Process planning for the rapid machining of custom bone implants

This thesis proposes a new process planning methodology for rapid machining of bone implants with customized surface characteristics. Bone implants are used in patients to replace voids in the fractured bones created during accident or trauma. Use of bone implants allow better fracture healing in the patients and restore the original bone strength. The manufacturing process used for creating bone implants in this thesis is highly automated CNC-RP invented at Rapid Manufacturing and Prototyping Lab (RMPL) at Iowa State University. CNC-RP is a 4th axis rapid machining process where the part is machined using cylindrical stock fixed between two opposing chucks. In addition to conventional 3 axes, the chucks provide 4th rotary axis that allows automated fixturing setups for machining the part. The process planning steps for CNC-RP therefore includes calculating minimum number of setup orientations required to create the part about the rotary axis. The algorithms developed in this thesis work towards calculating a minimum number of orientations required to create bone implant with their respective surface characteristics. Usually bone implants may have up to 3 types of surfaces (articular/periosteal/fractured) with (high/medium/low) finish. Currently CNC-RP is capable of creating accurate bone implants from different clinically relevant materials with same surface finish on all of the implant surfaces. However in order to enhance the functionality of the bone implants in the biological environment, it is usually advisable to create implant surfaces with their respective characteristics. This can be achieved by using setup orientations that would generally isolate implant surfaces and machine them with individual finishes. This thesis therefore focuses on developing process planning algorithms for calculating minimum number of orientations required to create customized implant surfaces and control related issues. The bone implants created using new customization algorithms would have enhanced functionality. This would reduce the fracture healing time for the patient and restore the original bone strength. The software package created using new algorithms will be termed as CNC-RPbio throughout in this thesis The three main tasks in this thesis are a) calculating setup orientations in a specific sequence for implant surfaces b) Algorithms for calculating a minimum number of setup orientations to create implant surfaces c) Machining operation sequence. These three research tasks are explained in details in chapter 4 of this thesis. The layout of this thesis is as follows. Chapter 1 provides introduction, background and motivation to the research in this thesis. Chapter 2 provides a literature review explaining different researches conducted to study the effects of different surface finish on the bone implants on their functionality. It also presents different non-traditional and RP techniques used to create bone implant geometries with customized surfaces, their advantages and limitations. Chapter 3 gives the overview of process planning algorithms used for CNC-RP and those needed for CNC-RPbio. Chapter 4 is the main chapter of the thesis including process planning algorithms for rapid machining of bone implants with customized surfaces using CNC-RP in details, while Chapter 5 provides Conclusions and Future work

Durable antimicrobial and superhydrophobic cotton fabrics

&nbsp;In this study, a durable dual functional (antimicrobial and superhydrophobic) coating for cotton fabrics was developed. A novel one-step coating method was devised which is simple and easy for scaling up for bulk-scale production. The fabrics have potential application in a hospital environment to contain the threat of nosocomial infections.<br /

Quantitative assessment of covariants of root canal treatment efficacy in human teeth

Clinically relevant cofactors that can demonstrate aspects of root canal treatment quality are of importance to clinicians, researchers and dental instrument manufacturers. Endodontics has been one of the most developing fields of dental science in recent years. There have been new instruments, materials, and methods introduced, which have been very rapidly adopted since most facilitate the root canal treatment process. Considering the current rate of technological developments and the long-term follow-ups required for clinical evaluation of root canal treatment success, clinical trials are not feasible for assessing every variable in treatment. In search of cofactors that could be used to demonstrate the efficacy and quality of a root canal treatment, the effect of surface roughness was investigated in the present thesis. Clinical relevance of surface roughness and its effect on endodontic treatments was assessed in the second chapter. This aim was achieved by comparing biofilm formation on rough and smooth dentine surfaces. Enterococcus faecalis was the microorganism tested to form biofilms on these surfaces because of its role as one of the most important endodontic pathogens in persistent endodontic infections. A novel methodology utilizing flow cytometry to quantify bacteria attached to the surfaces was designed for this experiment. The results showed that rough surfaces harboured a significantly higher number of bacteria compared to smooth surfaces. This indicated that achieving a final smooth surface in root canal treatment reduces the chance of bacterial biofilm formation. Considering the wide range of instrument designs and functions that are used in endodontic treatments, the results demonstrated the necessity for further investigations into their effect on a treated canal's final surface quality. Practical aspects of root canal treatment that may be effective on the canal surface roughness were the focus of the next experiments of this thesis. The third chapter compares the effect of two different filing motions, continuous rotary and adaptive reciprocation, on root canal surface roughness. Continuous rotation and reciprocation are the two most frequently used filing techniques in root canal instrumentation. In this experiment, a filing system that was compatible to work in both rotary and adaptive reciprocation modes was used to answer whether filing motion can affect surface roughness of a root canal. Experiments showed that surface roughness was significantly higher overall in the root canals of teeth prepared with adaptive reciprocation compared to continuous rotary. The results of this chapter showed that roughness of the root canal is a cofactor that can be modified by the clinician. Treatment strategies with different techniques can be implemented even while using identical instruments to achieve smoother treated surfaces. Based on the findings of this study, using a continuous rotary system to prepare canals or to finish the cleaning and shaping stage of a root canal treatment can be beneficial to reducing roughness of the canal surface. Differences between filing systems consists of differences in a mixture of variables including alloy, surface treatment, cross-section, taper, motion, design, etc. The fourth chapter in this series was aimed to evaluate the effect of three different filing systems with different concepts, on the final root canal surface quality. Cleaning and shaping was carried out on teeth with either a single-file reciprocating (Reciproc), continuous rotary (HyFlex EDM) or oscillating self-adjusting file (SAF) system. The results from this chapter showed that the three completely different filing systems resulted in similarly rough root canal surfaces. The high level of roughness in all groups suggested that the three filing systems tested in this experiment were relatively aggressive. File wear results in reduced cutting efficiency and aggressiveness. Since each file undergoes a life cycle and it is eventually worn out, the fifth chapter of this thesis was designed to assess how the effect of file wear translates into changes on the treated root canal surface roughness. In order to evaluate the impact of file wear effectively, Reciproc single-file reciprocating instruments were used for this study. Reciproc files endure the same stress that is usually distributed among a number of files in multi-file systems. This study showed that the amount of wear during three uses, which is within the range of use recommended by the manufacturer, does not affect the final root canal surface roughness. Without consideration of safety of these files in terms of file separation risk, these files can be used up to three times while expecting a similar treatment outcome. However, similar to the previous study, these files left a relatively rough surface in all cases. The key findings in the present thesis were that root canal surface roughness is an effective and modifiable cofactor that can be used to determine the quality of root canal instrumentation and the performance of the instruments used. The two new methodologies developed can be used to test other available endodontic instruments and techniques. These methods can provide a foundation for generating comparable and quantitative data regarding the roughness values and thresholds associated with biofilm formation and different endodontic instruments. Standard levels can be set for future instrument designs once enough research is available regarding the performance of the current instruments and the ideal levels of surface roughness

An engineering perspective of ceramics applied in dental reconstructions

The demands for dental materials continue to grow, driven by the desire to reach a better performance than currently achieved by the available materials. In the dental restorative ceramic field, the structures evolved from the metal-ceramic systems to highly translucent multilayered zirconia, aiming not only for tailored mechanical properties but also for the aesthetics to mimic natural teeth. Ceramics are widely used in prosthetic dentistry due to their attractive clinical properties, including high strength, biocompatibility, chemical stability, and a good combination of optical properties. Metal-ceramics type has always been the golden standard of dental reconstruction. However, this system lacks aesthetic aspects. For this reason, efforts are made to develop materials that met both the mechanical features necessary for the safe performance of the restoration as well as the aesthetic aspects, aiming for a beautiful smile. In this field, glass and high-strength core ceramics have been highly investigated for applications in dental restoration due to their excellent combination of mechanical properties and translucency. However, since these are recent materials when compared with the metal-ceramic system, many studies are still required to guarantee the quality and longevity of these systems. Therefore, a background on available dental materials properties is a starting point to provoke a discussion on the development of potential alternatives to rehabilitate lost hard and soft tissue structures with ceramic-based tooth and implant-supported reconstructions. This review aims to bring the most recent materials research of the two major categories of ceramic restorations: ceramic-metal system and all-ceramic restorations. The practical aspects are herein presented regarding the evolution and development of materials, technologies applications, strength, color, and aesthetics. A trend was observed to use high-strength core ceramics type due to their ability to be manufactured by CAD/CAM technology. In addition, the impacts of COVID-19 on the market of dental restorative ceramics are presented

Strain Mapping in Teeth with Variable Remaining Tooth Structure

Problem: The effect of remaining tooth structure on strain in compromised teeth is not fully understood. Different remaining tooth quantities may affect stress and strain concentration within the remaining structure and potentially the longevity of the related restoration. Objectives: The aim of this project was to map and evaluate tooth strain levels at different stages and areas of structural tooth loss created by dental preparation (simulating caries created lesions) or soft drink demineralisation (simulating external acid erosion lesions), before and after restoration, and to evaluate and compare different strain measurement techniques: strain gauges (SG), the surface displacement field measured using digital image correlation (DIC), electronic speckle pattern interferometry (ESPI), and finite element analysis (FEA). In addition, testing teeth affected by erosion required testing and verifying different acid demineralisation protocols. Material and methods: Part I: Enamel samples (sound, polished) were subjected to extended 25 hours (hr) soft drink immersion protocols (accelerated, prolonged) with different salivary protection conditions (no saliva, artificial saliva, and natural saliva) to compare enamel surface loss. Moreover, enamel surface loss of extended erosion periods simulating different levels of clinical erosion lesions was calculated by different imaging methodologies. Microscopic analysis was performed to compare subsurface changes of early and extended erosion protocols. Part II: Strain under static loading was compared in teeth with different stages of unrestored occlusal and buccal accelerated soft drink demineralisation lesions and after restoration using different techniques (strain gauges, electronic speckle pattern interferometry, and finite element analysis). Part III: Strain under static loading was compared in prepared teeth with different remaining tooth dimensions and different restorations using strain gauges and digital image correlation techniques. Results: Part I: No statistical significance was detected in enamel thickness loss between sound and polished enamel samples in the accelerated erosion groups under all salivary conditions or between early and extended erosion groups tested. Part II: All testing methodologies measured an increased strain reading after 1 day in occlusal erosion group followed by gradual decrease, while, continuous increase in strain was observed with buccal erosion progression. For both groups, all restorative materials used were able to restore strain close to pre-treatment level. However, strain distribution pattern was more favourable in ceramic and gold occlusal onlays than composite onlays. Part III: for both strain gauges and digital image correlation, remaining tooth height ≥ 3 mm and width of 1 to 1.5 mm of the remaining tooth structure had a positive effect on strain. Tooth compositions of enamel and dentine resisted strain better than dentine counterparts at all dimensions. Both core restorations (with and without cuspal coverage) were found to support the remaining tooth structure and reduce strain. However, only cuspal coverage recorded significantly lower strain than their unrestored counterparts. Conclusion: Restorations bonded to advanced erosion induced lesions restored strain levels to pre-treatment condition and produced a more favourable strain distribution pattern highlighting the role of adhesion in reducing strain. Remaining tooth structure suffers less strain under loading when enamel is part of the structure and when the minimum dimension of 3 mm in height and 1.5 mm in width is preserved. Bonding of core restoration or cusp coverage aids in reducing strain under loading. All strain measuring methodologies were comparable, where similar strain behaviour was recorded. Remineralisation of enamel and dentine is effective in the management of initial erosion

A Comprehensive Review on AISI 4340 Hardened Steel: Emphasis on Industry Implemented Machining Settings, Implications, and Statistical Analysis

Turning of hardened AISI 4340 steel is regarded as one of the demanding challenges in machining sectors where precision tolerances are essential for automobile parts. The AISI 4340 steel is broadly utilized in forged steel automotive crankshafts systems, hydraulic forged and additional machine tool purposes because of their improved characteristics.&nbsp; Moreover, one of the keys confronts in the machining of hard 4340 steel is the comparatively deprived machining behavior that reduces the functionality of the material and further leads to component&nbsp; rejection at the final inspection stage. In addition, accelerated tool wear necessitates for repeated changing of cutting tool that results in higher machining and tooling costs. This comprehensive review aimed to present in-depth features on the development of machining performances using various cutting tools. This review focus is to provide a broad perceptive of the role of controllable variables during machining of hardened steel. This review analysis examines the response variables and its advantages on chip morphology and heat generation. The comprehensive overview of machining settings, key machinability indicators and statistical analysis for AISI 4340 steel has been presented. This overview will provide academic, industrial and scientific communities with benefits and shortcomings through improved conceptual understanding towards further research and development