preparation for partial coverage crowns

 Its use is based on the premise that an intact surface of
tooth structure should not be covered by a crown if it is not
essential to the retention, strength or esthetic of
restoration.
Appearance of enamel
Gingival health (supragingival margins)
Pulpal problem (2.5 times)

 Tooth structure is spared
 Much of margin is accessible to dentist and patient
 Reducing the possibility of periodontal irritation
 Easily seated in cementation (hydraulic cylinder)
 Seating is more easily verified
 Electric pulp test

 Less retention
 Metal display
 Dexterity of operation

 Not as retentive as full crown
 Just used for single restoration or retainers for short-
span FPDs.
 Preparation feature used to compensate lost retention
& resistance.
 Commonly used feature is groove

Retention
 Less than full crown
 Adequate for single crown
 Adequate for Short-span FPD
 Features like Groove

preparation for partial coverage crowns

 Commonly used partial coverage
 If designed skillfully can be very esthetic:
 Conversational esthetics (moderate & reasonable
demands)

 Esthetic demands and ease of preparation have led to
near-total demise of anterior ¾ crown.
1. Short span
2. Caries
Path of insertion: incisal ½ to 2/3

 One of the disadvantages of conventional FPDs is
tooth structure destruction even in partial coverage.
 Inlay retainers
 Acrylic resin pontics
 Resin bonded FPD

 Rochette bridge: (Mechanical Retention)
 Funnel shape perforation
1. Weakening of the metal retainer by the perforations.
2. Exposure to wear of the resin at the perforations.
3. Limited adhesion of the metal provided by the perforations

Maryland bridge: (Micromechanical Retention)
 Electrochemical pit corroding tech.
 Technique sensitive
 Overetching: electropolished surface
 Chemical etching
 Air abrasion combined with silane

 Virginia bridge (lost salt tech.):
 Incorporating salt crystals into the retainer patterns,
leave cubic voids
 0.5 – 1 mm crystal-free margin

 Unfilled resin (Rochette)
 Unfilled/filled composite resin
 Chemically active (adhesive) resin: 4-MTE , MDP
 Rely on adhesion to metal (not microretention)
 Etching was no longer necessary
 Air abrasion with small particle for cleaning
 Tin plating for noble metal

 Advantages:
1. Reduced cost
2. No anesthetic needed
3. Supragingival margins
4. Minimal tooth preparation

 Disadvantages:
1. Irreversible
2. Longevity
3. No alignment correction

 Indication:
1. Caries free abutment teeth
2. Mandibular incisor replacement
3. Maxillary incisor replacement
4. Periodontal splints
5. Single posterior tooth replacement

 Contraindications:
1. Extensive caries
2. Nickel sensitivity: tin plated noble alloy can be used
3. Deep vertical overbite

 Axial reduction and guide plans
 Slight extensions to facial surface (180 degree)
 Finish line
 Occlusal clearance
 Vertical stops:
 Countersink on incisors
 Cingulum rest on canine
 Occ. rest on posteriors

0.5 mm, only on max. anterior teeth
• 1.5-2 mm from incisal edge
• Just incisal to the occ. contact
0.5 clearance
Flat notches or countersink

1 mm supragingival
Cingulum groove
Proximal groove

 Rubberdam
The casting:
 Air abrasion of retainers: 2-3 s per cm2, 60-100 psi
 Casting is washed:
 Running water : 1 min
 Ultrasonic unit: 2 min
 Tin plating(if noble metal): 5-10 s, 0.5 um
 Casting is rinsed: 2 min
 Blown dry

 The teeth:
 Pumice and rubber prophy cup
 Pumice is washed
 40_50 % phosphoric acid : 60 s
 Rinse and dry
 40_50 % phosphoric acid is reapplied: 15 s
 Rinse and dry: 20s
 Mylar strip is placed

 ED primer is mixed and applied on the preparation: 60s
 Pastes are mixed and applied on the retainers (not on the abutments)
 Oxyguard II on the margins: 3 min

preparation for partial coverage crowns

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preparation for partial coverage crowns