-E- OCCLUSION PROCEDURES ON IMPLANTS
Depending of the clinical case and the implant line, some prosthetic procedures are identical to those of natural teeth (like intermaxillary relationship, vertical dimension, impression), some need an adaptation (like occlusal static and dynamic balancing, impression…), others are different (like management of implant componentry…).
Implant systems protocols, range from very easy and simple to the most complex, with a lot of prosthetic components, without any relation with the quality grade of the results.
Privilege simplicity, it’s rapid more efficient and less expensive…
Fig. E7 Aesthetic and well balanced implant restoration, on a first mandible molar, with an occlusal face similar to a natural tooth
Immediate placement of a full arcade provisional restoration on implants. Initial balancing is limited to obtain immediately after the placement, a maximum of simultaneous contacts, in maximum occlusion, which must be well distributed on the arcade with the same intensity. To do more, is difficult, because the patient is still on the dental chair from almost 4 hours. The patient is asked to eat soft food during 2 or 3 weeks. Later on the final prosthesis, occlusion should be balanced during chewing function and swallowing.
Fig. E8: On extended immediate prosthesis, the occlusal balancing can be improved, in the next appointments. The steps of the protocol to be followed for the final restoration are summarized above. It must be followed in this order.
Occlusal management of the final prosthesis begin by the choice of the vertical dimension and the recording of the intermaxilla relationship, using anterior jig in addition to optimal position of the tongue. Because our natural closure position is maximum occlusion during swallowing, which occurs more than 1000 times a day. That position is a support to realize oesophagus peristaltic movement which transfer bolus toward stomach.
Fig. E9: After an approximate approach and tests on the provisional prosthesis, the final choice of the vertical dimension is done on the framework. The procedure takes into account: tongue position, phonetic and swallowing tests, in addition to facial aesthetic and morphologic classical criteria. A deprogramming jig realized on the framework, is progressively adapted in height to the retained VD, before recording the VD relationship in swallowing posture.
For a fixed restoration, the recording of intermaxilla relationship obey to a very acute protocol. It must be taken preferably with a Moyco® wax heated-up in warm water to reach the consistency of softened butter. The patient must close without any resistance in the wax and without any occlusal pressure of the elevator muscles, to obtain the exact mandible position. If there is a resistance of the recording material, too hard, the prosthesis will be in posterior overcontacts. If the closure is realized with muscular pressure, the prosthesis will be in posterior infracontacts.
Fig. E10: A silicon occlusion material can also be utilized for the record. But these impression materials are very acute, if you have residual small bubbles, on the opposite model, the recording material won’t find its proper position on the model.
During the realization of a full arch restoration, the jig-tongue is a relevant protocol to determine vertical dimension and record intermaxillary relationship. Vertical dimension is determined by setting the height of the jig in addition to S phonetic pronunciation tests and several swallowing. Mandible-maxilla relationship is recorded then, using bilateral Moïco® wax strips.
Fig. E11: Use simultaneously two strips of wax, one on each side, to record relationship. These strips allow the tongue to move easily toward palate. If a full sheet of wax crossing the palate is used, the optimal positioning of the tongue, against palate become impossible.
At the placement of the restoration, the protocol jig-tongue is used to balance swallowing occlusion. A deflecting overcontact is detected on the right second molar (fig.E12b) It is carefully suppressed by subtraction. On the right picture, occlusion ofswallowing is well balanced then.
Fig. E12: The colored paper must placed simultaneously on the two sides. Its placement on one side only, will result in a displacement of the mandible toward the side where is placed, the occlusal paper.
Chewing function is then tested on a similar colored paper. A cycle-out over-guidance, is visible on upper second molar (left picture a). It is suppressed carefully. On central pictures (b,c), one can see now, guidances well balanced for a mastication on the the right side and then the left side. The last step consist to check incision. This work has been realized by a lab technician which knows well functional occlusion and consequently there are very few corrections. It’s very rare…
Fig. E13 The area corrected must be carefully polished. The case is then finished
IMPLANTS: GUIDELINES FOR BALANCING OCCLUSION
In the presence of a complete fixed restoration, on implants connected, the rules for occlusal balancing are identiques to those of natural teeth. Because of extensive restoration, the rigid connection allows sharing the occlusal load on the entire prosthesis, while reducing or eliminating the consequences of overhangs and cantilever, on the bone of the underlying implants.
But when natural teeth and implants coexist on the same arcade, there are two main problems:
Firstly: the implant has not resilient ligament like teeth, in these condition, the usual balancing protocol, when the implant, is osseointegrated in a well adapted bone, is following:
– with light occlusal pressure : the contacts on implants must be lighter than on natural neighbouring teeth
– with stronger occlusal pressure : swallowing and chewing contacts and guidances must be well balanced with natural teeth.
When an implant is osseointegrated in a good quality, or cortical bone, it is reliable to support and share all of the functional forces without any restrictions.
This procedure should take account of the own tooth mobility for each patient. If natural teeth have a great clinical mobility, it may be necessary to make extensive connections and/or to connect rigidly teeth and implants, or to treat as below:
Secondly: at the first balancing of an implant, in a not adapted or a bone of poorly quality, the aim is to have only light stimulation forces to favor a rapid bone adaptation, without any uncontrolled overloading, possibly responsible for bone loss.
Taking into account the natural wearing of teeth, this result can be obtained when at the end of balancing, 1 or 2 layer of thin colored paper, so 20 to 40µ, can slide between the implant and its opposites. The thickness of the film depends on the clinical mobility of the next and opposite teeth and It can need more than 2 layers in some cases.
Excluding wearings from pathological habits (like bruxism), and from biocorrosion, enamel “normal” wearing has been measured at an average bone loss in height of 122µm each 3 year (Lambretch et al), which represent 0,4mm on 10 years, and a 2mm loss of vertical dimension on a life period of 50 years. It’s not negligible, but it’s more important, in parafunctional habits like bruxism or when biocorrosion is present. When these loss concern all the arcades they are not compensated by an extrusion of the teeth (continuous growth is not existing in human teeth).
When a natural tooth has not any antagonist, it extruded progressively, with all of its periodontal and alveolar tissues. An arcade in occlusion with permanent occlusal stimuli don’ react in the same way. We know that augmentations of the vertical dimension, even moderately (lower than 5mm), are followed by an intrusion of the teeth, but without never come back to the prior situation. It is then highly probable that, during slow and progressive wears, there are neither teeth extrusion, nor intrusion.
Referring to natural wear, the fact to balance an implant restoration with very light occlusal contacts and guidances, allows generally to observe during the following year, a progressive come back in a shared and balanced occlusion, by the natural wear of the next teeth, and may be a light displacement of the opposite (ligament adaptability). This procedure allows a progressive loading and an adaptation of the peripheral bone implant , without any risk of overload.
The follow-up of occlusion has allowed to observe routinely this progressive come back in occlusion, in parallel to the bone reinforcing (next chapter), so supporting the validity of the procedure.
Fig. E14: When an implant is osseointegrated in a good quality or cortical bone, it is reliable to support and share all of the functional forces. It’s not the case at the time of first loading and balancing, in a poor quality or not adapted bone. The protocol is then different
On this fixed restoration on implants, classical lateral movement allows to see an interference on left second bicuspid. After correction, classical occlusal balancing is finished, because during laterality movement only the cuspid guidance is visible.
Fig. E15: During laterality movement, only a limited part of the functional envelope is checked. Only big a interference is detected and corrected A theoretical rule has been respected …
However, a chewing function test (center) shows totally uncoordinated and traumatic occlusal guidance. The cuspid protection (left) is not efficient during chewing function. Right picture shows coordinated guidances after balancing. Occlusal forces on implants are now well shared and not traumatic.
Fig. E16 : …but in fact, the functional guidances are not balanced. Only the chewing simulation, allows to reveal and balance functional envelope, revealing overguidances that can be corrected by subtraction (like in this case) or infraguidances that must be corrected by addition and need a come back to laboratory. Unfortunately the classical articulators have not the ability to reproduce chewing cycles kinetics, and the final adjustment must be done in the mouth of the patient. When balanced, the cycle found again its optimal pattern and not any overloads are transferred to the peri-implant bone, but only positive stimulations.
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