Taurodontism

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Abstract

Taurodontism was hitherto considered to be a marker of oro-facial disorders. Since then, it has been reported with a moderately high-to-high prevalence on panoramic radiographs in case series of otherwise normal individuals in Brazilian, Middle Eastern and East Asian communities. This now understood higher than-formerly expected prevalence is important to the endodontist, orthodontist and restorative dentist. Therefore, the oral and maxillofacial radiologists should be aware of this phenomenon and its measurements to advise better their clinical colleagues.

Taurodontism as defined by Shifman and Chanannel “is a deformation of the internal morphology of the dental pulp cavity, characterized by an elongation of the pulp chamber extending into the root area” [1]. This vertical elongation of the pulp chamber of teeth, which displaces the furcation of the roots in multirooted teeth apically, changes the overall root shape of human molars from their classical hitherto most-commonly expected ‘cynodont’ shape to a more cylindrical taurodont shape. Cynodont means ‘dog-tooth’ from the classical (ancient) Greek Κύων, (pronounced Kýon) and ὀδούς (pronounced odoús), whereas ‘taurodont’ means ‘bull-tooth’ from the Latin Taurus for bull. Figure 1 schematically displays the progress of this change in shape in a mandibular molar from cynodont through hypo-taurodont and meso-taurodont to hyper-taurodont. Although this phenomenon is generally appreciated radiologically rather than clinically, it impacts many types of dental treatment; it complicates endodontics and it reduces the root surface area available for anchorage in orthodontics or adequate occlusal-load resistance for pontics. In a Brazilian study, Weckwerth et al. [2] recently reported taurodontism in 43% of their normal controls. This high prevalence in normal individuals reflected 44% prevalence in a young Chinese community 25 years earlier [3].

Fig. 1
figure1

A schematic diagram displaying the changing root shape of increasingly severe taurodontism from the initial normal tooth. The taurodont index is given for each

Prior to Shifman and Chanannel’s Israeli [1] and MacDonald-Jankowski and Li’s Chinese [3] reports, taurodontism was considered relatively uncommon as an isolated trait in normal modern humans (taurodontism has been reported in Neanderthals). Hitherto, taurodontism has been considered primarily as a marker of oro-facial abnormalities such as amelogenesis imperfecta [4] and cleft lip and palate; Weckwerth et al. [2] found taurodontism in 60–67% in the latter cases. Nevertheless, the high prevalence of taurodontism in normal Chinese and Brazilian individuals calls into question its central role as such a marker. There have been several methods for determining the presence of taurodontism and its severity [5]. Many of them were limited by the fact that teeth undergo attrition, particularly in adulthood and that the completion of root formation restricts which teeth can be used particularly in the younger patient, who are most likely to be in the care of the orthodontist and/or the pedodontist, specialists in dental development. Inspired by the unexpected observation of taurodontism in patients presenting for routine treatment [6], Shifman and Chanannel performed their aforementioned study in a cohort of patients in their third decade.

Shifman and Chanannel [1] developed a robust system for the radiological classification by objective measurements, which they called ‘variables’. There are three variables. These and their anatomical parameters are set out schematically in Fig. 2. In addition to their measurements, they developed a ‘taurodont index’ (TI), based on the ratio of two ‘variables’: TI = variable 1/variable 2 × 100) [1]. The values for TI are shown in Table 1 and given for all teeth, real or schematic.

Fig. 2
figure2

An adaptation of Shifman and Chanannel’s Fig. 1 setting out their three variables from which taurodontism could be objectively measured. 1 (Variable 1), the height of the pulp chamber, between the lowest point of the roof and the highest point of the floor; 2 (variable 2), the distance between the lowest point of the roof of the pulp chamber and the apex of the longest root; 3 (variable 3), the distance between the enamel-cemental junction and the highest point of the floor of the pulp chamber. The parameters for these variables have also been identified. Key: ECJ enamel–cemental junction. The taurodont index for this schematic figure is 20, which is exactly on the borderline between cynodont and hypo-taurodont

Table 1 Taurodont index

The periapical radiographs, Shifman and Chanannel [1] used, were derived from full-mouth surveys (FMS) that had been performed on 80% of their patients. Panoramic radiography has only come into general clinical use relatively recently [7]. Tulensalo et al. [8] were the first to use panoramic radiographs to detect taurodontism which they measured manually. Furthermore, as they used a small 10–16-year-old cohort, they clearly were unable to use the TI as the root formation would be incomplete for many molars during that age range. For this age range, they found variable 3 most useful. The aforementioned Chinese study [3] applied both Shifman and Chanannel measurements [1] and the implied finding that the age range in Tulensalo et al. study [8] was too young. The Chinese study used an older age group of 15–19 years [3].

The Chinese study was the first study in which measurements were made directly from the radiographs digitally. This digital measurement allowed measurements to be recorded at two decimal points, in contrast to the closest half millimeter. The Chinese study advocated a preference for the TI as it would not be affected by the magnification inherent to panoramic radiographs [7]. Most subsequent reports measuring from the panoramic radiograph used the TI. The almost 80% availability of FMS periapical radiographs to Shifman and Chanannel in the middle years of the 1970s is increasingly unlikely in jurisdictions which apply the tenets of the joint American Dental Association and US Food and Drug Administration’s (ADA/FDA) recommendations for patient selection and limiting radiation exposure, particularly when prescribing dental radiography for adolescents or young adults [9]. The ADA/FDA only recommends FMS for those patients with generalized oral disease or extensive dental treatment [9], precisely the patients to be excluded from such a study. Shifman and Chanannel also excluded such patients with ‘reparative dentine’ from their study [1].

Figure 3 displays the closeness of the roof of the pulp chamber to that of the enamel–cemental junction (ECJ). Indeed the lowest point of the roof of the pulp chamber, in 8% of the Chinese teeth, was actually apical to that of the ECJ [3]. In such cases, those teeth determined objectively, by digital measurement, would be less taurodontic. In addition to invalidating Variable 3, this could result in an under-reporting of taurodontism. This is even more so likely as the majority of taurodonts are hypo-taurodonts, with only a few hyper-taurodonts [1,2,3].

Fig. 3
figure3

Part of a panoramic radiograph displaying a left cynodontic mandibular first molar displaying in addition the measuring positions of Shifman and Chanannel’s three variables, the more apical position of the lowest point of the roof of the pulp chamber (blue line) to that of the line joining the enamel–cemental junctions (red line). This was found in 8% of MacDonald-Jankowski and Li’s young Chinese. Key: 1 (variable 1), the height of the pulp chamber, between the lowest point of the roof and the highest point of the floor; 2 (variable 2), the distance between the lowest point of the roof of the pulp chamber and the apex of the longest root; (3) (variable 3), the distance between the enamel–cemental junction and the highest point of the floor of the pulp chamber

Although there is a lower prevalence of taurodontism in normal communities of Israelis (6%) [1] and Germans (2%) [10], it has been found to be moderately higher in Turks (11%) [11] and Iranians (23%) [12]. As reported earlier, it is highest in at least one normal Brazilian (43%) [2] and in one normal Chinese (44%) [3] community.

Although these reports all used Shifman and Chanannel’s methodology as modified for panoramic radiographs, a focus on mandibular molars will result in a lower overall prevalence. Brkić and Filipović’s [13] Croatian study is a case in point; they reported a 2% taurodont prevalence in mandibular molars. Furthermore, Melo Filho et al. [14] reported that 9% of mandibular molars of their normal controls exhibited taurodontism in comparison to 18% of those with a cleft palate and lip. Weckwerth et al.’s [2] study also on Brazilians reported 43% to 60–67% respectively. The higher prevalence in Weckwerth et al.’s [2] study would be due to the inclusion of maxillary molars, which were more frequently affected by taurodontism. Similarly, exclusion of the third molars in the Chinese study simply because they had not yet fully completed root formation may also have led to under-reporting of taurodontism in this community, because Constant and Grine [15] reported that some reports reported that taurodontism was higher in third molars.

The Chinese report revealed that taurodontism was significantly more prevalent in females (56% in comparison to 36% in males, P < 0.001) [3]. It was found that in 22% of all first and second molar teeth examined, the prevalence was significantly greater in females (26% as compared with 17% in males, P < 0.001) [3]. This sex difference has since been reported in Weckwerth et al.’s controls; 49% in females to 32% in males (P < 0.01). These predilections for females are consistent with the relationship of taurodontism and X-chromosome polyploidy in XXX and XXXX Finnish females [16] and XXY Finnish Klinefelter syndrome males [17, 18]. The severity of the taurodontism (hypo-taurodont to meso-taurodont to hyper-taurodont) increased with each additional X-chromosome [16].

In addition to the definition for taurodontism set out earlier by Shifman and Chanannel [1], some authorities add a lack of constriction at the ECJ [5]. As Fig. 4 displays a first maxillary molar hypo-taurodontism exhibiting such a constriction, this feature should be considered only of secondary importance in the diagnosis of taurodontism.

Fig. 4
figure4

A panoramic radiograph taken for orthodontic purposes displaying taurodontism, particularly in the maxillary molars. Both first molars display complete root formation. Although the height of the pulp chamber in the mandibular first molar is higher than that in Fig. 3, its taurodont index is 13 and therefore is a cynodont, whereas the taurodont index of the maxillary first molar is 23 and therefore is a hypo-taurodont

The hitherto prevailing focus on taurodontism as it presents on conventional radiography, particularly panoramic radiographs, is that taurodontism in molars is clearly displayed on these projections as the central ray is orientated buccolingually. This projection will optimally display the taurodontism as the roots are arranged mesiodistally. The advent of cone-beam computed tomography and the ability to view teeth transaxially permit the detection of taurodontism in premolars; Fig. 5 displays such a case. Nevertheless, it was the unusual capturing on a conventional radiograph of taurodontism affecting a premolar which permitted the identification of a mass-disaster victim [19].

Fig. 5
figure5

Part of a cross-sectional image obtained by cone-beam computed tomography through the buccal and lingual roots of a left mandibular first premolar displaying hyper-taurodontism. Its taurodont index is 62

Change history

  • 01 June 2019

    In the original publication of the article, few errors were identified. The corrections are given below:

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Correspondence to David MacDonald.

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MacDonald, D. Taurodontism. Oral Radiol 36, 129–132 (2020). https://doi.org/10.1007/s11282-019-00386-1

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Keywords

  • Taurodontism
  • Panoramic radiography
  • Cone-beam computed tomography