Three-rooted permanent mandibular first molars of Asian and black groups in the Middle East Salwa Abdelsamad Younes, BDS, HDD, PhD,” Abdullah Rakeeb Al-Shammery, BDS, IQL!!,~and Mohammad Farouk Ei-Angbawi, BDS, HDD, PhD,’ Alexandria, Egypt, and Riyadh, Saudi Arabia KING SAUD UNIVERSITY The occurrence of supplementary roots of the lower first permanent molars is 2.33% for a Saudi group of Asiatic descendants and 0.65% for an Egyptian group of African descendants. The most prominent finding demonstrated in this study is the lower percentage of occurrence of the third root among the Saudi samples compared to other Asiatic samples in other studies. Furthermore, this study confirmed the occurrence of the anomaly in our African samples, and the clinical situation illustrates the importance of early diagnosis to avoid complications for such molars by dental practitioners. (ORAL SURC ORAL MED ORAL PATHOI.
3990;69:102-5)
C
linical situations vary widely, and more conservative designs will be required before the initiation of treatment, when three-rooted mandibular first molar traits dictate, to determine what special precautions must be taken. Some elective treatments might be eliminated or postponed because of the anatomic variations.‘-3 However, a number of investigations presenting data on the frequency of occurrence of three-rooted mandibular molars have been reported in studies of different races and populations. The three main ethnic groups, namely Asian, white, and black, all have some anatomic variations.‘-6 Mongoloids show a greater incidence of an additional distal root. The findings indicate that the anomaly occurs in as many as 43.6% of the Aleutians.4 In the Japanese, that figure was 20%.7In the Thai people, it was shown to be 19.2%.6The frequency of the anomaly in the Malay people reportedly varies from 12% to 16.3%.8.9In Eskimo populations, a figure of 12.5%,l” and in the Chinese, a figure of 8%,9were reported. ‘Associate Professor, Faculty of Dentistry, Alexandria University. Alexandria, Egypt. I,..:. .-...::. ,” . .v.eaavI .L,A ‘I’& ihd~i, iuiirge 0i L)entmry, Kmg Saud University Riyadh, Saudi Arabia. ‘Specialist, private clinic. Alexandria, Egypt. 7/15/11109
102
With respect to the other two main ethnic groups, the incidence of three-rooted permanent mandibular first molars, (TRPMFM) in white persons reportedly varies from 0.9% to 4.3%,2s7but it has never been reported in black persons.* In addition, the available data, on white and black people are sparse, and no published surveys have been taken for people of mixed races. Observations with respect to TRPMFM are important to clinicians and may be of interest to oral biologists, anthropologists, and forensic specialists. These facts persuaded us to conduct a study of the incidence of three-rooted permanent mandibular first molars of two well-defined racial group descendants of Asiatic and of African origin in the Middle East population. MATERIALS
AND METHODS
Observations were divided into three phasesin the two ethnic groups at the same time. The first phase was carried on 842 extracted lower first permanent mandibular molars. Asiatic descent was represented by 385 extracted teeth from Saudi patients treated in central Saudi hospitals (ElShemessiHospital) and the outpatient clinic of King Saud University College of Dentistry in Riyadh, Saudi Arabia; African descent was represented in 457 extracted teeth from Egyptian patients who
Volume Number
Three-rooted
69 1
permanent
mandibular
first molars
103
1. Examples of first permanent lower molars with (1) distal supplementary root, (2) mesial supplementary root, and (3) distal and mesial roots bifurcation.
Fig.
Table 1. Number and percentage of first lower permanent to ethnic group and for total sample Second First
Nationality
Saudi Egyptian Saudi and Egyptian
Extracted teeth 385 457 842
phase
Teeth with third root 9 3 12
9%
Extracted teeth
2.33% 0.65% 1.42%
56 12 128
molars with a supplementary
phase
Third
Extracted teeth with third root 2 1 3
%
No. of patients
3.57% 1.38% 2.34%
140 105 245
root according phase
No. of x-Rays of side 280 210 490
No. of patients with third root
%
6 2 8
2.14% 0.95% 1.63%
-
came to the Department of Oral Surgery at the College of Dentistry in Alexandria University in Egypt for extraction of their teeth or attended a private clinic. All extracted teeth were fixed in 5% formalin and examined for root anomalies. The second phase involved 56 extracted mandibular first molars of Saudi patients from the King Saud University College of Dentistry and 72 extracted mandibular molars of Egyptian patients from a private clinic. All patients were scheduled for teeth extraction. Radiographs of each extracted tooth were examined and compared with the results of the visual examination. The third phase consisted of examining the files and radiographs of 170 randomly selected Saudi patients who were being treated at the King Saud University College of Dentistry. Full-mouth periapical and bitewing radiographs were made as part of a routine examination at the college in Riyadh. A total of 280 molars of Saudi patients and 210 molars of Egyptian patients were examined radiographically.
In view of the small number of anomalies of the first lower permanent molar represented in this study, no attempt has been made to categorize the observations according to gender or tribe. Also, right and left teeth were grouped. Statistical analysis with the use of the computer was not possible because of the small number of anomalies of the TRPMFM compared to the sample size. The radiographically short cone technique was employed for radiographic examination to reveal the existence of the pulp in the third roots. Kodak Ultraspeed films were used, exposed, and processed according to the manufacturer’s instructions. In this study, we did not consider bifurcation of the root as a supplementary root. A real supplementary root is that which is found on the lingual side of the distal root of the lower first permanent molars. RESULTS
The frequencies of the TRPMFM are shown in Table I.
for both groups
104
Younes, Al-Shammery,
First
phase
and El-Angbawi
The results show that the occurrence of supplementary roots on the lower first permanent molars is 2.33% for Asiatic descendants and 0.65% for African descendants. Ethnic comparison reveals greater differences for Asiatic patients in this study. The number of extra roots on the lower first permanent molars of combined Saudi and Egyptian groups as samples of Middle Eastern population was small (1.42%) (Fig. 1). Second
phase
The results of the radiographic examination were compared with the results of the visual examination of the extracted teeth to determine their accuracy. In three mandibular first molars from the Saudi group thought to have three roots instead of two, the anomaly was not actually found until postextraction radiographs were examined. In the Egyptian group, one radiograph was thought to show a TRPMFM. But after extraction, no TRPMFM was present. In another patient, radiographs revealed no root variation, but after extraction, the tooth was found to have three roots. Third
phase
In a comparison of the radiographic results of the two ethnic groups, the radiographs of 140 Saudi patients were examined and were determined to show at least four mandibular first molars with three roots. Radiographs of Egyptian patients revealed that 2 of 105 had at least one TRPMFM. Morphologically, the supplementary root was situated distolingually, and it was a separated and independent root even when its base was in connection with the distal root. It was varied in size but smaller than both distobuccal and mesial roots and had a bent shape. The lower first permanent molar had a supplementary mesial root in 0.51% of Saudi patients and 0.21% of Egyptian patients. Radiographically, it revealed the presence of the pulpal extension into the supplementary root in the root canal, and its base was in connection with the main pulp cavity. DISCUSSION
The previous study”-l3 confirmed that the first permanent molar is the most important tooth in the dentition. This importance is mainly the result of its po;i:;,i; Ziiiu’ p..--r’-luu~clUll. ‘I Furthermore, histologically, there are certain unique characteristics attributed to the first permanent molar inasmuch as it is the only permanent tooth to be developed directly from
ORAL
SURG
ORAL
MED
ORAL PATHOL January 1990
the dental lamina.‘* However, the exact cause of the third root in the lower first permanent molars remains uncertain since the first description in 1908 as one of the anatomic variations.r3 Our results emphasize that the third root is separate, independent, and isolated, although its base is in connection with the distal root. Morphologically, as well as radiographically, it has a separate pulpal extension into the third root. These results agree with the findings of Freitas and coworkers* and other.+ I43I5 and refute Adloff s theoryi3 inasmuch as he stated that this root is a result of distal root bifurcation as well as refuting Balk’s theoryI since he stated that it is found only on the first molars and considers it as a last manifestation of monoplatyrrhiness third premolars, an element that in the monocatyrrines and in man was lost. The results of this study show that there are precentages of doubt of radiographic accuracy in the second and third phases. For this reason, the criteria established in the first phase were used to determine the frequency of the three-rooted mandibular first molars in both ethnic groups. In this study, the Saudi sample had a higher incidence of three-rooted lower first molar teeth than the Egyptian sample. This agrees with the other studies demonstrating that the Asiatic population has a higher incidence of anatomic variations.4*6-‘0 The most prominent finding demonstrated in this study is the lower percentage of occurrence of the third root among the Saudi samples as an Asiatic group compared to other Asiatic samples in other studies.3, G’O Turner4 in 197 1, found that a supplementary root was absent in some African tribes, but this study confirms the presence of teeth as equal the third phase only. In this study the method used to determine the frequency of TRPMFM was no more accurate than the crossing of the translucent lines to define the pulp space and the periodontal ligament as indicated by Walker and Quackenbush.3 We suggest more studies, as required, to provide special positions and angles for the x-ray tube or the use of special coloring agent injection before radiographs are taken to determine these anomalies with a higher percentage of accuracy. The third goal was formulated because the clinical situation of the third root has been reported by several authors.le3 The cases in this study also illustrate the importance of early diagnosis to avoid complications and to allow sufficient time for successful treatment by the dental practitioner. It is not within the scope of this article to describe all the clinical situations that might influence patient
Volume Number
69 1
treatment. However, there are some that occur frequently and should be appreciated by the patient and the dental practitioner. Often, extraction of these teeth proves very difficult and fracture of their supernumerary root occurs. Endodontic failure occurs if the presence of the third root canal is not well recognized. In orthodontic treatment, patients who have a third root may require special handling to move this tooth. On the other hand, an extra root can provide a firm anchor during orthodontic therapy. For the prosthodontist, selection of the artificial device type and design in both removable and fixed prosthodontics may be affected by the presence of the third root inasmuch as this multirooted distribution is an important point in the assessment of an abutment. CONCLUSION
Ethnic comparison reveals greater differences for Asiatic than for African patients in occurrence of TRPMFM. The Middle Eastern population shows the characteristic percentage more than the other various races reported. The combined data of the two ethnic groups in this study demonstrate lower prevalence of supplementary roots. These cases may serve to emphasize the incomplete knowledge of the exact anatomic variation of the lower first permanent molar roots in the two ethnic groups of the Middle Eastern population. Furthermore, this study shows the presence of variability of anomaly between the Middle Eastern population and other populations. The differences in the occurrence of TRPMFM between the Middle Eastern subjects and other Mongoloid and white persons may be due to diverse genetic, socioeconomic, and environmental factors and functional bases for these populations. This article advocates future studies by oral biologists and anthropologists as a first goal to determine the exact cause of the anomalies of the first lower molar. The second goal evolved from the finding that there is some doubt as to whether radiographic or visual examination of the extracted teeth provides the most accurate criteria for determining the incidence of the anomalies. This study advocates future investigations in three areas: 1. Determination of the exact cause of TRPMFM by oral biologists and anthropologists.
Three-rooted permanent mandibular first molars
105
2. Introduction of new practical radiographic methods to increase the accuracy of identification of the root anomalies by radiologists. 3. Introduction of special handling in treatment of TRPMFM by clinicians in the fields of endodontics, orthodontics, prosthodontics, periodontics, and oral surgery. REFERENCES 1 Jones AW. Dental morphology in people of Mongoloid origin. Odontostomatol Trop 1981;3:165-9. 2. Souza-Freitas JA, Lopez ES, Casati-Alvarez L. Anatomic variations of lower first permanent molar roots in two ethnic groups. ORAL SURG ORAL MED ORAL PATHOL 1971;31: 274-8. 3. Walker RT, Quackenbush LE. Three-rooted lower first permanent molars in Hong Kong Chinese. Br Dent J 1985; 159:298-9. 4. Turner CG. Three-rooted mandibular first permanent molars and the question of American Indian origins. Am J Phys Anthropol 1971;34:229-42. 5. Curzon MEJ. Three-rooted mandibular permanent molars in English Caucasians. J Dent Res 1973;52:181-5. 6. Reichart PA, Metacch D. Three-rooted permanent mandibular first molars in the Thai. Community Dent Oral Epidemiol 1981;9:191-2. I. Hjelman G. Morphologische Becobachtungen an den Zahnen der Finnen. Acta Sot Med Finn 1928;11:1-6. (Cited by Reichart and Metacch.“) 8. Jones AW. The incidence of three-rooted lower first permanent molar in Malay people. Sing Dent J 5:1. 9. Tratman EK. Three-rooted lower molars in man and their racial distribution. Br Dent J 1938;64:264-7. 10. Pedersen PO. The Cast Greenland Eskimo dentition. Numerical variations and anatomy. [Thesis.] Copenhagen: C.A. Reitzels forlag, 1949. (Cited by Reichart and Metacch.6) Il. Tsamtsouris A. A review of the importance of the first permanent molar. J Pedod 1980;236-48. 12. Noyes, Schour, Noyes. Dental histology and embryology 5th ed. Philadelphia: Lea & Febiger, 1938:16-49. 13. Adloff P. Das Gebiss des Menschen and der Anthropomorphen. Berlin: Springer-Verlag, 1908 (Cited by Souza-Freitas et aL2) 14. Curzon MEJ. Miscegenation and the prevalence of threerooted mandibular first molars in Baffin Eskimo. Community Dent Oral Epidemiol 1974;2: 130- 1. 15. Somogyi-Csizmazia W, Simons AJ. Three-rooted mandibular first permanent molars in Alberta Indian children. Can Dent Assoc J 1971;37:105-6. 16. Bolk L. Bumerkungen Uber Wurzeivariationen am Menschlichen Unteren Molaren. Zeitschrift fur Morphologie und Anthropologie 1915 (Cited by Souza-Freitas et al.“) Reprint
requests
to:
Abdullah Rakeeb Al-Shammery, BDS, MS Assistant Professor and Vice Dean College of Dentistry, King Saud University, Riyadh 11545 Saudi Arabia
P.O. Box 60169
3990;69:102-5)
C
linical situations vary widely, and more conservative designs will be required before the initiation of treatment, when three-rooted mandibular first molar traits dictate, to determine what special precautions must be taken. Some elective treatments might be eliminated or postponed because of the anatomic variations.‘-3 However, a number of investigations presenting data on the frequency of occurrence of three-rooted mandibular molars have been reported in studies of different races and populations. The three main ethnic groups, namely Asian, white, and black, all have some anatomic variations.‘-6 Mongoloids show a greater incidence of an additional distal root. The findings indicate that the anomaly occurs in as many as 43.6% of the Aleutians.4 In the Japanese, that figure was 20%.7In the Thai people, it was shown to be 19.2%.6The frequency of the anomaly in the Malay people reportedly varies from 12% to 16.3%.8.9In Eskimo populations, a figure of 12.5%,l” and in the Chinese, a figure of 8%,9were reported. ‘Associate Professor, Faculty of Dentistry, Alexandria University. Alexandria, Egypt. I,..:. .-...::. ,” . .v.eaavI .L,A ‘I’& ihd~i, iuiirge 0i L)entmry, Kmg Saud University Riyadh, Saudi Arabia. ‘Specialist, private clinic. Alexandria, Egypt. 7/15/11109
102
With respect to the other two main ethnic groups, the incidence of three-rooted permanent mandibular first molars, (TRPMFM) in white persons reportedly varies from 0.9% to 4.3%,2s7but it has never been reported in black persons.* In addition, the available data, on white and black people are sparse, and no published surveys have been taken for people of mixed races. Observations with respect to TRPMFM are important to clinicians and may be of interest to oral biologists, anthropologists, and forensic specialists. These facts persuaded us to conduct a study of the incidence of three-rooted permanent mandibular first molars of two well-defined racial group descendants of Asiatic and of African origin in the Middle East population. MATERIALS
AND METHODS
Observations were divided into three phasesin the two ethnic groups at the same time. The first phase was carried on 842 extracted lower first permanent mandibular molars. Asiatic descent was represented by 385 extracted teeth from Saudi patients treated in central Saudi hospitals (ElShemessiHospital) and the outpatient clinic of King Saud University College of Dentistry in Riyadh, Saudi Arabia; African descent was represented in 457 extracted teeth from Egyptian patients who
Volume Number
Three-rooted
69 1
permanent
mandibular
first molars
103
1. Examples of first permanent lower molars with (1) distal supplementary root, (2) mesial supplementary root, and (3) distal and mesial roots bifurcation.
Fig.
Table 1. Number and percentage of first lower permanent to ethnic group and for total sample Second First
Nationality
Saudi Egyptian Saudi and Egyptian
Extracted teeth 385 457 842
phase
Teeth with third root 9 3 12
9%
Extracted teeth
2.33% 0.65% 1.42%
56 12 128
molars with a supplementary
phase
Third
Extracted teeth with third root 2 1 3
%
No. of patients
3.57% 1.38% 2.34%
140 105 245
root according phase
No. of x-Rays of side 280 210 490
No. of patients with third root
%
6 2 8
2.14% 0.95% 1.63%
-
came to the Department of Oral Surgery at the College of Dentistry in Alexandria University in Egypt for extraction of their teeth or attended a private clinic. All extracted teeth were fixed in 5% formalin and examined for root anomalies. The second phase involved 56 extracted mandibular first molars of Saudi patients from the King Saud University College of Dentistry and 72 extracted mandibular molars of Egyptian patients from a private clinic. All patients were scheduled for teeth extraction. Radiographs of each extracted tooth were examined and compared with the results of the visual examination. The third phase consisted of examining the files and radiographs of 170 randomly selected Saudi patients who were being treated at the King Saud University College of Dentistry. Full-mouth periapical and bitewing radiographs were made as part of a routine examination at the college in Riyadh. A total of 280 molars of Saudi patients and 210 molars of Egyptian patients were examined radiographically.
In view of the small number of anomalies of the first lower permanent molar represented in this study, no attempt has been made to categorize the observations according to gender or tribe. Also, right and left teeth were grouped. Statistical analysis with the use of the computer was not possible because of the small number of anomalies of the TRPMFM compared to the sample size. The radiographically short cone technique was employed for radiographic examination to reveal the existence of the pulp in the third roots. Kodak Ultraspeed films were used, exposed, and processed according to the manufacturer’s instructions. In this study, we did not consider bifurcation of the root as a supplementary root. A real supplementary root is that which is found on the lingual side of the distal root of the lower first permanent molars. RESULTS
The frequencies of the TRPMFM are shown in Table I.
for both groups
104
Younes, Al-Shammery,
First
phase
and El-Angbawi
The results show that the occurrence of supplementary roots on the lower first permanent molars is 2.33% for Asiatic descendants and 0.65% for African descendants. Ethnic comparison reveals greater differences for Asiatic patients in this study. The number of extra roots on the lower first permanent molars of combined Saudi and Egyptian groups as samples of Middle Eastern population was small (1.42%) (Fig. 1). Second
phase
The results of the radiographic examination were compared with the results of the visual examination of the extracted teeth to determine their accuracy. In three mandibular first molars from the Saudi group thought to have three roots instead of two, the anomaly was not actually found until postextraction radiographs were examined. In the Egyptian group, one radiograph was thought to show a TRPMFM. But after extraction, no TRPMFM was present. In another patient, radiographs revealed no root variation, but after extraction, the tooth was found to have three roots. Third
phase
In a comparison of the radiographic results of the two ethnic groups, the radiographs of 140 Saudi patients were examined and were determined to show at least four mandibular first molars with three roots. Radiographs of Egyptian patients revealed that 2 of 105 had at least one TRPMFM. Morphologically, the supplementary root was situated distolingually, and it was a separated and independent root even when its base was in connection with the distal root. It was varied in size but smaller than both distobuccal and mesial roots and had a bent shape. The lower first permanent molar had a supplementary mesial root in 0.51% of Saudi patients and 0.21% of Egyptian patients. Radiographically, it revealed the presence of the pulpal extension into the supplementary root in the root canal, and its base was in connection with the main pulp cavity. DISCUSSION
The previous study”-l3 confirmed that the first permanent molar is the most important tooth in the dentition. This importance is mainly the result of its po;i:;,i; Ziiiu’ p..--r’-luu~clUll. ‘I Furthermore, histologically, there are certain unique characteristics attributed to the first permanent molar inasmuch as it is the only permanent tooth to be developed directly from
ORAL
SURG
ORAL
MED
ORAL PATHOL January 1990
the dental lamina.‘* However, the exact cause of the third root in the lower first permanent molars remains uncertain since the first description in 1908 as one of the anatomic variations.r3 Our results emphasize that the third root is separate, independent, and isolated, although its base is in connection with the distal root. Morphologically, as well as radiographically, it has a separate pulpal extension into the third root. These results agree with the findings of Freitas and coworkers* and other.+ I43I5 and refute Adloff s theoryi3 inasmuch as he stated that this root is a result of distal root bifurcation as well as refuting Balk’s theoryI since he stated that it is found only on the first molars and considers it as a last manifestation of monoplatyrrhiness third premolars, an element that in the monocatyrrines and in man was lost. The results of this study show that there are precentages of doubt of radiographic accuracy in the second and third phases. For this reason, the criteria established in the first phase were used to determine the frequency of the three-rooted mandibular first molars in both ethnic groups. In this study, the Saudi sample had a higher incidence of three-rooted lower first molar teeth than the Egyptian sample. This agrees with the other studies demonstrating that the Asiatic population has a higher incidence of anatomic variations.4*6-‘0 The most prominent finding demonstrated in this study is the lower percentage of occurrence of the third root among the Saudi samples as an Asiatic group compared to other Asiatic samples in other studies.3, G’O Turner4 in 197 1, found that a supplementary root was absent in some African tribes, but this study confirms the presence of teeth as equal the third phase only. In this study the method used to determine the frequency of TRPMFM was no more accurate than the crossing of the translucent lines to define the pulp space and the periodontal ligament as indicated by Walker and Quackenbush.3 We suggest more studies, as required, to provide special positions and angles for the x-ray tube or the use of special coloring agent injection before radiographs are taken to determine these anomalies with a higher percentage of accuracy. The third goal was formulated because the clinical situation of the third root has been reported by several authors.le3 The cases in this study also illustrate the importance of early diagnosis to avoid complications and to allow sufficient time for successful treatment by the dental practitioner. It is not within the scope of this article to describe all the clinical situations that might influence patient
Volume Number
69 1
treatment. However, there are some that occur frequently and should be appreciated by the patient and the dental practitioner. Often, extraction of these teeth proves very difficult and fracture of their supernumerary root occurs. Endodontic failure occurs if the presence of the third root canal is not well recognized. In orthodontic treatment, patients who have a third root may require special handling to move this tooth. On the other hand, an extra root can provide a firm anchor during orthodontic therapy. For the prosthodontist, selection of the artificial device type and design in both removable and fixed prosthodontics may be affected by the presence of the third root inasmuch as this multirooted distribution is an important point in the assessment of an abutment. CONCLUSION
Ethnic comparison reveals greater differences for Asiatic than for African patients in occurrence of TRPMFM. The Middle Eastern population shows the characteristic percentage more than the other various races reported. The combined data of the two ethnic groups in this study demonstrate lower prevalence of supplementary roots. These cases may serve to emphasize the incomplete knowledge of the exact anatomic variation of the lower first permanent molar roots in the two ethnic groups of the Middle Eastern population. Furthermore, this study shows the presence of variability of anomaly between the Middle Eastern population and other populations. The differences in the occurrence of TRPMFM between the Middle Eastern subjects and other Mongoloid and white persons may be due to diverse genetic, socioeconomic, and environmental factors and functional bases for these populations. This article advocates future studies by oral biologists and anthropologists as a first goal to determine the exact cause of the anomalies of the first lower molar. The second goal evolved from the finding that there is some doubt as to whether radiographic or visual examination of the extracted teeth provides the most accurate criteria for determining the incidence of the anomalies. This study advocates future investigations in three areas: 1. Determination of the exact cause of TRPMFM by oral biologists and anthropologists.
Three-rooted permanent mandibular first molars
105
2. Introduction of new practical radiographic methods to increase the accuracy of identification of the root anomalies by radiologists. 3. Introduction of special handling in treatment of TRPMFM by clinicians in the fields of endodontics, orthodontics, prosthodontics, periodontics, and oral surgery. REFERENCES 1 Jones AW. Dental morphology in people of Mongoloid origin. Odontostomatol Trop 1981;3:165-9. 2. Souza-Freitas JA, Lopez ES, Casati-Alvarez L. Anatomic variations of lower first permanent molar roots in two ethnic groups. ORAL SURG ORAL MED ORAL PATHOL 1971;31: 274-8. 3. Walker RT, Quackenbush LE. Three-rooted lower first permanent molars in Hong Kong Chinese. Br Dent J 1985; 159:298-9. 4. Turner CG. Three-rooted mandibular first permanent molars and the question of American Indian origins. Am J Phys Anthropol 1971;34:229-42. 5. Curzon MEJ. Three-rooted mandibular permanent molars in English Caucasians. J Dent Res 1973;52:181-5. 6. Reichart PA, Metacch D. Three-rooted permanent mandibular first molars in the Thai. Community Dent Oral Epidemiol 1981;9:191-2. I. Hjelman G. Morphologische Becobachtungen an den Zahnen der Finnen. Acta Sot Med Finn 1928;11:1-6. (Cited by Reichart and Metacch.“) 8. Jones AW. The incidence of three-rooted lower first permanent molar in Malay people. Sing Dent J 5:1. 9. Tratman EK. Three-rooted lower molars in man and their racial distribution. Br Dent J 1938;64:264-7. 10. Pedersen PO. The Cast Greenland Eskimo dentition. Numerical variations and anatomy. [Thesis.] Copenhagen: C.A. Reitzels forlag, 1949. (Cited by Reichart and Metacch.6) Il. Tsamtsouris A. A review of the importance of the first permanent molar. J Pedod 1980;236-48. 12. Noyes, Schour, Noyes. Dental histology and embryology 5th ed. Philadelphia: Lea & Febiger, 1938:16-49. 13. Adloff P. Das Gebiss des Menschen and der Anthropomorphen. Berlin: Springer-Verlag, 1908 (Cited by Souza-Freitas et aL2) 14. Curzon MEJ. Miscegenation and the prevalence of threerooted mandibular first molars in Baffin Eskimo. Community Dent Oral Epidemiol 1974;2: 130- 1. 15. Somogyi-Csizmazia W, Simons AJ. Three-rooted mandibular first permanent molars in Alberta Indian children. Can Dent Assoc J 1971;37:105-6. 16. Bolk L. Bumerkungen Uber Wurzeivariationen am Menschlichen Unteren Molaren. Zeitschrift fur Morphologie und Anthropologie 1915 (Cited by Souza-Freitas et al.“) Reprint
requests
to:
Abdullah Rakeeb Al-Shammery, BDS, MS Assistant Professor and Vice Dean College of Dentistry, King Saud University, Riyadh 11545 Saudi Arabia
P.O. Box 60169
