Factors to be considered in making the decision to use a post:
Many have stated that the main reason for placing a post is to strengthen the connection between the coronal build-up material or remaining tooth structure to the root portion of the tooth. In my opinion, that is only partially true. Additionally, the following potentially negative or positive factors should be considered in the decision to use a post. All of these factors should be observed before making the decision:

• Quantity of remaining tooth structure
• Quality of remaining tooth structure
• Remaining adjacent teeth
• Occlusion
• Planned restoration to be placed on the tooth

Quantity of tooth structure remaining
Some teeth have most of the coronal tooth structure remaining after endodontic treatment, and others have very little tooth structure remaining. What is the significance of the amount of remaining tooth structure? For simplicity, I’ll divide the discussion of remaining tooth structure into several categories, and I’ll list them in decreasing order of clinical success:

All of the coronal tooth structure present except the endodontic access hole.

If other negative factors (to be discussed later) are not present, such teeth usually do not require posts. After the endodontic procedure is completed, tooth colored resin-based composite should be bonded into the pulp chamber. These teeth usually continue to serve adequately as though they were vital teeth.

At least one-half of the coronal tooth structure remaining

This situation is one of the most common. Assuming the remaining coronal tooth structure does not have any of the negative characteristics discussed next, the occlusion is not heavy, and there are other teeth contiguous with the one being treated, this tooth may not need to have a post. The coronal tooth structure can be built up, usually with retentive resin-based composite build-up material, to provide additional retention for the subsequent restoration, and these teeth have excellent potential to serve uneventfully. However, if other negative factors are present, it is prudent to place a post. 

Quality of remaining tooth structure
Assuming that there is a significant amount of coronal tooth structure remaining, the quality of the remaining tooth structure should be considered. Often, remaining tooth structure has discoloured areas, slightly demineralised areas, cracks, undermined areas, or other negative characteristics. Removal of tooth structure with these characteristics allows a realistic and necessary appraisal of the amount of viable tooth structure remaining. After removing the affected areas, the same suggestions stated in the previous section on quantity of tooth structure remaining apply. Posts are often indicated.

Remaining adjacent teeth
If an endodontically treated tooth stands alone without adjacent teeth present, it will receive significantly more occlusal forces on it when compared to a tooth that has sound adjacent teeth. When restoring a tooth that has no or few surrounding teeth, it is appropriate to use a post or posts to augment the strength of the endodontically treated tooth, and to ensure that the remaining coronal tooth structure is strongly connected to the root portion.

Occlusion
One of the most important factors relative to the question of post placement in an endodontically treated tooth is the nature of the patient’s occlusion. Patients with bruxing or clenching habits place far more stress on teeth than those patients with normal occlusion. Usually, bruxers move their mandibles in left-right and forward-back movements, grinding off canine rise and incisal guidance. Enormous lateral stresses are placed on the teeth of these patients. Clenchers place forces in an apical direction with intense load and frequency. A logical decision is to place posts in bruxing and clenching patients.

Planned restoration to be placed on the tooth
An endodontically treated tooth planned to receive a single crown has minimal stress when compared to a tooth that is planned to be an abutment for a fixed prosthesis or an abutment for a removable partial denture. If an endodontically treated tooth is expected to have significant load placed on it in service, posts should be placed.