Posterior Crowns KM

8/11/2019 Posterior Crowns KM

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Dr. Keyvan Moharamzadeh

Academic Unit of Restorative Dentistry

The University of Sheffield

Posterior Full-Coverage Crowns


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Aims

The reasons for crowning acompromised tooth

Design and biological considerations

Materials

Full coverage crowns: FGC, PFM,All-ceramic

Tooth preparations

Clinical Sta es


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The reasons to restore a

compromised tooth Restoring function (first) and

aesthetics (second)

Restoring structural integrity andresisting fracture

Integrating with other prosthesis


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The Compromised Tooth

Restoring function (first) andaesthetics (second)


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Endodontically treated

teeth Weakened tooth due to access

cavity preparation

Loss of Structural integrity

associated with loss of roof of the

pulp chamber

Loss of dentine elasticity


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Posterior Teeth

Cuspal protection is required if:

Loss of marginal ridgesLoss of substantial tooth structure

Heavily restored tooth(Panitvisai P et al., J Endod 1995)


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Posterior Teeth

Cuspal protection can be achieved by:

Adhesive restorations Cusp-coverage cast restorations

Full-coverage restorations


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Restoring function (first) andaesthetics (second)


Integrating with other prosthesis


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Posterior Crowns

Design Considerations Is the tooth in function?

Appearance

Adjacent Teeth

Periodontal Tissues

Pulp Retention of the crown to the tooth

Materials


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Posterior Crowns

Periodontal Tissues Plaque control

Periodontal attachment

Alveolar bone levels

Status of periodontal disease


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Pulpal death following

crown preparationsAggressive insult to the tooth,

dentine and odontoblasts

Thermal damage

Local anaesthesia

Dessication Bacterial contamination


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Pulpal death following

crown preparations 10% - Hammerle 2000

19% - Saunders 1999 10% - Valderhaug 1997

6% - Jackson 1992

10% - Kerschbaum 1979 and 1993


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University of Graz

Austria

School of dentistry

Dep. of Prosthodontics

Gerwin Arnetzl


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Minimum of 0,7 mm dentine thicknesis recommended for pulpal protection

Gente 1995,Jde 1986, Robach 1982

0,7mm


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Courtesy G. Unterbrink


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A shoulder preparation of 1.2 mmResults in a remaining dentine width of 0.7 mm

only in50 % of maxillary molars

in all other premolars and molars theremaining dentine width is less than

0.7mm


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A 1.2mm shoulder crown preparationon a posterior tooth leaves 0.7mm

remaining dentine thickness


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Thermal

Chemical

Osmotic

Dessication


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Thermal

Chemical

Osmotic

Dessication

BacterialToxins


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Posterior Crowns

Materials

Balancing Functionand Aesthetics


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Posterior Crowns

MaterialsMetal

Metal-CeramicCeramic


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Posterior Crowns

MaterialsMetal (Full Gold Crown)

Minimal tooth reduction

Least aesthetic (? Not an issue)

Can be adjusted intra-orally (occlusion)


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Gold alloy types:

Type I (Soft) was hard enough to stand up to biting forcesbut soft enough to burnish against the margins of a cavitypreparation. It was used mostly for one-surface inlays.

Type II (Medium) was less burnishable but hard enough tostand up in small, multiple surface inlays that did not includebuccal or lingual surfaces.

Type III (hard) The most commonly used type of gold forall-metal crowns and bridges. A typical type III gold alloyincludes the following metals: Gold 75% Silver 10% Copper 10% Palladium 3% Zinc 2%

Type IV (Extra hard) was used for partial dentureframeworks but was not used in fixed prosthetics.


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Full Gold Crown

Donovan T, 2004: Retrospective clinicalevaluation of 1,314 cast gold restorationsin service from 1 to 52 years.

The survival rates at various time periods were97% at 9 years, 90.3% at 20 years, 94.9% at25 years, 98% at 29 years, 96.9% at 39 years,

and 94.1% for restorations in place > 40years. It appears that properly fabricated castgold inlays, onlays, partial veneer crowns, andfull veneer crowns can provide extremely

predictable, long-term restorative service.
http://www.ncbi.nlm.nih.gov/pubmed?term=Donovan%20T%5BAuthor%5D&cauthor=true&cauthor_uid=15597641http://www.ncbi.nlm.nih.gov/pubmed?term=Donovan%20T%5BAuthor%5D&cauthor=true&cauthor_uid=15597641


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Posterior Crowns

MaterialsMetal-Ceramic

Metal Core

Extensive buccal tooth reduction

Aesthetics at the cost of tooth tissue

Only the metal component can beadjusted intra-orally


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PFM alloy types:

High-noble alloys have a minimum of 60% noble metals (anycombination of gold, palladium, and silver) and a minimum of 40% byweight of gold. They usually contain a small amount of tin, indium, oriron which provides for oxide layer formation. These metals provide a

chemical bond for the porcelain. Noble alloys (gold, palladium, or silver) contain at least 25% by weight

noble metal. They have relatively high strength, durability, hardness, andductility.

Base-metal alloys contain less than 25% noble metal. They are muchharder, stronger and have twice the elasticity of the high-noble and

noblemetal alloys. Castings can be made thinner and still retain therigidity needed to support porcelain. They appear to be the ideal metalfor cast-dental restorations and were heavily used for PFM frameworksdue to their low cost and high strength characteristics. Unfortunately,nickel and beryllium, two of the most commonly used constituents ofbase-metal alloys can cause allergic reactions when in intimate contact

with the gingiva.


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Ceramic-Fused to metal Crown


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PFM crown

Pjetursson et al., 2007.A systematicreview of the survival and complicationrates of all-ceramic and metal-ceramicreconstructions after an observationperiod of at least 3 years. Part I: Singlecrowns.

In meta-analysis, the 5-year survival of all-ceramic crowns was estimated at 93.3% and95.6% for metal-ceramic crowns.
http://www.ncbi.nlm.nih.gov/pubmed/17594372http://www.ncbi.nlm.nih.gov/pubmed/17594372http://www.ncbi.nlm.nih.gov/pubmed/17594372http://www.ncbi.nlm.nih.gov/pubmed/17594372http://www.ncbi.nlm.nih.gov/pubmed/17594372http://www.ncbi.nlm.nih.gov/pubmed/17594372http://www.ncbi.nlm.nih.gov/pubmed/17594372http://www.ncbi.nlm.nih.gov/pubmed/17594372http://www.ncbi.nlm.nih.gov/pubmed/17594372http://www.ncbi.nlm.nih.gov/pubmed/17594372http://www.ncbi.nlm.nih.gov/pubmed/17594372http://www.ncbi.nlm.nih.gov/pubmed/17594372http://www.ncbi.nlm.nih.gov/pubmed/17594372http://www.ncbi.nlm.nih.gov/pubmed/17594372http://www.ncbi.nlm.nih.gov/pubmed/17594372http://www.ncbi.nlm.nih.gov/pubmed/17594372


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Posterior Crowns

MaterialsAll Ceramic

High strength ceramic core

Most aesthetic

Low edge strength

Requires extensive reduction

Intra-oral adjustment not possible


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All ceramic Crowns

Wang Xet al., 2012.A systematicreview of all-ceramiccrowns: clinical fracture rates inrelation to restored tooth type.

All-ceramic crowns demonstrated an acceptableoverall 5-year fracture rate of 4.4%irrespective of the materials used. Molar

crowns (8.1%) showed a significantly higher 5-year fracture rate than premolar crowns(3.0%), and the difference between anterior(3.0%) and posterior crowns (5.4%) also

achieved significance.
http://www.ncbi.nlm.nih.gov/pubmed?term=Wang%20X%5BAuthor%5D&cauthor=true&cauthor_uid=22930765http://www.ncbi.nlm.nih.gov/pubmed/22930765http://www.ncbi.nlm.nih.gov/pubmed/22930765http://www.ncbi.nlm.nih.gov/pubmed/22930765http://www.ncbi.nlm.nih.gov/pubmed/22930765http://www.ncbi.nlm.nih.gov/pubmed/22930765http://www.ncbi.nlm.nih.gov/pubmed/22930765http://www.ncbi.nlm.nih.gov/pubmed/22930765http://www.ncbi.nlm.nih.gov/pubmed/22930765http://www.ncbi.nlm.nih.gov/pubmed/22930765http://www.ncbi.nlm.nih.gov/pubmed/22930765http://www.ncbi.nlm.nih.gov/pubmed/22930765http://www.ncbi.nlm.nih.gov/pubmed/22930765http://www.ncbi.nlm.nih.gov/pubmed/22930765http://www.ncbi.nlm.nih.gov/pubmed/22930765http://www.ncbi.nlm.nih.gov/pubmed/22930765http://www.ncbi.nlm.nih.gov/pubmed?term=Wang%20X%5BAuthor%5D&cauthor=true&cauthor_uid=22930765


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Principles of ToothPreparation for crowns

Preservation of tooth structure

Retention

Resistance

Structural durability

Marginal integrity

P i C


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Posterior Crowns

Retention of the crown Retention Form: Prevents

dislodgement of the crown in an

axial direction.

Resistance Form: Prevents

dislodgement of the crown due torotation from a lateral load.


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Tooth Preparation Design

Preparations should be well-definedand well-finished


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Preparations should be well-defined andwell-finished

A clear finish line should be visible


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A clear finish line should be visible Ceramic margins should be a butt-joint rounded shoulder

- All Ceramic Crown -


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Contour togingiva

Shouldermargin


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A clear finish line should be visible Ceramic margins should be a butt-joint

rounded shoulder

Metal margins should have chamfermargins


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Chamfer margins
http://www.google.co.uk/url?sa=i&rct=j&q=chamfer+margin&source=images&cd=&cad=rja&docid=m-vagv_sEgStgM&tbnid=VFJhg_IveTC_zM:&ved=0CAUQjRw&url=http%3A%2F%2Fwww.technicdentallab.com%2Flava.asp&ei=B8kfUYTCFtGVswbRnYGwDw&bvm=bv.42553238,d.Yms&psig=AFQjCNEZ_zukXgFICW98kUO5wnHb6rKuYw&ust=1361123906528902


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A clear finish line should be visible Ceramic margins should be a butt-joint

rounded shoulder

Metal margins should have chamfer

marginsAll preparation line angles and point

angles are best rounded


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Tooth Preparation for All

Ceramic Crown

- All Ceramic Crown -


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Minimum occlusal reduction: 1.5mm

>2 mm inareas ofstress


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Occlusal reduction reflects the

morphology of the tooth and thefunctional pathways of the occlusion


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5 taper

Shouldermargin

Occlusalreduction:>1.5mm

>2 mm inareas ofstress


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Zone of retention


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Tooth Preparation for

PFM crown


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PFM crown prep
http://www.google.co.uk/url?sa=i&rct=j&q=pfm+crown+preparation&source=images&cd=&cad=rja&docid=0tSFYZHGZn-hDM&tbnid=tafO1cRdQRf_OM:&ved=0CAUQjRw&url=http%3A%2F%2Fwww.dentaljuce.com%2Ffruit%2Fpage.asp%3Fpid%3D106&ei=4tQfUYSGH6iP4gTimYDQCQ&bvm=bv.42553238,d.bGE&psig=AFQjCNF0rCiGqOhclU68gnVLLfciXkDmFw&ust=1361126919702959http://www.google.co.uk/url?sa=i&rct=j&q=pfm+crown+preparation&source=images&cd=&cad=rja&docid=0tSFYZHGZn-hDM&tbnid=z3h25lWGvXhQYM:&ved=0CAUQjRw&url=http%3A%2F%2Fwww.dentaljuce.com%2Ffruit%2Fpage.asp%3Fpid%3D106&ei=tNQfUbKVE7H24QTIpYCQBg&bvm=bv.42553238,d.bGE&psig=AFQjCNF0rCiGqOhclU68gnVLLfciXkDmFw&ust=1361126919702959


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PFM crown prep
http://www.google.co.uk/url?sa=i&rct=j&q=posterior+crown+preparation&source=images&cd=&cad=rja&docid=bCVfaJZdhl8iTM&tbnid=NcBOeWXljdmShM:&ved=0CAUQjRw&url=http%3A%2F%2Fdentistryandmedicine.blogspot.com%2F2011%2F07%2Fpfm-posterior-crown-restorations.html&ei=ydMfUeGALIfh4QSNpoD4DQ&bvm=bv.42553238,d.bGE&psig=AFQjCNFfu9lKTk-_j7m1AH2hO4EQ8VcuSg&ust=1361126691652584


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Tooth Preparation for Full

Gold Crown


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Full Gold Crown Prep

Posterior Crowns
http://www.google.co.uk/url?sa=i&rct=j&q=gold+crown+preparation+&source=images&cd=&cad=rja&docid=eEnG9rqSTdhI9M&tbnid=XBmEChIFFjndLM:&ved=0CAUQjRw&url=http%3A%2F%2Fwww.dentaljuce.com%2Ffruit%2Fpage.asp%3Fpid%3D417&ei=iNYfUamPIsrL4ATzg4HoDA&bvm=bv.42553238,d.bGE&psig=AFQjCNFMxbMm6D3REJPw8i2wG68GdhrF9Q&ust=1361127324841008


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Posterior Crowns

Clinical Stages-Phase I Pre-op clinical and radiographic

assessment

Further investigations, study models,diagnostic wax-up

Treatment Planning

Informed consent

Posterior Crowns


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Posterior Crowns

Clinical Stages-Phase II

Tooth build up (if necessary) and

Preparation Impression

Occlusal Record

Temporisation

Fabrication (Lab stage)

Posterior Crowns


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Posterior Crowns

Clinical Stages-Phase III Removal of temporary crown

Try-in of definitive crown

Cementation of definitive crown

Occlusal check

Review

Posterior Crowns KM

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