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TABLE 8.1

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Comparison between Different Methods of Aesthetic Restorations of Primary Teeth

Pre-Veneered

Zirconia Crowns

Aesthetic quality Good aesthetics with

good texture, translucency, and characterization

Thickness (1=lowest thickness,

4=highest thickness)

Ease of application (1=easiest, 4=most

difcult) Amount of tooth reduction Extensive Moderate Least Moderate Gingival integration The smooth surface

Durability Very durable Veneer chipping

Cost (1=cheapest,

4=most expensive) Retention Almost the same when properly seated and cemented

1 3 Depends on the

2 1 2 2

of the zirconia crown reduces plaque retention, therefore results in good gingival health.

4 3 1 2

Preformed Metal

Crowns

Fair but opaque due

to the underlying metal layer with less anatomical characterization

The two-layer

thickness is more inviting for plaque accumulation and gingival inammation.

reported

Composite Strip

Crowns

Good aesthetic quality,

but colour might change with time

operator skills

The non-standardized

thickness of the material and possible inadequate nishing at the gingival margin may result in gingival irritation.

Composite chipping

and fracture reported

Glass Fibre–

Reinforced Crowns

Fair quality, but may

change with time

The exibility and

nature of the material may allow for some irregular margins which may result in potential gingival irritation.

Crown wear

reported

111Aesthetic Full Coverage Restorations

Zirconia Crowns

Zirconia started to be used in the dental eld during the 1990s, in the form of root canal posts, and later as posterior xed protheses. It was mainly composed of zirconium oxide and introduced as a full ceramic restoration due to its biocompatible aesthetic and strong, metal-like properties that can efciently replace metal ceramic restorations. The zirconia dental prosthesis manufacturing process is based on either using a base of zirconia framework which is then veneered with ceramic layering or using a monolithic zirconia in non-veneered full zirconia restorations.

Zirconia crowns were recently introduced in paediatric dentistry, with many manufacturers producing different versions of both primary anterior and posterior zirconia crowns, each having different manufacturing methods, designs, means of retention, surface nish and gloss, and recommended methods of cementation. In addition to its high strength, zirconia offers remarkable biocompatibility to the gingival tissues. This was explained by its repelling effect of the adhesion to Streptococcus mutans and lesser plaque accumulation, consequently decreasing the overall plaque biolm and the microbial layer thickness.

Before zirconia crowns were rst introduced, concerns about the possible wear of their opposing natural teeth during function led manufacturers to work on the surface nish of the crown. Polished crown surfaces were found to have negligible wear effect when compared to glazed surfaces.

Zirconia Crown Design

Many crown designs have been proposed by various companies, with differences mainly in the external anatomical design (different degrees of taper, slopes, and occlusal or incisal forms). In order to improve crown

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retention, some manufacturers included retentive grooves on the tting surfaces, while others included tting surface treatment. Some manufacturers offer narrow sizes to accommodate for the possible loss of the regular mesio-distal dimension that occurs as a result of space loss. Other manufacturers provide universal sizes that can be used on either side for ease of use. Some manufacturers provide duplicate pink trial crowns that can be used in size selection and trial tness, while others require the use of the same crown, therefore resulting in the need for crown sterilization. The use of trial crowns prevents contamination of the crown tting surface with blood and saliva, consequently improving cement bonding, guarding against the development of possible minor cracks that may occur during repeated tting attempts and sterilization.

Zirconia Crown Tooth Preparation

The main zirconia crown tooth preparation principles are:

• Adequate crown preparation is required through occlusal clearance, clearing interproximal contact areas, as well as considerable buccal and lingual reduction.

• A suitable negative crown path of insertion (passive t) is required.

• A sub-gingival preparation is required in order to seat the crown sub-gingivally, without intentional creation of a nish line or the creation of cervical ledges that could obstruct the full seating of the crown.

• Adequate care is needed to prevent violation of the tooth biological width or laceration of the free gingiva.

• Line angles should be rounded, with circumferential undercuts eliminated.

• Crowns should be seated using balanced nger pressure in order to prevent the formation of micro-cracks or even fracture of part of the cervical margin of the crown.

Tooth Preparation Steps

FIGURE 8.1 The occlusal/incisal surfaces should be reduced by 1.5–2mm.

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FIGURE 8.2 A1mm supra-gingival circumferential preparation should be prepared, clearing interproximal contacts.

FIGURE 8.3 An additional 1–2mm circumferential sub-gingival preparation should be performed without the need

for creating a nish line or the formation of ledges/areas of undercut. Sharp edges should also be rounded.

Zirconia Crown Cementation

Different materials have been recommended for zirconia crown cementation, such as conventional glass ionomer cements (GICs), resin-modied glass ionomer cements (RMGIC), packable glass ionomer cements, resin cements, and bioactive cements.

Many studies reported a reliable retention level of zirconia crowns over periods up to three years. Both self-adhesive resin cements and resin-modied glass ionomer cements show superior marginal integrity when used in cementing zirconia crowns, while conventional glass ionomer cements show inferior adaptation quality.

Although conventional glass ionomer cements are widely used as an economic multi-purpose cement, both packable and resin-modied glass ionomer cements offer higher physical properties, which provide more reliable retention of the cemented crowns. In addition to their low cost, glass ionomer cements are less sensitive to blood and uid contamination. Resin-based cements, however, are more sensitive to such possible contaminations. In addition, conventional and packable glass ionomers offer easier removal of excess material after initial setting, as opposed to using light-cured resin-based cements.

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FIGURE 8.4 The most suitable zirconia crown size should be chosen and tried using balanced nger pressure. Trial

crowns, where appropriate, should be used to determine the correct size. The correct size depends on crown size, available space, adjacent teeth, and occlusion.

Cementation Steps

The following steps should be followed:

1. Crowns should be assessed prior to cementation using balanced pressure.

2. Cleaning and dryness of the prepared tooth are important prior to cementation. Haemostasis

can be achieved through the use of: a. Digital pressure with a wet gauze b. Haemostatic agents c. Retraction cord or paste d. Vasoconstrictor containing local anaesthesia The digital pressure is the easiest, most reliable, and least traumatic.

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FIGURE 8.5 Occlusion should be checked prior to crown cementation (best veried by opposite canine-to-canine

overbite).

3. While cementing the crown, the axial orientation of the crown should be consistent with

the inclination of the neighbouring teeth. In addition, the occlusion should also be checked

before the cement sets.

4. The following should be used when cementing multiple posterior crowns: a. Multiple crowns are best cemented together. b. When seating two crowns, the order with which the crowns were tried in should be

followed.

c. Gentle removal of the excess cement is very important in order to be able to realign teeth

before nal cement setting.

5. Special attention needs to be paid when cementing multiple anterior crowns. The fact that

the crowns are passively tted may result in slight rotation or shifting of the crown from

the proposed crown position; therefore, cementing the crowns together, especially in tight

contact cases, is advisable. In spaced cases, the centrals can be cemented rst, followed by

cementing both the lateral and canine of each side.

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Troubleshooting

Clinical Situation Possible Causes Management

Incomplete crown seating 1. Insufcient preparation Perform more reduction without

attempting to over-reduce and mutilate the tooth.

2. Improper crown size (larger or smaller)

3. Supra-gingival undercuts and sub-gingival ledges

Consider available space when

choosing the correct crown size. Neighbouring or contralateral crown size can be used as a reference.

Visually identify and remove

(preferably with magnifation) both undercuts and ledges.

4. Compromised available mesio-distal widths

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Try a smaller crown size. Use the narrow version of the same

size.

Use the contralateral upper rst molar

in the tight space of lower molar.

Minimal selective grinding of the

proximal surfaces of the neighbouring primary teeth.

Clinical Situation Possible Causes Management

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Crown malalignment 1. Decient preparation in one or more

areas, may guide the crown seating in the wrong direction

2. Rotation of a properly tted crown during cementation possible

Tactile and visual identication and

removal of the interfering area/ undercut/ledge.

Keep checking and adjusting the

alignment of the crown(s) before the cement nally sets.

117Aesthetic Full Coverage Restorations

De-bonding or crown loss

Inaccurate overbite 1. Zirconia crowns tted in cases of

1. Improperly seated and cemented crown

2. Defective cementation due to failure to follow the manufacturer’s instructions and/or inability to control the blood and saliva contamination

3. Failure to properly decontaminate the tting surface of a de-bonded crown before re-cementation

4. Frequent consumption of sticky food

extreme loss of vertical dimension

See management of incomplete crown

seating.

Strictly follow the manufacturer

instruction of the used crown and cement and control the contamination with proper isolation.

Use any of the recommended

methods of haemostasis described earlier.

Use sand blasting to refresh the tting

surface of the de-bonded crown, or use a new crown.

Patient and parent education.

Zirconia crowns are contraindicated

in these cases.

(Continued)

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(Continued)

Clinical Situation Possible Causes Management

2. The bite not properly assessed and adjusted

3. Incomplete seating of the crown See management of incomplete crown

Gingival inammation around

the crown margins

Gingival laceration 1. Use of wrong bur size while

1. Inadequate oral hygiene measures can cause inammation

2. In full mouth treatment cases, gingival inammation can be expected in the rst couple of weeks due to initial fear of cleaning or using the newly treated teeth.

3. Wrong placement of the crown margins supra-gingivally can result in plaque accumulation and subsequent inammation.

4. Excess cement, especially sub-gingivally, can cause inammation.

preparing the tooth sub-gingivally

2. Deep sub-gingival preparation (violating the biological width)

3. Direction of the bur against the gingivae rather than the tooth

Check the bite at the contralateral

side.

Further tooth reduction in the

proximal cervical area of the crown could help improve crown t, therefore, adjust the bite.

When crowning opposite canines, the

overbite should be properly checked before cementing the lower crown. More labial preparation of the lower abutment tooth and more palatal preparation of the upper one might solve this problem.

seating.

Proper oral hygiene instructions and

follow-up.

Parent re-assurance and education.

The crown margin should be placed

sub-gingivally.

Removal of excess cement.

Use the correct bur size.

Make sure not to exceed the

biological depth (maximum 1–2mm).

Careful tooth preparation.

Gingival recession

1. Over-extended preparations and aggressive gingival lacerations, causing recession

2. Gingival retraction using retraction cords or retraction pastes (especially those with astringent materials) resulting in post-operative recession

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Careful tooth preparation with

minimal gingival damage or deep gingival preparation.

Pressure using a wet gauze will

achieve the required haemostasis with less chance of gingival recession.

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Advancements in the Field of Full Coverage Primary Tooth Restoration

There is a growing need for new, exible, easy-to-t, and durable aesthetic full coverage restorations with reliable long-term success. Advancements in the eld of printable resin materials are growing widely and are expected to replace existing milled alternatives, such as the more rigid zirconia crowns. Prefabricated exible aesthetic crowns (Nusmile BioFlex crowns, Texas, USA) (Figures8.6–8.8) are now in the market, featuring many benets, such as exibility, wear resistance, relatively thin margins, natural anatomical forms, good gingival integration, and autoclavability, which can be cemented reliably using conventional glass ionomers. These crowns, however, lack the translucency and surface gloss of zirconia. Nevertheless, the exibility of such crowns guards against the possibility of fracture against undercut during seating. Such exibility is likely to allow these crowns to replace preformed metal crowns in restoring anterior and posterior primary teeth. These crowns, however, are relatively new and require extensive research in order to ascertain their long-term potential in the eld of paediatric dentistry.

FIGURE 8.6 Image showing grossly carious 85 and 84 (84 caries was conrmed radiographically).

FIGURE 8.7 Image showing size selection of the BioFlex aesthetic posterior crowns.

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FIGURE 8.8 Images showing cementation of the BioFlex crowns onto 84, 85, and 54. Of note is the bright white

colour of the BioFlex crowns in comparison to the natural colour of the teeth. Newer crown shades have been introduced in the market since the treatment of this case.