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Histological and chemical analyses of mesiodens development and mineralization
Archives of Oral Biology 87 (2018) 191–195
Contents lists available at ScienceDirect
Archives of Oral Biology journal homepage: www.elsevier.com/locate/archoralbio
Histological and chemical analyses of mesiodens development and mineralization Awady Muhamada, Moskovitz Motib, Cohen Ornita, Zilberman Uria, a b
T
⁎
Barzilai Medical University Center, Ashkelon, 7830604, Israel Department of Pediatric Dentistry, The Hebrew University – Hadassah School of Dental Medicine, Jerusalem, Israel
A R T I C L E I N F O
A B S T R A C T
Keywords: Supernumerary teeth Chemical analysis Mesiodentes Enamel
Objective: This study aimed to compare the developmental timing and mineralization quality of mesiodentes, i.e., supernumerary teeth located mainly in the midline of the maxilla between the central incisors, with the developmental timing and mineralization quality of permanent and primary central incisors. Design: Sixteen mesiodentes, nine permanent and seven primary central incisors were collected. The location of the neonatal line was determined using a light microscope at 10× or 20× enlargements. Chemical composition of the enamel at two locations was analyzed using energy dispersive X-ray spectrometer. Results: Neonatal lines were observed in eight out of 16 mesiodentes, in all primary central incisors and in none of the permanent central incisors. Chemical analyses showed that mesiodentes mineralization was impaired, resulting in higher amount of organic ions and reduced inorganic ions. Discriminant analysis showed minimal overlap of mesiodentes with either primary or permanent centrals. Conclusions: Mesiodentes development begins before birth in 50% of the cases but later than the primary centrals. Mineralization of mesiodens is impaired with less mineral content and higher organic content. The results showed that mesiodentes are a special group of teeth with defective morpho-differentiation and mineralization, with little similarity to primary or permanent central incisors.
1. Introduction
ratio (Van Buggenhout & Bailleul-Forestier, 2008; Ray, Bhattacharya, Sarkar, & Das, 2005). Variations due to differences in demographic and environmental susceptibilities may impact the reported prevalence. While the occurrence of mesiodens in primary dentition is quite rare, in permanent dentition it is considered to be the most common dental abnormality (Ferres-Padro, Prats-Armengol, & Ferres-Amat, 2009). In 82% of the cases it occurs in the maxilla (Ferres-Padro et al., 2009). Three common types of mesiodentes have been described: conical or peg-shaped, tuberculate and supplemental (Gallas & Garcia, 2000; Fernandez Montenegro et al., 2006; Prabhu, Rebecca, & Munshi, 1998). The main morphology pattern of mesiodentes is conical (Gallas & Garcia, 2000; Fernandez Montenegro et al., 2006; Prabhu et al., 1998). Conical teeth are the very primitive teeth during mammalian evolution. In humans, by 12 weeks in utero (stage II) the primary incisors crowns consist entirely of a single conical cusp, clearly delineated and occupying the incisal edge. One week later the mesial and distal portions of the incisal edge become elevated to such extent that the apex of the original cusp appears much reduced in size. Calcification of the central incisor begins at 14 weeks from only one center of calcification, and the calcification rate is faster than all other primary teeth (Kraus & Jordan,
Supernumerary teeth are extra teeth added to normal dentition. They can be single or multiple, unilateral or bilateral, erupted or impacted and located in the maxilla and/or in the mandible. These teeth are more common in the anterior region and mostly in the maxilla. The most common type of supernumerary teeth is the mesiodens, which is a supernumerary tooth located in the midline of the anterior maxilla between the maxillary central incisor teeth (Alberti, Mondani, & Parodi, 2006). The phenomenon of multiple supernumerary teeth in the midline is termed mesiodentes (Gallas & Garcia, 2000). In some syndromes, e.g. cleidocranial dysostosis, Gardner syndrome, Nance–Horan syndrome, Trichorhinophalangeal syndrome, Down syndrome and Ehlersedanlos syndrome, mesiodentes may be part of the oral signs (Van Buggenhout & Bailleul-Forestier, 2008). However, mesiodentes may also be found in normal individuals and a positive family history being one of the predisposing factors (Fernandez Montenegro, Valmaseda Castellon, Berini Aytes, & Gay Escoda, 2006). The reported prevalence in the general population ranges between 0.15–3.8%, and the phenomenon is more common in males with a 2:1
⁎
Corresponding author at: Barzilai Medical University Center, 2nd Hahistadrut st., Ashkelon, 7830604, Israel. E-mail addresses: [email protected] (A. Muhamad), [email protected] (M. Moti), [email protected] (C. Ornit), [email protected] (Z. Uri).
https://doi.org/10.1016/j.archoralbio.2017.12.020 Received 1 August 2017; Received in revised form 12 December 2017; Accepted 21 December 2017 0003-9969/ © 2017 Elsevier Ltd. All rights reserved.
Archives of Oral Biology 87 (2018) 191–195
A. Muhamad et al.
1865). In comparison with permanent peg shaped laterals, where morpho-differentiation of the crown had stopped at stage II, similar to most of the mesiodentes, the mesiodentes have shorter roots and crowns, similar to primary centrals. Mesiodentes may erupt normally but in some cases they remain impacted or erupt in an inverted position. Most are located palatal to the central incisors, and it is probable that these teeth follow an abnormal path of eruption or take an ectopic position. Unerupted mesiodentes can induce complications such as eruption path alteration of permanent teeth causing malocclusion, root resorption and cystic lesion formation (Meighani & Pakdaman, 2010). Recently it has been reported that 41% of non-extracted mesiodentes undergo a resorption of some degree, from limited to nearly complete without any pathologies involving adjacent permanent teeth (Mensah et al., 2015). The etiology of mesiodens remains unclear; but a few theories have been suggested. The genetic theory, based on the observations of familial high rate of hyperdontia (Stellzig, Basdra, & Komposch, 1997) is supported by current research that revealed that some genes may enhance the risk for dental anomalies. In syndromes where mesiodentes occur as part of the symptoms, the genetic basis might play an important role (Townsend, Richards, Hughes, Pinkerton, & Schwerdt, 2005). X-linked inheritance has been documented that may explain sex dominance in the supernumerary anomaly (Sedano & Gorlin, 1969). While according to the dichotomy theory splitting of the tooth bud into two equal or unequal sections may either form two equal sized teeth or one normal and one dysmorphic tooth (Rajab & Hamdan, 2002). The hyperactivity theory, that postulates the restricted increase in the activity of dental lamina, is considered the most etiologically acceptable (Rajab & Hamdan, 2002). It has been reported that the chronology of mesiodentes development differs from teeth of the other dentitions and their development was faster than ordinary teeth (Tyrologou, Koch, & Kurol, 2005). This study aimed to analyze the developmental chronology and mineralization quality of mesiodentes and compare these factors with the timing of development and mineralization quality of permanent and primary central incisors.
Fig 1. The location of ion content measurements at pre-natal and post-natal enamel.
2.2. Statistical analysis Using IBM SPSS software, statistical analyses (two-tailed student's ttest) were performed to compare the ion content of mesiodens and permanent or primary central incisors and also between the primary and permanent centrals, and P values were calculated. The level of statistical significance was set at P < 0.05. As a follow-up procedure for ascertaining how the groups of teeth (mesiodentes, primary and permanent incisors) differ on the composition of dependent variables, canonical discriminant functions were performed using the predictor variables, i.e., the ion contents of each tooth. Discriminant function analysis is a statistical analysis to predict a categorical dependent variable (grouping variable) by one or more continuous or binary independent variables (predictor variables). It is useful in determining whether a set of variables is effective in predicting category membership. It is used when groups are used apriori. In simple terms, discriminant function analysis is classification- the act of distributing things into groups of the same type. Discriminant analysis works by creating one or more linear combinations of predictors, creating a new latent variable for each function. The first function created maximizes the differences between groups on that function. The second function maximizes differences on that function, but also must not be correlated with the previous function. Each function is given a discriminant score to determine how well it predicts group placement.
2. Materials and methods This retrospective study included three groups of teeth – 16 mesiodentes, nine permanent central incisors and seven primary central incisors. The teeth were extracted during routine dental procedures or collected after normal exfoliation. The parents gave their approval for leaving the teeth at the clinic. The research was exempt from ethical committee approval since no personal data of the patients was used. 2.1. Scanning electron microscopy The teeth were embedded in epoxy (Epofix kit, Struers) and sliced bucco-lingually parallel to their sagittal axes, using a wafer blade (Isomet 1000, Buehler). A slice of approximately 150 μm was polished and photographed using a microscope (BestScope T3040) at ×10 and ×20 enlargements in order to detect the neonatal line. By using scanning electron microscopy (SEM; Quanta 200, Oregon, USA) under high vacuum mode in conjugation with an energy dispersive X-ray spectrometer (EDS), the ion content of two regions, squares of 0.2 × 0.2 mm, was determined in the three groups (Fig. 1). The two regions were: 1) The upper region of the crown close to the dentino-enamel junction (DEJ) representing pre-natal enamel formation in the primary centrals, 2) The cervical region of the crown close to the outer surface of enamel representing the post-natal enamel in primary centrals. On each square more than 5000 readings were performed by the EDS, and the results were given by mean and standard deviation (SD). The main ion content of each region was calculated, and the results were recorded in mol. wt% (molecular weight) units.
3. Results Table 1 shows the distribution of the mesiodentes by age and gender, Male to female ratio was 12/4. All mesiodentes were dysmorphic/conical. Neonatal lines were observed in all primary central incisors (Fig. 1) and in eight (7 males and 1 female) out of 16 mesiodentes (Fig. 2). The amount of pre-natal enamel in the mesiodentes was significantly lower than that of pre-natal enamel in the primary central incisors (Figs. 1 and 2). No neonatal line was observed in the permanent central incisors. 192
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Table 1 Distribution of the mesiodentes by age, gender, and neonatal line.
Table 2 Ion content of mesiodentes enamel in comparison to primary and permanent centrals.
Age (Y)
Gender
Type
Neonatal Line
Tooth
Ion
N
Mean
SD
9 9 6 10 12 14 9 7 12 11 10 8 9 7 8 7
M M M M F M M F F M M F M M M M
Conical Conical Conical Conical Conical Conical Conical Conical Conical Conical Conical Conical Conical Conical Conical Conical
+ + + − − − + − + + − − − + − +
Mesiodentes Primary centrals Permanent centrals Mesiodentes Primary centrals Permanent centrals Mesiodentes Primary centrals Permanent centrals Mesiodentes Primary centrals Permanent centrals Mesiodentes Primary centrals Permanent centrals Mesiodentes Primary centrals Permanent centrals Mesiodentes Primary centrals Permanent central Mesiodentes Primary centrals Permanent centrals
Ca
32 14 18 32 14 18 32 14 18 32 14 18 32 14 18 28 12 18 28 10 18 6 10 6
33.61 a,d 35.29 36.87 16.27 b,d 16.91 17.02c 41.94 a,d 40.03 39.40 6.75 c 6.11 5.30 0.77 b 0.95 d 0.76 0.44 0.40 0.40 0.27 0.22 0.24 0.16 0.28 0.16
2.05 2.41 2.03 0.59 0.58 0.77 2.32 2.35 1.55 1.87 1.65 1.87 0.18 0.20 0.15 0.19 0.17 0.17 0.10 0.06 0.07 0.06 0.29 0.03
P
O
C
Na
Cl
Mg
Si
Note: Ca = calcium, P = phosphate, O = oxygen, C = carbon, Na = sodium, Cl = chlorine, Mg = magnesium, Si = silica, N = number of measurements, SD = standard deviation. a P < .05 vs primary centrals. b P < .01 vs primary centrals. c P < .05 vs permanent centrals. d P < .01 vs permanent centrals. Table 3 Predicted group membership.
Mesiodentes Permanent Primary
Mesiodentes
Permanent
Primary
Total
13 (81.3%) 1 (11.1%) 1 (14.3%)
2 (12.5%) 7 (77.8%) 2 (28.6%)
1 (6.3%) 1 (11.1%) 4 (57.1%)
16 9 7
Note: Based on the functions created for the canonical discriminant analysis (see Fig. 3) the members of each group were analyzed in order to determine its classification to the original or other groups. The analysis showed that the mesiodentes are a specific group with 81.3% (13 out of 16 teeth) correct classification and minimal overlapping with the primary (6.3%-1 tooth) or permanent (12.5%-2 teeth) groups.
mesiodentes analyzed were grouped in the primary (1 tooth) and permanent (2 teeth) groups. These results are illustrated in Fig. 3, which demonstrate a high overlap between the areas of the primary and permanent central incisors while most of the mesiodentes are not included in either of these two groups.
Fig. 2. Location of neonatal line in a mesiodens teeth (arrow).
Table 2 shows the enamel ion content in the 32 areas measured of mesiodentes compared with the ion content of the 14 areas of primary central incisors and of the 18 areas of permanent central incisors. The statistical analyses for prenatal enamel and post natal enamel independently showed similar results so they were combined for each group for statistical purposes. The concentration of the inorganic ions, calcium and phosphate were reduced in the mesiodentes enamel in comparison to primary or permanent centrals and the differences highly significant. In the organic components, the oxygen content was significantly lower in comparison to primary or permanent centrals and the carbon content was lower but statistically significant to permanent centrals only. Of the residual ions, only sodium showed significant differences in contents between the groups. Predicted group membership found by the canonical discriminant functions analysis is shown in Table 3. Only three out of the 16
4. Discussion The hyperactivity theory considers mesiodentes to be an addition to the normal dentition. Since most mesiodentes are detected during radiographic examination of the upper anterior region, mainly during mixed dentition period or later, it may be postulated that mesiodentes are part of the permanent dentition, although a few reports have shown mesiodentes in the primary dentition (5,7). Our finding of a distinct neonatal line in 50% of the mesiodentes indicates that at least half of the mesiodentes began mineralization before birth, similar to primary dentition. The amount of prenatal enamel in mesiodentes was similar to the amount observed in the second primary molars (Keinan, Smith, & Zilberman, 2006), and less than in the primary centrals. That indicates that mesiodentes' mineralization starts during the last trimester of pregnancy. The mineral enamel content of mesiodentes was 193
Archives of Oral Biology 87 (2018) 191–195
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Fig. 3. Canonical discriminant function for the three groups of teeth analyzed.
University of Turku, Finland, for performing the SEM analyses of the enamel.
significantly different from that found in primary or permanent centrals. The main inorganic ions contents were reduced and the organic ions content was increased, showing that the mineralization process is both defective and incomplete. The content differences were more significant when compared to permanent central incisors. The canonical discriminant functions analysis showed that most mesiodentes (81.3%) did not fit in either primary or permanent teeth areas, while the permanent and primary centrals' areas overlap. The one mesiodens that did overlap with the primary teeth showed a neonatal line while in the two mesiodentes that were clustered in the permanent group no neonatal line was observed. Our finding that 50% of the mesiodentes are part of the primary dentition, may explain the resorption rate of unerupted mesiodentes found by Mensah et al. (2015). The resorption of primary teeth without a successor is a common finding, while in permanent dentition resorption is a very rare condition associated with pathological findings or hereditary abnormalities (Volodarsky, Zilberman, & Birk, 2015).
Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at https://doi.org/10.1016/j.archoralbio.2017.12.020. References Alberti, G., Mondani, P. M., & Parodi, V. (2006). Eruption of supernumerary permanent teeth in a sample of urban primary school population in Genoa, Italy. European Journal of Paediatric Dentistry, 7, 89–92. Fernandez Montenegro, P., Valmaseda Castellon, E., Berini Aytes, L., & Gay Escoda, C. (2006). Retrospective study of 145 supernumerary teeth. Medicina Oral Patologia Oral y Cirugia Bucal, 11, E339–344. Ferres-Padro, E., Prats-Armengol, J., & Ferres-Amat, E. (2009). A descriptive study of 113 unerupted supernumerary teeth in 79 pediatric patients in Barcelona. Medicina Oral, Patologia Oral y Cirugia Bucal, 14, E146–E152. Gallas, M. M., & Garcia, A. (2000). Retention of permanent incisors by mesiodens: A family affair. British Dental Journal, 188, 63–64. Keinan, D., Smith, P., & Zilberman, U. (2006). Microstructure and chemical composition of primary teeth in children with Down syndrom and cerebral palsy. Archives of Oral Biology, 51, 836–843. Kraus, B. S., & Jordan, R. E. (1865). The human dentition before birth. Philadelphia: Lea & Febiger. Meighani, G., & Pakdaman, A. (2010). Diagnosis and management of supernumerary (mesiodens): A review of the literature. Journal of Dentistry (Tehran), 7, 41–49. Mensah, T. M., Garvald, H., Grindefjord, M., Robertson, A., Koch, G., & Ullbro, C. (2015). Idiopathic resorption of impacted mesiodentes: A radiographic study. European Archives of Paediatric Dentistry, 16, 291–296. Prabhu, N. T., Rebecca, J., & Munshi, A. K. (1998). Mesiodens in the primary dentition – A case report. Journal of the Indian Society of Pedodontics and Preventive Dentistry, 16, 93–95. Rajab, L. D., & Hamdan, M. A. (2002). Supernumerary teeth: Review of the literature and a survey of 152 cases. International Journal of Paediatric Dentistry, 12, 244–254. Ray, D., Bhattacharya, B., Sarkar, S., & Das, G. (2005). Erupted maxillary conical mesiodens in deciduous dentition in a Bengali girl – A case report. Journal of the Indian Society of Pedodontics and Preventive Dentistry, 23, 153–155. Sedano, H. O., & Gorlin, R. J. (1969). Familial occurrence of mesiodens. Oral Surgery, Oral Medicine, Oral Pathology, 27, 360–361. Stellzig, A., Basdra, E. K., & Komposch, G. (1997). Mesiodentes: Incidence, morphology etiology. Journal of Orofacial Orthopedics, 58, 144–153. Townsend, G. C., Richards, L., Hughes, T., Pinkerton, S., & Schwerdt, W. (2005).
5. Conclusions Our results suggest that mesiodentes are a distinctive group of teeth with defective morpho-differentiation and mineralization. In at least 50% of cases the mineralization begins before birth later than the primary centrals, probably during the third trimester. Funding This research did not receive any specific grant from funding agencies in the public, commercial, or non-for-profit sectors. Acknowledgements Dr. Lippo Lasilla, Head of the Dental Laboratory, Turku Clinical Biomaterials Center, University of Turku, Finland, for his help with the chemical analyses. Dr. Linus Silvander, Abo Akademic Process Chemistry Center, 194
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Epigenetic influences may explain dental differences in monozygotic twin pairs. Australian Dental Journal, 50, 95–100. Tyrologou, S., Koch, G., & Kurol, J. (2005). Location, complications and treatment of mesiodentes – A retrospective study in children. Swedish Dental Journal, 29, 1–9. Van Buggenhout, G., & Bailleul-Forestier, I. (2008). Mesiodens. European Journal of
Medical Genetics, 51, 178–181. Volodarsky, M., Zilberman, U., & Birk, O. S. (2015). Novel FAM20A mutation causes autosomal recessive amelogenesis imperfecta. Archives of Oral Biology, 60, 919–922.
195
Contents lists available at ScienceDirect
Archives of Oral Biology journal homepage: www.elsevier.com/locate/archoralbio
Histological and chemical analyses of mesiodens development and mineralization Awady Muhamada, Moskovitz Motib, Cohen Ornita, Zilberman Uria, a b
T
⁎
Barzilai Medical University Center, Ashkelon, 7830604, Israel Department of Pediatric Dentistry, The Hebrew University – Hadassah School of Dental Medicine, Jerusalem, Israel
A R T I C L E I N F O
A B S T R A C T
Keywords: Supernumerary teeth Chemical analysis Mesiodentes Enamel
Objective: This study aimed to compare the developmental timing and mineralization quality of mesiodentes, i.e., supernumerary teeth located mainly in the midline of the maxilla between the central incisors, with the developmental timing and mineralization quality of permanent and primary central incisors. Design: Sixteen mesiodentes, nine permanent and seven primary central incisors were collected. The location of the neonatal line was determined using a light microscope at 10× or 20× enlargements. Chemical composition of the enamel at two locations was analyzed using energy dispersive X-ray spectrometer. Results: Neonatal lines were observed in eight out of 16 mesiodentes, in all primary central incisors and in none of the permanent central incisors. Chemical analyses showed that mesiodentes mineralization was impaired, resulting in higher amount of organic ions and reduced inorganic ions. Discriminant analysis showed minimal overlap of mesiodentes with either primary or permanent centrals. Conclusions: Mesiodentes development begins before birth in 50% of the cases but later than the primary centrals. Mineralization of mesiodens is impaired with less mineral content and higher organic content. The results showed that mesiodentes are a special group of teeth with defective morpho-differentiation and mineralization, with little similarity to primary or permanent central incisors.
1. Introduction
ratio (Van Buggenhout & Bailleul-Forestier, 2008; Ray, Bhattacharya, Sarkar, & Das, 2005). Variations due to differences in demographic and environmental susceptibilities may impact the reported prevalence. While the occurrence of mesiodens in primary dentition is quite rare, in permanent dentition it is considered to be the most common dental abnormality (Ferres-Padro, Prats-Armengol, & Ferres-Amat, 2009). In 82% of the cases it occurs in the maxilla (Ferres-Padro et al., 2009). Three common types of mesiodentes have been described: conical or peg-shaped, tuberculate and supplemental (Gallas & Garcia, 2000; Fernandez Montenegro et al., 2006; Prabhu, Rebecca, & Munshi, 1998). The main morphology pattern of mesiodentes is conical (Gallas & Garcia, 2000; Fernandez Montenegro et al., 2006; Prabhu et al., 1998). Conical teeth are the very primitive teeth during mammalian evolution. In humans, by 12 weeks in utero (stage II) the primary incisors crowns consist entirely of a single conical cusp, clearly delineated and occupying the incisal edge. One week later the mesial and distal portions of the incisal edge become elevated to such extent that the apex of the original cusp appears much reduced in size. Calcification of the central incisor begins at 14 weeks from only one center of calcification, and the calcification rate is faster than all other primary teeth (Kraus & Jordan,
Supernumerary teeth are extra teeth added to normal dentition. They can be single or multiple, unilateral or bilateral, erupted or impacted and located in the maxilla and/or in the mandible. These teeth are more common in the anterior region and mostly in the maxilla. The most common type of supernumerary teeth is the mesiodens, which is a supernumerary tooth located in the midline of the anterior maxilla between the maxillary central incisor teeth (Alberti, Mondani, & Parodi, 2006). The phenomenon of multiple supernumerary teeth in the midline is termed mesiodentes (Gallas & Garcia, 2000). In some syndromes, e.g. cleidocranial dysostosis, Gardner syndrome, Nance–Horan syndrome, Trichorhinophalangeal syndrome, Down syndrome and Ehlersedanlos syndrome, mesiodentes may be part of the oral signs (Van Buggenhout & Bailleul-Forestier, 2008). However, mesiodentes may also be found in normal individuals and a positive family history being one of the predisposing factors (Fernandez Montenegro, Valmaseda Castellon, Berini Aytes, & Gay Escoda, 2006). The reported prevalence in the general population ranges between 0.15–3.8%, and the phenomenon is more common in males with a 2:1
⁎
Corresponding author at: Barzilai Medical University Center, 2nd Hahistadrut st., Ashkelon, 7830604, Israel. E-mail addresses: [email protected] (A. Muhamad), [email protected] (M. Moti), [email protected] (C. Ornit), [email protected] (Z. Uri).
https://doi.org/10.1016/j.archoralbio.2017.12.020 Received 1 August 2017; Received in revised form 12 December 2017; Accepted 21 December 2017 0003-9969/ © 2017 Elsevier Ltd. All rights reserved.
Archives of Oral Biology 87 (2018) 191–195
A. Muhamad et al.
1865). In comparison with permanent peg shaped laterals, where morpho-differentiation of the crown had stopped at stage II, similar to most of the mesiodentes, the mesiodentes have shorter roots and crowns, similar to primary centrals. Mesiodentes may erupt normally but in some cases they remain impacted or erupt in an inverted position. Most are located palatal to the central incisors, and it is probable that these teeth follow an abnormal path of eruption or take an ectopic position. Unerupted mesiodentes can induce complications such as eruption path alteration of permanent teeth causing malocclusion, root resorption and cystic lesion formation (Meighani & Pakdaman, 2010). Recently it has been reported that 41% of non-extracted mesiodentes undergo a resorption of some degree, from limited to nearly complete without any pathologies involving adjacent permanent teeth (Mensah et al., 2015). The etiology of mesiodens remains unclear; but a few theories have been suggested. The genetic theory, based on the observations of familial high rate of hyperdontia (Stellzig, Basdra, & Komposch, 1997) is supported by current research that revealed that some genes may enhance the risk for dental anomalies. In syndromes where mesiodentes occur as part of the symptoms, the genetic basis might play an important role (Townsend, Richards, Hughes, Pinkerton, & Schwerdt, 2005). X-linked inheritance has been documented that may explain sex dominance in the supernumerary anomaly (Sedano & Gorlin, 1969). While according to the dichotomy theory splitting of the tooth bud into two equal or unequal sections may either form two equal sized teeth or one normal and one dysmorphic tooth (Rajab & Hamdan, 2002). The hyperactivity theory, that postulates the restricted increase in the activity of dental lamina, is considered the most etiologically acceptable (Rajab & Hamdan, 2002). It has been reported that the chronology of mesiodentes development differs from teeth of the other dentitions and their development was faster than ordinary teeth (Tyrologou, Koch, & Kurol, 2005). This study aimed to analyze the developmental chronology and mineralization quality of mesiodentes and compare these factors with the timing of development and mineralization quality of permanent and primary central incisors.
Fig 1. The location of ion content measurements at pre-natal and post-natal enamel.
2.2. Statistical analysis Using IBM SPSS software, statistical analyses (two-tailed student's ttest) were performed to compare the ion content of mesiodens and permanent or primary central incisors and also between the primary and permanent centrals, and P values were calculated. The level of statistical significance was set at P < 0.05. As a follow-up procedure for ascertaining how the groups of teeth (mesiodentes, primary and permanent incisors) differ on the composition of dependent variables, canonical discriminant functions were performed using the predictor variables, i.e., the ion contents of each tooth. Discriminant function analysis is a statistical analysis to predict a categorical dependent variable (grouping variable) by one or more continuous or binary independent variables (predictor variables). It is useful in determining whether a set of variables is effective in predicting category membership. It is used when groups are used apriori. In simple terms, discriminant function analysis is classification- the act of distributing things into groups of the same type. Discriminant analysis works by creating one or more linear combinations of predictors, creating a new latent variable for each function. The first function created maximizes the differences between groups on that function. The second function maximizes differences on that function, but also must not be correlated with the previous function. Each function is given a discriminant score to determine how well it predicts group placement.
2. Materials and methods This retrospective study included three groups of teeth – 16 mesiodentes, nine permanent central incisors and seven primary central incisors. The teeth were extracted during routine dental procedures or collected after normal exfoliation. The parents gave their approval for leaving the teeth at the clinic. The research was exempt from ethical committee approval since no personal data of the patients was used. 2.1. Scanning electron microscopy The teeth were embedded in epoxy (Epofix kit, Struers) and sliced bucco-lingually parallel to their sagittal axes, using a wafer blade (Isomet 1000, Buehler). A slice of approximately 150 μm was polished and photographed using a microscope (BestScope T3040) at ×10 and ×20 enlargements in order to detect the neonatal line. By using scanning electron microscopy (SEM; Quanta 200, Oregon, USA) under high vacuum mode in conjugation with an energy dispersive X-ray spectrometer (EDS), the ion content of two regions, squares of 0.2 × 0.2 mm, was determined in the three groups (Fig. 1). The two regions were: 1) The upper region of the crown close to the dentino-enamel junction (DEJ) representing pre-natal enamel formation in the primary centrals, 2) The cervical region of the crown close to the outer surface of enamel representing the post-natal enamel in primary centrals. On each square more than 5000 readings were performed by the EDS, and the results were given by mean and standard deviation (SD). The main ion content of each region was calculated, and the results were recorded in mol. wt% (molecular weight) units.
3. Results Table 1 shows the distribution of the mesiodentes by age and gender, Male to female ratio was 12/4. All mesiodentes were dysmorphic/conical. Neonatal lines were observed in all primary central incisors (Fig. 1) and in eight (7 males and 1 female) out of 16 mesiodentes (Fig. 2). The amount of pre-natal enamel in the mesiodentes was significantly lower than that of pre-natal enamel in the primary central incisors (Figs. 1 and 2). No neonatal line was observed in the permanent central incisors. 192
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Table 1 Distribution of the mesiodentes by age, gender, and neonatal line.
Table 2 Ion content of mesiodentes enamel in comparison to primary and permanent centrals.
Age (Y)
Gender
Type
Neonatal Line
Tooth
Ion
N
Mean
SD
9 9 6 10 12 14 9 7 12 11 10 8 9 7 8 7
M M M M F M M F F M M F M M M M
Conical Conical Conical Conical Conical Conical Conical Conical Conical Conical Conical Conical Conical Conical Conical Conical
+ + + − − − + − + + − − − + − +
Mesiodentes Primary centrals Permanent centrals Mesiodentes Primary centrals Permanent centrals Mesiodentes Primary centrals Permanent centrals Mesiodentes Primary centrals Permanent centrals Mesiodentes Primary centrals Permanent centrals Mesiodentes Primary centrals Permanent centrals Mesiodentes Primary centrals Permanent central Mesiodentes Primary centrals Permanent centrals
Ca
32 14 18 32 14 18 32 14 18 32 14 18 32 14 18 28 12 18 28 10 18 6 10 6
33.61 a,d 35.29 36.87 16.27 b,d 16.91 17.02c 41.94 a,d 40.03 39.40 6.75 c 6.11 5.30 0.77 b 0.95 d 0.76 0.44 0.40 0.40 0.27 0.22 0.24 0.16 0.28 0.16
2.05 2.41 2.03 0.59 0.58 0.77 2.32 2.35 1.55 1.87 1.65 1.87 0.18 0.20 0.15 0.19 0.17 0.17 0.10 0.06 0.07 0.06 0.29 0.03
P
O
C
Na
Cl
Mg
Si
Note: Ca = calcium, P = phosphate, O = oxygen, C = carbon, Na = sodium, Cl = chlorine, Mg = magnesium, Si = silica, N = number of measurements, SD = standard deviation. a P < .05 vs primary centrals. b P < .01 vs primary centrals. c P < .05 vs permanent centrals. d P < .01 vs permanent centrals. Table 3 Predicted group membership.
Mesiodentes Permanent Primary
Mesiodentes
Permanent
Primary
Total
13 (81.3%) 1 (11.1%) 1 (14.3%)
2 (12.5%) 7 (77.8%) 2 (28.6%)
1 (6.3%) 1 (11.1%) 4 (57.1%)
16 9 7
Note: Based on the functions created for the canonical discriminant analysis (see Fig. 3) the members of each group were analyzed in order to determine its classification to the original or other groups. The analysis showed that the mesiodentes are a specific group with 81.3% (13 out of 16 teeth) correct classification and minimal overlapping with the primary (6.3%-1 tooth) or permanent (12.5%-2 teeth) groups.
mesiodentes analyzed were grouped in the primary (1 tooth) and permanent (2 teeth) groups. These results are illustrated in Fig. 3, which demonstrate a high overlap between the areas of the primary and permanent central incisors while most of the mesiodentes are not included in either of these two groups.
Fig. 2. Location of neonatal line in a mesiodens teeth (arrow).
Table 2 shows the enamel ion content in the 32 areas measured of mesiodentes compared with the ion content of the 14 areas of primary central incisors and of the 18 areas of permanent central incisors. The statistical analyses for prenatal enamel and post natal enamel independently showed similar results so they were combined for each group for statistical purposes. The concentration of the inorganic ions, calcium and phosphate were reduced in the mesiodentes enamel in comparison to primary or permanent centrals and the differences highly significant. In the organic components, the oxygen content was significantly lower in comparison to primary or permanent centrals and the carbon content was lower but statistically significant to permanent centrals only. Of the residual ions, only sodium showed significant differences in contents between the groups. Predicted group membership found by the canonical discriminant functions analysis is shown in Table 3. Only three out of the 16
4. Discussion The hyperactivity theory considers mesiodentes to be an addition to the normal dentition. Since most mesiodentes are detected during radiographic examination of the upper anterior region, mainly during mixed dentition period or later, it may be postulated that mesiodentes are part of the permanent dentition, although a few reports have shown mesiodentes in the primary dentition (5,7). Our finding of a distinct neonatal line in 50% of the mesiodentes indicates that at least half of the mesiodentes began mineralization before birth, similar to primary dentition. The amount of prenatal enamel in mesiodentes was similar to the amount observed in the second primary molars (Keinan, Smith, & Zilberman, 2006), and less than in the primary centrals. That indicates that mesiodentes' mineralization starts during the last trimester of pregnancy. The mineral enamel content of mesiodentes was 193
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Fig. 3. Canonical discriminant function for the three groups of teeth analyzed.
University of Turku, Finland, for performing the SEM analyses of the enamel.
significantly different from that found in primary or permanent centrals. The main inorganic ions contents were reduced and the organic ions content was increased, showing that the mineralization process is both defective and incomplete. The content differences were more significant when compared to permanent central incisors. The canonical discriminant functions analysis showed that most mesiodentes (81.3%) did not fit in either primary or permanent teeth areas, while the permanent and primary centrals' areas overlap. The one mesiodens that did overlap with the primary teeth showed a neonatal line while in the two mesiodentes that were clustered in the permanent group no neonatal line was observed. Our finding that 50% of the mesiodentes are part of the primary dentition, may explain the resorption rate of unerupted mesiodentes found by Mensah et al. (2015). The resorption of primary teeth without a successor is a common finding, while in permanent dentition resorption is a very rare condition associated with pathological findings or hereditary abnormalities (Volodarsky, Zilberman, & Birk, 2015).
Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at https://doi.org/10.1016/j.archoralbio.2017.12.020. References Alberti, G., Mondani, P. M., & Parodi, V. (2006). Eruption of supernumerary permanent teeth in a sample of urban primary school population in Genoa, Italy. European Journal of Paediatric Dentistry, 7, 89–92. Fernandez Montenegro, P., Valmaseda Castellon, E., Berini Aytes, L., & Gay Escoda, C. (2006). Retrospective study of 145 supernumerary teeth. Medicina Oral Patologia Oral y Cirugia Bucal, 11, E339–344. Ferres-Padro, E., Prats-Armengol, J., & Ferres-Amat, E. (2009). A descriptive study of 113 unerupted supernumerary teeth in 79 pediatric patients in Barcelona. Medicina Oral, Patologia Oral y Cirugia Bucal, 14, E146–E152. Gallas, M. M., & Garcia, A. (2000). Retention of permanent incisors by mesiodens: A family affair. British Dental Journal, 188, 63–64. Keinan, D., Smith, P., & Zilberman, U. (2006). Microstructure and chemical composition of primary teeth in children with Down syndrom and cerebral palsy. Archives of Oral Biology, 51, 836–843. Kraus, B. S., & Jordan, R. E. (1865). The human dentition before birth. Philadelphia: Lea & Febiger. Meighani, G., & Pakdaman, A. (2010). Diagnosis and management of supernumerary (mesiodens): A review of the literature. Journal of Dentistry (Tehran), 7, 41–49. Mensah, T. M., Garvald, H., Grindefjord, M., Robertson, A., Koch, G., & Ullbro, C. (2015). Idiopathic resorption of impacted mesiodentes: A radiographic study. European Archives of Paediatric Dentistry, 16, 291–296. Prabhu, N. T., Rebecca, J., & Munshi, A. K. (1998). Mesiodens in the primary dentition – A case report. Journal of the Indian Society of Pedodontics and Preventive Dentistry, 16, 93–95. Rajab, L. D., & Hamdan, M. A. (2002). Supernumerary teeth: Review of the literature and a survey of 152 cases. International Journal of Paediatric Dentistry, 12, 244–254. Ray, D., Bhattacharya, B., Sarkar, S., & Das, G. (2005). Erupted maxillary conical mesiodens in deciduous dentition in a Bengali girl – A case report. Journal of the Indian Society of Pedodontics and Preventive Dentistry, 23, 153–155. Sedano, H. O., & Gorlin, R. J. (1969). Familial occurrence of mesiodens. Oral Surgery, Oral Medicine, Oral Pathology, 27, 360–361. Stellzig, A., Basdra, E. K., & Komposch, G. (1997). Mesiodentes: Incidence, morphology etiology. Journal of Orofacial Orthopedics, 58, 144–153. Townsend, G. C., Richards, L., Hughes, T., Pinkerton, S., & Schwerdt, W. (2005).
5. Conclusions Our results suggest that mesiodentes are a distinctive group of teeth with defective morpho-differentiation and mineralization. In at least 50% of cases the mineralization begins before birth later than the primary centrals, probably during the third trimester. Funding This research did not receive any specific grant from funding agencies in the public, commercial, or non-for-profit sectors. Acknowledgements Dr. Lippo Lasilla, Head of the Dental Laboratory, Turku Clinical Biomaterials Center, University of Turku, Finland, for his help with the chemical analyses. Dr. Linus Silvander, Abo Akademic Process Chemistry Center, 194
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Epigenetic influences may explain dental differences in monozygotic twin pairs. Australian Dental Journal, 50, 95–100. Tyrologou, S., Koch, G., & Kurol, J. (2005). Location, complications and treatment of mesiodentes – A retrospective study in children. Swedish Dental Journal, 29, 1–9. Van Buggenhout, G., & Bailleul-Forestier, I. (2008). Mesiodens. European Journal of
Medical Genetics, 51, 178–181. Volodarsky, M., Zilberman, U., & Birk, O. S. (2015). Novel FAM20A mutation causes autosomal recessive amelogenesis imperfecta. Archives of Oral Biology, 60, 919–922.
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