الفهرس 
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Abstract
Summary
I- Introduction:
The study of dental morphological characteristics is useful for providing information for phylogenic, anthropological, forensic and genetic studies and understanding variations within and among species.
Studying the external and internal anatomy of the permanent teeth especially the permanent molars has been the main scope for many morphometric and morphological studies in different populations, providing us with information about occlusal morphology, the shape and number of roots and root canals configuration.
So, the aim of this study was to investigate the occlusal morphology, root shape, root number and root canals configuration of the permanent maxillary molars in a sample of the Egyptian population.
II- Materials and methods:
A-Materials:
Extracted maxillary molars
Maxillary Dental casts
Digital caliper
CBCT
B-Methods:
1) Occlusal morphology:
a- Cusp number and groove pattern:
Examination of maxillary molars was done on the study cast.Teeth should be free from occlusal and proximal caries. After that , the occlusal pattern of each molar was classified according to the standards of morphological variants of permanent teeth of Arizona State University-Dento Anthropological system.This was determined after marking the developmental grooves using a pencil.
B- The frequency of molar tubercle (tubercle of carabelli).
C- Occlusal outline:
Occlusal outline of maxillary molars was done on study casts and classified into:
1-Rhomboidal occlusal outline.
2- Heart shaped occlusal outline.
3- Oval occlusal outline.
2) Measurement of mesio-distal crown width:
The mesio-distal crown width of each individual tooth was measured by a single examiner using a digital caliper on study casts. The measurements were performed by holding the cast vertically and placing the blades of the caliper on the molars’ contact points with the blade’s proximal sides parallel to the long axis of the tooth .
The measurments recorded three separate times and the mean value was taken .
3)Bucco-lingual diameter(BL):
The measurements were taken perpendicular to the MD width between their buccal and lingual crown maximum convexities. In upper molars these are across the paracone/protocone region of the crown and across the metacone/hypocone region .
The two diameters (MD & BL) are usually measured in order to obtain specific orthopometric index as
• Crown module (CM) = (MD + BL)/2
• Crown index (CI) = (BL / MD)*100
• Robustness index (RI) = MD*BL
4) Measurement of root to crown ratio (R/C):
The R/C ratio was measured using CBCT.The following definitions were used for CBCT-based measurements.
1- Crown length: distance between the tip of mesiobuccal cusp to the cementoenamel Junction (CEJ) on the buccal surface.
2-Root length: distance between the CEJ on the buccal surface and the root apex.
In triple-rooted teeth, the palatal roots were omitted and the longer one of the buccal roots was measured .
R/C was calculated by dividing the root length by the crown length.
5) Classification of the maxillary molars according to the shape and number of roots:
Classification of the maxillary molars according to the morphology and number of roots into 10 grades:
I- Three roots: all separate
II- Three roots: buccal roots fused
III- Three roots: one of the buccal fused with palatal root
IV- Three roots: all fused
V- Two roots: separate
VI- Two roots: fused
VII- One root: C-shaped
VIII- One root: conical
IX- Four roots: fused
X- Four roots: other
The maxillary molars were also classified according to the number and frequency of fusion of roots into:
1- Three rooted molars when the mesiobuccal ,distobuccal and palatal roots are widely separated.
2-Two rooted molars when either one of the two buccal roots fusing with the lingual root or through fusion of the two buccal roots with each other.
3-One rooted molars When all three roots are fused and there is no distinct interradicular projection.
6) Root canal morphology of maxillary molars:
Molds with the samples in were submitted for CBCT scan, CBCT images were acquired using i-CAT next generation device.
CBCT images were examined and evaluated types of root canals were categorized according to Vertucci’s classification .
III- Results:
Regarding cusp number and groove pattern of maxillary molars, M1 & M2 showed prevalence of 4H groove pattern while 3 cusps and U groove pattern was the most common pattern for M3.
Regarding the frequency of molar tubercle (tubercle of carabelli), M1 showed prevalence of type I molar tubercle (depression), while the absence of the molar tubercle was the most common pattern for M2 &M3.
Occlusal outline of M1& M2 showed prevalence of the rhomboidal outline while M3 showed prevalence of heart shaped outline. Statistical results showed significant difference between the maxillary molars.
Regarding mesio-distal crown width, buccolingual dimensions, crown module, crown index, robustness index and R/C. M1 showed higher value than M2 &M3.Significant difference was found between them.
Most of M1 has had three separate roots, two buccal and one lingual root. No M1 with three completely fused roots was found in our sample size As for M2, showed mostly three separate roots , while the rest of M2 showed partially and completely fused roots. For M3, showed mostly three fused roots, while the rest of M3 showed partially fused roots, four roots, two roots or one root.
Regarding the mesiobuccal root canal configuration for M1,In 2 canaled mesiobuccal canals ,type I was the most comman configuration and type II in single canaled mesiobuccal canals while that of M2 was type I and II and type II for M3, As for the distobuccal roots and palatal roots , type I was prevalent in all the maxillary molars.