J Adv Prosthodont.  2017 Jun;9(3):232-237. 10.4047/jap.2017.9.3.232.

Post and core build-ups in crown and bridge abutments: Bio-mechanical advantages and disadvantages

• Mamoun J

• KMID: 2382611
• DOI: http://doi.org/10.4047/jap.2017.9.3.232

Abstract

Dentists often place post and core buildups on endodontically treated abutments for crown and bridge restorations. This article analyzes the bio-mechanical purposes, advantages and disadvantages of placing a core or a post and core in an endodontically treated tooth and reviews literature on post and core biomechanics. The author assesses the scientific rationale of the claim that the main purpose of a post is to retain a core, or the claim that posts weaken teeth. More likely, the main function of a post is to help prevent the abutment, on which a crown is cemented, from fracturing such that the abutment separates from the tooth root, at a fracture plane that is located approximately and theoretically at the level of the crown (or ferrule) margin. A post essentially improves the ferrule effect that is provided by the partial fixed denture prosthesis. This paper also explores the difference between bio-mechanical failures of crowns caused by lack of retention or excess taper, versus failures due to a sub-optimal ferrule effect in crown and bridge prostheses.

Keyword

Post and core technique; Finite element analysis; Tooth crown; Dental abutments; Denture; Partial; Fixed

MeSH Terms

Crowns*
Dental Abutments
Dentists
Dentures
Finite Element Analysis
Humans
Post and Core Technique
Prostheses and Implants
Tooth
Tooth Crown
Tooth Root

Figure

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  Fig. 1 Finite Element Analysis Diagram shows how a crown transmits most occlusal force (in red) to the level of the crown margin (photo courtesy of Dr. Seung-Ryong Ha, with permission from J Adv Prosthodont1).

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  Fig. 2 Five examples of post/core restorations, where the core is retained only by the post, include situations where the abutment tooth structure has no undercuts to retain the core (A); the post is in a root tip (B); a tooth/core/post complex that fractured from the abutment was re-cemented and is retained only by a cement layer (C); a core separated from the post and was re-cemented and is retained only by the post cement (D); a core is not retained by tooth structure undercuts, but the crown margin is at 2.0 mm apical to the core on ferrule tooth structure (E). Only (E), and possibly (A), may be biomechanically stable.

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  Fig. 3 Finite Element Analysis Diagram of a post/core restoration shows how the post transmits moderate amounts of occlusal forces (in green) to the cemento-enamel-junction area of the post (where the crown or ferrule margin is often located), but also transmits most of the force (in red) to the root (photo courtesy of Dr. Prajna P. Shetty, with permission from Eur J Dent29).

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