Shmuel Shoshan

Gingival response to orthodontic force.

Orthodontic tooth movement is brought about by prolonged application of force on the attachment apparatus. This results in cellular and extracellular changes within the periodontium. As shown in numerous studies, tooth movement is achieved after the remodeling of alveolar bone and the response of the periodontal ligament to the mechanical force. Although gingival changes have also been found to be an important factor in the overall response, the effect of orthodontic tooth movement on the gingiva has been investigated to a lesser extent. Unlike bone and periodontal ligament, which regain their original structure after removal of force, the gingival tissue does not regain its pretreatment structure, a fact on which a hypothesis has been made that tooth relapse after removal of retention may be associated with changes in the gingiva. The present review summarizes available data on the effect of orthodontic force on collagen, elastin, and collagenase in the gingiva and its relevance to understanding the mechanism of tooth relapse.

The response of supraalveolar gingival collagen to orthodontic rotation movement in dogs

An orthodontically rotated tooth relapses toward its pretreatment position. Explanations for this phenomenon have been given after light microscopic studies, according to which it had been assumed that stretched supraalveolar gingival fibers pulled back the tooth and brought about relaxation of the stretched fibers. The rotational relapse, however, can be prevented by supraalveolar fiberotomy of the gingiva around the tooth. This investigation was initiated to reevaluate the validity of the hitherto assumed causes for the relapse, by obtaining ultrastructural data on the response of collagen fibers after orthodontic intervention. Lateral maxillary incisors in the dog were rotated with bonded fixed appliances. The teeth were divided into groups according to different orthodontic procedures. Scanning and transmission electron microscopic analyses were performed on gingival samples after proper processing. Analyses of the untreated control samples showed well-organized, parallel, and densely packed thick bundles of collagen fibers, interconnected with thin fibers. After rotation-followed-by-retention, the gingival fibers were torn, ripped, disorganized, and laterally spaced and of increased diameter. Thus it was concluded that all these patterns are incompatible with stretching. Also, an increased number of elastic fibers were seen in proximity to the torn collagen fibers. After gingival fiberotomy, most fibers resumed the appearance of the organized pattern of large fiber bundles similar to those seen in the controls.

Topically Applied Halofuginone, An Inhibitor of Collagen ~ Type I Transcription, Reduces Peritendinous Fibrous Adhesions Following Surgery

To test in vivo the effect of previously observed inhibition of collagen type I transcription by the plant alkaloid Halofuginone, deep flexor tendons of 12 chickens were severed and sutured, and Halofuginone was applied topically at the site of surgery. Intact tendons, and severed but untreated tendons served as controls. The effect of the treatment was assessed by histological, biochemical, and biomechanical examinations of the operated and intact tendons three weeks after surgery. The results indicated an almost complete absence of fibrous peritendinous adhesions in the histologic sections of the Halofuginone treated tendons. There was a statistically significant decrease in collagen contents of and in both force and energy required to pull out the Halofuginone treated tendons from their sheath, relative to the untreated controls. Halofuginone had no effect on the cellularity of the healing tissue. We conclude that Halofuginone is a potent inhibitor of fibrous peritendinous adhesions with potentially important clinical applications.

Inhibition of collagen breakdown by diphenylhydantoin

Gingival tissue obtained from diphenylhydantoin-treated patients was cultured in the presence of [14C]proline for 24 h. The radioactive medium was removed and the tissue cultured for three days more. DNA, protein, hydroxyproline, proline and radioactivity determinations in the tissue indicated increased cellular proliferation, increased collagen contents and decreased breakdown of collagen in the affected tissues. The media were assayed for dialyzable and non-dialyzable hydroxyproline contents. It was found that the media in which diphenylhydantoin tissues were cultured contained more than twice as much non-dialyzable hydroxyproline than the controls. It was concluded that diphenylhydantoin brought about a reduction in collagen breakdown thus explaining the accumulation of hydroxylated collagen in the tissue.

The Effect of Mechanical Force on mRNA Levels of Collagenase, Collagen Type I, and Tissue Inhibitors of Metalloproteinases in Gingivae of Dogs

Orthodontic force causes an injury to and subsequent degradation of the attachment apparatus, thus leading to the transposition of the tooth. The gingiva, however, is compressed and sometimes becomes hypertrophic with tooth movement and often shrinks after treatment. To study the effect of force on the gingiva, we applied orthodontic force in dogs and analyzed gingival tissues 1, 2, 3, 7, 14, and 28 days later as well as after removing the force. The effect of force on mRNA levels of collagen type I (col-I), matrix metalloproteinase-1 (MMP-1), and tissue inhibitors 1 and 2 (TIMPs) genes was analyzed by RT-PCR, and MMP-1 activity was determined by zymography. The results showed that force significantly increased both the mRNA levels of MMP-1 and its interstitial activity. After the removal of force, MMP-1 gene expression was significantly decreased. The results could partly explain the clinically observed shrinkage and adaptation of the gingiva during tooth movement. KEY WORDS: orthodontic force, MMP-1, gene expression.

The effect of cortisone on collagen synthesis in the secondary palate of mice

Abstract To measure the effect of cortisone on collagen formation in the secondary palates of foetal mice, [3H]-proline (Pro) was administered to the pregnant mothers and both the hydroxyproline (Hypro) contents and its specific activity were determined between day 15 and 15 1 2 of gestation. In the palates of the normal control animals, a significant increase in the Hypro contents was noticed at the time which demarcates the palatal closure in the embryo, while in the cortisone-treated mice a very slight change was apparent. The specific activities of both Pro and Hypro in the control animals decreased by 43.4 and 140.6 per cent, respectively, between day 15 and 15 1 2 . In the cortisone-treated animals, there was an increase in the specific activity of Hypro by 33.8 per cent and a decrease in that of Pro by 19.9 per cent at that time. The specific activity ratio of Pro/ Hypro was considerably higher in the palates of cortisone-treated animals than in the controls. It was concluded that incomplete closure of the secondary palate in mouse embryos, following cortisone administration to the pregnant mothers, may also be due to interference with the normal hydroxylation reactions during the biosynthesis of collagen polypeptide chains.

The effect of ascorbic acid on the cross-linking of collagen during its synthesis by cultured 3T6 fibroblasts

Abstract Since hydroxylysine has been shown to play a critical role in the intermolecular cross-linking of collagen and since the hydroxylation of lysine, like proline, is ascorbic acid dependent, it was argued that ascorbic acid deficiency should impair this type of cross-linking of collagen. This was tested in collagen newly synthesised in tissue culture by 3T6, a mouse fibroblast line. Ascorbic acid deficiency resulted in half the amount of hydroxyproline-containing material being laid down; this material was more salt soluble than the collagen from ascorbate-fed cultures, but behaved identically on disc gel electrophoresis, thus supporting the hypothesis that ascorbic acid affects the intermolecular cross-linking of collagen via certain hydroxylysine residues as well as affecting the hydroxylation of proline. Final proof must await the isolation of the cross-links.

Type I and Type III Collagen mRNA Levels in Kidney Regions of Old and Young Rats

Interstitial fibrosis is a common feature of renal aging. The steady-state levels of type I and type III collagen mRNAs as well as DNA, protein and collagen deposition were investigated in the cortex, inner and outer medulla of aged (22 months old) rats in comparison to young (5 months old) controls. Our data show that the cortex and outer medulla of old rats expressed significantly higher percentage of type I collagen mRNA compared to the respective regions in the young rat kidneys. Moreover, within the group of the old rats, the cortex expressed significantly higher percentage of type I collagen mRNA compared to the inner medulla whereas in the group of the young rats the expression was similar in all kidney regions. The ratio of extracellular collagen to DNA was significantly higher in the cortex, inner and outer medulla of old compared to young rats. The ratio of collagen to total protein, although showing a similar age-related difference, attained statistical significance in the cortex only. Thus, the present study indicates a close relationship between the expression of the mRNA for type I collagen, the major structural constituent of fibrotic tissues, and the deposition of collagen in both the cortex and outer medulla of the kidney. Moreover, the clear differences found between old and young rat kidneys can serve as markers for renal aging and might explain at least some of the kidney impairments caused by fibrosis during senescence.

Re-attachment of periodontal ligament by collagen in experimentally-induced alveolar bone dehiscence in dogs.

Fifty-four bone dehiscences were made in nine dogs by reflecting mucoperiosteal flaps on the labial aspect of lower and upper incisors and premolars and removing alveolar bone. One half of the dehiscences were treated with native enriched collagen solution (ECS) prepared from acid-soluble dog-skin collagen. Six weeks later, histologic sections were prepared from both the ECS-treated and untreated control sites. Re-attachment was promoted by the ECS preparation; there was arrest of epithelial migration apically and formation of new bone and cementum, as well as proliferation of fibrous connective tissue that became attached to the newly-formed cementum. This effect could be due to an influence of ECS on the chemotaxis of connective-tissue cells and to an anti-migratory (barrier) effect on gingival epithelium.

Enhanced healing of tooth-pulp wounds in the dog by enriched collagen solution as a capping agent

Abstract Pulpotomy was performed in 28 anterior permanent incisors of young dogs. In 18 the pulp chamber was filled with native enriched collagen solution and covered with dental wax. In 10, only dental wax was applied. The cavities were closed with silver amalgam. Pulp healing was followed histologically at 4, 7, 14 and 30 days. The collagen-treated pulps regenerated completely after 30 days when the controls were still inflamed.