PEOPLE: In memoriam Thorkild Karring (1937-2016) – a tribute from his colleagues

Prof Thorkild Karring, one of the pioneers of European periodontology, passed away on August 22 at the age of 78.  He made a major contribution to the development of periodontal science, notably through his work on tissue regeneration.  Here, the people who knew him well and who worked closely with him, offer their tributes to one of the ‘Perio Greats’.

It was with great sadness we received the news that Prof Thorkild Karring – one of the great names of periodontology – had passed away on August 22, after a short period of illness, write Anton Sculean, Andreas Stavropoulos, Jan Lindhe, Niklaus P. Lang, Nikos Donos, and Nikos Mardas.

Prof Karring spent most of his professional career at the department of periodontology of the Royal Dental College in Aarhus, Denmark (now the department of dentistry at Aarhus University), where he was the professor and chairman from 1983 until his retirement in 2007, and also served as dean for several terms. His work ranged from basic studies on soft-tissue wound healing in the 1970s to pre-clinical in vivo and clinical studies on periodontal hard- and soft-tissue wound healing and regeneration, and implant dentistry in later years.

Thorkild – he always preferred to be called by his first name – started his career under the mentorship of Prof Harald Löe, both in Aarhus and later at the University of Michigan in Ann Arbor. At that time, his main focus was gingival and connective-tissue graft wound healing. He contributed substantially to our understanding of the epithelial-connective tissue interactions in oral mucosal tissues.

Thorkild had a close relationship with Switzerland, dating back to the early 1970s, when Prof Niklaus Lang spent some time in Aarhus, working in the research group with Prof Löe. After that, these two disciples of Harald Löe continued to collaborate closely and Thorkild was a frequent speaker at meetings of the Swiss Society of Periodontology and at the legendary annual continuing-education weeks at Les Diableret, in the Swiss Alps.

He also had a close relationship with Sweden, dating back to the early 1980s, when he spent some years at the department of periodontology at the University of Gothenburg, together with Prof Jan Lindhe and Prof Sture Nyman. During that period, he focused on periodontal wound healing and developed (with Lindhe and Nyman) the biological principles of guided tissue regeneration (GTR). This principle represents without any doubt the only revolutionary treatment of periodontal disease in the twentieth century, and it is still applied today worldwide, forming the basis of all regenerative efforts in the oral cavity.

In 1993, this trio of professors – Karring, Lindhe, and Lang – initiated the concept of the European Workshops on Periodontology (now the EFP Perio Workshop), which soon became a tradition within the EFP. These workshops contribute immensely to the consolidation of global knowledge about periodontology and implant dentistry and the strengthening of collaboration and relationships between EFP member countries. Through these efforts, European periodontology has been promoted and has also gained worldwide respect.

Thorkild Karring also participated in the editorship of the widely accepted textbook Clinical Periodontology and Implant Dentistry, now in its sixth edition.

During his career, Thorkild was the president of several academic periodontology societies, including the Danish Society of Periodontology, the Periodontal Research Group (PRG) of the International Association of Dental Research (IADR), and the Scandinavian Society of Periodontology (ScSP).

His academic achievements were well recognised by his peers. In 1992, he received the most prestigious award in periodontal diseases issued by the International Association for Dental Research (IADR). In 2015, he received the EFP Distinguished Scientist Award for his contribution to the field.

In June 2016, the PRG announced the creation of an annual competitive award, the Karring–Nyman Sunstar Guidor Award, supporting studies on oral-tissue regeneration, to honour his and Prof Nyman’s contribution to this field. Thorkild was very happy to see this award established and also to receive a commemorative plaque bearing his name.

Thorkild retired in 2007, but was happy during the recent years to see several of his postgraduate students holding esteemed academic positions around the world, including Sweden, Switzerland, and the UK. They carry the torch of Thorkild Karring’s fire and enthusiasm for periodontal research and hence will ensure that his memory is honoured.

In these difficult times, our thoughts are with Thorkild’s wife Eva and his children Ann, Jakob, Gitte and Henrik. We all have lost a great human being.

Andreas Stavropoulos: ‘Thorkild had a special way to approach scientific questions’

I worked together with Thorkild for 11 years, from 1996 until 2007 when he retired. First as a postgraduate and PhD student, and later as a post-doc and staff member of the department. I was the last of a series of international – and especially Greek – people that went in Aarhus to work with him, and the one that stayed with him longest.

Thorkild gave one – at least, this was my personal experience – complete freedom in pursuing a scientific question, provided that this question was governed by common sense. He liked simple straightforward questions, and he generally used to give straightforward answers (and occasionally the answers could also be unpleasant). Sometimes he liked to answer with another question or a metaphor – then one knew that he did not necessarily like the original question!

Thorkild had a special way to approach a scientific question – often unconventional and full of fantasy – that was based on his unique charisma to sort the important from the irrelevant, even in cases involving complicated issues.

When writing an article, he used to say that it had to be written as a film: with a start, a story, and an end. Also he used to say: “Write exactly what you want to say – do not write anything more complicated!” He enjoyed correcting our articles, while drinking tons of thick, black coffee, which had been standing on his coffee machine for hours – when the articles were handed back, the pages were full not only of red marks but also of brown spots. However, the text was always smoother and easier to read.

Thorkild enjoyed drinking a beer or two, cigarettes, and discussions on non-scientific topics; he was very interested in politics, both national and international. He also liked to hear the gossip, but very seldom spread it. Thorkild had a strong belief that the world is becoming a better place to live and that good – and not evil – always wins in the end. 

Anton Sculean: ‘Thorkild, the genius of periodontology’

I recall the day I started my postgraduate training in periodontology at the Royal Dental College in Aarhus, Denmark and was introduced to Professor Karring. Having an educational background from a German university, I addressed him as “Professor Karring”, which he immediately corrected by asking me to call him “Thorkild”, according to the Scandinavian way.

After a short chat, he asked me directly about the topic of the research project that I would like to carry out for my master’s degree thesis. This question surprised me, as I was used to the “Professor” telling us what research we had to do without being asked about our ideas.

Thorkild was just the opposite of what I had known until then, as he expected his students to come up with their own novel ideas. And this was not easy for a beginner, because he always asked for the biological and/or clinical rationale to perform a certain project. This way of interacting with us was very demanding and one needed to have a thorough literature background on the topic before starting any discussion with him.

“Toni”, he said, “Before starting any new project, go and read carefully the available literature since there may also be other clever guys who have published a similar study.” These words are still in my mind whenever I am thinking about any new project.

Thorkild had a unique capacity to explain the most complicated things in a very simple and understandable way. He taught us that it does not make sense to perform any study if the question addressed lacks a potential clinical relevance and to try to express our thoughts concisely and clearly. He once told me, “Toni, you are writing the paper for the reader and not for yourself. Thus, the message has to be as short and clear as possible.”

In fact, this is true of the papers he authored: all of them are of clinical relevance, all of them are easy to read, and all of them are innovative. His studies have provided pivotal findings explaining the role of the various cell compartments in determining the healing of periodontal hard and soft tissues and alveolar bone defects, and they represent the basis of our current treatment concepts in regenerative and plastic aesthetic periodontal surgery.

For me, Thorkild was the genius of modern periodontology, a giant in dentistry, and a great human being who decisively influenced my professional future.

Nikos Donos: ‘A kind and very supportive mentor’

It was back in September 1992 when I arrived in Aarhus, Denmark to be part of the first cohort of the formal graduate programme in periodontology at the Royal Dental College. At that time, GTR was at its height and Professor Thorkild Karring and his research in the field of periodontal regeneration was the main reason that I decided to do my postgraduate studies in Aarhus.

I was at the department studying and working under Professor Karring for seven years, a period that I regard as one of the most influential in my professional life. Thorkild (as he always wished to be called) and his deep knowledge and understanding of wound healing, as well as his clarity of how biological phenomena were applied clinically, had a great impact in the field of periodontology and implant dentistry as we apply it and continue investigating it today.

His systematic approach in pre-clinical and clinical research and his unique way of interpreting the data led to scientific breakthroughs which are taught on postgraduate programmes today and which many clinicians continue to apply.

Thorkild was a pure researcher, constantly asking questions and developing new knowledge in new areas. One needs only to look at his research achievements and the areas that he investigated over the years. From (classic) studies on the basic anatomy of the periodontium, to periodontal wound healing and to his significant contribution to the development of GTR – which also continued into guided bone regeneration (GBR) – Thorkild was always among the pioneers in our field.

As a mentor, Thorkild was kind, very supportive, and provided positive feedback that promoted reflection, allowing his graduates to develop as individual researchers. Thorkild was always there when you needed guidance or scientific debate, and the available evidence and “common sense” were prominent items.

Thorkild was an inspiration for all of us, his graduates, and the fact that he continued to support us and follow our careers when many of us left Aarhus is a testament to his kind personality as a mentor and teacher.  On a personal level, it was a privilege and honour to study and work under his guidance and to consider him as my professional mentor.

Thorkild was one the “legends” of periodontology and the field has lost one of its brightest minds and teachers. 

Nikos Mardas: ‘A brilliant, innovative, and pioneering mind’

I first met Professor Karring in 1992 when I started my specialist training in periodontics at the Royal Dental College, University of Aarhus. At this time, Thorkild Karring was the professor and chairman in periodontology and also dean of the dental school. I was lucky enough to spent six full years working in his department as a specialist trainee and later as a PhD candidate and research/clinical associate.

I vividly remember his first words when I introduced myself during the initiation day of my studies: “Please call me Thorkild – in this country we prefer to call each other by our first names.” His “hard” face softened and, as we briefly talked, my stress and worries about all the years ahead of me as a trainee faded and I discovered maybe the biggest influence in my academic and professional career.

Thorkild was a pioneer in redefining the goals of periodontal treatment. He was able to simplify the mysteries of wound healing and to pair common sense and clinical relevance with biology. His extensive research work is just an example of these qualities. As a mentor, he guided us in acquiring a “thinking clinician” philosophy besides technical competence, always emphasising the importance of adopting a researcher way of thinking during our everyday clinical practice. His mind was always open to new thoughts and new ideas that he was able to push further and exploit to the maximum.

All of my peers during this period (many of whom now hold distinguished academic positions around the world) will remember being able to start a “debate” with him over one subject and enjoy his focus and depth of knowledge in the field but also his unconventional and sometimes “provocative” views. If he didn't know much about a subject, he would graciously accept this and inquire about it, inspiring us to do the same.

Thorkild was not always easy and pleasant but he was always true, honest, and direct. He had a good sense of humour that was coupled with his critical but polite and friendly approach towards his colleagues and collaborators. His way of motivating and engaging people to produce and create clinical and scientific work was unique.  Maybe, in the end, I learned more about the “man Thorkild” than about “Prof Karring”.

On 22 August 2016, the world of perio lost a brilliant, innovative, and pioneering mind. All of us – “his old students” – lost a teacher and a mentor, but most of all an inspiration for life.