Characterization of the peri-implant epithelium in hamster palatine mucosa: Behavior of Merkel cells and nerve endings

Abstract

The purpose of this study was to investigate the relationship between Merkel cells and nerve elements during tissue regeneration after receiving dental implants. Golden hamsters were divided into 3 groups and titanium alloy implants were fixed in their left-side maxilla through the third palatine ruga. Animals were sacrificed at 1, 2, 3, 4, 5, 6, and 7 days after the implantation and tissues were characterized at the immunohistochemical and morphological levels. CK 20 and PGP 9.5 antibodies which react with Merkel cells and nerve fibers were used. Immunohistochemically, no CK20-positive Merkel cells were seen in the peri-implant epithelium throughout the 7 days. However, starting at day 4, PGP 9.5-positive nerve fibers appeared in the connective tissue, and by day 7, nerve fibers had invaded the more superficial layer of the peri-implant epithelium compared to the mucosa removal control group. At the electron microscopic level, the intercellular spaces of the regenerating epithelium in the mucosa removal control group were small. In contrast, intercellular spaces of the peri-implant epithelium tended to be wide and regenerating nerve fibers invaded those intercellular spaces. In both the mucosa removal control group and the implantation group, the basal lamina and connective tissues regenerated completely. However, clear Merkel cells containing neurosecretory granules were not observed. Taken together, our results indicate that Merkel cells in the hamster palatine mucosa do not regenerate in the peri-implant epithelium. However, regenerative nerve fibers seem to play essential roles as part of the defense and sensory systems around the peri-implant epithelium to compensate for the weakened defense mechanism.It is well known that Merkel cells play an important role in tissues as a sensory system for pressure (8,16,28). Previous studies have revealed that Merkel cells are widely distributed in human oral mucosal tissues including the lip, hard palate and mandibular gingiva (1, 13). A fundamental, ultrastructural study of rodent oral mucosa demonstrated that two types of Merkel cells, with dendritic or roundish shapes, are recognized. Most dendritic Merkel cells are free of innervations while the roundish ones are innervated (26). In addition, Merkel cell-neurite complexes are considered to be slowly adapting type I mechanoreceptors in the oral mucosa of the hamster cheek pouch (28,29).The behavior of Merkel cells after denervation has also been elucidated (22), the conclusion being that Merkel cells survive with normal density and appearance in the epidermis after denervation. A study of the behavior of Merkel cells and nerve endings after partial excision of the lip has shown that Merkel cells and nerve fibers are regenerated (25). However, there have been no reports on the behavior of Merkel cells and/or nerve endings in re-

Osseoperception in Dental Implants: A Systematic Review

“…Neurophysiological evidence is provided by a series of neurophysiological studies in animals and in humans to prove the tactile function of dental implants (Table ) . Neurological research suggests that the sensory cortex can reorganize itself extensively, by training of or losing afferent inputs, even after the critical developmental time of the brain has expired .…”

“…Neurophysiological evidence is provided by a series of neurophysiological studies in animals and in humans to prove the tactile function of dental implants (Table 2). 4,11,[35][36][37][38][39][40][41][42][43][44][45][46][47][48][49][50][51][52] Neurological research suggests that the sensory cortex can reorganize itself extensively, by training of or losing afferent inputs, even after the critical developmental time of the brain has expired. 52 Table 1 Psychophysical studies to prove tactile function of dental implants Author Type Purpose Summary Outcome Jacobs et al 23 Human study Influence of temperature and foil hardness on interocclusal tactile threshold 20 subjects were tested for their absolute threshold level (RL)…”

Perceptual Changes in the Peri-Implant Soft Tissues Assessed by Directional Cutaneous Kinaesthesia and Graphaesthesia: A Prospective Study

“…They may respond to pain, touch, and pressure. 15 When applying forces to osseointegrated implants in the jaw bone, the pressure build-up in the bone is sometimes large enough to allow deformation of the bone and its surrounding periosteum. Merkel cells are important in tactile function and they are normally found in both the oral mucosa and in the gingiva.…”

“…11 These sensory receptors are more frequently found in the anterior part of the mouth. 15 Yet, the functional role of the peri-implant innervation remains unclear and when focused on the kinesthetic function of the oral mucosa, no information is present to enable to differentiate peri-implant from periodontal soft tissues. 12 They demonstrate a lower sensitivity when localized on the ridge (crest) when compared with the vestibular areas, suggesting that receptor density is more important in the former.…”

Response of Merkel cells in the palatal rugae to the continuous mechanical stimulation by palatal plate

“…Merkel cells proliferate in the elongated rete ridges of the oral epithelium when inflammation occurs in the underlying connective tissue 28) , while another report purports to demonstrate that Merkel cells are incapable of undergoing mitotic division and regeneration 36) . Thus, Merkel cells diminished in number due to excessive pressure stress by a inappropriate denture base may not be restored, and must change during oral functions such as the sensory system and swallowing.…”