Fabricating complete dentures with CAD/CAM technology

Fabricating complete dentures with
CAD/CAM technology
Luis Infante, DDS,a Burak Yilmaz, DDS, PhD,b
Edwin McGlumphy, DDS, MS,c and Israel Finger, DDS, MSd
School of Dentistry, Louisiana State University Health Sciences Center,
New Orleans, La; Division of Restorative and Prosthetic Dentistry, The
Ohio State University, College of Dentistry, Columbus, Ohio
Conventional complete denture prosthetics require several appointments to register the maxillomandibular relationship and
evaluate the esthetics. The fabrication of milled complete dental prostheses with digital scanning technology may decrease the
number of appointments. The step-by-step method necessary to obtain impressions, maxillomandibular relation records, and
anterior tooth position with an anatomic measuring device is described. The technique allows the generation of a virtual
denture, which is milled to exact speciﬁcations without the use of conventional stone casts, ﬂasking, or processing techniques.
(J Prosthet Dent 2014;-:---)
Present-day advances have led to
the incorporation of computer-aided
design/computer-aided manufacturing
(CAD/CAM) technology into the
design and fabrication of dental restorations, including complete dentures. Different systems for making
impressions and fabricating casts of a
patient’s dental structures have been
introduced,1,2 some of which also
allow for the production of speciﬁc
restorations in the laboratory, in the
dental ofﬁce, or at a centralized production center.3-5
The information for the development of a CAD/CAM cast or restoration can be acquired extraorally from
an impression or from a cast of
the object or intraorally by directly
recording the structures intraorally.
Different systems use different tools to
collect this information. Mechanical
digitizing systems rely on touch probes
(tactile),6,7 whereas optical digitizing
systems use cone beam computed tomography,8,9 laser,5 or light-emitting
diode scanners.5,6 These data are processed by software and then used
to fabricate the desired object or
a
restoration with the CAM portion of
the system.
In 2007, Quaas et al6 studied the
measurement uncertainty and the 3dimensional accuracy of a mechanical
digitizing system and concluded that
the measurement uncertainty for the
system was low and the precision was
high. However, they discouraged the
application of this method for the
digitization of ﬂexible impression materials because the physical contact of
the probe with the soft material might
lead to deformation and increased inaccuracy. In 2012, Goodacre et al2
proposed a technique to obtain maxillary and mandibular deﬁnitive impressions of the edentulous arches so these
could be scanned and data acquired to
mill denture bases with CAD/CAM
technology. They also described the
process for recording the neutral zone,
the maxillary and mandibular anterior
teeth position, the palatal morphology,
the occlusal vertical dimension, and the
interocclusal relation so these could be
included as part of the process of
fabricating the bases. Furthermore, they
used a prototype of 3-dimensional
software that allowed the milling of
the tooth sockets in the denture base
according to the desired arrangement.
The use of computer-generated
dentures is changing the procedures
for denture fabrication. CAD/CAM
technology differs from the conventional method in that the laboratory
work is simpliﬁed and fewer appointments are needed.10 Recently, Bidra11
reported the use of CAD/CAM technology for the fabrication of mandibular implant-retained overdentures in
only 2 clinical appointments. This
report describes a technique to fabricate a complete dental prosthesis with
CAD/CAM technology. The technique
presented uses a standard clinical procedure to fabricate dentures for a patient with existing dentures in only 2
appointments. The measurements were
recorded at the ﬁrst appointment and
inserted at the second appointment.
TECHNIQUE
1. Make a deﬁnitive impression
with the impression materials and thermoplastic moldable trays which are
Assistant Professor, Louisiana State University Health Sciences Center.
Assistant Professor, Division of Restorative and Prosthetic Dentistry, The Ohio State University.
c
Professor, Division of Restorative and Prosthetic Dentistry, The Ohio State University.
d
Adjunct Clinical Professor, Division of Restorative and Prosthetic Dentistry The Ohio State University.
b
Infante et al
2
Volume
available in different sizes (AvaDent).
Initially, mix the 2 part heavy-consistency
polyvinyl siloxane (PVS) and press it
into the existing denture to create a
PVS cast.
2. Measure the residual ridge and
select the appropriate thermoplastic
tray. Place the tray in a hot water bath
(77 C) and mold to the cast.
3. Evaluate the tray intraorally to
ensure it covers all the appropriate
anatomic areas and adjust the borders
as needed. As with any conventional
edentulous impression technique, dry
the tissue with gauze. First, border the
mold with heavy-body material and
make the deﬁnitive impression with a
regular-set light-body PVS material
(Figs. 1, 2).
4. Choose the correct size anatomic
measuring device (AMD) (1 of 3 available sizes) (AvaDent) by using the
caliper to measure the widest part of
the residual ridge (Fig. 3). If the residual
ridge is between sizes, use the smaller
AMD size. With the existing dentures in
the mouth, assess the occlusal vertical
dimension (OVD) and rest position
with a preferred assessment method.12
Establish whether these dimensions are
correct or whether they need to be
altered. Once established, place dots
on the patient’s facial features and record the OVD with a caliper.
5. Coat the AMD maxillary tray
with the speciﬁed adhesive (Express fast
set polyvinyl siloxane PVS maxillomandibular registration record; Xertec) material onto the tray and place
intraorally to stabilize the AMD on the
residual ridge before making the records. Coat the AMD mandibular tray
with adhesive, express the PVS maxillomandibular relationship record material onto the tray, and place the tray
in the mouth. Extend the mandibular
-
Issue
AMD as far posteriorly as possible and
place it horizontally (Fig. 4).
6. Place both AMDs into the
mouth and attach the AvaDent ruler
(Fig. 5). Align the ruler parallel to the
interpupillary line and record the angle
that will be used to correlate the
completed AMD to the virtual
mounting with software algorithms.
With the central bearing tracing device
resting on the mandibular tray, adjust
the OVD by turning the ﬁtting on the
side of the AMD to raise and lower the
central bearing pin (Fig. 6). Then
conﬁrm the OVD. To conﬁrm the
centric relation with a gothic arch
tracing, coat the tip of the bearing pin
with a marking agent, coat the
mandibular tray with occlusal spray, or
rub it with occlusal paper. Guide the
patient’s mandible back and trace
lateral, anterior, and posterior excursions on the mandibular tray with the
1 Maxillary deﬁnitive impression.
2 Mandibular deﬁnitive impression.
3 Maxillary and mandibular anatomic measuring devices
(AMDs).
4 Maxillomandibular relationship record material being
expressed into AMD maxillary tray.
The Journal of Prosthetic Dentistry
-
Infante et al
-
2014
3
5 Registration of interpupillary line.
6 OVD adjustment by turning screw on side of AMD.
7 Stabilization of AMD by injecting maxillomandibular
relationship record material into area between maxillary and
mandibular trays.
8 Use of composite resin to stabilize transparent guide.
bearing pin. Direct the patient to “keep
jaws together,” “slide lower jaw as far
forward as possible,” “as far back as
possible,” and “as far left and right as
possible.” Create the gothic arch
tracing accordingly.
7. Remove the mandibular tray and
drill a divot into the tray at the tip of
the arrow. Replace the tray intraorally,
place the tip of the pin into the divot,
and stabilize the AMD by liberally
injecting maxillomandibular relationship record material into the area between the maxillary and mandibular
AMD trays (Fig. 7). Remove any record
material from the maxillary AMD that
might interfere with the drape of the lip.
Adjust the lip support to the desired lip
fullness by turning the ﬁtting on the
anterior of the lip support.
8. As a guide for selecting the
appropriate denture tooth mold, overlay
Infante et al
the esthetic transparent guide onto the
existing denture. Use 1 of 3 overlay
esthetic transparent guides, which represent different tooth sizes. Once the
proper transparent guide is chosen,
establish the desired gingival height and
mark it on the prescription. Mark the
midline and incisal edge for the anterior
teeth on the lip support. Place composite
resin (Tetric EvoFlow; Ivoclar Vivadent)
onto the transparent guide and adhere
this to the lip support. With the AMD in
the mouth, verify the esthetics and OVD
(Fig. 8).
9. Send both the completed impressions and the ﬁnal AMD to the
laboratory for fabrication of the
dentures.
10. Examine the digital preview virtual setup sent by the laboratory, and
modify the design of the denture if
needed (Fig. 9).
11. Once processed, the dentures are
returned to the dentist for delivery to
the patient (Fig. 10).
DISCUSSION
Many materials have been used in
the fabrication of denture bases. From
wood to porcelain, no material has
received the same attention or gained
the same popularity as PMMA [poly(methyl methacrylate)].13-15 Although
it is the most common material
used today, PMMA is not without
problems. These problems are related to
processing, porosity, fracture strength,
dimensional stability, color stability,
and biocompatibility (allergenic reactions).16,17 Challenges with the use of
PMMA bases are being met by either
improving the qualities and properties
4
Volume
9 Virtual arrangement.
10 Maxillary and mandibular complete dental prosthesis.
of the material or the use of alternative
materials.18-22 The AvaDent dentures
are produced by machining a preformed cylinder of acrylic resin material. This cylinder is produced under
high pressure and heat, which prevents
shrinkage of the deﬁnitive milled prosthesis. As a result of the highly condensed resin, there is a decrease in free
monomer, a decrease in the porosity
when compared to a conventionally
processed denture, and a decrease in
the retention of Candida albicans by the
denture base.10 Manufactured acrylic
resin teeth, which are not CAD/CAM
produced, are used.
The fabrication in the laboratory
starts with relating the scanned maxillary and mandibular impressions to the
scanned AMD. The 2 ﬁles are digitally
overlaid and merged by best-ﬁt triangulation. Millions of digital triangles
overlap each other to form a vertical
representation of jaw position and
vertical height. A virtual record base is
created, and functional controls are
then applied. The algorithms for the
occlusal arrangement are written using
traditional rules.12 The occlusal plane
is set from the incisal edges of the
mandibular teeth to halfway up the
retromolar pad, and the curves of
Spee and Wilson are incorporated into
the software to create the optimum
occlusal arrangement on the basis of
the operator’s preference. Lingualized
or monoplane occlusal schemes may be
chosen.23 The designed software arranges the teeth according to the speciﬁc guidelines of the desired occlusion,
with the transparency being the guide
for the maxillary anterior teeth. A digital
preview is sent to the dentist, who can
examine the virtual setup and modify
the design of the denture.
Once the design of the teeth is
accepted by the clinician, the intaglio
surfaces of the denture and tooth
The Journal of Prosthetic Dentistry
-
Issue
-
sockets are milled with a 5-axis milling
machine. The sockets for the selected
teeth are milled according to the position of the selected teeth. The selected
teeth are chemically bonded to the
AvaDent base material by means of a
proprietary PMMA bonding technique
that uses heat and pressure, or if
requested, a clinical evaluation of the
denture can be selected. The teeth are
set into the milled sockets in wax and
returned to the dentist for evaluation,
allowing for movement of the anterior
and posterior teeth, adjustment of
the occlusion, and adjustment of the
denture base. In the wax evaluation
method, the teeth are attached to the
base with conventional techniques.
Should the patient not have existing
dentures, irreversible hydrocolloid impressions are made and casts are
poured. The thermoplastic trays are
adapted to these casts. The vertical
dimension of rest is obtained by the use
of phonetics, speciﬁcally the bilabial
sounds. Once obtained, the OVD is
calculated. The same technique is then
followed as with a patient who has
existing dentures.
The stability of a denture, that is the
ability to “resist displacement by functional horizontal or rotational stresses,”
depends to a great degree on the occlusion and base adaptation.24 The
transfer of concentrated stresses from
the denture base to the underlying
supporting structures has been associated with trauma to the tissues and
accelerated bone resorption.25-27 In the
currently described technique, there
should be reduced dimensional stability problems because the denture is
milled from preformed acrylic resin.
This quality should compare favorably
to bases fabricated with conventional
processing techniques. This may contribute to the improved stability and
retention of the denture base with less
trauma and fewer postinsertion adjustment visits.
The digital system facilitates the
completion of dentures in 2 visits. Impressions, occlusal relation records, and
an orientation record are made at the
ﬁrst visit and the dentures inserted at the
Infante et al
-
2014
second. This signiﬁcantly reduces the
time the patient spends in the dental
ofﬁce. Unlike in the fabrication of conventional dentures, there is no facebow
record. If the maxillomandibular record
is made at the correct OVD, the lack of
facebow should not cause any error. A
repository of the digital record is stored,
and an exact duplicate denture can be
reproduced at any time. The denture can
be designed according to the dentist’s
speciﬁcations. Bases can be fabricated
with various anatomic features, including stippling, rugae, thickness of
the actual base, and borders of the
dentures. A wax evaluation can also be
requested. Various shades of acrylic
resins are available for the fabrication of
the bases, and manufactured acrylic
resin teeth are used. The denture teeth
are placed virtually and the bases with
tooth sockets milled. The exact positions
of the teeth are recorded. These tooth
positions are compared to a scan made
of the denture and tooth positions after
the dentures have been fabricated. A
virtual remount is possible, and where
discrepancies are noted, the equilibration of the teeth is completed in the
milling center and clinical remount
procedures are avoided. A denture kit is
provided with all the materials required
to make the initial records and impressions. The actual scanning of records is
made off-site, eliminating the need for
the dentist to purchase expensive machines. Commercial laboratories can
now scan impressions and design the
dentures; however, all denture base
milling is done at the central laboratory.
Complete dentures, immediate dentures, and implant dentures can be
fabricated with this system.
Although initial results are promising, the technique has some disadvantages. The central bearing tracing
device can be a challenging method of
recording jaw relationships. Although
the recording of the gothic arch tracing
in some patients may be difﬁcult,
Infante et al
5
alternative techniques are being introduced. Further, the system does not
provide for all schemes of occlusion,
and no long-term results have been
published. Long-term clinical trials
should be performed to evaluate the
success of the technique presented.
SUMMARY
A technique for the fabrication of a
CAD/CAM denture is described. By using
an AMD, the dentist can make clinical
records in 1-step appointments. The
AMD allows the clinician to gather all the
clinical information needed with a single
intraoral device. The virtual denture is
milled to exact speciﬁcations without the
use of conventional stone models or
ﬂasking and processing techniques.
REFERENCES
1. Davidowitz G, Kotick PG. The use of CAD/
CAM in dentistry. Dent Clin North Am
2011;55:559-70.
2. Goodacre CJ, Garbacea A, Naylor WP,
Daher T, Marchack CB, Lowry J. CAD/CAM
fabricated complete dentures: concepts and
clinical methods of obtaining required
morphological data. J Prosthet Dent
2012;107:34-46.
3. E4D CAD/CAM systems. Put dental team in
control. Compend Contin Educ Dent
2012;33:542.
4. Christensen GJ, Child PL Jr. Fixed prosthodontics: time to change the status quo? Dent
Today 2011;30:66, 68, 70-73.
5. Beuer F, Schweiger J, Edelhoff D. Digital
dentistry: an overview of recent developments
for CAD/CAM generated restorations. Br
Dent J 2008;204:505-11.
6. Quaas S, Rudolph H, Luthardt RG. Direct
mechanical data acquisition of dental
impressions for the manufacturing of CAD/
CAM restorations. J Dent 2007;35:903-8.
7. Persson AS, Andersson M, Oden A, Sandborgh-Englund G. Computer aided analysis
of digitized dental stone replicas by dental
CAD/CAM technology. Dent Mater 2008;
24:1123-30.
8. Kanazawa M, Inokoshi M, Minakuchi S,
Ohbayashi N. Trial of a CAD/CAM system
for fabricating complete dentures. Dent
Mater J 2011;30:93-6.
9. Inokoshi M, Kanazawa M, Minakuchi S.
Evaluation of a complete denture trial
method applying rapid prototyping. Dent
Mater J 2012;31:40-6.
10. Bidra AS, Taylor TD, Agar JR. Computeraided technology for fabricating complete
dentures: systematic review of historical
background, current status, and future
perspectives. J Prosthet Dent 2013;109:
361-6.
11. Bidra AS. The 2-visit CAD-CAM implantretained overdenture: a clinical report. J Oral
Implantol. In press.
12. Boucher CO. Swenson’s complete dentures.
St Louis: Mosby; p. 125-6.
13. Moriyama N, Hasegawa M. The history of
the characteristic Japanese wooden denture.
Bull Hist Dent 1987;35:9-16.
14. Ladha K, Verma M. 19th century denture
base materials revisited. J Hist Dent
2011;59:1-11.
15. Yap CC. Developments in prosthetic dentistry
in the nineteenth century. Bull Hist Dent
1987;35:43-51.
16. Rickman LJ, Padipatvuthikul P,
Satterthwaite JD. Contemporary denture
base resins: part 1. Dent Update 2012;
39:25-8, 30.
17. Rickman LJ, Padipatvuthikul P,
Satterthwaite JD. Contemporary denture
base resins: part 2. Dent Update 2012;39:
176-8, 180-2, 184.
18. Matthews E, Smith DC. Nylon as a denture
base material. Br Dent J 1955;98:231-7.
19. Hargreaves AS. Nylon as a denture-base
material. Dent Pract Dent Rec 1971;22:
122-8.
20. Stafford GD, Huggett R, MacGregor AR,
Graham J. The use of nylon as a denture-base
material. J Dent 1986;14:18-22.
21. Jameson WS. Fabrication and use of a metal
reinforcing frame in a fracture-prone
mandibular complete denture. J Prosthet
Dent 2000;83:476-9.
22. Fredrickson EJ. A one-piece, all vinyl denture.
Quintessence Dent Technol 1979;3:9-12.
23. Lang BR. Complete denture occlusion. Dent
Clin N Am 2004:641-65.
24. The glossary of prosthodontic terms.
J Prosthet Dent 2005;94:10-92.
25. Carlsson GE. Responses of jawbone to pressure. Gerodontology 2004;21:65-70.
26. Jozefowicz W. The inﬂuence of wearing dentures on residual ridges: a comparative study.
J Prosthet Dent 1970;24:137-44.
27. Atwood DA. Some clinical factors related to
rate of resorption of residual ridges.
J Prosthet Dent 2001;86:119-25.
Corresponding author:
Dr Burak Yilmaz
The Ohio State University, College of Dentistry
Division of Restorative and Prosthetic Dentistry
Columbus, Ohio 43210
E-mail: [email protected]
Copyright ª 2014 by the Editorial Council for
The Journal of Prosthetic Dentistry.

Download Report