Changes in the force--intrusion relationship of the tooth with its resting position in macaque monkeys

Biomechanical considerations on tooth-implant supported fixed partial dentures

This article discusses the connection of teeth to implants, in order to restore partial edentulism. The main problem arising from this connection is tooth intrusion, which can occur in up to 7.3% of the cases. The justification of this complication is being attempted through the perspective of biomechanics of the involved anatomical structures, that is, the periodontal ligament and the bone, as well as that of the teeth- and implant-supported fixed partial dentures.

A morphometric, electron microscopic analysis of tissue channels shown by ionic tracer in normal and tensioned rat molar apical periodontal ligament

A 1.0 newton continuous, extrusive load was applied to the right maxillary molar for 30 min to determine the presence of channels as shown by the distribution of tracer across the interstitial compartment of normal and tensioned PDL. Sodium ferrocyanide (1% w/v), perfused via the common carotid arteries, was the tracer probe and tris(ethylenediamine) cobalt III chloride (1% w/v) the precipitating ion. Left molar control PDL had an overall mean of 0.43 +/- 0.05/microns2 tissue channels at 0.2 microns from the vascular endothelium, and 0.15 +/- 0.04/microns2 at 7-8 microns. On the experimental side, the overall mean number of tissue channels was 0.65 +/- 0.13/microns2 at 0-2 microns and 0.19 +/- 0.07/microns2 at 7-8 microns. A significant depth effect (P less than 0.01) was present in the control and experimental interstitial tissues for tissue channels adjacent to the endothelium of different categories of vessel. Extrusion increased the tissue channel density adjacent to arterial capillaries (P less than 0.01), venous capillaries (P less than 0.01) and postcapillary-sized venules (P less than 0.01). These findings implicate these three types of vessel as being functionally important in fluid exchange across endothelial boundaries in the PDL.

Short-term extrusion of isolated teeth of adult monkey (Macaca fascicularis)

By means of a variable capacitance device, the occlusal movements of 12 fully-developed teeth were recorded in 6 adult monkeys. Sustained extrusion was seen, with rhythmic pulsations due to the heart beat and to breathing. Extrusion varied from 10 to 138 micrometers over periods of 40-360 min, and became progressively slower with time. Because of the protracted nature of the extrusion, it is probable that these tooth movements were caused by forces generated in the periodontal ligament resulting from biochemical changes in the periodontium rather than by vascular alterations, and occurred as a result of the removal of intrusive loads from the opposing teeth.

Changes in axial mobility of undisturbed teeth and following sustained intrusive forces in adult monkeys (Macaca fascicularis)

The axial mobility and changes in rest position were studied over 3-h periods. No loads were applied to 10 teeth. All displayed reduction in mobility; eight became extruded. Other teeth were displaced into their sockets to a sustained level by a screw for 3 h. Mobility decreased for those teeth which were intruded a distance equivalent to less than 800 mN force, but increased following greater intrusion. It is argued that vascular changes played no part; it is more likely that aggregation of proteoglycans occurred in the periodontal ground substance when there was little or no displacement of the tooth. Displacement would have generated tension in the collagen fibres of the periodontal ligament, leading to smaller proteoglycan molecules being formed and a consequent increase in mobility.

The influence of vascular beta-adrenoceptors on the position and mobility of the rabbit incisor tooth

The influence of vascular beta-adrenoceptors on the tooth-supporting functions of the periodontal ligament were studied in 30 anesthetized rabbits. Propranolol and the beta 2-adrenoceptor antagonists ICI 118,551 and H 35/25 induced a marked extrusion of the incisor, probably due to reduced vasodilator tone in periodontal postcapillary blood vessels. Isoprenaline reversed the movement. beta 1- and beta 2-receptor antagonists decreased the intrusive responses to sympathetic nerve stimulation in teeth close to control position, but had no effect on responses in fully extruded teeth. Intrusive mobility, as tested by intermittent loading with 5-10 g, remained unaffected by beta-adrenoceptor blockade. The results suggest that vascular beta 2-adrenoceptors are important in the regulation of tooth position by their control of periodontal postcapillary resistance. Prejunctional beta-receptors enhancing the vasoconstrictor--and intrusive--responses to sympathetic nerve stimulation are probably a mixture of beta 1- and beta 2-receptors. It would seem that the periodontal vasculature is important for the position of the rabbit tooth but, due to rapid adaptive mechanisms of the tooth-supporting tissues, the vasculature contributes little to the resistance against load-induced intrusive movements of the tooth.