Association between posterior occlusal support and tooth loss in a population-based cohort: The OHSAKA study.

OBJECTIVES: This study aimed to assess the association between posterior occlusal support (POS) and the risk of tooth loss in older adults aged ≥75 years. METHODS: This longitudinal study analyzed 94,422 participants who participated in multiple dental check-ups provided as part of the public healthcare services in Osaka, Japan, from 2018 to 2022. The participants were categorized into nine groups (A1-3, B1-4, and C1 and C2) according to their POS status using the Eichner index at baseline. The dental charts were compared between the initial and final assessments to assess tooth loss. Logistic regression analysis was used to examine the association between POS status and tooth loss, adjusted for several covariates, including age, sex, body mass index, periodontal status, oral hygiene, history of diabetes, history of hypertension, attendance at the annual dental check-up, and observational period. Furthermore, stratified logistic regression analyses were conducted using anterior or posterior tooth loss. RESULTS: After controlling for confounders, POS status was associated with tooth loss. The odds ratios (ORs) with A1 as the reference were 1.74 in A2, 2.55 in A3, 3.40 in B1, 4.74 in B2, 5.79 in B3, 6.00 in B4, 4.44 in C1, and 3.00 in C2, respectively. The ORs for anterior tooth loss were higher than those for posterior tooth loss, with the highest OR observed in B4 (21.4). CONCLUSIONS: This large population-based cohort study showed that a decreased POS was a risk indicator for tooth loss; furthermore, the risk increased even further in the anterior teeth region.

Exploring the association between number of teeth, food intake, and cognitive function: A 9-year longitudinal study.

OBJECTIVES: This study aimed to investigate the association between the number of teeth, food intake, and cognitive function in Japanese community-dwelling older adults. METHODS: This 9-year longitudinal study included a total of 293 analyzable participants who participated in baseline and follow-up surveys. Dental status (number of teeth and periodontal pocket depth), dietary assessment using the brief-type self-administered diet history questionnaire, cognitive function, and the following confounding factors were evaluated: educational level, financial satisfaction, living situation, smoking and drinking habits, history of chronic diseases, apolipoprotein E-ε4 carrier, body mass index, handgrip strength, instrumental activities of daily living, and depressive symptomatology. The Japanese version of the Montreal Cognitive Assessment was used to evaluate cognitive function. A multinomial logistic regression analysis for the intake level of each food categorized into three groups (low, moderate, high), and a generalized estimating equation (GEE) for cognitive function over nine years were performed. RESULTS: After controlling for confounding factors, the number of teeth was shown to be associated with the intake of green-yellow vegetables and meat. Furthermore, the GEE indicated that the lowest quartile of intake of green-yellow vegetables significantly associated with lower cognitive function (unstandardized regression coefficient [B] = -0.96, 95 % confidence interval [CI]: -1.72 to -0.20), and the lowest quartile of intake of meat significantly associated with lower cognitive function (B = -1.42, 95 % CI: -2.27 to -0.58). CONCLUSIONS: The intake of green and yellow vegetables and meat, which is influenced by the number of teeth, was associated with cognitive function in Japanese community-dwelling older adults. CLINICAL SIGNIFICANCE: There are few studies that have examined the association between oral health, food intake, and cognitive function. This 9-year longitudinal study suggests that it is important to maintain natural teeth to enable the functional means to consume green-yellow vegetables and meat, and thereby help maintain cognitive function.

Survival time analysis of remaining teeth following replacement of unilateral free-end missing teeth: A comparison between fixed implant-supported prostheses and removable partial dentures.

OBJECTIVES: This retrospective study aimed to investigate the differences in tooth loss rate between fixed implant-supported prostheses (FISPs) and removable partial dentures (RPDs) in cases of unilateral free-end missing teeth. MATERIALS AND METHODS: The data of 324 patients who underwent treatment with FISPs or RPDs for unilateral free-end missing teeth and satisfied the applicable criteria, were evaluated (47 in the FISPs group and 277 in the RPDs group). After propensity score (PS) matching, which was used to extract patients with similar background factors related to prosthetic selection at baseline, survival time analyses were performed with tooth loss as the endpoint. The adjusted variables were age, sex, number of restored teeth, periodontal status, and the practicing dentist's experience in years. The remaining teeth were classified into subcategories in relation to the missing molars. RESULTS: Overall, 58 patients (29 in each group) selected by PS matching were evaluated in the final analysis. The total number of lost teeth was 35 (FISPs group: n = 10; RPDs group: n = 25). The mean (±SD) period to tooth loss and the 10-year survival rates in the FISPs and RPDs groups were 51.6 (±30.1) months and 42.3 (±29.7) months, 70.5% and 16.4%, respectively. The log-rank test showed that significantly longer survival time in FISPs compared with RPDs. CONCLUSIONS: After adjustments for confounding factors using PS matching, replacing unilateral free-end missing teeth with FISPs may exhibit a lower tooth loss rate in adjacent and contralateral teeth compared to replacing with RPDs.

Masseter and digastric muscle activity evaluation using a novel electromyogram that utilizes elastic sheet electrodes.

PURPOSE: To evaluate the reproducibility and reliability of a novel electromyogram (EMG) device with a flexible sheet sensor for measuring muscle activity related to mastication and swallowing. METHODS: We developed a new EMG device made of elastic sheet electrodes to measure the masseter and digastric muscle activities for evaluating mastication and swallowing. To examine the measurement reproducibility of the new EMG device, masseter muscle activity was analyzed using the intraclass correlation coefficient (ICC). Further, we measured the maximum amplitude, duration, integrated value, and signal-to-noise ratio (SNR) using the new EMG device and conventional EMG devices and evaluated the reliability using ICC and Bland-Altman analysis. RESULTS: We confirmed high ICC (1,1) and ICC (2,1) scores (0.92 and 0.88, respectively) while measuring the reproducibility of the new EMG device. When compared to the active electrode EMG device, we found a high correlation for the maximum amplitude (0.90), duration (0.99), integrated values (0.90), and SNR (0.75), with no observation of significant fixed errors. Moreover, the regression coefficient was not significant for any of the evaluation items and no proportional error was observed. Compared with the passive electrode EMG device, the maximum amplitude and duration were highly correlated (0.73 and 0.89). In addition, the SNR exhibited a significant fixed error. In contrast, the regression coefficient was not significant for any of the evaluation items and no proportional error was observed. CONCLUSIONS: Our results suggest that the new EMG device can be used to reliably and reproducibly evaluate muscle activity during mastication and swallowing.

Factors related to subjective evaluation of difficulty in chewing among community-dwelling older adults.

AIM: Awareness of difficulty chewing may limit the diversity of food intake in older adults. However, few studies have clarified which factors are related to subjective difficulty in chewing. The aim was to identify factors related to subjective difficulty in chewing in 70- and 80-year-old Japanese older adults. METHODS: A total of 1680 participants (792 men, 888 women) were surveyed. Difficulty in chewing was assessed with questionnaires regarding food intake, such as rice, apples, beef, and hard rice crackers. The participants were classified into two groups, the "with difficulty" group (participants who answered "cannot eat," "can eat with difficulty," and "can eat if small") and the "without difficulty" group (participants who answered "can eat without problems"), according to their answers to questionnaires for each food. A logistic regression analysis with subjective difficulty in chewing as the dependent variable was performed for each food. RESULTS: Subjective difficulty in chewing was associated with age, occlusal force, and depression for rice; age, number of remaining teeth, occlusal force, and depression for apples; number of remaining teeth, occlusal force, and depression for beef; and number of remaining teeth and occlusal force for hard rice crackers. CONCLUSIONS: Age, number of remaining teeth, and occlusal force, as well as depression, might be related to subjective evaluation of difficulty chewing in community-dwelling Japanese older adults. Geriatr Gerontol Int 2024; 24: 327-333.

The relationship between changes in occlusal support and masticatory performance using 6-year longitudinal data from the SONIC study.

OBJECTIVES: Reduced occlusal support is thought to be related to a decline in masticatory performance. However, previous research in this field was based on cross-sectional studies. In this study, we conducted a 6-year longitudinal observation of older adults living in the community and examined the associations of changes in occlusal support with masticatory performance. METHODS: Of the 864 participants aged 72-74 years in the SONIC study, 488 who were followed up (median follow-up period 5.92 years) and had no missing data were included in this study. Participants were divided into three groups according to the number of occlusal support zones in the posterior area: Complete occlusion (four zones), Reduced occlusion (one to three zones), and Collapsed occlusion (no occlusal support zone). Longitudinal analysis of the relationship between occlusal support and masticatory performance was undertaken with linear mixed-effects models. RESULTS: Sex, occlusal force, number of unreplaced missing teeth, aging, and occlusal support change were significantly related to masticatory performance. Furthermore, the interaction term between change in occlusal support and aging was a significant explanatory variable for the decline in masticatory performance. The interaction was strongest in the group that changed from Complete or Reduced occlusion to Collapsed occlusion. This result indicates that the loss of occlusal support is a major factor contributing to declining masticatory performance. CONCLUSIONS: The decline of occlusal support was greatly associated with the deterioration of masticatory performance. Our results suggest that older adults need to prevent the collapse of posterior occlusal support to maintain their masticatory performance. CLINICAL SIGNIFICANCE: Occlusal support is important for preserving masticatory performance in older adults. Preventing the loss of molars and retaining occlusal support may contribute to maintaining food intake diversity and nutritional status, thereby improving quality of life. Dental professionals need to carefully examine dental status to assess the risk of occlusal collapse.

Radiographic bone level and soft tissue dimensional changes following explantation of implants affected by peri-implantitis: A retrospective exploratory evaluation.

BACKGROUND: While the dimensional alteration of alveolar bone following tooth extraction have been extensively descripted in the literature, no information is available regarding potential hard and soft tissues changes following implant explantation. AIM: To evaluate the radiographic bone healing and the horizontal and vertical soft tissue dimensional alterations at implant extraction alveoli, 6 months following implant explantation. MATERIAL AND METHODS: Data from 31 patients scheduled for extraction of one implant with persisting peri-implantitis despite treatment were analysed. Bone crest level changes and the extent of bone healing at the apical aspect of the implant socket were assessed on the radiographs prior and 6 months following explantation. Regression analyses assessed the impact of various predictors (e.g., bone crest level, presence/absence of buccal bone) on bone level changes. Fisher's exact probability test was applied to assess the difference in probability to have mucosa recession of ≥2 mm in the presence or absence of alveolar buccal bone. RESULTS: A vertical bone loss of 0.8 mm (standard deviation [SD] = 1.3) of the peri-implant bone crest and a gain of 0.8 mm (SD = 1.1) from the bottom of the peri-implant defect were recorded. Complete healing was noted in the intact implant extraction socket (i.e., the part of the implant not affected by peri-implantitis). A reduction of 0.4 mm (SD = 0.7) of the alveolar mucosa height was recorded in concomitant with a decrease of 0.7 mm (SD = 0.8) of the mucosa width. These alterations were more pronounced in the absence of the alveolar buccal bone. CONCLUSION: The results of the present explorative study indicated a decrease in the height and width of the alveolar soft and hard tissues following explantation of peri-implantitis affected implants, and these changes were more pronounced in the absence of the buccal bone wall. Nevertheless, the apical portion of the implant alveolus (the intact implant socket) tend to heal with no further bone loss.

Relationship between the number of teeth, occlusal force, occlusal contact area, and dietary hardness in older Japanese adults: The SONIC study.

PURPOSE: Individuals with impaired masticatory function tend to prefer soft foods, which results in decreased masticatory muscle activity. This study examined the association between the oral condition (number of teeth, occlusal force, and occlusal contact area) and dietary hardness using a daily dietary questionnaire. METHODS: This cross-sectional study evaluated 1841 participants aged 69-71 and 79-81 years. Registered dentists examined the number of teeth, occlusal force, and occlusal contact area. Dietary hardness was defined as the estimated masticatory muscle activity required for a habitual diet. Habitual diet during the preceding month was assessed using a brief self-administered diet history questionnaire. Confounding factors, such as age, sex, socioeconomic status, smoking habits, history of chronic diseases (hypertension, hyperlipidemia, and diabetes), and cognitive function were also evaluated. Multivariate linear regression analyses were performed to assess the association between dietary hardness and each oral condition. RESULTS: Occlusal force (standardized regression coefficients [ß]=0.08, P < 0.01) and occlusal contact area (ß=0.06, P < 0.01) were significantly associated with dietary hardness after adjusting for the confounding factors. Number of teeth was not significantly associated with dietary hardness. In addition, the associations between dietary hardness, sex, and a history of diabetes were stronger than those between dietary hardness and oral factors. CONCLUSIONS: Occlusal force and contact area were significantly associated with dietary hardness as estimated from the masticatory muscle activity using a daily diet questionnaire.

Relationship between occlusal force and psychological frailty in Japanese community-dwelling older adults: The Septuagenarians, Octogenarians, Nonagenarians Investigation with Centenarians study.

BACKGROUND: Frailty increases the risk of negative health-related events, such as falls, disability, hospitalizations, and death. Although the association between oral health and physical frailty is well established, the relationship between oral health and psychological frailty has not yet been investigated. Therefore, we conducted a cross-sectional study to examine the association between maximal occlusal force and psychological frailty in Japanese community-dwelling older adults. METHODS: Psychological frailty was defined as a World Health Organization-5 scale (WHO-5) score of <13, cognitive and functional status was defined as a Japanese version of the Montreal Cognitive Assessment (MoCA-J) score of <23, and psychological robustness was defined as a WHO-5 score of ≥13 and a MoCA-J score of ≥23. We used a cross-sectional study design to measure maximal occlusal force in 1810 participants, and examined the following factors relevant to psychological frailty: educational level, financial status, living situation, history of chronic diseases, handgrip strength, and instrumental activities of daily living. We used propensity score matching to match the psychological frailty and psychological robustness groups according to demographic and confounding factors. This process, resulted in 344 participants, of whom 172 were in the psychological frailty group and 172 were in the psychological robustness group. In the matched cohort, differences between groups with and without psychological frailty were compared using generalized estimating equations for maximal occlusal force after adjusting for the number of teeth. RESULTS: After controlling for potential confounding factors of frailty, the psychological frailty group showed lower maximal occlusal force compared with the psychological robustness group (unstandardized regression coefficients = -72.7, 95% confidence interval: -126.3 to -19.1). CONCLUSIONS: Maximal occlusal force was associated with a reduced prevalence of psychological frailty among Japanese community-dwelling older adults participating in our study.

Longitudinal study on the effect of keratinized mucosal augmentation surrounding dental implants in preventing peri-implant bone loss.

Background: Dental implant therapy is a well-established method of prosthetic rehabilitation of missing teeth. To maintain the health of the surrounding tissue, management of risk factors/indicators and daily maintenance are important. It still remains controversial whether a certain amount of keratinized mucosal width is essential for maintaining the health of peri-implant tissue. The purpose of this multicenter retrospective study was to assess the correlation between bone loss around dental implant and the amount of keratinized tissue width. Methods: A total of 1,644 implants were evaluated. Data was collected about participants' general and dental history, as well as implant details. Bone resorption around implant was calculated from intra-oral radiographs taken after 1 year and more than 3 years of function. Implants were classified into three groups; received free gingival graft or apically repositioned flap surgery for increasing the keratinized mucosa ≥2 mm width (group A), keratinized mucosa width ≥2 mm (group B), and keratinized mucosa width <2 mm (group C). These data were analyzed by propensity score analysis and a generalized linear regression analysis was performed to compare the bone resorption among groups. Results: Mean functional time was 55.8 months (SD = 20.5) in group A, 67.6 months (SD = 28.1) in group B, and 74.5 months (SD = 32.9) in group C. Mean bone resorption of groups A, B, and C were 0.08 mm (SD = 0.40), 0.18 mm (SD = 0.66), and 0.44 mm (SD = 0.40). Groups A and B had significantly lower bone resorption than group C. Conclusion: The results in this study show the importance of keratinized mucosa in maintaining the peri-implant bone. Our findings also suggest that mucosal transplantation is useful, as opposed to narrowing of the keratinized mucosa.

Effective utilization of digital technology in complete denture fabrication.

Although digital technology is commonly used in various forms of dental treatment, its application to fabrication of removable dentures is still associated with limitations or challenges, such as the recording of occlusal vertical dimensions and determination of the occlusal plane. Here, a simple and inexpensive technique for fabrication of removable complete dentures, partly aided by digital technology, is proposed.

Association between gonial angle on orthopantomogram and reline frequency in removable partial denture wearers.

PURPOSE: Removable dentures are a reasonable option for prosthetic treatment. However, continuous residual ridge resorption and reline procedures are inevitable owing to the strong pressure exerted on the mucosa or inappropriate pressure distribution. This study aimed to elucidate the association between the gonial angle on orthopantomogram (GAO) with occlusal force and reline frequency in removable partial denture wearers. METHODS: Participants were patients who had previously received removable partial denture treatment for a free-end defect. Age, sex, number of remaining teeth, remaining opposing teeth, and occlusal support were investigated. GAO was measured using panoramic radiographs. The mean relining interval was calculated as the mean number of days between denture insertion and the first relining or subsequent relining. The association between the mean relining interval and each factor was investigated. RESULTS: Sixty-five subjects (33 females) were analyzed. The median value of the mean relining interval was 533.3 days, and the median GAO was 123°. There was a significant positive correlation between the mean relining interval and GAO (rs = 0.335). The number of remaining opposing teeth and occlusal support exhibited weak negative correlations with mean relining interval (rs = -0.187 and -0.214, respectively). Multivariate analysis using a generalized linear model showed that GAO was a significant explanatory variable for the mean relining interval. CONCLUSION: Within the limitations of this study, GAO was found GAO was found to contribute to the increased frequency of relining due to ridge resorption in patients with a small GAO.

Prevalence and risk indicators for peri-implant diseases: A literature review.

Peri-implant diseases are known as undesirable conditions that can occur after implant therapy. Although several risk indicators are becoming clear, the causes of peri-implant diseases have not been completely investigated. The purpose of this review was to summarize the prevalence and risk indicators for peri-implant diseases by referring to current papers from various angles. Many studies have reported the varied prevalence of peri-implant mucositis (23.9%-88.0% at the patient level and 9.7%-81.0% at the implant level) and peri-implantitis (8.9%-45% at the patient level and 4.8%-23.0% at the implant level). Additionally, several studies concluded that poor oral hygiene and lack of regular maintenance were strongly correlated with the development of both peri-implant mucositis and peri-implantitis. Diabetes and a history of periodontitis were revealed as risk indicators for peri-implantitis. However, there was no definitive conclusion about the correlations between peri-implant diseases and other factors such as smoking, the shape of the implant superstructure, and the condition of the keratinized mucosa. Further studies useful for evidence-based decision-making are needed for predictable implant therapy in the long term.

Predictive modeling for peri-implantitis by using machine learning techniques.

The purpose of this retrospective cohort study was to create a model for predicting the onset of peri-implantitis by using machine learning methods and to clarify interactions between risk indicators. This study evaluated 254 implants, 127 with and 127 without peri-implantitis, from among 1408 implants with at least 4 years in function. Demographic data and parameters known to be risk factors for the development of peri-implantitis were analyzed with three models: logistic regression, support vector machines, and random forests (RF). As the results, RF had the highest performance in predicting the onset of peri-implantitis (AUC: 0.71, accuracy: 0.70, precision: 0.72, recall: 0.66, and f1-score: 0.69). The factor that had the most influence on prediction was implant functional time, followed by oral hygiene. In addition, PCR of more than 50% to 60%, smoking more than 3 cigarettes/day, KMW less than 2 mm, and the presence of less than two occlusal supports tended to be associated with an increased risk of peri-implantitis. Moreover, these risk indicators were not independent and had complex effects on each other. The results of this study suggest that peri-implantitis onset was predicted in 70% of cases, by RF which allows consideration of nonlinear relational data with complex interactions.

Deep learning-based detection of dental prostheses and restorations.

The purpose of this study is to develop a method for recognizing dental prostheses and restorations of teeth using a deep learning. A dataset of 1904 oral photographic images of dental arches (maxilla: 1084 images; mandible: 820 images) was used in the study. A deep-learning method to recognize the 11 types of dental prostheses and restorations was developed using TensorFlow and Keras deep learning libraries. After completion of the learning procedure, the average precision of each prosthesis, mean average precision, and mean intersection over union were used to evaluate learning performance. The average precision of each prosthesis varies from 0.59 to 0.93. The mean average precision and mean intersection over union of this system were 0.80 and 0.76, respectively. More than 80% of metallic dental prostheses were detected correctly, but only 60% of tooth-colored prostheses were detected. The results of this study suggest that dental prostheses and restorations that are metallic in color can be recognized and predicted with high accuracy using deep learning; however, those with tooth color are recognized with moderate accuracy.

Two- and ten-year follow-up of patients responding and non-responding to the surgical treatment of peri-implantitis: A retrospective evaluation.

OBJECTIVES: To report a follow-up of patients following the surgical anti-infective treatment of peri-implantitis and to identify possible risk indicators for the progression of disease during supportive peri-implant therapy. MATERIAL AND METHODS: Following peri-implant surgery, 41 patients (213 implants) were enrolled in a supportive peri-implant therapy. At the 2-year follow-up, two groups of patients were identified, with or without residual peri-implant pockets (responding and non-responding group). Eighteen patients (85 implants) of the non-responding group were followed for further 8 years. RESULTS: At the 2-year examination, 73 of the 117 treated implants (62.4%) presented healthy peri-implant condition, while 44 (37.6%) presented persisting peri-implantitis associated with substantial bone loss before treatment. The 10-year examination of the non-responding group revealed that 1) 84% of the implants that regained health following surgery remained healthy during the entire observation period; 2) 66% of the implants with residual pockets following surgery maintained stable peri-implant condition; and 3) 29% of all treated implants showed disease progression, and 11 of those were extracted. Presence of pockets at 3-4 sites of the implants was identified as risk indicator for progression of peri-implantitis. CONCLUSION: The peri-implant health achieved following therapy was maintained for most of the implants during the follow-up. Residual pockets were a frequent finding at implants with substantial bone loss before treatment. Presence of pockets around the entire circumference of the implants resulted as a risk indicator for further disease progression. The probability of progression of peri-implant disease increased with increased observation time.

Identification of dental implants using deep learning-pilot study.

BACKGROUND: In some cases, a dentist cannot solve the difficulties a patient has with an implant because the implant system is unknown. Therefore, there is a need for a system for identifying the implant system of a patient from limited data that does not depend on the dentist's knowledge and experience. The purpose of this study was to identify dental implant systems using a deep learning method. METHODS: A dataset of 1282 panoramic radiograph images with implants were used for deep learning. An object detection algorithm (Yolov3) was used to identify the six implant systems by three manufactures. To implement the algorithm, TensorFlow and Keras deep-learning libraries were used. After training was complete, the true positive (TP) ratio and average precision (AP) of each implant system as well as the mean AP (mAP), and mean intersection over union (mIoU) were calculated to evaluate the performance of the model. RESULTS: The number of each implant system varied from 240 to 1919. The TP ratio and AP of each implant system varied from 0.50 to 0.82 and from 0.51 to 0.85, respectively. The mAP and mIoU of this model were 0.71 and 0.72, respectively. CONCLUSIONS: The results of this study suggest that implants can be identified from panoramic radiographic images using deep learning-based object detection. This identification system could help dentists as well as patients suffering from implant problems. However, more images of other implant systems will be necessary to increase the learning performance to apply this system in clinical practice.

Ideal placement of an implant considering the positional relationship to an opposing tooth in the first molar region: a three-dimensional finite element analysis.

BACKGROUND: Excessive loading from the occlusion is known as a major pathological factor in implant failure. The force applied to the implant varies depending on the positional relationship to an opposing tooth in clinical cases. However, no studies have clarified the relationship between the discrepancy and mechanical complications. MATERIALS AND METHODS: The study enrolled patients whose mandibular first molar was missing and was opposed by a natural maxillary first molar. The horizontal and vertical distance between the residual ridge and the occlusal surface of the maxillary first molar were measured from computerized tomograms. Subsequently, four finite element models were constructed in combinations of horizontal and vertical discrepancies. Additionally, the effect of inclined implantation and angled abutments were examined in a large clearance model. Maximum von Mises stress values generated in abutments under 90° or 60° loading vectors were compared with a three-dimensional finite element method. RESULTS: Data from 123 subjects (39 males and 84 females, average age 55.2 ± 11.4 (SD) years) were collected for the analyses. Under all conditions, the stress on the load side (the buccal side) was concentrated on the platform, and the stress on the opposite side (the lingual side) was concentrated on the top of the abutment tube inserted into the implant. In comparison to 90° loading vectors, the maximum von Mises stresses of each model were 1.20 to 2.67 times under 60° loading vectors. For inclined implantation, the maximum stress was 8.4% less at a 90° load and 9.7% less at a 60° load compared with vertical implantation. With angled abutments, the maximum stress was 15.7% less at a 90° load and 30.0% less at a 60° load compared with vertical implantation. CONCLUSION: In cases of progressive alveolar resorption with a large clearance between the implant and the opposing teeth, a higher stress concentration was observed at the joint between the implant and the abutment. Our findings also showed that stress concentration around this area can be reduced by the use of inclined implantation and angled abutments under the condition of a horizontal offset between the implant and opposing teeth.

Determination of the lingual border of lower complete dentures: How to use a silicone impression material?

OBJECTIVES: This study aimed to clarify the efficacy of a border-moulding procedure with low-flow silicone impression material compared with a conventional compound to complete denture fabrication. It also aimed to evaluate the influence of various functional tasks during the lingual-side moulding procedure regarding the depth and width of the border. METHODS: Ten dentate subjects (three men, seven women; average age 30 years) were enrolled in this study after giving informed consent. A specially designed custom impression tray for the mandibular lingual side was fabricated for each subject. With the tray and heavy-body-type silicone material, lingual border moulding was performed that included four functional tasks: tongue protrusion (TP), licking the upper lip with the tongue (UL), swallowing (SW), and placing the tongue tip to the palate (PP). RESULTS: Within the limitations of this study, the results suggested that heavy-body silicone impression material is satisfactory for use in the border-moulding procedure, giving reproducible results. CONCLUSION: There were no significant differences among the functional tasks regarding the depth and width of the lingual flange except for swallowing, which exhibited the largest values.

Risk indicators for marginal bone resorption around implants in function for at least 4 years: A retrospective longitudinal study.

BACKGROUND: Marginal bone stability is considered one of the most important issues in implant dentistry. It is essential to understand how various factors influence bone resorption around implants. The purpose of this retrospective longitudinal study was to identify potential risk indicators associated with marginal bone resorption around implants in function for at least 4 years. METHODS: Several systemic-related, intraoral-related, implant-related factors were collected. Marginal bone level change (MBLC) was determined by comparing intraoral radiographs taken at baseline (1 year after prosthesis delivery), and at follow-up (over 3 years from baseline). A hierarchical regression analysis using liner mixed-effects models was performed to examine correlations between MBLC and various factors. RESULTS: Overall, 514 patients with 1535 implants were analyzed. The mean age of the participants was 62.9 years. Mean annual MBLC was 0.048 mm, and mean functional time was 5.96 years. The result showed that the following explanatory variables had significant effects on MBLC: functional time, plaque control record > 20%, Eichner index C1-3, maxilla, cement-retained superstructure, and keratinized mucosa width < 2 mm. We did not find statistically significant associations between bone resorption and some variables known as risk factors, such as diabetes, smoking, and history of periodontitis. CONCLUSIONS: Within the limits of this study, longer functional time, poor oral hygiene, loss of occlusal support, location in the maxilla, cement-retained superstructure, and less keratinized mucosa should be considered as risk indicators for bone resorption around implants.