Illustrated Pediatric Dentistry - Part 3

Crown in Pediatric Dentistry

Anil Patil¹, *, Prathamesh P. Nikam¹, Dhanashree Sakhare²

¹ Department of Pedodontics and Preventive Dentistry, Bharati Vidyapeeth (deemed to be) University Dental College & Hospital, Maharashtra 400614, India

² Founder, Lavanika Dental Academy, Melbourne, Australia

Abstract

The basis for safe permanent teeth in infants and teens is laid during the first years of childhood. Several studies have linked dental caries in children to insufficient diet, unhealthy eating habits, and insufficient toothbrushing habits during the first two years of childhood. The emergence of caries in primary teeth increases the chance of developing caries in permanent teeth. Once a tooth has decayed in young children, the paediatric dentist plays a crucial role to return the tooth to its full functioning potential. The technical advancements in dental products utilized in children over the last few decades are a necessary prerequisite because what was acceptable in the past is not necessarily the safest way to treat young patients nowadays. Several alternatives exist to restore carious teeth in paediatric patients, ranging from stainless steel crowns to aesthetic crowns such as strip crowns and zirconium crowns, which are gaining popularity. This chapter contains a description of the crowns in paediatric dentistry.

Keywords: Stainless steel crowns, Open-faced stainless-steel crown, Polycarbonate, Strip crowns, Pedo jacket, new millennium, Cheng crowns, Kinder crowns, Nu-smile, Dura- crown, Pedo pearls, Zirconia crowns.

* Corresponding author Anil Patil: Department of Pediatric and Preventive Dentistry, Bharati Vidyapeeth (deemed to be) University Dental College & Hospital, Maharashtra 400614, India; E-mail: dranilp0888@gmail.com

INTRODUCTION

Oral wellbeing is a mirror of a person's lifestyle. Dental caries is now one of the most common multifactorial diseases on the planet. In infants, carious lesions begin with the destruction of tooth surface, which may influence aesthetics, self-esteem, mastication, speech, arch length maintenance, and the creation of oral habits, causing disorientation of overall health. So, it is essential to restore the deciduous carious teeth depending on their location, forces delivered to the tooth with various forms of crowns to maintain dental integrity before permanent teeth emerge.

The crowns are available into 2 categories [1]

1] Preformed crown and luting cement used for cementation

e.g. Stainless steel with facing, Cheng crowns, Kinder crowns, Nu-smile, Dura- crowns, Whiter bite, Pedo pearls

2] Crown which is bonded to the tooth

e.g. Polycarbonate, Strip crowns, Pedo jacket, new millennium

Stainless steel crown - The Preformed Metal Crown (PMC) most commonly known as the Stainless-steel crown (SSC). It is introduced by Humphrey in 1950 [2]. Stainless steel crown is most commonly used in deciduous dentition than permanent dentition (Tables 1 and 2).

Classification of Stainless-Steel Crown

Based on Composition

1] Stainless Steel crown (18-8) austenitic type: - 17-19% Chromium, 10-13% Nickel, 67% Iron, 4% Minor elements e.g.- Unitek and Rocky Mountain crowns

2] Nickel-Base crowns: -72% Nickel, 14% Chromium, 6-10% Iron, 0.004% Carbon, 0.35% Manganese, 0.2 Silicon e.g.- Ion Ni-chro from 3M

3] Tin Based crown

4] Aluminium Based crown

Based on Morphology

1] Uncontoured/ untrimmed crowns – This neither trimmed nor contoured and required lots of adaptation (Fig. 1a). They are longer in size, and it is time consuming. e.g. Unitek and Rocky Mountain crowns.

2] Pretrimmed crowns – It is straight and having non-contoured sides (Fig. 1b). This crown requires lots of contouring and trimming. It is festooned to follow gingival crest. e.g. 3M and Denovo crowns.

3] Precontoured crowns - This crown is festooned and having pre-contoured and pre-trimmed (Fig. 1c). Manufactures gingival crimp loss due trimming may cause difficulty in adaptation. e.g. Ni-chrome crowns and Unitek stainless steel crowns.

Table 1 Indications and contraindications of crowns (Fig. 2).

Table 2 Advantages and Disadvantages of crowns.

Fig. (1))

Types of crowns.

a - Untrimmed crowns b - Pretrimmed crowns c - Precontoured crowns.

Fig. (2))

Indications of crown.

Armamentarium

1] Burs and Stones - Burs no 169L or 69L friction grip shank (F.G.) (Fig. 3a) Tapered diamond F.G. (Fig. 3b), Green stones or heatless stone (Fig. 3c), Rubber wheel.

2] Pliers/Instruments - Ball and socket plier {#112} or Johnson’s Contouring pliers {#114 / #134} (Fig. 3d), Crown crimping plier {#800-417} (Fig. 3e), Howe plier {#110} (Fig. 3f), No 137 Gordon plier, Crown removal plier, Crown cutting scissor (Fig. 3g).

Preoperative Evaluation of Patients for Stainless Steel Crown Restorations [6]

Dental Age of the Patient:

This is recorded by the root development of the underlying tooth. When a primary tooth can be expected to exfoliate within 2 years of restoration, amalgam restoration can be done.

Co-operation of the Patient:

If the patient is uncooperative, due to younger age or due to negative behaviour, or if the child is stubborn and does not cooperate, first a positive behaviour has to be instilled. If the child is unable to co-operate because of age (i.e., <3yrs) then a general anaesthesia may have to be considered. In such cases, it is difficult to check the correct occlusion, so it is always better to keep the stainless-steel crown at the level or slightly below the level of the adjacent tooth, so that the child should not have disturbed occlusion due to premature contact.

Motivation of the Parents:

Parents should be educated regarding the various treatment modalities for their children’s carious teeth. They should be motivated for the treatment for their kids at the proper time.

Medically Compromised/Disabled Children:

For children with cardiac problems, prophylactic antibiotics should be administered before tooth reduction. Care should also be taken in treating children with leukaemia and bleeding disorders.

Fig. (3))

Armamentarium for stainless steel crown.

A - Burs no 169L, B - Tapered Diamond F.G, C - Green Stone, D - Johnson’s Contouring Plier, E - Crown Crimping Plier, F - Howe Plier, G – Crown Cutting Scissor

Clinical Procedure

A] Preoperative evaluation – First take putty or alginate impression of the upper and lower arch of patient to make a diagnostic cast. With the help of diagnostic cast evaluate space between upper central incisor, cusp relationship between two arches, canine relation, extrusion of opposing tooth and mesial drifting of adjacent teeth

B] LA Administration- It reduces the discomfort of patient during subgingival preparation

C] Isolation- Isolation has to be done with help of rubber dam and cotton rolls. Before isolation, check the child’s bite pattern. Rubber dam increases work quality as well as improve visibility and efficiency. Rubber dams protect the damage of surrounding tissues.

D] Caries removal- It is removed by large round bur in a slow speed handpiece. After caries removal and pulp therapy, it is filled or built up with GIC cement or Zinc oxyphosphate cement.

E] Crown selection- Crown selection involved following considerations.

Mesiodistal diameter (Fig. 4)

Light resistance to seating

Proper occlusal height

Before tooth preparation crown size may be selected by using Boley gauge. After tooth preparation crown size selected by trial-and-error procedure. The smallest crown should refer to fit on tooth preparation. While placing the crown friction to be felt when crown slips gingivally.

Fig. (4))

Measurement of mesiodistal diameter of crown with help of Boley gauge.

F] Tooth preparation-

Purpose of tooth preparation - To gain enough space for crown, to remove complete decay and caries tooth surface, to have sufficient tooth for retention of crown.

Occlusal Reduction

Humphrey in 1950 suggested that the occlusal cusps and all surfaces of tooth should be reduced. In 1966, Rapp advised that when occlusally reduction of tooth was done then gingival margin should be 4mm away from occlusal reduction. In 1968, Mink and Bennett suggested that 1mm of groove has to be made on occlusal surface that will help in a uniform occlusal reduction of 1 to 1.5mm (Fig. 5a,b,c). After that in 1976, Kennedy recommended that to preserve the tooth structure; bur should follow the anatomy of tooth [6].

Evaluation of Occlusal Reduction

The main aim of evaluation of occlusion is to preserve occlusal anatomy. Main motive of occlusal anatomy preservation is to maintain crown retention and decrease pulp exposure. It is done by visual examination. In 1981, Forrester advised to use wax sheet for evaluation of occlusal reduction.

Proximal Reduction

In second step, tooth preparation starts with interproximal reduction. It is marginal ridge and bur no-69L or 169L should move buccolingually. Proximal reduction should be10 degree converging towards occlusal surface. Proximal preparation should not be over taper. Finishing line of proximal reduction should be feather edge. During preparation, proximal contact with the adjacent teeth should be broken gingivally and buccolingually (Fig. 5c). Proximal slices converge slightly towards the occlusal and lingual surface, given by Meyers in 1976. The primary principle of the technique for fitting crown is to make the tooth preparation fit the crown form rather than attempt to make the crown fit the tooth preparation. Distal tooth surface reduction is necessary even when there is no growing tooth distally. Failure to follow this recommendation will result in on oversized crown being fitted, which may impede the eruption of first permanent molar [6].

Evaluation of Proximal Reduction

It is done by passing explorer through proximal area and check broken adjacent tooth contact.

Buccal And Lingual Reduction

During buccal and lingual surface reduction, it should be 0.5mm. It is deep enough to be (0.5 – 1mm) into gingival sulcus. Finishing line should be featheredge. Buccal bulge may require reducing in deciduous mandibular 1st molar. All sharp edges should be rounded [8].

Evaluation of Tooth Preparation

The occlusal clearance must be 1.5 to 2mm. Occlusal relationship is established by comparing adjacent marginal ridge heights. All line angles of tooth preparation should be rounded. Excessive gingival blanching should not be seen. Crown should be fitted sub gingival sulcus.

Adaptation of Crown

The adaption of crown is firstly tried on lingual surface of crowns then applying pressure in a buccal direction, so that crown easily fitted on buccal surface into the gingival sulcus (Fig. 5d,e). Resistance should be felt as the crown pass over the buccal bulge. Mark dotted line on crown surface to cut 1mm below line with scissors. After that, place the crown again, if gingival blanching is seen then remove the crown and retrim the crown surface [4].

The crown adaptation based on Spedding’s adaptation principle, and it is given in 1984 [3].

Spedding’s adaptation principle-1

The crown must be of correct length and its margins should closely resemble to the tooth. Any point on the tooth occlusal surface to the greatest diameter should be visible clinically and any point on the tooth apical to greatest diameter should be on undercut surface of tooth and should not be visible.

Spedding’s adaptation principle-2

The correct contours of buccal and lingual gingival margins of crown should have good adaptation to gingival tissue.

Crown Trimming

If the crown is longer than tooth, the crown margin may interfere complete seating, so in this case crown length may be adjusted by trimming and smoothing with an abrasive stone (Fig. 6a). Less trimming requires maintaining the retention of the crown [4].

Crown Contouring

The crown is contoured using a ball and socket plier (No-114) at middle third of crown for proper fit of crown (Fig. 6b). Contouring can be done with No 112 ball and socket plier, No 137 Gordan plier and No 114 Johnson plier. Buccal gingival contour of second primary molar look like smile. Buccal gingival contour of first primary molar resembles like stretched out S shape. Lingual contour of all primary molar form smile like shape. Proximal contour of all primary molar forms frown shape [4].

Crimping of Crown

The crimping of the crown is done using Johnson’s contouring plier (No 113) to adapt cervical margins of crown inwards and adapted into undercut area (Fig. 6c,d). If permanent molar is not erupted properly, little bit care must be taken for adaptation of distal margin of deciduous 2nd molar [4].

Evaluation of Crimping of Crown

It is evaluated using explorer. If margins of crown are open, then recrimping should be done. In 1987, Johnson suggested to check proper crimping of crown by blanching of gingival tissue. Bitewing radiograph technique also useful in evaluation of crimping of crown and it is given by More and Pink in 1973 [4].

Final Trial of Crown Adaptation

Crown should not be able to remove it with finger pressure. If crown is not properly seating and is without gingival blanching, then ledges can be found. If resistance to seating is there with blanching, then crown is wide or there may be tissue interfere.

Crown Finishing and Polishing

After polishing, crown margins should be blunt. If unpolished margin remains on crown it may lead to accumulation of plaque and can cause gingivitis. Rubber wheel helps to smoothen the rough margins of crowns. A large green stone is used to create a knife edge finish around the crown's cervical margin (Fig. 6e). Bur is rotated counter clockwise at a 45-degree angle. Iron rouge should be used to coat the crown. The final step before cementation is to create a bevelled gingival margin that can be polished.

Cementation of Crown

For cementation of crown GIC is much better than other cement. GIC cements have strengths as compared to zinc phosphate. GIC cement release fluoride as do the silico-phosphate, chelate or bond to tooth structure as the polycarboxylate and are as pulpally compatible as the polycarboxylates. The crown should be one half to two third filled with the cement (Fig. 7). Dry the tooth and seat the crown completely. Initially bite slowly with increasing pressure. Patient bite will help to seat the crown without distorting it. Cement should flow out from all ends of the crown. Remaining cement can be removed by spoon excavator or explorer. Recheck for excess cement [6].

Fig. (5))

Tooth preparation of stainless-steel crown.

A – Intra-oral image Showing occlusal reduction of 1 to 1.5mm, B – Occlusal view of tooth preparation, C – Intra-oral image Showing proximal contact break without touching to adjacent tooth, D, E – Intra-oral image Showing crown placement in oral cavity.

Fig. (6))

Adaptation of crown.

A - Crown trimming with scissor, B - Crown contouring with Johnson’s Contouring plier, C - Crown crimping with crimping plier, D - Crown crimping with howe plier, E - Crown finishing with green stone.

Fig. (7))

Cementation of crown.

A – Crown cementation done using luting cement, B – Remove excess cement with explore or dental floss.

Clinical Evaluation of Crown Cementation

1. The crown & its margins are smooth & polished properly

2. Properly adapted to the prepared tooth surfaces

3. The proximal contacts are established properly.

4. Crown should be in proper occlusion

5. Crown margins extended 0.5 -1mm into gingival crevice

6. Excess of cement is removed completely

Post-Operative Instructions

Patient should at least avoid sticky foods like caramel, gum, toffees, hard candies, chewing on ice, popcorn kernels and any other hard substances for next 1 hr.

Modifications of Stainless-Steel Crown (Mink and Hill, 1971)

Undersized Tooth or the Oversized Crown:

This mostly occurs in long untreated interproximal caries and space loss due to exfoliation or extraction. The crown circumference is decreased by a V cut made from the gingival surface to the occlusal surface of crown. To make crown circumference smaller the cutting edges are overlapped over one another (Fig. 8a,b,c). The crown is tried on the tooth preparation and amount of overlapping necessary is marked on the crown surfaces. Overlapping edges of crown close with spot welding machine. Rubber wheel used for polished the surface [5].

Oversized Tooth or the Undersized Crown:

In this V shape cut is made and make 2 separate edges on crown surface. To close that, a piece of 0.004 inches band material place over the cut surface. Then contouring is done and to reduce microscopic deficiency in seal by applying solder on it (Fig. 8d,e,f). After that, polish the soldered crown [5].

Deep Sub Gingival Caries:

Complete the indicated pulp treatment and then restore the cavity preparation. If subgingival caries occurs between proximal surfaces of tooth, the crown will extend to cover the caries (Fig. 8g) [5].

Fig. (8))

Modifications of stainless-steel crown.

A, B, C - Modification of stainless-steel crown for undersized tooth or oversized crown

D, E, F - Modification of stainless-steel crown for oversized tooth or undersized crown

G - Modification of stainless-steel crown using adding matrix band to caries side of crown to cover subgingival caries

Complications of Stainless-Steel Crown

The stainless-steel crown is not a cure-all or a miracle wand for treating extensive caries or preventing amalgam loss. When treated wrongly, these crowns can inflict just as much harm as a badly finished amalgam alloy. Some of the most common complications are mentioned below, along with necessary therapies [6].

Interproximal ledge: Because of the risk of iatrogenic pulpal exposure, further tooth reduction to remove this ledge should be attempted with caution. If the ledge is not removed, the crown will be unable to seat, and its borders will tie on the ledge. The interproximal slice is difficult to prepare when the neighbouring tooth is partly erupted, and the contact region is poorly defined. To clear the contact region, extensive subgingival tooth reduction is required; difficulty of access increases the risk of forming a ledge or destroying the erupting tooth, which would be unfortunate if it is the first permanent molar. In such cases, it could be prudent to postpone crowning until the contact areas are properly defined.

Poor margins: When a stainless-steel crown is imperfectly adapted, the crown's marginal dignity suffers. Open caries is a rarity around restorations and restorations are seldom precede the formation of caries However, as the anomaly grows, the odds of plaque retention, so does the likelihood of gum disease. On the other hand, it is believed that chronic inflammation and exposure of the supporting tissues may lead to premature tooth enamel loss, although this theory awaits confirmation in the future.

Crown tilt: If a full lingual or buccal wall is destroyed by caries or overzealous use of cutting tools, the finished crown can tilt to the deficient hand. This tilting is usually observed on the lingual side of mandibular primary molars due to a lack of tooth support. Prior to crowning, an amalgam alloy or glass-ionomer cement reconstruction is positioned to provide stability and avoid crown tilt (the restoration acting as a core). Crown tilting has no therapeutic importance until it occurs on young permanent molars, where it may result in unfavourable supra-eruption of the opposing tooth.

Nickel hypersensitivity: According to research, orthodontic treatment of nickel-containing stainless-steel instruments performed prior to ear piercing seems to decrease the occurrence of nickel hypersensitivity. When compared to skin, higher concentrations of contact allergen may be needed to induce a response from the oral mucosa, but the form, duration, and oral exposure required to trigger this potential remain uncertain (Table 2).

The crown is inhaled or consumed: Fortunately, these mishaps are uncommon, particularly where a rubber dam is used, which we recommend for all children's dentistry. If the rubber dam is not in place, abrupt, unexpected movement can result in inhalation or ingestion of the crown. If this occurs, an attempt at removal should be done as soon as necessary by turning the infant upside down; if this is insufficient, a prescription for an urgent chest X-ray is needed. If the crown is in the bronchi or lung, medical advice and referral will certainly result in a bronchoscope removal attempt. The presence of a cough reflex in a conscious infant decreases the chances of inhalation, though crown ingestion is more possible. Ingestion is less severe, but it must also be diagnosed on a chest radiograph from the absence of the crown. Within 5-10 days, the stainless-steel crown can pass through the alimentary tract without incident. The parent should take on the unenviable job of tracking down the ejected crown. Taking all practicable measures to avoid crown ingestion or inhalation reduces anguish and tension for the infant, adult, and clinician. As a result, with the rubber dam in place, crown preparing, trimming, and trail fitting can all be done. The interproximal rubber can be sliced, and the ligature withdrawn while a crown is being fitted next to the clamped tooth, revealing the gingival margins. With crown expertise, the operator will cement on the crown with the rubber dam in place, then lift the rubber dam and inspect the occlusion as the cement settles.

Failures in Stainless Steel Crowns can be Caused by a Variety of Factors

1. Inadequate tooth

2. Insufficient crown adaptation and as a result poor retention.

3. Inadequate cementation, resulting in a missing crown or open margins.

4. The pulp treatment failed.

5. Induced ectopic eruption of the permanent first molar.

6. Caries that recurs, especially in the interproximal areas.

7. Abrasion of the crown through the occlusal base.

Considerations for Successful use of Stainless-Steel Crowns

1. Caries removal and, if necessary, effective pulpal therapy

2. Optimal tooth structure reduction for proper crown retention.

3. Lack of damage to adjacent teeth after opening interproximal contacts.

4. Choose a crown that is the right height to keep the arch length.

5. Gingival wellbeing and accurate marginal adaptation

6. Good occlusion for practical purposes.

7. Cementation process that is optimal.

Hall Technique for Stainless Steel Crown

The Hall technique is a way of treating carious primary molars in which decay is sealed under a stainless-steel crown without the use of local anaesthesia, tooth cleaning, or caries removal. The Hall technique is one of the approaches used for biological sealing in primary molar carious lesions. As a result, the bacteria will be isolated from the oral system, and the caries will be rendered inactive. As opposed to traditional treatment modalities used in primary care environments, the Hall technique is regarded as a viable restorative alternative with high acceptability and longevity, as well as a low failure rate for treating carious primary molars. Furthermore, whether given using the Hall technique or conventional training by a paediatric dentist, the survival rate of stainless-steel crowns (SSCs) is considered high. As a result, the Hall procedure can be a useful complement to a clinician's care choices for carious primary molars. However, it can only be seen under limited circumstances [13], (Tables 3 and 4).

Table 3 Advantages and disadvantages of Hall technique.

Table 4 Indications and contraindications of Hall technique.

Procedure for Hall Technique

Determine the tooth shape, occlusion, and proximal contact region first. Where there are close contact, orthodontic elastic separators are used for 3-5 days in the mesial and distal contact areas. Crown positioning should take place after sufficient space has been gained. If the marginal ridge of one molar collapses, the adjacent tooth can move to the breakdown region. This complicates the Hall procedure of crown positioning without requiring modifications to the tooth or crown. In this case, reconstruct the marginal ridge and allow the separator to be mounted. Examine the occlusion in relation to the anterior overbite and the buccal connection of the tooth to be crowned with the opposing number. A cotton roll should be placed between the tongue and the tooth before the crown is placed. This protects the patient's airway. Try on various crown sizes to ensure a good match that protects all cusps. Choose the smallest crown size. If the crown is too big, there is a risk that the erupting pathway of permanent first molars would be messed with. Load the crown with GIC luting cement after determining the size and remove any excess cement from the tooth surface. Apply finger pressure to the crown and hold it in place until the cement hardens.

Success criteria of Hall technique crowns according to Innes et al (2007) [13].

1. The restorations or crowns are sufficient, and no treatments were necessary.

2. There were no clinical or radiographic symptoms of pulp disease.

3. Exfoliation of the teeth is normal.

Failure criteria of Hall technique crowns according to Innes et al (2007) [13].

1. Secondary caries or new caries are developed radiographically or clinically.

2. Repairing a crack or wear that necessitates attention.

3. An abscess or permanent pulpitis that indicates extraction or pulpotomy.

4. Internal root resorption or inter-radicular radiolucency.

5. If the restoration or crown were missing, or if the tooth could not be restored.

Open-Faced Stainless-Steel Crowns

Previously, there were fewer options for stainless steel crowns. Parents preferred prosthesis or extraction of individual teeth for grossly decayed anterior teeth because stainless steel crowns for anterior teeth did not look appealing. As an alternative to preformed metal crowns, open-faced stainless-steel crowns were added (Fig. 9, Table 5) (Croll, 1998).

Table 5 Advantages and disadvantages of open-faced stainless-steel crowns

Tooth Preparation of Open-Faced Stainless-Steel Crowns

Hartmann invented the open-faced stainless-steel crown tooth preparation method in 1983. When the cement has dried, continue expanding the window on the labial surface of the cemented crown with a no. 330 or no.245 bur. The incisal edge of the window should be low and gingivally to the height of the gingival crest when stretching it. The window should extend mesio-distally to the line angles. Following that, 1 mm of cement should be extracted from the sub gingivally. Smoothing the cut margin with a green stone bur. Both the bonding agent and the crown cementation, a glass ionomer lining is used. The resin-based composite should then be applied to the expanded window, and the composite should flow into the undercut and polymerize. For finishing restorations, abrasive discs are used [7].

Polycarbonate Crowns

Polycarbonates are aromatic linear carbonic acid polyesters. Polycarbonate crowns are heat-moulded acrylic resin shells that are self-cured acrylic resin-adapted to teeth. It is moulded as solids by a thermal distortion point of 270 degrees Fahrenheit. They are more visually appealing than stainless steel crowns. The polycarbonate composite is porous and cannot tolerate strong abrasive forces, resulting in regular fracturing and dislodgement (Fig. 10, Tables 6,