2017 Dr Ghazy DELTA LEVEL4 LECTURE 1 Partial Coverage crown preparation .pdf

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Class 2016/ 2017

Preparations for Partial coverage Restorations For the level level 4 DELTA UNIVERSITY UNIVERSITY students

By Dr. Mohamed H. Ghazy  September 24, 2016

Tooth preparation

extracoronal

Full coverage

Partial coverage

intracoronal

Inlays onlays

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An extr extra-coro a-coronal nal metal rest restorat oration ion that th at co cove vers rs on only ly pa parrt of th the e cl clin inic ical al crown.

It gene genera rall lly y in incl clud udes es all to toot oth h su surf rfac aces es except the buccal or the labial wall in the preparation.

Buccoo-lligual displacement of the rest re stor orat ation ion is pr prev even ente ted d by in inte tern rnal al fea fe atu turres (e (e.g .g.. pr prox oxiimal bo box xes an and d grooves).

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For posterior teeth: Three Thr ee-q -qu uarte terr, mod odif ifie ied d thrree th ee-quar qu arte ter, r, se seve venn-ei eigh ghts ts,, an and d ha half lf crowns.

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For anterior teeth: Three-quarter, Thr pinledges.

MacBoyl yle e,

and

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Indications: For posterior teeth: •  1. Restore posterior teeth if the buccal wall is intact  and well supported by sound tooth structure. •   2.

When restoration or alteration of the occlusal  surface is needed.

•

3. They can be used as a retainers for an FDP.

Indications: For anterior teeth: 1- Rarely suitable for restoring damage teeth but they can be used as a retainers for  FDP, to reestablish anterior guidance and to splint teeth.

2- They are suitable for teeth with sufficient bulk because they can accommodate the necessary retentive features.

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Contraindications: 1. Short clinical crown because retention may not be adequate. 2. As a retainer for long-span FDP 3. Rarely suitable for endodontically treated anterior teeth because insufficient supporting tooth  structure remain for the retentive features. 4. Shouldn't be used for endodontically treated  posterior teeth if the buccal cusps are weakened by the access cavity or on teeth with extensively damage crowns.

Contraindications: 5. They are contraindicated in dentitions with active caries or periodontal disease. 6. Proximally bulbous teeth because making of  the necessary proximal grooves is likely to leave unsupported enamel . 7. Shouldn't be used on thin teeth with restricted facio-palatal dimensions because it is impossible to place adequate retentive proximal grooves. 8. They can't be used with poorly aligned teeth as  problems with unsupported enamel often result.

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Advantages: 1. Conservative than the full coverage preparation because it   requires less reduction of sound tooth structure.

2. Reduced  preparation.

pulpal and

periodontal insult during

tooth

3. Access to the supragingival margins is rather easy and allows the operator to perform selected finishing procedures that are more difficult or impossible with complete coverage  restorations and also allow the patient for easy cleaning of the mouth.

Advantages: 4. Access is also better for oral hygiene because less of  the margin approximates the soft tissues subgingivally. There is less gingival involvement than the complete coverage restorations. 5. Luting agent can escape more easily during cementation which produce relatively good seating of the  restoration. 6. Because of direct visibility verification of seating and cement removal are simple. 7. The remaining intact facial or buccal tooth structure  permits electric vitality testing

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Disadvantages: 1. They have less retention and resistance than do complete cast crowns. 2. Preparation is more difficult. 3. Some metal is displayed in the completed  restoration which may be unacceptable to  patients with high cosmetic expectations.

Criteria:     

4 mm long axial walls Chamfer finish line 0.5 mm axial depth 0.5 mm supragingival 6-10º taper between opposing axial walls Armamentarium

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Armamentarium

1. Narrow (approximately 0.8 mm), round tipped, tapered diamond (regular or coarse grit): used for bulk reduction. 2. Regular size (approximately 1.2 mm), round tipped, tapered diamond (fine grit) or carbide: used for finishing.

Armamentarium 3. Football shaped or wheel shaped diamond (regular  grit): used for occlusal reduction. 4. Tapered carbide fissure burs: used for preparing grooves. 5. Inverted cone carbide bur: used for preparing incisal offset.

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Armamentarium

6. Finishing stones. 7. Mirror. 8. Explorer and periodontal prop: used for assessing various  steps. 9. Chisels: used for finishing proximal flares and bevels.

Its name is derived from the number of the axial walls involved. Except for a slight bevel or chamfer placed along the bucco-occlusal line angle the buccal tooth surface remains intact.

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Occlusal reduction: 1- Mark the proposed location of the margin of the completed restoration on the tooth with a pencil.

Occlusal reduction: 2. Initial depth holes are placed in the mesial and distal fossa approximately 0.8 mm deep. They are connected by the guiding grooves.

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Occlusal reduction: First, depth grooves are cut on the anatomical ridges and grooves of occlusal surface. The amount of occlusal reduction needed :  1.5 mm on functional cusp (palatal)  1.0 mm on non-functional cusp (buccal)

Assess the amount of the occlusal clearance in maximum intercuspation and in all excursive movements of the mandible. A clearance of at least 1.5 mm should exist on the functional cusp and at  least 1 mm on the nonfunctional cusp and in the central groove 

.

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Axial reduction: 

Reduction is done to eliminate cervical to the height of contour.

undercut

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-Mesio-distally-------------   reduction follows normal contour of the tooth.

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-Occluso-gingivally--------   reduction should be parallel to the long axis of the tooth (path of withdrawal) with slight occlusal convergence.

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-Finish line --------------mm width.

→

→

→

  chamfer 0.3 to 0.5

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