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Furcation Groove of Maxillary First Premolar,Thickness, and
Dentin StructuresPaola A. Lammertyn, DDS, PhD, Susana B. Rodrigo,
DDS, PhD, Mabel Brunotto, Dr. MSc,and Marta Crosa, DDS, PhD
Clinical Research
AbstractIntroduction: Few studies mention the presence
offurcation grooves in the palatal aspect of buccal rootsin upper
first premolars. Anatomic characteristics likeexternal grooves or
root curvatures predispose teethto weakening during post placement.
Roots with a largenumber of external sulci show more canal
variations.Previous research found that the palatal wall is
onaverage less than 1mm. There is a direct relationbetween the
volume of dental structures and thecapacity to resist occlusal
loads. The purpose of thisstudy was to evaluate the changes in
dentin thicknessand structures adjacent to the furcal
groove.Methods: The percentage that represented furcationgroove in
the buccal root was specified. The samplesize selected was n=20.
Three horizontal slices weremade to the buccal root, coronal,
middle, and apical.The angles of the grooves and dentin thickness
weremeasured with a profile projector. Results: In the cor-onal
third, the depth of the groove was correlativewith dentin thickness
negatively, ie, while the depthincreased, palatal dentin thickness
decreased or viceversa. In the coronal and middle thirds, the
palatalwall showed average dentin width smaller than thebuccal. In
some cases, the thickness was less than1mm. In the apical third,
palatal dentin thicknessesshowed higher averages than the buccal.
Structuralchanges were observed in dentin adjacent to the
furca-tion groove. These results are discussed in the context
ofother research. Methodologic differences do not enablecomparative
studies. Conclusions: Dentin thicknesscorresponding to the furcal
groove is variable; it pres-ents structural changes and must be
taken into accountin endodontic and prosthetic procedures. (J
Endod2009;35:814–817)
Key WordsDentin thickness, furcation groove, maxillary
firstpremolars
From the Department of Endodontics, Fundacion CREO,Cordoba,
Argentina.
Address requests for reprints to Dr Paola Adriana Lammer-tyn,
Franchini 108, 5186 Alta Gracia, Cordoba, Argentina.E-mail address:
[email protected]/$0 - see front matter
Copyright ª 2009 American Association of
Endodontists.doi:10.1016/j.joen.2009.03.012
814 Lammertyn et al.
Endodontic preparation and obturation in maxillary first
premolars (MFPs)frequently present serious complications. Lack of
knowledge of their variable andcomplex anatomy might lead to
procedural accidents.
Anatomic research relating to endodontics in general has focused
its attention onthe internal anatomy, describing the number of
roots, the characteristics of the canals,their locations,
diameters, shapes, and directions (1–4). Few studies mention the
pres-ence of a groove or invagination on the furcation aspect of
the buccal root (5–11).
This groove, described as development depression or furcal
concavity, starts ata point just apical to the bifurcation, travels
a mean distance of 5.38mm, and disappearstoward the apex. According
to different studies, it is found in between 62% and 100% ofcases
(4, 5, 7, 9–11) (Fig. 1A).
Previous anatomic research in MFPs concluded that the larger the
number ofexternal sulci present and the deeper and more extensive
they are, the more internalvariations they show (12). By using
high-resolution computed tomography, it wasdiscovered that changes
in root canal geometry after preparation are more dependenton the
type of canal than on the technique or instrument used to shape the
canals (13).In periodontics, there is a direct relation between
external concavities and periodontalattachment loss (9).
Morphometric studies on this groove of the buccal root and its
relation with thedentin width root found that the palatal wall in
unprepared roots is on average less than1mm. This fact assumes
importance if it is taken into account that there is approval
inprosthetic and endodontic areas; therefore, in canal enlargements
and post prepara-tions, a thickness less than 1mm must not be left
(14–16).
In pulpless teeth, loss of dentin as a result of previous
endodontic treatment andpost preparation are factors that affect
long-term prognosis. Studies have establisheda direct relation
between the volume of dental structure and the capability of the
toothto resist occlusal loads; therefore, the probability of
fracture of an endodonticallytreated tooth increases proportionally
to the amount of dentin removed (4, 17–19).
Root curvatures in combination with other anatomic
characteristics like cracks orroot grooves predispose roots to
weaken or perforate during post placement (4).Vertical root
fractures (VRFs) constitute the third cause of dental loss after
cariesand periodontal disease and are responsible for 4.3% of
endodontic failures. InVRFs 56% of cases relate to premolars (19,
20).
Local stress concentrations have been proposed as the causes of
VRFs. Clinically,the pattern of stress distribution might be the
result of both external root morphologyand root canal shape.
Localized irregularities in the canal wall might serve to
raisestresses even at the point of initiation of the fracture (21,
22).
To sum up, the presence of radicular grooves and variations in
dentin width arefactors to consider in the treatment of MFPs.
The objective of this study was to accomplish an anatomic study
of furcationgrooves and dentin width in buccal roots of MFPs.
Materials and MethodsThe study consisted of adult subjects aged
between 35 and 65 years whose 141
upper first biradicular premolars with well-formed roots without
endodontic treatmentformed the sample. Immediately after
extraction, these 141 upper first biradicularpremolars were cleaned
of calculus and remaining external tissue and stored in buff-ered
formalin solution until assessment.
JOE — Volume 35, Number 6, June 2009
mailto:[email protected]
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Figure 1. (A) Photomicrograph showing the furcation groove in a
proximal view (left), palatal view (center), and transversal cut
(right). (B) Photomicrographshowing transversal cut of an upper
first premolar in which the obtained measurements are shown. Blue
line, buccal wall width; yellow line, buccolingual canaldiameter;
red line, palatal dentin width; white line, furcal groove depth;
dotted white line, reference level for furcal groove measurement;
green line, angle of furcalgroove. (C, D) Photomicrograph showing
the slices made to 2 MFP buccal roots. Red arrow: dentin structural
changes; black arrow: canal invagination at groovelevel.
Clinical Research
A preliminary macroscopic study was carried out with a
magnifyingglass to determine the percentage of teeth of which
buccal roots pre-sented palatal invagination or groove along the
bifurcation aspect(Fig. 1A).
From the group that had furcation grooves (n = 117), 20
wererandomly selected for measurement of the groove depth and
dentinwidth in the buccal root.
The palatal root was eliminated by using a diamond disk,
perform-ing a transversal cut immediately apical to the
furcation.
Three horizontal slices were made with a cutting diamond disk
inthe buccal root. The first cut was 2mm from the furcation
(coronal), thesecond 2mm from the anatomic apex (apical), and the
third an equi-distant distance between the first and the second
(middle). In these 3slices coronal, middle, and apical, the
following measurements wereobtained (Fig. 1B): furcation groove
depth, buccolingual canal diam-eter, width of palatal canal wall,
width of buccal canal wall, and angleof the furcal groove.
These measurements were obtained by using a profile
projector(PRAZIS; Aro. S.A., Buenos Aires, Argentina), calibrated
according toISO/TS 16949. The projector performs an indirect
measurement byfocusing 2 beams of intense light that reflect the
tooth onto an enlargedscreen with projection lenses�50. A built-in
computer in the machine
JOE — Volume 35, Number 6, June 2009
records the desired measurement on an orthogonal projected
diagram(axes X-Y) scale of thousandths of a millimeter.
Statistical AnalysisThe correlations between the studied
variables were analyzed
statistically by using the coefficient of correlation of Pearson
(r2). Tostudy the relation between dentin thicknesses, the means
values ofbuccal wall and palatal wall measurements were subjected
to pairedt test. The test was considered statistically significant
when P
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Clinical Research
The average figures of diameters of canals were coronal
third,0.64mm, middle third, 0.42mm, and apical third, 0.28mm.
Widths of palatal canal wall had an average of 1.17mm in
thecoronal level, 0.97mm in the middle level, and 0.85mm in the
apicallevel. Variations in the coronal third were between 0.35 and
1.82mm(Table 1).
The average figures of widths of buccal canal wall obtained
were1.41mm in the coronal slice, 1.13mm in the middle slice, and
0.77mmin the apical slice (Table 1).
Angles could only be tested in 53.3% of the slices; generally,
acuteangles were obtained ðXangle ¼ 51:80Þ. The averages were
65.70degrees for the coronal third, 49.16 degrees for the middle
third,and 36.29 degrees for the apical third.
In the coronal third, the depth of the groove was negatively
correl-ative with dentin thickness of palate wall, ie, while the
depth increased,palatal dentin thickness decreased or vice versa
(r2 = –82). The furca-tion groove angle had a positive correlation;
the greater the depth, thegreater the angle or vice versa (r2 =
–0.83).
In the middle third, variable depth also correlated positively
withthe angle; the greater the depth, the greater the angle or vice
versa(r2 = –0.57).
DiscussionFew anatomic studies mention the presence of furcal
grooves.
Different authors found their presence varied between 62%
and100% of cases. In our study we used a sample of 141
bifurcatedMFPs, finding the groove in 83% (n = 117) of cases (6, 8,
10, 11, 23).
Tamse et al (11) carried out the first morphometric study.
Theydescribed it as a concavity that starts at bifurcation level
and reachesa maximum depth of 0.40mm at a mean distance of 1.18mm
fromthe bifurcation. In a previous study, Joseph et al (8) found
0.46mmaverage depth. In our work, the average figures of groove
depth fluctu-ated between 0.17 and 0.44mm, with maximum value of
0.89mm in themiddle third. This is important if we consider that
when the depthincreases, palatal dentin thickness decreases or vice
versa (r2 = –82).
A profile digital projector (PRAZIS) was used for
obtainingmeasurements; this equipment has been previously used in
dentalresearch (24–26), in periodontics for the study of furcation
anatomy(27), and in endodontics to test gutta-percha points and
root canalfilling materials microleakages (28, 29).
Tamse et al (11) mentioned that the furcal groove would bea
morphologic and not a development entity, because they did notfind
a depression on the buccal aspect. Gher and Vernino (5)concluded
that this groove would represent the partial formation of 2buccal
roots during development of the tooth. They based their opinionon
the fact that no furcal grooves were seen in premolars in which
bifur-cation was located in the apical third of the root. Mattuella
et al (12)reported the presence of a similar depression on the
buccal aspect ofthe root. The presence of the buccal groove was
detected in some casesin our study samples. A study of sequential
embryology of this tooth isnecessary to confirm that biologic facts
occur during the developmentof the tooth.
TABLE 1. Relation between Palatal Wall Dentin Width and Buccal
Wall DentinWidth in Different Thirds of the Buccal Root
PDW average±SD BDW average±SD P value
Coronal 1.17 � 0.08 1.41 � 0.17 .0242*Middle 0.97 � 0.05 1.13 �
0.13 .0047*Apical 0.85 � 0.06 0.77 � 0.16 .231
PDW, palatal wall dentin width; BDW, buccal wall dentin
width.
*Statistically significant differences for paired t tests.
816 Lammertyn et al.
Our research revealed histologic changes in dentin structure
adja-cent to root grooves, both buccal and furcal. Other studies
are necessaryto understand the structural changes in the type of
dentin (Fig. 1C).
Tamse et al (11) mentioned that in the canal level
correspondingto the furcal groove, a smaller identical invagination
was found. Eventhough this point was not in our study, in some
slices we observeda modification on the palatal wall of the canal
corresponding to the fur-cal groove invagination (Fig. 1D).
In the buccal root of MFPs, original dentin thickness had
beenpreviously measured. Tamse et al (11) determined an average
of0.81mm for the lingual aspect and 1.11mm for the buccal aspect
atcoronal level. In a later study, Bellucci and Perrini (30) found
the thick-nesses were 1.31mm for the lingual aspect and 1.45mm for
the buccalaspect. Subsequently, Katz et al (23) found the
thicknesses were0.99mm for the lingual wall and 1.16mm for the
buccal wall.
In the present study, averages similar to those of Bellucci and
Per-rini (30) were found, 1.18mm for the palatal wall and 1.41mm
for thebuccal.
Unlike in other studies, Bellucci and Perrini (30) took
intoaccount the patients’ ages at the time of the extraction, which
in theirstudy ranged between 35 and 55 years. However, they did not
mentionwhether the teeth had furcal grooves.
Regarding the selection of samples, we bore in mind that
premo-lars presented 2 well-formed roots. We considered the
patient’s ageolder than 35 years, taking into account that the
volume ratio of pulpcavity as well as the diameter of the root
canal orifices progressivelydecreased with age as a result of
apposition of secondary dentin.However, this change was not
gradual; in a comparative study betweendifferent age groups, the
major volumetric variations were between 20and 40 years, compared
with values observed between 40 and 60 years(31).
Bellucci and Perrini (30) found that the average width of
buccalroot was greater than the palate wall, with significant
differences(P < .05, t test). In our study, we observed that in
the middle andcoronal thirds, the dentinal width of the buccal root
was larger thanthat of the palatal wall, with statistically
significant differences(P < .05, paired t tests) (Table 1).
Therefore, the anatomic characteristics of buccal roots
examinedin this study and previous ones must be evaluated when
planning anydental treatment in MFPs.
From the endodontic point of view, we must take into account
thatcanal shape generally reproduces the external root anatomy, in
manycases presenting a kidney-shaped transversal section.
Conclusions(1) Eighty-three percent (n = 117) of studied teeth
had furcal
grooves in the buccal root. (2) The mean depth of this groove
was0.05mm in the apical third, 0.34mm in the middle third,
and0.36mm in the coronal third. (3) In many cases, palatal dentinal
widthwas smaller than 1mm.
Further investigation is needed to assess the relationship
betweenpreparation techniques and presence of the furcal
groove.
AcknowledgmentsThe authors thank Mr Mario Infante for his
assistance and
expertise with the profile projector and Mrs Marcela and Mr
NelsonAurich for translating the manuscript.
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Dentin Thickness and Structures Adjacent to Furcal Groove
817
Furcation Groove of Maxillary First Premolar, Thickness, and
Dentin StructuresMaterials and MethodsStatistical Analysis
ResultsDiscussionConclusionsAcknowledgmentsReferences