Dental Tribune Israel Edition

4 Dental Tribune Israel | 11/2016 Cord insertion is recommended not only to temporarily deflect the tissue laterally and retract it apically, but also as a security measure to remove thin remnants of torn impression material that might have been entrapped in the narrow sulci after the impression tray removal, which are inconspicuous to detect. Such remnants might result in a foreign body reaction of the tissue resulting in an inflammation and periodontal destruction. The Double-cord technique In the double-cord technique - the free gingiva and papillae should be properly and efficiently deflected in order to obtain an accurate and fully detailed blueprint of the prepared teeth. The size of the chosen cords depends on the tissue biotype and on the preparation depth into the sulcus. The first apically located cord is in general of smaller diameter and will remain in place during the entire procedure. The purpose of the first cord is to retract the tissue in an apical direction, to seal the sulcus from crevicular fluid seepage and to block (and then remove) any entrapped torn remnants of impression material upon removal of the impression. It is recommended to start rolling the cord gently from the interproximal area, where the depth of the sulcus is larger and the tissue (papilla versus free gingival margin) is stiffer, which allows the cord to be initially fixed easier. It is also recommended by the authors to roll the cord gently with very light strokes, beyond the finishing line, by utilizing a very thin flexible spatula that ensures its delicate insertion without exerting any unnecessary pressure. The tip of a thin spatula should be located over the cord, close to the tooth structure, and not in the middle of the cord width, to enable a controlled and easy sliding in a semi-rolling movement into the sulcus. There is no need to impregnate the first cord with a hemostatic solution (particularly if multiple abutments are to be treated) since the hemostatic or astringent solutions kept in contact with the tissue for a long time, might cause an adverse effect on the periodontal tissues (7, 8). The cord is inserted either dry or wetted with sterile saline solution. If the clinician decides to impregnate the cord with a hemostatic/astringent solution it should be kept in the sulcus no longer than 15 min, in order to avoid any damage to the periodontal tissues (9, 10). The second superficial cord is impregnated in most cases with hemostatic/astringent solution or gel and is placed at the level of the finishing line, so that its superficial part must always be visible after insertion. The superficial cord is typically thicker than the first cord and is aimed to laterally deflect the gingiva and to create enough space for the light body impression material to embrace and capture the preparation margin. In cases where the superficial cord is not completely visible – predominantly in the interproximal areas – an additional cord should be placed to deflect that part of the tissue away from the prepared tooth, and to prevent the collapse of the papillae tips. No rebound of the gingiva over the second cord should be allowed since it might block the light body material from penetrating areas apically to that tissue. After the insertion of the cord (or cords) a sufficient space should be created for the light body impression material to accommodate it. The width of the crevicular space obtained for the light body is influenced also by the time the second superficial cord remains in the sulcus. To create a minimum width of 0.2 mm - the cord should remain in the gingival crevice for at least 4 min prior to its removal before the impression (11, 12). This minimum width is necessary to ensure the minimal thickness of the light body required to prevent tearing of the material upon removal (regardless of the chosen technique) (13). The Clinical steps A case of two central maxillary incisors, as part of an interdisciplinary full mouth rehabilitation - one prepared for a crown and the second for a circumferential veneer is demonstrated, in order to describe the technique (Pic. 1). In cases in which multiple abutments need to be imprinted, a definitive path of insertion/removal of the set putty is mandatory in order to facilitate reinsertion of the tray loaded already with the set putty with no pressure on the putty material. Strict moisture control and cleansing the teeth from any temporary cements or debris is imperative (14). First, the teeth are properly cleansed with chlorhexidine solution (Ultrascrub, Ultradent Products, Inc. USA). In addition, an optional hemostatic solution might be used in some situations in order to arrest occasional local gingival bleeding (Viscostat, Ultradent Products, Inc. USA). The teeth are then thoroughly washed with copious amount of water and dried.The cords are chosen according to the previously performed mapping procedure. Step 1: In order to expose the margins of the preparation, a small diameter first cord was chosen and gently inserted (000 Ultrapack, Ultradent Products, Inc. USA) (Pics. 2, 3). After the first cord was placed, an initial impression (putty material, Zhermack, Spa, Italy) of the teeth was taken with a rigid stock tray, with no separation medium - directly over the teeth (Pic. 4). Step 2: The diameter of the second cord should be chosen according to the degree of deflection needed, taking under consideration the gingival biotype. Due to the difference in the positioning of the finishing line of the two treated teeth into the sulcus, two different diameters for the second cords were chosen. For tooth #11(8) being prepared for a full crown, that would need more deflection of the soft tissues in order to expose the preparation margin, a #0 cord size (Ultrapack, Ultradent Products, Inc. USA) was chosen. For tooth # 21(9) that was more minimally prepared for a circumferential veneer, a thinner cord #00 would ensure the necessary deflection (Pics. 5-7). The cords selected deflected the tissues horizontally and provided enough space for an easy penetration of the light body impression material. The insertion of the second cords followed the initial putty impression right after its removal. The cords were impregnated with a hemostatic- buffered aluminum chloride solution (Hemodent Gingival retraction cord, Premier Dental Products, U.S.A). Step 3: Modifications should then be made at the set putty. These alterations are imperative in order to create adequate space and routes of venting escapement for the light body material later on, but moreover - to enable its reinsertion to the same exact place over the teeth, with no disturbance of any undercuts. These modifications included cutting out all the undercuts of the interproximal gingival embrasures (Pic. 8) utilizing a 15C blade scalpel (or an 11 blade or any similar sharp knife). The interproximal release should ensure an easy and one- way insertion path of the set putty, which is crucial for avoiding distortions, pressure and even a possible folding or tearing of thin areas of the putty material. Then channels were carved in order to allow for the excess of the wash material to be vented away later and to avoid unnecessary hydraulic pressure that might disturb a proper seating of the loaded tray. This carving is performed using a Putty Cut (Zhermack clinical) (pic.9) or a Deta-Cut core, removal knife (Detax Dental GmbH &CO. KG) (pic. 10;11). The channels at the set putty were performed both externally to and within the areas of the abutments, at their axial and occlusal walls (Pics. 10-12). While doing so - special attention is required to avoid damage to the finishing line, captured already partially in the set putty. Following, an insertion verification test of the set putty tray was done to check the adequate release of the putty material from all undercuts and to indicate some landmarks of the tray relative to the jaw, to enable a precise and rapid insertion of the light body loaded tray at the following second impression step. Step 4: The second cord was gently removed and at the same time the low-viscosity light body PVS material was injected onto the set putty (Pic. 13). The loaded tray was then reinserted intraorally and placed over the prepared teeth and brought to a full seat, while the first deeper cords remained in place. The tray seating should be firm and straightforward utilizing the previously determined landmarks for its accurate positioning. After the setting of the light body material, the tray was removed. In order to break any vacuum seal between the set PVS and the intraoral tissues, before the tray removal, it is recommended to insert the tip of the triple syringe internal to the putty flange and blow in delicate air pressure in several locations. The impression was checked for any voids, distortions or other defects and was found to be flawless. Circumferential margin details should extend beyond the preparation margins. Often, the first cord might be removed along with the impression, which should not cause any problem for the technician as long as it is attached to the material and remains beyond Pic. 10: Channels were cut through the putty in vertical directions buccal and palatal to all teeth; Pic. 11: Channels were cut also at the buccal and lingual internal walls of the prepared teeth impression; Pic. 12: The modified putty is almost ready for reinsertion after all undercuts were removed and the escape channels created. Remaining debris from the cut putty material should be still removed. Pic. 13: The light body was injected over the putty. No need for intra-oral light body administration. At this stage the superficial cords were removed and the tray was then reinserted over the teeth, to its original position; Pic. 14: Final impression. Note the first deeper cords attached to the light body beyond the preparations margins (finishing lines). No need to detach them from the impression material. Only the loose parts should be cut away with caution; Pic. 15a: A buccal view of the alveolar (‘Geller’) master model. Pic. 15b: Palatal view – note the different position of the preparation margins of the prepared teeth; Pic. 16: e.max monolithic stained restorations on the master model. Pic. 10 Pic. 11 Pic. 12 Pic. 13 Pic. 14 Pic. 15a Pic. 15b Pic. 16

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