C.D. Lynch & F.M. Burke
Department of Restorative Dentistry, National University of Ireland, Cork, Ireland.

Introduction.
Complete or incomplete fracture of root-filled teeth has several aetiologies. It may arise from the excessive removal of tooth substance during instrumentation of the root-canal system (Rosen 1982), followed by the exposure of the already weakened tooth structure to mechanical pressures during obturation (Pitts & Natkin 1983, Dang & Walton 1989, Morfis 1990, Borelli & Alibrandi 1999). Tooth fracture can also occur when root-filled teeth are exposed to significant occlusal force. Such structurally compromised teeth – which may have a reduced level of ‘protective’ proprioception (Loewenstein & Rathkarnp 1955, Randow & Glanz 1986) and are sometimes regarded as more brittle than natural teeth (McLean 1998) – are noted to be at risk of fracture development (Shillingburg et al. 1997). The final coronal restoration should be designed to include adequate cuspal protection (Rosen 1982).
Extensively restored teeth are more likely to develop fractures (Cameron 1964). As rootcanal treatment is often performed on the teeth that have extensive restorations, these teeth should be investigated for existing fractures before commencing the treatment.
Tooth fractures impair the patient’s masticatory performance. They also compromise the survival of root-filled teeth, as they may contribute to the progression of periodontal destruction in the presence of apparently successful root fillings (Polson 1977).
The following case describes the development of an incomplete tooth fracture in a root filled mandibular molar.

Report.
A 39-year-old female patient was referred to the Department of Restorative Dentistry, University Dental School and Hospital, Cork, Ireland. Following root filling of the mandibular left first molar 2 years prior to the referral, a radiolucency suggestive of a fracture in the furcation area was noted (Fig. 1). The tooth had been restored with an extensive foursurface (mesio–occlusal–disto–buccal) intracoronal restoration of a silver-reinforced glassionomer cement (Ketac-Silver, ESPE Dental AG, Seefeld, Germany). An ‘overt’ fracture had developed clinically on the mandibular first left molar, running from the buccal surface to the distal surface, along the margins of the restoration, separating the tooth into two distinct components (Fig. 2). The fracture extended subgingivally (Fig. 3) and was associated with an extensive periodontal defect (8 mm) on the buccal surface (Fig. 4). The patient had a history of recurrent abscesses in this area following the completion of root-canal treatment. Treatment options offered to the patient included hemi-section and subsequent crowning, or extraction. The patient chose the latter option and the tooth was delivered completely. An incomplete vertical fracture was observed, extending from the crown on to the distal surface of the mesial root (Fig. 5).

Figure 1. Radiolucency suggestive of a fracture line in the furcation area of a root-filled mandibular first molar.



Figure 2. Fracture of the mandibular first molar extending along the margins of the intracoronal restoration.



Figure 3. The fracture extending subgingivally on the buccal surface.



Figure 4. Detection of an 8-mm periodontal defect in the region of the fracture.



Figure 5. Following extraction, an incomplete vertical fracture of the tooth extending from the crown on to the distal surface of the mesial root was evident.