Restoration of endodontically treated teeth :

Answers to important questions

Charles J. Goodacre, DDS, MSD Professor of Restorative Dentistry

Loma Linda University School of Dentistry This program of instruction is protected by copyright ©. No portion of this program of instruction may be reproduced, recorded or transferred by any means electronic, digital, photographic, mechanical etc., or by any information storage or retrieval system, without prior permission.

Do endodontically treated teeth need crowns?

•  Greater force required to activate proprioception (can bite harder before protective mechanism activated). One study showed 57% higher biting force required to activate pressoreceptors

•  Some physical properties are not affected and others are altered such as flexibility (decreased)

•  Greater cuspal deflection after RCT

Summary of Changes After RCT

Mandibular Molar Cuspal Deflection

•  Up to 1 µm with intact teeth •  MO cavity preparation causes < 2µm of

movement •  MOD cavity preparation produces 3 to 5 µm •  Endodontic access preparations produces 7 – 8 µm in the MO group and 12 – 17 µm of movement in the MOD group (a 2 – 3 fold increase) Panitvisai, J Endod 1995;21:57-61

Clinical Fractures •  1639 RCT posterior teeth were restored with

amalgam – no cusp coverage

•  Maxillary premolars with MOD amalgams had the highest fracture rate –  28% fractured within 3 years, –  57% fractured after 10 years, and –  73% fractured after 20 years

Hansen, Endod Dent Traumatol 1990;6:49-55

Survival of RCT Teeth & The Presence Of Crowns

•  RCT teeth without crowns lost at 6 times the rate of those with crowns (did not compare anterior vs. posterior teeth).

•  2nd molars had appreciably poorer 10 year survival than all other teeth.

•  Teeth with 2 proximal contacts had significantly longer survival than teeth with 1 or no proximal contacts. Aquilino, 2002

Survival of RCT Teeth & The Presence Of Crowns

•  116 RCT teeth that were extracted.

•  RCT teeth without crowns were lost after an average time of 50 months.

•  RCT teeth with crowns were lost after an average time of 87 months. Vire, 1991

Failure of Molars with No Crowns •  220 molars observed for time periods between 6

mo & 10.2 yrs •  101 teeth failed (46%) after 5 years (caries, crack

in tooth or filling, loss of filling, root fracture) •  14 of 101 teeth were unrestorable •  1, 2, 5 yr survival rates (96%, 88%, 36%) •  Teeth with maximum tooth structure (like Class I

filling) – 5 yr survival of 78% Nagasiri, J Prosthet Dent 2005;93:164-170

Composite Resin & RCT Molars

•  Completely intact except for conservative access opening

•  Can be successfully restored with composite resin and no crown Nagasari, J Prosthet Dent 2005

Crowns significantly improved the success of endodontically treated posterior teeth but did not improve the success of anterior teeth Sorensen, 1985

True or False Question

•  Crowns should be placed on all root canal treated teeth

•  False

•  Which teeth require crowns most of the time? •  Posterior teeth

Do posts improve the longevity of endodontically treated teeth or enhance strength?

Intact Anterior Crowns Provide Better Fracture Resistance Than Posts &

Cores

•  Maxillary incisors, without posts, resisted higher failure loads than the other groups with posts and crowns Pontius, J Endod 2002;28:710-715

•  Mandibular incisors with intact natural crowns

exhibited greater resistance to transverse loads than teeth with posts and cores Gluskin, J Endod 1995;21:33-37

Effect of Posts – Their Purpose

•  In laboratory tests on extracted teeth, posts either weakened the teeth or had a neutral effect.

•  There is no clinical data to show posts strengthen a tooth.

•  Therefore, there is no strengthening effect and the only function of a post is retention of a core.

Restorative Material Core vs

Post and Core •  Preference for restorative material core (without a

post) whenever it can be properly retained. This concept works best for molars but can work on premolars and anterior teeth where sufficient material bulk can be present.

•  Core retention can be obtained using undercuts, slots, grooves, boxes, pulp chamber, pins, bonding.

PULP CHAMBER RETENTION

Amalgam cores

Composite resin cores

With All Core Materials, There Needs to be Adequate Bulk To Resist Transverse Fracture. When The Bulk Is Not There, Then A Post Is Needed

True or False Question

•  Posts strengthen teeth.

•  False, except perhaps thin coronal tooth structure. They weaken roots.

•  The main purpose of a post is to retain a core. •  True

•  Post loosening (5%) •  Root fracture (3%) •  Caries (2%) •  Periodontal Health (2%) •  Root perforation (1%) •  Bent / fractured posts (1%)

What are the most common complications associated with posts

and cores?

•  As with all clinical procedures, we should focus upon preventing or minimizing complications associated with posts and cores.

Retention & Root Fracture

•  Threaded posts are the most retentive but clinical study data indicates they reduce tooth survival by about 10%

•  Parallel posts are more retentive than tapered posts. Parallel posts have a slightly lower tooth fracture incidence than tapered posts

Parallel vs Tapered Posts

•  It appears that prefabricated parallel – walled posts have some advantages

•  However, some teeth are not well suited for parallel posts

Post Form Summary

•  It is generally recommended that posts not be threaded. However, threaded posts may be useful in the presence of short roots that possess adequate root thickness, where retention is the primary concern and cemented posts will not be sufficiently retentive

Post Form Summary •  Parallel – walled cemented posts are

generally preferred over tapered cemented posts. However, custom cast, tapered posts are recommended for teeth with tapered roots and roots with substantial concavities such as mandibular incisors, maxillary first premolars and certain molar roots where preparation of round post spaces will result in excessive tooth reduction.

What is the optimal post length?

Short Posts Increase Stress

•  Standlee, 1972 •  Davy, 1981 •  Peters, 1983 •  Hunter, 1989 •  Standlee, 1992

Length & Fracture Resistance

•  Increasing length increases fracture resistance Trabert, 1978

• Posts should have maximal length and therefore extend to the gutta percha.

• How much gutta percha is need for a good apical seal?

Amount Of Gutta Percha •  32 of 88 specimens leaked at 2 mm

Camp, 1983

• Significantly more post-treatment periapical radiolucencies - < 3 mm Kvist, 1989

• Most 3 mm specimens leaked Portell, 1982

• Little leakage at 4 mm Zmener, 1980; Camp, 1983

• No leakage at 4 mm Neagley, 1969; Madison, 1984; Raiden, 1994

Due to radiographic angle variations, 5 mm of radiographic gutta percha should be retained.

The 5 mm Rule Works For All Teeth Except Molars

•  Based on perforation data from preparing extracted teeth, the post length should not exceed a length of 7 millimeters in the primary canals Abou-Rass, 1982

True or False Question

•  Post length is determined by retaining the amount of apical gutta percha required to maintain an apical seal

•  True

•  What is the appropriate amount of radiographic gutta percha that should be retained?

•  5 millimeters

Completion Question

•  Molar posts should not extend more than ____ millimeters apical to the canal orifice at the base of the pulp chamber

•  7 mm

What is the most appropriate post diameter?

Diameter & Root Fracture •  Large posts increase stress.

Mattison, 1982 Hunter, 1989

• With large diameter posts

(1.5 mm or more), root fracture increased sixfold for every mm of decreased root diameter. Deutsch, 1985

• Posts should not exceed

1/3rd the root diameter.

Avoiding Excess Diameter •  Controlling post diameter is best

accomplished by selecting instruments of the proper size.

•  Appropriate instrument size range is 0.6 to 1.2 millimeters in diameter.

Peeso Instruments

•  1 – 0.5 mm •  2 – 0.7 mm •  3 – 0.9 mm •  4 – 1.1 mm •  5 – 1.3 mm* •  6 – 1.5 mm*

* Do Not Use

Gates-Glidden Instruments

•  1 – 0.4 mm* •  2 – 0.6 mm •  3 – 0.8 mm •  4 – 1.0 mm •  5 – 1.2 mm •  6 – 1.4 mm*

* Do Not Use

Round Burs

•  2 – 0.8 to 1.0 mm •  4 – 1.2 to 1.4 mm* •  6 – 1.8 to 2.2 mm* •  Considerable diameter variation occurs between manufacturers

* Do Not Use

Para-Post Instruments •  3 – Brown 0.9 mm •  4 – Yellow 1.0 mm •  5 – Red 1.25 mm •  6 – Black 1.5 mm* •  7 – Green 1.75 mm*

4 5 6 7

* Do Not Use

Completion Question •  The diameter of posts should not

exceed ____ of the root diameter •  One-third

•  The diameter of posts should range between ___ and ___ millimeters, depending on the tooth

•  0.6-1.2 millimeters

Does the use of a cervical ferrule (circumferential band of metal that encompasses tooth structure) help prevent tooth fracture?

Crown Ferrule

Core Ferrule

•  Data indicates ferrules formed as part of the core are less effective than ferrules created by the crown engaging tooth structure.

•  Ferrule dimensions greater than 1 mm are needed to provide the tooth with adequate resistance to fracture. Therefore, 2.0 mm is proposed as an appropriate dimension to optimize resistance to fracture.

Effectiveness of Ferrules

Ferrule Uniformity •  2 mm uniform crown ferrule was compared with 2

mm non-uniform (only 0.5 mm on the proximal surfaces).

•  The uniform ferrule produced significantly greater fracture resistance than non-uniform ferrule but the non-uniform was better than none.

•  A post and core does not strengthen a tooth but it also does not weaken a tooth when there is a 2 mm ferrule. Tan, 2005

True & False and Completion Questions

•  Core ferrules are preferred over crown ferrules. •  False

•  Ferrules should ideally encompass ___ millimeters of apical tooth structure.

•  Two

•  Ferrules that encompass 2 mm on all 4 axial surfaces are the best and when present the negative affect of a post is counteracted.

•  True

•  Direct •  Indirect •  Prefabricated •  Custom cast

P & C Fabrication techniques

Direct Prefabricated Post & Restorative Material Core

•  One appointment •  Less expensive •  Judged to be easier by

many clinicians

Direct Pattern for Cast Post & Core

•  Resin or wax pattern •  With resin, be careful

not to lock pattern into the tooth

•  Five sizes: •  Five matching color

coded drills: Brown 0.09 mm Yellow 1.0 mm Red 1.25 mm Black 1.50 mm Green 1.75 mm

ParaPost System

Stainless Steel Parapost & Composite Resin Core

Charles J. Goodacre, DDS, MSD Professor of Restorative Dentistry

Loma Linda University School of Dentistry

Thank You For Your Kind Attention

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