RESTORATION OF BADLY BROKEN DOWN CARIOUS TOOTH
Meena Ranka*, Geera Modi*, Rohini Kharat**
*House Officer; **Unit Chief and Lecturer, Department of Dental Surgery, Seth GS Medical College and KEM Hospital, Mumbai, India.
Because of successful modern endodontic treatment many more teeth are retained today than formerly. However inadequate coronal restoration may reduce the length of time that such teeth remain as functional units. When root canal treated teeth must be removed the patient becomes disillusioned with the treatment programme. But restoration of endodontically treated teeth is complicated by the fact that much or all of the coronal tooth structure which normally would be used in the retention of restoration has been destroyed by caries, previous restorations, trauma and the endodontic access preparation itself. The dentist must employ the principle of substitution using posts or pins that are used to aid retention and to provide tooth support.
An 18 year old girl reported to the Out Patient Department of Dental Surgery with chief complaint of pain in lower left first molar. History revealed that patient had intermittent pain and food lodgement in relation to 36 since 2 months. Progressively patient was unable to take hot and cold food since last 5 days for which she had taken analgesics. On intraoral examination, a badly carious 36 with fractured distolingual cusp and gingival polyp extending from distolingual cusp region towards the centre of the tooth was seen (Fig. 1). An intraoral periapical X-ray showed radiolucency extending to the pulp. There was destruction of lamina dura around the mesial and distal root tips (Fig. 2).
Fig 1 : Badly carious 36 with fractured distal cusp and gingival polyp.
Fig. 2 : X-ray of 36 showing large radiolucent area extending to pulp chamber and loss of lamina dura around the root tips.
In view of severe carious destruction of 36 and young age of the patient it was decided to restore 36 rather than extract it. The patient was placed on anti-inflammatory, antibiotic drug regimen and the gingival polyp was excised under local anaesthesia with a bur and a proper gingival contour was achieved. An H2O2 wash and betadine dressing was given to control bleeding.
On second day under local anaesthesia, root canal was opened, pulp extirpation was done, biomechanical preparation started and a formocresol open dressing was given. After completion of biomechanical preparation, a diagnostic radiograph was taken and root canal filling was completed two days later. The post root canal X-ray showed well condensed root canal filling in relation to 36 (Fig. 3).
After two weeks, the patient was recalled and it was decided to give a post retained restoration to aid in retention of the post root canal restoration and to reinforce the remaining tooth structure. In view of the badly carious broken down distolingual cusp, a preformed threaded, parallel post with a tapered tip was selected for distal root canal. The parallel post with tapered tip was preferred because tapered post gives less retention and generates more stress. However, parallel sided post generates more stress in the apical area and so a tapered tip was chosen. The zincoxide eugenol cement was removed and the post hole was prepared. A long tapered diamond fissure bur was taken and access to the root canal was obtained. The gutta-percha filling in the distal root canal was removed, the length nearly matching the length of the crown to be restored (leaving approximately 4 mm of gutta-percha). This was done very carefully without damaging the endodontic seal, gouging or weakening the canal wall. The diamond bur was frequently removed during the procedure to check the direction of the progress. After this procedure, a radiograph was advised to determine the length of the prepared posthole in relation to the remaining distal root canal filling material. After viewing the radiograph, a post was chosen on the fact that it was as close fitting as possible but not too snug because this type of post distributes stresses evenly to the root and there are less chances of lateral distortion. The posthole was cleaned and dried for its full length with cotton wool on a barbed broach. The zinc phosphate cement was spun into the posthole with a lentulo and the post was also coated with the cement and seated (Fig. 4).
A composite restoration was done after removing the excess zinc phosphate cement and the original tooth anatomy was restored (Fig. 5).
Fig. 3 : X-ray showing well condensed root canal filling in 36.
Endodontically treated teeth have a number of special characteristics which demand particular attention during restorative treatment. Posts are normally used to aid core retention and to provide tooth support, although a significant minority question the use of posts in the latter role. A direct relationship is thought to exist between the quantity of sound tooth structure and tooth strength and care is required when preparing teeth to accept posts.
Fig. 4 : X-ray documenting cementation of post into the post hole made in the distal root canal.
Fig. 5 : Post root canal composite restoration of post retained 36.
Posts : The function of post is two fold
a) to retain prosthetic replacements for missing tooth structure and
b) to support or reinforce the remaining tooth structure.
It is considered that post placement will reinforce root-filled teeth by transferring load away from areas susceptible to stress concentration and by increasing their stiffness and resistance to bending.
Types : There is an enormous range of posts available. They may be custom made post either by free-hand waxing or based on a plastic burnout post, or they may be performed either cylindrical, threaded, smooth or serrated.
The most important indication for a custom-made post is for an irregular shaped root canal such as oval cross-section or variable taper. Where the root canal is regular the prefabricated post generally is preferred.
Post length : The length of the post must not be less than the length of the crown being restored. Recommendation of adequate length of gutta percha have ranged from 3 mm.[2-4] to 5 mm, but the recommendation to leave 4 mm. is considered to be most popular. On the basis of clinical studies, the longer post has better retention, because of the greater surface area in contact with dentine, and stress is distributed over a wider area reducing the chance vertical root fracture.
Post diameter : The actual post diameter is largely determined by the requirement that the post should fit the prepared root canal for a considerable portion of its length.
The other recommendations cited in the literature are:
1. The diameter should be not wider than 1/3rd the root width.
2. That at least 1 mm of sound dentine should remain around the circumference of the prepared post hole.
Post taper : Parallel sided posts are more retentive than tapered posts. The tapered dowel also generates greater stress than does parallel posts, showing a potential for splitting the root.
There is no universal technique suitable for the restoration of every badly carious tooth; however the Dentist should accept the challenge of preparation of an adequate tooth structure. The technique of employing posts to aid in retention is one of the preferred ways of restoration.
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