Occlusal Rest Research Articles

Seating accuracy of removable partial denture frameworks fabricated by different digital workflows in comparison to conventional workflow.

To evaluate the seating accuracy of removable partial denture (RPD) frameworks fabricated by two digital workflows involving selective laser melting (SLM) in comparison to the conventional workflow. A Kennedy class III modification 1 partially edentulous mandibular arch was used as a master model. Three RPD framework groups were included: (1) a conventional workflow group with conventional impression and casting (CC), (2) a partial digital workflow group with conventional impression and digital fabrication (CD), and (3) a complete digital workflow group with digital impression and digital fabrication (DD). A total of 10 frameworks were produced for each group. The marginal gaps at the occlusal rests, retention arms, and reciprocating arms were measured by a traveling microscope. The data were analyzed with the one-way analysis of variance test. At the framework level, the most superior fit was observed for the CD group (79.5µm) followed by DD (85.3µm) and CC (114.2µm) groups. The CD and DD groups were significantly superior to CC (p<0.001). This fit pattern was consistent for the retention and reciprocating arms, while the occlusal rest fit was similar among all the groups. The SLM frameworks had a promising seating accuracy in comparison to conventional frameworks. The type of impression, conventional or digital, did not affect the accuracy of SLM frameworks. The differences observed in the present study are likely to be of minimal clinical significance.

Fracture Resistance of Zirconia Surveyed Crowns With Digitally Designed and Hand-Modified Occlusal Rest Seats.

Background In light of the trend of using zirconia crowns, clinicians will likely face abutment included in removable partial dentures (RPD) designs with existing zirconia. However, the decision to replace the existing crown with a surveyed crown or modify the existing crown to accept the RPD is unclear. To the best of our knowledge, there is a lack of literature on the effect of preparing a rest seat on the existing monolithic zirconia crown in the patient's mouth on the fracture resistance of the crown. Therefore, in this study, we aimed to evaluate the fracture resistance of computer-aided design/computer-aided manufacturing (CAD/CAM) zirconia surveyed crowns with digitally designed rest seats and hand-modified rest seats. Methods Thirty CAD/CAM zirconia surveyed crowns were digitally designed and fabricated and divided into groups (n=10 per group) as follows: Group 1 comprised surveyed crowns with no occlusal rest seat; Group 2 comprised surveyed crowns with a digitally designed mesial rest seat; and Group 3 comprised surveyed crowns with a hand-modified mesial rest seat. Then, with all the crowns cemented to metal dies, the specimens were subjected to a fracture resistance test using a universal testing machine (Model 8501 Instron, Norwood, MA, USA). Results Surveyed crowns without any rest seat and those with digitally created and hand-modified rest seats displayed different fracture resistances: crowns with no rest seat offered the highest fracture resistance (5831 ± 895.15 N), followed by those with a digitally designed and milled rest seat (5280 ± 1673.33 N). Crowns with a hand-modified rest seat provided the lowest fracture resistance (4976 ± 322.5 N). Based on our results, surveyed crowns without a rest seat displayed higher fracture resistance than those with a rest seat. Conclusion The fracture resistance of crowns with a digitally designed and milled rest seat was statistically similar to that of control crowns with no rest seat, whereas hand-modified rest seats significantly reduced the fracture resistance of surveyed zirconia crowns.

Fracture strength of methacrylate resin based versus resin free composite restorations supporting occlusal rest of removable partial denture: In-Vitro Study

Fracture strength of methacrylate resin based versus resin free composite restorations supporting occlusal rest of removable partial denture: In-Vitro Study

Comparative analysis of the retention force and deformation of PEEK and PEKK removable partial denture clasps with different thicknesses and undercut depths

Statement of problemThe retentive force and deformation of milled polyetheretherketone (PEEK) and polyetherketoneketone (PEKK) removable partial denture (RPD) frameworks are not well understood. PurposeThe purpose of this in vitro study was to assess the retentive force and deformation of PEEK and PEKK Akers clasps with different designs and undercut depths. Material and methodsA master model containing the first and second molar abutments was used to design Akers clasps of different cross-sectional dimensions, undercut depths (0.5 and 0.75 mm), and materials. The components of the removable partial denture framework also included an occlusal rest and were manufactured using a milling machine (n=5). The fatigue resistance of the Akers clasps was measured before and after deformation regarding the retentive forces. ResultsThe PEEK2-U50 clasp had the largest retentive force with no significant difference among all groups before and after the insertion and removal cycle. In addition, the increased cross-sectional dimensions of the design resulted in significant differences in retentive forces between the PEEK1 and PEEK2 groups and between the PEEK and PEKK materials. ConclusionsIncreasing the clasp's cross-sectional dimensions significantly impacted retentive forces, especially between different PEEK groups and between PEEK and PEKK materials.

Wear, Fatigue and Fracture Resistance of Different Monolithic CAD/CAM Onlays As Abutments for Acetal Resin or Cobalt-Chromium Removable Partial Denture Frameworks.

To assess wear, fatigue, and fracture resistance of different CAD/CAM onlays, milled from monolithic Zirconia (Zr), hybrid ceramic (EN), and lithium disilicate (LS), when used as abutments for removable partial denture frameworks fabricated from acetal resin (AR) or cobalt-chromium (Co-Cr). Standard onlays and RPD framework were designed and milled using CAD/CAM. Onlays were cemented with resin cement to identical teeth models. The RPD's occlusal rest surface and the ceramic onlays' rest seats were both 3D scanned before and after 750,000 mechanical load cycles (50 N) and 8,000 thermal cycles (5-55°C) in a chewing simulator. The volumetric loss was measured using 3D image processing software, and the failure of the samples was detected using a stereomicroscope. The fracture resistance was tested by loading to failure in a universal testing machine. The fatigue failure results were analyzed with Fisher's exact probability test and the wear and fracture resistance data were analyzed using two-way ANOVA and Bonferroni Post-hoc test (P<0.05). A significant difference (p<0.05) was found between the tested experimental groups in wear, fatigue, and fracture resistance. Zr/Co-Cr combinations exhibited the least wear and the highest fatigue and fracture resistance (P<0.05), while the highest wear and least fatigue and fracture resistance were recorded for EN/AR group (p<0.05). Zr onlays demonstrated a conservative treatment option with superior mechanical behavior when used as an onlay abutment, regardless of the RPD framework material used. The AR framework is not recommended in the posterior region for removable partial dentures.

Comparison of the Retention and Fit of Polyether Ether Ketone Clasps during Fatigue Circulation Tests

PurposeThe purpose of this study was to evaluate the fit and retention of clasps made of polyether ether ketone (PEEK) or cobalt–chromium alloy (Co–Cr) at different tooth positions in experimental simulations of in vitro wear and removal for 5 years. MethodsStandard crowns of the right mandibular first premolar (44) and first molar (46) were selected, and a circular three-arm clasp was designed, scanned and fabricated. Ten PEEK clasps were used as the experimental group, and 10 Co–Cr clasps were used as the control group. The seating channel was parallel to the side of the abutment base in both groups. The oral environment was simulated, and each clasp was tested in artificial saliva for 7200 cycles while the change in clasp retention force was recorded. The fit before and after the fatigue cycles was measured by the silicone rubber film copying method. Data were statistically analyzed using the independent samples t-test (α = 0.05). ResultsBefore circulation, the retention forces of the clasps at position 44 were 4.61 ± 0.91 N (PEEK) and 47.50 ± 10.59 N (Co–Cr), and the forces at position 46 were 3.38 ± 0.49 N (PEEK) and 28.79 ± 10.99 N (Co–Cr). After circulation, the retention forces of the clasps at position 44 were 4.15 ± 0.91 N (PEEK) and 13.90 ± 6.59 N (Co–Cr), and the forces at position 46 were 2.93 ± 0.25 N (PEEK) and 11.56 ± 3.93 N (Co–Cr). Before circulation, the fit of each clasp at the reference points (clasp tip, clasp arm, and occlusal rest) was between 41.70 μm and 170.29 μm, and after circulation, they were between 64.05 μm and 182.59 μm. The retention force and fit of the PEEK clasps did not undergo statistically significant changes from before to after circulation (P > 0.05). However, there were statistically significant (P < 0.05) decreases in the retention force of the Co–Cr clasps and the fit of the clasp tip during circulation. In addition, there was a sudden and large change in the retention force of the Co–Cr clasps after approximately 360 cycles. ConclusionsThe retention force and suitability of the PEEK clasps met the requirements for clinical use during testing that simulated the in vitro wear and removal procedure for 5 years. Compared with the Co–Cr clasp, the PEEK clasp underwent less fatigue deformation, which makes it feasible for clinical applications.

Fracture resistance of zirconia surveyed crowns with four different occlusal rest seat designs.

To determine the fracture resistance of chairside computer-aided design and computer-aided manufacturing (CAD-CAM) zirconia surveyed crowns for a mandibular first molar without occlusal rest and with four different rest seat designs. Seventy CAD-CAM zirconia 4Y-PSZ (IPS e.max ZirCAD MT for CEREC A1, C15, Ivoclar Vivadent) crowns (14 specimens/group) were designed and fabricated with a dental chairside CAD-CAM system (CEREC PrimeScan, and CEREC MCXL Dentsply Sirona). The restorations were divided into groups according to the following rest seat designs: (1) Surveyed crown without rest seat, (2) surveyed crowns with disto-occlusal rest seat, (3) surveyed crowns with disto-occlusal extended rest seat, (4) surveyed crowns with interproximal rest seat, and (5) continuous rest seat. Crowns were treated with a primer system (Monobond Plus, Ivoclar Vivadent) and cemented using resin luting cement (Multilink Automix, Ivoclar Vivadent) to resin-printed dies (Grey Resin V4, FormLabs). Subsequently, the crowns were subjected to 200,000 load cycles at 1Hz with 20 N force and then loaded with a steel indenter until fracture. The test results were analyzed with one-way Analysis of Variance (ANOVA) and HSD Tukey post-Hoc test. The mean fracture resistance of surveyed crowns without and with different rest seats was significantly different from each other. Surveyed crowns with no rest seat displayed the highest resistance (4238 N) followed by crowns with continuous rest seat (3601 N), crowns with disto-occlusal extended rest seat (3283 N), and crowns with disto-occlusal rest seat (3257 N). Crowns with interproximal rest seat displayed the lowest fracture resistance (2723 N). Surveyed crowns without rest seats had a higher fracture resistance than crowns with rest seats Surveyed crowns with interproximal rest seats presented the lowest fracture resistance among all rest seat designs. Crowns with disto-occlusal rest seats, disto-occlusal extended rest seats, and continuous rest seats displayed similar fracture resistance.

Evaluation of the Retentive Forces from Removable Partial Denture Clasps Manufactured by the Digital Method

The purpose of this study was to evaluate the retentive forces over time of removable partial denture clasps fabricated by the digital method. Occlusal rest seats were fabricated on three premolar teeth fixed in acrylic blocks (9 × 20 × 40 mm). Digitization of the teeth was performed using a laboratory scanner (Zirkonzahn Scanner S600 GmbH, Gais, Italy). After the analysis and determination of the insertion axis, two types of clasps with mesial occlusal rests were designed per tooth: the back-action and the reverse back-action clasps, using the Partial Planner Zirkonzahn program. The file was sent for fabrication of six metal clasps from a cobalt-chromium SP2 alloy in the EOSINT M270 system by a direct laser sintering process. The Instron 5544 universal testing machine was used to perform 20,000 cycles of clasp insertion and removal in the corresponding tooth with a load cell of 100 N and a speed of 2.5 mm/s. The retentive force was recorded for each of the 1000 cycles, and the change in retention over time was calculated. Statistical analysis was performed using the nonparametric Mann–Whitney test and a significance level of 5%. At 16,000 cycles, a maximum change in retention of 3.74 N was recorded for the back-action clasps and a minimum of −24.28 N at 1000 cycles for the reverse back-action clasps. The reverse back-action clasps exhibited statistically significant lower change in retention than the reverse-action clasps at 4000 and 5000 cycles. No differences were observed in the remaining cycles. During the 20,000 cycles, the change in retention was low regardless of the type of clasp. For most cycles, there were no differences in the change in retention between the two types of clasps.

Fracture Strength of Composite Rest Seats: An In Vitro Comparative Study of Different Composite versus Amalgam Restorations

Occlusal rest provides support for removable partial dentures (RPD). Rest seats are ideally prepared in enamel, but the abutment teeth might be restored or need restorations. This study compared the fracture strength of abutments restored with composite to amalgam restorations after rest seat preparation. Disto-occlusal cavities were prepared in 30 extracted human maxillary premolars. The specimens were allocated in three groups (n = 10) based on the type of restoration. All the specimens were exposed to thermomechanical aging followed by cycling loading. Fracture strength was tested using a universal testing machine, and then, the fracture mode was recorded. The data were analyzed using Kruskal–Wallis test with a significance level set at 0.05. The fracture mode was recorded as catastrophic or non-catastrophic. The fracture strength between all tested groups showed no significant difference. The highest and lowest fracture strength were recorded on amalgam and Tetric N-Ceram groups, respectively. Composite Tetric N-Ceram showed equal distribution of fracture sites on the restorative materials and teeth, it also displayed the highest number of non-catastrophic fractures unlike other groups where the fracture occurred more within the restorations. The fracture strength of composite was comparable to that of amalgam restorations with prepared rest seats.

Performance of bulk-fill versus conventional nanocomposite resin restorations supporting the occlusal rests of removable partial dentures: An in vitro investigation

Statement of problemPlacing removable partial denture (RPD) rests on composite resin restorations has long been a debatable issue. Despite developments in composite resins such as nanotechnology and bulk-filling techniques, studies investigating the performance of composite resin restorations when used to support occlusal rests remain scarce. PurposeThe purpose of this in vitro study was to investigate the performance of bulk-fill versus incremental (conventional) nanocomposite resin restorations when they are used to support RPD rests under functional loading. Material and methodsThirty-five caries-free intact maxillary molars of similar coronal size were collected and divided into 5 equal groups (n=7): Enamel (Control) group: rest seats prepared entirely in enamel; Class I Incremental group: Class I cavities restored with incrementally placed nanohybrid resin composite resin (Tetric N-Ceram); Class II Incremental group: Mesio-occlusal (MO) Class II cavities restored with Tetric N-Ceram; Class I Bulk-fill group: Class I cavities restored with high-viscosity bulk-fill hybrid resin composite (Tetric N-Ceram Bulk-Fill); and Class II Bulk-fill group: MO Class II cavities restored with Tetric N-Ceram Bulk-Fill. Occlusal rest seats were prepared mesially in all groups, and clasp assemblies were fabricated and cast in cobalt chromium alloy. Specimens with their clasp assemblies were subjected to thermomechanical cycling using a mechanical cycling machine (250000 masticatory cycles) and 5000 thermal cycles (5 °C to 50 °C). Surface roughness (Ra) was measured with a contact profilometer before and after cycling. Fracture analysis was done using stereomicroscopy, and margin analysis was done with a scanning electron microscope (SEM) before and after cycling. Statistical analysis of Ra was conducted using ANOVA followed by the Scheffé test for between-group comparison and paired t test for within-group comparison. The Fisher exact probability test was used for fracture analysis. The Mann–Whitney test was used for between-group comparison and Wilcoxon signed rank test for within-group comparison for the SEM images (α=.05). ResultsMean Ra increased significantly after cycling in all groups. Significant differences in Ra were found between enamel and all 4 resin groups (P<.001), with no significant differences between incremental and bulk-fill resin groups for both Class I and II specimens (P>.05). No significant differences were found between the 2 resin groups with regard to fracture and margin analysis (P>.05). ConclusionsThe surface roughness of enamel was significantly lower than that of both incremental and bulk-fill nanocomposite resins before and after functional loading. Incremental and bulk-fill nanocomposite resins showed comparable performance in terms of surface roughness, fracture behavior, and marginal adaptation.

Fully digital workflow for retrofitting a new crown to an existing removable partial denture.

A fully digital technique for retrofitting a new crown to a removable partial denture (RPD) is presented. The conventional crown preparation was followed by intraoral scanning of the preparation, the antagonists, and the occlusal relationship and by scanning the RPD both in situ and outside the oral cavity. All the standard tessellation language (STL) files were indexed in a design software program, and the new crown was designed. After conventional dynamic adaptation against the antagonist teeth in the software program, the existing RPD was designated as the antagonist cast, and a second regular static adaptation was performed. This straightforward approach produced a crown which fit the occlusal rest and reciprocating arm without sending the existing prosthesis to the dental laboratory.

Monitoring of the Inverted Relation of Gingival Pads in a Non-Syndromic Infant

BACKGROUND: Monitoring the occlusal relationship of the infant’s gum pads is not a common practice in pediatric dentistry. In general, pediatric dentists are used to observe the conformation of the arches and clinical findings that may be outside of the infant’s normal oral anatomy. Here we tested the hypothesis that intervention before eruption of the primary dentition will minimize anterior crossbite in the primary dentition. To address our hypothesis, we used one case to demonstrate the importance of monitoring the relationship of the gum pads and primary teeth eruption to avoid possible deviations in the pattern of orofacial development and prevent future malocclusions.MATERIALS AND METHODS: After proper consenting and anamnesis, an inverted relationship of the gum pads was observed in a 7-month-old baby while sleeping and at occlusal rest. Given that the patient was exclusively breastfeeding, adjustments of the catch were made, such as a greater opening towards the areola and nipple, and adjustments in the position and posture of the baby.RESULTS: During the eruption phase of the anterior teeth, an anterior crossbite was observed. Caregivers were prescribed exercises that were to be performed in the maxillary and mandibular arches to stimulate maxillary growth and guide the posture of the mandible. The exercises were intensified during the eruption phase of the lateral incisors and molars and the occlusion was stabilized with bilateral masticatory guidance and different textures to be offered during food transition. CONCLUSION: Based on the results observed for this case, the interventions allowed for a more satisfactory occlusion.

Evaluation of PEEK and zirconia occlusal rest designs for removable partial dentures based on finite element analysis.

Purpose We aimed to assess removable partial denture occlusal rests composed of polyether-ether-ketone (PEEK) and zirconia, using finite element analysis.Methods Three-dimensional PEEK and zirconia rest models, including the occlusal rest (1.5 mm thickness at the basal portion, 3.0 mm width) and minor connector (1.5 mm thickness, 6.0 mm height), and rest seat models with mechanical properties of enamel were constructed. The radius of transitional curvature between the rest and minor connector was 0.1-0.5 mm. The rest and rest seat model interfaces were set as frictional contacts (μ = 0.1), and the base of the rest seat model was restrained in all the directions. A 100 N downward load was applied perpendicular to the bottom surface of the minor connector. The maximum value of the first principal stress (Max-S1) was compared to the flexural and fatigue strengths of each material. Occlusal rests with 1.0-2.0 mm thickness, 2.0-3.5 mm width, and 0.5 mm radius of transitional curvature were analyzed.Results Max-S1 was observed at the transitional part and decreased with increasing radius of the transitional curvature, rest width, and thickness. PEEK rests with at least 1.5 mm thicknesses and 3.0 mm widths showed lower Max-S1 than the flexural strength. Max-S1 of all PEEK rests exceeded the PEEK fatigue strength, whereas Max-S1 of the zirconia rests was lower than the zirconia fatigue strength.Conclusions Zirconia occlusal rests with conventional metal rest designs have sufficient fatigue strength. PEEK occlusal rests have insufficient fatigue strength and may not withstand repeated mastication.

Definitive obturator rehabilitation on the maxilla defect post-tumor surgery

Background: Obturator is a prosthesis to replace tissue lost post tumor surgery in the maxilla called maxillectomy. Obturator is made of acrylic and consists of surgery, intermediate, and definitive obturator. Definitive obturator is made using Hollow bulb technique to be light and stable when used. In this case, a definitive obturator was made for a patient using intermediate obturator. Objectives: To inform that obturator can rehabilitate maxillary defect to restore the patient’s mastication, digestive, phonetic, aesthetic and psyche functions. Case report: A 28-year-old man came for postoperative cleft management. Diagnosis is Post OP Hemi maxillectomy Dextra. The procedure begins with impression to obtain study model and the making of individual tray. The next visit is grinding the remaining teeth for occlusal rest placement. Double impression is done to obtain working model and making the bite block. The third visit is bite block try-in on the patient and placed to working model for fixation on the articulator, followed by tooth color determination and laboratory instructions. The fourth visit is wax obturator try-in and checking occlusion, articulation, aesthetics and phonetics. The fifth visit is definitive obturator insertion and follow up. Conclusion: Definitive obturator can rehabilitate defects post maxillary tumor surgery.Keywords: Maxillary defect, definitive obturator, Hollow bulb technique

Fracture resistance of CAD/CAM restorative materials in mismatched removable partial denture rests: An in vitro experimental and finite element analysis.

To evaluate the fracture resistance of computer-aided design and computer-assisted manufacturing restorations as the abutment of removable partial dentures, experimental blocks, with the rest seat made of feldspar, hybrid resin composite, lithium disilicate glass ceramic, or zirconia, were subjected to loading by a metallic occlusal rest. The rest contacted the rest seat with an accurate fit and two mismatch contact conditions: bottom and sidewall contact. Zirconia exhibited the highest fracture load, and the fracture load of the accurate fit was significantly higher than that of the sidewall contact (p<0.05) and insignificantly higher than that of the bottom contact (p>0.05). A finite element analysis of the sidewall contact revealed a higher tensile stress concentration at the bottom of the rest seat than the other contact conditions. The mismatch between the rest and the restoration reduced fracture resistance, while zirconia as the abutment withstood the average occlusal force of the posterior region.

Comparative clinical evaluation of removable partial denture frameworks fabricated traditionally or with selective laser melting: A randomized controlled trial

Statement of problemThe clinical efficacy of selective laser melting (SLM) for fabricating removable partial dentures (RPDs) is not well established. PurposeThe purpose of this clinical study was to compare the performance of SLM-fabricated frameworks with that of those fabricated via traditional lost wax casting. Material and methodsA double-blind, randomized, crossover design was used to compare cobalt chromium partial denture frameworks (n=29) fabricated by using SLM or traditional methods. The time taken for adjustments and the clinical fit and stability of the adjusted frameworks were appraised. The accuracy of the frameworks was assessed by measuring the space between the occlusal rest seat and the corresponding rest seat. Statistical comparisons between the 2 frameworks were carried out by using a linear mixed-effect model for repeated measurements (α=.05). ResultsFrameworks fabricated by using both SLM and traditional techniques had an acceptable fit based on subjective clinical evaluation. The overall mean ±standard deviation space between the occlusal rest and rest seat for SLM frameworks (273.7 ±44.5 μm) was comparable with that of traditional frameworks (242.2 ±44.5 μm). The clinical fit adjustment time, 7.76 ±6.43 minutes for SLM and 5.49 ±6.39 minutes for traditionally fabricated frameworks, was statistically similar (P=.067). ConclusionsDentures fabricated via SLM and traditional techniques had comparable accuracy of fit and clinical fitting time.

ЛАБОРАТОРНОЕ ИЗУЧЕНИЕ АДГЕЗИВНЫХ МОСТОВИДНЫХ ПРОТЕЗОВ В БОКОВЫХ ОТДЕЛАХ ЗУБНЫХ РЯДОВ. ЧАСТЬ 2. МЕХАНИЧЕСКИЙ ЭКСПЕРИМЕНТ

Background. To date, numerous retrospective studies on the use of resin-bonded fixed partial dentures (RBFPD) have proven their reliability. Nevertheless, there are still questions about the design of posterior resin-bonded fixed partial dentures for replacing 1 and 2 missing teeth.&#x0D; Objectives. The present research was an in vitro study of the fracture strength of resin-bonded fixed partial dentures (RBFPD) with movable connector on the heat-pressed ceramic minor retainer when replacing 1 or 2 missing premolars. &#x0D; Methods. The laboratory research was carried out to study the fracture strength of fixed/movable RBFPD on acrylic moulds with a space equivalent to one or two premolars. The nature of RBFPD destruction and breaking loads in newtons were assessed by comparing the mean values according to the t-test. We studied 4 groups of RBFPD, depending on the type of retainer and the number of lost teeth.&#x0D; Results. The smallest fracture strength (1017.0 ± 49.0 N) was observed in the group with two missing teeth. In groups with 1mm thick occlusal rest, its deformation was observed. In the groups with 2 mm thick occlusal rest, partial fracture of the ceramic minor retainer was observed. Fixation loss of the adhesive wings or cast crowns as a large retainer was not observed. &#x0D; Conclusions. Fixed/movable RBFPD replacing two missing premolars are less fracture resisted then when replacing one missing premolar. Fixation loss of the large retainers was not observed. Adhesive wings were as effective as cast crowns as a large retainer.

Finite Element Analysis of Restored Principal Abutment in Free-End Saddle Partial Denture.

PurposeThis study analyzed the stress distribution of restored principal abutments in free-end saddle partial dentures.Materials and MethodsThe mandibular second premolar was modeled with class II cavity restored with composite resins (Tetric N Ceram and Charisma Smile). Finite element analysis (FEA) was used to examine the stresses under 200-N static load vertically and horizontally and the results were graphically illustrated in the form of von Mises stresses.ResultsThe von Mises stress distribution patterns of two different composite resins (Tetric N Ceram and Charisma Smile) were very similar in all modes of loading.ConclusionComposite resins with a similar modulus of elasticity in class II cavities with occlusal rest seat preparation had similar stress distributions.Clinical SignificanceNanohybrid composite resin restorations may be a possible method for preparing abutments for receiving elements of the removable partial denture (RPD).

Fit accuracy of removable partial denture metal frameworks produced by CAD-CAM – a clinical study

Objectives: To assess the effect of a CAD-CAM protocol fabrication on the clinical fit accuracy of removable partial denture metal frameworks to abutment teeth. Methods: Fifteen patients with partial edentulism were selected to participate in this clinical study, and twenty dental arch rehabilitations were planned. For each dental arch (n=20), two cobalt-chromium frameworks were produced through two protocols: CAD-CAM production (experimental group); and conventional lost-wax casting technique (control group). Clinical fit accuracy was assessed using an indirect quantitative method to evaluate the gap between the framework occlusal rest and the corresponding rest seat. A silicone mold of that gap was obtained, digitized, and analyzed by micro-computed tomography. The two silicone molds obtained for each occlusal rest were overlapped and evaluated for thickness and volume. Data were analyzed with the paired t test for silicone thickness results and the Wilcoxon test for silicone volume results (α= 0.05). Results: Considering the two dependent variables under study, no statistically significant (p=0.441 for silicone thickness and p=0.204 for silicone volume) differences were found between groups. Conclusions: The results of this study suggest that the CAD-CAM protocol applied is a viable method for the production of removable partial denture metal frameworks. (Rev Port Estomatol Med Dent Cir Maxilofac. 2021;62

Retention Assessment of High Performance Poly-etheretherketone Removable Partial Denture Frameworks Constructed by Various Techniques (in vitro Study).

Statement of the Problem: Poly-etheretherketone is a novel material used in the construction of the removable partial dentures frameworks instead of the metal frameworks. This material can be fabricated by various techniques. Most common methods are the injection molding or Computer Aided Design/Computer Aiding Manufacturing (CAD/CAM) milling techniques. The fabrication technique may affect the adaptation of the frameworks by influencing the retention.Purpose: To assess the effect of the processing techniques of high performance Poly-etheretherketone either by injection molding (pressing) or CAD/CAM milling techniques on removable partial denture frameworks retention for rehabilitation of upper class I Kennedy classification.Materials and Method: This in vitro study was performed on one epoxy resin model representing the partially edentulous maxillary arch with natural teeth extending from first premolar to first premolar. First premolars and canines were reduced to receive porcelain fused to metal crowns with 0.50mm mesio-buccal retentive undercuts, distal guiding planes and mesial occlusal rest seat on first premolars and cingulum rest seat on canines. Considering the construction technique of frameworks, twenty samples were divided into two groups. In the group I, ten frameworks were fabricated by injection molding, and in the group II, ten frameworks were fabricated by CAD/CAM. The removal and insertion was carried out at 120, 720 and 1440 cycles for both groups, respectively. The retention values were measured by using Universal Testing Machine before cycling and after each interval.Results: Independent t-test showed significant difference on retention at different simulation cycles between groups. Group II exhibited significantly less retention than group I (p< 0.001), while comparing the retention at different cycles within each group by paired sample t-test exhibited significant decrease of retention till the end of the cycling (p< 0.001).Conclusion: From the retention point of view, high performance poly-etheretherketone frameworks fabricated by injection molding technique provided a promising method over CAD/CAM technique milling method.