Secondary and tertiary dentinogenesis oral histology

 Seondary dentin formation starts after the completion of root formation. 

=> It is formed by the same odontoblast which forms the primary dentin. But the rate of secondary dentin formation is slower than that of primary dentin. 

=> Secondary dentin differs slightly from primary dentin in staining and organization of dentinal tubules or somtimes dentinal tubules are absent.

Tertiary dentin is deposited at specific sites like damage to odontoblast or carious lesion or a site of restorative dental procedure.

=> Rate of tertiary dentin deposition is rapid and it may results in entrapment of cells. 

=> During formation of tertiary dentin collagen, DSP and DMP1 are down regulated and BSP, osteopontin are up regulated.

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Mid face fractures and classification

 Mid face fractures classified by Le fort in 1901 as : 

◦ Le fort 1 / horizontal fracture

◦ Le fort 2 / pyramidal fracture 

◦ Le fort 3 / transverse fracture 

Lefort 1 : It runs laterally from pirifirm aperture below zygomatic buttress and then from lower third of pterygoid plates joining behind maxillary tuberosity. 

SIGNS AND SYMPTOMS: 

◦ Palatal ecchymosis or Gurein sign 

◦ deranged occlusion 

◦ bruising of buccal sulcus and upper lip 

Le fort 2 : It runs from middle of nasal bone to frontal process of maxilla and then to lacrimal bone behind lacrimal sac to medial wall of orbit, crossing infrraorbital foramen and then laterally downwards below zygomaticomaxillary suture and then to pterygoid plates 

SIGNS :

◦ anesthesia and paresthesia of cheek 

◦ deranged occlusion with retropositioned maxilla

◦ step deformity and tenderness at infraorbital margin 

Le fort 3 : It runs from frontonasal suture involving ethmoid and cribriform plate entering in to inferior orbital fissure , extending backward in to pterygomaxillary fissure and laterally across lateral wall of orbit passing through frontozygomatic suture. It is also known as craniofacial dysjunction.

SIGNS: 

◦ moonlike face 

◦ hooding of eyes 

◦ Dishface appearence 

◦ diplopia 

◦ stepdeformity at frontozygomatic suture 

◦ epistaxis

By Dr. Aleena Fatima

Pattern of mineralization in dentin

Dentin is first deposited as an unmineralized matrix which consist of mainly collagen type I and small amount of ground substance which is glycosaminoglycans. 

Mineraliztion of dentin starts after the deposition of mantle dentin ( first layer of dentin ).

On the basis of rate of dentin formation histologically dentin calcification occurs in two patterns which are:

1. Globular or (calcospheric) calcification 
2. Linear calcification

1. Globular calcifiication of dentin 

It involves the deposition of crystals in several discrete areas of matrix by heterogenous capture in collagen. With the growth of crystal globular masses are formed. These masses then fuses to form a single large calcified mass.

 This pattern is most commonly seen in circumpulpal dentin.

 2. Linear calcification of dentin

When rate of dentin deposition is slow the mineralization front appears more uniform and the process is said to be linear.

 This pattern is most commoly seen in mantle dentin.

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Acid etching of enamel

Acid etching of the enamel, or enamel conditioning is an important technique in clinical practice.  37% phosphoric acid is used for this procedure. 

Stages in acid etching of enamel

Stage 1: Acid removes plaque and other debris along with thin layer of enamel. 

Stage 2: It inceases the porosity of exposed surfaces through selective dissolution of crystals which provides a better bonding surface for the restorative and adhesive materials.

Patterns in acid etching of enamel

Type I: It is the most common characterized by preferential removal of rods.

Type II: It preferentially removes the interrod enamel and rod remains intact.

Type III: It is irregular and indiscriminate. 

Uses

It is used for 

1. Fissure sealants

2. Bonding of restorative materials to enamel

3. Cementing of orthodontic brackets to the tooth surfaces

Classification of impacted teeth and its management in exodontia

Impacted Teeth:

Impacted teeth is the one whose eruption in dental arch is impeded by physical barrier within stipulated time. 

The order of impaction: 3rd molars> maxillary canine > mandibular premolars (2nd premolar most commonly) 

Management of Impaction

Surgical extraction of impacted tooth.

Indications for extraction for the extraction of impacted tooth

Following are the indications for the extraction

a) Periodontitis 

b) Odontogenic cyst or tumors 

c) Caries 

d) Pericorinitis 

e) Root resorption 

f) Jaw fractures 

Contraindications for extraction of impacted tooth 

a) Advanced age 

b) Medically compromised 

c) Damage to adjacent structures ( nerves and teeth ) 

 Classification System for Mandibular Third Molar Impactions

 1. Winter's classification

It is based on angulation of the long axis of the impacted third molar with respect to the long axis of the adjacent second molar.

1. Mesioangular impaction

2. Horizontal impaction

3. Vertical impaction

4. Distoangular impaction

The order is based on easiest extraction.

Mesioangular being the easiest to extract. 

Mesioangular > vertical > horizontal > distoangular 

Other angulations are buccal, lingual/palatal and transverse

2. Pell and Gregory classification

 It is based on relation to anterior border of ramus and occlusal plane.

 Following are the subclasses

Class 1: Impacted 3rd molar anterior to anterior body of ramus.

Class 2: It is posterior to ramus. 

Class 3: It is within ramus .

Class A: Occlusal plane of impacted mandibular 3rd molar is at occlusal plane of mandibular 2nd molar. 

Class B: It is in the middle  of occlusal and cervical third. 

Class C: It is at cervical level. 

Class 3 and C are difficult to extract and class 1 and A are easier to extract. 

Basic necessities for oral surgery

 There are two principal requirements.

1. Adequate Visibiltiy

2. Assistance

1. Adequate Visibility

It depends on the following three factors

a) Adequate access which depends on patients ability to open the mouth widely, increased exposure with proper retraction and proper creation of surgical flaps.  

b) Adequate light which is an absolute necessity. Surgeon and assistance should continously repositioned light or use more than one overhead light or use headlight for better visibility of the field.

c) A surgical field free of excess of blood and other fluids and debris which can be achieved by high volume suctioning with relatively small tip.

2. Assistance 

An assistant should properly trained and be familiar with the procedure. 

Cross striations in enamel

Cross striations in enamel represents the daily rhythmic pattern of enamel of formation. Enamel is formed at the rate of 4mm per day and these are visible under microscope in the form of cross striations.

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