Page 16 - SPRING 2016

To Screw or Not to Screw?

By Chanda Kale, DDS

The answer overwhelmingly is, “Yes,” in Europe and “reluc- F engaging design. The engaging screw-retained type has all the
Cast to gold engaging and non-engaging abutments.
tance” in North America. I find these answers surprising. advantages of an abutment, so you can play with emergence

However, I do understand “why” and therefore the reason for this profile, margins, and esthetics and have 100% retrievability.

F
Cast to gold engaging and non-engaging abutments.
article. I tried to fortify my position with an examination of some In the non-engaging, the main retention is the screw and the
studies on PubMed. When searching the term “screw-retained fixture does not engage the internal retentive connection at all.

implant crown”, I found 272 hits of which about 10-12 articles In the combination type, you are converting an implant from

were relevant to the topic, and with the term “screw versus an internal connection to an external connection with the use

cement-retained implant”, about 23 hits of which 4-5 were rele- of an extra transmucosal abutment such as the Tapered

vant. After a few more attempts, I came to the conclusion that any Abutment (Zimmer) or Multi-Unit Abutment (Nobel

aid from solid literature was not likely to support my hypothesis. 1 Biocare). The advantage is that the clinician can change the

emergence angle and also connect multiple units together for

Let us try to separate different scenarios to make sense of this
a screw-retained restoration.
dilemma. Your decision to use a screw or to cement is not a per-

sonal preference nor should it be. Every case should be thought 2. Anterior or posterior restorations: Screw-retained restorations

out on its own individual merits and needs. Let us look at factors (Figures 2, 3) have an access hole on the occlusal or lingual,

affecting this decision. but not on the buccal for obvious esthetic concerns. For pos-

terior scenarios, patients as well as clinicians, find the access
1. Single unit or multiple units
2. Anterior or posterior restorations
3. Morphology and dimensions of the bone
4. Esthetic case or non-esthetic case
5. Is it important for the clinician to be able to retrieve a case if
necessary?
6. Are you an implant surgeon or a restorative dentist?
We are being bombarded with “proofs” of how cement is destroy-
2
ing dental implants and how certain types of cements should
never be used. The fact is that a cement retained implant crown
2,3
is one of the easiest and most reliable methods of restoring Figure 2. Screw-retained #3 single crown.
Figure 2. Screw-retained #3 single crown.
implant-retained crown and bridge. There is no doubt that excess Figure 2. Screw-retained #3 single crown.
4
cement poses a risk for peri-implantitis and, at the same time, we
know a screw-retained case is the best scenario for retrieving a
case. So, how do we make a decision?
1. Single or multiple units: First of all, most of us may be famil-
iar with two types of screw-retained scenarios. However, there
are actually three: engaging, non-engaging and combination.
So, now we can do more with screw-retained prostheses than
earlier in implant dentistry. In addition, CAD/CAM technolo-
gy has made tremendous advancements so that we can deliv-
3
er quality restorations faster, cheaper (?), and with fewer com- Figure 3. Screw-retained #7 single crown.
Figure 3. Screw-retained #7 single crown.
plications. But let us just look at the engaging and non-engag- Figure 3. Screw-retained #7 single crown.
ing scenarios (Figure 1). The engaging screw-retained restora-
hole annoying and difficult to maintain. In anterior scenarios,
tion is the most desirable in my opinion, but it is only possi-
the access hole must be on the lingual and there are challenges
ble for a single restoration. Multiple units require the non-
to make that possible surgically. The first challenge is having
a conceptual idea how the implant emergence should be for
the prosthesis, and second, and most importantly, having
enough bone volume to make such a placement possible.
Again, CAD/CAM technology has aided us greatly in visual-
izing, as well as making it possible to plan a guided surgery.
In many cases, bone volume deficit can be overcome with
guided bone regeneration (GBR). However, any extra effort
obviously adds to the stress level to achieve success and try-
ing to keep the procedure affordable for the patient.

Cast to gold engaging and non-engaging abutments.
F Figure 1. Cast to gold engaging and non-engaging abutments.
www.nysagd.org | Spring 2017 | GP 16

Figure 2. Screw-retained #3 single crown.

Figure 3. Screw-retained #7 single crown.