CLINICAL RESEARCH

Evidence-based concepts and

procedures for bonded inlays
and onlays. Part II. Guidelines for
cavity preparation and restoration
fabrication
Giovanni Tommaso Rocca, DMD
Senior lecturer, Division of Cariology and Endodontology,
University Clinic of Dental Medicine, Geneva, Switzerland

Nicolas Rizcalla, DMD

Senior lecturer, Division of Cariology and Endodontology,
University Clinic of Dental Medicine, Geneva, Switzerland

Ivo Krejci, Prof, DMD,PD

President, University Clinic of Dental Medicine, Geneva, Switzerland
Director, Department of Preventive Dental Medicine and Primary Dental Care,
Head, Division of Cariology and Endodontology,
University Clinic of Dental Medicine, Geneva, Switzerland

Didier Dietschi, DMD, PhD, PD

Senior lecturer. Division of Cariology and Endodontology,
University Clinic of Dental Medicine, Geneva, Switzerland
Adjunct Professor, Department of Comprehensive Dentistry,
Case Western University, Cleveland, Ohio
Private Education Center, The Geneva Smile Center, Geneva, Switzerland

Correspondence to: Giovanni Tommaso Rocca, DMD

School of Dentistry, Faculty of Medicine, University of Geneva, 19 rue Barthélémy-Menn, 1205 Geneva, Switzerland;

E-mail:giovanni.rocca@unige.ch

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Abstract after a multifactorial analysis, which in-

cludes cavity dimensions and the result-
The second part of this article series pre- ing tooth biomechanical status, as well
sents an evidence-based update of clin- as occlusal and esthetic factors. The clin-
ical protocols and procedures for cavity ical impact of the modern treatment con-
preparation and restoration selection for cepts that were outlined in the previous
bonded inlays and onlays. More than article – Dual Bonding (DB)/Immediate
ever, tissue conservation dictates prep- Dentin Sealing (IDS), Cavity Design Op-
aration concepts, even though some timization (CDO), and Cervical Margins
minimal dimensions still have to be con- Relocation (CMR) – are described in de-
sidered for all restorative materials. In tail in this article and discussed in light of
cases of severe bruxism or tooth fra- existing clinical and scientific evidence
gilization, CAD/CAM composite resins for simpler, more predictable, and more
or pressed CAD/CAM lithium disilicate durable results. Despite the wide choice
glass ceramics are often recommend- of restorative materials (composite resin
ed, although this choice relies mainly on or ceramic) and techniques (classical or
scarce in vitro research as there is still CAD/CAM), the cavity for an indirect res-
a lack of medium- to long-term clinical toration should meet five objective cri-
evidence. The decision about whether teria before the impression.
or not to cover a cusp can only be made (Int J Esthet Dent 2015;10:392–413)

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Introduction has the potential to resolve most of the

clinical difficulties usually encountered
The first part of this series of articles was during the preparation, isolation, impres-
presented as a comprehensive, revised sion taking, and cementation of tooth-
treatment rationale and as clinical pro- colored inlays and onlays, while improv-
cedures for bonded inlays and onlays, ing treatment quality and longevity.
based on scientific and long-term clin-
ical evidence. The most relevant princi-
ples reported were the absence of tissue Occlusal considerations
removal following materials’ properties
and tooth preparation
or technical requirements, and the ef-
fective preparation of dental tissues fol- Restoration material choice
lowing Dual Bonding (DB)/Immediate
Dentin Sealing (IDS) concepts,1-8 Cav- Regarding the restorative material used
ity Design Optimization (CDO), and Cer- for inlays and onlays, ceramics (pressed
vical Margins Relocation (CMR), or fired) were traditionally preferred, as
depending on the clinical situation and they were thought to be stronger and
needs. The aforementioned procedures more reliable than their composite coun-
aim to avoid any additional tooth prep- terpart. However, the referred literature
aration and tissue removal required to never clearly confirms the advantage of
create the geometry for indirect pos- ceramics, especially taking into consid-
terior restorations and to protect the eration disparate testing environments
pulpodentinal structures from any con- for both restorative materials.14-16 Ac-
tamination/disturbance during the tem- tually, the patient selection and clinic-
porary phase, as well as to stabilize and al environment were manifestly more
improve the adhesive interface quality. favorable to ceramic restorations, as
When needed, the CMR technique (also indirect ceramic restorations were nei-
known as Deep Margin Elevation – DME) ther placed in social clinics nor in pa-
helps to raise deep cervical margins to a tients with severe bruxism, while such
visible and accessible level (supragingi- restrictions did not normally apply (or
vally), easing impression and cementa- did not apply as strictly) to composite
tion procedures. Moreover, due to an studies. Despite this, composite resins
even cavity design, the CDO and CMR have been widely used for the fabrica-
techniques facilitate the placement of tion of inlays and onlays due to a simpler
temporary restorations (non-cemented) manufacturing process (and thus lower
and the restoration fabrication. Regard- cost), as well as their excellent esthet-
ing cementation, the use of a highly ics and easier reparability. A more “re-
filled, light-curing restorative material is cent” and increasingly used alternative
recommended instead of a dual-curing is CAD/CAM restoration, made in either
composite cement because of its super- ceramic or composite resin blocks (ie,
ior mechanical properties and wear re- IPS Empress or e.max CAD, Ivoclar
sistance, as well as its practicality.
Overall, this updated clinical protocol this large choice with regard to materials

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 ROCCA ET AL

and fabrication methods, the tooth prep- ment of the in vivo performance of new
aration for all kinds of modern bonded monolithic ceramic restorations in a criti-
restorations relies on similar specific cal biomechanical environment.
principles, which differ from those for
traditional cast-gold inlays and onlays, Preparation extent and restoration
and even the first generation of fired thickness
porcelain restorations, whose limited
mechanical resistance imposes more All tooth-colored materials (composite
demanding and invasive preparations. resin or ceramic) used for the fabrica-
The occlusal environment has to be tion of posterior indirect restorations are
evaluated, as it plays an important role submitted to high occlusal functional
in restoration longevity and can also stresses; consequently, their inherent
influence material choice. Extensive vulnerability needs to be compensated
restorations with generally large and for by restoration thickness and proper
deep cavities (mainly non-vital teeth) adhesive cementation. Although the res-
in high load-bearing areas (especially torations should therefore be as thick as
the second molars) associated with an possible, this approach is tempered by
unfavorable occlusal context (such as the fundamental principles of minimal
patients with bruxism) have to be con- invasiveness.29 Moreover, an unconsid-
sidered biomechanically vulnerable and ered sacrifice of enamel and dentin could
more susceptible to failure. In the latter also directly weaken the tooth. For exam-
unfavorable situation, only the strong- ple, Fennis and co-workers have dem-
est materials should be chosen, based onstrated that thick overlay restorations
mainly on their superior mechanical show higher static fracture strength com-
properties. Today, new CAD/CAM com- pared to conservative ones, although
posite resin blocks (ie, Lava Ultimate, they present more drastic and irrevers-
ible failures; ie, thicker restorations may
based restorations (ie, IPS e.max Press be stronger but simultaneously imply
or CAD, Ivoclar Vivadent) are preferred, thinner and weaker dental tissues under-
the former option having some interest- neath them. At the same time, extremely
ing stress-absorbing properties,17 while thin material is not systematically and un-
requiring simpler procedures when a conditionally recommended. If one takes
surface modification or repair is need- into consideration that a few tenths of a
ed.18 Recent in vitro studies on the frac- millimeter can considerably strengthen a
ture and fatigue resistance of direct and restoration, the best compromise would
indirect restorations of a severely eroded be between material resistance and the
tooth model demonstrated the favorable clinical situation. We should therefore
behavior of CAD/CAM composite ma- move away from the blind application of
terials.17,19-24 Apart from the non-vital “minimally invasive dentistry” to a more
tooth configuration, the aforementioned realistic concept of “minimally hazard-
findings are well supported by clinical ous dentistry”, which is particularly per-
trials.25-28 However, less information is tinent to large and deep cavities and to
available to date regarding the assess- non-vital teeth.

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ials, including composite resins, pressed

ceramics, and CAD/CAM blocks (apart
from traditional feldspathic and leucite-
reinforced ceramics), while the stabil-
ity and impact of thinner material lay-
ers on restoration longevity is still under
evaluation. Moreover, it is important to
note that minimal material thicknesses
should be limited to monolithic/mono-
laminar restorations, as a layering pro-
cedure could mean including imperfec-
Fig 1 Oscillating selectively coated diamond in- tions in the narrow available space, thus
struments for the finishing of the interproximal zone.
weakening the system. Finally, esthetic
considerations will also have an impact
on restoration thickness (see “Esthetic
considerations” below).
In conclusion, a good compromise
between tissue preservation and a suita-
The minimal occlusal thickness al- ble restoration thickness has to be found
lowed for a material depends on its in- and adapted to each case or tooth-spe-
trinsic mechanical features (static and cific occlusal and esthetic context.
dynamic reaction to stresses) and is
therefore material- and even brand- Clinical guidelines
dependent. Thus, usual recommenda-
tions based on clinical experience and It follows, then, that while the cavity de-
in vitro testing suggest to attain at least sign and extent is largely dictated by
1 mm thickness for composite resins, conservation principles, together with
and 2 mm for low-strength ceramics, occlusal and esthetic parameters, the
such as feldspathic (eg, Vita Mark II, overall cavity design is related to the
Vita) and leucite-reinforced (IPS Em- pathology and presence of decayed tis-
press I, Ivoclar Vivadent) ceramics. sues rather than the need for macrore-
For new lithium disilicate-reinforced ce- tention or friction.
ramics (ie, IPS e.max Press or CAD), Practically, preparation starts with the
the minimal recommended thickness removal of the existing restoration and
seems to be closer to that recommend- decayed tissues without initially finishing
ed for composite resin, ie, between 1 the enamel margins. In less accessible
and 1.2 mm. The presence of areas (usually interproximally), oscillat-
enamel under these thin ceramic res- ing, selectively diamond-coated instru-
torations has also been recently proven ments (ie, PCS, EMS or Sonicsys, KaVo)
to yield a certain positive effect. facilitate the preparation and finishing
Overall, a restoration thickness between of cavities (Fig 1). When cavity margins
1.0 and 1.5 mm seems to be advisable violate the biological width, a crown-
for all modern “white” restorative mater- lengthening procedure may be needed,

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 ROCCA ET AL

while for subgingival/intracrevicular cer- to follow aforementioned conservation

vical margins (a more frequent condi- principles, thin and undermined cavity
tion), a conservative CMR is advised. walls can be maintained and reinforced
The decision to use a specific technique with composite resin during the adhe-
depends less on ultra-strict biological sive resin lining of the cavity. The au-
width considerations and more on the thors recommend a minimum of 1 mm
future accessibility of the margins to se- as minimal wall width/thickness before
cure the clean and dry environment nec- reinforcement. In cases where the mini-
essary for proper adhesive techniques. mal residual thickness is below this
Fissures (in dentin or enamel) should measurement, cusp coverage is indi-
ideally be included in the preparation, cated (this guideline seems to be the
considering potential bacterial leakage accepted general clinical consensus
or structural weakening, although their nowadays). The aim is to have a more
extension in inaccessible zones often homogeneous biting force distribution
prevents these flaws from being fully and offer a “protective effect” for the un-
eliminated. derlying weakened tooth structure. The
resulting “invasiveness” could, howev-
Thin cavity walls and occlusal er, increase the risk of irreversible tooth
fracture (below the cementoenamel
coverage
junction – CEJ), as is shown in vitro by
Little is known scientifically about the Fennis et al, although such clinical ob-
minimal thickness needed to maintain servation is extremely rare in vital teeth.
thin tooth walls and what is to be con- Finally, the systematic occlusal cover-
sidered totally safe and conservable, age of functional and/or non-function-
knowing that a multitude of parameters al cusps is not yet advocated, as it is
will impact such a decision process. The seemingly not proven to increase the
presence of thin walls around an exten- final strength of the tooth-restoration
sive cavity is, in any case, considered a system, both for composite resins40 and
strong indication for indirect restorations ceramics.41-44
rather than direct fillings, as polymeriza- In conclusion, occlusal coverage is
tion might deform the remaining facial recommended for cavity walls of 1 mm
and lingual tooth structures, potentially or thinner, while for “intermediate” thick-
inducing cracks due to the inward cusp ness (1 to 2 mm), the occlusal context
movement that follows. The cavity including tooth position, presence of
size and design (C-factor), as much as parafunctions, and the kind of lateral
the stratification technique, will impact guidance (canine or group guidance)
such stresses on residual tooth struc- should be taken into account when mak-
ture. This is why indirect techniques ing the therapeutic decision. The cavity
are generally preferred, because poly- configuration, and in particular the pres-
merization shrinkage is confined to the ence or absence of the marginal ridges,
thin layer of luting resin cement. can also play a role in the final strength
Different options are available with an of the residual walls, especially in endo-
indirect approach. First, in an attempt dontically treated teeth.45

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Fig 2 The “smile space” of two different patients. The visibility of the treated tooth during smile has to be
verified before cavity preparation. The patient’s lips can act as a curtain behind which the tooth–restoration
transition can be hidden.

Esthetic considerations esthetic zone is generally unknown. As

the removal of undermined, fissured or
For restorations extending into the buc- thin buccal cusps could bring the res-
cal-esthetic zone (the virtual space be- toration into a visible and more critical
tween the upper and lower lips during esthetic zone, this occurrence must be
full smile), margin positioning plays an taken into account and a shade selec-
important role (Fig 2). Actually, the sim- tion systematically performed before the
plest and most ideal situation is for the preparation. Otherwise, tissue dehydra-
restoration margins to be located in the tion will prevent the clinician from later
incisal or cervical thirds. In both situa- choosing a precise and reliable shade
tions, a good esthetic integration of the registration because it only takes a few
restoration can easily be achieved due seconds of tissue dehydration to impact
to a simpler tissue arrangement; practi- shade perception.
cally, almost only one tissue is present
– enamel in the incisal third, and dentin Shade selection
in the cervical third. This makes the es-
thetic integration of the restoration tech- Additionally, metallic and temporary res-
nically and optically more predictable torations, caries, and – in general – any
discolored, decayed tissue may alter
low, margins can be left elsewhere on dentin and enamel shades; thus, they
the buccal cusp, depending only on the should be removed beforehand under
restorative needs. water spray, to preserve tissue hydra-
While the esthetic impact of the res- tion. As an alternative, tooth shade can
toration should theoretically be analyzed be recorded and crossed-matched with
before the cavity preparation, the final a non-restored, contralateral or neigh-
extent of the restoration in the buccal- boring tooth.

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