Fundamentals of Tooth Preparations for Cast Metal and Porcelain Restorations.pdf

Contents www.alllsJam.net http://dentalbooks-drbassam.blogspot.com/ Problem

Introduction

9

Chapter 1

Biomechanical Principles of Preparations

13

Chapter 2

Finish Lines and the Periodontium

45

Chapter 3

Instrumentation

61

Chapter 4

Full Veneer Crowns

83

Chapter 5

Maxillary Posterior Three-Quarter Crowns

95

Chapter 6

Mandibular Posterior Three-Quarter Crowns

115

Chapter 7

An terior Three-Quarter Crowns

133

Chapter 8

Pin-Modified Three-Quarter Crowns

153

Chapter 9

Seven-Eighths Crowns

173

Chapter 10

Proximal Half-Crowns

189

Chapter 11

tnlays

205

Chapter 12

MOD Ontays

237

Chapter 13

Anterior Porcelain-Fused-Io-Metal Crowns

259

Chapter 14

Posterior Porcelain-Fused-Io-Melal Crowns

279

Chapter 15

All-Ceramic Crowns

295

Chapter 16

Preparation Modifications for Damaged Teeth

321

Chapter 17

Preparation Modifications for Special Situations

359

Author Index

377

Subject Index

385

7

Chapter 1

Biomechanical Princ iples of Preparations www.slllslsm.net Problem The design and preparation of a tooth for a cast metal or porcelain restoration are governed by five princi p les: 1. 2. 3. 4. 5.

Preservation of tooth st ructure Retention and resistance form Structural durability of the restoration Marginal integrity Prese rvation of the pe riodontium

At times it may be necessary to compromise one or more for the sake of another. For example, sound tooth structure may have to be sacrificed in order to produce a more retentive form, to create space for the bulk of restorative material necessary for structural durability or an esthetic veneer, and to allow the restoration to seat with closefitting margins. Sound judgment must be exercised in making these compromises , with the requirements of the individual situation taken into careful conside ration.

Preservation of tooth structure Excessive removal of tooth structu re can have many ill effects. If a tooth is overtapered or shortened too much, there will be an unnecessary sacrifice of retention and resistance. Thermal hypersensitivity, pulpal inflammation, and necrosis can result from approaching the pulp too closely. As a guide to how

much tooth structu re can be safely removed, or how deeply a preparation may extend, the average thicknesses of enamel and dentin for permanent maxillary teeth are given in Table 1-1. Those for mandibular teeth are shown in Table 1-2. One of the most common violations of this principle is seen in the indiscriminate use of full-coverage porcelain veneered crowns in situations where partial veneer coverage with an allmetal restoration could be used. It is true that fUll-coverage restorations have long been recognized by clinicians as offering superior retention and resistance . 1 This has been borne out in recent years by several studies. 2-4 Howeve r, the shift in emphasis from partial venee r to full veneer restorations is more probably related to the ease and convenience associated with the design. 5--7 The decision to use full coverage should be reached only after a partial veneer crown has been considered and found wanting because of inadequate retention or esthetics . 8-- 11 Preservation of tooth structure entails more than simply avoiding excessive destruction. II also requires designing the restoration so that it will reinforce and protect the remaining enamel and dentin even when this means sacrificing a small amount of additional tooth structure on the occlusal surface to protect underlying cusps.

13

"-

Table ,-,

Enamel and dentin thicknesses in maxillary teeth (mm)" Midcrown

Occlusal Material

Incisal

CEJ

M

F

D

L

M

F

D

L

0.9 3.4

0.7 1.6

1.0 1.4

0.7 1.6

0.7 1.0

2.2

2.5

2.3

3.1

0.9 3.3

0.8

1.0

0.6

0.7

1.2

1.1

1.2

0.9

1.8

2.2

1.7

2.4

1.1

0.7 1.8

0.8 2.0

0.8 2.2

0.7 2.0

2.0

2.7

2.2

2.9

1.2

1.3

1.3

1.4 2.2

2.6

2.2

2.7

2.0

2.2

1.9

2.3

2.5

2.8

2.6

2.8

2.6

2.9

2.6

3.0

F

Cent

L

Central incisor

Enamel Dentin

Lateral Incisor

Enamel Dentin Canine

Enamel Dentin

4.4 Cusp

Cusp

1 .5

Groove 1 .3

3.0

3. 1

3.3

Cusp

Groove

1.7

1.3

Cusp 1.7

3.3

3.2

3.4

MF

DF

Cent

ML

DL

Cusp 1.8

Cusp 1.9

Fossa 0,6

Cusp 1.9

Cusp 1.9

First premolar

Enamel Dentin Second premolar

Enamel Dentin

First molar

Enamel Dentin Second molar

Enamel Dentin

3.9

1.8

1.1

1.3

1.1

1.4

1.31.51 .41.6

4.0

Cusp

Cusp

2.0 3.8

1.9

Fossa 0.5

Cusp 2.1

Cusp 1.9

1.3

1.4

1.3

4.4

'Mod,toed from H T ShoIIingburg and C S Grace. ThIckness of enamel and denim. J Soutn. Calil Dent Assoc_. 41 33. 1973

1.6

Table 1-2

Enamel and dentin thicknesses in mandibular teeth (mm)" Occlusal

Material

Incisal

F

Cent

CEJ

Midcrown M

F

D

L

M

F

D

L

0.9 3.7

0.6

0.9

1.1

1.1

0.7 1.2

0.6 0.9

15

23

1.5

2.4

1.0 3.6

0.6 2.0

0.8 2.0

0.8 2.1

0.6 2.1

2.8

22

2.9

1.0

1.2

1.0

1.1

2.1

2.5

2.1

2.8

22

2.6

2.2

2.5

2.5

2.8

2.7

2.6

2.5

3.0

2.8

2.6

L

Incisor Enamel Dentin Canine Enamel

Dentin First premolar

Enamel Dentin

Second premolar Enamel Dentin

First molar

Enamel Dentin Second molar

Enamel Dentin

Cusp

Groove

Cusp

1.3 3.2

1.2 2.0

1.1

3.0

Cusp

Groove

Cusp

1.6 3.4

1.3 2.7

1.6 3.8

1.1

MF

DF

D

CENT

ML

DL

Cusp

Cusp 1.8

Cusp 1. 9

Fossa 0.5

Cusp

Cusp

1.9 3.7

1.8 3.3

2.0 3.8

3.3

Cusp

Cusp

Fossa

Cusp

Cusp

2.0 3.6

1.9 36

0.5

1.8

1.8 3.6

3.3

1.2

1.4

1.3

1.5

1.6

1.1

1.3

1.5

~

Ul

"MOd,had from H T Shillingburg and C S, Graco, Thickness 01 enamel and denlln. J South Cal"

Dent Assoc ,