Standardization and classification of injection needles
Needles for the maxillofacial region are classified according to several strict criteria to ensure the safe delivery of anesthetics. First, the cannula may have a smooth inner surface or a thread for rigid fixation onto the syringe. Second, the shaft (the distance from the tip to the cannula) is strictly regulated in length:
- Ultrashort needles: from 2 to 8 mm.
- Short needles: from 16 to 25 mm.
- Long needles: from 32 to 44 mm.
International diameter standardization is applied to dental cartridge syringes. The size of the inner lumen is designated in G (Gauge) units, which corresponds to a specific outer diameter in millimeters. The higher the G value, the thinner the needle:
| Lumen size (G) | Outer diameter (mm) |
|---|---|
| 20G | 0,9 |
| 21G | 0,8 |
| 25G | 0,5 |
| 27G | 0,4 |
| 30G | 0,3 |
Systematization of syringes in dentistry
Syringes are used for temporary storage, dosing, and generating injection pressure. Disposable plastic models with a graduated barrel require pre-filling with the drug. Metal reusable (cartridge) systems are designed to work with pre-filled dental cartridges.
According to the cartridge fixation mechanism, they are classified as:
- Spring-loaded: feature a return mechanism on the plunger for aspiration control.
- Bayonet: cylindrical, visually resembling a pen, equipped with a side clamping lever.
- Breech-loading (hinged): equipped with an angular hinge mechanism for working in hard-to-reach areas.
- For intraligamentary anesthesia: pistol-type with a powerful lever that creates high pressure to deliver the solution into dense periodontal tissues.
Bone surgery instruments and their parameters
Surgical interventions use instruments with strictly defined parameters of action on the bone.
- Bone scrapers: collect bone chips into a hollow body, keeping them saturated with plasma to maintain osteocyte viability.
- Trephine burs / burr forceps: available with a straight (for the anterior segment) and curved (for lateral segments) working part. The end section features symmetrical openings for passage of the trephine.
- Chisels and osteotomes: equipped with measurement notches on the working part, serving as a visual marker of safe insertion depth.
- Bone rongeurs / forceps: double-hinged provide a wide gripping area for compressive fragmentation, while triple-hinged allow for localized fragment removal without destroying adjacent healthy bone.
Instruments for sinus grafting
Specific instruments for elevating the Schneiderian membrane and sinus floor are also standardized in shape and function.
Elevators (bone expanders) can be straight or bayonet-shaped. Their conical working part is equipped with circular notches for depth control. To prevent sinus perforation, models with removable stoppers are used.
Curettes have a rounded spoon-shaped working part. Their connecting shank has a complex geometry (curved in a multi-link broken line), which allows precise adaptation of the instrument to the complex anatomy of the maxillary sinus while minimizing the risk of membrane rupture.
Measuring devices
For precise planning of implantation, high-precision calibrated instruments are used:
- Micrometer: allows determining both the maximum thickness of the bone tissue and its parameters at a specific point. The data are plotted on a millimeter scale and fixed with a screw clamp.
- Osteometer: is used to measure the true width of the alveolar process. The sharp spikes on the instrument's jaws allow piercing the soft mucosal tissues and excluding their thickness from the final calculations.
Briefly: answers to topical questions
What are the functional differences between spring-loaded, bayonet, and block syringes?
The functional differences between spring-loaded, bayonet, and block syringes lie in the method of carpule fixation and design features that facilitate the injection.
| Type of syringe | Method of carpule fixation | Design features |
|---|---|---|
| Spring-loaded | The plunger is pulled back and returns to its place under spring action, clamping the carpule | Equipped with a return spring mechanism on the plunger for ease of aspiration |
| Block | The piston part is retracted at an angle, and returns to its original position after the carpule is inserted | Features a hinge (angled) mechanism facilitating access to hard-to-reach areas |
| Bayonet | The piston part is fixed to the barrel using a half-turn snap-lock | Has a cylindrical shape and is equipped with a lateral clamping lever |
Additionally, the plunger of spring-loaded and block syringes may be equipped with a return mechanism for fluid aspiration.
Class and exam questions
How does the needle gauge in G relate to its thickness in millimeters?
The Gauge (G) system measures the size of the internal lumen. The larger the G number, the thinner the needle. For example, a 20G needle has an outer diameter of 0.9 mm, while a 30G needle is only 0.3 mm.
What is the feature of the osteometer compared to the micrometer?
The osteometer is equipped with special spikes on its jaws that pierce the mucous membrane. This makes it possible to measure the true width of the bone tissue alone, neutralizing the thickness of the gingiva.
What are the parameters of ultra-short needles?
Ultra-short injection needles have a shaft length of 2 to 8 millimeters.
How is the depth of chisel penetration into the bone controlled?
The working part of chisels and osteotomes features special measurement notches that serve as a marker of the allowable depth pre-calculated from the X-ray.
What else to study on this topic
- Surgical and instrument clamps
- Hemostatic chisel and its application
- Classification of retractors and mouth gags
- Types and purpose of bone rasps
- Condensers for bone cavity preparation
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Other topics in «Chapter 3. Dental Instruments»
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