Implications of Vertebrate Craniodental Evo-Devo for Human Oral Health

Food texture and vitamin D influence mouse mandible form and molar roots

Industrialization influenced several facets of lifestyle, including softer nutrient-poor diets that contributed to vitamin D deficiency in post-industrzialized populations, with concomitantly increased dental problems. Here we simulated a post-industrialized diet in a mouse model to test the effects of diet texture and vitamin D level on mandible and third molar (M3) forms. Mice were raised on a soft diet with vitamin D (VitD) or without it (NoD), or on a hard diet with vitamin D. We hypothesized that a VitD/hard diet is optimal for normal mandible and tooth root form, as well as for timely M3 initiation. Subsets of adult NoD/soft and VitD/soft groups were bred to produce embryos that were micro-computed tomography (μCT) scanned to stage M3 development. M3 stage did not differ between embryos from mothers fed VitD and NoD diets, indicating that vitamin D does not affect timing of M3 onset. Sacrificed adult mice were μCT-scanned, their mandibles 3D-landmarked and M3 roots were measured. Principal component (PC) analysis described the largest proportion of mandible shape variance (PC1, 30.1%) related to diet texture, and nominal shape variance (PC2, 13.8%) related to vitamin D. Mice fed a soft diet had shorter, relatively narrower, and somewhat differently shaped mandibles that recapitulated findings in human populations. ANOVA and other multivariate tests found significantly wider M3 roots and larger root canals in mice fed a soft diet, with vitamin D having little effect. Altogether our experiments using a mouse model contribute new insights about how a post-industrial diet may influence human craniodental variation.

Does the "Root Removal First" strategy prevent postoperative complications in the surgical removal of impacted mandibular third molars in the Pell and Gregory class C and horizontal position? - a randomized clinical trial

OBJECTIVE

To evaluate the clinical outcomes of the "Root Removal First" strategy in the surgical removal of impacted mandibular third molar (IMTM) in the class C and horizontal position.

MATERIALS AND METHODS

A total of 274 cases were finally included in the statistics. The positions of IMTM in the horizontal position were confirmed by cone-beam computed tomography (CBCT). Cases were randomly divided into two groups: the "Root Removal First" strategy was applied in the new method (NM) group, and the conventional "Crown Removal First" strategy was executed in the traditional method (TM) group. The clinical information and relevant data upon follow-up were recorded.

RESULTS

The duration of the surgical removal and the incidence rates of lower lip paresthesia in the NM group were significantly lower than those in the TM group. The degree of mobility of the adjacent mandibular second molar (M2) in the NM group was significantly lower than that in the TM group at 30 days and 3 months post-operation. The distal and buccal probing depth of the M2, as well as the exposed root length of M2 in the NM group, were significantly lower than those in the TM group 3 months post-operation.

CONCLUSIONS

The "Root Removal First" strategy can reduce the incidence rate of inferior alveolar nerve injury and periodontal complications of the M2 in the surgical removal of IMTM in class C and horizontal position with high efficiency.

TRIAL REGISTRATION

ChiCTR2000040063.

Medium-Term Effect of Treatment with Intra-Articular Injection of Sodium Hyaluronate, Betamethasone and Platelet-Rich Plasma in Patients with Temporomandibular Arthralgia: A Retrospective Cohort Study

Temporomandibular joint disorders are associated with pain and reduced jaw mobility. The aim of this study was to compare the long-term effect on pain of intra-articular TMJ injections of betamethasone, sodium hyaluronate and platelet-rich plasma. The sample was made up of 114 patients, who were randomly distributed into three groups at least three years ago and who achieved a total remission of pain after treatment. We found that the median number of months without pain was, according to each group, as follows: platelet-rich plasma: 33; sodium hyaluronate: 28; betamethasone: 19. Both platelet-rich plasma and sodium hyaluronate lead to significant pain-free time after treatment; when we compare bethametasone with the two other substances, it proved to be very ineffective.

Unexpected variation of human molar size patterns

A tenet of mammalian, including primate dental evolution, is the Inhibitory Cascade Model, where first molar (M1) size predicts in a linear cline the size and onset time of the second (M2) and third (M3) molars: a larger M1 portends a progressively smaller and later-developing M2 and M3. In contemporary modern Homo sapiens, later-developing M3s are less likely to erupt properly. The Inhibitory Cascade Model is also used to predict molar sizes of extinct taxa, including fossil Homo. The extent to which Inhibitory Cascade Model predictions hold in contemporary H. sapiens molars is unclear, including whether this tenet informs about molar initiation, development, and eruption. We tested these questions here. In our radiographic sample of 323 oral quadrants and molar rows from contemporary humans based on mesiodistal crown lengths, we observed the distribution of molar proportions with a central tendency around parity (M1 = M2 = M3) that parsed into 13 distinct molar size ratio patterns. These patterns presented at different frequencies (e.g., M1 > M2 > M3 in about one-third of cases) that reflected whether the molar row was located in the maxilla or mandible and included both linear (e.g., M1 < M2 < M3) and nonlinear molar size ratio progressions (e.g., M1 > M2 < M3). Up to four patterns were found in the same subject's mouth. Lastly, M1 size alone does not predict M3 size, developmental timing, or eruption; rather, M2 size is integral to predicting M3 size. Our study indicates that human molar size is genetically 'softwired' and sensitive to factors local to the human upper jaw vs. lower jaw. The lack of a single stereotypical molar size ratio for contemporary H. sapiens suggests that predictions of fossil H. sapiens molar sizes using the Inhibitory Cascade Model must be made with caution.

Timing of Mouse Molar Formation Is Independent of Jaw Length Including Retromolar Space

For humans and other mammals to eat effectively, teeth must develop properly inside the jaw. Deciphering craniodental integration is central to explaining the timely formation of permanent molars, including third molars which are often impacted in humans, and to clarifying how teeth and jaws fit, function and evolve together. A factor long-posited to influence molar onset time is the jaw space available for each molar organ to form within. Here, we tested whether each successive molar initiates only after a minimum threshold of space is created via jaw growth. We used synchrotron-based micro-CT scanning to assess developing molars in situ within jaws of C57BL/6J mice aged E10 to P32, encompassing molar onset to emergence. We compared total jaw, retromolar and molar lengths, and molar onset times, between upper and lower jaws. Initiation time and developmental duration were comparable between molar upper and lower counterparts despite shorter, slower-growing retromolar space in the upper jaw, and despite size differences between upper and lower molars. Timing of molar formation appears unmoved by jaw length including space. Conditions within the dental lamina likely influence molar onset much more than surrounding jaw tissues. We theorize that molar initiation is contingent on sufficient surface area for the physical reorganization of dental epithelium and its invagination of underlying mesenchyme.

Silver-Albumin Tissue Staining Protocol to Visualize Odontogenesis in Whole Embryos

Visualizing tooth organs from their earliest inception as they actually appear in three dimensions has, until recently, been difficult due to the technical obstacle of imaging these tiny, translucent, low-density embryonic craniodental tissues. Related to this obstacle, quantifying craniodental morphology has been confounded by the time consuming need to physically section and then digitally photograph and reconstruct these images of tissues into 3D volumes. Here we provide a simple solution in the form of an overnight silver albumin tissue stain for whole embryos. Because it is differentially absorbed by embryonic tissues, this stain generates the contrast needed to detect and visualize unmineralized dental tissues. Stained specimens can be scanned using either desktop or synchrotron micro-computed tomography systems, generating digital 3D datasets of whole embryos that can immediately be used to assess dental morphology and histology. Craniodental structures can then be measured with high precision and accuracy using 3D image analysis software.

Allometry predicts trabecular bone structural properties in the carnivoran jaw joint

Because overall cranial morphology-biomechanics linkage in carnivorans is significantly influenced by both feeding and non-feeding ecological variables, whole-skull mechanical performance measures may be less sensitive to feeding ecology than regional characteristics within the skull. The temporomandibular joint could be one regional characteristic that is highly sensitive to feeding ecology considering that this joint is used in prey capture, food processing, and experiences compressive loading during mastication. Through 3D model construction, 3D printing, and compression tests, morphological and mechanical performance measures were determined for the temporomandibular joint trabecular bone structure of 40 species representative of the phylogenetic and ecology diversity of Carnivora. Remarkably, the results indicate that relative fill volume, relative structural complexity, elastic modulus, and relative maximum compressive strength of trabecular bone structure are not significantly related to phylogeny or ecology. The results reveal that morphological and mechanical performance attributes of trabecular bone structure are primarily influenced by body size, and that positive centroid size allometry and positive body mass allometry are present for structural complexity. The lack of feeding ecological signal in dorso-ventral compressive loading of temporomandibular joint models indicates that carnivoran temporomandibular joint trabecular structures may not undergo significant differential remodeling as an evolutionary response to different mechanically demanding feeding tasks.

Part II: Temporomandibular Joint (TMJ)-Regeneration, Degeneration, and Adaptation

PURPOSE OF REVIEW

Elucidate temporomandibular joint (TMJ) development and pathophysiology relative to regeneration, degeneration, and adaption.

RECENT FINDINGS

The pharyngeal arch produces a highly conserved stomatognathic system that supports airway and masticatory function. An induced subperiosteal layer of fibrocartilage cushions TMJ functional and parafunctional loads. If the fibrocartilage disc is present, a fractured mandibular condyle (MC) regenerates near the eminence of the fossa via a blastema emanating from the medial periosteal surface of the ramus. TMJ degenerative joint disease (DJD) is a relatively painless osteoarthrosis, resulting in extensive sclerosis, disc destruction, and lytic lesions. Facial form and symmetry may be affected, but the residual bone is vital because distraction continues to lengthen the MC with anabolic bone modeling. Extensive TMJ adaptive, healing, and regenerative potential maintains optimal, life support functions over a lifetime. Unique aspects of TMJ development, function, and pathophysiology may be useful for innovative management of other joints.

Upper jaw development in the absence of teeth: New insights for craniodental evo-devo integration

In p63-null mice (p63^-/- ), teeth fail to form but the mandible forms normally; conversely, the upper jaw skeleton is malformed. Here we explored whether lack of dental tissues contributed to midfacial dysmorphologies in p63^-/- mice by testing if facial prominence defects appeared before odontogenesis failed. We also investigated gene dose effects by testing if one wild type (WT) p63 allele (p63^+/- ) was sufficient for normal upper jaw skeleton formation. We micro-CT scanned PFA-fixed p63^-/- , p63^+/- , and WT (p63^+/+ ) adult and embryonic mice aged E10-E14. Next, we landmarked mandibular (MdP), maxillary (MxP) and nasal prominences (NPs), and facial bones. 3D landmark data were assessed using Principal Component, Canonical Variate, Partial Least Squares, and other statistical analyses. The p63^-/- embryos showed MxP and NP malformations by E12, despite the presence of dental tissues. MdP shape was comparable among p63^-/- , p63^+/- , and p63^+/+ embryos. Upper jaw shape was comparable between p63^+/+ and p63^+/- adults. The upper jaw and its dentition both require p63 signaling, but not each other's presence, to form properly. One WT p63 allele enables normal midfacial morphogenesis; gene dose may be a target for jaw macroevolution. Jaw-specific genetic mechanisms likely integrate the evo-devo of dentitions with upper versus lower jaws.