Won Hee Lim

Palatal Bone Density in Adult Subjects: Implications for Mini-Implant Placement

OBJECTIVES To evaluate palatal bone density to allow for better selection of palatal implant anchorage sites. MATERIALS AND METHODS Computed tomographic (CT) images were obtained from 15 males and 15 females (mean age, 27 years; range, 23-35 years). Bone density was measured in Hounsfield units (HU) at 80 coordinates at regular mediolateral and anteroposterior intervals along the midpalatal suture. RESULTS Bone densities ranged from 805 to 1247 HU. A significant difference between male and female groups was noted, although no difference was found between left and right sides of individual palates. Palatal bone densities showed a tendency to decrease laterally and posteriorly. The midpalatal area within 3 mm of the midsagittal suture had the densest bone in the entire palate. CONCLUSION Results suggest that mini-implants for orthodontic anchorage may be effectively placed in most areas with bone density equivalent to the palatal area if they are placed from 3 mm posterior to the incisive foramen and 1 to 5 mm to the paramedian side.

Quantitative evaluation of cortical bone thickness and root proximity at maxillary interradicular sites for orthodontic mini-implant placement.

Few studies have evaluated interradicular anatomy for cortical bone thickness and root proximity when placing a mini‐implant for orthodontic anchorage. The purpose of this study was to provide a clinical guideline to indicate the best location, according to different insertion angles, for placement of a mini‐implant with respect to the thickness of cortical bone and root proximity. CT images from 14 men and 14 women (mean age, 27 years; range, 23–35 years) were used to evaluate the buccal interradicular cortical bone thickness and root proximity from and mesial to the central incisor to the second molar. A measure of cortical bone thickness was performed at four different angles. Generally, thin cortical bone thickness was found in the central/central incisors and central/lateral incisors interradicular sites. Cortical bone thickness increased significantly as the insertion angle increased except for interradicular sites at the 2 mm level from the alveolar crest. The volume of cortical bone engagement increased significantly at the 4 and 6 mm levels from the alveolar crest with an insertion angle of 30° and 45° in most interradicular sites. The lateral incisor/canine and second premolar/first molar interradicular sites showed greater space between roots compared with other sites, although this was not statistically significant. Based on the findings of this study, we recommend that mini‐implants be placed at the 4 and 6 mm levels from the alveolar crest with 30° and 45° angles for the majority of interradicular sites to ensure better cortical bone to mini‐implant contact without root damage. Clin. Anat. 21:486–491, 2008.

Treatment of ankylosed mandibular first permanent molar

This report describes the treatment of a 21-year old patient with an ankylosed mandibular right first permanent molar. The tooth was noticeably infraoccluded when the patient was first seen, at age 9. Over the next 11 years, several interventions, as well as periods of observation, were undertaken to bring the infraoccluded tooth into occlusion. This was finally accomplished by using a microscrew implant. The final treatment and the treatment procedures during the adolescent period are reported here.

Wnt signaling regulates pulp volume and dentin thickness.

Odontoblasts, cementoblasts, ameloblasts, and osteoblasts all form mineralized tissues in the craniofacial complex, and all these cell types exhibit active Wnt signaling during postnatal life. We set out to understand the functions of this Wnt signaling, by evaluating the phenotypes of mice in which the essential Wnt chaperone protein, Wntless was eliminated. The deletion of Wls was restricted to cells expressing Osteocalcin (OCN), which in addition to osteoblasts includes odontoblasts, cementoblasts, and ameloblasts. Dentin, cementum, enamel, and bone all formed in OCN‐Cre;Wlsfl/fl mice but their homeostasis was dramatically affected. The most notable feature was a significant increase in dentin volume and density. We attribute this gain in dentin volume to a Wnt‐mediated misregulation of Runx2. Normally, Wnt signaling stimulates Runx2, which in turn inhibits dentin sialoprotein (DSP); this inhibition must be relieved for odontoblasts to differentiate. In OCN‐Cre;Wlsfl/fl mice, Wnt pathway activation is reduced and Runx2 levels decline. The Runx2‐mediated repression of DSP is relieved and odontoblast differentiation is accordingly enhanced. This study demonstrates the importance of Wnt signaling in the homeostasis of mineralized tissues of the craniofacial complex.

Alveolar Bone Turnover and Periodontal Ligament Width Are Controlled by Wnt

BACKGROUND The molecular signals responsible for maintaining homeostatic control over the periodontal ligament (PDL) are unknown. The purpose of this study is to investigate the role of Wnt signaling in this process using gain- and loss-of-function approaches. METHODS The function of endogenous Wnt signal in the PDL was evaluated in Lrp5(ACT) mice in which a mutation in the low-density lipoprotein receptor-related protein 5 Wnt coreceptor causes constitutive activation of Wnt signaling, and in adenovirus Dkk1-treated mice in which overexpression of the Wnt inhibitor Dkk1 causes transient Wnt signal inhibition. PDL in both animal models was examined using histology and immunohistochemical analyses for osteopontin, runt-related transcription factor 2 (Runx2), fibromodulin, osterix, ki67, receptor activator of nuclear factor-κB ligand (RANKL), and alkaline phosphatase activity. RESULTS Lrp5(ACT) mice exhibited a significant narrowing of the PDL space caused by an increase in osteogenic gene expression, a reduction in RANKL expression and osteoclast activity, and an increase in alveolar bone formation. Conversely, adenovirus Dkk1-treated mice showed decreased expression of osteogenic markers, coupled with an increase in osteoclast activity, which resulted in a slight increase in PDL width. CONCLUSION The Wnt pathway is involved in the homeostatic control of the PDL, and conditions that elevate or repress Wnt signaling alter the expression of osteogenic genes within the PDL space, which in turn affects its overall width.

Wnt Signaling and Its Contribution to Craniofacial Tissue Homeostasis

A new field of dental medicine seeks to exploit nature’s solution for repairing damaged tissues, through the process of regeneration. Most adult mammalian tissues have limited regenerative capacities, but in lower vertebrates, the molecular machinery for regeneration is an elemental part of their genetic makeup. Accumulating data suggest that the molecular pathways responsible for the regenerative capacity of teleosts, amphibians, and reptiles have fallen into disuse in mammals but that they can be “jumpstarted” by the selective activation of key molecules. The Wnt family of secreted proteins constitutes one such critical pathway: Wnt proteins rank among the most potent and ubiquitous stem cell self-renewing factors, with tremendous potential for promoting human tissue regeneration. Wnt reporter and lineage-tracing strains of mice have been employed to create molecular maps of Wnt responsiveness in the craniofacial tissues, and these patterns of Wnt signaling colocalize with stem/progenitor populations in the rodent incisor apex, the dental pulp, the alveolar bone, the periodontal ligament, the cementum, and oral mucosa. The importance of Wnt signaling in both the maintenance and healing of these craniofacial tissues is summarized, and the therapeutic potential of Wnt-based strategies to accelerate healing through activation of endogenous stem cells is highlighted.

Variation of the intermaxillary tooth-size relationship in normal occlusion

The purpose of this study was to explore the intermaxillary tooth-size relationship that is attributed to normal occlusion using multivariate cluster analysis, while simultaneously incorporating the full dentition as a data set. From the central incisor to the second molar, the tooth sizes of 307 subjects (188 males and 119 females; mean age ± standard deviation, 19.9 ± 3.3 years) with normal occlusion were investigated. Tooth-size data were analysed separately for the maxilla and the mandible. When clustering, the partitioning around medoids (PAM) algorithm was performed with the transformed data based on principal component analysis (PCA). After the subjects were classified into four groups, the cluster memberships were cross-classified, and the distribution pattern and intermaxillary tooth-size relationships were explored. Bolton tooth ratio showed a relatively wide range, and this was indicative of the variability in tooth size in subjects with a normal occlusion. However, the patterns of the intermaxillary tooth-size relationship were similar for males and females, and this result was concordant with the findings of the classic Bolton analysis. Using the multivariate approach to analyse the tooth-size data set of an individual patient and then comparing the results with the normal occlusion cluster has possible clinical applications in determining the amount and location of tooth-size control in orthodontics.

The molecular and cellular effects of ageing on the periodontal ligament.

AIM Many in vitro studies have investigated age-related biological changes in cells comprising the periodontium but the basic question of whether the periodontium can maintain its integrity with age remains unanswered. Thus, the aim of this study was to understand how, in the absence of disease, advancing age impacts the structure of the periodontium. MATERIALS AND METHODS Of 4, 10, 25, and 50-week-old mice were examined using histology and immunohistochemical analyses for cell proliferation, cell turnover, collagen quantity and quality, osteogenic markers, bone turnover, and cytokine expression. RESULTS The periodontal ligament (PDL) space shows a gradual decrease in width over the lifespan of the mice. Cell proliferation as well as the quantity and quality of collagen fibres decreased with age although cell density did not appear to be altered. Osteoprogenitor markers in the PDL maintained their expression with increasing age. Alkaline phosphatase (ALP) activity decreased, but osteoclast activity increased with age. CONCLUSIONS Ageing is associated with a decline in the quality and quantity of collagen and an increase in bone resorption, all of which can diminish the function of the periodontium even in the absence of disease.

Three-dimensional analysis of tooth movement after intrusion of a supraerupted molar using a mini-implant with partial-fixed orthodontic appliances

OBJECTIVE To evaluate three-dimensional (3D) positional changes of an intruded tooth, a neighboring tooth, and a tooth connected to a mini-implant following intrusion of a single supraerupted molar, using a mini-implant with partial-fixed orthodontic appliances. MATERIALS AND METHODS The study consisted of 14 adult patients (two males and 12 females, mean age 41.9 years) with a supraerupted molar due to loss of an antagonist. Intrusion was performed using a mini-implant with a partial strap-up. The mean treatment time was 11.9 months, and the mean retention time was 23.3 months. To quantify the positional changes of the teeth, 3D models using a laser-based, dental scanning system and 3D software at pretreatment, posttreatment, and retention were oriented in a coordinate system and superimposed using nonmoved teeth as references. The changes on the x-, y-, and z-axes were measured at the tip of each cusp in the involved teeth. RESULTS A supraerupted molar was intruded by a mean amount of 1.35 ± 0.48 mm and was well maintained during the retention period. The overall change in the neighboring tooth was insignificant, although it showed opposite movement compared to the intruded tooth during the intrusion. The tooth connected to a mini-implant exhibited a secure anchorage. CONCLUSION 3D analysis showed the detailed positional changes of each tooth, and the involved molars were well maintained after intrusion.

Influence of temporomandibular joint disc displacement on craniocervical posture and hyoid bone position

INTRODUCTION The purpose of this study was to evaluate craniocervical posture and hyoid bone position in orthodontic patients with temporomandibular joint (TMJ) disc displacement. METHODS The subjects consisted of 170 female orthodontic patients who consented to bilateral magnetic resonance imaging of their TMJs. They were divided into 3 groups based on the results of magnetic resonance imaging of their TMJs: bilateral normal disc position, bilateral disc displacement with reduction, and bilateral disc displacement without reduction. Twenty-five variables from lateral cephalograms were analyzed with 1-way analysis of variance to investigate differences in craniocervical posture and hyoid bone position with respect to TMJ disc displacement status. Pearson correlation coefficients were calculated to analyze the relationships between craniofacial morphology and craniocervical posture or hyoid bone position. RESULTS Subjects with TMJ disc displacement were more likely to have an extended craniocervical posture with Class II hyperdivergent patterns. The most significant differences were found between patients with bilateral normal disc position and bilateral disc displacement without reduction. However, hyoid bone position in relation to craniofacial references was not significantly different among the TMJ disc displacement groups, except for variables related to the mandible. Pearson correlation coefficients indicated that extended craniocervical posture was significantly correlated with backward positioning and clockwise rotation of the mandible. CONCLUSIONS This suggests that craniocervical posture is significantly influenced by TMJ disc displacement, which may be associated with hyperdivergent skeletal patterns with a retrognathic mandible.