|Year : 2012 | Volume
| Issue : 1 | Page : 42-46
Kinesthetic ability with osseointegrated implants
Varun Dahiya1, Puneet Sharma2, Palwinder Kaur2
1 Department of Periodontics, D. J. Dental College, Modinagar, Uttar Pradesh, India
2 Department of Prosthodontics, Swami Devi Dyal Dental College, Panchkula, Haryana, India
|Date of Web Publication||24-May-2012|
D. J. Dental College, Modinagar, Uttar Pradesh
Source of Support: None, Conflict of Interest: None
| Abstract|| |
Least consensus is available on implant proprioception, which is the basis of restoring missing teeth with implants, in particular. This is the reason that implants are still not popular in many countries. If we understand the sensory motor function improvement with the implant-supported fixed prosthesis and removable restoration, we can inculcate the implants in our practice more routinely. In the present review many studies are critically evaluated to understand the phenomenon of proprioception for controlling the position and movement of the jaw. This is very important in adjusting the muscular movement accurately to maintain neuromuscular balance. Kinesthetic ability is a muscle memory that can result in precise jaw movements after the tooth loss. It is a proven fact that training can improve this muscle memory and coordination if the neural input is strong. Studies say that the removal of intra-dental and periodontal mechanoception accompanying tooth loss changes are the fine proprioceptive control of jaw function. It can influence the precision of magnitude, direction, and rate of occlusal load application, which can be detrimental to the stomatognathic tissues if not within the physiologic limits. If we provide implant-supported prostheses, which will improve proprioception as compared to tissue-supported prostheses, it will definitely improve the muscle sense and control.
Keywords: Dental implants, kinesthesia, neuromuscular control, osseoception
|How to cite this article:|
Dahiya V, Sharma P, Kaur P. Kinesthetic ability with osseointegrated implants. J Dent Implant 2012;2:42-6
| Introduction|| |
Molecular and cell biology has tremendously widened the present prospects of osseointegrated implants. Continuous research and clinical use of osseointegrated implants has given a new horizon to restorative dentistry. As tactile sensation is popular with periodontal ligament receptors, osseoperception is associated with endosseous innervations. Osseoperception describes the patient-reported feeling of increased perception to the load applied on to the osseointegrated implant retained prosthesis. This sensory function is important for implant acceptance in the oral physiology. ,, The techniques of restoring the missing part can be variable but until the patient accepts it nicely and is comfortable with the restoration, future prognosis cannot be decided.
Till date it is not clear how the neurophysiologic mechanisms that modulate jaw arrangement are associated with osseointegrated implants; however, patients with implant-supported prostheses definitely have better tactile discriminative capabilities and improved motor function compared with when they wear complete dentures. This type of functioning with the osseointegrated implant restoration avoids overloading to the oral tissues; although, their sensory and motor capabilities do not appear to match those of dentate individuals.
| Neurophysiology|| |
Periodontal neural receptors exert a negative feedback on maximal clenching forces. It is observed that jaw muscles are fatigue-resistant during repeated maximal clenching efforts. Researches show that the periodontal neural input is must for the jaw-muscle coordination and precise jaw movements.
Discriminative contraction of various masticatory muscles is necessary to move the mandible precisely. A highly refined neurological control system regulates and coordinates the activities of masticatory system. , The basic understanding of neuromuscular coordination is essential to understand the tooth contact.
Two major components of neuromuscular system are neurological structures and muscles. Information from the tissues away from central nervous system is transferred into CNS and on higher center of brain stem through sensory receptors. Once the information is evaluated appropriate action is taken. Higher centers then send impulses down the spinal cord to the efferent organs. Various types of sensory receptors are located in the tissues of masticatory system. The receptors which provide information regarding the position and movement of mandible and associated structure are called proprioceptors. Out of four receptors seen in masticatory system nociceptors are found in tendon, periosteum, joint fascia and subcutaneous tissues. Nociceptors are low threshold receptors specific to light touch and pressure. These receptors mainly function to monitor the position and movement of tissues in the masticatory system. When conditions exist that actually can cause injury, these receptors relay information to CNS and prevent injury to the stomatognathic tissues.
| Tactile Discrimination|| |
Tactile sensation is studied by many authors for comparison of implant-supported prosthesis, natural teeth and complete denture. Periodontal receptors have great role in tactile discrimination. There are two types of tactile discrimination Active and Passive.
Passive discrimination is dependent upon periodontal mechanoreceptors, which is assessed by applying force on the tooth. In the passive psychophysical discrimination, test of magnitude estimation is done where forces are applied to teeth and compared with the previously applied force. Implant-restored responses are compared with those of natural teeth; , although various studies have shown that there is no difference in sensitivity between natural teeth and implant-retained restorations. Karayannin found that passive discrimination is higher in implants almost 10 times than natural teeth.  (34N and 0.3N, respectively).
Active discrimination involves number of mechanoreceptors in teeth periodontium, jaw muscles, TMJ capsule and ligaments. Jacob found implant threshold is 50 times. Threshold for active discrimination is proven to be lowest for natural teeth (8 um), higher for implants (50 um) and highest for complete denture wearer (100 um). 
In case of natural teeth, periodontal neural receptors play tactile discriminative role. In complete denture therapy, mucosal receptors are the primary receptors that play role but they are not in direct contact with the prosthesis. As a result, the neural input sent to CNS is weak and patient cannot perceive fine tactile discrimination. In osseointegrated implants, other receptors take over this function, like receptors in the periosteum, remaining periodontal receptors, and mucosal receptors. Their neural endings are in close proximation with the implant in the osseointegrated sites. This type of connection will result in higher intensity neural inputs as compared to removable prosthesis and play role in precision in the jaw movements.
| Stereognosis Ability|| |
Stereognosis ability is to identify the objects of various shapes and sizes placed between teeth to know the discriminative ability without disclosing the identity of the object being placed. This ability decreases with age but the period of edentulousness does not influence this ability. PD and intradental mechanoreceptors allows for high degree of oral stereognosis.  With tooth loss this ability decreases. Still our neuromuscular system is maintaining in function either restored with Complete dentures or implant retained prosthesis. Mc Closkey proved that in absence of periodontal mechanoreceptors, Muscle spindles afferent take over supported by afferents from TMJ, mucosa and periosteum.  A comparison of teeth and implants confirmed the superior stereognostic ability of dentate individuals and reduction in that ability in both complete dentures and implant supported overdentures with the same degree. , Although on contrary many studies have proved that there is better stereognostic abilities with the Implant supported fixed prosthesis as well as overdentures. ,,
Stereognosis and osseointegration
Stereognosis is a function of both peripheral and central integrating process working together. It gives knowledge on daily functioning and measures sensory impairment because of presence of general and local pathology like tooth loss. A change in the oral cavity by means of partial or complete loss of dentition creates a change in the oral sensory function. In dentate individuals periodontal neural receptors and tongue plays important role in stereognosis. In complete denture wearers, it is observed that after removing the denture there is marked reduction in the stereognostic ability. Muller et al., Lundquist demonstrated even more improvement after rehabilitation with oral implants.  Jacob instead noted no significant difference in this ability with implant-supported fixed or removable prosthesis even when eliminating the involvement of tongue and lip receptors. ,
| Rationale of Incorporating Implant in Practice|| |
It is evident that some sensory mechanism is present in peri-implant environment. Either residual periodontal ligament or free nerve endings from the mucosal connective tissues, periosteum and mandibular bone are responsible for peri-implant proprioception. In the bone, myelinated and non-myelinated fibres are present in Haversian system and marrow spaces in histomorphometric analysis. It is noticed in various studies that nerve fiber density is more around the loaded implants than unloaded implants. ,,,,
Researches suggest that osseoperception is secondary to nerve ingrowth into remodeling bone, as controlled by neuropeptides such as calcitonin gene-related peptide. Osseoperception has been quantified using Vibrometry as a measure of neural sensory function, which is advantageous to dentists to incorporate implant in their practice more routinely. There is intriguing ongoing research work on osseoperception in Sweden and at the VA Healthcare Center, San Diego, and the University of California, San Diego, focusing on the relationship between nerve injury and remapping of the somatosensory cortex. Already, clinical studies have supported this way of practice in the clinics. ,,,
| Theories of Proprioception|| |
Based on the nerve stimulation or neural inputs, which change the jaw movement patterns, there are various theories suggested by different authors. These theories are beneficial to understand the implant-related osseoception [Table 1]. 
Suggests that periosteum may be a source of proprioceptive response. Mechanoreceptors, which are in the periosteum, are around the implants and send the proprioceptive impulses.  This theory is most acceptable but only few receptors are present in the periosteum, which may not suffice for the neural input that can result in precise jaw movements.
Postulates that occlusal load results in strain of bone that is interpreted by the cytostructure of osteocytes resulting in action potential generated in axons of adjacent Haversian systems. This theory was suggested based on the ingrowth of nerve fibers in the threads of the implant that is osseointegrated. This theory can be given weightage in terms of good neural inputs.
Associates these responses with muscle spindle and joint receptors that substitute for periodontal ligament of natural teeth. However, because these receptors are not in direct contact with the implants, these may not have role in better osseoceptive ability with osseointegrated implants. Also these receptors are functional even with removable prosthesis.
Suggests that bone in the regions adjacent to implant contains nerve fibers that may serve as sensory nerve response. This theory carries good support as far as intensity of neural input is concerned.
Linden and Scott
Postulates that following tooth extraction, although periodontal tissues breakdown and are absorbed, some PD receptors remain within the bone. Further responses can be recorded in the trigeminal mesencephalic nucleus following electrical but not mechanical stimulation of the bone. These receptors can also play major role in jaw muscle coordination, but one cannot decide that the extraction was atraumatic and remaining periodontal receptors were not damaged.
Documented that reinnervation in association with controlled forces directed to implants occur that result in proprioception. ,, This theory got the maximum support because it is fact that loaded implants show better proprio ception than immediate non-functional implants. The reason could be that with physiologic loading, osseointegration is near to woven bone with the development of new nerve fibers around the implant.
| CNS Plasticity or Stomatognathic Kinesthesia|| |
Patient with altered somatosensory mechanism following tooth loss and restoration with implant-supported prostheses instead of complete dentures may develop a new intraoral environment by selectively attending to specific orofacial afferent information and the functional accommodation to new prosthesis. Implant-supported prosthesis will cause a change in somatosensory input to brain that will be different from that occurring with complete dentures. Cortical areas will play role in focusing attention on the special sensory input from the orofacial mechanoreceptors and prepare the individual to accommodate to altered intraoral environment. As cortical representation of the trained hand is more complex than the untrained hand, it is quite possible that after removal of periodontal input and restoration with the implant-supported prosthesis, plastic changes occur in somatotopic map. These plastic changes may be directly associated with the individuals to accommodate to new prosthesis. ,, The extent of changes in the cortical area depends upon the specific treatment and individual orodental characteristics. That is why some individuals experience more and some less difficulty in accommodating with the new prosthesis. It is a well-known fact that better the quality of the prostheses in serving function, form and esthetics, early will the somatomotor system adapt. So in a nutshell, closer the final prostheses come to restoring function, closer will the sensory motor system re-establish its original characteristics. 
| Factors Influencing Proprioception|| |
- Force: Sensory responses from peri-implant area may modulate jaw reflexes utilize occlusal pattern similar to natural dentition. As mentioned earlier, loaded implant show more proprioceptive responses than unloaded implants.
- Sex: Women have higher frequencies to muscle and temporomandibular-related signs because of constitution of female hormone to muscle pain. So females may show greater inadaptability to new prostheses but as such there are no marked gender effects on stereognostic ability or jaw function.
- Age: Temporomandibular disorders are more common in young age. However stereognostic ability declines with age. This could be because of the senile degenerative changes and lack of tissues regenerating power for proper osseointegration.
- Proprioceptive discriminative ability (dexterity): It is also a patient-related variable. There is some relation between masticatory performance and dexterity but it is not related to tactile function or stereognosis. 
- Experiment design: An assessment of interocclusal foil hardness and the influence of temperature were done. Foil at room temperature may serve as cold stimulus but with increase in temperature may cause stimulation because of pulpal thermosensitive units. The conductivity of material used in psychophysical tests varies significantly and influence foil temperature. 
| Clinical Implication of Implant-Mediated Sensory Motor Interaction|| |
If perception with the implant stimulation is working well, peripheral feedback may be restored and may help in tuning of the motor control and improve the kinesthetic ability of the stomatognathic system after the teeth loss. This implant-mediated sensory-motor interaction will help to achieve a more natural function with the bone-anchored prosthesis. ,,, This type of coordinated function can only be seen with the gradual healing period and it does not come immediately. This is important when we plan for the immediate loading of implant-retained prostheses. So in the immediate loading implants, the patient perception to closer to natural occlusal function may not be achieved; rather tactile perception gradually increases. So if we plan to do the immediate loading, patient should be encouraged to limit the chewing forces during the healing period. Parafunctional habits can be bad for the implant healing, so bruxism and clenching are the contraindication for the immediate loading protocols. ,
When dental implants are loaded mechanically, a sensation called, osseoperception, is evoked. The sensory signals underlying this phenomenon are qualitatively different from the signals evoked when loading a natural tooth. In contrast with osseointegrated dental implants, natural teeth are equipped with periodontal mechanoreceptors that signal information about tooth loads. Patients with implant-supported prostheses have improved tactile discriminative capabilities. The patients with implant-retained prostheses show improved kinesthesia as compared to those wearing complete dentures although those sensory motor abilities do not match the dentate individuals. With the loss of periodontal and dental mechanoreceptors, other peripheral receptors dominate and provide the neural basis perpetual abilities of implant patients. It is proved that accurately designed implant-retained prosthesis being fixed to bone more closely resembles dentate situation. This type of prosthesis can restore optimal motor and sensory function of the masticatory system.
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