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Esthetic Dentistry
Recent trends in esthetic restorations for posterior teethDidier
Dietschi* / Pascal Magne** / Jacqties Holz***
The increase in the demands made by patients for esthetic or
metal-free restorations, togetherwith the ever-growing interest
shown by the dental profession for tooth-colored materials
andtechniques, led to the current development of posterior adhesive
restorations. This paper re-views critical elements such as
adhesion to dental hard tis.sues as well as current properties
ofbases/liners, fdling materials, and luting materials. A rationale
for the succe.s.iful use of cur-rently available restorative
.n'stems is presented. (Quintessence
Introduction
The interest for esthetic intracoronal restoration is nota
modern concept. As early as 1856. prefabricated ce-ramic inlays
were employed as esthetic obturations tobe sealed with gold foils,'
Other examples are the de-velopment of fired ceramic inlays in
lSfi2 by Herbst inCiermany — reported in the dental literature for
thefirst time in 1S91- — and the fabrication of fired ceram-ic
inlays over platinum foil developed a few years later,in 1888. by
Land.' ' Ceramic inlays were introduced inthe dental profession
well before amalgam (1895),''The absence of a high-performance
luting material has.however, been a serious obstacle to the
clinical successof these techniques' until recently, when resin
andporcelain etching were used to bond the restorationstrongly to
the tooth''''(Figs la and Ib),
The development of direct esthetic materials reallybegan in
1871. with silicate cements,'* It was followedonly later, in 1937,
by the advent of unfilled resins, ad-vocated for esthetic
obturations since 1945.' The mostsignificant events in that field
were probably the devel-
Lecturer, Department of PrevenLive and Restorative Dentist-ry,
University of Geneva. School of Dental Medicine, 19,
rueBartliélemy-Menn. 1205 Geneva, Switzerland,Lecttirer, Deparimenl
of Preventive and Restorative Dentist-ry, Department of
Presthodontics. University o[ Geneva,Professor and Director.
Department of Preventive and Resto-rative Dentistry, University of
Geneva,
opmentsof enamel etching by Buonocore'"in 1955 andof the
composite resin material derived from Bowen'sbis-GMA formulation."
This was the beginning ofmodern cosmetic adhesive dentistry.
Until a few years ago. posterior esthetic materialsand
techniques could not compete with amalgam orgold obturations
because of their biologic and physico-chemical shortcomings,"""
Durability of esthetic resto-rations was limited by marginal
degradation, wear, andmechanical failure''"" (Fig 2), Recurrent
caries, pulpalinjuries, or loss of function were therefore
commonclinical findings,'^"' Fortunately, recent improvementsin Ihe
physicochemical properties and development ofnew techniques have
made possible the use of thesematerials in posterior teeth with a
reasonable certaintyof success'-'(Fig3),
Patients' requests for and clinicians' interest in pos-terior
esthetic restorations have grown considerablyover the last decade.
Because of preventive dentistryand improved oral hygiene habits, a
dramatic decreasein caries was observed.'^ As a consequence, the
con-cepts of traditional denlistry were progressively ques-tioned
and a new impetus was given to the more con-servative adhesive
techniques,-" Al the same time, thesafety of amalgam and other
metals used in the mouthwas increasingly controversial, despite the
absence ofdefinitive scientific proof,^'" Patients' concerns
aboutpotential mercury toxicity and related ecological
con-siderations often led them to reject traditional materi-als and
techniques (Figs 4a and 4b). These concerns,among other reasons,
justify today's need for alterna-tive restorative techniques.
Quintessence Inlernational Volume 25, Nutnber 10/1994 659
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Esthetic Dentistry
Fig 1 a Ceramic overlay on its master cast. Fig lb Ceramic
overlay in mouth after cementation. Thesuccessful bonding of
ceramic to tooth has increased theindications for indirect adhesive
restorations.
Fig 2 Failed composite resin restoration after a few yearsof
clinicaf service, resulting from insufficient physicochemi-cal
characteristics of early materials.
Fig 3 Clinical appearance ot 8-year-old Class I compositeresin
restorations, revealing the satisfactory performance ofmodern
products.
Fig 4a Maxillary arch in preoperative state. Fig 4b Same arch
after rehabilitation with nonmetallic res-torations (all-ceramic
crcwns, composite resin inlays, andceramic overlay). This treatment
option is frequently desiredand even demanded by the patient.
660 Quintessence International Volume 25, Number 10/1994
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Esthetic Dentistry
Desptle the increasing number of esthetic materialsand
techniques available, the ideal system, covering allchntcal
tndications. does not exist. The aim of this arii-cle is to present
the basic and theoretical elements toenable the clinician to choose
the appropriate restora-tive system for each clinical
situation,
Eslhelk restorative materials
Esthetic restorative materials have to fulfill both me-chanical
and biologic functions; they tnust optimally re-store the
morphology and the original mechanical re-sistance of the tooth so
it may resume its function in aproper way; ensure external and
internal adaptationand seal the restoration to prevent recurrent
caries,pulpal injury, and dentinal sensttivity; and be
biologi-cally compatible with the underlying vital substrate. Asa
tentative answer to these challenging requisites, dif-ferent
materials may be used lo restore posterior teeth.These materials
can be roughly classified according totheir function (adhesives,
bases/hners, luting materials,filling materials) or to their
physicochetnical structure(ceramics, composite resin, and
cements),
Adhesives
The efficiency of the adhesive system is undoubtly es-sentiai to
ensure the success and longevity of the resto-ration. It has to
provide a long-standing bond betweenthe luting or filling material
and the dental tissues. Theefficiency ofthe micromeehanical
adhesion of resins toetched enamel'" is now well established,
Buonocore'sgroup not only introduced enamel etching, but alsotried,
as early as 1956. to bond to etched dentin,-' Thisprocedure
unfortunately met with limited success be-cause of the poor wetting
of dentin by the hydrophobicrestns available at the time. Moreover,
the etching ofdentin to obtain a micromechanical bond was
suspect-ed of potential harmful effects to the pulp.'''-'
Subse-quently, researchers and manufacturers tried to devel-op
chemical dentinal bonding agents to be placed onthe smear layer.
This was the first generation of denti-nal adhesives. the poor
performances of which resultedmainly from the weak adhesion of the
smear layer tothe underlying dentin,-'̂ The next generation of
adhe-sives was characterized by the development of differ-ent
treatments of the smear layer, resulting in an im-proved but still
insufficient dentinal bond,-'
Most of the latest-generation systems rely on thecomplete
removal of Ihe smear layer and partial décal-cification ofthe
dentin̂ ** (Fig 5a), The demineraliiiation
resulting from the acid treatment exposes collagen fi-bers on
the dentinal surface that ean later be impreg-nated with
hydrophilic resin monomers. This results ina resin-infiltrated
collagen network called the hybridlayer or interdiffusion
zone.-''-^" The rationale that liesbehind this procedure is to
obtain simultaneous bond-ing and sealing of the dentin and thus
theoretically toprevent baeterial leakage, which is presumed to be
thecause of most biologic failures encountered with adhe-sive
restorations,'' This procedure is. however, chal-lenging because
complete diffusion of the resinthrough the demineralized collagen
fibers networkmay be affected by the formation of a new
collagensmear layer,'^ This superficial layer presumably
resultsfrom the collagen fiber collapse following acid etchingand
air drying. The subsequent reduction in dentinalporosity may also
create a weakness of the bond be-eause of a localized decrease of
resin concentration.Recent scanning electron microscopic (SEM)
andconfocal observations of dentin-bonded restorationsusing the
total-etch technique support these findings(Fig 5b), The problem of
studying the dentin is furthercomplicated by the differential
permeability of thistissue, depending on various anatomic,
pathologic, andphysiologic factors,̂ "
Use of a new-generation bonding agent can, howev-er, be
recommended whenever enamel is absent or isunable to provide a
satisfactory marginal seal.'*-' In suchsituations, a combined
amalgam-composite resin res-toration has been proposed as an
alternative to im-prove gingivoproxitnal seal of deep Class II
obtura-tions,'"'"
The applieation of a bunding agenl on internal denti-nal
surfaces not covered with a baseliner is also advis-able to prevent
postoperative sensitivity.̂ ^ Instead oftrying to seal the dentin
with a complete adhesivesystem, some authors advocate the placement
of a var-nish hner to isolate the internal dentinal surfaces,-'̂
Be-cause the biocotnpatibility of these materials has notbeen
conclusively proven (Figs 6a to 6c), applieation ofa calcium
hydroxide liner in deep areas of the cavitystill appears to be a
justifiable procedure,'^""
Bases/liners
With the development of higher performance adhe-sives, the use
of and indications for bases/liners havedecreased. This group of
materials traditionally hadmany different functions, including
partial lining as abiologic protection for deep preparation areas,
totallining fur dentinal insulation against chemical or ther-
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Esthetic Dentistry
Fig 5a Successfui dentin adhesion: fluorescein-iabeleddentinal
bonding agent appears on both sides of the iutingcomposite resin.
Resin tags penetrate the etched dentin.(Original magnification
x180.)
Figs 5a and 5b Confocai images of in vitro bonded ceram-ic
restorations. Section of the adhesive interface.
Fig 5b Dentin bonding ¡aiiure. Faiiure presumably oc-curred
between the hybrid iayer and the overlaying resinand luting
composite resin. (Originai magnification x 180.)
Figs 6a to 6c Histologie section of human puip under an adhesive
restoration 50 days postoperatively. (Hematoxyiin-eosinstaining;
courtesy of Drs Virgiiiito and Hoiz.)
Fig 6a General view of (arrows) pulp. (Original magnifica-tion
x35,)
Fig 6b Control side of the pulp horn. (Original magnifica-tion
x350).
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Esthetic Dentistry
Fig 6c Pulpal area near the cavity shows reduced dentino-genesis
as well as a severely altered odontoblastic layer,(Original
magnification x 350), Special staining of adjacentsections did not
reveal the presence of bacteria.
mal injuries, and as dentinal replacement (as a base)prior to
further restorative procedures if the restora-tive material itself
cannot fulfill these requirements."'-"'-'Today, the indication for
placing a liner under an adhe-sive restoration has evolved mainly
to protective par-tial lining {calcium hydroxide cements) because
mod-ern adhesives can assume the total lining function ofpreviously
used varnishes and cements. The rationalefor this procedure has to
be confirmed, however, withbiologic and clinical studies.
The main role of base materials is currently to re-store the
geometry of large preparations for inlays andonlays. With direct
restorations, the placement of abase is also indicated to reduce
the volume ofthe obtu-ration material.''-^-" This allows better
control of theshrmkage and reduces the influence of the high
ther-mal expansion of composite resin materials. For thesepurposes,
application of glass-ionomer cements is awidespread practice. Other
materials, such as îincphosphate or polycarboxylate cements and
specialcomposite resins, are also used. The resin
modifiedglass-ionomers, a new class of materials, have recentlybeen
developed to overcome the handling shortcom-ings of conventional
cements. -
Glass-ionomer cements. Glass-ionomer cementsresult from Ihe
combination of polycarboxylate cementliquid (polyearboxylic acid)
and silicate cement pow-der (aluminosilicate glass). This original
cement""'offers some unique features:
1. Significant fluoride release2. Potential chemical adhesion to
hard tissues3. Superior mechanical resistance to that yielded
by
formerly available cements4. Compatibility of the thermal
expansion coefficient
with hard tissues5. Compatibility of chemistry with substrate
moisture.
However, the benefits of these interesting character-istics,
mostly demonstrated in vitro, are limited in vivo.For the time
being, the controversial biocompatibility(Figs 7a and 7b) as well
as the still-insufficient adhesionand wear resistance limit their
use as ahase.'*''^ More-over, clinical procedures are extremely
sensitive be-cause of the relatively long setting time that
requires asteady cement hydration.""̂
Composite resins. To overcome the manipulationshortcomings of
traditional glass-ionomer cements,manufacturers developed
low-viscosity light-curingcomposite resin materials. Different
fillers, such as syn-thetic hydroxyapatite hydroxide and
aluminosilicateglass, were incorporated in the resin matrix.
Manipula-tion is easy because it requires only the application of
asingle component and enables immediate light curing.These
characteristics, as well as fluoride release,'" arethe main
advantages of these products. However, thepoor adhesion to dentin''
and high bonding capacity tothe overlying composite resin
restoration or luting ce-ment made questionable the internal seal
quality ofsuch based/lined restorations,'-'^ unless a dentinal
ad-hesive was applied first,'"'
Resin modified glass-ionomers. Resin modifiedglass-ionomers were
developed to combine some ad-vantages of glass-ionomer cements and
composite res-ins. This new generation of dental materials is made
ofboth polyacryhc and methacrylate matrix that reactswith an
aluminosilicate glass filler.''' The unique fea-ture of these
products is the dual setting through theimmediate light-activated
polymerization and delayedchemical curing. The expected benefits of
resin modi-fied glass-ionomers are ¡1) ease of manipulation
be-cause of the too long working time and rapid set
(lightactivation); (2) resistance to early contamination by
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Esthetic Dentistry
Figs 7a and 7b Histologie section of human puip under
glass-ionomer iining 29 days postoperatively. (Hemaioxylistaining;
courtesy of Drs Virgillito and Holz )
Fig 7a Gênerai view of (arrow) puip, {Originai magnifica-tion
x20,) Puip bénéficiâtes from a thick remaining dentinwall.
Fig 7b in comparison with the control side of the puiphorn, the
puipai area in near the cavity shows the cessationof dentinogenesis
related to the complete odontobiasficatrophy, ¡Originai
magnification x350.)
Fig 8 Scanning eiectron microscopic view of mica crys-tals
protruding from Ihe glassy matrix (90-second hydro-fluoric
acid-etched Dicor specimen), (Original magnification
X 1,500,]
Fig 9 Scanning electron microscopic replica photographof a
composite resin restoration 1 year posto pe rative i y. Be-cause of
wear, a negative ledge was created by puiiing outofthe filler
particles. This is typical of old-formufation poste-rior composite
resins. (Original magnification x i ,000,)
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Esthetic Dentistry
water atid to dehydration: (3) higher early strength(compared
with that of traditional glass-iotiomer ce-ments): (4) potential
adhesion to hard tissues: and (5)fluoride release.
However, the present fortnnlution of resiti
modifiedglass-ionomers also suffers from an insufficient denti-nal
adhesion when they are submttted to the polymer-ization stress of
the material itself or of the overlyingcomposite resin,"
Other cements. Calcium hydroxide cements stillhave an indication
as a partial lining for protecting thepulp in deep areas of
preparations.'^
In more than a century of practical use, the classiczinc
phosphate cement has demonstrated its satisfacto-ry ciinical
performance. Its has also been shown to bereliable from a
histologie standpoint,'^ Clinicians knowthat old zinc phosphate
linings are difficult to remove.Despite the lack of any scientific
proof, it appears obvi-ous that the apparent adhesion of this
cement to dentinresults from a long-term interaction with dental
tissues.Its utilization as a base/liner in modern
restorativetechntques should therefore not be neglected as long
asmarginal seal is achieved through proper adhesive pro-cedures. As
with the traditional glass-ionomer cements,the long setting time of
zinc phosphate cements is aproblem.
Filling materials
Ceramics. The microstrueture of a fired dental porce-lain
usually consists of two phases; a glassy matrix thatsurrounds
crystalline inclusions.'"' The ceramics used inrestorative
dentistry are mainly reinforced porcelains.The first generation of
these materials was introducedby McLean and Hughes" in 1965,
Compared to theconventional fused-to-metal porcelain, these
ceramicscontain a higher amount of crystal phase. The
strength-ening results from different procedures,^'' The mostcommon
among these is the inclusion of high-elasticitymodule crystals
(mostly alumina and leucite) in theglassy matrix to form
crystal-glass composites (eg. Vi-tadur. Vita Zahnfabrik: Empress.
Ivoclar), In glass ce-ramics (eg. Dicor. Dentsply: Cerapearl.
Kyocera), thecrystal phase (mica, apattte) is created by the
"ceram-ization" of glass through thermal treatment-'""' (Ftg
8),Another promising procedure is slip casting."'-*- In theIn-Ceram
material {Vita Zahnfabrik), the matrix,made of sintered Spinell
(MgAlO;). is infiltrated withglass. This characterizes a new class
of dental ceramtcs.the matrix of whtch is crystalline. However, all
highly
crystalline ceramics present a reduced translucencyand are
therefore only indicated for fabricating a coreto be covered by a
cosmetic porcelain.
The ceramic materials can be processed in differentways: firing,
casting, pressing, slip casting, or machin-ing. Firing of porcelain
over a platinum foil ur refracto-ry die is a traditional but still
widespread method for in-lay fabrication (eg, Vitadur alpha: Optec,
Jeneric/Pen-tron; Mirage, Myron International: LFC. Ducera),More
recently, fabrication methods have been devel-oped or updated to
simplify or even eliminate laborato-ry steps as well as to improve
tbe material's physico-ehcmical characteristics. The application of
low-fusingceramic over a conventional ceramic core appearspromising
thanks to some unique characteristics: sim-plified laboratory
procedures {ceramic layering direct-ly on the master cast), the
possibility to make correc-tion firings, as well as excellent
io-mouth polishabilityand "physiologic" abrasion of opposing
teeth," Castceramics (CeraPearl and Dicor) did not encounter
adurable success in posterior teeth^' because of practicalor
physical shortcomings. Cold or hot pressing of ce-ramic ( Alceram
or Empress] is an interesting develop-ment, but it offers only a
slight improvetuent over tra-ditional methods with regard to
mechanical properties.The application of the In-Ceram system and
recentlythe ln-Ceram Spinell to the inlay technique
appearspromising (high mechanical resistance and improvedmarginai
adaptation),*' Innovative computer-aidedfabrication methods and the
pantograph device (Celay.
-Mikrona) allow the milling of prefabricated homoge-neous and
pore-free ceramics yielding improved physi-cal characteristics and
polishability,^*''' With the mo-bile station of the Cerec system
(Siemens), chairsideceramic restorations can be realized without
laborato-ry intervention.
To date, none of the available systems allow a "sim-ple"
realization of esthetic ceramic restorations provid-ing a high
intrinsic mechanical resistance. Therefore,satisfactory clinical
longevity rests on the efficiency ofthe restoration's bond to
dental tissues with adhesivecements,''^''' Moreover, many of the
new technologiesapplied to the fabrication of intracoronal
restorationsrequire expensive equipment that increases tbe cost
oftreatment for the patient.
Composite resins. Composite resins basically con-sist of an
organic phase, the resin matrix (acryiic poly-mers), and an
inorganic phase, the mineral filler {parti-cles). Both phases are
chemically or micromechanical-ly linked,^"" This bond is a weak
point of composite
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Esthetic Dentistry
Table I Current classification of composite resin materials
according to filler composition
Compositeresin type
Macro filled(traditional)
Stnall-particleSpheroidal
HomogeneousMicrofilledInhomogeneousMicrofilled
Hybrid
Small-particleHybrid(Fine hybrid)
Fillertype
Monomodal:Milled, edge-shapedmacroparlicles
Monotnodal:Milled, spheroidalsmall particles
Monotnodal:Pyrolitic silica
Monotnodal:Pyrolitic silica plusresin filler complex
Bimodal:Milled, edge-shapedmacroparticlesPyrolitic silica
Bimodal:Milled, edge-shapedsmall particlesPyroiitic silica
Ftllerconic ni(wt %)
60-80
85
35^5
45-79
70-80
70-80
Averageparticlesize(M-ni)
>5(variable)
0,6
0,04
0,04
2-10
0,04
0,5-1
0,(14
Particledistribution(^m)
1-40
0.01-3,5
1-200
0,5-30
0,1-10
Typicalbrands forposterior use
Estilux posterior(old formulation)
ZIOO
Dual (luting)
HeliomolarDistalite
FulfilOcclusinP-50
Herculite XRVPrisma A PHPorcelite (luting)Dicor (luting)
resins^" {Fig 9). A remarkable effort was made by man-ufacturers
to improve the silanization process (themost commonly used chemical
coupling) mainly to in-crease wear resistance,
Bowen's bis-GMA resin is still commonly used as theprincipal
constituent of the matrix, Hydrophobic resinswere recently
developed on the assumption that thedetrimental effects of the
water sorption on compositeresin chemistry would be reduced.^'Tlie
future as far asresin polymers are concerned certainly lies in the
de-velopment of nonshrinking materials using, for in-stance,
ring-opening monomers,''*'''
Light activation is now preferred to traditionalchemical curing.
The main advantages of light-activat-ed composite resins are their
pore-free structure, thehomogeneity of activation (improved
physicochemiealcharacteristics and wear resistance), and the
possibilityof multilayer application (improved adaptation and
es-thetics),"'''•̂ **"™ Nevertheless, the relative practical
ad-vantage of itnmediate curing is counteracted by thestress
development during rapid polymerization. Thedelayed curing of
chemically activated products prob-
ably allows a better stress absorption by the restorationand
dental tissues,''' The advantages of both curingsystems could be
combined by obturating the bottomof the cavity with a slow,
chemical-sett ing compositeresin and restoring the sutface with
light-curing ma-terial.
The filler is of pritnary concern for the clinical
andphysicochemieal properties ofeomposite resins,"" Thecurrent
classification of composite resins is thereforebased on the filler
characteristics'*' (Table 1), The trendtoday is to reduce the
particle size and to increase thefiller content in the tnaterial.
This kind of compositionis found in small-particle hybrids (eg,
Brilltant, Col-tene; Hereulite XRV. Kerr/Sybron: APH and
TPH,De-Trey Dentsply).'̂ - These submicron-particle com-posite
resins exhibit good surface characteristics (pol-ishability and
wear resistance) atid excellent physico-chemical properties.
Recently, spheroidal milled mac-roparticles were incorporated in a
new kind of macro-filled composite resin (ZIOO, 3M Dental). The use
ofsuch a filler, with a broad distribution of particle
sizes,instead of conventional shatp-edged glass ceramics
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Esthetic Dentistry
with a more regular size, led to the manufacturing of
ahtgh-density macrofilled composite resin.'*^ The bene-fits of this
structure still have to be established. Atpresent, composite resin
materials or adhesives canalso benefit frotii potential fluoride
release because ofthe incorporation of special fillers such as
ytterbiumfluoride (Hehomolar and Tetric, Vivadent),*-*-̂ '
Most of the new-generation products available onthe market today
exhibit similar physicochemical char-acteristics. Their esthetic
potential, however, can varyaccording to the diversity of shades
and opacities used.Some manufacturers offer excellent kits
including allVita shades in dentin and enamel opacities, as well
asdifferent incisai and cervical masses (eg.
HerculiteXRV)(Figin).
Polymerization shrinkage is still the main shortcom-ing of all
composite resin materials. This inherent dis-advantage of
fortrtcrly and currently available productsjustifies the need to
improve dentinal adhesion and de-velop placement techntques to
maintain satisfactoryadaptation and seal of esthetic
restorations.
Luting materials
Although glass-ionomer cements were at one time ad-voeated for
cementation of tooth-colored restorations,chnieal experience
demonstrated that they were inap-ropriate for thts purpose. The
high rate of clinical fail-ures observed was due to insufficient
mechanical resis-tance and poor adhesion to dental hard tissues or
resto-ration material.*'*
To lute resin and eeramic inlays, special compositeresins were
developed. Tlie association of light activa-tion and chemical
curing is necessary to ensure suffi-cient working time as well as
optimal polymerization ofthe luting cement. Unlike filling
materials, these two-component products are characterized by a
lower vis-cosity, which facilitates hand mixing and full
restora-tion seating. This reduced viscosity results from a
re-duction in filler content and an increased percentage oforganic
solvent (low molecular monomers).*** The phy-sicochemical
shortcomings of such materials are in-creased linear shrinkage and
lower wear resistance. Inpractice, these products easily flow in
approximalundercuts, and the removal of excess cement
remainsproblematic. Ultrasonic energy can be used to assist
theseating of tooth-colored restorations luted with a dual-curing,
highly filled hybrid composite resin (eg. Sono-Cem, ESPE,
Varia-link ultra, Vivadent). This energytemporarily increases ihe
flowability of the compositeresin (thixotropicity).^'
Fig 10 Composite resin inlays made chairside, demon-strating
naturai coior and transiucency effects because ofthe use of
diflerent material opacities and shades.
The efficiency of chemical activation is limited, how-ever, and
a proper illumination of the dual-curing ce-ment through the
restoration is preferable to ensure asufficient conversion rate
ofthe composite resin.̂ " Thisunderlines the necessity to fabricate
luted restorationswith minimal transiucency.
The use of highly filled composite resin cements istheoretically
necessary to facilitate removal of excess.to improve wear
resistance of the layer, and to providesatisfactory marginal
adaptation.'*"*" Currently, noneofthe available cementation kits
provide materials thatideally fulfill these requirements. Further
research andchnieal tests are therefore needed to improve the
adap-tation and seal of esthetic inlays and onlays, which re-main
the weakpoint of luted restorations (Fig 11).
Esthetic restorative techniques
There are several treatment modalities that make useofthe
previously described materials (Fig 12). In the di-rect technique,
all restorative steps are rcahzcd intra-orally, lasting a single
appointment. The semidirecttechnique also requires a single
appointment but dif-fers from the direct one by a number of
extraoral steps.The semidirect restoration is then luted, as is the
casewith the indirect technique, which requires at least
twoappointments and the collaboration of a dental labora-tory. Only
direct and semidirect restorations are madeentirely chairside.
This terminology (direct, semidirect, and indirecttechniques)'^"
is interesting because it simplifies andclarifies the
classification of the numerous current res-torative procedures as
regards their respective indica-tions.
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Fig 11 Scanning electron microscopic photograph of abonded fired
ceramic inlay in vivo. Examination after 1 yearrevealing
considerable wear of the (LC) luting compositeresin. (CER) Ceramic;
(E) enamel. (Original magnificationx200.)
Fig 12 Classification and maincharacteristics of the three
differenttypes of adhesive restorations.
Direct techniques
There are many different direct restorative techniques,including
simple ones, such as the hulk restoration, andmore sophisticated
ones, such as the three-sited light-curing technique,'''' The
peculiarity of direct compositeresins is that the placement
technique has to compen-sate for the unavoidable composite reshi
polymeriza-tion shrinkage, especially for Class II and larger Class
Tpreparations. To that effect, numerous procedtircshave been
proposed: segmentation of the polymeriza-tion by multilayer
techniques (horizontal, three-sited,or oblique),''-'^- use of
condensation and polymeriza-tion tips,''•'•''•' or placement of
glass inserts to reduce the
volume ofthe shrinking material,''^ Because a perfectgingival
seal and adaptation of direct composite resinrestorations cannot
predictably be obtained despite theuse of the aforementioned
placemen! techniques, the"rebonding" of the restoration margins
with a low-vis-cosity resin is highly recommended,'^
Compared with other esthetic treatment modalities,direct
restorations are relatively simply and rapidlyperformed. However,
polymerization shrinkage can heonly partially compensated for, and
adequate proximalcontacts of Class II restorations may be difficult
toachieve. These concerns led to the development oísemidirect
techniques for large restorations.
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Semidirect techniques
These techniques are primarily distinguished accord-ing to tbe
restorative material used, ie, composite resinor ceramic.
Composite resin. Composite resin semidirect resto-rations can be
fabricated intraorally^' after cavity insu-lation, or extraorally
on a fast-setting cast (usually sili-con) tnade from a synthetic
elastomer or alginate im-pression. After the restoration is made,
it is recom-mended that the piece be subjected to a thermal
orphotothermal process (postpolymerization) in a smallfurnace or in
boihng water, before cementation, I'hepostpolymerization was
supposed to improve thematerial's physicochemical properties. In
fact, the mainbenefits of this treatment are improved wear
resis-tance''̂ and dimensional stability of the material,""Marginal
adaptation and seal are potentially improvedbecause polymerization
shrinkage is confined to thesole luting composite resin
layer,'""'"'
From a practical viewpoint, extraoral fabrication ofthe
restoration on the cast (eg, EOS. Vivadent; InlaySystem.
DeTrey/Dentsply) has a substantial advantageover direct and
semidirect intraoral (eg, DI, Coltene;CS Inlay. Kulzer) techniques.
This is particularly truefor mesio-occlusodistal cavities and for
the most poste-rior teeth or when access Is hmited. However,
supple-mental procedures are required to make such
extraoralrestorations, and these increase the time needed
forcompletion as well as the related treatment fees.
Ceramic. There are several semidirect systems thatcan produce a
milled ceramic restoration: theCAD/CAM and pantograph systems. The
costs ofCAD/CAM systems are very high and the resulting
res-torations yield limited esthetic results compared withother
restorative leehniques, Tlic well-known Cerecsystem is undoubtedly
the most practical and integrat-ed one. It represents a concrete
contribution of newtechnologies to the dental profession and it
probablyreflects the future of restorative dentistry. The
Celaypantograph is a totally computer-free system that al-lows the
replication of an intraorally made resin inlayinto a ceramic inlay.
This replication consists in themining of a ceramic block by burs
and disks directed bythe movement of similar form guides touching
the resininlay, Tlic main disadvantage of the Cerec and
Celaysystems is having to cut the occlusal anatomy inside
theceramic or resin. This procedure is time consuming andgenerally
results in a simplified morphology: the occlu-
sal function of such restorations is therefore not ideal.An
additional cosmetic firing may improve fhe finalesthetics.
Indirect techniques
Ceramics are still the choice material for indirect
resto-rations,'"""'"-^ Adequate bonding of ceramic to resinrests on
micromechanical adhesion (ceramic etchingwith hydrofluoric acid)
usually in association withchemical coupling (silanization),*-'
Chemical adhesionalone also seems possible."* '̂"'' For indirect
inlays, new,highly filled, small hybrid composite resins can also
beused when poslpolymerized.
Treatment options and relaied clinical considerations
The success of a restorative procedure depends onwell-defined
requirements: use of biocompatible mate-rials, resistance ofthe
restored tooth, satisfactory adap-tation and seal, wear resistance
of the restoration and"physiologic" abrasion of opposing teeth,
ideal esthet-ics and function, practicability of the system, and
lowcosts.
Because no ideal material exists that can be easilyhandled and
applied to every chnical situation withpredictable success, today's
clinician has to select theproper materials and techniques
according to each par-ticular case. New adhesive materials,
including thosecapable of fluoride release, have still not
clinicallyproven their cariostatic potential. Posterior
estheticrestorations are therefore still considered to be
indicat-ed for patients with good oral hygiene, low caries
sus-ceptibility, and true esthetic demands. Because adhe-sive
techniques cannot compete with the reasonablecost of amalgam
restorations, the economic concernshould not be neglected when
treatment is planned.Local parameters also have to be considered
becausethey will define which materials and techniques have tobe
applied.
Location ofthe margins. It is generally accepted thatthe
presence of enamel all around the cavity is essentialto provide a
satisfactory adaptation and seal of the res-loration,''' However,
the thickness and amount of re-,sidual enamel at the gingival limit
as well as the margi-nal design may strongly influence the quality
of the res-toration,'* It has been shown that a minimal
enamelthickness of 1,0 mm wilh a bevel is required for
directtechniques (multilayer), whereas luted
restorations(semidirccf or indirect techniques) require only l),5
mmto provide satisfactory adaptation and seal whatever
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Esthetic Dentistry
Figs 13a and 13b Sections of in uitro Class II restorations
(view of the cervical area;
Fig 13a Severe leakage occurred with the direct tech-nique and
butt preparation (residual enamel is 1 mm thick].
Fig 13b Semidirect restoration (inlayl with butt prepara-tion
provided a perfect seal despite the extremely thin re-maining
enamel.
Figs 14a and 14b Class II cavitiesextendingdistally below the
cementoenamel junction.
Fig 14a Cavity preparation includes retention form. Fig 14b An
amalgam base will provide the dentinal seal fora combined
amalgam-composite resin restoration.
the marginal design may be (Figs l.'ía and 13b). Whenresidual
enamel is less than 11,5 mm or totally absent,only tbe most recent
dentinal bonding agents in combi-nation with a luted restoration
seem able to improvemargin quality,'"^ A mixed restoration
(self-retentiveamalgam to obturate the bottom of the proximal
cavityand composite resin to restore the remaining volume)
is also an alternative^''-'' {Figs 14a and 14b), However,the
clinical benefits of these procedures still have to
bedemonstrated.
Location ofthe tooth inside the dental arch. This pa-rameter has
to be considered not only for esthetic pur-poses, but also to
determine tbe mecbanical strain therestoration will sustain.
Restorations in the anterior
670 Quintessence International Volume 25, Number 10/1994
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Esthetic Dentistry
Fig 15 Typical cusp fissure associated with amaigam
res-toration. This situation resuils from an improper seieetion
ofrestorative material or preparation design.
Fig 16a Indications for direct restorations: treatment of
alimited number ot smail carious lesions or faulty
existingrestorations.
Fig 16b Preop e rat i ve situation.
Fig 16c Adhesive preparations. Fig 15d Finai restorations.
Quintessence iniernationai Voiume 25, Number 10/1994 671
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Esthetic Dentistry
SEMI-DIRECT RESTORATIONS
Fig 17a Indications for semidirect restorations: treatmentofa
iimited number of large carious lesions or faulty
existingrestorations.
Fig 17b Preoperative view.
Fig 17c Chairside composite resin inlays (made extraoral-iy) on
their silioon cast.
Fig 17d Restorations after oementation.
area of the arch present a good prognosis because ofthe lower
functional stress and wear developedthere.""'"'
Tooth anatomy. The lack of tooth reinforcement bytraditional
metallic materials frequently leads to fis-sures or fractures of
dental tissues (Fig 15). For ana-tomic reasons, maxillary premolars
and mandibularmolars, as well as teeth presenting a high cuspal
inclina-tion, are at-risk teeth."-"^ Only adhesive techniqueshave
demonstrated their ability to reinforce the pre-pared tooth."''
Consequently, these techniques shouldbe considered for prevention
of such mechanical fail-ures as well as for conservative treatment
of fissured orfractured teeth. In the case of a deep mesiodtstal
fts-sure. the tooth shouid preferably be endodonticallytreated and
crowned."" As a result ofthe unfavorable
anatomy of premolars (mainly their reduced size) di-rect
restoration of these teeth is often preferred be-cause tbe tootb
preparation is more conservative.
Size and number of restorations. Clinicians agree thatdirect
obturations should be strictly restricted to smalland medium
intracoronal cavities (Figs 16a to 16d).Wide Class I atid Class II
preparations as well as partialcoverages represent typical
indications for luted resto-rations. A limited number (two or three
teeth distribut-ed within different quadrants) of such restorations
maybe ideally realized with semidirect techniques (Figs 17ato 17d).
Currently, optimal functional and anatomic oc-clusal surfaces
cannot be produced with the basic pre-cedures of semidirect
techniques (cutting or carvingthe restorative material without
proper reference totheopposingarch). As long as these techniques
are not
672 Quintessence International Volume 25, Number 10/1994
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Esthetic Dentistry
INDIRECT RESTORATIONS
Fig 18a Indications tor indirect restorations: treatment
ofmultiple carious lesions or faulty existing restorations
andcomplete-quadrant rehabilitation.
Fig 18b Preoperative view.
JJilFig 18c Composite resin inlays on the master cast. Fig 18d
Restorations after cementation.
considerably modified, clinical experience demon-strates that
the proposed indications for semidirect res-torations appear
pertinent. When several teeth have tobe treated simultaneously in
the same quadrant or evenfor complete posterior rehabilitations,
indirect tech-niques should be employed (Figs 18a to lSd), A
bet-ter occlusion and esthetic control can be achieved
withlaboratory-fabricated restorations. For extendedcoverage
(single or multiple restorations), indirect ce-ramic onlays and
overlays are recommended.
Based on the reviewed biologic and physicochemicalproperties of
restorative materials as well as practicaland clinical criteria,
guidelines for a logical treatmentchoice are summarized in Table
2,
Quinlessence Inlernational Volume 25, Number 10/1994 673
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Esthetic Dentistry
Table 2 Clinical guidehnes for posterior esthetic
restorations.
Cavity size and class
Small Class I
Small Class IIMedium Class I
Medium Class IIor
Large Class I or II(MO/OD, coverage)(easily accessible)
Large Class I or II(MOD, coverage)
Serial Class I or II(without coverage)
Single, serial resto-rations with extendedor complete
coverage
Restorative material
Composite resin
Composite resin/ceramic
Ceramic
Restorative technique
Direct
Semidirect
Indirect
Most appropriate options
Bulk •
Horizontal layeringHori;iontal and oblique layering
Three-sited and oblique layeringceramic inserts and polymerized
tips
Celay or Cerec intraoral inlay
Celay or Cerec, extraoral inlay
Laboratory fabrication
Conclusions
Since the early 196üs, adhesive techniques and materi-als have
improved tremendously, Tliere are probablyno other restorative
systems that have been so inten-sively and critically investigated.
In vivo and in vitrotrials have demonstrated their main advantages
overtraditional metallic restorations: esthetics,
maximumconservation of sound tissue, and tooth reinforcement.While
waiting for a unique and ideal esthetic restora-tive material,
dentists still have to deal with a widerange of materials and
techniques. Most cases in resto-rative dentistry can be
successfully treated as long as anappropriate choice of esthetic
products and proceduresismade,Todate, the weakpoinf of this type of
restora-tion remains the problematic adhesion fo dentin andthe
related bacterial leakage and postoperative sensi-tivity
problems.
Acknowledgments
We express our gratitude to Mrs M, Turner for her help in
reviewingthe manuscripl and to Mr M, Magne and Mr D, Vinci
(denlalteclini-cians) for Ihe labora lory-made restorations
presented here.
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