Mechanical Failure of Endocrowns Manufactured with Different Ceramic Materials: An In Vitro Biomechanical Study.

PURPOSE: To evaluate the effect of different silica-based ceramic materials on the mechanical failure behavior of endocrowns used in the restoration of endodontically treated mandibular molar teeth. MATERIALS AND METHODS: Thirty-six intact mandibular molar teeth extracted because of a loss of periodontal support received root canal treatment. The teeth were prepared with a central cavity to support the endocrowns, replacing the occlusal surface with mesial-lingual-distal walls. Data acquisition of the prepared tooth surfaces was carried out digitally with a powder-free intraoral scanner. Restoration designs were completed on manufactured restorations from three silicate ceramics: alumina-silicate (control), zirconia-reinforced (Zr-R), and polymer-infiltrated (P-I). Following adhesive cementation, endocrowns were subjected to thermal aging, and then, each specimen was obliquely loaded to record the fracture strength and define the mechanical failure. For the failure definition, the fracture type characteristics were identified, and further analytic measurements were made on the fractured tooth and ceramic structure. RESULTS: Load-to-fracture failure did not differ significantly, and the calculated mean values were 1035.08 N, 1058.33 N, and 1025.00 N for control, Zr-R, and P-I groups, respectively; however, the stiffness of the restoration-tooth complex was significantly higher than that in both test groups. No statistically significant correlation was established in paired comparisons of the failure strength, restorative stiffness, and fractured tooth distance parameters. The failure mode for teeth restored with zirconia-reinforced glass ceramics was identified as non-restorable. The resin interface in the control and P-I groups presented similar adhesive failure behavior. CONCLUSION: Mechanical failure of endocrown restorations does not significantly differ for silica-based ceramics modified either with zirconia or polymer.

Effect of digitizing techniques on the fit of implant-retained crowns with different antirotational abutment features.

STATEMENT OF PROBLEM: The development of computer-aided design/computer-aided manufacturing technology has enabled the fabrication of implant-retained restorations. However, information on the marginal and axial accuracy of restorations fabricated by different digitizing techniques with different antirotational abutment features is not sufficient. PURPOSE: The purpose of this in vitro study was to evaluate the influence of digitizing techniques on the fit of implant-retained crowns with 2 antirotational features. MATERIAL AND METHODS: An experimental working cast housing a tissue-level dental implant was created. Resin-retained abutments with different antirotational features were connected to the implant. Optical impressions of 2 abutment types were obtained separately with 1 chairside and 2 laboratory approaches. Alumina silicate restorations were milled from chairside optical impressions, and ceramic oxide cores were milled from laboratory optical impressions. Restoration fit was evaluated from axial sections of restorations with silicone materials representing the marginal and axial gaps. Axial and marginal fits were measured on digital photographs of the sectioned specimens with a computer program. Two-way ANOVA was used to compare differences between abutments with 2 different antirotational features and digitizing techniques separately for the marginal and axial fits of single implant-retained crowns. A post hoc least significant difference test was used to compare digitizing techniques (α=.05). RESULTS: Significant differences in the marginal fit of single-implant-retained crowns were found among digitizing techniques (P=.011) and between antirotational features (P<.001). No significant difference in the axial fit of single-implant-retained crowns was found among digitizing techniques (P=.905) or between antirotational features (P=.075). CONCLUSIONS: Within the limitations of this in vitro study, the marginal fit of single-implant-retained crowns was affected by antirotational abutment features. Furthermore, digitizing techniques were found to play an important role in the marginal fit of single-implant-retained restorations.

Low-level laser therapy vs. pulsed electromagnetic field on neonatal rat calvarial osteoblast-like cells.

To compare the effects of pulsed electromagnetic field (PEMF) and low-level laser therapy (LLLT) on osteoblast cells in a cell culture model. Fifty thousand neonatal rat calvarial osteoblast-like cells per milliliter were seeded and 0.06 mT PEMF, 0.2 mT PEMF, and LLLT at 808 nm were applied for 24 and 96 h on the cells. To evaluate cellular proliferation and differentiation, specimens were examined for DNA synthesis, alkaline phosphatase (ALP) activity, cell numbers, and viability of the cells. Morphological appearances of the cells were observed using scanning electron microcopy after 24 and 96 h of incubation. At 24 and 96 h, the control group had a higher cell proliferation than 0.06 and 0.2 mT PEMF groups (p=0.001). At 96 h, 0.2 mT PEMF group had higher cell proliferation rate than 0.06 mT PEMF and LLLT groups (p=0.001). The cell count and cell viability in 0.2 mT PEMF group were higher than the 0.06-mT PEMF and LLLT groups, although these differences were not statistically significant at 96 h (p>0.05). At 24 and 96 h, cell viability in the control group was higher than the test groups. Alkaline phosphatase levels of the groups were comparable in both time intervals (p>0.05). 0.2 mT PEMF application on osteoblast-like cells led to cell proliferation and differentiation better than 0.06 mT PEMF and LLLT at 808 nm, although a remarkable effect of both PEMF and LLLT could not be detected. The ALP activity of 0.2 and 0.06 mT PEMF and LLLT were comparable.

The effects of pulsed electromagnetic field (PEMF) on osteoblast-like cells cultured on titanium and titanium-zirconium surfaces.

BACKGROUND: Commercially pure Ti, together with Ti Ni, Ti-6Al-4V, and Ti-6Al-7Nb alloys, are among the materials currently being used for this purpose. Titanium-zirconium (TiZr) has been developed that allows SLActive surface modification and that has comparable or better mechanical strength and improved biocompatibility compared with existing Ti alloys. Furthermore, approaches have targeted making the implant surface more hydrophilic, as with the Straumann SLActive surface, a modification of the SLA surface. PURPOSE: The aim of this study is to evaluate the effects of pulsed electromagnetic field (PEMF) to the behavior of neonatal rat calvarial osteoblast-like cells cultured on commercially pure titanium (cpTi) and titanium-zirconium alloy (TiZr) discs with hydrophilic surface properties. MATERIALS AND METHODS: Osteoblast cells were cultured on titanium and TiZr discs, and PEMF was applied. Cell proliferation rates, cell numbers, cell viability rates, alkaline phosphatase, and midkine (MK) levels were measured at 24 and 72 hours. RESULTS: At 24 hours, the number of cells was significantly higher in the TiZr group. At 72 hours, TiZr had a significantly higher number of cells when compared to SLActive, SLActive + PEMF, and machine surface + PEMF groups. At 24 hours, cell proliferation was significantly higher in the TiZr group than SLActive and TiZr + PEMF group. At 72 hours, TiZr group had higher proliferation rate than machine surface and TiZr + PEMF. Cell proliferation in the machine surface group was lower than both SLActive + PEMF and machine surface + PEMF. MK levels of PEMF-treated groups were lower than untreated groups for 72 hours. CONCLUSIONS: Our findings conclude that TiZr surfaces are similar to cpTi surfaces in terms of biocompatibility. However, PEMF application has a higher stimulative effect on cells cultured on cpTi surfaces when compared to TiZr.

Occlusal adjustment of 3-unit tooth-supported fixed dental prostheses fabricated with complete-digital and -analog workflows: A crossover clinical trial.

AIM: This prospective crossover clinical trial aimed to compare the complete-digital and -analog workflows in terms of occlusal adjustment of 3-unit tooth-supported fixed dental prostheses, operator, and patient preferences. MATERIALS AND METHOD: This study included twelve patients receiving fourteen 3-unit posterior FDPs. 2 FDPs were made for each restoration site: one fabricated in complete-digital workflow comprising intraoral scan with static bite registration (Trios 3) and a monolithic zirconia FDP (test); the other fabricated in complete-analog workflow comprising conventional impression/face-bow transfer and a porcelain-fused-to-metal FDP (control). The FDPs (n=28) were intraorally/provisionally fixed, and quadrant-like intraoral scans were taken for every FDP before & after their occlusal adjustments. Pre- and post-adjustment scans of each FDP were then superimposed using best-fit alignment (GOM Inspect) to measure the volumetric occlusal adjustment amount (mm3) (3Matic) (Mann Whitney U, α=0.05). The patient and operator experience for digital and analog workflows were evaluated using visual analog scales (Wilcoxon test, α=0.05). RESULTS: Mean occlusal adjustments were 7.63 mm3 [±7.02] and 25.95 mm3 [±39.61] for test and control groups, respectively. The volumetric adjustment difference was clinically noticeable but not significant (P=0.12). The impression and digital workflow adjustment were perceived more favorably by both operator (P=0.003, P=0.046, respectively) and the patients (P=0.003, P=0.002, respectively). CONCLUSIONS: Within the limitations of this clinical study, the complete digital workflow with digital static bite-registration provided high occlusal accuracy for short-span tooth-supported FDPs. In addition, the patient and operator preferences significantly favored the digital workflow. CLINICAL SIGNIFICANCE: Complete-digital workflow employing intraoral scanning and model-free fabrication of monolithic-Zr short-span tooth-supported FDPs offers an effective treatment modality with sufficient occlusal accuracy. Therefore complete-digital workflow is a valid alternative for complete-analog workflow comprising conventional impression, face-bow transfer, and use of a semi-adjustable articulator.

Efficacy of resonance frequency analysis in the diagnosis of compromised bone-implant interface.

PURPOSE: To investigate the sensitivity level of resonance frequency analysis (RFA) in the identification of contact loss at compromised bone-implant interfaces. METHODS: Twelve cylindrical acrylic experimental models housing a perpendicularly positioned dental implant were generated. Two different compromised bone-implant interfaces to simulate the loss of bone-to-implant contact were created in 8 models, whereas the resting 4 simulated the intact relationship between implant and bone. Each implant received RFA and subjected to serial sectioning to evaluate bone-acrylic interface microscopically. Implant stability quotient values were statistically compared among groups. Correlation level between the implant stability quotient values and bone-acrylic interface conditions was assessed. RESULTS: RFA was not sensitive to recognize the lack of horizontal contact (approximately 0.276 mm), but it was able be to discriminate the additional loss of approximately 0.1 mm at the bone-implant interface. CONCLUSION: RFA is not a reliable method in the assessment of the initial contact loss at bone-implant interface.

Fatigue resistance of 2 different CAD/CAM glass-ceramic materials used for single-tooth implant crowns.

PURPOSE: To evaluate the fatigue resistance of 2 different CAD/CAM in-office monoceramic materials with single-tooth implant-supported crowns in functional area. MATERIALS AND METHODS: A metal experimental model with a dental implant was designed to receive in-office CAD/CAM-generated monoceramic crowns. Laterally positioned axial dynamic loading of 300 N at 2 Hz was applied to implant-supported crowns machined from 2 different glass materials for 100,000 cycle. Failures in terms of fracture, crack formation, and chipping were macroscopically recorded and microscopically evaluated. RESULTS: Four of 10 aluminasilicate glass-ceramic crowns fractured at early loading cycles, the rest completed loading with a visible crack formation. Crack formation was recorded for 2 of 10 leucite glass-ceramic crowns. Others completed test without visible damage but fractured upon removal. DISCUSSION: Lack in chemical adhesion between titanium abutment and dental cement likely reduces the fatigue resistance of machinable glass-ceramic materials. However, relatively better fractural strength of leucite glass-ceramics could be taken into consideration. Accordingly, progress on developmental changes in filler composition of glass-ceramics may be promising. CONCLUSION: Machinable glass-ceramics do not possess sufficient fatigue resistance for single-tooth implant crowns in functional area.

Spontaneous early exposure and marginal bone loss around conventionally and early-placed submerged implants: a double-blind study.

PURPOSE: The aim of this retrospective study was to compare the frequency of spontaneous early exposure of cover screws and marginal bone resorption in conventionally and early-placed submerged implants before second-stage surgery. MATERIALS AND METHODS: A total of 103 Nobel Biocare Branemark implants were conventionally (Group 1), or early-placed (Group 2) in 46 consecutive patients following the two-stage surgical protocol. Patients in both groups received oral hygiene training in self-performed plaque control measures, including exposure of cover screws during healing. Spontaneous cover screw exposure (CSE) of each implant was recorded for both groups and scored from Class 0 (no perforation) to Class 4 (complete exposure). Plaque index scores were recorded and marginal bone-level (MBL) changes were measured in radiographs before second-stage surgery in a blind manner. RESULTS: MBL in Group 2 was higher than Group 1 in patients with or without interim prosthesis (P<0.05). The use of interim prosthesis did not increase MBL in Group 1, but led to higher MBL in Group 2. The percentage of non-exposed implants in Group 1 was higher than Group 2 (P=0.007, odds ratio=7). Group 1 implants had 11.5 times greater plaque index score 0 than those in Group 2 (P=0.031, odds ratio=11.5). The differences between MBL with regard to CSE scores 0 and 1-4 was significant for both sides in Group 2 and the mesial side in Group 1 (P<0.05). The difference between MBL with regard to plaque index scores 1-3 was similar in both groups (P>0.05). CONCLUSIONS: There is a direct relation between spontaneous early cover screw perforations with early crestal bone loss. Early-placed implants experienced more spontaneous perforations and associated bone loss in comparison with conventionally placed submerged implants. The use of interim dentures may lead to more CSE and consequent MBL in the early-placement protocol.

A systematic review of marginal bone loss around implants retaining or supporting overdentures.

PURPOSE: To evaluate, through a systematic review of the literature, the effects of implant design and attachment type on marginal bone loss in implant-retained/supported overdentures. MATERIALS AND METHODS: With the combined search terms "implant and overdenture," "implant-supported overdenture," "implant-retained overdenture," and "implant-anchored overdenture," along with specific inclusion and exclusion criteria, eligible articles between 1997 and 2008 (up to April 1) were retrieved from PubMed, EMBASE, OVID, the Cochrane Library databases, and seven journals by hand searching. Marginal bone loss values with regard to time, attachment type, and implant system used were compared by Kruskal-Wallis tests. Means and standard deviations of data were combined using fixed- and random-effect models and evaluated using meta-analysis. RESULTS: Forty-six articles were included in the analyses; data extraction and meta-analysis were able to be conducted on eight studies. Data regarding maxillary overdentures could not be analyzed statistically. Bone loss around mandibular implants did not seem to be influenced by implant system or attachment design (bar, ball, magnet, and other types) in the first year, from 1 to = or < 5 years, and even after 5 years (P > .05). Meta-analysis could not detect differences in implant systems or attachment types (P > .05). CONCLUSIONS: Based upon a systematic review and meta-analysis of the literature that identified a total of 4,200 implants from 13 manufacturers, there was no difference in marginal bone loss around implants retaining/supporting mandibular overdentures relative to implant type or attachment designs.

Fresh-frozen vs. embalmed bone: is it possible to use formalin-fixed human bone for biomechanical experiments on implants?

PURPOSE: As formalin is an extremely reactive electrophilic chemical that reacts with tissues, the purpose of this study was to explore whether formalin fixation could potentially alter the mechanical properties of bone tissue and have an effect on the primary stability measurements of implants. MATERIAL AND METHODS: Ø 3.3 x 8 mm, Ø 4.1 x 8 mm, and Ø 4.8 x 8 mm implants were placed on sockets prepared into the anterior surface of the radius of two fresh-frozen human cadavers. The insertion torque of each implant was quantified using a strain-gauged torque-wrench connected to a data acquisition system at a sample rate of 10 KHz, and resonance frequency analysis measurements were also undertaken for each implant. The cadavers were then subjected to embalment with 10% formalin for 3 months, and the same experiments were undertaken on the contra lateral radius of the cadavers. RESULTS: The insertion torques before and after chemical fixation were similar for Ø 3.3 mm (P>0.05), and higher values were obtained for Ø 4.1 mm and Ø 4.8 mm implants after chemical fixation (P<0.05). The resonance frequency analysis values before and after chemical fixation were similar for all implants (P>0.05). CONCLUSIONS: Implants have higher insertion torque values in formalin-fixed bone than fresh-frozen human bone, but similar implant stability quotients in both cases. The insertion torque technique can detect the difference between formalin-fixed and fresh-frozen human bone, but resonance frequency analysis cannot.

Implant stability and bone density: assessment of correlation in fresh cadavers using conventional and osteotome implant sockets.

OBJECTIVE: To compare the primary stability of implants placed in conventional and osteotome sites and to evaluate the level of correlation between cutting torque measurements, resonance frequency analysis (RFA), and bone density. MATERIALS AND METHODS: Eight human femoral heads were scanned with computed tomography for bone density measurements as Hounsfield units (HU), and individualized computed tomography-based surgical stents were prepared for placement of implants. Five implant sockets were prepared in each collum (CoF), caput (CaF), and trochanter (Tr-MM) section of the femoral heads using the conventional drilling technique or by a combination of drilling and use of an osteotome. Cutting-torque values (CTV) of the implants were measured by a manual torque wrench, followed by determination of implant stability quotients (ISQ) by RFA. RESULTS: The CTVs of implants were similar in the conventional group, but different in the osteotome group (P<0.05). There was a general tendency toward achieving higher CTV and ISQ values in CoF than CaF and Tr-MM (P<0.05), and measurements in CaF and Tr-MM were comparable (P>0.05). The mean HU of sites were similar, although CoF had higher HU values (P>0.05). CTV of implants in CaF and Tr-MM and ISQ values in CoF in the conventional groups were higher than those in the osteotome groups (P<0.05). The correlation between CTV and HU in Tr-MM was significant in the osteotome group, although no other correlations between CTV, ISQ, and HU could be detected (P>0.025). CONCLUSIONS: Conventional placement led to higher implant stability than the drilling and osteotome technique used in the study. No correlation could be found between CTV, RFA, and bone density.

Nonlinear finite element analysis versus ex vivo strain gauge measurements on immediately loaded implants.

PURPOSE: To evaluate the level of agreement between nonlinear finite element stress analysis (NL-FEA) and ex vivo strain gauge analysis (EV-SGA) on immediately loaded implants. MATERIALS AND METHODS: Four 4.1-mm-diameter, 12-mm-long implants were placed bilaterally into the lateral and first premolar regions of completely edentulous maxillae of four human cadavers. Two-element 90-degree rosette strain gauges were bonded to the labial cortical bone around the implants, and 100 N maximal load was applied over two miniature load cells on bar-retained overdentures while simultaneous data acquisition from load cells and strain gauges was performed at a sample rate of 10 KHz. Individualized numeric models of the cadavers were constructed, and contact analysis with normal contact detection and separation behavior was performed between the implants and bone. Upon simulation of the loading regimen, axial and lateral strains were recorded. The NL-FEA data and EV-SGA data were compared. RESULTS: There was a high level of agreement regarding the quality of strains, as determined by both techniques, although the mean values obtained with EV-SGA were higher than those found with NL-FEA. However, the strains recorded by NL-FEA did not differ significantly (P<.05) from the strains recorded by EV-SGA. CONCLUSION: Considering the complex biomechanical behavior of human hard and soft tissues, EV-SGA and NL-FEA did not suggest inconsistency in the detection of the quality of strains. Further, the methods provided comparable values for the quantification of strains on implants supporting maxillary overdentures.

Numeric simulation of time-dependent remodeling of bone around loaded oral implants.

PURPOSE: The objective of this study was to investigate the time-dependent biomechanics of marginal bone around osseointegrated dental implants within physiologic loading conditions. MATERIALS AND METHODS: The remodeling of marginal bone around a 4.1-mm-diameter, 10-mm-long implant was studied by implementing the Stanford theory into axisymmetric mathematical models simulating different bone support at the implant neck: 1-mm-thick cortical bone (model 1), 0.5-mm-thick cortical bone (model 2), absence of cortical bone (model 3), and absence of cortical bone with 0.5 mm of resorption of marginal trabecular bone (model 4). The results were examined separately for all models at five time intervals: the first loading after osseointegration and 3, 6, 9, and 12 months after osseointegration. Minimum principal stress, maximum principal stress, strain energy, total equivalent strain, displacement, average elastic modulus, and bone density were evaluated. RESULTS: In models 1 and 2, the magnitude of the stresses increased during the 1-year period. The distributions of stresses in models 3 and 4 were less variable and lower than models with cortical bone. The region of high stresses enlarged during the first 3 months and then decreased over time. There was a time-dependent increase in strain energy density around the neck of the implant in models 1 and 2. The time-dependent displacement values of implants were almost constant over time (maximum 1 Mum change). The lowest implant displacement values were observed in model 1. There was a slight increase in the elastic modulus of cortical bone and a decrease in trabecular bone (maximum 1% change). CONCLUSION: The time-dependent increase in stresses in the marginal zone of the implants with cortical bone support was higher than that of the implants supported solely by trabecular bone in the first year of function. Higher strain energy density around the implants with cortical bone support might indicate apposition and increase in interface stiffness, whereas lower strain energy density around implants supported solely by trabecular bone could be associated with skeletal tissue loss.

Meta-analysis of methods used to assess implant stability.

PURPOSE: To evaluate correlations between Periotest, cutting torque or insertion torque, and/or the reverse torque test with resonance frequency analysis measurements. MATERIALS AND METHODS: The combined search terms dental implant, primary stability, resonance frequency analysis, removal torque, vibration analysis, torque, Periotest, cutting torque, and insertion torque and specific inclusion and exclusion criteria were used to retrieve eligible articles published between 1998 and 2008 (up to April 1) from PubMed, EMBASE, OVID, The Cochrane Library databases, and 10 journals by hand-searching. The pooled P value was calculated with the Fisher method. The correlation coefficients (r) were combined using fixed and random effect models. Heterogeneity of the studies was tested by performing the homogeneity test. RESULTS: Fifty articles were identified, but 3 studies were excluded because of limitations in study design. Studies that fulfilled the inclusion criteria fell into a variety of categories (11 human cadaver, 16 clinical, 15 animal, and 5 in vitro studies). Assessment of P values revealed that correlation between cutting torque or insertion torque and resonance frequency analysis was significant (6 studies; P = .0022). Correlation between Periotest and cutting torque or insertion torque was significant (1 study; P = .015), and correlations between resonance frequency analysis and reverse torque test values (1 study; P = .319; r = 0.405) and Periotest and resonance frequency analysis (P = .28) were insignificant. Nine articles provided r values, and cutting torque or insertion torque and resonance frequency analysis showed a statistically significant and direct relationship of 55.4% (P = .000). One study provided an r value of -0.149. A statistically significant and direct relationship of 87.6% was found between cutting torque or insertion torque and reverse torque (2 studies; P = .000). CONCLUSION: This meta-analysis of 47 studies showed a statistically significant correlation between cutting torque or insertion torque and resonance frequency analysis.

Two-year prospective follow-up of implant/tooth-supported versus freestanding implant-supported fixed partial dentures.

The aim of this study was to compare the prosthetic outcomes of implant/tooth-supported three-unit fixed partial dentures (FPDs) with those of freestanding implant-supported FPDs after 2 years of function. Twenty-nine partially edentulous patients presenting with unilateral or bilateral distal-extension edentulous areas received FPDs and were followed for a minimum of 24 months. In all, 49 FPDs were fabricated. In 34 FPDs, implants were connected to teeth and thus the FPDs were categorized as mixed (m-FPDs), whereas 15 FPDs were supported by freestanding terminal implants (fs-FPDs). Evaluation of prosthetic parameters including mechanical complications was performed. Changes in marginal bone level (DeltaMBL) around implants in both treatment groups were measured on digitalized periapical radiographs. Neither loss of osseointegration of an implant nor intrusion of abutment teeth was recorded. All FPDs were functioning after 24 months. Mean DeltaMBLs of posterior implants supporting m-FPDs and fs-FPDs at 24 months were 0.189 mm and -0.285 mm, respectively, representing a significant difference (P < .05). Mean DeltaMBLs at the mesial and distal surfaces of anterior and posterior implants supporting fs-FPDs were similar (P > .05). In the treatment of short-span distal-extension edentulous areas, similar clinical outcomes may be obtained for implant- and tooth/implant-supported three-unit FPDs in the early stages of function.

A photoelastic and strain-gauge analysis of interface force transmission of internal-cone implants.

The objective of this study was to compare force transmissions in the peri-implant bone region of implants with various conical implant-abutment mating designs. Photoelastic models of solitary Bicon, Astra Tech, and synOcta and monoblock ITI implants were fabricated. Static vertical and 20-degree oblique forces of 75 N were applied on the implants in separate loading cases, and the generation of isochromatic fringes was observed and photographed in the field of a circular polariscope. Three-element strain gauges were bonded on the models in close proximity to the implants. Under the same loading protocol, the strain-gauge signals were digitized by a data-acquisition system and displayed on a computer using corresponding software at a sample rate of 10 kHz, and the principal strains were calculated. Isochromatic fringe orders around ITI and Astra Tech implants were similar at the collar region and slightly higher than around the Bicon implant under both loading conditions. Strains around the Bicon implant were lower than those around all implants tested under vertical loading (P < .05), whereas the strains around both ITI implants were similar and lower than those around the Astra Tech implant (P < .05). Under oblique loading, strains around both ITI implants were higher than those around other implants tested (P < .05). However, these differences do not seem to have any clinical relevance. Internal-cone implants have similar interface force transfer characteristics that resemble a one-part implant. To reduce stresses in the peri-implant region, implant diameter may be more effective than the type of implant.

Effect of compromised cortical bone on implant load distribution.

PURPOSE: To investigate photoelastically the difference in load distribution of dental implants with different implant neck designs in intact and compromised bone. MATERIALS AND METHODS: Composite photoelastic models were fabricated using two different resins to simulate trabecular bone and a 1-mm thick layer of cortical bone. The following parallel-sided, threaded implants were centrally located in individual models representing intact and compromised cortical bone: Straumann (4.1-mm diameter x 12-mm length), AstraTech (4.0-mm diameter x 13-mm length), and 3i (3.75-mm diameter x 13-mm length). The compromised cortical bone condition was simulated by contaminating a 1-mm neck portion with Vaseline to impair the implant-resin interface. Vertical and oblique static loads were applied on the abutments, and the resulting stresses were monitored photoelastically and recorded photographically. RESULTS: For the fully intact condition, the highest stresses were observed around the crest and apical region for all implant designs under vertical and inclined loads. There were no appreciable differences in magnitude or distribution between implant types. With compromised cortical bone, for all designs and load directions, higher stresses in the supporting structures were observed. Increased stresses were noted especially at the cortical bone-trabecular bone interface. Somewhat lower stress levels were observed with the 3i implant. CONCLUSIONS: The condition of implant-cortical bone contact has considerable influence on stress distribution. A compromised cortical bone condition caused higher level stresses for all implant designs tested.

Bone strains around immediately loaded implants supporting mandibular overdentures in human cadavers.

PURPOSE: To compare the biomechanical effect of splinted versus unsplinted mandibular implants supporting overdentures subjected to experimental static immediate load on bone tissue deformation using strain gauge analysis. MATERIALS AND METHODS: Strain gauges were bonded on the labial cortical bone adjacent to 2 Straumann dental implants placed in the mandibular interforaminal region of 4 completely edentulous mandibles of fresh human cadavers. The installation torque value (ITV) of each implant was measured using a custom-made torque wrench, and implant stability quotients (ISQs) were also obtained using resonance frequency analysis. Three overdentures (ODs), 2 splinted (bar- and cantilevered bar-retained) and 1 unsplinted (ball-retained), were fabricated for each edentulous mandible. Two experimental loads were applied subsequently via 2 miniature load cells that were placed bilaterally 10 mm (anterior loading) and 15 mm (posterior loading) from the implant. Strain measurements were performed at a sample rate of 10 KHz and under a maximum experimental static load of 100 N; they were simultaneously monitored from a computer connected to a data acquisition system. Finally, the removal torque values (RTV) of the implants were measured. RESULTS: Strains on the labial cortical bone around implants supporting mandibular ODs under anterior loading were significantly higher than measured under posterior loading for all attachment types (P < .05). All strain values were compressive in nature, and the minimum strain (-19 microepsilon) was recorded for bar-retained ODs under 25 N posterior loading, while the maximum strain (-797 microepsilon) was for recorded for retentive anchor-retained ODs under 100 N anterior loading. Nonparametric correlations between ISQs, ITVs, and RTVs identified significant correlations only for ITVs and RTVs (P < .05). CONCLUSION: Splinting of 2 interforaminal dental implants, regardless of attachment type, to support mandibular ODs subjected to immediate load significantly reduced initial bone tissue strains experienced on the labial cortical bone in comparison with the use of unsplinted implants.

Effect of surgical techniques on primary implant stability and peri-implant bone.

PURPOSE: To evaluate the primary stability of dental implants placed with condensing-osteotome versus drilling-osteotome techniques and to explore peri-implant mircromorphologic consequences of lateral bone condensing. MATERIALS AND METHODS: The experimental model designed for the study comprised bilateral iliac crests from 3 fresh frozen human cadavers. Two AstraTech dental implants (AstraTech AB, Mölndal, Sweden) were consecutively placed with condensing- and drilling-osteotome techniques in bone with a 10-mm interimplant distance. Six experimental bone sites received a total of 12 implants. Installation torque values (ITVs) and implant stability quotients (ISQs) were measured to quantify primary implant stability. Bone specimens including implants were removed to quantify the peri-implant relative bone volume and bone microstructural parameters in the 1-mm circular vicinity of implants using desktop computed tomography (microCT). The Mann-Whitney U test was used to evaluate the differences in primary implant stability values and microCT data for the surgical placement techniques. RESULTS: ITVs and ISQs were similar for both surgical placement techniques without statistical significance (P > .05). Relative bone volumes around implants placed with the condensing-osteotome technique were significantly (P < .05) higher than those around implants placed with the drilling-osteotome technique. Microstructural parameters, such as trabecular thickness, separation, and number, differed significantly between the 2 osteotome techniques. CONCLUSIONS: Managing implant sites with the condensing-osteotome technique results in notable changes in peri-implant bone architecture but might not be as promising in improving primary implant stability compared with the drilling-osteotome technique.

Bone strains around apically free versus grafted implants in the posterior maxilla of human cadavers.

The objective of this study was to compare the bone strains of apically free versus grafted implants in the posterior maxilla. The experiments were undertaken in four edentulous maxillary posterior regions of fresh human cadavers, having a minimum bone height of 8 mm. In each bone fragment, two Ø 4.1 mm x 12 mm Straumann implants were placed, and insertion torque values (ITV) and implant stability quotients (ISQ) of the implants were quantified to determine implant anchorage. Two splinted crowns were fabricated for each experimental model. Strain gauges were bonded on the buccal and sinus floor cortical bones around apically free and grafted implants. Microstrains were recorded by a data acquisition system and corresponding software at a sample rate of 10 KHz under central and buccally oriented lateral-axial static loads of 100 and 150 N in separate cases. The data were compared by independent T test at a significance level set at P<0.05. Bone tissue strains on the buccal cortical areas adjacent to apically free implants were higher than those of apically grafted implants (P<0.05). The differences ranged between 10 and 48 mu epsilon under central and lateral axial loads of 100 and 150 N. The shift in load application from central to buccally oriented lateral axial mode increased strains between 60 and 201 mu epsilon on buccal cortical bone around apically free and grafted implants (P<0.05). Bone strains around anterior implants were higher than those of posterior implants. Microstrains in the sinus floor cortical bone in apically grafted models were slightly higher than apically free models. Bone tissue strains on the buccal cortical areas adjacent to apicallyfree implants are higher than those of apically grafted implants. Sinus lifting, resulting in an enhanced apical support, slightly increases strains at the sinus floor region, but leads to a decrease in bone strains around the collar of supporting implants.