Journal of Oral Rehabilitation 2004 31; 562–567
The bitewing radiograph as an assessment tool in fixed
prosthodontics
D. G. PURTON, B. P. NG, N. P. CHANDLER & B. D. MONTEITH
Department of Oral Rehabilitation,
University of Otago School of Dentistry, Dunedin, New Zealand
SUMMARY Molar crown preparations, as described in
the literature, have standard forms dictated by the
demands of retention, resistance and the physical
properties of materials. Standard designs may not be
appropriate for all patients because of ethnic variations in tooth shape, pulp size and dentine thickness. Accurate data on these features could assist
clinicians to minimize the risk of accidental pulpal
injury. The aim of this study was to compare the
first molar crown and pulp dimensions between
Asian (Chinese, Korean, Malay) and other ethnic
groups, using measurements from the bitewing
radiographs of 121 subjects. Comparisons revealed
the following significantly different features of
Asian first molars: larger total pulp areas in uppers
(P < 0Æ0005); shorter crowns (P < 0Æ0005); narrower
upper teeth at the cervix (P < 0Æ0005); wider pulps at
Introduction
Anthropological studies describe differences in molar
tooth crown morphology between ethnic groups (1).
Little information is available on the subject of coronal
pulp morphology in different ethnic groups. The combination of crown and pulp dimensions defines the
hard tissue structure of the crown, and is directly
relevant to operative dentistry and fixed prosthodontics. Shillingburg and Grace (2) measured the dentinal
thickness at several levels in horizontally sectioned first
molars from Caucasian subjects of unspecified age and
sex. They reported on 22 maxillary first molars and 20
mandibular first molars. Stambaugh and Wittrock (3)
similarly reported on four upper and four lower first molars
without documenting the race or sex of the subjects.
Informal, undocumented accounts from colleagues
had drawn the authors’ attention to the possibility
ª 2004 Blackwell Publishing Ltd
the cervix of lowers (P < 0Æ02); more bulbous crowns
(P < 0Æ0005 for uppers; P < 0Æ01 for lowers), and
finally significantly thinner dentine interproximally
at the cervix (P = 0Æ001 for uppers; P = 0Æ011 for
lowers). Preparations with wide shoulders could
pose hazards to the pulps in Asian subjects. This
study emphasizes the value of bitewing films in
assessing crown and pulp size and shape before
making crown preparations. The experienced practitioner may intuitively include tooth and pulp
morphology in treatment planning, but this appears
not to be taught or documented in textbooks.
KEYWORDS: pulp size, dentine thickness, bitewing,
ethnicity
Accepted for publication 27 November 2002
that Asian (Chinese, Korean, Malay) patients are at a
greater risk than others of suffering pulp exposure
during the preparation of teeth for crowns or bridges.
Accurate data on tooth shape, pulp size and dentine
thickness in ethnic groups could guide clinicians during
treatment planning and tooth preparation, to minimize
the risk of accidental pulp exposure or inflammatory
changes.
The aim of this study was to compare the first molar
crown and pulp dimensions between Asian and other
ethnic groups, using data from bitewing radiographs.
Materials and methods
Bitewing radiographs were taken of 121 University of
Otago undergraduate dental students up to 25 years of
age, over three successive years, as part of a teaching
exercise. Ethical approval was gained for the study and
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BITEWING RADIOGRAPH AS AN ASSESSMENT TOOL IN FIXED
PROSTHODONTICS
the students signed a consent form which also provided
details of their age, sex and the ethnicity of their
parents and grandparents. The subjects were grouped
into two ethnic groups: Asian and others.
Kodak Ektaspeed Plus E speed film*, supported in a
Rinn bitewing holder and beam alignment device† was
exposed using the same X-ray machine for all subjects.
Processing was automatic using Kodak GBZ developer
and fixer solutions. The 242 bitewing films were mounted in slides, coded and digitally scanned using a Nikon
Scan 2 scanner‡. A radiograph of a standard measuring
grid with 1-mm squares was also taken and scanned.
An operator, who was unaware of the origin of the
images, measured the maxillary and mandibular first
molars using Scion Image software§ on a desktop
computer. The reliability of his measurements using
this method had been checked in three pilot tests,
revealing a high correlation of his repeat measurements
(r ¼ 0Æ90, 0Æ92 and 0Æ92, respectively) with regression
slopes not differing significantly from 1Æ00. The software was calibrated from the digital image of the
measuring grid film. A baseline was drawn between the
mesial and distal cemento-enamel junctions, the area
above this line being termed the clinical crown. The
following were measured (Fig. 1): crown width and
crown height, crown width at the cervix (the baseline)
and pulp area in the clinical crown (above the
baseline). The total pulp area above a line drawn across
the most superior part of the pulpal floor (parallel to the
baseline), the pulp width at the cervix (along the
baseline) and the heights of the mesial and distal pulp
horns were also measured (Fig. 2).
Statistical analysis of the results was performed using
SPSS release 11 statistical software¶. Student’s t-test
was used to test for equality of means and Levene’s test
for equality of variances. When data were found not to
be normally distributed, the non-parametric Mann–
Whitney U-test was employed.
Results
From the 242 bitewing films, data were available from
445 first molars. Thirty-nine teeth were not available
*Kodak Co., Rochester, NY, USA.
Dentsply Rinn, Weybridge, UK.
‡
Nikon Corp., Tokyo, Japan.
§
Scion Corp., Frederick, MD, USA.
¶
SPSS Inc., Chicago, IL, USA.
†
Fig. 1. Measurements made on bitewing films; 1, crown width; 2,
crown height; 3, crown width at the cervix; 4, pulp area in the
clinical crown.
because they had been extracted, crowned, endodontically treated or because one of the required measurements could not be accurately made. The distributions
of the teeth by ethnic group, sex and jaw are shown in
Table 1.
Pulp areas
For upper molar teeth, Asian subjects had a mean total
pulp area of 8Æ04 2Æ02 mm2 compared with
6Æ95 1Æ91 mm2 in the other subjects. The difference
was statistically significant. There were no significant
differences between groups in either total pulp area of
lower molars or pulp area in the clinical crowns of
uppers or lowers (Table 2).
The presence of restorations led to a significant
reduction in pulp area. For all subjects, the mean pulp
area in the clinical crowns of the 302 unrestored teeth
was 3Æ61 1Æ54 mm2 and of the 143 restored teeth was
3Æ13 1Æ50 mm2 which was a significant reduction
(P < 0Æ001).
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D . G . P U R T O N et al.
7Æ76 0Æ54 mm for the other subjects. The difference
was statistically significant. The mean values for lower
molars were 7Æ05 0Æ56 mm for Asian subjects and
7Æ32 0Æ56 mm for the others. This difference was also
statistically significant. Asian subjects thus had significantly shorter upper and lower molar crowns. Crown
widths were not significantly different between groups
(Table 2).
Crown and pulp widths at the cervix
The upper molar crowns of Asian subjects had a mean
width at the cervix of 8Æ59 0Æ66 mm compared with a
mean of 8Æ94 0Æ83 mm in the other subjects. The
difference was statistically significant. For lower molars
the Asian group had a mean pulp width at the cervix of
4Æ28 0Æ59 mm compared with 4Æ06 0Æ83 mm for
the other subjects. The difference was statistically
significant. There were no other significant differences
between groups for these measurements (Table 2).
Fig. 2. Measurements made on bitewing films; 5, total pulp area;
6, pulp width at the cervix; 7, mesial pulp horn height; 8, distal
pulp horn height.
Table 1. Distributions of the first molar teeth by ethnic group, sex
and jaw
Upper
Lower
Total
Asian
male
Asian
female
72
68
n ¼ 229
43
46
Other
male
63
60
n ¼ 216
Other
female
Total
47
46
225
220
There were too few carious lesions into dentine
(n ¼ 11) to draw any conclusions about the effect of
caries on pulp area.
Pulp horn heights
Student’s t-tests revealed that there were no significant
differences in mesial or distal pulp horn heights
between the two groups (Table 2).
Crown heights and widths
The upper molars in Asian subjects had a mean
crown height of 7Æ39 0Æ56 mm compared with
Crown bulbosity
Subtracting crown widths at the cervix from the crown
widths provided further information about crown
shapes. This difference defines the bulbosity of the
teeth (Table 3).
For upper molars the Asian subjects had a mean
difference of 2Æ77 0Æ45 mm and the other subjects
had a mean of 2Æ50 0Æ51 mm. The upper molars were
significantly more bulbous in the Asian subjects.
For lower molars the Asian subjects had a mean
difference of 2Æ38 0Æ52 mm and the other subjects
had a mean of 2Æ21 0Æ40 mm. The lower molars were
also significantly more bulbous in the Asian subjects.
Dentine thickness at the cervix
The thickness of dentine at the cervix of the teeth was
derived by subtracting the pulp width at the cervix from
the crown width at the cervix. Halving this difference
defines the dentine stock available at the mesial and
distal aspects of the teeth for operative procedures such
as class II cavities or full-crown preparations.
For upper molars the Asian subjects had a mean
dentine thickness of 2Æ77 0Æ30 mm and the other
subjects had a mean of 2Æ92 0Æ29 mm. The difference
was significant. For lower molars, Asian subjects had a
mean dentine thickness of 2Æ67 0Æ23 mm and the
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BITEWING RADIOGRAPH AS AN ASSESSMENT TOOL IN FIXED
PROSTHODONTICS
Table 2. Mean values for pulp and crown dimensions
Asian
Other
Asian
Upper
Lower
Total pulp area (mm2; s.d.)
8Æ04 2Æ02*
8Æ82 2Æ14
6Æ95 1Æ91*
8Æ52 2Æ33
Pulp area in the clinical crown (mm2; s.d.)
3Æ32 1Æ46
3Æ23 1Æ48
3Æ61 1Æ37
3Æ66 1Æ83
Upper
Lower
Mesial pulp horn height (mm; s.d.)
1Æ48 0Æ55
1Æ40 0Æ53
1Æ76 0Æ52
1Æ74 0Æ54
Distal pulp horn height (mm; s.d.)
1Æ00 0Æ51
1Æ03 0Æ50
1Æ09 0Æ44
1Æ20 1Æ14
Upper
Lower
Crown height mm; (s.d.)
7Æ39 0Æ56*
7Æ05 0Æ56*
Crown width mm (s.d.)
11Æ36 0Æ66
12Æ04 0Æ57
Upper
Lower
Crown width at the cervix (mm; s.d.)
8Æ59 0Æ66*
8Æ94 0Æ83*
9Æ66 0Æ58
9Æ69 0Æ58
7Æ76 0Æ54*
7Æ32 0Æ56*
Other
11Æ44 0Æ78
11Æ90 0Æ66
Pulp width at the cervix (mm; s.d.)
2Æ96 0Æ58
2Æ86 0Æ72
4Æ06 0Æ83†
4Æ28 0Æ59†
*Significant difference between Asian and others at the P < 0Æ0005 level.
†
Significant difference between Asian and others at the P < 0Æ02 level.
Table 3. Mean values for crown bulbosity and dentine thickness
Asian (mm; s.d.)
Other (mm; s.d.)
Table 4. Crown and pulp dimensions that were significantly
larger in male subjects than in females, with P-values for the
comparisons
Crown bulbosity ¼ crown width minus crown width at the cervix
Upper
2Æ77 0Æ45*
2Æ50 0Æ51*
Lower
2Æ38 0Æ52†
2Æ21 0Æ40†
Dentine thickness ¼ (crown width at the cervix minus pulp width
at the cervix)/2
Upper
2Æ77 0Æ30‡
2Æ92 0Æ29‡
§
Lower
2Æ67 0Æ23
2Æ74 0Æ20§
*Significant difference at P < 0Æ0005.
†
Significant difference at P < 0Æ01.
‡
Significant difference at P ¼ 0Æ001.
§
Significant difference at P ¼ 0Æ011.
other subjects had a mean of 2Æ74 0Æ2 mm. The
difference was significant. The Asian subjects thus had
significantly less dentine stock at the cervix of upper
and lower teeth (Table 3).
Asian
Upper
Total pulp area
Pulp area in clinical crown
Mesial pulp horn height
Distal pulp horn height
Crown height
Crown width
Crown width at the cervix
Pulp width at the cervix
Crown bulbosity
Dentine thickness
Other
Lower
Upper
0Æ01
Lower
0Æ039
0Æ037
0Æ001
0Æ000
0Æ010
0Æ000
0Æ000
0Æ05*
0Æ010
0Æ014
0Æ000
0Æ000
Student’s t-test for all comparisons, except ‘*’ which was Mann–
Whitney U-value because of non-normal distribution of data.
Pulp horn height and bulbosity were not related to the
sex of the subjects.
Sexual dimorphism
Male subjects were found to have significantly larger
tooth and pulp dimensions for some of the measurements made. The significance levels of these differences
appear in Table 4.
In summary, the lower molar crowns, pulps and
cervical dentinal stock of Asian males were wider than
those of Asian females. In the other subjects, the males
had wider upper and lower crowns, thicker dentine in
the uppers, and the lowers were taller with larger pulps.
Discussion
Molar tooth preparations for prosthetic crowns, as
described in the dental literature, have standard forms
dictated by the demands of retention, resistance and the
physical properties of materials. The application of such
standard designs may not be appropriate for the
treatment of all patients.
The requirement to provide adequate height for
retention in a crown preparation could create problems
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in the first molar teeth of Asian patients. These teeth
have significantly shorter natural crowns, which means
that other features being equal, crown preparations on
these teeth will provide less retention than preparations
in other patients. Maximizing the gingival extension of
the proximal walls to gain height will bring the gingival
margin into the cervical region where the Asian teeth
become significantly narrower. To maintain shoulder
width and avoid undercuts the operator must place the
proximal preparation walls more centrally in the tooth
bringing the preparation closer than ideal to the pulp
chamber. This threat to the pulp is thus an effect of
tooth shape not of pulp area. The pulp areas in the
clinical crowns of the teeth in Asian subjects were not
different from those in the other subjects, nor were the
pulp horns different in height.
This problem of proximity to the pulp will be most
acute with preparations for all-ceramic crowns. Allceramic crowns require gingival shoulders in the
preparations of at least 1 mm uniformly around their
periphery, with up to 1Æ5 mm recommended for some
systems (4). Such a preparation encroaches heavily on
the dentine stock at the cervical area of the tooth.
Because the density and diameter of dentinal tubules
increase with proximity to the pulp, the prospects of
creating more pronounced hydrodynamic effects and
pathways for bacterial penetration of the pulp will be
greatest with these preparations in bulbous, Asian
teeth.
Ceramo-metal crowns requiring 1Æ2–1Æ5 mm of shoulder width in areas of porcelain coverage may similarly
endanger the pulps of bulbous teeth. However compromises are possible with these crowns because metal
alone may be acceptable in the interproximal cervical
regions, depending on the aesthetic demand of the case.
In the present study the mean thickness of interproximal cervical dentine, measured from the radiographs of non-Asian subjects was 2Æ92 mm in upper
first molars and 2Æ74 mm in lowers. Shillingburg and
Grace (2) recorded mean values of 2Æ53 mm and
2Æ59 mm for upper and lower first molars, respectively,
in Caucasian subjects. Stambaugh and Wittrock (3)
reported 2Æ67 mm and 2Æ60 mm, respectively, in subjects not specified by ethnic group. The differences
between the studies no doubt reflect the different
populations studied and the different techniques used.
However, the thinner dentine apparent in the sectioned
teeth of these two earlier studies further highlights the
need for care in planning preparation designs. Shilling-
burg et al. (5) cautioned against the indiscriminate use
of full coverage ceramo-metal crowns when more
conservative designs in metal could be used.
Cast metal crowns would seem to offer the least
threat to pulps, as they require the least occlusal
reduction and the narrowest marginal shoulder width.
This applies to all patients but may be rather more
strongly indicated in Asian patients.
Class II cavities for plastic restorations are also
invasive of proximal dentine. The extent of the lesion
largely dictates the form of the preparations. The
acceptability or even desirability of undercuts makes
these preparations more adaptable to individual tooth
forms and thus less threatening to pulps than crown
preparations.
The present study considered the first molars in young
adult patients. Older adults would be expected to have
smaller pulps and thicker dentine. However it is unlikely
that this would be clinically significant. Murray et al. (6)
found that the mean rate of increase in dentine
thickness was 6Æ5 lm year)1. Thus the subjects in this
study would expect to gain only 0Æ065 mm of dentine by
their early thirties. Deferring crown preparation solely
on the basis of age does not seem appropriate.
Most teeth being crowned will previously have had
restorations placed, many interproximally. As described
in the results this will have affected pulp size. However
the reduction will be unpredictable and asymmetrical
making it difficult to factor this effect into crown
preparation designs.
This study emphasizes the value of bitewing films in
assessing crown and pulp size and shape before making
crown preparations. It is noteworthy that no authoritative textbooks on operative dentistry or fixed prosthodontics could be found which referred to this use of the
bitewing film. In general, this film is recommended for
detecting caries, assessing restorations, determining
bone levels and so on. The experienced practitioner
may use bitewing films and intuitively include tooth
and pulp morphology in treatment planning, but such
use appears not to be taught or at least not documented
in textbooks.
Prosthetic crowns are known to be associated with a
high incidence of post-operative sensitivity and a
significant incidence of pulpal necrosis. In reporting a
prospective study, Johnson et al. (7) reported that one
quarter of crowned teeth were sensitive to cold
3 months after cementation. From a radiographic
study Valderhaug et al. (8) estimated that after
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BITEWING RADIOGRAPH AS AN ASSESSMENT TOOL IN FIXED
PROSTHODONTICS
10 years, 8% of teeth that were vital at crowning
would have signs or symptoms of pulpal deterioration.
The use of bitewing radiographs to assess tooth and
pulp morphology when treatment planning for crowns
on molars, especially in Asian patients, may help to
reduce these problems, and the possibility of unexpected pulp exposures.
References
1. Kieser JA. Human Adult Odontometrics. Cambridge: Cambridge University Press; 1990: 128.
2. Shillingburg HT, Grace CS. Thickness of enamel and dentin.
J South Calif Dent Assoc. 1973;41:33–52.
3. Stambaugh RV, Wittrock JW. The relationship of the pulp
chamber to the external surface of the tooth. J Prosthet Dent.
1977;37:537–546.
4. Pröbster L. Survival rate of In-Ceram restorations. Int J
Prosthod. 1993;6:259–263.
5. Shillingburg HT, Jacobi R, Brackett SE. Fundamentals of Tooth
Preparations for Cast Metal and Porcelain Restorations.
Chicago, IL: Quintessence Publishing Co; 1987: 13.
6. Murray PE, Stanley HR, Matthews JB, Sloan AJ, Smith AJ.
Age-related odontometric changes of human teeth. Oral
Surg Oral Pathol Oral Med Oral Radiol Endod. 2002;93:
474–482.
7. Johnson GH, Powell LV, Derouen TA. Evaluation and control of
post-cementation pulpal sensitivity: zinc phosphate and glass
ionomer luting cements. J Am Dent Assoc. 1993;124:39–46.
8. Valderhaug J, Jokstad A, Ambjørnsen E, Norheim PW. Assessment of the periapical and clinical status of crowned teeth over
25 years. J Dent. 1997;25:97–105.
Correspondence: David G. Purton, Department of Oral Rehabilitation,
University of Otago School of Dentistry, PO Box 647, Dunedin, New
Zealand.
E-mail david.purton@stonebow.otago.ac.nz
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