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Evaluation of the printing trueness of CAD-CAM maxillary complete denture bases fabricated by using two different DLP 3D printers

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Evaluation of the printing trueness of CAD-CAM maxillary complete denture bases fabricated by using two different DLP 3D printers

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Content Evaluation of the printing trueness of CAD-CAM maxillary complete denture
bases fabricated by using two different DLP 3D printers
by
Mostafa Ibrahim, BDS

A Thesis Presented to the
FACULTY OF THE USC HERMAN OSTROW SCHOOL OF DENTISTRY
UNIVERSITY OF SOUTHERN CALIFRONIA
In Partial Fulfillment of the
Requirement for the Degree
MASTER OF SCIENCE
BIOMATERIALS AND DIGITAL DENTISTRY

December 2020

Copyright 2020 Mostafa Ibrahim
ii
ACKNOWLEDGEMENTS
I would like to express my gratitude and appreciation to all my committee members, Dr.
Sillas Duarte and Dr. Jin-Ho Phark for their countless hours of guidance and support throughout
this research project.
Thank you to my advisor Dr. Sillas Duarte for encouraging me all the time and providing
me the tool that I want to achieve my goals and complete my research project.
Thank you for my co-advisor Dr. Jin-Ho Phark who taught me the principles of doing a
high standard research project. Thank you for being enthusiastic, patient, and very
knowledgeable.
I would like also to thank Mrs. Karen Guillen for continuous support and assistant. Also,
special thanks to my co-residents for the collaborative work and knowledge especially in the
statistical analysis work.
Finally, I would like to acknowledge with gratitude my family, especially my parents for
continuous love and support throughout my life and work.

iii

TABLE OF CONTENTS

Acknowledgments........................................................................................................................... ii
List of Tables ................................................................................................................................. iv
List Of Figures ............................................................................................................................... v
Abbreviations…………………………………………………………………………………….vii
Abstract ........................................................................................................................................ viii
Introduction ..................................................................................................................................... 1
Specific aim .................................................................................................................................... 6
Materials and Methods .................................................................................................................... 7
Results ........................................................................................................................................... 11
Discussion ..................................................................................................................................... 13
Conclusion……………………………………………………………………………………… 20
Conflict of Interest…………………………………………………………………………….... 21
Funding ………………………………………………………………………………………… 22
References ..................................................................................................................................... 23
Tables and Figures ........................................................................................................................ 27

iv

LIST OF TABLES
Table 1: Technical specifications of the DLP printers. ............................................................... 27
Table 2: technical specifications of dentca denture base ii, shade: original pink. ....................... 28
Table 3: Mean absolute deviation, standard deviation, mean difference, standard error, and
pairwise comparison of printers at intaglio and cameo surface. ................................................... 29
Table 4: Pairwise comparison of printers at intaglio and cameo withing each group. ................ 30
Table 5: Tests of between-subjects effects and the analysis of variance table of mean square, f-
value and p-value. ......................................................................................................................... 31

v
LIST OF FIGURES
Figure 1: Virtual reference denture base...................................................................................... 32
Figure 2: Asiga MAX/MAX UV Printer (Asiga). ....................................................................... 33
Figure 3: Cara Print 4.0 Printer (Kulzer). .................................................................................... 34
Figure 4: Asiga MAX/ MAX UV printer - virtual reference denture base with supports (frontal
view). ............................................................................................................................................ 35
Figure 6: Asiga MAX/ MAX UV printer - virtual reference denture base with supports (bottom
view). ............................................................................................................................................ 37
Figure 7: Cara Print 4.0 printer - virtual reference denture base with supports (bottom view). .. 38
Figure 8: Dentca denture base II, shade: original pink (Dentca). ................................................ 39
Figure 9: Asiga MAX/ MAX UV printer sample with support structure (frontal view). ............ 40
Figure 10: Cara Print 4.0 printer sample with support structure (frontal view). ......................... 41
Figure 11: Asiga MAX/ MAX UV printer sample with support structure (posterior view). ...... 42
Figure 12: Cara Print 4.0 printer sample with support structure (posterior view). ...................... 43
Figure 13: Cara Print 4.0 printer sample: a, intaglio surface. b, cameo surface. ......................... 44
Figure 14: Asiga MAX/ MAX UV printer sample: a, intaglio surface. b, cameo surface. ......... 45
Figure 15: Flowchart of the study protocol. ................................................................................ 46
Figure 16: Mean absolute deviation and 95% confidence interval of both printers. ................... 47
Figure 17: Mean absolute deviation and 95% confidence interval of both printers at intaglio and
cameo surfaces. ............................................................................................................................. 48
Figure 18: Color-coded 3d surface deviation maps of one random sample from each group. a
and c: intaglio and cameo surfaces of dentures bases fabricated by Asiga MAX/ MAX UV
vi
printer. b and d: intaglio and cameo surfaces of dentures bases fabricated by Cara Print 4.0
printer. ........................................................................................................................................... 49
vii
ABBREVIATIONS

1. AM: Additive Manufacturing

2. 3D: Three Dimensional

3. CAD: Computer-Aided Design

4. CAM: Computer-Aided Manufacturing

5. DLP: Digital Lighting Processing

6. SLA: Stereolithography

7. DLMS: Direct Laser Metal Sintering.

8. LCD: Liquid Crystal Display

9. SLS: Selective Laser Sintering

10. LED: Light Emitting Diode

11. ISO: International Organization for Standardization

12. STL: Standard Tessellation Language

13. PVS: Polyvinyl siloxane

14. PMMA: Polymethyl methacrylate

15. RMSE: Root Mean Square Value

16. SD: Standard Deviation

17. ANOVA: Analysis of variance

viii
ABSTRACT
Keywords: CAD-CAM complete dentures, Additive and Subtractive Manufacturing, Digital
Light Processing, 3D printers, PMMA material, Trueness, Surface matching.
Objective: The aim of this in vitro study was to assess the printing trueness of CAD-CAM
maxillary complete denture bases fabricated by using two different 3D printers.
Materials and methods: A maxillary complete denture base was digitally designed based on the
virtual reference model of the maxilla which was obtained from scanning of a polyvinyl siloxane
(PVS) impression of the edentulous maxilla of one patient. A total of 20 CAD-CAM maxillary
complete denture bases were fabricated based on the virtual reference maxillary denture base
from an ultraviolet light-curable resin material by utilizing two different Digital Light Processing
(DLP) 3D printers (Asiga MAX/ MAX UV and Cara Print 4.0 printers). The intaglio and cameo
surfaces of all printed complete denture bases were scanned and superimposed on the
corresponding virtual reference maxillary denture base to assess the printing trueness of all
printed maxillary complete denture bases using a surface matching software (Geomagic Qualify
12). Statistical analysis was conducted with two-way ANOVA and Tukey post-hoc, α=0.05.
Results: The printing trueness of the maxillary complete denture bases fabricated by the Asiga
MAX/ MAX UV printer was significantly more accurate than those fabricated by the Cara Print
4.0 printer (p<0.001). ANOVA test showed a significant effect of printers (p<0.001) and surface
(p=0.047) with no significant interaction between printers and surface (p=0.249).
Conclusion: There was a statistically significant difference in the printing trueness of CAD-
CAM Maxillary complete denture bases fabricated by two different 3D DLP printers. The Asiga
MAX/ MAX UV printer was more accurate than the Cara Print 4.0 printer in terms of the
printing trueness of the intaglio and cameo surfaces.
Clinical Significance: Additive manufacturing (AM) technique represented by digital light
processing (DLP) 3D printer provide an appropriate method for fabricating CAD-CAM
removable complete dentures. 3D printed CAD-CAM removable complete dentures can be
considered a reliable alternative option for the edentulous patient offering the advantages of
improved accuracy, less clinical time, and cost-effectiveness.
1
INTRODUCTION
In prosthodontic rehabilitation of edentulous individuals, the removable complete denture
is considered a less invasive and cost-effective choice.
1
An essential factor that determines the
quality of complete dentures is the fit of the denture.
2
Well-fitting complete dentures demonstrate
a higher comfort and minimize the incidence of traumatic ulcers.
3, 4
The retention of complete
dentures impacts the speaking and masticatory ability of the patient and has a strong influence on
the quality of life of the patient.
5

Removable complete dentures fabricated by computer-aided design (CAD) and
computer-aided manufacturing (CAM) were first discussed in 1994
6
and now exemplify an
enhancement over the production of conventional dentures.
6, 7
The manufacturing of complete
dentures by CAD-CAM technique has developed extensively in both laboratory and clinical
practice in recent years.
8
In comparison to conventionally made complete dentures, CAD-CAM
made complete dentures exhibit important advantages such as minimization of residual
monomer, decreased polymerization shrinkage, enhanced physical characteristics of the acrylic
resin, better retention, less patient visits and clinical treatment time, less microbial colonization
and higher patient satisfaction.
9, 10
In addition, CAD-CAM technologies permit the effective
manufacturing of a spare prostheses from the stored digital data.
9-11

Two main CAD-CAM methods are available, the subtractive method utilizing a milling
process and the additive method utilizing various 3D printing processes to construct digital
complete dentures. 3D methods are advantageous due to fewer materials required to create the
intended prostheses or models as well as the capacity to generate various prostheses at once.
12

Disadvantages of subtractive methods, such as milling, include the cost of the equipment, wear
of the milling tools that need to get changed and unintentional material loss while milling.
12

Subtractive methods utilize computer software and 3-, 4-, or 5-axis milling devices that are
equipped with drills or burs to cut through prefabricated and pre-polymerized polymethyl
methacrylate (PMMA) blocks.
13
Additive methods consist of various printing technologies that
include stereolithography (SLA), jet printing (PolyJet and ProJet), digital light processing (DLP),
selective laser sintering (SLS), and direct laser metal sintering (DLMS).
13

2
Stereolithography (SLA) is a 3D printing method that utilizes an ultraviolet laser beam as
a light source to cure the unpolymerized resin material layer by layer to create a desired solid
shape. The laser beam is directed onto the top surface of a light curable resin that is contained in
a vat. The vat also contains a moving platform which is covered with a thin layer of the liquid
resin. Once the laser beam passes over this layer and hardens it, the platform travels downward.
Then, the just hardened layer is covered with fresh resin again, which then is hardened after
another pass of the laser beam thereafter. These steps in the printing process are repeated until
completion.
14, 15
Photopolymerization is the method used to harden the photosensitive resins used
in the SLA technique. Both, radical and cationic polymerization could be performed at the SLA
laser beam wavelength of 355 nm, depending on the photoinitiator.
15, 16

Supporting structures are required to attach the printed object to the building platform
and avoid deflection of the printed object due to gravity. These supporting structures are created
by the software of the 3D printer. After completion of the printing process, the printed model is
cleaned in an alcohol bath eliminate the unpolymerized residual resin layer. Supporting
structures are often removed manually.
15, 17
Then, post-printing curing is required to complete the
polymerization process for uncured remaining resin material. Stereolithography (SLA) has the
advantages of wide material selection. However, some limitations exist, such as low printing
resolution (depending on the laser beam size), expensive cost of the printing materials, the
difficulty of handling due to the light sensitivity of the resin material, and poor mechanical
properties of the printed object.
15, 17

Digital light processing (DLP) is also a 3D printing method and is similar to
stereolithography (SLA) in many aspects.
15
However, there is one major difference, the light
source. Digital light processing utilizes an arc lamp to produce ultraviolet light as a light source
using a projector based on liquid crystal display (LCD) technology.
18
Also, instead of a
projector, LED display could be used. DLPs use a bottom-up approach where the exposure
direction of the light is from the transparent bottom of the resin vat. With this technique, a
moving platform is hanging into the liquid resin in the vat. Between the surface of the platform
and the transparent bottom of the vat is a thin space filled with uncured resin.
19
As the light
projection hardens the resin, the then hardened material stays attached to the platform surface.
The platform moves up and the hardened resin detaches from the transparent bottom of the vat,
3
creating a space with is subsequently filled with liquid resin again.
20
This liquid resin can now be
light cured from the bottom and it stays attached to the previous layer. These steps are repeated
until the object is completed.
20

Free radical photopolymerization is usually utilized in Digital light processing (DLP).
Cationic photopolymerization is not utilized due to a few reasons. A cationic photoinitiator
would insufficiently function under 405 nm irradiation. Furthermore, the light intensity of DLP
printer is not sufficient to photolyze the cationic photoinitiators, which, as a result, would fail to
catalyze the photopolymerization.
15
Digital light processing (DLP) has many advantages, such as
high printing resolution and faster printing process.
15
In contrast, the size of the printed object is
a limitation for DLP 3D printing. Supporting structures and post-printing curing is also required
for DLP.
Jet printing technique utilizes multiple inkjet printing heads that deposit a small drops of
resin material on the building platform or print bed. After jetting one-layer, ultraviolet light is
used to harden the resin material. Then another layer is added on top of the previous one. The jet
printing technology has the advantage of eliminating the need for resin tank and post-printing
curing. For fabrication of metallic restorations, selective laser sintering (SLS) and direct laser
metal sintering (DLMS) printing techniques utilize a high-power beam of laser light to hit
metallic powder. As a result, the metallic powder particles melt and are fused together creating a
solid 3D structure based on the 3D model.
17
These technologies are used in dentistry to produce
metal frameworks for removable partial dentures.
Currently, there are many digital systems available for fabrication of complete dentures.
However, only two studies assessed the procedures for the construction of digital complete
dentures and explained the existing popular digital systems for complete dentures.
8, 21

Additionally, there are other new digital systems available for the dental practitioners to
manufacture CAD-CAM complete dentures such as Vita Vionic, Lucitone Digital Print,
NextDent, but there is few information in the literature about these systems.
22-24

To fabricate digital complete dentures clinically, two appointments are needed using
digital systems, such as Avadent (AvaDent Digital Dental Solutions, Scottsdale, Arizona, United
states of America) and Dentca (Dentca, Torrance, California, United States of America).
8
During
4
the first appointment, final impressions for the edentulous arches are taken utilizing prefabricated
trays that come with each system. Next, the vertical and horizontal jaw relation records are
registered by utilizing anatomical recording devices or conventional techniques. Then, the type,
size, and shade of artificial teeth are selected.
8
After that, the final impressions and the jaw
relation records are disinfected and sent to the dental laboratory or the manufacturer. There, the
impressions and the connected jaw relation records are scanned and digitized utilizing a desktop
scanner. Computer software is used to mark and identify the denture borders. The teeth are
arranged virtually with proper position and occlusal plane orientation and the virtual denture
base is established with proper morphology. Once the design of the complete denture has been
done virtually, the denture base is either milled or printed according to the desired manufacturing
system.
8
After fabricating the denture base, teeth are bonded to the denture base and checked for
proper position and orientation. Dentists can request a trial denture as an option. In the second
appointment, the CAD-CAM complete denture is delivered, and post-delivery adjustments are
made in a similar manner of the conventional complete denture delivery.
8

As described by the International Standards Organization standard ISO 5725-4:2020, the
accuracy is described by two terms, trueness and precision.
25
“Trueness is defined as the
closeness of agreement between the arithmetic mean of many test results and the true or accepted
reference value”. “Precision refers to the closeness of agreement between test results”.
25
Chen et
al. stated that the wax patterns of the maxillary complete denture fabricated by 3D printing
process have comparable adaptation with the wax pattern fabricated by the conventional
method.
26
Another study was conducted by Lee et al. and they concluded that the accuracy of the
complete denture bases fabricated by milling and rapid prototyping methods is superior to those
denture bases fabricated by injection molding technique.
23
Also, Hwang et al. revealed that the
3D printed maxillary denture base showed superior tissue surface adaptation and trueness in
comparison with a denture base made by either milling or pack and press techniques.
27
However,
Kalberer et al. reported that milled complete dentures displayed higher trueness and adaptation of
the intaglio surface.
28
To this date, there is no study comparing 3D DLP printers for the printing
trueness of CAD-CAM complete denture bases for their intaglio and cameo surfaces. So, the
purpose of this laboratory study is to compare and evaluate the printing trueness of CAD-CAM
maxillary complete denture bases for their intaglio and cameo surfaces fabricated by using two
different DLP 3D printers. The first null hypothesis was that there is no difference in the printing
5
trueness of CAD-CAM Maxillary complete denture bases fabricated by two different 3D DLP
printers. The second null hypothesis was that there is no difference in printing trueness for the
intaglio and cameo surface of these denture bases.
6
SPECIFIC AIM
The aim of this laboratory study is to compare the printing trueness of CAD-CAM
maxillary complete denture bases fabricated by two different DLP 3D printers.
7
MATERIALS AND METHODS
Sample preparation
A Polyvinyl siloxane (PVS) impression (Heavy and light body Flexitime, Kulzer, Hanau,
Germany) was taken of the edentulous maxilla of one patient only. A large impression tray
(DENTCA Tray, Dentca, Torrance, California, United States of America) was used to take the
final impression. CaviCide disinfectant (CaviCide, Metrex, Orange, California, United states of
America) was utilized to decontaminate the PVS impression. After that, the PVS impression was
lightly spray-coated with anti-reflection coating (Spotcheck spray, Magnaflux, Glenview,
Illinois, United States of America). The polyvinyl siloxane (PVS) impression was scanned using
a desktop scanner (D710 Dental Scanner, 3Shape, Copenhagen, Denmark) and digitized using a
desktop scanner software (ScanItOrthodontics, 3Shape, Copenhagen, Denmark). According to
the technical specifications of the desktop scanner (D710 Dental Scanner, 3Shape, Copenhagen,
Denmark), as described by the manufacturer, the accuracy was < 20 microns.
29

The digitized 3D data was saved as a standard tessellation language (STL) format file.
The STL file of the digitized PVS was exported to the Dentca denture design software (CAD -
Dentca denture design software, Dentca, Torrance, California, United States of America) and the
virtual reference model of the edentulous maxilla was prepared and saved as a separate STL file.
After that, a reference denture base with posterior palatal seal was designed based on the
obtained reference model of the maxilla. Default settings of the Dentca denture design software
were used in preparation of virtual reference model of the edentulous maxilla and designing of
the virtual reference denture base (
Figure 1).

Two different DLP 3D printers were used to print the reference denture bases: Asiga
printer (Asiga MAX/ MAX UV, Asiga, Alexandria, Australia; Figure 2: Asiga MAX/MAX UV
Printer (Asiga).) and Cara printer (Cara Print 4.0, Kulzer, Hanau, Germany;

8

Figure 3: Cara Print 4.0 Printer (Kulzer).

). These two printing systems employ digital light processing (DLP) with a light emitting
diode (LED) generated light source at a peak wavelength of 405 nm (violet light). Additionally,
the Asiga printer used LED light at a wavelength of 385 nm (ultraviolet UV light). Both 3D
printers utilized its software to operate the printing process. The printing resolution of the Asiga
printer was 62 μm, while for the Cara printer it was 53.6 μm. The technical specifications of both
3D printers, as described by the manufacturer, are listed in Error! Reference source not
found..
30, 31

The STL file of the reference denture base was exported to the software of both printers (Cara
print CAM, Kulzer, Hanau, Germany; Asiga composer, Asiga, Alexandria, Australia). The
printing layer thickness was set to 100 μm for both printers. The number of supports were
designed by the printers’ software programs automatically, with a 45-degree build angle for the
Asiga printer and a 30-degree for the Cara printer (Error! Reference source not found., Error!
Reference source not found., Figure 5, Figure 6).
9
The resin material (DENTCA Denture Base II, shade: Original Pink, Dentca, Torrance,
California, United States of America) was used as printing material, with shade not being a
relevant factor (FIGURE 7). Also, the resin material was cured by both, violet and ultraviolet UV
light. The mechanical properties of the resin material meet the requirement of ISO 20795-1:
2013 and the technical specifications of this resin material, as described by the manufacturer, are
listed in (TABLE 2).
32
The absorption spectrum of the resin material was mentioned in (Table 2)
based on the communication with Dr. Jason Lee (the director of material department, Dentca,
Torrance, California, United States of America).
A total of 20 samples were printed and divided into two groups. 10 samples were printed using
the Asiga MAX/ MAX UV printer and the other 10 samples using the Cara Print 4.0 printer. All
samples were printed from the same reference denture base (Figure 8FIGURE 9Figure 10Figure
11). According to the manufacturer instructions, the building platform for the Cara Print 4.0
printer was able to print one denture base in 56 minutes while the Asiga MAX/ MAX UV printer
was able to accommodate and print two denture bases at once in 150 minutes.

Testing Procedure
After printing, supports were trimmed and removed manually from the printed samples by using
a clipper (Kaisi KS-107, Kaisi Industry, Yongkang, China). Each sample was cleaned in a 99%
isopropyl alcohol bath (IPA, Del Amo Chemical, California, United States of America) for 10
minutes according to the manufacturing instructions (Figure 12Figure 13). Immediately after
cleaning in the alcohol bath, each sample was wrapped in aluminum foil (Kirkland Signature,
Costco, Issaquah, Washington, United States of America) to eliminate any possible curing by
any source of light. Each printed sample was lightly spray-coated with an anti-glare scan spray
(Helling 3D, Laser Design, Minneapolis, Minnesota, United States of America)
33
and scanned
two times using the desktop scanner (D710 Dental Scanner, 3Shape, Copenhagen, Denmark).
10
With the first scan, the intaglio surface was scanned. With the second scan, the cameo surface
was scanned.
After completing the scanning process of all printed samples, all STL files were exported from
the desktop scanner (D710 Dental Scanner, 3Shape, Copenhagen, Denmark) to a surface
matching software (Geomagic Qualify 12, 3D Systems, Rock Hill, South Carolina, United Stated
of America). In this software, the STL files of all scanned printed samples of both groups were
subjected to a surface to surface matching by superimposition with the STL file of the reference
denture base.
27
The nominal deviation to define the increments of the color spectra 3D analysis
was set at ±50 μm and the maximum values was set at ±300 μm.
27, 34
Color-coded 3D surface
deviation maps were generated to visually display the matching areas (green) and the areas of
positive (red-surface higher compared to reference) and negative (blue-surface lower compared
to reference) deviation. All values were averaged for each printer system (Figure. 18). Each
scanning and superimposition process were performed by a single investigator. FIGURE 14
shows the flowchart of the protocol for this laboratory study.
Statistical Analysis
The means of the average positive and average negative deviations as well as the standard
deviation of all the measured surface deviations were calculated and exported as pdf-file by the
surface matching software. Due to the limitation of the surface matching software (Geomagic
Qualify 12), the software was unable to provide the root mean square values (RMSE). Therefore,
the mean absolute deviation values were calculated for each sample
to express the deviation information and account
for trueness. Also, the mean absolute deviation is a suitable parameter to evaluate the trueness
because it measure the average deviation from the reference model since we have positive and
negative deviations.
35
All the mean absolute deviation values and standard deviations of all
printed samples were saved in an Excel file (Microsoft 365, Microsoft Corporation,
Albuquerque, New Mexico, United Stated of America). The data was imported into a statistical
software package (SPSS Statistics V16.0, IBM Corp, Armonk, New York, United Stated of
America) in order to perform the statistical analysis. Descriptive statistics of means and standard
deviation were calculated. A two-way ANOVA test was conducted to evaluate and compare the
11
trueness among the two tested groups as well as to determine whether the differences between
both 3D printers are statistically significant. Tukey HSD was used for post-hoc analysis. For
statistical analysis alpha was set at 0.05.
12
RESULTS
A total of 20 samples were printed and divided into two groups. 10 samples were printed
using the Asiga MAX/ MAX UV printer and the other 10 samples using the Cara Print 4.0
printer. The mean absolute deviation of the Cara Print 4.0 printer at the intaglio surface ±
standard deviation was 0.12 mm ±0.01, and at the cameo surface was 0.13 mm ± 0.007. For the
Asiga MAX/ MAX UV printer, the intaglio surface mean deviation was 0.09 mm ± 0.008 and
0.09 mm ± 0.007 at the cameo surface (TABLE 3, FIGURE 15 andFIGURE 16). Withing Asiga
MAX/ MAX UV printer, there was no significant difference between cameo and intaglio
surfaces with p=0.054. Within Cara Print 4.0 printer, there was a significant difference between
cameo and intaglio surfaces with p=0.03 (Table 4).
Two-way ANOVA assumptions were met. The null hypothesis of Levene’s test of
homogeneity of variance was not rejected with p=0.77, and Kolmogorov–Smirnov test showed
normally distributed data with p=0.15. The ANOVA showed a significant effect of printers
(p<0.001) and surface (p=0.047) with no significant interaction between printers and surface
(p=0.249) (TABLE 5). Pairwise comparison analysis showed a significant difference between
the two printers for the intaglio surface (p<0.001) as well as for the cameo surface (p<0.001;
TABLE 3).
The color-coded 3D surface deviation maps were generated to visually display the areas
of positive and negative deviation (FIGURE 17). To evaluate these deviations, the surface
matching software has shown positive and negative surface deviation values in green, blue, and
red colors on the color-coded 3D surface deviation map. The positive deviation was shown as
yellow to red and indicates a space between the virtual printed denture bases and the virtual
reference denture base. However, the negative deviation was shown as cyan to blue and
represents the impingement of the virtual printed denture bases with the virtual reference denture
base. Green color represents a good match with a surface deviation below 50 μm. For both
groups of printed samples (Cara Print 4.0 and Asiga MAX/ MAX UV groups), no sample has
shown a color-coded 3D surface deviation map that was completely green. However, the
statistical analysis of the mean (The positive and negative average deviation) and the standard
deviation of all the measured surface deviations confirmed the finding that the Asiga MAX/
13
MAX UV printer more accurate than the Cara Print 4.0 printer in terms of the printing trueness
of the intaglio and cameo surfaces.
FIGURE 17 shows the color-coded deviation maps of a random sample from each group.
Visualization of the 3D surface deviation maps was done for all Asiga MAX/ MAX UV and
Cara Print 4.0 samples. For Cara Print 4.0 samples, 6 of 20 samples showed a patterns of positive
deviation (yellow to red) on the posterior palatal side of the intaglio surface and cameo surface,
and a pattern of negative deviations (cyan to blue) on the side of ridge area of the intaglio surface
and on the posterior palatal side if the cameo surface. However, For Asiga MAX/ MAX UV
samples, 8 of 20 samples showed the same patterns of surface deviations that was noticed with
Cara Print 4.0 samples.

14
DISCUSSION
In all complete denture manufacturing techniques, accuracy is the main focus and
concern for all dentists and dental technicians.
2
In this in vitro study, two different DLP 3D
printers were utilized to fabricate CAD-CAM maxillary complete denture bases from the same
virtual reference denture base. All 3D printed denture bases were cleaned, scanned, and
superimposed with the virtual reference denture base to evaluate the printing trueness of these
CAD-CAM maxillary complete denture bases. According to the results of this laboratory study,
it was shown that the printing trueness of maxillary complete denture bases fabricated by the
Asiga MAX/ MAX UV printer was superior to those made by the Cara Print 4.0 printer.
Furthermore, for both printers, the printing trueness of the intaglio surface was more accurate
than the printing trueness of the cameo surface. Consequently, both null hypotheses were
rejected.
Many studies have indicated that the polymerization shrinkage leads to the deformation
of the complete denture base, and thus has a negative influence on the retention, support, and
stability of the removable complete denture.
36, 37
Therefore, the quality of patient’s life could be
affected. So, it is necessary to use other alternative manufacturing techniques, such as subtractive
or additive methods using CAD-CAM technology that can minimize polymerization shrinkage
and produce well-fitting removable complete denture.
The subtractive method utilizes burs or diamond disks to mill the desired parts from
prefabricated and prepolymerized blocks of polymethylmethacrylate material (PMMA). The
subtractive method has the advantage of fabricating the desired objects completely with a
minimum amount of distortion as the polymerization shrinkage already occurs before them
milling step. However, it has the disadvantages of wasting large parts of the prefabricated
PMMA while milling, wear of the milling tools that need to get changed, and consumption of
large amounts of energy.
12, 13
Additive method on the other hand utilize an ultraviolet laser beam
or violet light as a light source to cure a unpolymerized resin material layer by layer, thus
creating the desired solid object. The model of the desired object is sectioned virtually into many
layers by using the computer-aided design CAD, then the 3D printer uses these 3D data to build
the desired object by stacking the layers accordingly. The additive method has the possibility of
15
overcoming the disadvantages of subtractive methods by utilizing less resin material, consume
less energy, and being more efficient. However, while the subtractive technique does not
encounter polymerization shrinkage after the milling process, the additive techniques require
light-curing after the printing process, which on the other hand can cause distortion due to
polymerization shrinkage.
12, 13

Nonetheless, in this study an additive method was used by utilizing two different 3D
printers (Cara Print 4.0 and Asiga MAX/ MAX UV printer) to construct digital complete denture
bases from one virtual reference denture base. These printers employ digital light processing
(DLP) with light emitting diodes (LED) as the light source at peak wavelengths of 385 nm
(ultraviolet/UV light) and of 405 nm (violet light). A photosensitive unpolymerized resin
material is used to fabricate the digital complete dentures. According to the technical
specifications of this resin material, as described by the manufacturer, it is compatible with the
light wavelength ranged from 315 - 410 nm. The printing layer thickness was set at 100 μm for
both 3D printers. According to the manufacturing specifications of these two 3D printers, the
building platform for Cara Print 4.0 printer was smaller in size and able to print one denture base
in 56 minutes while the Asiga MAX/ MAX UV printer was bigger and able to print two denture
bases in 150 minutes. Both 3D printers utilized its software to operate the printing process. The
printing resolution of the Asiga printer was 62 μm, while for the Cara printer it was 53.6 μm
(Error! Reference source not found.).
The Trueness of the printed denture bases for both printers could have been impacted by
various possible factors such as 3D software program, amount of supporting structures, building
angle of the printer, number of printed layers, post-processing method, and the light intensity of
the printer.
23
It is important to consider the limitations of methacrylate-based resins despite their
demonstrated efficacy in 3D photopolymerization. During the polymerization process, these
resins often undergo shrinkage. These pure resins have the tendency to become thick at low
conversion rates.
18
As a result, the residual uncured resin will experience limited flow.
Additional shrinkage or stress will be introduced with the newly created bonds if further
photopolymerization applied. The degree of shrinkage is depending on the molecular structure of
these pure resins. The result of the shrinkage and the associated stress may present as curling and
deformation during 3D process. In turn, the trueness of the final printed product may be
16
adversely affected.
18
In theory, polymerization shrinkage is possible after completing the printing
process because the resulting printed denture base is not completely polymerized during the
actual printing process with a residual layer of resin material still unpolymerized.
38
For this
reason, it is always recommended to rinse the printed complete denture with an appropriate
solvent to eliminate the residual resin material followed by an additional step of light
polymerization to finalize the process and to produce a fully polymerized complete denture.
38

Another possible factor that may influence the trueness of 3D printed objects is the
oxygen inhibited layer. Monomers and photoinitiators are the essential components of the any
polymerization reaction. The photoinitiators will split into primary radicals if the light is applied
to them. Then, these photoinitiators will react with double bonds that exist in the monomers
creating a network. If these reaction processes are exposed to oxygen, the oxygen will react with
the primary radicals and convert them to less active radicals.
39
In the DLP technique, light is
irradiated from the bottom of the resin vat. At the same time, the building platform sinks into the
liquid resin tank from the opposite direction. As the curing process of the resin material happens
at the bottom of the resin vat, surrounded by liquid resin in the absence of oxygen, the DLP
technique is less influenced by the oxygen inhibited layer than the SLA technique.
18, 38
The
oxygen inhibited layer has the disadvantage of interfering with polymerization process and forms
a sticky layers. However, it can be advantageous. A recent experiment was conducted by Zhao et
al. studied the influence of the oxygen inhibited layer on the interfacial strength during
incremental photopolymerization of 3D printed materials. They found that the presence of
oxygen during the incremental photopolymerization can enhance the strength of the interfaces
between the printed layers.
39
However, Gojzewski at al. conducted a laboratory study using
atomic force microscopy (AFM) to evaluate the mechanical properties of the interface between
the printed layers formed by digital light processing technology. They stated that there are
differences in the elastic properties of the interfaces between the printed layers and these
differences attributed to many possible factors such as the oxygen inhibited layer, variations in
the photopolymerization reaction and molecular diffusion across the printed layer’s interface.
40

According to the technical specifications of the resin material used in this study, the resin
material is compatible with wavelengths ranging from 315 - 410 nm.
32
The Asiga MAX/ MAX
UV printer employ LED light with a wavelength of 385 nm (ultraviolet UV light) while the Cara
17
Print 4.0 printer uses light with a wavelength of 405 nm (violet light).
30, 31
The printing layer
thickness was set at 100 μm for both printers. The parameter printing layer thickness is
determined by the setting of light intensity. Upon selecting the appropriate layer thickness,
prevention of over curing or inadequate curing should be monitored.
41
This can happen during
the printing process as the printer’s light penetrates further into the object than the specific layer
thickness. On the contrary, it can further occur when the light does not penetrate sufficiently to
cure the entire material.
41
Consequently, this can result in inaccuracies in the final printed
product. This difference in light intensity of both printers in relation to the layer thickness may
have a potential effect on the printing trueness of both printers. However, there is still
insufficient data regarding the effect of light intensity and the relevant layer thickness on the
accuracy of the 3D printed object. Additional post-printing curing was avoided in this study to
prevent any other influencing factors and to evaluate accuracy in terms of printing trueness.
One important and critical factor that determines the required amount of supporting
structure is selection of the appropriate build angle, which may influence the accuracy of 3D
printed object. So, changing the build angle will increase or decrease the amount of supporting
structures that are needed to support the printed object during the 3D printing process.
42
In this
study, each 3D printer has its own 3D software, the supporting structures were designed by each
printing software automatically, with a 45° build angle for the Asiga MAX/ MAX UV printer
and 30° angle for the Cara Print 4.0 printer (Error! Reference source not found.Error!
Reference source not found.). The supporting structures in this study were created on the
cameo surface of the denture base rather than the intaglio surface since the intaglio surface is
more important and had to match with the palatal soft tissue to provide retention and being well
fit. On the other hand, the cameo surface is in most parts touching mobile tissues, such as lips,
cheeks, tongue, or in parts nothing. The amount of supporting structures created by the Cara
Print 4.0 printer was larger than those created by the Asiga MAX/ MAX UV printer (Figure
5Figure 6). Also, the configuration of the supporting structures created by the Asiga MAX/
MAX UV printer was more uniform than those created by the Cara Print 4.0 printer (Figure
8FIGURE 9). As mentioned before, all supporting structures were removed manually.
Consequently, the printed denture bases using the Asiga MAX/ MAX UV printer will have less
support removal induced surface discrepancy than those printed by the Cara Print 4.0 printer.
The supporting structures are necessary for the 3D printing process to hold the resin material
18
during the 3D printing process. The form or structure of the 3D printed object may deform or sag
during the 3D fabrication process if there is no enough amount of the supporting structures.
43

Previous studies have indicated that the building angle, and the amount and configuration of the
supporting structures have a potential effect on the mechanical properties and accuracy of the
printed objects fabricated by DLP printers.
23, 42, 43
Hence, the previously mentioned differences
and factors may be a possible explanation for the finding of this study which showed that the
Asiga MAX/ MAX UV printer is more accurate than the Cara Print 4.0 printer in terms of the
trueness of the intaglio and cameo surfaces.
Multiple 3D software programs were used in this study such as CAD - Dentca denture
design software, Cara print CAM, Asiga composer, and Geomagic Qualify 12 surface matching
software. All these software programs have a potential influence on the printing trueness of the
printed denture bases. However, there are no studies in the scientific literature has evaluated the
effect of the CAD - Dentca denture design software, Cara print CAM and Asiga composer
software on the accuracy of printed dentures bases. Another possible factors that may affect the
trueness of the printed denture bases are the desktop scanner and the powder coating that was
utilized before scanning the printed denture based. According to the technical specifications of
the desktop scanner (D710 Dental Scanner), the accuracy was < 20 microns.
29
Lee et al. stated
that the desktop scanner and surface treatment with coating powder used in fabrication of CAD-
CAM denture bases may introduce small degree of inaccuracies that may not be critical to the
clinical outcome of the CAD-CAM complete denture.
23

The 3D deviation analysis was conducted by utilizing surface matching software
(Geomagic Qualify 12). The nominal deviation for the color spectra 3D analyses was set at ±50
μm and ±300 μm, one value was for the increments and the other was the maximum value.
27, 34

This software provided different values and deviations in the result report of 3D surface
comparisons such as maximum upper deviation, minimum upper deviation, positive average
deviation, negative average deviation, and standard deviations. Several studies have evaluated
the trueness of the 3D printed fixed dental restorations bases on the root mean square values
(RMSE) and deviations patterns on the color-coded 3D map.
42, 44
The root mean square values
(RMSE) were calculated and evaluated in these studies by utilizing the Geomagic Studio 2014
surface matching software. However, in this study, the Geomagic Qualify 12 surface matching
19
software was used as a surface matching software and was not able to provide the root mean
square values (RMSE). Also, the precision evaluation was not conducted due to the limitation of
the Geomagic Qualify 12 surface matching software. The mean absolute values were calculated
for each sample to express the deviation
information and account for trueness only. Also, the mean absolute deviation is a suitable
parameter to evaluate the trueness because it measures the average deviation from the reference
model since we have positive and negative deviations.
35
However, the printing trueness is still an
important parameter to investigate.
27, 28
Further studies are required to investigate effect of
printing speed, and light intensity of the 3D printer on the accuracy of the printed complete
denture bases.
Due to the dynamic movement of the oral mucosa, the ability of the soft tissue to tolerate
displacement of the complete denture is large. Previous articles stated that mucosal displacement
in the range of 375 and 500 μm was recorded and assumed to be acceptable from the clinical
standpoint.
34, 45
However, in our study, the critical positive deviation was 300 μm which below
the range of mucosal displacement. Therefore, from the clinical standpoint, the complete denture
bases fabricated by Asiga MAX/ MAX UV and Cara Print 4.0 printer could be acceptable.
Previous studies explained the importance of the fit of the complete denture and the
influence of the overall fit of complete denture on the quality of life of the patient.
2-4
In fixed
prosthodontics, it’s much easier to talk about the fit of fixed restorations because we can measure
it to see if the restorations’ margins are open or not by using a dental explorer or radiographs. If
the fixed restoration is well fitted, then we can consider it as a successful restorative treatment.
However, in removable prosthodontics, it’s more challenging to talk about fit of the complete
denture and how it’s related to the success of the complete denture treatment. The complete
denture treatment is considered successful when the patient accepts the complete denture and is
satisfied with it. Patient acceptability for complete dentures is dependent not only on the fit of
the complete denture but it also on other influencing factors such the psychological and physical
factors.
46, 47
Even though the results of this study showed that both printers gave us clinically
acceptable denture bases, we still have to consider the other factors that may influence the
overall success of complete denture treatment. So, if the dental laboratory doesn't necessarily
have the printer that showed the best results, then clinically, patient acceptability for the
20
complete denture would be still compensated, probably by the other influencing factors that are
related to the overall success of the complete denture treatment. Further studies are required to
investigate the effect of printing speed, post-processing method, and light intensity of the 3D
printer on the accuracy of the printed complete denture bases.

21

CONCLUSION
Within the limitation of this laboratory study, there was a statistically significant
difference in the printing trueness of CAD-CAM Maxillary complete denture bases fabricated by
two different 3D DLP printers. The Asiga MAX/ MAX UV printer was more accurate than the
Cara Print 4.0 printer in terms of printing trueness of the intaglio and cameo surface.
22

CONFLICT OF INTEREST
The authors of this research study declare no conflict of interest.
23
FUNDING
This research study was funded and supported by the master program in biomaterials and
digital dentistry (BMDD) in the Division of Restorative Sciences at the Herman Ostrow School
of Dentistry of University of Southern California.
24
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28
TABLES AND FIGURES
Table 1: Technical specifications of the DLP printers.
The technical specification Cara Printer Asiga Printer
Printing technology Digital Light Projection DLP Digital Light Projection DLP
Resolution 53.6 µm 62 µm
LED Wavelength 405 nm (violet) 385nm (UV) and 405nm (violet)
Building area 103 × 58 × 130 mm 119 × 67 × 7 5mm
Software Cara print CAM Asiga composer
Printing speed 56 minutes for one denture base 2.5 hours for two denture bases
Printer dimensions and weight 267 × 420 × 593 mm / 21 kg 260 × 385 × 370mm / 19.3 kg

29
Table 2: technical specifications of dentca denture base ii, shade: original pink.
The technical specification Units Specifications
Before curing (Liquid state)
Viscosity at 25 ± 0.5 °C cps 1000 < × < 2000
Density g/cm
3
1.05 < × < 1.20
Surface curing rate Second 119 × 67 × 7 5mm
After curing
Density g/cm
3
1.15 < × < 1.25
Flexural strength MPa >65
Flexural Modulus MPa >2000
Degree of conversion % >70
Absorption spectrum nm 315 - 410

30
Table 3: Mean absolute deviation, standard deviation, mean difference, standard error,
and pairwise comparison of printers at intaglio and cameo surface.

Surface (I) Cara (J) Asiga (I-J) SE P-value
Mean ± SD Mean ± SD
Intaglio 0.12 ± 0.01 0.09 ± 0.008 0.03 0.004 <0.001
Cameo 0.13 ± 0.007 0.09 ± 0.007 0.04 0.004 <0.001
31
Table 4: Pairwise comparison of printers at intaglio and cameo withing each group.

Printer
(I) Surface (J) Surface
Mean
Difference
(I-J)
Std.
Error
Sig.
b

P-value
Lower
Bound
Upper
Bound
Cara
Intaglio
Cameo
-.009 .004 .029 -.016
-.001
Cameo Intaglio .009 .004 .029 .001 .016
Asiga
Intaglio
Cameo
-.002 .004 .537 -.010
.005
Cameo Intaglio .002 .004 .537 -.005 .010
32
Table 5: Tests of between-subjects effects and the analysis of variance table of mean
square, f-value and p-value.

Variable

Mean Square

F

P-value
Printer 0.011 152.60 <0.001
Surface 0.001 4.22 0.047
Printer *Surface

0.001 1.37 0.249

33
Figure 1: Virtual reference denture base.

34
Figure 2: Asiga MAX/MAX UV Printer (Asiga).

35
Figure 3: Cara Print 4.0 Printer (Kulzer).

36

Figure 4: Asiga MAX/ MAX UV printer - virtual reference denture base with supports
(frontal view).

37

Figure 5: Cara Print 4.0 printer - virtual reference denture base with supports (frontal view).

38

Figure 5: Asiga MAX/ MAX UV printer - virtual reference denture base with supports
(bottom view).

39

Figure 6: Cara Print 4.0 printer - virtual reference denture base with supports (bottom
view).

40

Figure 7: Dentca denture base II, shade: original pink (Dentca).

41

Figure 8: Asiga MAX/ MAX UV printer sample with support structure (frontal view).

42

Figure 9: Cara Print 4.0 printer sample with support structure (frontal view).

43

Figure 10: Asiga MAX/ MAX UV printer sample with support structure (posterior
view).

44

Figure 11: Cara Print 4.0 printer sample with support structure (posterior view).

45

Figure 12: Cara Print 4.0 printer sample: a, intaglio surface. b, cameo surface.

A B
46

Figure 13: Asiga MAX/ MAX UV printer sample: a, intaglio surface. b, cameo surface.

A B
47

Figure 14: Flowchart of the study protocol.

PVS impression
3D scan data of the PVS impression
Virtual reference model of edentulous
maxilla - STL file
Scanning of the PVS impression by desktop 3D scanner
CAD - DENTCA denture design software
Printed denture base n=10 Printed denture base n=10
3D scan data of all printed samples
Surface matching by superimposition of
the STL files of all printed samples with
STL file of reference denture base
Edentulous patient – Edentulous Maxilla
Scanning all printed samples by desktop scanner
Virtual reference denture base - STL file
CAD - DENTCA denture design software
Asiga MAX/MAX UV Printer Cara Print 4.0 Printer
48

Figure 15: Mean absolute deviation and 95% confidence interval of both printers.

49

Figure 16: Mean absolute deviation and 95% confidence interval of both printers at
intaglio and cameo surfaces.

50

Figure 17: Color-coded 3d surface deviation maps of one random sample from each group. a
and c: intaglio and cameo surfaces of dentures bases fabricated by Asiga MAX/ MAX UV
printer. b and d: intaglio and cameo surfaces of dentures bases fabricated by Cara Print 4.0
printer.

A B
C D

Abstract (if available)

Abstract Objective: The aim of this in vitro study was to assess the printing trueness of CAD-CAM maxillary complete denture bases fabricated by using two different 3D printers. ❧ Materials and methods: A maxillary complete denture base was digitally designed based on the virtual reference model of the maxilla which was obtained from scanning of a polyvinyl siloxane (PVS) impression of the edentulous maxilla of one patient. A total of 20 CAD-CAM maxillary complete denture bases were fabricated based on the virtual reference maxillary denture base from an ultraviolet light-curable resin material by utilizing two different Digital Light Processing (DLP) 3D printers (Asiga MAX/ MAX UV and Cara Print 4.0 printers). The intaglio and cameo surfaces of all printed complete denture bases were scanned and superimposed on the corresponding virtual reference maxillary denture base to assess the printing trueness of all printed maxillary complete denture bases using a surface matching software (Geomagic Qualify 12). Statistical analysis was conducted with two-way ANOVA and Tukey post-hoc, α=0.05. ❧ Results: The printing trueness of the maxillary complete denture bases fabricated by the Asiga MAX/ MAX UV printer was significantly more accurate than those fabricated by the Cara Print 4.0 printer (p<0.001). ANOVA test showed a significant effect of printers (p<0.001) and surface (p=0.047) with no significant interaction between printers and surface (p=0.249). ❧ Conclusion: There was a statistically significant difference in the printing trueness of CAD- CAM Maxillary complete denture bases fabricated by two different 3D DLP printers. The Asiga MAX/ MAX UV printer was more accurate than the Cara Print 4.0 printer in terms of the printing trueness of the intaglio and cameo surfaces. ❧ Clinical Significance: Additive manufacturing (AM) technique represented by digital light processing (DLP) 3D printer provide an appropriate method for fabricating CAD-CAM removable complete dentures. 3D printed CAD-CAM removable complete dentures can be considered a reliable alternative option for the edentulous patient offering the advantages of improved accuracy, less clinical time, and cost-effectiveness.

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Asset Metadata

Creator Ibrahim, Mostafa Jaleel (author)

Core Title Evaluation of the printing trueness of CAD-CAM maxillary complete denture bases fabricated by using two different DLP 3D printers

School School of Dentistry

Degree Master of Science

Degree Program Biomaterials and Digital Dentistry

Publication Date 10/05/2020

Defense Date 09/29/2020

Publisher University of Southern California (original), University of Southern California. Libraries (digital)

Tag 3D printers,additive and subtractive manufacturing,CAD-CAM complete dentures,digital light processing,OAI-PMH Harvest,PMMA material,surface matching,trueness

Language English

Contributor Electronically uploaded by the author (provenance)

Advisor Phark, Jin-Ho (committee chair)

Creator Email mjibrahi@usc.edu,mostafa.ibrahim@ibrahimdentoffice.com

Permanent Link (DOI) https://doi.org/10.25549/usctheses-c89-380628

Unique identifier UC11666398

Identifier etd-IbrahimMos-9027.pdf (filename),usctheses-c89-380628 (legacy record id)

Legacy Identifier etd-IbrahimMos-9027.pdf

Dmrecord 380628

Document Type Thesis

Rights Ibrahim, Mostafa Jaleel

Type texts

Source University of Southern California (contributing entity), University of Southern California Dissertations and Theses (collection)

Access Conditions The author retains rights to his/her dissertation, thesis or other graduate work according to U.S. copyright law. Electronic access is being provided by the USC Libraries in agreement with the a...

Repository Name University of Southern California Digital Library

Repository Location USC Digital Library, University of Southern California, University Park Campus MC 2810, 3434 South Grand Avenue, 2nd Floor, Los Angeles, California 90089-2810, USA