Effect of guide sleeve material, region, diameter, and number of times drills were used on the material loss from sleeves and drills used for surgical guides: An in vitro study.

STATEMENT OF PROBLEM: How material loss from sleeves and drills is affected when different guide sleeve materials and different sizes of implant drills are used for different regions of surgical guides is unclear. PURPOSE: The purpose of this in vitro study was to compare the amount of material loss from different guide sleeves (zirconia and cobalt-chromium) and drills of different diameters during osteotomy preparation in different regions. MATERIAL AND METHODS: Three tooth-supported surgical guides with sleeve holes positioned in the first premolar and second molar sites were prepared. Guide sleeves (Ø 2.20 mm, 3.40 mm, and 4.05 mm) were milled from zirconia (n=60) and cobalt-chromium (n=60) blocks. A total of 12 titanium nitride-coated stainless steel twisted drills (n=6 per sleeve material) of different diameters (Ø 2.00, 3.20, 3.85 mm) were used with corresponding sleeves during the drilling. The weight loss from the drills and the volume loss from the guide sleeves after drilling were analyzed by using multiple linear mixed effect models (α=.05). RESULTS: According to the 4-way ANOVA for volume loss from sleeves, no significant interaction was found among the 4 main effects (number of times a drill was used, region, diameter, and material), but interactions between the number of times a drill was used and diameter (P=.001) and between the number of times the drill was used and material were significant (P<.001). For weight loss from the drills, a significant interaction was detected between the number of times the drill was used and diameter (P=.024). CONCLUSIONS: Less sleeve material was lost when zirconia sleeves were used. All sleeves had more material loss in the molar region than in the premolar region. The diameter had varying effects on the amount of material loss from drills and sleeves. The sleeve material and the region did not affect the material loss from drills.

A Technique to Fabricate an Interim Implant-Supported Fixed Complete Denture for Immediate Loading.

Converting an acrylic resin removable complete prosthesis into a fixed implant-supported prosthesis to immediately load the implants can be a challenging procedure. Using acrylic resin to secure titanium interim copings intraorally may be a difficult task, and any process to facilitate this procedure may be advantageous for the clinician and the patient. This report describes a technique for facilitating the fabrication of an interim immediately loaded implant-supported fixed complete prosthesis. This technique and the materials used enabled the efficient fabrication and delivery of the prosthesis with an appropriate soft-tissue surface and acrylic resin thickness without irritating newly sutured soft tissues.

Evaluation of the Precision of Different Intraoral Scanner-Computer Aided Design (CAD) Software Combinations in Digital Dentistry.

BACKGROUND The aim of this study was to evaluate the precision of correlation between intraoral scanners and computer aided design (CAD) software programs used during scanning and designing phases of digital dentistry. In the present study, CAD software programs that accept data in Standard Tessellation Language (STL) and proprietary format have been evaluated and data loss has been examined in the scanned data. MATERIAL AND METHODS A single unit crown preparation was conducted for maxillary right first molar on a fully dentulous model. The prepared tooth was scanned with a high precision industrial scanner (ATOS Core 80) and the reference digital model was obtained. The dental model was further scanned 10 times using 3 different intraoral scanners (CEREC Omnicam AC, TRIOS 3 Color Pod, and Aadva IOS 100). The data obtained from the reference scanner and intraoral scanners were transferred to different CAD programs (CEREC inLab, TRIOS Design Studio, Exocad) and digital crowns were designed for each scanned data-CAD combination. After that, the data losses that occurred between these transfers were evaluated by superimposition technique in a special software (VR Mesh v7.5) (alpha=0.05). RESULTS Among the all combinations of scanner and software, Omnicam AC-InLab was determined to be the most precise combination through the full digital workflow since the Omnicam AC-Exocad combination showed the highest deviations. CONCLUSIONS Within the limitations of this in vitro study, it was determined that the combinations of scanners and associated CAD programs yielded more accurate results, and data loss was revealed when the scanned data converted from the proprietary format to the STL format.

Does the application of surface treatments in different sintering stages affect flexural strength and optical properties of zirconia?

OBJECTIVE: To investigate the influence of surface treatments conducted in presintering and postsintering stages on flexural strength and optical properties of zirconia. MATERIALS AND METHODS: Specimens were milled from partially sintered zirconia blocks in different geometries and divided into three main groups as presintered, postsintered, and control groups. Test groups were further divided into three subgroups (n = 10) according to the surface treatments conducted (grinding, Er,Cr:YSGG laser irradiation, air-borne particle abrasion [APA]). Four-point flexural strength (σ) test and Weibull analysis were conducted. Color differences (ΔE00 ) and translucency parameter (TPab ) were calculated with a spectrophotometer. Surfaces of specimens were scrutinized under FESEM. Data were statistically analyzed. RESULTS: Postsintered groups exhibited higher σ values (P < .05). Within all groups, highest and lowest σ values were detected at postsintered and presintered APA groups, respectively (P < .05). All ΔE00 values were above the perceptibility threshold (ΔE00 > 0.8). Higher TPab values were obtained and deeper scratches were observed in presintered groups. CONCLUSIONS: Surface treatments performed at postsintering stage had a favorable effect on the flexural strength of all specimens. Surface treatments performed before sintering increased translucency and caused higher ΔE00 values. CLINICAL SIGNIFICANCE: Surface treatments performed at different sintering stages can alter mechanical and optical properties of zirconia.

Accuracy of different definitive impression techniques with the all-on-4 protocol.

STATEMENT OF PROBLEM: A nonpassive fit of implant-supported restorations can jeopardize the biological and mechanical success of the treatment. Data regarding the fit of different impression techniques for the all-on-4 protocol are limited. PURPOSE: The purpose of this in vitro study was to digitally evaluate 4 different impression techniques used with the all-on-4 protocol, with distal multiunit analogs positioned in 4 different angulations. MATERIAL AND METHODS: Four maxillary definitive cast models with 4 multiunit analogs (T0 32202; NucleOSS) were fabricated according to the all-on-4 treatment protocol. In the anterior region, the analogs were positioned in a parallel direction, whereas in the posterior region, they were positioned in different angulations (0, 10, 20, and 30 degrees). One hundred and sixty models were obtained by using 4 different impression techniques (closed tray without plastic cap, closed tray with plastic cap, splinted open tray, sectioned resplinted open tray) (n=10) and polyvinyl siloxane impression material. Definitive casts and definitive duplicate casts were scanned using a modified laser scanner (Activity 880; Smart Optics Sensortechnik GmbH), and data were transferred to a software program (VRMesh Studio; Virtual Grid Inc). The definitive casts and definitive duplicate cast scans were digitally aligned. Angular and linear deviations in all axes (x, y, and z) of the analogs between definitive and duplicate casts were calculated and subjected to statistical analyses (α=.05). RESULTS: Mean angular deviations were in the range of 0.03 to 0.16 degrees, and linear deviations were in the range of 0.10 to 0.75 mm. The increased angulation between impression copings caused higher linear and angular deviations when closed-tray impression techniques were used (P<.05). CONCLUSIONS: Reduced linear and angular displacements were obtained from the open-tray impression techniques compared with the closed-tray impression techniques in the angulated groups. Angular and linear deviations increased with the increase in the angulation of the posterior analog.

The effect of removable partial dentures on alveolar bone resorption: a retrospective study with cone-beam computed tomography.

PURPOSE: The aim of this study was to compare vertical and horizontal mandibular alveolar bone resorption by measuring bone morphological variation in Kennedy Class II removable partial denture (RPD) wearers and non-wearers using cone-beam computed tomography (CBCT). MATERIALS AND METHODS: In total, 124 sites in the CBCT scans of 62 (29 RPD non-wearers, 33 RPD wearers) Kennedy Class II patients were analyzed retrospectively. Three-dimensional representations of the mandible with superimposed cross-sectional slices were developed with the CBCT scans to evaluate the mandibular alveolar height and width by measuring distances between the mandibular canal, mylohyoid ridge, alveolar crest, and lower border of the mandible in four regions (eight sites) of Kennedy Class II non-wearers and wearers of RPDs. RESULTS: Mandibular alveolar bone height and width were significantly lower in edentulous sites when compared with dentate sites in both Kennedy Class II non-wearers and wearers of RPDs (p < 0.05). Additionally, mean vertical and horizontal mandibular bone resorption was significantly higher in RPD wearers than in non-wearers (p < 0.05). CONCLUSIONS: Vertical and horizontal alveolar bone resorption was found to be higher in the RPD wearing patients when comparing the dentate and edentulous sites.

Effect of angulation on the 3D trueness of conventional and digital implant impressions for multi-unit restorations.

PURPOSE: The study aimed to determine the influence of implant angulation on the trueness of multi-unit implant impressions taken through different techniques and strategies. MATERIALS AND METHODS: As reference models, three partially edentulous mandibular models (Model 1: No angulation; Model 2: No angulation for #33, 15-degree distal angulation for #35 and #37; Model 3: No angulation for #33, 25-degree distal angulation for #35 and #37) were created by modifying the angulations of implant analogues. Using a lab scanner, these reference models were scanned. The obtained data were preserved and utilized as virtual references. Three intraoral scanning (IOS) strategies: IOS-Omnicam, ISO-Quadrant, and IOS-Consecutive, as well as two traaditional techniques: splinted open tray (OT) and closed tray (CT), were used to create impressions from each reference model. The best-fit alignment approach was used to sequentially superimpose the reference and test scan data. Computations and statistical analysis of angular (AD), linear (LD), and 3D deviations (RMS) were performed. RESULTS: Model type, impression technique, as well as interaction factor, all demonstrated a significant influence on AD and LD values for all implant locations (P < .05). The Model 1 and SOT techniques displayed the lowest mean AD and LD values across all implant locations. When considering interaction factors, CT-Model 3 and SOT-Model 1 exhibited the highest and lowest mean AD and LD values, respectively. Model type, impression technique, and interaction factor all revealed significant effects on RMS values (P ≤ .001). CT-Model 3 and SOT-Model 1 presented the highest and lowest mean RMS values, respectively. CONCLUSION: Splinted-OT and IOS-Omnicam are recommended for multi-unit implant impressions to enhance trueness, potentially benefiting subsequent manufacturing stages.

Clinical application of stereolithographic surgical guide with a handpiece guidance apparatus: a case report.

The success of implant-supported restorations depends on the treatment planning and the transfer of planning through the surgical field. Recently, new computer-aided design and manufacturing (CAD/CAM) techniques, such as stereolithographic (SLA) rapid prototyping, have been developed to fabricate surgical guides to improve the precision of implant placement. The objective of the present case is to introduce a recently developed SLA surgical guide system into the rehabilitation of a 62-year-old male patient with mandibular edentulism. After obtaining a cone-beam computerized tomography (CBCT) scan of the mandible with a radiographic template, the images were transferred into a 3-dimensional (3D) image-based software for implant planning. The StentCad Beyond SLA surgical guide system, which is a combination of a currently used surgical template with pilot hollows and a surgical handpiece guidance apparatus, was designed to transfer a preoperatively defined implant position onto the surgical site without any drill-surgical guide contact. For the fabrication of this system, a surgical handpiece was scanned by a laser optical scanner and a mucosa-supported surgical guide was designed according to the patient's 3D model, which was attained from the CBCT images. Four dental implants were inserted through the SLA surgical guide system by a torque-controlled surgical handpiece to the interforaminal region via a flapless surgical procedure. Implants were assessed 3 months after surgery, and an implant-retained mandibular overdenture was fabricated. The present case emphasizes that CAD/CAM SLA surgical guides, along with CBCT images and scanning data, may help clinicians plan and place dental implants.

Influence of the Angulation and Insertion Depth of Implants on the 3D Trueness of Conventional and Digital Impressions.

PURPOSE: To study the influence of insertion depth and implant angulation on the 3D trueness of models obtained with different impression techniques. MATERIALS AND METHODS: Four different reference models (model 1: parallel, depth of 1.5 mm; model 2: parallel, depth of 4 mm; model 3: 20-degree angle, depth of 1.5 mm; and model 4: 20-degree angle, depth of 4 mm) of partially edentulous maxillae were generated by altering implant angulations and subgingival depths. All scans of reference models were done with a laboratory scanner, and obtained data were exported into standard tessellation language format to be used as virtual reference images. Impressions were obtained from each reference model via three conventional techniques (closed tray [CT], non-hexed open tray [NHOT], and hexed open tray [HOT]) and one digital technique (intraoral scanning [IOS]). A total of 160 impressions were made. The reference and experimental scan data were superimposed by using the best-fit alignment algorithm. Angular (AD), linear (LD), and 3D (RMS) deviations were computed, and obtained data were statistically analyzed. RESULTS: In premolar implant sites, AD and LD values were significantly affected by model type (P ≤ .001 for AD and LD) and impression technique (P = .001 for AD, P = .002 for LD). However, no significant interaction was detected (P = .703 for AD, P = .768 for LD). Model 1 (0.44 ± 0.25 for AD, 7.79 ± 6.29 for LD) and the NHOT technique (0.49 ± 0.43 for AD, 9.04 ± 8.14 for LD) exhibited the lowest mean AD and LD values. In molar implant sites, AD and LD values were significantly affected by model type (P ≤ .001 for AD and LD) and impression technique (P ≤ .001 for AD and LD), as well as by their interaction terms (P = .037 for AD, P = .005 for LD). Considering interaction terms, while the highest and lowest mean AD values were exhibited by IOS-model 4 (1.56 ± 0.25) and NHOTmodel 2 (0.46 ± 0.28), respectively, the highest and lowest mean LD values were exhibited by CT-model 4 (41.40 ± 14.48) and NHOT-model 2 (8.03 ± 4.86), respectively. RMS estimate values were significantly influenced by model type (P ≤ .001) and impression technique (P ≤ .001), as well as by their interaction terms (P = .019). The highest and lowest mean RMS values were exhibited by IOS-model 4 (70.02 ± 4.74) and NHOT-model 2 (25.96 ± 17.67), respectively. CONCLUSION: In the case of angulated and deeply placed implants, splinted NHOT and HOT techniques can be recommended for better trueness.

Correlation between bone density and angular deviation of implants placed using CT-generated surgical guides.

BACKGROUND: The aim of this study was to evaluate the correlation between the density of bone where implants were placed and the angular deviations that occurred between the virtually planned and actually placed implants using 2 different stereolithographic surgical guides. METHODS: The study population consisted of 54 patients who received 216 implants. Computed tomography machine was used for preoperative evaluation of the jawbone for implant therapy as well as determination of the bone density values (Hounsfield units [HU]) of the implantation site. All implant sockets were prepared using 2 different types of stereolithographic surgical guide. Ninety-four implants were installed using the surgical guides (Stentcad Beyond, Ay-Design; Kos-gep, ODTU, Ankara, Turkey) in the mouth, whereas 122 implants were placed after the surgical guides (Stentcad Classic; Kos-gep, ODTU) were removed. RESULTS: The mean bone densities of maxilla and mandible were 561.36 (SD, 229.46) HU and 890.63 (SD, 361.85) HU, respectively. The mean angular deviations between planned and placed implants using Stentcad Classic and Stentcad Beyond surgical guides were 5.32 (SD, 1.96) degrees and 3.73 (SD, 1.14) degrees, respectively. Highly negative correlation was found between the bone density of the placed implant sites and angular deviations in the group in whom implants were installed with freehand. CONCLUSIONS: The lower bone density values have resulted in the greater angular deviations in the group, in whom the implants were placed after the surgical guides were removed. This deviation might have been derived from the freehand placement of the implants and the poor quality of the bone.

Numb chin syndrome as a manifestation of possible breast cancer metastasis around dental implants.

Numb chin syndrome, sometimes called numb lip syndrome, is an uncommon but well-recognized symptom in medical oncology. It may be a metastatic neurologic manifestation of malignancy, often with no clinically visible pathologic finding. The authors report a numb chin syndrome as a manifestation possible breast cancer metastasis around dental implants in a 69-year-old woman. The patient was presented with complaint of numbness in the lower jaw. Medical anamnesis revealed a metastatic breast carcinoma (CA). Radiographic imaging with conventional panoramic radiography and cone beam computed tomographic examination, revealed a moth-eaten shape, radiolucent, and radiopaque mixed appearance around the dental implants that was related with possible metastasis of the breast cancer. Numb chin syndrome is almost unknown within the dental and oral and maxillofacial community, despite being well reported in the medical literature. General dentists, oral medicine specialists, and oral and maxillofacial surgeons must be aware of this condition to consider metastatic cancer in patients with unexplained facial hypoesthesia. Moreover, although the development of metastatic lesions around implants is an uncommon pathologic finding, the examination of peri-implant lesion should be performed carefully considering the entire pathologic situations.

Evaluation of Stresses on Implant, Bone, and Restorative Materials Caused by Different Opposing Arch Materials in Hybrid Prosthetic Restorations Using the All-on-4 Technique.

The long-term success of dental implants is greatly influenced by the use of appropriate materials while applying the "All-on-4" concept in the edentulous jaw. This study aims to evaluate the stress distribution in the "All-on-4" prosthesis across different material combinations using three-dimensional finite element analysis (FEA) and to evaluate which opposing arch material has destructive effects on which prosthetic material while offering certain recommendations to clinicians accordingly. Acrylic and ceramic-based hybrid prosthesis have been modelled on a rehabilitated maxilla using the "All-on-4" protocol. Using different materials and different supports in the opposing arch (natural tooth, and implant/ceramic, and acrylic), a multi-vectorial load has been applied. To measure stresses in bone, maximum and minimum principal stress values were calculated, while Von Mises stress values were obtained for prosthetic materials. Within a single group, the use of an acrylic implant-supported prosthesis as an antagonist to a full arch implant-supported prosthesis yielded lower maximum (Pmax) and minimum (Pmin) principal stresses in cortical bone. Between different groups, maxillary prosthesis with polyetheretherketone as framework material showed the lowest stress values among other maxillary prostheses. The use of rigid materials with higher moduli of elasticity may transfer higher stresses to the peri implant bone. Thus, the use of more flexible materials such as acrylic and polyetheretherketone could result in lower stresses, especially upon atrophic bones.

Comparison of the accuracy of different impression procedures in case of multiple and angulated implants : Accuracy of impressions in multiple and angulated implants.

BACKGROUND: There is no consensus in the literature regarding the impression procedures in the presence of multiple and angulated implants. METHODS: Three maxillary master models with 6 implants bilaterally positioned in anterior, premolar and molar regions were fabricated. In model 1, all implants were placed in parallel; in models 2 and 3, anterior implants were buccally inclined and posterior implants were distally inclined in 10- and 20-degrees, respectively. Three different impression copings (hexed, non-hex, multi-unit) and two different impression techniques (splinting and non-splinting) were tested. A total of 180 impressions (n = 10 per group) were made using mono-phase vinyl poly-siloxane. Master models and duplicate casts were scanned by a 5-axis laboratory scanner and data were transferred to a software program for the alignment of master and duplicate copings. Coronal and angular deviations were calculated, and data were statistically analyzed. RESULTS: For angulated models, the lowest deviation values were detected at the splinted non-hex coping group (P < 0.05). CONCLUSIONS: Implant angulation, impression coping type, and splinting the impression copings had significant effects on the accuracy of impressions. TRIAL REGISTRATION: Not applicable.

Biomechanical comparison of the All-on-4, M-4, and V-4 techniques in an atrophic maxilla: A 3D finite element analysis.

BACKGROUND: Patients with severely atrophied jaws can be challenging in implantology. The All-on-4 treatment concept eliminates advanced augmentation procedures in highly resorbed ridges by preserving the relevant anatomic structures. In addition, the inclination of the distal implants enables the placement of longer implants. Hence, tilting the anterior implants allows longer implant placement, in line with the distal implants of the All-on-4 concept. This study compared the biomechanical aspects of the standard All-on-4 treatment concept with the M-4 and V-4 techniques. METHODS: A three-dimensional model of an edentulous maxilla was created to perform three-dimensional finite element analysis. Three different configurations (All-on-4, M-4, and V-4) were modeled by changing the tilt angle of the anterior implants. In each model, to simulate a foodstuff, a solid spherical material was placed on the midline of the incisors and the right first molar region, separately applying an occlusal load of 100 Newtons. The maximum principal stress and minimum principal stress values were acquired for cortical bone, and von Mises stress values were obtained for ductile materials. RESULTS: According to the present study's findings, although there were no considerable differences among the models, in general, the All-on-4 group demonstrated slightly higher stresses and the M-4 and V-4 group showed lower stresses. CONCLUSION: M-4 or V-4 configurations may be used in cases of severely atrophied anterior maxillae to achieve better primary stabilization.

Cone Beam CT Evaluation of Maxillary Sinus Floor and Alveolar Crest Anatomy for the Safe Placement of Implants.

BACKGROUND: Alveolar bone height in the posterior maxillary region is very important and critical for dental implant planning and placement. OBJECTIVES: This study aimed to evaluate the anatomy of the maxillary sinus floor in relation to the alveolar crest and to determine variations in the vertical measurements between the maxillary sinus floor and the alveolar bone crest tip in the posterior edentulous maxilla with the use of cone beam computerized tomography. METHODS: This analysis enrolled 234 retrospectively selected patients (123 males with mean age 52.95±11.74 (range 32-76 years) and 111 females with mean age 58.14±11.92 (range 32-75 years)) with edentulous posterior maxillary regions. The maxillary sinus floor was divided into three anatomical segments (anterior, median and posterior) in relation to the transverse palatine suture. The measurements were performed on 3D surface rendered volumetric images by using rotation and translation of the views. Landmarks for measurement were specified by using a cursor driven pointer. Vertical lines were marked on the cross-sectional images between the alveolar ridge and the deepest point of the maxillary sinus floor for each of the three regions. P < 0.05 was regarded as statistically significant. RESULTS: The mean distance values between the sinus floor and the alveolar crest in the anterior, median and posterior regions were 8.74±3.97 mm, 5.37±3.23 mm and 7.06±3.28 mm, respectively. Measurements in the anterior region were found to be high in both total and gender groups compared to other regions. Also, subsinus alveolar bone heights decreased with increasing age in both genders in all three regions. CONCLUSION: This study emphasizes that the mean subsinus alveolar bone height is highest in the anterior segment of the edentulous posterior maxilla. These results may guide clinicians to make the decision of implant placement area and lead to less invasive alternative surgery methods for edentulous posterior segments.

The use of a computerized tomography-based software program with a flapless surgical technique in implant dentistry: a case report.

Successful implant treatment includes osseointegration, as well as prosthetically optimal positions of the implants for esthetics and function. The aim of this study is to evaluate a patient that was treated with an implant-supported fixed prosthesis with the help of computer-assisted three-dimensional planning. A 52-year-old edentulous man underwent computerized tomographic (CT) scanning, and the cross sections were reformatted. The cross sections were used to construct a surgical guide. Eight ITI Straumann dental implants were placed using a series of supramucosal surgical stents. Following a 5-month healing period, the stability of the implants was confirmed with the use of an Osstell device. Because satisfactory stability was observed, implant-supported fixed partial dentures, incorporating 12 units in all, were made. After 6 months, a second CT evaluation was carried out and the positions of the implants were compared with the treatment planning data. The CT-based software program and surgical stents contributed to the success of this case.

Clinical accuracy of 3 different types of computed tomography-derived stereolithographic surgical guides in implant placement.

PURPOSE: Presurgical planning is essential to achieve esthetic and functional implants. The goal of this clinical study was to determine the angular and linear deviations at the implant neck and apex between planned and placed implants using stereolithographic (SLA) surgical guides. PATIENTS AND METHODS: A total of 110 implants were placed using SLA surgical guides generated from computed tomography (CT). All patients used the radiographic templates during CT scanning. After obtaining 3-dimensional CT scans, each implant insertion was simulated on the CT images. SLA surgical guides using a rapid prototyping method including a laser beam were used during implant insertion. A new CT scan was made for each patient after implant insertion. Special software was used to match images of the planned and placed implants, and their positions and axes were compared. RESULTS: The mean angular deviation of all placed implants was 4.1 degrees+/-2.3 degrees, whereas mean linear deviation was 1.11+/-0.7 mm at the implant neck and 1.41+/-0.9 mm at the implant apex compared with the planned implants. The angular deviations of the placed implants compared with the planned implants were 2.91 degrees+/-1.3 degrees, 4.63 degrees+/-2.6 degrees, and 4.51 degrees+/-2.1 degrees for the tooth-supported, bone-supported, and mucosa-supported SLA surgical guides, respectively. CONCLUSION: The results of this study suggested that stereolithographic surgical guides using CT data may be reliable in implant placement, and tooth-supported SLA surgical guides were more accurate than bone- or mucosa-supported SLA surgical guides.

Reliability of implant placement with stereolithographic surgical guides generated from computed tomography: clinical data from 94 implants.

BACKGROUND: Dental implant placement requires precise planning with regard to anatomic limitations and restorative goals. The aim of this study was to evaluate the match between the positions and axes of the planned and placed implants using stereolithographic (SLA) surgical guides. METHODS: Ninety-four implants were placed using SLA surgical guides generated from computed tomography (CT) between 2005 and 2006. Radiographic templates were used for all subjects during CT imaging. After obtaining three-dimensional CT images, each implant was virtually placed on the CT images. SLA surgical guides, fabricated using an SLA machine with a laser beam to polymerize the liquid photo-polymerized resin, were used during implant placement. A new CT scan was taken for each subject following implant placement. Special software was used to fuse the images of the planned and placed implants, and the locations and axes were compared. RESULTS: Compared to the planned implants, the placed implants showed angular deviation of 4.9 degrees+/-2.36 degrees, whereas the mean linear deviation was 1.22+/-0.85 mm at the implant neck and 1.51+/-1 mm at the implant apex. Compared to the implant planning, the angular deviation and linear deviation at the neck and apex of the placed maxillary implants were 5.31 degrees+/-0.36 degrees, 1.04+/-0.56 mm, and 1.57+/-0.97 mm, respectively, whereas corresponding figures for placed mandibular implants were 4.44 degrees+/-0.31 degrees, 1.42+/-1.05 mm, and 1.44+/-1.03 mm, respectively. CONCLUSION: SLA surgical guides using CT data may be reliable in implant placement and make flapless implant placement possible.

Biomechanical Comparison of Different Implant Inclinations and Cantilever Lengths in All-on-4 Treatment Concept by Three-Dimensional Finite Element Analysis.

PURPOSE: The aim of this study was to evaluate the effect of implant inclination and cantilever length on the stress distribution in mandibular cortical bone, implant, abutment, prosthetic framework, and prosthetic screw via three-dimensional (3D) finite element analysis (FEA). MATERIALS AND METHODS: Four different finite element models (0-0, 17-17, 30-30, 45-30) were designed according to the tilting angle (0, 17, 30, and 45 degrees) of the posterior implant and angle of multiunit abutments (0, 17, and 30 degrees). Screw-retained fixed prostheses with different cantilever lengths in accordance with implant inclination were modeled. A foodstuff was used for the 100-N load application. Maximum principal (Pmax) and minimum principal (Pmin) stresses were calculated for cortical bone, and von Mises stress values were calculated for the implant, abutment, metal framework, and prosthetic screw. RESULTS: The highest stress values were observed in the anterior implant, surrounding bone, and prosthetic components of the 0-0 configuration. Pmin stress values in bone were gradually decreased with the increasing inclination of both anterior and posterior implants. Peak Pmax stress values were detected in the 0-0 group. For the cortical bone around the posterior implant, the 30-30 group showed the lowest Pmax value. The highest von Mises stress on implants was found at the posterior implant of the 30-30 group. The stress values on abutments gradually decreased with the increase of the angulation of the posterior implants. For prosthetic screws, the 30-30 and 45-30 groups exhibited lower stress values, and for the metal framework, the 30-30 group exhibited lower stress values. CONCLUSION: Biomechanical comparison via 3D FEA revealed that decreasing the cantilever length by tilting the posterior implants resulted in a reduction in stress values in the peri-implant bone, abutment, prosthetic screw, and metal framework. The groups with 30- and 45-degree tilted posterior implants and shorter cantilever lengths showed better stress distributions in comparison to the straight and 17-degree tilted groups.

Effect of Implant Height Differences on Different Attachment Types and Peri-Implant Bone in Mandibular Two-Implant Overdentures: 3D Finite Element Study.

Implant-supported overdentures with self-aligning attachment systems are preferred to improve the stability and retention of complete dentures. The positioning of the implant attachments is a very important aspect of two-implant overdentures in obtaining better stress distribution. Therefore, the objective of this study was to compare two different attachment systems in a two-implant overdenture by evaluating the stress distributions in peri-implant bone and stresses on the attachments with positioning at different height levels using the 3D FEA method. Six models with ball attachments and 6 models with locator attachments-totaling 12 models (including 2 controls)-with the left implant positioned unilaterally at different height levels were subjected to 3 loading conditions (anterior, right posterior, and left posterior). Data for Von Misses stresses were produced numerically, color coded, and compared among the models for attachments and peri-implant cortical bone. The configurations in which implants presented 3 mm height differences in the bone level showed the most successful results in the peri-implant bone. When stresses on the attachments were compared, greater stress values were obtained from the ball attachments. As a conclusion, the configurations with a considerable (3 mm) height difference between quadrants of the mandible in the anterior segment showed the most successful results in the peri-implant bone. On the contrary, peak stress values around the implant observed from the models with less (1 mm) bone height difference may require leveling of the bone during surgery. However, these findings should be corroborated with clinical studies.