Morphometric Analysis of Furcation Areas of Multirooted Teeth in a Tunisian Population

Aims The aim of the study was to evaluate the morphological characteristics of furcation of permanent molars in Tunisian population. Materials and Methods One hundred and four extracted maxillary and mandibular permanent molars were included in this study; comprising 34 maxillary first molars, 18 maxillary second molars, 33 mandibular first molars, and 19 mandibular second molars. For each tooth, the vertical dimension of the root trunk, root length, and interradicular space width were assessed with a micrometer caliber. Different types of root trunk in maxillary and mandibular molars were also analyzed. Statistical analysis was performed using a t-test. Results Root length decreased from the first to the second molars. This decrease seems to be pronounced at mandibular molars. The most observed root trunk type was type B, with a prevalence of 67.30% in maxillary molars and 51.92% in mandibular molars. The root trunk length increased from the first to the second molars in both maxillary and mandibular. The average width of the interradicular spaces varied on the same tooth and between the teeth. Conclusion This study provides epidemiological data about molars root length, interradicular space, and root trunk vertical dimension in a Tunisian population that could help clinicians in periodontal and endodontic therapy.


Introduction
Furcation is defined by the glossary of periodontal terms as "the anatomic area of the multirooted tooth where the roots diverge" and "furcation invasion refers to the pathologic resorption of bone within a furcation" [1,2].
Furcation morphology of multirooted teeth has been addressed extensively in the literature. ere are some anatomical variations that contribute to the etiology and the compromised prognosis of furcation involved teeth. ese factors include furcation entrance width, root trunk length, root concavities, enamel projections, and enamel pearls which influence the onset and progression of periodontal disease as well as the development of interradicular lesions [3][4][5].
Furcation areas present some of the greatest challenges of the success of periodontal therapy [4]. It has been demonstrated that many variables could alter the oral environment, such as the presence of osseointegrated implants [6], orthodontic appliances [7], or topographic hard-to-reach areas [8].
Many studies assessed the influence of topographic anatomy of molars on periodontal therapy and have shown that inaccessibility of these areas for cleaning as well as the narrowness of the furcation entrance makes adequate instrumentation and plaque control difficult. It leads to a lack of proper access for instrumentation and consequently, a persistence of pathogenic microbial flora [9]. A better understanding of the furcation and root surface anatomy is necessary for effective management of the furcation area [3,4]. e purpose of this work was to assess the characteristic of furcation areas, the root trunk dimensions, and type of maxillary and mandibular molars and to analyze their influence on the diagnosis and management of molars with furcation involvement.

Materials and Methods
e sample of this study was composed of 430 multirooted teeth selected from a collection of extracted human teeth of a Tunisian population, obtained from different private clinics. e reasons for extractions were following advanced periodontal disease, caries and endodontic infection, or orthodontic reasons. e extracted teeth were placed in a solution of sodium hypochlorite 3% during one day, identified based on tooth morphology characteristics, and classified into four groups: first maxillary molars, second maxillary molars, first mandibular molars, and second mandibular molars [10,11].
Only maxillary molars with three roots and mandibular molars with two roots were included in this study. Intact cementoenamel junction (CEJ) and intact crowns were also criteria of inclusion.
ird molars, molars with fused or fractured roots, caries or restorations in the furcation areas were excluded.
A final sample of 104 teeth was retained and composed by 34 maxillary first molars, 18 maxillary second molars, 33 first mandibular molars, and 19 second mandibular molars. Teeth were cleaned under running water to remove debris and then disinfected in a solution of sodium hypochlorite 3%. If any calculus obscured the furcation entrances or the root trunk, this calculus was removed gently using a manual curette scaler (Periodontal scaler 651/11Ti.HL8. MEDESY s.r.l. Italy).

Morphometric Analysis
e following parameters were measured on the selected molars: (1) e length of each root from the enamel-cementum junction to the apex of each root (2) e length of each root trunk from the enamelcementum junction to the entrance of furcation (3) e width of the interradicular space, 1 mm apically from the furcation entrance, measured between the internal sides of the roots ( Figure 1) Measurements were carried out using a digital micrometer caliper (Fowler & NSK MAX-CAL 6" Electronic Digital LCD Caliper, Japan) with an electronic display of nearly 10 −2 . Two measurements were made separately, realized by the same operator, and the average of these measurements was calculated. If the two measures were different by more than 0.2 mm, tooth was reviewed, and the results were remeasured. All data were expressed as the mean ± standard deviation.
Using Ochsenbein's classification, the root trunk was classified into three types: A (short), B (medium), and C (long) [5,10]. Maxillary molars with root trunks of 3 mm or less were classified as short, 4 mm trunks were classified as medium, and 5 mm or more trunks were classified as long.
For mandibular molars, a short root trunk was considered to be 2 mm or less, medium root trunks were 3 mm, and long root trunks were 4 mm or longer.
For the evaluation of the variables, root length, root trunk, and interradicular space width, statistical analysis was performed using a t-test. Statistical analysis was performed using IBM statistical package for the social sciences statistics 21 programs (IBM SPSS statistics, Armonk, NY, USA). Correlations between root trunk length and interradicular space width, root trunk length, and root length were calculated using Pearson's correlation coefficient. e level of significance was set as p < 5.10 − 2 .

Results
e mean values of root length (RL), root trunk length (RTL), and interradicular space (IRS) width of the examined teeth are presented in Tables 1 and 2. Table 3 illustrates the comparison of the different studied parameters.

Root Length.
At maxillary molars, distobuccal root was the shortest (p � 0.002) followed by the mesiobuccal root and the palatal root (12.32 mm, 13.17 mm, 13.38 mm), respectively (Table 1). However, this order was not always conserved as the palatal root was not always the longest one (p � 0.747). Some molars with mesial roots longer than the palatal one were also noticed.
At mandibular molars, the mesial root was the longest (14.69 mm) followed by the distal root (13.74 mm), and this result seemed to be statistically significant (p � 0.002) ( Table 3). Root lengths decreased from the first to the second molars. is decrease seemed to be pronounced at mandibular molars.

Root Trunk Length.
e length of the root trunk increased from the first to the second molars in both maxillary and mandibular. e order of the increasing average of root trunks was the same for the first molars and second maxillary molars: buccal, distal, and mesial (Table 2).
It can be perceived that in the Tunisian population, the mesial root trunk was the longest one on maxillary molars. e buccal root trunk was the shortest one in comparison with other root trunks in both arches (Table 3). Table 4 shows that the most observed root trunk type was type B with a prevalence of 67.30% in maxillary molars and 51.92% in mandibular molars. e mean value of root trunk length for maxillary molars ranged from 3.96 mm to 4.90 mm, while for mandibular molars, root trunk length varied from 3.75 mm to 4.47 mm. Table 2 lists the mean values of the width of the interradicular spaces in maxillary and mandibular first and second molars. e mean width of the interradicular spaces varied on the same tooth and between the teeth. Regarding the interradicular space dimensions of maxillary molars, the buccal interradicular space was the narrowest, followed by the mesial than the distal one (p � 10 − 3 ), whereas in mandibular molars, the buccal interradicular space was larger than the lingual one.

Interradicular Space Width.
It can also be observed that with the increasing mean of root trunk length, there was a decrease in the interradicular space width. It was interesting to note that for mandibular molars, lingual furcation was characterized by a long root trunk associated with narrower interradicular space.

Discussion
Our study was based on measurements using a micrometric caliper with an electronic display with an accuracy of 10 −2 ; the reading was difficult. However, it was done by one operator which minimized the risk of error. Moreover, dental anatomy is highly variable; the random collection of teeth in our study overcame the anatomical diversity of the molars.
e finding of the present study showed that the mean length of the mesiobuccal and palatal roots, in maxillary first molars, was, respectively, 13.17 mm and 13.38 mm. e distobuccal root was the shortest. is order was the same for the second maxillary molars.
However, for mandibular first molars, the means of the mesial and distal roots were, respectively, 14.69 mm and 13.74 mm. In mandibular second molars, the root length means were 14.04 mm in mesial side and 13.34 mm on the distal side of the tooth. ese results were in accordance with those reported by Dababneh et al. [11] who found that for maxillary first molars, the mean lengths of the mesiobuccal and palatal roots were closer (12.9, 13 mm) and longer than the distobuccal root (11.9 mm), while for mandibular first molars,   the means of the mesial and distal roots were, respectively, 14 and 13.5 mm. Different results were obtained by Roussa [12] for the maxillary molars who found that the distobuccal was the longest root (12.2 mm) compared to 11.3 mm and 11.2 mm for, respectively, the mesiobuccal and palatal roots. On the other hand, for mandibular molars, they found that the means for the mesial and distal roots were, respectively, 14.2 mm and 14 mm. Distal roots were found to be longer than mesial roots. ese morphometric measurement variations could be attributed to geographic and ethnic differences. e root trunk is defined as the area of the tooth extending from the cementoenamel junction to the furcation [3].
e present study showed that the most observed type was type B followed by type A and type C for both maxillary and mandibular molars. e prevalence of type C in the present study (13.46% in maxillary molars and 3.84% in mandibular molars) was higher than those reported in other studies such as those cited by Hou et al. and Dababneh et al. [11,13]. e root trunk length increased from the first to the second molars at both maxillary and mandibular arches.
is finding was in accordance with those reported by Kerns et al. [5]. e main finding of the present study was that the buccal furcation was anatomically different from the lingual, mesial, and distal furcations for all the evaluated measurements [13]. e buccal root trunk length was shorter than the mesial and distal root trunk and the mesial root trunks were the longest root trunk in maxillary molars. is data was in agreement with others founded in other studies [11,14]; however, it disagreed with some other studies that found that the distal root trunk was longer than the mesial one [12,15,16].
In mandibular molars, the buccal root trunk was shorter than the lingual root trunk. is finding was in accordance with the morphometric studies of root trunk [5,13,17,18] ( Table 5).
Root trunk length has an important impact on the pathogenesis of the periodontal disease. is is one of the keys to anatomical factors that make molars particularly susceptible to periodontal disease [21,22]. Short root trunk is more likely to develop early furcation involvement and attachment loss in the presence of periodontal disease because it has less surface area for periodontal attachment. Even though, once the disease is installed, reduced root trunk length tends to lead to satisfactory periodontal treatment outcomes because of its easier access [3].
On the other hand, a long root trunk makes access to the proximal furcation more difficult compared to the other sides, particularly when neighboring teeth are present. Diagnosis and treatment could be better with surgical exposure in the case of furcation involvement because of a lack of access [23,24]. e furcation entrance measure is extremely important in anticipating the success of periodontal therapy. In this study, buccal furcation was statistically the narrowest for maxillary molars, while the lingual furcation was narrower than the buccal furcation for mandibular molars. ese results were comparable to other results in other studies [13,15,17,20,25]. Narrow furcation implies an increased difficulty of access through furcation entrances for complete root debridement leading to a poor periodontal outcome.
is fact seemed to be accentuated in the present study because of the long lingual root trunk in mandibular molars associated with a narrower furcation [24]. e present study showed that the mean of the interradicular space width was superior to 0.98 mm at 1 mm of the furcation entrance. is result could be a micrometric characteristic of the Tunisian population, which seemed to be similar to the dimension of standard Gracey curettes (75 to 0.95 mm). is finding indicated that the use of curettes alone might be suitable for root preparation in the furcal area.
However, the micrometric measurements of the present study were more important than those reported in several studies. In fact, Kodovic et al. [22] reported that 81% of all furcation entrances diameters were <1 mm and 58% were <0.75 mm. Sixty-three percent of maxillary molars and 50% of mandibular molars were <0.75 mm. Different findings   [23]. e small number of teeth used in the present study could be considered as a limitation. In fact, the main inclusion criteria were intact crown and roots. However, most of the first and second permanent molars extracted were severely affected by decay or badly destructed which impeded tooth measurement.
is fact can limit the extrapolation of the results, particularly concerning the distribution of root trunk in maxillary and mandibular molars to the entire population. Nevertheless, no survey on the anatomy of the furcation of permanent molars in the Tunisian population has been published at the time of the preparation of this study. erefore, the results of this study may provide useful data of the micrometer measurements of permanent molars roots and the anatomy of the root trunk and furcation which can help in defining new strategies for treatment and prevention of periodontal diseases. Further studies involving a larger sample will be an essential step in improving the periodontal health status of the Tunisian citizens.

Conclusion
e data of the present study provide reference measurements for therapeutic applications in molars of the Tunisian population within the limits of the sample studied. Furcation areas of multirooted teeth are extremely complex and must be carefully understood to improve the success rate of periodontal therapy. Knowledge of root trunk characteristics and interradicular dimensions, coupled with furcation and osseous architecture, should aid the clinician in the diagnosis, management, and prognosis of periodontally involved molars.
Data Availability e data of the assessed parameters used to support the finding of the present study are available from the corresponding author upon request. International Journal of Dentistry 5