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【技术交流】——DISMANTLING CORONAL RESTORATIONS  

2014-03-22 16:35:30|  分类: 技术交流 |  标签: |举报 |字号 订阅

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DISMANTLING CORONAL RESTORATIONS

INTRODUCTION

Gaining access to root canals for non-surgical retreatment is relatively easy when a direct intracoronal restoration is in place. However,dismantling cast restorations, posts and cores can be challenging. The techniques described in this chapter will allow predictable disassembly for non-surgical root canal retreatment.

REMOVING CROWNS

It is not uncommon for a crown to be removed in order to complete root canal retreatment. It is therefore always wise to warn a patient that a new restoration may be required before embarking on dismantling the root-treated tooth. Patients are more likely to accept the potential additional cost of a new restoration if they have been advised that the existing one may be damaged or destroyed in the process of root canal retreatment. The quality of coronal seal should be assessed preoperatively. Where a crown is obviously leaking or has been undermined by recurrent caries, it should be removed. Removing the coronal restoration will obviously give much better information about the state of the remaining tooth substance. There is little justification in attempting to retain an existing restoration if it is going to jeopardize successful root canal retreatment. Removing the coronal restoration may also be important in deciding whether a tooth is actually restorable. After all, unless the foundation work can be completed successfully, extraction may be the only course of action. Removing a restoration, therefore, allows thorough investigation, assessment of restorability, removal
of caries and location of orifices which may not be possible when working through an access cavity. Difficulty in locating canals can be especially relevant if the crown does not conform to the original anatomy of the tooth, thereby giving a false indication of where the canal orifices may lie (Figure 3.1).1 From a technical viewpoint, it can sometimes be difficult to achieve good positioning of the rubber dam clamp when a crown has been removed. In this case it may be recemented as 【技术交流】——DISMANTLING CORONAL RESTORATIONS - 牙医张文鑫 - 上海牙医张文鑫
  a temporary measure with glass ionomer following caries removal2 or a temporary restoration may be constructed. Alternatively, a split dam technique may be required. If there is insufficient tooth substance remaining onto
which a rubber dam clamp can be placed, then one must question whether the tooth is actually restorable. If the crown is of good quality and has only recently been fitted, root canal retreatment can normally be carried out through a conservative access cavity which will be sealed using adhesive restorative materials following treatment.







【技术交流】——DISMANTLING CORONAL RESTORATIONS - 牙医张文鑫 - 上海牙医张文鑫
 
【技术交流】——DISMANTLING CORONAL RESTORATIONS - 牙医张文鑫 - 上海牙医张文鑫
 

 METHODS FOR REMOVING CROWNS

Careful placement of a chisel, flat plastic or Coupland’s chisel into a marginal deficiency can be sufficient to cause the cement lute tofail. Force should be applied along the path of insertion to avoid fracture of the underlying tooth substance and core material. The chisel should be held in the palm of the hand with the forefinger near the tip so that if the instrument slips there is no risk of injury to the patient. The margin of the crown can be undermined using a small diamond bur or an ultrasonic tip, creating a gap into which the chisel is placed (Figures 3.2–3.5). An access cavity can be cut in the occlusal surface and the instrument inserted between underlying core material and the crown. By
cutting an access cavity, retention of the crown is significantly reduced and should therefore make crown removal easier. There are numerous burs available for preparing an occlusal cavity through crowns. Usually, a diamond bur is preferred for cutting porcelain and a tungsten carbide bur used to cut through the metal part of any restoration.
 
 【技术交流】——DISMANTLING CORONAL RESTORATIONS - 牙医张文鑫 - 上海牙医张文鑫
 
 Forceps

Special forceps for crown removal are available with rubber cups on the beaks. These are coated in carborundum powder to prevent slipping. Some practitioners prefer to use extraction forceps, but great care must be exercised to
ensure that the instrument does not slip or that excessive force is placed on the tooth, thereby damaging it. Generally, forceps are applied to the crown that needs to be removed and a gentle wiggling action used to loosen the restoration.
One must be careful not to damage adjacent or opposing teeth (Figures 3.6, 3.7).

【技术交流】——DISMANTLING CORONAL RESTORATIONS - 牙医张文鑫 - 上海牙医张文鑫

The Richwell Crown and Bridge Remover

This is essentially a tablet of water-soluble pliable resin which is softened in hot water and placed on the restoration that needs to be removed. The patient is asked to bite down and compress the resin block to about two-thirds of its original thickness. It is then allowed to cool. When the resin is set, the patient is asked to open quickly, which, in theory, will generate sufficient force to loosen and lift the restoration. This technique tends not to be particularly effective. There is also a risk of removing the restoration from an opposing tooth!
 
Ultrasonics

Ultrasonics is sometimes useful to loosen the cement from around the margins of a poorly fitting crown. This could be a simple ultrasonic scaler tip vibrated at high power with a water spray or a specialist tip such as the CT4 (SybronEndo, Orange, CA, USA). If a porcelain crown needs to be removed with little damage, then ultrasonics should not be used
as there is the potential risk of porcelain fracture. Undermining the crown or opening up a marginal deficiency will allow the placement of a crown remover, chisel or flat plastic (Figure 3.8)

【技术交流】——DISMANTLING CORONAL RESTORATIONS - 牙医张文鑫 - 上海牙医张文鑫
 
 

Chisel and Mallet

A straight chisel and mallet can be used to tap off the crown. However, there are obvious risks involved in this method and it is perhaps not that pleasant for the patient!

Crown Removers

This instrument consists of a hook that is
inserted under the margin of a restoration. The hook is in turn connected to a rod with either a weight or a spring-loaded device which can apply a sudden force to break the
cement lute. Well-fitting restorations obviously present a problem, as it is difficult to find a margin under which the instrument can be inserted. The KaVo Coronaflex (KaVo Dental Ltd, Amersham, Buckinghamshire, UK) works by delivering a pneumatic force. Special forceps or bands are provided which can be linked to either crowns or bridges. On depressing the trigger, a force is generated along the long access of the tooth, enabling removal of the restoration. This is an excellent device for removing restorations with little risk of damage (Figures 3.9–3.13). 

【技术交流】——DISMANTLING CORONAL RESTORATIONS - 牙医张文鑫 - 上海牙医张文鑫
 
【技术交流】——DISMANTLING CORONAL RESTORATIONS - 牙医张文鑫 - 上海牙医张文鑫
 


 
 

The WamKey

The WamKey (Dentsply, Weybridge, Surrey,UK) looks rather like a small key and can be effective for crown and bridge removal. A small access is cut in the buccal or lingual surface of the crown such that space is made between the underside of the restoration and any core material. The key is then inserted and, when rotated, separates the crown from the underlying core material (Figures 3.14–3.17).

【技术交流】——DISMANTLING CORONAL RESTORATIONS - 牙医张文鑫 - 上海牙医张文鑫
 
 

Sectioning

If a crown is to be replaced, it can simply be removed by sectioning with a bur and the separate pieces elevated. Metal restorations can easily be cut using a tungsten carbide fissure bur such as a Jet Beaver bur (Beavers Dental, Morrisburg, Ontario, Canada).
The crown is partially sectioned by cutting a groove from the gingival to the occlusal surface and then a crown remover, flat plastic or Coupland’s chisel can be used to open up the groove and flex the restoration, breaking the cement lute. One should make sure that the restoration has been completely severed at the gingival margin. Some crowns, if particularly well cemented, will need to be ‘peeled’ off the tooth. Cutting a slot and prizing the crown loose is probably the least traumatic method of removing a cast restoration. Even though the crown may be destroyed, damage to the tooth is avoided (Figures 3.18, 3.19).

【技术交流】——DISMANTLING CORONAL RESTORATIONS - 牙医张文鑫 - 上海牙医张文鑫
 
 
Bridges

The abutment teeth of bridges can normally be treated as individual crowns and access is often made in the occlusal surface in the normal manner. A split dam technique can be useful to gain isolation and caulking will be required
to block out the area under pontics.2 If the bridge is to be sectioned and removed, it is important that the remaining portion, if cantilevered, does not allow excessive force to be placed on the abutment so risking fracture. In the anterior region of the mouth where aesthetics are important, it may be easier and beneficial to construct a temporary bridge using an acrylic material. When glazed and polished a very good cosmetic result can be achieved. Alternatively, a temporary denture may be provided (Figure 3.20).
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