Class III Denture

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Arrangement of Teeth in Class 3 Jaw Relations

Problems associated with class 3 relations…

The condition is characterized by the lower anterior ridge being forward in relation to maxillary ridge that may vary from edge to edge relation OR marked prognathism of mandible.

Class 3 upper and lower jaw relation

Management of Problems Associated with class 3 Relations

When ridges are edge to edge:

  • Incisal edges of upper and lower incisors and cuspids also meet in edge to edge.
  • Upper and lower teeth are placed as near as possible to the labial plates of bone in their respective ridges.
  • Normal horizontal overlap can be given only if it is possible.
Normal horizontal overlap can be given only if it is possible
  • Normal horizontal overlap should not be attempted when ridge relation does not permit-if done then stability of denture will be greatly hampered.
  •  Edge to edge relation enhances stability.

Extreme protrusion of the mandible:

  •  Negative or reverse horizontal overlap should be used (magnitude depends on degree of  protrusion).

Canine relationship in CLASS 3 cases:

  • Relationship – usually does not pose much of a problem.
  • Distal surface of lower canine coincides with the tip of the upper canine.
  • If it finishes mesial to the canine tip, the discrepancy can be rectified using small spaces between the lower anterior teeth so that the canine will have normal relation.
Distal surface of lower canine coincides with the tip of the upper canine

Setting  Posterior  Teeth in Class 3 Cases

Arrangement of posterior teeth

  • Crest of the lower arch is located further buccally than that part of the upper residual ridge which leads to a problem of developing an adequate occlusal relationship between upper and lower teeth.
  • To ensure there is normal occlusal contact with the lower teeth, the upper posterior teeth can be set slightly buccal to the crest of the ridge,  therefore results in a wider arch form.

When the Lower Arch is Too Wide…

  • Interchange using upper teeth on the lower denture and lower teeth on the upper denture.
  • Interchange is made across the arch as well (e.g. right upper teeth are placed on left lower ridge, left lower teeth are placed on right upper arch).

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Class II Denture

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Image source from internet

About teeth setting in abnormal jaw relations…

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Upper-lower ridge relationship is an individual problem for each complete denture patient. For abnormal ridge relations, it is needed to modify normal guidelines necessary to fulfill all demands.


Maxillary Protrusion Problems Faced & Arrangement of Teeth

Changes in anterior arrangement

1) Increased overjet – Due to maxillary prognathism, there will be increased overjet. It leads to abnormal upper and lower canine tooth relationship. No attempt should be made to reduce it by moving upper teeth palatally or lower teeth labially.

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Increased Overjet

2) Changes in canine relationship – Normally, the distal surface of lower canine tooth (located at) tip of the cusp of upper canine, whereas in maxillary prognathism it leads to the lower canine tooth finishing anywhere from the tip to distal surface of upper canine. Excessive prognathism leads to distal incline of cusp of lower canine posterior to distal surface of upper canine tooth.

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Changes in Canine Relationship


Setting Upper Posterior Teeth in Class 2 Relation

Upper first premolar setting

  • If necessary, the palatal cusps of the 1st premolar is flattened.
  • This is done to get good intercuspation with lower premolar.

Upper second premolar setting

  • Upper 2nd premolar is set with its flattened lingual cusp occluding with the flattened buccal cusp of the lower second premolar.
  • There is less buccal overlap and a larger area of contact is possible between this teeth.

Setting upper molars

  • Upper molars are set in normal relation as done in class 1 teeth arrangement.

Setting Lower Anterior Teeth in Class 2 Relation

Lower anteriors are set according to normal principles. The overbite is maintained at 2mm. However, there will be increased overjet.

Setting of Lower Posteriors

  • The lower first molar is placed in Class I relation. (Key of Occlusion).
  • The remaining space for premolar is assessed. Usually there will be space for only 1 premolar. The lower premolar is set in the remaining space. The buccal cusp of lower premolar occludes with the palatal cusp of upper second premolar.
  • The lower second molar is set in normal relation with the upper second molar.

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Tooth Morphology

CENTRAL INCISORS

Maxillary Central IncisorMOR_UCI00

MOR_UCI01


 

Mandibular Central Incisor

MOR_LC00MOR_LCI01


 

LATERAL INCISORS

Maxillary Lateral Incisor

MOR_ULI00

 


 

Mandibular Lateral Incisor

MOR_LLI00


 

CANINES

Maxillary Canine

MOR_UC00

MOR_UC01


 

Mandibular Canine

MOR_LC00MOR_LC01


 

PREMOLARS

Maxillary 1st Premolar

MOR_U1P01

 

 


 

Maxillary 2nd Premolar

 

MOR_U2P01.jpg


 

Mandibular 1st Premolar

MOR_L1P01

MOR_L1P02


 

Mandibular 2nd Premolar

MOR_L2P01


 

MOLARS

Maxillary 1st Molar

MOR_U1M01


 

Maxillary 2nd Molar

MOR_U2M01.jpg


 

Mandibular 1st Molar

MOR_L1M01


 

Mandibular 2nd Molar

MOR_L2M01.jpg

 

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References:
Tooth morphology – Wheelers

Tooth Anatomy

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Anatomy of Human Tooth

The main structure of the tooth consists of:

  • Enamel
  • Dentin
  • Cementum
  • Pulp

 

 

WHAT IS ENAMEL ?

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Microscopic view of the enamel

It is a protective outer covering of the crown which is the hardest substance in the human body.

It doesn’t contain any nerves or blood vessels therefore it is insensitive to pain.

However, it cannot undergo repair when damage is caused by decay or injury is permanent.

Microscopically, it consists of long solid rods – prisms.

 

 

WHAT IS DENTIN ?

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Magnified view of the dentine

 

The dentin forms the interior of the crown and root.

It is highly sensitive to pain therefore protected from painful stimuli by enamel of crown and cementum of root.

It contains dentinal tubules which make it slightly elastic – like a shock absorber.

It is softer than enamel, less mineralised.

 

 

WHAT IS CEMENTUM ?

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Cementum under the microscope

 

The cementum is a calcified substance covering the root of tooth which is formed by cementoblasts.

It anchors the tooth to bone via periodontal ligament.

 

 

 

 

WHAT IS PULP ?

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Pulp under the microscope

 

It is a purely soft tissue, unlike the enamel, dentine and cementum where nerves & blood vessels enter root apex through apical foramen and pass up through root to the pulp chamber.

It contains odontoblasts (dentine forming cells) at the outermost layer,  next to dentine. Odontoblasts contain dentinal fibrils which pass into dentine through tubules.

The secondary dentine is produce slowly throughout life whereas the reparative dentine is produced quickly in response to damage.

 


 

Supporting Structures of the Tooth

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i) BONE

Jaws bones contain dense outer layer (compact  bone) and softer interior (spongy/cancellous bone)

Alveolar process – It is a ridge of bone containing tooth sockets

Lamina dura – is compact bone lining of tooth socket where a well defined lamina dura is an indicator of good periodontal health.

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Normal lamina dura
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Thickening of lamina dura due to periodontal disease
Could you identify the differences?

 

ii) GINGIVA

The gingiva is firmly attached to underlying alveolar bone that fits around the neck of each tooth like tight cuff.

Gingival crevice – A shallow crevice present between tooth surface or gum margin

Interdental papilla – A triangular mound of  gum in between teeth

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iii) PERIODONTAL LIGAMENT

A soft fibrous tissue which attaches each tooth to its socket (cementum to lamina dura) which also acts as a shock absorber.

It contains nerves, blood vessels and bundles of fibres are also attach the  gingival margin to the tooth or alveolar bone and each tooth to its neighbour.

 

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References:
Dental anatomy – Julian B.Woelfel,Rickne C.Scheid – 6th edition

Dental Anatomy

WHAT IS DENTAL ANATOMY ABOUT?

It is the study of the development, morphology, function, and identity of each of the teeth in the human dentitions, as well as the way in which the teeth relate in shape, form, structure, color, and function to the other teeth in the same dental arch and to the teeth in the opposing arch.

WHAT ARE THE TYPES OF HUMAN DENTITION?

A) Deciduous (baby) teeth 

– Twenty ( 20) primary teeth.

– Arches – maxillary and mandibular.

– Quadrants – each arch divided in half.

(i)  Maxillary right and left.

(ii)  Mandibular right and left.

– Anterior and posterior teeth.

(1)  Anterior – centrals, laterals, and cuspids.

(2)  Posterior – molars.

 

B) Permanent teeth

– 32 permanent teeth.

– Arches – maxillary & mandibular

– Quadrants.

(1)  Maxillary right and left.

(2)  Mandibular right and left.

– Anterior and posterior teeth.

(1) Anteriors – central, lateral and cuspids.

(2)  Posteriors -bicuspids and molars.

 

Tooth Identification Systems | Numbering or Coding Systems

Palmer Notation System

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Universal System

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International FDI System (two digit system)

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WHAT ARE THE TOOTH SURFACES?

Line and Point Angles:

Line angle:

It is formed by the junction of two surfaces and its name is derived from both surfaces.

 

Point angle:

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It is formed by the junction of three surfaces and its name is derived from these surfaces.

 

Division into Thirds:

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Anatomical Landmarks of the Crown:

Lobe

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Primary centers of calcification and growth formed during the crown development.

Each tooth begins to develop from four lobes or more.

The pulp chamber has pulp horns corresponding to these lobes.

 

Crown Elevations

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Mamelons:

3 small rounded projections of enamel present in the incisal third of newly erupted permanent incisors.

 

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Cingulum:

A bulge on the cervical third of lingual surface of the crown in anterior teeth.

 

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Cusps:

Pyramidal projections on the incisal edges of canines and on the occlusal surfaces of the premolars and molars. Each cusp has four cusp ridges.

 

Tubercle:

It is a small elevation produced by excessive formation of enamel.

Tubercle is noticed at :

  • the palatal surface of E & 6
  • sometimes at the lingual surface of incisors over the cingulum.

N.B. Tubercle differs from cusp , it is formed of enamel only while cusp is formed of pulp horn covered by dentin and enamel.

 

Ridges:

Ridge or elevation of enamel forming the margin of the surface of a tooth; on mesial /distal margins of lingual surfaces – anterior teeth ; mesial & distal margins of occlusal surfaces – posterior teeth.

ANA_017 Marginal ridges

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Linear ridge

Crown Depressions

a) Linear Depressions:

  • Developmental grooves: Sharply defined narrow grooves that separate cusps or primary parts of teeth.
  • Supplemental grooves: Small , irregularly placed  auxiliary grooves ; Branches from developmental grooves ; They do not denote union of primary lobes ; The third molars followed by second permanent molars are characterized by high number of supplemental grooves.

b) Irregular Depressions:

  • Fossa: Depression or cavity
  • Fissures:  Narrow crevice at the depth of developmental grooves.Caused by incomplete fusion of enamel during tooth development . Decay mostly begins in deep fissure .
  • Pits: Occurs at the depth of fossa where two or more grooves join.Also, enamel defects where caries begin . 

     


WHAT ARE THE ANOMALIES?

Anomalies in number: anodontia, hypodontia, hyperdontia

Anomalies in size: macrodontia, microdontia, fusion, gemination

Anomalies in shape:  dens evaginatus (Leong’s premolar ),dens invaginatus, taurodontism, peg laterals, dilaceration

 

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References:
Tooth morphology – Wheelers
Dental anatomy – Julian B.Woelfel,Rickne C.Scheid – 6th edition
Dental Embryology. Histology and Anatomy-Mary Bath – Balogh , Margaret J Fehrenbach – second edition