|Year : 2014 | Volume
| Issue : 1 | Page : 33-40
Coronal disassembly systems and techniques: An overview
Kavitha Janardanan, Vini K Varkey, M Lovely, A Anuroopa
Department of Prosthodontics, Government Dental College, Thiruvananthapuram, Kerala, India
|Date of Web Publication||21-Jun-2014|
Department of Prosthodontics, Government Dental College, Thiruvananthapuram, Kerala
Source of Support: None, Conflict of Interest: None
| Abstract|| |
To create a general awareness among the clinicians regarding the appropriate choice of crown removal systems and techniques in various clinical situations. Fixed prosthodontic treatment is often faced with complications involving failure of restoration or of the abutment due to improper treatment planning. In such situations, further management can be accomplished either by removal and replacement or repair of the restoration. Removal of the crown and bridges for refabrication is extremely tedious and can lead to unpredictable consequences if proper technique is not used. An external device is always required for the removal of the failed restorations. Decrowning devices are a boon to dentistry to deal with such situations. Numerous decrowning devices are available commercially. This review describes and demonstrates the various available devices based on the mode of action. Literature search was carried out using PubMed and Google Scholar from 1970's to till date. Any decrowning device will be successful only if used appropriately. Hence, this literature attempts to suggest the possible application of each system based on clinical situations. A few modified techniques have also been discussed in this article for ease of the clinician.
Clinical Relevance to Interdisciplinary Dentistry
The field of fixed prosthodontics warrants the use of coronal disassembly systems in situations such as loosened retainer of a bridge, fractured facing, unesthetic patient appeal, loosened abutment of an implant, etc.Removal of a crown or bridge is important for conservative retreatment in conditions such as secondary caries underneath a cemented crown or recurring periapical infection of a root canal treated tooth restored with a crown.Special care should be exercised while removing fixed restorations from a periodontally compromised abutment.Safe removal of crowns is also important in the field of implant dentistry.
Keywords: Coronal disassembly, crown and bridge remover, pneumatic crown remover
|How to cite this article:|
Janardanan K, Varkey VK, Lovely M, Anuroopa A. Coronal disassembly systems and techniques: An overview. J Interdiscip Dentistry 2014;4:33-40
|How to cite this URL:|
Janardanan K, Varkey VK, Lovely M, Anuroopa A. Coronal disassembly systems and techniques: An overview. J Interdiscip Dentistry [serial online] 2014 [cited 2020 Aug 4];4:33-40. Available from: http://www.jidonline.com/text.asp?2014/4/1/33/135009
| Introduction|| |
Any prosthesis in the dynamic oral environment has limited longevity and crowns and bridges are no exception. They need to be removed at one stage or other due to functional, biological or aesthetic reasons. Some of the common clinically encountered situations requiring retrieval of a fixed restoration include the need for endodontic retreatment, gingival recession resulting from crown margin encroaching the biologic width, extension of the bridge span, refiring of a fractured ceramic layer, loosened retainer of a bridge, fractured laminate veneer, grossly decayed crown due to secondary caries, etc. The patient often demands an unmarried restoration after removal due to economic, esthetic and psychological reasons. The five factors, which can affect the removal of a cemented restoration are the taper of the preparation, restoration design and structure, restorative material used, cementing agent employed, and the removal device selected. 
Various methods have been described in the literature for the safe removal of a fixed prosthesis. These may vary from simple instruments available in dental operatory such as a large spoon excavator, a scaler tip, brass ligature wires, matrix band, chisel and hammer to specific coronal disassembly instruments such as crown remover forceps, impact delivering devices, crown sectioning burs, crown splitters, etc. A clear understanding of the functioning of these devices is vital for a safe and effective practice of crown and bridge prosthodontics. The aim of this article is to review the various systems and techniques available and to suggest the best option in each clinical situation.
| Data acquisition|| |
PubMed and Google Scholar were used for literature search related to coronal disassembly systems and techniques. A thorough search of literature was carried out from 1970's to 2012 using the keywords coronal disassembly, crown and bridge removal systems, and laser decrowning and implants retrieval. Based on the data obtained, a newer classification system has been put forward encompassing the devices as well as the techniques employed.
Ingle has classified coronal disassembly devices into grasping instruments, percussive instruments and active instruments. According to the classification suggested by the authors they are divided into:
Devices permitting reuse of the prosthesis
- Adhesive resins
- Grasping instruments
- Forceps which provide a firm grip over the crown
- Forceps engaging the margins
- Impact delivering devices
- Manual back action
- Spring loaded back action
- Spring loaded semi-automatic
- Spring loaded automatic
- Devices that actively engage the restoration.
Instruments that does not permit reuse of the prosthesis
- Crown splitters
- Crown spreaders.
Radiations for safe removal of the fixed prosthesis
| Adhesive resins|| |
They are mainly indicated for the removal of temporarily cemented crowns and loose deciduous teeth. The Richwil Crown and Bridge Remover (Almore International Ltd., Portland, Ore) [Figure 1]a is a water soluble resin which becomes pliable at 145° F. Softened resin is placed on the incisal or occlusal surface of the prosthesis to be removed. The patient is instructed to occlude and to compress it to two-third of its original size. Once cooled, the sudden opening motion will remove the crown due to breakage of the cement seal. Their use becomes limited if there is any nonsecure restoration in the opposing arch.
| Grasping instruments|| |
These forceps like instruments work by applying inward pressure on two opposing handles. They are best suited for removing temporary restorations. They provide a firm grip over the crown by means of rubber inserts at the beak end and release the restoration without producing any damage. Some of them are provided with turn screws to prevent crushing of the crown [Figure 1]b. A few commercially available grasping instruments are K. Y. Pliers (G C America, Alsip, IL), CK pliers (C-K Dental, San Diego, CA), Nordent crown adaptor pliers (Nordent Manufacturing, IL, United States), Trial Crown Remover (Hu-Friedy Co., Chicago), Wynmann Crown Gripper (Miltex Instrument Company, Lake success, New York, PA), Trident Crown Placer or Remover (C-K Dental, San Diego, CA), TempOff crown removers (David Fyffe, DDS, Dallas, US).
Another type of grasping instrument engages the margins of the crown. The Roydent Bridge Remover forceps (Roydent Dental Products, Rochester Hills, MI) has tips, which engage the margins of the crown, while the adjacent tooth is used as the fulcrum. The crown will be elevated off the tooth when the handles are squeezed together. However, they may produce damage to the fragile margins.
| Manual back action instruments|| |
These groups of instruments engage the margins by a tip, which is attached to a shaft. The shaft has a sliding weight and impact force is applied by activation of the weight manually [Figure 1]c. It is mainly indicated for the removal of a temporarily cemented prosthesis. Activation of the load may cause the rod to shift away easily from the intended axis of removal. Instruments in this category include Morrell crown remover (Henry Schein, Port Washington, NY), Miltex crown remover (Integra York PA Inc., Davies Drive, York, PA), Pulpdent Crown and Bridge Remover (Pulpdent Corporation, Watertown, USA), Osung Crown Remover (Osung MND Co., Ltd, Kimpo, KS), Shen crown remover, etc. These traction based devices may cause considerable patient trauma and luxation of the ligament. Furthermore, it is difficult to ascertain that the forces are exerted along the long axis of the preparation. 
| Spring loaded back action|| |
These are back action hammers that are spring loaded. The spring is compressed manually and released to deliver the impact force [Figure 1]d. Instruments in this category include Kohler spring loaded (Pearson Dental) and Kentzler Kaschner Dental Type C crown remover (Kentzler Kaschner Dental GmbH, Ellwangen, Germany).
| Spring loaded semi automatic|| |
This class of the instrument can be operated easily with one hand while the other can be used to secure the device at the crown margin. Hence, they have better directional control when tapping forces are applied. The spring is compressed by sliding the outer tube over the inner tube. Pressing the button provides back action to remove the prosthesis [Figure 1]e. However, the instrument should be removed and reactivated each time it is operated. The Bontempi, Toronto. Ont, Crown-A-Matic (Peerless International, Inc. S.Easton, MA), Kentzler Kaschner Dental Type A, semiautomatic crown remover Medesy belong to this class.
|Figure 1: Richwil adhesive crown and bridge remover (a), trial crown remover with rubber inserts and turn screws (b), manual back action instrument (c), spring loaded back action hammer (d), spring loaded semiautomatic (e), and spring loaded automatic (f)|
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| Spring loaded automatic crown remover|| |
The automatic crown removers can be used in a single handed manner, and they need not be removed for reactivation. By pressing the handle, the shock impulses are released successively [Figure 1]f. A few instruments in this category include Dexell automatic crown remover, Kentzler Kaschner Dental Type B, Medesy Crown clix, etc. These types can be attached with loops, which are passed through the connector area to deliver impulses for removal of bridges.
| Pneumatic crown remover|| |
This class of instruments makes use of compressed air in the dental unit to break the cement seal. The purchase point is placed at the margin of the restoration and short, repeated, low impact force is delivered. Reactivation is automatic due to the compressed air flowing through the unit. The Easy Pneumatic Crown and Bridge Remover II (Dent Corp., White Plains, NY) [Figure 2]a, Saferelax (Anthogyr, Sallanches, France), ATD Automatic crown and bridge remover (J. Morita, Irvine, CA) are automatic crown removers that can be attached to the compressor. For the Coronaflex (KaVo, Lake Zurich, IL) [Figure 2]bthe main component is a gun like a barrel with a small extension at the end rotating at 360°, which delivers the impact force. Forceps or clamps can be used for the removal of crowns and a loop holder and loops are used for bridge removal.
|Figure 2: Easy pneumatic crown and bridge remover (a), coronafl ex forceps, clamp and loop holder to which the impact is delivered (b)|
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| Active instruments|| |
These instruments actively engage the restorations by means of a small access window cut through the crown, in order to support the abutment while the lifting force is applied on the restoration. The Metalift (Classic Practice Resources, Baton Rouge, LA) [Figure 3]a is one such instrument which creates a threaded channel in the restoration to engage the self-tapping instrument thread into the metal. Turning of the instrument against the dentin past the metal causes the cement layer to break. The Kline crown remover (Brasseler, Savannah, GA) is a stainless steel plier like instrument with one end having a pin 6 mm long and 1.6 mm diameter and the other end being flat and pointed. The pin engages a hole created on the cusp tip and the flat end engages the margin or a created notch. Squeezing the handle produces pressure causing the cement seal to break. The Higa Bridge Removal System (Higa Mfg Ltd., West Vancouver, B.C. Canada), [Figure 3]b makes use of a cable system that pulls up the bridge, while a support peg holds down the prepared tooth. The support pin is inserted into the hole on the occlusal surface. Tightening of the cable causes equal pressure to be applied to the bridge in the upward direction causing it to lift up while the pin supports the abutment. The Wamkey System (Dentsply, Ballaigues, Switzerland) [Figure 3]c makes use of oval shaped keys of dimensions ranging from 2.5 to 5 mm 2 . A Wamkey is inserted into the tunnel created between the occlusal surface of the preparation and the intaglio surface of the crown and rotated. The crown follows the path of least resistance and lifts up from the preparation.
|Figure 3: Metalift self-tapping instrument engaging a threaded channel in the restoration (a), tightening of the cable of Higa Remover (Higa Manufacturing, West Vancouver, B.C) causes the bridge to lift up while the pin supports the abutment (b), Wamkey inserted into the tunnel between the preparation and inner surface of crown (c)|
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| Devices which does not permit safe removal of the prosthesis|| |
When the underlying tooth is mobile, root canal treated, or resists removal due to adhesive cementation, the crown should be splitted and removed. The crosscut tungsten carbide burs are indicated for sectioning of base metal alloys, whereas medium grit diamond burs are indicated for high noble metals.  The crowns are splitted from both buccal and lingual sides and joined at the incisal edge. The Brasseler Crown Removal System (Brasseler, Savannah, GA), The Great White Burs (S.S. White Burs Inc., Lakewood, NJ, USA), Crown Removal Set LS -102 (Axis Dental Corporation, Coppell, Texas), (Axis Dental Corporation) have special burs for sectioning diamond and metal. Tri hawk (Trihawk Inc., Luxemberg) has standard carbide burs as well as special Talon burs [Figure 4]a to accomplish this purpose. Hyperbolic shaped Talon metal and crown cutter have blades at the top and sides, allowing them to cut vertically as well as horizontally.
|Figure 4: Talon burs with blades at sides and tip allowing them to cut vertically and horizontally (a), double ended spreaders with flat ends (b), "T" shaped spreaders with flat ends (c), elevator type spreaders with notched tips (d), squeezing the handle of the spreader causes the beaks to separate (e)|
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| Crown spreaders|| |
Once the crowns are split open they need to be spreader to release the metal substructure from the tooth. Crown spreaders are inserted into the groove and rotated to break open the cement seal. One hand held instrument is the Nemetz crown remover (Gingi-Pak, Division of Belport) whose unique double action opens up the crown with both frontal and lateral displacement and also have a soft silicone grip providing a tactile feel. Zoll dental has provided for double ended rigid crown removers with flat ends. Similar instruments in this category include Nash/Taylor crown spreader (Hu-Friedy Mfg Co., Inc.) [Figure 4]b, Brasseler Crown Spreader, USAB 134, USAEB 134 (Brasseler, Savannah, GA), Trident crown splitter (C-K Dental, San Diego, CA) etc.
These are also available in the form of "T" shaped keys with flat ends. Goldstein crown remover keys (Hu-Friedy Co., Chicago) [Figure 4]c are available as straight, 45° angled and 90° angled tips making it possible to be used anywhere in the mouth.
The heavy duty elevator types of crown spreaders provide for a better grip. The Zena Spreader or Elevator (Brasseler, Savannah, GA) is a stainless steel instrument with octagonal tapered handle resembling a straight surgical elevator, but with a flat end without serrations on the tip. The Christensen Crown Remover (Hu-Friedy Mfg Co., Inc.) may be straight or angled with a flat tip. The Nordent, Osung RECDA and Medesy [Figure 4]d crown spreaders are single ended with notched tips ("+" shaped) with more efficiency than flat ended types.
The forceps type of spreaders engages a slot created on the surface of the crown. Gently squeezing the handle allows the beaks to separate and split the crown [Figure 4]e. The Dexell Crown Spreader Forceps, Xcision crown spreader Miltex Instrumental Company, Lake Success, NY, Medesy Crown Splitting forceps Zoll Dental Crown Removers are all based on this type.
| Ultrasound|| |
This is an atraumatic technique for decrowning. It makes use of special scaler tips (Piezon Ultrasonic, EMS, Fotips rest gate, Dallas, USA), which are placed in a groove cut in the restoration. However, the application of vibration over a long period of time may cause ceramic to become detached from the coping. The heat generated can cause damage to the pulp and supporting structures. Hence, copious water spray is essential. Furthermore, this procedure is time consuming. Although the effect of ultrasonic vibration on retention of cast restorations has been proved to be negative in previous studies,  Melo Filho et al.  had found that the application of ultrasonic vibration at the cervical margin of the crown for 15 s caused a considerable reduction in tensile bond strength due to fracture of cement layers.
| Lasers|| |
Mainly indicated for debonding porcelain laminate veneers Er, Cr: YSGG lasers 2780 nm can be used for this purpose.  The wavelength of this laser cannot be absorbed by porcelain compounds. Hence, they pass through porcelain and are absorbed in the luting agent as Erbium is absorbed in the water present in the luting agent. Application of Er, Cr: YSGG, 20 Hz for approximately 1-2 min on each side will aid in the removal of the restoration. A study by Oztoprak et al.  have shown that Er-YAG (erbium- doped: yttrium aluminium garnet) laser at a wavelength of 2940 nm, when applied for 9 s on the labial surface in horizontal strokes caused a nine-fold reduction in bond strength of luting composite to enamel. The mode of action of laser during removal is by thermal softening of the resin without any damage on the tooth enamel. Morford et al.  have made use of Er-YAG laser at a wavelength of 2940 nm and 133 mJ output with the fiber tip positioned 3-6 mm from the veneer surface for debonding porcelain laminate veneers within a period of 113 ± 76 s.
| Techniques for safe removal of crowns and bridges|| |
Recent tools in combination with simple techniques can also be efficiently used for easy crown removal. In the Bucco-Lingual Dimple technique  dimples are created on the buccal and lingual surfaces in the gingival one third to act as a receptacle for Baade Pliers. The twisting motion of the hands and wrist helps to remove the crown by breaking the cement seal. For removing cast metal onlays and partial coverage restorations three dimples are created on the buccal and lingual surface of the restoration. The Baade Pliers can then engage and torque the casting in a variety of directions. This technique is contraindicated in periodontally compromised dentition. Similar techniques were suggested by Garver and Wisser  and Liebenberg,  where autopolymerizing resin was applied onto the ceramic veneer to serve as undercuts for application of the tip of the forceps. For removal of the loosened retainer of a fixed partial denture (FPD) Verrett and Mansueto  made use of a two piece matrix on the buccal and lingual surface of the bridge, connected to each other by means of a nut and bolt. Application of tapping force through the matrix created on the resin aids in the safe removal. Sutherland and Cheeseman  have advocated a technique in which a permanent crown remover forceps PermGripper (HolmesDental Co., Hatboro, PA, US) can be used along with a mechanical impact device (Peerless Crown-A-Matic, Henry Schein, Port Washington, New York) for efficient removal of crown. The tip of the Crown-A-Matic is placed adjacent to the tip of the forceps on the vestibular or lingual surface to deliver the impact force. A custom made FPD remover by Oruη  makes use of ligature wires passing through the embrasures of the bridge and connected to a cone, which is attached to a horizontal bar on which the impact can be delivered. Although, it requires significant time for fabrication, cost and chair side time are considerably reduced. Sharma et al.  have made use of a polyvinyl siloxane impression material in a quadrant disposable tray for crown removal. The application of tray adhesive on the crown allows the impression material to adhere to the crown. Removal of the impression enables the detachment of the crown from the tooth surface. The crown remains adhered to the impression tray. Whitehead et al.  have introduced a method for debonding porcelain laminate veneer by incorporating a fluorescent dye into the luting agent to differentiate it from the tooth, which aided in veneer removal without much damage to the remaining tooth structure.
| Retrieval of implant crowns|| |
Sectioning and removing a loosened implant crown with loosened abutment screw has limited usefulness as the metal of the restoration is much thicker and cutting it open may damage the abutment screw head making it nonretrievable. The use of a standard back action hammer may result in stresses being transmitted to the loosened abutment screw resulting in damage to the threads or fracture of the abutment.
When the abutment screw is loosened for a cement retained implant supported fixed partial denture, precise location of the screw head is the first requirement. Exact location of the access opening for the retrieval of a cemented implant supported crown using cone beam computed tomography was advocated by Wicks et al.  A technique described by Prestipino et al.  makes use of retrieval slots that are incorporated at the crown abutment interface on the lingual side at the time of waxing up. The aim is to hold the abutment down while pushing up on the prosthesis with a flat ended instrument hence that tension on the screw retaining the abutment can be reduced. In a technique described by Rajan and Gunaseelan  the screw access channel is maintained with the hexagonal screw driver during the wax up of the implant crown coping as well as during addition of the ceramic. The same technique can be used for the fabrication of metal free implant supported prosthesis. Doerr  employed a vacuum formed clear retaining screw location guide fabricated over the cast of a cemented restoration. This guide is then placed on the implant level or abutment level cast and access holes are drilled on the guide visualizing the location of the screws. This guide is then placed in the mouth crown is drilled to locate the abutment screw using the access holes as a guide. Another technique for locating the implant abutment screws involves putting a stain on the ceramic restoration occlusally to indicate the location of the abutment screw. Ichikawa et al.  had described two techniques for the retrieval of a cement retained prosthesis. In the first technique, a removal screw was incorporated on the lingual surface of the implant superstructure and cemented with temporary cement. Turning the screw clockwise will cause it to push against the abutment resulting in separation of the crown. In the second technique, a dimple was created on the abutment, which could be accessed through a vent in the superstructure. A modified explorer can be inserted through the vent and rotated in an upward direction to break the cement seal. Similar techniques were described by Okamoto and Minagi  and Valbao et al.  Gupta and Verma  made a putty index over the faulty implant restoration and the adjoining teeth to minimize vibrations during cutting. Sectioning of the index over the implant restoration makes way for the air rotor carbide bur. The index not only stabilizes the implant restoration during cutting, but also aids in tongue and cheek retraction.
| Conclusion|| |
From the many systems and techniques discussed in this review, it is difficult to suggest a universal system for coronal disassembly. Selection of an ideal crown removal system depends on a particular clinical situation. The advantages and disadvantages of various crown disassembly techniques [Table 1] should be kept in mind before a final decision is made. Any back action hammer will serve best if there is a sound underlying tooth structure with a favorable path of insertion provided the luting agent is of conventional type. If the abutment is grossly decayed or periodontally compromised, the use of back action hammer is contraindicated. The safest options in such situations are the use of ultrasonics, lasers or splitting the crown and prying with a spreader. Irrespective of the luting agent employed, splitting and spreading of the crown can be done for preventing the damage to the abutment during retrieval. Any device in the category that permits safe removal of the crown can be employed if reuse of the crown is desired. In case of apprehensive patients, the pneumatic crown removers that work by breaking the cement seal through vibrations rather than the typical jack hammer effect can be suggested. An active instrument can be an option in case of thin abutment vulnerable to fracture, crowns with unfavorable path of insertion and also in dowel core treated teeth. This system can also be used when adhesive cements are employed.
|Table 1: Comparison of advantages and disadvantages of various crown disassembly systems|
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The successful use of any coronal disassembly device thereby depends on the judicious selection of the instrument or technique. Ensuring an ideal preparation taper and parallel path of insertion, using luting agent in the correct consistency, application of the luting agent on the inner axial surface of the crown rather than on the entire intaglio surface and proper maintenance and sterilization of the instrument are the duties to be perfected by the clinician for an effective crown removal.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4]