Ectocranial suture fusion in primates: pattern and phylogeny

Age estimation in the harbour seal (Phoca vitulina) based on the closure of skull sutures and synchondroses

Age estimation of individuals is an important tool for the management of marine mammals and is mostly done by microscopic analysis of growth layer groups (GLGs) in teeth (cementum and dentin) and bone. The present study evaluated the use of sutural and synchondrosal closure in the skull of the harbour seal (Phoca vitulina) as a potential non-destructive alternative for age estimation. For that, we scored the ectocranial closure of 12 selected sutures and synchondroses in a sample of 303 Eastern Atlantic harbour seals (P. v. vitulina; 138 males, 165 females), for which data on age at death were available, based on determined gross-morphological criteria in individuals younger than 1 year and cement layer analysis in canines in older individuals. A strong positive relationship between the sum of closure level scores (SCS) and age (males: r = 0.8797, females: r = 0.8825) was recorded, which was stronger than that for the relationship between age and condylobasal length (CBL, males: r = 0.7085, females: 0.7086) (all p-values <0.0001). In adult individuals (≥5 years), CBL was higher in males than females (p < 0.0001), while SCS did not significantly differ between the two sexes (p = 0.148). Our findings show that the analysis of sutural/synchondrosal closure is a valid alternative for age estimation in harbour seals, thereby confirming results of previous studies on other pinniped species.

Sagittal suture maturation: Morphological reorganization, relation to aging, and reliability as an age-at-death indicator

OBJECTIVES

The sagittal suture (SS) is assumed to be an initial site for the commencement of cranial suture closure as well as the most frequent spot of isolated craniosynostosis. The present study aimed to inspect the reorganization of the SS at the microlevel to assess the relation between its closure and aging and to establish whether it could be used as a reliable indicator in age-at-death prediction.

MATERIALS AND METHODS

The SS was investigated in 68 dry contemporary adult male skulls of known age-at-death. An additional series of 20 skulls was used for verification. The skulls were scanned using a micro-computed tomography system. The SS closure degree was assessed along the three bone layers on cross-sectional tomograms by using a scoring scale.

RESULTS

In the entirely open SS, the bone edges consist of compact bone and are widely separated. With SS maturation, the bone edges come into contact, and the remodeling process leads to a decrease in the sutural area and bone homogenization across all three layers. SS closure is an irregular process roughly related to aging, beginning in the early 20s, reaching its peak at about 30 years of age and abating in the late 40s.

DISCUSSION

Although related to aging, SS closure is not a simple function of it. Rather, the underlying factors inducing and managing this process are multifaceted and complex. Although the etiology of SS maturation remains unclear, it is reasonable to use SS closure cautiously and only as a supportive method for age prediction.

Intraspecific variation of the interparietal suture closure in Siberian roe deer Capreolus pygargus from Jeju Island

The sequence of cranial suture closure among cervids is reported to be generally species-specific and highly conservative within species. On the other hand, it is known that intraspecific variation often exists to some extent in other mammalian taxa. Here we studied the cranial suture closures of Capreolus pygargus from Jeju Island and compared it with other cervid species. We found that the timing of the interparietal suture closure is highly variable within C. pygargus. Capreolus capreolus similarly shows intraspecific variation of the interparietal suture closure, whereas other cervid species studied to date do not show any intraspecific variation in the sequence of cranial suture closure. Such high intraspecific variation of the interparietal suture may be a derived character for Capreolus.

Stretch force guides finger-like pattern of bone formation in suture

Mechanical tension is widely applied on the suture to modulate the growth of craniofacial bones. Deeply understanding the features of bone formation in expanding sutures could help us to improve the outcomes of clinical treatment and avoid some side effects. Although there are reports that have uncovered some biological characteristics, the regular pattern of sutural bone formation in response to expansion forces is still unknown. Our study was to investigate the shape, arrangement and orientation of new bone formation in expanding sutures and explore related clinical implications. The premaxillary sutures of rat, which histologically resembles the sutures of human beings, became wider progressively under stretch force. Micro-CT detected new bones at day 3. Morphologically, these bones were forming in a finger-like pattern, projecting from the maxillae into the expanded sutures. There were about 4 finger-like bones appearing on the selected micro-CT sections at day 3 and this number increased to about 18 at day 7. The average length of these projections increased from 0.14 mm at day 3 to 0.81 mm at day 7. The volume of these bony protuberances increased to the highest level of 0.12 mm³ at day 7. HE staining demonstrated that these finger-like bones had thick bases connecting with the maxillae and thin fronts stretching into the expanded suture. Nasal sections had a higher frequency of finger-like bones occuring than the oral sections at day 3 and day 5. Masson-stained sections showed stretched fibers embedding into maxillary margins. Osteocalcin-positive osteoblasts changed their shapes from cuboidal to spindle and covered the surfaces of finger-like bones continuously. Alizarin red S and calcein deposited in the inner and outer layers of finger-like bones respectively, which showed that longer and larger bones formed on the nasal side of expanded sutures compared with the oral side. Interestingly, these finger-like bones were almost paralleling with the direction of stretch force. Inclined force led to inclined finger-like bones formation and deflection of bilateral maxillae. Additionally, heavily compressive force caused fracture of finger-like bones in the sutures. These data together proposed the special finger-like pattern of bone formation in sutures guided by stretch force, providing important implications for maxillary expansion.

Osteoprotegerin deficiency results in disruption of posterofrontal suture closure in mice: implications in nonsyndromic craniosynostosis

BACKGROUND

Little is known about the role of osteoclasts in cranial suture fusion. Osteoclasts are predominantly regulated by receptor activator of nuclear factor kappa B and receptor activator of nuclear factor kappa B ligand, both of which lead to osteoclast differentiation, activation, and survival; and osteoprotegerin, a soluble inhibitor of receptor activator of nuclear factor kappa B. The authors' work examines the role of osteoprotegerin in this process using knockout technology.

METHODS

Wild-type, osteoprotegerin-heterozygous, and osteoprotegerin-knockout mice were imaged by serial micro-computed tomography at 3, 5, 7, 9, and 16 weeks. Suture density measurements and craniometric analysis were performed at these same time points. Posterofrontal sutures were harvested from mice after the week-16 time point and analyzed by means of histochemistry.

RESULTS

Micro-computed tomographic analysis of the posterofrontal suture revealed reduced suture fusion in osteoprotegerin-knockout mice compared with wild-type and heterozygous littermates. Osteoprotegerin deficiency resulted in a statistically significant decrease in suture bone density in knockout mice. There was no reduction in the density of non-suture-containing calvarial bone between wild-type and osteoprotegerin-knockout mice. Histochemistry of suture sections supported these micro-computed tomographic findings. Finally, osteoprotegerin-knockout mice had reduced anteroposterior skull distance at all time points and an increased interorbital distance at the week-16 time point.

CONCLUSION

The authors' data suggest that perturbations in the expression of osteoprotegerin and subsequent changes in osteoclastogenesis lead to alterations in murine cranial and posterofrontal suture morphology.

The effect of factors other than age upon skeletal age indicators in the adult

CONTEXT

Estimation of adult age from skeletal remains is problematic due to the weak and variable relationship between age indicators and age.

OBJECTIVES

To assess the proportion of variation in age indicators that is associated with factors other than age and to attempt to identify what those factors might be.

METHODS

The paper focuses on frequently used adult bony age markers. A literature search (principally using Web of Science) is conducted to assess the proportion of variation in age indicators associated with factors other than age. The biology of these age markers is discussed, as are factors other than age that might affect their expression.

RESULTS

Typically, ∼60% of variation in bony age indicators is associated with factors other than age. Factors including inherent metabolic propensity to form bone in soft tissue, vitamin D status, hormonal and reproductive factors, energy balance, biomechanical variables and genetic factors may be responsible for this variation, but empirical studies are few.

CONCLUSION

Most variation in adult skeletal age markers is due to factors other than age; dry bone study of historic documented skeletal collections and high resolution CT scanning in modern cadavers or living individuals is needed to identify these factors.