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Isabel C.C.M. Porto IJRD ISSUE 1, 2012

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Post-operative sensitivity in direct

resin composite restorations:

Clinical practice guidelines

Isabel C.C.M. Porto, PhD

Department of Operative Dentistry, Cesmac University Center and Federal University of Alagoas, Maceió,AL, Brazil

Address for correspondence: Isabel Cristina Celerino de Moraes Porto, Centro Universitário Cesmac, Rua Cônego Machado, 918, Farol,

CEP: 57051-160, Farol, Maceió, Alagoas, Brazil. Tel.: +55 82 3215 5031; fax: +55 82 3215 5214.e-mail: [email protected] / [email protected]

Abstract : Pain is one of the most frequent reasons for seeking dental treatment and clinical observations confirm that patients

complain of dentinal sensitivity under different conditions and degrees of intensity. This is a very frequent problem after dentalrestorations with resin composite, even when there is no visible failure in the restoration. The aim of this bibliographic review was toidentify the causes of post-operative sensitivity in resin composite restorations and how it can be avoided so that professionals can usethis information to reduce the occurrence of this inconvenience in their daily practice. Complete texts of relevant articles on the subject

were analysed. There are various causes of post-operative sensitivity in direct resin composite restorations related to failures indiagnosis and indications for treatment and/or cavity preparation, the stages of hybridization of hard dental tissues, insertion of thematerial, and finishing and polishing the restoration. To avoid or minimize the occurrence of post-operative sensitivity, it is imperative to

make a good diagnosis and use the correct technique at all stages of the restorative procedure.

Keywords: composite resins, dental restoration, operative dentistry, toothache.

Introduction

Dentistry has possibly evolved more in the lastfew years than in all of its previous history, andthis is due to a physicochemical phenomenoncalled adhesion. The adhesive,which previouslyrequired different treatments for different dental

substrates, can now be used on both enamel anddentin, and it may be possible to dispense withacid etching. The latest generation of adhesiveshas attained a bond strength of 30 MPa,or more,and they are formulated to interact simultane-ously with enamel and dentin after total acidetching of the tooth surface (total etch) (1) or, inthe so-called self-etching adhesives, to etch,

prepare and bond to the tooth surface simulta-neously (2,3), forming an interdiffusion zonecalled the hybrid layer (1). An understanding ofthe principles of adhesion has allowed satisfactoryaesthetic procedures to be performed, with a

protective effect on the remaining tooth (4).

In the last few years, there has been a trend towardsreplacement of amalgam restorations by moreaesthetic restorations, especially using resincomposite. This trend leads one to believe that formost restorations, the dentist’s first choice is

restorations using adhesive characteristics, andconsequently, resin materials are used. Thus, tounderstand the reasons for post-operative sensitivity,it is natural to focus on the bonding procedures(5,6).

Despite great progress, restorative techniques still present a certain rate of failures (7,8). Discoloration,marginal leakage, recurrent caries and loss of therestoration are the main problems related torestoration failures. Class I and II resin compositerestorations are the most predisposed to failure.Perhaps the most intriguing and challenging

problem is post-operative dentin sensitivity, one ofthe disadvantages of using direct resin composites in

posterior teeth (7).

REVIEW RTICLE

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After restorations with resin composite, especially in posterior teeth, clinical observation has shown that patients complain of dentinal sensitivity at differentlevels and in different situations. This is a common

problem, even with no visible failures in therestoration (9). Pain is always a warning signal of

possible aggression, and although it does not have a

direct relationship with the pathological processes, itis one of the most common reasons for seekingdental treatment, either in public service or privateclinics (4).

Post-operative sensitivity in resin compositerestorations is a common occurrence that causesdiscomfort in the patient and inconvenience to the

professional, because it has various causes.Although frequent, it has still not been fullyexplained. Therefore, it is important to study the

problem to establish a work routine to avoid it.The aim of this bibliographic review was to identifythe causes of post-operative sensitivity in resincomposite restorations and how it can be avoided, toenable professionals to reduce the occurrence of thisinconvenience in their daily practice.

Dentinal sensitivity

The main morphological characteristic of dentin isthat it is a tubular structure, filled with fluid,

connecting the pulp to the enamel – dentine junction.The lumen of dentinal tubules are surrounded bythin cuffs of mineralized tissue, called peritubulardentin. The matrix interposed between thiscylindrical structure, the intertubular dentin,contains around 30% by volume of mineralizedcollagen type I fibrils (10,11) perpendicular to thelong axis of the tubules (11). Much smallerquantities of collagen (10% by volume) are presentin peritubular dentin (10). Dentinal permeability is,therefore, a direct consequence of this structural

pattern.The closer one gets to the pulp, the greater is thevalue of this porosity (45,000 – 65,000; 29,500 – 35,000; 15,000 – 20,000/mm2) and the diameter ofthe tubules (2.5 µm close to the pulp; 1.2 µm in theintermediate region; 0.5 µm at the enamel – dentine

junction). This explains the increase in dentin permeability in the area close to the pulp chamber(12).

The widely accepted hydrodynamic theory proposed

by Brännström and Ästron in 1964 (13) seeks toexplain the painful phenomenon that occurs indentin by the movement of fluid within the dentinal

tubules after certain stimuli, which causesintratubular pressure changes, thus leading toexcitation of the pulp nerve terminals, producing asensation of pain (4,14). Therefore, due to thedisposition, size and pattern of dentinal tubules, thetype of dentin has a direct relationship with dentinalsensitivity.

Reduction in fluid movements and propagation ofmolecules through dentin occur due to reduction inthe tubular openings with the deposition of

peritubular dentin or the formation of otherintratubular material. Reparative dentin, in contrastto secondary dentin, does not have continuoustubules, thus leading to diminished permeability andfluid movement, and this results in a reduction insensitivity (14). Therefore, teeth with recently cutsecondary dentin have a greater propensity to

develop sensitivity after direct restorations.

Post-operative sensitivity in resin

composite restorations

Sensitivity is characterized as being a responsegiven by the body to say that something is wrong,and this response may be originated by anaggressive stimulus or in a spontaneous manner(15). The sensory potential of the pulp makes itcapable of reaction with an immediate painful

response, even when the stimulus is applied at adistance from the pulp tissue, such as in thesuperficial layers of dentin (4).

Clinical studies on sensitivity arising after resincomposite restorations have reported a frequent andvery variable prevalence of between 0 and 50% (16 – 20), with predominance in posterior teeth and ClassII restorations. As the patient can have considerablediscomfort, professionals are sometimes obliged tochange restorations because of the inability toeliminate the problem (21). Patients have describedit as a moderate pain, of short duration, that appearsspontaneously when chewing, with hot and coldfoods (4,8) and on rare occasions with sweet andacid foods, and it disappears when the stimulus isremoved (4).

Innumerable restorative procedures are performedon a day-to-day basis in dental offices, and somestages of the procedure may generate stimuli thatresult in pain or potentiate already existingsensitivity. Therefore, it is important to know what a

resin composite restoration is not: simply removingcarious tissue and inserting restorative material insmall increments. Instead, it comprises various stepsthat must be carefully performed so that the

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restoration will be successful; that is, a perfectlysealed restoration that restores the shape andfunction of the tooth, and is comfortable for the

patient (15).

Post-operative sensitivity can be caused by multiplefactors and does not originate from one isolated

aspect. It results from the interaction between therestorative technique, the clinical condition of thetooth to be treated (health of the pulp and remaininghard dental tissue) and the restorative material.Therefore, there is a permanent and unpredictable

possibility of sensitivity occurring (4). In addition,there are other factors related to the cause of post-operative sensitivity, such as the individual profileof each patient, the shape and extension of the cavity

preparation and protection of the dentin – pulpcomplex (22).

Pre-operative causes

It is extremely important to establish a precisediagnosis before any restorative procedure, in orderto be certain that the pain reported by the patientdoes not originate from pre-existing causes, such ascracks, tooth fractures, dentinal sensitivity resultingfrom dentin exposure in the cervical region, orreversible or irreversible inflammatory processes inthe pulp. A meticulous anamnesis associated withcareful clinical and radiographic examination willallow other pathological processes that can affect the

pulp and the dental periapex to be excluded.

Cracks and fractures

Cracked tooth syndrome is an entity characterized by the presence of incomplete cracks or fractures ofthe enamel or enamel and dentin in a tooth, withsymptoms of pain when chewing and inexplicablesensitivity to cold (23). The difficulty in visualizingthe crack and the patient’s report of symptoms,

which are not always well explained, sometimesmake it a complex diagnosis, and the symptoms may

be confused with post-operative sensitivity.

Cervical dentinal exposure

Areas of cervical dentinal exposure may present asinsensitive before the restoration, and may bestimulated during the operative procedure due to

prolonged contact with the clip, or inadvertently, bythe prolonged presence of phosphoric acid duringcavity etching, which could lead to difficulties in

diagnosing the pain, and may lead to re-interventionin the restoration (4). Thus, a meticulousexamination should be performed to identify the

presence of exposed dentin, whether there is a

record of painful symptoms or not, and avoid possible procedures that may trigger or exacerbateexisting pain.

Pulp condition

A determinant factor before restoring the tooth is toestablish the condition of the pulp. Radiographic

examination should be done, previous proceduresshould be observed, the presence or absence ofsymptoms reported by the patient should berecorded and pulp vitality tests should be performed.All these procedures are essential to minimize therisks of sensitivity. Frequently, inadequateinstrumentation during cavity preparation, without adetailed analysis of the pulp condition, may causeirreversible pulp damage due to the increase inharmful stimulus on pulp that has been debilitated

by pre-existing conditions (15). In the presence of pulp inflammation, it is necessary to make ameticulous evaluation of the condition of the pulp toconsider whether endodontic treatment should bedone before the restoration.

Operative causes

Pain of dentinal origin is intimately related torestorative procedures, and may occur by cutting andexposing healthy dentin due to dentin dehydrationand the release of toxic substances from the

restorative material, among other causes. Abusive dental structure wear

The use of burs and diamond tips with excessivecutting or wearing pressure, without the use ofadequate cooling, may generate frictional heat anddentin dehydration. Even if this happens for only ashort time, it causes displacement of the tubularfluid and a painful pulp response. Zach and Cohen(24) have shown that an increase in temperature of5.6 ºC may trigger various degrees of inflammation

or even pulp necrosis. Blunt burs and diamond tipsdemand greater pressure during cavity preparation,inducing a rise in temperature. Diamond tips aresubject to increasing degrees of wear and diamond

particle loss, as they are submitted to a largernumber of cavity preparations, and must bereplaced. A previous study has attested that their useafter the fifth preparation is questionable, and theymust therefore be replaced after the fourth

preparation (the author’s unpublished data).

Excessive dentin dehydration may also occur by repetitive cavity drying during preparation of thetooth and/or while performing the restoration,causing pain due to pulp fluid displacement, with

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pulp alterations that are generally reversible.Dehydration is limited by the resultant smear layer,

but prolonged exposure, especially after acidetching, may induce a more severe pulp trauma dueto dehydration (25). These types of damage can beavoided with the use of new burs and diamond tips,adequate cooling and cutting with intermittent

movements.

Incomplete carious tissue removal

The environment found under restorations presentsfavourable conditions for microbial growth betweenthe restorative material and the cavity wall (26).Incomplete carious tissue removal leads to the

possibility of bacteria remaining between therestoration and the cavity wall, increasing thesusceptibility of the pulp to leakage of the bacteriathemselves and their toxins (4). Bacterial activityresults in pulp infection or inflammatory reactionsresulting from bacterial products (26).Consequently, post-operative sensitivity results from

pulp aggression caused by the presence of cariousdentin and the low quality of the adhesive bond todentin. The deficient bond causes marginal gaps andconsequently, microleakage, recurrent caries and

pulp inflammation (4).

The presence of bacteria and their products may bedetected at any stage of the restorative procedure.

Contamination of the cavity may occur during cavity preparation with the presence of carious dentin, bysaliva penetration during cavity preparation, while

performing the restoration, with the use ofcontaminated instruments, or in the post-operativestage due to the presence of marginal leakage (4).

Negligence in protecting the dentin – pulp complex

Undoubtedly, dentin is the best pulp protectionmaterial. At the time of deciding about protectingthe dentin – pulp complex during a resin composite

restoration, dentinal permeability and the type andquality of remaining dentin should be assessed.Whether dentin is removed by pathological or

professional means, if its thickness is reduced thedentinal tubule openings are increased, making itmore permeable and consequently, more susceptibleto irritation by chemical or bacterial agents.

Another very important factor is cavity depth, whichvaries from shallow to medium and deep, and it isfundamental to know how to act in each case.

Shallow and medium cavities present a largerquantity of dentin, which favours the maintenance ofthe number of odontoblasts. The larger the numberof odontoblasts, the greater the repair capacity of the

pulp. In deep cavities, there is a smaller quantity ofodontoblasts remaining, which may be diminishedeven further during the restorative procedure,drastically reducing the chances of pulp recovery(15).

The increase in cavity depth is proportional to the

dentinal permeability and significantly predisposesthe dentin to post-operative sensitivity. Restorationsin deep cavities present four times greater risk offailure, whereas cavities with pulp exposure have a14 times higher risk of failure, compared withrestorations in cavities with a greater dentinthickness (8).

The quality of remaining dentin found between thecavity floor and the pulp is of important in

preventing pulp complications caused by operative procedures. The patient’s age must also be

considered. A young tooth has a larger pulp cavitythan an adult tooth, which has received more

physiological stimuli or injuries during the course oflife, and in which more reparative dentin hasformed, and consequently, the pulp chamber isreduced in size (15).

The use of resin composite materials duringrestorations is a controversial but important topic. Ithas been questioned whether it is really necessary touse a lining material under a composite restoration,

when a good seal can be obtained with theapplication of an adhesive system. Furthermore,why cover the dentin, which is an excellent bondsurface, with a lining of questionable value? (27 – 29).

To some authors, an almost perfect seal is verydifficult to achieve clinically, therefore, under thecondition of a not so perfect seal, a cavity floorlining may still be of great value. Liners, when used,must support (and continue to support) the

restorations superimposed upon them, since anydecomposition will result in a defective base,causing a pumping action and marginal percolationduring chewing, resulting in sensitivity (14,15). Theindiscriminate use of calcium hydroxide linings tostimulate secondary dentin formation continues to

be controversial. On the one hand, it is argued thatsecondary dentin will form in any case, as aresponse to the repair process. On the other hand,the need to form secondary dentin is questionedwhen there is good cavity sealing (22,30 – 34).

Irrespective of this, the use of calcium hydroxide isrecommended in very deep cavities in which theremaining dentin thickness (

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undesirable effects of toxicity of adhesives andcomposite resin (35,36).

Post-operative sensitivity may be minimized withthe use of protective materials that will act on thedentin – pulp complex, such as glass ionomer cement,calcium hydroxide and resin-based adhesive

systems. These materials must present bacteriostaticand bactericidal characteristics, protect the pumpagainst thermal or electrical stimuli, and have goodcompatibility with the pulp and restorative material.It is desirable for these characteristics to be presentsimultaneously, however, there is still no materialthat presents all these features. The professionalmust have full knowledge of the type of action thatis required for each cavity in order to select the best

protective material possible (37). Consideration ofthe need for mechanical protection (tubular

obliteration) or biologic protection (need for amaterial with greater biologic compatibility andcapacity to induce reparative dentin formation) may

be the key to improved protection of the dentin – pulpcomplex.

The thickness of the adhesive layer applied to thetooth may also help to reduce sensitivity, andmultiple layers of adhesive may have a better effectthan one thinner layer. The use of resin-reinforcedglass ionomer cement as a lining on the pulp and

axial walls before the use of acid has produced thesame effect (16). All these procedures lead toobliteration of the dentinal tubules, andconsequently, to eliminating or lowering theincidence of cases of post-operative sensitivity.

Inadequate isolation of the operative field

Absolute isolation is indicated to reduce two issuesthat cause post-operative sensitivity generated by

penetration of saliva into the operative field:contamination of the cavity by microorganisms that

cause pulp inflammation and contamination byhumidity, which harms the bond and facilitatesmarginal leakage (4). The study of Auschill et al. (8)showed that the type of isolation, with a rubber dykeor cotton wool rolls, has no influence on theoccurrence of post-operative pain, provided thatcavity contamination is avoided.

Failure in dental tissue hybridization

Hybridized dentin is prepared at the interface of thesurface demineralized by previous acid etching to

expose the collagen fibers in the dentin matrix andallow infiltration of adhesive monomer into theexposed fiber network (38). Therefore, dentinhybridization is a process that creates a mixed layer

of resin monomers and collagen fibrils, altering the physical and chemical properties of this tissue (39).

The formation of a bond interface that is as perfectas possible and minimizes or prevents the entry of

bacterial fluids is fundamental to guarantee greaterlongevity of resin composite restorations. Inadequate

formation results in marginal leakage, resindiscoloration and post-operative sensitivity(3,33,40,41). Therefore, dentin hybridization, acidetching, application and light activation of theadhesive system must be meticulously performed.

Previous acid etching transforms the tooth surface,making it more receptive to bonding with theadhesive system and resin composite, andfacilitating the formation of resin tags within thedentinal tubules, which gives the restoration greaterresistance and durability (34,42).

Acid etching for a longer time than thatrecommended by the manufacturer leads to manyconditions that result in sensitivity. Most acids arehypertonic and cause pulp fluid displacement,leading to movement of the odontoblasts as a pulpresponse. Acid solutions used in excess of therecommended time (15 s) denature the collagenfibers, increase dentin permeability and humidity,facilitate chemical aggression by the adhesivesystem and bacterial infiltration, and for all these

reasons, harm the bond and may cause pain (4).Dentin demineralization of over 5 µm is not of muchvalue to the clinical procedure, and may result fromlonger exposure of dentin to the acid. An increase inthe demineralized dentin layer will not guarantee theformation of a thicker hybrid layer and a better

bond, as the primer/adhesive may not have thecapacity to infiltrate throughout its entire thickness,causing exposure of the collagen within and at the

base of the hybrid layer, which could lead to

degradation and leakage. The greater the flow ofadhesive between the collagen fibrils and throughthe complex of demineralized channels, the betterwill be the quality of the hybrid layer, giving it ahigher degree of resistance to hydrolysis andoffering greater protection against microleakage(4,43). An increased dentin etching time is anotherclinical error responsible for the occurrence of post-operative sensitivity (4).

With the advancements in adhesive dentistry,simplified techniques and improved clinicaldevelopments are increasingly being sought.Adhesive systems began to present two forms ofapplication according to whether or not previous

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acid etching was necessary. Self-etching adhesiveshave an advantage over adhesives that require acidetching. As the primer is acidified, acid etching is

performed without the need for washing. Althoughthe hybrid layer formed is thinner, the entire etchedarea is occupied by adhesive, thus diminishing thechances of hydrolysis occurring in the area.

Research has indicated that one of the disadvantagesis lower resin bonding to enamel as a result of theacidic primer buffering. Due to this limitation,attempts have been made to combine the twotechniques and tests have suggested the use of

phosphoric acid on enamel before the self-etchingadhesive is applied throughout the cavity, with theintention of enhancing the bond to enamel,

providing good marginal sealing and greaterlongevity of the restoration (44). The use of total-etch or self-etch adhesives presented no statisticallysignificant difference with regard to the occurrenceof post-operative sensitivity (45,46).

For the step-by-step performance of hybridization,the tooth must be kept moist. Without adequatehumidity, the exposed collagen fibrils collapse andmake it difficult for the adhesive system to penetrateinto the demineralized tissue. The exposed fibrils atthe margins and within the restoration allow the

passage of fluids and bacterial enzymes that mayattack the collagen (47 – 50). The cumulative effect

of these actions may be debilitation of the integrityof the restoration margin (43).

The definition of humidity may vary from oneoperator to another, and a larger or smaller quantityof water on the dentin, available for interacting withthe adhesive system, may interfere in the adequateformation of the hybrid layer, favouring the presenceof gaps and fluid accumulation at the tooth – restoration interface.

Although good bond efficiency can be obtained with

acetone-based adhesives in vitro, the high sensitivityof these types of adhesives, particularly the two-steptype, may lead to poorer results in the long term(3,51 – 53). Acetone in contact with moist dentininduces an increase in the remaining water vapor

pressure (54), which, if it is not in a sufficiently highquantity, rapidly reduces dentin permeability,making it difficult for the resin monomers to

penetrate (55) and form the hybrid layer. Thedifficulty of standardizing dentinal humidity may bemore prejudicial to the bond strength of acetone-

based adhesive system than that of water andalcohol-based systems (56). Thus, the use ofadhesives with acetone as solvent may increase the

possibility of developing dentinal sensitivity afterrestorative treatment and demands greater attentionfrom the professional with regard to the applicationtechnique.

Handling restorative material

Resin composites are have a broad range of

indications in clinical dentistry. They consist of anorganic matrix permeated with inorganic particlessurrounded by a bonding agent that makes themadhesive to the resin matrix. The organic base ofcontemporary resin composites is composed of themonomer bisphenol A-glycidyl dimethacrylate (bis-GMA) in combination with other di-methacrylatessuch as triethylene glycol dimethacrylate(TEGDMA), urethane dimethacrylate (UDMA) and

bisphenol A-glycidyl dimethacrylate ethoxylate(BisEMA) (57). Despite the differences in theirformulations, all the methacrylate-based compositeare polymerized by the generation of free radicals(58). In this process, the approximation of themethacrylate monomers to establish covalent bondswith one another during the polymerization reactioncauses a significant reduction in the volume of resinafter polymerization (59), thereby leading to thegreatest inconvenience of resin composites:

polymerization shrinkage (60).

To reduce the polymerization shrinkage stress of

dental composites, a new compound, called Siloranewas developed using a monomer system with lowshrinkage, derived from the combination of siloxaneand oxirane radicals. It has a different

polymerization mechanism based on the opening ofcationic rings of the oxirane radicals (61), which isresponsible for the low shrinkage and low stressgeneration, while siloxane give the material itshydrophobic properties. Thus, the maincharacteristic of the new composite is less than 1%

polymerization shrinkage, in comparison with more

than 2% in methacrylate-based resins (59,61).

Although reduced in the more recent resins, polymerization shrinkage of resin composites duringthe polymerization process persists, and is theconsequence of the reaction of monomertransformation into polymers, with the change fromthe viscous to the solid state. During thistransformation, the resin develops forces that maycause rupture of the bond between the adhesivesystem and cavity walls, reducing the useful life of

restorations because of the existence of microscopicgaps at the tooth/restoration interface. These gapsallow entry of bacteria, and may lead to the

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formation of caries, staining and post-operativesensitivity.

Various recommendations have been made to reducethe effects caused by polymerization shrinkage ofresin composites. The use of gradual and carefullight activation techniques and care with maintaining

the wavelength emitted by the light source, insertingthe resin in small increments and the use of a base ofmaterials with a low modulus of elasticity are someof the suggestions (62 – 65).

Incomplete resin composite polymerization is alsoresponsible for post-operative sensitivity (4).Problems associated with inadequate polymerizationinclude inferior physical properties, diminishedretention, greater degradation in the oralenvironment and adverse pulp responses. In clinical

practice, only one appliance is bought and used to polymerize all the materials available in the dentaloffice, as it is not possible for dentists to suit theirappliances to the different materials. Inadequate

power due to degradation of the components (bulbs,reflectors, filters and light conducting tips), whichoccurs with use over time, contributes to difficultiesin polymerizing these materials (65).

It is impossible for the naked eye to identifydifferences between the types of light sources,variations in wavelength and changes in pulse and

intensity. The light intensity is directly proportionalto the number of photons that stimulate the

photoinitiator, which is responsible for initiating theresin polymerization reaction (66,67). Therefore,frequent evaluation of the light intensity and care inthe maintenance of light sources used for

polymerization are among the ways of preventing post-operative sensitivity (65).

Many light polymerizing appliances used in dentaloffices are operating at a light intensity below the

recommended level, and this means that insufficientresin composite polymerization is occurring and alarger quantity of substances harmful to the pulp,such as unreacted resin monomers andcamphorquinone, may be released (16,65).Moreover, the bond and sealing present failures thatmay trigger pain and reduce the useful life ofrestorations (16).

The contraction stress that occurs during polymerization has received considerable attention.A recommendation for reducing the stress caused by

polymerization shrinkage is to activate the resincomposite in small increments within the cavity(65), observing the size of the increment to be

polymerized (up to 2 mm) and the number of wallswith which the resin comes into contact (4). Thesmaller the number of bonded faces, the greater will

be the resin’s capacity to flow and release stress,

favouring the resin bond to the tooth (4,65).

In addition to resin composite insertion in small

increments and gradual light activation, the use ofmaterials with a low modulus of elasticity, such asresin flow or ionomer materials has been proposedin an attempt to minimize the effects of shrinkageand increase the longevity of the restoration,especially of the Class II type (68 – 71).

In cavities that present margins limited to coronalenamel, the beveled and etched enamel helps tocontain the contraction forces. In Class II cavitiesthat present the cervical margin located apically tothe cement/enamel line, in an area with no enamelwhere the material bond to dentin is weaker, ruptureof the bond between the material and cavity wallmay occur due to the polymerization shrinkageforces of the resin composite. This rupture of the

bond causes the formation of spaces, which serve asa port of entry to bacteria and their products, leadingto secondary caries, marginal stains, pulpinflammation and hypersensitivity to cold (72,73).Due to the deficient seal at the tooth/restorationinterface, the free extremities of the tubules are

exposed, generating a flow of fluids due todifferences in gradient when they come into contactwith the external medium (16). The sensitivity tocold that is present in this situation may beexplained by a small change in the fluid volume

present at the gap. When it receives the cold thermalstimulus, contraction of the fluid within the gapoccurs, which causes rapid movement within thedentinal tubules, leading to stimulation of the pulpnerve fibers, causing the painful sensation (26). Thisoccurs mainly in the presence of infection, as in

cases in which there is communication with the oralcavity. With elimination of the gap and any existinginfection, the sensitivity rarely persists unless the

pulp has been irreversibly compromised (74). Verysevere pulp inflammation may present even in the

presence of small gaps, therefore the size of the gapmay be of less importance than the other factors,such as bacterial invasion and their toxic products,and the effects these could have on the pulp.

Recent studies have shown that patients with resincomposite restorations with low polymerizationshrinkage have not presented post-operativesensitivity (75). It is possible to eliminate post-operative sensitivity, even in restorations with

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cavities that have a high C factor value, when theyare restored using small increments and gradual lightactivation (76).

Therefore, to perform a resin composite restoration,all the clinical stages must be strictly followed.Among these, knowledge, skill and professional

organization must be included. It is essential for professionals to have full understanding of howcomplex the adhesive restorative technique is, sothat they obtain adequate aesthetics and seal thecavity, thereby guaranteeing the success of therestorative treatment, without complaints of painfrom their patients.

Post-operative causes

Restoration finishing and polishing

Finishing and polishing are commonly performed bydentists. Restorations must be done in such a waythat the finishing and polishing stages are restrictedto small adjustments in the shape and superficialsmoothness of the restoration. Purposely inserting alarge excess of material and then performingfinishing is extremely unfavourable to the tooth andthe restoration (4). Immediate and excessivesuperficial wear of a recently placed resin compositegenerates alterations in the resin matrix by the heat

produced, disturbs the post-irradiation phase of

polymerization, and removes the superficial layer,which theoretically obtains the highest degree ofconversion. The possibility of pulp injury due to theexaggerated frictional heat generated by the highspeed bur is increased. The careful use of burs andabrasive instruments at this stage avoids possibledamage to the restoration margins and adjacentdental tissue, avoiding failures at thetooth/restoration interface.

Occlusal interference

During mastication of solid foods, or when therestoration is in occlusion with the antagonist tooth,deformation of the margins and interfaces occurs,and this may lead to a dimensional change that couldcause fluid movement within the dentinal tubulesand cause pain (4,16).

Cervical dentin exposure

The restorative procedure may trigger or increase pain coming from areas of exposed dentin in thecervical region of the tooth. Inadequate use of clips

may result in traumatic gingival displacement andconsequent cervical dentinal exposure. Similarly, theinadvertent permanence of acid in this region can

lead to pain and can be avoided by paying attentionto all stages of the restorative procedure.

Final considerations

The clinical performance of resin compositerestorations in posterior teeth can be maintained atsatisfactory levels, and post-operative sensitivity can

be avoided or maintained at minimal levels whenrestorations are inserted strictly in accordance withthe technical recommendations (18). Several causesof sensitivity result from errors in technique before,during and after placement of the restoration. Thedynamics of a poorly conducted restoration may alsotrigger post-operative dentinal sensitivity.

Dentistry demands complicity between professionalsand the material they use. The material must offer

properties that justify their choice and it is the

responsibility of professionals to be familiar withthese properties, understand their indications, andknow how to apply them with the necessary skill(4). Many procedures performed using the samerestorative materials, applied with the sametechnique and under similar clinical conditionsgenerate sensitivity in some cases and not in others.Only by allying knowledge and command of thetechnique and the material applied is it possible toensure the placement of adequate restorations, andthe patient’s physical and psychological well-beingin return.

Briefly, the causes of post-operative sensitivity indirect resin composite restorations are diverse, andcomprise failures in the diagnosis and indication forthe procedure, cavity preparation and/or stages ofinsertion of the material, finishing and polishing therestoration, through to occlusal adjustment of therestoration.

The recommendations for avoiding or minimizing post-operative sensitivity involve all the principlesfor attaining excellence in restorative dentistry; thatis, making a good diagnosis before performing therestoration; analysing the initial health of the pulpand periapical region; the use of new burs withabundant cooling; use of adequate isolation to

prevent contamination; not dehydrating dentin withexcessive drying; strictly following all the criteriaindicated in the stages of hybridization, insertion,finishing, polishing and occlusal adjustment of therestoration.

References

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