A Zygomatic Bone Study Using Virtual Dental Implant Planning Software.

This study evaluated the anatomical factors that influence the virtual planning of zygomatic implants by using cone-beam computerized tomography (CBCT) scans. CBCT scans of 268 edentulous patients were transferred to specialized implant planning software for the following measurements: maxillo-sinus concavity size (small, medium, and large), zygoma width, implant insertion angle, implant length, and implant apical anchorage. Concavity sizes found were as follows: 34.95% small, 52.30% medium, and 7.35% large. The mean insertion angle was 43.2 degrees, and the average implant apical anchorage was 9.1 mm. The most frequent implant length was 40 mm. Significant differences were found when the different types of concavities in relation to the installation angle, the distance of the apical portion of the implant in contact with the zygomatic bone, and the lateral-lateral thickness of the zygomatic bone were compared (P < .001). Medium-sized maxillary sinus concavity presented greater apical anchorage of the implant (9.7 mm) and was the most frequent type (52.30%). The zygomatic bone is a viable site for zygomatic fixtures, and the use of specialized implant planning software is an important tool to achieve predictable outcomes for zygomatic implants and allows good visualization of the relation between implants and anatomical structures.

A comparison between visual, intraoral scanner, and spectrophotometer shade matching: A clinical study.

STATEMENT OF PROBLEM: Visual shade matching is subjective and a cause of concern for clinicians. Different measurement devices have been developed to assist in tooth color selection and to achieve better esthetic results. However, consensus is lacking as to which method of tooth shade selection provides more predictable results. PURPOSE: The purpose of this clinical study was to compare the reliability of different visual and instrumental methods for dental shade matching. MATERIAL AND METHODS: Visual shade matching was performed by 3 experienced clinicians using 2 different shade guides (VITA Classical A1-D4 and VITA Toothguide 3D-MASTER with 29 tabs; VITA Zahnfabrik) with and without the aid of a light-correcting device (Smile Lite; Smile Line). An intraoral scanner (TRIOS; 3Shape A/S) and a spectrophotometer (VITA Easyshade Advance 4.0; VITA Zahnfabrik) were also used for color shade matching. The instrumental methods were repeated 3 times to determine repeatability. Shade-matching sessions for each method were performed under controlled lighting on the middle third of the maxillary right central incisor of 28 participants. The Fleiss' kappa statistical test was used to assess the reliability of each method. The weighted kappa statistical test was used to assess the agreement between the shades matched by different methods (α=.05). RESULTS: Instrumental methods were more accurate than visual methods. The best performance was found for the intraoral scanner configured for the 3D-MASTER scale (Fleiss' kappa value of .874) and for the spectrophotometer configured for the VITA Classical scale (Fleiss' kappa value of .805). The best visual shade-matching method was the VITA Classical scale associated with the light-correcting device (Fleiss' kappa value of .322). The Classical scale without the light-correcting device showed the poorest reliability (Fleiss' kappa value of .177) (P<.05). CONCLUSIONS: Instrumental methods for color shade matching were more reliable than the visual methods tested.

Strain transfer behavior of different planning options for mandibular single-molar replacement.

STATEMENT OF PROBLEM: The loss of the first molar and second premolar could lead to mesial movement of the second molar, thus limiting the restoration space for the 2 missing teeth. Placement of a larger first molar is a common choice, but the best implant number and position option remain controversial. PURPOSE: The purpose of this in vitro study was to test different planning options for replacing the mandibular first molar. MATERIAL AND METHODS: Two polyoxymethylene models simulated first molar edentulous spaces of 11 mm (conventional size first molar: control group) and 14 mm (enlarged first molar: all remaining groups other than control). Models included acrylic resin replicas of a first and second premolar, a second molar, and the first molar edentulous space. The following groups were established: control (CO), ø3.5-mm center implant; center implant (CI), ø3.5 mm; mesial implant (MI), ø3.5 mm; distal implant (DI), ø3.5 mm; center implant (WI), ø5.0; 2 implants (2I), 2 ø3.5-mm implants. Three Co-Cr molar crowns were fabricated for each group by using a computer-aided design and computer-aided manufacturing (CAD-CAM) technique. Model surface strains under a 250-N first molar load were calculated by 3-dimensional digital image correlation. Three regions of interest below the first molar were selected for comparison among groups. A test for unequal variances and a follow-up Welch ANOVA were used for statistical analysis (α=.05). RESULTS: The highest strains were found when the first molar was restored by using a 5.0-mm-wide implant (P<.05). Region of interest 1 showed that two 3.5-mm implants replacing the lost molar showed strain distribution similar to that of only one 3.5-mm implant (P>.05). Mesial and distal placement of the implant showed more neutral strain results than other restoration options (P<.05). CONCLUSIONS: Two small-diameter implants in an increased edentulous space show more optimized surface strain behavior than a single wide-diameter implant. However, a single 3.5-mm implant also showed reduced strains in the restoration of the same edentulous space.

Effect of different implant placement depths on crestal bone levels and soft tissue behavior: a randomized clinical trial.

OBJECTIVES: This randomized clinical trial analyzed crestal bone changes and soft tissue dimensions surrounding implants with an internal tapered connection placed in the mandible anterior region at different depths (equicrestal and subcrestal). MATERIALS AND METHODS: Eleven edentulous patients (five implants per patient) were randomly divided in a split-mouth design: G1, 28 equicrestal implants; and G2, 27 subcrestal implants. All implants were immediately loaded. Correlation between keratinized tissue width (KTW) and vertical mucosa thickness (MT) with soft tissue recession was analyzed. Intraoral radiographs were used to evaluate crestal bone changes. Patients were assessed immediately, 4-, and 8-months after implant placement. Rank-based ANOVA-type statistical test was used for comparison between groups (α = 0.05). RESULTS: Fifty-five implants (G1 = 28 and G2 = 27) were assessed in 11 patients. Implant survival rate was 100% for both groups. Both tested implant placement depths presented similar crestal bone loss (P > 0.05). Significant crestal bone loss for each group was found in the different measurement times (T4 and T8) (P < 0.05). Implant placement depths, KTW, and vertical MT had no effect on soft tissue recession (P > 0.05). CONCLUSIONS: Different implant placement depths do not influence crestal bone changes. Soft tissue behavior is not influenced by different implant placement depths or by the amount of keratinized tissue.

A Digital Image Correlation Analysis of Strain Generated by 3-Unit Implant-Supported Fixed Dental Prosthesis: An In Vitro Study.

OBJECTIVE: To evaluate the influence of different veneering materials (porcelain and resin) and implants (short and conventional) in the strain distribution of implant-supported splinted fixed partial dentures (FPDs) using digital image correlation (DIC). MATERIAL AND METHODS: Four polyurethane models were fabricated with resin replicas (first premolar) and short and/or conventional implants replacing the second premolar and first and second molars, according to the following configurations: G1, 2 conventional (second premolar and first molar) and 1 short (second molar) implant; G2, 1 conventional (second premolar) and 2 short (first and second molar) implants; G3, 3 short implants; G4, 3 conventional implants. Porcelain- and resin-veneered splinted FPDs were screwed to the implant abutments. The DIC system was used to calculate strains during application of occlusal load (250 N). RESULTS: Porcelain- and resin-veneered showed similar strain distribution for all groups (P > 0.05). Concentration of compressive strains was higher in G3P and G3R with maximum compressive strains of -1271.50 and -1026.88 µs, respectively. G4 transferred the best strain distribution (porcelain, -275.14 µs; resin, -254.44 µs), followed by G2 (porcelain, -306.79 µs; resin, -310.63 µs). CONCLUSION: The veneering material used did not influence the strain distribution. In addition, conventional implants generate less strain concentration, although the combination of 2 short and 1 conventional implant seems to be a viable plan.

Influence of Cyclic Fatigue in Water on Screw Torque Loss of Long-Span One-Piece Implant-Supported Zirconia Frameworks.

PURPOSE: It is still unclear whether four, six, or more implants should be used when restoring fully edentulous maxillae. This research evaluated the in vitro screw torque loss of zirconia frameworks supported by six implants and cantilevered zirconia frameworks supported by four implants. MATERIALS AND METHODS: Computer aided design/computer-assisted machining was used to fabricate 10 one-piece frameworks. Standardized pressable porcelain crowns were fabricated and luted to the frameworks. Specimens were divided into two groups (n = 5): AO4, cantilevered 12-unit full-arch fixed dental prosthesis supported by four implants; AO6, 14-unit supported by six implants. An opposing mandibular dental arch was fabricated with bis-acrylic composite resin. Specimens were submitted to 200 N underwater cyclic load at 2-Hz frequency for 1 × 106 cycles in a controlled 37°C temperature. A digital torque gauge assessed the initial and postload screw removal torque. Linear mixed-effects model was used for statistical analysis (α = 0.05). RESULTS: Significant screw torque loss was found for AO6 after cyclic loading (before: 36.20%/after: 52.82%; p < 0.05). Group AO6 (36.20%) presented lower preload loss before the cyclic loadings compared with AO4 (60.10%) (p < 0.05). CONCLUSIONS: Cyclic loading and lower implant-to-replaced-units ratio do not seem to compromise screw stability compared with higher implant-to-replaced-units ratio; however, a steep drop in preload was found before cyclic loading for both groups.

Predictable Outcomes with Porcelain Laminate Veneers: A Clinical Report.

This clinical report describes how to achieve predictable outcomes for anterior teeth esthetic restorations with porcelain laminate veneers by associating the digital planning and design of the restoration with interim restorations. The previous digital smile design of the restoration eliminates the communication barrier with the patient and assists the clinician throughout patient treatment. Interim restorations (diagnostic mock-ups) further enhance communication with the patient and prevent unnecessary tooth reduction for conservative tooth preparation. Adequate communication between patient and clinician contributes to successful definitive restorations and patient satisfaction with the final esthetic outcome.

A randomized controlled trial comparing interim acrylic prostheses with and without cast metal base for immediate loading of dental implants in the edentulous mandible.

OBJECTIVES: This randomized controlled trial used resonance frequency analysis (RFA) to assess the effects of the presence or absence of a cast rigid bar splinting multiple implants in the stability of immediately loaded implants. MATERIAL AND METHODS: Twenty-nine edentulous patients were randomly divided into two groups: G1 with full-arch implant-fixed prostheses and G2 with multiple implant splinting via acrylic resin denture bases. All implants were immediately loaded. RFA measurements assessed implant stability at three different times (T0--at baseline, T1--4 months, and T2--8 months. Wilcoxon and Friedman tests and a multivariate model with repeated measures for longitudinal data were used for statistical comparison (α = 0.05). RESULTS: Twenty-nine patients were assessed (G1 = 15 and G2 = 14). Implant and prostheses survival rates were 100% for both groups after the 8-month observation period and no significant differences in the mean ISQ values were found at the different implant stability assessment times (P > 0.05). CONCLUSIONS: The different splinting protocols did not appear to affect implant stability during the 8-month observation period.

Partially Edentulous Arches: A 5-Year Survey of Patients Treated at the Fluminense Federal University Removable Prosthodontics Clinics in Brazil.

PURPOSE: This study investigated the number and Kennedy Classification of the edentulous arches in patients treated at the Removable Partial Denture (RPD) Clinics of the Fluminense Federal University School of Dentistry (FO-UFF) in Rio de Janeiro, Brazil, from 2005 to 2010. MATERIALS AND METHODS: A cross-sectional retrospective survey was conducted on patient record charts to identify gender, age, number, and location of the edentulous arches, and Kennedy Class type. RESULTS: One hundred and forty-six patients were analyzed for this study (96 [65.8%] women and 50 [34.2%] men). Two hundred and ninety-two arches were analyzed: 74 arches (25%) were found with intact dentitions, 18 (6.1%) were edentulous arches, and 200 (68.8%) were partially edentulous arches. Ninety-one patients (62.3%) needed oral rehabilitation with RPDs on one arch and 55 (37.7%) in both arches. One hundred and eight (53.2%) partially edentulous mandibles and 92 (46.8%) partially edentulous maxillae were found. Kennedy Class I was more frequent in the mandibular arch (58 patients; 29%) whereas Kennedy Class III was more frequent in the maxillary arch (40 patients; 20%). Patients aged between 51 and 60 years presented the highest percentage of partially edentulous arches (33.6%). CONCLUSION: Mandibular Kennedy Class I and maxillary Kennedy Class III presented the highest frequency in patients treated at the FO-UFF. These results are in agreement with previous studies that evaluated the different Kennedy classes in partially edentulous arches.

Torque loss under mechanical cycling of long-span zirconia and titanium-cemented and screw-retained implant-supported CAD/CAM frameworks.

OBJECTIVES: This study evaluated the screw joint stability after cyclic loading of implant-supported titanium and zirconia CAD/CAM frameworks for fixed dental prostheses (FDPs) with different retention methods. MATERIAL AND METHODS: Twenty four one-piece frameworks supported by six threaded implants placed in the maxilla were fabricated using a CAD/CAM technique (NeoShape). Dry-pressed porcelain crowns were luted to the frameworks to standardize the specimens. The specimens were then divided into four groups (n = 6) according to framework material (titanium or zirconia) and retention method for the prosthesis (cement- or screw-retained): G1, Ti-cemented; G2, Ti-screw-retained; G3, Zr-cemented; and G4, Zr-screw-retained. A digital torque ratchet was used to assess the initial preload removal torque. Torque was then reapplied and the specimens were submitted to a 200 N cyclic load, at a frequency of 2 Hz, underwater in controlled temperature of 37°, and for 1 × 106 cycles. An opposing lower dental arch was fabricated using bis-acrylic resin to simulate occlusal contacts in centric. After cyclic loading, postload removal torque was measured. Preload and postload torque loss was expressed as a percentage of the initial load. Data were submitted to a linear mixed-effects model for statistical significance (α = 0.05) to evaluate the effect of cyclic loading in the screw torque loss used with frameworks of different materials and retention methods. RESULTS: Significant screw torque loss (%) was found for the tested groups (before/after cyclic loading, respectively): G1 (39.77/61.83), G2 (37.57/50.96), G3 (34.87/54.10), and G4 (47.56/73.50) (P < 0.05). CONCLUSIONS: The screw removal torque was significantly reduced for all groups in this study after cyclic loading the specimens. Screw-retained zirconia specimens presented the highest torque loss before and after the cyclic loadings compared with the other specimens that were tested.

Effect of surface treatment on the bond strength between yttria partially stabilized zirconia ceramics and resin cement.

STATEMENT OF PROBLEM: No consensus has been reached on the best bonding protocol between a zirconia ceramic surface and the tooth structure. PURPOSE: The purpose of this study was to evaluate the extrusion shear strength between yttria partially stabilized zirconia ceramics and resin cement (Panavia F) after different surface treatments. MATERIAL AND METHODS: The surface treatments evaluated (n=7) included the following: G1-control group (no surface treatment); G2-treated with MDP primer (Alloy Primer); G3-treated with 40% hydrofluoric acid (210 seconds); and G4-treated with 40% hydrofluoric acid (210 seconds) followed by MDP primer. The specimens were bonded to 2.5-mm-thick disks of bovine root dentin, and the extrusion shear tests were performed after they had been stored for 24 hours in distilled water at 37°C. The surface modifications were assessed on 2 specimens that were selected from each group by scanning electron microscopy. Data were analyzed with 1-way ANOVA and the Tukey-Kramer honestly significant difference test (α=.05). RESULTS: G4 (mean 2.84, standard deviation [SD] 0.43 MPa) presented significantly higher (P<.001) extrusion shear strength when compared with the other groups in the study (G1: mean, 1.57; SD 0.28 MPa; G2: mean 1.46, SD 0.28 MPa; G4: mean 1.16, SD 0.41 MPa). No significant differences were found among the other groups in the study. CONCLUSIONS: Yttria partially stabilized zirconia ceramics can be treated with 40% hydrofluoric acid for 210 seconds to increase the bond strength with the resin cement.

Effect of cyclic loading on the vertical microgap of long-span zirconia frameworks supported by 4 or 6 implants.

STATEMENT OF PROBLEM: Few studies have investigated the microgap of long-span complete-arch fixed dental prosthesis zirconia frameworks. PURPOSE: The purpose of this study was to evaluate the effects of cyclic loading on the vertical microgap of maxillary 12-unit prostheses supported by 4 implants and on 14-unit prostheses supported by 6 implants. MATERIAL AND METHODS: One-piece zirconia frameworks were fabricated with a computer-aided design/computer-aided manufacturing technique and divided into 2 groups (n=5): a group of 12-unit prostheses and a group of 14-unit prostheses. The vertical microgap between the frameworks and prosthetic abutments was measured with an optical microscope (80×) under 2 reading conditions. Condition 1 (1-screw test): 1A, the screw on implant 1 was tightened and readings were made on all implants; 1B, the screw was changed to implant 4 (implant 6 for the 14-unit group) and readings were made on all implants. Condition 2: the microgap was measured with all screws tightened before cyclic loading (2A). Specimens were submitted to 200 N underwater (37°C) cyclic loading at a 2-Hz frequency for 1×10(6) cycles. Microgap reading condition 2 was repeated after cyclic loading (2B). The data were submitted to a linear mixed-effects model for statistical comparison (α=.05). RESULTS: A lower (P<.05) vertical microgap (µm) was found for the 12-unit group (reading conditions: 1A, 47.93; 1B, 43.83; 2A, 11.77; and 2B, 11.25) compared to the 14-unit group (1A, 94.87; 1B, 112.56; 2A, 21.28; and 2B, 16.90). No differences were found when each group was compared before and after cyclic loading (P>.05). CONCLUSIONS: The vertical microgap was significantly reduced after tightening all the screws in the framework, possibly leading to a nonpassive situation. Longer-span frameworks showed an increased microgap. Cyclic loading had no influence on the vertical microgap within each group.

Comparison of the correlation of photoelasticity and digital imaging to characterize the load transfer of implant-supported restorations.

STATEMENT OF PROBLEM: Whether splinting or not splinting adjacent implants together can optimize the stress/strain transfer to the supporting structures remains controversial. PURPOSE: The purpose of this study was to compare the photoelasticity and digital image correlation (DIC) in analyzing the stresses/strains transferred by an implant-supported prosthesis. MATERIAL AND METHODS: A polymethylmethacrylate model was made with a combination of acrylic resin replicas of a mandibular first premolar and second molar and threaded implants replacing the second premolar and first molar. Splinted (G1/G3) and nonsplinted (G2/G4) metal-ceramic screw-retained crowns were loaded with (G1/G2) and without (G3/G4) the presence of the second molar. Vertical static loads were applied to the first molar implant-supported crown (50 N-photoelasticity; 250 N-DIC). The resulting isochromatic fringes in the photoelastic models were photographed, and a single-camera 2-dimensional DIC system recorded the deformation at the surface of the resin models. RESULTS: Residual stresses were present in the photoelastic model after screw fixation of the crowns. The following average photoelastic stress results (MPa) were found around the loaded implant: G1 (20.06), G2 (23.49), G3 (30.86), G4 (37.64). Horizontal strains (εxx, %) between the molars averaged over the length of the loaded implant were found by DIC: G1 (0.08 ± 0.09), G2 (0.13 ± 0.10), G3 (0.13 ± 0.11), G4 (0.16 ± 0.11). Splinted crowns transferred lower stresses to the supporting bone when the second molar was absent. The second molar optimized the stress distribution between the supporting structures even for nonsplinted restorations. CONCLUSIONS: Both methods presented similar results and seemed capable of indicating where issues associated with stress/strain concentrations might arise. However, DIC, while apparently less sensitive than photoelasticity, is not restricted to the use of light-polarizing materials.

Occlusal concepts application in resolving implant prosthetic failure: case report.

The prosthetic management of a poor implant treatment is presented in this case report. The recommended occlusion concepts for implant-supported prostheses were applied for the resolution of the case. The rehabilitation of the posterior segments provided a mutually protected occlusion with adequate distribution of the axial and lateral bite forces with stable posterior occlusion. The clinical exam indicated the need for modification in the vertical dimension of occlusion. Sufficient interocclusal rest space was present to test the alteration in the vertical dimension. The aim was to achieve an occlusion scheme that followed four specific criteria: (1) centric contacts and centric relation of the jaw-to-jaw position; (2) anterior guidance only; (3) shallow anterior angle of tooth contact; and (4) vertical dimension of occlusion with acceptable tooth form and guidance. The success of an oral rehabilitation relies in following the aforementioned criteria, appropriate interaction between the dental laboratory technician and the clinician, careful elaboration of the provisional rehabilitation with all the desired details to be reproduced in the final prosthetic restoration and sufficient follow-up time of the provisional prostheses before placing the final restoration.

Attachment-retained gingival prosthesis for implant-supported fixed dental prosthesis in the maxilla: a clinical report.

The rehabilitation of edentulous maxillae is a complex procedure due to the involvement of esthetic and functional requirements. A trial maxillary denture can be used to identify the need for adequate upper lip support when replacing removable complete dentures by implant-fixed dental prostheses. This clinical report describes the outcome of the rehabilitation of an edentulous atrophic maxilla with unfavorable maxillomandibular relationship and deficient upper lip support. A trial denture was fabricated and used to diagnose the need for a prosthesis capable of restoring the upper lip support. The reduced upper lip support was also confirmed by a lateral cephalogram. The patient was rehabilitated by an implant-fixed dental prosthesis associated with an attachment-retained gingival prosthesis. The case presented shows that when loss of upper lip support is detected and the patient does not wish to undergo further surgical reconstruction procedure, the retention of a gingival prosthesis using a ball attachment is a satisfactory treatment option.

Comparison between visual and instrumental methods for natural tooth shade matching.

Tooth shade matching in daily clinical practice is still a cause of discomfort for many professionals due to the subjectivity of the process and the need for advanced training; this discomfort may lead to unsatisfactory results for the clinician and the patient. Instrumental methods were developed to simplify daily color matching procedures and to provide better esthetic outcomes. This study compared the accuracy of shade matching by both visual and instrumental methods to determine whether the instrumental method would significantly improve the process. Visual shade matching was performed by 4 dentists using a classic shade guide; instrumental shade matching was performed with a spectrophotometer by a previously calibrated examiner. Shade matching was conducted in a dental clinic under controlled illumination on the middle third of the right central incisor tooth of 30 subjects. Data were analyzed by Cohen's Kappa inter-rater agreement and by the equality of 2 proportions test (α = 0.05). Results showed statistically significant differences between the groups (76.7 ± 11.1% and 32.4% ± 7.8% for the instrumental and visual methods, respectively). Shade matching by clinicians using the instrumental method presented more agreement, and was more effective than shade matching by clinicians using the visual method.

Photoelastic analysis of stresses transmitted by universal cast to long abutment on implant-supported single restorations under static occlusal loads.

OBJECTIVES: The aim of this study was to compare the stresses resulting from cemented or screw-retained dental prostheses using universal cast to long abutment by the photoelastic method. MATERIAL AND METHODS: A photoelastic resin model was fabricated to simulate a segment of the mandibular arch with resin replicas of a first premolar and a second molar, and two 3.75 × 11-mm implants replacing the second premolar and the first molar. Vertical static loads were individually applied on the occlusal surface of the premolar and the molar (5 kgf) and simultaneously on both crowns (10 kgf). RESULTS: Results found variable stress patterns around each implant and concentrated stresses in the individually loaded crowns. Force transfer characteristics of each situation and quantification of the isochromatic fringes were evaluated. CONCLUSIONS: Within the limitations of this study and based on the results obtained for implant-supported prosthesis with internal hexagon connection/universal cast to long abutment, it could be concluded that single adjacent screw-retained prosthetic restorations lead to higher stresses around the implants when compared with cement-retained restorations.

Implant stability measurements of two immediate loading protocols for the edentulous mandible: rigid and semi-rigid splinting of the implants.

AIM: Primary and secondary stabilities of immediately loaded mandibular implants restored with fixed prostheses (FP) using rigid or semi-rigid splinting systems were clinically and radiographically evaluated. METHODS: Fifteen edentulous patients were rehabilitated using hybrid FP; each had 5 implants placed between the mental foramens. Two groups were randomly divided: group 1-FP with the conventional rigid bar splinting the implants and group 2-semi-rigid cantilever extension system with titanium bars placed in the 2 distal abutment cylinders. Primary stability was evaluated using resonance frequency analysis after installation of the implant abutments. The measurements were made at 3 times: T0, at baseline; T1, 4 months after implant placement; and T2, 8 months after implant placement. Presence of mobility and inflammation in the implant surrounding regions were checked. Stability data were submitted to statistical analysis for comparison between groups (P < 0.05). RESULTS: Implant survival rate for the implants was of 100% in both groups. No significant differences in the mean implant stability quotient values were found for both groups from baseline and after the 8-month follow-up. CONCLUSION: The immediate loading of the implants was satisfactory, and both splinting conditions (rigid and semi-rigid) can be successfully used for the restoration of edentulous mandibles.

Strain Behavior of Implant-Supported Full-Arch Fixed Dental Prostheses Supported by Four or Five Implants.

PURPOSE: Strains transferred to the supporting simulated bone structure by implant-supported full-arch fixed dental prostheses (FAFDPs) were analyzed by digital image correlation (DIC). MATERIALS AND METHODS: Polyurethane models were made using 3.75 × 11-mm implants and divided into the following groups with different implant numbers and design: EH5 (five implants/external hexagon), MT5 (five implants/internal taper), EH4 (four implants/external hexagon), and MT4 (four implants/internal taper). Both qualitative and quantitative (one-way analysis of variance [ANOVA] statistical comparison) analyses were performed by the DIC method after the application of a 250-N load in the central fossa of the mandibular first molar. Different regions of interest were selected in the polyurethane model for comparison between groups. RESULTS: Compressive strains were found in the cervical region of the models, and tensile strains were found in the apical region of the models. Significant differences were found in the different analyzed regions of interest for the different number of supporting implants and implant designs (P < .05). CONCLUSION: Groups with five implants showed more regions with less strain concentration compared to groups with four implants, but strain distribution was similar between groups. The different tested implant designs showed similar strain concentration and distribution to the supporting structures.

Photoelastic stress analysis of different designs of cement-retained fixed partial dentures on Morse taper oral implants.

There is no consensus in literature regarding the best plan for prosthetic rehabilitation with partial multiple adjacent implants to minimize stress generated in the bone-implant interface. The aim of this study was to evaluate the biomechanical behavior of cemented fixed partial dentures, splinted and nonsplinted, on Morse taper implants and with different types of coating material (ceramic and resin), using photoelastic stress analysis. A photoelastic model of an interposed edentulous space, missing a second premolar and a first molar, and rehabilitated with 4 different types of cemented crowns and supported by 2 adjacent implants was used. Groups were as follows: UC, splinted ceramic crowns; IC, nonsplinted ceramic crowns; UR, splinted resin crowns; and IR, nonsplinted resin crowns. Different vertical static loading conditions were performed: balanced occlusal load, 10 kgf; simultaneous punctiform load on the implanted premolar and molar, 10 kgf; and alternate punctiform load on the implanted premolar and molar, 5 kgf. Changes in stress distribution were analyzed in a polariscope, and digital photographs were taken of each condition to allow comparison of stress pattern distribution around the implants. Cementation of the fixed partial dentures generated stresses between implants. Splinted restorations distributed the stresses more evenly between the implants than nonsplinted when force was applied. Ceramic restorations presented better distribution of stresses than resin restorations. Based on the results obtained, it was concluded that splinted ceramic restorations promote better stress distribution around osseointegrated implants when compared with nonsplinted crowns; metal-ceramic restorations present less stress concentration and magnitude than metal-plastic restorations.