Effectiveness of Implant Therapy Analyzed in a Swedish Population: Prevalence of Peri-implantitis

by Emil L.A. Svoboda, PhD, DDS

I have been placing and restoring dental implants for over 25 years and was intrigued by an article by J. Derks et al. “Effectiveness of Implant Therapy Analyzed in a Swedish Population: Prevalence of Peri-implantitis” JDR January 1, 2016, 95: 43-49. A copy of this article was sent to all dentists in Ontario, Canada, by the Royal College of Dental Surgeons of Ontario (RCDSO). I have some serious reservations regarding the potential interpretation of the results from this article.

1) J Derks et al. acknowledges the large variation in the literature regarding the criteria used to diagnose mucositis and peri-implantitis. Their selection of criteria used for the diagnosis of peri-implant disease may mislead the reader to a biased conclusion of an Exaggerated Prevalence of Peri-implant Disease.

2) When I look at the post treatment care received by their nine-year sample of implant patients, I suggest that the results of their study describe “What can happen to a group of heavily restored implant patients when they receive Inappropriate Professional Care”.

Exaggerated Prevalence of Peri-implant Disease
It is true that there is a lot of variation in the criteria used to diagnose peri-implant disease in previous publications. This variation is probably due to the fact that the tests used to diagnose gingivitis and periodontitis around natural teeth has been applied to dental implants. Dental Implants are not teeth. We know that the gingival tissues do not connect to dental implants in the same way as it does to natural teeth. Dental implants are frequently surrounded by cuffs of soft tissue covered with a fragile thin layer of epithelium adjacent to the dental implant. Probing of this epithelium can easily make it bleed. This bleeding may not be a sign of pathology, but a sign of injury.

There are other signs that could be used, to help interpret pathology. Perhaps some of the signs of inflammation like redness of the tissue, swelling of the tissue and the existence of exudate would also be helpful to tabulate. Unfortunately, the investigators chose to lump bleeding on probing together with suppuration, and did not mention redness or swelling of tissues. Why would they do this? Suppuration, together with redness, swelling and bleeding could be a much more convincing indicator for peri-implant disease. The grouping of bleeding on probing together with suppuration unfortunately increases the numbers involved in their diagnoses of mucositis and peri-implantitis and thus exaggerates its prevalence.

In the article, the authors use the measure of bone loss as a sign of peri-implantitis and as an indication about the severity of the disease. Does bone loss of 1 or 2 mm signify disease or is a function of homeostasis after the trauma of surgery, the effect of the local bacterial flora and the occlusal load in the particular individual? With the absence of redness, tissue enlargement, exudate, and other signs of pathology, is it really pathology? With natural teeth gingival recession and loss of facial bone can result in a very stable condition that can support function for a lifetime. Teeth with bone loss and shrunken gingiva can be stable for years. Similarly, implants with over 2 mm of bone loss can be stable for many years with appropriate care. The results of this study are difficult to interpret. Certainly, moving the inclusion criteria from 2 to 3 mm of lost bone has a huge negative effect on their reported prevalence of disease. It would be helpful if other signs of active pathology were presented, to give readers a more objective view of the condition of the test group.

This study reports peri-implant disease at the patient level. The patients in the sample group had an average number of dental implants that was almost double what my patient base has. This increased number of implants per patient, of course increases the frequency of patients with peri-implant disease. If the average number of implants were even higher, the percentage of patients affected would also be higher. Reporting this number can exaggerate the prevalence of peri-implant disease. I would suggest that if we study the prevalence of periodontitis in the natural dentition on the patient level, the prevalence would be very high. How many patients do you know that do not have a single 5 mm pocket around one of their teeth?

When we compare the incidence of periodontitis with the incidence of peri-implant disease on a patient level, perhaps the peri-implant disease levels might look a little more appealing. I am happy that the investigators also tabulated the result at the implant level. In my opinion, this gives a better indication of the prevalence of peri-implant disease. Considering the diagnosis issues mentioned above and the aftercare issue that is discussed below, treatment with dental implants is starting to look much safer.

Inappropriate Professional Care
The above article reports that 80% of the patient group studied had regular recalls on an annual basis and that about 18% were irregular. There are no details about what was done at the recall visits over the nine years of the study. The average number of implants per patient was about four, 20% of the patients were smokers and 24% were diagnosed with existing periodontitis. Eighteen percent of the prosthetics in their sample were installed by an intra-oral cementation technique, and 77% by a screw-in technique.

In this group of patients with many failed teeth, multiple implants, a large percentage of smokers (20%) and a large percentage of existing periodontitis (24%), do you feel that an annual recall or less is an appropriate post-treatment protocol? I would call the professional care regime used for the patients in this study inappropriate!

The periodontitis group (24%) would probably benefit from a three-month recall protocol to help stabilize their condition. The smoker group (20%) could also benefit from more frequent care. This study group of patients had already lost many natural teeth and had treatment worth thousands of dollars, in their mouths. This oral condition would “scream” for a more frequent and comprehensive recall regime.

About 18% of the patients studied had their prosthetics cemented intra-orally. If this group of patients displayed signs of persistent inflammation, according to the study by Wilson (2009)1, at least 74% of these mucositis cases could have been cured by removal of residual subgingival cement. Why was this group of patients neglected for nine years? Did anyone attempt to prevent the progress of mucositis to peri-implantitis by the removal of residual subgingival cement? A more frequent and comprehensive post-treatment examination protocol might have stimulated the clinician to investigate and remove any residual subgingival cement. Thus, the inappropriate level of care delivered to this vulnerable population of patients, further exaggerated the incidence of reported mucositis and peri-implantitis.

The rest of the peri-implant disease cases (78%) can be attributed to prosthetics installed by the screw-in technique. According to this study, those patients with four or more implants had 15 times the incidence of peri-implantitis, as compared to the group of patients with less than four implants. The question is, “What is causing this large rise in peri-implantitis rate?” There is no residual subgingival cement to suspect, as any cementation would have been done extra-rally in the dental laboratory. The big problem with screwed-in prosthetics installation technique is that the abutment-prosthesis complex is assembled on an inaccurate model before being transferred to the mouth. This process can cause an implant-abutment misfit at the deep tissue level and thus create both mechanical and biological complications for the patient.2 The incidence of peri-implantitis is significantly increased when the implant-abutment misfit is present in conjunction with a history of periodontitis, existing plaque or bleeding on probing and other factors.3,4 In reference 4, Dr. Paulo Malo, of All-on-Four fame, is a co-author of the article that describes a risk profile algorithm to organize patients into risk groups for the purpose of implementing an appropriate recall treatment frequency to attempt to stabilize the patient’s condition. All cases that had a history of periodontitis and had a gross implant-abutment misfit fell into his high and very high-risk group. The article suggests a three and two month recall frequency respectively for these risk groups. This is a far cry from the post-prosthetic care received by the Swedish group of patients.

What can the clinician do to correct an implant-abutment misfit? Perhaps through frequent scaling and surgery, the clinician can change the peri-implant environment by pocket reduction; that in effect makes the implant-abutment connection “less-subgingival”. This may improve the patient’s ability to maintain and tolerate the implant-abutment misfit. Perhaps, it may be better to try to understand and prevent this “misfit problem” in the first place. Together with appropriate aftercare, this may have reduced the incidence of peri-implant disease by 60%.5,6

Further Discussion
I have lectured about “Implant Prosthesis Installation Techniques and their Contribution to Peri-implant Disease” in Boston, Vancouver and New Orleans and will present again in Chicago, Las Vegas and Missisauga in 2017. A copy of my Chicago Presentation and supporting articles are available for study at www.ReverseMargin.com. It discusses the prevention of residual subgingival cement and optimization of the implant-abutment junction and promises to help the clinician mitigate some of the problems related to current prosthesis installation techniques.

My work suggests that we can now optimize the fit of the implant-abutment connection while preventing the occurrence of residual subgingival cement. This alone promises to reduce iatrogenic complications by 60%, extrapolated from the results of Wilson (2009). I have already implemented the necessary changes in the restoration of 600 dental implants in my practice. I am confident that controlling the above two variables, is a significant improvement to the level of care that I offer my patients.

Knowing what I know now, I can no longer return to the old ways of installing prosthetics for my implant patients. I am hopeful that some forward-thinking university will begin the large-scale clinical trials necessary to confirm the value of my work. However, in the meantime, do we want to continue causing unnecessary complications?

My experiments are simple to understand and simple to repeat. There is no complicated technology that requires sophisticated interpretation. My results are visual and logical. It is easy for an experienced practitioner to judge its validity. To date, I have not found anything that invalidates the interpretation of my results.

Now “more than ever”, those providing implant services must be seen by the public as doing something different, that promises to reduce the incidence of peri-implant disease. The “status quo” prosthesis installation techniques are not working as well as we had all wished. “It is not what we don’t know that gets us into trouble. It’s what we know for sure, that just ain’t so” (Mark Twain). I would like you, my colleague, to consider the information I have shared with you, and apply it to your treatment. We need to get serious about preventing peri-implantitis.

With regard to the J Derks et al. article, the study clearly shows that annual recalls and intermittent recalls are not consistent with optimal oral health maintenance around dental implants.

There can be serious complications related to treatment with dental implants. The professionals delivering implant-based treatment should identify the sources of their patient’s complications and when possible, make the necessary changes to their protocols to prevent them. OH

Oral Health welcomes this original article.


  1. The positive relationship between excess cement and peri-implant disease: a prospective clinical endoscopic study. Wilson, T.G., J Periodontol 2009;80:1388.
  2. Dental Implant Prosthetics. Carl Misch, 2nd Edition, Elsevier-Mosby, 2015,Ch 28.
  3. Top factors leading to dental implant abutment/implant fixture misfit: The dreaded microgap. Scott Froum, Editorial Director, Feb 6, 2017 Clinical Associate Professor – Periodontist NYU
  4. Attributable fractions, modifiable risk factors and risk stratification using a risk score for peri-implant pathology. de Araújo Nobre M, Mano Azul A, Rocha E, Maló P, Salvado F. J Prosthodont Res. Mar 28, 2016.
  5. Controlling Excess Cement During the Process of Intra-Oral Prosthesis Cementation: Overcoming the Gingival Effects. Svoboda ELA. OralHealth October 2015, pp 52-66
  6. Dental Implant Prosthetics: Achieving Retrievability and Reducing Treatment Complications by Using a Modified Installation Technique. Svoboda E. OralHealth October 2016, pp 8-18
  7. Can We Make Intra-oral Cementation Safer? Svoboda ELA. 2017. www.ReverseMargin.com

Dr. Emil L.A. Svoboda earned his PhD and DDS at University of Toronto. He is an Honored Fellow of the AAID (AAID.com) and a Diplomate of the ABOI/ID (ABOI.org). After placing and restoring thousands of dental implants, he began a research project to identify and prevent the causes of peri-implant disease by safer prostheses installation techniques. More information is available about the progress of his work at www.ReverseMargin.com. Contact Dr. Svoboda at drsvoboda@rogers.com.

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