Operative Instrumentation

Operative Instrumentation

Introduction

  • Importance in Restorative Dentistry:

    • Removal and shaping of tooth structure are crucial for effective restorative dentistry.

    • Hand instrumentation alone may not suffice for intricate and detailed operative procedures.

  • Knowledge of Dental Instruments:

    • Understanding various dental instruments is essential for performing detailed procedures in operative dentistry.

Rotary Instruments

  • Components of Rotary Instruments:

    • Handpieces

    • Burs

    • Polishing instruments

Handpieces

  • Classification Based on Driving Mechanism:

    • Gear Driven Handpiece:

    • Rotary power transferred via a belt from an electric motor.

    • Functions best at low speeds, though capable of variable speeds.

    • Water Driven Handpiece:

    • Introduced in 1955, operates at approximately 100,000 rpm.

    • Uses high-pressure water to rotate turbines.

    • Belt Driven Handpiece:

    • Also introduced in 1955, works at speeds greater than 100,000 rpm.

    • Air Driven Handpiece:

    • Introduced in 1957, can reach speeds between 300,000 and 400,000 rpm.

  • Types of Handpieces:

    • Straight Handpiece:

    • Long axis of the bur is aligned with that of the handpiece.

    • Primarily used in oral surgery and laboratory procedures.

    • Contra-Angled Handpiece:

    • The head of the handpiece is angled from the long axis for better accessibility, visibility, and stability during use.

Classification of Rotary Instruments Based on Speed Range

  • Speed Measurement:

    • Rotational speed is measured in revolutions per minute (rpm).

    • Speed Categories:

    • Slow Speed: Below 12,000 rpm.

    • Intermediate Speed: Between 12,000 and 200,000 rpm.

    • High Speed: Above 200,000 rpm.

  • Surface Speed Consideration:

    • Surface speed, or the velocity at which cutting edges move across the surface, is a crucial factor for operation.

Detailed Classification of Rotary Instruments by Speed

  • High Speed Instruments:

    • Typically operate between 100,000 to 300,000 rpm.

    • Generate considerable heat.

    • Used for gross tooth reductions and exclusively with tungsten carbide burs.

    • Advantages:

    • Less force required on the bur reduces operator fatigue.

    • Disadvantages:

    • Reduced tactile perception.

  • Slow Speed Instruments:

    • Available as straight and contra-angle types.

    • Suitable for both steel and carbide burs, offering greater tactile feedback.

    • Useful for deep caries removal and refinement procedures.

    • Disadvantages include:

    • Time-consuming.

    • Increased force leads to elevated heat and operator fatigue.

    • Generates high amplitude vibrations, potentially causing discomfort.

    • Results in decreased lifespan of carbide burs due to vibration-induced skipping.

Dental Burs

  • Function of Burs:

    • Dental burs attach to handpieces for cutting or polishing hard tissues in the mouth.

    • Main Types of Burs:

    • Diamond Burs: Highly effective for cutting hard tissues.

    • Tungsten Carbide Burs: Known for durability and effectiveness.

    • Steel Burs: For general purposes.

Structure of a Bur

  • Three Parts of a Bur:

    • Shank:

    • Connects to the handpiece; available in three common types: straight, latch-type, and friction grip.

    • Neck:

    • Connects the shank to the head; must be adequately strong and allow for coolant flow to the head.

    • Head:

    • The working part of the bur responsible for cutting and shaping tooth structure.

  • Design Considerations for Burs:

    • Must be harder than the material being cut, with tungsten carbide being preferred for enamel cutting due to its superior properties at high speeds.

    • Comprised of metal cutting edges, known as blades, teeth, and flutes.

    • Generally designed to cut when rotating clockwise.

Bur Design Features

  • Cutting Efficiency vs. Surface Finish:

    • Burs with a higher number of cutting blades tend to create smoother surfaces but are less efficient.

    • Fewer blades resulting in more effective cutting but may leave a rougher finish.

Steel Burs

  • Characteristics:

    • Known for flexibility and edge retention, designed for slow speeds under 5000 rpm.

    • Effective for dentin removal but blunt faster than tungsten carbide and prone to corrosion.

Tungsten Carbide Burs

  • Manufacturing Process:

    • Created by alloying tungsten carbide powder with cobalt-nickel powder under pressure and sintering in a vacuum.

    • Three times harder than steel, allowing a smoother finish when reducing tissue.

    • Commonly used in operative procedures, often with a carbide tip and steel shank.

Diamond Burs

  • Properties and Use Cases:

    • Most commonly used burs with high-speed applications.

    • Excellent for grinding hard tissues, leaving a rough surface.

    • Constructed by bonding small diamond particles to a substrate.

    • Frequently employed in crown and veneer related procedures, albeit with a shorter lifespan compared to other burs.

Bur Shapes

  • Classification By Contour:

    • Common shapes include round, inverted cone, pear, straight fissure, and tapered fissure.

    • Within any series, smaller numbers correspond to smaller burs and larger numbers to larger burs.

Specific Bur Types

  • Round Burs:

    • Spherical in shape, cutting on both ends and sides.

    • Diameter numbers range from ¼ to 10, ideal for initial tooth entry and caries removal.

  • Elliptical Burs (Pear-Shaped):

    • Tapered cone design for creating undercuts, commonly used types include 330 and 331.

  • Long Pear Burs with Rounded Corners:

    • For use in Class II proximal boxes, exemplified by numbers 245 and 246.

  • Carbide Finishing Burs:

    • Designed for finishing procedures, with increased flutes for smoother cuts but decreased efficiency.

    • Flame, tapered, or football-shaped burs reserved for finishing composite resins; round finishing burs can finish silver amalgam work.

Cutting Recommendations

  • Optimal Use of Handpieces and Burs:

    • Use contra-angle handpieces for high speed with air-water spray for cooling.

    • Apply light pressure with carbide burs for intra-coronal tooth preparations and amalgam removal.

    • Diamond burs are preferred for both intra-coronal and extra-coronal preparations, including beveling enamel margins.

Hazards with Rotary Instruments

  • Key Risks:

    • Pulpal Precautions: Prolonged use can induce discomfort and damage.

    • Mechanical Vibration: Extended use of carbide burs may cause discomfort to patients.

    • Heat Generation: Excessive heat from bur use may harm tooth pulp.

    • Microcracks: Preparation with diamond burs may induce microcracks in enamel; size and orientation depend on diamond particle characteristics.

    • Desiccation of Teeth: Potential drying of tissues during procedures.

    • Transection of Odontoblastic Processes: Possible injury to dental pulp nerves and cells.

Factors Influencing Tooth Temperature During Cutting Procedures

  • Key Factors Include:

    • Diameter and Sharpness of the Bur: Smaller and sharper burs generate less heat.

    • Bur/Tooth Contact Time: Longer contact increases temperature.

    • Type of Coolant Used: Water is the best coolant; air may dehydrate and cause hypersensitivity.

    • Force Applied to the Bur: Greater force produces more heat.

    • Dull Burs: Produce heat and are less efficient without coolant.

  • Use of Coolants:

    • Air-water sprays moisten tissues, clean and cool cutting tools, extending tool lifespan and enhancing operating site visibility.

Soft Tissue Precautions

  • Injury Risks:

    • Risks to lips, tongue, and cheek during procedures.

    • Rubber dams may isolate soft tissue effectively.

    • Patient instruction to avoid sudden movements is crucial; finger rests enhance stability.

    • Mechanical Pulp Involvement: Greater risk during caries excavation with hand versus rotary instruments.