Oral Anatomy - Molars
Permanent Molars: General Features
Positioning
Permanent molars are the most posterior teeth in the permanent dentition, located distal to the premolars.
Each dental arch usually contains six molars, with three in each quadrant (if all have erupted).
Types of Molars
Three types of molars exist:
First Molars: Also known as 6-year molars, they erupt around age 6.
Second Molars: Also known as 12-year molars, they erupt around age 12.
Third Molars: Commonly referred to as wisdom teeth, erupt around ages 17-21, marking the end of jaw growth.
Eruption Timeline
All three types of molars erupt in sequence distal to the primary second molars, long after all primary teeth have emerged and begun functioning.
Permanent molars are nonsuccedaneous, meaning they do not replace any primary teeth.
Functionality
Molars have the largest and strongest crowns in the permanent dentition and, with the help of premolars, are primarily involved in grinding food during mastication.
Their occlusal surfaces are wide, featuring prominent cusps that allow for effective grinding. They have more cusps than other types of teeth.
Crown Shape
Viewed from the buccal or lingual side, the crown outline of both maxillary and mandibular molars is trapezoidal or four-sided.
From the proximal view: maxillary molars' crowns are trapezoidal, while mandibular molars' crowns are rhomboidal.
Crown Size and Structure
The first molar is the largest, while the second and third molars are progressively smaller.
Each molar has a substantial crown size but is shorter occlusocervically compared to anterior teeth.
Surface Features
Each buccal surface contains a significant cervical ridge in the cervical third, running in a mesiodistal direction.
The occlusal surface has three or more cusps, generally with at least two being buccal.
No buccal developmental depressions are present.
The occlusal table features bordered cusp ridges and marginal ridges, along with grooves and pits found on both maxillary and mandibular molars' occlusal surfaces. In addition, grooves are found on the lingual surfaces of maxillary molars and buccal surfaces of mandibular molars.
Root Structure
Molars are multi-rooted:
Maxillary molars typically have three roots (trifurcated).
Mandibular molars have two roots (bifurcated).
Molars originate as a single root from the crown, referred to as the root trunk, with the number of roots bifurcating from there.
The multiple roots provide additional periodontal support.
Third Molar Removal
The removal of third molars is a common but controversial procedure during adolescence.
Approximately 25% of individuals may require extraction of their third molars before the age of 25.
Many patients are unaware of potential complications associated with their third molars.
Over 40% of adults who retained their third molars during adolescence may face complications such as infections, caries, cyst formations, or periodontal disease by age 45, necessitating extraction.
The risk of surgical complications in adults increases by 30% compared to adolescents.
It is generally recommended that third molars be evaluated by the age of 25.
Periodontitis
With periodontitis, the root features—such as furcations, furcation crotches, and root concavities—of the molars can lose their periodontal support to varying extents, leading to furcation involvement.
Biofilm and other deposits can accumulate in exposed furcation areas and root concavities, further worsening periodontal disease.
Molars are more susceptible to loss from periodontal disease compared to single-rooted teeth.
Mulberry Molars
In children affected by congenital syphilis, molars are often affected similarly to incisors.
The crowns exhibit an abnormally shaped occlusal surface, characterized by berry-like nodules or tubercles of enamel rather than traditional cusps.
Enamel Pearl
Primarily located on the buccal surfaces of second molars, enamel pearls are deposits of enamel at the cementoenamel junction (CEJ) and have a tapered shape extending into root furcation areas.
They are present in over 28% of maxillary molars and 17% of mandibular molars.
Enamel pearls cannot be removed with standard dental instrumentation.
Dilaceration
The presence of dilaceration in the roots can complicate extraction procedures and endodontic treatments.
Root Fusion
Root fusion leads to deep developmental grooves in molars.
These fused areas can accumulate deposits that are not easily accessible for periodontal therapies or home care.
After the third molars, the highest prevalence of root fusion occurs in maxillary second molars, followed by mandibular second molars, maxillary first molars, and then mandibular first molars. It is noted that women generally have a higher incidence of root fusion compared to men.
Permanent Maxillary Molars: General Features
Eruption Timing
Maxillary molars typically erupt between 6 months and 1 year after the corresponding permanent mandibular molars.
They are usually the first permanent teeth to appear in the maxillary arch.
Size and Strength
Maxillary molars are the largest and strongest teeth in the maxillary arch.
Shorter in occlusocervical height than the crowns of anterior teeth but larger in all other measurements compared to other maxillary teeth.
Physical Features
Maxillary molars have a crown outline that is typically rhomboidal or four-sided when viewed from the occlusal aspect.
From the buccal view, the outline shows that these molars are wider buccolingually than mesiodistally.
Each maxillary molar possesses four major cusps (two on the buccal side and two on the lingual side).
Unique to most maxillary molars, except the third molar, is the presence of an oblique ridge that crosses the occlusal table obliquely, formed by the union of the distobuccal cusp and the mesiolingual cusp.
Root Structure
Maxillary molars usually have three roots, composed of the mesiobuccal (MB), distobuccal (DB), and lingual (or palatal) roots.
The lingual root is generally the largest and longest.
The roots of maxillary molars tend to decrease in size and become less divergent as one moves distally through the arch.
The first molar has longer, more divergent roots than the third molar, and maintains a more consistent size and shape.
Furcation and Contact Areas
There are three furcations located on the buccal, mesial, and distal surfaces, originating near the junction of the cervical and middle thirds of the root.
Lingual Pit Risk
A possible lingual pit on the maxillary molars is at an increased risk of caries due to the retention of dental biofilm and the thinness of the enamel surrounding the pit.
Maxillary Sinus Involvement
The roots of maxillary molars may penetrate into the maxillary sinus during tooth extraction or due to trauma, due to their close proximity to sinus walls.
Concrescence
Maxillary molars are commonly involved in concrescence, which is the union of roots of two or more teeth through cementum only.
Initially separate teeth that join due to excessive cementum deposition from eruption, often due to crowding or trauma.
This condition can lead to complications during extraction and root canal treatments.
Permanent Maxillary First Molars
Identification Numbers: Universal #3 and #14; International #16 and #26.
Eruption and Form
Erupt between 6 and 7 years of age, with root completion occurring between ages 9 and 10.
They are the first permanent teeth to erupt into the maxillary arch, distal to the primary maxillary second molars, and they do not replace any primary teeth.
Notably, the first molar is the largest tooth in the maxillary arch and possesses the largest crown in the entire permanent dentition.
Among all maxillary molars, the first is the least variable in form.
Root Characteristics
Its roots are larger and more divergent than those of the second molars, and more complex than those of the maxillary premolars.
The roots are generally twice the length of the crown, with the lingual (palatal) root being the largest and longest, inclining lingually to extend beyond the crown outline.
Root Overview
The mesiobuccal root is the second largest, longest, inclined mesially and buccally, curving distally in its apical third.
The distobuccal root is the smallest and shortest, inclined distally and buccally, with a mesial curve in its apical third.
There are three furcations located on the buccal, mesial, and distal sides, with pulp cavities generally presenting one horn for each major cusp and three main canals for pulp.
Buccal View Features of Permanent Maxillary First Molars
The overall shape is trapezoidal from this view, with the buccal surface larger than adjacent premolars.
Visibility of parts of all four major functioning cusps: mesial buccal (MB), distal buccal (DB), mesial lingual (ML), and distal lingual (DL).
The MB cusp is the widest, but the DB cusp tip is sharper.
The two buccal cusps have nearly the same height, with the ML cusp tip nestled between them.
The occlusal outline is divided by a buccal groove, running apically to the CEJ, fading out into a buccal pit.
Mesial Outline
Flat from the CEJ to the mesial contact area, which is at the junction of the occlusal and middle third.
Distal Outline
Rounded from CEJ to occlusal surface, with distal contact in the middle third.
Lingual View Features of Permanent Maxillary First Molars
Lingual surface resembles the buccal in being nearly as wide mesiodistally and trapezoidal, but is more rounded.
The mesial lingual (ML) cusp outline is longer/larger but less sharp than the distal lingual (DL) cusp.
The cusp of Carabelli, a common but variable fifth nonfunctioning cusp, is often present starting from the ML cusp, separated by a cusp of Carabelli groove.
The DL groove divides the lingual outline, often ending in a lingual pit.
Proximal View Features
Only the MB and ML cusps are visible from the mesial aspect.
The mesial marginal groove typically notches the mesial marginal ridge about midway along its length.
The distal view shows a similar outline to the mesial; however, the mesial cusp tips project beyond the outline of the DB and DL cusps.
The distal marginal ridge is less prominent and dips more cervical than the mesial ridge, often accompanied by a distal marginal groove halfway along its length.
The CEJ curves slightly toward the occlusal, with potential straight lines on some teeth at the distal surface.
Occlusal View Features
The overall outline of the occlusal surface appears rhomboidal.
The buccal outline is unevenly divided by the buccal groove, while the lingual outline is split by the distolingual groove.
The mesial marginal ridge is more prominent and longer than the distal marginal ridge.
Occlusal Table Components
The MB cusp has a sharp cusp tip and is noted as the second largest.
The DB cusp contributes with the sharpest cusp tip and ranks as the third largest.
The ML cusp is the largest with a rounded tip, and the oblique ridge extends from the DB to the ML cusp.
Transverse ridges connect the ML and MB cusps, while the DL is the smallest and most variable among the cusps.
The minor cusp of Carabelli is considered the smallest when present.
Three occlusal pits are noted: central, mesial, and distal, while the buccal groove extends onto the buccal tooth surface.
Tooth Loss and Implications
Permanent maxillary first molars, because of their position as the first permanent maxillary teeth, are vital for creating functional occlusion.
Loss typically results from periodontal disease, leading to mesial inclination and mesial drift of the maxillary second molar into the resultant gap.
The mandibular first molar can also experience overeruption in response to this gap.
The overall occlusion and mastication can be negatively impacted, increasing risks for caries and periodontal issues, thereby necessitating prosthetics for restoration.
Tooth Deposits
Increased supragingival tooth deposits can often be found on the distal buccal surfaces owing to their fighting position opposite the duct openings of the parotid salivary glands.
The mineral content of saliva can lead to quicker biofilm mineralization.
Permanent Maxillary Second Molars
Identification Numbers: Universal #2 and #15; International #17 and #27.
Eruption and Form
Erupt between 12 and 13 years of age, with root completion by ages 14 to 16.
They erupt distally to the first molars and are also nonsuccedaneous.
The maxillary second molars generally show variation in form, particularly in the size of the distolingual (DL) cusp.
Crown Structure
Typically, the crown comprises four major cusps similar to the first molar, although it can also have three.
The three roots are smaller and less divergent relative to the first molar.
The lingual root is still the largest and longest, extending beyond the crown outline, but it is straighter compared to the curvature seen in the first molar.
Furcations
There are furcations on the buccal, mesial, and distal surfaces.
The pulp chamber typically includes three main pulp canals correlating to the three roots together with pulp horns aligned with each major cusp.
Buccal View Features
The maxillary second molars are shorter occlusocervically than the first molar and narrower mesiodistally.
The buccal groove is positioned further distally on the buccal surface than that of the first molar.
The MB cusp is longer and possesses a less sharp cusp tip with contact areas typically within the middle third.
Lingual View Features
The DL cusp can be smaller and shorter than that of the first molar, with the ML cusp classically being the largest in comparison.
A lingual pit might be present at the end of the distolingual groove, further exacerbating caries risk.
Proximal View Features
Mesial contact area typically larger than that of the first molar, while both the DB and DL cusps are considerably smaller compared to the first molar.
Occlusal View Features
The crown contours narrower mesiodistally compared to the first molar yet maintains equal buccolingual width.
Two outlines are possible: rhomboidal and heart-shaped—rhomboidal being the more frequently observed form.
The heart-shaped outline features a smaller or absent distolingual cusp.
Occlusal Table Components
Surrounding a cross-shaped groove pattern, occlusal features share resemblance to the first molar's characteristics but with fewer supplemental grooves and a less pronounced oblique ridge.
Three occlusal pits are present: central, mesial, and distal.
Permanent Maxillary Third Molars
Identification Numbers: Universal #1 and #16; International #18 and #28.
Eruption Timing
May erupt between ages 17 and 21, with root completion occurring between ages 18 and 25.
When erupted, they are positioned distally to permanent second molars, rendering them nonsuccedaneous.
Physical Characteristics
Known as the smallest molars with highly variable crown shape; describing a typical third molar can be challenging.
It is generally smaller in every dimension when compared to maxillary second molars, often displaying poorly developed crowns.
The occlusal outlines can appear heart-shaped or rhomboidal.
Common Features
Heart-shaped is the most typical; these molars often exhibit numerous supplemental grooves.
Usually possess three cusps (MB, DB, ML) with the DB cusp being considerably shorter than the MB cusp.
If a fourth cusp is present, it typically appears as small and nonfunctional. In some cases, an additional cusp can emerge with no oblique ridge present.
Root Characteristics
Roots tend to be poorly developed—generally shorter than those of second molars and may be completely or partially fused.
The roots curve distally, helping to determine tooth orientation when distinguishing right from left.
Pulp cavity structure remains similar to other molars, usually consisting of a pulp chamber and three pulp canals, though variations can exist.
Arch Position
Instrumentation and restorations can be problematic due to the extreme posterior position of these teeth, leading to increased deposits and susceptibility to periodontal disease and caries.
Clinical considerations may require the patient to adjust their mouth position for proper care access.
Impaction Risk
Maxillary third molars can become impacted if they fail to erupt due to underdeveloped maxillae, leaving insufficient space in the arch. Surgical intervention may become necessary.
Microdontia
These molars can exhibit partial microdontia, leading to smaller molar crowns with possibly only one cusp (sometimes termed peg molars), which may occur bilaterally or unilaterally.
Permanent Mandibular Molars: General Features
Erupt between 6 months to 1 year earlier than the corresponding maxillary molars.
Crowns generally feature four or five significant cusps, with always two of them being lingual.
Mandibular molars are consistently wider mesiodistally compared to buccolingually, conversely to the maxillary counterparts.
Overview of Permanent Mandibular Molars
Identification Numbers: Universal #19 and #30 for the first molar; #18 and #31 for the second molar; #17 and #32 for the third molar.
Mandibular First Molars
Erupt approximately between ages 6 and 7, with root completion from age 9 to 10.
Considered the first permanent teeth in the oral cavity, they emerge distal to the primary second mandibular molars.
Crown typically shows five cusps: three on the buccal and two on the lingual side. A missing distal cusp or an adjacent sixth cusp can occasionally develop on larger specimens.
The roots are bifurcated, leading to a mesial and a distal root, larger and more divergent than those seen in the second molar, with pronounced fluting on mesial surfaces.
Pulp Canal Features
Feature three approachable canals; namely: distal, mesiobuccal (MB), and mesiolingual (ML) comprising five pulp horns overall.
Buccal Features of Mandibular First Molars
The crown size from a buccal view is significantly wider mesiodistally than occlusocervically.
It stands out as the widest MD permanent tooth due to its fifth cusp, with visible portions of all five cusps.
Notably, the MB cusp is the largest, widest, and highest on the buccal side, whereas the DB cusp is slightly shorter and sharper than the MB cusp.
Occlusal Surface Segmentation
The crown's occlusal outline is divided into three distinct sections by two buccal grooves, identified as the MB and DB grooves leading into a buccal pit.
Groove Significance
The MB groove of the mandibular first molar has implications for classification under the Angle classification of malocclusion relative to the maxillary arch.
This groove has a cervically extending path and usually concludes at a buccal pit proximal to the buccal cervical ridge located in the cervical third of the buccal surface.
Lingual View Features
The lingual surface displays smaller dimensions compared to the buccal surface but retains a similar mesiodistal outline. The occlusal outline is divided by a lingual groove separating the mesiolingual and distolingual cusps.
Proximal View Features
Yo the general shape is smaller buccolingually than mesiodistally and occlusocervically.
The crown leans toward the lingual side, characteristically rhomboidal in its outline. The CEJ showcases soft curves.
Mesial surfaces are similar to distal but with notable size differences; the mesial marginal groove here notches the marginal ridge distinctly.
Occlusal View Features
Crown outline appears roughly pentagonal where the distal aspect of the buccal outline narrows to form a fifth side, and the buccal outline is rounded, segmented by two distinct buccal grooves (mesiobuccal and distobuccal grooves). The length of buccal cusps diminishes toward the distal side.
Lingual outlines highlight two distinct components divided by a lingual groove, similarly, the mesial outline further displays segmentation attributed to a mesial marginal groove.
Occlusal Table Components
Functional cuspage counts vary, yet this form typically showcases five major cusps arranged from largest to smallest: MB, ML, DL, DB, and a distal cusp.
Disturations in terms of height can be acknowledged as ML cusp maintaining the highest stature while ultimately ranking the DB cusp with a rounded tip as one of the more supplemented characteristics overall.
Y-shaped grooves define the occlusal table groundbreaking with multiple pits including mesial, central, and distal pits.
Buccal Pit Risk
Risk of developing caries is notably elevated on any buccal pit surface due to increased biocream retention.
Tooth Loss Considerations
The loss of mandibular first molars heavily influences functional occlusion and results in mesial inclination of adjacent molars, leading to better conversion at their care needs.
Permanent Mandibular Second Molars
Eruption occurs between ages 11 and 13, with subsequent root completion at ages 14-15.
These molars erupt distal to the first molars and are nonsuccedaneous; they exhibit smaller crown measurements compared with the first molar.
The four cusps are almost symmetric in size.
Two roots exist, shorter and less divergent than those of the first molar.
Pulp Canal Overview
Typically featuring two pulp canals, equivalently designed for both roots; however variations can be observed where a third canal mirroring features of the first molar can occasionally become present.
The common viewpoint details each major cusp corresponding to its respective pulp horn.
Buccal View Features of Mandibular Second Molars
Characteristically identical sizes evident on both MB and DB cusps, defined by a mesial contact at the occlusal and middle thirds junction.
Lingual View Features
The ML and DL cusps are similarly sized to buccal forms, although they manifest sharper cusp tips due to lingual convergence.
Proximal View Features
Descriptive highlights on proximal surfaces display a less pronounced buccal cervical ridge relative to the first molar, with observations made on marginal ridge characteristics.