Eastman Institute for Oral Health, Periodontology Resident
Dental implants are used in dentistry to replace missing teeth. Implants integrate into the jawbone through a process called osseointegration. Branemark first described osseointegration as the direct contact of bone with the implant under load. This is without intervening soft tissue. There are many factors to consider when treatment planning for dental implants. These include both systemic and local risk factors of the particular patient as well as characteristics of the implant itself. Additionally, there are many different designs of implants, including different thread size and topography. Implant surface characteristics are a crucial element when considering implants as a treatment modality. A rough implant surface is thought to increase bone to implant contact and, therefore, promote osseointegration. There are many ways to roughen the surface of a dental implant, including acid-etching and sandblasting.
For this project, a failed dental implant with unknown material and an unused dental implant were imaged using scanning electron microscopy. These dental implants were compared to study the surface characteristics. Also, identification of the composition of the unknown material was done.
Several techniques were used in the process of studying these samples. The first was sample preparation with sputter coating to prepare the used implant with unknown material for microscopy. The dental implants were imaged using secondary electron imaging with both the secondary electron and backscattered electron detectors. Energy dispersive x-ray spectroscopy was used to determine the elemental composition of implant surfaces. Elemental maps were done of the failed dental implant with unknown material. Finally, an image of the unknown specimen was colorized using Adobe Photoshop.
Prior to any electron imaging, the failed implant with unknown material required some preparation.
In preparation for SEM imaging, the samples were mounted on stubs using carbon tape and graphite adhesive glue. Once secured on the stub, the failed implant with unknown material was sputter coated with 60 Angstroms of gold/min at 15 mA current. Dental implants themselves are a conductive surface. Thus, coating the unknown material was important for preventing charging of the sample and increasing the number of secondary electrons emitted from the sample.
Scanning electron microscope (SEM) is an instrument used to produce high resolution images of a sample surface using electrons. Imaging of a sample can be obtained through several different mechanisms including the signal from secondary electrons (SE2) as well as using backscattered electrons (BSD). They are commonly used for imaging the surface structure of materials. All images were collected on a Zeiss Auriga CrossBeam SEM-FIB at the University of Rochester.
The SE2 and BSD detectors were used to collect images of both the failed and unused dental implant.
From the images obtained from the secondary electron detector, the macrotopography of the dental implants can be appreciated. The failed dental implant appears to have spiral threads, with the depth between each thread being larger than that of the unused dental implant. The unused dental implant has more square shaped threads with decreased distance between the threads. In general, the larger the surface area of the threads, the greater bone-to-implant contact. The microtopography of the dental implants can also be appreciated. A moderately rough surface seems to be the best for use in dentistry, especially if the bone quality of the patient is poor or if the patient has parafunctional habits.
The back scattered electron signal shows “phase” contrast in a sample, because it is caused by the collision of the primary electron beam with the nucleus in the sample. The higher the atomic number phase, the more backscattering produced. This is because there are more collisions likely when the nuclei, and therefore, the atomic number, are larger. More backscattering corresponds to a brighter image. From the backscattered images shown, it can be seen that the failed dental implant has different materials on top of the surface of the implant. The surface of the implant appears brighter, corresponding to a higher atomic number element. The unknown material appears dark, corresponding to a lower weight element.
Energy dispersive spectroscopy is a technique used to analyze the elemental composition of the sample. In this technique, the x-rays are arranged according to their atomic number and energy. The y-axis of an EDS analysis shows the number of x-rays processed by the detector. The x-axis shows the energy level of those counts. This was done with EDAX-EDS. Dental implants are mostly made from grade IV commercially pure titanium. When exposed to the environment, an oxide layer develops which promotes integration into the bone by absorption of calcium and phosphate ions. Spot identification of the unknown specimen on the used implant shows calcium and phosphorus which is consistent with the implant still having a piece of bone attached to it. The main inorganic portion of bone is formed from salts of calcium and phosphorus forming hydroxyapatite. It is important to note that since this is a failed implant, there is a chance that it can be calculus, which is calcified bacterial plaque also made of hydroxyapatite. However, the images and location of the specimen on the implant are more consistent with that of bone. Elemental mapping was also completed to show the distribution and proportion of the previously identified elements over a certain area. The results showed that the majority of calcium and phosphorus in the area of the unknown specimen, while the titanium, was mainly in the area surrounding the specimen which corresponds to the implant surface. Oxygen, nitrogen and carbon were also identified throughout the sample.
Adobe Photoshop was used to colorize the unknown specimen on the failed dental implant. The roughened surface of the dental implant can be appreciated in the background of the image.
Studying dental implants through microscopic techniques allowed for visualization of the rough surface characteristics of the dental implants, the design of the threads, and possible identification of a specimen remaining on a failed dental implant. Elemental analysis showed that the unknown specimen was composed of calcium and phosphorus mainly, which could be due to bone remaining on the dental implant or perhaps a piece of calcified plaque. However, the location of the specimen on the implant is more consistent with bone.
I would also like to thank my instructor, Brian McIntyre and my TA, Caleb, for guidance with the course, project and SEM labs.