Basics of Dental Technology
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About the Companion Website ix
Chapter 1 Introduction 1
1.1 Introduction 1
1.2 How to use this book 1
1.3 Equipment and instruments 1
1.4 Health and safety in the dental laboratory 5
1.5 Sterilisation and impression handling 6
1.6 Introduction to model making 8
1.7 Models for prosthodontics - casting primary impressions 9
1.8 Models for prosthodontics - boxing-in impressions 12
1.9 Models for prosthodontics - casting working (secondary) impressions 13
1.10 Models for prosthodontics - models for cobalt-chromium frameworks 13
1.11 Orthodontic study models 14
1.12 Introduction to sectional models 16
1.13 Producing a sectional model using a tray system (Figure 1.13.1) 17
1.14 Producing a sectional model using a pinned system 19
1.15 Sectioning the model 20
1.16 Introduction to articulating models 22
1.17 Articulating models on a simple hinge articulator 22
1.18 Articulating dentate models using the average position 23
1.19 Articulating edentulous models using the average position 25
1.20 Articulating models using a facebow 26
Chapter 2 Complete Prosthetics 31
2.1 Introduction to complete prosthetics 31
2.2 Construction of a close-fitting custom impression tray 32
2.3 Construction of a tray with spacer for edentulous cases 34
2.4 Construction of a tray for dentate or partially dentate cases 35
2.5 Construction of a windowed close-fitting tray 37
2.6 Construction of occlusal registration rims 38
2.7 Setting up denture teeth 42
2.8 Denture processing 47
2.9 Grinding and finishing the dentures 53
2.10 Denture repair 57
2.11 Relining a denture in the laboratory 60
2.12 Copy dentures 62
Chapter 3 Partial Prosthetics 65
3.1 Introduction to partial prosthetics 65
3.2 Classification 65
3.3 Component parts of partial dentures 66
3.4 Surveying 68
3.5 Designing partial dentures 71
3.6 Partial denture construction - acrylic resin 75
3.7 Partial denture construction - cobalt-chromium 77
Chapter 4 Fixed Prosthodontics 85
4.1 Restoration design 85
4.2 Metal restorations 86
4.3 Ditching the die 88
4.4 Producing a wax pattern 88
4.5 Investing the wax pattern 90
4.6 Casting and de-vesting the pattern 92
4.7 Finishing the casting 94
4.8 Metal-ceramic restorations 98
4.9 Producing a wax pattern for a metal bonded to ceramic framework 99
4.10 Investing the wax pattern 102
4.11 Casting the pattern 102
4.12 De-vesting and surface preparation 104
4.13 Ceramic application and build-up 105
4.14 Ceramic restorations 112
4.15 Producing a high-strength ceramic substructure 114
4.16 Veneering a high-strength ceramic substructure 115
4.17 Producing a resin-bonded crown on a refractory die 115
4.18 Post crowns 117
4.19 Bridges 118
4.20 Producing a cast metal fixed-fixed restoration 121
4.21 Producing a soldered metal fixed-fixed restoration 122
4.22 Soldering 123
4.23 Minimal preparation bridges 125
4.24 Producing a minimal preparation bridge (Maryland technique) 126
4.25 Digital dentistry 128
4.26 Using a laboratory-based CAD-CAM system 131
4.27 Producing a posterior single-unit substructure or restoration using a reduction technique 132
4.28 Producing a bridge substructure 134
4.29 Removable Partial Denture Design 134
4.30 Implant-supported prosthodontics 139
Chapter 5 Orthodontics 141
5.1 Introduction to orthodontics 141
5.2 Classification of malocclusions 142
5.3 Theory of tooth movement 143
5.4 Basic wire bending techniques 144
5.5 Making passive components 146
5.6 Producing ball-ended clasps 146
5.7 The Adams clasp 147
5.8 Producing a southend clasp 148
5.9 Active appliances 149
5.10 Palatal finger spring (guarded) 150
5.11 Making a T-spring 152
5.12 Double cantilever or Z-spring 152
5.13 Buccal canine retractor 153
5.14 The Roberts retractor 154
5.15 Producing baseplates 155
5.16 Producing biteplanes 156
5.17 Extra-oral anchorage 156
5.18 Functional appliance design 157
5.19 Producing an Andresen appliance 157
5.20 Twin-block appliance 158
5.21 Fixed orthodontic appliances 160
5.22 Retainer appliance design 160
5.23 Repair and modification of orthodontic appliances 162
5.24 Making tooth positioners 164
5.25 Sports Mouthguards 165
Chapter 6 Occlusion 167
6.1 Introduction to occlusion 167
6.2 Occlusal schemes 168
6.3 Articulators 170
6.4 Facebows 171
6.5 Summary 171
Chapter 7 Shade, Colour and Size Determination for Dental Appliances 173
7.1 Introduction to aesthetics 173
7.2 Colour terminology 173
7.3 Shade guides 173
7.4 Selecting teeth for complete denture patients 175
Appendix Tooth Morphology 177
Glossary 179
Index 181
Chapter 1
INTRODUCTION
1.1 Introduction
This book has been designed for use in the dental laboratory as a guide for the novice dental technician. Described in the manner of a 'cook book', the procedures in this handbook have been designed to be followed step by step. Presented in sections ordered by specialty, each procedure has been completed in a dental laboratory, with photographs illustrating all the important steps of each procedure. The work shown in this book has not been edited or tweaked, but is presented as the instructions given in this book were followed, to ensure that the outcomes are achievable by anyone following the guides (perhaps with a little practice!).
1.2 How to use this book
This book is designed for the student of dental technology for use on the bench in the dental laboratory. The construction of many dental prostheses and appliances requires progression through a series of stages, often from impression through to the finished product. You can use this book to work through each procedure step by step.
The graphic at the beginning of the sections will help you to see where any given procedure fits into the production process. An example of this is shown on the right.
For each procedure you will find a brief introduction, a list of the tools and equipment required, guidance on working safely and an illustrated step-by-step basic procedure.
In addition, the hints and tips sections give techniques to expand or refine the process, and the extended information sections give an insight into the scientific and clinical aspects that can enhance your understanding of the topic.
1.3 Equipment and instruments
The equipment listed below is commonly found in a dental laboratory, and with which any technician should be familiar.
Plaster bowl, spatula and knife (Figure 1.3.1)
Common to all plaster rooms, these items are used for mixing, shaping and trimming plaster of Paris, Kaffir and die stone materials. Cleanliness of these items is important to prevent rapid setting of materials.
Wax knives and carvers
These instruments are commonly used in the laboratory for a number of procedures. You should purchase your own good-quality knives and carvers.
- Small wax knife: Most commonly used in the fabrication of crowns for placing and carving inlay wax. You may see technicians using two, a cold and a hot knife, to save time (Figure 1.3.2, instrument on the left).
- Large wax knife: Used for melting, placing and carving modelling wax in the production of dentures. Again, it is common to see two knives being used, a cold and a hot knife (Figure 1.3.2, instrument on the right).
- LeCron carver: This carver is popular for the carving of inlay wax in the production of crowns. It is used cold, but some techniques use it slightly warm, but not hot (Figure 1.3.3, instrument on the far right).
- Ash 5: This carver is used cold to shape modelling wax in the production of dentures (Figure 1.3.3, instrument in the centre).
- Hylin carver: This carver is popular for the carving of inlay wax in the production of crowns. It is used cold (Figure 1.3.3, instrument on the far left).
- PKT (PK Thomas): A set of instruments (examples of two shown) designed to aid the precise positioning of molten wax in the production of crowns (Figure 1.3.4).
Other hand instruments
- Ceramic brushes: Available in a range of sizes similarly to artists' brushes (Figure 1.3.5), with sizes from 0 to 20 with 0 being the smallest and 20 the largest. These brushes are made from sable and should be treated with care. A size 6 brush is popular for the placement of ceramics in the production of crowns. Smaller brushes are useful for staining, and a larger brush for condensing ceramic.
- Ceramic spatulas: These instruments (Figure 1.3.6) are used for mixing, placing and carving of ceramic powders. They are produced from a material that will not contaminate the ceramic with metal particles that may cause discoloration.
- Micromotors: Modern micromotors (Figure 1.3.7) are very advanced in terms of engineering, control and quality. They are powered by low voltage electricity and usually controlled via a foot or knee controller, allowing the speed to be set anywhere between 5000 and 40 000 rpm. The chuck is opened and closed by twisting the handpiece to secure or remove a bur.
Burs
There is a huge range of burs currently on the market and manufacturers devote several pages of their catalogues to them. Below is a brief outline of the main types.
- Tungsten carbide (TC): These are very popular burs used for many applications within the laboratory from trimming plaster to acrylic and metal. They are available in a large selection of shapes and sizes (Figure 1.3.8). The most useful are the plaster trimmers, flame-shaped for trimming acrylic and small round (often called rosehead) burs for accessing small areas.
- Steel burs: As above, but not as hard wearing (and cheaper).
- Stone burs: Abrasive stone burs are available in different grades, shapes, sizes and materials. The shapes range from cones to points to discs (Figure 1.3.9) and the different materials are indicated (often by colour) for different applications, that is, for the trimming and finishing of ceramics, acrylics or alloys.
- Diamond discs and burs: Increasingly popular over the past decade, these tools are used for the shaping of ceramics and composites. They are available in many shapes and sizes (Figure 1.3.10).
- Rubber abrasives for metals: These are available as wheels, cones or points and are used mainly in the finishing of metal surfaces (Figure 1.3.11).
- Abrasives for acrylics: The simplest is a mandrel that holds a small piece of sandpaper, but rubber-bonded abrasives are now popular (Figure 1.3.12).
- Brushes and mops: The main application of these is the polishing of metal surfaces in combination with wax-based polishing compounds (Figure 1.3.13).
Pliers and cutters
For orthodontic appliance manufacture (or for any other occasion where a wire may need to be bent or cut) the technician will have a selection of tools.
- Adams 65: Square-ended pliers used in the bending of orthodontic stainless steel wire (Figure 1.3.14).
- Adams 64: Square- and round-ended pliers used in the forming of springs and curves in orthodontic wires (Figure 1.3.15). (Sometimes referred to as 'half-round'.)
- Maun cutters: Used for the cutting of orthodontic stainless steel wires (Figure 1.3.16).
- Parallel pliers: Used for firmly griping a variety of items (Figure 1.3.17).
Large laboratory equipment
Most laboratories will have most or all of the following (illustrations of some of the following equipment will appear later in the book).
- Model grinder: A bench-mounted, water-lubricated, tungsten carbide wheel used to grind plaster products (Figure 1.3.18).
- Polishing lathe: Used with brushes and pumice, or mops and polishing wax in the polishing of acrylics and alloys (Figure 1.3.19). Modern lathes have integrated dust extraction and lighting and have two speeds: 1500 or 3000 rpm. The polishing lathe can be fitted with a variety of brushes and mops, for example, a bristle brush for applying abrasive pumice to acrylics (Figure 1.3.20) or a cotton mop for polishing acrylics or alloys (Figure 1.3.21).
- Steam cleaner: Used extensively in the dental laboratory for cleaning models and restorations.
- Pressure bath: These use compressed air to keep self-curing acrylics under pressure during curing. They also have the facility to keep water warm to aid the process.
- Hydroflask: Used full of water for putting self-curing acrylic under pressure whilst curing, in the repair of dentures, for example (Figure 1.3.22).
- Vibrating table: Used during the mixing and pouring of plaster materials to help avoid air bubbles.
- Vacuum mixer: Essential in the production...
