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: paolammertyn@hotmail.com.0099-2399/$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.

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mailto:paolammertyn@hotmail.com

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

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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

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