| Abstract | Augmentacija kosti oralno-kirurški je zahvat kojim se nadomješta nedostatan volumen bezubog čeljusnog grebena, najčešće s ciljem ugradnje dentalnih implantata. Augmentacijske tehnike kod horizontalnih koštanih defekata u suvremenoj oralnoj kirurgiji daju predvidljive rezultate, dok su rezultati kod opsežnijih vertikalnih i horizontalnih defekata manje predvidljivi, s manjim postotkom uspješnosti. Pored konvencionalnih tehnika koštane augmentacije, suvremena tehnologija otvara potencijalnu mogućnost upotrebe novih materijala i tehnika u regenerativnoj oralnoj kirurgiji. Razvojem biomaterijala omogućena je upotreba prirodnih i sintetskih polimera u biomedicini, s velikim potencijalom u koštanoj regeneraciji. Svrha ovog rada bila je istražiti i analizirati učinkovitost 3D tiskane individualne biorazgradive augmentacijske mrežice (IBAM) izrađene od polilaktične kiseline (PLA) putem uspostave procesa izrade, definiranja pravila dizajna i laboratorijskih ispitivanja mehaničkih svojstava prototipa
IBAM-a u dinamičkim in vitro uvjetima. Odabirom ciljnoga gradivnog materijala omogućena je izrada varijantne konstrukcije i definiranje pravila dizajna IBAM-a. Prvi korak uključivao je utjecaj procesa 3D tiska na osnovna mehanička svojstva PLA polimera. Nakon definirane orijentacije uzoraka u 3D tisku, computer-aided design (CAD) modeliranjem dizajniran je pojednostavljeni model IBAM-a, koji je omogućio laboratorijsko ispitivanje mehaničkih svojstava tijekom zadanog razdoblja od 16 tjedana u dinamičkim uvjetima. Prije laboratorijskih ispitivanja izvršena je analiza metodom konačnih elemenata (MKE) na osnovi definiranih rubnih uvjeta opterećenja. Dobiveni rezultati pokazali su kako planirani dizajn IBAM-a zadovoljava predviđena opterećenja. Nakon računalne analize MKE-om provedena su laboratorijska ispitivanja mehaničkih svojstava IBAM-a mjerenjem
tlačnog i vlačnog opterećenja. Uzorci su ispitani u razdoblju od 16 tjedana, simulirajući biorazgradnju otapanjem u Hankovoj izbalansiranoj otopini. Rezultati laboratorijskih ispitivanja pokazali su da zadana opterećenja i biorazgradnja nemaju statistički značajan učinak na mehanička svojstva IBAM-a. Ovo istraživanje postavlja IBAM kao potencijalno sredstvo u augmentaciji bezubog čeljusnog grebena i otvara nove mogućnosti u koštanoj regeneraciji. |
| Abstract (english) | Objectives: Bone augmentation is an oral surgery procedure that replaces bone where there is insufficient volume of the edentulous alveolar ridge and is most commonly used to enable the placement of dental implants. Augmentation techniques of horizontal defects give predictable results in contemporary oral surgery, while results in combined defects are less predictable, with a lower percentage of success. Titanium augmentation meshes and reinforced membranes play a key role in such defects, because of their mechanical properties that enable them to stabilize the bone transplant and provide a stable three-dimensional space for adhesion, proliferation, and differentiation of bone cells. Their main deficiency is the non-resorbable aspect and the need for another explantation surgical procedure. The development of biomaterials has enabled the use of natural and synthetic polymers in biomedicine, with great potential in bone regeneration. The aim of this research was to develop and determine the efficiency of 3D printed individualized biodegradable augmentation scaffold made of polylactic acid (PLA). The mechanical characteristics of the scaffold were evaluated under dynamic conditions, simulating biodegradation and the influence of masticatory forces.
Materials and methods: Synthetic PLA polymer Lactoprene® 7415 was the material of choice for the fabrication of individualized biodegradable augmentation scaffolds used in this research. Following material selection, a 3D printing process was established. The influence of the 3D printing process, specifically the orientation of samples, on the fundamental mechanical properties of the PLA polymer was examined in three different print orientations: flat, on-edge and upright. The following mechanical tests were performed: static tensile test, three-point flexural test and Charpy impact (V-notch) test. Five samples were fabricated in each of the mentioned orientations for each mechanical test. Static tensile and three-point flexural tests were conducted using the universal testing machine Inspekt table 50 kN. Fracture toughness was tested using a Charpy impact testing machine. The hardness of differently oriented samples was also measured using Zwick 3106 hardness tester. Additionally, equipment for filament extrusion was chosen to determine additional fabrication parameters for the raw PLA filament. After defining the sample orientation in 3D printing, a prototype of a PLA scaffold was designed through CAD modeling to allow laboratory testing of mechanical characteristics. The scaffolds were 3D-printed using a MakerBot Method X Carbon fiber printer. The FEM model was proposed to simulate the structural behavior of the PLA scaffold prior to the mechanical tests, enabling a realistic simulation of the scaffold’s response under different loading conditions simulating masticatory forces. The purpose of the FEM analysis was to determine whether the scaffold could
withstand the required forces. Two different loading scenarios were used for the simulation of occlusal and lateral masticatory forces and their effects on the stress and deformation of the PLA scaffold. Universal testing machine Inspekt table 50 kN was used for compression tests. The values of 150 N for occlusal load and 50 N for lateral load were determined. Mechanical characteristics of 3D-printed scaffolds were evaluated under dynamic in vitro conditions for a total period of 16 weeks. A total of 54 scaffolds were 3D-printed and divided into two groups of 27 scaffolds according to the mechanical testing procedures (occlusal and lateral). In each of the main groups, nine subgroups of three scaffolds were formed for different testing periods. Following the compression testing procedure of the initial subgroup of dry scaffolds, the rest were soaked in Hank’s balanced salt solution (HBSS) for 16 weeks. HBSS served as a dissolving agent simulating biodegradation. Both occlusal and lateral compression tests were performed every 2 weeks on scaffold subgroups.
Results: The initial mechanical tests for raw PLA filament showed tensile strength values of 49.96 ± 0.54 MPa. Regarding the influence of sample orientation on fundamental mechanical properties of the PLA polymer, maximum tensile strength values were recorded for flat oriented PLA samples (34.1 ± 1.4 MPa). Tensile strength observed for on-edge oriented samples was 28.28 ± 1.41 MPa, while the lowest values and the widest scattering of results (9.74 ± 5.31 MPa) was recorded for upright positioned samples. The three-point flexural test results were analogous to the mentioned results, where the flat oriented samples again achieved maximum forces and flexural strength values. Fracture energy values obtained by Charpy impact test were highest for on-edge oriented samples (0.41 J). Flat oriented samples gave the similar fracture energy of 0.40 J. The hardness test was the only mechanical test where upright positioned PLA samples performed the best (HR = 0.26). Based on the results of initial mechanical tests, the flat orientation was chosen for 3D printing of the PLA scaffold model. The results of the FEM analysis showed that the PLA scaffold was able to withstand both occlusal
and lateral forces without breaking or deformation exceeding 4 mm. The maximum stress for occlusal loading was 151.9 MPa, with maximum displacement of 1.88 mm. A laterally loaded PLA scaffold withstood maximum stress of 252 MPa with 2.51 mm displacement. Finally, compressive modulus of the scaffolds calculated using force displacement graphs for both
lateral and occlusal mechanical tests showed no statistically significant difference among time points (p = 0.119 for occlusal, and p = 0.175 for lateral compression tests).
Conclusion: According to the findings of this research, the biodegradation process, coupled with occlusal and lateral loads, did not exert a statistically significant impact on the mechanical characteristics of the individualized biodegradable augmentation scaffold. The scaffold was able to withstand determined forces during the 16-week period of biodegradation in vitro. Considering the limitations of this study, the PLA augmentation scaffold nevertheless represents a viable solution from a mechanical point of view. Despite these results, it is imperative to acknowledge the complexities that persist in clinical application. These findings give important evidence to support further studies with the intention of creating a standardized protocol for clinical use. |
