Conservative Approach for Esthetic Repair of Fractured Ceramic Facing in Ceramic-Fused-to-Metal Crowns: A Case Series

Metal-ceramic restorations (porcelain-fused-to-metal [PFM] crowns) are commonly advocated and used in restorative dentistry and prosthodontics. Because of the brittle nature of ceramic, occasional fractures are observed. The fracture (failure) of the ceramic portion can occur due to occlusal disharmony, parafunctional habits, trauma, laboratory mistakes, iatrogenic factors, or the inherent structure of the ceramics.^1,2 Keeping in mind the cost of a metal-ceramic restoration (crown) and the number of appointments required, replacement of such fractured crowns is a time-consuming and expensive matter in dentistry. With the introduction of new adhesive restorative materials and techniques, replacement of such defective restorations is no longer the only valid option; instead, a more conservative repair approach can easily be applied in clinical practice.

The techniques for repair of fractured ceramic restorations (facings) include re-bonding of the fractured chip to the fixed restoration, bonding a porcelain veneer to the fractured porcelain, or using a resin-based composite (RBC) to restore the fractured porcelain.³ Among these, use of resin-based composite (RBC) to restore the fractured ceramic chip of the fixed restorations seems to be an easier, faster, and less expensive technique. With the introduction of aluminium oxide (Al2O3)-air abrasion, airborne abrasion with diamond particles,⁴ hydroflouric acid,⁵ silane-coupling agents,⁶ newer-generation bonding agents, 4-META resin,⁷ 10-MDP (methacryloyoxy decyldihydrogen phosphate),⁸ irradiation with Nd:YAG laser,⁹ silica coating,¹⁰ use of glass fiber-reinforced resin-based composite (RBC),¹¹ the Rocatec™ system (3M ESPE, www.3MESPE.com ), etc., it is now possible to achieve a good clinical bond between metal and ceramic, metal and RBC, RBC and ceramic, and amalgam and RBC.¹² Although replacement is an optimum treatment, with the advent of these new technologies, repair (as a conservative approach) provides an excellent alternative option and temporary solution to such clinical situations.¹³ It is now possible to perform a functional and esthetic chairside repair of these fractured facings that is economical, less time-consuming, and requires a single appointment.

The following article describes a conservative chairside repair protocol for fractured ceramic facing of PFM crowns that is esthetic, fast, and affordable, and includes an overview of several cases involving the above-mentioned repair treatment protocol.

The protocol described below is based on the clinical technique that is being used for the repair treatment of fractured ceramic facings (Figure 1) in dental clinics. The first and foremost step is to diagnose the underlying etiology that resulted in the fracture of ceramic facing, which can be attributed to traumatic impact, occlusal interferences, or a parafunctional habit. Any occlusal interference in the existing dentition—both in centric and eccentric relation—must be rectified before the repair can be undertaken.

Following oral prophylaxis, shade selection is completed using a universal shade guide (VITA System 3D-MASTER^®, www.vita-zahnfabrik.com) (Figure 2). With a rubber dam, quadrant isolation is done as required, depending on the tooth under treatment (Figure 3). Sharp edges of fractured ceramic facing are smoothened and beveled using a diamond bur. A long bevel is created on the fractured edge of ceramic facing in order to achieve esthetically merging margins of RBC and ceramic. If the ceramic facing has been lost completely, the metal surface is roughened using a bur (Figure 4). An initial treatment with phosphoric acid (Total Etch, Ceramic Repair, Ivoclar Vivadent, www.ivoclarvivadent.us) for 10 seconds is done to remove the debris produced during mechanical roughening from the ceramic (or metal) surface (Figure 5). Hydrofluoric acid (HF) (IPS^® Ceramic Etch, Ivoclar Vivadent) is applied on the exposed ceramic surface for 30 seconds followed by rinsing for 15 seconds with an air-water jet system (CoJet™ Intraoral Repair System, 3M ESPE). Alternatively, the CoJet system can also be used to aid in repair with cold silicatisation of the restoration surface.

Depending on the extent of fracture, this is followed by application of a silanating agent (SA) (Monobond-S™, Ivoclar Vivadent) on the ceramic surface and/or of metal zirconia primer (Metal/Zirconia Primer, Ivoclar Vivadent) on the metal surface for 60 seconds and drying it with an air syringe (Figure 6). Two coats of bonding agent are applied for 10 seconds on the entire primed surface (ceramic and/or metal) to ensure better bonding between the two different substrates (Figure 7). They are then dried using an air syringe, then cured according to the manufacturer’s instructions (usually 40 seconds). An opaque RBC (Tetric^® EvoFlow Bleach XL or Monopaque^®, Ivoclar Vivadent) is applied to mask the black-grey metal color of the crown and is then light-cured (Figure 8). In certain commercial ceramic-repair kits, the bonding agent (eg, Heliobond^®, Ivoclar Vivadent) is applied following the application of an opaque composite.

Following this, a direct composite veneering technique is use to repair the defect using an appropriate RBC (Esthet.X^®, DENTSPLY Caulk, www.caulk.com). Depending on the extent of the repair, either a single selected shade or multiple shades in layers are applied and cured, then re-checked for occlusal interferences (Figure 9). Finally, finishing (Sof-Lex™ discs, 3M ESPE) and polishing (Enhance^®, DENTSPLY Caulk) is accomplished using an appropriate agent (Enhance^® Composite Finishing and Polishing system, DENTSPLY Caulk).

A brief description of four cases reported to the Department of Conservative Dentistry and Endodontics are discussed below. They were treated using the above-described repair protocol to achieve a functional and esthetic outcome.

A patient reported with a partial fracture and wear-off of the ceramic facing of a metal-ceramic crown (Figure 10) cemented on the maxillary right second premolar (tooth No. 4) due to eccentric movements interference. Following examination and removal of observed occlusal interferences, the above-mentioned repair protocol was used, retaining the remaining porcelain facing and masking the exposed metal surface with an opaque RBC to obtain an esthetic final outcome (Figure 11).

This patient reported with a complete dislodgement of the ceramic facing (Figure 12) in relation to the maxillary left first premolar (tooth No. 12) during mastication, which was attributed to improper metal-ceramic bonding. A full-veneer preparation was done on the metal backing, masking the black metal color with an opaque RBC. The suggested repair protocol was carried out to obtain a good esthetic and functional outcome (Figure 13).

A patient reported with a complete loss of the ceramic facing in relation to the maxillary left first premolar (tooth No. 12), which was attributed to faulty occlusal contacts in centric relation to the mandibular partial denture (Figure 14). After relieving occlusal interferences, a repair procedure similar to that described in Case 2 was used, and a RBC veneering was done to match the shade of the lower partial denture teeth for a better esthetic outcome (Figure 15).

The patient reported with fractured ceramic facing at the disto-incisal angle extending up to the cervical margin (Figure 16) of a metal-ceramic crown on the maxillary right central incisor (tooth No. 8). A long bevel was created on the fractured edge of the ceramic facing. Following masking of the metal with an opaque RBC, the highlighted repair protocol was carried out using a layering technique (Esthet•X^®, DENTSPLY Caulk; or Z100™, 3M ESPE) to obtain a 3-dimensional (3-D) color match with the existing retained ceramic facing (Figure 17). Finally, occlusal interferences from the mandibular complete denture on protrusive movements were removed.

The above-mentioned case studies describe a conservative chairside protocol for the repair of ceramic facings that are either fractured and/or worn-off and is based on the authors’ clinical experience. The technique is economical, less time-consuming, preserves and conserves both the restoration and tooth structure,¹² and, if done meticulously, can yield good esthetic and functional results. A variety of pretreatment options, as mentioned earlier, for different substrates are available (Table 1).^14-18

A combination of airborne particle abrasion (50-µm Al2O3), etching with HF acid, and application of silane is the recommended treatment method for intraoral repair of ceramics.^14,15 For alumina- and zirconia-reinforced ceramics, use of air abrasion (diamond burs) is preferred over acid etching, as acid etchants do not roughen the surface of these ceramics sufficiently.¹⁴ Use of air abrasion is also advocated in cases involving pretreatment of metal and RBCs (indirect) before bonding.^16,17 In addition, for the intraoral repair of exposed metal surfaces or alumina-reinforced ceramic, the Rocatec silica-coating system is advocated.^18,19 This system applies a tribochemical silica coat that allows for chemical bonds with the silane coupling agent and RBCs. For slightly retentive or nonretentive designs, methacryloyloxydecyl dihydrogen phosphate (MDP)-based primers (eg, Z-Prime™ Plus, BISCO, Inc., www.bisco.com) have been shown to achieve long-term durable bonding of zirconia surfaces with indirect substrates (metal).^20,21 The phosphate ester group chemically bonds to metal oxides such as zirconium dioxide.

In the above-described cases a combination of phosphoric acid/hydrofluoric acid and a silanating agent was used to improve the adhesion between resin-based composite-ceramic and/or resin-based composite-metal and to facilitate the repair procedure. This pretreatment combination has shown either higher or equivalent bond strength values as compared to other treatments. A recent study²² compared the microtensile bond strength of a repair resin composite to an alumina-reinforced feldspathic ceramic using three different conditioning methods (hydrofluoric acid, alumina-oxide air abrasion, and tribochemical silica coating), followed by the application of a silane coupling agent. The results of the study showed that the repair microtensile bond strength is higher after HF acid application and silanization as compared to other tested groups. Frankenberger et al (2000)10 observed that the repair with a silica coating achieved equal or higher bond strengths than the etching technique did. Sandblasting under a rubber dam is another good alternative to make the ceramic surface more amenable to adhesion.¹ There is paucity of literature regarding the longevity of such repair protocols in a clinical practice; thus, more in-vivo studies with adequate follow-ups are required to evaluate the long-term success of such repair techniques and procedures.

The described clinical repair technique is a good alternative for an esthetic and functional repair of defective ceramic facings in metal-ceramic crowns as opposed to replacements of such crowns.

Neeraj Malhotra, MDS, PGDHHM
Reader
Department of Conservative Dentistry and Endodontics
K.D. Dental College
Mathura, U.P., India

Shashirashmi Acharya, MDS
Professor
Department of Conservative Dentistry and Endodontics
Manipal College of Dental Sciences
Manipal University
Manipal, India