As usual when I read an article, I pretty much ignore the marketing fluff known as the abstract. Reading the abstract gives you the conclusions without the underlying data and can bias your critique of the materials, methods and most importantly, the assumptions.
The second paragraph into the introduction brings a statement with potential to go wrong.
"Improving the prognosis of endodontically treated teeth requires understanding their bio-mechanical properties".
The danger in that statement is that it can fool us into thinking that understanding biomechanical properties gives us an ability to predict outcome.
Unfortunately, outcomes in dentistry are devilishly difficult to predict and often teeth do not behave as instructed by in vitro/modelling tests. I would prefer a statement like;
"Improving the prognosis of endodontically treated teeth requires observing various types of treatments over a long period of time in the mouth whilst observing particular patient characteristics such as bruxism".
After some discussion on how removing structure makes teeth weaker, there is a significant error introduced.
"..it was generally necessary to retain non-adhesive indirect core buildups by placement of indirect cast endodontic posts........resulted in further loss of healthy tooth structure".
Firstly, despite the loss of tooth structure, well done cast post restorations seem to be the oldest post and core restorations I see in my practice, some of them pre-dating my birth in teeth with no ferrule. So from an outcome basis, rather than a ideological one, there seems to be a problem with this. Secondly, cast posts are not considered in the experiment so this statement is pure conjecture.
A little further on we are advised that posts must involve the preparation of the root canal. This is not true as most people now use thinner posts that do not require any further removal of tooth structure than was needed for the endo.
This is followed by another major error that betrays an academic's lack of long term relationships with patients in a practice.
"The main goal for any treatment - and even more so for severely broken down teeth - must be to preserve as much dental hard tissue as possible".
Dear patient, your $1500 crown fell off a month later, but at least we preserved all your dental hard tissue. The goal of any treatment will be established by the patient's values and for many, it will be their dental work giving good value for money by lasting as long as possible. It is very important to not get distracted from the patient in establishing what is successful treatment.
As we move into the materials and methods we can see that they are using freshly cut dentine from extracted third molars. This of course does not replicate the poor condition of the dentine in your average in-vivo tooth requiring buildup so they likely get completely different bonding results.
They use weaker empress crowns supposedly to help test the core more quickly than say emax, but this again is rarely used, so complicates the extrapolation of results.
Now we reach the biggest problem. This test was done using a machine that applied repetitive cycles to the tooth in increasing loading. This gives us no confidence that it simulates the mouth.
We are told that this protocol has been shown by Fennis and others that it better simulates clinical conditions better than other static load tests. This is like saying a paper aeroplane better simulates the conditions of an Airbus A380 than does an unfolded flat piece of paper. It's a true statement, but not one I'd buy an airfare on.
In any case, I looked up the article by Fennis and it's also a very theoretical in vitro test that is entirely removed from such distractions as...er...patients. And clinical outcomes.
Interestingly, they could not get the crowns to fail with vertical or tripodised occlusion, and had to resort to the 30 degree offset to get them to fail within their time and money budget. So perhaps occlusion is the most important factor after all. Classic pros for the win.
Amusingly, we are advised that they great advantage of the in vitro study is "high level of standardisation with well defined parameters". There is no mention of the fact that it's drawback is that it relates to absolutely no clinical situation we will ever encounter.
One of the interesting things we get out of this paper is that often bonded crowns do not fail by debonding, but by catastrophic failure where the strong bond of the crown takes a large piece of tooth with it when it fractures. This mirrors my clinical experience which is bonded crowns rarely fail by just dislodging and often take a palatal or buccal cusp with them leaving a subgingival margin to repair. This flies in the face of the "at least it is the restoration that failed" ideology.
The conclusions of this article should be soundly ignored unless one has a patient with a virgin third molar that you wish to cut to gingival level, do RCT and then place a composite core and an empress crown and only allow the patient to bite on it at 30 degrees for slightly less than a year until it fails.
We can also conclude that in a laboratory setting doing a large prep (which most people do not do) to place posts does not help.
This is not to take away from the important work that academic researchers do in dentistry, nor Magne's contributions, but to merely make sure we do not take confidence in articles when making clinical decisions where the article is not applicable to clinical situations.
There is nothing we can take from this article and extrapolate to the mouth with confidence and prognosticate about longevity. On a scale of evidence, this would rank below the anecdotal observations of long established and obsessively documenting dentist that treats many patient's over a long period of time with long term clinical follow ups in a single location.
As a final parting shot, the conflict of interest statement states "The authors have no proprietary, financial, or personal interest of any nature or kind in any product, service and or company that is presented in this article" This is extremely doubtful given that at least one of the authors earns much or most of his income from speaking and each time he speaks, only sponsorship by large companies such as 3M, Ivoclar and Sirona make this possible.
I am certain that this article will be heavily mis-used and quoted in lectures erroneously.
Detailed review of Magne's latest article, here is the link to this article.
Dr Lincoln Harris has been completely focused on excellence and quality from the beginning of his career as a dentist. He established the first private dental practice in Bargara – Harris Dental Boutique in 2000. Since graduation he has trained extensively in Aesthetic Implant Techniques and Full Mouth Rehabilitation to attain immense skill and knowledge. With his vast dental knowledge Dr Harris coaches and trains dentists from all over the world on complex aesthetic dentistry, surgical techniques and business management. Dr Harris is the founder of RIPE. Restorative Implant Practice Excellence: Full Protocol group an international forum of over 70,000 members worldwide. The purpose of the group is to share information and excellence in the dental industry. He has also lectured in multiple cities throughout Australia, North America, Asia, Singapore, United Kingdom and Europe.