Debonding of Fixed Restorations PDF

DTC200 2. Class Theoretical Committee CS2 Fixed Prosthodontics Subcommittee Debonding of Fixed Restorations Muhammad. Saleh, DDS, PhD Near East University faculty Dentistry- Department of Prosthodontic dentistry The Learning Goals Student will have the ability to mention indications for debondin...

DTC200 2. Class Theoretical Committee CS2 Fixed Prosthodontics Subcommittee Debonding of Fixed Restorations Muhammad. Saleh, DDS, PhD Near East University faculty Dentistry- Department of Prosthodontic dentistry The Learning Goals Student will have the ability to mention indications for debonding prosthesis. Student will be able to classify available techniques for prosthesis debonding . Student will be able to mention the advantages and disadvantages of every retrievability technique Fixed dental constructions possess a predefined period of use. Most often they are removed by means of sectioning after which they are unusable. we can distinguish two groups of clinical situations: 1. Cases, when due to a mistake, removal must be implemented immediately after cementing. 2. Cases, when the cement has reached its maximal hardness qualities and strength potential. In the second group of clinical situations, we can observe two main approaches: 2.1. Without preserving the construction. 2.2. With preserving the construction. As it was previously discussed, fixed prosthetic restorations have a determined life duration. According to literature data, the average life duration of crowns is 7-8 years. Reasons for that may be for instance the necessity to treat root canals, secondary caries under construction to repair fractured porcelain, correction of mistakes made in shade selection, form and outline of the porcelain or acrylic veneering, etc. Other factors demanding intact removal of a fixed restoration are patient’s age and health status, time spent on the case, esthetics, financial costs, social and psychological problems The removal of a prosthetic construction, are divided into four main groups. ✓ Biological - inflammatory processes in the pulp of the prepared teeth, abutment fracture, traumatic occlusion, pressure on soft tissues, poor oral hygiene, the necessity of retreatment, allergies to metal alloys, etc. ✓ Mechanical - inadequate restoration due to an absence of appropriate metal substructure, marginal distortion,etc. ✓ Aesthetical - improper shade selection of the veneeringmaterial and the cement, over contouring or protrudingcrowns or bridge, etc. ✓ Cementing agent - improper mixing technique, inadequateisolation, incomplete removal of the temporary cement,etc. The three main groups of techniques are as follows: destructive, conservative and semi-conservative techniques. 1. Destructive techniques - the dental restoration is completely destroyed since it is cut and removed. 2. Conservative techniques - the dental restoration is preserved and may be reused. Usually, this method demands grip and a hit. 3. Semi-conservative techniques - these methods allow the dentist to re-cement the construction after adjustments. 1. More conservative techniques: we aim at breaking down the luting cement layer - this approach is the least dangerous for the restoration. It can be re-cemented again. 1.1. Ultrasonic The technique for removing prosthetic restorations using special scalar tips. The approach might be applied alone or in conjunction with other techniques. It successfully destroys luting cement layers without damaging the restoration. Melo Filho et al. stated that implementing ultrasound vibration at the gingival margin for 15 seconds causes a reduction in bond strength resulting in a breakdown of the cement layer. Disadvantages: time consuming approach, ceramic veneering may get fractured, heat generated can cause damage to the pulp (profound water spray is obligatory), proved the negative effect of ultrasound vibration on retention of restorations. Ultrasound techniques are contraindicated in patients with Hepatitis B and herpes simplex, as well as in patients with cardiac pacemakers. Manufacturers warn that this approach is not successful with restorations cemented with zinc polycarboxylate and glass-ionomer cement. 1.2. Decementing with Richwill resin Richwill is a water-soluble thermoplastic resin which,when compressed, generates strong temporary adhesive properties. According to Oliva, Richwill is suitable to remove temporarily and permanently fixed restorations. The resin is softened in hot water for 2-3 minutes and then placed on the occlusal /incisal surface of the construction. The patient is then instructed to occlude and compress the resin block to 2/3 of its original size. The resin block is cooled with water. After around 10 seconds, the patient is instructed to suddenly open mouth rapidly and forcefully - the restoration gets fixed on the opposing teeth along with the resin. This technique is described as the most effective approach towards dislodgement cast restorations. Oliva reports 100% success rate of this method towards removing temporarily cemented restorations and 60% successful for permanently cemented cast restorations combined with the ultrasound technique. The success rate is bound as well to patient’s cooperativeness. Disadvantages: In some cases, the procedure needs repetition. The technique is contraindicated if the opposing tooth or the restoration are lacking stability. To prevent accidental aspiration of the resin block, the manufacturer recommends tying dental floss to it. 1.3. Lasers Lasers such as Er, Cr: YSGG 2780 nm may be used for the safe removal of all ceramic restorations. The procedure is fast, and there is no iatrogenic danger for the underlying structures. The wavelength of the laser is absorbed not by the porcelain structure - it passes through it, but by the water in the luting cement. Using Er, Cr: YSGG, 20 Hz for 1- 2 minute for each side will contribute towards removing of the ceramic restoration. Application of lasers saves time and expenses, thermally softens the resin without any negative effect on the enamel. Disadvantages: Limited application - mainly used for debonding all-ceramic restorations. Hazardous for hard and soft tissues if the tip is not positioned appropriately. 2. Removal with back-action instruments 2.1. Back-action instruments with a weight. Those instruments engage the margins of the restoration with a tip, attached to a shaft, which has a sliding weight. Force is applied by manually activating the weight. Disadvantages: A traumatic system for the patient. May cause discomfort and luxation of the periodontal ligament. It is mainly indicated for removing temporarily cemented restorations. Activation of the weight may cause the rod to shift away from the long axis of the tooth. 2.2. Spring loaded back-action remover. They are spring loaded, manually compressed and released to deliver the impact force. Disadvantages: The rod may easily shift away from the long axis of the tooth. 2.3. Spring loaded Semi-automatic remover. Operated easily with one hand, the other hand may be used to secure the tip of the remover at the crown margin. They have better directional control over the force delivered. Spring is compressed by sliding the outer cylinder over the inner one. Pressing the button provides back-action to remove the restoration. Devices of this type should be reactivated each time they are used. Disadvantages: The tip may easily shift away from the margin and the long axis of the tooth/crown. More hazardous for the underlying substructures. 3. Semi-conservative techniques with partial destruction of the restoration. These approaches include making a small access hole through the prosthesis. They are more convenient for patients, time-savers, force is inflicted less traumatically, restorations may be reused as provisional ones. The hole can be obturated using composite materials. Different instruments are developed for access through the hole made. The tooth is used as an anchor point, while the traction force is applied on the prosthesis. That breaks down the luting agent. 4. Destructive techniques with full destruction of the restoration Applying this method, most common for all practitioners, restorations are usually sectioned with a diamond and/or tungsten-carbide bur. The technique can be combined with an ultrasound instrument to disrupt the luting cement layer. Present-day adhesively bonded all-ceramic restorations may be extremely difficult to remove. A cut through the lingual surface might be necessary as well which renders the restoration totally unusable. Additionally, inserting a crown spreader/lever or the special Mitchell’s trimmers in the groove made on the surface of the restoration, using rotational moves split is spread evenly, and The rod may easily shift away from the long axis of the tooth cement layer breaks down. Other instruments are Christen-son Crown Remover trimmers. The crown spreads evenly, reducing the tension on the tooth/core when using levers and trimmers.