Case Conference Screw Retention vs. Cement Retention with Dr. Effie Habsha
January 16, 2017
Dr. Effie (Effrat) Habsha comes back with a new case conference.
If you have any questions, Dr. Habsha has kindly agreed to provide brief responses. Email Dr. Habsha at ehabsha@buildyoursmile.com
Highlights
In this short case presentation, Dr. Habsha discusses a situation that clinicians may encounter when following patients who have had implant restorations. Final implant restorations are either screw-retained or cement-retained. This case relates to a patient who presented with a loose cement-retained crown.
Two questions:
1. What importance do you attach to the replacement of the retaining screw prior to replacement? Screw loosening often occurs because of stretching of the screw. Some authorities have suggested that screw replacement is important in order to overcome problems that might occur as the result of using a deformed component.
2. Given that this problem is likely generated by stress, might you recommend a re-evaluation of the distribution and intensity of occlusal contacts, with a view to controlling the severity of forces exerted particularly in lateral excursions?
Thank you for engaging with CDA and the profession.
Dr. Habsha’s response:
Thank you for taking the time to watch the video and sending your questions! Please see my comments below:
1. In a situation where the screw comes loose after being in function for a while I recommend replacement of the screw. I concur with the suggestion that the retrieved screw may be distorted and should be replaced. A new screw offers the mechanical advantage of achieving optimum screw joint pre-load which is achieved when the screw is torqued into place. One can think of a screw as a spring, that is stretched by the pre load and the stretch is maintained by the frictional force in the threads. So the screw elongates when torqued. Once that connection is lost (due to a host of potential contributing factors) the screw distorts hence a new screw is recommended.
2. When dealing with a prosthetic complication such as a loose screw, one has to consider the etilogic factors. The potential reasons for abutment screw loosening include inadequate preload, excessive occlusal forces, inadequate occlusal support, inadequate occlusal scheme or crown anatomy, inappropriate implant position, variations in hex dimension, coupled with equal variations in the abutment counterparts, fit and accuracy of the restoration, tension on abutment and cylinder from ill-fitting restorations and improper screw design. So in this case, the lack of occlusal support and excessive occlusal contact likely contributed to screw loosening. Modifying occlusal load by adjusting the occlusal table and relieving centric and excursive contact is indicated. Furthermore, increased occlusal support by replacement of posterior teeth is indicated. This case demonstrates that proper treatment planning is essential to achieving predictable results.
A few articles pertaining to biomechanical implant complications are listed below:
1. Biomechanical implant treatment complications: a systematic review of clinical studies of implants with at least 1 year of functional loading. In J Oral Maxillofac Implants 2012 July-Aug;27(4):894-904
2. Int J Prosthodont. 2015 Mar-Apr;28(2):127-45. doi: 10.11607/ijp.3947. Screw- versus cement-retained implant prostheses: a systematic review of prosthodontic maintenance and complications.