Ultrasonics in Endodontics

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CONTENTS

INTRODUCTION

     The use of ultrasonics or ultrasonic  instrumentation was first introduced to dentistry for cavity preparations using an abrasive slurry .Although the technique received favorable reviews,it never became popular ,because it had to compete with the much more effective and convenient high-speed handpiece.

             However,a different application was introduced in 1955, when Zinner reported on the use of an ultrasonic instrument  to remove deposits  from the tooth surface. This was  improved upon by Johnson and Wilson ,and the  ultrasonic scaler  became an established tool in the removal of dental calculus and plaque. The concept to using Ultrasonic in endodontics was first introduced by Richman in 1957.  However, it was not until Martinetal ,demonstrated the ability of ultrasonically activated K-type files to cut  dentin that this application found common use in the preparation of rootcanals before  filling and obturation. The term endosonics  was coined by  Martin and Cunningham  and was defined as the ultrasonic and synergistic system of rootcanal instrumentation and disinfection.

               Ultrasound is sound energy with a frequency above the range of human hearing, which is 20kHz. The  range of frequencies employed in the original ultrasonic units was between 25and40kHz .Subsequently the so-called low-frequency ultrasonic hand pieces operating from 1to8kHz were developed ,which produce lower shear stresses ,thus causing less alteration to the tooth surface

              There are two basic methods of producing ultrasound.The first is magetostriction ,which converts electro magnetic energy into mechanical energy. A stack of magnetostrictive metal strips in a hand piece is subjected to a standing and alternating magnetic field, as a result of which vibrations are produced. The second method is based on the piezoelectric principle, in which a crystal is used that changes dimension when an electrical charge is applied. Deformation of this crystal is converted into mechanical oscillation without producing heat

ULTRASONIC CLEANING

It is an excellent cleaning method, as it reduces direct handling of instrument.It is safer and more effective

MECHANISM OF  ACTION

Ultrasonic energy generated in ultrasonic cleaner produces billions of tiny bubbles which further collapse and create high turbulence at the surface of the instrument. this turbulence dislodges the debris . The time may vary due to nature of the instrument amount of debris and efficiency of ultrasonic unit. Usually time ranges from 4-16 minutes.

 ULTRASONIC IMAGING

It can be used to detect early caries on smooth surfaces. Ultrasonic probe is used to send and receive sound waves from the surface of teeth.Normal enamel produce no echoes while initial surface lesion produce weak surface echoes and areas with cavitation produce echoes of higher amplitude.

APPLICATION OF ULTRASONICS IN ENDODONTICS

1.    Access refinement , finding calcified canals ,and removal of attached pulp stones

2.    Removal of intra canal obstructions (separated instruments ,root canal posts, silver points, and fractured metallic posts)

3.    Increased action  of irrigating solutions

4.    Ultrasonic condensation of gutta-percha

5.    Placement of mineral trioxide aggregate(MTA)

6.    Surgical endodontics: Root-end cavity preparation and refinement and placement of root-end obturation material

7.    Root canal preparation

ACCESS REFINEMENT ,FINDING CALCIFIED CANALS, AND REMOVAL OF ATTACHED PULP STONES

            One of the challenges in endodontics is to locate canals, particularly in cases in which the orifice has become occluded by secondary dentin or calcified dentin secondary to the placement of restorative materials or pulpotomies. With every access preparation in a calcified tooth, there is the risk  of perforating the root or, when incorrectly performed, of complicating each subsequent procedure.

                 A lack of a straight- line access is  arguably the leading cause of separation. In conventional access procedures , ultrasonic tips are useful for access refinement ,location of MB2  canals in upper molars and accessory canals in other teeth ,location of calcified canals in any  tooth,  and removal of attached pulp stones. One of the more important advantages of ultrasonic tips is that they do not rotate  ,thus enhancing safety and control, while maintaining a high cutting efficiency .This is especially important when the risk of perforation is high.

               

 REMOVAL OF INTRA CANAL OBSTRUCTIONS

                  Clinicians are frequently challenged by endodontically treated teeth that have  obstructions such as hard impenetrable pastes ,separated instruments ,silver points ,or  posts in their roots.If endodontic treatment has failed, these obstructions need to be removed to perform non surgical retreatment. Many instruments and techniques have been reported.They include appropriate burs special forceps; ultrasonic instruments indirect or in direct contact;peripheral filing techniques in the presence of solvents ,chelators ,or irrigants ;micro tube delivery using mechanical adhesion techniques; and different kits and extractors.

                Ultrasonic energy has proven effective as  an adjunct in the removal of silverpoints, fractured instruments ,and cemented posts. The prognosis of these cases mainly depends on the preoperative condition of the periapical tissues If an instrument can be removed or by passed and the canal can be properly cleaned and filled, nonsurgical endodontics is a more desirable and conservative approach.The removal of an obstacle from a root canal must be performed with a minimum of damage to the tooth and the surrounding tissues.Too much destruction of tooth structure will complicate the restorative phase and as a result will most likely decrease the overall prognosis.

   The relative ease of removing prefabricated parallel posts with the use of ultrasound is probably related to their design, as they do not adapt well to the coronal third of most root canals. This allows for easy break down of

the cement in the coronal third and subsequent shifting of the fulcrum

point toward the apical end of the post.

INCREASED ACTION OF IRRIGATING SOLUTIONS

The flushing action of the irrigant solution may be more important than the ability of the irrigant solution to dissolve tissue.  Most of the dentine debris is inorganic matter that cannot be dissolved by NaOCl. Therefore, removal of dentine debris relies mostly on the flushing action of irrigant.

Ultrasonic Irrigation

The enhancement of the flushing action of an irrigant solution by using ultrasound is well documented.  The ultrasound device allow the endodontic irrigant to pass along the ultrasonic files. The irrigant is activated by the ultrasonic energy imparted from the energized instruments producing acoustic streaming and eddies.

   More bacterial spores and dentine debris were removed during ultrasonic irrigation than hand irrigation. Ultrasonic proved superior to syringe irrigation alone when the canal narrowed to 0.3 mm (size 30 instrument) or less.

Causes continous flow of irrigantin the canal,thus prevents accumulation of debris the canal

Mechanism  of action

When a small file is placed in the canal and ultrasonic activationis given,the ultrasonic energy passes through the irrigating solution and exerts its acoustic streaming or scrubbing effect on the canal wall.This  mechanical energy warms the irrigant solution and dislodges debris from canal.

                                           

ADVANTAGES

·         Cleans better

·         Remove smear layer efficiently

·         Dislodges debris from the canal better

DISADVANTAGES

·         Is unpredictable

·         It can lead to excessive cutting of canalwalls and damage finished preparation

ULTRASONIC CONDENSATION OF GUTTAPERCHA

                                    

               Ultrasonically activated spreaders have been used to thermoplasticize gutta-percha in a warm lateral condensation technique. Ultrasonic spreaders that vibrate linearly and produce heat, thus thermoplasticizing the gutta-percha achieved a more homogeneous mass with a decrease in number and size of voids and produced a more complete three-dimensional obturation of the root canal system.

 PLACEMENT OF MINERAL TRIOXIDEAGGREGATE(MT

                       Witherspoon and Ham described the use of ultrasound to aid in the placement of MTA. The inherent irregularities and divergent nature of the recommended placement method consists of selecting a condenser tip ,then picking up and placing the MTA with the ultrasonic tip, followed by activating the tip and slowly moving the MTA material down using a 1-to2 mm vertical packing motion. Direct ultrasonic energy will vibrate and generate a wave like motion, which facilitates moving and adapting the cement to the canal walls

SURGICALENDODONTICS

Root-End Cavity Preparation and Refinement and Placement of Root-End Obturation Material

                                      

      Root-end cavities have traditionally been prepared by means of small round or inverted cone burs in a micro handpiece. The development of ultrasonic and sonic retrotips has revolutionized root-end therapy ,improving the surgical procedure with better access to the root end, resulting in better canal preparation.

Ultrasonic tips canals to be used to polish root end material and apical surfaces. Utilizing specific ultrasonic tips for refinement of the external radicular surface may be beneficial in the elimination of extra radicular bacteria, which may be responsible for infection.

Advantages

·         Smaller preparation size and better access

·         Less or no need for root end beveling

·         A deeper preparation possible

·         More parallel walls for better retention

·         Less debris and smear layer than those prepared with bur

ROOT CANAL PREPARATION

1.    Ultrasonic handpiece

2.    Ultrasonics used in endodontics is called as endosonics intrduced by RICHMAN

MECHANISM OF ACTION

 It uses   sound as a energy source (20-40khz) activates  a endodontic file resulting in three dimnsional activation of file in the surrounding medium.Ultrasonic system involve a power source to which an endodontic file is attached with a holder and an adaptor

It uses k file as a canal instrument 

CAVITATION AND ACOUSTIC STREAMING

    Cavitation is defined as the growth and subsequent violent collapse of small gas filled pre existing inhomogenicity in the bulk fluid.This results in development of shock wave,increased temp,pressure and free radicalformation in the fluid.

 Acoustic streaming

It is the generation of time independent ,steady unidirectional circulation of fluid in the vicinity of small vibrating object.Production of large hydrodynamic shear stress around file    

CONCLUSION

Main reasons to use ultrasonics in endodontic applications

“Improved visualization combined with a more conservative approach when selectively removing tooth structure, particularly in difficult situations in which a specific angulation or tip design permits access to restricted areas, offers opportunities that are not possible with conventional treatment”

Compared to burs/rotating instruments: better view of the operative field , greater cutting precision (better control of the amount of dentin removed)