Researchers investigate possibility of regrowing teeth news For certain animals, the loss of teeth does not always pose a problem: sharks and crocodiles have the abil- ity to regrow their teeth repeatedly. Researchers from the Technische Universität Berlin (TU Berlin) are ex- ploring the possibility that this can be applied to humans and are work- ing on a new method to develop teeth from the human body’s own tissue. “It’s true that there are isolated reports of people growing third teeth or even a third complete set of teeth, but why this should be possible for some people and not for others re- mains unknown,” said Prof. Roland Lauster, Head of the Institute of Bio- technology at TU Berlin. “Essentially science assumes that over the course of a lifetime the human jaw also possesses the information nec- essary for the growth of new teeth,” said Dr Jennifer Rosowski, research as- sistant to Lauster. The question is what exactly triggers this process. Under natural conditions, hair, teeth and even nails grow as a result of what is termed mesenchymal con- densation. In the case of teeth, certain precursor cells cluster together in the jaw beneath the outer skin layer. These cells condense and form a kind of embryonic tooth germ. As a result of this condensation, the embryonic tooth germ begins to interact with sur- rounding cell layers in the jaw via spe- cific messengers. “Within the tooth bud created by this process, a differen- tiation of various cell types occurs: the enamel organ, the dental papilla, and the dental lamina. These tissues con- tinue to differentiate until a complete tooth is formed,” said Rosowski. The approach adopted by the re- search team for the natural growth of third teeth is as simple as it is ingen- ious. They remove dental pulp cells from the interior of an extracted tooth, and these are then cultivated and dedifferentiated in such a way as to produce an active embryonic tooth germ. If this embryonic tooth germ were to be implanted into a patient, it would begin to communicate with the surrounding tissue, initiating the process of tooth development. Competing research groups have already provided conceptual evi- dence in an animal model system and have demonstrated that an embry- onic tooth implanted into the jaw ac- tually develops into a complete tooth. The TU Berlin research team, however, sees a decisive competitive advantage to their method. All other competing research groups use em- bryonic stem cells to produce embry- onic tooth germs. “This makes a real application of the process impossible as the use of stem cells is ethically highly contentious and not permitted The Department of Oral and Max- illofacial Surgery at Charité–Univer- sity Medicine provides the research- ers with the teeth they require for their research in the form of ex- © TU Berlin/Tobias Rosenberg Embryonic tooth germs are generated from dental pulp cells in a laboratory using a special method of cultivation. by law in most countries,” explained Rosowski. “We would only use cell material taken from the patient’s own teeth. This enables us to bypass all ethical and legal considerations, providing us with the decisive advan- tage that our procedures focus on an actual application of the body’s own tissue. Using the body’s own tissue means that no rejection reaction will occur.” tracted third molars. The researchers have developed a special cultivation method to allow the adult cells in these teeth to dedifferentiate back into a type of embryonic state and fi- nally form an embryonic tooth germ. The dental pulp cells are isolated, cleansed and then cultivated in micro- titre plates whose upper surfaces have been coated with a hydrogel. The hydrogel prevents the cells ad- hering to the walls of the plates. They float freely in the medium but are ac- tually programmed to achieve a 3D structure. As a result, they condense independently, without external pres- sure, into a kind of cell ball. This pro- cess takes 24 hours and the resulting ball is about 200–500 μm in size. “We are the only group world- wide who have been able to demon- strate that this process of creating a ball through independent mesen- chymal condensation triggers the expression of various genes, thus setting in motion the production of specific messengers. These messen- gers are required to interact with the surrounding jaw tissue,” said Rosowski about the method, which has since been patented globally. In order to prove the validity of this, the researchers co-cultivated the embryonic tooth germs together with gingival cells. During embry- onic tooth development, these two cell types interacted, initiating tooth formation. Thus, the researchers were able to prove precisely this in- teraction. Now that all the in vitro tests have been successfully completed, the embryonic tooth germs are ready for the first preclinical tests. Study determines reasons for dental implant failure and removal techniques Long-term study analyses risk factors for short dental implants Dental implants have become a great treat- ment option to replace missing teeth, and vari- ous treatment concepts have reported high suc- cess rates. Nevertheless, like in every medical procedure, biological complications can occur which may lead to complete implant failure and, consequently, in the worst-case scenario, to the removal of the implant. A recent study by re- searchers from the University of Zurich has re- ing or maintaining osseointegration, or bone overheating or site contamination. Late implant failure is triggered by implant fractures, malpo- sitioned implants and progressive peri-implanti- tis. The last causes 81.9 % of late implant fail- ures. Early implant failure results in implants that are normally mobile and easy to remove. Late implant failure means the implants can be at least partly osseointegrated and, therefore, © Kasama Kanpittaya/Shutterstock.com more difficult to remove. As options for implant removal, the study determined tooth extraction, tre- phine burs, piezo-surgery, laser sur- gery, the counter-torque ratchet tech- nique (CTRT) and electrosurgery. Even though trephine burs seem to be the best-known method for implant re- moval, the CTRT method, alone or com- bined, should be the first choice for the clinician because of its low invasive- ness. According to a recent study, peri-implantitis is currently the main reason for dental implant failure. The use of standard dental implants has be- come a widely accepted treatment modality for the rehabilitation of complete and partial eden- tulism. However, in severe alveolar resorption, standard-length implant placement is not possi- ble without additional surgical intervention. For such cases, the use of short implants is consid- ered a major contribution to the field of implant dentistry. Now, a study has determined the risk factors for short dental implant survival. The study, conducted by the Ankara Yildirim Beyazit University in Ankara, the Cumhuriyet University in Sivas in Turkey and a private den- tal practice in Ankara, aimed to identify the dif- ferent implant- and patient-related risk factors for long-term short dental implant success. Through a retrospective chart review of three centres, patient information regarding demo- graphic variables, smoking habits, history of periodontitis and systemic diseases, and medica- tions was collected. In addition, information was gathered relating to the parameters for short im- plant placement, including implant manufac- turer, design, anatomical location, diameter and length, and type of placement. For the statistical analysis, univariate re- gression models were used at implant and pa- tient levels. A total of 460 short implants—rang- ing from 4 to 9 mm in length—placed in 199 pa- tients and followed up for up to nine years were reviewed. Survival rates of the short implants were 95.86 % and 92.96 % and success rates were 90.00 % and 83.41 % for implant- and pa- tient-based analysis, respectively. Peri-implanti- tis was reported as the cause of short dental im- plant failure in 73.91 % of the cases. Univariate regression models revealed that the female sex was strongly related to short implant success. In addition, smoking and a history of periodontitis were found to have a significant negative influ- ence on short implant success at the implant and patient levels. These results support the use of short im- plants as a predictable long-term treatment op- tion; however, smoking and a history of perio- dontitis are suggested to be the potential risk factors for short implant success. According to the researchers, these outcomes are consistent with the findings of other long-term studies. The study, titled “Risk factors associated with short dental implant success: A long-term retrospective evaluation of patients followed up for up to 9 years”, was published in Brazilian Oral Research. © DenDor/Shutterstock.com The study, titled “Removal of failed dental implants revisited: Questions and answers”, was published in Clinical and Experimental Dental Research. In a long-term study, researchers have reported high survival rates for short dental implants. Furthermore, the research team found that implantation in previously failed sites, irrespective of early or late failure, results in a 71–100 % survival rate over five years. Regarding zirconia implant removal, little data is available. Because of zirconia’s physical properties, it is supposed that these implants re- quire a different approach to removal compared with titanium implants. “If removal is required, interventions should be based on considerations regarding minimally invasive access and management, as well as predictable healing. (Post)Operative con- siderations should primarily depend on the de- fect type and the consecutive implantation plans,” concluded the authors in their paper. visited the reasons for implant failure and com- pared different removal techniques. A literature search included 28 studies which had been conducted up to 2018. The stud- ies assessed titanium implant failure, removal techniques and the reinsertion of implants in a previously failed site. The research team identified different cate- gories of factors causing implant failure. Biolog- ical factors include peri-implantitis and failure to attain or to maintain osseointegration. Im- plant fracture is an example of a mechanical factor. Medical errors causing implant failure in- clude bone overheating, site contamination and malpositioning. Functional reasons for implant failure include design of prosthesis and func- tional overload. The researchers found that early implant failure is normally caused by the lack of attain- 4 28 th EAO Annual Scientific Meeting