Association between oral tori, occlusal force, and mandibular cortical index

Association between oral tori, occlusal force, and mandibular cortical index

MENA Dental Science

15. April 2019

Ziad N. Al-Dwairi, Ala’ N.F. Al-Daqaq, Andrej M. Kielbassa, Edward Lynch

Objective: To assess possible associations between torus palatinus (TP), torus mandibularis (TM), occlusal force (OF), Klemetti’s classes, mandibular cortical index (MCI), and sociodemographic variables in a selected sample of Jordanians. Previous studies have suggested that oral tori are benign anatomical variations probably related to several factors such as functional stress, gender predisposition, number of teeth present, and nutritional factors. Method and Materials: A total of 130 Jordanian adults were included. Shape, location, and appearance of tori were recorded from study casts. Size was measured using digital calipers. OF was recorded in Newtons. MCI and Klemetti’s classification were assessed using panoramic radiographs. Data were statistically analyzed, and level of significance was set at P < .05. Results: The mean ± SD recorded OF was 524 ± 183 N in the tori group, compared to 417 ± 172 N in controls (P = .001). OF was significantly higher in males compared to females (P < .001), and was significantly higher in subjects with TM only (543 ± 201 N) (P < .001). TP and TM were predominantly more than 6 mm in size. The average OF in subjects with Klemetti class 3 was 418 ± 174 N, while OF in Klemetti class 1 subjects amounted to 535 ± 187 N (P = .043). Conclusion: Average OF was significantly higher in tori subjects and in males (if compared to controls and female subjects, respectively). The presence of oral tori, Klemetti’s classification, and MCI ratio seems to be positively correlated with OF. (Quintessence Int 2017;48:–849; doi: 10.3290/j.qi.a38856)

The etiology of oral tori has not been clearly determined, and both genetic aspects1-4 xand causes of multifactorial origin are thought to be involved.2,4 Although some reports suggested that these nonpathologic, localized exostoses arising from cortical bone may be related to an autosomal4 (but nongonosomal5) dominant trait, environmental and functional factors have been postulated that may account for a more complex etiology than simply genetics.2,6,7 Several other factors such as gender and age5-13 have been identified for oral tori, but this relationship has not been confirmed unani­mously.14-18 Beneath these aspects, functional stresses, parafunctions, and masticatory forces,12,16,19,20 temporomandibular joint (TMJ) pathology,12 high bone mineral density (BMD),21 as well as nutritional factors and marine diet5,20,22 may also be involved.

The prevalence of oral tori has been reported to be quite common. In different ethnic groups, there is a wide variation, ranging from 1.3% for torus palatinus (TP) in normal patients8 to 56.8% for torus mandibularis (TM) in those with genetic predisposition,1 and with a slight preponderance of mandibular tori.14,17,23 With an increasing number of teeth, the frequency of bony protuberances would seem to be higher,24-26 but the latter have been observed even with edentulous patients.10,27 There is a strong relationship between mandibular and maxillary tori.7,17,21-23,27,28

It has been reported that panoramic radiographs could be useful for identifying patients with low BMD or osteoporosis.29,30 A simple method to classify the radiographic image of the mandible is the mandibular cortical index (MCI),31-34 which can be defined as the ratio of the thickness of the inferior mandibular cortex in the mental region over the distance between the lower border of the mandible and either the inferior or the superior border of the mental foramen.32 The morph­ology of the mandibular inferior cortex can be determined by observing both sides of the mandible distally from the mental foramen using the classification published by Klemetti and colleagues.34-36 The MCI has been developed to assess osteoporosis in the cortical area of the mandible based on panoramic radiographs.35 MCI readings reflect the solidity of cortical bone in the mandibular base, since structural changes in cortical bone tissue are manifested by the resorption both on the outer and inner sides of the mandibular cortical layer.36 Both MCI and Klemetti’s classification have been considered to be simple methods to assess the radiographic image of the mandible as they can be easily and effectively used by general practitioners and dental specialists.35

Previously, there has been controversy regarding the etiology of tori, even though their existence, histology, and prevalence have been thoroughly investigated. In particular, the relationships between oral tori, occlusal force (OF), morphology of the inferior mandibular cortex (Klemetti’s classification), and MCI have not been previously studied. Therefore, this study aimed to assess associations between TP and TM with age, gender, body mass index (BMI), chewing side, OFs, Klemetti’s classification, and MCI in a selected sample of Jordanians. The null hypothesis stated that no relationship exists between the OF and the occurrence of oral tori and MCI in adult Jordanians. This null hypothesis was tested against the alternative hypothesis of a difference.

Method and Materials

After obtaining ethical approval by the Institutional Review Board of Jordan University of Science and Technology (Vote Number: GM7601), 130 subjects were enrolled in this study (65 with TP and/or TM, and 65 controls matched for age and sex). Demographic data obtained included age, gender, and chewing side. Subjects’ ages ranged between 20 and 50 years. BMI of the patients was classified according to the formula used by the Centers for Disease Control and Prevention37 as follows:

  • Underweight: BMI ≤ 18.5
  • Normal: 18.5 ≤ BMI ≤ 24.9
  • Overweight: 25 ≤ BMI ≤ 29.9
  • Obese: BMI ≤ 30.

Subjects were recruited from different areas in Jordan, and examination was carried out at the Department of Prosthodontics of the Jordan University of Science and Technology. Participants included undergraduate and graduate students, as well as patients seeking regular dental treatment at the Faculty of Dentistry.

Subjects presenting with TP and/or TM, and having at least a full set of first molars were included in the study. Edentulous patients with partial or complete dentures, subjects who were reported to have diurnal or nocturnal bruxism or TMJ dysfunction, and subjects with systemic disorders affecting bone density (endocrine, metabolic, or skeletal disorders, or any local bone pathology) were excluded.

Clinical examination

Extraoral examination of the muscles of mastication and TMJ was carried out to test for the presence of pain, TMJ sounds, TMJ locking, ear pain, or headaches. Tori were examined by clinical inspection and digital palpation. This was followed by maxillary and mandibular irreversible hydrocolloid impressions (Algeniux, Major Prodotti Dentari). A study cast poured using gypsum material (Elite Model, Zhermack) was used to evaluate the location and size of TP and/or TM.

Occlusal force measurement

A portable OF gauge (GM10, Nagano Keiki) consisting of a hydraulic pressure gauge, and a biting element made of a vinyl material encased in a polyethylene tube was used to measure the OF, which was displayed digitally in Newtons.

Before recording the OF, subjects were seated in an upright position and asked to perform their strongest bite over the device (after previous training). The OF-meter bite fork (GM10, Nagano Keiki) was covered with a disposable plastic cap to prevent the individuals from cross infection. The measurements were exclusively performed at the first molar region. Two readings were recorded on both the right and the left sides, respectively, and an average was obtained.

Assessment of oral tori

Tori were assessed both clinically and on the casts for size and site (unilateral or bilateral). The size of tori was measured twice at the highest elevation of the outgrowth using calipers (Model 505, Mitutoyo) to the nearest 0.01 mm. The average size of tori was recorded and categorized according to the classification by Reichart et al:18

  • small (< 3 mm)
  • medium (3–6 mm)
  • large (> 6 mm).

Measuring MCI and Klemetti’s classification

All subjects were assessed for the MCI using an ortho­pantomogram based on Klemetti’s classification.34 Panoramic radiographs of subjects were obtained (Cranex Tome Ceph, Soredex) at 63 to 83 kV and 10 mA for 10 seconds. The head of each subject was positioned so that the line from the tragus to the outer canthus was parallel to the floor; the anteroposterior position of the subjects was ensured by placing the incisal edges of their maxillary and mandibular incisors into the bite block. All films were processed in an automatic x-ray processor (Periomat Plus, Dürr Dental) with a processing time of 2.45 minutes. Panoramic radiographs with diagnostic contrast and density, and absence of positioning errors, were evaluated by two consultant radiologists. The morphology of the mandibular infer­ior cortex was determined by assessing both sides of the mandible distally from the mental foramen.34

  • C1: The endosteal margin of the cortex is even and sharp on both sides (Fig 1a)
  • C2: The endosteal margin shows semilunar defects (resorption cavities) with cortical residues one- to three-layers thick on one or both sides (Fig 1b)
  • C3: The cortical layer contains heavy endosteal cortical residues and is clearly porous (Fig 1c).

Panoramic radiographs of the two groups were mixed, and calculations of MCI and Klemetti class morphologies were carried out independently by the two radiologists (with assured 1-week intervals). Each radiologist examined the panoramic radiograph under the same environment and using the same viewer. The MCI was calculated for both right and left sides of the mandible on panoramic radiographs as the ratio of the thickness of the inferior mandibular cortex in the mental region over the distance between the lower border of the mandible and either the inferior or the superior border of the mental foramen, as shown in Fig 2.

Fig 2  Calculating MCI on panoramic radiographs: The ratio of the thickness of the inferior mandibular cortex in the mental region (B) over the distance between the lower border of the mandible (a) and either the inferior (I) or the superior (S) border of

Statistical analysis

Data were analyzed using SPSS software application (version 22.0, IBM). The weighted kappa index was used as a measure of inter-observer agreement for Klemetti class evaluation, while Pearson’s correlation coefficients were used as a measure of inter-observer agreement in the MCI measurements. Means ± standard deviations (SDs) were calculated for continuous variables (such as OF and age). A frequency distribution of categorical variables was provided. One-way analysis of variance (ANOVA) and independent sample’s t test analysis were used to compare individual continuous variables by presence of tori. Categorical variables’ association with presence of tori was analyzed using chi-square cross-tabulations together with Fisher’s exact test in case of cell counts less than 5. Values of continuous variables are expressed as means ± SD, while categor­ical distributions were expressed as n (%). The level of significance was set at P < .05.


Controls were selected to match the tori subjects with regard to gender, age, chewing side, and BMI. For this reason, these aspects did not reveal any significant differences (Table 1). In subjects with tori, OF on the right side had a mean ± SD of 520 ± 190 N compared to 416 ± 188 N in the control group (P = .001), while the mean on the left side was 582 ± 192 N compared to 417 ± 179 N in controls (P = .002). The average OF in males was 572 ± 190 N and 411 ± 155 N in females (P < .001). There was no significant association between the average OF and any of the two chewing sides (P = .273). In addition, there was a significant increase in the average OF from Klemetti class 3 to class 1 on both the left (P = .010) and the right side (P = .043) (Table 2). Overall, there was a significant correlation between the average MCI ratio and OF on both left and right sides of the mandible (P > .010) (Table 3).

Table 1  Distribution of the study population by age, sex, body mass index (BMI), and chewing side

Parameter Control (n = 65), N (%) Tori (n = 65), N (%) P value
Sex Female 41 (63.1) 41 (63.1) 1.000
Male 24 (36.9) 24 (36.9)
BMI score Underweight 4 (6.2) 3 (4.6) 411
Normal 37 (56.9) 44 (67.7)
Overweight 18 (27.7) 16 (24.6)
Obese 6 (9.2) 2 (3.1)
Age group (y) 20–29 43 (66.2) 44 (67.7) 880
30–39 11 (16.9) 9 (13.8)
40–50 11 (16.9) 12 (18.5)
Chewing side Both 24 (36.9) 30 (46.2) 553
Left 15 (23.1) 12 (18.5)
Right 26 (40.0) 23 (35.4)

Table 2  The association between occlusal force (right side, left side, average) and other variables (sex, study group, chewing side, Klemetti class)

Right side OF (N) Left side OF (N) Average OF (N)
Mean ± SD Mean ± SD Mean ± SD
Sex Female 397.5 ± 154.3 424.0 ± 165.2 410.8 ± 154.9
Male 589.4 ± 199.7 554.8 ± 209.9 572.1 ± 189.5
P value† < .001* < .001* < .001*
Group Control 416.4 ± 188.3 417.0 ± 178.6 416.7 ± 172.3
Tori 520.3 ± 189.5 527.6 ± 191.9 524.0 ± 183.0
P value† .002* .001* .001*
Chewing side Both 503.3 ± 198.7 497.9 ± 198.0 500.6 ± 188.8
Left 434.5 ± 193.4 484.4 ± 203.3 459.5 ± 191.5
Right 448.4 ± 190.2 437.4 ± 179.5 442.9 ± 175.9
P value‡ 219 265 273
Klemetti class (left) C3 407.9 ± 193.3a 419.9 ± 212.8a 413.9 ± 188.3a
C2 455.1 ± 194.8a 464.9 ± 187.7ab 460.0 ± 186.2a
C1 561.2 ± 169.6b 543.5 ± 166.4b 552.4 ± 154.2b
P value‡ .006* .038* .010*
Klemetti class (right) C3 415.1 ± 178.9a 421.5 ± 194.9a 418.3 ± 173.6a
C2 474.8 ± 193.3a 481.5 ± 187.6a 478.2 ± 185.1a
C1 539.1 ± 208.9b 531.7 ± 190.5b 535.4 ± 186.7b
P value‡ .044* 73 .043*

†Independent samples’ t test; *indicates significant associations (P < .05).

‡One-way ANOVA (values with same superscript letters are not significantly different).

Table 3  Association between occlusal force and mandibular cortical index in the study population

Parameter Right side OF (N) Left side OF (N) Average OF (N)
Left MCI ratio Pearson’s r .300** .250* .287**
P value 5 21 8
N 85 85 85
Right MCI ratio Pearson’s r .252* .230* .251*
P value 13 24 14
N 96 96 96
Average MCI ratio Pearson r .314** .67** .303**
P value 2 8 3
N 97 97 97

*Correlation is significant at the .05 level (two-tailed).

**Correlation is significant at the .01 level (two-tailed).

The majority of oral tori (50% of TP and about 72% of TM) were more than 6 mm in size, while only 16.7% of TP and 10% of TM were less than 3 mm. There was a significant difference between males and females in the distribution of Klemetti classes on both the right and the left sides of the mandible (P < .001). However, Klemetti classes did not differ significantly with regard to the preferred chewing sides (P < .050).

In addition, there was no significant difference between the control and tori groups regarding average MCI (P = .227). In females, the average MCI value was of 0.375, whilst in males it was 0.378 (P = .818). As for the chewing side, there was no significant difference between right and left sides regarding the average MCI.

In Table 4, with subjects of Klemetti class 1, the right side MCI had a mean of 0.386 ± 0.1 in the tori group compared to 0.364 ± 0.1 in the control group (P = .521). In subjects with Klemetti class 2, the right side MCI had a mean of 0.409 ± 0.1 in the tori group compared to 0.377 ± 0.1) in the control group (P = .146). However, within each of the tori and control groups there was a significant increase in the average MCI value from Klemetti class 3 to class 2 to class 1 (P > .05). A high level of agreement (76%) was found between the two radiologists regarding Klemetti’s classification ratings and calculation of the average MCI (P < .001).

Table 4  Association between MCI value and Klemetti class on both the right and left sides of the mandible in the study population

Control right MCI ratio (mean ± SD) Tori right MCI ratio (mean ± SD) P value
Klemetti class (right) C3 0.364 ± 0.0988a 0.386 ± 0.0711a 521
C2 0.377 ± 0.0772a 0.409 ± 0.0788a 146
C1 0.461 ± 0.1100b 0.499 ± 0.1536b 611
P value .031* .034*
Klemetti class (left) C3 0.375 ± 0.0895a 0.389 ± 0.1138a 763
C2 0.372 ± 0.1034a 0.421 ± 0.0622a 58
C1 0.559 ± 0.1018b 0.523 ± 0.1216b 538
P value < .001* .005*

*Correlation is significant at the .05 level (two-tailed); values with same superscript letters are not significantly different.

**Correlation is significant at the .01 level (two-tailed).


Several previous studies have been conducted to determine the prevalence of oral tori.1,3,5,7-11,13-18,20-25,27,28,38-40 The reasons behind the selection of the specific age group assessed in the current study was related to the hypothesis that oral tori occur in early adult life,6,17 as a result of maturation of the dentition,26 the strength of the jaw-closing muscles, the pain threshold of the subjects,25 and/or the risk of reduction in BMD as result of increased age.41,42

With regard to Jordanian patients, the prevalence of TP and TM was studied in 338 edentulous subjects in Jordan, and has been recorded as 29.8% for TP and 42.6% for TM. Both types of tori were associated with each other in 27.7% of cases, with no significant differences between males and females, implying that a sex-based factor has negligible influence on the prevalence of tori.16 Based on these data, the tori and non-tori (control) groups were matched in the present study (see Table 1).

The requirement for a full set of first molars in the present study was based on the effect the number of teeth have on the presence of tori, as proposed by several studies.24,26 In the first molar area, however, wide variations in human OF measurement have been recorded.43-45 Those variations can be explained by the fact that these studies have been performed on different populations using different measuring instruments and techniques.46 The selection of first molars as the preferred site for OF measurements was based on the well-accepted concept that OF is regarded as highest in that area, with a majority of vertical vectors of force. In addition, variations in OF that can occur within different regions of the oral cavity make the first molar area the first choice position for maximum voluntary OF measurements.47

The OF-meter used in the present study has been recommended for measuring the OF of subjects in dental research.43 In comparison to other devices such as deformation sensitive piezoelectric film (bite fork), novel miniature OF recorder, pressure-sensitive sheet and tube, gnathodynamometer, quartz and foil force transducer, strain gauge OF transducer, force sensitivity resistor, or electromyogram, the GM10 OF-meter was considered to be simple and accurate, and has repeatable measurements at the center of the bite element. Its accuracy is position-sensitive, in particular in anterior/posterior areas to the center; the device does not need a special mounting procedure, has a small thickness (4.5 mm), does not interfere with the tongue, is easy to change and to disinfect, and is easy to use and carry around.44 The GM10 comprises an 8.6-mm-thick bite fork and digital body. It has a high-precision load cell and uses an electronic circuit for indicating force providing precise measurements that are easy to read from its digital screen. Moreover, this appliance presents a scale in Newtons.43

It is well known that OFs in living Inuits is surprisingly high (if compared to non-circumpolar populations),48 and Alaskan Eskimos present high prevalence rates of oral tori.18,38 Consumption of dry, raw, or frozen food can lead to the production of increased loads, and this would explain an increase in OF levels.49 In the current investigation, the type of diet was not recorded as all subjects were from the same demographic area, thus sharing similar eating habits. In a previous study in Jordan, OF of subjects revealed a mean of 573 ± 140 N.46 This was comparable to the outcome of the current study; mean OFs of 524 ± 183 N was measured in subjects with oral tori (compared to 417 ± 172 N in the control group), with significant differences between males and females. The mean OF was found to be higher in males compared to females. It has been shown that muscle strength in males and females was as strong and as large until puberty.50 Moreover, it is believed that gender-related OF differences develop during the post-pubertal period in association with greater muscle development influenced by androgenic steroids in males.48,49

Calibration between observers is an important issue in measuring MCI and Klemetti’s classifications, and many previous studies reported satisfactory levels of inter- and intra-observer agreement.2,30,50 In the current study, levels of inter-observer agreement were high (76%). For the MCI measurements, inter-observer agreement was 69% (when taking into account the magnification coefficient based on the manufacturer’s instructions). Moreover, BMD was significantly related to MCI, thus indicating a direct association.

Regarding the distribution of oral tori in relation to gender, the most common type of tori in females was TP (compared to males). This is in agreement with previous studies.11,22,26,28 Statistically, the tori group revealed an increased OF of some 100 N compared to the non-tori control group. Accordingly, the null hypothesis stating “no relation between presence of tori and OF” was rejected. The location of TP and TM might suggest an exit-point for the force concentration in these areas, and deposition of exostotic bone could be stimulated by teeth, jaw bones, and/or muscles of mastication, with continuing growth later during life. This finding indeed does support the previously reported concept that functional forces are important factors in the etiology of oral tori.25,26

In terms of size, tori of more than 6 mm were the most predominant finding of the present study, followed by the 3- to 6-mm group, and finally the less than 3-mm group. This observation is in contrast to a previous investigation,28 and can be explained by skeletal and muscular maturation of an individual and the structure and number of permanent teeth as they reach adolescence.

Klemetti’s classification was positively correlated with the average OFs. Also, a positive correlation was found between MCI and the mean OF. This finding might be interpreted as an increase in OF alters the bone structure as morphologically observed, as an adaptive mechanism, and this would underline the idea of the “hard-chewing” hypothesis48 responsible for formation of exostoses.

Klemetti’s class C1 was more common in males. However, mean MCI was not statistically different between males and females. This observation could be related to fluctuation of hormones in females that might affect the morphology of the cortex, thus resulting in more frequent observations of Klemetti’s class C3 with females (being more susceptible to reduced BMD and osteoporosis).50

According to the present authors’ knowledge, the MCI has not been correlated with Klemetti’s classification or the OF in any of the previous studies. In the present investigation, Klemetti classes and MCI meas­urements were positively correlated with right, left, and mean OFs. When relating the mean MCI to Klemetti’s classification, there was an increase in the MCI mean values when there was a change in Klemetti’s class from C3 to C2 or from C2 to C1.

Dental clinicians are likely to encounter tori in daily practice. An understanding of this condition and its consequences may help make decisions regarding specific treatment plans. Based on the outcomes of the current study, recording a patient’s OF using a simple OF registration device before the initiation of treatment may help with selection of the type of restoration and the prediction of future problems due to high loads. It would seem plausible to extend the same experimental methodology to a larger sample, and to conduct a reliability trial in measuring MCI (including intra-observer reliability).


Males and patients revealing oral tori present an increased average OF. Within the limitations of the current study, it is concluded that the presence of oral tori, Klemetti’s classification, and MCI ratio could be used as indicators of an increased OF.


This work was supported by Deanship of Scientific Research/Jordan University of science and Technology (Grant Number: 2015/106). The authors thank all who contributed to this work, especially Dr Belal Al-Hazymieh (Department of Radiology, Ibn Al-Haytham Hospital, Amman, Jordan), who helped with the radiologic section of the current study.



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Ziad N. Al-Dwairi, BDS, MFDSRCS(Glasg), MFDSRCS Ed, PhD1/Ala’ N.F. Al-Daqaq, DDS, MclinDent (Prosthodontics)2/ Andrej M. Kielbassa, Prof Dr med dent Dr h c3/Edward Lynch, BDentSc, MA, FDSDentSc, PhD4