Dental implant treatment has greatly improved the level of care offered to patients. According to Misch 2015, implant retained prosthetics are usually installed by a means of intra oral cementation or by a screw-in method, that involves the extra-oral cementation of the abutment-prosthesis complex on a model.
The screw-in technique is commonly referred to as retrievable. It is implied that this installation process allows the prosthesis to be removed from the mouth and reinstalled without any critical damage to the prosthesis. It also implies that a prosthesis that is cemented intra orally is not easily retrievable and that it would have to be critically damaged during its removal.
No differences in complication and failure rates have been found in reviews that compare the two installation systems. The cited reviews indicate that 31- 33% of the fixed prostheses retained by dental implants are associated with mucositis, 10-16% peri-implantitis and that the survival rates of the implants are about 96% over five years and 92% over 10 years. The biological complications of treatment manifest themselves as peri-implant inflammation, exudate, loss of gingiva and supporting hard tissues. All these complications require treatment and can cause a “less than happy” experience for the patient and the dentist. Yes, treatment complications can be emotionally and financially taxing for all involved. The question is, “Can we reduce these complications?”
What is the main difference between the two installation systems? The main difference appears to be related to where the prosthesis is cemented to its’ abutment or abutments. In a traditional setting, the screwed-in prosthesis is assembled on a model that is not a precise representation of the mouth. This extra-oral assembly of the abutment-prosthesis complex thus forms an imprecise rigid structure that, when transferred to the mouth, causes a misfit at the implant-abutment junction. This misfit problem can be exacerbated by tight contacts with adjacent tooth structures, which also can prevent the abutment from seating fully onto its implant retainer.
A misfit at the implant-abutment junction is not optimized for stability and is also more susceptible to invasion by oral pathogens. This can create problems for the patient. These problems can include loose and broken screws, foul odour and taste, and the abovementioned complications including mucositis, peri-implantitis and implant failure. The misfit of the implant-abutment junction is a known risk factor for peri-implant disease. These complications can be difficult to mitigate because the implant-abutment misfit cannot be easily rectified. In addition, one must consider the possibility that uneven loading of an ill-fitting connection by the abutment screw tightening process and/or intraoral camera function could also cause damage to the adjoining components. It is possible to replace a damaged abutment, but how does one repair a damaged implant top? In conclusion, the major weakness of the screw-in prosthesis technique, appears to result from a misfit at the implant-abutment connection that is difficult to correct.
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