Prosthodontics is the dental speciality involved in the restoration of normal teeth and replacement of missing teeth or structures in the oral cavity with artificial apparatuses [1]
To achieve their goals prosthodontists require a large armamentarium with a wide range of tools. Each instrument has a specific function and are built by manufacturers for an intended use. It is vital for the prosthodontist not only to be familiar with the instruments, but also know and understand how to use the instruments correctly and in a safe fashion.
The ability to use an instrument well and with skill comes with practice, many prosthodontists may have a preferred tray setup for certain procedures which may be completely different to other prosthodontists.
Instruments in prosthodontics are designed to be able to
- prepare tooth structures for artificial restorations
- manipulate and create the best environment for impression materials
- alter prostheses from dental laboratories
Without these tools the prosthodontist would be unable to achieve the acceptable conditions for reinstating dental function resulting in defective prostheses with a high failure rate.
The ever-changing and evolving nature of dentistry means that there are many instruments available on the dental market, this can be confusing and overwhelming for a new dentist and therefore it is imperative that new graduates familiarise themselves with the standard and most common armamentarium.
Mixing Bowl
The dental mixing bowl is designed for mixing and preparing impression material, e.g. alginate or dental plaster
Dental mixing bowls may be made of rubber or silicone, these are inert and are designed to not interfere with the chemistry of the impression material. Latex-free forms have been developed to protect patients with latex allergies
Mixing bowls are also available in a plastic disposable form. These have the advantage of lower risk of cross-infection, the patient sees a clean bowl and because it is disposed of immediately there is no problem with blocking sink holes with impression material.
It is used with a spatula to mix the impression powder with water to form a paste
They come in sizes of 150cc to 1000cc according to the manufacturer
Manual mixing has largely been replaced by auto-mixing devices. Reasons for this are to prevent the risk of cross-infection, obtain a homogenous mix and decrease bubble formation which all affect the overall quality of the final impression and therefore the dental model. [2]
Spatula
The dental spatula is used with the mixing bowl to combine the impression powder with water to form the impression material. They may be made from plastic, silicone, metal, or metal with a wooden handle.
Modern spatulas can generally be autoclaved (According to the brand)
Dental spatulas are designed to mix the material into a homogenous substance within about 30s, as some materials are dimensionally unstable and need to be poured almost immediately.[3]
Dispensing Guns
Dispensing guns, also known as automix dispensors, are instruments used to extrude dental impression materials from specially made cartridges.
They automatically mix and deliver dental materials such as
They consist of a large hand-held gun device with a lever, plunge and trigger.
The lever and plunge work together to load and unload special cartridges. The trigger is pulled to press out the material.
A long removable, disposable tip can be attached to aid delivery around the tooth preparation.
According to the manufacturer, they are available in many mixing ratios, ranging from 1:1 to 10:1
Special cartridges are also available on the commercial market usually of size 25ml or 50ml.
The advantages of dispensing guns are that they generally produce a more homogenous mix, free of bubbles compared to standard hand mixing.
For inexperienced dentists or nurses they are easier to handle and give a reliable result.
Notable disadvantages are that they are quite difficult to reliably sterilize totally, and due to their large size they may add to any already present patient anxiety.
Impression Trays
Impression trays are dental trays designed to hold impression material. The tray is used as a vehicle to carry the impression material into the mouth and press it against the structures of the oral cavity.
Impression trays may be disposable: designed for one use and then discarded. These are made of plastic (usually nylon or polystyrene)
They are available in 5 sizes: 0, 1, 2, 3, 4
Stainless steel trays can be placed in an autoclave for sterilization and are designed to be reusable.
Trays may be perforated offering retention to the impression material, or they may be without perforation in which case a dental adhesive can be used to hold the impression material in place.
Dental Adhesives may be solutions of resins in alcohol (delivered in a spray form) these are for alginate. Rubber solutions in acetone are used for polysulphides and isopropylalcohol is used as a silicone adhesive.[4]
Individual Trays
Also known as custom trays, these are fabricated on a premade “diagnostic” cast of edentulous patients and are used to make the final impression.
They are an important step in the construction of complete removable dentures as they allow for improved retention via precise moulding of the borders.
Most importantly they allow realistic recording of soft tissues including vestibular and frenal attachments.
During individual tray fabrication, a wax spacer can be used to replicate the thickness of any impression material used.
Tray usually requires some trimming in order to find the best possible fit for taking the final impression.
Individual trays are usually made from acrylic, shellac or tray compound materials.
Alginators
Alginators give the dentist or dental nurse an alternative to manual hand-mixing.
An alginator is an electrical device that spins a dental mixing bowl. The benefit of using an alginator is that it creates a consistent homogenous mixture free of bubbles or porosities. It is simple to use with a predictable outcome. [5]
The dentist or dental nurse only needs to load the alginator with the alginate powder and water (according to the brand instructions) and then press the mixture against the side of the bowl with a spatula as the alginator spins the bowl.
The disadvantages of alginators is their cost to buy and repair, they require a flat, immovable surface and a power source.
Retraction Cord
A retraction cord is a length of thin woven string, it is designed to be pressed into the gingival sulcus completely pushing the free gingiva away from the cervical region of the tooth crown.
It may consist of cotton or silk, some even have copper filament to provide better resistance
It provides space for dental impression material to capture the form of the crown in its entirety.
The cord has an absorbent property and so isolates the tooth crown from sulcular fluid providing moisture control.
The retraction cord is usually invested in a haemostatic agent such as epinephrine to help control bleeding. However, it is important to note that epinephrine impregnated cords are contraindicated in patients with cardiac arrhythmias.
The cord is pre-packaged, and the dentist cuts the necessary length required and uses a special gingival retraction cord instrument to press the cord into the sulcus.
Gingival Retraction Cord Instrument
It is used to press the gingival retraction cord into the gingival sulcus.
They have two fine working ends which may be serrated or non-serrated. They may have a straight or round edge. They are designed to be minimally traumatising to the gingival tissue during packing of the cord.
This instrument is also known as a cord packer.
Crown and Bridge Scissors
Crown and bridge scissors are curved scissors designed to trim stainless steel crowns, aluminium temporary crowns, custom temporary crowns, gingival retraction cords and matrix bands
They have a short cutting blade which may be straight or curved and narrow or wide.
Some crowns are prefabricated and therefore their final shape must be adapted to fit the prepared tooth. Crown and bridge scissors can remove excess material from the cervical region of these crowns to obtain a more accurate fit. The dentist can mark a line on the crown with a sharp probe to indicate where to cut. [6][7]
Crown-Removing Forceps
Crown-removing forceps are designed to aid the removal of provisional crowns, or permanent crowns during the try in phase.
They are made of stainless steel and may or may not have replaceable rubber pads, to give a nonslip tight grip. They are either specifically for the upper jaw or lower jaw.
They can be sterilized in an autoclave after removal of the rubber grips.
Crown removing forceps can also be used to remove failed crowns. Crown failure may be due to marginal caries, poor cementation or breakage.
Contouring Pliers
Contouring pliers are designed to bend stainless steel and temporary crowns at the cervical margin and for improving the interproximal contacts.
They are made of stainless steel and can be sterilized by autoclave.
By adapting the crown to the tooth shape and into the gingival margin, they improve the retention of the crown and minimize the risk of failure.
Shade Guides
Dental shade guides are a set of various colour examples available from manufacturers of artificial teeth and tooth coloured material such as resins and porcelains.
Shade guides depend on the ability of the dentist to read the tooth and choose the best possible match from the examples in the shade guide.
The dentist must read the tooth in natural light and assess the hue, value, chroma of the tooth, and also recognize any distinctive features in the tooth, for example fluorosis.
It is usually necessary to combine different shades, as the tooth structure itself has range of shades according to its natural morphology. For example, where the enamel is thin in the cervical region there is greater colour representation of the underlying dentin.
Each shade has a specific code assigned, for example A1 or C3, the dentist then takes the material (from the same manufacturer’s box) with the same code and uses it in the reconstruction process.
Modelling Wax
Modelling wax is a malleable dental wax used to record the bite registration, make occlusal rims and also the preliminary denture.
It usually is made in a red/pink colour to match the oral environment and is available in a range of types and thickness.
Modelling wax is composed of a varied mixture of paraffin, beeswax, carnauba wax and resins.
It is gently heated under warm water or a soft yellow flame, this allows the wax to be moulded into the required form.
Wax knife
Wax knives are used to cut and trim wax during the modelling process. They can also carry molten wax.
The knife is heated over a soft yellow flame or in placed in hot water to make the cutting easier.
They are fitted with a wooden shaft for better gripping and have two functional ends. One end is a blunt blade and the other is flat and curved.
For more precise and fine trimming a Lecron carver can be used. It is made of stainless steel and unlike the wax knife does not have a wooden handle.
Diamond Burs
Diamond burs are used in crown preparation procedures and for polishing and finishing composite restorations. They allow the prosthodontist to make a fast reduction of the tooth structure with high accuracy.
Diamond burs vary in grit size from super-coarse (rough) to superfine (smooth) [X]
SF: Super Fine 30micrometres
F: Fine 50micrometres
M: Medium 120micrometres
C: Coarse 150-180micrometres
SC: Super Coarse 180-250micrometres
They are available in many sizes and shapes and designed for use in high-speed handpieces. [Y]
Flat-End Taper – Provides a rectangular shoulder
Flat-End Cylinder – Give parallel walls and flat cavity floors
Flame – Allows access to prepare subgingival margins and creating fine detail
Wheel – For preparing the lingual surface of anterior teeth and reducing incisal edges
Diamond burs are available as single or multi-use depending on the prosthodontists preference.
Finishing burs are designed for smoothing and finishing metal restorations and aesthetic materials and are either fine or super fine.
Prefabricated Crowns
Prefabricated Crowns( also known as preformed, provisional or temporary crowns) are used as temporary restorations whilst waiting for a definitive crown to be manufactured. They are especially useful in emergency situations.
The prosthodontist will buy the crown as part of a kit with many different shapes and sizes.
They may be made of stainless steel, aluminium or acrylic resin and cemented with a temporary adhesion system such as zinc-oxide eugenol, zinc phosphate or flowable composites.
Stainless steel are designed for use in the primary dentition where caries has damaged posterior teeth, they can be temporary or permanent.
Temporary crowns should provide adequate protection to the tooth from further damage or fracture until a permanent crown is made available. This includes pulpal protection, positional stability, occlusal function, ease of cleaning, smooth margins, retention and aesthetics. [Z] The disadvantages of prefabricated crowns are that they need to be adjusted to achieve a sufficient marginal fit, this can be time-consuming. They have a lower resistance to mechanical force compared to permanent crowns and may fall out or become loose.
Dental tray setup
A dental tray setup is a term used to describe the organization of certain dental instruments in a small tray.
The instruments are chosen according to the course of treatment the patient is about to undergo.
Instruments are all sterilized and if provided in a bag or wrap will remain in the bag until they are need during the procedure.
The instruments are positioned from left to right in the order that they will be used by the dentist. This saves time for the dentist and avoids confusion during the treatment.
For example, a crown and bridge setup [8]:
- Gingival retraction cord
- Gingival retraction cord instrument
- Dental Floss
- Dental Burs
- Dental mirror
- Explorer
- Tweezers
- Spoon excavator
- Crown and bridge scissors
- Cement spatula
- Articulating paper
- Crown-removing forceps
- Anaesthetic syringe
Articulator
A dental articulator is an instrument used to reproduce and make perfect the relationship between the positions of the mandible to the maxilla.
It is used to help create removable prosthesis’, fixed prosthesis’ and also for orthodontic treatment.
Effectively it is a mechanical representation of the temporo-mandibular joint, the maxilla and the mandible.
Its function is to hold the cast of the maxilla and mandible in an exact and chosen fixed position, it provides a simulation of the movement of the jaw and is able to produce lateral and protrusive movements.
From an articulator we can identify the occlusal status, build a treatment plan and arrange positions of artificial teeth.
Articulators are classed as
1. Simple Hinge Articulators
2. Mean Value Articulators (Anatomical)
3. Adjustable Articulators
a) semi-adjustable
b) fully adjustable
Articulators can be aided by the use of a facebow – an instrument used to record the relationship of maxilla to the temporo-mandibular joint. Usually these are used in conjunction with semi-adjustable articulators.
References
[1] American Dental Association – Dental Speciality Education and Training (beyond a 4-year college degree) http://www.ada.org/4504.aspx#specialty
[2] Ahmad, I. “Impression materials” Prosthodontics at a Glance. 1st ed. Blackwell Publishing Ltd, 2012
[3] Ahmad, I. “Impression techniques and armamentarium” Prosthodontics at a Glance. 1st ed. Blackwell Publishing Ltd, 2012
[4] “Adhesives and Perforations”. Impression Trays. University of Birmingham, The School of Dentistry http://www.dentistry.bham.ac.uk/cal/impress/imptray.htm
[5] Blaes J. 2001 “Pearl 121 The Alginator”. Pearls for Your Practice. Tulsa, Ok : PennWell Corp., 2001.
[6] 3M ESPE Prefabricated Crowns. User Guide. A 3M ESPE Technical Service Publication. http://multimedia.3m.com/mws/mediawebserver?mwsId=66666UF6EVsSyXTtn8TyLxF6EVtQEVs6EVs6EVs6E666666–
[7] Bartolomucci Boyd L.R. 2009 “Crown and Bridge Scissors”. Dental Instruments, A Pocket Guide. 3rd Ed. Saunders Elsevier.
[8] Bartolomucci Boyd L.R. 2009 “Crown and Bridge Preparation”. Dental Instruments, A Pocket Guide. 3rd Ed. Saunders Elsevier
[X] Johnson Promident – Diamond burs. http://www.johnsonpromident.com/diamond-burs/
[Y] Ncbeyer – Dental Burs and Rotary Attachments for Handpieces. http://quizlet.com/2515135/dental-burs-and-rotary-attachments-for-handpieces-flash-cards/
[Z] Shillingburg, H. “Provisional Restorations” Fundamentals of Fixed Prosthodontics. 4th ed.Quintessence Publishing Co, Inc 2012
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