Ting-Hsun Lan

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.

Influence of different implant materials on the primary stability of orthodontic mini-implants

This study evaluates the influence of different implant materials on the primary stability of orthodontic mini‐implants by measuring the resonance frequency. Twenty‐five orthodontic mini‐implants with a diameter of 2 mm were used. The first group contained stainless steel mini‐implants with two different lengths (10 and 12 mm). The second group included titanium alloy mini‐implants with two different lengths (10 and 12 mm) and stainless steel mini‐implants 10 mm in length. The mini‐implants were inserted into artificial bones with a 2‐mm‐thick cortical layer and 40 or 20 lb/ft3 trabecular bone density at insertion depths of 2, 4, and 6 mm. The resonance frequency of the mini‐implants in the artificial bone was detected with the Implomates® device. Data were analyzed by two‐way analysis of variance followed by the Tukey honestly significant difference test (α = 0.05). Greater insertion depth resulted in higher resonance frequency, whereas longer mini‐implants showed lower resonance frequency values. However, resonance frequency was not influenced by the implant materials titanium alloy or stainless steel. Therefore, the primary stability of a mini‐implant is influenced by insertion depth and not by implant material. Insertion depth is extremely important for primary implant stability and is critical for treatment success.

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.

Fracture resistance of monolithic zirconia crowns with different occlusal thicknesses in implant prostheses.

STATEMENT OF PROBLEM The use of monolithic zirconia crowns in implant prostheses is increasing, especially when the interdental space is insufficient. However, fractures have been reported in clinical practice. PURPOSE The purpose of this study was to determine the minimal thickness of a complete zirconia crown used for an implant prosthesis in the posterior dental region. MATERIAL AND METHODS Fifty complete zirconia crowns were produced using a computer-aided design/computer-aided manufacturing technique. In each group, 5 crowns of varying thicknesses (0.4, 0.5, 0.6, 0.7, and 0.8 mm) were subjected to cycles of vertical and 10-degree oblique compressive loading at 5 Hz and 300 N in a servohydraulic testing machine. Five finite element models comprising 5 different occlusal thicknesses (0.4, 0.5, 0.6, 0.7, and 0.8 mm) were simulated at 2 loading angles (0 and 10 degrees) and 3 loading forces (300, 500, and 800 N). Data were statistically analyzed, and fracture patterns were observed with a scanning electron microscope. RESULTS Cyclic loading tests revealed that the fracture resistance of the specimens was positively associated with prosthesis thickness (P<.01). Low von Mises stress values were obtained for prostheses with a minimal thickness of 0.7 mm under varying loading directions and forces. CONCLUSIONS Zirconia prostheses with a minimal thickness of 0.7 mm had a high fracture resistance and the lowest stress values. Therefore, dentists and laboratory technicians should carefully choose the optimum thickness of zirconia prostheses.

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.

Milling properties of low temperature sintered zirconia blocks for dental use

To investigate the milling properties of different yttria-tetragonal zirconia polycrystalline (Y-TZP) block materials by applying a dental computer numerical control (CNC) milling center. Low temperature sintering zirconia block denoted by KMUZ (experimental) with two commercial zirconia blocks for T block made in Taiwan and a G block made in Germany were compared for the milling properties. Seventy-two specimens were milled using the same CNC milling center, and properties were evaluated by measuring the weight loss (g), milling time (s), margin integrity (%) and broken diameter (μm). The crystalline phases contents were identified by X-ray diffraction and the microstructures of the sintering specimens were observed by scanning electron microscopy and transmission electron microscopy. The mean milling time of G and KMUZ were significantly shorter than T (P<0.05). The KMUZ samples exhibited the least weight loss among the three kinds of blocks (P<0.05). The percentages of marginal integrity after milling were high in G and KMUZ but low in T (P<0.05). The mean broken diameters were from 90μm to 120μm. The phase transformation of t-ZrO2 (KMUZ: 7.4%, G: 5.9%, T: 3.2%) to m-ZrO2 when facing the milling pressure in ZrO2 blocks was observed by XRD. The result of TEM microstructure of KMUZ revealed that Y and Si were soluble in grain boundaries. The results show that the milling properties of KMUZ were better than one commercial T and near the G. The hindered grain growth, as a result of the Y3+ content in the grain boundaries, also plays a role in promoting the abnormal grain growth of 3Y-TZP.

Dental implant navigation system guide the surgery future

No study has investigated the effect of learning curves on the accuracy of dental implant navigation systems. This study evaluated the accuracy of the dental implant navigation system and established the learning curve according to operation site and operating time. Each dental model was used for drilling 3 missing tooth positions, and a patient tracking module was created. The same dentist performed the drilling test for 5 sets of dental models. CT back scanning was performed on the dental models. Customized implants based on the drilled holes were inserted. The relative error between the preoperative planning and actual implant was calculated. Using the dental navigation system could help dentists position implants more accurately. Increasing the frequency with which a dentist used the navigation system resulted in shorter operations. Longitudinal and angular deviation were significantly (P < 0.0001 and P = 0.0164). We found that the same level of accuracy could be obtained for the maxilla and mandible implants. The Students t test demonstrated that the longitudinal error, but not the total or angular error, differed significantly (P = 0.0012). The learning curve for the dental implant navigation system exhibited a learning plateau after 5 tests. The current system exhibited similar accuracy for both maxillary and mandibular dental implants in different dental locations. The one‐way ANOVA revealed that the total, longitudinal, and angular errors differed significantly (P < 0.0001, P < 0.0001 and P = 0.0153). In addition, it possesses high potential for future use in dental implant surgery and its learning curve can serve as a reference for dentists.

Craniofacial features of cleidocranial dysplasia

Cleidocranial dysplasia (CCD) is an autosomal-dominant malformation syndrome affecting bones and teeth. The most common skeletal and dental abnormalities in affected individuals are hypoplastic/aplastic clavicles, open fontanelles, short stature, retention of primary teeth, delayed eruption of permanent teeth, supernumerary teeth, and multiple impacted teeth. Treatment of CCD requires a multidisciplinary approach that may include dental corrections, orthognathic surgery and cranioplasty along with management of any complications of CCD. Early diagnosis of this condition enables application of the treatment strategy that provides the best quality of life to such patients. Notably, Runx2 gene mutations have been identified in CCD patients. Therefore, further elucidation of the molecular mechanism of supernumerary teeth formation related to Runx2 mutations may improve understanding of dental development in CCD. The insights into CCD pathogenesis may assist in the development of new treatments for CCD.

Method of Retention Control for Compromised Periodontal Bone Support Abutment of Conical Crown Retained Denture

Conical crown‐retained dentures (CCRD) show a higher survival rate and greater patient satisfaction than transitional removable partial dentures during long‐term follow‐up. However, unsustainable denture retention force on supporting abutments after initial delivery and loss retention are frequently seen in long‐term follow‐up of clinical cases. The main causes are insufficient information concerning denture retention designs and the retention‐tolerance of the supporting abutments. Monitoring by dental technicians of the quality of dental prostheses is critical. This case report describes an optimal method for CCRD construction that determines and distributes an optimal denture retention force on the supporting abutments to allow the patient to easily remove the denture while ensuring that the CCRD remains in place during physiologic activities. Oral rehabilitation with CCRD should consider the condition of the abutment periodontal support, the interarch occlusal relationship, supplemental fatigue of the terminal abutment, and patients estimated bite force. The effects of friction on the abutments inner crown were based on an optimal a angle. The dental laboratory used these measurements to fabricate a CCRD using a Koni‐Meter to adjust the retention of the inner crown. This method protects the abutments and reduces the wear between the inner and outer crowns. The CCRD achieved good esthetic results and physiologic functions. Periodic long‐term follow‐up of the patient and CCRD after initial placement is recommended.