According to biocompatibility of GIC and biological characteristic of GIC for releasing florid and ionic adhesion with tooth structure, I guess that GIC has more advance than ZNP cement, in condition that setting is properly done.

In response to the question and expanding on What Hixcham Nuaimi said, I would like to add that the fluoride released from glass ionomers is only relevant in primary teeth and not of sufficient quantity to be of anti-cariogenic effect  adult teeth.

I am more interested as to why one would use a ZNP cement as a liner ?  It has an unfavourable low pH of 2.1 and stabilises at 4.6 which is still lower than ideal. Although it does have significant compression strength of approx 100 MPa its use as a luting agent has diminished in most of the Academic institutions i have been at.  

I agree these two answers. Amalgam restaurations weakens the tooth. If the cavity is voluminous and requires a GIC base, the use of composite ( direct or indirect method) is preferable for the longevity of the tooth.

Dear Ina Schueler, very fruitful your question. Here in Brazil we are in a true "state of war" with respect to amalgam. The novelty now is that they are studying the removal of the matter from the undergraduate curriculum or by the maintenance of it. I still believe that despite the obvious lack of aesthetics, when it is required (ie, where is preserved 50% of the mineral mass of the tooth crown) amalgam is the only restorative "ultimate" material with sufficient longevity (I have 25-30 years cases that I controll). If we consider the constant changes of composite restorations that always lead to (further) loss of mineralized tissue, we must also consider the amalgam restoration. As to your specific question is always important to remember that cement setting zinc phosphate occurs in short time allowing the condensation of amalgam in the same clinical session. As for glass ionomer cements, even to the dual cure ones, it is always advisable to wait 48-72 hours (according to the manufacturer's instructions) before condensation of the amalgam. If restoration in the same session is required, depending on the depth I advise the pulp capping with calcium hydroxide cement and the base with zinc phosphate cement or dentin opaque composite (with characteristics of resilience closer to dentin) resin. It is my clinical opinion!

Thanks a lot for your honest answers. In Germany, amalgam restorations are the restoration payed by health assurances and therefore still in wide use. Since decades ZnOP-Cement is used as "underfilling" with or without pulp capping with Calcium hydroxyde and this is considered "lege artis". The longevity of amalgam restorations is without any question. I was wondering if there are any trials where the success of amalgam restorations was observed regarding the liner underneath. I was not able to identify any RCT comparing this. I hope sincerelly that amalgam will persist as filling material for posterior stress bearing restorations, even if modern composites are deveoped and developing.

Dear Ina, I will forward your kind answer to Profa. Alma Blásida Concepcion Elizaur Benitez Catirse, she is a colleague from department (Dental Materials and Prosthesis) and also teach, research and work with amalgam. Her email is [email protected] Best Regards, Vinícius

Because of financial considerations, I have often placed alloys for 48 years in my private dental practice.  My patients and I enjoy our biyearly appointments and reviewing the alloys that have functioned very well for 40+ years.  They are stained chipped and tarnished but still chewing.  Many were 4 and 5 surfaces because of the damage of decay or trauma of chewing.  Realizing that this is, at best, a large case study in a single center.  Being a private practice that is not a very controlled research situation.  When the composites have lasted that long, I might consider changing.  As an insurance consultant, I have seen submissions, many a week, asking to crown teeth because the 2-3 surface  composite has failed in less than 5 years.  I have an alloy, a DLi on an upper cuspid that was placed when I was 10, 64 years ago.  I think the most functional filling is an stained chipped ugly alloy.  If it get that way, it has chewed for decades. 

Interesting Question. Alloy restorations would generally fail over Zinc Phosphate due to the solubility of the ZnP. What we have seen is 30 and forty year old Amalgam over thick red copper cement base replacing  the lost dentin. Amalgam is simply incompatible with dentin..

When we added GIC in 1983, we did not immediately quit using amalgam. We continued on using amalgam over Miracle Mix for around a year and a half, mimicking the red copper cement based restorations we knew worked.. Again, particularly if we were using an inlay or convex prep, some of these restorations are still there thirty years later. Otherwise, we have not used amalgam for thirty years now.

What I have a hard time reconciling is the terrible and inexcuesable advice to use Dycal as a base under amalgams. All of my instructors had seen the long term benefits of red copper cement, so why were we flagged off of this very good combination given the fact that we were stuck with amalgam at the time?

I have an extensive photo album of red copper cement fillings in my archives, and an extensive collection of thirty year old "bondings" with GIC base. Eliminating the expansion of amalgam against dentin assured long range success. We also have 30 year old GIC's that were placed as "temporaries" and nothing has happened to the teeth since.

I too havent come across any literature suggesting the ZnP or GIC liner contributes to amalgam failure. GIC under composite resin, on the other hand, has been shown to cause failures, presumably from the compromise in bonding. This might be solved by using RMGI. All said and done, good old amalgam restorations serve you the longest of all direct restorations. 

in olden days amalgam restoration was the gold standard but with change in cavity designs then minimal invasive technique and upgradation of materials gic is tooth friendly and preferred material

I would like to see some long term research before dismissing alloy.  The first composites looked very good at 1 years, 2 years even 5 years, but by 10 years the failure rate was too high.   New and better ones came out but they too had higher failure rates than alloy.  As one well known lecturer said, "You can be beautiful for 5 years or ugly for the rest of your life."  Alloy is ugly but it lasts.  What we really need is a way to speed up aging, so we can know more about how the new materials last.  Small conservative preps help; but, as this month's JADA suggests, a lot of the incipient lesions are better off being observed because they never progress.  If we look at cost vs. longevity and function it is hard to beat alloy. 

Thank you for this answer - If I could, I would give 10 flags!

To answer the question, and as already said before: there is no evidence that any base or liner contributes to the longevity of amalgam (and also composite) restorations. so why use them?

commenting the also adressed question whether amalgam is still superior to composite restorations: this is all to be considered within the perspective of modern dentistry, where overtreatment is more a problem then undertreatment, especially in countries where the number of dentists is exploding (Brazil).

Being known as the researcher showing that amalgam and composite restorations have comparable longevity, my clinical guidelines would be:

1. Be very conservative to intervene in a still unrestored tooth, as you'll start up the restorative cycle.

2. don't replace a still functioning restoration just because of dubious reasons, like 'insufficient marginal quality, unacceptable colour match etc. etc. It will contribute to the longevity of any type of restoration.

3. If a restoration is really clinically failing, don't replace as a first option, but do a repair!

4. considering longevity: amalgam and composite are comparable, but adhesive techniques enable to reduce the amount of sound tooth substance to be removed.

5. Use gold standard materials: 3-step etch and rinse or two step self etch adhesives and hybrid composites.

It's not a black and white discussion, it's a question how we serve the dental health of our patient in the best possible way. For me that means that I am not placing amalgams anymore since 1996, after having placed them in massive numbers between 1982 and 1996. And several of these are still functioning fine. But this will happen also with the composite restorations.

Finally: the most important factor is probalby not the material but the patient: high or low caries risk, bruxing habits etc........

Dear Ina, we do have excellent prospects with the contribution of several researchers regarding your great quesiton. As specialist both endodontics and prosthodontics, I (unfortunately) done (many) canal treatments in teeth restored with composites simply because of the "cosmetic dentistry" have routinely neglected the protection of the dentin-pulp complex, and we know that this well accepted kind of restorations are usually accompanied of miscellaneous of chemicals such as acids, self-etching primers, etc. etc. etc. Thus, a good basis over the dentinopulpar complex as protection is still desirable, since such as individuals we are different as our immune resistance qualities, allergies, etc. etc. Yet, here I leave my humble opinion to recommend (very) careful regarding restorations repairs at fault, so do not become "patches", since there is often resistance mismatch between the restorative materials, each presenting different ductbility, other showing higher hardness, and the clinician do not always have access through radiographs or surveys on the quality of both mineral and organic tissue that is under a restoration that has failed. I consider very dangerous practice in repairs of universities without prior guidance based on scientific evidence for the students understand the risks of a "burial" of active caries. It is the opinion of a clinician and clinical supervisor at the university that as we will train future dentists that will serve a population that does not always have sufficient access to relevant information such as those offered by the Cochrane Library that offers both abstract and plain language abstract for clinicians, researchers and population.

1. There is no proof that composite restorations result in more endodontic treatments.  A cement layer is not necassary and may lead to a weakening of the restoration and even more failure.

2. Dentists have to learn that a complete replacement, including all the risks and effects on the tooth prognosis, is not always good dentistry. Monitoring and repair are the better alternatives in many cases that are treated by full restoration replacement. This is not patch-dentistry, but state-of-art!

A point of view can be seen all from just a point .... there is strong evidence that the burial of micro-organisms does not take its impracticability (there are several types of nutrition and viability in cases os anaerofilia and also microaerophilic). State of the art must be based on clinical evidence and should not be disseminated a technique without longitudinal strong studiesto very few learners (undergraduate). And bases weaken restorations? Hummmm depends on how they are inserted and from the respect you have with the substrate and with the technique of handling / application manufacturers.

I think what is missing is an understanding that much of the research that comes out of dental school is, at most, 2 to 3 years in duration, the length of the graduate students research project. 

Dentistry needs studies out of practices that go on for 20, 30 or 40 years.  I would have loved to have had a graduate student come to my office and mine information from my charts, many go back in excess of 45 years.   How long did alloys last?  How long did repairs last?  Can you repair the margins of crowns?  I have photos of crowns that were placed 30 years ago and repaired multiple times over the next 30 years.  The gingival tissues receded exposing root surfaces.  The root surface decayed and it was repaired every decade or so as other decay happened. 

I think such studies out of a number of practices would lead to very valuable information about what does and does not work.  Success after 2 years is not always an indication of success for life.  We all too often call this patchwork dentistry.  I think age relevant dentistry or dentistry for life might be a better name. 

It is not as profitable as crowning everything after there is secondary decay,  nor does it lead to as many root canals and the crowns may well need repairs also.

There is loads of very interesting data in long standing dental offices that should be mined. 

My answer is based on my personal experience with amalgam. lining material does not affect directly the amalgam longevity and failure, it is the surface that we can create under this filling. Smooth horizontal surface with identified internal linear angels will provide long term survival, any material can do the job would be fine. 

Great Dr. Abdul!

I find it interesting that the topic has gone from what liner/base is best to what material is best.  I am old enough to have been exposed to the concept that a preparation that is larger than "ideal" should have a base placed until it is ideal.  I have seen copper cement, zinc phosphate cement and IRM used.  I think we are currently out of the era of using a cement in this manner because conventional wisdom is that natural tooth structure is the best base (noting that pulpal issues are addressed).  Many of us have seen failure of an amalgam restoration due to an underlying base washing out over a period of time.  We should always aspire to preserve tooth structure and in minimal carious lesions, this would favor a composite material over amalgam, due to the necessity of having a bulk of amalgam for resistance to fracture (G.V.Black Resistance Form).  In moderate sized lesions, there is a greater variance of opinion as to what material is best, and this often depends: on the area to be restored, forces on the restoration, and in some cases the desires of the patient or here in the U.S. what is covered by the patient's insurance or what the patient is willing to pay.  In very large lesions, either metal or ceramic coverage is indicated.  To get back to your original question, I think that GIC is less toxic to the pulp than zinc phosphate and can be applied in a thinner layer, decreasing the potential for creating a large void under the restoration leading to eventual fracture.. (these are my opinions and don't reflect that of the University of Maryland SOD)

In my personal experience there is no difference.

With today's EXCELLENT adhesive materials, why would anyone place an amalgam?

I am a dentist for the past 28 years and have place thousands of fillings. Many of my patients are family members and I can assure you that amalgam filling is the best filling material I ever used in the term of longevity and oral health care in the posterior region. 

Dear Niek Opdam, thank you very much for your answer, highlighting the important factors in making decisions regarding restorative treatment. I especially agree with your recommandation to focus on repair before replacing and to the minimisation of tooth substance "sacrifice" in preparing cavities for restoration.

Did I understand you well, that even under amalgam fillings you would recommend not to place any liner/cement? 

I placed thousands of amalgams in my general practice from 1980-1996. And thousands of posterior composites from 1988 until today. since 1996 I stopped placing amalgams and I seldom place an indirect restoration: large build-ups with amalgam as well as composites were and are routine. Results of this is published in JDR (2010) showing a better performance of composite especially in the larger restorations in low caries risk patients (80% of the population) and a tendency for more failure with composite in the high caries risk group, mainly because composite has the tendency to have more secondary caries.

amalgam and composites were/are placed without liners. In the early years I used a glass-ionomer lining cement with composite but this resulted in more failure (9 year results: J Adh Dent 2007). Of the failing composite restorations in my GDP, more then 50% was repaired. Results of this treatment is published in JDent 2012.

So: liners or base: not necassary. amalgam: good material, but it will disappear for sure and has the disdavantage of non-adhesive technique and esthetics. However, is not obsolete in my view, but I will not use it in any case anymore, because we have suitable alternatives.

moreover: minimally invasive is the norm: pro-active in prevention, reactive in restorative treatments........

Posterior composite: standard direct restorative material, placed with a gold standard etch-and-rinse or 2-step self etching system.

GIC and zinc phosphate cements were designed to be pulpal obtundants, to minimize the galvanic and thermal shocks transmitted  to the tooth through highly conductive metal-based amalgam. Composite resin restorations acts as insulants, both galvanic and thermal, making these liners and bases obsolete. 

You are partially wrong and you should be able to correct your proper statement. You are missing the link between tooth structure and the composite resin. This link is the major problem of the most post sensitivity of  all tooth color restorations until now . Composite resin and amalgam are great restorative materials we should know when we can use them. Glass ionomer is a great material to use as a base when we are dealing with deep restorations.

I assume that everyone understands the mandatory use of a dental adhesive between the tooth and the composite resin restorative. Pure glass ionomers have a weak bond to tooth structure and tend to break down at their surface (although they do not exhibit much marginal leakage). Bonded composite resins have a strong bond to tooth structure, and done properly, they have excellent marginal longevity and functional stability. Resin ionomers combine some of the best features of each category. None of these more modern materials require a liner or a base.

You still don’t understand the main problem when colleagues do composite restorations in posterior teeth. As I said, the main problem that we have in restorative dentistry today, is the micro mechanical interface between the composite resin and the dentinal substrate. This interface, is the weakest link of any resin restorations that manufacturers could not find the proper solution yet. I understand the adhesive dentistry has revolutionized restorative dental practice during the past of 35 years going through generation number eight in the adhesive systems but the interface integrity still leaking because we couldn’t achieve a chemical bonding yet like we have with glass ionomer. Furthermore, even, we went back to the golden standard of the adhesive system to achieve a great bonding supported by a series of researches which is the generation number four.

It is very important to undertand the pulp biology and how this component is going to behave with the presence of bacteria, fluid, nano debris at the tooth-composite interface. I am sure you know the consequences of the penetration of microorganisms and micro/nano fluid into the dentin and dental pulp because of micro/nano leakage around the margins of any composite restorations which should received considerable attention.

As you have said, “the glass ionomer exhibit very little marginal leakage” because the glass ionomer bond very well chemically to the dentin and it doesn’t break down at the interface of any resin restoration. That is the main reason why we advice to use glass ionomer in deep restorations to prevent the micro and nano leakage and to protect the health of the pulp. Remember we have two great direct restorative materials and we should know when we can use them clinically. They are: Composite resin and dental amalgam.

Dear Esteban D. Bonilla, my congratulations on your position, with which I agree in number and gender. The Nakabaiashi hybrid layer  - see: Nakabayashi N, Nakamura M, Yasuda N.Hybrid layer to the dentin-bonding mechanism. J Esthet Dent. 1991 Jul-Aug; 3 (4): 133-8. Did u have talked a few hours with Prof. Nakabayashi? The "father of adhesion" was in an important workshop in Brazil at the University of São Paulo talking about the hybrid layer and the adhesiveness was a wrong term for adhesive systems (he is biochemical by formation) and the term adhesive  would be one of pure adhesive cement polycarboxylate and also glass ionomer cements derived from the first - cement like ASPA 1 (polycarboxylate and silicate) and that the "stickiness" of the composites is just a mechanical micro-interlock. Mechanical systems fail, as the interfaces of titanium dental implants. Continuity solutions simply pass as nanostructures from outside to inside and from inside to outside. I asked him within 400 or more researchers in the event: Prof. Nakabayashi, would you use all those chemicals in your teeth? He look at me and talk: Well, as a researcher I work for this to be used, but in my teeth I always demand protection of life tissues. That's it! I agree, that both composites and amalgam are great materials for direct restorations, but the pulp vitality must be preserved.

Dr. Pedrazzi thank you for your outstanding information and great meeting with the "Father of Adhesion", Prof. Nakabayashi in Brazil. I agreed with you totally, when we do any restorative procedure our main goal is to preserve and to maintain the vitality of the dental pulp.

Dear Dr. Bonilla... perfect your position! BTW, as clinician we must to fight pain and discounfort and preserv life, promoting health in all levels! Big hug, I wish u a nice and healthfull weekend!

If this interface really would be the problem, how can it be that we have excellent results in class 5 restorations and posterior composites in observation times exceeding 10 years and annual failure rates of 1-2%. We teach our dental studnets to do total -etching for already 20 years and at the same time we have a shortage of endodontic treatments for the undergraduate program.

The trouble with in-vitro studies is that you can show all kind of effects and problems, but the question is if these findings are related to clinical problems. With the good results we have you cannot say that the interface is a real problem affecting clinical outcome.

The primary interface objective of a restoration is to seal the dentinal and/or enamel interface so that bacteria cannot proceed deeper into the tooth structure and eventually into the pulp. The best material for this interface sealing is an adhesive resin, whose attachment is micromechanical, not chemical. An effective bonding procedure develops a completely competent interface seal in approximately 30 seconds. The easiest, least technique sensitive, and most predictable bonding agent is a one-step, one-component 7th generation material.

Greetings, Dr. Freedman,

Could you kindly provide any clinical study reference for your statement on the predictability of the 7th generation bonding material? I ask because I have come across only in vitro studies which invariably excuse themselves from the burden of justifying their findings in clinical situations.

Thank you.

Here is a good survey source:  http://www.dentalaegis.com/id/2009/02/update-on-seventh-generation-bonding-agents 

Considering the best choice for adhesives, a recent systematic review published in Dental Materials by Peumans et al (http://www.ncbi.nlm.nih.gov/pubmed/25091726), measuring the clinical effectiveness of adhesives in restoring NCCL's reveils that the best retention is achieved with 3 step etch and rinse, 2 step mild self etch, one step self etch adhesives and glassionomer restorative cement.

We have recently published a meta-analysis  in JDR based on 12 clinical studies on posterior composites. (http://www.ncbi.nlm.nih.gov/pubmed/25048250) We couldn't demonstrate any effect of the material on survival. At the same time, the caries risk of the patient strongly influenced the results, doubling annual failure rates for the high risk group.

So I think it is too simple to say that the choice for a 7th generation (= 1step-self etching) is the best choice. I would stick to gold standard materials like 3 step etch and rinse and two step (mild )self etching materials. 

I you would go for a 7th generation, at least choose a mild etching adhesive, as the strong etching adhesives really perform inferior......

The 4th generation adhesives involve more components (3 or more), require more procedural steps (3 or more), and are inherently more prone to clinical error and technique sensitivity. On the other hand, 1-component,1-step 7th generation adhesives are simple and intuitive to use. The older, 1990-era 4th generation adhesives are called the "golden standard" for 2 reasons: more research has been done with them, and as a corporate marketing tool for companies that have not progressed beyond that state. The retentive values to dentin and enamel are higher with 7th than with generation, even though 17MPa is the important base value, with anything over 20-25MPa actually quite redundant. An intermediate glass ionomer layer simply weakens the interface and the entire restoration..

Dear colleague, I am not agreed with you at all what you are stating. You have said the “4th generation adhesives are inherently more prone to clinical error and technique sensitivity. On the other hand, 1-component,1-step 7th generation adhesives are simple and intuitive to use”. We are using the 4th generation for at least 22 years at UCLA and USC on posterior teeth in Class I, II and V and we have very little problems with post operative sensitivity (0.5% of restorations done by dental students). There was a short time we have tried the adhesive system of 5th and 7th generations and we got a lot of failures cases such as debonding between the the tooth structure and resin restoration causing problems such as reduced fracture resistance, increased microleakage and high post operative sensitivity on posterior teeth especially on chewing. Then we went back to gold standard adhesive system like 3 steps system etch/rinse, primer and adhesive application. We have better control of each component because they are applied separately in a carefully controlled sequence. We allow the primer and adhesive to get in contact directly with the dentin in order to form the hybrid layer. Furthermore we can get a very strong bonding in the enamel to seal and to hold the resin restorations properly. I believe we need to see at least 7 to 10 years clinical study before we say the 7th generation will give us an outstanding outcome. Now with the latest adhesive system, 8th generation (Dual-cured self-etch adhesive) we should be very cautious as well and we can not start doing some experiments with our patients who deserved the best dental restorative treatment to achieve a wonderful esthetic result, excellent function and great longevity.

Despite the good results achieved by the three-step etch-and-rinse adhesive systems, several studies have reported excellent performance of self-etch products in laboratorial (Marchese et al., 2014, Nairet al., 2014, Sahin et al., 2012) and clinical studies (Perdigão, 2014; van Dijken, 2012; van Dijken, 2013). Recently, clinical studies have observed promising results with one-step self-etch adhesive systems (Perdigao, 2014; van Dijken, 2012; van Dijken, 2013). Santos et al. (2014) in a systematic review about the retention of restorations placed in NCCLs observed no significant difference in a risk of loss of restorations between a three-step etch-and-rinse adhesive system and either a two-step self-etch system or a one-step self-etch system (Santos MJ, Ari N, Steele S, Costella J, Banting D. Retention of tooth-colored restorations in non-carious cervical lesions--a systematic review. Clin Oral Investig. 2014 Jun;18(5):1369-81).

I do agree with Niek J M Opdam

No evidence to suggest that the use of liners under amalgam adds to its success. The success is more related to preparation designs and expertise

The Council of Scientific Affairs of the American Dental Association (ADA) concluded in 1998 that amalgam continues to be a safe and effective restorative material in view of scientific information available at that time [44], and the ADA affirmed this statement in 2002, 2003, and 2009 [1, 7, 66]. The ADA stated that if the organization considered that dental amalgam posed a threat to the health of dental patients, they would advise their members to cease using this material for restorations. The ADA has concluded that dental amalgam offers a safe and cost-effective treatment option. Recently, the Council of European Dentists (CED) declared that dental amalgam continued to be the most appropriate material for many restorations due to its ease of use, durability, and cost-effectiveness (CED, 2010) [67]

It is good to line the deep restorations. The conductivity of hot and cold sensations will be reduced. In case of failure of restoration, it is easy to remove the restoration.