1
Q
Mesiobuccal cusp
A
- The mesiobuccal cusp is approximately the same height as the distobuccal cusp according to three experts.
- Traditionally however, the mesiobuccal cusp is generally accepted as wider (mesiodistally) as well as slightly taller than the distobuccal cusp.
- The mesial and distal slopes of the mesiobuccal cusp form an obtuse angle.
2
Q
Distobuccal cusp
A
- The distobuccal cusp is the sharpest of the cusps.
- The mesial and distal slopes of the distobuccal cusp form approximately a right angle, making this cusp sharper than the mesiobuccal cusp about 72% of the time.
3
Q
Buccal groove
A
- The buccal groove is located approximately equidistant between the mesiobuccal and distobuccal line angles, or it may be oriented slightly to the distal (shown).
- It slants occlusocervically at such an angle that it parallels the long axis of the distobuccal root.
- This feqture could be helful for endo.
- The groove terminates about halfway between the cervical line and its origin on the occlusal aspect of the buccal surface.
- There may be a slight depression for some distance mesial and distal to the gradual termination of the groove.
- The groove may terminate by splitting into two diagonally slanting grooves that fade out after a short distance.
- Although the Tooth Atlas says that there may be a pit where the groove terminates, this is extremely rare.
4
Q
Mesial Crown Form
A
- The mesial crown surface follows a nearly straight line from the cervical line toward the area of greatest convexity.
5
Q
Mesial Proximal contact
A
- The mesial proximal contact has been located at the junction of the occlusal and middle thirds.
- It has also been located three-fourths of the distance between the cervical line and marginal ridge which could put it in the occlusal third (Charlick).
6
Q
Cervical line form
A
- The cervical line may possess a slight convexity toward the roots.
- Or it may consist of two slightly curved segments separated by a sharp, apically directed peak over the buccal furcation (shown)
7
Q
Distal Crown Form
A
- The distal crown surface is more convex than the mesial surface i spite of it being nearly flat in the cervical thid (not a good drawing of this feature).
- The distal surface around the area of the proximal contact is spheroidal.
8
Q
Distal proximal contact
A
- The distal proximal contact has been located halfway between the cusp tip and cervical line, at the occlusocervical midpoint, and in the middle third near the occlusocervical center.
- It has also been located farther cervically than the mesial contact, three-fifths of the distance between the cervical line and marginal ridge
- All of those descriptions put the distal contact approximately in the same place, and it follows the usual trend: distal contacts are located farther cervical than mesial contacts.
9
Q
Roots
A
- The three roots are nearly the same length (within 1.5 millimeters) but the palatal (lingual) root is the largest and longest
- The two buccal roots are approximately the same length, with the distobuccal root being slightly shorter and therefore the shortest of the three roots.
- The mesiobuccal root is larger buccolingually (not visible in this view) and narrower mesiodistally than the distobuccal root (true but the drawing shows the opposite)
10
Q
Cross-sectional root form
A
- The roots are described as all being roughly ovoid in cross-sectional form at the mid-root area.
- Comparing the two buccal roots, however, the distal will have a more round cross section than the mesial.
11
Q
Root trunk form
A
- There is a deep developmental depression on the buccal surface of the root trunk that begins in the bifurcation and terminates in a shallow depression at the cervical line.
12
Q
Buccal Bifurcation
A
- The buccal bifurcation is often near the junction of the cervical and middle third of the root.
- The buccal bifurcation is located about 4 millimeters apical to the cervical line.
13
Q
Root Separation
A
- The lateral separation (spread) of the two buccal roots is nearly as wide as the mesiodistal crown dimension (roots should be drawn wider).
- The separation and form of these roots resemble the handles on a pair of pliers.
14
Q
Mesiobuccal Root Angulation
A
- The cervical half of the mesiobuccal root projects mesially and then curves toward the distal.
15
Q
Root separation and angulation
A
- All of these root features serve to lock this tooth into the bone, making it difficult to extract.
16
Q
Distal crown height
A
- The distal half of the crown is shorter occlusocervically than the mesial half.
- This is a general rule for the molar teeth that distal features are smaller and less well-formed than the mesial features, a remnant of our evolution.
17
Q
Mesiolingual cusp
A
- The mesiolingual cusp is the largest and tallest cusp on the first molar.
- The width of the mesiolingual cusp is 3/5 of the mesiodistal crown dimension.
- The mesial and distal slopes of the mesiolingual cusp form an obtuse angle.
18
Q
Distolingual cusp
A
- The distolingual cusp is slightly shorter than the mesiolingual cusp.
- The distolingual cusp is narrower than the mesiolingual cusp.
19
Q
Cusp of Carabelli
A
- The Cusp of Carabelli (5th cusp) may be present on the lingual surface of the mesiolingual cusp
- The cusp of Carabelli is present in some form about 70% of the time.
- It may be quite large, medium-sized like a cusplet, even smaller like a tubercle, or still smaller, just a bump (medium size is shown).
- When present, it will be identical on both the left and right sides of the arch (#3 & #14), never unilaterally.
- Although the Cusp of Carabelli is usually located about 2 mm apical to the mesiolingual cusp tip, there are instances where it is virtually as tall as the mesiolingual cusp.
20
Q
Lingual Groove
A
- The lingual groove (commonly called the distolingual groove) originates on the occlusal surface and traverses onto the lingual surface distal to the middle of the crown.
- The lingual groove may be continuous with the longitudinal depression that usually occurs on the lingual surface of the palatal root.
- The termination point of the groove on the lingual surface is frequently the site of a deep pit.
21
Q
Palatal (Lingual) Root
A
- The palatal root is the longest, largest, and strongest of the 3 first molar roots.
- It is the third longest root in the maxilla after the canine and second premolar.
- The palatal root has a greater mesiodistal dimension than buccolingual dimension
- The palatal root is conical and has a bluntly rounded apex.
- The palatal root apex is almost directly aligned with the mesiodistal center of the crown.
22
Q
Crown Dimensions
A
- The buccolingual crown width is greater than the mesiodistal width
- The average difference is as great as 1.1 mm and as small as 0.5 mm.
- Although the inequity of the two measurements appears slight from an occlusal view, it is traditionally accepted that the tooth is wider buccolingually than mesiodistally.
- One expert indicates the two dimensions are the same
23
Q
Lingual Crown Dimension
A
- On many first molars, the lingual half of the crown is wider mesiodistally than the buccal half of the crown.
24
Q
Distal Crown Dimension
A
- The crown is narrower buccolingually in the distal half of the crown.
- All of the decrease in measurement is due to the lingual slant of the buccal surface.
25
Crown outline
* The outline of the occlusal surface may resemble a *parallelogram* with 2 acute and 2 obtuse angles.
* The acute angles are *mesiobuccal* and *distolingual* angles.
* The crown has also been described as appearing *rhomboidal (* diamond-shaped) from an occlusal view.
* *Rhomboid* and *parallelogram* are both possibilities in this tooth.
26
Mesial proximal contact
* The buccolingual position of the mesial proximal contact has been located *buccal* to the center of the crown.
27
Buccal groove location
* The distance from the mesial surface to the buccal groove is *greater* than the distance from the buccal groove to the distal surface.
* Simply stated, the buccal groove is located slightly *distally*.
28
Distal proximal contact
* The buccolingual position of the distal proximal contact has traditionally been located at the *center* of the crown.
* The location is an *exception* to the usual rule that contacts of posterior teeth are located to the *buccal of the mesio-distal center* of the tooth.
* The distal proximal contact is usually *broad* and *flat* and assigning it to a specific point is *misleading*. It's better described as an area than as a point.
* In spite of the *traditional centered location*, if visualized as an area, the center of the distal proximal contact *is* frequently off slightly to the buccal.
29
Distolingual groove location
* The distance from the mesial surface to the distolingual groove is *greater* than the distance from that groove to the distal surface.
* Simply put, the distolingual groove is located slightly *distal* on the lingual surface as the name suggests (similar to the buccal groove)
30
Cusps
* The size of the five cusps (from largest to smallest) has traditionally been listed in the following order:
1. Mesiolingual
2. Mesiobuccal
3. Distobuccal
4. Distolingual
5. Cusp of Carabelli
* The order, however, has also has been listed as a switch between 3 & 4
1. Mesiolingual
2. Mesiobuccal
3. Distolingual
4. Distobuccal
5. Cusp of Carabelli d
* The mesiolingual cusp is the *largest* cusp 95% of the time.
* There is a distinct triangular arrangement of the mesiobuccal, distobuccal, and mesiolingual cusps (termed a *trigon*, the form of the original *reptile tooth*).
31
Cusp of Carabelli
* The Cusp of Carabelli (5th cusp) is present on first molars about 70% of the time.
* The Cusp of Carabelli may be distinctly formed or it may be barely visible.
* A groove may be present between the Cusp of Carabelli and the lingual surface of the mesiolingual cusp.
* The groove is sometimes quite deep and *may* *become carious*.
32
Fossae
* There are 4 fossae on the occlusal surface; their order of size from largest to smallest:
1. Central (C)
2. Distal (D)
3. Mesial triangular (MT)
4. Distal triangular (DT)
* There are 2 major fossae (C, D) & 2 minor fossae (MT & DT)
* The central fossa is the *largest* and *deepest* of the 4 fossae.
33
Oblique ridge
* The oblique ridge is formed by the union of the *distobuccal triangular cusp ridge* and the *distal ridge of the mesiolingual cusp*.
* The oblique ridge crosses the occlusal surface in a *diagonal* direction between the *obtuse angles* of the parallelogram.
* The enamel is usually *fused* and there will be a shallow *depression* where the two ridges join each other, but the ridge is *rarely* crossed by a groove on the first molar (drawn too deep in the drawing however).
* The point where the two ridges join is located at about the *same level* occlusocervically (the same height) as the marginal ridges.
34
Transverse Ridge
* It is *possible* for the triangular ridge of the mesiobuccal cusp to meet the triangular ridge of the mesiolingual cusp to form a true transverse ridge.
* TRADITIONALLY, this is defined as a transverse ridge in *rare* cases where the enamel from the triangular ridges is fused (like the oblique ridge) and the central groove is interrupted.
* The enamel fusion is *rare* and the drawing in the Tooth Atlas does NOT show a true transverse ridge.
* *However,* along with the maxillary first premolar, a true transverse ridge is *possible* on this tooth.
* When this occurs the tooth will have an *elongated oval* shape.
* In any case do NOT confuse the oblique ridge with the *rarely* occuring transverse ridge.
35
Mesiolingual cusp triangular ridges
* A single expert describes the mesiolingual cusp as having two triangular ridges.
* Every other expert describes this cusp as having the usual *single triangular ridge* and the usual mesial and *distal cusp ridges*
36
Developmental grooves
* There are 5 major grooves present:
1. Central (C)
2. Buccal (B)
3. Distal oblique (DO)
4. Lingual (LO
5. Transverse groove of the oblique ridge (TG)
* The distal oblique and lingual grooves are combined by some experts as the *distolingual groove*, the common name.
* The transverse groove of the oblique ridge is a short developmental groove that radiates *distolingually* from the *central fossa*, up the mesial slope of the oblique ridge.
* It usually fades out before reaching the ridge crest. It *rarely* crosses the oblique ridge in the first molar.
37
Buccal groove angle
* The buccal groove is angled towards the mesial, forming an *acute angle* with the central groove.
* In the Tooth Atlas, Wheeler says it's an obtuse angle; it could be obtuse, but NOT usually; the drawing shows the groove accurately.
38
Stuart Groove
* The groove present between the *distal cusp ridge* and the *triangular ridge of the mesiolingual cusp* is called the *Stuart Groove*.
39
Buco-Lingual Crown Form
* When viewed mesially, the crown is *wider* buccolingually at the cervical line than it is in the occlusal third, which is the *opposite* of a buccal or lingual view.
40
Mesiolingual cusp location
* The mesiolingual cusp is located on the long axis line of the *palatal root*.
* The *largest strongest root* supports the *largest cusp*.
* The *greatest occlusal force* is therefore aligned with the long axis of the tooth; this has been the case with every tooth where we have noted the long axis alignment.
41
Marginal Ridge Groove
* The mesial marginal ridge usually has a shallow supplemental groove notching the ridge about halfway along its length.
* Although termed a marginal ridge groove, this is NOT comparable to the deep mesial marginal ridge groove that was present on the maxillary first premolar
42
Tubercles
* Unworn marginal ridges of maxillary molars may have one or more projections called "tubercles"; these are more common on the mesial than on the distal marginal ridges.
43
Mesiobuccal root width
* The mesiobuccal root is very wide buccolingually.
* The buccolingual width of the mesiobuccal root at its base equals *two-thirds* of the buccolingual width of the root trunk.
44
Palatal (Lingual) Root Form
* The palatal root diverges sharply to the lingual and is bent like a banana.
45
Mesial Bifurcation
* The mesial bifurcation is located closer to the cervical line (less than 4mm) than the buccal bifurcation.
* THe shorter bifurcation results in a longer root, which increases the bony anchorage.
* The roots provide considerably more anchorage than the root trunk.
* There is a smooth concavity extending occlusally and lingually from the furcation almost to the cervical line.
46
Palatal (Lingual) Root Extension
* The palatal root extends *lingually* beyond the lingual surface of the crown
47
Mesiobuccal root extension
* The convex buccal surface of the mesiobuccal root often extends buccally beyond the buccal surface of the crown (close but not shown).
48
Mesiobuccal root form
* The lingual aspect of the mesiobuccal root is relatively straight
49
Mesiobuccal root surface
* The mesial surface (as well as the hidden distal surface) of the mesiobuccal root has a depression, *frequently* deep and dividng the pulp into *two canals*
50
Cusp Visibility (distal view)
* *All four cusps* are visible from a distal view.
* The mesial cusp tips are visible as they project beyond the outline of the smaller distal cusps.
* There is also a tendency for the crowns of all posterior teeth to be tipped slightly to the *distal*, making more of the occlusal surface visible from the distal.
51
Marginal Ridge
* The distal marginal ridge is *closer* to the cervical than the mesial marginal ridge.
* The distal marginal ridge is narrower *buccolingually* and is more *concave* than the mesial marginal ridge.
52
Marginal ridge groove
* The distal marginal ridge usually has a shallow groove crossing.
* On first molars, 50% of the teeth had distal marginal ridge grooves.
53
Tubercles
* The distal marginal ridge sometimes has accessory tubercles but they are *rarer* than on the mesial marginal ridge (tubercles not shown on the drawing)
54
Proximal Cervical Crown Form
* The distal surface may be slightly convex, flat, or concave; *concave* especially near the distobuccal root.
* Although not mentioned in the Tooth Atlas, the distobuccal line angle also exhibits a *significant flattening in the cervical third of the crown*
* Charlick describes this line angle as being "tucked in". This is especially troublesome area for plaque and calculus accumulation and a frequent site of periodontal problems.
55
Root trunk form
* A *continuation* of the *proximal crown concavity* occurs frequently, extending onto the root trunk, and it may be fairly deep.
* When exposed in the mouth by gingival recession in middle-aged and older patients, this is an area of *significant plaque accumulation.*
* Dental floss will bridge across the concave area without cleaning it, contributing further to the periodontal problems already noted from the flattened line angle.
56
Distal Bifurcation
* The distal bifurcation is located 5 or more mm apical to the cervical line, thereby being the *most apically* located furcation.
57
Distobuccal root
* The distobuccal root is the *smallest, shortest, and weakest* root.
* The distobuccal root is shorter than the mesiobuccal root and NOT as large buccolingually.
* The distobuccal root is *narrower* at its base than either of the other two roots.
* The buccal surface of the distobuccal root is not located as far buccally as the mesiobuccal root.
* The distal surface of the distobuccal root has NO longitudinal depressions
* The distobuccal root apex is fairly *sharp* and it is *sharper* than the mesiobuccal root apex
* Due to its smaller size and lack of features, the distobuccal root does NOT contribute as much as the other roots to the anchorage into the alveolar bone.
* Bottom line, all around small/short/insignificant.
