Design and Manufacturing of Spatially Distributed and Interconnected Porous Architectures for Smart Dental Implants

Abstract

Dental implants serve as a prosthetic for missing teeth, aimed to replicate the natural tooth function. Titanium is the preferred material in the dental implant industry due to its biocompatibility with natural bone. Despite their widespread use, high associated risks persist, often detectable only long after insertion. Significant failures arise during the wound healing or bone remodeling phase accompanied by common occurrences of bone loss. Peri-implantitis, occurring post-insertion, leads to progressive bone loss attributed to a significant stiffness mismatch between the titanium implant and mandibular/maxillary bone. This mismatch creates non-uniform stress distributions, forming stress shields at the interface between the dental root and patient bone resulting in bone resorption. Additionally, edentulous patients with preexisting diseases causing low quality of bone, face even higher risks and, in some instances, are ineligible for dental implants due to weak metal-natural bond formation during the wound healing phase. Recent research focuses on inducing interconnected porous networks to encourage bone ingrowth and reduce stiffness to mimic bone properties. Pore characteristics, encompassing size, interconnectivity, porosity, and architecture, significantly influence cell attachment and mechanical structure properties. While existing research explores various porous architectures, a notable gap exists in comprehensive studies that evaluate and compare thier biological and mechanical performance. This work presents a novel approach to designing and additively manufacturing (3D printing) a titanium dental implant. The design incorporates an embedded spatially distributed and interconnected microporous architecture with functionally graded properties that closely replicate the physical, biological, and mechanical behavior of bone. Two optimal porous architectures for biomedical applications, the triply periodic minimal surface (TPMS) gyroid variants and Voronoi stochastic are compared based on manufacturability, cell infiltration and adhesion, simulation, and compression testing. Understanding the impact of additive manufacturing on porous structure resolution facilitates the optimization of porous architectures and geometries. Using computer-aided design (CAD), the TPMS gyroid and Voronoi stochastic structures were modeled. A study on the feasibility of 3D printing porous titanium structures determined that the most favorable porous interconnectivity and distribution were achieved at a pore size of approximately ≥250µm. Subsequently, porous constructs were fabricated based on manufacturability for a set of in-vitro experiments, wherein a variant of the TPMS gyroid demonstrated superior cell adhesion and proliferation. Given its outperformance in biologically and manufacturing aspects, The TPMS solid gyroid variant underwent mechanical testing at a range of pore size and porosity combinations to produce a functionally graded porous structure. The mechanical behavior is validated from a 2D digital image correlation developed compression test, micro computed tomography (micro-CT), and microscopy. Ultimately, the TPMS solid gyroid structures with a gradient of pore size (6-34%) and porosity (approximately 100-400 µm) demonstrate promising results. In summary, this dissertation developed a framework for fabricating a functionally graded porous dental implant with enhanced biological and mechanical properties, along with methods for comprehensive characterization.