Implantable screw-retained crown
The main types of crown materials are either ceramic fused to metal or metal-free prosthesis like full zirconium crowns. The restoration is sent back from the laboratory as one piece for delivery; an intermediate try-in step is unnecessary especially when an accurate impression is taken. The following steps are presenting the clinical steps of the screw-retained crown delivery after receiving a full-ceramic zirconium crown from the dental laboratory:
DISCUSSION
The choice of a screw-retained versus a cemented crown is a decision that involves several points of consideration. The clinician should have good awareness regarding the advantages and disadvantages of using a screw-retained versus a cemented crown. Here are some factors the clinician should put in consideration when choosing which type to use:
Retrievability:
The main advantage of screw-retained crowns is retrievability. It is always nice to have the option to easily remove an implant crown or re-tighten the screw whenever it is needed without any damage to the restoration. In the case of crown loosening, crown fracture, screw replacement, implant assessment, and cleaning of the surrounding tissue, the crown can easily be removed. While the screw-retained crown is certainly retrievable, removing a cemented crown can be problematic particularly if full ceramic crowns are used.
Hygiene
Excess cement left behind cemented restoration is a major problem and can result in soft tissue damage, bone loss, and/or chronic inflammation; however, by removing cement thoroughly, the risk of leaving cement subgingivally that could cause peri-implantitis is reduced significantly.
Retention
Abutment height, degree of taper and surface area are all factors that affect the retention of cemented crowns. Abutment height is an important factor for proper retention. Longer abutment walls have more surface area,and are consequently are more retentive. At least 5mm of abutment height is needed for proper retention of cemented crowns. Because of this, screw-retained crowns are necessary in situations when limited inter-arch space dictates an abutment that would be shorter than 5mm.
Aesthetics
In screw-retained restorations, the access hole will exit through the central fossa of the prosthetic crown. The screw hole in prosthesis may compromise aesthetic, occlusion, and porcelain strength, especially if the diameter of the screw was wide. The cemented crown obviously has no entrance cavity. All-ceramic screw-retained crowns reduce the challenge of masking underlying discoloration from showing through the occlusal access opening once it is sealed by resin cement.
Accessibility
Placing a screw-retained restoration in a patient with a limited opening and/or in the posterior area of the mouth can be challenging if there is not sufficient space for the screw-driver to be inserted.
Screw loosening
Screw-retained restorations are associated with screw loosening complication especially in single crown restoration. The frequency of screw loosening is reported to be between 5% and 65%. Using a mechanical torque instrument to tighten the screw to a recommended torque level (20-30 Ncm) has greatly diminished this prosthetic complication. In a study simulating clinical settings, 60 dental students applied their maximum controlled torque to the head of a screw-driven, the mean torque value obtained by hand was 11.5 Ncm. In this way, the over-estimation of the hand-driven forces can be avoided. In Addition, re-tightening abutment screws 10 min after initial torque applications has been shown to increase stability and decrease screw loosening.
In a recent long-term systematic review conducted by Jung RE, Zembic A, Pjetursson BE, Zwahlen M, and Thoma DS, "The survival rate and the incidence of biological, technical, and aesthetic complications of single crowns on implants.", reported that survival of implant-supported single crowns was 96.3% after 5 years and 89.4% after 10 years. Technical complications reached a cumulative incidence of 8.8% for screw-loosening, 4.1% for loss of retention, and 3.5% for fracture of the veneering material after 5 years. No statistical differences were detected when comparing survival rates of screw-retained and cemented single crowns; there was no statistically significant difference between all-ceramic and metal-ceramic single crowns.
Another review, conducted by Pjetursson, reported that the survival rate of metal–ceramic implant supported fixed dental prosthesis was 96.4% after 5 years and 93.9% after 10 years. The most frequent complications over the 5-year observation period were fractures of the veneering material (13.5%), loss of access hole restoration (5.4%), abutment or screw loosening (5.3%), and loss of retention of the cemented prosthesis (4.7%).
CONCLUSION
When it comes to the restoration of implants, we typically have two treatment options: Screw-retained or cement-retained crowns. Although both treatment options can be used predictably, they have their own advantages and disadvantages; known retention, retrievability, re-tightening possibility, and the risk of not leaving residual cement are the main advantages of screw-retained crowns. While improved aesthetic outcome and better occlusion are the main advantages of cemented crowns, their main disadvantages are less retention and difficulty of removal.