Ultrastructure of cementogenesis as affected by growth hormone in the molar periodontium of the hypophysectomized rat

Are Cementoblasts a Subpopulation of Osteoblasts or a Unique Phenotype?

Experimental studies have shown a great potential for periodontal regeneration. The limitations of periodontal regeneration largely depend on the regenerative potential at the root surface. Cellular intrinsic fiber cementum (CIFC), so-called bone-like tissue, may form instead of the desired acellular extrinsic fiber cementum (AEFC), and the interfacial tissue bonding may be weak. The periodontal ligament harbors progenitor cells that can differentiate into periodontal ligament fibroblasts, osteoblasts, and cementoblasts, but their precise location is unknown. It is also not known whether osteoblasts and cementoblasts arise from a common precursor cell line, or whether distinct precursor cell lines exist. Thus, there is limited knowledge about how cell diversity evolves in the space between the developing root and the alveolar bone. This review supports the hypothesis that AEFC is a unique tissue, while CIFC and bone share some similarities. Morphologically, functionally, and biochemically, however, CIFC is distinctly different from any bone type. There are several lines of evidence to propose that cementoblasts that produce both AEFC and CIFC are unique phenotypes that are unrelated to osteoblasts. Cementum attachment protein appears to be cementum-specific, and the expression of two proteoglycans, fibromodulin and lumican, appears to be stronger in CIFC than in bone. A theory is presented that may help explain how cell diversity evolves in the periodontal ligament. It proposes that Hertwig’s epithelial root sheath and cells derived from it play an essential role in the development and maintenance of the periodontium. The role of enamel matrix proteins in cementoblast and osteoblast differentiation and their potential use for tissue engineering are discussed.

Periodontal disease in adults with untreated congenital growth hormone deficiency: a case-control study

AIM

The aim of this study was to investigate the possible associations between isolated growth hormone deficiency (IGHD) and periodontal attachment loss (PAL) in adults affected by congenital IGHD.

MATERIALS AND METHODS

Forty-five previously identified IGHD subjects were eligible for this study. The final study sample comprised 32 cases (gender:20M/12F; age:44.8 ± 17.5) matched for age, gender, diabetes, smoking status and income to 32 controls (non-IGHD subjects). Participants were submitted to a full-mouth clinical examination of six sites per tooth and were interviewed using a structured, written questionnaire. Periodontitis was defined as proximal PAL≥5 mm affecting ≥30% of teeth.

RESULTS

No significant differences were observed in the percentage of sites with visible plaque between IGHD and non-IGHD subjects (59.4% versus 46.9%, p=0.32). IGHD subjects had significant less supragingival calculus (31.3% versus 59.4%, p=0.02) and more bleeding on probing (71.9% versus 18.8%, p<0.01) than controls. PAL≥5 mm was significantly more prevalent (100% versus 71.9%, p<0.01) and affected more teeth (30.5% versus 6.7%, p<0.01) in cases than in controls. After adjusting for supragingival calculus, IGHD cases had a higher likelihood of having periodontitis than controls (OR=17.4-17.8, 95% CI=2.3-134.9, p=0.004-0.005).

CONCLUSION

Congenital IGHD subjects have a greater chance of having PAL.

Mouse molar dentin size/shape is dependent on growth hormone status

Growth hormone (GH) status affects dental development, but how GH influences tooth size/shape is unclear. Since GH affects dental epithelial proliferation, we hypothesized that GH influences the tooth crown and root dimensions. Dentin matrix dimensions were measured in longitudinal sections of decalcified first mandibular molars from 3 genetically modified mice: giant (GH-Excess) mice and dwarf (GH-Antagonist and GH-Receptor-Knockout) mice. GH status was found to influence crown width, root length, and dentin thickness. Analysis of these data suggests that GH influences both tooth crown and root development prior to dentinogenesis as well as during appositional growth of dentin. This is concordant with the expression of paracrine GH and GH receptors during tooth bud morphogenesis, and of GH receptors in the enamel organ, dental papilla, and Hertwig's epithelial root sheath during dentinogenesis. Based on prior studies, these GH morphogenetic actions may be mediated by the induction of both bone morphogenetic protein and insulin-like growth factor-1 expression.

Mouse cellular cementum is highly dependent on growth hormone status

Cementum is known to be growth-hormone (GH)-responsive, but to what extent is unclear. This study examines the effects of extremes of GH status on cementogenesis in three lines of genetically modified mice; GH excess (giant), GH antagonist excess (dwarf), and GH receptor-deleted (GHR-KO) (dwarf). Age-matched mandibular molar tissues were processed for light microscope histology. Digital images of sections of first molar teeth were captured for morphometric analysis of lingual root cementum. Cross-sectional area of the cellular cementum was a sensitive guide to GH status, being reduced nearly 10-fold in GHR-KO mice, three-fold in GH antagonist mice, and increased almost two-fold in giant mice (p < 0.001). Cellular cementum length was similarly influenced by GH status, but to a lesser extent. Acellular cementum was generally unaffected. This study reveals cellular cementum to be a highly responsive GH target tissue, which may have therapeutic applications in assisting regeneration of the periodontium.

Growth hormone induces bone morphogenetic proteins and bone-related proteins in the developing rat periodontium

The hypothesis that growth hormone (GH) up-regulates the expression of enzymes, matrix proteins, and differentiation markers involved in mineralization of tooth and bone matrices was tested by the treatment of Lewis dwarf rats with GH over 5 days. The molar teeth and associated alveolar bone were processed for immunohistochemical demonstration of bone morphogenetic proteins 2 and 4 (BMP-2 and -4), bone morphogenetic protein type IA receptor (BMPR-IA), bone alkaline phosphatase (ALP), osteocalcin (OC), osteopontin (OPN), bone sialoprotein (BSP), and E11 protein (E11). The cementoblasts, osteoblasts, and periodontal ligament (PDL) cells responded to GH by expressing BMP-2 and -4, BMPR-IA, ALP, OC, and OPN and increasing the numbers of these cells. No changes were found in patterns of expression of the late differentiation markers BSP and E11 in response to GH. Thus, GH evokes expression of bone markers of early differentiation in cementoblasts, PDL cells, and osteoblasts of the periodontium. We propose that the induction of BMP-2 and -4 and their receptor by GH compliments the role of GH-induced insulin-like growth factor 1 (IGF-1) in promoting bone and tooth root formation.

A histological study of the effect of growth hormone on odontogenesis in the Lewis dwarf rat

The effect of growth hormone (GH) on the dentition has been described in children with pituitary dwarfism where teeth fail to form; those that do form tend to be reduced in size and the eruption potential is diminished. The aim here was to examine the effect of GH on odontogenesis via molar development in Lewis (control), dwarf (Dw) and Dw GH-treated (Dw+GH) rats aged 3, 6, 9, 12 and 15 days. Dw+GH animals received a twice-daily dose (65 microg/kg) of GH which commenced at 2 days of age. Animals were killed, mandibles removed, processed to embedding in paraffin, sectioned and stained for histological examination of molar morphology during development. Variations in enamel mineralization and root development were observed. In 6-day-old animals, enamel mineralization was delayed in Dw and Dw+GH animals. Root initiation was evident at 6 days of age in controls but was not observed until 9 days of age in Dw and Dw+GH animals. At 12 days of age, maturation of enamel in Dw and Dw+GH animals remained delayed. By 15 days of age no variation in tooth development was evident. These data indicate that enamel mineralization is affected by the level of circulating GH in the rat. A specific deficiency of GH did not appear to delay bone resorption prior to tooth emergence.

Net-shaped hydroxyapatite implants for release of agents modulating periodontal-like tissues

Periodontal-like tissues and, in particular, alveolar bone- and root cementum-like material can theoretically be modulated by release of biochemical agents such as bisphosphonate (PCP), growth hormone (GH) and alkaline phosphatase (ALP) from the implant surface. The present research focused on porous ceramic hydroxyapatite (PCHA) implants. In the past the PCHA implants were machined on a lathe out of simple blocks of PCHA ceramic. This was a tedious and cumbersome method, often resulting in implants with undesirable characteristics: different porosities, cracks and fractures. Therefore a moulding technique was developed to sinter near-net-shaped PCHA implants at 2 different sintering temperatures: 1170 degrees C and 1280 degrees C, resulting in PCHA implants with porosities of 62.06% (PCHA type 1) and 40.74% (PCHA type 2), respectively. After 1 h incubation in a 10(-2) M solution of PCP, the total amounts adsorbed onto PCHA type 1 and type 2 were 114.9 +/- 2.1 micrograms and 46.1 +/- 1.5 micrograms, respectively. This was approximately 5 times higher than after incubation for 1 wk in a 10(-4) M solution of PCP. The total amounts of PCP released after the observation period of 75 d from PCHA type 1 and type 2 after incubation in the 10(-2) M solution were 103.1 +/- 1.8 micrograms and 42.8 +/- 1.5 micrograms, respectively. The total amounts released from type 1 and 2 after incubation in the 10(-4) M solution were 7.4 +/- 0.4 micrograms and 4.1 +/- 0.1 micrograms, respectively. After 2 wk of incubation in a liver/bone/kidney ALP solution the total amount of ALP adsorbed onto PCHA type 1 implants was 5039 +/- 412 mU/ml. The total amounts of ALP released were 4674 +/- 438 mU/ml and 53 +/- 20 mU/ml after 1 and 2 wk, respectively. The release of ALP was high at the beginning but slowed down thereafter. It was evident that despite the well-known high bonding affinity of PCP to HA the release of PCP occurred steadily, over a long period of time in vitro.

Dual X-ray absorptiometry for alveolar bone: precision of peri-implant mineral measurements ex vivo

The precision of measurements of minor mineral changes in alveolar bone mineral content (ABMC) and alveolar bone mineral density (ABMD) on implant surfaces was determined in small regions (0.03 +/- 0.005 cm2) using dual X-ray absorptiometry (DXA). Dog hemimandibles with alveolar processes containing 17 implants were studied ex vivo. The precision was expressed as the coefficient of variation in percent (c.v. %). The ultra-high resolution protocol was applied to the mesial, distal and apical subregions of each implant. The line spacing was 0.0254 cm and the point resolution was 0.0127 cm. The mean c.v. (%) +/- s.d. for the ABMC in the mesial, distal and apical regions were 0.42 +/- 17, 0.47 +/- 0.21 and 0.48 +/- 0.18, respectively. For the ABMD these values were 0.42 +/- 0.16, 0.47 +/- 0.19 and 0.48 +/- 0.16. For each region approximately 68% of the 17 c.v. values were distributed within 1 s.d. from the mean c.v. These results indicate that measurements are highly reproducible (better than 0.48%) and that there are no differences in precision between several peri-implant regions. Changes as small as 0.85% in ABMC and ABMD in small areas adjacent to implant surfaces are measurable with a confidence level of 95%. Therefore the DXA technique will be expedient for our research evaluating the efficacy of the ceramic hydroxyapatite implant releasing agents affecting or inducing alveolar bone- and root cementum-like materials on its surface.