DIGITAL DENTISTRY FOR COMPLETE DENTURES A REVIEW OF DIGITAL DENTISTRY VERSUS CONVENTIONAL APPROACHES TO COMPLETE DENTURES

Abstract

There is a wide array of treatments for complete edentulism, and each option has its advantages and drawbacks. In a nutshell, treatment of the edentulous patient can be divided into fixed and removable prostheses. Recently, computer aided design/ computer aided manufacturing (CAD/ CAM) technology has been used to design and fabricate complete dentures. This article briefly reviews digital removable complete dentures and demonstrates a simple, time saving technique in a treatment report.

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IN DENTISTRY • September 2020 DecisionsInDentistry.com
There is a wide array of treatments for complete edentulism, and each
option has its advantages and drawbacks. In a nutshell, treatment of the eden-
tulous patient can be divided into fixed and removable prostheses. A fixed pros-
thesis, either cement- or screw-retained, involves four or more implants, while
removable treatment consists of conventional complete dentures and overden-
tures supported by teeth, solitary implant attachments, or implant-supported
bars. This article will focus on removable prostheses.
For close to a century, polymethyl methacrylate has been used in the fab-
rication of dentures. Polymerization is catalyzed by heat or chemical reaction
and, over the years, numerous techniques have been developed. Recently, com-
puter aided design/ computer aided manufacturing (CAD/ CAM) technology
has been used to design and fabricate complete dentures. This article briefly
covers advances in digital dentures.
Digital design and manufacturing was introduced to dentistry by
Andersson, who developed the Procera system in 1983, and Mörmann,
C
omplete edentulism is a debilitating condition that negatively affects a person’s well-
being. Associated with a diminished quality of life and health challenges — including
comorbidities, such as malnutrition and obesity — it affects professional opportunities,
as well as social and personal relationships.1,2 Although the incidence of complete edentulism
has decreased in recent decades, the growth and aging of the population is expected to
increase the number of edentulous patients from 33.6 million in 2016 to 37.9 million in 2020.2
Digital dentistry and dental implants have revolutionized treatment for completely and partially
edentulous patients, but not everyone is a candidate or can afford implants. As a high number
of individuals affected by this condition are from a lower socioeconomic background, with
limited access to care, cost effective and efficient treatment in the realm of complete edentulism
is becoming increasingly necessary.3
who introduced the CEREC system in 1985.4Earlier CAD/ CAM innovations
were mostly geared toward indirect, tooth-borne restorations. The first
report of CAD/ CAM use for dentures is attributed to Maeda et al,5who, in
1994, employed additive manufacturing technology.
As seen in Figure 1, the three components of using CAD/ CAM technology
for digital dentures are:
1. Data acquisition
2. Prosthesis design
3. Manufacturing
DATA ACQUISITION
With the conventional complete denture process, master casts are obtained
by border molding a custom tray and using an elastomeric impression mate-
rial. Similarly, in the CAD/ CAM process, the initial step requires the acquisi-
tion of data. Two options are available: direct intraoral scanning, or making
DIGITAL
DENTISTRY
FOR COMPLETE
DENTURES
A REVIEW OF DIGITAL DENTISTRY VERSUS
CONVENTIONAL APPROACHES TO
COMPLETE DENTURES
By Amit Punj, BDS, DMD, MCR, FACP,
and Francois Fisselier, DDS

a conventional impression that can be scanned with a desktop scanner or
poured in gypsum to obtain the master casts that, in turn, are scanned.
Advantages: In general, taking a digital impression has many advantages,
including the possibility of performing an immediate chairside analysis (e.g.,
to evaluate the anatomy, residual ridges, presence of undercuts, or necessity of
preprosthetic surgery). This approach saves on impression material, and can
be quicker than a conventional impression (two minutes for the maxilla, and
five minutes for the mandible when possible). In addition, it is convenient in
cases involving patients with a gag reflex or limited opening. It is a true muco-
static impression; in addition, there is no need for disinfection, it has a faster
turnaround time, and the data can be archived for future use without occupy-
ing physical space.6
Disadvantages: This technology has some challenges, such as the initial
high cost, learning curve, and possible subscription fees for the equipment
and software. Clinically, using an intraoral scanner for edentulous patients
can be tricky. The posterior palatal seal in the maxilla and complicated floor
of the mouth anatomy — with interference from the tongue and saliva in
the mandible — can be difficult to capture. In cases with a limited amount
of keratinized tissue, the mucosa is more movable and needs to be recorded
in one pass since returning later over a missed area results in a different
position of the soft tissue, leading to an error in the digital impression.6
Hence, it is advisable to make a conventional impression and scan the
impression or master cast. Table 1 summarizes the advantages and disadvan-
tages of scanning technology.
PROSTHESIS DESIGN
Denture-designing software offers a powerful tool that lets clinicians select
molds from a library of teeth to generate the tooth arrangement automatically
— although it is still possible to customize the tooth setup. It is the authors’
opinion that use of CAD technology for complete dentures can be a great
teaching tool for students, as it can show them the proper positioning of the
denture teeth in terms of esthetics, relationship to the residual ridge, location
of the occlusal plane, and occlusal relationship.
MANUFACTURING TECHNOLOGIES
Since the introduction of polymethyl methacrylate by Wright in 1936, many
issues of conventional complete denture materials have been associated with
polymerization shrinkage, leading to issues of fit, strength, and also release of
monomer.7,8 With CAD/ CAM technology, two types of fabrication methods can
be used to overcome these shortcomings.
Subtractive manufacturing (milling): In the subtractive approach, a puck
(block) of material is milled by automated control of specialized cutting tools
that receive information from a computer algorithm known as computer
numerical control technology.
As the block of acrylic resin comes prepolymerized, there are no shrinkage
issues. Also, as the puck is prepolymerized under high temperature and pres-
sure, there may be less monomer release, which, in turn, reduces irritation to
the soft tissues. The precision of milling is directly related to the milling unit’s
number of axes and size of the burs. The reported precision is between 5 and
25 microns.9,10
Additive manufacturing (three-dimensional printing): In this method,
material is stacked layer by layer, one over the other, to create a three-dimen-
sional structure. Furthermore, additive manufacturing offers the ability to
produce structures with complex geometries. It also reduces material waste
by 40% and allows finer detail compared to subtractive technology9
Compared to conventional fabrication methods, delivering complete den-
tures with CAD/ CAM technology requires fewer appointments (two to three
visits), saving chairtime. This can be beneficial for older adults (Table 2).11,12 The
two-visit procedure generally skips the try-in appointment — although the
authors highly recommend this step. One advantage of a try-in prosthesis is
that the patient can take it home for a few weeks to evaluate function and
esthetics, which is not possible with traditional wax try-in setups.
The following case report demonstrates the use of this CAD/ CAM technology
wherein the surgical guide was used for the mandibular implant placement, and
also served as a custom tray, record base, and artificial tooth arrangement guide.
CASE REPORT
A 75-year-old male presented with a chief concern that his mandibular
teeth were sensitive and breaking down (Figure 2). His medical history
was unremarkable, although he complained of mild xerostomia. The
DecisionsInDentistry.com September 2020 •
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IN DEN TIS TRY 13
FIGURE 1. Computer aided design/computer aided manufacturing workflow.
Manufacturing
DesigningData Acquisition
Direct intraoral scan
Indirect extraoral scan
of cast or impression
and occlusal record
Printed denture
Proprietary denture
design software
Milled denture
AMIT PUNJ, BDS, DMD, MCR, FACP, is a diplomate of
the American Board of Prosthodontics, a clinician and an educator.
He maintains a private practice and is an assistant professor at
Oregon Health & Science University, School of Dentistry in Portland.
He can be reached at punj@ohsu.edu.
FRANCOIS FISSELIER, DDS, is an assistant professor at
Tufts University School of Dental Medicine in Boston, where he
teaches prosthodontics and implant dentistry.
The authors have no commercial conflicts of interest to disclose.
TABLE 1. Pros and Cons of Digital Impressions
Advantages Disadvantages
Chairside analysis High initial cost
Cost saving of impression materials Steep learning curve
True mucostatic impression Possible scanning fees
Easy for patients with a gag reflex Often not possible for the mandible
Easy for patients with limited opening Often not possible with lack of keratinized tissue
No need for disinfection Must be done in one pass
Ability to print or mill master casts Difficult to scan movable soft tissue
Digital archivability Capturing the posterior palatal seal area is difficult

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IN DENTISTRY • September 2020 DecisionsInDentistry.com
of the mandibular arch. Maxillomandibular relation records were obtained
and an artificial tooth arrangement was set up for a mandibular immediate
complete denture. Once the immediate denture was processed and finished,
it was duplicated in clear acrylic resin to serve as a surgical/ radiographic
guide. All the mandibular teeth were extracted uneventfully under local anes-
thesia and the mandibular immediate denture delivered. After two months,
the surgical/ radiographic guide was placed on the mandibular arch, and a
cone beam computed tomography (CBCT) scan was taken to plan the
implant positions. Two implants were placed in sites #22 and 27 and buried
for three months.
DEFINITIVE PROSTHESIS
With the immediate complete dentures, the patient’s existing occlusal ver-
tical dimension (OVD) was evaluated using phonetics, facial profile and
esthetics. It was recorded for future reference by measuring the distance
between two marked reference points: one on the tip of the patient’s nose,
and the other on the most anterior point of the chin. The healing abutments
were removed and the gingival cuff height was measured to select the
appropriate attachment system abutments, which were installed per the
manufacturer’s recommendations (Figure 3).
Next, abutment level impression copings were placed and the surgical
guide seated and modified to provide at least 5 mm of clearance around
the impression copings (Figure 4). The access openings in the surgical
guide were covered with a light-polymerizing material (Figure 5).
The surgical guide was used as a custom tray and relieved appropriately
on the intaglio surface and borders to ensure passive seating with 1 mm of
space for the impression material. The OVD was reevaluated with the surgical
guide based on the previously recorded measurements (Figure 6).
A VPS interocclusal material was used to record the maxillo-mandibular
relationship. Tray adhesive was applied on the intaglio surface of the surgical
guide, and the definitive impression was made using heavy body VPS around
the impression copings and medium body VPS for all other areas. Once the
tray was placed in the oral cavity, border molding movements were per-
formed and the patient was asked to close down into the interocclusal record
that was previously obtained. The OVD and centric relation were reverified
and held steady until the impression material set (Figure 7).
The definitive abutment level impression that was made with the surgical
guide, along with the interocclusal record and opposing cast, were sent to
the laboratory, where the items were scanned. Instructions were given regard-
ing the shade and midline. The mold characteristics could be identified from
the intact denture teeth on the surgical guide. The occlusal scheme was spec-
ified for bilateral balanced occlusion. Denture designing software was used
to design the teeth and denture base according to the work authorization,
and a digitally designed preview file was sent to the clinician for approval.
patient had a maxillary complete denture that was recently made and
that he was satisfied with. On the mandibular arch, the patient had a his-
tory of failing restorations, primary and secondary caries, and an ill-fitting
mandibular removable partial denture. After a thorough discussion of his
treatment options, the patient decided to receive a two-implant-retained
overdenture.
Extraoral, intraoral, oral cancer screening and occlusal examinations were
performed. Diagnostic casts were obtained, mounted and evaluated. An algi-
nate impression was made of the maxillary prosthesis to serve as the oppos-
ing cast, and a vinyl polysiloxane (VPS) impression in a stock tray was made
FIGURE 5. Access openings covered with a light-
polymerizing material.
FIGURE 6. Reevaluate the
occlusal vertical dimension.
FIGURE 2. Preoperative radiographs of mandibular arch.
FIGURE 3. Measure the gingival cuff
height in order to select the abutment.
FIGURE 4. Create clearance around the
impression coping.
key takeaways
• The growth and aging of the population is expected to increase
the number of edentulous patients from 33.6 million in 2016 to
37.9 million in 2020.2
• As such, cost effective and efficient treatment in the realm of
complete edentulism is becoming increasingly necessary.3
• Compared to conventional fabrication methods, delivering
complete dentures with computer aided design/computer aided
manufacturing technology requires fewer appointments (two
to three visits), saving chairtime.
• Digital denture technology has simplified the designing and
manufacturing process for complete dentures, and produces
better-adapted prostheses with superior material properties.
TABLE 2. Comparison of Conventional and Digital
Approaches to Complete Dentures
Conventional Approach
Visit 1 Preliminary impressions
Visit 2 Definitive impressions
Visit 3 Maxillomandibular relation records
Visit 4 Artificial tooth arrangement try in
Visit 5 Delivery
Digital Approach
Visit 1 Definitive impressions and
maxillomandibular record; select
arrangement of artificial teeth
Visit 2 Artificial tooth arrangement try in
(optional visit)
Visit 3 Delivery

Once approved, the milling process was initiated and
completed (Figure 8).
The mandibular overdenture (which was made using
a monolithic dual-shaded block with the teeth and den-
ture base together) was milled in one piece and returned
finished. The prosthesis was tried in, adjustments were
made for fit and comfort, and the occlusion was verified.
As the master cast incorporated abutment analogues, the
attachment housing could be picked up in the laboratory
or returned to the clinician to perform an intraoral pickup
procedure. Alternatively, the impression can be made without abutment level
impression copings directly over the abutments provided there is sufficient
clearance made for the impression material. In this situation, the primary
author decided to perform an intraoral pickup of the housings and, as the
recesses were already created by the CAM process, minimal modifications
were done to the denture. Once the patient and clinician were satisfied with
the prosthesis, the next step of connecting the denture to the implant abut-
ments was performed, as per the manufacturer’s instructions (Figure 9). Next,
home care instructions and follow-up appointments were made (Figure 10).
This clinical treatment highlights the versatile use of the surgical guide as
a custom tray, record base, and denture tooth mold selection guide. This
helps eliminate additional patient visits, reduces costs associated with addi-
tional laboratory procedures, and produces a high-quality prosthesis.
DISCUSSION
The use of CAD/ CAM in digital dentistry remains an exciting topic with tremen-
dous growth potential. However, challenges can be encountered, as well. With
the subtractive method, denture teeth often need to be placed into the dedi-
cated sockets, which can lead to deviations from planned arrangement, and
the strength of the bond still needs to be assessed.13 These complications could
be overcome by milling one-piece monolithic dentures, as shown in the above
case report. Using additive or subtractive manufacturing, dentures can be fab-
ricated with a combination of methods. These include fabricating a milled den-
ture base or a printed denture base, with prefabricated denture teeth bonded
into the sockets. However, denture teeth can also be milled or printed sepa-
rately and bonded to a milled or printed denture base (Figure 11).
Milling technology has been used for a longer period and therefore is
supported by more research, especially regarding material properties.
Although additive manufacturing is fast catching up, clinicians need to be
cautious when making choices regarding materials for printed dentures. In
the near future, multi-material printing will become available that will allow
clinicians to print monolithic dentures with different material properties within
the same denture.14 This denture technology has many additional advantages,
such as the ability to superimpose images from preoperative facial scans,
digital photographs, smile design programs, or CBCT images. With advanced
software features, these overlays can be toggled on or off, depending on what
the dentist or technician would like to accomplish.
CONCLUSION
Digital denture technology has simplified the designing and manufacturing
process for complete dentures, and produces better-adapted prostheses with
superior material properties. However, as of today, this technology does not
compensate for poor diagnosis or the inability to make adequate conventional
impressions and establish proper jaw relation records.
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FIGURE 10.
Definitive mandibular implant-
retained overdenture prosthesis.
FIGURE 11.
Printed denture teeth fitted
into the printed denture base sockets.
FIGURE 7. Surgical guide utilized as a custom tray, record
base, and artificial tooth arrangement try-in template.
FIGURE 8. Finished monolithic, milled, mandibular
complete denture.
FIGURE 9. Attachment housings being picked up with
autopolymerizing resin.