A. Al-Wahadni & D. L. GutteridgeFaculty of Dentistry, Jordan University of Science and Technology, Irbid, Jordan.
Division of Restorative Dentistry, Leeds Dental Institute, Leeds, UK .Introduction.
Posts are normally used to aid core retention. A direct relationship exists between the quantity of sound tooth structure and tooth strength and care is required when preparing teeth to accept posts (Hunter & Flood 1989a,b). The emphasis of many restorative techniques is now on the preservation of tooth structure, wherever possible. Following root canal treatment, where the provision of a post and core restoration may be indicated, a successful post restoration should minimize loss of tooth structure, reduce unnecessary stresses and maintain the seal of the root filling (Sokol1984).
The importance of retaining the maximum amount of sound dentine when restoring root-filled teeth has been emphasized (Trabert et al. 1978, Mattison 1982). Caputo & Standlee (1976) and Tjan & Whang (1985) made recommendations on the amount of sound dentine that should remain around a post. The importance of retaining sound dentine in the distribution of post stress to the remaining root has also been emphasized (Goerig & Mueninghoff1983, Halpern1985, Stokes1987).
Kafalias (1969) also recommended retaining self-supported coronal dentine as it produced an irregular joint between the tooth and casting which would increase retention and resistance to dislodgement. Perel &Muroff (1972) reported that dentine should not be sacrificed to be replaced by a cast core. Baraban (1967) recommended that remaining dentine should be well supported, and criticized the practice of removing coronal tooth structure to the level of the gingival margin prior to the provision of post and core restorations.
Although recommendations based on clinical experience have been made, little scientific evidence has been reported on the advantages of retaining sound coronal dentine. Ina photoelastic study, Henry (1977) found that stress transmission to the root became more favourable as coronal dentine was retained and stress concentration at the shoulder reduced. Hunter & Flood (1989a,b) agreed that incorporating sound dentine as part of the core increased cast core retention and reduced stress transmission to the root. Retained coronal dentine can also increase post length, improve retention and give resistance to rotation of the post and core (Mckerracher 1981). However, the effect on the strength of the restored tooth is more difficult to assess. In fact, Patel & Gutteridge (1996) concluded that retained coronal dentine would not strengthen a tooth restored with a cast post and partial core, reporting that retained buccal coronal dentine significantly reduced the fracture strength of samples in vitro. In conclusion, most authors agree that retaining sound coronal tooth structure has benefits in terms of retention and improvements in stress distribution, but the effect of preserving coronal dentine on the strength of the teeth restored with post and core restorations requires further investigation. The aims of this study were:
- To investigate the effect of retained sound coronal dentine on the strength of teeth restored with cemented post and partial core restorations under direct loading.
- To investigate the effect of different heights of residual coronal dentine on the strength of the teeth restored with a cemented post and partial core restoration.
- To observe the pattern of fracture and mode of failure of the teeth and restorations.