Fractographic ceramic failure analysis using the replica technique

Abstract

Objectives: To demonstrate the effectiveness of in vivo replicas of fractured ceramic surfaces for descriptive fractography as applied to the analysis of clinical failures.

Methods: The fracture surface topography of partially failed veneering ceramic of a Procera Alumina molar and an In-Ceram Zirconia premolar were examined utilizing gold-coated epoxy poured replicas viewed using scanning electron microscopy. The replicas were inspected for fractographic features such as hackle, wake hackle, twist hackle, compression curl and arrest lines for determination of the direction of crack propagation and location of the origin.

Results: For both veneering ceramics, replicas provided an excellent reproduction of the fractured surfaces. Fine details including all characteristic fracture features produced by the interaction of the advancing crack with the material's microstructure could be recognized. The observed features are indicators of the local direction of crack propagation and were used to trace the crack's progression back to its initial starting zone (the origin). Drawbacks of replicas such as artifacts (air bubbles) or imperfections resulting from inadequate epoxy pouring were noted but not critical for the overall analysis of the fractured surfaces.

Significance: The replica technique proved to be easy to use and allowed an excellent reproduction of failed ceramic surfaces. It should be applied before attempting to remove any failed part remaining in situ as the fracture surface may be damaged during this procedure. These two case studies are intended as an introduction for the clinical researcher in using qualitative (descriptive) fractography as a tool for understanding fracture processes in brittle restorative materials and, secondarily, to draw conclusions as to possible design inadequacies in failed restorations.

Fig. 1

Fracture of the veneering porcelain (AllCeram) of an upper left Procera alumina molar after 4.2 years of intra-oral function

Fig. 2

After having cleaned the fractured surface with an alcohol cotton pellet and air-dried, the silicone impression material is injected first on the fractured zone.

Fig. 3

The silicone impression material continues to be injected over the occlusal surface

Fig. 4

a,b: The impression is poured with epoxy resin reproducing the fractured crown.

Fig. 5

a: Occlusal view (at 10x) of the Procera AllCeram crown showing the veneer failure on the palatal-mesial cusp. Major wear is visible on all four cusps. The frame near the mesial gingival margin is magnified in Fig.5b and Fig.5c b and c: Higher magnifications within the frame (Fig.5a) near the interproximal mesial margin show hackle and wake hackle indicating the direction of crack propagation towards the margin.

Fig. 5

a: Occlusal view (at 10x) of the Procera AllCeram crown showing the veneer failure on the palatal-mesial cusp. Major wear is visible on all four cusps. The frame near the mesial gingival margin is magnified in Fig.5b and Fig.5c b and c: Higher magnifications within the frame (Fig.5a) near the interproximal mesial margin show hackle and wake hackle indicating the direction of crack propagation towards the margin.

Fig. 5

a: Occlusal view (at 10x) of the Procera AllCeram crown showing the veneer failure on the palatal-mesial cusp. Major wear is visible on all four cusps. The frame near the mesial gingival margin is magnified in Fig.5b and Fig.5c b and c: Higher magnifications within the frame (Fig.5a) near the interproximal mesial margin show hackle and wake hackle indicating the direction of crack propagation towards the margin.

Fig. 6

Side view of the Procera AllCeram crown (at 15x). Major arrest lines are recognizable as well as hackle lines. The circled occlusal broken edge shows some surface damage.

Fig. 7

Higher magnification (31x) of the circled area in Fig.6. Several arrest lines are visible (concave well delimited lines). Areas of interest (frames) are scrutinized at higher magnifications in the following figures.

Fig. 8

Detailed view (127x) of the occlusal damaged edge (larger frame in Fig.7). Two indented (crater type) areas are identified as the origin sites from which failure started followed by an arrest line. The area near the arrest line delimited by a frame is blown-up in Fig. 9.

Fig. 9

High magnification at 1019x of the frame in Fig.8. Many wake hackle are visible starting from pores within the Procera veneering porcelain (AllCeram). The direction of propagation goes from top to bottom along the trail of the wake hackle.

Fig. 10

Higher magnification of the smaller frame area in Fig. 7. Wake hackle are clearly recognizable indicating the direction of crack propagation (from top to bottom i.e. from occlusal surface to gingival margins).

Fig. 11

Additional occlusal view at an angle and low magnification (31x) of the crack initiation sites (origins). Note the occlusal worn ceramic surface and resin pouring artifacts (black spots) resulting from poor resin wetting at sharp angles of the replica impression.

Fig. 12

Summary image with circled area for crack initiation and arrows indicating the general direction of crack propagation.

Fig. 13

Gold-coated replica of an In-Ceram Zirconia veneering porcelain fracture of an upper first premolar. The naked eye recognizes many hackle lines and a damaged buccal edge with several smaller edge chips.

Fig. 14

The SEM view at 18x shows evidence of ceramic wear near the fractured edge, arrest lines, hackle and wake hackle (zoom within the image). The frame area is analyzed in Fig. 15.

Fig. 15

Higher magnification (97x) of the frame delimited occlusal edge area in Fig. 14 showing many arrest lines, hackle, wear and one of several origins on that edge.

Fig. 16

Summary of the failure event with the initiation site on the occlusal buccal edge (cusp tip) and the crack front moving along the arrowed path towards the gingival margins.

Fig. 17

The clear details obtained from replicas viewed here at 4027x. Twist hackle looking like ripples are visible perpendicular to a wake hackle (detailed view of Fig. 10). The twist hackle are obtained from final lateral link up of overlapping crack segments.