From Science Fiction Back to Reality?

I vividly remember a particular oral examination in Kuwait when the external examiner, a professor from Sweden, had not shown and I and then chairman of the surgical department, Tryggve Lie from Norway, had to quiz the bright candidate by ourself. It was quite an inspired exam, much about figuring out whether deeper understanding of underlying biological mechanisms of pathogenesis and healing of periodontal disease was present or not [1].

When we discussed periodontal regeneration, I asked the candidate at one point whether she could recall the cover of the new edition (the fourth, of 2003) of what is still referred to as Lindhe’s textbook. No, she said but we had a copy at hand. It had actually puzzled me for some time, in particular the authors had not mentioned their source. It apparently showed a histological section of an implant which was in touch with two remaining roots. On page 658, in chapter 28 on Regenerative Periodontal Therapy, the image appears again. The legend tells,

” Fig. 28-13. Microphotograph of a titanium implant placed in contact with retained root tips (a). A distinct cementum layer (arrows) and periodontal ligament (PL) in continuity with that on the roots (R) is visible on the implant surface.”


A higher magnification in polarized light clearly showed the cementum layer with Sharpey’s fibers present at the implant surface. Principal fibers, oriented perpendicular to the surface, were running across the ligament space and were inserting in the adjacent bone as in natural teeth. Reference to a research group in Arhus was made (Buser et al. 1990, Warrer et al. 1993). According to the authors of the chapter, the ultimate proof that progenitor cells for new attachment formation were residing in the periodontal ligament. And, periimplant ligament rather than osseointegration had apparently been a research topic in the early 1990s; sort of science fiction which had meanwhile been abandoned [2].

This spring, the sixth edition of Clinical Periodontology and Implant Dentistry was published. As in its fifth edition, the work appears in two volumes called basic concepts and clinical concepts. A change among the editors has occurred, Lindhe and Lang are responsibe for the first volume while Lang and Lindhe for the second. The work is heavy, both in its content as physically. Many of my colleagues have already striked the previous 5th edition of Lindhe’s textbook from the recommended reading list for undergraduates. Two volumes with more than 1400 pages altogether appears inappropriate for a topic which may or may not be regarded a core discipline in dentistry [3]. The same applies to the main American textbook on Periodontology, Carranza’s. Sometimes less is more. For postgraduate training, both works are indispensable, of course. Not for undergraduates.

What the cover of Volume 1, Basic Concepts, displays is anyway remarkable. Bad dentistry on the cover of a 21st century textbook edited by the two leading dental researchers?


The 1 mm or so bacteria-filled gap between the metal crown and the preparation line is, of course, shocking. Who had advised the editors to choose such an example? The acceptable fitting accuracy of cemented restorations may be as poor as 100 micrometer, allowing 1 micrometer large bacteria to party in crowds. That’s why subgingival margins of zinc phosphate cemented restorations are so deleterious for the periodontium. That’s why, the biological width has to be respected in those cases [4]. That’s why modern restorations are nowadays cemented with adhesive systems closing the gap provided excess material is carefully removed.

But what is it that the editors want to point to? Blaming the common colleague of practicing outdated dentistry with implications for periodontal tissues [5]? Well, it may at least again serve for broader discussions with students about, e.g.,  the perio-prosthetic interface, the biological with, cause and effect, nonspecificity of dental biofilm-induced periodontal disease and non-specific tissue response.


[1] As part of the former British Empire, Kuwait largely follows the respective system of higher education. The dental curriculum is completed with a BDS, not a master’s. A written exam may be followed, according to very strict rules, by an oral exam. So, a student with a B+ grade may gain another two marks to get an A. Or a B- after a C+. Likewise, a student who had flunked by a very narrow margin, say 59 marks, would have a chance to gain one additional mark and so just pass the exam.  The oral exam was voluntary, students who were satisfied with their grades, would not show on invitation. But Kuwaitis were eager to prove excellence. And, they could not lose marks. So, exams were usually delightful for all parties, including the impressed external examiner. In the written exams, a mix of multiple choice questions (type A with one correct answer out of five possible; type B, i.e., a to be specified number of correct answers, was utterly discouraged as too confusing in an exam), short answer questions and essays was demanded since students may differ in their capabilities of performing well in all kinds of questions. The exam was meant to be fair, transparent and waterproof. The latter was considered important since students’ complaints reflected badly on teachers.

[2] And, I have to admit, forgotten, at least in my case. This highlights again the genius of one of the book’s editors, Thorkild Karring of Arhus University, who deserves most of the credits for what was then called guided tissue regeneration and who does no longer belong to the editorial team of this remarkable work.

[3] The EFP is still aiming at establishing Periodontology in all European countries as a specialty. Even in 2015, not all university clinics in Germany have independent departments of Periodontology, especially negative examples comprise Cologne, Hamburg, Munich, Regensburg, Nuremberg, Homburg, and Mainz. Here at Tromsø University, a decision by the founding administration to abandon sections and establish a new topic of education, i.e. clinical odontology, comprising Cariology, Endo, Perio, Prostho, Oral Surgery and Medicine, and Gerodontology, has created both praise and scepticism among experienced teachers.

[4] That’s also why possible violation of the biological width by accurately placed composite resin material would not lead to deleterious effects since there is no gap between restoration margin and dentin. I have reported some time ago about the claim a decade-long paradigm was shattered by a case report published in Operative Dentistry, see here. Not the short distance between the restoration margin and the bone had concerned me, of course, but rather maltreatment of soft tissues during the operation including electrosurgery in close spatial relation to the alveolar bone and cementum, as well as application of hemostatic chemicals on top of the bone.

[5] Bad dentistry is, of course, still common, in Germany as well as in Norway. See, for instance, the case below. That severe periodontitis at abutment teeth had been ignored when it was decided to insert a four-unit dental prosthesis, which did not fit and was thus “too high”, closely relates to the decision to “adjust occlusion” in the opposite jaw with grinding off the cusps. The gap between crown margins and preparation lines resembles that displayed on the cover of Lindhe and Lang (2015).

Patient 2(3)

Posted 2 August 2015 @ 10:44 am.

Last modified September 2, 2015.


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