Full Coverage Restoration in Pediatric Dentistry

 In the pediatric dentistry the restorative techniques to restore a primary tooth are both demonstrable and time-tested (Waggoner & Welson, 2019). Many of these techniques haven’t changed for decades, such as the use of full-coverage metal crown restoration (Garg et al., 2016). However, due to the current advances in dental materials leaning toward more preventive and minimal preparation restorations, tooth bonded full coverage restorations were developed (Waggoner & Welson, 2019).

A full-coronal restoration or a crown is defined as the synthetic replacement of missing tooth structure surrounding most of the remaining clinically exposed tooth structure, this in turn should replace shape, form, and function of the normal tooth (Seale & Randall, 2015). Full-coronal coverage of primary teeth in general have shown to be more superior to extensive and multi-surfaced adhesive restorations with a considerable clinical life span (Randall, 2002).

Indications

 Extensive dental decay in young children represents what is called early childhood caries (ECC), this oral health disease is a significant public health problem affecting almost 50% of preschool children. These statistics of ECC were reported from 29 of 195 countries by the WHO (Uribe et al., 2021). Lesions in ECC were found to be multi-surfaced and with cervical decalcifications, this leads to an increased implications on the treatment of the teeth and therefore suggesting the use of full coverage restorations (AAPD, 2019).

ECC lesions that involve the incisal edges most likely in the maxillary anteriors suggest the use of tooth-colored crowns for its aesthetic properties (Champagne et al., 2007).

Additionally, hereditary disorders of the enamel and dentine structure such as amelogenesis imperfecta, dentinogenesis imperfecta and molar incisor hypomineralization (MID) represent defective and weak tooth structure, therefore, early diagnosis and full coverage restoration can help in prevention of pulpal involvement (AAPD, 2019). On the contrary, if there is pulp involvement in the primary teeth that lead to pulp therapy such as pulpotomy or pulpectomy, this will lead to a weakened tooth structure, hence the use of a crown is necessary (AAPD, 2019).   Special needs patients that demonstrate high caries risk and who cannot practice a good oral hygiene are considered an indication for full coronal restorations specially under general anesthesia (Waggoner & Welson, 2019).

Tooth wear facets and bruxism related attrition in primary and permanent dentition prevents the use of intra-coronal restorations, thus the use of crowns can be indicated in this case (AAPD, 2019).

Contraindications

 Mainly when the teeth are expected to exfoliate in 6 to 12 months, placement of full-coronal restoration is not indicated (Garcia et al., 2015). Furthermore, to be able to retain the full coronal seal it is required to assess the remaining tooth structure, if the level of the tooth structure is below the bone, then extraction should be indicated (Randal, 2002). It can be difficult to do a crown preparation and cementation on uncooperative patients, as this can be a time-consuming procedure, therefore, patient behavioral assessment must be considered (Randal, 2002).

Classifications

 The crowns can be classified into two types, the first being crowns that are cemented using a luting cement and they include: Stainless steel crowns (SSC), Zirconia crowns and pre-veneered crowns. On the other hand, bonded crowns comprise of polycarbonate crowns, Strip crowns and Pedo jacket crowns (Waggoner & Welson, 2019).

Stainless Steel crowns (SSC):

SSC were introduced in the 1950’s as prefabricated metal crowns used in the permanent and primary dentition (Roberts & Sherriff, 1990). Indications of SSC can include traumatized teeth, fractured cusps and caries involving three or more surfaces (AAPD, 2019). The objective of using SSC was initially when amalgam fillings were to fail in proximal surfaces when the cavity extend beyond line angels (Roberts & Sherriff, 1990). However, at the present time SSC are used to form a biocompatible, cost effective and clinically competent restoration (AAPD, 2019).

In addition to them being durable and have a good longevity, these crowns can be used in junction with a space maintainer in the crown and loop form (Qudeimat & Sasa, 2015). Conversely, many articles discussed their used because of the dislodgement of the crown by a failed loop (Randal, 2002).  However, the literature still supports the use of crown and loop in comparison to a band and loop over the crown (Qudeimat & Sasa, 2015).

As mentioned above, SSC has many advantages as a restoration in the pediatric dentistry, in cases of MIH, when compared to resin restorations they were found to be 94% successful in comparison to 46% respectively (Farias et al., 2021). On the other hand, it was found that if the SSC wasn’t adapted and contoured to the prepared tooth structure margin, it was shown to lead to gingival inflammation (AAPD, 2019).

Despite the poor aesthetic properties of stainless-steel crowns and advances in tooth-colored crowns, nonetheless, SCC is still the gold standard for badly decayed posterior teeth (Seale & Randall, 2016).

Clinical Steps

In this section we are going to discuss the clinical procedure of selecting, preparing and

cementation of a SSC.

When SSC is indicated as a treatment of choice, the first step involves the selection of a crown that has a surface area or mesiodistal distance similar to the tooth involved (Randal, 2002).

It is important to note that if the primary second molar SSC was oversized, this can potentially prevent and interfere with the eruption of the permanent molar.In addition, the clinician must pay attention to the primate spaces when placing a crown on the first deciduous molar, if impingement of the space occurs, it can prevent the late mesial shift of the permanent first molar (Waggoner & Welson, 2019).After crown selection is done, the clinician is recommended to administer local anesthetic and then place rubber dam which can prevent dislodgement of the crown in the throat and can provide isolation (AAPD, 2019)

The preparation for the tooth is done on the occlusal and proximal surface for 1-1.5mm reduction, however, the buccal and lingual surfaces are not prepared, unless there is a significant bulge that prevent crown fitment (AAPD, 2019). The literature suggests the use of wedges or separators to create space to prevent causing a ledge on the adjacent tooth (Soxman, 2015).

Two main types of SSC are present, festooned, or pre-contoured and non-festooned crowns, it was found that using pre-contoured crowns provide more accurate contact with the tooth and is less time consuming (Kindelan et al., 2008). However, when there is a very deep proximal cavity, non-festooned crowns can help encompass the margins sub-gingivally, and then contoured using a plier (Kindelan et al., 2008).  In other instances, when encountered by space loss in the mandibular first deciduous molar, it is suggested to use the opposite side maxillary 1^st molar crown. This is possible because the gingival margin on the mesiobuccal surface fits the mandibular mesiobuccal cervical area (Waggoner & Welson, 2019).

Care must be taken to assess that the crown is 1 mm subgingival or at the gingival level, while doing try-in of the crown, the clinician must note blanching of the gingival tissue which could demonstrate an over extended crown (AAPD, 2019).

The use of crimping pliers, scissors and polishing cups is also recommended to further adapt the margins to the tooth structure, this can be assessed by a pre-cementation x-ray (AAPD, 2019).

Hall technique 

This technique was first found in Scotland, it was published as a new simple and pain free technique to restore deciduous teeth with preformed metal crowns (Kindelan et al., 2008).There is no involvement of any preparation, caries removal or anesthesia. However, this technique is only indicated with teeth that lack any clinical or radiographical pulp involvement and is free of symptoms (Innes et al., 2007). The idea behind the Hall technique is to isolate the bacteria involved in the dental caries from the oral environment where they obtain nutrients, thus, stopping the progression of the dental lesion. The pulp dentine produces reparative dentine and the caries arrest (Innes et al., 2007).  

As a consequence of not reducing the teeth occlusal surface there was a concern in regards of the temporomandibular joint (TMJ) pain and increased vertical dimension of occlusion. Current studies suggest that the vertical dimension in children and young patients can correct itself and the literature behind TMJ pains was insignificant (Ludwig et al., 2014) Success rates of using the hall technique was reported in a 10 years-retrospective study to be over 90% of the cases (Innes et al., 2017). Therefore, although the hall technique was controversial in the beginning due to lack of understanding the carious process. However, now it became a common practice in the Pediatric dentistry around the world due to its high success rate and simplicity and cost efficiency (Pinheiro et al., 2020).

Preveneered stainless steel crowns

This modification of stainless-steel crowns where initially used to incorporate an aesthetic component to the metal frame of the crown. This was done with combining a resin composite facing on the labial and occlusal surface this led to parental satisfaction because of the aesthetics and durability of the SSC (Gill et al., 2020).

However, there were many disadvantages with their use, such as, the fracture and loss of retention of the veneer facing and increased preparation to accommodate for the thickness of the resin composite (Al Shobber et al., 2017).

Moreover, the crown inability to be crimped and contoured affects its adaptability to mimic the normal anatomy of the tooth and possibly leading to gingival inflammation. Success rates of pre-veneered stainless steel crowns were found to be less than 50% due to fractures in the composite veneer after 3 years (O’Connell et al., 2014). A study by MacLean et al. (2007) also clinically assessed the aesthetics of the crowns, it was shown that the majority of the crowns were lighter in shade than the natural teeth, therefore, questioning its aesthetic purposes.

Strip crowns 

 Composite resin strip crowns are among the most popular and aesthetic treatment choices of badly carious primary anterior teeth (Garg et al., 2016). Additionally, it is particularly used when the incisal edge is involved in the cavity, fractured incisors and malformed teeth which are aesthetically unpleasing (Waggoner, 2002). On the other hand, this technique can be challenging when there is insufficient tooth structure for bonding the restoration. Patients with edge-to-edge occlusion or deep bite which can lead to detachment or fracture of the restoration are contraindicated for this technique (AAPD, 2019). In addition, technique sensitivity of using strip crowns can limit its use. In such cases when the patient is uncooperative, high caries risk and moisture control is difficult to maintain (Yang & Mani, 2016). Gingival bleeding can also influence the quality of the restoration and subsequently lead to failure (Yang & Mani, 2016). However, this type of crown is easily manipulated and simple to fit and trim, the aesthetics are very high because the crown design can allow different shades to be used to match the natural tooth color (Garg et al., 2016).

Clinical Steps

Clinically prior to preparation local anesthesia is administered followed by shade selection, it is advisable to choose a slightly lighter shade, then the correct crown size is selected roughly according to the mesiodistal length (Waggoner & Welson, 2019). Rubber dam placement is then recommended if feasible. The preparation is usually around 1-1.5 mm all around the tooth surfaces, on the mesial and distal surfaces the finish line should be a tapered knife edge (Kupietzky, 2002). Before placing composite in the crown, two openings are created at the mesial and distal line angle, this provides an escape for excess composite and air bubbles (Waggoner & Welson, 2019). The crown is then trimmed to the correct length, the tooth will be then isolated, etched, and bonded (AAPD, 2019).

Moreover, two thirds of the crown is then filled with composite, the crown is then fitted and the excess composite escape through the vents created (Kupietzky, 2002).  The use of a plastic instrument will help remove the excess before curing. It must be noted that the clinician must avoid excess pressure to avoid splitting the crown (AAPD, 2019).

Rum & Fuks (2006) evaluated the success rate of strip crowns in 387 children for a period of at least 24 months follow up, the parameters evaluated were, chipping, decay, and detachment of the strip crowns. They have found that 80% of the restorations were successful, another study found 56% failure rates at 33 months follow up, however, majority of the crowns were done on patients with high caries risk under general anesthesia. Additionally parental satisfaction was assessed for the use of composite strip crowns and found that results were positive (Kupietzky & Waggoner, 2004).

Pedo jacket crowns

This type of crowns functions like a strip crown, however, the shell of the crown is made from a tooth-colored polyester material which is filled with a resin material (Garg et al., 2016), the difference lays in the fact that the shell will not be removed after curing the material (Sahu et al., 2016).

An advantage of using this crown is that it can be simple to place and can be trimmed with a crown and bridge scissor to fit the correct size of the tooth (Anuradha et al., 2015). Nevertheless, one of the downfalls of using this crown is that it cannot be reduced, finished, or polished with a high-speed handpiece since it can lead to melting of the polyester (Garg et al., 2016). Secondly, using pedo jacket crowns is inaesthetic because these crowns come in only one shade, which is considered to be very white in color, therefore, it is used as an interim restoration for using strip crowns in uncooperative patients (Garg et al., 2016).

Polycarbonate crowns

 Polycarbonate crowns are acrylic heat molded resin prefabricated crowns, they were introduced in the 1970’s as a more aesthetic full coverage restoration than the SSC and acrylic crowns (Sahana et al., 1999). Furthermore, these crowns are flexible and can be crimped to adapt to the tooth structure (Weinberger, 1989). 

On the contrary, the preparation for these crowns required more tooth structure which made them less conservative. Studies have shown that polycarbonate crowns to be brittle, can fracture easily and were reported lose retention after 12 months of cementation. Thus, it led to limiting their use in modern dentistry (Garg et al., 2016).

Zirconia crowns

 Zirconia crowns were introduced in the early 2000’s to be used in dentistry, zirconia is a metal like structure that has the strength and aesthetics of natural tooth (Garg et al., 2016). Their use in the permanent dentition is very popular because of their aesthetics and strength in the anterior and posterior teeth (Anuradha et al., 2015). When SSC and zirconia crowns are compared in gingival plaque accumulation, detachment, and fracture, it should that zirconia crowns have less plaque accumulation but less retention than SSC (Taren & Kaya, 2018).

In addition, aesthetics and patient satisfaction is significantly high and is comparable to composite strip crowns (Alaki et al., 2020). However, not enough long term randomized clinical trials are found in the literature to support its use in primary dentition, yet, in the permanent dentition it has shown promising results (Holsinger et al., 2016). Alaki et al. (2020) also compared the loss of opposing tooth structure between strip crowns and zirconia and have found that zirconia crowns cause more tooth structure loss. Moreover, it is important to note that tooth preparation is more extensive when using zirconia crown as it requires at least 1.5-2 mm of reduction, secondly, crowns can fracture and lead to cracking if adjustments were to be made, since the material is brittle and can’t be crimped (Khatri, 2017). Lastly, due to its high inventory cost, their use is limited in underprivileged societies or third world countries (Bona et al., 2015).

Resin modified glass ionomer cement were recommended for the cementation with zirconia crowns to maximize its retention. Therefore, its mandatory to obtain proper isolation from bleeding or saliva to minimize contamination between the resin cement and the crown (Waggoner & Nelson, 2019). Some companies aim to increase retention by providing internal groves to obtain more mechanical retention (Waggoner & Nelson, 2019). Other companies like Nu Smile provide a try-in crowns that are pink in color, which are used to prevent saliva contamination before cementation (Waggoner & Nelson, 2019).

The preparation for a zirconia crown includes 1.5-2mm incisally or occlusally, followed by 1.5mm clearance on the labial and lingual surface and subgingivally the preparation extends 1-2mm (Khatri, 2017). Better gingival health is obtained with a knife-edge finish line which can provide a flush terminal between the preparation and the crown (Khatri, 2017).

Success rates from the current literature around the use of zirconia crowns is in favor of their use. Reports comparing zirconia crowns with SSC and strip crowns retention and gingival health after 6 months, provides results that support zirconia crowns when there is sufficient tooth structure remaining for the preparation. However, it must be noted that preparation and cementation of this crown is more time-consuming, therefore, patients’ behavior must be monitored to avoid failure of the restoration (Waggoner & Nelson, 2019).

Conclusion

The gold standard full coronal restoration for the posterior teeth is the SSC, due to its low cost, adaptability, ease of adjustments and comparable retention. Parent satisfaction was, however, higher with strip crowns and zirconia crowns, however the use of strip crowns should be when aesthetics are the main concern of the patient/patient and when there is enough tooth structure for bonding. If tooth structure is limited, pre-veneered SSC is still a feasible and successful option. reports for zirconia crowns in the permanent dentition is good, However, due to limited randomized clinical trials around the use of zirconia crowns in the primary dentition, we cannot draw a clear recommendation around their use.

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