Indications and potential limitations of Gates Glidden drills (GGDs) in endodontics

            
         

Gates Glidden Drill Basics

GGDs have been used for decades to shape the orifice and canal above the point of first curvature in endodontic procedures. 

Traditionally they come in lengths of 28, 32 and 38 mm and in sizes #1-6, with size #1 being the smallest in diameter and #6 the largest.

Football shaped at the cutting end and smooth shafted, after insertion they are used in a coronal brushing motion against the canal wall possessing the greatest width of dentin. 

The diameter of the cutting bud on the GGD #1 is 0.5 mm, #2 is 0.7 mm, #3 is 0.9 mm, #4 is 1.10 mm, #5 is 1.3 mm and #6 is 1.5 mm. 

Not all GGDs are made from the same stainless steel, for example, Mani GGDs are made from a corrosion resistant hard fiber austenite stainless steel.

 Relatively inexpensive, GGDs are a far more economical option than their rotary nickel titanium (RNT) counterparts. 

Additionally, when a GGD fractures, it generally breaks at the latch end rather than the bud end. In the rare instances when a fracture at the bud does occur, the clinician must generally utilize a surgical operating microscope and ultrasonics to facilitate removal.

Gates Glidden Drills in Use

GGDs are used sequentially to achieve the desired taper in the coronal and middle third of canals. 

When more taper is desired, a larger GGD is taken to the greatest depth apically. Conversely, when less taper is desired, a smaller GGD is taken to the greatest depth apically.

For example, in preparing a minimal taper, the #1 GGD is taken furthest apically—usually to the point of first canal curvature or a clinically appropriate depth. Next the #2 is taken to a depth 1-2 mm coronal to the #1, the #3 is taken to a depth 1-2 mm coronal to #2, and the rest continue in this sequence. Generally, the #5 and #6 are used only at the orifice.

Overzealous and forceful GGD insertion, especially of the larger sizes, can lead to “screwing in,” excessive dentin removal and furcal perforation. Maintaining tactile control of a GGD can prevent this tendency. Maintaining a firm grip on the slowspeed handpiece and only taking the drill to its desired apical depth of insertion can go far toward minimizing these challenges

Creating appropriate taper with GGDs requires the clinician to take into account the root morphology including the degree of root fluting, width, length, curvature, calcification, and whether the root has been previously treated with endodontics, among other factors. The initial GGD taken apically must be carefully chosen.

Regardless of whether a GGD or a RNT orifice opener is used to shape the coronal aspect of the preparation, the final prepared canal shape should resemble a tornado, i.e. a tapered funnel with narrowing cross sectional diameters. Using too large a GGD initially, without giving thought to the desired final taper can make achieving this shape all but impossible.

                        

For example, a large canal that narrows rapidly or curves dramatically at mid root can easily be over shaped with excessive dentin removed from the canal above the point of first curvature if the first GGD chosen is too large making a tapering funnel impossible to achieve. Clinically, it is best to be conservative with the first GGD entered into the canal to act as an orifice opener as more dentin can always be removed later if needed.

Blockage is a risk in some canal anatomy after insertion of a GGD if the clinician does not assure all debris is removed both from the chamber floor after access and again before the first GGD is used. Enlarging just the coronal 1-2 mm of the canal first and subsequently using hand K files initially to scout the canal to its terminus also can be beneficial to assure the clinician that the canal is open and negotiable. Such an action will minimize blockage.

This can be contrasted with a procedure where, after using a GGD, the canal is not patent and the clinician does not know if they blocked the canal with debris or whether the canal was never patent in the first place. Assuring patency as described is a precaution that will prevent subsequent iatrogenic events such as blockage or possible perforation in some complex cases.

In summary, GGDs are a time honored way to open orifices and do bulk shaping in the coronal and middle third. Generally very safe and cost effective, it is necessary for the clinician to use them conservatively, especially at first, to assure that only the desired taper is created through blending the various GGDs and avoiding excessive dentin removal.