Original study - ZZI 01/2009

Load distribution and loading concepts on teeth and implants

K. Tokmakidis1, B. Wessing2, K. Papoulia3, H. Spiekermann1

Tactile sensitivity and the function regulation of jaw movements with partially or completely implant-based restorations are very different and imprecise compared with the natural dentition. This systematic review shows certain correlations between the bite force and how the dentures are anchored. Twenty-two English and German publications were analyzed. The loads are three times higher on removable implant-borne prostheses and nine times higher on fixed single-tooth implant-borne restorations than on the natural dentition. This can lead to premature fatigue of the materials used, as well as to overloading of the implant abutments. This phenomenon can be reduced with the use of rigid materials (metal framework and porcelain veneering); splinting implants with natural teeth can also provide afferent feedback and thus prevent functional overloading. In regard to a satisfactory long-term prognosis, the type of splinting requires special attention.

Keywords: Dental implant-supported, dental implant splinting, bite load, bite force, overload, tactility

 

1 Introduction

Successful long-term integration of an implant-borne restoration in the stomatognathic system depends in part on optimal load distribution on the bearing tissue. Because of the different anchorage mechanisms of teeth (desmodontal suspension) and implants (osseointegration) there is a fundamental difference in the perception and control of the loading [7, 17, 19, 30, 33].

The masticatory bite forces are greatly influenced by mandibular kinaesthesia and neurophysical processes [1, 3, 5, 7]. Evaluations of the significance of periodontal receptors differ greatly.

Purely implant-retained prostheses are expected to show much higher loads than similar constructions on natural teeth. This suggests a correlation between the bite force employed and the fact that natural teeth (periodontal ligaments) were involved.

In association with extensive implant-retained restorations of both jaws carried out in the Department of Prosthodontics and Biomaterials in the Medical Centre of the University of Aachen (RWTH) differences were found from restorations largely periodontally retained or at least with natural teeth integrated into the restoration. In purely implant-retained restorations of both jaws there was an increase in material fatigue of every kind (ceramic chipping, severe abrasion in the case of acrylic teeth).

The aim of this systematic review was to analyze the available literature on this topic in order to find whether the tactile sensitivity of osseointegrated implants is markedly lower than that of natural teeth. In addition, recommendations are deduced as to whether it is useful to include natural teeth as tactile elements in implant-retained restorations for the above reasons.

The literature search was conducted with Ovid-Medline and PubMed. The date of the last search was 12.01.2007. The analysis included publications in English and German, which were found under the listed search words. Only journals were read which have at least one peer-review procedure as a criterion for acceptance.

 

Search words:

Biomechanical considerations, tooth-supported, implant-supported, mechanoperception, tactile sensibility, tactile sensitivity, finite element analysis, masticatory forces, implant loads, bite loads, chewing forces, occlusal force, bite force, occlusal perception, biomechanische Betrachtungen, zahngestützt, implantat-gestützt, Mechanoperzeption, Tastempfindlichkeit, Tastsensibilität, Finite-Element Analyse, Kaukraft, Kaukraftmessung, Implantatbelastung, Okklusalkraft, Beißkraft.

 

2 Basic principles

The tooth root and alveolar bone are joined in a syndesmosis by the periodontal ligament (PDL). The proprioceptors of the PDL are linked with the main sensory nucleus of the trigeminal nerve through the mesencephalic nucleus. These proprioceptors monitor the forces when biting and chewing and detect the tiniest obstacles to occlusion.

The PDL is particularly important for neuromuscular and tactile activity in the stomatognathic system as it is responsible for load perception [16, 56]. As early as 1970, Catton pointed out the neurophysiological tactility of the teeth and PDL [56]. There has been scientific interest in the tactile perception of intercuspidation since the 19th century [1, 6, 10, 12, 14, 16, 18, 21, 26, 27, 38, 45, 50–52]. Therefore, numerous experimental designs for measuring tactile sensitivity have been presented over the years.

It is thus beyond doubt that the periodontal receptors play a large part in sensing and distinguishing mechanical oral stimuli. The sensitivity and location of the periodontal receptors on the abutment teeth are altered by any prosthetic restoration because of the different distribution of force in the course of the body’s reaction [11]. Tactile sensitivity diminishes drastically in the case of tooth loss [13, 56].

Successful implant prosthetic restorations of the stomatognathic system require anatomical (osseointegration) and functional integration of the endosseous implant in the orofacial system. However, dental implants have no PDL and thus no periodontal tactility. Accordingly, this perception must be provided in other ways.

The CNS can receive information about the position and movements of the mandible as well as the force of the masticatory muscles through two mechanisms [19, 29]: the first mechanism is based on monitoring efferent muscle stimulation and thus monitoring the indicated afferent muscle force and tension from the central nervous system [19]. The second mecha-nism is calculated by the mechanoreceptors activated during mandibular movement in different mandible positions.

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