Byoung-Duck Roh

Computed Tomography as a Diagnostic Aid for Extracanal Invasive Resorption

A case of multiple extracanal invasive resorption is reported. The patient had a history of hypothyroidism for approximately 1 yr before the dental visit. Utilization of computed tomography and a rapid prototyping tooth model in diagnosing the exact location and the size of the resorption area are discussed.

The effect of preparation designs on the marginal and internal gaps in Cerec3 partial ceramic crowns

OBJECTIVES The purpose of this study was to evaluate the marginal and internal gaps in Cerec3 partial ceramic crowns (PCCs) of three different preparation designs in vitro using microcomputed tomography (microCT). METHODS Cerec3 PCCs of three different preparation designs (n=20) were fabricated according to the following: Group I-conventional functional cusp capping/shoulder preparation, Group II-horizontal reduction of cusps and Group III-complete reduction of cusps/shoulder preparation. After fixation of PCCs, the microCT scanning was performed. For obtaining the average internal gap (AIG), the microCT sections were reconstructed 3-dimensionally, and then the total volume of the internal gap was divided by the contact surface area. The 2-dimensional (2D) microCT views were used to investigate the gaps at predetermined key positions in seven bucco-lingual sections and three mesio-distal cross sections. The gaps were measured using the microCT at each reference point. Statistical analysis was performed using one-way ANOVA and Tukeys test. RESULTS For the 3D reconstruction technique, the AIGs were as followed: Group I 197.3+/-48.2microm, Group II 171.2+/-45.1microm, and Group III 152.7+/-27.1microm. For the 2D microCT views, the gaps of each group were the smallest on the margins ranging from 35.4+/-32.2 to 128.4+/-69.5microm, and the largest on the horizontal or angle walls ranging from 184.5+/-41.2 to 406.5+/-176.1microm. According to the results, Group I showed larger marginal and internal gaps compared with the other groups. CONCLUSIONS For the PCCs, the simplified designs (Groups II and III) demonstrated superior results compared to the traditional cusp capping design (Group I). The marginal gaps were smaller than the internal gaps in all groups.

Prognostic Factors for Clinical Outcomes in Autotransplantation of Teeth with Complete Root Formation: Survival Analysis for up to 12 Years.

INTRODUCTION Tooth autotransplantation is a treatment option that has the potential to restore masticatory function and esthetics to edentulous spaces resulting from extracted teeth. The purpose of this study was to investigate the prognostic factors and clinical outcomes for autotransplanted teeth with complete root formation. METHODS Patients who had received tooth autotransplantation in the Department of Conservative Dentistry, Yonsei University Dental Hospital, Seoul, Korea, from July 2001 to August 2010 were electronically searched, and a total of 105 cases of autotransplanted teeth met the inclusion criteria. Tooth survival, inflammatory root resorption (IRR), ankylosis, and related prognostic factors were assessed by using the survival analysis that was based on clinical and radiographic examination. RESULTS The cumulative tooth survival rate was 68.2% at 12 years after the tooth autotransplantation. According to the Cox proportional hazard regression analysis, patient age, donor position, and extraoral time were significantly associated with tooth survival (P < .05). Donor extraction type was significantly associated with IRR (P < .05), and transplantation timing and initial stability were significantly associated with ankylosis (P < .05) CONCLUSIONS: Patients less than 45 years of age, maxillary donor teeth, and an extraoral time of less than 15 minutes were associated with significantly higher tooth survival. Surgical extraction of the donor tooth was associated with a significantly higher incidence of IRR. Immediate transplantation after the extraction of the recipient sites tooth and low initial stability were associated with a significantly lower incidence of ankylosis.

Inhibition of Streptococcus mutans biofilm formation on composite resins containing ursolic acid

Objectives To evaluate the inhibitory effect of ursolic acid (UA)-containing composites on Streptococcus mutans (S. mutans) biofilm. Materials and Methods Composite resins with five different concentrations (0.04, 0.1, 0.2, 0.5, and 1.0 wt%) of UA (U6753, Sigma Aldrich) were prepared, and their flexural strengths were measured according to ISO 4049. To evaluate the effect of carbohydrate source on biofilm formation, either glucose or sucrose was used as a nutrient source, and to investigate the effect of saliva treatment, the specimen were treated with either unstimulated whole saliva or phosphate-buffered saline (PBS). For biofilm assay, composite disks were transferred to S. mutans suspension and incubated for 24 hr. Afterwards, the specimens were rinsed with PBS and sonicated. The colony forming units (CFU) of the disrupted biofilm cultures were enumerated. For growth inhibition test, the composites were placed on a polystyrene well cluster, and S. mutans suspension was inoculated. The optical density at 600 nm (OD600) was recorded by Infinite F200 pro apparatus (TECAN). One-way ANOVA and two-way ANOVA followed by Bonferroni correction were used for the data analyses. Results The flexural strength values did not show significant difference at any concentration (p > 0.01). In biofilm assay, the CFU score decreased as the concentration of UA increased. The influence of saliva pretreatment was conflicting. The sucrose groups exhibited higher CFU score than glucose group (p < 0.05). In bacterial growth inhibition test, all experimental groups containing UA resulted in complete inhibition. Conclusions Within the limitations of the experiments, UA included in the composite showed inhibitory effect on S. mutans biofilm formation and growth.

Influence of Apical Root Resection on the Biomechanical Response of a Single-rooted Tooth: A 3-dimensional Finite Element Analysis

INTRODUCTION Apical root resection is a biologically essential component in endodontic microsurgery. However, because it reduces the total root length and supported root surface, it changes the biomechanical response of the tooth. The purpose of this study was to analyze the biomechanical effect of apical root resection and to compare apical root resection with periodontal bone loss from a biomechanical standpoint. METHODS Finite element models of the maxillary central incisor were reconstructed. First, preoperative and surgically treated models were generated to assess the factors altering the biomechanical response of the tooth. Then, apically resected models with different amounts of resection (3, 4, 5, 6, 7, and 8 mm) were created to estimate the clinically applicable limit of apical root resection. Periodontally destructed models with varying degrees of bone loss (0.5, 1, 1.5, 2, and 3 mm) were also created to compare the effect of apical root resection with periodontal bone loss. Stress distribution, tooth displacement, and effective crown-to-root ratio (α) were analyzed for each condition. RESULTS Apical root resection did not significantly alter the maximum von Mises stress or tooth displacement until it reached 6 mm (α = 0.67) when the tooth was supported by normal periodontium. In contrast, periodontal bone loss had a greater impact on biomechanical response change compared with apical root resection. CONCLUSIONS For a tooth supported by normal periodontium, 3 mm of apical root resection (α = 1.07) appeared to be mechanically acceptable. The biomechanical influence of apical root resection was weak compared with that of periodontal bone loss.

Influence of preparation design on fit and ceramic thickness of CEREC 3 partial ceramic crowns after cementation

Abstract Objective. This study investigated the influence of preparation design on the marginal and internal gap and ceramic thickness of partial ceramic crowns (PCCs) fabricated with the CEREC 3 system. Materials and methods. Sixteen extracted human mandibular molars were prepared according to two different preparation designs (n = 8): a retentive preparation design with traditional cusp capping (Group I) and a non-retentive preparation design with horizontal reduction of cusps (Group II). PCCs were fabricated from IPS Empress CAD with the CEREC 3 system. The parameters for luting space and minimum occlusal ceramic thickness were set to 30 μm and 1.5 mm, respectively. The fabricated PCCs were cemented to their corresponding teeth with self-adhesive resin cement and were then scanned by micro-computed tomography. The marginal and internal gaps were measured at pre-determined measuring points in five bucco-lingual and three mesio-distal cross-sectional images. The ceramic thicknesses of the PCCs were measured at the measuring points for cusp capping areas. Results. Group II (167.4 ± 76.4 μm) had a smaller overall mean gap, which included the marginal and internal gap measurements, than that of Group I (184.8 ± 89.0 μm). The internal gaps were larger than the marginal gaps, regardless of preparation design. Group I presented a thinner ceramic thickness in the cusp capping areas than the minimum occlusal ceramic thickness parameter of 1.5 mm. Conclusion. Preparation design had an influence on fit, particularly the internal gap of the PCCs. Ceramic thickness could be thinner than the minimum ceramic thickness parameter.

Invasive cervical resorption: treatment challenges

Invasive cervical resorption is a relatively uncommon form of external root resorption. It is characterized by invasion of cervical region of the root by fibrovascular tissue derived from the periodontal ligament. This case presents an invasive cervical resorption occurring in maxillary lateral incisor, following damage in cervical cementum from avulsion and intracoronal bleaching procedure. Flap reflection, debridement and restoration with glass ionomer cement were performed in an attempt to repair the defect. But after 2 mon, more resorption extended apically. Considering root stability and recurrence potential, we decided to extract the tooth. Invasive cervical resorption in advanced stages may present great challenges for clinicians. Therefore, prevention and early detection must be stressed when dealing with patients presenting history of potential predisposing factors.

Effect of Insufficient Light Exposure on Polymerization Kinetics of Conventional and Self-adhesive Dual-cure Resin Cements

OBJECTIVES The purpose of this study was to investigate the influence of insufficient light exposure on the polymerization of conventional and self-adhesive dual-cure resin cements under ceramic restorations. METHODS Two conventional dual-cure resin cements (Rely-X ARC, Duolink) and two self-adhesive resin cements (Rely-X U200, Maxcem Elite) were polymerized under different curing modes (dual-cure or self-cure), curing times (20 and 120 seconds), and thickness of a ceramic overlay (2 and 4 mm). Polymerization kinetics was measured by Fourier transform infrared spectroscopy for the initial 10 minutes and after 24 hours. Data were analyzed using mixed model analysis of variance (ANOVA), one-way ANOVA/Student-Newman-Keuls post hoc test, and paired t-test (α=0.05). RESULTS When light-curing time was set to 20 seconds, the presence of the ceramic block significantly affected the degree of conversion (DC) of all resin cements. Especially, the DC of the groups with 20 seconds of light-curing time under 4 mm of ceramic thickness was even lower than that of the self-cured groups at 24 hours after polymerization (p<0.05). However, when light-curing time was set to 120 seconds, a similar DC compared with the group with direct light exposure (p>0.05) was achieved in all dual-cure groups except Maxcem Elite, at 24 hours after polymerization. CONCLUSIONS For both conventional and self-adhesive dual-cure resin cements, insufficient light exposure (20 seconds of light-curing time) through thick ceramic restoration (4 mm thick) resulted in a DC even lower than that of self-curing alone.

Evaluation of the marginal and internal discrepancies of CAD-CAM endocrowns with different cavity depths: An in vitro study

Statement of problem. The marginal and internal discrepancies of computer‐aided design and computer‐aided manufacturing (CAD‐CAM) endocrowns are unknown. Purpose. The purpose of this in vitro study was to evaluate the marginal and internal discrepancies of endocrowns with different cavity depths by measuring them with microcomputed tomography (&mgr;CT). Material and methods. Endocrowns (n=48) of 2 different cavity depths (2 mm and 4 mm) were fabricated in 2 different chairside CAD‐CAM systems (CEREC AC and E4D). A &mgr;CT scan was made before and after cementation. For analysis of the marginal and internal discrepancies, reference points were selected in 2‐dimensional views of 3 buccolingual cross‐sections and 3 mesiodistal cross‐sections. To calculate the total discrepancy volume, the &mgr;CT sections were reconstructed 3‐dimensional views, and changes in volume and surface area were examined. Statistical analysis was performed using 2‐way ANOVA with Bonferroni correction (&agr;=.05). Results. An endocrown with a 4‐mm cavity showed a larger marginal and internal volume than one with a 2‐mm cavity. Cementation did not show significant differences in total discrepancy thickness. Discrepancies on the pulpal floor were largest in other sites. Both chairside CAD‐CAM systems showed similar discrepancy in the endocrowns. Conclusions. Based on the present study, marginal and internal discrepancies increased depending on cavity depth. Cementation did not increase the dimension of the discrepancy between the restoration and the cavity wall. The discrepancy on the pulpal floor appeared to affect these results.

Influence of Apical Root Resection on the Biomechanical Response of a Single-rooted Tooth—Part 2: Apical Root Resection Combined with Periodontal Bone Loss

INTRODUCTION In a clinical situation, an apically resected tooth is often accompanied by a varying degree of periodontal bone loss. The purpose of this study was to assess the influence of apical root resection combined with periodontal bone loss on the biomechanical response of a single-rooted tooth. METHODS A basic intact model and a basic apically resected model of the upper central incisor were selected for the numerical analysis. From each basic model, 6 models were developed assuming different amounts of periodontal bone loss (0, 0.5, 1, 1.5, 2, and 3 mm). Maximum von Mises stress (σ max), maximum tooth displacement (ΔR max), and effective crown-to-root ratio (α) were calculated for each condition. RESULTS There were only marginal differences (a 2.1% difference in σ max and a 16.9% difference in ΔR max) between the biomechanical responses of the intact model and the apically resected model when the tooth was supported by a normal periodontium. However, when destruction of the periodontium was assumed, the intact model and the apically resected model responded differently. The difference increased as the periodontal bone loss progressed, resulting in a 68.7% difference in σ max and a 56.3% difference in ΔR max when the periodontal bone loss increased to 3 mm (α = 0.48). CONCLUSIONS Although the biomechanical response of an apically resected tooth was relatively stable when the tooth was supported by a normal periodontium, the apically resected tooth showed a more deteriorated response compared with the intact tooth as the periodontal bone loss progressed.