Researching the Research: Which Statistics Can We Truly Rely On?

  • by Gerard Scannell, DDS
  • Jan 9, 2023
1-9-23_Comm_BWe have all had patients ask how long our dental work will last. Most of us have an answer memorized — whether it’s a crown, implant or other treatment. And we likely have had the same answer for years. Chances are it’s either a vague answer or an estimate based on scientifically proven studies or our experience. 

As a new dentist, it isn’t enough to reassure a patient that my work will last based on my one year of experience. Sometimes my response is something I learned in school or read in an article. But I’ve realized that many of my answers to how long something will last are statistics I’ve heard cited by colleagues or mentors. 

However, I’ve recently wondered if those answers have just been passed down from colleague to colleague — like a game of telephone. If this is the case, very few may actually know their origins. 

An example that comes to mind is when a patient inquires, “How long will my crown last?” I’ve told patients, “If this crown can last 10 years, it’s a success.” Where did this statistic come from? I believe I overheard another dentist mention this to a patient and thought to myself, “That sounds like an adequate answer.” So, I asked as many dentists as I could for their thoughts. Most mentioned numbers in a range from five to 25 years. However, only one dentist could provide the evidence on which they based their answer. 

The one dentist who had “evidence” for their answer is a classmate from dental school. The website of the office they work for references a study that shows the survival rate of dental crowns. The 2013 study, by Terry Walton, BDS, MDSc, MS, FRACDS, in the International Journal of Prosthodontics, demonstrates evidence of a survival rate of 97% after 10 years and 85% after 25 years.1 This was exactly the kind of statistic I’d been looking for — or so I thought. What the website fails to mention is that all of those single-unit crowns in the study were high gold-based metal-ceramic crowns. So, if that is the type of crown you are providing to patients, then this is a great study to reference. However, if you are telling patients a zirconia crown has a 97% chance of lasting at least 10 years, this study doesn’t exactly support that claim. 

Patients place a lot of trust in what we do and recommend. That trust deserves accurate representation of what we’re telling them. Wouldn’t you want to know the success or failure rate of a heart surgery you may be undergoing rather than the statistics of a related, but different, procedure? 

Another example I found is a 2008 study published in the Journal of Endodontics comparing the success of implants versus endodontically treated teeth. The authors found that implants had a success rate of 98.4% and endodontically treated teeth had a success rate of 99.3%.2 They explained that there was no statistically significant difference in these percentages, but added the caveat that “implants required more postoperative treatments to maintain them.” Even though these are evidence-based statistics, we should always keep in mind potential author bias. In this case, the study was published by endodontists from the University of Alabama Birmingham Department of Endodontics. 

Success and failure of what we do in dentistry can be defined in numerous ways, too. Another article, headed by Carl E. Misch, DDS, MDS, PhD, discusses implant success, survival and failure. It includes a few concrete definitions that I like. It states that implant success “should include a time period of at least 12 months” and include ideal clinical conditions.3 In addition, “implant failure is the term used for implants that require removal or have already been lost.” These definitions could be applied to other procedures we do in dentistry, too. 

Whatever answers we are giving to patients to explain how long they can expect a prosthesis to last or what qualifies as a successful procedure, caveats of proper home care, diet, effects from medications, and regular professional cleanings and maintenance should be mentioned. Managing a patient’s expectations appropriately can have a positive outcome on whatever we recommend and ultimately do. 

I was hoping to provide concrete scientifically proven studies you can reference to patients in order to increase case acceptance or, at least, reassure patients that what we’re recommending to improve their oral health will have a lasting positive effect. But what I’ve unfortunately concluded from researching the research is that there are way too many studies that claim to prove something but may not come from a trusted source or even pertain to what we do. 

However, there are many great and reliable resources, especially through AGD, so take advantage of them and continue to educate yourselves. Make sure that what we ultimately tell our patients is coming from an honest place and for the benefit of their overall well-being. 

Gerard Scannell, DDS, is a general dentist practicing in his hometown of St. Petersburg, Florida. He is the former AGD Impact Student Perspectives columnist. To comment on this article, email


1. Walton, T. R. “The Up to 25-Year Survival and Clinical Performance of 2,340 High Gold-Based Metal-Ceramic Single Crowns.” International Journal of Prosthodontics, vol. 26, no. 2, 2013, pp. 151–160.
2. Hannahan, J. P., and P. D. Eleazer. “Comparison of Success of Implants Versus Endodontically Treated Teeth.” Journal of Endodontics, vol. 34, no. 11, 2008, pp. 1302–1305.
3. Misch, Carl E., et al. “Implant Success, Survival, and Failure: The International Congress of Oral Implantologists (ICOI) Pisa Consensus Conference.” Implant Dentistry, vol. 17, no. 1, 2008, pp. 5–15.