Peri-Implant Bone Evolution

-E-  FUNCTIONAL OCCLUSION AND PERI-IMPLANT BONE LEVEL EVOLUTION

The aim of this chapter is to try to assess the impact of the load or the occlusal overload on the level of the peri-implant bone. It was first necessary to remove at best all the risks of infection around the implant and to compare the capacity of key concepts occlusal to balance and get atraumatic occlusal surfaces on implants. 

Then from two lines of implants, of same concept, to make a comparison of the evolution of the peri-implant bone between a group balanced canine protection and a second group balanced by simulating the actual chewing function. In order to know if there is really a correlation between the occlusal concept applied to an implant prosthesis and evolution of peri-implant bone level (Le Gall and Gall JPIO Jan-Feb 2016).

Fig. E17 A single implant on a lower second left bicuspid, showing an increasing bone level of 2,75mm, 44 months later. That is exceptional

 

 

 

 

 

OCCLUSION and BONE LOSS ON NATURAL TEETH

For occlusal schools bone loss can only be infectious, but can also be caused by a single traumatic occlusion. This statement is presumed but not actually proven.
For the Swedish School of Periodontology bone loss is still infectious. The occlusion is only a cofactor.
In periodontology, the role of occlusion in bone loss on natural teeth was discussed and challenged and ultimately brought to an infectious etiology, by the fact that polymorphic microflora is always present in the mouth and around the periodontal tissues and has a key role in bone loss. It was concluded that the natural teeth in the presence of a premature contact, there was always a microbial flora that was the primary etiology of bone loss. In fact this flora can be physiological or pathogen and the host response is of paramount importance in the installation of an infectious process or not. Practically it was not possible to prove that around a tooth, the presence of a suspected bone loss of occlusal origin, could exist in the absence of germs.

OCCLUSION and BONE LOSS ON IMPLANT

According implantologists, there are two possible local etiologies to explain the peri-implant bone loss:
The first is infectious, as periimplantitis reported or not the surface condition, the presence of permanent microgap responsible for infectious exudates, peripheral sockets … may be responsible for bone loss.
The second is the presence of occlusal interferences and overloads that may be solely responsible for the fracture of implant components and / or bone loss (Misch et al 2005, Chiba and all 1993 Frost 2004), since the lack of mobility and avoidance mechanisms, amplifies the consequences occlusal loads that are easy to relate to bone loss which is specific clinical aspect.

Fig. E18: In implantology, generally, a bone loss lesion in basket shape, is related to infectious origin (central X-ray), when a bone loss in V form is related to occlusal overload (Fig E20, left lower X-ray).

Studies show that loads of moderate intensity applied to the bone (total hip arthroplasty, orthodontics treatment, implantology) can cause bone loss, even in the absence of infectious germs (Chiba et al 1993, Frost 2003). Other publications show that low forces can stimulate and induce bone remodeling (Cowin et al 1991, Frost 2004). Misch (2005) found a direct relationship between occlusal trauma and bone loss around dental implants.

Fig. E19: In implantology forces exceeding 1500 microstrains (mst) can be responsible only for bone loss and those exceeding 10,000 to 20,000 mst may be responsible for bone fractures and implant components. Between 50/100 mst and 1500 mst there is stimulation and bone remodeling and below 50/100 mst, there is no longer any stimulation, therefore bone atrophy.

PREREQUISITES For a study on BONE LOSS or GAIN
The prerequisites for such a study is first to compare the levels of bone implants of same emergence profile and concept. The selected implants must have specific features and protocols of use that allow them to withstand and dissipate harmoniously chewing forces (Le Gall et al 2005), while eliminating the risk of infection to the best that can cause bone loss whose origin is not mechanical. In particular, all contributing factors mucositis and peri-implantitis, which can be related to:
➤The surface condition of the body and the emergence of the implant neck and shape:
–    In proscribing surface-processing too rough and porous, in the bone area of the implant neck. The surface condition of an implant depends on the scale at which it is observed, it is a fractal (Mandelbrot 1973): the more it is magnified, most irregularities occur. The balance of the microstructure must allow good bone attachment while controlling the risk of bacterial colonization.
–   By favoring on the neck of the implant at the transmucosal level or bone level, a machined surface but not polished as a miror, excluding rough surfaces,
–    By choosing an emergence of simple form which is easy to ensure hygiene by the patient and allowing optimal aesthetic results (watch mode effects of prosthetic components of complex shape whose effectiveness is questionable).
➤The lack of stability and leakproofness of the abutment-implant interface, by using:
–   An internal connection, strong, waterproof, by morse taper or related, so without any micro-gap at bone or biologic space level, responsible for bacterial contamination, away from any means of hygiene, and subject to bio-corrosion (Ektessabi, Mouhyi et al 1997). 
–   A remote connection of the bone by a transmucous neck (it could be suppressed now, by using a monobloc implant).
➤The leaking of the prosthetic connection:
–   Avoiding screw-retained prosthesis, with a non-functional unsightly screws on the occlusal face and whose prosthetic limit is subgingival and not waterproof, like for abutment. Bio-corrosion is present in the micro-gap (Ektessabi, Mouhyi et al 1997) and toxins leakage is also responsible for a permanent contamination of the peripheral mucosa with an increased risk of mucositis, peri-implantitis and bone loss.
–    By preferring the permanent sealing of the prosthesis, without occlusal screw, which enables optimum adjustment of the occlusion, with meticulous removal of excess subgingival cement. If the emergence neck is well designed without overhang, or rough surface, the cement is easy to eliminate and later, the prosthetic dismantling for cleaning-up  is no longer necessary. Therefore, the requirement of a close and scheduled maintenance is deleted for the patient.

Implants selected for this study, are one-stage implants. Their emergence flared head and neck, share the same patent, with a body almost similar:
– Straumann Sin Octa® is cylindrical. These implants have been used for a study, developed below, on bone level evolution (Akça et Çerheli, 2008).

– Zimmer SwissPlus® is slightly tapered. These implants are used in clinical practice in our office for over 15 years(Le Gall and Le Gall 2005, 2006).
The implants of these two brands are directly comparable. The only real difference is the occlusal concepts applied to balance occlusion, CPO and CR /-VS-/ Functional Occlusion.

Clinical study: Straumann® Implants
A clinical study of 2 years (Akça and Çerheli, 2008) compare the evolution of the bone level on 15 fixed restorations of 3 units on 2 implants with 34 fixed restorations of 3 units supported by one tooth and one implant, rigidly connected. Against all expectations they measured a significant bone level augmentation around the implants connected to natural teeth, and a decreasing bone level around the implants connected together. 

An other study (Lindh and al 2001) found similar results and not knowing how to interpret their results, the authors considered that any attempt of interpretation was speculative.

Fig. E20 Note the positive remolding of bone around the implant connected to a tooth, it is the opposite of what says the theoretical analysis. Conversely bone loss is observed around the implants connected 3 units bridges. For conventional concepts, it is inexplicable…

An attempt at interpretation can now be offered. The occlusal concept applied in these studies is the canine protection, with a high probability of the presence of incoordination chewing guidances or interference on the occlusal surfaces of posterior teeth.

In the case of bridges, connecting one tooth and one implant, two mechanisms can be retained without being able to specify their level of involvement: on the one hand the differential damping between tooth and implant which generates low forces on the implant neck, so stimulating for bone, where the bone gain. On the other hand, avoidance mechanisms generated by the mechanoreceptors of the natural teeth, that moderate the impacts on malocclusions.
Regarding implant supported restorations, mechanoreceptors are absent, the forces are poorly regulated and patients chew on malocclusions.  without control. The developed forces are stronger and responsible for bone loss (Chiba et al. 1994 Frost, 2003).

Fig. E21 These logical functional interpretations begin to prove that an approximate balancing of implant supported restorations can be dangerous to the long lasting of implants.

Clinical Study: SwissPlus® Implants
This comparative study has been published  in the 2016  January / February JPIO. You will find below several clinical cases of this study:

Fig. E22: Clinical case connecting a tooth and an implant . Before extraction bone was very resorbed around cuspid. Appeared missing buccal plate. At the implant insertion, none membrane has been used, only a bone substitute (tricalcium-phosphate) has been placed around. Six years later, look at the bone level improvement and the well balanced chewing guidances, the same day. None occlusal alteration has been done from the initial balancing. Light balanced occlusal forces are responsible for bone stimulation and the gain on distal face of the connected implant, similar to Akça result, but opposite to theoretical analysis expectations. Measurement:  13 Mesial 0s (0mm) Distal +2,15 threads (1,95mm) Average +0,97mm.

Fig. E23: Atraumatic functional balancing can be associated to positive bone stimulation 4 years later.
Right first lower molar. Immediate provisional crown in underguidance. Mesial 2,5t (2,25mm) Distal 3t (2,7mm) Average 2,48mm.
Second left bicuspid Immediate placement in extraction site with temporary crown: 35 Mes 2t (1,8mm) Dist 1,8t (1,62mm) Average 1,71mm.
Measurement reference: the last thread plus one, to avoid any overrating.

Fig. E24 Immediate placement in extraction site, consequently bone gain is  difficult to evaluate. In these cases the measurement reference is the last thread plus one, to avoid any overrating. Measurement: Mesial 1,3 thread (1,17mm) Distal 1,3t (1,17mm) Average 1,17mm. The real gain can’t be lower than 1,1mm.

 

Fig. E25:  General follow-up of the case: 26 years.  Immediate placement of a single implant in the extraction site of a central incisor. An immediate provisional tooth has been realized, without any occlusal contact and instruction to the patient to eat soft food on the lateral sectors during the first month

Fig. E26 Single implant replacing upper right central incisor. Follow-up documented: 3 years. Measurement: Mesial 1,1tr (1mm) Distal 1tr (0,9mm) Average bone gain 1mm. Note the bone densification

Fig. E27  Single implant Immediately placed in the extraction site of the first right lower bicuspid, with an immediate provisional restoration.The follow-up is only 20,5 months after placement and at this time bone adaptation is far to be finished. Measurement: Mesial: 1 thread (+0,9mm) Distal 1,3 t (+1,17mm) Average +1mm

Fig. E28 immediate placement in extraction site of first mandible molar. The follow-up is 16 months. Bone cicatrization is completed, but progressive adaptation is far to be finished. The measurement reference is the last thread plus one, to avoid any overrating.  Mesial 1,7t (+1,53mm) Distal 2t (+1,8mm) Average +1,7mm (13,5months)

This is a retrospective study of a randomized group of 30 patients and 40 single or two connected implants. Only one implant was connected to a natural tooth. The prostheses were all sealed and the cement was thoroughly cleaned. These implants were all placed and the prostheses balanced by both authors. The follow-up period ranges from 1 to 8 years. All the clinical cases illustrated above show an increase in the bone level and an improvement in its density, unexpected at the time of implant placement. The average bone gain is 1.33 mm with an average follow-up of 43.7 months. The general standard deviation is  = 1.51, indicating homogeneous, non-dispersed data. The average bone gain is high and significant.

The implications are interesting. They show that the remodeling is not limited to one year, for it continued for a long time, it’s similar for the bone density. They also point-out that if overloadings, or occlusal traumas, can result in bone loss, a well balanced loading is stimulating and result in bone augmentation. The occlusal faces must be finely balanced to maintain the occlusal forces in the stimulation range. The classical occlusal concept allows to balance, a reduced share of the functional envelope only, and is not capable of such results.
Moreover these bone results were obtained on a simple emergence machined titanium. Without any microthreads or switching platform, with a rough processing surface. One can question oneself about the real utility of these specificities, because in fact it’s occlusion balancing the real mechanical key of bone long lasting at the neck level, where transverse forces are concentrated.
Only the natural model of chewing function and swallowing, as a reference, allow to reach this level of balancing, a key condition to maintain and increase the level of the peri-implant bone.
Conversely the classical concept of occlusion must be abandoned in implantology, because its restricted possibilities make it dangerous for the implant perenniality. (the pdf of this article is available> publication>Dropbox link)

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