For clinics that do not have access to facilities and systems that enable them to produce immediate final teeth often use one of the two alternative methods:
Staged treatment with delayed fitting of teeth
This was the traditional way to do implants. After loss or removal of teeth, the implants would be surgically positioned under the gums and covered up. They would remain submerged for 3-6 months to allow for gum and bone healing to take place. A second surgery was then required to expose the heads of the implants, and only then the dentist or prosthodontist would commence the process of making the final teeth and connect them to the supporting fixtures.
What is the problem with the staged technique?
The main issue with this method is that a removable denture would typically be used during the healing phase, which can disturb the adaptation of the implants. The interim denture used during healing is often loose and its movement in function can traumatise the gum and break the seal causing ingress of bacteria and inflammation around the implants. The denture pressure also results in a concentration of force over individual implants causing micromovement or overload which tips the biomechanical balance resulting in bone loss and/or failure.
The staged procedure is appropriate for individual implants when replacing only one or two teeth, because pressure can be kept off the healing implants by alternative methods of temporisation, which are supported by adjacent teeth without impacting on the gum. However in full set replacement there are no teeth remaining to absorb the functional loads, and the size and looseness of the denture can result in a significant concentration of pressures on the implants during function, regardless of whether a soft liner is used.
Why do some clinicians still use this technique?
This technique is mostly popular with doctors or specialists who are trained in either the surgical component of the treatment or the restorative component of the treatment, but not both. As such the patient needs to move from the care of one specialist to another, and there is a loss of continuity and passage of time. This technique may also be used if the implant system is not suitable for immediate loading, or in cases where adequate stability of the implants could not be achieved at surgery, but in those situations to avoid the issues mentioned above it is preferable that the patient does not wear a temporary denture.
Immediate loading using temporary teeth
Also Known as DENTURE CONVERSION TECHNIQUE
In the mid-late 90’s there was significant research into immediate loading – being able to connect the teeth to the supporting implants immediately or shortly after surgery without having to wear a removable denture described in option 1 above. Since then this concept has been well documented and supported in the literature.
To enable immediate loading there are a number of pre-requisites that must be fulfilled:
- the surgeon and the restorative dentist would need to work together during the operation, unless the one person is trained in both streams; and,
- the implants must be stable at surgery – this depends on technique and experience of the surgeon as well as on the brand of implants and available components; and,
- the teeth must be produced in advance or within a short timeframe from the surgery. The teeth are the structure that connect the implants to each other and allow them to work in a group and dissipate the functional loads, avoiding the concentration of force on individual implants.
The biological process of osseointegration is such that the old bone around the body of the supporting fixture is replaced with new bone that actually attaches to the surface. As the old bone is replaced there is a known phenomenon of relaxation (and a loss of stability) of the bone around the implants during the initial 3-4 weeks after surgery, before the stability is regained and improved over the subsequent 3 months.
Simunek A, Kopecka D, Brazda T, Strnad I, Capek L, Slezak R. Development of Implant stability during early healing of immediately loaded Implant. Int J Oral Maxillofac Implants 2012;27:619-27.
Sennerby L, Meredith N. Implant stability measurements using resonance frequency analysis: Biological and biomechanical aspects and clinical implications. Periodontol 2000 2008;47:51-66.
For the reasons above it is critical to immediate loading the prosthetic teeth are fitted onto the dental implants immediately or shortly after surgery, and then not removed for 3 months. This means that an additional level of sophistication and manufacturing system is required to be able to produce the teeth immediately unless they are produced in advance.
As it is not possible to determine the precise positions of the implants when producing the teeth in advance, the teeth are made like a denture with holes in the approximate positions of the implants in order to enable these dentures to be retrofitted and connected to the implants with glue-like acrylic material. This is called the Denture Conversion Technique.
What is the problem with the Denture-Conversion technique?
The main advantage of the denture conversion technique is that it is cheap to produce and requires a minimal setup or sophistication. It is literally making a denture and gluing it to the implants.
The disadvantages of this technique are as follows:
- Whilst the implants are connected to each other via the denture with the aim that they work in a group to dissipate functional loads, the connection using with a glue-like substance makes it unreliable, and any debonding or micro cracks can effectively detach one or more implants from the group and render the entire system ineffective and the implants subject to overloading;
- Since the denture is hollowed to accommodate the implant posts, it is weakened, so to avoid it breaking when attempting to fit it it is made bulkier. Added bulk means discomfort for the patient, but more importantly it makes it very difficult (or impossible) to clean around the implants, causing accumulation of food and plaque which leads to inflammation or infection by the time the patient is ready for the final teeth, often at a substantial additional cost, down the track.
Once there is overload (uncontrolled excessive pressure on individual posts), or inflammation or infections around the implants, even when the implants survive and are still partly encased in bone, the recession and soft tissue problems may be difficult to treat and may result in a cascade of problems even after the final teeth are eventually fitted. The known and potential biomechanical issues with the denture conversion technique were the primary reason for the development of the All On 4 Plus ® system and Immediate Final Teeth.
Why do some clinicians still use Denture Conversion technique?
Simply put, the denture-conversion technique is often used for no reason other than limitations in the facilities and the experience of the surgeon. Typical dental clinics do not have production facilities in-house.
The Denture Conversion method is also cheaper to produce and makes the initial price more attractive because of the often unaccounted future costs (and additional dental procedures) when eventually producing the final teeth.
In Summary, the denture conversion technique may appear to be cheaper initially, but there are often hidden costs, and also a biological cost that comes with potential complications to do with the unreliable connections and the rough and bulky surfaces.