Choosing the ideal crown for your implant can be difficult. Our Master Implant Program can help guide your decision on which is best for your patient. Here at ARIA, we’ll go through the three main types: cemented, screw-retained and cross-screw.
Cemented crowns directly adhere onto the implant’s abutment. This makes their force distribution passive, potentially reducing crown fracture risk. (Al‐Omari, Shadid, Abu‐Naba’a, & Masoud, 2010) (Jivraj & Chee, 2006). No visible screws also enhance aesthetics. Successful placement requires 6-8mm of inter-arch space, and for aesthetics the abutment margin should be sub-gingival anteriorly.
Cement choice can be difficult; it should be strong enough to retain the crown, while weak enough that it allows crown retrievability. Realistically this can cause complications. Weak cement can lead to debonding at inopportune moments, and potentially patient harm and dissatisfaction. On the other hand, a stronger cement reduces the ability for retrievability. Excess cement may also cause peri-implantitis, and improper seating can lead to malocclusion. Maintaining hygiene with such crowns can therefore be difficult (Pauletto et al., 1999).
We discuss such cases at our Melbourne and Adelaide courses. Therefore, while these are cheaper and simpler to place, cemented crowns are seldom recommended due to these serious complications.
Our specialist prosthodontist and periodontist lecturers usually advise these. The main benefits of screw access implant crowns are that they are retrievable, fit the abutment more precisely, and are suitable for limited inter-arch room. While there should be a minimum 4mm inter-arch space (Jivraj & Chee, 2006), it should realistically be 6mm. This still allows for placement of shorter crowns compared to cemented crowns.
The screw provides a strong connection to the implant, better suiting them to bridges and longer spans. Nevertheless, stress distribution is not as even as in cemented crowns, and thus crown fracture is more likely (Al‐Omari et al., 2010).
Retrievability, however, is a huge asset. The porcelain crown can be repaired if there is a fracture (Pauletto et al., 1999), or built-up if adjacent teeth undergo passive eruption. The underlying abutment screw can also be accessed and retightened, angle-corrected or cleaned as needed. Since the screw requires occlusal or lingual access, however, aesthetics is somewhat compromised, and limited access may make placement difficult.
Cross-screw implants are another screw-retained option with the similar benefit of retrievability. This involves two screws: one screw holds the abutment into the implant, while a transverse screw (the cross-screw) holds the crown onto the abutment. The cross-screw itself does not provide the sole retention for the crown, but does prevent its dislodgement along the path of insertion, and allows retrievability of the crown and implant abutment (Gervais, Hatzipanagiotis, & Wilson, 2008).
Drawbacks can include difficult or limited access, stripping of the cross-screw head, a bulky lingual surface, and continual loosening (Gervais et al., 2008). These also require at least 6mm of inter-arch space.
Abutments in this case are usually custom CAD/CAM or UCLA , in order to provide adequate thickness of metal and thus strength. Our specialist educators usually recommend these when there are angulation issues greater than 30 degrees.
Considering these factors for each individual case during the planning process improves chances of implant and crown long-term success. Let our clinical specialists help you in the process.
Images courtesy of Dr Praveen Nathaniel
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Al‐Omari, W. M., Shadid, R., Abu‐Naba’a, L., & Masoud, B. E. (2010). Porcelain Fracture Resistance of Screw‐Retained, Cement‐Retained, and Screw‐Cement‐Retained Implant‐Supported Metal Ceramic Posterior Crowns. J Prosthodont, 19(4), 263-273. doi:10.1111/j.1532-849X.2009.00560.x
Gervais, M. J., Hatzipanagiotis, P., & Wilson, P. R. (2008). Cross‐pinning: the philosophy of retrievability applied practically to fixed, implant‐supported prostheses. Aust Dent J, 53(1), 74-82. doi:10.1111/j.1834-7819.2007.00013.x
Jivraj, S., & Chee, W. (2006). Screw versus cemented implant supported restorations. Br Dent J, 201(8), 501-507. doi:10.1038/sj.bdj.4814157
Pauletto, N., Pauletto, N., Lahiffe, B. J., Lahiffe, B. J., Walton, J. N., & Walton, J. N. (1999). Complications associated with excess cement around crowns on osseointegrated implants: a clinical report. Int J Oral Maxillofac Implants, 14(6), 865-868.