Crown

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Crown

  1. 1. CONTENTS 1. STAINLESS STEEL 2. INTRODUCTION TO STAINLESS STEEL CROWN 3. INDICATION 4. FACTORS TO BE CONSIDERED IN PRE-OPERATIVE EVALUATION 5. TOOTH PREPERATION 6. CROWN ADAPTATION 7. COMPLICATIONS. STAINLESS STEEL CROWN When 12.30% of chromium is added to steel containing 1.2% carbon alloy called stanless steel. COMPONENTS Chromium Nickel Carbon Ferritic 11.5-26% 0% 0-20% Martensitic 16-26% 7-22% 0-25% Austenitic 11.5-12% 0-25% 0.5-1.25% PROPERTIES: 1. Resistts furnish and corrosive because of fascinating effect chromium. 2. A thin, transparent yet tough and in porous adherence layer of G2O3 forms on the surface of stainless steel when exposed to oxidizing atmosphere. 3. If oxide layer ruptures by mechanical or chemical agents a temporary loss of protection against carosin occurs. The stainless steel crown, developed for use in pediatric dentistry in the early 1950’s has helped ro solve the problem of the extensively carious tooth.Because of the alarming rate of failure of class II amalgam restorations in the primary molars, particularly the pediatric dentist has used the stainless steel crowns as a certain treatment in selected cases. The crown is prefabricated in a variety of sizes for each tooth. Tooth preparation precedes the fitting contouring if necessary and cementation all at one appointment. INTRODUCTION Stainless steel crown: It is a semi-permanent restoration used in the primary and young permanent teeth. It was introduced as chrome stel crown by Humhry in 1950, which proved to be a fovaour to the pediatric dental practice. Stainless steel crown is more frequently found in deciduous dentition than in permanent dentition. 1. In small deciduous teeth neglected caries can destroy tooth’s integrity faster than in the larger teeth of permanent teeth. 2. The deciduous teeth pulp is larger than permanent pulp in relation to it dentin and enamel envelop. Thus it is difficult to make the dentinal stump for a gold casting or to use a pin system of retention for more extensive amalgam restoration. ADVANTAGES;  The most advantageous system of restoration because of its retention and resistance.
  2. 2.  They are acceptable to both the patient and the dentist.  They are also more cost effective because of comparatively simple procedures involved in restorating even severely affected primry molars.  OBJECTIVES:  To achieve biologically compatible, masticatory compotent and clinically acceptable restoration.  To maintain the form and function and where possible, the vitality of tooth should be maintained COMPOSITION. Stainless steel crowns (18-8) /austantic type of alloy is used. 17-19% chromium 10-13% nickel 67% iron 4% ninor elements. NICKEL BASED BASE CROWNS 72% nickel 14% chromium 6-10% Fe 0.04% carbon 0.35% manganese 0.2% silicon INDICATIONS 1. Extensive decay in primary teet  A crown is indicated whenever one or more cusps are destroyed or weakened by caries. This commonly occurs in the 1st primary molr when the distal interproximal lesions is not treated early when decayed it involves whole of broad, flat contact area, the disto lingual and distobuccal cusps or both weakened. AZttempts at a Class II cavity preparation would result in proximal bone whose buccal and lingual walls flare amrked by towards the embrasure, this would encourage failure of the amalgam at these margins. When a primary tooth can be expected to enfoliate within a year of restorationHowever parent child and operator may all be frustrated by the failure of extensive amalgam restorations in primary teeth. The experience clinician can place stainless steel crown faster than a three surface amalgam alloy restoration and so disadvantage of additional time is overcome. 2. Following pulp therapy: In both primary and permanent teeth, pulp therapy leaves the treted teeth more brittle. That the tooth structure might subsequently fracture has led to the accepted wisdom of cuspal coverage after endodontics in permanent teeth. This should also apply to primary teeth. Post operative fgailure be prcvented by placing a stainless steel crown in first place. A tooth that is a candidate for pulp therapy will probably also be a candidate for a crown. 3. As a preventive restoration- If the patient has a high susceptibility to caries manifestating it either by numerous gross carious lesions or by rampant
  3. 3. caries and in a handicapped child whose luck of oral hygiene may encourage further dcay. Evidence of a developing Class V lesion is a sign of lapse in dietary and oral hygiene habits. When this occurs in the preschool child. Who also has a Class II lesion in the same tooth. The stainless steel crown should be considered . 4. For teeth developmental defects: Linear hypoplastic defects can undermine the occlusal surface of first primary molars if the etilogical systemic upset occurred at or around birth. Similarly amalfenesis and dentinogenesis impefecta can alter tooth morphology and predispose the dentition to excessive wear and loss of the vertical dimension. Hypoplastic and hypocalcified defects on the teeth may be more susceptible to caries if the anatomy encourages plaque retention although this does not always occur. In placements of stainless steel crown on hypoplastic teeth treatment may involve crowing of teeth in all four quadrants. Thus there is a danger of altering the vertical dimension by impinging on the free way space. So the crown should be fitted quadrant wise. FACTORS TO BE CONSIDERED IN PRE OPERATVE EVALUATION Dental age of the patient.  This is recrded by the root development of the underlying tooth. When the primary tooth can be expected to enfoliate within 2 years of restoration, amalgam restoration in the primary teeth can be frustrating.  Co-operation of the patient: If the patient is un co-operative whether it is due to age or due to megative behaviour of child is strubbarn and does not want to co-operative because of age a chair side GA amy have to be considered.  Motivation of parents: whether the patents are willing to come for dental dental visits for the follow up. TOOTH PREPERATION ANTERIOR: With the development of the acid etch retained composite strip crown, the indications for anterior steel crowns have fallen markedly. Although stainless steel crowns are very functional and long lasting . Their appearance provide a great carrier to their acceptance by both patients and parents.The aims of tooth reduction are to provide sufficient space for the steel crown, remove the caries and leave. The sufficient tooth substance for creation of the crown. Mesial and distal reductions are required to clear the interproximal contacts. The anterior steel crown can be closed, or open faced for better aesthetics. In this latter existence of the crown should be fitted up to the point of cementation before its labial surface is finally removed. POSTERIOR:The aims of tooth reduction are the same as the described for the anterior crowns and reduction is accomplished using a N0.699 tapered fissure, turbine bur throught. The steps in its placement are described n the following sub sections. CARIES REMOVAL This is best accomplished before the main preparation for the crown lesions. If the pulp thrapy is subsequently required , it will not be compromised by the gingival
  4. 4. bleeding that might result from the crown preparation,A temporary dressing is easier to place into a class I and II cavity than over a tooth prepared for a crown. OCCLUSAL REDUCTION This should approximately follow the anatomy of the tooth to a depth of 1.0 – 1.5 mm, which allows sufficient space for the metal crown. It maintains the original contour of the cusps. Reduction of occlusal surface can be judged by comparision with the marginal ridges of the adjacent teeth. PROXIMAL SLICES We have to place the wooden wedges in the interproximal embrasures. The wedges separate the adjacent teeth, thus minimizing the risk of damaging the tooth enamel. The bur is moved across the proximal surface ,beginning at the marginal ridges and at angle slightly convergent to occlusal surface. Preperation should be taken gingivally for enough to avoid the development of the ridge, which would make it difficult to seat the crown properly . because of cervical constriction of the primary tooth, adequate depth of the proximal preparation will result in a feather edge finish line. DISTAL REDUCTION UNDER RUBBER DAM. As preparation of a second primary molar is being carried out under rubber dam it may be that this tooth also being clamped. Therefore a problem arises when the distal proximal slice needs to be made without snagging the rubber dam in the bur.This can be dealt with by simply pushing the rubber away from distal tooth surfacewith a large flat-plastic instrument. BUCCO-LINGUAL REDUCTION Reduction of the buccal and lingual surface is either unnecessary or very minimal. Natural undercuts of these surfaces assists the retention of stainless steel crown. FINISHING Any remaining caries should be removed with a slow running round bur. The preparation is completed by leveling the eternal line angles around the occlusal part and where the proximal reduction meets the buccal and lingual surfaces. This will ensure proper seating of the stainless steel crown whose internal contour s is force from sharp angles. When caries has been removed and a Pulpotomy or Pulpectomy has not been completed, then pulp protection is required. Therefore, after final caries removal, a suitable protective base should be placed. The tooth is now ready for trial fitting of the crown. CROWN ADAPTATION SEATING THE CROWN Now the crown is tried on the preparation of acting the lingual first and applying pressure in a buccal direction so that the crown slides over the buccal surface into the gingival sulcus. Resistance should be felt as the crown slip over the buccal bulge. Each time the crown is placed on the tooth, gingival tissue should be carefully examined. They should meet compress and produce blanching of the marginal gingival tissue. CROWN CONTOURING Initial crown contouring is performed with a 114 plier in the middle 1/3rd of the crown to produce a belling effect. This will give the crown a more even curvature.
  5. 5. Contouring of proximal metal surface is not done with these pliers as they are already in contact with the adjacent teeth. FINISHING AND POLISHING Accumulation of the plaque and inflammation of gingiva is commonly seen in practice of restorative dentistry due to rough and unpolished restoration. To avoid these compications the crown should be polished prior to cementation with a cubber wheel to remove all scratches. PROCEDURE OF POLISHING While polishing the crown, margin should be blunt since knife edge finish produces sharp ends which act as areas of plaque retention. A broad stone wheel should run slowly in light brushing strokes, across the margins towards the centre of the crown. This will draw the metal close to the tooth without reducing the crown height and thus improves the adaptation of crown. CEMENTATION It should be cemented only on clean dry tooth. Isolation of tooth with cotton rolls is recommended.  Rinse the dry the crown inside and outside and prepare to cement it. ZnPO4 or GIC is preferred.  If Zn PO4 is used 2 coats of cavity varnish should be applied on vital tooth before cementation and cement should be of consistency so that it strings from mixing pad with the spatula.  Seat the crown completely on dried tooth surface preparation. Final placement should follow an established path of insertion of the crown. Cement should be expressed around all margins.  Before the cement sets, ask the patient to close into centric occlusion by applying pressure through a cotton roll and confirm that the occlusion has not been altered. COMPLICATIONS a) Inter proximal ridge: Incorrect angultion of the tapered fissure bur can produce a ridge instead of shoulder-free interproximal slice. further
  6. 6. Contouring of proximal metal surface is not done with these pliers as they are already in contact with the adjacent teeth. FINISHING AND POLISHING Accumulation of the plaque and inflammation of gingiva is commonly seen in practice of restorative dentistry due to rough and unpolished restoration. To avoid these compications the crown should be polished prior to cementation with a cubber wheel to remove all scratches. PROCEDURE OF POLISHING While polishing the crown, margin should be blunt since knife edge finish produces sharp ends which act as areas of plaque retention. A broad stone wheel should run slowly in light brushing strokes, across the margins towards the centre of the crown. This will draw the metal close to the tooth without reducing the crown height and thus improves the adaptation of crown. CEMENTATION It should be cemented only on clean dry tooth. Isolation of tooth with cotton rolls is recommended.  Rinse the dry the crown inside and outside and prepare to cement it. ZnPO4 or GIC is preferred.  If Zn PO4 is used 2 coats of cavity varnish should be applied on vital tooth before cementation and cement should be of consistency so that it strings from mixing pad with the spatula.  Seat the crown completely on dried tooth surface preparation. Final placement should follow an established path of insertion of the crown. Cement should be expressed around all margins.  Before the cement sets, ask the patient to close into centric occlusion by applying pressure through a cotton roll and confirm that the occlusion has not been altered. COMPLICATIONS a) Inter proximal ridge: Incorrect angultion of the tapered fissure bur can produce a ridge instead of shoulder-free interproximal slice. further

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