PRINCIPLES OF TOOTH PREPARATION
Preservation of the tooth structure - 4 models of preparations

1. THREE QUARTER CROWN
i. Occlusal + proximals + lingual
ii. Labial is untouched
iii. They are retained by grooves on mesial, distal & occlusal surfaces.
iv. For all teeth
v. Bur used to add retentive groove is – Tapered (/radial) fissure bur*
vi. Always made of cast metal.

2. REVERSE / MODIFIED ¾ CROWN
 Preserves lingual surface
 Commonly for mandibular molars
 Damaged buccal surface with intact lingual side
 Also useful on lingually tilted molar, coz lare amount of tooth
structure may need to be removed, might involve the pulp.
So to avoid that.

3. MESIAL / PROXIMAL HALF CROWN
vii. Mesially tilted mandibular molars

4. SEVEN BY EIGHT CROWN
 For posterior esthetics
 On maxillary molars
 Mesiobuccal area not prepared or crowned
 Mesial 1/3rd of buccal surface — unprepared.
 Useful in distal surface caries
 More coverage than a ¾ th crown

Mesially Tilted crown cases — mandibular molars.
b. Orthodontic uprighting (theoretically 1st choice , for exam point of view)
c. Use of non-rigid connectors (key and key hole, tenon-mortis etc)
d. Mesial half crown
e. Telescopic crown (least preferred type)


Retention and Resistence
a) Degree of taper - 6° tapering
b) Best bur — tapered fissure
---------i. Diamond coated
---------ii. Or tungsten coated carbide bur, known as 159L bur

TWO PLANE PREPARATION *

COMPLICATIONS OF 1 PLANE
A. Incisal only — food lodgement
i. Poor oral hygiene
ii. Gingival health compromised
B. Gingival only — opaqueness on incisal edge

Q. The ideal post drill for most posterior teeth is: peso drill size 2-3.

Q. Instrument used for wax grooving for a die in FPD: * Instrument we use to make a groove in the wax is: PKT no3.