Finally, we are reaching the conclusion of our summary of bonding agents! I know everyone will be thoroughly excited to talk about something different.

Seventh generation bonding agents are truly one bottle systems. Within that bottle, etch, primer, and adhesive resin are all present. Seventh generation products do not require a preemptive etch, just prep, isolate, and apply. Unlike sixth generation adhesives, seventh generation adhesives do not require mixing. As incredibly convenient as these products could be, they do not perform well in trials. Bond strength is consistently lower than both 4th and 5th generation adhesives.

While I think that seventh generation bonding agents could simplify bonding considerably, the data does not support their use in practice. With some tinkering, it is possible that a one bottle system will emerge with good clinical success and ease of use, but that product is not here yet. Stick to 4th or 5th generation. You and your patients will be happier!

And now a short break from bonding!

A few times a year I get a publication from the American Association of Endodontists. As a general dentist, I am not a member of the AAE, but this particular publication is not meant for endodontists. They publish a few of these a year and target them for general dentists. I am not sure how I got on their mailing list, but I am glad I did.

Each of these pubs covers one specific component of endodontics. This newest issue is all about access. It covers everything from pre-access analysis to trouble shooting. It’s a great publication with excellent illustrations and photos. If you aren’t receiving this pub, by all means, visit the website and get signed up here.

In our last few blog posts and in an upcoming column in the magazine, we have been covering bonding. As I have stated before, bonding transcends all disciplines of dentistry and a firm understanding is essential.

Again, we all know that 4th generation bonding systems yield the highest bond strengths according to countless studies. In the name of ease, manufacturers have continuously attempted to simplify bonding. One of their key strategies is to combine different steps of the bonding process. With each iteration, a new generation of bonding agent is born.

Fifth generation bonding agents combine the primer and adhesive step. These still require a total etch with phosphoric acid etch. Fifth generation bonding agents are very popular on the market. Some of these systems can yield bond strengths almost comparable to 4th generation agents. If I were to deviate from 4th generation, I would use a 5th generation.

Sixth generation bonding agents consist of self-etch adhesives. There are two different types of 6th generation agents. One type consists of a self-etching primer and a separate adhesive. The other type combine conditioner, primer, and adhesive but require mixing. Sixth generation bonding agents generally have lower bond strengths than 4th or 5th generations. In my opinion, 6th generation bonding agents really have little use in dentistry. The point of deviating from the tried and true 4th generation bonding agents is to reduce the number of steps and simplify. Having to mix three different agents mitigates this and ends up netting no gain in simplicity or time. Even in the two-bottle 6th generation agents, the number of steps is not reduced from 5th generation bonds which yield much higher bond strengths.

Last post we discussed 1st-3rd generation bonding agents, which brings us to 4th generation.  We often read that 4th generation bonding agents are the cream of the crop and have the best results in trials.  Often times we blow right through that without any thought of what 4th generation bonding agents actually means.

What sets 4th generation bonding agents from it’s predecessors is the use of a pretreatment to the dentin that makes the dentin more receptive to bonding.  This is what we call a primer.  This primer is applied after total-etching with phosphoric acid.  In the past, there was some concern about damaging pulps when etching dentin with phosphoric acid etch.  This would lead to some practitioners just etching enamel and n0t dentin.  That lead to the use of the term “total-etch” which I used earlier meaning etching both enamel and dentin.

As a final step in a 4th generation bonding system, unfilled or semi-filled low-viscosity adhesive resin in applied to both enamel and dentin.

So to recap, 4th generation bonding systems involve three steps.

1) Total etch with phosphoric acid etch

2) Primer

3) Adhesive

These can be quite technique sensitive which is a disadvantage to these systems.  The research shows clearly that bond strengths with 4th generation bonding agents are higher than all other systems.  Personally, I use a 4th generation bonding agent in my practice and recommend all practitioners do the same.

Often times I throw around terminology that may be confusing to those reading from different schools or countries. In a recent entry, I mentioned bonding systems and used the terminology of “4th generation.” Some of us may take for granted our understanding of this, so I thought I might recap bonding agents over a few articles in order to increase our knowledge of the subject.

Dental literature and manufacturers use the terminology of generations when describing bonding agents. While somewhat confusing, there seems to be little movement amongst the industry to move away from generational classification of bonding agents.

Today I will discuss 1st thru 3rd generation bonding agents. They are of little importance to us today, as 4th generation and above are the only generations currently available on the market.

1st generation bonding agents- Date back to early 50’s; achieved dentin bond strengths of 2-3 MPa that were unstable in water; Cervident by SS White was the first commercially sold dentin bonding agent “theoretically bonding to enamel and dentin by chelation with calcium on the tooth surface and had improved water resistance.” Obviously, a dentin bond that is unstable in water is no good intraorally. I think it is interesting to note that dentin bonding was being explored as far back as the 1950’s.

2nd generation- introduced in 1978; relied mainly on enhancing ionic interactions within the dentin structure; yielded bond strengths of 5-6 MPa; clinical trials yielded poor results; most bond strength probably came from bonding to the smear layer and not to the dentin itself.

3rd Generation- developed in early 1980’s; first bonding agents that utilized the philosophy of acid etching dentin to remove smear layer; served as basis for some bonding systems available today like Amalgambond and C&B Metabond; adhesives were mainly self-curing resins; Scotchbond 2 was first product to receive provisional acceptance from ADA which was followed by full acceptance.

There we have it. A brief look at 1st thru 3rd generation bonding agents. I will be back soon with a summary of 4th thru 7th generation bonding agents.

Always remember, the generational classifications pertain to dentin bonding only. Enamel bonding has been successful for many years with an acid etch technique. Dentin bonding requires the presence of adhesives and primers. Just an afterthought worth noting…

The November/December issue of “General Dentistry” (the peer-reviewed journal of the AGD) has a great article written by Dr. Michael Miller who is the president and editor of REALITY. The article is titled “The Gold Standard” and has brief summations of some things in dentistry that reach the highest level of achievement.

There are very few surprises in the article but of note is his section on bonding agents. He gives a very good quote that we should all keep in mind. Miller says “If you could have only one bonding agent in your office, it should still be a total-etch version.”

I think this statement is of significant importance. Fourth generation bonding materials still outperform all other generations in studies. While I feel there is a place for some other types of bonding agents, Fourth generation agents should be our work horses and be doing most of the bonding in our practices.

In a future entry, I will summarize the different generations of bonding agents and review some literature on the subject.

There are some really cool things going on in endodontic research these days.  One of which has to do with endodontic regeneration.

An in progress case report can be found on PubMed here.

What the researchers are finding is that in young permanent teeth with necrotic pulps and periapical pathology, revascularization can actually return vitality to the tooth.  As a result the periapical pathology can resolve as well.  The thought is that stem cells around the apex of young teeth can be utilized to regenerate a dental pulp.  There is some argument as to the best procedure to do this.  In the PubMed case report I listed above, the endodontist utilized coronal irrigation with no instrumentation.  Other procedures utilize taking endodontic files out of the apex to draw stem cells back into the tooth.  MTA is of great use during these procedures as well.
There is some thought in endodontic circles that this could eventually lead to a product with growth factors that could be injected into a necrotic pulp that could return a tooth to vitality without performing endodontic treatment.  This is some ways away, but steps are being made in that direction.  A good friend of mind did research on this during his endo residency.  I will try and get some periapical radiographs of some cases he did and post them here.

Several weeks ago, I received a fax from an allergist regarding a mutual patient. The patient had gone through a routine allergy skin test and some interesting results came up.

The patient tested positive for gold sodium thiosulfate which is a gold derivative used for screening of contact allergy to dental gold materials. I found these results quite surprising. We are all familiar with allergies to nickel and other base metals, but I had yet run across a patient with this allergy. I spoke to some colleagues who were also unfamiliar with any patients with gold allergies. We are taught that gold is a noble metal producing the most ideal of gingival responses.

After a quick PubMed search, I found the following article:
Investigation of contact allergy to dental metals in 206 patients.
Raap U, Stiesch M, Reh H, Kapp A, Werfel T.
Contact Dermatitis. 2009 Jun;60(6):339-43.

The authors found that out of 206 patients, 28 had positive patch tests to some dental metal. The number of positive patch test reactions was highest for gold sodium thiosulfate, palladium chloride, and nickel sulfate.

Wow! So out of dental metals, gold is one of the most common allergies. The sample size is quite small on this study. It would be interesting to see the results with a sample size of 1000 or 2000. My instinct tells me that we would see a much higher incidence of nickel allergy with a larger sample size, however those results are not evident with the smaller sample size.

It is with great pride that I make my first post here with The New Dentist.  I joined The New Dentist team several weeks ago, taking the role as clinical blogger.  Previously, my blog was self published as The New Dentist Blog.  Now as Clinical Buzz, I will be posting very similar type stories.  The previous posts you see were previously published at The New Dentist Blog.  Starting tomorrow, you will begin seeing new clinical posts here at Clinical Buzz.

I look forward to many valuable interactions with readers of Clinical Buzz!

Joshua Austin, DDS

In this recent blog entry, we discussed the hierarchy of evidence and briefly touched on the different types of weak evidence. Today I would like to begin to review stronger evidence as we move up the chart.

After opinions, case reports, and case series we have case control studies. I know, all the terminology gets confusing. A case control study is a retrospective study of patients who already have a certain condition compared with control subjects.

That almost reads like a foreign language. The best way to understand this is with an example. Let’s say that we are setting up a case control study on lung cancer. We would compare patients who already have lung cancer with patients who don’t have lung cancer. We would ask the patients with lung cancer how much they smoked in the past. These answers would be compared to the answers of the control patients who do not have lung cancer.

Case control studies can be somewhat less reliable than stronger forms of evidence like randomized clinical trials or cohort studies. This is because a statistical relationship between two conditions does not mean that one condition actually caused the other. For instance, lung cancer rates are higher for people without a college education (who tend to smoke more). But this does not mean that you can reduce the risk of lung cancer just by getting a college education.

Our next article will discuss cohort studies. I am sure that all of you are elated with joy [/sarcasm].

Posted by Joshua Austin, DDS