Molar Cusp Research Articles

Dental morphology evolution in early peratheriines, including a new morphologically cryptic species and findings on the largest early Eocene European metatherian

ABSTRACT The initial stages of the evolutionary history of peratheriines, the European herpetotheriid metatherians, are largely unknown, primarily due to their limited morphological dental disparity throughout the Palaeogene, coupled with significant intraspecific variation. Based on eleven molars, we document a new early peratheriine species, Peratherium musivum sp. nov. which is larger than and morphologically similar to the earliest peratheriine, Peratherium constans (MP7). Subtle molar characters are shared with the largest early Eocene peratheriine, Peratherium maximum comb. nov. We illustrate the importance of studying possible changes in molar cusp – basin proportions and correlated characters that occured during peratheriine evolution. Peratherium musivum sp. nov. which spanned only part of the MP7-MP8 + 9 time interval, and the ~MP8 + 9 Peratherium maximum comb. nov. were probably widespread in Western Europe. The description of a well-preserved mandible of the latter, from La Borie (~MP8 + 9), reveals original features concerning relative size and shape of dental alveoli, partly corroborated using isolated molars. These traits are absent in the younger, most representative species of both peratheriine genera, Peratherium and Amphiperatherium. Based on the aforementioned data and a critical review, it is demonstrated that peratheriine genera lack consistent definitions, so that the Peratherium/Amphiperatherium dichotomy is plausibly inapplicable to early Eocene representatives. This article is registered in ZooBank under urn:lsid:zoobank.org:pub:A2B4DE58-855C-4CB8-BC1D-C9677E6DF97D

Monson’s sphere in Chinese young adult females with individual normal occlusion: a preliminary study using digital models

BackgroundThis study investigated the characteristics of Monson’s sphere in Chinese young adult females with individual normal occlusion to provide a reference for oral rehabilitation in prosthodontic and orthodontic treatments.MethodsPoints at the dental cusps and incisal edges were selected from 51 digital mandibular dental models of Chinese young adult females (aged 18–22 years) with individual normal occlusion. Monson’s spheres were fitted to the selected points based on the least-squares principle and the radii were calculated. The deviation of each selected point from its relative spherical surface was also calculated. The radii and deviations of these points were examined using conventional descriptive statistics and distributions of the most deviated points inside and outside the spheres were analyzed.ResultsThe mean radius of Monson’s sphere in Chinese young adult females was 79.60 ± 14.13 mm. The deviation of each selected point from its relative sphere surface was 0.38 ± 0.30 mm. The maximum deviations inside and outside the sphere were 0.93 ± 0.25 mm and 0.95 ± 0.30 mm, respectively. The most deviated points outside the spheres were mainly distributed at the distolingual cusps of the mandibular second permanent molars (31.37%), while those inside the spheres were mainly distributed at the mesiolingual cusps of the mandibular first permanent molars (45.10%).ConclusionsThe radius of Monson’s sphere in Chinese young adult females was smaller than the classic four-inch value suggested by Monson. Deviation was observed from all selected points to their Monson’s sphere surface, with the most deviated points distributed primarily in the molar region.

Testing the patterning cascade model of cusp development in Macaca fascicularis mandibular molars

ObjectiveMolar crown configuration plays an important role in systematics, and functional and comparative morphology. In particular, the number of cusps on primate molars is often used to identify fossil species and infer their phylogenetic relationships. However, this variability deserves renewed consideration as a number of studies now highlight important developmental mechanisms that may be responsible for the presence of molar cusps in some mammalian taxa. Experimental studies of rodent molars suggest that cusps form under a morphodynamic, patterning cascade model of development (PCM) that involve the iterative formation of enamel knots. This model posits that the size, shape and location of the first-forming cusps determines the presence and positioning of later-forming cusps. DesignHere we test whether variation in accessory cusp presence in 13 Macaca fascicularis mandibular second molars (M2s) is consistent with predictions of the PCM. Using micro-CT, we imaged these M2s and employed geometric morphometrics to examine whether shape variation in the enamel-dentine junction (EDJ) correlates with accessory cusp presence. ResultsWe find that accessory cusp patterning in macaque M2s is broadly consistent with the PCM. Molars with accessory cusps were larger in size and possessed shorter relative cusp heights compared to molars without accessory cusps. Peripheral cusp formation was also associated with more centrally positioned primary cusps, as predicted by the PCM. ConclusionsWhile these results demonstrate that a patterning cascade model is broadly appropriate for interpreting cusp variation in Macaca fascicularis molars, it does not explain all manifestations of accessory cusp expression in this sample.

Comparison of the Haas Expander and the Elastodontic Device for the Resolution of Transverse Discrepancies in Growing Patients: A Single-Centre Observational Study

Background: This study aimed to compare the clinical outcomes of using two different devices to treat upper palatal discrepancies evaluated with a digital intraoral scanner. Methods: A total of 64 patients were enrolled and treated with either an elastodontic expansion device (32 patient test group, 16 females and 16 males, mean age 7.08 ± 0.44) or Haas expander (32 patient control group, 16 females and 16 males, mean age 7.32 ± 0.50). The two groups exhibited similar orthodontic features. The orthodontic criteria were: skeletal class I relationship; molar class I relationship; complete eruption of upper sixths; presence of unilateral or bilateral cross bite. All dental casts were examined and subsequently scanned with an intraoral scanner (I-Tero) pre-treatment (T0) and 12 months after the onset of therapy (T1) to assess the distance between the decidous upper canines (ICW, intercanine width) and the distance between the mesiopalatal cusps of the upper first molars (IMW, intermolar width). For statistical analysis, the t-test for continous variables and the chi-square test for categorical variables were used, respectively. Results: There were no statistically significant differences between the mean and SD of the expansions that resulted from the Haas expander and the elastodontic devices (Haas expander vs. Eptamed: ICW_T1 (Haas) = 42.34 (3.09), ICW_T1 (Eptamed) = 42.69 (2.77); p = 0.743; IMW_T1 (Haas) = 34.22 (2.29), IMW_T1 (Eptamed) = 34.00 (2.56); p = 0.800). The two devices were similarly effective. Conclusions: Elastodontic devices and the Haas expander can successfully help the orthodontist to conduct upper arch expansion treatment. However, elastodontic devices are more comfortable during the resolution of palatal discrepancies compared to palatal expander devices.

Differences in Volumetric Tooth Loss for Monolithic Ceramic Crowns, Occlusal Overlays, and Partial-Coverage Onlays.

To compare the volumetric loss of clinical crown structure in commonly encountered clinical situations for monolithic ceramic crowns, occlusal overlays, and partial-coverage onlays. Typodont teeth made with preexisting mesio-occlusodistal (MOD) preparations for mandibular first molars and maxillary first premolars were prepared with three different preparations: a full-contour monolithic zirconia crown, a lithium disilicate occlusal overlay, and mesio-occlusodistobuccal/mesio-occlusodistolingual (MODB/MODL) lithium disilicate onlays for premolars and molars. 3D-metrologic software was used to evaluate the volumetric loss of clinical crown structure for each preparation type. Subsequently, the mesiolingual cusps of mandibular molars and buccal cusps of maxillary premolars were excluded for a separate analysis to simulate patient presentation with an existing restoration and sheared-off cusp. Full-coverage monolithic zirconia crowns removed 45.37 to 219.53 mm3 of the remaining clinical tooth structure, depending on the clinical scenario and tooth position, while lithium disilicate overlays removed 27.48 to 105.13 mm3 and MODB/MODL lithium disilicate onlays removed 5.48 to 47.45 mm3. In each scenario tested, MODB/MODL onlays removed significantly less clinical crown structure than overlays (P < .001); both MODB/MODL onlays and overlays removed significantly less structure than full-coverage crowns (P < .001). Monolithic zirconia crown restorations require significantly more removal of remaining tooth structure than lithium disilicate occlusal overlays and partial-coverage onlays for commonly occurring clinical situations requiring indirect restorations.

Three-dimensional molar enamel thickness and distribution patterns in Late Miocene Lufengpithecus lufengensis from Shihuiba, Southwest China.

Enamel thickness and distribution provide dietary insights in hominoids. Yet, three-dimensional (3D) enamel analysis of the Late Miocene Lufengpithecus from southwest China is lacking. We digitally reconstructed 68 unworn or lightly worn Lufengpithecus (L.) lufengensis molars using micro-computed tomography (micro-CT). Comparisons with modern humans, Homo erectus, extant/fossil Pongo, Pan, and Gorilla reveal L. lufengensis has "intermediate/thick" enamel, thicker than Pongo and Gorilla, but thinner than modern humans and H. erectus. In enamel distribution, relatively thicker enamel lies on the lingual cusps of the maxillary molars. The hypoconid, hypoconulid, and entoconid exhibit relatively thicker enamel compared to the metaconid and protoconid of the mandibular molars. L. lufengensis also exhibits an uneven pattern on the lingual and buccal walls. With relatively intermediate/thick enamel and distinctive distribution pattern, L. lufengensis may be able to respond to dietary variation in seasonal habitats.

Human-like enamel growth in Homo naledi.

A modern pattern (rate and duration) of dental development occurs relatively recently during human evolution. Given the temporal overlap of Homo naledi with the first appearance of fossil Homo sapiens in Africa, this small-bodied and small-brained hominin presents an opportunity to elucidate the evolution of enamel growth in the hominin clade. Here we conduct the first histological study of two permanent mandibular canines and one permanent maxillary first molar, representing three individuals attributed to H. naledi. We reconstruct the rate and duration of enamel growth and compare these findings to those reported for other fossil hominins and recent humans. Thin sections of each tooth were produced using standard histological methods. Daily and longer period incremental markings were measured to reconstruct enamel secretion and extension rates, Retzius periodicity, canine crown and molar cusp formation time. Daily enamel secretion rates overlapped with those from recent hominins. Canine crown formation time is similar to that observed in recent Europeans but is longer than canine formation times reported for most other hominins including Australopithecus and H. neanderthalensis. The extended period of canine formation appears to be due to a relatively tall enamel crown and a sustained slow rate of enamel extension in the cervical portion of the crown. A Retzius periodicity of 11 days for the canines, and nine days for the molar, in H. naledi parallel results found in recent humans. An 11-day periodicity has not been reported for Late Pleistocene Homo (H. erectus, H. neanderthalensis) and is rarely found in Australopithecus and Paranthropus species. Enamel growth of H. naledi is most similar to recent humans though comparative data are limited for most fossil hominin species. The high Retzius periodicity values do not follow expectations for a small-brained hominin.

Evaluation of Palatal Thickness for the Placement of MARPE Device among a Cohort of Iraqi-Kurdish Population: A Retrospective CBCT Study.

This study aimed to evaluate and compare palatal thickness in adults for the placement of mini-implants for miniscrew-assisted rapid palatal expansion (MARPE) appliances using cone-beam computed tomography (CBCT) in a sample of Iraqi-Kurdish people. CBCT scans from 68 Kurdish patients, aged between 18 and 30 years, were assessed retrospectively. Of these, 37 were males and 31 were females. The measurements were performed at 3 mm from the mid-palatal suture. T-zone was selected for the anterior points, at the level of the palatal cusps of 2nd premolars, and the posterior point at the level of mesio-palatal cusps of 1st molars bilaterally. Palatal thickness of males and females bilaterally, as well as anterior and posterior areas, were measured and compared. An independent t-test was applied for comparison for normally distributed data, and the Mann-Whitney test was utilized for nonnormally distributed data. Additionally, Bonferroni correction was implemented for p-value adjustment. The mean palatal thickness at the anterior area was 6.06 mm for males, 6.17 mm for females on the right side, 5.94 mm for males, and 5.99 mm for females on the left side. The mean palatal thickness at the posterior area was almost the same for both genders (4.40 mm for males and 4.44 mm for females) on the right side, 4.35 mm for males, and 4.54 mm for females on the left side. Statistically, no significant difference was recorded between males and females, as well as right and left sides in both anterior and posterior regions; however, a very highly statistically significant difference (p < 0.001) was recorded when comparing total thickness, including both hard and soft tissue, between anterior and posterior regions. CBCT proves a highly effective modality in assessing palatal thickness and suggesting ideal locations for orthodontic mini-screw placement. Our examination of palatal thickness in a sample of Iraqi-Kurdish individuals revealed no statistical difference between genders or sides, but significant variations were noted between anterior and posterior thicknesses. Comprehensive clinical and pre-expansion CBCT evaluations are crucial for precisely determining the optimal placement of MARPE devices in each patient, ensuring successful outcomes.

Accuracy of arch expansion with two thermoplastic materials in Invisalign® patients: EX30® and SmartTrack®.

The purpose of this retrospective study was to compare accuracy of arch expansion using two different thermoplastic materials in Invisalign aligners: EX30® (Polyethylene Terephthalate Glycol, or PETG) and SmartTrack® (polyurethane). The study sample comprised 65 adult patients consecutively treated with Invisalign from two private practices: group 1 - treated with EX30® (358 teeth) and group 2 - treated with SmartTrack® (888 teeth). Six hundred and twenty-three measurements were assessed in three digital models throughout treatment: model 1 - initial, model 2 - predicted tooth position, and model 3 - achieved position. Sixteen reference points per arch were marked and, after best alignment, 2 points per tooth were copied from one digital model to another. Linear values of both arches were measured for canines, premolars, and first molars: on lingual gingival margins and cusp tips of every tooth. Comparisons were performed by Wilcoxon and Mann-Whitney test. Both termoplastic materials presented significant differences between predicted and achieved values for all measurements, except for the lower molar cusp tip in the SmartTrack® group. There is no statistical difference in the accuracy of transverse expansion between these two materials. Overall accuracy for EX30® aligners in maxilla and mandible were found to be 37 and 38%, respectively; and Smarttrack® presented an overall accuracy of 56.62% in the maxilla and 68.72% in the mandible. It is not possible to affirm one material expands better than the other. Further controlled clinical studies should be conducted comparing SmartTrack® and EX30® under similar conditions.

An Evaluation of the Curve of Spee in the Maxilla and Mandible of Human Permanent Healthy Dentitions: A Cross Sectional Analytical Study in a Group of Nepalese Population

Introduction: Familiarity with the typical measurements of the maxillary and mandibular curves of Spee can assist clinicians in formulating sagittal plane occlusion and proves beneficial in delivering prosthetic rehabilitation for patients with occlusal derangement. The objective of this study is to evaluate and compare the radius and depth of the Spee curve in the maxillary and mandibular arches among both male and female individuals within young Nepalese population. Materials and Methods: The study comprised 21 men and 21 women aged between 18 and 30 years. Alginate impressions were made for both the maxillary and mandibular arches and dental stone casts were subsequently created. Digital images of the right side of maxillary and mandibular dental casts were captured using a digital camera and subsequently transferred to a computer. The tips of the distal cusps of molars, premolars, and canines in both the maxillary and mandibular arches were identified. Utilizing the computer software (Corel DRAW), the radius and depth of the Spee curve were measured based on the digital photographs of the dental casts. Results: The results indicated a substantial difference in the depth of the Spee curve between the mandibular and maxillary arches (p&lt;0.001), with the mandibular arch displaying a significantly greater depth. Furthermore, the Spee curve was notably deeper in females (p=0.045) compared to males. However, there was no statistically significant difference in the depth of the Spee curve in the mandible between genders (p=0.171). Conclusions: The radius of the Spee curve was unaffected by the gender or arch of the subjects under investigation. Nevertheless, the Spee curve was observed to be significantly flatter in the maxillary arch when contrasted with the mandibular arch. Additionally, a notable difference in the depth of the Spee curve was identified between females and males, with females displaying a greater depth.

The Correlation between Mandibular Arch Shape and Vertical Skeletal Pattern.

Background and Objectives: The aim of this study was to evaluate the correlation between the mandibular arch shape and the vertical skeletal pattern in growing patients. Materials and Methods: A total of 73 Caucasian patients (33 males and 40 females; mean age 9.4) were retrospectively enrolled from a pool of patients treated in chronological order at the Department of Orthodontics, University of Foggia, Italy, from April 2018 to December 2021. Each patient received a laterolateral radiograph and a digital scan of the dental arch. Eight cephalometric parameters (lower gonial angle, intermaxillary angle, divergence angle, Wits index, Jarabak ratio, OP-MP angle, PP-OP angle, and ANB) and five dental measurements (posterior mandibular arch width, anterior mandibular arch width, mandibular occlusal angle, posterior width on distobuccal molar cusps, and molar angle) were analyzed and then compared. A Spearman's rho correlation test between the cephalometric measurements and the dental measurements was performed. Statistical significance was set at p < 0.05. Results: A negative statistically significant correlation was found between the Jarabak ratio and the intermolar angle; a statistically significant correlation was also observed between the Wits index, the posterior mandibular width, and the occlusal mandibular angle; the ANB angle and the occlusal mandibular angle; the intermaxillary angle (PP-PM) and the mandibular occlusal angle, posterior mandibular width on the disto-vestibular cusp, and the intermolar angle; and the OP-MP angle and mandibular occlusal angle and the posterior mandibular width on the disto-vestibular cusp. Conclusions: The mandibular arch form may be related to certain predisposing features in craniofacial morphology, such as jaw divergence, the Jarabak ratio, and the intermaxillary angle.

Variation in enamel mechanical properties throughout the crown in catarrhine primates

Enamel mechanical properties vary across molar crowns, but the relationship among mechanical properties, tooth function, and phylogeny are not well understood. Fifteen primate lower molars representing fourteen taxa (catarrhine, n = 13; platyrrhine, n = 1) were sectioned in the lingual–buccal plane through the mesial cusps. Gradients of enamel mechanical properties, specifically hardness and elastic modulus, were quantified using nanoindentation from inner (near the enamel-dentine junction), through middle, to outer enamel (near the outer enamel surface) at five positions (buccal lateral, buccal cuspal, occlusal middle, lingual cuspal, lingual lateral). Cuspal positions had higher mechanical property values than lateral positions. Middle enamel had higher mean hardness and elastic modulus values than inner and outer locations in all five crown positions. Functionally, the thicker-enameled buccal cusps of lower molars did not show evidence of increased resistance to failure; instead, lingual cusps—which show higher rates of fracture—had higher average mechanical property values, with no significant differences observed between sides. Preliminary phylogenetic results suggest there is relatively little phylogenetic signal in gradients of mechanical properties through the enamel or across the crown. There appears to be common mechanical property patterns across molar crowns in Catarrhini and potentially among primates more broadly. These results may allow more precise interpretations of dental biomechanics and processes resulting in mechanical failure of enamel in primates, such as wear and fracture.

Dentoalveolar Alterations in an Adenine-Induced Chronic Kidney Disease Mouse Model.

Chronic kidney disease (CKD) is characterized by kidney damage and loss of renal function. CKD mineral and bone disorder (CKD-MBD) describes the dysregulation of mineral homeostasis, including hyperphosphatemia and elevated parathyroid hormone (PTH) secretion, skeletal abnormalities, and vascular calcification. CKD-MBD impacts the oral cavity, with effects including salivary gland dysfunction, enamel hypoplasia and damage, increased dentin formation, decreased pulp volume, pulp calcifications, and altered jaw bones, contributing to clinical manifestations of periodontal disease and tooth loss. Underlying mechanisms are not fully understood, and CKD mouse models commonly require invasive procedures with high rates of infection and mortality. We aimed to characterize the dentoalveolar effects of an adenine diet (AD)-induced CKD (AD-CKD) mouse model. Eight-week-old C57BL/6J mice were provided either a normal phosphorus diet control (CTR) or adenine and high-phosphorus diet CKD to induce kidney failure. Mice were euthanized at 15 weeks old, and mandibles were collected for micro-computed tomography and histology. CKD mice exhibited kidney failure, hyperphosphatemia, and hyperparathyroidism in association with porous cortical bone in femurs. CKD mice showed a 30% decrease in molar enamel volume compared to CTR mice. Enamel wear was associated with reduced ductal components, ectopic calcifications, and altered osteopontin (OPN) deposition in submandibular salivary glands of CKD mice. Molar cusps in CKD mice were flattened, exposing dentin. Molar dentin/cementum volume increased 7% in CKD mice and pulp volume decreased. Histology revealed excessive reactionary dentin and altered pulp-dentin extracellular matrix proteins, including increased OPN. Mandibular bone volume fraction decreased 12% and bone mineral density decreased 9% in CKD versus CTR mice. Alveolar bone in CKD mice exhibited increased tissue-nonspecific alkaline phosphatase localization, OPN deposition, and greater osteoclast numbers. AD-CKD recapitulated key aspects reported in CKD patients and revealed new insights into CKD-associated oral defects. This model has potential for studying mechanisms of dentoalveolar defects or therapeutic interventions. © 2023 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).

Disentangling morphology and genetics in two voles (Microtus pennsylvanicus and M. ochrogaster) in a region of sympatry.

Species in recent, rapid radiations can be difficult to distinguish from one another due to incomplete sorting of traits, insufficient time for novel morphologies to evolve, and elevated rates of hybridization and gene flow. The vole genus Microtus (58 spp.) is one such system where all three factors are likely at play. In the central United States, the prairie vole, Microtus ochrogaster, and the eastern meadow vole, M. pennsylvanicus, occur in sympatry and can be distinguished on the basis of molar cusp patterns but are known to be exceptionally difficult to distinguish using external morphological characters. Using a combination of morphometrics, pelage color analyses, and phylogenetics, we explored which traits are most effective for species identification and whether these same traits can be used to identify the subspecies M. o. ohionensis. While we were able to identify six traits that differed significantly between M. ochrogaster and M. pennsylvanicus, we also found substantial measurement overlap which limits the utility of these traits for species identification. The subspecies M. o. ohionensis was particularly difficult to distinguish from M. p. pennsylvanicus, and we did not find any evidence that this subspecies forms a distinct genetic clade. Furthermore, the full species M. ochrogaster and M. pennsylvanicus did not form reciprocal clades in phylogenetic analyses. We discuss several possible reasons for these patterns, including unrecognized variation in molar cusp patterns and/or localized hybridization. Overall, our results provide useful information that will aid in the identification of these species and subspecies in the future, and provides a case study of how genetics, morphometrics, and fur color analyses can be used to disentangle signatures of evolutionary history and hybridization.

Characteristics of Spatial Changes in Molars and Alveolar Bone Resorption among Patients with Loss of Mandibular First Molars: A CBCT-Based Morphometric Study

To investigate the characteristics of spatial changes in molars and alveolar bone resorption among patients with loss of mandibular first molars. A total of 42 CBCT scans of patients with missing mandibular first molars (3 males, 33 females) and 42 CBCT scans of control subjects without loss of mandibular first molars (9 males, 27 females) were evaluated in this cross-sectional study. All images were standardized using the mandibular posterior tooth plane with Invivo software. The following indices regarding alveolar bone morphology were measured, including alveolar bone height, bone width, mesiodistal and buccolingual angulation of molars, overeruption of maxillary first molars, bone defects, and the capability of molar mesialization. The vertical alveolar bone height in the missing group was reduced by 1.42 ± 0.70 mm, 1.31 ± 0.68, and 1.46 ± 0.85 mm on the buccal, middle, and lingual side, respectively (no differences among the three sides; p > 0.05). Alveolar bone width was reduced the greatest at the buccal CEJ level and the least at the lingual apex level. Mandibular second molar mesial tipping (with mean of the mesiodistal angulation = 57.47 ± 10.34°) and lingual tipping (with mean of the buccolingual angulation = 71.75 ± 8.34°) were observed. The mesial and distal cusps of maxillary first molars were extruded by 1.37 mm and 0.85 mm, respectively. Buccal and lingual defects of alveolar bone occurred at the CEJ, mid-root, and apex levels. Through 3D simulation, the second molar cannot be successfully mesialized into the missing tooth position, and the difference between the available and required distances for mesialization was the greatest at the CEJ level. The duration of tooth loss was significantly correlated with the mesio-distal angulation (R = -0.726, p < 0.001), buccal-lingual angulation (R = -0.528, p < 0.001) and the extrusion of the maxillary first molar (R = -0.334, p < 0.05). Both vertical and horizontal resorption of alveolar bone occurred. Mandibular second molars exhibit mesial and lingual tipping. Lingual root torque and uprighting of the second molars are needed for the success of molar protraction. Bone augmentation is indicated for severely resorbed alveolar bone.

Variability in molar crown morphology and cusp wear in two Western chimpanzee populations.

Chimpanzees (Pan troglodytes) possess a relatively generalized molar morphology allowing them to access a wide range of foods. Comparisons of crown and cusp morphology among the four subspecies have suggested relatively large intraspecific variability. Here, we compare molar crown traits and cusp wear of two geographically close populations of Western chimpanzees, P. t. verus, to provide further information on intraspecific dental variability. Micro-CT reconstructions of high-resolution replicas of first and second molars of two Western chimpanzee populations from Ivory Coast (Taï National Park) and Liberia, respectively were used for this study. First, we analyzed projected tooth and cusp 2D areas as well as the occurrence of cusp six (C6) on lower molars. Second, we quantified the molar cusp wear three-dimensionally to infer how the individual cusps alter with advancing wear. Both populations are similar in their molar crown morphology, except for a higher appearance rate of a C6 in Taï chimpanzees. In Taï chimpanzees, lingual cusps of upper molars and buccal cusps of lower molars possess an advanced wear pattern compared to the remaining cusps, while in Liberian chimpanzees this wear gradient is less pronounced. The similar crown morphology between both populations fits with previous descriptions for Western chimpanzees and provides additional data on dental variation within this subspecies. The wear pattern of the Taï chimpanzees are in concordance with their observed tool rather than tooth use to open nuts/seeds, while the Liberian chimpanzees may have consumed hard food items crushed between their molars.

Investigating the accuracy of mandibulectomy and reconstructive surgery using 3D customized implants and surgical guides in a rabbit model

BackgroundThis study aimed to analyze the accuracy of the output of three-dimensional (3D) customized surgical guides and titanium implants in a rabbit model, and of mandibulectomy, reconstructive surgery, and surgical outcome; additionally, the correlation between surgical accuracy and surgical outcomes, including the differences in surgical outcome according to surgical accuracy, was analyzed.ResultsThe output of implants was accurately implemented within the error range (− 0.03–0.03 mm), and the surgical accuracy varied depending on the measured area (range − 0.4–1.1 mm). Regarding surgical outcomes, angle between the mandibular lower borders showed the most sensitive results and distance between the lingual cusps of the first molars represented the most accurate outcomes. A significant correlation was noted between surgical accuracy in the anteroposterior length of the upper borders pre- and postoperatively and the angle between the mandibular lower borders (regression coefficient = 0.491, p = 0.028). In the group wherein surgery was performed more accurately, the angle between the mandibular lower borders was reproduced more accurately (p = 0.021). A selective laser melting machine accurately printed the implants as designed. Considering the positive correlation among surgical accuracy in the mandibular upper borders, angle between the mandibular lower borders, and more accurately reproduced angle between the mandibular lower borders, the angle between the mandibular lower borders is considered a good indicator for evaluating the outcomes of reconstructive surgery.ConclusionTo reduce errors in surgical outcomes, it is necessary to devise a positioner for the surgical guide and design a 3D surgical guide to constantly maintain the direction of bone resection. A fixed area considering the concept of three-point fixation should be selected for stable positioning of the implant; in some cases, bilateral cortical bone fixation should be considered. The angle between the mandibular lower borders is a sensitive indicator for evaluating the outcomes of reconstructive surgery.

Clinical longevity of extensive direct resin composite restorations after amalgam replacement with a mean follow-up of 15 years

ObjectivesThe aim of this retrospective clinical study was to determine the survival of extensive direct resin composite restorations after amalgam replacement on vital molars and premolars after a mean observation period of 15 years. MethodsBetween January 2007 and September 2013, a total of 117 extensive cusp replacing direct resin composite restorations were placed in 88 patients in a general dental practice. These were indicated for replacement of existing amalgam restorations. Tooth vitality, the absence of at least one cusp in premolars, and at least two cusps in molars were considered for inclusion. The long-term follow-up of the restorations, re-evaluated after up to 17 years using the original evaluation criteria is reported. Results81 of 88 patients (92.1%) and 106 of 117 restorations (90.6%) were available for follow-up. The cumulative success rate was 62.0% (95% CI: 47.3–76.2, AFR 2.79%) after a mean observation time of 163.4 months, the cumulative survival rate was 74.7% (95% CI: 59.8–89.6%, AFR: 1.70%) after a mean observation time of 179.1 months. The number of cusps replaced in premolars had a statistically significant influence on the success and survival rate of the restorations (HR of respectively, 2.974 and 3.175, p = <0.0005). Premolars with two cusps replaced had 297% more chance of failure than premolars with one cusp replaced. ConclusionsExtensive direct resin composite restorations placed after amalgam replacement showed good survival after a mean observation period of 15 years. The number of cusps involved had a statistically significant influence on the longevity of the restorations in premolars. Clinical SignificanceWith good survival and low annual failure rates, direct resin composite restorations are a suitable treatment for repairing extensive defects in posterior teeth involving multiple cusps and surfaces, provided that they are placed by a dentist who has long experience and is skilled in the placement of direct composite materials.

The prevalence of Brodie bite in untreated orthodontic patients in Nigeria.

The Brodie bite (BRB) is a rare posterior crossbite affecting the transverse occlusal relationship with the palatal cusps of the upper molars, biting into the vestibule and outside the buccal cusps of the lower molar teeth. The BRB is a highly challenging orthodontic problem and is an extreme form of scissors bite. Patients with this problem present with facial deformity and inability to chew on the affected side. The problem is usually not identified until it becomes severe. This study aimed to identify the prevalence of BRB among untreated orthodontic patients in two geo-political zones in Nigeria. A total of 1,041 untreated orthodontic patients who presented to two different orthodontic centres located in two geo-political zones (South/South-Benin City and North Central-Abuja, Nigeria) over a 3-year period were evaluated for the presence of BRB. The transverse dimension of the occlusion was examined for the presence of a crossbite or scissors bite. The molar teeth were used as the reference point for occlusion with Angle's classification of malocclusion. Four groups were identified, namely, teeth in occlusion (TIO) (Angle's Classes I, II or III malocclusion served as the control group), scissors or lingual crossbite (LCB), buccal crossbite (BCB) and BRB. A posterior crossbite was confirmed when the upper molar teeth were biting outside the buccal groove of the lower molar teeth either lingually or buccally. A BRB was identified when the palatal cusps of the upper molars were biting into the buccal vestibule of the lower jaw, with the deviation of the face to that side. Statistical analyses were performed using SPSS version 21; frequencies were determined for the variables, and cross-tabulations between the variables were established. P values < 0.05 were considered significant. The overall prevalence of BRB in this study was 0.6% (six patients). The values in the South/South (Benin City) were 997 untreated orthodontic patients, with a prevalence of 0.5% (five patients). The North Central (Abuja) zone had a total of 44 untreated orthodontic patients, with a prevalence of 2.3% (one patient). Unilateral BRB was seen in five patients (80%), and bilateral BRB was seen in one patient (20%). The condition was more prevalent among women (four patients, 80%) and on the right side (three patients, 60%). Angle's relationship in Classes I, II and III (TIO or control group) was seen in 911 patients (87.5%). The LCB and BCB groups comprised 39 (3.8%) and 85 patients (8.1%), respectively. Posterior crossbite was seen in 130 patients (12.5%). The prevalence of BRB in this study was found to be 0.6%, with the condition being more prevalent in women and on the right side.

Evaluation of maxillary canine and molar movement during the first phase of extraction space closure: a multilevel analysis.

This study was designed to analyze and compare the cusp and apex movements of the maxillary canines and first molars during canine retraction in the first step of extraction space closure, and to evaluate if these teeth follow a curvilinear (acceleration and/or deceleration) movement rate. Twenty-five patients (23.3 ± 5.1 years of age) were enrolled. The retraction of the maxillary canines was accomplished using nickel-titanium closed coil springs (100gf) on 0.020-in stainless steel archwire. Oblique cephalograms were traced and superimposed on the anatomic best fit of the maxilla (before the retraction [T0], and after one month [T1], three [T3], five [T5] and seven [T7] months). Statistics was based in a normally distributed data. Multilevel procedures were used to derive polynomials for each of the measurements. Student's t-test and one-way repeated measures ANOVA were conducted. The level of significance of 5% was adopted. Canine cusps and apexes did not follow a quadratic curve regarding horizontal movement (neither accelerate nor decelerate). Canine and molar cusps showed more horizontal movement than apexes (4.80 mm vs. 2.78 mm, and 2.64 mm vs. 2.17 mm, respectively). Canine did not accelerate or decelerate overtime horizontally; the cusps and apexes of the canines and molars showed more horizontal movement and larger rate at the beginning of canine retraction, followed by significantly smaller and constant movement rate after the first month.