The natural history of the helicoidal occlusal plane and its evolution in early Homo

In modern man the pitch of the occlusal plane may vary along the tooth-row. When anterior cheek-teeth show a plane sloping upward palatally, whilst that on posterior cheek-teeth slopes upward buccally, there results a twisted or helicoidal occlusal plane (Ackermann). Several hypotheses have been proposed for the structural basis of the helicoidal occlusal plane. Campbell's proposal ('25) has gained widest acceptance, namely that the helicoid results from anteroposterior differences in upper and lower alveolar arch width. In the early 1960s, while studying the Olduvai hominids assigned to Homo habilis, the author noted changing occlusal slopes along the tooth-row and a slight helicoid, although these featues had not been noted in other early hominids. Subsequently, Wallace showed a total absence of the helicoid from South African australopithecines, and its presence in Swartkrans Homo, SK 45 and SK 80. Recent studies confirm the presence of the helicoid in all available specimens of H. habilis, including Stw 53 found at Sterkfontein in 1976. Hence, this trait may distinguish between Australopithecus and early Homo. Measurements of the maxillary arch widths have shown that, whereas in Australopithecus arch widths increase to a maximum at M3, in early Homo maxillary arch widths are greatest at M2. The decline in posterior maxillary arch width is part of a general reduction of that region. Thus despite striking elongation of premolars and M1 in early Homo, M2 and M3 are mesiodistally abbreviated. It is hypothesized that the onset of posterior arch reduction, with the appearance of a helicoid, was a structural and functional concomitant of the transition from the presumed australopithecine ancestor to H. habilis.     

Intersession reliability of a posturo-stabilometric test,using a force platform

Aim of the studyTo evaluate the intersession reliability of a posturo-stabilometric examination.MethodsSingle blind clinical trial conducted in two sessions over two weeks.44 healthy volunteers free from postural and temporomandibular disorders. All the subjects complied with the criteria for completing the study.All the subjects underwent two sessions of posturo-stabilometric examinations in different visual and mandibular conditions.Sway area, sway length and the coordinates of the center of pressure were evaluated and statistically analyzed using the Intraclass correlation coefficient (ICC).ResultsAll the posturo-stabilometric parameters seemed to have an excellent reproducibility with overall ICCs higher than 70% and good confidence intervals except for the sway area (ICC 0.422 with CI 0.283–0.560 with open eyes and ICC 0.554 with CI 0.424–0.683 with closed eyes).ConclusionsThe posturo-stabilometric examination carried out using a force platform has a good intrasession and intersession reliability, especially considering sway velocity, COP X and COP Y parameters. The force platform usefulness in analyzing static posture is confirmed in any medical field.     

Patterns of dental wear in the Lengua Indians of Paraguay

Wear patterns were examined on dental casts of 202 living Lengua Indians from the Chaco area of Paraguay. Consideration was given to the development of the molar helicoidal plane, age-related changes in occlusal attrition, coalescence of dentine exposures, interproximal attrition, and erupted crown height. This study lends support to Osborn's theory of the helicoidal plane development by showing that attrition enhances rather than modifies posteruption molar occlusal planes. The rate of interproximal attrition was found to slow down with the eruption and functional initiation of the third molars. Sinuous and cavo-convex interproximal contact areas that are generated with age, however, appeared to be less abrasion resistant than straight surfaces, hence leading to an increase in interproximal attrition rates with advanced age. Maximum crown height reduction occurred between the ages of 20 and 40 years in central incisors, canines, and first molars. Kruskal-Wallis tests and log linera models failed to demonstrate significant sexually dimorphic or antimeric differences in wear patterns of Lengua teeth.     

Protonmotive force driven 6-deoxyglucose uptake by the oral pathogen,Streptococcus mutans Ingbritt

Streptococcus mutans Ingbritt was grown in glucose-excess continuous culture to repress the glucose phosphoenolpyruvate phosphotransferase system (PTS) and allow investigation of the alternative glucose process using the non-PTS substrate, (³H) 6-deoxyglucose. After correcting for non-specific adsorption to inactivated cells, the radiolabelled glucose analogue was found to be concentrated approximately 4.3-fold intracellularly by bacteria incubated in 100 mM Tris-citrate buffer, pH 7.0. Mercaptoethanol or KCl enhanced 6-deoxyglucose uptake, enabling it to be concentrated internally by at least 8-fold, but NaCl was inhibitory to its transport. Initial uptake was antagonised by glucose but not 2-deoxyglucose. Evidence that 6-deoxyglucose transport was driven by protonmotive force (p) was obtained by inhibiting its uptake with the protonophores, 2,4-dinitrophenol, carbonylcyanide m-chlorophenylhydrazine, gramicidin and nigericin, and the electrical potential difference () dissipator, KSCN. The membrane ATPase inhibitor, N,N¹-dicyclohexyl carbodiimide, also reduced 6-deoxyglucose uptake as did 100 mM lactate. In combination, these two inhibitors completely abolished 6-deoxyglucose transport. This suggests that the driving force for 6-deoxyglucose uptake is electrogenic, involving both the transmembrane pH gradient (pH) and . ATP hydrolysis, catalysed by the ATPase, and lactate excretion might be important contributors to pH.Abbreviations DNP 2,4-dinitrophenol - CCCP carbonylcyanide m-chlorophenylhydrazone - DCCD N,N¹-dicyclohyxyl carbodiimide - p protonmotive force - pH transmembrane pH gradient - transmembrane electrical potential difference     

Initiation of acellular extrinsic fiber cementum on human teeth

Summary The development of acellular extrinsic fiber cementum (AEFC) has never before been studied in human teeth. We have therefore examined the initiation of AEFC in the form of a collagenous fiber fringe and its attachment to the underlying dentinal matrix, in precisely selected, erupting human premolars with roots developed to 50%–60% of their final length. Freshly extracted teeth were prefixed in Karnovsky's fixative, decalcified in EDTA and subdivided into about 10 blocks each, cut from the mesial and distal root surfaces, vertical to and along the root axis. The blocks were postfixed in osmium tetroxide, embedded in Epon and cut for light- and electron-microscopic investigation. Starting at the advancing edge of the root, within a region extending about 1 mm coronal to this edge, fibroblast-like cells were seen closely covering the external root surface. Along the first 100 m from the root edge, these cells extended cytoplasmic processes and contacted the dentinal collagen fibrils. Between these cells and the dentinal matrix, new collagen fibrils and very short collagen fibers gradually developed. Within the second 100 m from the root edge, this resulted in the formation of a cell-fiber fringe network. Newly formed fibers of the fringe were directly attached to the non-mineralized matrix containing dentinal collagen fibrils and could be distinguished from the latter by differences in fibril orientation. During the process of dentin mineralization, the transitional zone between the fiber-fringe base and the dentinal matrix, i.e., the future dentino-cemental junction, also mineralized. It is suggested that this fiber fringe is the base of AEFC, which later increases in thickness by fiber extension and subsequent mineralization.Abbreviations AEFC acellular extrinsic fiber cementum - AIFC acellular intrinsic fiber cementum - CIFC cellular intrinsic fiber cementum - CMSC cellular mixed stratified cementum - ARE advancing root edge - CP cytoplasmic process - D dentin - DCJ dentinocemental junction - E enamel - EBL external basal lamina - EC epithelial cell - EDTA ethylene diaminetetraacetic acid - ERM epithelial rests of Malassez - FF fiber fringe - HRS Hertwig's epithelial root sheath - IBL internal basal lamina - MD mineralized dentin - NMD non-mineralized dentin - OB odontoblast - PD predentin - PL periodontal ligament     

Occlusal variation in Australian aboriginals

Variation of dental occlusion around established norms has frequently been related to industrialized or modernized life habits. This tendency has been tested among samples (n = 48) of older (originally nomadic) and younger (settled and rationed) Australian Aboriginals. Although significant differences are found in incisor relation traits, tooth malalignment, and relative arch breadth, these are slight compared to some other studies of peoples undergoing one-generation dietary westernization. Reasons for this might relate to concomitantly subtle differences in diet or masticatory habits, genetic buffering, attrition gradient, tooth size, biased sampling according to tooth retention, or fluoride in water supplies.     

Hanuman Langur: Monkey of India

An apparently new type of dental wear pattern, lingual surface attrition of the maxillary anterior teeth (LSAMAT), has been found in 85% of 46 adult crania from a 3000–4200 BP Archaic site called Corondó near the Atlantic Ocean coast of Brazil. LSAMAT is associated with a high caries rate (60% of 77 adults; 11% of 1,219 permanent teeth) in what on archeologica grounds alone would be considered a mainly meat-eating population. It is suggested that both LSAMAT and caries resulted from eating some starchy plant like manioc.     

Influence of transmucosal height in abutments of single and multiple implant-supported prostheses: a non-linear three-dimensional finite element analysis

The aim of this study was to analyze the influence of three different transmucosal heights of the abutments in single and multiple implant-supported prostheses through the finite element method. External hexagon implants, MicroUnit, and EsthetiCone abutments were scanned and placed in an edentulous maxillary model obtained from a tomography database. The simulations were divided into two groups: (1) one implant with 3.75 × 10 mm placed in the upper central incisor, simulating a single implant-supported fixed prosthesis with an EsthetiCone abutment; and (2) two implants with 3.75 × 10 mm placed in the upper lateral incisors with MicroUnit abutments, simulating a multiple implant-supported prosthesis. Subsequently, each group was subdivided into three models according to the transmucosal height (1, 2, and 3 mm). A static oblique load at an angle of 45 degrees to the long axis of the implant in palatal-buccal direction of 150 and 75 N was applied for multiple and single implant-supported prosthesis, respectively. The implants and abutments were assessed according to the equivalent Von Mises stress analyses while the bone and ceramics were analyzed through maximum and minimum principal stresses. The total deformation values increased in all models, while the transmucosal height was augmented. The transmucosal height of the abutments influences the stress values at the bone, ceramics, implants, and abutments of both the single and multiple implant-supported prostheses, with the transmucosal height of 1 mm showing the lowest stress values.     

Endothelin-1 regulates the dorsoventral branchial arch patterning in mice

Endothelin-1 (ET-1), a 21-amino acid peptide secreted by the epithelium and core mesenchyme in the branchial arches as well as vascular endothelium, is involved in craniofacial and cardiovascular development through endothelin receptor type-A (EdnrA) expressed in the neural crest-derived ectomesenchyme. Here we show that ET-1(-/-) mutant mice exhibit a homeotic-like transformation of the lower jaw to an upper jaw. Most of the maxillary arch-derived components are duplicated and replaced mandibular arch-derived structures, resulting in a mirror image of the upper and lower jaws in the ET-1(-/-) mutant. As for hyoid arch-derivatives, the ventral structures are severely affected in comparison to the dorsal ones in the ET-1(-/-) mutant. Correspondingly, the expression of Dlx5 and Dlx6, Distalless-related homeobox genes determining the ventral identity of the anterior branchial arches, and of the mandibular marker gene Pitx1 is significantly downregulated in the ET-1(-/-) mutant, whereas the expression of Dlx2 and the maxillary marker gene Prx2 is unaffected or rather upregulated. These findings indicate that the ET-1/EdnrA signaling may contribute to the dorsoventral axis patterning of the branchial arch system as a mediator of the regional intercellular interactions.     

Genetic structure of a tribal population, the Yanomama Indians. XIII. Dental microdifferentiation.

Data are presented on the frequency of the following eight dental traits in 635 Yanomama and 65 Makiritare Indians: upper central incisor rotation or winging, shoveling of maxillary incisors, maxillary molar hypocone reduction, Carabelli's trait, mandibular molar cusp number, mandibular molar cusp pattern rotation of second lower premolar, and pattern of second lower premolar cusps. Yanomama dentition is unusual in the high frequency of six cusps on the mandibular molars. There is marked dental microdifferentiation between villages; significant agreement was observed between a matrix of pairwise "dental distances" based on six morphological traits and corresponding matrices based on 11 genetic systems and on geographic location.