Retrospective analysis of 10 Zirconia crown cases in primary teeth with its

clinical considerations.

Abstract - Early childhood caries (ECC) is a widespread global affliction and a leading cause
of premature deterioration and loss of primary front teeth in children. Managing and
addressing this issue during early childhood is crucial, given the vital roles these affected
teeth play in appearance, speech, eating, and oral function. Additionally, they are instrumental
in providing sensory feedback to the premaxilla and preserving space for the proper eruption
of permanent teeth. Recent advancements have introduced aesthetic alternatives to traditional
preformed metal crowns. This paper outlines the clinical considerations, implementation
protocol, and upkeep necessary for the successful restoration of ECC-affected anterior teeth
using preformed zirconia crowns.

Keywords - Aesthetics; Crown; Dental Caries, Primary Teeth, Zirconium

Introduction –

Early childhood caries (ECC) presents a significant public health challenge, impacting both
developing and industrialized nations. It can initiate in infancy, progress rapidly in high-risk
individuals, and frequently remains untreated. The repercussions extend beyond the affected
child's immediate family, affecting their quality of life and carrying substantial social and
economic implications.1 Clinically, ECC is defined as the presence of decayed, missing, or
filled surfaces in primary teeth of children aged birth to 71 months. Severe early childhood
caries (S-ECC) is identified by any indication of smooth-surface decay in children under 3
years old.2 ECC, marked by formidable infectious challenges and linked to atypical dietary
habits, can severely damage primary dentition, often necessitating hospital visits for young
children. It disproportionately affects disadvantaged ethnic and socioeconomic groups,
impacting over half of children within these demographics. 3 ECC progression can be swift,
from minor lesions to extensive decay requiring urgent dental intervention within months,
potentially leading to serious infections and necessitating hospitalization, antibiotics, and
even tooth extraction in toddlers as young as 2-3 years old. 4 Beyond tooth loss, ECC
compromises speech development and nutritional intake, potentially leading to
developmental delays and impacting body mass index.5 Hence, early detection, diagnosis, and
treatment are imperative. Recent years have seen the emergence of advanced aesthetic
restoration options like preformed zirconia crowns, which offer superior strength, aesthetics,
biocompatibility, and resistance to decay compared to traditional options. 6,7 These crowns,
made entirely of ceramic materials, are anatomically shaped, metal-free, bio-inert, and less
prone to plaque accumulation and colour changes. 8–10 Various brands provide zirconia crowns
for primary teeth, catering to different tooth types, including incisors, cuspids, molars, and
even permanent first molars. They are available as NuSmile Zr crowns (NuSmile Ltd,
Houston, Tx. USA), EZ-Pedo (Loomis, California, USA), Cheng Crowns zirconia
(Orthodontic Technologies Inc., Houston, Tx. USA), HuFriedy Mfg. Co., LLC, Chicago, IL,
USA; Kinder Krowns (St. Louis Park, Minn., USA) and more recently Kids-e-Crowns (Kids-
e-dental LLP, Mumbai, IN).

Indications –

1. Teeth exhibiting significant coronal damage (involving more than two surfaces) or
teeth displaying coronal fractures warrant special attention.
2. Particularly for endodontically treated teeth, there's a heightened risk of coronal
fractures and the need for thorough sealing.
3. Additionally, conditions such as amelogenesis imperfecta, dentinogenesis imperfecta,
hypoplasia’s, and hypomineralization, which lead to defects in enamel and dentin,
must be addressed.
4. Furthermore, aesthetic considerations are paramount in treatment planning.

Contraindications –

1. Extensive damage preventing reconstruction.

2. Root resorption, whether physiological or pathological, affecting over two-thirds of
the root.
3. Persistent bruxism.
4. Cases of anterior crossbites and severe crowding.
Clinical Considerations

In contrast to preformed stainless steel crowns, zirconia crowns lack the flexibility for
crimping. Fitting a Pediatric zirconia crown on a mandibular molar proves simpler than
fitting anterior teeth or upper molars. Initially, performing a single-unit restoration is less
challenging than consecutive restorations. Optimal patient cooperation is essential, with
sedation potentially aiding the process. Compared to preformed metal crowns, zirconia
crowns demand more meticulous preparation.8

Zirconia crown selection

The crucial aspect of zirconia crowns lies in accurately selecting the crown size. This
selection involved aligning the incisal edge of the zirconia crown with that of the tooth. We
evaluated the mesiodistal dimension and determined the crown size to match the tooth's
original size.

Tooth preparation

Prior to tooth preparation, it's essential to administer local anesthesia and ensure isolation of
the operative area. Given the specific attributes of preformed zirconia crowns—being rigid,
thicker, and larger—it's advisable to adhere to the reduction protocols outlined by the
manufacturer to prevent undue excessive reduction. Proper tooth preparation greatly
enhances aesthetics, crown fit, and saves time during the procedure. The tooth should be
prepared to accommodate the crown in a manner that ensures passive fitting without any
pressure during seating.

Incisal reduction

Using a tapered diamond bur in a high-speed handpiece, reduce the incisal length by
approximately 1.5-2 mm. Adequate occlusal reduction is crucial for ensuring proper fit and
positioning of zirconia crowns. The final occlusal plane of the seated zirconia crown depends
on the extent of occlusal reduction. Preparations should exhibit convergence towards the
incisal edge without any retention areas to facilitate the passive seating of the crowns.
Carefully extend and refine the preparation margin to create a feather-edge, ensuring no
undercuts or subgingival ledges remain, with margins positioned approximately 1-2 mm
subgingivally on all surfaces.

Peripheral reduction

Preparations consistently converge towards the occlusal surface, ensuring removal of line
angles and point angles to achieve slight rounding on all surfaces of the prepared tooth.
Circumferential reduction of the tooth by approximately 0.5-1.25 mm as needed is vital for
passive seating of the crown and should be carried out gradually across all planes of the
tooth. This process yields a preparation that is either parallel or slightly converging
incisally/occlusally, adhering to the natural contours of the existing clinical crown. For
anterior teeth, this results in a thin, tapered incisal edge.

On the lingual surface, a minimum reduction of 1-1.25 mm of tooth structure is necessary,

extending from 1 to 1.5 mm subgingivally to the middle of the incisal edge of the preparation,
while still following the natural contours of the existing clinical crown to facilitate passive fit.
Subsequently, the preparation is rounded, and any sharp angles are eliminated. 11

Subgingival extension

Subgingival extension guarantees the absence of crown margin exposure, promotes healthy
gingival adaptation, and maximizes retention. Utilize a thin, tapered diamond bur to prevent
tissue maceration during subgingival tooth reductions. These principles are equally applicable
to the preparation of primary molars.11

Try-in and adjustment

The crown is meticulously tried on, considering the rigidity of preformed zirconia crowns. A
minor cervical reduction of the crown may be performed using a bur under a water spray to
ensure a consistent fit. However, if the crown proves to be ill-fitting, further adjustments in
the form of incisal and sub-gingival steps can be re-evaluated.
Cementation

Before cementation, it is essential to ensure that the teeth are free from saliva, blood, or any
debris, and to reasonably control gingival bleeding. Pressure, tissue infiltration, or a
haemostatic agent may be employed as needed to achieve this objective.
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