Digital design of open hollow obturator framework using existing dentures: A dental technique.

Computer-aided design and computer-aided manufacturing technology has been applied to the fabrication of maxillary obturator frameworks, both directly and indirectly. However, with earlier techniques, it was not possible to accurately determine the position of the framework conforming to the palate, an issue that has been resolved in current fabrication methods. Using the patient's existing denture, prosthodontists can determine where the framework should be positioned in the defect area. This allows the obturator bulb to be hollowed, thereby reducing weight and making adjustment easier. The most appropriate position for the finish line can be determined by accurately establishing the arrangement of the artificial teeth as well as the most appropriate polishing surface morphology. In maxillofacial prosthetics, restoring proper articulation and the swallowing function through rehabilitation is important, and determining the proper palatal morphology enables good tongue movement and facilitates the restoration of adequate function. The lighter weight contributes to protecting the remaining teeth and improves patient comfort.

Predicting maximum occlusal force and tongue pressure using decision tree analysis in patients diagnosed with head and neck tumors.

STATEMENT OF PROBLEM: Preserving and restoring oral functions, especially mastication and swallowing, is important to the quality of life of patients being treated for head and neck tumors. Studies that help predict maximum occlusal force and tongue pressure during prosthetic treatment, necessary for providing comprehensive, appropriate treatment and encouraging patient adherence and confidence are lacking. PURPOSE: The purpose of this clinical study was to develop a decision tree model for predicting maximum occlusal force and tongue pressure in patients diagnosed with head and neck tumors that could help both experienced and less experienced prosthodontists and oral surgeons optimize the treatment plan and support patient compliance and their quality of life. MATERIAL AND METHODS: A total of 80 patients who had been treated for head and neck tumors were enrolled in the study. Their maximum occlusal force was measured using a pressure-sensitive film and tongue pressure using a tongue pressure measurement device. Data, including basic characteristics, were transferred to a comma separated values file, which was then imported into a statistical software package to produce a decision tree. The classification and regression tree method was used to construct a predictive model. RESULTS: The number of occlusal contacts associated with not wearing a prosthesis, flap reconstruction, radiotherapy, chemotherapy, the number of teeth present, age, tumor stage, and tumor type were found to be associated with maximum occlusal force, with a prediction accuracy of 96.3%, area under the receiver operating characteristic curve of 0.99, sensitivity of 97%, and specificity of 94%. The number of occlusal contacts associated with wearing and not wearing a prosthesis, tumor stage, age, radiotherapy, and surgery type were found to be associated with tongue pressure, with a prediction accuracy of 96.3%, area under the receiver operating characteristic curve of 0.97, sensitivity of 97%, and specificity of 93%. CONCLUSIONS: The decision tree model can be an effective tool for the prediction of maximum occlusal force and tongue pressure in patients diagnosed with head and neck tumors, helping both experienced and less experienced prosthodontists and oral surgeons to provide early, appropriate, and necessary treatment before starting prosthetic treatment and helping patients with treatment compliance and communication with medical staff.

Advancing maxillofacial prosthodontics by using pre-trained convolutional neural networks: Image-based classification of the maxilla.

PURPOSE: The study aimed to compare the performance of four pre-trained convolutional neural networks in recognizing seven distinct prosthodontic scenarios involving the maxilla, as a preliminary step in developing an artificial intelligence (AI)-powered prosthesis design system. MATERIALS AND METHODS: Seven distinct classes, including cleft palate, dentulous maxillectomy, edentulous maxillectomy, reconstructed maxillectomy, completely dentulous, partially edentulous, and completely edentulous, were considered for recognition. Utilizing transfer learning and fine-tuned hyperparameters, four AI models (VGG16, Inception-ResNet-V2, DenseNet-201, and Xception) were employed. The dataset, consisting of 3541 preprocessed intraoral occlusal images, was divided into training, validation, and test sets. Model performance metrics encompassed accuracy, precision, recall, F1 score, area under the receiver operating characteristic curve (AUC), and confusion matrix. RESULTS: VGG16, Inception-ResNet-V2, DenseNet-201, and Xception demonstrated comparable performance, with maximum test accuracies of 0.92, 0.90, 0.94, and 0.95, respectively. Xception and DenseNet-201 slightly outperformed the other models, particularly compared with InceptionResNet-V2. Precision, recall, and F1 scores exceeded 90% for most classes in Xception and DenseNet-201 and the average AUC values for all models ranged between 0.98 and 1.00. CONCLUSIONS: While DenseNet-201 and Xception demonstrated superior performance, all models consistently achieved diagnostic accuracy exceeding 90%, highlighting their potential in dental image analysis. This AI application could help work assignments based on difficulty levels and enable the development of an automated diagnosis system at patient admission. It also facilitates prosthesis designing by integrating necessary prosthesis morphology, oral function, and treatment difficulty. Furthermore, it tackles dataset size challenges in model optimization, providing valuable insights for future research.

Use of digital technology in prosthesis fabrication for an elderly patient with a maxillectomy and severe trismus: A clinical report.

This clinical report describes a novel approach based on digital technology to fabricate a maxillofacial prosthesis for a 90-year-old woman with severe trismus who had undergone maxillectomy on the right side. The approach was safe, rapid, and less burdensome on this elderly patient, and the storage and communication of intraoral and maxillofacial prosthesis data without temporal and spatial constraints was helpful. A combination of digital and analog technology provided a maxillofacial prosthesis that improved the quality of life of this elderly patient with head and neck cancer and severe trismus.

Combined digital-conventional workflow to fabricate a definitive obturator from an interim obturator for a patient with an anterior maxillectomy defect.

An existing interim obturator can be reproduced as the definitive one using digital technology, with benefits for a patient with a maxillectomy. By digitally scanning the oral condition and the existing interim obturator, a definitive obturator, including a computer-aided designed and computer-aided manufactured metal framework, was fabricated and delivered to a patient with an anterior maxillectomy defect by following a combined digital and conventional workflow. This technique can hasten the adaptation of the patient to the new obturator and ensure a more comfortable and safer clinical procedure.

Creating and analyzing digital scans of a mandibulectomy cast with simulated trismus.

STATEMENT OF PROBLEM: Trismus associated with maxillofacial defects resulting from tumor resection or radiotherapy can make dental treatment uncomfortable for patients. Using an intraoral scanner instead of making a conventional impression could help to make prosthetic rehabilitation more comfortable. However, limited information is available regarding the feasibility and accuracy of intraoral scanners for scanning mandibular defects. PURPOSE: The purpose of this in vitro study was to evaluate the feasibility and accuracy of using an intraoral scanner to digitize a cast of a mandibular defect under various simulated trismus conditions. MATERIAL AND METHODS: An intraoral scanner was used to scan the mandibular cast under different simulated degrees of trismus (mouth opening 10, 20, and 30 mm) and nontrismus (mouth opening 40 mm). The surface areas captured were compared. The datasets were loaded into a 3-dimensional (3D) evaluation software program and then superimposed for precision analysis and on reference data for trueness analysis. One-way analysis of variance was used to compare surface area captured, precision, and trueness of the measurement under the different mouth opening conditions (α=.05). RESULTS: The surface area for which 3D data were obtained by the intraoral scanner ranged from 3199.1 to 6161.6 mm2. The area differed significantly under all mouth opening conditions (P=.001), with a smaller scanned surface area captured in severe trismus (10 mm). Precision ranged from 0.032 to 0.056 mm, and trueness from 0.037 to 0.076 mm. No significant differences were seen in precision (P=.312), but significant differences were seen in trueness (P=.016) under all trismus conditions. CONCLUSIONS: Using an intraoral scanner appears feasible for digitizing mandibular defect casts with simulated mild and moderate trismus. The accuracy of the obtained data was clinically acceptable.

Effect of cut-out rescan procedures on the accuracy of an intraoral scanner used for digitizing an ear model: An in vitro study.

PURPOSE: The purpose of this study was to evaluate the impact of the rescanning of mesh holes of different diameters on the accuracy of an intraoral scanner (IOS) used to digitize an ear model. MATERIALS AND METHODS: An ear model was digitized using an intraoral scanner (Medit i500) to obtain a reference mesh. A baseline experimental scan was created by editing a duplicate of the reference mesh using the cut-out tool of the IOS software. Three equal groups were created based on the diameter of the cut-out areas: 2 mm (G1), 5 mm (G2), and 8 mm (G3) (n = 15). The cut-out areas were rescanned and a total of 45 digital files were exported. The discrepancy between the reference and the experimental digital scans was measured using the root mean square calculation (RMS). The data were analyzed by a Kruskal-Wallis test followed by a post hoc Dunn's test with Bonferroni correction. RESULTS: The trueness values ranged from 19.53 to 27.13 µm. There were significant differences in the RMS error values among the groups tested (p < 0.001) and post hoc multiple comparisons showed significant differences between the G1 and G2 groups (p = 0.04), G1 and G3 groups (p < 0.001), and G2 and G3 groups (p = 0.004). Overall, the precision values ranged from 4.93 to 7.73 µm and significant differences in the RMS values were only found between the G1 and G2 groups (p = 0.014). CONCLUSIONS: Mesh hole rescanning affected the scanning accuracy (trueness and precision) of the IOS tested. The larger the diameter of the mesh holes, the less the trueness of the IOS tested. The precision values seemed to be less affected compared with the trueness by the cut-out and rescanning procedures.

Inhibitory effect of 405-nm blue LED light on the growth of Candida albicans and Streptococcus mutans dual-species biofilms on denture base resin.

We investigated whether irradiation with 405-nm blue LED light could inhibit the growth of not only single- but dual-species biofilms formed by Candida albicans and Streptococcus mutans on denture base resin and cause the alteration in gene expression related to adhesion and biofilm formation. C. albicans and S. mutans single-/dual-species biofilms were formed on the denture base specimens. The biofilms were irradiated with 405-nm blue LED light (power density output: 280 mW/cm2) for 0 (control) and 40 min. Dual-species biofilms were analyzed using CFU assay and fluorescence microscopy, and single-/dual-species biofilms were analyzed using alamarBlue assays and gene expression analysis. To assess the inhibitory effect of irradiation on dual-species biofilms, specimens after irradiation were aerobically incubated for 12 h. After incubation, the inhibition of growth was assessed using CFU assays and fluorescence microscopy. Data were analyzed using the Mann-Whitney U or Student's t test (p < 0.05). Irradiation produced a significant inhibitory effect on biofilms. Fluorescence microscopy revealed that almost all C. albicans and S. mutans cells were killed by irradiation, and there was no notable difference in biofilm thickness immediately after irradiation and after irradiation and incubation for 12 h. alamarBlue assays indicated the growth of the biofilms was inhibited for 12-13 h. The expression of genes associated with adhesion and biofilm formation-als1 in C. albicans and ftf, gtfC, and gtfB in S. mutans-significantly reduced by irradiation. Irradiation with 405-nm blue LED light effectively inhibited the growth of C. albicans and S. mutans dual-species biofilms for 12 h.

Microbicidal effect of 405-nm blue LED light on Candida albicans and Streptococcus mutans dual-species biofilms on denture base resin.

This study investigated: (1) the microbicidal effect of 405-nm blue LED light irradiation on biofilm formed by Candida albicans hyphae and Streptococcus mutans under dual-species condition on denture base resin, (2) the generation of intracellular reactive oxygen species (ROS) induced by irradiation, and (3) the existence of intracellular porphyrins, which act as a photosensitizer. Denture base resin specimens were prepared and C. albicans and S. mutans dual-species biofilms were allowed to form on the specimens. The biofilms were irradiated with 405-nm blue LED light and analyzed using the colony-forming unit assay, fluorescence microscopy, and scanning electron microscopy (SEM). Single-species biofilms of C. albicans and S. mutans formed on the specimens were irradiated with 405-nm blue LED light. After the irradiation, the intracellular ROS levels in C. albicans and S. mutans cells were measured. In addition, the level of intracellular porphyrins in C. albicans and S. mutans were measured. Irradiation for more than 30 min significantly inhibited the colony formation ability of C. albicans and S. mutans. Fluorescence microscopy revealed that almost all C. albicans and S. mutans cells were killed by irradiation. SEM images showed various cell damage patterns. Irradiation led to the generation of intracellular ROS and porphyrins were present in both C. albicans and S. mutans cells. In conclusion, irradiation with 405-nm blue light-emitting diode light for 40 min effectively disinfect C. albicans hyphae and S. mutans dual-species biofilms and possibly react with intracellular porphyrins resulting in generation of ROS in each microorganism.

A new masticatory performance scale to integrate food biting, comminution and mixing ability in removable partial denture wearers.

BACKGROUND: The existing masticatory performance (MP) tests cannot comprehensively evaluate objective masticatory function. OBJECTIVES: We aimed to examine the construct validity and responsiveness and determine the clinically minimum important difference (MID) and related factors of a newly developed MP scale to integrate food biting, comminution and mixing ability in patients with removable partial dentures (RPDs). METHODS: Masticatory performance tests using gummy jelly, peanuts and colour-changeable gum were performed before and 3 months after RPD treatment in 248 partially dentate patients. A 10-point ordinal subscale was created for each MP test based on the distributions of MP values, and the three subscales were integrated into a single scale (iMP scale). We analysed the correlations between MP values and iMP scores and determined the effect size for RPD treatments and the MID on the basis of patient perception of chewing ability. RESULTS: iMP scores exhibited moderate correlations with the three MP values (|ρ| = 0.73-0.79, p < .001) and with the change scores (|ρ| =0.61-0.64, p < .001). The mean iMP score significantly increased after RPD treatment (p < .001), and the effect size was 0.35. Of the 248 patients, 55 (22%) reported a slight improvement in chewing ability with a mean iMP score change of 2.1 points. Sex and the number of missing teeth were significantly associated with iMP scores (p < .05). CONCLUSIONS: The iMP scale comprehensively evaluated objective masticatory function, including food biting, comminution and mixing ability in RPD wearers, and an increase of two points on the iMP scale was considered to be the MID in RPD treatments.

Responsiveness of methods to evaluate chewing ability after removable partial denture treatments.

BACKGROUND: The ability of an instrument to detect a clinically important change in patient-reported outcomes following prosthetic treatment is critical for its use in clinical practice and research settings. OBJECTIVES: This study aimed to examine the responsiveness of instruments in evaluating patient perception of chewing ability after removable partial denture (RPD) treatment in a prospective cohort. METHODS: A single 100-mm visual analogue scale (VAS), 20-item food intake questionnaire (FIQ) and 6-point chewing difficulty scale (CDS) were administered to 248 partially edentulous patients to evaluate chewing ability pre- and post-RPD treatment. We conducted a statistical comparison between the pre- and post-treatment scores and determined the effect size (r) of RPD treatment for the instruments. RESULTS: A significant improvement in chewing ability after RPD treatment was identified by VAS and CDS (P < .05), but not by FIQ (P = .16), which identified an improvement after controlling for sex, age, the number of missing teeth and presence/absence of existing removable dentures. The effect size was medium for VAS (r = .54), weak for CDS (r = .14-.17) and absent for FIQ (r = -.09). The increase in r was significantly associated with impaired chewing ability before treatment (ρ = -0.87, P < .001). CONCLUSIONS: These results suggest that the 100-mm VAS, followed by CDS, is the most responsive instrument to detect an improvement in chewing ability after RPD treatment. Pre-treatment impairment of chewing ability was associated with better responsiveness of the instruments.

Accuracy of cone beam computed tomography in evaluation of palatal mucosa thickness.

AIM: The purpose of this study was to investigate the accuracy of the measurement of palatal mucosa thickness using cone beam computed tomography (CBCT) and to create a conversion formula to evaluate palatal mucosa thickness more accurately. We then evaluated the palatal mucosa thickness in a Japanese population using CBCT and the conversion formula. MATERIALS AND METHODS: We evaluated palatal mucosa thickness in 10 healthy subjects at 15 sites using CBCT, digital impression, and K file. Multiple regression analysis was performed to create a conversion formula to measure thickness accurately. We then obtained CBCT data from 174 patients retrospectively, applied the conversion formula, and evaluated palatal mucosa thickness. RESULTS: Sites of measurement affected measurement error. Measurement using CBCT was 0.34 ± 0.04 mm smaller than actual measurement; therefore, a conversion formula was created. Male, age ≥60 years, and probing pocket depth ≥4 mm had significant and positive associations with palatal mucosa thickness; however, no association was observed between bleeding on probing and palatal mucosa thickness. CONCLUSION: CBCT is useful for the noninvasive and accurate measurement of palatal mucosa thickness.

Does oral dryness influence pressure pain sensitivity in the oral mucosa of removable denture wearers?

OBJECTIVE: This study aimed to determine if oral dryness is associated with oral pain sensitivity in removable denture wearers. MATERIALS AND METHODS: The pressure pain threshold (PPT) in the mucosa at the midline between the central incisors in the maxilla and mandible was evaluated in 333 removable denture wearers (mean age 71.2 years, male 33.3%). The frequency of oral dryness and severity of anxiety were evaluated using self-reported questionnaires. Multilevel analyses considering the correlated data structure (jaws nested within individual) adjusted for age, sex, number of missing teeth, anxiety level, smoking status, and systemic diseases were performed to examine the association between PPT and oral dryness. Further subgroup analysis stratified by number of missing teeth was performed. RESULTS: Oral dryness was present in 122 (21.6%) of 566 jaws in 73 (21.9%) of the 333 subjects. The mean (standard deviation) of the log PPT was 2.00 (0.26) in the subjects who perceived oral dryness and 2.04 (0.22) in those who did not. Oral dryness was associated with a lower log PPT, but the relationship was not significant (coefficient - 0.017; 95% confidence interval - 0.071, 0.038). Subjects with oral dryness and edentulous oral mucosa had a significantly lower PPT (coefficient - 0.145; 95% confidence interval - 0.283, - 0.006) than their partially dentate counterparts. CONCLUSION: There was a significant association of oral dryness with increased pressure pain sensitivity in the oral mucosa only in jaws with complete dentures. CLINICAL RELEVANCE: The approach to oral dryness could contribute to reduction of oral pain sensitivity.

Pre-treatment impairment of oral health-related quality of life is associated with variations in minimal clinically important differences among patients with removable partial denture treatment.

BACKGROUND: The minimal clinically important differences (MID) of the Oral Health-related Quality of Life (OHRQoL) are the benchmark to meaningfully interpret treatment outcomes. However, there is no available information regarding the factors impact the MID variations after removable partial denture (RPD) treatment. OBJECTIVE: The purpose of this study was to determine the influence of the pre-treatment OHRQoL impairment on the MID in the oral health impact profile (OHIP) after RPD treatment. METHODS: In this prospective study, OHIP and Self-reported Oral Health (SROH) questionnaires were administered to patients before and 3 months after RPD treatment. The MID in each OHIP version (OHIP-49, OHIP-20, OHIP-14 and OHIP-5) was the mean score of patients who showed a minimum SROH improvement. Multiple linear regression analysis was conducted to determine the influence of the pre-treatment OHIP summary score on the MID score. RESULTS: Among 248 participants who completed both evaluations, 85 (34%) patients had minimum SROH improvements after RPD treatment. Multiple regression analysis indicated that each 10-point increase in the pre-treatment summary OHIP score was associated with an increase in the MID score of three points for OHIP-49 and four points for OHIP-20, OHIP-14 and OHIP-5 (P < .05), after controlling for age, sex and the number of missing teeth. Therefore, the MID increased as the pre-treatment OHRQoL was impaired. CONCLUSIONS: The MID was accounted for by approximately one-third of the pre-treatment summary score, independent of the OHIP version, in the interpretation of the effects of RPD treatment on patients' OHRQoL.

Influence of the Covering Area of Major Connectors of Mandibular Dentures on the Accuracy of Speech Production: A Pilot Study.

BACKGROUND/OBJECTIVES: Speech impairment during the initial phase of removable partial denture (RPD) treatment can prevent patient adaptation to RPDs. This quasi-experimental study aimed to investigate the influence of the covering area of major connectors located in the mandibular anterior region on the accuracy of speech production. METHODS: Fifteen adults (12 men and 3 women aged 26-40 years) with healthy dentition were recruited. Four target syllables were used for the assessments: [ʃi], [ʧi], [çi], and [ki]. There were four speaking conditions: without a connector (control), wearing lingual bar (5 mm width), wearing lingual plates (12 mm width), and wearing connectors covering the occlusal surface of lower dentition (16 mm width; CO). The accuracy of speech production was evaluated by mean appearance ratio of correct labels (MARC) and incorrect labels (MARIC) of the phonetic segments which were calculated with a speech evaluation system (VoiceAnalyzer). RESULTS: The MARC in the 3 target syllables [ʃi], [ʧi], and [ki] significantly decreased with CO. For the target syllable [ʃi], the MARICs of [ʧi], [ʤi], and [çi] with CO were significantly lower than that in the control. For the target syllable [ʧi], the MARIC of [ki] with CO was significantly higher than that in the control. For the target syllable [çi], the MARIC of [gi] with CO was significantly higher than that in the control. CONCLUSION: RPDs with major connectors covering the lower dentition could disturb speech production during the initial phase of RPD treatment. Prosthodontic treatment with such RPD designs requires further consideration regarding the information given to patients before starting the treatment.

Biomechanical Effect of an Exposed Dental Implant's First Thread: A Three-Dimensional Finite Element Analysis Study.

BACKGROUND The purpose of this study was to assess the effect of different exposure levels of a dental implant's first thread on adjacent bone stress and strain using the finite element analysis method. MATERIAL AND METHODS Three-dimensional models of 2 threaded implants and abutments with a mandibular bone segment were constructed to represent the covered (C) and exposed models. In the exposed models, the implant was first placed in the bone, and rotated around its axis a quarter-turn each time to simulate 4 different levels of first thread exposure at the mid-lingual side: Upper Flank (UF), Thread Crest (TC), Lower Flank (LF), and Thread Root (TR) models. Oblique forces were applied and analysis was performed. RESULTS Maximum compressive stress magnitude and distribution varied according to the exposed thread profile. In the exposed group, peak stress ranged from 136 MPa to 197 MPa in TC and LF models, respectively, compared to 141 MPa in C model. In LF, UF, and C models, peak stress was observed at the mid-lingual side of the crestal region, while in TC and TR models, peak stress shifted distally in accordance with thread profile. However, alveolar bone volumes which exhibited compressive microstrain levels within the physiological loading and maintenance windows were relatively close in all models. CONCLUSIONS Results suggest that the exposed thread profile influences stress and strain outcomes in the adjacent bone; however, this influence is only limited to a small region around the exposed thread.

Effectiveness of 405-nm blue LED light for degradation of Candida biofilms formed on PMMA denture base resin.

This study investigated (i) the degradation effect of 405-nm blue light-emitting diode (LED) light irradiation on Candida albicans and C. glabrata biofilms formed on denture base resin and (ii) the effects of 405-nm blue LED light irradiation on the mechanical and surface characteristics of the resin. Polymethyl methacrylate denture base resin discs were prepared, and C. albicans or C. glabrata biofilms formed on the denture base resin discs. Each biofilm was irradiated with 405-nm blue LED light under a constant output power (280 mW/cm2) for different times in a moisture chamber with 100% relative humidity. Postirradiation, each biofilm was analyzed using a colony-forming unit assay, fluorescence microscopy, and scanning electron microscopy (SEM). Parallelepiped specimens of acrylic resin were prepared, and changes in their flexural strength (FS), flexural modulus (FM), and surface roughness (Ra) preirradiation and postirradiation with 405-nm blue LED light were evaluated. Irradiation for 30 min completely inhibited colony formation in both Candida species. Fluorescence microscopy showed that almost all Candida cells were killed because of irradiation. SEM images showed various cell damage patterns, such as wrinkles, shrinkage, and cell surface damage. An increase in FS was noted postirradiation, but no significant changes were observed in FM and Ra preirradiation and postirradiation. In conclusion, irradiation with 405-nm blue LED light induces degradation of C. albicans and C. glabrata biofilms on denture base resin, even in the absence of photosensitizers, without resin surface deterioration.

The association between mucosal pain and subjective masticatory function in patients with partial removable dental prostheses.

BACKGROUND: Improvement of masticatory function is critical in prosthetic treatment. Multiple factors are related to patients' perception of chewing ability in denture wearers. However, the associations between such factors and chewing ability have not yet been fully elucidated. OBJECTIVE: To investigate the association between mucosal pain and subjective masticatory function in patients with partial removable dental prostheses (PRDPs). METHODS: This cross-sectional study included 333 consecutive patients with PRDPs (mean age 71.2 years, male 33.3%) who were recruited from the prosthetic clinic of a dental hospital in Japan. Patients' perception of chewing ability was evaluated using a food intake questionnaire consisting of 20 items, and chewing difficulty was rated by patients using an 11-point numerical scale. Participants rated the pain intensity of the denture-supporting mucosa and oral dryness while chewing. In addition, the bilateral maximal biting force (MBF) was recorded. A structural equation model was used to identify the factors associated with chewing ability and chewing difficulty. RESULTS: The model indicated that mucosal pain, oral dryness, the number of occluding pairs, the denture type (interim/definitive PRDPs) and the MBF were significant independent predictors of chewing ability and chewing difficulty (P < 0.01). CONCLUSIONS: Our findings suggest that mucosal pain is a risk factor for impairment of subjective masticatory function in patients with PRDPs. It is clinically important to consider the denture design and to select denture base materials with regard to the prevention of mucosal pain.

Influence of Oral Morphology on Speech Production in Subjects Wearing Maxillary Removable Partial Dentures with Major Connectors.

BACKGROUND/AIMS: Speech impairment during the initial phase of removable partial denture (RPD) treatment can prevent patient adaptation to RPDs. This study was undertaken to investigate the influence of oral morphology on speech production in subjects wearing RPDs with major connectors. METHODS: Two types of connectors were fabricated for 17 subjects with normal dentitions: covering the middle palate (M-bar) and the anterior/posterior palate (AP-bar). Four target sounds ([∫i], [t∫i], [çi], and [ki]) were evaluated under 3 recording conditions: no connector, M-bar, and AP-bar. The mean appearance ratios of correct labels (MARCs) were calculated as parameters representing speech production accuracy with the speech evaluation system. Subgroup analysis was conducted based on palate height, dental arch width, and front space volume of the oral cavity. RESULTS: Based on the multiple linear regression test, a significant association was found between the MARCs of [∫i] with M-bar and front space (p = 0.036). In the subgroup analysis, the AP-bar had a significant effect on the MARCs of [∫i] among subjects with high palate (p = 0.026), narrow arch (p = 0.004), and small front space (p = 0.014). CONCLUSION: RPDs with major connectors could disturb speech production among patients with high palates, narrow arches, and small front spaces.

A comparison of the fitting accuracy of thermoplastic denture base resins used in non-metal clasp dentures to a conventional heat-cured acrylic resin.

OBJECTIVE: To incorporate a metal framework into removable partial dentures, the dimensional accuracy of thermoplastic resins requires precision equivalent to conventional acrylic resins. This study aimed to evaluate the fitting accuracy of thermoplastic resins compared to heat-cured acrylic resin. MATERIALS AND METHODS: Four thermoplastic resins (polyethylene terephthalate [EstheShot, ES; EstheShot Bright, ES-B], polyamide [Lucitone FRS, LF], polycarbonate [Reigning Resin N, RN] and a heat-curing acrylic resin [Acron, AC]) were used. The specimens were created on master casts constructed of high-strength stone that simulated a maxillary edentulous ridge. Additionally, high-expansion stone was used as the master cast for RN specimens. The ES-B, LF and RN specimens were prepared with and without annealing after injection molding. The gaps between the molded resin and the cast were measured. RESULTS: ES had the smallest gap and was significantly smaller than AC (p < 0.05). The gap sizes of ES-B, LF and RN (high-expansion stone) without annealing were similar to AC (p > 0.05), while the gap size of RN (high-strength stone) with and without annealing was significantly greater than AC (p < 0.001). The gap sizes of ES-B and LF with annealing were significantly less than AC (p < 0.05). Further, the gap sizes of ES-B, LF and RN with annealing were significantly smaller than the gaps without annealing (p < 0.05). CONCLUSIONS: The results suggested that ES, ES-B and LF have adequate fitting accuracy for incorporating metal framework into dentures and that annealing effectively improved the fitting accuracy of ES-B, LF and RN.