Restorative dentistry: Tooth preparation techniques for porcelain laminate veneers
ABSTRACT Objective The purpose of this study was to determine the effect that two guides to tooth preparation had on an operator's ability to appropriately and consistently prepare teeth for porcelain laminate veneers.Study designIn-vitro studyMaterials and methods Thirty typodont central incisor teeth were randomly allocated into three groups and a general dental practitioner was asked to prepare the teeth for porcelain laminate veneers. Group A were prepared freehand while Groups B and C were prepared with the assistance of a silicone index and depth preparation bur respectively. Images of the prepared teeth were used to calculate the mean labial depth of preparation and incisal reduction of teeth in each group.Results The mean labial reduction for Groups A, B and C was 0.37 mm (SD 0.13), 0.62 mm (SD 0.17) and 0.61 mm (SD 0.15) and the mean incisal reduction for Groups A, B and C was 1.0 mm (SD 0.28), 1.0 mm (SD 0.38) and 1.03 mm (SD 0.26) respectively.Conclusion It is suggested that consideration be given to the use of a silicone index or depth gauge bur when teeth are prepared for porcelain laminate veneers.
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ABSTRACT: Objective The purpose of this study was to determine the effect that two guides to tooth preparation had on an operator's ability to appropriately and consistently prepare teeth for porcelain laminate veneers.Study designIn-vitro studyMaterials and methods Thirty typodont central incisor teeth were randomly allocated into three groups and a general dental practitioner was asked to prepare the teeth for porcelain laminate veneers. Group A were prepared freehand while Group B and C were prepared with the assistance of a silicone index and depth preparation bur respectively. Images of the prepared teeth were used to calculate the mean labial depth of preparation and incisal reduction of teeth in each group.Results The mean labial reduction for Groups A, B and C was 0.37 mm (SD 0.13), 0.62 mm (SD 0.17) and 0.61 mm (SD 0.15) and the mean incisal reduction for Groups A, B and C was 1.0 mm (SD 0.28), 1.0 mm (SD 0.38) and 1.03 mm (SD 0.26) respectively.Conclusion It is suggested that consideration be given to the use of a silicone index or depth gauge bur when teeth are prepared for porcelain laminate veneers.British dental journal 01/2000; 189(5):256-256. · 0.81 Impact Factor
260BRITISH DENTAL JOURNAL, VOLUME 189, NO. 5, SEPTEMBER 9 2000
preparations for porcelain laminate veneers require the operator to
reduce the labial surface uniformly, within enamel, by 0.5 mm.7
Inadequate labial reduction can potentially lead to increased bulk
in the veneer8while over reduction needlessly results in more
extensive dentine exposure.9In cases where the operator fails to
achieve uniform reduction of the labial surface, taking account of
the facial contours of the tooth, it is common to find areas of both
inadequate and unnecessarily extensive reduction within the same
Initially four types of preparation were described for porcelain
laminate veneers; only two of which required the incisal edge to be
prepared.10Currently it is accepted however that when teeth are
prepared for porcelain laminate veneers the incisal edge should be
reduced by 1.0 mm and finished with a bevel or overlapped onto
the palatal surface.11The requirement to reduce the incisal edge has
recently been questioned in two studies, which reported equivalent
longevity for porcelain laminate veneers with and without incisal
overlap.12–13It is suggested however that until further evidence is
forthcoming the incisal edge be reduced when teeth are prepared
for porcelain laminate veneers.11Two studies have reported a ten-
dency for practitioners to under prepare teeth for porcelain lami-
nate veneers with under preparation of the middle incisal third of
the tooth being especially common.14–15
The aim of this study was to investigate the effect that guides to
depth preparation have on an individual practitioner’s ability to cor-
rectly and consistently prepare teeth for porcelain laminate veneers.
Methods and materials
Thirty typodont, upper right incisor, teeth (Riverside Dental Man-
ufacturers, London, UK) were mounted singly in plaster blocks and
randomly allocated to three equal groups (A, B and C) using ran-
dom number tables. A prosthodontist with suitable postgraduate
training, attuned to the preparation required for porcelain lami-
nate veneers, was invited to prepare each tooth for a porcelain lam-
inate veneer restoration using standard burs (Burs 0835, 0835F,
Shofu Inc, Kyoto, Japan). The practitioner was not told of the pur-
pose of the study until all the preparations had been completed.
Group A teeth were prepared freehand, Group B teeth were pre-
pared using a sectioned index (Fig. 1) formed from an addition
cured silicone impression material (Provil, Heraeus Kulzer Ltd,
UK) and the Group C teeth were prepared using a depth gauge (0.5
mm) bur (S4 bur, Intensiv SA, Lugano, Switzerland) (Fig. 2).
The technique for measuring depth of preparation originally
described by Nattress et al.,15was modified for the purposes of the
study. Prior to tooth preparation a sectional index that could be
reconstructed over the original tooth was produced using an addi-
tion cured silicone impression material. Following tooth prepara-
tion the index was reconstructed and a light body addition cured
silicone, of contrasting colour, injected into the index to occupy the
space created by tooth preparation. The index was then sectioned
axially along the midline of the prepared tooth with a scalpel and
the left-hand side mounted on a microscope slide.
Tooth preparation techniques for
porcelain laminate veneers
P . A. Brunton,1A. Aminian,2and N. H. F. Wilson,3
Objective The purpose of this study was to determine the effect
that two guides to tooth preparation had on an operator’s ability
to appropriately and consistently prepare teeth for porcelain
Study design In-vitro study
Materials and methods Thirty typodont central incisor teeth
were randomly allocated into three groups and a general dental
practitioner was asked to prepare the teeth for porcelain laminate
veneers. Group A were prepared freehand while Groups B and C
were prepared with the assistance of a silicone index and depth
preparation bur respectively. Images of the prepared teeth were
used to calculate the mean labial depth of preparation and incisal
reduction of teeth in each group.
Results The mean labial reduction for Groups A, B and C was
0.37 mm (SD0.13), 0.62 mm (SD0.17) and 0.61 mm (SD0.15)
and the mean incisal reduction for Groups A, B and C was
1.0 mm (SD 0.28), 1.0 mm (SD0.38) and 1.03 mm (SD0.26)
Conclusion It is suggested that consideration be given to the use
of a silicone index or depth gauge bur when teeth are prepared for
porcelain laminate veneers.
teeth is the provision of porcelain laminate veneers.1The porcelain
laminate veneer restoration, as first described by Horn2gained
widespread acceptance with a survey of 200 practitioners in the US
in the late 1980s and early 1990s reporting that practitioners placed
a mean of 200 porcelain laminate veneer restorations over a 3-year
period.3 There is evidence, however, that the numbers of porcelain
laminate veneers prescribed in England and Wales is falling, and
practitioners would seem to prefer more destructive techniques
including full veneer crowns for the management of unattractive
anterior teeth.4It has been suggested that the lack of a predictable
outcome with porcelain laminate veneer restorations, invariably
as a result of poor tooth preparation, may be responsible for the
practitioner’s reticence to continue to prescribe them in prefer-
ence to more extensive forms of restoration.4Such a trend is cause
for concern given that full coverage restorations are less preserva-
tive5of tooth tissue and are associated with an increased incidence
of periradicular periodontitis.6
Accepted recommendations, although not evidence based, for
ith the exception of vital bleaching, the most used preserva-
tive treatment for unsightly, but otherwise sound, anterior
1*Lecturer,2General Dental Practitioner, 3Professor, Unit of Operative Dentistry
and Endodontology, University Dental Hospital of Manchester, Higher
Cambridge Street, Manchester M15 6FH
*Correspondence to: Dr P. A. Brunton
Received 22.11.99; Accepted 15.03.00
© British Dental Journal2000; 189: 260–262
BRITISH DENTAL JOURNAL, VOLUME 189, NO. 5, SEPTEMBER 9 2000 261
An optical microscope, with a resolution of ±0.02 mm, attached
to a personal computer was used to capture an image of the sec-
tioned relined index (Fig. 3), which was subsequently analyzed by
an image analysis package (HL Image ++, Data Translation Lim-
ited, Basingstoke, UK; Sigma Scan, SPSS ASC Erkrath, Germany).
Five measurements (Fig. 3) of the labial reduction and one of the
incisal reduction were obtained on two occasions. These results
were averaged to give a mean labial and incisal reduction for each
preparation. The data were analyzed using a one way analysis of
variance and Scheffe’s post hoc statistical test.
The mean labial reduction for Groups A, B and C was 0.37 mm
(SD 0.13), 0.62 mm (SD 0.17) and 0.61 mm (SD 0.15) respectively.
The mean incisal reduction for Groups A, B and C was 1.0 mm
(SD 0.28), 1.0 mm (SD 0.38) and 1.03 mm (SD 0.26) respectively.
There was a statistically significant difference (P < 0.05) between
the three groups with respect to the labial reduction. In contrast,
there was no significant difference (P > 0.05) between the three
groups with respect to incisal reduction. The labial reduction for
Group A was less than that of Groups B and C, which were similar.
Scheffe’s test revealed that this difference was significant at the 5%
level of significance.
The labial reduction for teeth in Group A was accomplished free-
hand, which it is suggested is typical of clinical practice. The
results of this study suggest that teeth prepared in this way for
porcelain laminate veneers would tend to be under prepared. This
supports the findings of a previous clinical study, which reported
that clinicians tend to under prepare the labial aspect of teeth for
porcelain laminate veneers,4which produces overcontouring of
the restored tooth.16
Under preparation creates a technical problem when the lami-
nate veneer restoration is produced in the laboratory. To compen-
sate for under preparation the technician often has to over bulk the
restoration. It has been shown that excessive bulk in the gingival
part of the restoration can adversely effect the emergence profile,
which may initiate inflammation of the adjacent gingivae.17
Increased bulk in the incisal part of the restoration produces poor
aesthetics but more importantly it can alter the protrusive relation-
ship leading to atypical occlusal loading of the veneer and possible
subsequent fracture. Under preparation of severely discoloured
teeth especially will also result in a poor aesthetic outcome. A thin
layer of porcelain has a limited ability to disguise severely dis-
coloured underlying tooth tissue.18
Teeth prepared with a silicone index or a depth gauge bur
(Groups B and C) were slightly over prepared. It is therefore likely
that increased amounts of dentine will be exposed within the
preparation. This is particularly the case in the cervical third of the
preparation where the enamel is very thin.19This will not compro-
mise the ultimate restoration, provided such dentine exposure is
embodied within the preparation and all margins are within
enamel. Whenever porcelain laminate veneers are cemented
Fig. 1 Sectioned silicone index
Fig. 2 Depth preparation bur (0.5 mm)
Fig. 3 Captured image
of tooth tissue
removed, when a
silicone index is used,
illustrating the points
taken (L1–L5 labial and
262 BRITISH DENTAL JOURNAL, VOLUME 189, NO. 5, SEPTEMBER 9 2000
however the use of a dentine-bonding agent and associated resin-
based luting system is therefore recommended.15
When a silicone index is used to prepare teeth for porcelain lami-
nate veneers the results of this study suggest that an operator’s abil-
ity to distinguish comparative depths of preparation is accurate to
within 0.1 mm given that the teeth prepared with a silicone index
were over prepared by 0.1 mm. The use of a depth gauge bur
involves additional smoothing out of the grooves produced by the
bur. When this is done it appears that there is a tendency to slightly
over prepare the labial surface of the preparation by 0.1 mm.
Further research is needed to establish whether the use of a 0.4 mm
depth gauge bur would enable practitioners to correctly reduce the
labial aspect of a preparation for a porcelain laminate veneer.
It could be considered a limitation of this study that the teeth
were prepared in isolation with the sole operator not being able to
use abutment teeth to help gauge tooth reduction. It is question-
able however whether the presence of abutment teeth would have
affected tooth preparation given that practitioners still under pre-
pare teeth for porcelain laminate veneers clinically even when abut-
ment teeth are present.14Should the adjacent teeth be worn or have
atypical morphology not common to the tooth being prepared,
using such a tooth as a guide during tooth preparation may well
result, for example, in an over prepared tooth if the adjacent tooth
has significant non-carious tooth tissue loss.
Given the tendency to under preparation when teeth are pre-
pared freehand, it is recommended that either an index or appro-
priate depth gauge bur are used when teeth are prepared for
porcelain laminate veneers. Some freehand preparation of severely
discoloured teeth will still be required so as to ensure a successful
aesthetic outcome, an increased thickness of porcelain and/or lut-
ing cement in the final restoration having a greater masking
ability.20 Similarly teeth, which have suffered some degree of non-
carious tooth surface loss should be prepared accordingly with a
combination of margin definition and selected free hand reduction
where appropriate. Blanket preparation with an index or depth
gauge bur would not be appropriate in such cases.
The present trend when teeth are prepared for porcelain lami-
nate veneers is to include the incisal edge either by bevelling or by
means of overlapping. A silicone index is more helpful than a depth
gauge bur when preparing the palatal surface and reducing the
incisal edge, a depth gauge bur having limited application in these
situations. It could be considered that a disadvantage of making an
index of addition cured silicone is the expense in terms of material
and time required to produce such an index. It is suggested how-
ever that the benefits to the patient and the operator from using a
silicone index far exceed the additional cost of fabricating the
index. A further advantage of a silicone index is that it can be sec-
tioned so that the parts can be relocated accurately. The index can
then be reconstructed and used to fabricate a temporary restora-
tion. If a depth gauge bur is used in preference to a silicone index
minimal smoothing of the labial face to prevent over preparation is
It is concluded that freehand preparation of teeth for porcelain
laminate veneers results in under preparation of the labial aspect of
the preparation. The use of a silicone index or a depth gauge bur
with minimal additional smoothing is recommended to produce
appropriate reduction of the labial surface of teeth when preparing
teeth for porcelain laminate veneers.
Paul A Brunton was awarded the British Society for Restorative Dentistry Research
Prize 1999 for this research.
1 Christensen G J. Veneering of teeth. State-of-the-art. Dent Clin North Am
1985; 29: 373-391.
Horn H R. Porcelain laminate veneers bonded to etched enamel.Dent Clin
North Am1983;27: 671-684.
Christensen G J. Have porcelain laminate veneers arrived? J Am Dent Assoc
1991; 122: 81.
Brunton P A, Wilson N H F. Preparations for porcelain laminate veneers in
general dental practice. Br Dent J 1998; 184: 553-556.
Anusavice K. Materials of the future: Preservative or Restorative? Oper Dent
1998; 23: 162-167.
Saunders W P, Saunders E M. Prevalence of periradicular periodontitis
associated with crowned teeth in an adult Scottish subpopulation. Br Dent J
1998; 185: 137-140
Garber D A. Rational tooth preparation for porcelain laminate veneers.
Compend Contin Educ Dent 1991; 12: 316, 318, 320 and 322.
Pameijer C H. Porcelain laminate veneers. J Calif Dent Assoc 1991; 19:
Weinberg L A Tooth preparation for porcelain laminates. N Y State Dent J
1989; 55: 25-28.
10 Clyde J S, Gilmour A. Porcelain veneers: A preliminary review. Br Dent J
1988; 164: 9-14.
11 Calamia J R. Materials and techniques for etched porcelain facial veneers.
Alpha Omega1988; 81: 48-51a.
12 Meijering A C, Creugers N H, Roeters F J, Mulder J. Survival of three types
of veneer restorations in a clinical trial: a 2.5 year interim evaluation. J Dent
1998; 26: 563-568.
13 Nordbo H, Rygh-Thoresen N and Henaug T. Clinical performance of
porcelain laminate veneers without incisal overlapping: 3-year results. J
Dent1994; 22: 342-345.
14 Brunton P A, Richmond S, Wilson N H F. Variations in the depth of
preparations for porcelain laminate veneers. Eur J Prosthodont Restor Dent
1997; 5: 89-92.
15 Nattress B R, Youngson C C, Patterson C J W, Martin D M, Ralph J P. An in
vitro assessment of tooth preparations for porcelain veneer restorations. J
Dent 1995; 23: 165-170.
16 Meijering A C, Peters M C R B, DeLong R, Pintado M R, and
Creugers N H J. Dimensional changes during veneering procedures on
discoloured teeth. J Dent1998; 26: 569-576.
17 Perel M L. Axial Crown Contours. J Prosthet Dent 1971; 25: 642-649.
18 Barghi N, McAlister E. Porcelain for veneers. J Esthetic Dent1998; 10:
19 Shillingburgh H T, Scottgrace C. Thickness of enamel and dentine. J South
Calif Dent Assoc 1973; 41: 33-52.
20 McLaughlin K, Morrison J E. Porcelain fused to tooth-The state of the art.
Restorative Dent1988; 4: 90-94.