Comparative Study of Retention of Mandibular Denture Bases Three-dimensional (3D) Printing Technique and Metal-reinforced Acrylic Resin
Phase: NA
Conditions: Edentulous Alveolar Ridge
Sponsor: National Research Centre, Egypt

 
 
 
 
 
 
 
 
Comparative study of retention of 
mandibular denture bases three-
dimensional (3D) printing technique 
and metal-reinforced acrylic resin 
 
 
21/7/2022 
 
 
 
 
 
 
 

 
Abstract  
Objective: retention evaluation of mandibular complete denture fabricated by different method 
Methods: This in-vivo study was conducted over mandibular complete denture for completely edentulous 
patients.  This study consisted of 2 groups according to method of fabrication of mandibular complete 
denture: Group I: mandibular complete denture fabricated by 3D printing technique, Group II: mandibular 
complete denture with metal reinforced fabricated by conventional technique. Retention were evaluated 
for both groups 
Results:  
Conclusion:  
 
Keywords: complete denture, metal reinforced denture, retention, Digital, 3D printing 
 
 
 Introduction:  
 
Edentulism has been a serious public health problem in industrialized countries 
due to population aging and in developing countries due to poor oral care. The life 
quality and nutrition intake are impacted for edentulous patients due to edentulism. 
Despite an anticipated decrease in the age-specific rates of edentulism, the demand 
for complete dentures will continuously increase in the next decades (1). Edentulism 
is even classified as a physical handicap by the World Health Organization (2).  
Retention plays a vital role in the success of the complete denture, and therefore 
every stage of denture construction should be given due importance. Effective 
retention is attained by the close mucosal contact of the denture base. Polymethyl 
methacrylate (PMMA) is the material of choice for the fabrication of the majority 
of dentures. During the polymerization process, dimensional shrinkage of the resin 
occurs. Shrinkage, which is caused by the differences in the densities of the 
monomer and the polymer, results in a lifting of the denture base away from the 
posterior palate as a result of polymerization (3). 
Alternative materials and techniques are available to overcome the 
shortcomings of heat cured PMMA, including metal alloys and digital technique. 
Metal alloys, offer superior mechanical and physical properties in comparison with 
PMMA. They are stronger, with higher fatigue and fracture strengths. In addition, 
they can be cast in thin sections without compromising their rigidity or fracture 
resistance. This property, in addition to their high thermal conductivity, provides 
patients with a natural “feel” to the prosthesis (4).  
Metallic denture bases are also biocompatible, dimensionally stable with high 
surface polish which facilitates hygiene maintenance. They are particularly useful 

in situations with high risk of fracture that require strengthening of the denture 
base, as in cases with bruxism or in single maxillary dentures (5). 
CAD- CAM technology has been widely used in the field of prosthodontics. 
Construction of complete denture using CAD- CAM is characterized by ease of 
fabrication with reduced laboratory procedures. It also leads to higher dimensional 
accuracy and standardized fabrication (6). 
Digital design ensures consistent thickness of denture bases which can be 
adjusted and kept minimal. In addition, the presence of digital data enables future 
fabrication of dentures in case of lost ones (7). 
Al helal in 2017 stated that the retention of milled dentures from pre-
polymerized poly-methyl methacrylate is better than that of conventional heat 
polymerized acrylic resin due to less polymerization shrinkage with subsequent 
superior adaptation. (8) 
 
            Soygun et al in 2013  compared the mechanical properties of polyamide 
with the conventional PMMA and fiber reinforced PMMA denture base materials; 
it was revealed that the polyamide denture base material had the highest transverse 
strength, without any fracture. It was also observed that the values of maximum 
impact strength were the highest for polyamide (9) 
 
Retention measured by Strain gauge which is a sensor device which is used 
to convert force, pressure and tension (mechanical strain) in to change in electric 
resistance (voltage output) that can be measured, it can be used in in-vivo and in-
vitro studies.(10) 
 
 
Materials and Methods:  
Study design: 
The National Research Centre's Medical Research Ethics Committee accepted the research 
protocol on 21/07/2022 (no. of approval: 8887082022). 
Completely edentulous patients were selected from the outpatient clinic of the 
Medical Excellence Centre of the National Research Centre, Cairo, Egypt and 
College of Oral and Dental surgery, Misr University for Science and technology 

according to the following inclusion criteria: patients aged from 45-75 years and 
had been completely edentulous for a minimum period of 1-year, normal 
maxillary-mandibular relationship, healthy mucosa, and normal salivary flow. 
While the exclusion criteria were: smoker patients or patients having hard or soft 
tissue pathology, severe ridge undercut, and patients who had received radiation to 
the head and neck region. 
This study divided into 2 groups according to type of denture received by the 
patients: 
Group I:  Patients received maxillary and mandibular rapid prototype complete 
denture  
- Retention was measured at time of insertion and after 3 weak and after 6 
weak  using the retention force gauge device 
 
Group II: Patients received mandibular complete denture constructed from 
polyamide reinforced with metal frame work and maxillary dentures constructed 
from conventional Poly-Methyl Methacrylate  
- Retention was measured at time of insertion and after 3 weak and after 6 
weak  using the retention force gauge device 
 
Sample Size Calculation: 
A total sample size of 12 will be sufficient with the power of 80% and 5% significance level. 
This number will be increased to 20 (10 in each of the two groups) to compensate for follow-up 
losses. The sample size was determined through the application of the G Power program. 
Construction of the 3D model: 
For rapid prototype complete denture base, Preliminary impressions was made 
using irreversible Hydrocolloid Alginate (Cavex Holland BV) then definitive 
impression and recorded horizontal relationship were done in one visit and sent to 
a digital laboratory for scanning and 3D printing of the CDs. 
 
The master casts were digitalized using and extraoral 3D scanner * , at which the 
cast holder used to fix the cast in place, 
The digital image (STL file) were imported to Exocad* digital design software to 
oriented the cast according to proposed insertion and removal pathway and to draw 
extension of denture base at the depth of vestibules and make design of denture 
base. 

Printing step: the designed denture base were export as STL file and sent to 3D 
printer software, the denture base were printed according to Digital Light 
projection (DLP) technology * using Next Dent Baes Liquid* which is a monomer 
based on acrylic ester. Then the denture base were finished and polished except 
area at crest of the ridge. 
Bite registration using printed denture base: wax occlusal rim were made on the 
printed denture base, then inserted in patient mouth to adjust lip support and 
vertical diminution and for registration jaw relation (centric relation) 
Setting artificial teeth were carried on the same way as in conventional complete 
denture, after try in maxillary and mandibular denture, the artificial teeth attached 
to digital denture base by self cured acrylic resin. 
Finally the finished denture was inserted in patient mouth to checking retention 
and stability and occlusion  
* info@doflab.com +82 70-5057-5577 601-602, 77, Seongdong-gu, Seoul, 04790 Korea 
* Exocad GmbH Julius- Reiber- StraBe 37 64293 Darmstadt Germany 
* Digital light projection (DLP): Mogassam Dentcase printer, Delaware, USA 
* Next Dent base liquid: by 3D systems, Soesterberg, Netherlands 
Construction of metal reinforced complete denture: 
Maxillary and mandibular preliminary impressions were made for each patient 
using irreversible hydrocolloid impression material (alginate) in stock tray then  
special trays were constructed for final impression registration. 
Centric relation at the proper vertical dimension of occlusion was recorded 
using wax wafer registration, and then Trial dentures were tried in the patient's 
mouth for appropriate vertical and horizontal maxilla-mandibular relation 
Finally, duplication of the master cast using silicon material was done to obtain 
a refractory cast for the construction of the metal framework 
Metal framework: Two rows of mesh wax pattern were adapted on the 
refractory cast, followed by spruing, investing, burning out and casting of the 
metal framework. 

The metal framework was returned in to the master cast and checked for 
adaptation. Sealing of the mandibular trial denture base to the master cast, 
waxing up and attaching the sprue formers was done to make the channels for 
injection of polyamide into mold, The cartridge was placed in a cartridge carrier 
which was then placed in electric cartridge furnace* used for softening of 
thermoplastic denture base material. The cartridge was placed on the inlet of the 
flask and was compressed in mechanical compressor.  
Finally Denture insertion was made checking extension, retention, stability and 
occlusion 
* Thermopress Flask, Bredent, GmbH, Senden/ Witzighausen, Germany 
Retentive force Measurements 
The measuring device used to meseaure retention is Digital force gauge *(is an 
advanced type of force meter device used to Measure Tension or Compression 
force. 
After determining the geometric center for mandibular denture, then mark a point 
on the plaster base. 
Three “V” shaped grooves were created on the polished surface of the lower 
denture. (Two grooves were created at the retromolar pad area just distal to the 
second molar of both sides. The other one was made on the lingual flange at the 
midline region below the central incisors) 
A wrought wire of 1 mm in diameter was then bent at its center and adjusted so as 
not to encroach on the tongue space and to run 2 cm above the occlusal plane from 
the retromolar pad groove of one side to the retromolar pad groove of the other 
side. 
                                                          
* Digital Force Gauge EXTECH 475044.   

Then free ends of the three wires were then fixed to the polished surface of the 
lower denture by self-cured acrylic resin.  
Retention of mandibular dentures was assessed as follows: 
After denture insertion, The metallic probe of the digital force-meter was then 
attached to the c-shaped metal hook created at the geometric center of the 
mandibular dentures and a vertical pulling force was applied to measure denture 
retention. Retention strength was measured in newtons.  
 
Statistical analysis:  
All data were presented as mean &standard deviation. Data were presented 1 
table & 1 graph. Statistical analysis was performed with SPSS 16 ® (Statistical 
Package for Scientific Studies), Graph pad prism & windows excel 
Exploration of the given data was performed using Shapiro-Wilk test and 
Kolmogorov-Smirnov test for normality which revealed that the significant level 
(P-value) was insignificant as P-value > 0.05 which indicated that all data 
originated from normal distribution (parametric data) resembling normal Bell 
curve.  
Accordingly, comparison between different groups was performed by using 
Independent t-test, while comparison between different intervals was performed by 
using One Way ANOVA test followed by Tukey`s Post Hoc test for multiple 
comparisons. 
Effect of time (table 1 and figure 1): 
In group I, there was a significant difference between all intervals as P<0.05, 
at  delivery was significantly the lowest retention (10.58 ± 0.31), while there was 

insignificant difference between after 3 months (11.92 ± 0.56) and after 6 months 
(12.17 ± 0.49) with 15.9% percent of increase in retention for 6 months. 
In group II, there was a significant difference between all intervals as 
P<0.05, at  delivery was significantly the lowest retention (16.54 ± 0.52), then after 
3 months (18.49 ± 0.58), while after 6 months (19.87 ± 0.59) was significantly the 
highest with 20.00% percent of increase in retention for 6 months. 
Effect of different construction techniques (table 2 and figure 2): 
Comparison between group I & II revealed that group II was significantly 
higher than group I at all intervals as P <0.05 
 
Table (1): Mean and standard deviation of retention in both groups and 
comparison between different intervals with percent of change in each group: 
  
Follow up 
M 
SD 
% change 
P value 
Group I   
(3D printed 
denture) 
At delivery 
10.58 a 
0.31 
15.90% 
<0.0001* 
After 3 weeks 
11.92 b 
0.56 
After 6 weeks 
12.17 b 
0.49 
Group II  (metal 
reinforced 
denture) 
At delivery 
16.54 a 
0.52 
20.00% 
<0.0001* 
After 3 weeks 
18.49 b 
0.58 
After 6 weeks 
19.87 c 
0.59 
M: mean            SD: standard deviation       *Significant difference at P <0.05 
Means with different superscript letters were significantly different as P <0.05 
Means with the same superscript letters were insignificantly different as P >0.05 
 

 
Figure (1): line chart representing retention changes of both groups during different intervals. 
 
 
Table (2): Comparison between group I & II regarding retention at 
different intervals using Independent t-test: 
  
 Interval 
N   
Group I 
Group II 
Independent t-test 
P value 
MD ± SEM 
95% CI 
M 
SD 
M 
SD 
L 
U 
At time delivery 
7 
10.58 
0.31 
16.54 
0.52 
0.0001 * 
5.9 ± 0.2 
5.4 
6.4 
After 3 weeks 
7 
11.92 
0.56 
18.49 
0.58 
0.0001 * 
6.6 ± 0.3 
5.9 
7.2 
After 6 weeks 
7 
13.24 
0.49 
19.87 
0.5 
0.0001 * 
6.63± 0.3 
6.05 
7.21 
M: mean            SD: standard deviation       *Significant difference at P <0.05 
Difference between means (B - A) ± standard error of mean 
CI: confidence intervals at 95% (U; upper / L: lower) 
 
0
5
10
15
20
25
At time delivery
After 3 weeks
After 6 weeks
Mean 
Retention 
Group I
Group II

 
 
Figure (2): Bar chart representing retention in both groups. 
 
 
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