2.2 Morphology of incisors, canines and premolars

what are the planes of orientations?

sagittal

medial

horizontal

frontal

What are the 4 types of ways to divide teeth into according to shape and function?

1. Incisors - cutting/tearing food, lip+tongue support, provides incisal guidance, enables speech

2. Canine - cutting food, corner of dental arch, canine guidance, labial contour, part of aesthetic quadrant, lip support

3. Premolars - mixed function, cutting+grinding , known as transition teeth, initial mastication, maintain vertical dimensions, canine assistance in cutting food

4. Molars - grinding food, main mastication, maintain vertical dimensions, less aesthetic influence.

List the cusps of teeth

1. Mesial cusp ridge

2. Distal cusp ridge

3. Buccal cusp ridge

4. Triangular ridge

The Cusps - Mesial cusp ridge

slope that faces towards the front of the mouth

The Cusps - Distal cusp ridge

slope that faces towards back of the mouth

The Cusps - Buccal cusp ridge

slope on cheek side for most teeth, but for canines, it’s called the labia; ridge since it’s more towards the lips

The Cusps - Triangular Ridge

Slope you’ll find on posterior teeth (like molars), on the tongue side. For canines, this is known as the lingual ridge

Describe morphology of Incisors (central/lateral, maxillary/mandibular)

• slightly more rounded on distal side of incisal ridge

• more angled on mesial side

• apex of root usually curves distally

Describe morphology of maxillary lateral incisors

• smaller than maxillary central incisor

• crown and root are narrower mesiodistally (about 2mm narrower) in facial view compared to the central incisor

What is the contact points of maxillary lateral incisors?

• mesially at the junction of the middle third and incisal third

• distally, at the centre of the middle third

Describe morphology of maxillary central incisor

• Generally wider labiolingually from the proximal view than the maxillary lateral incisor

What are the 4 developmental lobes of maxillary central incisors?

• facial aspect

• lingual aspect

• proximal aspect

• incisal aspect

maxillary central incisors: facial aspect

nearly straight incisal edge, mesially straight and while distally rounded

Development lobe of maxillary central incisors: lingual aspect

• lingual fossa, cingulum and incisal edge

Development lobe of maxillary central incisors: Proximal aspect

mesial and distal aspect present a triangular outline

developmental lobes maxillary central incisors: incisal aspect

developmental lobes are the primary growth centers from which teeth form. Each tooth develops from multiple lobes that eventually fuse

Anterior Teeth (Incisors & Canines) – Typically develop from four lobes: three facial lobes and one lingual lobe (which forms the cingulum).

what are the 4 developmental lobes of maxillary lateral incisors?

• mesial

• labial

• distal

• lingual

developmental lobe of maxillary central incisor - lingual aspect

prominent marginal ridges and cingulum

developmental lobe of maxillary central incisor - proximal aspect

same as the central but the roots are longer

developmental lobe of lateral central incisor - Incisal aspect

narrower mesiodistally than the central but same thickness labiolingually, shaped more like a diamond

developmental lobe of maxillary lateral incisor - facial aspect

narrower mesiodistally than central and has more rounded incisal edge

what are 4 developmental lobes of mandibular central incisor?

3 facial and 1 lingual (form cingulum)

Development lobe of mandibular central incisor - facial aspect

smallest tooth in dental arch, long and narrow with straight incisal edge

Development lobe of mandibular central incisor - Lingual aspect

concave surface with small cingulum

mandibular central incisor - Proximal aspect

mesial and distal surface present a triangular outline

Development lobe of mandibular central incisor - Distal aspect

incisal edge is at right angle

Developmental lobe of mandibular lateral incisor - facial aspect

develops from four developmental lobes—three facial lobes and one lingual lobe (which forms the cingulum)

Developmental lobe of mandibular lateral incisor - lingual aspect

same as the central but has no symmetry

Developmental lobe of mandibular lateral incisor - proximal aspect

has a triangular outline

Developmental lobe of mandibular lateral incisor - incisal aspect

the edge is twisted from 90 degree angle

What are the 4 developmental lobes of canines?

3 facial one lingual (forms cingulam)

what are the functions of a canine?

• cut food

• lip support

• canine guidance

• labial contour

• part of aesthetic quadrant

Discuss the size of roots and crowns of canines

• Canines have particularly long and thick roots (labiolingually) that help to anchor them securely in the alveolar process

• Mandibular canine CROWN is longer than maxillary canine crown

what is the longest tooth in each arch?

canines

……have the longest root and is the longest tooth in the mouth

maxillary canines have the longest root

What do canines have instead of a straight incisal ridge and what do they usually not have?

• Rather than being straight, incisal ridge of canines is divided into two inclines: mesial and distal cusp ridge (also called cusp slopes or arms)

• Don’t usually have mamelons but may have notch on either cusp ridge

From the facial view, what does the crown of canines resemble?

five-sided pentagon

which cusp ridge is shorter in canines?

mesial cusp ridge is shorter than distal cusp ridge

what is cusp slopes or cusp arms?

it is the incisal ridge of canines made by mesial and distal cusp ridges

Talk about labial contour of maxillary and mandibular canines

• Labial surface is convex with vertical labial ridge

Which teeth has buccal ridge?

premolars

which teeth are the only ones to have a labial ridge?

Canines

in which way is the measurement of the canine crown greater?

What shape are root cervix measurements labiolingually?

• measurement of maxillary+mandibular canine crowns is greater (this applies to mandibular incisors as well) labiolingually than mesiodistally

• Root cervix measurements are even more oblong labiolingually

what other teeth share the quality of having crowns that are greater in size labiolingually than mesiodistally?

Mandibular incisors

what are some canine traits that are similar to incisors?

• similar contact points to most incisors a (except mandibular central incisor)

• location of incisal edge wear, similar to incisors

Where is the height of contour on facial and lingual surface of canines?

Both have height of contour at cervical third with the lingual having the contour end on the cingulum

From proximal view what is the shape of canine crowns?

wedge or triangular shaped

The crown outline is more…..on distal than on the mesial surface

convex

For canines the distal contact point is more…..than mesial contact area?

cervical

Where does tooth wear occur on canines?

• location of incisal edge wear, similar to incisors

Where does facets form on mandibular canines, compared to maxillary canines?

• Facets on mandibular canine cusp tip and cusp ridge usually form more on the labial border, not on lingual border as seen in maxillary canines.

Development lobe of maxillary canine: Facial aspect

• 1mm narrower than central incisor

• distal cusp ridge is longer than mesial

• smooth labial surface

maxillary canine: Lingual aspect

well developed cingulum with distinct distal and mesial marginal ridges

Development lobe of maxillary canine: Proximal aspect

mesial and distal aspect present triangular outline

Development lobe of maxillary canine: Incisal aspect

thicker labiolingually than mesiodistally

Development lobe of mandibular canine: facial aspect

narrower and shorter than upper but wider mesiodistally

Development lobe of mandibular canine: lingual aspect

less prominent marginal ridge and cingulum

Development lobe of mandibular canine: proximal aspect

mesial and distal aspect give a triangualr outline with less developed cingulum

Development lobe of mandibular canine: incisal aspect

mesiodistally shorter than labiolingually

function of upper premolars

• initial mastication

• maintain vertical dimensions of face (between nose and chin)

• canine assistance in cutting food

What separates buccal/labial (same as vestibular) cusp and lingual cusp in upper premolars?

• two vertical ridges on sides (separating vestibular and lingual cusps)

Describe the buccal cusp and buccal ridge of upper premolars?

Buccal cusp is long and buccal ridge extends down to base of tooth

Where is the highest points of upper premolars located on front and back surface?

On front - in cervical third

On back - in cervical third

What is the shape of the buccal surface of upper premolars and which does it resemble?

Rounds buccal surface and resembles canines

what is the widest part of upper premolars?

the middle cervical thirds

From which side is the crown narrower in upper premolars?

Crown narrower towards bottom from buccal/labial side (same as vestibular side)

where is upper premolars located?

between molars and canines

In which of the upper premolars is the buccal ridge more prominent in?

Buccal ridge more prominent on first premolar

In which of the upper premolars is the buccal cusp longer?

First upper premolars have a longer and sharper buccal cusp

in second upper premolar it is more obtuse and less pointed

Which cusp ridge is shorter and longer in second upper premolars?

Shorter mesial cusp ridge than distal cusp ridge

Which cusp ridge is shorter and longer in first upper premolars?

Longer mesial cusp ridge than distal cusp ridge

What are the contact points of upper premolars?

• Mesial contact in middle third

• Distal contact, slightly more cervical, still middle third

In which of the upper premolars is the crown larger and in in which is the roots longer?

Crown is larger in first premolar

Root is longer in second premolar

Which way do the roots of upper premolars bend and at what end?

• Can bend distally at apical end, but can also be straight

Which tooth has the greatest root-to-crown ratio among maxillary teeth?

second upper premolar (1.8/1)

How many roots does second upper premolar have?

one root

How many roots does first upper premolar have?

two roots

What do both the type of upper premolars have in common in terms of their roots?

• Both first and second premolar roots taper narrower to the lingual

Which one of the upper first premolars roots is shorter?

Lingual root of the first upper premolar is shorter than the buccal root

Which marginal ridge is more cervical in both types of upper premolars?

Distal marginal ridge

Towards the mesial of whats axis line is the peaks of the lingual cusps of both types of upper premolars facing?

The peaks of both premolar’s lingual cusps are consistently positioned to the mesial of the mid-root axis line

What is the difference in how the mesial and distal ridges of lingual cusp meet in first and second upper premolars?

• Mesial and distal ridges of lingual cusp of first premolar meet at somewhat rounded angle

• On second premolar the tip of lingual cusp is relatively sharp

Is the lingual cusp longer or shorter than buccal in upper premolars?

• lingual cusp shorter than buccal cusp (especially on first premolar)

• Lingual cusp and buccal cusp nearly same length on second premolar

Is there a difference in the average length between buccal and lingual cusp peaks of first and second premolar?

• Average distance between buccal and lingual cusp peaks of first and second premolar is about the same

From proximal and lingual aspect, is the buccal or lingual cusp longer in first upper premolar?

what about in second upper premolar?

• The buccal cusp is longer than lingual

• In second upper premolar, both cusps are nearly equal in length

When viewed from proximal aspect what is the shape of the upper premolars?

What does the shape consist of?

• both upper premolars resemble trapezoid when viewed from proximal angle

• Trapezoid features two parallel sides and two nonparallel sides

In what aspect do upper premolars show distinctive concavity and where does it extend to?

• Mesial aspect has distinctive concavity in cervical third that extends onto root

Is it the first or second upper premolar that has developmental depression on the distal aspect?

First upper premolar

What is a distinctive feature of upper premolars?

mesial marginal developmental grooves

Do upper premolars have well defined buccal and lingual cusps?

yes

What are the contact points of the upper premolars?

Mesial contact - near junction of buccal and middle third

Distal contact - middle third

Compare the difference in sizes of cusp ridges of upper second and first premolars

• Second premolar has symmetrical occlusal outline so most mesial and distal cusp ridge is even

• First premolar the mesial cusp ridge is longer than distal cusp ridge

Describe the shape of the buccal outline of first upper premolars?

Rounded and almost V-shaped

Mesiodistally is the lingual half of upper premolars (especially seen in first premolars) wider or narrower?

Lingual half is narrower mesiodistally

What is the outline of the crowns of both the upper premolars?

oblong