Veterinary dental instruments: dental unit and accessories

As in every medical discipline, odontostomatology mandatorily requires, besides suitable scientific preparation, technical knowledge about the instruments needed to perform dental procedures. The equipment that the professional decides to purchase has to be proportionate to the volume of work expected and to the type of operations she/he expects to perform most often. Some equipment and some instruments are often unnecessary in daily practice, while others are essential, hence it is not easy to orient oneself among the many products proposed by the industry; in addition, materials derived from human dentistry, which are totally useless, if not actually harmful, are often offered.

Note: The equipment and materials reproduced in photos or videos are the author’s property; any references to brands and/or manufacturers are purely accidental and are not for advertising purposes.

DENTAL UNIT

The dental unit is a piece of equipment that allows controlling the handpieces (turbine, micromotor, air/water syringe, scaling handpiece, etc.) by driving them with compressed air and pressurised water (Fig. 1); dental units powered by electricity are also widely used in veterinary medicine.

Dental units driven by compressed air can have an internal compressor or use an external power supply (dry compressor or medical air cylinders): it is important for the air to be oil-free, as oil interferes negatively with some materials and can seriously damage the head of the instruments.

Besides cart mounted dental units, specific for veterinary medicine, there are also integrated units fastened to the dental table. These instruments (Fig. 2) are usually derived from human medicine and have a mobile appendage, called “holder bar”,  to which the handpieces are connected (Fig. 3).

The dental unit allows the use of rotating instruments, scalers, air/water syringes and, optionally, it can be fitted with a surgical aspirator. These instruments are connected to the hoses (for the supply of air and water) with special fittings, called connectors: there are 2 main types of connectors, Borden and Midwest. The two connectors are available in the following versions: 2-way Borden, 3-way Borden, 4-way Midwest, electrified Midwest and Midwest USA (Fig. 4).

Rotating instruments

Turbines: these are air powered rotating instruments with a coupling for high speed burs,  diameter 1.59/1.60 mm, called “FG” (Friction Grip); locking occurs through friction (locking with a special key or with an automatic push-button mechanism) (Video 1). Connection to the hose is through direct coupling or through special automatic connectors. The turbine is basically made up of two main parts (Fig. 5): the casing, called body, normally made of anodized aluminium or other light alloys like titanium, and the rotor, which performs several functions and is located inside the head; indeed, besides locking the bur, its main task is to make the bur rotate. The rotor is usually made up of a hollow metal cylinder on which the rotary fan and the bearings are connected. The air, which exercises a thrust on the fan blades, is driven through a duct inside the body. The rotor can reach a rotation speed of over 400,000 RPM (Revolutions per Minute). The head is also provided with a series of outlet nozzles for the bur cooling spray. Optical-fibre models also have a system for the illumination of the operating area (see Fig. 16). Unlike the contra- angle, the turbine is less resilient to wear and to blows or jolts.

Turbines are in fact instruments characterized by an extremely high rotational speed, compared to micromotors (40,000 RPM), and with a great cutting capacity; however the twisting torque (i.e. the force developed per unit area, expressed in Newton/cm_²) is in fact inferior compared to the one of micromotors which, in the case of special units mainly used in the field of endodontics (Figs. 6 and 7) and implantology (Figs. 8 and 9), are capable of developing extremely high and predefined twisting moments.

In view of the speed reached, turbines allow making quick and precise cuts. Their fields of use in veterinary medicine are: cutting crowns to separate roots (extraction of teeth with many roots), alveolotomy, access to the pulp canal in root treatments, preparation of the enamel for conservative treatment, etc. Turbine heads come in several shapes and sizes (standard, mini standard [Fig. 10], semispherical, mini semispherical, etc.) and can be provided or not with fibre-optic lighting (Figs. 15 and 16); the type of head chosen depends on the function that the instrument has to perform. It is necessary to recall that the surgical sensitivity associated with use of the turbines is lower than that related to use of micromotors, as the latter are more controllable, especially when using speed reducers and/or multiplier handpieces.

Micromotors: similarly to turbines, mircomotors can be driven by compressed air (Fig. 11) or be real miniature electric motors (Fig. 12) on which terminals are fitted which, depending on the angle, are called “contra angles” and “straights” (Fig. 13). Micromotors can also reach speeds suitable for the cutting of enamel; these speeds, encoded around 200,000 RPMs, can be reached using multiplier contra angles. Multiplier contra angles which can, in fact, multiply up to five times an initial speed of 40.000 RPM, have been in use for many years. Compared to turbines, they have a much more advantageous twisting moment, which translates into greater control of the instrument. Also in this case the connection to the hose is through direct coupling or through special automatic connections.

Contra angle: these belong to the category of rotating instruments that operate through coupling with the micromotors. Contra angles have a coupling for 2.35 mm diameter burs fitted with a locking groove for the head of the contra angle, called “CA” or “W” (Fig. 17). The name contra angle[20] comes from the particular shape, which is more angled compared to the turbine. Contra angles are used when higher torque and relatively low speeds are required.  Several types of instruments exist with different multiplication and/or reduction ratios depending on the number of revolutions of the micromotor. A coloured ring is marked by the manufacturer on each instrument indicating the ratio of gearing down, or of multiplication, of the revolutions:

• Green ring and double green ring: reduction in number of revolutions
• Blue ring: 1:1 ratio
• Red ring: multiplication of number of revolutions

The contra angles developed for surgery, endodontics and implantology (see Figs. 6 and 7) are operated by special equipment which allow to control the exact number of revolutions of the bur, the operating and interruption torque under excessive load and, last but not least, to control the bur cooling physiological solution flow. Contra angles are extremely sturdy and require little maintenance; they are made up of two main parts, the body and the head.

The contra angle head can usually be unlocked from the body, not only to allow better cleaning and lubrication of the two parts, but also in order to replace it in the event of irreparable damage. The internal rotation mechanism is made up by a transmission tang integral with a drive shaft which, through a crown wheel, allows rotation of the rotor inside the head. The hollow shaft of the rotor is thus inserted in a pair of bearings and, in the case of models with extremely high reduction ratios, the lower bearing is a bushing. The bur locking system can be automatic, push-button, or use a much simpler locking system, defined as "knife" or "guillotine" (Video 2). Clearly, a careless maintenance of this instrument can, over time, cause problems that go from excessive oscillation of the bur to seizing.

Contra angles have a universal coupling, with two variants: the system for supplying atomized water and air, which are drawn directly through the micromotor from the hose, and the lighting system for optical-fibre models (Fig. 14); these come with an Intramatic coupling. Contra angles for specific use in implantology or surgery are normally fitted with an external physiological solution supply system. Through special pipes, the peristaltic pump supplies the physiological solution directly in the vicinity of, or inside the bur. It is important to remember that also these instruments require constant and continuous lubrication. This operation must be performed with the aid of special plastic or metal fittings which, simulating the micromotor connection, allow the oil to penetrate inside the body, removing debris and lubricating all transmission components. It is a good rule to perform a cleansing and lubrication cycle before each sterilization cycle (Video 3).

Straight handpiece: in human medicine this rotating instrument is mainly used in dental laboratories, but in veterinary medicine it is widely used to even out the molariform teeth of lagomorphs and rodents. The burs mounted on this instrument have a 2.35 mm diameter and a smooth end; they are locked to the handpiece by friction (HP connection, see Fig. 17). The straight handpiece can be equipped or not with internal spray, for bur irrigation and, as for contra angles, the multiplication speed is indicated by the colour of the ring on the instrument.

Prophylaxis handpiece: this is a special contra angle, usually without fibre optic lighting and water spray. The head of this rotating instrument ends with a female screw coupling that accepts the male screw of dedicated prophylaxis (prophy) cups (Fig. 18) (Video 4), or with a fixed "Snap On" coupling.

This instrument allows to save on expensive contra angles, which are stressed considerably during polishing operations following ultrasonic scaling. Veterinarians who decide to only perform oral hygiene sessions as their only dental practice, may purchase, apart from the ultrasonic scaling equipment, this handpiece instead of a contra angle, thus allowing a considerable saving.

It should be pointed out that Snap-On – CA adapters for contra angle do exist (Fig. 19).

Air/water syringe: unlike the other handpieces, this instrument is generally fastened permanently to the air/water hose; it can supply compressed air, water or a spray of air and water by pressing on the proper push-buttons. The syringe comes in varied shapes; the tip can have from one to four nozzles, be fixed or interchangeable with other tips (single use or autoclavable). The air/water syringe is used to cleanse and dry the operation site; the strength of the jet is regulated with the pressure exercised on the control push-buttons.

“Scaler” handpiece for scaling procedures: this is an instrument which allows the removal of bacterial plaque and tartar by means of ultrasonic vibrations. The scaler has a rounded metal tip that vibrates with ultrasonic frequency, delivering at the same time a jet of water; the ultrasounds break up the tartar, making its removal from the tooth possible, and the extremely fast vibrations of the tip create some microscopic air bubbles inside the jet of water which, bursting, break the bacterial membrane: this phenomenon is called cavitation. There are various types of ultrasound scalers: piezoelectric ultrasonic, magnetic ultrasonic, sonic and rotosonic. Although all four types of scalers have the same function, it is useful to know that the piezoelectric ultrasonic scaler removes tartar above the gum line more quickly than the other three and that the rotosonic type is the one that causes the most damage, as it causes deep damage to the enamel of the crown.

Independently from the type of scaler used, after ultrasonic scaling it is necessary to polish the surface of the treated teeth using prophy cups with special polishing paste or special polishers that do not require the use of paste (Figs. 20 and 21). The more modern instruments have special inserts that allow removing plaque and tartar below the gum line. Scalers come with the dental unit or they can be purchased as a separate unit.

Air-powder scaler: an instrument can be connected to the outlet of a hose of the dental unit which mixes micronized sodium bicarbonate powder with air and water (powder scaler) which, coming out under pressure, generates a spray capable of removing plaque and tartar from the surface of the tooth. Air-powder scalers make it possible to reach every recess and, if used with an angle of incidence of 30 – 60°, do not damage the enamel.

Aspirator: some dental units are fitted with a surgical aspirator.

Protections: to avoid the transmission of infections from patient to patient, turbines, micromotors, contra angles, scalers and air/water syringes can be used with special disposable covers, as well as be sterilized in an autoclave.

BURS

Turbine burs (FG coupling): burs for turbines can be made of steel, stainless steel, tungsten carbide or constructed with diamond grains deposited on a steel support (diamond burs); the material the bur is made of and its shape must be carefully associated with the type of work to be performed.

Contra angle burs (CA or W coupling): burs for contra angles can be made of steel, stainless steel, tungsten carbide or constructed with diamond grains deposited on a steel support (diamond burs); the material the bur is made of and its shape must be carefully associated with the type of work to be performed.

Other abrasivesfor contra angles

• Prophy cups are used to polish teeth following ultrasonic scaling. Before use, the polisher assembled on the handpiece is filled with polishing paste; it should however be pointed out that specific models exist which can be used without paste (Fig. 22). Several types of cups are manufactured:
  • Preassembled on a mandrel (CA coupling) (Fig. 27)
  • With screw connection (a prophylaxis handpiece [see Fig. 18] or a screw – CA adapter is required [Fig. 23])
  • Snap-On coupling (to be assembled on special cup holder mandrels or on special Snap-On - CA adapters [see Fig. 19])
• Prophylaxis polishers are used to polish teeth following ultrasonic scaling. These products are preassembled on a mandrel (CA coupling) or with a screw connection and come in various shapes (point, minipoint, cup and webbed cup) and with several degrees of stiffness (soft and stiff); some polishers have to be used with polishing paste, while this is not required for others.
• Prophylaxis brushes are used during oral hygiene sessions for cleaning areas of the teeth which are difficult to access. They may be used alone or with disinfectants. They are available with screw connection (a prophylaxis handpiece or a screw – CA adapter is required [Fig. 23]) or preassembled on a mandrel (CA coupling). The bristles can be made of nylon, pig bristle, white goat hair, Kevlar, etc. (Fig. 24).
• Abrasive discs, mounted or not mounted on a mandrel: useful for modelling, finishing and polishing composites, amalgams, metals and alloys, they are generally available in 4 sequential grains (coarse, medium, fine and extra-fine) marked with different colours (Fig. 25). It is first necessary to check the material on which the discs are to be used on; a disc for metals would for example stain a restoration made of composite and, vice versa, a disc for composites would not be very effective on metals.
• Abrasive polishers for composite materials assembled on a mandrel (Fig. 26): these are used for the finishing of restorations made of composites; they come in several shapes (minipoint, point, flame, cup and disc) and are made of rubber or silicone to which several materials are added (diamond dust, aluminium oxide, etc.).
• Abrasive polishers for amalgams, metals and alloys assembled on a mandrel (Fig. 28): these are used for the finishing of restorations made of materials other than composites; they come in several shapes (minipoint, point, flame, cup and disc) and are made of rubber or silicone to which several materials are added (diamond dust, aluminium oxide, etc.). These abrasives should only be used on  materials for which they have an indication because, if used on composites, they can stain them, causing serious imperfections.
• Abrasive points for finishing ceramic, gold, amalgams and for rough grinding or finishing of composites assembled on a mandrel (shapes: minipoint, point, cup, disc). Their particular field of use limits their use in the veterinary field.

Burs for straight handpieces: also called laboratory burs, burs for dental technicians, cutters, etc. These come in different shapes, sizes and bit finishes (Fig. 32).

“Cutters” are used mainly to even up the molariform teeth of lagomorphs and rodents and, for those involved in orthodontics, for finishing touches/adjustments to the manufactured articles provided by the dental technician. Generally speaking, cylindrical and tapered cutters with standard simple toothing (Fig. 29) or standard cross toothing (Fig. 30) (blue ring) are used to even out the molariform teeth of lagomorphs and rodents; the shapes used most often for this operation are shown in Figure 31.

Other abrasivesfor straight handpieces: apart from the cutters, there is the availability of abrasives with FG connectors (diamond discs, polishing discs, etc.) which are of little importance in veterinary medicine (Fig. 33).

Brass brushes for the cleaning of burs: During their operation, besides wearing out, burs collect fragments of the material that they abrade and loose efficiency. To protect their operation, they must be cleaned thoroughly after use. The first phase consists of manual cleaning with a brass brush (Fig. 34), then followed by further treatments: enzyme bath, ultrasound cleaning tank and drying.