Screw Retained Versus Cement Retained Implant Parts
Posted on 07/27/2011
Although the parts listed in yesterday's blog (7/26/2011) apply to most situations, there are some parts which will vary depending on the final restoration type: screw retained versus cement retained. As listed yesterday, there are five parts required by the lab: (1) impression coping, (2) impression coping screw, (3) implant analog, (4) abutment, (5) abutment screw.
It is specifically part #4 - the abutment, that depends on the final restoration type. Here are the general rules of thumb:
1. Single Restoration - Screw Retained or Cement Retained: A single unit (non-bridge) restoration whether screw retained or cement retained requires an ENGAGING ABUTMENT. An engaging abutment is an abutment with an extension into the implant that "locks" into place. This secures the abutment in a specific position to avoid rotations.
2. Bridge - Cement Retained: A cement retained bridge also requires an ENGAGING ABUTMENT. This is because the abutment is separate from the crown, so the position of the abutment must be secure without consideration to the crown. If there is any path of insertion issue, this will be addressed through contouring the abutment and design of the crown. But the abutment itself cannot be allowed to rotate - and thus an "engaging" abutment is required.
3. Bridge - Screw Retained: A screw retained bridge requires a NON-ENGAGING abutment. A non-engaging abutment is an abutment that has no extension directly into the implant - i.e. it does not engage the implant. Essentially, it merely sits on top of the implant and is secured to the implant using the final abutment screw. The reason why a non-engaging part is used is because the abutment and crown are one single unit - which thus creates a severe path of insertion issue if it is bridged with other screw retained crowns. Essentially, with a screw retained bridge, no individual units should lock the others into place as the path of insertion is so difficult as to make it almost impossible to achieve a complete seating. As a result, the non-engaging part is used which will allow for a small amount of rotation of each abutment over the implant. Securing the abutments with the screw is sufficient to ensure retention.
It is specifically part #4 - the abutment, that depends on the final restoration type. Here are the general rules of thumb:
1. Single Restoration - Screw Retained or Cement Retained: A single unit (non-bridge) restoration whether screw retained or cement retained requires an ENGAGING ABUTMENT. An engaging abutment is an abutment with an extension into the implant that "locks" into place. This secures the abutment in a specific position to avoid rotations.
2. Bridge - Cement Retained: A cement retained bridge also requires an ENGAGING ABUTMENT. This is because the abutment is separate from the crown, so the position of the abutment must be secure without consideration to the crown. If there is any path of insertion issue, this will be addressed through contouring the abutment and design of the crown. But the abutment itself cannot be allowed to rotate - and thus an "engaging" abutment is required.
3. Bridge - Screw Retained: A screw retained bridge requires a NON-ENGAGING abutment. A non-engaging abutment is an abutment that has no extension directly into the implant - i.e. it does not engage the implant. Essentially, it merely sits on top of the implant and is secured to the implant using the final abutment screw. The reason why a non-engaging part is used is because the abutment and crown are one single unit - which thus creates a severe path of insertion issue if it is bridged with other screw retained crowns. Essentially, with a screw retained bridge, no individual units should lock the others into place as the path of insertion is so difficult as to make it almost impossible to achieve a complete seating. As a result, the non-engaging part is used which will allow for a small amount of rotation of each abutment over the implant. Securing the abutments with the screw is sufficient to ensure retention.
