Evaluation of complete denture trial method applying rapid

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					 Dental Materials Journal 2012; 31(1): 40–46

Evaluation of a complete denture trial method applying rapid prototyping
Masanao INOKOSHI, Manabu KANAZAWA and Shunsuke MINAKUCHI

Complete Denture Prosthodontics, Department of Oral Masticatory Function Rehabilitation, Division of Oral Health Sciences, Graduate School of
Medical and Dental Sciences, Tokyo Medical and Dental University, 1-5-45 Yushima, Bunkyo, Tokyo 113-8549, Japan
Corresponding author, Manabu KANAZAWA; E-mail:

A new trial method for complete dentures using rapid prototyping (RP) was compared with the conventional method. Wax dentures
were fabricated for 10 edentulous patients. Cone-beam CT was used to scan the wax dentures. Using 3D computer-aided design
software, seven 3D denture images with different artificial teeth arrangements were made and seven trial dentures per patient were
fabricated accordingly. Two prosthodontists performed a denture try-in for one patient using both conventional and RP methods. The
prosthodontists and patients rated satisfaction for both methods using a visual analogue scale. Satisfaction ratings with both
conventional and RP methods were compared using the Wilcoxon signed-rank test. Regarding prosthodontist’s ratings, esthetics and
stability were rated significantly higher with the conventional method than with the RP method, whereas chair time was rated
significantly longer with the RP method than with the conventional method. Although further improvements are needed, the trial
method applying RP seems promising.

Keywords: Complete denture, CAD/CAM, Rapid prototyping, Evaluation, Trial

                                                                         using CAD/CAM with a computerized numerical control
                                                                         (CNC) processor and ball-end mills. Sun et al.17)
In dentistry, computer-aided design (CAD)/computer-                      constructed virtual flasks according to the finished CAD
aided manufacturing (CAM) technologies have been                         digital models of removable complete dentures and
applied in the field of prosthodontics since the 1980s1).                created individual physical flasks using a 3D printer.
More specifically, the application of CAD/CAM                            The artificial teeth were inserted one by one, and the
technologies to restorative dentistry and fixed                          complete denture was finally finished with traditional
prosthodontics has increased considerably in recent                      laboratory procedures such as packing and polishing.
years. Computer-aided technologies allow more precise                    They indicated that a 3D printer would be useful for
and systematic modeling, and could therefore reduce the                  fabricating complete dentures. The arrangement of
burdensome steps of both chair-side and laboratory                       artificial teeth, flasking and resin packing can thus be
work, saving vital time2). Rapid prototyping (RP) is a                   improved successfully. Despite these reports, however,
CAD/CAM technology that was originally developed to                      applying these methods in a clinical setting has remained
fabricate prototypes for industrial purposes. This method                difficult.
automatically constructs physical models from                                 To further enhance the implementation of CAD/
computerized three-dimensional (3D) data. RP has                         CAM technologies successfully to design complete
recently seen successful application in various medical                  dentures, a new method has been developed2). In this
fields, such as in the fabrication of implant surgical                   method, the pre-existing dentures that the patient has
guides3,4), maxillofacial prosthetics5-7) and frameworks for             been using are scanned using cone-beam computed
removable partial dentures8,9). The manufacturing of                     tomography (CBCT) to obtain data of the mucosal surface
complete dentures in the conventional manner was                         and jaw relationship records. The pre-existing dentures
introduced about 70 years ago10), and is cumbersome and                  are modified, if necessary. Data for the denture space are
dependent on proficient skills from dentists and dental                  registered and imported to a workstation. Using 3D CAD
technicians. This new technology of RP might therefore                   software, denture shapes are designed. In this step, only
also help to reduce the complexity and technical                         the artificial teeth arrangement and polishing surface
sensitivity of creating complete dentures11).                            are designed. The complete denture bodies are then
     To date, the use of CAD/CAM technologies has                        developed by applying a CNC processor. Next, complete
primarily been focused on fixed prosthodontics1,12-14). In               dentures are completed by inserting artificial teeth into
contrast, few reports have been published on the use of                  dimples in the denture bodies. Thus far, however, with
CAD/CAM technologies for denture prosthetics. Maeda                      the use of this method, performing a trial insertion,
et al.15) were the first to fabricate complete dentures                  discussing the arrangement of the anterior teeth with
using 3D laser lithography to fabricate plastic shells of                the patient and verifying jaw relationship records at the
the dentition and record base. Kawahata et al.16)                        trial insertion appointment are still not feasible.
developed a removable-denture duplication procedure                           The trial insertion appointment is an important step
                                                                         in complete denture treatment18). This step not only
                                                                         needs the patient to make judgments of esthetics and
Color figures can be viewed in the online issue, which is avail-
able at J-STAGE.
Received May 10, 2011: Accepted Sep 2, 2011
doi:10.4012/dmj.2011-113 JOI JST.JSTAGE/dmj/2011-113
                                             Dent Mater J 2012; 31(1): 40–46                                         41

pronunciation19), but also requires verification of jaw
relationship records, including orientation of the occlusal
plane, vertical dimension, tongue space, tooth positioning,
palatal seal and soft tissue support for proper external
form20,21). This should be viewed as a time of approval
and acceptance by both the dentist and patient. Finally,
any instructions to be provided to the patient must be
given. Fabrication of complete dentures without a trial
insertion appointment is thus not practical. For this
reason, to enable the successful trial insertion
appointment with the use of CAD/CAM technologies, the
following steps were added to the procedures of
fabricating complete dentures. After registration of the
denture space, data for trial dentures with different
denture shapes are designed using 3D CAD software.
Trial dentures are then fabricated by applying RP. With
these trial dentures, arrangement of the anterior teeth
can be discussed with the patient and jaw relation
records verified at the trial insertion appointment.
     To date, however, no study has examined try-in of a
trial denture using RP. Efficiency of the try-in with a
trial denture applying RP thus remains unclear. The
purpose of this study was to evaluate a new method of
fabricating trial dentures using RP and to compare this
approach with the conventional method using wax
dentures. The null hypothesis of this study was that no
difference exists between the RP method and the               Fig. 1   Flow chart of the study set-up. STL: standard
conventional method.                                                   triangulated language.

Participants                                                      All research protocols were approved by the ethics
Ten edentulous patients under maintenance control             review board at Tokyo Medical Dental University,
(mean age, 78.1 years; standard deviation (SD), 5.6           Faculty of Dentistry (No. 372). No conflicts of interest
years) and 20 prosthodontists (mean age, 35.2 years; SD,      were present in this study.
7.9 years; mean clinical experience, 10.0 years; SD, 7.5
years) were enrolled in this study at the University          Fabrication of the trial denture
Hospital of Dentistry at Tokyo Medical and Dental             Figure 1 provides a simplified flow chart for this study.
University. Power analysis was performed to estimate          For each patient, maxillary and mandibular duplicate
the sample size needed to achieve at least 80% power          dentures were made using an auto-polymerizing resin
and a significance level of 0.05. Data from a preliminary     (Fit Resin, Shofu, Kyoto, Japan) at the first appointment.
study were used to estimate the necessary sample size.        These dentures were based on dentures that had been
     Inclusion criteria for patients for this study were      made properly by experienced prosthodontists in the
edentulous patients who wore complete dentures made           Prosthodontic Department of the University Hospital of
in the University Hospital of Dentistry, Tokyo Medical        Dentistry at Tokyo Medical and Dental University. The
and Dental University. Patients were excluded if they         shape of duplicate dentures and jaw relation records
were rated ≤20 points on the Revised Hasegawa                 were modified using a self-cured acrylic resin (Unifast
Dementia Scale, which is a scale of dementia, or if they      III, GC Corporation, Tokyo, Japan), if necessary.
had symptoms of severe myopia or daltonism. Patients          Duplicate dentures were used to take impressions and
using complete dentures rated<80 points according to          jaw relation records with a silicone impression material
the method of Sato et al.22) were also excluded. This         (Exadenture, GC Corporation, Tokyo, Japan) and a vinyl
method is a quantitative assessment of complete denture       polysiloxane impression material (Correct Plus Bite
quality to clarify the degree of contribution of each         Superfast, Jeneric/Pentron, Wallingford, CT, USA)23).
clinical factor on a scale from 0–100 and is considered to    The final impressions were taken without border
objectively assess complete dentures. No patient was          molding. The final casts were made and mounted to the
excluded after these preliminary examinations. Inclusion      articulator. Wax dentures were then made according to
criteria for prosthodontists for this study were dentists     the conventional method24). Figure 2 shows a wax
who had been working at the University Hospital of            denture. A CBCT (Finecube, Yoshida Dental
Dentistry at Tokyo Medical and Dental University for          Manufacturing, Tokyo, Japan) scanned the wax dentures.
more than 4 years.                                            CT images were reconstructed and transferred into 3D
42                                             Dent Mater J 2012; 31(1): 40–46

images using a Digital Imaging and Communication in             software. According to these 3D images, a RP machine
Medicine (DICOM) Viewer (OsiriX, The OsiriX                     (EDEN250, Objet Geometries, Rehovot, Israel) was used
Foundation, Geneva, Switzerland). These 3D images               to fabricate the seven trial dentures for each patient.
were imported into a workstation as standard                    Figure 4 shows the RP machine, which was used in this
triangulated language (STL) files. Using 3D CAD                 study. This RP machine sprays state-of-the-art
software (CATIA V5R19, Dassault Systemes, Vélizy-               photopolymer materials in subsequent ultra-thin layers
Villacoublay, France; and FreeForm, SensAble                    onto a building tray until the part is completed. Each
Technologies, Woburn, MA, USA), the following seven             photopolymer layer is cured by ultraviolet light
denture 3D images were made: one denture with the               immediately after it is sprayed, producing completely
same shape as the wax dentures (a); two dentures with           cured models that do not require any post-curing. The
changes in the size of the artificial teeth (one size smaller   RP machine was used with ultraviolet-cured acrylic-
and larger; b and c); two dentures with lip support             based resin material (FullCure720, Objet Geometries,
adjusted by 2 mm (backward and forward; d and e); and           Rehovot, Israel), which is approved for medical use in
two dentures with the position of occlusal plane changed        terms of cytotoxicity, irritation and sensitization
by 2 mm (lower and higher; f and g). Figure 3 shows             according to the United States Pharmacopeia (USP)
artificial tooth arrangement after application of 3D CAD        Class VI. Trial dentures were painted using prosthetic
                                                                composite resins (Gradia Gum GUM Opaque, HPO-04
                                                                OB3, GC Corporation, Tokyo, Japan) by one of the
                                                                authors. Figure 5 shows a completed trial denture after
                                                                application of RP. One experienced prosthodontist took
                                                                the final impressions and determined jaw relation
                                                                records, made the wax dentures, operated the 3D CAD
                                                                software and completed the trial dentures applying RP.
                                                                     To evaluate the accuracy of the trial denture after
                                                                application of RP, some of the above-mentioned
                                                                (a)-shaped RP dentures were scanned using CBCT
                                                                (Finecube, Yoshida Dental Manufacturing, Tokyo,
                                                                Japan). Using the DICOM Viewer (OsiriX, The OsiriX
                                                                Foundation, Geneva, Switzerland), CT images were
                                                                reconstructed and transferred into a 3D image. These 3D

Fig. 2   One of the wax dentures.
         Wax dentures were made according to the
         conventional method.

Fig. 3   Complete denture design using 3D CAD software.
         This figure shows artificial teeth arrangement
         using 3D CAD software (CATIA, Dassault
         Systemes). A data library for artificial tooth
         arrangement can reduce the time for denture
         design using 3D CAD software.                                Fig. 4   The RP machine used in this study.
                                             Dent Mater J 2012; 31(1): 40–46                                           43

images were then imported into a workstation. Deviation        prosthodontists performed arrangement of the artificial
analysis between wax dentures and RP dentures was              teeth. The order of the two trial insertion methods was
performed using 3D CAD software (CATIA V5R19,                  decided using a random number table and the blocked
Dassault Systemes, Vélizy-Villacoublay, France). This          randomization method. With the RP method, the
analysis allowed evaluation of deviation between all           prosthodontists placed a few trial dentures that had
nodes in both forms of CAD data.                               been judged suitable in terms of esthetics into the
                                                               patient’s mouth. In this study, neither patients nor
Evaluation of the trial insertion applying the conventional    prosthodontists could be blinded to the methods, since
and RP methods                                                 the appearance of trial dentures was easily distinguished.
Twenty prosthodontists evaluated trial insertions. Each        The 10 patients as well as the 20 prosthodontists rated
patient was assigned two prosthodontists, creating ten         satisfaction levels with the two methods on a 100-mm
test groups. Two prosthodontists performed a trial             visual analogue scale (VAS). Prosthodontists were
insertion for one patient using the conventional method        blinded to each other’s scores. Items on the patient
and the RP method. They evaluated esthetics, stability,        questionnaire were: esthetics; predictability of final
and occlusion of the trial dentures. Only one of the two       denture shape; stability; comfort of the dentures; and
                                                               overall satisfaction. Items on the prosthodontist
                                                               questionnaire were: esthetics; stability; operator
                                                               friendliness for verifying jaw relation records; chair
                                                               time; and overall satisfaction.

                                                               Statistical analysis
                                                               Ratings of satisfaction with each conventional and new
                                                               method were compared using the Wilcoxon signed-rank
                                                               test. Significance level was set at the level of p=0.05.
                                                               Data were analyzed using a statistical program (SPSS.
                                                               Version 16.0 for Windows, SPSS, Chicago, IL, USA).

                                                               Deviation analysis
                                                               The results of deviation analysis for wax dentures and
                                                               trial dentures applying RP were as follows. On the
                                                               maxillary denture, about 92% deviation ranged from
Fig. 5   Trial dentures applying RP.                           −0.4 mm to 0.4 mm. Mean deviation was −0.0051 mm
         A RP machine fabricated trial dentures with UV        (SD, 0.19 mm). On the mandibular denture, about 95%
         curable resins. The trial dentures were further       deviation ranged from −0.3 mm to 0.3 mm. Mean
         manually completed using prosthetic composite         deviation was −0.023 mm (SD, 0.16 mm). Figure 6 shows
         resins.                                               the results of deviation analysis for one of the maxillary

(a)                                                             (b)

Fig. 6   (a) Results of deviation analysis for one of the maxillary trial dentures at the occlusal surface.
         The deviation range was −0.63 mm to 1.04 mm. The histogram and noted percentages show the frequency
         The green area represents no deviation, while the red and blue areas represent a positive and negative deviation,
         (b) Results of deviation analysis for one of the maxillary trial dentures at the mucosal surface.
         The facial surface of denture teeth shows the maximum deviation.
44                                               Dent Mater J 2012; 31(1): 40–46

(a)                                                                     (b)

Fig. 7    (a) Results of deviation analysis for one of the mandibular trial dentures at the occlusal surface.
          The deviation range was −0.53 mm to 0.80 mm. The histogram and noted percentages show the frequency
          The green area represents no deviation, while the red and blue areas represent a positive and negative deviation,
          (b) Results of deviation analysis for one of the mandibular trial dentures at the mucosal surface.
          The facial surface of denture teeth also shows the maximum deviation.

Table 1     Ratings from 100-mm VAS in 10 patients comparing conventional and RP methods

                             Esthetics           Predictability               Comfort             Stability

                           RP             C       RP             C       RP             C       RP             C       RP             C

Median                     87.0          89.5    95.0           96.0     93.0          92.5    94.5           95.5    97.0           98.0

Maximum score             100            100     100            100     100            100     100            100     100            100

Minimum score              50.0           40.0    48.0           64.0    39.0           50.0    48.0           37.0    36.0           35.0

Mean                       85.4           81.7    89.9           89.9    87.4           85.7    88.6           87.5    89.3           89.9

Standard deviation         14.3           20.4    15.2           12.5    17.0           17.6    15.6           18.4    18.9           18.9

p                                 0.61                   0.93                   0.86                   0.68                   0.59
RP, RP method; C, conventional method.
p=Wilcoxon signed-rank tests.

Table 2     Ratings from 100-mm VAS in 20 prosthodontists comparing conventional and RP methods

                                                                         Verifying jaw                                   Overall
                             Esthetics              Stability                                    Chair time
                                                                        relation records                               satisfaction

                           RP             C       RP             C       RP             C       RP             C       RP             C

Median                     23            86.5    80.5           82.5     83            92      84             44.5    73.5           75

Maximum score              93            100      95            100     100            100     100             84      91             86

Minimum score               0             44      30             41      58             37      34              0      28             31

Mean                       29.2           81.2    73.1           81.9    83.0           87.9    74.1           41.6    69.2           71.3

Standard deviation         24.4           15.4    18.7           12.7    13.2           14.5    20.6           26.1    17.4           13.4

p                               >0.00*                 0.04*                    0.15                 >0.00*                   0.87
RP, RP method; C, conventional method.
p=Wilcoxon signed-rank tests. * Significant difference (p<0.05).
                                              Dent Mater J 2012; 31(1): 40–46                                           45

trial dentures. Figure 7 shows the results of deviation        resulting in significantly lower scores. Improved teeth
analysis for one of the mandibular trial dentures.             and gum-colored RP materials will eventually be
                                                               developed. If these materials are correctly applied,
Patient ratings                                                esthetics will improve greatly.
Table 1 shows the results of the 100-mm VAS for the 10              Ratings of chair time were significantly higher with
patients. No significant difference was seen between the       the RP method than with the conventional method. In
two methods in esthetics, predictability of final denture      the future, the population of elderly edentulous patients
shape, stability, comfort of the dentures or overall           will only increase26). For this reason, the short chair time
satisfaction.                                                  of the RP method is highly advantageous. Chair time
                                                               with the conventional method was apparently shorter
Prosthodontist ratings                                         than that with the RP method when the dentist did not
Table 2 shows the results of the 100-mm VAS for all            arrange the artificial teeth at the chair-side, but
prosthodontists. Ratings of esthetics and stability were       rearrangement is necessary in most cases during this
significantly higher with the conventional method than         time. On the other hand, a key disadvantage of the RP
with the RP method (p<0.05). Ratings of chair time were        method is that arrangement of artificial teeth in the RP
significantly higher with the RP method than with the          dentures cannot be altered at the chair-side, since
conventional method (p<0.01). No significant differences       several trial dentures of different tooth arrangements
between methods were seen for operator friendliness or         need to be fabricated well in advance. With the
overall satisfaction (p>0.05).                                 conventional method, moving the anterior artificial teeth
                                                               is easy. However, some time is required to modify the
                                                               arrangement of artificial teeth. The RP method is thus
                                                               much more favorable than the conventional method.
In this study, trial dentures were fabricated applying              Although RP has a high processing accuracy, RP
RP. The results of deviation analysis indicate that RP         dentures showed inferior stability compared to wax
offers high processing accuracy compared to conventional       dentures. The cause of this difference has been the
wax dentures. The mucosa has a displaceability of about        scanning process using CBCT. In particular, three
0.14–0.34 mm25). Taking the displaceability of the mucosa      factors are regarded as important. First, the partial
into consideration, these deviations can be compensated        volume effect can introduce imprecision to the digital
for in the clinical situation. Trial dentures can thus be      image. Second, using the DICOM Viewer, threshold
fabricated by applying RP. With this method using CAD/         values can often lead to error. Third, imported data in
CAM technologies, the trial insertion appointment can          the CAD software can introduce imprecision to the
still be included to advance the quality of denture            digital image27). Although a 3D laser scanner would be
fabrication.                                                   able to solve these problems, such equipment is very
     With regard to the sample size, no research has yet       expensive. The scanning data could potentially be
been published in the field of CAD/CAM technologies            compensated for before fabrication by adjusting the CAD
regarding trial insertion with RP. While a sample size of      data using CAD software during data construction.
10 does indeed seem small, it was determined in advance             No significant differences were seen between the
by power analysis using data from a preliminary study.         two methods in terms of operator friendliness for
We will be continuing this study to increase the sample        verifying jaw relation records and overall satisfaction.
size.                                                          The null hypothesis of this study was thus partially
     According to patient ratings, RP dentures and wax         rejected.
dentures were evaluated equally in terms of esthetics,              To date, it is still necessary to take impressions, in
predictability of final denture shape, stability, comfort of   the same way as it is done with the conventional method.
dentures and overall satisfaction. RP is thus quite            In the future, the impression procedure might be
applicable to clinical use. At the trial insertion             replaced by scanning the patient’s jaw with CBCT or
appointment, the dentist should offer to send the trial        Magnetic Resonance Imaging (MRI). In terms of patient
dentures home with the patient, since RP dentures are          safety, MRI might be better to discard the difficult
no longer necessary in the following laboratory work19).       impression taking.
The dentist can reflect on the suggestions of other family          Further studies should be performed to evaluate the
members concerning final denture appearance. Within            quality of complete dentures by applying CAD/CAM
the short term, it is also possible to use RP denture.         technology, to examine the arrangement of artificial
Regarding esthetics, the RP method is able to take the         teeth using a virtual articulator, and to develop new
opinions and personal preferences of the patient into          denture base materials that can be used with RP.
consideration. However, this may be difficult to achieve       Moreover, studies are presently underway to investigate
using the conventional method, as the wax dentures are         face-simulation technology. This technology will enable
commonly used for further processing of the final              dentists to determine the shape of dentures properly and
dentures.                                                      to reduce the number of trial dentures. To date,
     At the moment, only one RP material is safe to use        fabricating complete dentures with RP is expensive. If
orally. As a result, RP dentures have always had inferior      face-simulation technology can be applied properly,
esthetics compared to conventional wax dentures,               savings will be achieved in the costs of the dentures. In
46                                                 Dent Mater J 2012; 31(1): 40–46

addition, with this technology, dentists and patients will                  technique for complete dentures in an undergraduate dental
be able to discuss the arrangement of artificial teeth.                     curriculum. J Prosthet Dent 2001; 85: 121-125.
                                                                      12)   Wittneben JG, Wright RF, Weber HP, Gallucci GO. A
    Although further improvements are needed in
                                                                            systematic review of the clinical performance of CAD/CAM
esthetics and processing of 3D data, the present results                    single-tooth restorations. Int J Prosthodont 2009; 22: 466-471.
demonstrate that trial insertion can be accomplished                  13)   Harder S, Kern M. Survival and complications of computer
when the dentures are fabricated by RP.                                     aided-designing and computer-aided manufacturing vs.
                                                                            conventionally fabricated implant-supported reconstructions:
                                                                            a systematic review. Clin Oral Implants Res 2009; 20 Suppl 4:
                  ACKNOWLEDGMENTS                                           48-54.
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Shonan Institute of Technology.                                             Oral Implants Res 2007; 18 Suppl 3: 205-217.
                                                                      15)   Maeda Y, Minoura M, Tsutsumi S, Okada M, Nokubi T. A
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