTURE (529)
After construction of the S/L RPD framework
using one of the methods that mentioned before, the
t accuracies of the labial part were measured. Then
the labial section was sectioned and removed to
allow construction of the S/L RPD framework using
the other method on the same lingual part. Then the
t accuracies of the labial part were measured.
Statistical analysis
The SPSS statistical package for social science
v.17 (SPSS Inc., Chicago, IL) was used for data
analysis. Shapiro-Wilk test was used to test the
normality of the data. The data was parametric and
normally distributed. Paired samples t-test was used
to compare the t between the two groups S/L RPD
with and without reduplication of the master cast. P
was signicant if < 0.05 at condence interval 95%.
RESUL
The mean and standard deviation of measured
gaps (in micrometer) for double casting technique
with and without reduplication of the master
cast were presented in (Table 1). No signicant
difference was present between the two different
methods for double casting technique of S/L RPD
where P = 0.062.
TABLE (1) The mean and standard deviation and
statistical comparison of the measured
gaps (in micrometer) for double casting
technique with and without reduplication
of the master cast.
Measured gaps
of double casting
technique with
reduplication
Measured gaps
of double casting
technique without
reduplication
mean 67.1 64.6
Standard
deviation 16.8 ± 16.7 ±
T value 1.999
P value 0.062
*Signicant different at P ≤ 0.05.
DISCUSSION
Improvements in imaging, data processing
and rapid prototyping technologies have allowed
the fabrication of RPD framework patterns and/
or RPDs entirely in a new methodology.19-25. The
conventional laboratory construction of the RPD is
still used until now.
This in vitro study simplies the conventional
laboratory process for construction of S/L RPD. The
construction of S/L RPD is more complex than that
of a conventional RPD.17 The material of choice for
S/L RPD framework should be cobalt- chromium
alloys to provide rigidity, strength, and wear
resistance that required for the hinge and locking
mechanisms.15
The hinge and latch may be cast separately
from prefabricated plastic patterns or purchased in
already cast form. They are secured to the wax-up
of the main framework being placed in the same
horizontal plane and parallel to each other. A careful
casting technique is required10 to avoid welding of
the molten metal alloy to the precast hinge and latch
mechanism and destroy the mechanism. In double
casting technique of S/L RPD, the lingual section is
cast rstly then it must be repositioned on the master
cast for the second casting of the labial section.14 In
this study, the second casting of the labial section
can be done either with or without reduplication of
master cast.
In the rst method of this study, the reduplication
of the master cast was done using agar reversible
hydrocolloid material. The lingual section remains in
the duplicating agar and the refractory material was
poured against it. On this refractory cast, the labial
component was waxed to the rst lingual section.
Then it was sprued and casted to the rst casting.
But in the second method, without reduplication
of the master cast, after application of separating
medium to the master cast the rst lingual section
remains on the master cast and a light curing resin
was used directly to form a rigid core of the labial
(530) Aisha. Z. H. MustafaE.D.J. Vol. 62, No. 1
section with hinge and latch component. Blue inlay
wax was used to complete the contouring. After
spruing of this part, the latch opened carefully and
the rst casting with waxed labial part was removed
from the master cast and was invested to casting the
labial part.
A precise hinge and latch results from the
double casting technique, since the thin oxide
layer that formed on the rst part of casting when
it is placed in the furnace to burn out the second
waxed up segment (labial bar), well create freedom
of movement in hinge and latch.1 This technique
gives the possibility to make smaller and more
precise joints than one can achieve with commercial
components.
The results of this study accept the null hypotheses,
where there was no signicant difference between
the two different methods used for double casting
of S/L RPD. The double casting method, without
reduplicating the master cast, gives accurate casting
as well as the double casting method, but it saves
the time. Neither method was able to accomplish an
optimal t. One cause for the absence of complete
t is the high linear solidication shrinkage of
cobalt-chromium based alloys.35 hence, it is difcult
to achieve complete t of the metal framework.31,36
The t of the cobalt – chromium PRDP may
be compromised by errors in wax blocking out
and duplication, variability in the expansion of the
refractory material, and the techniques used for
tting and polishing the metal frameworks.37 In the
casting, the agar duplicating material is suffering
dimensional variations of syneresis and imbibition,
which may unfavorably affect the accuracy of the
refractory cast.29 Therefore, it is practical to have an
accurate t with the second method because there
is no reduplication of the master cast, and the light
cured resin is adapted directly to the hinge and latch
component in accurate position on the master cast.
The vertical mist of a fabricated Co-Cr alloy
framework was inuenced by manufacturing
technique. After denitive t measurement, a better
passive t would be found for Co-Cr frameworks
processed by CAD/CAM technology in comparison
with conventional casting.38 there are no any study
that use the CAD/CAM technology in the swing-
lock RPD construction.
The result of this study found no difference
between the two methods. This result was not in
agreement with the studies29,31 that found a more
accurate t of the metal frameworks constructed with
light cured resin in comparison to the conventional
method. This may attribute to the difference in the
prosthesis design and technique. In the other hand,
Sushma39 found that: the inlay wax pattern give
better vertical marginal t in comparison to the light
cured modeling resin material and autopolymerized
resin material.
One limitation of this in vitro study was that the t
accuracy was evaluated just at the vertical projection
of the labial bar. Further investigation is required to
study the t accuracy of all the labial part including
the hinge and latch to detect the meticulous area of
the interference. In addition, an in vivo study of the
t accuracy must be made, to notice whether it is
clinically tolerable. Also, it is interesting to compare
the t accuracy of S/L RPD constructed by the use
of the CAD/CAM technology with that constructed
with the double casting method.
CONCLUSION
Within the limitation of this study, the double
casting method, without reduplicating the master
cast for the second casting, gives accurate casting
as well as the double casting method, with
reduplicating the master cast but it saves the time.
This double casting technique can be used with
many prosthetic devices other than a swing-lock
removable partial denture such as stress breaker
removable partial denture (hidden-lock), disjunct
denture, and metallic framework constructed on
xed crown or bridge before cementation of crown
or bridge.
FIT ACCURACIES OF THE SWING LOCK REMOVABLE PARTIAL DENTURE (531)
CONFLICT OF INTEREST
No conict of interest.
ACKNOWLEDGEMENT
Author thanks Prof. Ibrahim Elewa (Professor
of Industrial Production Engineering, Faculty of
Engineering, Mansoura University) for his guidance
in the measurement of the t accuracy.
REFERENCES
1. Brudvik JS. Advanced Removable Partial Dentures.
Chicago: Quintessence; 1999. p. 107-10.
2. Antos EW, Renner RP, Foerth D. The swing-lock partial
denture: An approach to conventional removable partial
denture service. J Prosthet Dent 1978;40:257-62.
3. Schulte JK, Smith DE. Clinical evaluation of swinglock
removable partial dentures. J Prosthet Dent 1980;44:595-
603.
4. Sadig W, Fahmi F. 5 modied swing-lock: A new approach.
J Prosthet Dent 1995;74:428-31
5. Barclay CW, Russell MD, Murphy P. A three- part bilateral
swing lock design denture revisited. Case report. Br Den J
2001;190:538-40.
6. Car AB, Brown DT. McCracken’s Removable partial
prosthodontics. 12th ed. St. Louis: Elsevier Mosby; 2011.
p. 38, 333-334, 341.
7. Roberts HW. Swing-lock partial dentures. Gen Dent
2001;49:366-72.
8. Lynch CD, Allen PF. The swing-lock denture: its use in
conventional removable partial denture prosthodontics.
Dent Update 2004;31:506-8.
9. McAndrew R. Prosthodontic rehabilitation with a swing-
lock removable partial denture and a single osseointe-
grated implant: A clinical report. J Prosthet Dent 2002;88:
128-31.
10. Bolender CI, Becker CM. Swing-lock partial denture
where and when. J Prosthet Dent 1981;45:4-10.
11. Talbot TR. Review of swing-lock partial denture. Int J
Prosthodont 1991; 4: 80-8.
12. Turkyilmaz I. Prosthodontic management or patient with
cleft lip/palate using maxillary overdenture and swing-
lock attachment mechanism. Clinical report. N Y State
Dent J 2008;74:62-4.
13. Ersu B, Hekimoglu C, Özyar E, Aslan Y. A hinged ange
radiation carrier for the scalp: A clinical report. J Prosthet
Dent 1998;79:369-71.
14. Rudd KD, Morrow RM, Eissmann HF. Dental laboratory
procedures. Removable partial dentures. Vol 3. St. Louis:
Mosby; 1981. p. 491-524.
15. Phoenix RD, Cagna DR, DeFreest CF. Stewart’s Clinical
removable partial prosthodontics. 3rd ed. Chicago: Quin-
tessence; 2003. p. 398-506.
16. Cameron DA, Lyons MF. Properties of a custom-made
hinge clasp compared with a conventional circumferential
clasp. J Prosthet Dent 1996;75:326-31.
17. Schwalm CA, La Spina FV. Fabricating swing-lock re-
movable partial denture frameworks. J Prosthet Dent
1981;45:216-20.
18. Minagi S, Tanaka T, Sato T, Matsunaga T. Double-casting
method for xed prosthodontics with functionally gener-
ated path. J Prosthet Dent 1998;79:120-24.
19. Kattadiyil MT, Mursic Z, AlRumaih H, Goodacre CJ. In-
traoral scanning of hard and soft tissues for partial re-
movable dental prosthesis fabrication. J Prosthet Dent
2014;112:444-8.
20. Beguma, Z. and P. Chhedat, Rapid prototyping--when vir-
tual meets reality. Int J Comput Dent 2014;17: p. 297-306.
21. Bibb RJ, Eggbeer D, Williams RJ, Woodward A. Trial t-
ting of a removable partial denture framework made using
computer-aided design and rapid prototyping techniques.
Proc Inst Mech Eng H 2006; 220: p. 793-7.
22. Eggbeer D, Bibb R, Williams R. The computer-aided design
and rapid prototyping fabrication of removable partial denture
frameworks. Proc Inst Mech Eng H. 2005;219:195-202.
23. Williams RJ, Bibb R, Rak T. A technique for fabricating
patterns for removable partial denture frameworks using
digitizedcasts and electronic surveying. J Prosthet Dent
2004;91(1):85-8.
24. Lang LA, Tulunoglu. A critically appraised topic review of
computer-aided design/computer-aided machining ofre-
movable partial denture frameworks. Dent Clin North Am
2014;58:247-55.
25. Bohnenkamp, D.M., Removable partial dentures: clinical
concepts. Dent Clin North Am 2014;58:69-89.
26. Dunham D, Brudivik J, Morris J, Plummer K, Cameron
S. A clinical investigation of the t of removable partial
(532) Aisha. Z. H. MustafaE.D.J. Vol. 62, No. 1
dental prosthesis clasp assemblies. J Prosthet Dent 2006;
95:323-6.
27. William RJ, Al-Hourani TR. An Electronic method for
measuring the t of removable partial denture frame-
worksz to dental casts. The journal of engineering research
2009;6:15-20.
28. Takaichi A, Wakabayashi N, Igarashi Y. Prefabricated light-
polymerizing plastic pattern for partial denture framework.
Contemp Clin Dent 2011;2:402–4.
29. Kumar MV, Murugesan K, Bhagath SN. The accuracy of
t of cast clasps designed with conventional wax pattern
and light cured patterns: a comparative in vitro study. SRM
Univ. J. Dent. Sci. 2010;1:10–3.
30. Swelem AA, Abdelnabi MH, Al-Dharrab AA, AbdelMa-
guid HF. Surface roughness and internal porosity of partial
removable dental prosthesis frameworks fabricated from
conventional wax and light-polymerized patterns: a com-
parative study. J Prosthet Dent 2014;111:335–41.
31. Anan MT, Al-Saadi MH. Fit accuracy of metal partial re-
movable dental prosthesis frameworks fabricated by tra-
ditional or light curing modeling material technique: An
in vitro study. The Saudi Dental Journal 2015;27:149-54.
32. Stern MA, Brudvik JS, Frank RP. Clinical evaluation of
removable partial denture rest seat adaptation. J Prosthet
Dent 1985;53:658–62.
33. Fritell DN, Muncheryan AM, Green AJ. Laboratory accu-
racy in casting removable partial denture frameworks. J
Prosthet Dent 1985;54:856–62.
34. Murray MD, Oyson JE. A study of clinical t of cast cobalt-
chromium clasps. J Prosthet Dent 1988;16:135–9.
35. Anusavice KJ, Shen C, Rawls HR. Philips’ Science of dental
materials. 12th ed. Elsevier Saunders Inc., 2012. p.199-386.
36. Gebelein M, Richter G, Range U, Reitemeier B. Dimen-
sional changes of one-piece frameworks cast from tita-
nium, base metal, or noble metal alloys and supported on
telescopic crowns. J Prosthet Dent 2003;89:193-200.
37. Brudvik JS, Reimers D. The tooth-removable partial den-
ture interface. J Prosthet Dent 1992;68:924-7.
38. de Franca DG, Morais MH, das Neves FD, Barbosa GA.
Inuence of CAD/CAM on the t accuracy of implant-
supported zirconia and cobalt-chromium xed dental pros-
theses. J Prosthet Dent 2015;113:22-8.
39. Sushma R, Farias A, Soni R. Vertical marginal discrepan-
cies of metal castings obtained using different pattern ma-
terials: A scanning electron microscope study. J Int Clin
Dent Res Organ 2014;6:98-102.
40. Javid NS, Michael CG, Mohammed HA, Colaizzi FA.
Three- dimensional analysis of maxillary denture displace-
ment during reline impression procedure. J Prosth Dent
1985; 54: 232- 237.
