Full Coverage Aesthetic Restoration of Anterior Primary Teeth Zirconia Crowns

Sep 20, 2019|

Zirconia (zirconium dioxide) crowns are made of solid monolithic zirconia ceramic material. Although discovered in 1789 by the German chemist Martin Heinrich Klaproth, zirconia has been used as a biomaterial since the late 1960s. Its use as a dental restorative material became popular in the early 2000s with the advent of CAD-CAM technology. In the later part of the decade they became available as preformed crowns for primary teeth.

Advantages

1.They are very aesthetic, with greater durability than composite strip crowns and pre-veneered crowns.

2.They are not as technique sensitive as composite strip crowns as the fabricated crown is cemented with self-adhesive resin cement rather than bonding.

3.They take a bit longer to place than stainless steel crowns and composite strip crowns, about the same as pre-veneered crowns, and less than open faced stainless steel crowns.

Disadvantages

1.They are not recommended in patients that are heavy bruxers.

2.Greater tooth reduction is required.

Zirconia Crown Technique (technique description and illustrations courtesy of EZ Pedo Crowns)

Select the correct crown size by placing the incisal edge of the crown against the incisal edge of the tooth.

Reduce the incisal edge1.5 - 2mm.

Reduce the labial surface a minimum of 0.5-1.0 of tooth structure in three planes (gingival-middle-incisal thirds). These three planes extend from 1-2mm subgingivally all the way to the middle of the incisal edge of the prep.

Reduce the lingual surface by removing .75-1.25mm of tooth structure from the lingual surface, extending from 1-2mm subgingivally to the middle of the incisal edge of the prep following the natural contours of the existing clinical crown. The facial and lingual preps should meet in a thin incisal edge. Check the occlusion to insure there is adequate clearance from opposing dentition.

The red arrows mark the most common areas of internal interference that, if under-prepared, will make it difficult to seat zirconia crowns. Lingual and facial reductions should meet at a thin incisal edge of the final restoration. This thin incisal edge helps to reduce internal interferences between the tooth and the internal surface of the crown.

Completed tooth preparation. The circumference of the overall prep should be ovoid when viewed from the incisal edge. Facial and lingual surfaces should not be prepared flat, but rather curved interproximally. Removing extra material in these areas will insure an easier fit with less internal interference and allow mesia/distal rotation for a better alignment of the crown during final cementation.

Ceramic crown adjustment. It is possible to adjust a pedo ceramic crown. However because it is ceramic and cannot be trimmed with scissors like a traditional stainless steel crown, it is necessary to use a high speed, fine diamond with lots of waters because excessive heat could cause fractures in the crown’s ceramic structure. Occlusal and interproximal adjustments are not recommended, as these will remove the crown’s glaze and possibly create a weak area of thin ceramic.

Passive fit. It is very important that zirconia pedo crowns fit passively. Because they are zirconia and do not flex, pushing harder will not work. Do not attempt to force a crown to fit. Excessive pressure may fracture the crown. The appropriate size crown should fit passively and completely subgingivally without distorting the gingival tissue. EZ- Pedo Crowns have internal ZirLock grooves that increase the overall surface area of the restoration, providing more retention and improving overall clinical success.

Preparation for Cementation

Rinse the preparation and remove all blood and residue from the tooth. If bleeding continues, squeeze the preparation with a moist 2x2 gauze or carefully apply Superoxol to the tissue using a micro brush. Using peroxide or alcohol, thoroughly clean the internal surface of the crown so that all blood residue is removed.

Cementation

Cementation is the most important step to creating a beautiful smile. Tooth orientation and emergence profile are key. Centrals should always be cemented together first and then the laterals. Apply consistent, firm finger pressure during cementation using glass ionomer cement. The crown should remain undisturbed until the cement has completely hardened. Wiping excess cement from the facial embrasure will allow a clearer facial view and insure a better final alignment, dramatically improving the final esthetic result. Tooth labeling can be scratched off with a spoon or polished off with coarse prophy paste.

With all full coverage restorations parents must be advised to institute appropriate preventive health practices (elimination of sugar containing drinks, regular tooth brushing and topical fluoride application) to maximize gingival health and minimize the recurrence of caries under the restorations.

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