Comparative Evaluation of Occlusal Bite Force in Relation to the Muscle Activity in the Mixed Dentition Children of Age Group 9-12 Years: A T-scan Analysis

Aim and objective

Compare and evaluate the muscle activity and the occlusal force between the mixed dentition boys and girls of 9-12 years.

Materials and methods

The study included 15 boys and 15 girls. The occlusal force and activity of the masseter and temporalis muscle were measured with a T-scan device using a sensor, a module to transmit the signals to a computer and the complete data of the bite force and muscle activity with the EMG recordings and data were collected and evaluated.

Results

Relative occlusal force in the primary and permanent molars between the boys and girls showed no significant difference on the left side compared to the right. The electromyography values of masseter and temporalis in boys and girls showed a significant difference in which (TAR and MMR), (TAR and MML), (TAL and MMR), and (TAL and MML) are significant. The overall paired sample statistics showed higher muscle activity in masseter.

Conclusion

T-scan analysis has proved to be a dependable method for the evaluation of occlusal bite force with the muscle activity interpretation using EMG. This study concluded that there is a difference in the occlusal pattern and muscle activity in the mixed dentition that showed the maximum force was on the permanent molars and the symmetry of EMGs activity in children was on the right masseter comparatively with higher bite values in boys compared to girls.

Clinical significance

T-scan is a computerized analysis system that helps in the proper assessment of the patient's occlusion and assists in the proper treatment planning and diagnosis accurately without much effort.

How to cite this article

Prabahar T, Gupta N, Chowdhary NR, et al. Comparative Evaluation of Occlusal Bite Force in Relation to the Muscle Activity in the Mixed Dentition Children of Age Group 9-12 Years: A T-scan Analysis. Int J Clin Pediatr Dent 2021;14(S-1):S29-S34.

Comparative evaluation of bite force in patients treated for unilateral mandibular condylar fractures by open and closed methods

BACKGROUND/AIM

Condylar fractures account for a large proportion (20% to 52%) of mandibular injuries. The goal of treating these fractures is to restore the occlusion, thereby re-establishing the masticatory function as close as possible to the patient's pre-trauma state. The aim of this study was to compare the bite forces following unilateral condylar fractures treated by open reduction and internal fixation (ORIF) with those managed by the closed method.

METHOD

Patients with unilateral mandibular condylar fractures were divided into two groups (n = 20) using a simple randomization method. Patients in group I were treated by open reduction and internal fixation (ORIF) using titanium miniplates and screws. Patients in group II were treated by the closed method with inter-maxillary fixation. Patients in both groups were evaluated pre-operatively and then post-operatively at one week, one month and three months for maximum bite force achieved at the central incisor, premolar and molar regions.

RESULTS

Pre-operative bite forces on the unaffected site were significantly higher than the affected site in both groups, whereas no significant difference was observed in bite forces between the unaffected and affected sites in both groups post-operatively. The bite forces achieved at both the unaffected and affected sites in the ORIF group were significantly higher than in the closed group.

CONCLUSION

Maximum bite forces differed significantly when the treatment was done with the open method, and the patients treated with the open method needed less time to achieve the maximum bite forces, thereby making an earlier return to function.

Bite Force, Occlusal Contact and Pain in Orthodontic Patients during Fixed-Appliance Treatment

Previously, bite force, occlusal contact and pain were investigated in orthodontic patients with moderate-to-severe malocclusion, but not in patients with minor malocclusion. The purpose of this study was to investigate changes in bite force, teeth in occlusal contact and pain in orthodontic patients with minor crowding before orthodontic treatment (T0), after bonding (T1), during treatment (T2), post-treatment (T3) and during retention (T4). In total, 27 patients (21 females, 6 males, median age 15.3 years) with neutral occlusion and normal craniofacial morphology were treated with non-extractions and fixed appliances. Differences in the registered data were analysed by a mixed linear model with repeated measures. Bite force and teeth in occlusal contact significantly decreased between T0 and T1 (p < 0.0001, respectively) and between T0 and T2 (p < 0.01, respectively). Bite force and teeth in occlusal contact significantly increased between T1 and T4 (p < 0.05, p < 0.0001, p < 0.001, respectively) and between T2 and T4 (p < 0.05, p < 0.0001, p < 0.01, respectively). No significant difference in pain was found. The results indicate that bite force and teeth in occlusal contact significantly decreased during treatment and reached baseline level at retention. The findings may prove valuable for informing orthodontic patients with minor malocclusion.

The Reliability of a New Device for Measuring the Maximum Bite Force

Objective. To test the inter- and intraexaminer reliability of a recently developed instrument for measuring the maximum bite force (MBF). Material and Methods. Sixty patients who were clinically confirmed as having Oral Submucous Fibrosis (OSMF) and 60 healthy controls were included in this study. For each subject, age, gender, weight, height, and body mass index (BMI) were recorded. The maximum bite force was recorded in alternate order with a bite force sensor (D1) and an occlusal force meter (D2). Bite force was measured in the first molar region. Pearson’s correlation coefficient and kappa statistic were applied to assess the reliability between D1 and D2 in the assessment of maximum bite force. The independent $t$ -test was performed to find the statistical significance between the two study groups. The paired $t$ -test was applied to find out the difference between the right and left disease in groups of two devices separately. The one-way analysis of covariance (ANOVA) was performed to find the significant difference between grades of OSMF. Results. The results of the kappa values were $0.8531\pm 0.0724$ and $0.7336\pm 0.0737$ for interdevice reliability in OSMF patients in right and left sides. Similar findings were obtained in right and left sides of healthy individuals ( $0.7549\pm 0.0816$ and $0.9440\pm 0.0806$ ) and in the total sample ( $0.8132\pm 0.0544$ and $0.8303\pm 0.0538$ ). Pearson’s correlation coefficient between two devices revealed a high and significant positive correlation between D1 and D2 separately and in the whole sample. Conclusion. The observations of the present study suggest that the bite force sensor can be used as a reliable device for measuring bite force.

Mechanical Stability of Screw-Retained Monolithic and Bi-layer Posterior Hybrid Abutment Crowns after Thermomechanical Loading: An In Vitro Study

To evaluate the failure-load and survival-rate of screw-retained monolithic and bi-layered crowns bonded to titanium-bases before and after mouth-motion fatigue, 72 titanium-implants (SICvantage-max, SIC-invent-AG) were restored with three groups (n = 24) of screw-retained CAD/CAM implant-supported-single-crowns (ISSC) bonded to titanium-bases: porcelain-fused-to-metal (PFM-control), porcelain-fused-to-zirconia (PFZ-test) and monolithic LDS (LDS-test). Half of the specimens (n = 12/group) were subjected to fatigue in a chewing-simulator (1.2 million cycles, 198 N, 1.67 Hz, thermocycling 5–55 °C). All samples were exposed to single-load-to-failure without (PFM0, PFZ0, LDS0) or with fatigue (PFM1, PFZ1, LDS1). Comparisons were statistically analyzed with t-tests and regression-models and corrected for multiple-testing using the Student–Neuman–Keuls method. All PFM and LDS crowns survived fatigue exposure, whereas 16.7% of PFZ showed chipping failures. The mean failure-loads (±SD) were: PFM0: 2633 ± 389 N, PFM1: 2349 ± 578 N, PFZ0: 2152 ± 572 N, PFZ1: 1686 ± 691 N, LDS0: 2981 ± 798 N, LDS1: 2722 ± 497 N. Fatigue did not influence load to failure of any group. PFZ ISSC showed significantly lower failure-loads than monolithic-LDS regardless of artificial aging (p < 0.05). PFM ISSC showed significantly higher failure loads after fatigue than PFZ (p = 0.032). All ISSC failed in a range above physiological chewing forces. Premature chipping fractures might occur in PFZ ISSC. Monolithic-LDS ISSC showed high reliability as an all-ceramic material for screw-retained posterior hybrid-abutment-crowns.

Bending Fracture of Different Zirconia-Based Bioceramics for Dental Applications: A Comparative Study

The fabrication of fixed dental prostheses using aesthetic materials has become routine in today’s dentistry. In the present study, three-unit full zirconia fixed prosthetic restorations obtained by computer-aided design/computer-aided manufacturing (CAD/CAM) technology were tested by bending trials. The prostheses were intended to replace the first mandibular left molar and were manufactured from four different types of zirconia bioceramics (KatanaTM Zirconia HTML and KatanaTM Zirconia STML/Kuraray Noritake Dental Inc.; NOVAZir^® Fusion float^® ml/NOVADENT/Dentaltechnik; and 3D PRO Zirconia/Bloomden Bioceramics). In total, sixteen samples were manufactured—four samples per zirconia material. Additionally, the morphology, grain size area distribution, and elemental composition were analyzed in parallelepiped samples made from the selected types of zirconia in three different areas, noted as the upper, middle, and lower areas. The scanning electron microscope (SEM) analysis highlighted that the grain size area varies with respect to the researched area and the type of material. Defects such as microcracks and pores were also noted to a smaller extent. In terms of grain size area, it was observed that most of the particles in all samples were under 0.5 μm², while the chemical composition of the investigated materials did not vary significantly. The results obtained after performing the bending tests showed that a zirconia material with fewer structural defects and an increased percentage of grain size area under 0.5 µm², ranging from ~44% in the upper area to ~74% in the lower area, exhibited enhanced mechanical behavior. Overall, the resulting values of all investigated parameters confirm that the tested materials are suitable for clinical use.

Contact fracture test of monolithic hybrid ceramics on different substrates for bruxism

OBJECTIVES

To determine the minimum thickness required for a monolithic hybrid ceramic crown on different substrates (soft vs stiff) used in posterior dentition for bruxism.

METHODS

80 polymer-infiltrated ceramic networks Vita Enamic (PICN VE) disc specimens with four different occlusal thicknesses (0.8, 1.2, 1.6 and 2.0 mm), were produced using a computer-aided design/manufacturing system, and cemented on a stiff (zirconia) or soft (polyamide) substrate of 4-mm thickness. The ten specimens, in soft or stiff groups, were subjected to compressive loading by a MTS machine until fracture or maximum load (4500 N) was reached. The unbroken specimens were examined using optical coherence tomography. Eight axisymmetric finite element models and eight 3D models comprising the four different occlusal thicknesses and two substrates under different vertical loads and sliding movements were constructed. The maximum principal stress was selected to evaluate the stress distribution in this study.

RESULTS

The fracture resistance of the specimens was significantly different between the two substrates (P < 0.001). Fracture resistance was positively associated with specimen thickness (r = 0.597 and 0.896 for the soft and stiff substrate respectively). Specimens on the soft substrate had lower fracture loads, whilst cone cracks were observed in unbroken samples on different soft/stiff substrate prior to final fracture. The finite element analysis confirmed that samples on the stiff substrate had lower maximum principal stress values than those on the soft substrate. For the maximum principal stress not to exceed the flexural strength of PICN VE, a stiff substrate and minimum thickness of 2.0 mm are required for the prostheses.

SIGNIFICANCE

A minimum 2.0 mm thick, stiff substrate was needed for bruxism as shown by the effect of high/large chewing force on the posterior dentition of monolithic PICN VE crowns.

Influence of one-wall remaining coronal tooth with resin abutment and fiber post on static and dynamic fracture resistance

The objective of this study was to determine the influence of height and thickness of the one wall remaining coronal tooth structure on the fracture resistance of an endodontically treated root with resin abutment build-up using resin composite and fiber-reinforced resin composite post. Static and dynamic fracture tests were performed by placing the remaining tooth wall on the tensile side and applying loads at an angle of 30° from the tooth axis. Superior static fracture resistance was observed when the wall remaining on the tooth had a height and thickness greater than 1.0 mm. The dynamic fatigue test showed high loading capacity or fracture resistance in specimens with large height and thickness. The dynamic fatigue test showed the influence of the remaining tooth structure on fracture resistance clearly. In conclusion, the static and dynamic fracture resistances increased with the height and thickness of the one wall remaining tooth structure.

Maximum Voluntary Molar and Incisor Biting Force and Morphological Variables in Subjects With Different Vertical Skeletal Patterns

Objective:

To estimate the maximum voluntary molar biting force (MBF) and incisor biting force (IBF) and their relationship to morphological variables in subjects with different vertical skeletal patterns.

Materials and Methods:

Maximum voluntary MBF, IBF, and morphological variables were recorded in 120 subjects (60 males and 60 females) with skeletal class I pattern in the age range of 14 to 24 years. All subjects were divided into 3 groups: Normodivergent, hypodivergent, and hyperdivergent, according to the maxillomandibular plane angle and Jarabak ratio. Bite force measurements were undertaken using a custom-made portable digital gnathodynamometer on the left and the right sides of the jaw in the molar and incisor regions during maximal clenching. Statistical analysis was performed using independent t-test, chi-square test, and ANOVA test using SPSS version 22.0.0.0 software.

Results:

MBF and IBF are influenced by gender with higher values obtained for male subjects in all groups in the following order: hypodivergent > normodivergent > hyperdivergent. No significant changes were seen with morphological variables in different groups.

Conclusion:

Molar and incisor biting forces are highest in hypodivergent subjects and least in hyperdivergent subjects as a reflection of jaw morphology and muscular efficiency. In all groups, males exhibit higher force values than females, underlining a strong gender influence on biting force and facial pattern.

Effect of cementation techniques on fracture load of monolithic zirconia crowns

Aim

The aim of this study was to evaluate the effect of cement on the fracture load of monolithic zirconia crowns with different yttria content (3 and 5 mol%).

Methods

A total of 62 monolithic zirconia crowns, 40 3Y-zirconia crowns (Prettau^® Zirconia, Zirkonzahn) and 22 5Y-zirconia crowns (Prettau^® 4 Anterior^®, Zirkonzahn) were produced to a shallow chamfer molar preparation. The 3Y-crowns were divided into four groups and attached to composite abutment duplicates (SDR^® flow+, Dentsply DeTrey GmbH) using the following four cementation techniques; (1) Self-adhesive resin-based cement, (2) Pre-treatment with air-abrasion and self-adhesive resin-based cement, (3) Zinc phosphate cement, (4) Glass-ionomer cement. The 5Y-crowns were divided into two groups and attached to the duplicates with; (1) Self-adhesive resin-based cement, or (2) Air-abrasion pre-treatment and self-adhesive resin-based cement. All crowns were loaded axially (0.5 mm/min) on the occlusal surface until fracture occurred.

Results

Among the 3Y-zirconia groups, the zinc phosphate cement group fractured at lower loads compared to the resin-based cement groups, with and without air-abrasion, (p < .012). Among the 5Y-groups the air-abraded crowns fractured at statistically significant lower loads compared to the untreated crowns (p < .028). Load at fracture values were significantly different between the two zirconia materials (p < .001), with fracture loads ranging from 3873 to 7500 N in the 3Y-groups, and 2100 to 4948 N in the 5Y-groups.

Conclusions

Resin-based cementation increased the fracture load compared to non-adhesive cementation. The 3Y-crowns fractured at almost twice the loads of the 5Y-crowns. Pre-treatment with air abrasion reduced the strength of the 5Y-crowns only, showing the importance of differentiating the treatment of the two materials.

Comparison of Fracture Strengths of Three Provisional Prosthodontic CAD/CAM Materials: Laboratory Fatigue Tests

Temporary restorations play a fundamental role in oral rehabilitation. They can be used on teeth or implants for a variable period of time during the period prior to rehabilitation with definitive restorations. Temporary or provisional restorations manufactured via CAD/CAM methods are becoming increasingly used in the intermediate phase of the treatment of complex cases. The main objective of this study was to compare the fracture resistance of three materials used in the creation of provisional crowns on implants: polymethyl methacrylate (PMMA), composite resin, and polyether ether ketone (PEEK). Fracture resistance in PMMA (Zirkonzahn Temp Basic® , Gais, South Tyrol, Italy) ranged from 1216.0 N to 1461.2 N, with a mean of 1300.4 N (SD = 97.09). In the composite material (3M Lava Ultimate®, Minnesota, USA), fracture resistance varied between 1343.5 N and 1490.6 N, with a mean of 1425.9 N (SD = 49.03). Lastly, in PEEK (Tecno Med Mineral®, Zirkonzahn®, Gais, South Tyrol, Italy), fracture resistance ranged from 2294.8 N to 2451.7 N, with a mean of 2359.5 (SD = 50.01). The crowns made with the PEEK Tecno Med Mineral® (Zirkonzahn®, Tyrol, Italy) material presented the best fracture resistance, followed by the crowns made with the Lava Ultimate® (3M® ESPE, Minnesota, USA) composite resin material and, finally, those made with the PMMA Temp Basic® (Zirkonzahn®, Tyrol, Italy) material.

Affordable oral health care: dental biofilm disruption using chloroplast made enzymes with chewing gum delivery

Current approaches for oral health care rely on procedures that are unaffordable to impoverished populations, whereas aerosolized droplets in the dental clinic and poor oral hygiene may contribute to spread of several infectious diseases including COVID-19, requiring new solutions for dental biofilm/plaque treatment at home. Plant cells have been used to produce monoclonal antibodies or antimicrobial peptides for topical applications to decrease colonization of pathogenic microbes on dental surface. Therefore, we investigated an affordable method for dental biofilm disruption by expressing lipase, dextranase or mutanase in plant cells via the chloroplast genome. Antibiotic resistance gene used to engineer foreign genes into the chloroplast genome were subsequently removed using direct repeats flanking the aadA gene and enzymes were successfully expressed in marker-free lettuce transplastomic lines. Equivalent enzyme units of plant-derived lipase performed better than purified commercial enzymes against biofilms, specifically targeting fungal hyphae formation. Combination of lipase with dextranase and mutanase suppressed biofilm development by degrading the biofilm matrix, with concomitant reduction of bacterial and fungal accumulation. In chewing gum tablets formulated with freeze-dried plant cells, expressed protein was stable up to 3 years at ambient temperature and was efficiently released in a time-dependent manner using a mechanical chewing simulator device. Development of edible plant cells expressing enzymes eliminates the need for purification and cold-chain transportation, providing a potential translatable therapeutic approach. Biofilm disruption through plant enzymes and chewing gum-based delivery offers an effective and affordable dental biofilm control at home particularly for populations with minimal oral care access.

Reliability of Class II Bulk-fill Composite Restorations With and Without Veneering: A Two-year Randomized Clinical Control Study

Bulk-fill composites are increasingly used in stress-bearing areas in posterior teeth, with a diversity of reports concerning their effectiveness and clinical reliability. The objective of this randomized clinical control study was to investigate the effectiveness of bulk-fill versus veneered bulk-fill Class II composite restorations. A double-blind split-mouth technique was employed in 80 subjects recruited for restoring Class II caries in one molar bilaterally in the same arch following respective inclusion and exclusion criteria and after obtaining written consent. While one molar was randomly restored with bulk-fill composite using the sealed-envelope technique, Tetric N-Ceram Bulk Fill (TBF), the contralateral was restored with a bulk-fill composite veneered with an increment of a heavy-body microhybrid composite-Tetric-Ceram HB (TBF/V). Box-only cavities were prepared and received etch-and-rinse adhesive bonding and Tetric N-Bond treatment before composite insertion. Restorations were assessed at 24 hours, 2 weeks, 6 months, 12 months, and 24 months for esthetic, functional, and biological quality employing the FDI ranking criteria. Friedman repeated-measures analysis of variance, the McNemar test, and the Cohen's kappa statistical test were used for statistical analysis. Over a 24-month interval, none of the test restorations were ranked as clinically unsatisfactory. In terms of functional criteria, clinically excellent restorations were significantly more prevalent in TBF/V than in TBF (p<0.05). For long-term satisfactory performance of Class II bulk-fill composites, an occlusal veneering increment of conventional heavy body microhybrid composite appears to be favorable.

Bite force changes after surgical correction of mandibular prognathism in subjects with increased vertical dimension : A prospective clinical trial

PURPOSE

Occlusal bite force (OBF) is the most important parameter in assessing biting efficiency. The aim of this study was to record OBF changes after surgical correction of high angle maxillary/mandibular (Max/Mand) class III patients and to compare these with that recorded in class III patients with average Max/Mand angle.

MATERIALS AND METHODS

Initially included were 42 patients with severe class III skeletal malocclusion who were scheduled for orthodontic surgery: group 1-22 patients with increased vertical relationship scheduled for bimaxillary surgery; group 2-20 patients with average vertical relationship scheduled for mandibular setback only. OBF measurements before surgery (T0), at debonding (T1) and at least 3 months after debonding (T2) were recorded using a portable occlusal force gauge. The following were also measured: maximum OBF (MOBF) achieved by the subject on each side, averaged OBF on each side (AOBF) and maximum OBF at the incisal region (MIOBF). At T2, only 33 patients (group 1: 17 and group 2: 16) were included in the analysis due to loss to follow-up.

RESULTS

MOBF increased significantly in group 1, while no significant changes were detected in group 2. MIOBF increased after surgical correction in both groups. Significant increase in MIOBF was observed at T1 (P < 0.001) followed by an insignificant decrease during the observation period (3-6 months after treatment; P > 0.05). The two groups differed significantly in MOBF at T1 and T2, while no statistically significant differences were detected between the groups for MIOBF changes at the various time intervals (P > 0.05). The number of posterior teeth with occlusal contacts increased in both groups. Relapse was detected in group 1 where the number of posterior teeth in contact decreased during the observation period (T1-T2).

CONCLUSION

OBF greatly improved after surgical correction of the vertical morphology. Correction of high angle mandibular prognathism improves oral function in addition to esthetics.

Biomechanical evaluation of caudally and buccally screwed customised reconstruction plates for lateral segmental defects of mandible

The aim of this study was to compare locking reconstruction plates with caudobuccally screwed custom mandibular reconstruction plates in bridging lateral mandibular segmental defects. The in vitro study was conducted on 13 polyurethane mandibles. A total of 7 mandibles with lateral segmental defects were bridged with locking reconstruction plates in group I, 6 mandibles with the same standard defect were bridged with caudobuccally screwed customised reconstruction plates in group II. Mean yield displacement, yield load, and displacement at 80 N (Newtons), 100 N, 200 N, 300 N loading were compared among the 2 groups. The mean (SD) displacement for Group I was 11.27 (3.6) mm, Group II was 21.08 (2.5) mm. Group II had significantly greater (p=0.0001) displacement when compared with Group I. The mean (SD) force before failure for Group I was 638.4 N (127.2), Group II was 1398. 3 N (162.7). Group II withstood significantly greater force than Group I (p=0.0001). The study reveals that the caudobuccally screwed custom reconstruction plates can significantly enhance yield load as preserving the preoperative shape of the face and mandible.

Fracture Resistance of Single-Unit Implant-Supported Crowns: Effects of Prosthetic Design and Restorative Material

PURPOSE

To evaluate the fracture resistance and fracture patterns of single implant-supported crowns with different prosthetic designs and materials.

MATERIALS AND METHODS

One hundred and forty-four identical crowns were fabricated from zirconia-reinforced lithium silicate (ZLS), leucite-based (LGC), and lithium disilicate (LDS) glass-ceramics, reinforced composite (RC), translucent zirconia (ZR), and ceramic-reinforced polyetheretherketone (P). These crowns were divided into 3 subgroups according to restoration design: cementable crowns on a prefabricated titanium abutment, cement-retained crown on a zirconia-titanium base abutment, and screw-cement crown (n = 8). After adhesive cementation, restorations were subjected to thermal-cycling and loaded until fracture. The fracture patterns were evaluated under a stereomicroscope. Statistical analysis was performed by using 2-way ANOVA/Bonferroni multiple comparison post hoc test (α = 0.05).

RESULTS

For each prosthetic design, ZR presented the highest fracture resistance (p ≤ 0.005). Other than the differences with ZLS and RC for screw-cement crowns (p > 0.05) and RC for crowns on zirconia-titanium base abutments (p > 0.05), LGC showed the lowest fracture resistance. P endured higher loads than LDS (p < 0.001), except for the crowns on zirconia-titanium base abutments (p > 0.05). Cementable crowns presented the highest fracture resistance (p < 0.001), other than LGC and LDS. The differences between LGC crowns (p > 0.05) or LDS crowns on prefabricated titanium and zirconia-titanium abutments were nonsignificant (p = 0.133). Fragmented crown fracture was predominant in most of the restorations. Screw and abutment fractures were observed in ZR screw-cement crowns, and all P crowns were separated from the abutments.

CONCLUSIONS

Restorative material and restoration design affect the fracture resistance and fracture pattern of implant-supported single-unit restorations. Clinicians may restore single-unit implants in premolar sites with the materials and prosthetic designs tested in the present study.

Chewing function and related parameters as a function of the degree of dementia: Is there a link between the brain and the mouth?

Background

To date, no study has investigated the association between chewing function and related parameters as a function of the degree of dementia using a finer subdivision of the values of the Mini‐Mental State Examination (MMSE).

Objective

This study aimed to investigate the differences in chewing function and related parameters as a function of the degree of dementia.

Methods

An analysis of cross‐sectional data obtained from the OrBiD (Oral Health, Bite Force, and Dementia) pilot study was performed. The participants were stratified into five groups based on the outcomes of the MMSE (no dementia, MMSE 28–30; mild cognitive impairment, MMSE 25–27; mild dementia, MMSE 18–24; moderate dementia, MMSE 10–17; severe dementia, MMSE <10). The chewing efficiency, maximum occlusal force and related parameters (number of supporting zones, number of teeth, Eichner index, tooth/denture status, denture quality, and dental treatment needs) were recorded.

Results

The MMSE groups showed significantly different chewing efficiencies (p = .003, Jonckheere‐Terpstra test) and maximum occlusal forces (p = .003, Jonckheere‐Terpstra test), but the number of supporting zones (p = .055, chi‐square test) and the number of natural teeth (p = .126, chi‐square test) were not different. The Eichner index, tooth/denture status, denture quality and dental treatment need showed no significant associations with the degree of dementia.

Conclusion

An improvement in the usability of the measurement methods for assessing chewing function in people with dementia is needed. Research involving people with dementia is necessary because the nutritional situation often deteriorates rapidly within a multifactorial system, which includes chewing ability and oral health.

Analysis of maximum bite force and chewing efficiency in unilateral temporomandibular joint ankylosis cases treated with buccal fat pad interpositional arthroplasty

There is limited knowledge about masticatory function after the release of temporomandibular joint (TMJ) ankylosis. In this study, masticatory function was evaluated by measuring maximum voluntary bite force (MVBF) and chewing efficiency in 30 unilateral TMJ ankylosis patients who were treated with buccal fat pad (BFP) interpositional arthroplasty. Eighteen subjects over 12 years of age were included in study Group A and 12 subjects below 12 years of age in study Group B. Patients in the study groups had completed a minimum follow up of one year after surgery. Control groups C (over 12 years of age, n = 18) and D (under 12 years of age, n = 12) consisted of age, sex, and weight-matched normal subjects. The mean MVBF was measured between occluding molar teeth with a strain gauge transducer. Chewing efficiency was measured with two different coloured chewing gum strips. These were chewed for 5, 10, 20, 30, and 50 strokes. Compared with normal subjects, the study groups (A and B) could generate 64.7% (p = 0.004*) and 89.8% (p = 0.121) of MVBF, respectively. Overall chewing efficiency was 88.7% in Group A and 92.9% in Group B (p = 0.014* and p = 0.138, respectively) when compared with normal subjects. The study has shown that BFP interpositional arthroplasty effectively restores masticatory function.

Influence of Preparation Design and Restorative Material on Fatigue and Fracture Strength of Restored Maxillary Premolars

STATEMENT OF PROBLEM

Extensive carious lesions and/or large preexisting restorations possibly contribute to crack formation, ultimately resulting in a fracture that may lead to the loss of a tooth cusp. Hence, preparation design strategy in conjunction with the restorative material selected could be influential in the occurrence of a cuspal fracture.

PURPOSE

The purpose of this in vitro study was to evaluate the fatigue behavior and fracture strength of maxillary premolars restored with direct composite and indirect ceramic inlays and overlays, with different preparation depths in the presence or absence of cuspal coverage, and analyze their failure types.

METHODS AND MATERIALS

Sound maxillary premolars (N=90; n=10) were divided into nine groups: group C: control; group DCI3: direct composite inlay 3 mm; group DCI5: direct composite inlay 5 mm; group ICI3: indirect ceramic inlay 3 mm; group ICI5: indirect ceramic inlay 5 mm; group DCO3: direct composite overlay 3 mm; group DCO5: direct composite overlay 5 mm; group ICO3: indirect ceramic overlay 3 mm; group ICO5: indirect ceramic overlay 5 mm. In indirect ceramic, lithium disilicate restoration groups, immediate dentin sealing was applied. After restoration, all specimens were tested in fatigue (1,200,000 cycles, 50 N, 1.7 Hz). Samples were critically appraised, and the specimens without failure were subjected to a load to failure test. Failure types were classified and the data analyzed.

RESULTS

Zero failures were observed in the fatigue testing. The following mean load to failure strengths (N) were recorded: group ICO5: 858 N; group DCI3: 829 N; group ICO3: 816 N; group C: 804 N; group ICI3: 681 N; group DCO5: 635 N; group DCI5: 528 N; group DCO3: 507 N; group ICI5: 482 N. Zero interaction was found between design-depth-material (p=0.468). However, significant interactions were found for the design-depth (p=0.012) and design-material (p=0.006). Within restorations at preparation depth of 3 mm, direct composite overlays obtained a significantly lower fracture strength in comparison to indirect ceramic onlays (p=0.013) and direct composite inlays (p=0.028). In restorations at depth 5 mm, significantly higher fracture load values were observed in indirect ceramic overlays compared with the inlays (p=0.018). Indirect ceramic overlays on 3 mm were significantly stronger than the deep inlays in ceramic (p=0.002) and tended to be stronger than the deep direct composite inlays. Severe, nonreparable fractures were observed with preparation depth of 5 mm within ceramic groups.

CONCLUSIONS

The preparation depth significantly affected the fracture strength of tooth when restored with either composite or ceramic materials. Upon deep cavity preparations, cuspal coverage proved to be beneficial when a glass ceramic was used as the restorative material. Upon shallow cavity preparations, a minimally invasive approach regarding preparation design used in conjunction with a direct composite material was favorable.

Fracture resistance of maxillary premolars restored with different endocrown designs and materials after artificial ageing

PURPOSE

To evaluate the effect of three different designs and two monolithic ceramic materials on the durability and fracture resistance of endocrowns on maxillary first premolars, in comparison to post-and-core crowns.

METHODS

Fifty-six maxillary premolars were endodontically treated and shortened to a level of 2 mm from the cervical line, and randomly categorized into six endocrown groups and post-and-core crown control group (n=8); E1; endocrowns with flat occlusal table (without ferrule), E2; endocrowns with 1.5 mm circumferential ferrule, E3; endocrowns with 1.5 mm buccal ferrule preparation. Two materials were used for endocrowns: zirconia (4YSZ; Z), and lithium disilicate (L). The control group was restored with zirconia posts, and lithium disilicate crowns. All restorations were bonded using Panavia V5 and its respective primers and underwent thermo-mechanical fatigue with a 10 kg dynamic load for 1,200,000 cycles and thermocycling between 5 and 55 °C. Thereafter all survived specimens were loaded to fracture. The results were statistically analyzed using ANOVA and T-Test.

RESULTS

None of the specimens showed any signs of debonding or fracture caused by the fatigue test. The PC control group showed no statistically significant difference in comparison to groups ZE1, ZE2 and LE2 ( p > 0.05 ). However, it was significantly different from groups LE1, LE3, and ZE3 ( p ≤ 0.05 ).

CONCLUSIONS

Preparation designs and materials affected the fracture resistance of endocrowns. The results showed a superiority of the post-and-core crowns,zirconia/lithium disilicate endocrowns with 1.5 mm circumferential ferrule, and zirconia endocrowns with the flat occlusal table.

Gastrointestinal jabberwocky to bioengineering design: using function diagrams to teach physiology

Function diagrams put the focus on physiology and physiological concepts rather than the associated anatomy. Function diagrams could potentially serve as an elaboration tool and memory aid (mnemonic) to improve learning and recall. The function diagram prototype of the gastrointestinal system can aid in the instruction of difficult gastrointestinal physiology topics using a sequential focus on fundamental gastrointestinal functions.

Periodontal Clinical Parameters as a Predictor of Bite Force: A Cross-Sectional Study

OBJECTIVE

To investigate the correlation of periodontal parameters and bite force in different stages of periodontitis after phase I periodontal therapy.

METHODS

Periodontal clinical parameters such as mobility, attachment loss, gingival recession, and percentage of bone remaining were recorded at the mandibular first molar region after phase I therapy in subjects categorized according to the stage of periodontitis. Corresponding bite force was recorded at the first mandibular molar region using a bite force device after phase I therapy. ANOVA test was used to assess the significant difference among different groups. Pearson correlation coefficient was used to assess the correlation between measured variables.

RESULTS

The ANOVA test represents that there is no statistical significant difference between the bite force in stage I, stage II, and stage III type of periodontitis. A strong positive correlation was found (r = 0.537) between bite force and percentage of remaining alveolar bone support whereas negative correlation was observed in measured parameters such as mobility (r = -0.0181), attachment loss (r = -0.608), and gingival recession (r = -0.435).

CONCLUSION

Among all periodontal clinical parameters, the percentage of remaining alveolar bone is the strong predictor of bite force and mobility; attachment loss and gingival recession cannot predict the bite force in the first molar region. Bite force is variable in different stages of periodontitis.

Biomechanical Assessment of the Validity of Sheep as a Preclinical Model for Testing Mandibular Fracture Fixation Devices

Mandibular fracture fixation and reconstruction are usually performed using titanium plates and screws, however, there is a need to improve current fixation techniques. Animal models represent an important step for the testing of new designs and materials. However, the validity of those preclinical models in terms of implant biomechanics remains largely unknown. In this study, we investigate the biomechanics of the sheep mandible as a preclinical model for testing the mechanical strength of fixation devices and the biomechanical environment induced on mandibular fractures. We aimed to assess the comparability of the biomechanical conditions in the sheep mandible as a preclinical model for human applications of fracture fixation devices and empower analyses of the effect of such defined mechanical conditions on bone healing outcome. We developed 3D finite element models of the human and sheep mandibles simulating physiological muscular loads and three different clenching tasks (intercuspal, incisal, and unilateral). Furthermore, we simulated fractures in the human mandibular body, sheep mandibular body, and sheep mandibular diastema fixated with clinically used titanium miniplates and screws. We compared, at the power stroke of mastication, the biomechanical environment (1) in the healthy mandibular body and (2) at the fracture sites, and (3) the mechanical solicitation of the implants as well as the mechanical conditions for bone healing in such cases. In the healthy mandibles, the sheep mandibular body showed lower mechanical strains compared to the human mandibular body. In the fractured mandibles, strains within a fracture gap in sheep were generally not comparable to humans, while similar or lower mechanical solicitation of the fixation devices was found between the human mandibular body fracture and the sheep mandibular diastema fracture scenarios. We, therefore, conclude that the mechanical environments of mandibular fractures in humans and sheep differ and our analyses suggest that the sheep mandibular bone should be carefully re-considered as a model system to study the effect of fixation devices on the healing outcome. In our analyses, the sheep mandibular diastema showed similar mechanical conditions for fracture fixation devices to those in humans.

Evaluation of fracture resistance of zirconia modification/polishing around implant abutments

Subcrestal placement of implants may have interproximal bone proximity issues that interfere with submucosal contour of the implant-supported Zirconia restorations during delivery of these restorations.  Modification of the mesial distal submucosal areas may be necessary to fully seat the restoration without impingement of the interproximal bone. Our aim was to determine if modification of submucosal cervical contour of implant supported zirconia titanium base (Zi-Ti base) restorations result in a significant change in fracture strength compared to Zi-Ti base restorations without any modification near the cervical submucosal area. Implant Zi-Ti base restorations, designed in the form of a maxillary premolar was made for the Straumann implant lab analog. Zirconia samples were cemented onto the Ti-base and the test group (N=20) underwent recontouring and polishing at the junction of the Zi-Ti-base cervical areas. The control group (N=20) did not undergo any modifications. All 40 samples underwent fracture testing with an Instron machine. We assessed differences between modified and unmodified implant restorations using a two-tailed t-test for independent samples.   Fracture strength values (N) ranged from 4,354.68 to 6,412.49 in the test group (N=20) and from 5,400.31 to 6,953.22 in the control group (N=20). The average fracture strength in the control group (6,154.84 ± 320.50) was higher than in the modified group (5,593.13 ± 486.51; p<.001)). Modification of submucosal contour significantly decreased the fracture strength. However, the average fracture strength exceeded the masticatory forces of humans.

Maximum voluntary molar bite force in subjects with malocclusion: multifactor analysis

OBJECTIVE

This study was performed to determine the maximum voluntary molar bite force (MVMBF) in relation to age, sex, lip competency, midline shifting, dental and skeletal malocclusion, overjet, overbite, and crowding.

METHODS

One hundred Saudi patients with orthodontic malocclusion aged 14 to 25 years (51 male and 49 female patients) were investigated in this cross-sectional study. The baseline MVMBF on the right and left side was evaluated in all patients before commencing any orthodontic treatment. The MVMBF was registered with a portable occlusal force gauge in the first molar region during maximal clenching.

RESULTS

The MVMBF significantly varied with respect to all nine confounding variables. The MVMBF significantly increased with an age of >18 years, male sex, right-side lip competency, no midline shift, dental and skeletal Class I malocclusion, normal overjet, normal overbite, and mild crowding.

CONCLUSION

All nine variables examined in the present study significantly influenced the MVMBF.

The Influence of Dentin Wall Thickness and Adhesive Surface in Post and Core Crown and Endocrown Restorations on Central and Lateral Incisors

CLINICAL RELEVANCE

Post and core crowns and endocrowns perform similarly on fracture strength, but endocrowns have more repairable fractures.

SUMMARY

Mechanical behavior of nano-hybrid composite in comparison to lithium disilicate as posterior cement-retained implant-supported crowns restoring different abutments

OBJECTIVE

Resin-based materials are gaining popularity in implant dentistry due to their shock absorption capacity. Therefore, the aim of this study was to evaluate the fracture strength and failure mode of resilient materials for both crowns and abutments and compare them to the most widely used materials in different combinations after subjection to long-term fatigue loading.

METHODS

Forty-eight cement-retained implant-restorations were assembled on titanium implants. Identical custom-made CAD/CAM abutments were milled out of 3 different materials (n = 16); T: titanium, Z: zirconia and P: ceramic-reinforced PEEK. Each group was subdivided, according to the restorative crown material, into two subgroups (n = 8); C: nano-hybrid composite and L: Lithium disilicate. Specimens were subjected to dynamic load of 98 N for 1,200,000 cycles with integrated thermal cycling. The surviving specimens were subjected to quasi-static loading until failure. Shapiro-Wilk test was used to test for normality. One-way ANOVA followed by Tukey's post-hoc test was used to detect statistically significant differences between groups.

RESULTS

All specimens withstood 1,200,000 load cycles. The fracture strength values varied from a minimum of 1639 ± 205 N for group PL to a maximum of 2949 ± 478 N for group ZL.

SIGNIFICANCE

The abutment material influenced the fracture strength and failure mode of the restoration. A combination of zirconia abutments and nano-hybrid composite showed the most favorable mode of failure within the test groups. Therefore, this combination might be recommended as an alternative for restoring single implants in the posterior area.

Failure Load of Monolithic Lithium Disilicate Implant-Supported Single Crowns Bonded to Ti-base Abutments versus to Customized Ceramic Abutments after Fatigue

PURPOSE

This laboratory study analyzed the influence of retention mode (screw- vs cement retained) and fatigue application on the failure load of monolithic lithium-disilicate (LDS) implant-supported single crowns (ISSC).

MATERIAL AND METHODS

A total of 72 samples of monolithic LDS (*Ivoclar Vivadent) ISSC were divided into three groups (n = 24) according to their type of retention mode: Group Ti-CAD: Titanium base (SICvantage CAD/CAM Abutment red (SIC invent AG), screw-retained milled monolithic LDS (IPS e.max CAD*); Group Ti-P: Titanium base (SICvantage CAD/CAM Abutment red), screw-retained pressed monolithic LDS (IPS e.max Press*) and Group Ti-Cust: Titanium base with cemented press LDS (IPS e.max Press*) crown on a LDS (IPS e.max Press*) custom abutment. A mandibular first molar implant-supported single crown model was investigated (Titanium implant: SICvantage-max, SIC invent AG, diameter: 4.2 mm, length: 11.5 mm). Half of each group (n = 12) w​ere exposed to fatigue with cyclic mechanical loading (F = 198 N, 1.2 million cycles) and simultaneous thermocycling (5-55°C). Single load to failure testing was performed, before (Subgroups Ti-CAD, Ti-P, and Ti-Cust) and after (Subgroups Ti-CAD-F, Ti-P-F, and Ti-Cust-F) fatigue. Weibull distribution was used to determine the characteristic strength and Weibull modulus differences between groups. Probability of survival at 900N load was calculated.

RESULTS

No samples failed during fatigue. Characteristic strength values were as follow: Ti-CAD: 3259.5N, Ti-CAD-F: 2926N, Ti-P: 2763N, Ti-P-F: 2841N, Ti-Cust: 2789N, Ti-Cust-F: 2194N. Whereas no difference was observed between pressed or milled monolithic crowns cemented to Ti-base, regardless of loading condition, fatigue decreased the characteristic strength of crowns cemented to custom abutments. Probability of survival at 900 N was not significantly different between groups.

CONCLUSIONS

Screw-retained pressed or milled monolithic LDS ISSC, cemented directly to Ti-base abutments or LDS crowns cemented to custom ceramic abutments resist physiological chewing forces after simulated 5-year aging in the artificial mouth and presented equally high probability of survival. However, a significant decrease in load to failure was observed in LDS crowns cemented to custom ceramic abutments after fatigue. Prospective clinical trials are needed to confirm the results of this laboratory investigation.

Failure Load and Fatigue Behavior of Monolithic Translucent Zirconia, PICN and Rapid-Layer Posterior Single Crowns on Zirconia Implants

This laboratory study aimed to evaluate the thermo-mechanical fatigue behavior and failure modes of monolithic and rapid-layer posterior single-crowns (SCs) supported by zirconia implants. Methods: 120 all-ceramic crowns supported by one-piece zirconia implants (ceramic.implant; vitaclinical) were divided into five groups (n = 24 each): Group Z-HT: 3Y-TZP monolithic-zirconia (Vita-YZ-HT); Group Z-ST: 4Y-TZP monolithic-zirconia (Vita-YZ-ST); Z-XT: 5Y-TZP monolithic-zirconia (Vita-YZ-XT); Group E: monolithic-polymer-infiltrated ceramic network (PICN,Vita-Enamic); Group RL (rapid layer): PICN-“table-top” (Vita-Enamic), 3Y-TZP-framework (Vita-YZ-HT). Half of the specimens of each group (n = 12) were exposed to fatigue with cyclic mechanical loading (F = 198N, 1.2-million cycles) and simultaneous thermocycling (5–55 °C). Single-load-to-failure testing (Z010, Zwick) was performed for all specimens without/with fatigue application. Data analysis was performed using ANOVA, Tukey’s post-hoc test, two-sample t-test and Bonferroni correction (p < 0.05). Results: All specimens survived fatigue exposure. Significant differences in failure loads were detected among groups (p ≤ 0.004). Materials Z-HT and Z-ST showed the highest failure loads followed by Z-XT, RL and E. The influence of fatigue was only significant for material RL. Conclusions: All types of tested materials exceeded clinically acceptable failure load values higher than 900N and can be recommended for clinical use. Z-HT and Z-ST appear to be highly reliable towards fatigue. Rapid-layer design of PICN and YZ-HT might be an interesting treatment concept for posterior implant SCs.

Mechanical stability of dental CAD-CAM restoration materials made of monolithic zirconia, lithium disilicate, and lithium disilicate-strengthened aluminosilicate glass ceramic with and without fatigue conditions

STATEMENT OF PROBLEM

Studies investigating the mechanical stability of lithium disilicate-strengthened aluminosilicate glass ceramic that do not require sintering after milling compared with other computer-aided design and computer-aided manufacturing (CAD-CAM) materials are lacking.

PURPOSE

The purpose of this in vitro study was to investigate the flexural strength of CAD-CAM zirconia, lithium disilicate, and lithium disilicate-strengthened aluminosilicate glass ceramics with and without fatigue conditions.

MATERIAL AND METHODS

Specimens (N=90, n=15) (12×4×3 mm) from the following CAD-CAM materials were prepared and polished: lithium disilicate glass ceramic (IPS e.max CAD); lithium disilicate-strengthened aluminosilicate glass ceramic (N!ce); and zirconium dioxide ceramic (IPS e.max ZirCAD). All specimens were divided into 2 subgroups: immediate testing without aging and simulation of aging by using a mastication simulator for 1 200 000 cycles (5 °C-55 °C). Thereafter, flexural strength testing was performed by using a universal testing machine (1 mm/min) on nonaged and aged specimens. The data were evaluated by using nonparametric 2-way ANOVA and Wilcoxon rank post hoc tests (α=.05).

RESULTS

Both the material type and aging significantly affected the results (P<.001). The interaction was not significant (P>.05). Under nonaged conditions, zirconium dioxide ceramic (1136 ±162 MPa) showed significantly higher mean ±standard deviation flexural strength (P<.001) than lithium disilicate (304 ±34 MPa) and lithium disilicate-strengthened aluminosilicate glass ceramic (202 ±17 MPa). The glass ceramic groups were also significantly different from each other (P<.001). After aging, zirconium dioxide (1087.9 ±185.3 MPa) also presented significantly higher mean ±standard deviation flexural strength (P<.001) than lithium disilicate (259 ±62 MPa) and lithium disilicate-strengthened aluminosilicate glass ceramic (172 ±11 MPa) (P<.001). Aging significantly decreased the flexural strength of lithium disilicate (14.6%) (P=.03) and lithium disilicate-strengthened aluminosilicate glass ceramic (14.5%) (P=.01) but had minimal effect on the zirconium dioxide ceramic (4.3%) (P=.29).

CONCLUSIONS

Among the tested CAD-CAM materials, the mechanical performance of lithium disilicate-strengthened aluminosilicate glass ceramic was comparable with that of lithium disilicate and considerably lower than that of zirconia. Aging decreased the flexural strength of both lithium disilicate and lithium disilicate-strengthened aluminosilicate glass ceramic.

Biomechanical characterization of human temporal muscle fascia in uniaxial tensile tests for graft purposes in duraplasty

The human temporal muscle fascia (TMF) is used frequently as a graft material for duraplasty. Encompassing biomechanical analyses of TMF are lacking, impeding a well-grounded biomechanical comparison of the TMF to other graft materials used for duraplasty, including the dura mater itself. In this study, we investigated the biomechanical properties of 74 human TMF samples in comparison to an age-matched group of dura mater samples. The TMF showed an elastic modulus of 36 ± 19 MPa, an ultimate tensile strength of 3.6 ± 1.7 MPa, a maximum force of 16 ± 8 N, a maximum strain of 13 ± 4% and a strain at failure of 17 ± 6%. Post-mortem interval correlated weakly with elastic modulus (r = 0.255, p = 0.048) and the strain at failure (r =  − 0.306, p = 0.022) for TMF. The age of the donors did not reveal significant correlations to the TMF mechanical parameters. Compared to the dura mater, the here investigated TMF showed a significantly lower elastic modulus and ultimate tensile strength, but a larger strain at failure. The human TMF with a post-mortem interval of up to 146 h may be considered a mechanically suitable graft material for duraplasty when stored at a temperature of 4 °C.

Crystal misorientation correlates with hardness in tooth enamels

The multi-scale hierarchical structure of tooth enamel enables it to withstand a lifetime of damage without catastrophic failure. While many previous studies have investigated structure-function relationships in enamel, the effects of crystal misorientation on mechanical performance have not been assessed. To address this issue, in the present study, we review previously published polarization-dependent imaging contrast (PIC) maps of mouse and human enamel, and parrotfish enameloid, in which crystal orientations were measured and displayed in every 60-nm-pixel. By combining those previous results with the PIC maps of sheep enamel presented here we discovered that, in all enamel(oid)s, adjacent crystals are slightly misoriented, with misorientation angles in the 0°-30° range, and mean 2°-8°. Within this limited range, misorientation is positively correlated with literature hardness values, demonstrating an important structure-property relation, not previously identified. At greater misorientation angles 8°30°, this correlation is expected to reverse direction, but data from different non-enamel systems, with more diverse crystal misorientations, are required to determine if and where this occurs. STATEMENT OF SIGNIFICANCE: We identify a structure-function relationship in tooth enamels from different species: crystal misorientation correlates with hardness, contributing to the remarkable mechanical properties of enamel in diverse animals.

Fracture resistance of additive manufactured and milled implant-supported interim crowns

STATEMENT OF PROBLEM

Interim dental prostheses can be fabricated by using subtractive or additive manufacturing technologies. However, the fracture resistance of implant-supported interim crowns fabricated by using vat-polymerization additive manufacturing methods remains unclear.

PURPOSE

The purpose of this in vitro study was to evaluate the fracture resistance of anterior and posterior screw-retained implant-supported interim crowns fabricated by using subtractive and vat-polymerization direct light processing (DLP) additive manufacturing procedures.

MATERIAL AND METHODS

An implant (Zinic Implant RP ∅4.0×10 mm) was placed in a 15×15-mm polymethylmethacrylate block. An implant abutment (ZiaCam, nonrotatory RP) was positioned on each implant. The virtual implant abutment standard tessellation language (STL) file provided by the manufacturer was imported into a software program (Exocad v2.2 Valletta) to design 2 anatomic contour crowns, a maxillary right central incisor (anterior group) and a maxillary right premolar (posterior group). Each group was subdivided into 2 subgroups depending on the manufacturing method: milled (milled subgroup) and additive manufacturing (additive manufacturing subgroup). For the milled subgroup, an interim material (Vivodent CAD Multi) and a milling machine were used to fabricate all the specimens (N=40, n=10). For the additive manufacturing subgroup, a polymer interim material (SHERAprint-cb) and a DLP printer (SHERAprint 30) were used to manufacture all the specimens at a 50-μm layer thickness and 45-degree build orientation as per the manufacturer's instructions. Then, each specimen was cemented to an implant abutment by using composite resin cement (Multilink Hybrid Abutment HO) as per the manufacturer's instructions. A universal testing machine was used for fracture resistance analysis, and the failure mode was recorded. The Shapiro-Wilk test revealed that data were normally distributed. One-way ANOVA and Tukey multiple comparison were selected (α=.05).

RESULTS

One-way ANOVA revealed significant differences among the groups (P<.05). The anterior milled subgroup obtained a significantly higher fracture resistance mean ±standard deviation value of 988.4 ±54.8 N compared with the anterior additive manufacturing subgroup of 636.5 ±277.1 N (P<.001), and the posterior milled subgroup obtained significantly higher mean ±standard deviation of 423.8 ±68 N than the additive manufacturing subgroup of 321.3 ±128.6 N (P=.048). All groups presented crown fracture without abutment fracture.

CONCLUSIONS

Manufacturing procedures and tooth type influenced the fracture resistance of screw-retained implant-supported interim crowns. Milled specimens obtained higher fracture resistance compared with the DLP additive manufacturing groups. The anterior group was higher than the posterior group.

Low-Profile Electromagnetic Field Sensors in the Measurement and Modelling of Three-Dimensional Jaw Kinematics and Occlusal Loading

Dynamic occlusal loading during mastication is clinically relevant in the design and functional assessment of dental restorations and removable dentures, and in evaluating temporomandibular joint dysfunction. The aim of this study was to develop a modelling framework to evaluate subject-specific dynamic occlusal loading during chewing and biting over the entire dental arch. Measurements of jaw motion were performed on one healthy male adult using low-profile electromagnetic field sensors attached to the teeth, and occlusal anatomy quantified using an intra-oral scanner. During testing, the subject chewed and maximally compressed a piece of rubber between both second molars, first molars, premolars and their central incisors. The occlusal anatomy, rubber geometry and experimentally measured rubber material properties were combined in a finite element model. The measured mandibular motion was used to kinematically drive model simulations of chewing and biting of the rubber sample. Three-dimensional dynamic bite forces and contact pressures across the occlusal surfaces were then calculated. Both chewing and biting on the first molars produced the highest bite forces across the dental arch, and a large amount of anterior shear force was produced at the incisors and the second molars. During chewing, the initial tooth-rubber contact evolved from the buccal sides of the molars to the lingual sides at full mouth closure. Low-profile electromagnetic field sensors were shown to provide a clinically relevant measure of jaw kinematics with sufficient accuracy to drive finite element models of occlusal loading during chewing and biting. The modelling framework presented provides a basis for calculation of physiological, dynamic occlusal loading across the dental arch.

Factors associated with bite force in people with Parkinson's disease

ABSTRACT Purpose: to assess the bite force in people with Parkinson’s disease and correlate it with age, sex, stage and time of the disease, dentures use, presence of temporomandibular disorder, side of symptom onset, and masticatory preference. Methods: the Research Diagnostic Criteria for Temporomandibular Disorders and the Hoehn & Yahr Parkinson’s disease scale were used, and the participants’ oral cavity was clinically examined. Then, the bite force was measured with an analog dynamometer, whose bar was adapted for mouth grip. The bite force results and their correlation with the variables were analyzed with the independent t-test (p<0.05). Results: the sample comprised 42 parkinsonians at a mean age of 64 years, 67% of whom were males. No difference was observed in the correlation with age, temporomandibular disorder, stage and time of Parkinson's disease; or between the sides, symptom onset and masticatory preference. However, there was a significant association between the sexes (males and females) for both sides (right - p=0.002; left - p=0.04) and denture use for bite force on the right side (p=0.03). Conclusion: being a female and using dentures are factors associated with decreased bite force in people with Parkinson’s disease.

Harnessing biomolecules for bioinspired dental biomaterials

Dental clinicians have relied for centuries on traditional dental materials (polymers, ceramics, metals, and composites) to restore oral health and function to patients. Clinical outcomes for many crucial dental therapies remain poor despite many decades of intense research on these materials. Recent attention has been paid to biomolecules as a chassis for engineered preventive, restorative, and regenerative approaches in dentistry. Indeed, biomolecules represent a uniquely versatile and precise tool to enable the design and development of bioinspired multifunctional dental materials to spur advancements in dentistry. In this review, we survey the range of biomolecules that have been used across dental biomaterials. Our particular focus is on the key biological activity imparted by each biomolecule toward prevention of dental and oral diseases as well as restoration of oral health. Additional emphasis is placed on the structure-function relationships between biomolecules and their biological activity, the unique challenges of each clinical condition, limitations of conventional therapies, and the advantages of each class of biomolecule for said challenge. Biomaterials for bone regeneration are not reviewed as numerous existing reviews on the topic have been recently published. We conclude our narrative review with an outlook on the future of biomolecules in dental biomaterials and potential avenues of innovation for biomaterial-based patient oral care.

Effect of luting agent type on fracture loads of implant-supported ceramic premolar prostheses

To investigate the effect of luting agent type on fracture loads of implant-supported ceramic prostheses in premolar region. Ninety-nine implant-abutment complexes were divided into three different implant-supported prostheses: monolithic yttria-partially stabilized zirconia (Y-PSZ) restorations (MPZ specimens), porcelain layered on yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) restorations (PLZ specimens), and monolithic lithium disilicate ceramic restorations (MLD specimens). Implant-supported prostheses were luted with adhesive resin luting agent (RLA), glass ionomer cement (GIC), or zinc phosphate cement (ZPC). For MPZ and MLD specimens, fracture loads were significantly higher for RLA group than for GIC and ZPC groups. For PLZ specimens, fracture loads did not significantly differ in relation to luting agent. Fracture loads were significantly higher for MPZ specimens than for other test specimens, regardless of luting agent. Use of an adhesive resin luting agent is recommended for placement of premolar implant-supported monolithic Y-PSZ and lithium disilicate ceramic prostheses.

In vitro performance and fracture resistance of interim conventional or CAD-CAM implant-supported screw- or cement-retained anterior fixed partial dentures

STATEMENT OF PROBLEM

Interim restorations represent an essential clinical treatment step; however, limited information is available concerning the performance of computer-aided design and computer-aided manufacturing (CAD-CAM) interim materials.

PURPOSE

The purpose of this in vitro study was to evaluate the performance and fracture load of resin anterior implant-supported interim fixed partial dentures (IFPDs).

MATERIAL AND METHODS

Identical anterior resin IFPDs (maxillary central incisor to canine; n=16 per material) were milled from polymethylmethacrylate (PMMA) or di-methacrylate (DMA) systems with different filler content. The IFPD groups were split to simulate a chairside (cemented implant-supported prosthesis) or laboratory procedure (screw-retained implant-supported prosthesis). A cartridge DMA material served as a control. After interim cementation, combined thermocycling and mechanical loading (TCML) was performed on all restorations to approximate a maximum of 2.5 years of clinical function. Behavior during TCML and fracture force was determined, and failures were analyzed. The data were statistically investigated (Kolmogorov-Smirnov test, 1-way-ANOVA; post hoc Bonferroni, Kaplan-Meier survival, α=.05).

RESULTS

Drop out during TCML varied between no failures and complete failure during loading. For most systems, failure occurred between 120 000 and 600 000 mechanical loading cycles. For IFPDs without a screw channel fracture, values varied between 644 ±263 N and 987 ±101 N. Those with a screw channel fracture failed between 493 ±89 N and 951 ±248 N. Individual IFPDs had significantly higher mean fracture loads (P<.002), but the mean fracture values between IFPDs with and without a screw channel were not significantly different (P>.137). Failures were characterized by fracture of the connector (n=53) followed by mixed failures (n=22) or fractures at the abutment (n=21).

CONCLUSIONS

These interim materials are sufficiently fracture resistant for the fabrication of implant-supported anterior IFPDs and are expected to survive between 6 months and 2 years before failure. The stability of IFPDs depended on the type of material but not on the restoration design (with or without a screw channel).

In vitro performance and fracture resistance of pressed or CAD/CAM milled ceramic implant-supported screw-retained or cemented anterior FDPs

PURPOSE

This study investigated the in-vitro performance of anterior implant-supported fixed dental prostheses (FDP). The effect of ceramics, fabrication, finalization and the presence of a screw-channel wa s investigated.

METHODS

Identical anterior ceramic FDPs (tooth 11-13; n=80) were milled (Lithiumdisilicate (LiSiCAD, emaxCAD, Ivoclar-Vivadent), Lithiumaluminiumsilicate (LiAlSi, experimental material) or pressed (Lithiumdisilicate (LiSiPress, emaxPress, Ivoclar-Vivadent), Lithiumsilicate (ZLS, CeltraPress, Dentsply Sirona). FDP-groups (n=8 per material and group) simulated a cemented or screw-retained approach. After cementation or screwing on titanium abutments, thermal cycling and mechanical loading (TCML) was performed on all restorations to mimic 5-year clinical performance. Performance and fracture force were determined and failures were analyzed.

STATISTICS

(Kolmogorov-Smirnov-test, one-way-ANOVA; post-hoc-Bonferroni, multivariate-regression, α=0.05).

RESULTS

All FDPs survived TCML without aging, cracks, fractures or chipping. For FDPs without screw channel fracture values varied between with 839.8±112.3N (LiAlSi glazed) and 1485.9±232.6N (LiSiCAD). With screw channel, fracture results varied between 701.4±220.1N (LiALSi glazed) and 1516.3±253.7N (LiSipress). The type of material had a significant influence on the fracture results (LiSi>ZLS>LiAlSi; p≤0.012). Fabrication and finalization had no influence on the results. A screw channel did not significantly (p≥0.135) reduce the fracture force of the FDPs. Type of failure was mostly characterized by a fracture of the connector (LiSi, LiAlSi) or the abutment (ZLS, LiAlSi).

CONCLUSIONS

FDPs survived TCML without failures indicating that the in vitro performance was not influenced by the tested parameters. Composition of ceramic material has significant influence on the fracture resistance of implant supported LiSi based FDPs. Screw channel, fabrication or finalization did not weaken the FDPs.

Influence of fatigue loading on fracture resistance of endodontically treated teeth restored with endocrowns

PURPOSE

This in vitro study aimed to evaluate the influence of fatigue loading on fracture resistance of endodontically treated molars restored with endocrowns using different machinable blocks.

METHODS

Endodontically treated mandibular first molars were prepared using a standardized method. Specimens were divided into 4 groups (n = 10).Anatomically shaped endocrowns groups were manufactured using VITA ENAMIC (VE) and KATANA Zirconia (KZ). Layered endocrowns groups were manufactured using IPS e.max CAD (EM) and BioHPP (BH). Half of the specimens of each group were subjected to fracture resistance test, while the other half were subjected to thermocycling and chewing simulation. After fatigue loading, specimens were loaded until failure. Specimens were examined using stereomicroscopy. Data were analyzed using ANOVA analysis of variance and Bonferroni post hoc test (α=0.05).

RESULTS

KZ group had the highest initial fracture resistance value (1810.20± 119.56 N) and BH had the lowest value (579.50± 76.15 N). The reduction of fracture resistance after fatigue loading was significant for KZ group (1588.30±216.25 N) and BH group (502.60±11.53 N) and non-significant to VE group (1101.70±77.05 N) and EM group (1112.10±74.12 N). Failure modes of KZ and EM groups showed high percentage of non-restorable fractures, while VE and BH groups showed high percentage of restorable fractures.

CONCLUSIONS

Within the limitations of this study, the following can be concluded: Poly infiltrated ceramics should be considered as a proper material to be used as an endocrown material because of its ability to be restorable if failure occurred.

Influence of different surface treatments on two-body wear and fracture load of monolithic CAD/CAM ceramics

OBJECTIVES

To investigate two-body wear (2BW) and fracture load (FL) of monolithic ceramics after different surface pretreatments.

MATERIALS AND METHODS

Zirconia (MOZ), lithium-disilicate (LIT), and leucite-reinforced (LEU) specimens (n = 60/group) were manufactured with CAD/CAM-technology and underwent (n = 15/subgroup): 1) grinding + polishing (GrPo), 2) grinding + glazing (GrGz), 3) grinding (Gr), or 4) glazing (Gz). Scanning electron microscope (n = 3/subgroup) and 3D measurements of the ceramic crowns and antagonists (N = 180) were performed to determine 2BW before and after 120,000/1,200,000 masticatory cycles. FL was examined for all specimens (N = 180). Data were analyzed using Kolmogorov-Smirnov, one-way ANOVA, Scheffé post hoc, Kruskal-Wallis, Mann-Whitney-U, and Wilcoxon (p < 0.05).

RESULTS

MOZ presented the highest FL independent on pretreatment (6960-9250 N), while LEU (1405-2320 N) showed the lowest (p < 0.001). Ceramic and antagonist wear increased between 120,000 and 1,200,000 masticatory cycles (p < 0.001). For pretreatments GrPo, GrGz, and Gz, MOZ showed the lowest wear of the ceramic, while causing the highest antagonist wear (p < 0.001). GrPo resulted in the lowest wear for MOZ (p < 0.001), with Gr leading to the highest antagonist wear (p = 0.008). LIT specimens presented the highest wear of the ceramic and antagonist after Gz (p < 0.001), while GrPo resulted in the lowest antagonist wear (p < 0.001). GrGz led to the highest antagonist wear for LEU (p < 0.001).

CONCLUSIONS

With FL exceeding maximum masticatory forces, the three tested ceramics can be recommended for restorations, even in posterior regions. While glazing resulted in higher wear and impaired FL, polishing improved mechanical properties while largely preserving the antagonist.

CLINICAL RELEVANCE

While surface pretreatment after grinding is vital to ensure a ceramic's optimal mechanical properties, glazing and polishing varies with regard to material properties, costs, and time.

The fracture strength of endocrowns manufactured from different hybrid blocks under axial and lateral forces

AIM

This in vitro study was conducted to compare the fracture strength of endocrowns manufactured from different hybrid blocks under axial and lateral forces.

MATERIAL AND METHODS

Following root-canal treatment, 100 permanent mandibular first molars were randomly distributed among 5 groups according to restoration material. Endocrown restorations were produced from IPS e.max CAD (IPS), Vita Enamic (VE), GC Cerasmart (GC), Shofu (SH), and Brilliant Crios (BC) using CAD/CAM technology. Specimens were cemented, subjected to artificial aging, and further divided into 2 subgroups (n = 10) per group for fracture testing. Each specimen was placed on a universal testing machine and subjected to axial or lateral forces applied at a crosshead speed of 1 mm/min. Fracture data were analyzed using one-way ANOVA, Tukey, Tamhane T2, and Weibull tests.

RESULTS

Statistically significant differences in fracture-strength (FS) values under axial and lateral forces were observed among the groups (P < 0.05). Group BC had the highest FS value under axial forces, whereas group IPS had the highest FS value under lateral forces. According to Weibull analysis, VE exhibited the highest reliability under axial forces (7.62), whereas IPS exhibited the highest reliability under lateral forces (4.68). No statistically significant differences were detected in the distribution of failure types under either axial or lateral forces among the groups (P > 0.05).

CONCLUSION

All of the hybrid blocks tested showed sufficient fracture strength for use as CAD/CAM-fabricated endocrowns.

CLINICAL RELEVANCE

Hybrid blocks can be used as an alternative to lithium disilicate blocks in endocrown restorations.

Fracture resistance, failure mode and stress concentration in a modified endocrown design

Purpose

The purpose of this study was to assess fracture resistance, failure mode and stress concentration of a modified endocrown preparation design, under axial and lateral forces.

Materials and Methods

Forty lower molars were divided into two groups (n = 20) and were restored with lithium disilicate glass-ceramic endocrowns following 2 preparation designs: Conventional, with circumferential butt margin 2 mm above the cemento–enamel junction; and Modified, by adding 2 grooves on the mesial side of the vestibular dentinal wall and on the distal side of the lingual dentinal wall. After cementation and thermomechanical cycling loading, half of the samples (n = 10) from each group were loaded axially and the other half (n = 10) was loaded laterally. Fracture resistance and failure modes were observed and the finite element analysis (FEA) was used to identify the stress concentration. Two-way ANOVA and Chi-square tests (α = 0.05) were used for in vitro data analyzes.

Results

Fracture resistance showed a statistically significant difference between conventional and modified preparations (p < .001), and between axial and lateral loadings (p < .001). Conventional preparation recorded 2914 N under axial loading and 1516 N under lateral loading, while modified preparation recorded 3329 N under axial loading and 1871 N under lateral loading. FEA showed that retention grooves have reduced the stress concentration under both loads for the tooth and the restoration.

Conclusion

Modified endocrown design showed higher fracture resistance than conventional endocrown. Lateral loading displayed a high percentage of severe fracture but under higher load to failure than the values reported for normal masticatory forces.

Influence of Deep Margin Elevation and preparation design on the fracture strength of indirectly restored molars

The objectives of this in-vitro study were to investigate the influence of Deep Margin Elevation (DME) and the preparation design (cusp coverage) on the fracture strength and repairability of CAD/CAM manufactured lithium disilicate (LS₂) restorations on molars. Sound extracted human molars (n = 60) were randomly divided into 4 groups (n = 15) (inlay without DME (InoD); inlay with DME (IWD); onlay without DME (OnoD); onlay with DME (OnWD)). All samples were aged (1.2 × 10⁶ cycles of 50N, 8000 cycles of 5-55 °C) followed by oblique static loading until fracture. Fracture strength was measured in Newton and the fracture analysis was performed using a (scanning electron) microscope. Data was statistically analyzed using two-way ANOVA and contingency tables. DME did not affect the fracture strength of LS₂ restorations to a statistically significant level (p = .15). Onlays were stronger compared to inlays (p = .00). DME and preparation design did not interact (p = .97). However, onlays with DME were significantly stronger than inlays without DME (p = .00). More repairable fractures were observed among inlays (p = .00). Catastrophic, crown-root fractures were more prevalent in onlays (p = .00). DME did not influence repairability of fractures or fracture types to a statistically significant level (p > .05). Within the limitations of this in-vitro study, DME did not statistical significantly affect the fracture strength, nor the fracture type or repairability of LS₂ restorations in molars. Cusp coverage did increase the fracture strength. However, oblique forces necessary to fracture both inlays and onlays, either with or without DME, by far exceeded the bite forces that can be expected under physiological clinical conditions. Hence, both inlays and onlays are likely to be fracture resistant during clinical service.

Temporary materials: comparison of in vivo and in vitro performance

OBJECTIVE

The aim of this investigation was to compare clinical performance and in vitro wear of temporary CAD/CAM and cartridge crowns. This study is an approach to estimate the influence of in vivo use and laboratory simulation on temporary crowns.

MATERIALS AND METHODS

A total of 90 crowns were fabricated from each temporary CAD/CAM or cartridge material. Also, 10 crowns of each material were clinically applied for 14 days, and 80 identical duplicate restorations were investigated in the laboratory after storage in water (14 days; 37 °C) and subsequent thermal cycling and mechanical loading (TCML, 240.000 × 50N ML, 600 × 5°C/55 °C). After in vivo application or in vitro aging, facture force, superficial wear (mean and maximum), surface roughness (Ra, Rz), thermal weight loss (TGA), and heat of reaction (DSC) were determined for all crowns.

STATISTICS

Bonferroni post hoc test; one-way analysis of variance (ANOVA); α = 0.05).

RESULTS

The fracture resistance of the temporary materials varied between 1196.4 (CAD in vivo) and 1598.3 N (cartridge crown in vitro). Mean (maximum) wear data between 204.7 (386.7 μm; cartridge in vitro) and 353.0 μm (621.8 μm; CAD in vitro) were found. Ra values ranged between 4.4 and 4.9 μm and Rz values between 36.0 and 40.8 μm. DSC and TG analysis revealed small differences between the materials but a strong influence of the aging process.

CONCLUSIONS

Comparison of in vivo and in vitro aging led to no significant differences in fracture force and wear but differences in roughness, DSC, and TGA. SEM evaluation confirmed comparability. Comparison of CAD/CAM and cartridge temporary materials partially showed significant differences.

CLINICAL RELEVANCE

In vitro aging methods might be helpful to estimate materials' properties before principal clinical application. CAD/CAM and cartridge temporary materials provided comparable good clinical performance.

Application Solid Laser-Sintered or Machined Ti6Al4V Alloy in Manufacturing of Dental Implants and Dental Prosthetic Restorations According to Dentistry 4.0 Concept

This paper presents a comparison of the impact of milling technology in the computer numerically controlled (CNC) machining centre and selective laser sintering (SLS) and on the structure and properties of solid Ti6Al4V alloy. It has been shown that even small changes in technological conditions in the SLS manufacturing variant significantly affect changes from two to nearly two and a half times in tensile and bending strengths. Both the tensile and bending strength obtained in the most favourable manufacturing variant by the SLS method is over 25% higher than in the case of cast materials subsequently processed by milling. Plug-and-play SLS conditions provide about 60% of the possibilities. Structural, tribological and electrochemical tests were carried out. In vitro biological tests using osteoblasts confirm the good tendency for the proliferation of live cells on the substrate manufactured under the most favourable SLS conditions. The use of SLS additive technology for the manufacturing of dental implants and abutments made of Ti6Al4V alloy in combination with the digitisation of dental diagnostics and computer-aided design and manufacture of computer-aided design/manufacturing (CAD/CAM) following the idea of Dentistry 4.0 is the best choice of technology for manufacturing of prosthetic and implant devices used in dentistry.