TBU # 022: Stress Reduced Direct Composites: 11 Factors For Success

In this article you are going to read about the: Stress Reduced Direct Composite (SRDC) technique. SRDC is one of the techniques in Biomimetic Restorative Dentistry.  It will help you in some (not all) cases to avoid, for example, a crown lengthening surgery

To begin with, I want to thank Dr. Jeff Davies his invitation to participate on his web 

Let me introduce myself: 

I am Dr. Luis Marcano, writing these lines from Caracas, Venezuela

I’ve been learning and practicing Biomimetic Dentistry, first on my own.

And now, in the Academy of Biomimetic Dentistry.

I’ve been “online” for more than three years with my own blog on Dentistry, written in Spanish, with thousands of readers each month

And now, thanks to Dr. Davies, I will share with you the stress reduced direct composite technique.

Keep reading and you will discover its details.

What are the stress reduced direct composites?

Stress reduced direct composites are single visit direct resin-bonded composites, which are an alternative to conventional indirect restorations.

The goal is reducing stress on hybrids layers and teeth while restoring them

According to a Clinical Evaluation Published by: Deliperi, Bardwell & Alleman, SRDC are now possible thanks to the evolution on:

• Composites 
• Bonding agents (adhesives)
• Light curing units.

And let me add one more: 

• The improvement of scientific evidence through decades.

Shrinkage: a composite-related problem.

Shrinkage through/after light-curing is a constant in all composites

Nowdays it goes from 1% to 5%.

No matter what system of composites you’re using, it shrinks during and after light curing it

And, according to Dr. Deliperi it:

• Could create a gap from 1.67% to 5.68% of the total volume of the restoration

Indications

•  Cases where we would resort to semidirect or indirect restorations.
•  But the patient prefers a solution in a single appointment 

That means:

•  Isthmus greater than two thirds of the intercuspal distances.

There are different criteria among authors.

For example, Dr. David Alleman recommends:

•  Onlay non functional (tension) cups thinner than 3mm
•  Onlay functional (compresion) cusps thinner than 2mm

In the other hand Dr. Simon Deliperi will keep 1.5 (and biggest) cusps.

Using methods such as the wallpapering technique

Which one should you use? 

It will depends on your diagnostic, training and expertise.

And the wishes of your patient

There is no such thing as an universal answer

Regarding training and expertise, you will get them, here, in Dr. Jeff Davies’ online course on Biomimetic Dentistry.

11 factors for success

According to a case report published by Dr. Simon Deliperi in Operative Dentistry, they are:

•  Occlusion. Preoperative analysis.
•  Excavation of dental caries. 
•  Cavity preparation. 
•  Analysis of residual tooth structure. 
•  Immediate dentin sealing. 
•  Layering technique. 
•  Occlusal force equilibration.

Alleman & Nejad (Inside Dentistry, 2017) proposed a few more:

•  Remove dentin cracks. 
•  Decouple with time.
•  Fiber inserts.
•  Light curing technique.

Stress reduced direct composite Technique (step-by-step)

So,

How could you perform a stressed reduced direct composite?

First of all, knowing when to use this technique

Then, following these steps:

Analysis of the occlusion

We need to perform a preoperative occlusal analysis, in order to:

•  Find where the bigger concentration of the occlusal load is.
•  Know which ones will be the final occlusal load points. 

Selective caries removal:

In biomimetic dentistry we do not use the traditional visual and tactile techniques.

In order to differentiate outer carious dentin, from inner carious dentin.

And then creating a peripheral seal zone.

Our goal is to remove both of them (outer and inner) carious dentin in the peripheral seal zone

To achieve a long term marginal seal, so the restoration lasts for many years 

(provided that the patients take care of their oral health during that time)

Excavate

First of all, we advise you to use rubber dam, because:

•  The isolation will give you a better visualization of the operative field. 
•  Dental bonding systems and composites are sensitive to moisture.

Once the rubber dam is placed you will:

•  Remove decay dental tissue. Max. 5mm from the occlusal surface and 3mm from the proximal wall to avoid pulpal exposure 

If the tooth has pulp vitality, you should stop in those caries removal endpoints

The same applies to cracks:

•  Remove cracks within 2mm of the dentin-enamel junction

5mm from the occlusal surface (max.) and 3mm from the proximal wall is where you should stop (crack removal endpoints)

In this way, we will avoid pulp exposure and preserve tooth vitality

What we are doing is taking care of the tooth, working in order it lives even beyond the restoration lifetime

Peripheral Seal Zone

Make sure you create a peripheral seal zone (2-3mm within the enamel dentin junction free of caries/hard tissue dyed)

This, to make sure a good seal of the restoration with an average bond strength of 50MPa

Cavity preparation

•  Remove sharp edges on enamel and unsupported prisms

Analysis of residual tooth structure

At this point:

•  Onlay functional cusps thinner than 2mm.
•  Onlay non-functional cusps thinner than 3mm.

Immediate dentin sealing

Immediate dentin sealing is one of the cornerstones on Biomimetic Dentistry.

And of course, it is another step in our stress reduced direct composites restorations.

  Tooth preparation can produce a lot of dentin exposure.

According to Dr. Pascal Magne, immediate dentin sealing (IDS):

•  Prevents dentin contamination.
•  Prevents any susceptibility of the hybrid layer.
•  Allows to work with more conservative tooth preparation. (An overlays saves up to 50% of tooth structure in comparison with dental crowns preparations) 
•  Improves bond strength.
•  Avoids gap formation.
•  Protects the tooth against bacterial leakage. 

Magne et al (2005) found that teeth treated through IDS showed microntensile bond strength (MTBS) values between 53.61 and 61.96 MPa.

On the other hand, teeth treated with delayed dentin sealing showed MTBS values between 0.36 to 26.52 MPa.

That is a significant difference.

Therefore:

•  freshly cut dentin is the best one for dentin bonding.
•  Polymerization of the dentin bonding agent as a separate step (in time and technique) improves bond strength. (we´ll talk about this in the “decouple with time” section)

But immediate dentin sealing is a technique that relies on:

•  The dentist’s expertise.
•  The type of dentin bonding system.

This article is specifically about stress reduced direct composites.

In other article in this web, Dr, Davies addressed the subject of the bonding agents.

Here, we recommend two type of adhesives

They’re two gold standard bonding agents:

• Optibond FL (Kerr). Recommended by Dr Pascal Magne.

• Clearfill SE Bond 2 (Kuraray). Recommended by Dr David Alleman 

Each one has its own set of techniques

Optibond FL

Dr. Pascal Magne´s article on IDS (2005) used OptiBond FL as bonding agent.

Which is the DBA recommended by him.

Which will require we use a total etch technique.

• Start applying 37% phosphoric acid on the enamel.

• Then continue to dentin.

• For 15 seconds

• Wash with water for another 15 seconds

It’s important to rinse the tooth for that time, beyond “removing the blue gel”

Because we need to remove the salts produced during the etching

• Now apply 2% clorhexidine for 30 seconds

Clorhexidine will deactivate the MMPs that, otherwise, would decrease our bond strengths in time

Opening a door to the failure of our SRDC restorarion

• Wash with water for 15 seconds 

So, clorhexidine will: 

• Deactivate the MMPs (that we activate using phosphoric acid on dentin)

• Increase the wetting capacity of dentin. Therefore, improving adhesion

• Increase the microtensile bond strenghts between restorations and dentin 

Warning: use only systems of clorhexidine for cavity cleaning, never clorhexidine mouthwashes, since those have other components that will hurt your bonding protocols, and outcomes.

•  After clorhexidine, remove excess and getly air dry
•  Apply Optibond FL primer with a gently scrub motion for 15 seconds
•  Gently air dry for 5 seconds until the point the dentin shows a shiny appearance.
•  Light cure

Then:

•  Apply Optibond FL adhesive over enamel and dentin uniformly.
•  Remove any excess using a micro-applicator
•  Light cure for at least 10 seconds with a wavelength : 400-515nm (more on this later in this article)

Clearfill SE Bond

This adhesive requires using a self-etching technique on the dentin.

Dr. Junji Tagami (Japan) has published some scientific evidence about this bonding agent.

After they selective caries removal:

•  Sandblast the teeth. Using 50 µm oxide aluminum particles

This will help you to discover any remaining cracks in dentin

And it’ll be useful to achieve a thin smear layer. 

•  Apply clearfill SE Bond primer for 20 seconds.
•  Evaporate the volatil ingredients with an air stream.

Then:

•  Apply the Bond (second bottle)
•  Light cure for at least 10 seconds using a curing light with an irradiation of wave length : 400-515nm)

Resin coating

Resin coating, also called “reinforced IDS”, is a thin layer of flowable composite over the IDS, to protect the hybridized dentin

It is another step in the stress reduced direct composites restorations, because:

•  Positive pulpal pressure can push the penetration of dentinal fluid in the hybrid layer causing gap formation (even of the thick layer of the OptiBond FL adhesive)
•  There is some risk of dentin exposure. For example, if we use air abrasion.

A thin layer (0.5mm) of flowable composite will help us to avoid these risks.

Decoupling with time

Each hybrid layer will need at least 5 minutes to reach their maximum strength

Pascal Magne and David Alleman found that IDS + decoupling with time will help us to achieve 400% more bond strength.

This, because after the polymerization of the dentin boding agent, the dentin bond strength has its own time to develop, stress-free, over time.

The goal is:

•  The maximum monomer conversion possible. This continues happening after we stop light curing the adhesive system.

There are two ways of decoupling with time:

•  Placing small increments of composites. Our first layer should not be thicker than 1.5mm the first 5 minutes.
•  Waiting at least 5 minutes after light curing the DBA we place over the dentin.

As a matter of fact, according to Deliperi, Alleman & Rudo:

•  We have to perform stress reduction steps in the first 5-30 minutes after the polymerization of the dentin bonding agent.

Whatever be your choice, this will give time to the hybrid layer to mature and develop the best bond strength possible.

Remember, we are talking about a stress reduced direct restoration, so we have to use time as a tool.

Due the hierarchy of bondability composites flows towards the most mineralized surface during polymerization.

Layering technique

As you read a few paragraphs above, shrinkage is a composite-related issue in all composites.

Resin-based composites have become one of the first options to restore teeth.

They have advantages like:

•  We can reproduce the tooth´s color and tones with them.
•  Make possible a minimally invasive dentistry.
•  Make possible ealier treatments. For example, the infiltrative composites.
•  Patient can use their new teeth immediately.
•  Composites can be repaired.

And some of them offer advantages for biomimetic restorative dentistry, for example:

•  Fiber reinforced composites (E.g. Ever x) make possible to create a safe-fail mechanism in our restorations.
•  Some composites (like APX) has mechanical properties that help us to use them as dentin replacement.

In the cases of indirect restorations, shrinkage is away from the tooth

And our hybrid layers have a lot of time to mature.

But:

While layering a stress reduced direct composites we need to choose how we are going to do it

Since polymerization shrinkage is present in composites that are bonded, it is mandatory to prevent gap formation. 

What incremental technique should we use?

•  Horizontal?
•  Vertical?
•  Oblique?

Nikolaenko et al. found that:

•  There are differences in bond strengths when different layering techniques are used.
•  The first composite increment is crucial.
•  The vertical and oblique technique showed almost no adhesion to the cavity floor. 
•  Horizontal increments are the best way to get a good bond of the cavity floor.
•  Thicker adhesive layers in DBS (like OptiBond FL) may have increased to a slightly dentin bond strengths

So we advise you:

•  to use 1mm horizontal increments when performing a stress reduced direct composite (the thicker the layer the less curing-light penetration)
•  Each increment should be placer to only two bonded surfaces, in order to decrease the C-factor ratio.

Fiber inserts

Polyethylene fibers, such as Ribbond, place after the resin coating, functions as a fail-safe mechanism in the Biobase.

Indications:

•  Pulpal floor. 
•  Pulpal chamber.
•  Axial walls. Only dentin (or dentin replacement)

By placing the fiber insert so close to the dentin, composite on one side of the fiber moves in a different direction than the fiber on the other side.

There is a highly connected polymer network without stressing the hybrid layer.

The more tooth structure is compromised (e.g. decay) the more the potential of a catastrophic failure

We, as Dentists, take patients with previous large amalgam restorations o metal-porcelain crowns, which:

•  Are not bonded to the tooth structure.
•  Causes occlusal stresses on the tooth.
•  Resistance forms create areas of big stress concentrations.

All of this increase the risk of cracks.

By using fiber inserts in our stress reduced direct composites, we aim to:

•  Increase the composite toughness.
•  Mimic the crack shielding mechanism of the dentin enamel complex.

How to place polyethylene fiber inserts? The wallpapering technique

This step comes after we perform the IDS + resin coating.

Remember you have decoupling with time is needed in that phase.

At this point you will have to:

•  Estimate if the tooth needs one or more fiber inserts. (are one or more cusps missing? Does the pulpal chamber need to be restored?
•  Choose length and width of the fiber.

Then:

•  Wet the fiber insert (s) with an unfilled resin. For example Ribbond wetting resin.
•  Remove the excess of unfilled resin.
•  Cover the fiber with flowable composite. (or place the fiber on a thin layer of AP-X)
•  Bond to the surface (axial wall, pulpal floor or pulpal chamber)

Two important tips:

•  Each fiber will stop at an imaginary (or real) DEJ line.
•  Adapt the fiber(s) as closely as possible against the residual tooth. To replicate the DEC mechanism of protection against cracks.

In biomimetic restorative dentistry we call biobase the set composed of: 

•  immediate dentin sealing.
•  + resin coating.
•  + fiber insert.

Advantages of fibers

•  Polyethylene fibers as Ribbond distribute the stresses of the occlusal load over a greater region. 
•  This helps to control shrinkage and occlusal load stress.

Now, let’s talk about curing lights

Light curing technique

From the IDS to the final layer of composite (and beyond) we have to light cure the DBA and each layer of composite.

The question is: how?

I´d say not trying to rush it.

We may:

•  Use a slow start polymerization.
•  Use a pulse activation.
•  Or perhaps we may light cure through the tooth walls.
•  Or start the light activation getting the curing light a few millimeters away from the tooth.

Take into account:

•  Each light curing led is different. And have different wave length, intensity and features.

Each light curing unit differs in the amount of radiant emittance and the energy source to power it.

•  Different resin-based composite requires different light energy levels at specific wavelengths (we recommend reading the manufacturer´s instructions regarding each type of composite)
•  The intensity of the curing lights diminishes with the distance (e.g. proximal boxes, pulpal chambers)
•  Shades, translucency and filler load change the time each composite needs to be light cured.
•  The degree of conversion (DC) is paramount in the success of the stress reduced direct composites.

What is the degree of conversion?

It is the percentage of monomers that become a polymer.

This conversion implies one thing.

•  Shrinkage of the composite during the light curing.
•  Less than ideal mechanical properties of composites before poor curing protocols or flaws in the light-curing equipments.

Photopolimerization has three stages: initiation, propagation and termination.

Let me explain this stages:

•  We use our curing lights. This causes that photoinitiators absorb photons and generate free radicals (initiation)
•  These free radicals react with the monomers causing a polymer chain.
•  The polymer chain increases the cross linking of the chain to another polymer. The composite become rigid (propagation)
•  After this, the free radicals forms a stable covalent link (termination)

Considerations for choosing a light curing unit

•  Irradiance.
•  Energy.
•  Beam Uniformity.

Any flaw in these features could lead to secondary caries.

Why?

Because of the undercuring of the composite (or even the dentin bonding system)

Undercuring is caused by an insufficient energy delivery on the composite, leading to a less than optimal degree of conversion.

High degree of conversion values are needed to achieve get the best mechanical properties from composites

That means: 

•  good compressive strength
•  fracture toughness
•  good bonding.

Given we are talking about stress reduced direct composites, the question arises:

How to light cure the composites minimizing the stress?

And at the same time delivering the adequate amount of energy to achieve an excellent degree of conversion.

Equipment

•  It is mandatory to use an excellent light curing unit.

Your LCU will be with you a lot of time, and will be responsible (in part) of the success or failure of many of your restorations

So, spare no expenses.

Maybe in another article will be addressed this subject specifically, but I will mention some good LCUs here:

•  Valo Grand (Ultradent). Wavelength range 385 to 515 nm, collimasion across its 12mm lens, light intensity from 1.000 mW/cm 2 to 3.200 mW/cm 2
•  Elipar (3M). 430-480nm wavelength, 10mm lens, light intensity 1.470 mW/cm 2
•  Bluephase (Ivoclar). Wavelength range 385 to 515 nm, light intensity from 1.200 mW/cm 2 to 3.050 mW/cm 2. 
•  S.P.E.C 3 (Coltene). Wavelength range 430-490nm, light intensity from 1.600 mW/cm 2 to 3.500 mW/cm 2

Time

•  Start far, star slow.

Another to achieve a stress reduced direct composite is by starting light curing the composite with the lens of the LCU a few millimeters apart from the cavity, for the initial seconds.

Doing it in this way, you will have to spend more time light curing the composite.

But you will make sure you are reducing the stress on the tooth, the hybrid layer and every layer of composite you place.

•  The farther is the light surface from the composite, the more time you have to light cure it.

Examples: proximal boxes, pulpal chamber.

Your curing light loses intensity with each millimeter of distance

And you will have to make up for that lost by increasing the curing time.

How much? 

Read the manufacturer´s instructions first to find out what the standard light curing time for your DBA and composite.

Then, increase the light curing time in radical scenarios such as the examples above.

•  As you read some paragraphs above, we need to decouple with time after light curing our DBAs, at least 5 minutes, this is a must.

A stress reduced direct composite needs to separate the time the hybrid layer requires to mature from the stress of the following layers of composites.

So, by doing so, you will prevent any microleakage.

•  Spent time light curing, not the tooth, but each layer of composite.

Spend specific time to light cure proximal boxes and proximal walls.

The tip of the light curing units not necessarily emits the same level of light (some light is dispersed, some is collimated)

Specific time of light curing will make up for any loss or lack of energy.

•  Light cure separate portions of composite.

Make sure each layer of composite is over one or two surfaces, no more

•  Make sure the light cure tip is perpendicular to the area to be light cure. To avoid lack of exposure in some areas

Verticalizing occlusal forces

By verticalizing occlusal forces we will reduce tensile stress on the stress reduced direct composite.

Well.

That is all for now. 

I know this article will help you to understand and make confidently a stress reduced direct composite on your patients.

And if you want training on Biomimetic Dentistry, you will find an excellent online course here.

I want to thank Dr. Jeff Davies for his invitation to write an article for this web.

Be well.

References

•  Utilizing Light Cure Units: A Concise Narrative Review. Fatin A. Hasanain and Hani M. Nassar. Polymers (Basel). 2021 May; 13(10): 1596.
•  Immediate Dentin Sealing: A Literature Review. Samartzi TK & cols. Clinical cosmetic and investigational dentistry. 20 May 2021
•  Effect of 2% Chlorhexidine Following Acid Etching on Microtensile Bond Strength of Resin Restorations: A Meta-Analysis. Tasnim Hamdan-Nassar & cols. Medicina (Kaunas). 2019 Dec; 55(12): 769
•  Factors influencing success of radiant exposure in light-curing posterior dental composite in the clinical setting. Haifa maktabi, BDS, MSc & cols. American Journal of Dentistry. 2018 Dec;31(6):320-328.
•  Stress-reduced Direct Composites for the Restoration of Structurally Compromised Teeth: Fiber Design According to the ‘‘Wallpapering’’ Technique. S Deliperi, D Alleman, D Rudo. Operative Dentistry. 2017 May/Jun;42(3):233-243
•  The Protocols of Biomimetic Restorative Dentistry: 2002 to 2017. David Starr Alleman, DDS | Matthew A. Nejad, DDS | Capt. David Scott Alleman, DMD. Inside Dentistry. June 2017. Volume 13, Issue 6.
•  Immediate dentin sealing improves bond strength of indirect restorations. Pascal Magne , Tae Hyung Kim, Domenico Cascione, Terence E Donovan. The Journal of Prosthetic Dentistry. 2005 Dec;94(6):511-9.
•  Influence of c-factor and layering technique on microtensile bond strength to dentin. Sergej A. Nikolaenko, Ulrich Lohbauer, Matthias Roggendorf, Anselm Petschelt, Walter Dasch, Roland Frankenberger. Dental Materials. 2004 Jul;20(6):579-85.