Messung der Knochendichte durch intraoralen Ultraschall für eine sichere Implantatinsertion
In der Ausgabe 2-2021 des englischsprachigen Magazins ceramic implants ist Dr. Johann Lechner mit einem Fachbeitrag zum Thema „Messung der Knochendichte durch intraoralen Ultraschall für eine sichere Implantatinsertion“ vertreten:
In the medical field, ultrasonography is widely used to image various types of soft tissue. In principle, images of structures in the body are generated by analysing the reflection of ultrasonic waves. To derive useful information concerning the status of jawbone, different ultrasonic techniques must be employed, as the ultrasonic waves are almost completely reflected at the bone–soft-tissue interface. The in vivo measurement of ultrasonic velocity in human cortical bone was introduced as a rapid, reliable and non-invasive method which could be used to analyse the mechanical properties of bone. Is a newly available ultrasonic device for the radiation-free measurement of bone density (CaviTAU®; Digital Dental & Healthcare Technology) suitable for visualising the condition of jawbone density?
Is the jawbone ready for implant insertion?
Researchers have reported microscopically proven chronic ischemic/inflammatory or fatty degenerative osteonecrosis of the jawbone (FDOJ):2 FDOJ was found in > 50% of 154 clinically and radiographically unremarkable edentulous jaw areas into which dental implants were to be placed. The following question is therefore justified: can aseptic bone necrosis pose a risk to implant placement? The currently available literature offers an insight into anecdotal reports of “poor quality” alveolar bone discovered during implant surgery in edentulous sites. This poses a risk for the uninterrupted osseointegration of implants. Aseptic bone necrosis has been reported after surgery, trauma and immunosuppressive therapy. The evolution of aseptic necrosis is documented in the
maxillomandibular region, particularly after osteotomies. It has been found that micromotion of implants in soft bone is consistently high and that this can result in failed osseointegration. Scientists—such as those who have reported FDOJ from the Division of Periodontics of the University of Maryland School of Dentistry in Baltimore in the US1—speak of the phenomenon of a chronic ischemic/inflammatory or FDOJ. This pathology is thus internationally recognised and was first included in the tenth revision of the International Statistical Classification of Diseases
under “aseptic ischemic osteonecrosis”.
Assessing stability of the bone bed with ultrasound
Whether implants can be embedded in the jaw for extended periods depends primarily on the condition of the bone. In the anterior of the lower jaw, conditions are usually ideal. However, in the upper jaw, the bone is naturally less dense. The dentist often only notices whether an implant will stay in place here when drilling or when cutting the thread for the implant into the bone, and
even this impression can be deceptive: “There is no reliable method for predicting the success of dental implant insertion before the dental procedure,” according to Prof. Robert Sader from the clinic for oral and facial plastic surgery at the Frankfurt university hospital in Germany. One solution is determining the density of the bone using ultrasound. This is because the propagation of ultrasonic waves in bone tissue depends on its density: the more stable the bone, the faster the waves move through it. Scientists at Johannes Gutenberg University Mainz have now investigated for the first time whether the method also allows conclusions to be drawn on the condition of the jawbone. Prof. Bilal AI-Nawas from the clinic for oral and maxillofacial surgery has investigated ultrasonic transmission velocity (UTV) in the lower jaw and pelvic bone of pigs. The results indicate that UTV is an accurate measurement of the level of mineralisation: bone sections with a critical bone density that would prohibit implant insertion were detected by the method in 75% of cases. Thus, determining the quality of the bone in the jaw with the help of ultrasound may even be more effective than radiography. Torque and UTV were used to assess the bone implant sites in these studies. UTV can be used to analyse the mechanical properties of the teeth after
in vitro, in situ and in vivo loading.
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