The Good, The Bad & The Ugly - now available for CE Credits on DentalTown

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What's the Deal With GentleWave?

We have been asked by many dentists regarding our thoughts on a new irrigating technology called GentleWave by Sonendo Inc.  After meeting with the GentleWave representatives, an in-office demonstration, performing the procedure on extracted teeth, discussing with colleagues using the product and critically reviewing the clinical research  on this technology, we are prepared to answer the question so many of you have asked, "What's the deal with GentleWave?"

"Thrill of the Fill" accomplished using the EndoActivator

At SSE, we have been early adopters of many new, and lasting technologies in endodontics such as microscopes and CBCT.  Our process in adapting a new technology, like GentleWave, is to carefully evaluate the technology, including the claims made by the manufacturers and a critical evaluation of whether the published evidence supports those claims.

 It is also important to evaluate the financial side of any large investment to make sure that it is a fiscally sound decision that makes sense for our patients  and our practice.  Failure to do so leaves a practice in a position where a financial commitment to a technology then determines how the technology is applied to the patient's care.

In the #1 bestselling book, Good to Great by Jim Collins, he makes a point about  our "cultural obsession with technology and technological-driven change". Nowhere can you find a group of professionals more obsessed with technology than in dentistry!

EndoActivator

However, in Collins extensive study of what made good companies become lasting, great companies, he noted that the great companies "maintained a balanced perspective on technology, while most companies become reactionary, lurching and running about like Chicken Little..."  Collins finds that technology alone is never a primary cause of either greatness or decline.

If you are following the information that the GentleWave manufacturer is delivering to offices throughout the greater Phoenix area it is obvious they are making a sizable marketing investment. With a clever marketing approach, they have included in the purchase price of the system, a marketing budget to promote the system and the practice who has invested in it.  You have likely received several invitations to CE events promoting the technology.  There are several phrases being used by the sales-force to excite dentists about GentleWave such as "the thrill of the fill", "this is the new standard of care",  "anatomy like never before seen" and "becoming part of the club". There appears  be an effort by the manufacturers and early adopters to create an impression that the evidence is in and this technique is proven to be superior to conventional irrigation methods.  If you are not adopting the technology now, you will be left behind...

A short summary of our decision regarding the GentleWave procedure as to why we have decided not invest in the technology yet because it will cost patients more, increase treatment time, and decrease our productivity without clinical evidence of improved outcomes was posted on the blog several months ago. We will continue to watch the technology, its improvement and evaluate  the evidence published over time.

The following sections provide more detail into our evaluation regarding the claims made by GentleWave.

What Does the Research Say About GentleWave?

The initial clinical study which made claims of 97% success rates, improved cleaning of canals, isthmuses &  lateral canals & improved cleaning had some major design flaws and biases. Design bias, attrition bias, selection & sampling bias and sponsorship bias were all evident in this study, including a failure to include proper positive and negative controls.

The second clinical study improved upon many of major design flaws & biases of the first study, yet again failed to include positive and negative controls.

Failure to include controls in the clinical studies is concerning to us.  This failure in study design, is hard to comprehend, unless a direct comparison with conventional techniques was not desired or conventional techniques were equally effective.  We have also asked why there has not yet been a double blind, randomized, controlled study performed?

EndoActivator

Why have the universities and residency programs not published about the Gentlewave technique? After discussing this with several people involved at that level, the  reason appears to be that if a university accepts any financial support from the company, including providing the unit, the company insists on controlling the publication of any research results.

So while we can understand the company's desire to protect its significant investment in the development of it's technology, their scientific research appears designed as a marketing tool to support manufacturer claims.  A properly designed study, (randomized, double blinded study with proper controls) will go a long way to overcome sponsorship bias that up to now has been evident in the research.  In fact we have not been able to find one study where the authors are not directly tied to and supported by Sonendo.  We will continue to watch  for this evidence and keep you updated.

3 Dimensional Cleaning, Shaping & Filling 

EndoActivator

One of the biggest claims made regarding the GentleWave technique is "improved removal of organic matter" and creating a "higher standard of clean". Evidence provided for this claim are usually images of more complex anatomy picked up when the tooth is obturated. The advocates call this "the thrill of the fill".

However, the idea of cleaning and filling lateral canals and isthmuses is not unique to GentleWave.  In our practice we have used both ultrasonic and sonic activation of irrigating solutions which has provided 3D cleaning and shaping of complex canal anatomy.

EndoActivator

I have included several radiographic that demonstrate the "Thrill of the Fill" routinely seen at SSE using sonic activation of irrigating solutions. After our hands on demonstration with the GentleWave, I began putting aside radiographs after using sonic activation and found that the fill results were equally impressive.

 In the end, we need to be honest with ourselves. How many teeth are really returning to our office as failures because we didn't clean the tooth well enough?  From our experience - very few.  When patients return to our office with a non-healing root canal procedure, typically it is because the tooth is fractured, not because it wasn't clean. We would love to add the Gentlewave technology to our office but first we need to see a tangible benefit to our patients. That day may come, but for now we would like to see more evidence than "because the company says it's better", before we invest in this technology.

Don't Just Assume A Root Is Fractured When You See Lateral Bone Loss

Sometimes we are quick to assume a tooth is fractured when we see lateral bone loss.  But that radiographic finding alone isn't enough to make that determination.  If you cannot visualize a fractured, and the tooth is diagnosed as a necrotic pulp, it doesn't matter how big the lucency is, it can and should be given the opportunity to heal.  Proper diagnosis to determine vitality is the most important test for the prognosis of this tooth.  In this case, with definite necrotic pulps on #26 and #27 and no periodontal defects, endodontic therapy is recommended.

Necrotic pulp with sinus tract on the buccal of #26.

CBCT shows the apical and lateral bone loss on #26 and #27.  The lateral bone loss on #27 is also suggestive of a possible root fracture, but since the tooth is necrotic, radiographic appearance alone is not enough evidence to diagnose this with a root fracture.  CBCT also shows a 2 canaled root form on #26.

There was concern of a possible root fracture, but none could be see internally with microscope.  CaOH medicated dressing was placed after initial debridement and NaOCl irrigation.

After 3 months in CaOH, we opened and examined again and could find no fractures.  Another application of CaOH medicated dressing was placed.

After 6 months of CaOH therapy we saw significant bone healing. The canals were obturated and case completed.

Sometimes we are quick to assume a tooth is fractured when we see lateral bone loss.  But that alone isn't always enough to make that determination.  Even with CBCT available, I tell my patients the only way to be 100% of a vertical root fracture is to see it.

Finding the Right People for Your Practice

In Jim Collins' bestselling book, Good to Great, he discussed the importance of getting the right people on your team.  He describes your team as a bus and if you get the right people on your bus, it doesn't matter where you take your bus, you will be successful.  The follow concepts are a summary of Collins's concepts of finding the right poeple from Chapter 3, p. 41-63.

In “Great” businesses, people are not your most important asset. The right people are.   Great businesses make a priority on finding the right people.

CONCEPT:  If you have the right people on the bus, the problem of how to motivate and manage people largely goes away.  With the right people, you can take the bus anywhere it needs to go. 

CONCEPT: If you have the right people on the bus, they will do everything within their power to build a great company, not because of what they will “get” for it, but because they cannot imagine settling for anything less.  The purpose of a compensation system is not to get the right behaviors from the wrong people, but to get the right people on the bus and keep them there.

CONCEPT: In finding the “right” people, greater weight is placed on character attributes than on specific educational background, practical skills, specialized knowledge or work experience.

CONCEPT:  Great companies have rigorous – not ruthless – cultures. A rigorous culture means consistently applying exacting standards at all times and at all levels – especially in upper management.  The only way to deliver to the people who are achieving is to not burden them with the people who are not achieving. 

·     To let people languish in uncertainty for months/years, stealing precious time in their lives that they could use to move on to something else, when knowing that they are not going to make it – that is ruthless

·     To deal with it right up front and let people get on with their lives – that is rigorous

CONCEPT: Practical disciplines for being rigorous – not ruthless

1.    When in doubt, don’t hire – keep looking.  The ultimate throttle on growth is not markets, technology, competition or products. It is the ability to get and keep enough of the right people.

2.    When you know you need to make a people change, ACT.  The right people don’t need to be managed.  Guided – Yes, Taught – Yes, Lead – Yes, - but not tightly managed.

a.    Great leaders don’t rush to judgment. They invest substantial effort in making sure they have someone in the right seat before concluding  they have the wrong person on the bus.  Instead of firing honest and able people who are not performing well, it is important to try to move them once or even two or three times to other positions where they might blossom.

3.    Put your best people on your biggest opportunities, not your biggest problems. Managing problems can only make you good whereas building your opportunities is the only way to become great.

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CONCEPT:  Right People + Great Company = Great Life.  Balance in work and life is possible when you have the right people on the bus.  Finding the right people is key in finding that balance and having a great life.  If we are not spending the vast majority of our time with people that we love and respect – how will we ever have a great life? Great life is made up of people who love what they do and love who they do it with.

Single-Visit vs. Multiple-Visit Endodontic Treatment: A Review

There are differing opinions regarding single-visit vs. multiple-visit endodontics.  Some clinicians feel strongly that teeth with apical periodontitis (necrotic or retreatment) need the extra step of CaOH therapy to be successful while others are comfortable with these cases being done in a single visit.  What does the research say regarding this?  Here's a summary of the more recent research:

Please note that the systematic reviews, in an effort to summarize the existing research and find the best evidence, exclude review papers, case studies, review studies and studies that are determined to be "low evidence" and focus on randomized clinical trials or quasi-randomized clinical trials.  However, like most of our dental research, there is a serious lack of studies that can be considered "high-level" evidence, large enough sample size, good research design and proper identification of study bias.  This is a problem found throughout our scientific research and requires the reader to evaluate the quality of research on a study by study basis.

Single versus Multiple Visits for Endodontic Treatment of Permanent Teeth (A Cochrane Review) by Manfredi et. al. 2016, included in their review, 25 randomized controlled trials, of which only 3 studies were found to be a low risk of bias, 8 unclear bias levels and 14 high bias levels.  They found no evidence of a difference between single visit or multiple visit treatment in terms of radiological failure, immediate post operative pain, swelling or flare-up incidence, sinus tract formation or complications.  There was moderate evidence that patients undergoing single step treatment were more likely to use painkillers over those undergoing multiple visit treatment.

A Systematic Review of Nonsurgical Single-Visit Versus Multiple-Visit Endodontic Treatment by Wong et. al 2014 which reviewed a total of 47 papers of clinical trials on the subject.  Meta-analysis showed that post-operative complications of both groups were similar.  Neither group could guarantee the absence of post-operative pain.  Neither single-visit or multiple-visit treatment had superior results in terms of healing or success rates.

Single-Visit or Multiple-Visit Root Canal Treatment: Systematic Review, Meta-Analysis and Trial Sequential Analysis by Schwendicke et. al. 2017 included 29 trials (4341 patients), of which all but 6 showed high risk of bias. Based on 10 trials, risks of complications was not significant. Based on 20 studies, risk of pain was not significant. Based on 8 studies, risk of flare-up was higher in single-visit treatment.  Conclusion was insignificant evidence to rule out whether important differences between these strategies exist.

Outcome of Single- vs. Multiple-Visit Endodontic Therapy of Non-Vital Teeth: A Meta-Analysis by Almeida et. al. 2017 is a review of 17 randomized clinical trials of non-vital teeth.  They found no difference between single or multiple visit treatment in regard to peri-apical repair or microbiological control.  They did find that single-visit treatment results in 21% less post-operative pain.

Single-Visit More Effective Than Multiple-Visit Root Canal Treatment? by Hargreaves 2006 is a review that includes 3 randomized controlled trials including 146 cases. In this review, included NSRCT of teeth with necrosis or signs of periapical bone loss - excluding pretreatment and surgical tx. It was concluded that single-visit root canal treatment was slightly more effective than multiple-visit treatment with a 6.3% higher healing rate. However this difference was not statistically significant (P = 0.3809).

Single Versus Multi-visit Endodontic Treatment of Teeth with Apical Periodontitis: An In Vivo Study with 1-Year Evaluation by Gill et. al 2016, found no significant differences in healing between teeth treated in single visit, multi-visit without dressing and multi-visit with CaOH dressing.

Treatment Outcomes of Single-Visit Versus Multiple-Visit Non-Surgical Endodontic Therapy: A Randomized Clinical Trial by Wong et. al. 2015, was a university study performed by general dentists, on 220 patients followed for at least 18 months. They reported no significant difference in success rate or prevalence of post-operative pain between the single visit or multiple visit treatments.

In my opinion, the evidence does not support that multi-step initial endodontic treatment, even of necrotic teeth, has any significant improvement in outcomes over single step treatment.  In my experience, patients usually prefer to have their endodontic treatment in single-step treatment as well.

BIAS ALERT:  In an effort to identify my own biases, I would share that I perform the majority of my endodontic procedures in a single-step.  I do use CaOH occasionally on retreatment cases that are not healing as expected or when I run out of time to complete treatment in a single step.

GentleWave by Sonendo: A Third Look

We recently had an in-office demo of the GentleWave procedure by Sonendo, Inc. (Laguna Hills, CA).  We had a great team from Sonendo who came to our office and gave a us a presentation and demonstration, including the opportunity to perform the procedure on an extracted tooth.  We spent almost 3 hours together learning about GentleWave.

The presentation was very informative and clearly explained the unique approach of the GentleWave system.  This included a history of its development with some amazing visual imaging of the technology and how the multi-sonic energy and fluid dynamics are used to clean the canal system.  We also had Dr. Mehrzad Khakpour, a GentleWave co-founder, on a conference call to answer any questions.

There is no doubt that the GentleWave system by Sonendo is a novel and unique approach to the endodontic challenge of cleaning root canal systems.  There are a several things I find very interesting about the GentleWave approach which I really like.

1. The multi-sonic energy and fluid dynamic approach to enhance irrigation and cleaning is very interesting.
2. The minimalization of canal shaping with files continues to move us in a conservative direction to preserve maximum tooth structure.
3. The concept of a negative pressure and evacuation of the irrigants and debris through the treatment instrument is a great idea.
4. The de-gassed irrigants ability to penetrate the complexities of the canal system.
5. The removal of smear layer using multi-sonic and fluid dynamics.
6. For those who do 2-step treatment, this may be a way for them to feel more comfortable with single step treatment - which patients prefer.
7. Sonendo insists that they are focused on continuing the clinical research.
8. Sonendo does have a volume discount for treatment instruments, which gives the endodontist a slight economic advantage over a general practicioner.
9. The technology is really cool. Who doesn't like new technology?

 Here are some of the questions or concerns that I have about the GentleWave procedure:

1. We have current ways to create sonic or ultrasonic activation in the canal system.  These work very well and are much faster and less expensive the GentleWave.
2. With the GentleWave procedure, you still have to locate all the canals, including calcified canals, get patency and open them up to a minimal size.  This is the most difficult and time consuming part of the endodontic procedure.  GentleWave does not solve those problems.  No time saved there.
3. Cost of the treatment instrument, materials to create the platform, additional volume of irrigants and sealers double or triple the material overhead costs of the treatment.
4. Using the GentleWave procedure will add time to the procedure. It has been estimated by one clinician currently using it that it takes 30% more time per case (20 min for this practitioner).  This would decrease the number of patients that could be treated each day.
5. The claims being made regarding improved success rates and decreased post-op sensitivity are anecdotal.
6. Hidden costs of ownership make this technology much more expensive than it appears.  A business model that requires up to 73% of the cost of the initial investment in disposable, single use treatment instruments per year (in order to get the discounted rate) ends up being a much bigger investment.
7. Will insurance companies really allow contracted clinicians to charge additional "non-covered" fees to the root canal procedure?

Being among the earliest adopters of microscopes and CBCT in Arizona, we have been through the process of evaluating new technologies and their impact on the clinical practice of endodontics.  When it comes to incorporating a new technology into practice, it should be able to:

1. Make you better - improve outcomes
2. Make you faster - more efficient
3. Make you more profitable

The GentleWave procedure will not make you faster or more profitable and there is not enough evidence to determine if it would make you better by improving outcomes significantly for patients.

This technology is fascinating. However, for such a large expense, it would be foolish to incorporate any technology into a practice that can so profoundly affect the overhead and productivity of the practice without doing an adequate cost benefit analysis, measuring the opportunity cost and evaluating the return on investment.

GentleWave by Sonendo: A Second Look

A new research article titled, "Healing of Periapical Lesions After Endodontic Treatment with the GentleWave Procedure: A Prospective Multicenter Clinical Study" by Asgeir Sigurdsson, Randy W. Garland, Khang T. Le, and Shabriar A. Rassoulian, was just published in the March 2018 Journal of Endodontics.

This new study did a great job and addressing some of the design problems with the previous study reviewed in our post titled, GentleWave by Sonendo: A First Look.  While the previous study showed that the new GentleWave procedure could be considered a good alternative to conventional endodontic therapy, I felt that it failed support its claims of superiority over conventional endodontic treatment and specifically the claim to better remove the microbial load of the affected tooth.

The main issue with the study is that it again fails to have any positive or negative controls.  It would have been easy to create a randomized, double-blinded study to compare the new GentleWave procedure with a conventional endodontic treatment.  In stead, it simply evaluates the GentleWave technique and then goes to the literature to compare its success with conventional treatment.

The major improvements in this study are:

1. Selection/Sampling Improvement:  This study evaluated teeth with periapical lesions.  These are the teeth that have bacterial issues and give us the most challenge in cleaning and obturation.  This change in the study design, makes this study much more relevant and important.
2. Attrition Improvement:  This study lost only 1 of 45 patients in the study, while the previous study lost 16% to attrition.
3. Standardization & Calibration of Examiners: training, calibration, independent scoring and consensus scoring of the periapical index (PAI) scores all demonstrate a desire for accuracy.
4. Citation Bias:  The comparisons made in the discussion to other studies, specifically Orstavik et. al. was more relevant because both studies were evaluating healing of patients with periapical lesions.  Comparing two similar samples (teeth with periapical lesions using the PAI)  makes for a more relevant discussion.  The GentleWave success rate was listed at 97.7% at one year, while Orstavik's study reported 88% success rate at one year.
5. Sponsorship Bias:  While the study was still "funded in part" by Sonendo, the study design, proper selection/sampling, standardization of examiners all significantly improve the quality of the study design and do a better job at supporting the claims made by the manufacturer.

Overall, I think this new study is much more helpful and relevant.  The next step is a larger, randomized, double-blinded clinical trial comparing GentleWave side by side with conventional treatment on teeth with periapical lesions.

Source:

1. Healing of Periapical Lesions after Endodontic Treatment with the GentleWave Procedure: A Prospective Multicenter Clinical Study Sigurdsson, Asgeir et al. Journal of Endodontics , Volume 44 , Issue 3 , 510 - 517

GentleWave by Sonendo: A First Look

We have had some recent questions about a new technology for cleaning and disinfecting the root canal system that is being heavily marketed in the dental community.  This system, known as the GentleWave System, by Sonendo Inc. (Laguna Hills, CA), consists of a console that is used to deliver the traditional irrigating solutions through a proprietary treatment instrument (TI).  The tooth is accessed, canals are located, patency established and canals shaped to #20 .07 taper, the TI is sealed to the access of the tooth.  The console then systematically delivers the irrigating solutions through the tip of the TI.  Through the TI, irrigating solutions are delivered in a "degassed" state (no air bubbles) using acoustic  and hydrodynamic cavitation.  The solutions are simultaneously removed using built-in vented suction through the same TI.

While Sonendo Inc. has been around for close to 10 years, this company has made a significant investment into the marketing of this product.  The clinical claims made by the company include:

• the technique provides improved removal of organic matter (pulp tissue and biofilm) a "higher standard of clean"
• the technique allows for minimal instrumentation of the canals, preserving valuable tooth structure
• the technique allows for improved cleaning of canals, lateral canals, isthmus
• 97% success rate of endodontic cases - in initial clincial studies

Like many new technologies and materials that are introduced in dentistry, much of the research supporting the new technology or product comes from the manufacturer or studies that are supported by the manufacturer.  It is well known that studies supported by a manufacturer tend to have bias that favors the funding source known as funding bias.   As clinicians, it is up to us to evaluate the research that is presented to us as we make important decisions.

A recent study titled, "12-Month Healing Rates After Endodontic Therapy Using the Novel GentleWave System: A Prospective Multicenter Clinical Study" by Sigurdsson et. al. published in the Journal of Endodontics, July 2016 is a perfect example of this problem. (click here to see the study)

The study concludes, "...the GentleWave System showed a high level of success after 12-month follow-up".   The abstract states, "The cumulative success of endodontic therapy was 97.3%.  The success rates of necrotic and irreversible pulpits were 92.9% and 98.4% respectively".  The failures in design of this cohort, uncontrolled study, make these numbers less impressive than they sound.

The problem with the study design is:

• Design Bias:  Bias that occurs when the design of a study selects or encourages a specific outcome.  This is 12 month prospective study with no controls.  How easy would it have been to make this a randomized, double blinded study and compare this new technology to the conventional endodontic approach. Then we might have a better idea if this technology actually improves the outcomes of treatment.  Design bias is also evident in the discussion of this study by its failure to acknowledge the one-sided study design and in the analysis of what the results mean (see below)  
• Attrition Bias: Systematic error introduced into a study by loss of participants: 75 of the 89 patients in the study returned for the 12 month follow-up.  This is a drop-out rate of 15.7%.  A major problem with almost all of our medical/dental studies is that we make assumptions about that 15%.  Since we don't have information on them, we exclude them from the study results.  So when the study says they have 97.3% success rate - they are assuming that the 15.7% that dropped out were also successes.
• Selection/Sampling Bias: Bias introduced by the selections of participants: 72 of the 89 patients included in this study were diagnosed with irreversible pulpitis.  Only 14 of 89 patients in the study had a necrotic pulp.  Cases of irreversible pulpitis have the highest success rates in endodontics.  To heavily weight a study with irreversible pulpitis cases creates a significant bias.  A study focused on treating necrotic pulpal tissue would have been much more meaningful - especially if the study aims to prove that the GentleWave procedure will better remove the microbiota from the canal system.
• Sponsorship Bias: Refers to the overwhelming tendency of a scientific study to support the interests of the study's financial sponsor. While the financial sponsorship is noted in the footnotes of the article, the tendency toward this bias requires a stricter methodology and implementation to reduce bias and a more clear and open discussion regarding analysis of results and clinical interpretation of these results.

The problems that we find in the discussion include:

• Citation Bias: The success rate of this study (comprised mostly of irreversible pulpitis cases) is then compared to the success rates of other previous studies (comprised of teeth with periapical radiolucencies - which means necrotic cases) as an argument of improved cleaning and efficacy is an example of selection and citation bias together.
• Internal Validity Bias:  Refers to the author and reviewer's confidence that the study design, implementation and data analysis have minimized or eliminated bias.  There appears to be no effort on the part of the authors to evaluate or report any bias in the study design, implementation or data analysis.
• External Validity Bias: Refers to the degree to which the study's design allow its findings to be able to be generalized to other groups or populations. The failure in methodology of this prospective study without positive or negative controls, make the comparisons made in the discussion in regards to improved clinicial efficacy unsubstantiated.
• The discussion regarding single visit vs. multiple visit endodontic treatment is again not a fair comparison when 89% of the cases in the study were irreversible pulpitis.  Those who advocate for multiple visit endodontic therapy are recommending that for necrotic cases and usually treat irreversible pulpitis in single visit as well.
• The discussion about reduced post-operative pain is again biased by a study heavily weighted with irreversible pulpitis.

So a closer review of this study shows that the study design has major flaws and multiple unidentified and unreported biases.  These biases are then ignored and assumptions are made regarding superior cleaning of the new technology.

Obviously, the GentleWave procedure can be an effective alternative technique for irrigation and cleaning of the canals.  It does not provide evidence that the GentleWave procedure is superior over conventional endodontic therapy.  The series of case reports and in vitro studies available on the Sonendo website are a good beginning to provide evidence to support the claims made by the manufacturer (click here), but there is not evidence of superiority over conventional endodontic treatment at this point.

In order to substantiate the claims being made by the manufacturer, we need randomized, double-blinded, controlled clinical trials focusing on necrotic teeth.  With this kind of data, we would be able to better evaluate the effectiveness of the GentleWave procedure over conventional endodontic therapy.

In our practice at SSE, we are committed to providing the highest levels of endodontic care.  If any technology can demonstrate a significant improvement over conventional approach with serious randomized, controlled studies, rather than cohort  studies, case reports and in vitro studies, we will be interested in incorporating that technology.  We look forward to learning more about the GentleWave procedure in an upcoming office demonstration. We will also be watching for better scientific evidence to be published and will do our best to keep you up to date with our findings.

SOURCES:

Elemam RF, Pretty I. Comparison of the Success Rate of Endodontic Treatment and Implant Treatment. ISRN Dentistry. 2011;2011:640509. doi:10.5402/2011/640509.

12-month Healing Rates after Endodontic Therapy Using the Novel GentleWave System: A Prospective Multicenter Clinical Study Sigurdsson, Asgeir et al. Journal of Endodontics , Volume 42 , Issue 7 , 1040 - 1048.

Pannucci CJ, Wilkins EG. Identifying and Avoiding Bias in Research. Plastic and reconstructive surgery. 2010;126(2):619-625. doi:10.1097/PRS.0b013e3181de24bc.