How Many Implants for a Full-Arch Prosthesis?
There are staunch advocates for both sides of this debate. On one side of the extreme there are the minimalists who ask “What is the minimum number of implants that we can place?” The other side asks, “Why not place as many as possible just in case one fails?”
This picture is from a study by Rivaldo et al. 2012 at the Branemark institute in Brazil. They placed 3 implants in the mandible and followed an immediate load protocol. At 1 year out, they had a 98% survival rate: 98% and had a marginal bone loss similar to that of protocols including more implants.
If that is surprising, check this out:
This is from a Randomized Control Trial by Cannizzaro et al (2011). They compared the immediate load protocol of All-on-2 with the All-on-4.
At 1 yr out, they found…
- implant survival rate: 100% for both
- prosthesis survival rate: 100% for both
- no statistically sig diff in post-op complications
This evidence notwithstanding, you’ll understand if I’m not ready to start doing this type of treatment just yet. Perhaps it may be best to wait for longer term studies….
On the other side are those who would rather “be safe than sorry.” I’ve heard any arguments for overengineering, including:
- If one fails, there are more to fall back on
- Natural gingival emergence is more esthetic than porcelain gums
- Better hygiene access
And we all know that the All-on-Four technique has a significant amount of literature (and marketing) behind it. It cannot be argued that the technique doesn’t work.
Here’s some of the stats:
- Studies by Malo et al:
- (2015) 5 yr data
- Prosthetic Survival 100%
- Implant survival 95.5%.
- More mechanical complications for both arches restored with All-on-4, than single arch.
- (2011) 10 yr data (mandibular)
- Prosthetic survival 99.2%
- implant survival 94.8%.
- (2015) 5 yr data
- Systematic Review by Heydecke et al (2012) w/ 4-6 implants
- 5 yr prosthetic survival 97.5%
- 10 yr prosthetic survival 95%
- 5 yr prosthetic survival 97.9%
- 10 yr prosthetic survival 95.9
Also, an engineering study conducted at Stanford University by Brunksi et al (2014) found that “with respect to axial loads on implants, there is no significant benefit to selecting 6 rather than 4 as long as the 4 implants span the same arc length as the 6.”
I have had some All-on-Four cases where the distal implant fails. In this situation, what can you do? Do you destroy your final prosthesis and jerry-rig a connection to a new implant?
None of these philosophies is “absolute.” I don’t think that many of us would say we “always” place 4, 6, or 8 implants. The astute practitioner takes into considerations the many individual patient factors such as:
- parafunctional habits
- opposing dentition
- alveolar ridge width
- Anterior-Posterior spread attainable
Each approach has pros and cons. What is your philosophy? I encourage you to share your experiences or questions below.
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by the way…
You also got this type of “philosophy”… Where do you stand?