Chau-Hsiang Wang

The biomechanical analysis of relative position between implant and alveolar bone: finite element method.

BACKGROUND The purpose of this study is to analyze biomechanical interactions in the alveolar bone surrounding implants with smaller-diameter abutments by changing position of the fixture-abutment interface, loading direction, and thickness of cortical bone using the finite element method. METHODS Twenty different finite element models including four types of cortical bone thickness (0.5, 1, 1.5, and 2 mm) and five implant positions relative to bone crest (subcrestal 1, implant shoulder 1 mm below bone crest; subcrestal 0.5, implant shoulder 0.5 mm below bone crest; at crestal implant shoulder even with bone crest; supracrestal 0.5, implant shoulder 0.5 mm above bone crest; and supracrestal 1, implant shoulder 1 mm above bone crest) were analyzed. All models were simulated under two different loading angles (0 and 45 degrees) relative to the long axis of the implant, respectively. The three factors of implant position, loading type, and thickness of cortical bone were computed for all models. RESULTS The results revealed that loading type and implant position were the main factors affecting the stress distribution in bone. The stress values of implants in the supracrestal 1 position were higher than all other implant positions. Additionally, compared with models under axial load, the stress values of models under off-axis load increased significantly. CONCLUSIONS Both loading type and implant position were crucial for stress distribution in bone. The supracrestal 1 implant position may not be ideal to avoid overloading the alveolar bone surrounding implants.

Stress Analysis of Different Angulations of Implant Installation: The Finite Element Method

Clinically, many implant cases with different angulation over the lower posterior area have been found. The purpose of this study was to analyze the bony stress with different implant tilting during normal masticatory load using the finite element method (FEM), with the hope of discovering a desirable installation of implant. Athree‐dimensional finite element method was employed to analyze the bony stress generated by different angulation designs (15°) of implant bodies. Eight solid models of the mandibular first and second molars were built up and then transferred to a mesh model in FEM (ANSYS) to perform a stress analysis. A simulated load (400N) was applied to the splinted crowns with vertical and horizontal forces. The loading sites were on the central fossa of the splinted crowns. For stress distribution, some designs will be better than a parallel installation. The results suggested that not all implant bodies tilting with the splinted crowns lead to stress concentration.

Effects of denture maintenance on satisfaction levels of Taiwanese elderly using removable partial dentures: a pilot study

OBJECTIVE The aim of this study was to evaluate the correlation between patient satisfaction with removable partial dentures and denture maintenance by patients, including regular application of denture adhesives and cleansers. BACKGROUND The success of removable partial dentures depends on patient satisfaction with dentures and their regular denture maintenance. MATERIALS AND METHODS Demographic information, the Oral Impacts on Daily Performance (OIDP) indicator and details of denture maintenance (including the use of denture cleansers and adhesives) were collected from 193 (41.5% men and 58.5% women) participants by using questionnaires. A dentist performed oral examinations to evaluate denture function according to the OIDP items photographically and recorded the number of remaining teeth and Kennedys classification. RESULTS Most participants were satisfied with their removable partial dentures and tended to have higher satisfaction levels than the dentists estimation. Further, those using denture adhesives and cleansers had higher satisfaction levels than those not using such denture maintenance. CONCLUSIONS Appropriate education regarding denture use is important because regular denture maintenance by patients affects their degree of satisfaction with dentures, as well as the dentists skill and the patients oral condition. Dentists could use this information to predict the potential success of dentures.

Horizontal pull-out strength of orthodontic infrazygomatic mini-implant: an in vitro study.

Purpose:New modified mini-implants have recently come into use for reinforcing skeletal anchorage in orthodontic application. The aim of this study was to investigate the influence of the design of a mini-implant on its mechanical strength. Materials and Methods:We measured the insertion torques and horizontal pull-out strengths of 3 brands of infrazygomatic mini-implants (AbsoAnchor, Bioray, and Lomas; 2 mm for all). Five implants of each brand were manually driven 6 mm into the artificial bone. Significant differences in various parameters among the brands were investigated with the Kruskal–Wallis test. Results:There was no significant relationship between insertion torque and horizontal pull-out strength. The Bioray mini-implants had significantly greater horizontal pull-out strength than the AbsoAnchor mini-implants. Conclusions:The design of the mini-implant can influence its insertion torque and horizontal pull-out strength. In our findings, the horizontal pull-out strength of all mini-implants placed in the infrazygomatic crest was significantly greater than the orthodontic force applied.

Emergence Angles of the Cementoenamel Junction in Natural Maxillary Anterior Teeth

STATEMENT OF THE PROBLEM   Fabrication of normal crown contour to maintain gingival health is difficult in the absence of emergence angle data. PURPOSE   The aim of this study was to measure the geometric values of the emergence angles on the cementoenamel junction (CEJ) for natural maxillary anterior teeth. MATERIAL AND METHODS   This study collected 148 natural permanent maxillary anterior teeth (74 central incisors, 59 lateral incisors, and 15 canines) with intact cervixes for this study. The teeth were scanned with a three-dimensional (3D) scanner to construct 3D models. This study measured the emergence angles of the cervical CEJ on the zenith of labial, palatal, mesial, and distal, for each tooth. RESULTS   Measurements made on 148 maxillary anterior teeth showed the emergence angle to be within a narrow range from 11.30° to 15.26°, irrespective of the tooth location. There were no statistically significant differences between any two groups (p > 0.05). CONCLUSIONS   On the basis of measurements taken from natural teeth, we conclude that the emergence angles of the CEJ in natural maxillary anterior teeth should be 15° from the root surface. CLINICAL SIGNIFICANCE The information presented in this article may be useful in helping to create dental restorations with optional emergence angles over the CEJ in natural maxillary anterior teeth. Prior to the treatment the dentist should consider not only the fit of the crown, but also the emergence angles and contours of the soft tissues surrounding the involved teeth.

PAIN PERCEPTION DURING MINIPLATE-ASSISTED ORTHODONTIC THERAPY

Miniplate and screw devices are widely used for fracture repair and fixation of osteotomies. Currently, these miniplate systems are being used as orthodontic treatments for skeletal anchorage. However, despite the widespread use of these treatments, patients are apprehensive when they need to undergo miniplate procedures. Recently, we assessed pain perception using the visual analog scale (VAS) score (0–100 mm) in patients who had undergone miniplate procedures. Thirty miniplates were positioned in the maxilla as skeletal anchors for orthodontic treatment. On the first day after insertion of the fixed orthodontic appliances, the mean VAS score was 36.3 mm. The mean VAS score at 24 hours after insertion of the miniplate was 58 mm. Three months after orthodontic force was applied to the miniplate, the mean VAS scores during eating and speaking gradually decreased to 20 mm and 15 mm, respectively. The mean VAS score at 24 hours after removal of the miniplate was 41.3 mm. Three months after removal of the skeletal anchors, the VAS score decreased to 5 mm. Eighty‐eight percent of patients stated that they would be prepared to undergo these new and more efficient treatment modalities in the future. The miniplate system was successfully used in this study as a skeletal anchor, and the patients could endure the pain and discomfort of this orthodontic treatment.

Reconstruction of the Soft Palate In Oral Cancer to Repair an Operative Defect with Speech Aid Prosthesis: A Case Report

A soft palate defect may result from surgical resection, and its consequences could include hypernasal speech and nasal regurgitation of food and liquids. A speech aid prosthesis fabricated for patients can improve nasal emission during speech, and assist in preventing nasal regurgitation of food. This article presents a case of the reconstruction of a soft palate defect by prosthetic obturation.

Mechanical strength of orthodontic infrazygomatic mini-implants

Orthodontic anchorages have recently been reinforced by newly developed mini-implants. The aim of the present study was to investigate the mechanical strengths of infrazygomatic mini-implants. We measured the insertion torque and pull-out strength of three brands of infrazygomatic mini-implants (AbsoAnchors, Bioray, and Lomas). All three mini-implants were 2 mm in diameter, and five of each brand were manually driven 6 mm into artificial bone. Significant differences among the brands were investigated with Kruskal-Wallis tests. We found no significant relationship between insertion torque and pull-out strength in any individual brand. Among the three brands of infrazygomatic mini-implants, we found no significant difference in mechanical strength. The design of an infrazygomatic mini-implant may be the most important factor determining its mechanical strength.

Biomechanical Analysis of Distal Extension Removable Partial Dentures with Different Retainers

The purposes of this study were to compare various retainer designs with different design philosophies based on stress breakers and rigid support. The technique of quasi-3-dimensional photoelastic stress analysis was used for this investigation. A photoelastic model was made with individual simulative materials for tooth structure and alveolar bone. The model was fabricated to simulate a mandibular Kennedy class Ⅱ modification 1 edentulous state with the right 1st premolar as the terminal abutment Six types of retainers were fabricated for the analysis: a wrought wire clasp; rest, proximal plate, Ⅰ-bar (RPI) system; conical crown telescopic retainer; rest, bi-proximal plate, Ⅰ-bar (RPPI) system; ring clasp, and cast circumferential clasp. For each experimental removable partial denture (RPD), a micro-load cell transducer was placed under the denture base to measure the denture base shearing load of the occlusal force. After 18 kg was loaded vertically on the occlusal table of the RPD, photoelastic stress distribution isochromatics and the denture base shearing load were obtained. Results indicated that an unfavorable stress gradient was found with the wrought wire clasp design, with the maximum stress (5.59 kg) being concentrated at the residual ridge while the minimum stress occurred at the abutment. A favorable stress gradient was found with the conical crown telescopic retainer design, with the stress (1.05 kg) being concentrated at the residual ridge. Within the limitations of this experiment, different retainer designs had different effects on the abutment and residual ridge. The retainers designed based on a rigid support philosophy concentrated more stress at the abutment and generated less stress at the residual ridge than those retainers designed with a flexible support.

The Difference Between Two Oral Appliances in Treating Obstructive Sleep Apnea: A Case Report

Oral appliances are a range of devices that are designed to alter upper airway patency. The efficiency of these appliances for treatment of obstructive sleep apnea (OSA) has been rarely discussed. This case report describes two designs of mandibular repositioning appliances used to treat OSA. A 36-year-old man was diagnosed with mild OSA by his physician. A single-piece, soft oral appliance and a two-piece, acrylic appliance were used in this patient. Polysomnography was performed three times (baseline, and with the single-piece, and two-piece appliances). The apnea/hypopnea index was improved significantly with both appliances, but to a greater degree with the single-piece soft appliance. Our study concluded that oral appliances may assist in the management of OSA.