In primary dentition, large, multisurface carious lesions often advocate the use of a full-coverage restoration. Full coverage is likewise indicated in deep approximal cavities, circumferential caries, bilateral approximal cavities and history of root canal treatment. The American Academy of Pediatric Dentistry also included children at high risk with anterior and/or posterior decay, and children requiring general anesthesia.
Historically, such restorations have been in the form of stainless steel crowns (SSCs). Stainless steel crowns were introduced in 1947 by the Rocky Mountain Company and popularized by Humphrey in 1950. With only 0.2 mm metal thickness, these crowns are strong, resilient and malleable.
Stain Steel Dental Crowns for Pediatrics
They do not fracture and can be modified by crimping to ensure proper adaptation to the prepared tooth structure. Several studies have reported their superiority, in terms of better retention and less recurrent decay, relative to posterior composite resin and amalgam Class II restorations. Yilmaz et al. 2006 showed that after two years of clinical use, the rate of perforations or dents of SSCs was only 12%. Also SSCs do not require complete isolation for bonding, as do crowns made of composite resin, nor do they require a preparation incorporating mechanical retention into the design, as do amalgam restorations.
Over the years, design modifications have simplified the fitting procedure and improved the morphology of the crown so that it more accurately duplicates the anatomy of primary molar teeth and thus, the SSC have become the standard for restoration of compromised pediatric dentition and proved to function satisfactorily for over 36 months. However, these crowns have one potential drawback owing to the unattractive color of the restorative material, which fails to meet the esthetic demands of patients’ parents. In order to address parents’ esthetic wishes while effectively treating the decay, Pre-veneered Stainless Steel Crowns “PSSCs” were introduced in the early 1990’s, initially developed for anterior teeth, but later for primary molars.
These are basically SSC with a tooth colored material (either a resin composite or porcelain) coating that is chemically or mechanically attached to the metal coping. The composite veneer covers the facial, occlusal, mesial, and distal aspects of the crown, and its thickness varies from 0.6 mm at the mesiobuccal to 1.5 mm at the occlusal surface in order to withstand the patient’s occlusal forces. These crowns combine the thin strong foundation of stainless steel, with the tooth colored appearance of composite or porcelain. As such, they can provide full coverage, durability, ease of placement and aesthetics.
Although PSSCs resolve some problems associated with SSCs, they still have several shortcomings; they require a greater reduction of tooth structure during preparation than is the case for traditional SSCs. The greater occlusal reduction can increase the risk of exposing vital pulp, necessitating vital pulpotomy, a procedure which increases chair time and cost.
In addition, these crowns cannot always be crimped to fit to the prepared tooth. Crimping could cause fracture or chipping of the esthetic facing. Esthetic facing may also get fractured if exposed to uniaxial force and repair of fractured coatings may entail complete replacement. Fracture of an esthetic SSC can lead to loss of space in the developing pediatric dentition, as well as increased retention of plaque.
Zirconia Dental Crowns for Pediatrics
For decades, dentists had been limited to those two types of full coronal coverage for primary molars. However, the overwhelming need for lifelike restorations that mimic natural tooth have driven the profession towards metal free whenever possible. In pediatric dentistry, this is represented through the use of zirconia crowns which are considered “cosmetic” in nature compared to other alternative crown materials. Initially, zirconia crowns were predominantly fabricated with a zirconia coping layered or pressed with different types of porcelain. Recently, monolithic (full-contour) zirconia crowns have been developed, which are extraordinarily strong, and argued to be just as aesthetic as layered zirconia crowns.
Initially, zirconia ceramic parts were just applied as the cores for manufacturing dental crowns in the form of bi-layer restorations, with veneer porcelain shells fused on them. Therefore, the porcelain made of softer amorphous silicates is the one that comes in contact with the natural tooth structure. Nowadays, by increasing the translucency of zirconia ceramics, full contour zirconia crowns are used to reestablish the posterior teeth. This type of ceramic restorations made of one single material by computer assistant design (CAD) and computer assistant machining (CAM) approach shows excellent mechanical properties.
They were proved to be extraordinarily strong, and argued to be just as aesthetic as layered zirconia crowns. While using different restorations, it always remains the issue of avoiding or minimizing the pathological damage of natural teeth during the friction process between restorations and natural teeth. Surface wear of enamel is a physiological process going with the opposite movement between upper and lower teeth through mastication. This natural process may be accelerated by the introduction of restorations whose properties of wear differ from those of the tooth structure that they slide against.
Therefore and despite the truth that a constant wear of the entire dentition is possible independent of dental restorations, it is desirable that wear behavior of restorative materials is similar to natural enamel, because excessive wear could lead to clinical problems such as damage of teeth occluding surfaces, loss of vertical dimension of occlusion, poor masticatory function associated with temporomandibular joint remodeling, dentine hypersinsivity or death of the tooth and at least may lead to esthetic impairment. It is therefore of particular interest to carry out in vitro friction tests between dental materials and natural teeth.
With the increasing development of new esthetic full coverage’s for primary teeth, and the relatively short application time of the newest addition of zirconia crowns, there is an increasing demand for analyzing the resultant pathological tooth wear against these types. Unfortunately, clinical documentation of enamel wear, when opposing restorative materials, is difficult to obtain. However, these data can be acquired from in vitro studies.
Analyzing enamel wear after in vitro cycling and loading. The present study investigated the amount of wear in primary enamel, caused by zirconia crowns, pre-veneered stainless steel crowns and stainless steel crowns. In addition, the wear behaviors and patterns were characterized by examination using scanning electron microscopy.