In vitro evaluation of shape-memory hydrogels for removable dental prostheses and optimization of phase-transition temperature for intraoral use.

STATEMENT OF PROBLEM: Removable dental prostheses require periodic relining with the loss of intaglio surface fit because of mucosal shape changes over time. Therefore, a new material with high adaptability to tissue changes over time would be beneficial. PURPOSE: This study focused on a shape-memory gel (SMG) that softens when heated, retains its shape when cooled, and returns to its original shape when reheated. The purpose was to optimize SMG for intraoral use by controlling the ratio of 2 acrylate monomers and to evaluate the changes in the shape memory and physical properties of SMG with temperature and to evaluate biocompatibility. MATERIAL AND METHODS: SMG specimens were synthesized using the following mixing ratios of 2 monomers, docosyl acrylate (DA) and stearyl acrylate (SA): 0:100, 25:75, 50:50, 75:25, and 100:0. SMG specimens were photopolymerized using a fluorescent light-polymerizing unit. To evaluate shape memory as a function of temperature, permanent deformation was measured based on the standardized compression set test for thermoplastic rubber. For evaluation of the physical properties and cytotoxicity, a 3-dimensionally printed denture base material was used as the control material. All assessments were compared between the groups by using 1-way analysis of variance followed by the Tukey-Kramer multiple comparison test (α=.05). RESULTS: SMGs with a higher amount of DA maintained their compressed shape at room and intraoral temperatures. However, the SMG matrices softened and recovered their original shapes above 60 °C. SMGs showed Shore A hardness equivalent to that of the denture-base polymer material at intraoral temperatures because of the high phase-transition temperature. The low water solubility of SMGs supported the biocompatibility test results. CONCLUSIONS: SMG, in which the phase-transition temperature was controlled by mixing acrylate monomers with different melting points, exhibited shape memory in the intraoral environment. The results indicate the feasibility of applying SMG for the fabrication of removable dental prostheses because of its high adaptability to tissue changes over time and biocompatibility.

Medical-Dental Collaboration and Interprofessional Training for Maxillofacial Diseases at Tohoku University Hospital.

The Tohoku University Hospital has been a clinical and research facility for all the related departments of Tohoku University. Medical-dental and interprofessional collaboration has resulted in special treatment teams, made up of members of departments such as the center for head and neck cancer, the center for dysphagia, and the cleft lip and palate center. Those treatment teams held conferences, case study meetings, reading sessions, and in-hospital seminars. The purpose of this study was to evaluate the outcomes of various medical-dental and the interprofessional collaboration at Tohoku University Hospital and training program to equip hospital dentists in higher medical institutions. The attainment targets are the acquisition of basic medical skills and knowledge under the guidance of supervising doctors. As a result, the hospital dentists could acquire their own specialized knowledge and skills certificated by each academic society. The smooth team treatment has been achieved, and the number of cases discussed by cancer boards and center for dysphagia has increased year by year due to the efficiency of their clinical pathways. On the dental care side as well, the wearing rates of maxillofacial prosthetic devices such as maxillofacial prostheses and palatal augmentation prostheses (PAP) have improved, which have contributed to improving patient's stomatognathic function. Tohoku University Hospital has been practicing collaboration between medical and dental professionals and it has produced mutual benefits. Our interprofessional training system based on the medical-dental collaboration could develop professionals who have acquired cross-disciplinary knowledge and skills from experienced doctors.

Hermeticity of a hollow obturator model using CAD and rapid prototyping technologies.

STATEMENT OF PROBLEM: Although closed hollow obturator prostheses provide the benefit of minimized weight, they also pose challenges. They are complex to fabricate, and contaminated water can easily enter the hollow section through the joined part, making them unsanitary and leading to malodor and increased weight. PURPOSE: The purpose of this in vitro study was to investigate the hermeticity and durability of a hollow obturator model fabricated by using computer-aided design (CAD) and rapid prototyping (RP) techniques and to evaluate the possibility of its clinical use. MATERIAL AND METHODS: Leak testing was used to evaluate the hermeticity and durability of hollow spherical obturator specimens with an outer diameter of 30 mm and 2 different wall thicknesses (1.5 and 2.0 mm). Six specimens were fabricated for each of the wall thicknesses by using CAD and RP techniques. The accumulation of fluids in the hollow obturator specimens was evaluated every day by using megascopic observation with photoirradiation from the base of the specimens. The amount of water absorption and the rate of increase in the weight of the 2 specimens were calculated and compared. Statistical analysis was performed by using the Mann-Whitney U test (α=.05). RESULTS: The application of CAD and RP techniques made it possible to fabricate a hollow obturator model specimen with completely unified parts. The 1.5-mm specimen showed an absorption rate (2.61%) that significantly exceeded that of the 2.0-mm specimen (2.53%) on day 130 (P=.006). By the end of the observation period, the 1.5-mm specimen exhibited large amounts of water absorption and destruction. The 1.5-mm-thick wall had reduced hermeticity than the 2.0-mm-thick wall. CONCLUSIONS: A fully unified hollow obturator model with 2.0-mm-thick walls was fabricated by using CAD and RP techniques. The absence of any joints prevented fluid accumulation, making this method suitable for the fabrication of hollow prostheses.

A workflow for fabricating a hollow obturator by using 3D digital technologies.

Conventional methods used for fabricating hollow obturator prostheses have numerous problems. The workflow presented in this article integrates 3D digital technologies into a functional protocol, enabling the fabrication of single-piece hollow prostheses with no joints by using an optical 3D scanner and a laminating molding device.

Dental implant care and trouble among dependent patients based on the questionnaire survey among Japanese dental practitioners.

BACKGROUND: Self-care and professional care of implants may prove difficult for elderly people who require nursing care. However, the actual state of care and problems remains unknown. In this study, we investigated the actual state of implant problems in elderly people living in their own home or in a nursing home who received visiting dental treatment. METHODS: We mailed questionnaire survey forms to 2339 representatives or specialists who were members of the Japanese Society of Oral Implantology, the Japanese Society of Gerodontology or the Japan Prosthodontic Society. We narrowed down the respondents to those who provided visiting dental treatment, and analyzed the actual state of implants observed during visiting dental treatment (type, care, problems, countermeasures, etc.). RESULTS: Of the 924 dentists who responded to the questionnaire survey, 291 (22%) provided visiting dental treatment. While the majority of implant types encountered in the previous 12 months were root-form implants, there were still a certain number of blade and subperiosteal implants. Daily implant care involved mostly cleaning with a toothbrush + auxiliary tools. The most frequent implant problems encountered in the past were difficulty in cleaning and peri-implantitis. Medication and antiphlogistic treatment were most frequently adopted as countermeasures to implant problems, followed by observation. When we classified the results into those for the dentists who provided implant treatment and those for the dentists who did not, we found that many of the dentists who did not provide implant treatment opted for observation or medication, while those who provided implant treatment also implemented removal of superstructure, retightening of screws, repair and so forth. CONCLUSIONS: We found that many of the implant troubles encountered by dentists who provided visiting dental care were difficulty in cleaning or peri-implantitis, and that the actions taken against these troubles varied depending on the experience of the dentist performing the implant treatment. Our study also revealed that dentists who provide visiting dental care need to acquire knowledge and skills of implant treatment, to have actions prepared in case they encounter such cases, or to closely coordinate with dentists who specialize in implants.

Influence of maxillary obturator prostheses on facial morphology in patients with unilateral maxillary defects.

STATEMENT OF PROBLEM: Facial asymmetry is prominent with individuals with unilateral bone resorption and can lead to decreased quality of life. PURPOSE: The purpose of this study was to investigate the influence of maxillary obturator prostheses on facial morphology of individuals with unilateral maxillary defects by using 3-dimensional digital stereophotogrammetry. MATERIAL AND METHODS: The facial data of 8 participants with unilateral maxillary defects were acquired with a noncontact 3-dimensional digitizer, both with and without maxillary prostheses. The mid-facial plane was established by overlapping an original facial image with its mirror image. Displacement at 18 measurement points, including 7 bilateral pairs, was compared between the 2 sides, with and without the prostheses. Asymmetry indices of these 7 pairs also were calculated. Multivariate repeated-measures ANOVA was used to determine differences. RESULTS: Displacements of the lateral and inferior points at the ala of the nose were significantly greater on the defect side than on the normal side. The distances between the ideal and defect side points at the superior ala, the upper lip, and the angle of the mouth decreased significantly with the prosthesis. No significant differences were found in asymmetry indices, but the angle of the upper lip line to the mid-sagittal plane increased significantly with the prosthesis. CONCLUSIONS: The 3-dimensional analyzing method developed in this study can be useful in evaluating facial reconstruction with maxillary obturator prostheses with individuals with unilateral maxillary defects. The prostheses affect the region of the nasal ala, the upper lip, and the angles of the mouth.

Influence of immediate and early loading on bone metabolic activity around dental implants in rat tibiae.

OBJECTIVES: The aim of this study was to examine the influence of immediate and early loading on dynamic changes in bone metabolism around dental implants using bone scintigraphy. MATERIAL AND METHODS: Two titanium implants were inserted in the right tibiae of 21 rats. Closed coil springs with 4.0-N loads were applied parallel to the upper portion of the implants for 35 days. According to the load application timing, rats were divided into three groups: immediate loading (IL) group, early loading 1 day after implant insertion (1-D early loading [EL]) group, and loading 3 days after implant insertion (3-D EL) group. Rats were intravenously injected with technetium-99 m-methylene diphosphonate (Tc99 m-MDP) (74 MBq/rat) and scanned by bone scintigraphy at 1, 4, 7, 11, 14, 21, 28, and 35 days after load application. The ratio of accumulation of Tc99 m-MDP around the implants to that of a reference site (uptake ratio) was calculated to evaluate bone metabolism. RESULTS: In every group, the uptake ratio increased until 7 days after load application and then gradually decreased. It was significantly higher than baseline at 4, 7, 11, and 14 days (P < 0.001). The uptake ratio in the 1-D EL and 3-D EL groups were significantly higher than that in the control group and also that in the IL group (P < 0.001). CONCLUSIONS: Bone metabolism initially increased and then gradually decreased to baseline despite differences in load timing. Increases in bone metabolic activity differed according to load application timing; the later the load application, the more enhanced the bone metabolism.

Tongue pressure during swallowing in adults with down syndrome and its relationship with palatal morphology.

In individuals with Down syndrome, hypotonicity of the tongue and an underdeveloped maxilla may lead to poor oral motor coordination, which adversely affects the oral phase of swallowing. This study aimed to evaluate the characteristics of pressure produced by the tongue against the hard palate during swallowing in individuals with Down syndrome. In addition, the relationship between tongue pressure and palatal morphology was examined. We studied nine adults with Down syndrome and ten healthy adults as controls. Tongue pressure while swallowing 5 mL water was recorded by a sensor sheet system with five measuring points attached to the hard palate. Palatal length, depth, width, curvature, and slope were measured by three-dimensional digital maxillary imaging. The order of onset of tongue pressure on the median line of the hard palate was the same in all participants, except for three with Down syndrome. The duration and maximal magnitude of tongue pressure on the median line in nine participants with Down syndrome were significantly shorter and lower than those of controls. In participants with Down syndrome, significant positive correlations were observed between the duration of tongue pressure at the mid-median part of the hard palate and palatal depth and width, and between the duration and maximal magnitude of tongue pressure at the posterior-median part and palatal length. These findings suggest that impaired tongue activity, poor tongue control, and constrained tongue motion due to a short and narrow palate contribute to swallowing difficulty in individuals with Down syndrome.

Bone response to immediate loading through titanium implants with different surface roughness in rats.

Because of its high predictability of success, implant therapy is a reliable treatment for replacement of missing teeth. The concept of immediate implant loading has been widely accepted in terms of early esthetic and functional recovery. However, there is little biological evidence to support this concept. The objective of this study was to examine the interactive effects of mechanical loading and surface roughness of immediately loaded titanium implants on bone formation in rats. Screw-shaped anodized titanium implants were either untreated (smooth) or acid-etched. Two implants were inserted parallel to each other in the tibiae of rats, and a closed coil spring (2.0 N) was immediately applied. Trabecular and cortical bone around both implants was analyzed using microtomographic images, and a removal torque test was performed at weeks 1, 2, and 4. Immediate loading of acid-etched implants resulted in significant decreases in bone mineral density, contact surface area, and cortical bone thickness. These effects were not observed after immediate loading of smooth implants. Conversely, loading did not influence acid-etched implant fixation; however, smooth implant fixation at week 1 was significantly reduced. These results imply that surface roughness regulates bone response to mechanical stress and that immediate loading might not inhibit osseointegration for smooth and rough implants in the late healing stages.

Postoperative Rehabilitation with a CAD/CAM-fabricated Occlusal Splint Following Plate Reconstruction after Hemimandibulectomy and Condylectomy: A Case Report.

Mandibular deviation (MD) is a common reconstruction sequela after segmental mandibulectomy. Although proper postoperative rehabilitation is critical for MD management and minimization, the information available is limited. This report describes postoperative rehabilitation with an occlusal splint fabricated using computer-aided design (CAD) and computer-aided manufacturing (CAM) (CAD/CAM-OS) and the results of a threedimensional occlusal analysis using an intraoral scanner after hemimandibulectomy and plate reconstruction. Despite the short follow-up, adherence to postoperative rehabilitation with CAD/CAM-OS for MD correction, even during radiotherapy, was demonstrated by the digital workflow and analysis results.

Effects of maxillofacial prosthetic treatment on oral health-related quality of life and masticatory ability of patients with head and neck tumors.

PURPOSE: Using multivariate analysis, this study investigated the effectiveness of maxillofacial prosthetic treatment in relation to oral health-related quality of life (OHR-QoL), masticatory ability (food intake status score and gum-jelly test score) and related factors in patients who had undergone surgery for head and neck tumors. METHODS: The study cohort comprised 112 patients who underwent surgical resection and prosthetic treatment among 224 patients with head and neck tumors seen at the Maxillofacial Prosthetics Clinic of Tohoku University Hospital in a 2-year period. Correlations between OHR-QoL, food intake status score, and gum-jelly test score (criterion variables), and age, sex, maxillary defect, tongue/soft tissue defect, reconstructive surgery, and chemoradiotherapy (explanatory variables) were investigated, and the data were examined statistically. RESULTS: Maxillary defect, tongue and soft palate tissue defect, and chemoradiotherapy were identified as factors that hindered the effectiveness of maxillofacial prosthetic treatment for improvement of the OHR-QoL, food intake status score, and gum-jelly test score. On the other hand, reconstructive surgery was a factor that facilitated the improvement of OHR-QoL and masticatory ability with maxillofacial prosthetic treatment. CONCLUSION: The factors identified to be related to the success or failure of maxillofacial prosthetic treatment suggest the importance of combining prosthetic intervention with surgical reconstruction.

Prosthodontic treatment can improve the ingestible food profile in Japanese adult outpatients.

PURPOSE: To investigate the effect of prosthodontic treatment on the ingestible food profile in adult Japanese outpatients, and to identify the related risk factors that can deteriorate the profile. METHODS: The participants were 277 outpatients who visited university-based specialty clinics in Japan for prosthodontic treatment. The demographic data, number of present teeth assessed via intraoral examination, and oral health-related quality of life assessed by the total Oral Health Impact Profile (OHIP-J54) scores of all participants were recorded before treatment. Ingestible food profile score (IFS) was recorded using a validated food intake questionnaire. Eligible participants who answered the questionnaire before and after treatment were categorized into five groups based on the prosthodontic treatments they received (i.e., crowns, bridges, removable partial dentures, removable complete dentures, and removable complete and partial dentures). RESULTS: Multivariate analysis of covariance revealed a statistically significant main effect of prosthodontic intervention (time course: before and after treatment) on mean IFS (P=0.035, F=4.526), even after adjusting for covariates (age, number of present teeth, and treatment modality). Multiple linear regression analysis revealed that the low number of present teeth (r=0.427, P<0.001) and a high OHIP-J54 total score (r=-0.519, P<0.001) of the patients at the baseline were significantly associated with their baseline IFSs, even after adjusting for confounding variables. CONCLUSIONS: The findings of this multicenter follow-up study indicate the importance of prosthodontic rehabilitation in improving patients' ingestible food profiles.

Quantification and identification of bacteria in acrylic resin dentures and dento-maxillary obturator-prostheses.

PURPOSE: To quantify and identify bacteria detected in acrylic resin dentures and dento-maxillary obturator-prostheses after long-term use. METHODS: The internal layer of denture bases from 13 daily-use removable acrylic resin dentures was sampled, while the inner fluid samples/no-fluid samples of obturators were collected from 11 in-use acrylic resin dento-maxillary obturator-prostheses. Samples were cultured, and isolated bacteria were counted and identified by molecular biological methods. RESULTS: Bacteria were detected in five (38.5%) acrylic resin dentures and six (54.5%) acrylic resin obturators. Four Lactobacillus species and one Propionibacterium species were isolated from three repaired denture bases, and from two non-repaired dentures, two Actinomyces species and Streptococcus mutans were isolated. On the other hand, 17 bacterial species, belonging to the family and genera of Olsenella, Bacillus, Citrobacter, Enterobacteriaceae, Lactobacillus, Pantoea, Peptoniphilus, Klebsiella and Pseudomonas, were isolated from obturators. Several species of viable bacteria were detected in acrylic resin denture bases and obturators.

Bone remodeling following mandibular reconstruction using fibula free flap.

To investigate bone remodelling responses to mandibulectomy, a joint external and internal remodelling algorithm is developed here by incorporating patient-specific longitudinal data. The primary aim of this study is to simulate bone remodelling activity in the conjunction region with a fibula free flap (FFF) reconstruction by correlating with a 28-month clinical follow-up. The secondary goal of this study is to compare the long-term outcomes of different designs of fixation plate with specific screw positioning. The results indicated that the overall bone density decreased over time, except for the Docking Site (namely DS1, a region of interest in mandibular symphysis with the conjunction of the bone union), in which the decrease of bone density ceased later and was followed by bone apposition. A negligible influence on bone remodeling outcome was found for different screw positioning. This study is believed to be the first of its kind for computationally simulating the bone turn-over process after FFF maxillofacial reconstruction by correlating with patient-specific follow-up.

Changes in tongue pressure and dysphagia at oral cancer patients by palatal augmentation prosthesis.

BACKGROUND: The palatal augmentation prosthesis (PAP) is an intraoral prosthesis used in the treatment of dysphagia. AIM: The objective of the study is to examine the effect of PAP using tongue pressure and the Videofluoroscopic Dysphagia Scale (VDS) to understand the precise mechanism for improvement in swallowing function with PAP for oral cancer at retrospective survey. METHODS AND RESULTS: Fifteen patients were provided PAPs. Tongue pressure and VDS were evaluated with and without PAP. After intervention with PAP, tongue pressure significantly increased as compared to when without PAP (p < .05). The total mean VDS score with PAP was found to have significantly improved (p < .05). The mean VDS score of the oral phase also significantly improved with the PAP compared to without the PAP group (p < .05). Significant differences (p < .01) were found in each category, such as tongue to palate contact and pyriform sinus residue. CONCLUSION: PAP can improve tongue pressure, tongue to palate contact, and pyriform sinus residue.

The potential of cohesive silicone for facial prosthetic use: a material property study and a clinical report.

PURPOSE: Prosthetic reconstruction of a facial defect can help to reduce disfigurement and restore the social functioning of the patient. Several methods for holding a prosthesis in place exist, including the use of osseointegrated implants and medical adhesive agents; however, since the treatment options for some patients may be restricted by various health conditions and other limitations, including allergies to adhesive agents, a history of radiation therapy, and financial issues, other options that suit individual demands are required. The objectives of this study were to test the hypothesis that adhesive characteristics could be bestowed on silicone elastomers by altering their catalyst/base silicone ratios (CBR) and to examine the effect of the thickness of the cohesive silicone layer of a prosthesis on its initial adhesive strength. MATERIALS AND METHODS: The adhesive strengths of specimens with CBRs ranking from 1/10 to 1/70 were examined by the rolling ball tack test. A tensile test was used to evaluate the tensile adhesive strengths of specimens made of layers of cohesive silicone (CBR 1/60) and normal silicone (CBR 1/10) with different thicknesses. Auricular prostheses containing cohesive silicone on the skin side were applied to a 50-year-old man with defects in both auricular regions and with reduced manual dexterity due to serious burns. RESULTS: The rolling distance was reduced with a decrease in CBR, and a thinner cohesive silicone (CBR 1/60) layer demonstrated a higher peak load. On clinical application, the adhesion of the auricular prosthesis containing cohesive silicone was improved by expanding the adhesive area and altering the thickness of the cohesive silicone layer, resulting in sufficient adhesion and easier handling than that achieved using an adhesive agent 1 year post delivery. CONCLUSION: These results suggest that cohesive silicone can be used as a glueless retentive material for facial prostheses.

Questionnaire survey on nurses and speech therapists regarding dysphagia rehabilitation in Japan.

OBJECTIVE: Current interventions of dysphagia are not generalizable, and treatments are commonly used in combination. We conducted a questionnaire survey on nurses and speech therapists regarding dysphagia rehabilitation to understand the current situation in Japan. METHODS: The questionnaire was sent to 616 certified nurses in dysphasia nursing and 254 certified speech-language-hearing therapists for dysphagia. Based on "Summaries of training methods in 2014" by JSDR, 24 local indirect exercises, 11 general indirect exercises, and 13 direct exercises were selected. The Likert scale "How do you feel about each method" was used as follows: A; Frequency, B; Ease, C; Adherence, D; Effectiveness (1-5))?". RESULTS: Two hundred fifty (40%) nurses and 145 (57%) speech-language-hearing therapists (ST) responded to the questionnaire. The direct exercise was associated with a significantly high score in every question. In indirect exercises, "Cervical range of motion exercise," "Orofacial myofunctional exercise," "Lip closure exercise." "Ice massage of pharynx" and "Huffing" were used relatively frequently. "Balloon dilatation therapy" and "Tube exercise" was associated with a relatively high discrepancy for two questions. Frequency" and the sum of "Ease," "Adherence," and "Effectiveness." was significantly correlated for local indirect exercises (r2 = 0.928, P < 0.01), general indirect exercises (r2 = 0.987, P < 0.01), and direct exercises (r2 = 0.996, P < 0.01) (Fig. 5). CONCLUSION: This study examined the current situation of dysphagia rehabilitation in Japan. Our results aid to increase understanding and selection of rehabilitative treatments for dysphagia patients in Japan.

Questionnaire survey on pharyngolaryngeal sensation evaluation regarding dysphagia in Japan.

OBJECTIVE: The objective is to conduct a questionnaire survey regarding pharyngolaryngeal sensation evaluation in dysphagia to understand the current situation in Japan. METHOD: The questionnaire was sent to the councilor of the Society of Swallowing and Dysphagia of Japan and the Japanese Society of Dysphagia Rehabilitation-Certified Clinician. The prospective questionnaire survey included the questions listed below: Q1: What do you think of the importance of pharyngolaryngeal sensory evaluation? Q2: Select one of the essential swallowing sensations. Q3: Select one of the following regarding the frequency of sensory examination of the larynx. Q4: Select the proportion of cases the sensory test results affect. Q5: As a pharyngolaryngeal sensory evaluation method in swallowing function evaluation, please fill in the table below for the frequency, difficulty, and effectiveness of the following tests, such as gag reflex, touching the larynx by endoscopy, touching the larynx by the probe with endoscopy, cough reflex test, swallowing provocation test. RESULTS: The essential swallowing sensations of mechanical stimulation, chemical stimulation, thermal stimulation were 84.9%, 5.4%, and 9.7%, respectively. The frequency of touching the larynx by endoscopy in the otolaryngology group and cough reflex test in dentistry was significantly higher than the other groups (p < 0.05). The correlation between the frequency and difficulty or effectiveness of the sensory tests indicated that the frequency and difficulty are significantly correlated between each item. CONCLUSION: Our results aid in increasing understanding and selection of pharyngolaryngeal sensation evaluation for dysphagia patients.

Effects of buccal thickness augmentation on bone remodeling after maxillary anterior implantation.

The biomechanics associated with buccal bone thickness (BBT) augmentation remains poorly understood, as there is no consistent agreement in the adequate BBT to avoid over-loading resorption or over-augmenting surgical difficulty. This study utilizes longitudinal clinical image data to establish a self-validating time-dependent finite element (FE)-based remodeling procedure to explore the effects of different buccal bone thicknesses on long-term bone remodeling outcomes in silico. Based upon the clinical computed tomography (CT) scans, a patient-specific heterogeneous FE model was constructed to enable virtual BBT augmentation at four different levels (0.5, 1.0, 1.5, and 2.0 mm), followed by investigation into the bone remodeling behavior of the different case scenarios. The findings indicated that although peri-implant bone resorption decreased with increasing initial BBT from 0.5 to 2 mm, different levels of the reduction in bone loss were associated with the amount of bone augmentation. In the case of 0.5 mm BBT, overloading resorption was triggered during the first 18 months, but such bone resorption was delayed when the BBT increased to 1.5 mm. It was found that when the BBT reached a threshold thickness of 1.5 mm, the bone volume can be better preserved. This finding agrees with the consensus in dental clinic, in which 1.5 mm BBT is considered clinically justifiable for surgical requirement of bone graft. In conclusion, this study introduced a self-validating bone remodeling algorithm in silico, and it divulged that the initial BBT affects the bone remodeling outcome significantly, and a sufficient initial BBT is considered essential to assure long-term stability and success of implant treatment.

Influence of bone condition on implant placement accuracy with computer-guided surgery.

BACKGROUND: The impact of the jaw bone condition, such as bone quantity and quality in the implant placement site, affecting the accuracy of implant placement with computer-guided surgery (CGS) remains unclear. Therefore, this study aimed to evaluate the influence of bone condition, i.e., bone density, bone width, and cortical bone thickness at the crestal bone on the accuracy of implant placement with CGS. METHODS: A total of 47 tissue-level implants from 25 patients placed in the posterior mandibular area were studied. Implant placement position was planned on the simulation software, Simplant® Pro 16, by superimposing preoperative computed tomography images with stereolithography data of diagnostic wax-up on the dental cast. Implant placement surgery was performed using the surgical guide plate to reflect the planned implant position. The post-surgical dental cast was scanned to determine the position of the placed implant. Linear and vertical deviations between planned and placed implants were calculated. Deviations at both platform and apical of the implant were measured in the bucco-lingual and mesio-distal directions. Intra- and inter-observer variabilities were calculated to ensure measurement reliability. Multiple linear regression analysis was employed to investigate the effect of the bone condition, such as density, width, and cortical bone thickness at the implant site area, on the accuracy of implant placement (α = 0.05). RESULT: Intra- and inter-observer variabilities of these measurements showed excellent agreement (intra class correlation coefficient ± 0.90). Bone condition significantly influenced the accuracy of implant placement using CGS (p < 0.05). Both bone density and width were found to be significant predictors. CONCLUSIONS: Low bone density and/or narrow bucco-lingual width near the alveolar bone crest in the implant placement site might be a risk factor influencing the accuracy of implant placement with CGS.