In the present investigation, spring specimens were 3D printed using MAX (Asiga, Sydney, Australia) with DLP (digital light processing) technology via the experimental flexible printable material (Code:BM2008, GC, Tokyo, Japan) which contains a 3D resin material as its main ingredient. The specimens were designed by the computer aided program Autodesk Netfabb (San Rafael, CA, USA). The post processing of the specimens was performed by GC-Europe according to the manufacturer’s instructions. Unheated ultrasonic bath (Bandelin, Berlin, Germany) reusable isopropanol solution with a concentration of 96% was utilized to clean the specimens for 2 minutes followed by 2 more minutes of a clean isopropanol bath with the same concentration.
The specimens were withdrawn from the solution and dried with compressed air in-between the two cleaning cycles. Surface polymerization was done using Labolight DUO (GC, Tokyo, Japan) with double wavelength LED technology in a range of 380nm – 510nm with spectrum range peaks of 465nm - 485nm (12 Blue LED’s) and 390nm - 400nm (3 Violet LED’s). Two periods of 3-minute durations each were applied, and the samples were turned for curing from both sides. After post curing, carbide bur and nipper were used to remove supports.
After eliminating all specimens’ printable supports, the specimens were divided into three different groups according to their different design parameters, control group (n=18), length group (n=19) and thickness group (n=22) (Table 1 & Figures 1-3). The specimen groups did not have equal numbers due to springs destruction during the post-processing.
Group
|
Control group
|
Length group
|
Diameter group
|
Specimens
|
18 specimens
|
19 specimens
|
22 specimens
|
Feature
|
Two identical springs
|
different coil numbers
|
different coil radius
|
(n1 = 4, n2 = 6)
|
(Δρ = 0.15mm)
|
Table.1: Overview of the group classification
The control group consisted of the same material and design parameters used in recent study conducted by Othman et al. who found that the 3D resin used material provides an acceptable force in comparison to NiTi material (16). Accordingly, the control group was characterized by two in design identical springs with radius 0.75 and four coils, while the length group was characterized by two springs with a difference in coil-number (n1 = 4, n2 = 6) and the diameter group was defined by two coils with different radius (Δρ = 0.15mm).
A reference key was designed using Autodesk Netfabb (San Rafael, CA, USA) and printed with the Varseowax Model material using Varseo S 3D printer (BEGO, Bremen, Germany), which acted as a spring’s attachment to the torque measuring device (Sauter DB 0.5-4, Grindelwald, Switzerland) in which the values were automatically recorded with an implemented software in the device itself. In order to assure pointed force exertion upon the springs base, a C shaped 3D printed key was loaded into the universal testing machine (Z010 Zwick/Roell, Ulm, Germany). The C shaped key was designed using Autodesk Netfabb (San Rafael, CA, USA) and printed with the Varseowax Model material using Varseo S 3D printer (BEGO, Bremen, Germany). (Figure.4)
Parameters for the universal testing machine were predefined by speed starting position with 50 mm/min and 5 seconds holding time for torque measuring between the clockwise and counter clock wise directions. In the torque measuring device, the reference key which acted as a holder for the specimens was attached to the device and loaded in the universal testing machine for measuring both directions for five cycles each (Figure.4). All results of both clockwise and counter clockwise force exertion was recorded in N (Newton) using the torque measuring device itself which has an internal software for displaying the values and the maximum for each specimen were recorded.
Descriptive analysis:
Results were divided in the three groups: control, length and thickness with clockwise as well as counter clockwise testing for each of the three groups. Statistical analysis was performed via Steel-Dwass test which is primary used to evaluate non-parametric distributions of multiple comparisons to determine which ones are different. Accordingly, in this study the median values of the three groups in both testing direction were compared (p<0.001).