Bite Force Evaluation in Complete Denture Wearer with Different Denture Base Materials: A Randomized Controlled Clinical Trial

Effects of Loading Forces, Loading Positions, and Splinting of Two, Three, or Four Ti-Zr (Roxolid®) Mini-Implants Supporting the Mandibular Overdentures on Peri-Implant and Posterior Edentulous Area Strains

Clinical indications for the Ti-Zr alloy (Roxolid®) mini-implants (MDIs) in subjects with narrow ridges are still under review. The aim was to analyze peri-implant and posterior edentulous area strains dependent on the MDI number, splinting status, loading force, and loading position. Six models were digitally designed and printed. Two, three, or four Ti-Zr MDIs, splinted with a bar or unsplinted (single units), supported mandibular overdentures (ODs), loaded with 50-300 N forces unilaterally, bilaterally, and anteriorly. The artificial mucosa thickness was 2 mm. Strain gauges were bonded on the vestibular and oral peri-implant sides of each MDI, and on the posterior edentulous area under the ODs. Loadings were performed through the metal plate placed on ODs' artificial teeth (15 times repeated). Arithmetic means with standard deviations and the significance of the differences (MANOVA, Sheffe post hoc) were calculated. Different MDI numbers, loading positions, forces, and splinting elicited different peri-implant microstrains. In the two-MDI models, 300 N force during unilateral loading elicited the highest microstrains (almost 3000 εμ on the loaded side), which can jeopardize bone reparation. On the opposite side, >2500 εμ was registered, which represents high strains. During bilateral loadings, microstrains hardly exceeded 2000 εμ, indicating that bilateral chewers or subjects having lower forces can benefit from the two Ti-Zr MDIs, irrespective of splinting. However, in subjects chewing unilaterally, and inducing higher forces (natural teeth antagonists), or bruxers, only two MDIs may not be sufficient to support the OD. By increasing implant numbers, peri-implant strains decrease in both splinted and single-unit MDI models, far beyond values that can interfere with bone reparation, indicating that splinting is not necessary. When the positions of the loading forces are closer to the implant, higher peri-implant strains are induced. Regarding the distal edentulous area, microstrains reached 2000 εμ only during unilateral loadings in the two-MDI models, and all other strains were lower, below 1500 εμ, confirming that implant-supported overdentures do not lead to edentulous ridge atrophy.

Mechanical properties of conventional versus microwave-polymerized denture base acrylic resins

STATEMENT OF PROBLEM

New denture base acrylic resins have been introduced that are specifically formulated for microwave polymerization. Microwave polymerization is a time-efficient procedure, but few studies have evaluated how these new acrylic resin formulations compare with conventionally processed acrylic resins.

PURPOSE

The purpose of this in vitro study was to compare the stiffness and strength of denture base acrylic resins formulated for microwave polymerization with conventionally processed acrylic resin.

MATERIAL AND METHODS

Rectangular beams were fabricated from 2 microwave-polymerized denture base acrylic resins, microwave-specific resin (Nature-Cryl MC), resin with the option of microwave polymerization (Diamond D), and a conventionally processed resin as a control (Lucitone 199). Specimens (n=10) were stored in water for 1 week and subjected to a 3-point bend test to determine the flexural modulus (stiffness) and flexural strength before (initial properties) or after 120 000 load cycles. The load cycles, conducted between 5 and 25 N at 2 Hz, simulated 6 months of mastication. Data were analyzed by using 2-way ANOVA, followed by pairwise comparisons (α=.05).

RESULTS

The initial flexural modulus (mean ±standard deviation) was conventionally processed resin, 2.65 ±0.33 GPa; microwave-specific resin, 3.01 ±0.20 GPa; and microwave-option resin, 2.63 ±0.04 GPa. After load cycling, the mean flexural modulus was conventionally processed resin, 2.34 ±0.32 GPa; microwave-specific resin, 2.69 ±0.20 GPa; and microwave-option resin, 1.96 ±0.11 GPa. The initial flexural strength was conventionally processed resin, 77.6 ±11.0 MPa; microwave-specific resin, 83.6 ±3.5 MPa; and microwave-option resin, 78.9 ±2.6 MPa. After load cycling, the mean flexural strength was conventionally processed resin, 68.7 ±9.0 MPa; microwave-specific resin, 73.3 ±3.3 MPa; and microwave-option resin, 65.5 ±3.5 MPa. Resin and loading state significantly affected the stiffness and strength (P<.01); the interaction resin×state was not significant (P≥.558).

CONCLUSIONS

Microwave-polymerized denture base acrylic resins were comparable in stiffness and strength with conventionally processed acrylic resin. All acrylic resins decreased in stiffness and strength after load cycling. The microwave-specific resin was significantly stiffer and stronger than the other denture base acrylic resins, initially and after 120 000 load cycles.

Evaluation and comparison of patient satisfaction with VertexThermosens and conventional acrylic complete dentures

OBJECTIVES

Patient perception and satisfaction with dentures are important indicators in prosthodontic treatment. This study aimed to compare patients' satisfaction with VertexThermosens dentures versus conventional acrylic dentures during a 12-month study period.

MATERIAL AND METHODS

This randomized study involved 60 participants aged between 45 and 80 with representation of both sexes. The patients were divided into two groups: The first group (experimental group), which had complete dentures from VertexThermosens base material included 30 participants. The second group (control group), which had complete dentures from convectional rigid acrylic base material, included 30 participants. Patient satisfaction with the dentures was assessed in each of the two Vertex/Acrylic groups through a specially created questionnaire of five questions with a five-point Likert scale of possible answers (0 = never; 1 = rarely; 2 = occasionally; 3 = often; and 4 = very often).

RESULTS

After 12 months, intergroup comparison with Mann-Whitney U Test related to Q2 (p = 0.193), Q3 (p = 0.960), Q4 (p = 0.317), Q5 (p = 1.000) patient satisfactions indicated that there was no significant difference between the two groups (Vertex/Acrylic), except  Q1 (p = 0.010) question, Vertex group was more satisfied. The results regarding the patients of both groups (Vertex/Acrylic) showed that after 12 months of wearing the denture, the satisfaction level regarding to all questions increased, except Q5-question for Vertex group, where the difference was not significant due to the already achieved maximum satisfaction at zero time.

CONCLUSION

Based on the findings of this clinical study, it can be concluded that higher satisfaction is seen in patients rehabilitated with VertexThermosens dentures than with conventional rigid acrylic dentures.

A modal analysis of implant-supported overdentures installed on differently positioned sets of dental implants

This study evaluated the three vibration characteristics, namely, natural frequency, damping ratio, and natural mode, together with maximum displacement of a two-implant-supported overdenture (IOD) at different locator attachment positions using experimental modal analysis (EMA). Edentulous mandibular models with a gingival thickness of 1 mm or 3 mm were prepared, into which dental implants were placed using a fully guided surgical template designed with simulation software, the locator abutments were fastened, and the IODs were then fabricated. The implant positions were bilaterally marked at the lateral incisor, first premolar, and first molar regions. EMA was performed by hammering the test structures to measure the impulse response and obtain the vibration characteristics (n = 5). The Kruskal-Wallis test was performed for natural frequency and maximum displacement, and the Games-Howell test for damping ratio. The significance level was set at α = 0.05. The study indicated that the gingival thickness had a significant effect on the vibration characteristics. Moreover, the natural frequency and damping ratio results showed that the vibration subsided faster when the attachment was placed on the molar implants in the thick gingival model. Furthermore, according to the effect of lateral force on IODs, the difference in maximum displacement between the anterior and posterior regions of the IOD was smaller when the attachments were designed on the pair of lateral incisors. Thus, within the limits of this experiment, our results suggested that two anterior implant-supported IODs are preferable treatment designs in terms of vibration engineering, especially when the gingiva is thick; the molar attachment design could be considered for thin gingival conditions. The differences in gingival thickness and abutment position affected the vibration characteristics of the IOD. Further in vivo studies would be necessary to validate the implant positions and their IOD designs for the mandibular edentulous shapes and the occlusal relationship.

The Effects of Wearing a Removable-Partial-Denture on the Bite Forces: A Cross-Sectional Study

Background: Removable partial dentures are a frequently used prosthetic treatment in the elderly population, but different types or RPDs might guarantee different chewing capabilities. In many studies, the relationship between chewing and aging has been reported and it has been shown that efficient chewing can improve the overall quality of life. Objectives: In the present study, the relationship between maximum bite force (MBF) and RPDs was studied. A relationship between the body mass index (BMI) and the type of prosthesis was also analyzed. Methods: 240 elderly patients, 120 males and 120 females, with bilateral posterior edentulism (class 1 of Kennedy classification) who had been wearing an RPD for at least a year, were recruited. Patients were divided into two groups: Group 1: male (n = 60) and female (n = 60) patients with bilateral edentulous areas located posterior to the remaining natural teeth and natural teeth in the opposite dental arch. Group 2: male (n = 60) and female (n = 60) patients with maxillary and mandibular bilateral edentulous areas located posterior to the remaining natural teeth. Their Body Mass Index (BMI) and Maximum bite force (MBF) were measured and compared according to the material and design of their RPD. Results: In both Groups, patients wearing cobalt-chrome alloy RPDs (Co-Cr-RPD) (Group 1: 20.25 ± 6.7 MBF, p < 0.001; Group 2: 16.0 ± 5.7 MBF, p < 0.001) had an increased MBF when compared to polymethylmethacrylate RPD (PMMA-RPD) (Group 1: 12.9 ± 3.36 MBF; Group 2: 10.4 + 2.8 MBF), and Valplast RPD (V-RPD) (Group 1: 14.3 ± 4.7 MBF; Group 2: 11.3 ± 3.4 MBF) users. There were no significant differences in bite force between patients wearing PMMA-RPD and V- RPD in both Groups. Patients in Group 2 showed a lower MBF than those in Group 1 (Group 1: 16.05 ± 6.13 MBF; Group 2: 12.6 ± 4.84 MBF; p < 0.001). Conclusions: A reduction in chewing force can lead to choosing softer foods for nutrition, which can lead to an increase in BMI. Our results show that only CoCr-RPD wearers were able to chew consistent food, whereas PMMA- RPD and V-RPD, due to the properties of the materials, their instability, and the possibility of causing pain during mastication, determined a limitation in the choice of food for many of the participants.

The Relationship between Dentofacial Vertical Pattern and Bite Force Distribution among Children in Late Mixed Dentition

Background: Digital bite measurement systems such as the T-Scan III allow for the computerized measurement of occlusal force distribution. This study aimed to establish the relationship between dentofacial vertical pattern and bite force distribution among children in late mixed dentition. Materials and Methods: In total, 86 children (45 male, 41 female) aged between 9 and 11 years with short (n = 28), medium (n = 28), and long (n = 30) facial heights were included in this study. The height, weight, age, and gender were recorded. Occlusal bite force distribution and time of occlusal cycle were recorded using a T-Scan III device (Tekscan Corp. Boston, MA, USA). The bite force distribution was compared among facial types using a One-Way ANOVA and post hoc test, a linear regression model with time of occlusion as dependent variable was developed. Results: No significant differences were observed in occlusion time between genders. Children with long facial height had a significantly lower anterior bite force distribution (p < 0.05) and significantly higher posterior bite force distribution (p < 0.05) than those with average or short facial height. Age, gender, height, and weight had no significant association with time of the occlusal cycle. Conclusion: Children with an increased vertical facial height have a more posterior distribution of force than children with average or short facial heights in the late mixed dentition.

Association of facial type with possible bruxism and its related clinical features in adolescents: A cross-sectional study

OBJECTIVES

The assessment of bruxism and its clinical characteristics is acknowledged in literature. This study aimed to evaluate the association of adolescents' facial patterns with bruxism and its related clinical features in the form of signs and symptoms.

MATERIALS AND METHODS

Four hundred and three adolescents answered a questionnaire evaluating sleep bruxism (SB) and awake bruxism (AB). Parents/caregivers answered a questionnaire evaluating the adolescents' sleep features (drooling on the pillow, snoring). Adolescents' facial (dolichofacial/brachyfacial/mesofacial) and clinical features (pain in masseter/temporal muscle, indentations marks on the tongue, linea alba, tooth attrition, mouth's maximum opening and masseter electrical activity) were evaluated. Multinomial regression was performed. Odds ratio (OR) and confidence intervals (CI) were provided.

RESULTS

Brachyfacial adolescents were less likely to present possible AB compared to mesofacials (OR=0.46, CI=0.21-0.98). Brachyfacial adolescents were more likely to present pain in the temporal muscle (OR=6.59, CI=2.18-19.87) and a higher number of posterior teeth with attrition (OR=1.25, CI=1.02-1.57) compared to mesofacials. Dolichofacial adolescents were more likely of not presenting pain in the masseter muscle (OR=2.23, CI=1.03-4.83), had a higher mouth's maximum opening (OR=1.43, CI=1.04-1.97), had a higher number of posterior teeth with attrition (OR=1.17, CI=1.00-1.37) and were more likely to drool on the pillow (OR=2.05, CI=1.15-3.67) compared to mesofacials. Dolichofacial adolescents were more likely of not presenting pain in the temporal muscle (OR=6.36, CI=2.30-17.54), to present themselves without marks on the tongue (OR=2.26, CI=1.09-4.69) and present a higher mouth's maximum opening (OR=2.09, CI=1.40-3.13) compared to brachyfacials.

CONCLUSION

Bruxism and its clinical features differ among dolichofacial, brachyfacial and mesofacial adolescents.

Did expanded access to denture services improve chewing ability in the Korean older population? Results of a regression discontinuity analysis

The Korean National Health Insurance expanded the dental insurance in 2012 to cover denture services for older adults. We analyzed whether the new policy improved of chewing ability in the eligible population. We used regression discontinuity (RD), a quasi-experimental design, to analyze the effects of the expanded dental insurance. We analyzed data from the Korea National Health and Nutrition Examination Survey conducted in 2010 and 2015. The study population consisted of two groups: the treatment group, aged 65 and above who were eligible; and the control group, under 65 years of age who were not eligible for the dental insurance benefit. The main outcome evaluated was self-reported chewing difficulty. The RD analysis showed that in 2015, the chewing difficulty in aged above 65 was 2.2% lower than in those aged under 65. However, the difference was not statistically significant (P = 0.76). The results from the falsification testing of predetermined covariates, placebo cut-offs, and bandwidths validated our main conclusion. The expansion of dental insurance benefits to include dentures for the older adults did not improve the chewing ability in the eligible population. Future studies should evaluate long-term outcomes of oral health as well as the social impacts on the elderly.

Masticatory function parameters in patients with removable dental prosthesis

This study aimed to assess the masticatory efficiency in patients with a removable dental prosthesis, presenting different systemic, oral and prosthetic states while chewing different foods. The study was conducted on a convenient sample of patients aged 45 and above, with removable prostheses in at least one jaw. Patients were asked to chew samples of digestive biscuits, apple, and carrot, until the sensation of swallowing. The recorded masticatory function parameters were: chewing time, the number of mastication cycles, mean masticatory cycle duration, and chewing frequency. We found out that the masticatory functional parameters registered statistically significant differences according to the chewed food (e.g., generally the highest values were recorded for carrot and lowest for apple), most likely this being in relation to food’s consistency, wetting, and adherence. High positive correlations were found between the chewing time and the number of mastication cycles for all three foods taken into consideration. Higher values for chewing time and number of mastication cycles were found for all foods in patients with complete dentures and overdentures, and while chewing carrot in patients with altered general status and of advanced age. Therefore, it that it takes a different time and number of mastication cycles to complete chewing, in relation to individual and food characteristics, to the systemic, oral and prosthetic patient’s status. The residual teeth number and the type of prosthetic rehabilitation favor the adaptation and improvement of masticatory parameters and can have marker value for masticatory efficiency.