Tooth structure removal associated with various preparation designs for

anterior teeth
Daniel Edelhoff, Dr Med Dent,a and John A. Sorensen, DMD, PhDb
School of Dentistry, Medical Center, University of Aachen, Germany; and School of Dentistry, Oregon
Health Sciences University, Portland, Ore.
Statement of problem. The conservation of sound tooth structure helps preserve tooth vitality and
reduce postoperative sensitivity. Innovative preparation designs, like those for porcelain laminate veneers,
are much less invasive than conventional complete-coverage crown preparations. However, no study has
quantified the amount of tooth structure removed during these preparations.
Purpose. The purpose of this study was to quantify and compare the amount of tooth structure
removed when various innovative and conventional tooth preparation designs were completed on different
teeth.
Material and methods. A new comprehensive tooth preparation design classification system was intro-
duced. Typodont resin teeth representing the maxillary left central incisor, maxillary left canine, and
mandibular left central incisor were prepared with the following designs: partial (V1), traditional (V2),
extended (V3), and complete (V4) porcelain laminate veneer preparations; resin-bonded retainer prepara-
tion with grooves (A1) and with wing/grooves (A2); all-ceramic crown preparation with 0.8 mm axial
reduction and tapering chamfer finish line (F1), all-ceramic crown preparation with 1.0 mm axial reduc-
tion and rounded shoulder finish line (F2), and metal-ceramic crown with 1.4 mm axial reduction and
facial shoulder finish line (F3). After tooth preparations (10 per group), the crown was separated from the
root at the CEJ. The removed coronal tooth structure was measured with gravimetric analysis. Means and
standard deviations for tooth structure removal with different preparation designs were calculated and
analyzed with analysis of variance at a significance level of P<.05.
Results. Significant differences in the amount of tooth structure removal were noted between prepara-
tion designs. Ceramic veneers and resin-bonded prosthesis retainers were the least invasive preparation
designs, removing approximately 3% to 30% of the coronal tooth structure by weight. Approximately 63%
to 72% of the coronal tooth structure was removed when teeth were prepared for all-ceramic and metal-
ceramic crowns. For a single crown restoration, the tooth structure removal required for an F3
preparation (metal-ceramic crown) was 4.3 times greater than for a V2 preparation (porcelain laminate
veneer, facial surface only) and 2.4 times greater than for a V4 preparation (more extensive porcelain lami-
nate veneer).
Conclusion. Within the limitations of this study, tooth preparations for porcelain laminate veneers and
resin-bonded prostheses required approximately one-quarter to one-half the amount of tooth reduction of
conventional complete-coverage crowns. (J Prosthet Dent 2002;87:503-9.)

CLINICAL IMPLICATIONS
The innovative preparation designs evaluated in this study conserved significant
amounts of sound tooth structure.

A fundamental principle in replacing missing

tooth structure or missing teeth is the restoration of
function and esthetics at minimal biologic cost. Given
their reliability and durability, conventional metal-
ceramic restorations with a complete-crown
preparation design generally are the treatment of
This study was supported in part through research grant ED 69/1-1 choice for anterior single tooth restorations and fixed
from the German Society of Research (Deutsche partial dentures (FPDs).1 However, this technique
Forschungsgemeinschaft) and the OHSU Applied Prosthodontic requires considerable reduction of tooth structure. For
Materials Research Lab. a metal-ceramic shoulder preparation, a facial tooth
aAssociate Professor, Department of Prosthodontics, University of

Aachen School of Dentistry.

reduction of about 1.3 to 1.5 mm is recommended.2,3
bODA Centennial Professor of Restorative Dentistry, Department of In certain situations, it may be necessary to increase
Prosthodontics, Oregon Health Sciences University School of axial tooth reduction to between 1.75 and 2 mm in
Dentistry. order to achieve the desired esthetic result.4

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THE JOURNAL OF PROSTHETIC DENTISTRY EDELHOFF AND SORENSEN

Table I. Codes and armamentarium employed for the veneer preparation designs
Code Tooth Preparation design Dimensions (mm) Burs Fig. Ref.

V1 Maxillary left central Partial veneer, incisal Extension: horizontal 4.0, Set #2590* 3, 9 32
incisor third, mesial edge up vertical 3.5
Incisal clearance: 1.0
Margin depth: 0.7
Maxillary left canine Partial veneer to reestablish Incisolingual extension: 6856-31-014 2 33
canine guidance horizontal 4.0, vertical 4.0 88011-31-021
Incisal clearance: 1.0
Margin depth: 0.7
Mandibular left central Partial veneer, incisal third, Margin location: 3.0 apical Set #2590* 1 32
incisor circular edge up from incisal edge
Incisal clearance: 1.0
Margin depth: 0.7
V2 All Traditional veneer, medium Margin: 0.5 incisal from CEJ TFC-1† 4, 9 34-36
wrap, preservation of Facial reduction: cervical third 868A.314-018
interproximal contacts, 0.2-0.3, middle third 0.5, 686-31-014
chamfer finishing line incisal third 0.5-0.7 686-31-016
H375R-31-014
H375R-31-016
V3 All Extended veneer. See V2. See V2. Additional incisal See V2 4, 9 34, 37
Additional oral overlap clearance: 1.0 (man LCI),
1.5 (max LCI and C).
Additional lingual overlap: 1.0
V4 All Full veneer. See V3. See V3. Except incisal See V2. Additional 4, 9 34, 35,
Additional long wrap design clearance: 1.5 (man LCI) or 5858-31-014 37
with removal of 2.0 (max LCI and C) (removal of IP)
interproximal contacts
*Manufactured by Hager & Meisinger (Düsseldorf, Germany).
†Manufactured by Brasseler (Savannah, Ga.).

The introduction of modified complete-crown endodontic intervention.18 The combination of high-

preparations for cast metal and metal-ceramic crowns ly translucent porcelains and composite cements has
has been correlated with increased pulpal complica- facilitated the clinical use of the adhesive technique
tions. In a 1966 study, only 0.4 to 2% radiographic and launched a new era of restorative treatment
periapical pathologies were found; in 1970, 2.9% was options.
reported, and 10 years later, up to 4.0% periapical Due to their excellent clinical performance, out-
pathologies were detected.5-7 These results can be standing esthetics, and minimal invasiveness,
explained by the increased use of air turbines and more resin-bonded veneers19 and FPDs20 offer an excellent
invasive shoulder or chamfer preparations for metal- treatment option with an ever-expanding range of
ceramic restorations compared to the feather-edge indications.21,22 However, the tooth preparation
design used in the 1960s and 1970s.8 requires a careful and meticulous technique.23
The introduction of new ceramic materials, as well Restorative techniques are considered advantageous
as advances in the field of adhesive cementation tech- for both maintenance of tooth vitality and economy of
niques, have increased the use of all-ceramic crowns hard tissues.24 Data on the loss of vitality are limited
and have facilitated innovative, conservative prepara- among the clinical studies on veneer restorations. A
tion designs for single tooth and FPD restorations.9-15 5-year clinical study on ceramic veneers recorded a
The reliable bond to enamel achieved with the adhe- 2.3% loss of vitality, which was related to preexisting
sive technique has greatly impacted preparation deep interproximal composite restorations.25 Reports
design, resulting in significant preservation of tooth of endodontic complications with single full-crown
structure.16 The retention of enamel has become an restorations vary from 3% after 5 years to 5% after 8
important issue for preparation design.17 Increased years.26,27 The higher incidence of vitality loss with
preservation of enamel promotes a superior bond over FPD abutments (reported in a range of 3% after 5
dentin, lower post-cementation sensitivity, improved years to 21% after 6 years) is probably related to the
support of the ceramic restoration, and reduced greater tooth reduction required to align multiple

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EDELHOFF AND SORENSEN THE JOURNAL OF PROSTHETIC DENTISTRY

Table II. Codes and armamentarium employed for the adhesive attachments and complete-crown preparation designs
Code Tooth Preparation design Dimensions (mm) Burs* Fig. Ref.

A1 Maxillary left central incisor Adhesive attachment, Facial groove: 4.5 × 1.0 × 0.8 8847KR-31-016 9 10
grooves (all-ceramic) Oral groove: 2.0 × 1.0 × 0.8
Maxillary left canine Adhesive attachment, Facial groove: 3.5 × 1.0 × 0.8 8847KR-31-016 9 10
grooves (all-ceramic) Oral groove: 2.0 × 1.0 × 0.8
Mandibular left central incisor Adhesive attachment, Facial groove: 4.0 × 1.0 × 0.8 8847KR-31-016 9
grooves (all-ceramic) Oral groove: 2.0 × 1.0 × 0.8
A3 All Adhesive attachment, Margin: 1.0 incisal from CEJ 878-31-010 9 38
wing/2 grooves Lingual reduction: 0.5 8878-31-010
(metal-ceramic), 8856-31-012
chamfer finishing line 8862-31-012
88011-31-021
F1 All Full crown (all-ceramic), Margin: 0.5 incisal from CEJ 828-31-030 5, 9 39
chamfer finishing line Margin depth: 0.8 6878-31-016
Incisal clearance: 1.5 8878-31-016
Axial convergence: 6° 379-31-023
379EF-31-023
F2 All Full crown (all-ceramic), Margin: 0.5 incisal from CEJ 828-31-030 5, 9 40, 41
rounded shoulder Margin depth: 1.0 847KR-31-016
finishing line Incisal clearance: 1.5 H336-31-016
Axial convergence: 6° 1089-31-012
379-31-023
379EF-31-023
F3 Maxillary left central Full crown (metal-ceramic Margin: 0.5 incisal from CEJ 828-31-030 5, 9 42
incisor and canine Facial: rounded shoulder Facial margin depth: 1.4 847KR-31-016
Oral: chamfer finishing line Lingual margin depth: 0.7 H336-31-016
Incisal clearance: 2.0 H283-31-012
Axial convergence: 6° H158-31-014
1089-31-016
379-31-023
379EF-31-023
*Manufactured by Brasseler (Savannah, Ga.).

abutment teeth.6,28,29 In contrast, a clinical evaluation tubules, and water content that would influence gravi-
of different resin-bonded FPDs with 1560 abutments metric (weight-based) measurements were avoided. A
found only 0.13% loss of vitality after 5 years.30 standardized preparation technique was ensured due
Although clinicians may believe that innovative to lack of decay and preexisting restorations. To
preparation designs are much less invasive than con- approximate the clinical situation, the teeth were pre-
ventional esthetic crown preparations, no studies have pared on a Typodont model (Nissin Kilgore
quantified the tooth structure removal associated with International) with a missing maxillary right lateral
these preparations. The purpose of this study was to incisor.
gravimetrically quantify the amount of tooth structure Resin materials tend to absorb water depending on
removed for anterior preparations for single tooth and storage conditions.31 This could affect the gravimetric
FPD retainers. evaluation of resin teeth after preparation with tur-
bine/spray application. A pilot study therefore was
MATERIAL AND METHODS
performed to measure the effect of storage conditions
Three different morphologies of artificial resin teeth on water uptake and weight change of the resin teeth.
(maxillary left central incisor, maxillary left canine, and In the first part of the pilot study, the relative
mandibular left central incisor; Nissin Kilgore increase in weight after 10 days of water storage at
International Inc, Coldwater, Mich.) were used for the 23°C was determined for 2 types of the unprepared
study. Due to the homogeneous structure of artificial resin teeth: the maxillary and mandibular left central
teeth, undesirable individual differences like morpho- incisors (10 per group). Their weight increased by
logic variation, extension of the pulp and dentin 2.02% (mandibular left central incisor) to 2.61% (max-

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THE JOURNAL OF PROSTHETIC DENTISTRY EDELHOFF AND SORENSEN

Fig. 1. Edge-up preparation design on mandibular central. Fig. 2. Partial veneer preparation to reestablish canine guid-
ance.

Fig. 3. Anatomical crowns of maxillary left central incisors Fig. 4. Porcelain veneer preparation designs (V2, V3, and
with edge-up preparation design after root removal prior to V4) for maxillary left central incisor.
testing.

weight by evaporation was determined after 12, 24,

and 48 hours and 1 week of storage in the incubator.
No significant weight decrease occurred when the
storage time exceeded 24 hours. Based on these
results, prior to the testing procedure, all resin teeth in
the study were prepared under turbine/spray applica-
tion and dried for at least 24 hours in an incubator
under the conditions just described.
Ten teeth per group were prepared by a single per-
son. The codes for the preparation designs and the
armamentarium employed in the present study are list-
ed in Tables I32-37 and II38-42 (Figs. 1 through 5).
Fig. 5. Complete-crown preparation designs for maxillary When possible, a transparent template was employed
left central incisor (left to right): 0.8 mm circumferential as a guideline for the preparation. The preparation
chamfer (F1), 1.0 mm rounded circumferential shoulder depth was controlled with the template and a scaled
(F2), 1.4 mm labial rounded shoulder and lingual 0.7 mm periodontal probe (UNC15; Hu-Friedy, Chicago,
chamfer (F3). Ill.). Structure removal was determined exclusively for
the anatomical crown of the Typodont tooth.
Therefore, after completion of the preparation, the
illary left central incisor). In the second part of the CEJ area was marked, and the root was cut off with a
pilot study, the pretreated teeth were stored at 60°C in precision low-speed saw (Isomet, Buehler, Ill.) and
an incubator to evaporate the water uptake. The loss of refined with a carbide cutter (H29DF-023; Brasseler,

506 VOLUME 87 NUMBER 5

EDELHOFF AND SORENSEN THE JOURNAL OF PROSTHETIC DENTISTRY

Fig. 6. Tooth structure removal of maxillary left central Fig. 7. Tooth structure removal of maxillary left canine with
incisor with various preparation designs. various preparation designs. Columns marked with same
lowercase letter were not significantly different.

Savannah, Ga.) (Fig. 3). Prior to the determination of

weight in a high-precision balance (Type B6; E.
Mettler, Zürich, Switzerland), the prepared and decap-
itated anatomical crowns were cleaned with
isopropanol (70%) and dried with air pressure. The
mean weight of the unprepared, decapitated anatomi-
cal crowns (10 per tooth type) was employed as a
reference. The percentage of structure removal (Rs)
was calculated as follows:
W0 – W
Rs = × 100
W0
where W0 is the mean weight of 10 unprepared, decap-
itated anatomical crowns and W is the mean weight of
10 prepared, decapitated anatomical crowns. Means Fig. 8. Tooth structure removal of mandibular left central
incisor with various preparation designs.
and standard deviations for tooth structure removal
with different preparation designs were calculated and
analyzed with analysis of variance (P<.05).
(Fig. 8), and preparation A3 from 10.7% (Fig. 7) to
RESULTS
18.9% (Fig. 8). Analysis of variance showed no signifi-
The amount of tooth structure removal for the cant differences for the remaining preparation designs
preparation designs increased in the following order dependent on the tooth type employed. An overview
(mean % of typodont teeth): A1 (5.2), V1 (8.2), A3 comparison of structure removal associated with the
(14), V2 (16.7), V3 (22.1), V4 (30), F1 (64), F2 (70), tested preparation designs is given for a maxillary cen-
and F3 (71.9) (Figs. 6 through 8). The F3 design tral incisor in Figure 9.
could not be prepared on a mandibular central incisor
DISCUSSION
due to inadequate tooth structure in the gingival third
of the anatomical crown (Fig. 8). For single tooth Different methods have been described to measure
restorations, an F3 preparation required removal of the amount of tooth structure removal associated with
4.3 times more tooth structure than a V2 preparation preparation designs for metallic and metal-supported
and 2.4 times more tooth structure than a V4 prepa- ceramic restorations. Given its accuracy, ease, and sim-
ration. plicity, gravimetric analysis was employed to measure
For FPD abutment preparations, tooth structure tooth structure removal. It should be noted that in
removal varied from approximately 5% (A1) to 72% these ideal preparation designs, only the specific
(F3). The invasiveness of the preparation was signifi- requirements of the material were considered as a fac-
cantly (P < .05) influenced by tooth morphology: tor for tooth structure removal. Beyond that, other
Preparation V1 varied from 3.6% (Fig. 7) to 14.2% important clinical criteria controlled the preparation
(Fig. 8), preparation A1 from 3.1% (Fig. 6) to 8.9% design. This criteria included condition of the tooth,

MAY 2002 507

THE JOURNAL OF PROSTHETIC DENTISTRY EDELHOFF AND SORENSEN

Numerous publications have focused on prepara-

tions for all-ceramic crowns. These studies have been
contradictory with regard to the geometry of the
margin, angle of convergence, and extent of tooth
removal.11,39 In vitro investigations have shown that
a supporting structure with a high elastic modulus
increases the strength of all-ceramic crowns; the
residual dentin thickness after preparation therefore
may influence the life expectancy of the restoration.12
The authors of the present study believe that a prepa-
ration design that requires the removal of large
amounts of hard tooth structure must be rejected for
a number of reasons: exposure of dentin near the
pulp with a high proportion of dentin tubules,
increased secretion of dentinal fluid, adverse influ-
ence on the ratio of residual dentin to cavities (pulp
cavity, dentin tubules), increased risk of postoperative
sensitivity, and contraindication for young patients
with large pulps. A clinical study showed that a cham-
fer finish line only 0.8 mm deep with a maximum
convergence angle of 10 degrees was a relatively easy
and minimally traumatic complete-crown preparation
Fig. 9. Comparison of structure removal associated with dif- for heat-pressed glass-ceramic crowns.39 No adverse
ferent preparation designs for maxillary left central incisor. effect on longevity was observed, in contrast to other
Pink areas represent proximal contact location. clinical studies on the same all-ceramic crowns with a
1.0- to 1.3-mm deep shoulder margin or 1.2- to 1.5-
mm depth.13-15
esthetic and functional aspects, orientation of the The tooth preparation classification system intro-
tooth, tooth retention, reconstruction of the occlu- duced in this study is a comprehensive and systematic
sion, and patient desires. In contrast to some method for describing a broad range of tooth prepa-
recommended clinical procedures,24 in the present ration designs. The study results should be
study, pilot grooves were employed only to create considered for sound clinical tooth preparation
reproducible standardized preparations. design criteria. Use of the tested innovative prepara-
The results of the present study suggest that the tion designs may result in the conservation of sound
minimally invasive veneer preparation offers a tremen- tooth structure and maintenance of tooth vitality in
dous advantage over conventional crown preparations. comparison to traditional, more invasive fixed
Even for a complete veneer preparation (V4), less than prosthodontic designs.
half the amount of the tooth structure was removed
CONCLUSIONS
compared to the most conservative complete crown
preparation (F1). Within the limitations of this in vitro study, the fol-
For resin-bonded prostheses, a large variety of lowing conclusions were drawn:
preparation designs have been reported.20,30 Wing- 1. When resin typodont teeth were evaluated, com-
shaped retainers with retentive elements (grooves) plete-coverage all-ceramic and metal-ceramic crown
have demonstrated a remarkable long-term success preparations required the removal of 63% to 72% (by
rate when the clinical protocol was followed careful- weight) of the total unprepared crown weight. Tooth
ly.20,30 These classic design principles cannot be preparations for ceramic veneers (porcelain laminate
applied directly to resin-bonded prostheses made of veneers) and resin-bonded prostheses removed 3% to
metal-free materials, as more removal of the tooth 30% by weight of the crown.
structure is necessary to fulfill the specific require- 2. For a single crown restoration, the tooth struc-
ments of greater bulk of framework materials. ture removal required for a metal-ceramic crown (F3)
Therefore, in many situations, wing-shaped retainers was 4.3 times greater than for a ceramic veneer prepa-
cannot be used in limited space and dental enamel ration (V2) and 2.4 times greater than for a complete
must be preserved for successful bonding.17 These ceramic veneer preparation (V4).
complications have led to innovative preparation 3. The preparations for all-ceramic crowns (F1)
designs, including the 2-groove design described by were approximately 11% less invasive than for metal-
Pospiech10 and evaluated in the present study. ceramic crowns (F3).

508 VOLUME 87 NUMBER 5

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