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dental practices have embraced the process of bonding to natural tooth structure
to combine function and esthetics. Direct composite resin restorations have
replaced amalgam and gold in many clinical situations where esthetics is of
primary concern and an adequate amount of sound natural tooth structure remains.
When more extensive reconstruction is required or elective treatment requires
covering larger areas of the tooth, indirect laminates of processed composite
resin or ceramic materials can be used. A laminate can cover only the facial
surface of a tooth or it can wrap around to inter-proximal or lingual areas
where esthetics or function demands more aggressive treatment. Where
conventional treatment may call for a full crown, a 360-degree laminate can
accomplish the same result while requiring a thickness of as little as 0.5 mm.
While ceramic materials are inherently brittle and can be broken easily when
unsupported, they become quite strong when laminated to an underlying durable
material. The lamination process is why porcelain fused to metal has been so
successful in dentistry. The fact that the porcelain is laminated to a metal
understructure gives it the strength to hold up under heavy functional stresses
in the oral cavity.
Now that we can bond ceramics and composite resins to natural tooth structure,
the tooth itself becomes the supporting structure and no metal foundation is
needed for many clinical situations. Because there is no need for metal and an
opaque layer of porcelain to block out the color of the metal, the restoration
can be thinner so less tooth reduction is required. More of the patient's
natural tooth structure can be maintained.
But as we communicate these facts about advances in materials to our patients, we
must temper our enthusiasm and provide balance. The word "permanent"
should be eliminated from our dental vocabulary. Even natural teeth wear away as
we age. Gold is the closest thing to permanent we can use for dental
reconstruction. However, today most patients prefer tooth-colored alternatives.
Bonded composite resin and ceramic materials can deliver the desired result
while providing longevity that is acceptable to most patients. Still, it is very
likely that the restoration a patient receives today will need replacing
sometime in the future. While most dentists agree that bonded ceramics provide
greater longevity than composite resin, ceramic materials are more difficult to
Composite resin can be removed with carbide finishing burs and it is easy to
detect when natural tooth structure is reached, so little or no additional tooth
removal may result. Porcelain, however, must be ground off using diamond burs
and it is very likely that more tooth structure will be removed at each new
preparation. I prefer to prepare conservatively so the patient will have as much
natural tooth structure as possible left for future treatment.
Direct composite resin restorations require the least tooth reduction since they
are built directly on the prepared tooth. They can be paper-thin in areas and
still perform well. Laboratory-fabricated processed composite resin restorations
need slightly more preparation because they must have a certain thickness (as
little as 0.3 mm) to be held in the technician's hand and finished without
breaking. Stacked porcelain needs only a little more thickness (0.3 to 0.5 mm)
but still can be very thin and function well after being bonded to the natural
tooth. Pressed ceramics require more aggressive tooth reduction (0.6 mm and up)
because they are fabricated using the lost wax technique. The process simply
requires more thickness to allow for fabrication of the ceramic core and
overlaying of low-fusing porcelain for esthetics.
The Lamination Process
Regardless of the material chosen, the bonding process requires attention to detail and
flawless clinical technique. There is no span between excellent and poor in
adhesive dentistry. If the clinical result is not excellent, it is no good at
all. Inadequate bonding can lead to marginal leakage, tooth sensitivity,
recurrent decay, de-bonding and loss of the restoration.
Current science advocates wet bonding. Our modern bonding agents are
hydrophilic, allowing for bond strengths on dentin and enamel that exceed the
cohesive strength of both the natural tooth and the restorative material. The
luting composites for indirect laminates of composite resin and ceramic
materials are of major importance in the success of the restorations. Indirect
inlays, onlays and full crowns rely on composite luting agents for their
retention and marginal seal.
The bonding process actually results in a strengthening of the remaining natural
tooth structure since the remaining parts are held together instead of being
wedged apart, as was the case with amalgam fillings.
What About Sensitivity?
Post-operative sensitivity has been one of the major areas of concern for most dentists who
perform adhesive procedures for their patients. While some clinicians have
claimed no problems with sensitivity, the vast majority of dentists are
concerned about this phenomenon. Cold sensitivity is the most common complaint.
This can occur due to open margins and resultant micro-leakage. However, even
dentists who are sure that a marginal seal has been achieved have expressed
frustration that cold sensitivity can still exist.
The most likely explanation is that a hybrid layer has not been achieved in the
dentin bonding process or there are open dentin tubules which have not been
sealed. By acid etching the enamel for 15 seconds with 37% phosphoric acid, part
of the enamel matrix is dissolved, leaving thousands of tiny micro-pores in the
A liquid resin is flowed into these pores and allowed to harden, forming
thousands of fingers of resin into the enamel. The bond is tremendous and is
stronger than the tooth. The same acid removes the smear layer from the dentin
in just five seconds, leaving the dentin tubules open. A hydrophilic resin flows
into these open tubules and into the inter-tubular dentin, forming a
"hybrid" layer consisting of resin and dentin which is mechanically
and chemically locked together at a strength which is higher than the tooth
itself. If this hybrid layer is incompletely formed or absent, the dentin
tubules remain open and a negative pressure results when temperature or osmotic
changes occur in the oral cavity. This results in the sensation of pain.
Given enough time, cold sensitivity usually goes away. I believe many endodontic
procedures have been prematurely performed by well-meaning dentists who did not
understand this process. However, with proper technique, post-operative
sensitivity can be nearly eliminated today.
A dentin desensitizer and wetting agent used after acid etching and before
applying the bonding agent can be very beneficial in helping form this important
hybrid layer. Several formulas are currently on the market. One of the popular
brands contains gluteraldehyde as its anti-microbial agent. This chemical can
tan gingival tissues, so it must be used carefully in order to confine it to the
tooth structures. I prefer another well-known brand (Hurriseal, Beutlich
Pharmaceuticals) that uses benzalchonium chloride as the anti-microbial agent.
It is kind to all tissues and can be used anywhere in the oral cavity.
Fourth-generation bonding agents utilized a primer followed by an adhesive. Fifth-generation
bonding agents combine these into one solution. Both can work effectively when
used properly. Film thickness is the major concern for one-step bonding agents
since they must be light cured before a luting agent is placed between them and
Many current one-step bonding agents exhibit a very low film thickness and can
be used successfully for indirect procedures. When in doubt, a fourth-
generation bonding agent can be used since it is cured only after the
restoration is placed.
Luting composites can be either microfills or micro-hybrids. Handling properties
usually determine the choice by the clinician. Some are less viscous and flow
readily. Others exhibit a higher viscosity. I like the higher viscosity resins
and find clean-up procedures less difficult with their use.
Luting composites can be light cured or dual cured. I find dual-curing resins
more efficient to use as long as a distinct gel state occurs during the curing
process. At this stage (approximately three minutes after the start of the mix
of the catalyst and base for most materials), the excess can be easily peeled
away with a gentle touch of a scaler or explorer. Nearly total clean up can be
accomplished before light curing.
For those who are concerned about stresses that may be caused by high-speed
curing, the dual-cure technique will eliminate this problem. Some clinicians
have expressed concern that dual-cure resins can darken with time, as did
self-cure resins of the past. I must say that I have never seen this phenomenon
clinically and I have been using dual-cure luting agents routinely for years.
It is hypothesized by some that sensitivity is created by aggressive finishing
procedures. Care should be taken to minimize use of rotary instruments at the
marginal areas where dentin and cementum are present. Careful technique must be
used with light-cured luting resins. You must be sure to remove as much excess
resin as possible before light curing. This will minimize the need for
finishing. By using a dual-cure resin, most of the excess can be removed before
light-curing, so post-cure finishing is automatically minimized. Of course,
excellent margins that are clinically undetectable and flow into the natural
tooth anatomy allow for maximum dental health and reduce the likelihood of any
post-operative problems. Esthetic supra-gingival margins are usually possible
and preferable when metal-free restorations are used.
The choice of direct or indirect composite resin, stacked porcelain or pressed
ceramic materials depends on many factors. When considering the restorative
material, conservation of tooth structure will often lead to the correct choice.
Sometimes other considerations, such as the presence of old restorations or
broken down tooth structure, may dictate or allow the use of materials which
require more aggressive preparation.
A desensitizer and wetting agent can help eliminate post- operative sensitivity
and ensure a complete hybrid layer. The use of a fourth- or fifth-generation
dentin and enamel and bonding agent will assure bond strengths that exceed the
cohesive strength of the tooth structure or the restoration. Modern luting
composites can be light cured or dual cured. The dual-cure technique can result
in easier clean up and less need for marginal finishing which may also result in
less post-operative sensitivity.
Shade selection and Management
Obstructive Sleep Apnea- Do you know about it?
Genetically modified bacteria may prevent cavities - Put you out of Business?
Fiber Reinforced composites
A primer on all composite class materials
Immediate and Early loading of Implants
Treatment of Fluorosis Stains
Emergency in a Dental Clinic
Preparation of Root Canal
Placement of gingival restorative margins
Bonding for the New Millennium
Nanodentistry- the Future
Access Cavity Preparation
Access Cavity Preparation - Molars
Selection of Analgesics
Fifth generation bonding
About whitening agents
Caries disclosing agents
LED curing lights
Recurrent Aphthous Stomatitis
New cavity-fighting agent shows promise
Tooth Loss Linked to Pancreatic Cancer in Smokers
2-min brush helps achieve cleaner teeth: Study
Snoring can kill
Gum disease raises death risk in diabetics: study
Brushing Right After Drinking Soda may Harm Teeth
What are Giomers
Benefits of Pre-procedural mouth rinsing?
To Bond Or not to Bond Amalgam
Restoration of endodontic teeth
Options for esthetic restorations
Oral Prophylaxis made Easy
Teeth Whitening Facts and Myths
Fiber reinforced composites in dentistry
Changing concepts in Class I and II cavity preparation
Curing lights for composite resins
Preventing dental diseases
Caries Prevention in Children - The Indian Challenge
Mouth Rinsing before dental procedures.
Aids and Dentistry
Dental Journals by Subject