MECHANISM OF ULTRASONICS - ACOUSTIC STREAMING

¢ Acoustic streaming is the rapid movement of particles of fluid in vortex(circular)-like motion about a vibrating object.

¢ When a vibrating file is immersed in a fluid, the file is observed to generate a streaming fluid comprising two components:

¢ Primary field consisting of rapidly moving eddies in which the fluid element oscillates about a mean position, and a superimposed secondary field consisting a patterns of relatively slow, time independent flow. Characteristically the fluid is transported from the apical end to the coronal end.

¢ In a endosonic file the greatest shear stresses will be generated around points of maximum displacement, such as the tip of the file and the antinodes along its length

¢ it is probable that will also be important in moving the associated irrigant around the canal so that maximum benefit is achieved from the chemical irrigant.

Martin H. the ultrasonic synergistic system. Int Dent J 1984;34:198 –203.

Martin H. the ultrasonic synergistic system of endodontics. Endod Dent Traumatol 1985;1:201– 6.

Ahmad M. Ultrasonic debridement of root canals: acoustic cavitation and its relevance. J Endod 1988;14:486 –93.

PROCEDURAL ERRORS DURING CLEANING AND SHAPING

TRANSPORTATION

It is moving the position of canal’s normal anatomic foramen to a new location on the external root surface.

It Occurs apical to curvature.

Transportation occurs when the angle of access and angle of incidence differ.

The angle of access refers to the orientation of the instrument as it slides down the body of the root canal.

The angle of incidence refers to the turn required to follow the path of the root canal.

EXTERNAL TRANSPORTATION

• Occurs mainly due to failing to precurve files, using large instruments.

Original apical foramen is torn.

• When the instrument is overused - the elastic memory of the instrument may create the teardrop and tearing of the apical foramen

• Another form of external transportation is direct perforation.

• begins with a ledge or apical blockage.

• continues its misdirection until it perforates the root surface.

INTERNAL TRANSPORTATION

• occurs when foramen is clogged with dentin mud.

• perforate the external root surface through a false path.

LEDGING

• leding is Iatrogenically created root canal wall irregularity .

• it Impedes the placement of instrument

• Caused by

– forcing uncurved instrument in a curved canal.

– Rapid advancement in file size.

• Identified by Loss of tactile sensation on instrument - loose feeling instead of binding at the apex.

ZIPPING

• It is transposition of the apical portion of the canal.

• Causes

– failure to precurve the files

– Forcing the instrument in curved canal.

– Use of large , stiff instruments.

files placed in a curved canal will cut more on the outer portion of the canal wall.

ELBOW

• Creation of an ‘elbow’ is associated with zipping

• narrow region of the root canal at the point of maximum curvature as a result of the irregular widening.

• Elbow prevents obturation in the apical portion of the canal

STRIP PERFORATION

Strip perforation occurs in the middle part of the inner curve of a root canal if excessive dentine is removed by over instrument.

cross section of hand instruments in endodontics

MECHANISM OF SODIUM HYPOCHLORITE

PECORA ET AL,1999

NaOCl + H2O « NaOH + HOCl « Na+ + OH- + H+ + OCl-

SODIUM HYPOCHLORITE EXHIBITS DYNAMIC BALANCE

Saponification reaction

Sodium hypochlorite acts on fatty acids, transforming them into fatty acid salts (soap) and glycerol (alcohol), that reduces the surface tension of the remaining solution.

Neutralization reaction

NaOCl neutralizes amino acids and forms water and salt. With the exit of hydroxyl ions, there is a reduction of ph.

Chloramination reaction

Hypochlorous acid, present in NaOCl solution, when in contact with organic tissue acts as a solvent, releases chlorine that, combined with the protein amino group, forms chloramines, that interfere in cell metabolism.

Hypochlorous acid (hocl-) and hypochlorite ions (ocl-) lead to amino acid degradation and hydrolysis.

Chlorine (strong oxidant) presents antimicrobial action inhibiting bacterial enzymes leading to an irreversible oxidation of SH groups (sulphydryl group) of essential bacterial enzymes.

Braz Dent J (2002) 13(2): 113-117

Mechanism of xylitol in remineralization

Xylitol prevents the decalcification by inhibiting the translocation of dissolved calcium(Ca2+) and phosphate(PO43–) ions from lesions.

Xylitol may act as Ca2+ ion carrier supplying the middle and deep layers with Ca2+ ions from the oral environment, thus enhancing remineralization by providing the Ca2+ ions for crystal repair.

It may also accelerate remineralization by lowering the diffusion coefficients of calcium and phosphate ions within the demineralized layers.

The greater extent of mineralization in seen in deeper layer.

Journal of Electron Microscopy 52(5): 471–476 (2003)

CRITERIA FOR EVALUATION OF RESTORATION

COLOUR MATCH