Effect of occlusal hypofunction on centre of resistance in maxillary central incisor using the finite element method.

OBJECTIVES: To determine differences in the location of centre of resistance (Cres) between functional and hypofunctional teeth and to evaluate the relationship between the pulp cavity volume and locations of the Cres, using the finite element (FE) method. DESIGN: Retrospective cohort study. PARTICIPANTS: FE models of right maxillary central incisor, derived from cone-beam computed tomography (CBCT) images of 46 participants, were divided into normal function (n = 23) and hypofunction (n = 23) groups using anterior overbite and cephalometric measurements. METHODS: Measurements of the tooth and pulp cavity volume were made from the CBCT. Cres levels were presented as percentages of the root length from the root's apex. All data were analysed and compared using the independent t-test (P < 0.05). The relationship between the location of Cres and volume ratios were evaluated statistically. RESULTS: The means of the pulp cavity/tooth volume and root canal/ root volume ratio of the maxillary central incisor in the anterior open bite group were significantly greater than those in the normal group. The average location of Cres in the anterior open bite group was 0.6 mm (3.7%) apically from the normal group, measured from root apex. The difference was statistically significant (P < 0.01). There was a significant correlation between root canal/root volume ratio and locations of Cres (r = -0.780, P < 0.001). CONCLUSIONS: The Cres in the hypofunctional group was located more apical than the functional group. As the pulp cavity volume increased, the level of Cres shifted apically.

Heterozygous Variants in FREM2 Are Associated with Mesiodens, Supernumerary Teeth, Oral Exostoses, and Odontomas.

BACKGROUND: Supernumerary teeth refer to extra teeth that exceed the usual number of dentitions. A mesiodens is a particular form of supernumerary tooth, which is located in the premaxilla region. The objective of the study was to investigate the genetic etiology of extra tooth phenotypes, including mesiodens and isolated supernumerary teeth. METHODS: Oral and radiographic examinations and whole-exome sequencing were performed on every patient in our cohort of 122 patients, including 27 patients with isolated supernumerary teeth and 94 patients with mesiodens. A patient who had multiple supernumerary teeth also had odontomas. RESULTS: We identified a novel (c.8498A>G; p.Asn2833Ser) and six recurrent (c.1603C>T; p.Arg535Cys, c.5852G>A; p.Arg1951His, c.6949A>T; p.Thr2317Ser; c.1549G>A; p.Val517Met, c.1921A>G; p.Thr641Ala, and c.850G>C; p.Val284Leu) heterozygous missense variants in FREM2 in eight patients with extra tooth phenotypes. CONCLUSIONS: Biallelic variants in FREM2 are implicated in autosomal recessive Fraser syndrome with or without dental anomalies. Here, we report for the first time that heterozygous carriers of FREM2 variants have phenotypes including oral exostoses, mesiodens, and isolated supernumerary teeth.

Mutations in the WLS are associated with dental anomalies, torus palatinus, and torus mandibularis.

BACKGROUND: Canonical and non-canonical WNT signaling are important for odontogenesis. WNT ligand secretion mediator (WLS; MIM611514) is required to transport lipid-modified WNT proteins from the Golgi to the cell membrane, where canonical and non-canonical WNT proteins are released into the extracellular milieu. Biallelic pathogenic variants in WLS are implicated in autosomal recessive Zaki syndrome (ZKS; MIM 619648), the only genetic condition known to be caused by pathogenic variants in WLS. OBJECTIVE: To investigate molecular etiology of dental anomalies in 250 patients with or without oral exostoses. PATIENTS AND METHODS: Clinical and radiographic examination, and whole exome sequencing, were performed in the case of 250 patients with dental anomalies with or without oral exostoses. RESULTS: Four extremely rare heterozygous missense variants (p.Ile20Thr, p.Met46Leu, p.Ser453Ile and p.Leu516Phe) in WLS were identified in 11 patients with dental anomalies. In five of these patients, a torus palatinus or a torus mandibularis was observed. CONCLUSION: We report for the first time the heterozygous WLS variants in patients with dental anomalies. Root maldevelopments in patients with WLS variants supports the role of canonical and non-canonical WNT signaling in root development. We also show that variants in WLS were implicated in torus palatinus and torus mandibularis. In addition, this is the first time that heterozygous carriers of WLS variants were found to manifest phenotypes. WLS variants were likely to have adverse effects on the concentration of WNT ligands delivered to the cell membrane, resulting in aberrant canonical and non-canonical WNT signaling, and subsequent phenotypes. LIMITATIONS OF THE STUDY: Patient's positioning during the acquisition of panoramic radiography might have affected the appearance of the tooth structures. If we had all family members of each patient to study co-segregation between genotype and phenotype, it would have strengthened the association of WLS variants and the phenotypes.

Effects of the cone-beam computed tomography protocol on the accuracy and image quality of root surface area measurements: An in vitro study.

Purpose: The objective of this study was to evaluate and compare the accuracy and image quality of root surface area (RSA) measurements obtained with various cone-beam computed tomography (CBCT) protocols, relative to the gold standard of micro-computed tomography (CT), in an in vitro setting. Materials and Methods: Four dry human skulls were scanned using 8 different protocols, with voxel sizes of 0.15 mm, 0.3 mm, and 0.4 mm. Three-dimensional models of the selected teeth were constructed using CBCT and micro-CT protocols, and the RSA was automatically measured by the image-processing software. The absolute difference in the percentage of the RSA (%ΔRSA) was calculated and compared across the 8 CBCT protocols using repeated-measures analysis of variance. Finally, image quality scores of the RSA measurements were computed and reported in terms of percent distribution. Results: No significant differences were observed in the %ΔRSA across the 8 protocols (P>0.05). The deviation in %ΔRSA ranged from 1.51% to 4.30%, with an increase corresponding to voxel size. As the voxel size increased, the image quality deteriorated. This decline in quality was particularly noticeable at the apical level of the root, where the distribution of poorer scores was most concentrated. Conclusion: Relative to CBCT protocols with voxel sizes of 0.15 mm and 0.3 mm, the protocols with a voxel size of 0.4 mm demonstrated inferior image quality at the apical levels. In spite of this, no significant discrepancies were observed in RSA measurements across the different CBCT protocols.

Mutations in LRP5 and BMP4 are associated with mesiodens, tooth agenesis, root malformation, and oral exostoses.

WNT/ß-catenin and BMP signaling pathways play important roles in the process of tooth development. Dysregulation of WNT/ß-catenin and BMP signaling is implicated in a number of human malformations, including dental anomalies. Whole exome and Sanger sequencing identified seven patients with LRP5 mutations (p.Asn1121Asp, p.Asp856Asn, p.Val1433Met, and p.Val1245Met) and six patients with BMP4 mutations (p.Asn150Lys, p.Gly168Arg, p.Arg269Gln, and p.Ala42Glu). All patients were affected with isolated dental anomalies (dental anomalies with no other structural defects), including mesiodens, tooth agenesis, unseparated roots, narrow roots, shortened and tapered roots, and taurodontism. Five patients with LRP5 and one with BMP4 mutations had oral exostoses. Protein models of LRP5 mutations indicate the possible functional effects of the mutations. Here we report for the first time that mutations in LRP5 are associated with dental anomalies. LRP5 appears to be the first gene related to pathogenesis of mesiodens. We also show for the first time that in addition to tooth agenesis, mutations in BMP4 are also implicated in root maldevelopment and torus mandibularis. Sharing of the phenotypes of the patients with LRP5 and BMP4 mutations, which include root maldevelopment, tooth agenesis, and torus mandibularis, implicates cross talks between the WNT/ß-catenin and BMP signaling pathways, especially during root development.

Does pulp cavity affect the center of resistance in three-dimensional tooth model? A finite element method study.

OBJECTIVES: To compare the center of resistance (Cres) of the maxillary central incisor in models with and without the pulp cavity and to evaluate the association of pulp cavity/tooth volume ratio and difference in Cres position between the two models. MATERIALS AND METHODS: CBCT images of the right maxillary central incisor were collected from 18 subjects. Pulp cavity/tooth volume ratio was measured, and finite element models of teeth and periodontal structures were generated. Cres location was presented as a percentage of root length measured from the root apex. Differences in Cres positions between models were compared using the paired t-test, while the correlation between pulp cavity/tooth volume ratio and a difference in Cres was evaluated by Pearson's correlation coefficient. RESULTS: For the pulp cavity model, the average location of the Cres measured from the apex of the root was 58.8% ± 3.0%, which resulted in a difference of 4.1% ± 1.1% (0.5 mm) apically, when compared with the model without pulp cavity. Differences in Cres between the models were statistically significant (P < 0.01), while the correlation between pulp cavity/tooth volume ratio and a difference in Cres between models was significantly positive (r = 0.709, P = 0.001). CONCLUSIONS: In the pulp cavity model, the Cres was located in a more apical position. The difference in Cres between models increased as the pulp cavity/tooth volume ratio increased. CLINICAL RELEVANCE: The line of force must be applied more apically in the pulp cavity model to achieve the desired orthodontic tooth movement.

Three-dimensional volumetric evaluation of dental pulp cavity/tooth ratio in anterior open bite malocclusion using cone beam computed tomography.

OBJECTIVES: To assess and compare pulp cavity/tooth volume ratio of maxillary permanent teeth between patients exhibiting anterior open bite malocclusion and those exhibiting anterior normal overbite using cone beam computed tomography (CBCT). MATERIALS AND METHODS: 3D dental images from 44 patients aged between 15 and 29 years were analyzed. The DICOM files of all dental images were imported into an image processing software for calculating pulp cavity volume and tooth volume. Differences of pulp cavity volume, tooth volume, and pulp cavity/tooth volume ratio of each tooth type from both types of occlusions were analyzed using the independent t test. The intra-class correlation coefficient was used to evaluate intra-examiner reliability. RESULTS: The means of pulp cavity/tooth volume ratio in anterior open bite group were significantly greater than those in anterior normal overbite group (central incisor p = 0.001; lateral incisor p = 0.00025 and canine p = 0.004). The means of root canal/root volume ratio in anterior open bite group were significantly greater than anterior normal overbite group (central incisor p = 0.00001; lateral incisor p = 0.00007; and canine p = 0.001), whereas there were no significant differences of the means of pulp chamber/crown volume was observed. CONCLUSION: Anterior open bite malocclusion might lead to an increase of the pulp cavity volume and decrease of the tooth volume due to occlusal hypofunction. CLINICAL RELEVANCE: Orthodontic force should be carefully determined in anterior open bite patient due to the greater root canal volume and lesser root volume.

Treacher Collins syndrome: A novel TCOF1 mutation and monopodial stapes.

Treacher Collins syndrome (TCS: OMIM 154500) is an autosomal dominant craniofacial disorder belonging to the heterogeneous group of mandibulofacial dysostoses. OBJECTIVE: To investigate four Treacher Collins syndrome patients of the Sgaw Karen family living in Thailand. METHOD: Clinical examination, hearing tests, lateral cephalometric analyses, Computed tomography, whole exome sequencing and Sanger direct sequencing were performed. RESULTS: All of the patients affected with Treacher Collins syndrome carried a novel TCOF1 mutation (c.4138_4142del; p.Lys1380GlufsTer12), but clinically they did not have the typical facial gestalt of Treacher Collins syndrome, which includes downward-slanting palpebral fissures, colobomas of the lower eyelids, absence of eyelashes medial to the colobomas, malformed pinnae, hypoplastic zygomatic bones and mandibular hypoplasia. Lateral cephalometric analyses identified short anterior and posterior cranial bases, and hypoplastic maxilla and mandible. Computed tomography showed fusion of malleus and incus, sclerotic mastoid, hypoplastic middle ear space with a soft tissue remnant, dehiscence of facial nerve and monopodial stapes. CONCLUSION: Treacher Collins syndrome in Sgaw Karen patients has not been previously documented. This is the first report of monopodial stapes in a TCS patient who had a TCOF1 mutation. The absence of a common facial phenotype and/or the presence of monopodial stapes may be the effects of this novel TCOF1 mutation.

TRPS1 mutation associated with trichorhinophalangeal syndrome type 1 with 15 supernumerary teeth, hypoplastic mandibular condyles with slender condylar necks and unique hair morphology.

Trichorhinophalangeal syndrome type 1 (TRPS1; Online Mendelian Inheritance in Man #190350) is an autosomal dominant disorder caused by mutations in TRPS1. We report a Thai male with TRPS1 who carried a c.1842C>T (p.Arg615Ter) mutation. He had 15 supernumerary teeth, double mental foramina, hypoplastic mandibular condyles with slender condylar necks and unique ultrastructural hair findings. Body hair was absent. The hair in the area of a congenital melanocytic nevus had a greater number of hair cuticles than normal. Occipital hair had abnormal hair follicles and cuticles. The scale edges of the hair cuticles were detached and rolled up. Hypoplastic mandibular condyles with slender condylar necks, double mental foramina and the rolled up edges of hair cuticles have not been reported in patients with TRPS1.