Subcrestal Position Research Articles

Influence of crestal and sub-crestal implant position on development of peri-implant diseases: a 5-year retrospective analysis.

The aim of the present study was to evaluate the influence of crestal and subcrestal implant position on development of peri-implant diseases. The study was designed as a retrospective clinical and radiographic analysis. Implant-supported fixed dental prostheses were allocated in two groups: with the shoulder (i) placed in sub-crestal level and (ii) placed at bone level. For each patient, the following clinical variables were assessed: FMPS, FMBS, PlI, BOP, and PD. After prothesis delivery, an intraoral radiograph was obtained; this exam was performed also at 5years of observation period. No statistically significant difference was found in terms of FMPS and FMBS at baseline and after 5years follow-up (P < 0.05). A statistically significant difference was assessed between PD of control group and test group (P = 0.042). Patient-based analysis showed a 25.6% of peri-implant mucositis and 32.6% of peri-implantitis for implants placed with the shoulder in crestal position, while for implants inserted in sub-crestal position the percentage of peri-implant-mucositis and peri-implantitis were 19%; no statistically significant difference was found between groups after 5years (P < 0.05). Within the limitation of the present study, the clinical and radiographic outcomes showed that the percentage of peri-implant mucositis and peri-implantitis was not statistically significant for both groups after 5years follow-up. The outcomes of present study clinically demonstrated that a deep position of implant shoulder did not provide any benefits. On the contrary, it may be considered a possible risk indicator for implant diseases.

Crestal and Subcrestal Placement of Morse Cone Implant-Abutment Connection Implants: An In Vitro Finite Element Analysis (FEA) Study.

The issue of dental implant placement relative to the alveolar crest, whether in supracrestal, equicrestal, or subcrestal positions, remains highly controversial, leading to conflicting data in various studies. Three-dimensional (3D) Finite Element Analysis (FEA) can offer insights into the biomechanical aspects of dental implants and the surrounding bone. A 3D model of the jaw was generated using computed tomography (CT) scans, considering a cortical thickness of 1.5 mm. Subsequently, Morse cone implant-abutment connection implants were virtually positioned at the model's center, at equicrestal (0 mm) and subcrestal levels (-1 mm and -2 mm). The findings indicated the highest stress within the cortical bone around the equicrestally placed implant, the lowest stress in the -2 mm subcrestally placed implant, and intermediate stresses in the -1 mm subcrestally placed implant. In terms of clinical relevance, this study suggested that subcrestal placement of a Morse cone implant-abutment connection (ranging between -1 and -2 mm) could be recommended to reduce peri-implant bone resorption and achieve longer-term implant success.

Influence of Placement of Ultrashort Implant at Sub-Crestal, Crestal and Supra-Crestal Level with Titanium or Polyetheretherketone Hybrid Abutment: 3D Finite Element Analysis

The aim of this study was to evaluate and compare the stress concentration of short dental implants supporting different conical abutments using 3D finite element analysis (3D-FEA). A tridimensional model of single-unit short dental implants (5.2 mm × 5 mm) was designed using the computer-aided design (CAD) software based on the manufacturer’s stereolithography. The short implants were positioned in a bone model to support titanium or ceramic-reinforced PEEK conical abutments considering different bone levels (supra-crestal, crestal or sub-crestal). With the aid of a computer-aided engineering (CAE) software, the finite element model was created and an axial load of 500 N was applied. Observing the mechanical response of the implant, abutment and screw, both evaluated materials resulted in homogeneous stress and could be indicated for implant-supported restorations with short fixtures. However, aiming to decrease the strain in the bone tissue, placing the implant in the sub-crestal position is a preferable option; while the supra-crestal placement decreases the stress at the screw and implant.

Influence of implant length and insertion depth on primary stability of short dental implants: An in vitro study of a novel mandibular artificial bone model

Background/purposeDental implants are a mainstream solution for missing teeth. For the improvement of dental implant surface treatment and design, short dental implants have become an alternative to various complex bone augmentation procedures, especially those performed at the posterior region of both the maxilla and mandible. The objective of this study was to evaluate the effect of various insertion methods on the primary stability of short dental implants. Materials and methodsCommercial dental implants were inserted into artificial mandibular bone specimens using various insertion methods (equicrestal position, subcrestal position 1.5 mm, and lateral cortical anchorage) in accordance with an implant surgical guide. Insertion torque value (ITV) curves were recorded while implant procedures were performed. Both maximum ITVs (MITVs) and final ITVs (FITVs) were evaluated. Subsequently, Periotest values (PTVs) and implant stability quotients (ISQs) were measured for all specimens. A Kruskal–Wallis test was conducted to analyze the results for four primary stability parameters, and the Dunn test was used for a post hoc pairwise comparison when a difference was identified. ResultsFor all groups, their mean MITVs ranged from 33.6 to 59.4 N cm, whereas their mean FITVs ranged from 17.5 to 43.5 N cm. Insertion torque value, ISQ, and PTV decreased significantly when implants were inserted into subcrestal positions. When implants were inserted in the lateral bicortical position, the four aforementioned parameters yielded greater values. ConclusionWhen 6-mm short implants were inserted in a lateral cortical anchorage position, high primary stability was yielded.

Biomechanical behavior analysis of four types of short implants with different placement depths using the finite element method

Statement of problemThe clinical application of short implants has been increasing. However, studies on the marginal bone loss of short implants are sparse, and clinicians often choose short implants based on their own experience rather than on scientific information. PurposeThe purpose of this finite element analysis study was to evaluate the microstrain-stress distribution in the peri-implant bone and implant components for 4 types of short implants at different placement depths of platform switching. Material and methodsBy using short implants as prototypes, 4 short implant models were 1:1 modeled. The diameter and length of the implants were 5×5, 5×6, 6×5, and 6×6 mm. The restoration was identical for all implants. Three different depths of implant platform switching were set: equicrestal, 0.5-mm subcrestal, and 1-mm subcrestal. The models were then assembled and assigned an occlusal force of 200 N (vertical or 30-degree oblique). A finite element analysis was carried out to evaluate the maximum equivalent elastic strain and von Mises stress in the bone and the stress distribution in the implant components. ResultsThe 5×5 implant group showed the largest intraosseous strain (21.921×103 με). A 1-mm increase in implant diameter resulted in a 17.1% to 37.4% reduction in maximum intraosseous strain when loaded with oblique forces. The strain in the bone tended to be much smaller than the placement depth at the equicrestal and 0.5-mm subcrestal positions than that at the 1-mm subcrestal position, especially under oblique force loading, with an increase of approximately 37.4% to 81.8%. In addition, when the cortical bone thickness was less than 4 mm, 5×6 implants caused significantly higher intraosseous stresses than 6×6 implants. ConclusionsLarge implant diameters, rather than long implants, led to reduced intraosseous strain, especially under oblique loading. Regarding the implant platform switching depth, the short implant showed small intraosseous strains when the platform switching depth was equicrestal or 0.5-mm subcrestal.

Effect of Implant Length and Insertion Depth on Primary Stability of Short Dental Implant

Purpose: To evaluate the effect of insertion depth, bone type, and implant diameter on the primary stability of short implants. Materials and Methods: Commercial dental implants with different lengths (6 and 8 mm; BLX, Straumann) were inserted into artificial bone specimens of good and poor quality at three different depth positions: equicrestal, 1-mm subcrestal, and 2-mm subcrestal. Insertion torque values were recorded spontaneously during the implant procedure. Both maximum insertion torque values (MITVs) and final insertion torque values (FITVs) were recorded. Subsequently, Periotest values (PTVs) and implant stability quotients (ISQs) were measured for all specimens. Results: The mean MITVs of all groups ranged from 31.8 to 46.2 Ncm. However, the mean FITVs of all groups ranged from 8.8 to 29 Ncm. Torque values decreased significantly when the implants were inserted into their final positions. When insertion depth was increased, the PTV and ISQ decreased. Long implants and implants inserted into good-quality bone yielded greater primary stability, and bone quality appeared to have a greater effect on primary stability. Conclusion: When 6-mm short implants are inserted in a subcrestal position, low primary stability may be yielded, particularly in poor-quality bone.

Influence of the abutment height on marginal bone level changes around two-piece dental implants: Meta-analysis and trial sequential analysis of randomized clinical trials.

The focused question was: "In systemically healthy individuals with at least one two-piece dental implant, what is the efficacy of long (≥2 mm; intervention) compared with short (<2 mm; comparison) shoulder height abutments in peri-implant marginal bone level (MBL) changes at <1 year and ≥1 year reported by randomized controlled clinical trials?" An electronic and hand search was conducted to identify RCTs published up to August 2022. The primary outcome variable was changed in MBL from implant surgery to subsequent follow-ups. Mean values and standard deviations for each study were extracted. Weighted mean differences and 95% confidence intervals were calculated. Meta-analysis for MBL changes was performed through a random-effect restricted maximum-likelihood model at early (<1year) and late (≥1year) stages of bone remodeling. Publication bias and sensitivity tests were also applied. Subgroup analysis was performed to further explore possible sources of heterogeneity in the estimated treatment effect. Trial sequential analysis was performed to assess the required information and false-positive results. Six randomized clinical trials fulfilled the inclusion/exclusion criteria and were included in the qualitative and quantitative analysis with a follow-up range from 6 to 36 months after implant surgery. Meta-analysis revealed that long abutments significantly exhibited 0.27 mm (CI 95% -0.60, 0.06) and 0.33 mm (CI 05% -0.50, -0.16) lower MBL changes compared with short ones at <1year and≥1year, respectively. Subgroup meta-analysis revealed that studies with implants placed in a more subcrestal position significantly exhibited less differences in MBL changes between long and short abutments. No meta-analysis was conducted for peri-implant clinical parameters, and soft-tissue changes provided that reported data were scarce. Trial sequential analysis revealed insufficient information size to provide a definitive answer on the effect of abutment height in MBL. It might be cautiously concluded that two-piece implants with long abutments (≥2 mm) may display a protective role against marginal bone loss when compared with short ones (<2 mm) at <1year and ≥1year. A more subcrestal implant position seemed to minimize the effect of the abutment height in terms of MBL.

Subcrestal Positioning of Implants with a Convergent Hyperbolic Collar Profile: An Experimental Study in Dogs.

To evaluate the influence on peri-implant soft and hard tissues of one-piece implants with a convergent hyperbolic profile collar placed at different depths with respect to the bone crest. Six dogs were included in the experiment. Three months after mandibular tooth extractions, two one-piece implants carrying a 2.8-mm-high convergent hyperbolic profile collar were placed in the alveolar crest with the coronal margin of the rough surface either 0.8 mm (test-1) or 1.8 mm (test-2) deeper with respect to the bone crest (Ct0). Two similar implants were instead placed flush to Ct0 as controls (control-1 and control-2, respectively). Healing screws were connected, and nonsubmerged healing was allowed. After 4 months, block sections were harvested, and histologic slides were prepared in a buccolingual plane. In the histologic analyses, both the buccal crest and coronal level of osseointegration were located more coronally at the test compared to the control implants concerning the implant. However, the buccal bone crest with respect to Ct0 presented a loss of 0.8 ± 0.4 mm at the test-1 and 0.5 ± 0.4 mm at the control-1 implants (P = .028), and a loss of 2.0 ± 1.0 mm and 0.7 ± 0.4 mm at the test-2 and control-2 implants (P = .028), respectively. At the control implants, the collars were exposed above the peri-implant mucosa, while those of the test implants were not. However, the coronal level of the peri-implant mucosa with respect to Ct0 was located more apically at the test compared to the control implants. The placement of implants with a hyperbolic convergent profile collar in the subcrestal position resulted in higher buccal bone resorption and more soft tissue recession compared to the crestal implants with respect to the level of the bone crest at placement.

Marginal bone loss around crestal or subcrestal dental implants: prospective clinical study

ObjectivesThe stability of crestal bone has been reported as a major factor in the success of dental implants. Implants can be placed in an equicrestal (crestal) or subcrestal position. The aim of this study was to evaluate the effect of implant depth placement on marginal bone loss.Materials and MethodsThe study was created in a split-mouth design. Immediately after implant surgery, digital parallel radiographs were prepared and levels of bone were measured where marginal bone loss and bone level changes occurred. These measurements were repeated at 3-month and 6-month follow-up periods.ResultsIn this interventional study, 49 implants were evaluated in 18 patients. Primary bone height was not significant between the intervention and control groups in both mesial and distal aspects at 3 months and 6 months from the baseline. The mean marginal bone loss on the mesial side was 1.03 mm in the subcrestal group and 0.83 mm in the crestal group. In addition, mean marginal bone loss on the distal side was 0.88 mm and 0.81 mm in the subcrestal and crestal groups, respectively. Marginal bone loss was not significantly different between sexes, the maxilla or mandible, and in the anterior or posterior regions as well as between different lengths and diameters of implants.ConclusionBased on the results of this study, there was no significant difference in terms of marginal bone loss between crestal and subcrestal implants.

Does Subcrestal Position Affect Insertion Torque of Different Implant Designs at Different Bone Densities? An In Vitro Model Study.

To evaluate the insertion torque at the equicrestal and subcrestal positions of three implant designs in synthetic polyurethane blocks simulating different bone conditions. Overall, 72 implants with three different designs (two conical and one cylindrical) were inserted at equicrestal and subcrestal positions (-2 mm) into polyurethane blocks simulating the anterior (0.32 g/cm3) and posterior (0.48 g/cm3) regions of the maxilla. The final insertion torque of all implants was measured using a digital torque meter, and the results were evaluated and statistically analyzed. For all implant systems, insertion torque decreased significantly when placed at the subcrestal position (P < .05), except for cylindrical implants placed in the bone blocks with high cancellous density. The implants with higher body conicity and square threads had higher insertion torque values than the cylindrical and conical implants with a lower body conical angle and trapezoidal threads. The implants inserted into higher-density blocks showed greater stability. The different implant systems lost insertion torque in a nonuniform manner at the subcrestal position and varied according to bone density. Implant design significantly influenced the initial stability at the equicrestal and subcrestal positions, especially in lower-density bone.

Five Degree Internal Conical Connection and Marginal Bone Stability around Subcrestal Implants: A Retrospective Analysis

Background: There is limited information on the effect of the connection between subcrestally placed implants and abutments on marginal bone levels. The aim of the present retrospective study was to evaluate marginal bone levels after definitive prosthesis delivery around implants with an internal 5° conical connection placed in a subcrestal position. Materials and methods: Patients treated with fixed prostheses supported by implants placed at a subcrestal level between 2012 and 2018 were recalled for a follow-up examination. All implants had 5° internal conical connection with platform switching. Radiographic marginal bone level (MBL) was measured. MBL change between prosthetic delivery (t0) and follow-up examination (t1) was calculated. A multiple regression model was performed to identify the most significant predictors on MBL change. Results: Ninety-three patients and 410 implants, with a mean follow-up of 2.72 ± 1.31 years, were examined. Mean MBL was −1.09 ± 0.65 mm and −1.00 ± 0.37 mm at t0 and t1, respectively, with a mean bone remodeling of 0.09 ± 0.68 mm. An implant’s vertical position in relation to the bone crest, the year of follow up and the presence of type-2 controlled diabetes were demonstrated to be influencing factors for MBL modifications. Conclusions: Subcrestally placed implants with platform switching and internal conical connection maintained stable bone levels over a mean follow-up of more than 2 years. How a tight internal conical connection between abutment and implant may contribute to this clinical evidence should be more deeply investigated. MBL variations seem to be mostly influenced by an implant’s vertical position and presence of type-2 controlled diabetes.

The Effect of Insertion Angles and Depths of Dental Implant on the Initial Stability

The objective of this study was to evaluate the effect of the measurement directions of the Periotest value (PTV) and implant stability quotient (ISQ) of dental implant fixtures inserted at various angles and depths. Five groups were organized: vertically inserted implants in an evencrestal position; implants inserted at a 17° tilt in a distal subcrestal position; implants inserted at a 17° tilt in a mesial supracrestal position; implants inserted at a 30° tilt in a distal subcrestal position; and implants inserted at a 30° tilt in a mesial supracrestal position. The PTV and ISQ were measured along four directions (buccal, lingual, mesial, and distal directions) in all specimens. The PTV and ISQ exhibited a highly negative correlation when the fixture was vertically inserted. Compared to the implants inserted vertically and at the distal subcrestal position, the fixture with a greater tilt and inserted at the mesial supracrestal position had a lower stability. The PTV and ISQ of the tilted implants were affected by the measurement direction, inserted angulation and depth.

Effect of different implant placement depths on crestal bone levels and soft tissue behavior: A 5-year randomized clinical trial.

This randomized clinical trial analyzed the long-term (5-year) crestal bone changes and soft tissue dimensions surrounding implants with an internal tapered connection placed in the anterior mandibular region at different depths (equi- and subcrestal). Eleven edentulous patients were randomly divided in a split-mouth design: 28 equicrestal implants (G1) and 27 subcrestal (1-3mm) implants (G2). Five implants were placed per patient. All implants were immediately loaded. Standardized intraoral radiographs were used to evaluate crestal bone (CB) changes. Patients were assessed immediately, 4, 8, and 60months after implant placement. The correlation between vertical mucosal thickness (VMT) and soft tissue recession was analyzed. Sub-group analysis was also performed to evaluate the correlation between VMT and CB loss. Rank-based ANOVA was used for comparison between groups (α=.05). Fifty-five implants (G1=28 and G2=27) were assessed. Implant and prosthetic survival rate were 100%. Subcrestal positioning resulted in less CB loss (-0.80mm) when compared to equicrestal position (-0.99mm), although the difference was not statistically significant (p>.05). Significant CB loss was found within the G1 and G2 groups at two different measurement times (T4 and T60) (p<.05). Implant placement depths and VMT had no effect on soft tissue recession (p>.05). There was no statistically significant difference in CB changes between subcrestal and equicrestal implant positioning; however, subcrestal position resulted in higher bone levels. Neither mucosal recession nor vertical mucosa thickness was influenced by different implant placement depths.

Radiological implications of crestal and subcrestal implant placement in posterior areas. A cone-beam computed tomography study.

BackgroundSubcrestal implant placement has been suggested as a method that could contribute to maintain the periimplant soft and hard tissues in comparison with crestal placement. The objective of this study was to investigate the relationship between implant placement at different depths in the alveolar bone and (a) the thickness of the buccal bone plate (BBP); and (b) crestal cortical bone thickness, based on the use of cone-beam computed tomography (CBCT). Material and MethodsA cross-sectional study was performed, analyzing CBCT scans from the database of the Oral Surgery Unit of the University of Valencia. Individuals with single missing teeth in posterior sectors were included. Two trained dentists used a software application to plan implant placement at four different depths from the bone crest (from 0-2 mm subcrestal). The thickness of the BBP was measured at each established depth, tracing a line from the implant platform to the outermost part of the facial alveolar bone, and the ratio between the implant platform and cortical bone thickness was calculated. ResultsThe study sample consisted of 64 patients. In the case of implants placed in a crestal position, the distance from the platform to the BBP was 1.99±1.10 mm. This distance increased significantly (p<0.001) with the planned implant placement depth, reaching an average of 2.90±1.22 mm when placement was 2 mm subcrestal. Subcrestal implant placement at this depth implied surpassing the cortical bone in 91% of the cases. ConclusionsRadiological planning of implant placement in a subcrestal position results in a greater distance from the implant platform to the BBP. In general terms, planning implant placement at a depth of 2 mm subcrestal surpassed the cortical bone in 91% of the cases. Key words:Subcrestal implant, cortical bone thickness, buccal bone plate, cone-beam computed tomography.

Tapered Screw Implants With Different Machined Neck Designs: A 3-Year Split-Mouth Randomized Controlled Prospective Study.

Tapered Screw Implants With Different Machined Neck Designs: A 3-Year Split-Mouth Randomized Controlled Prospective Study.

Factors Influencing Early Marginal Bone Loss around Dental Implants Positioned Subcrestally: A Multicenter Prospective Clinical Study.

Early marginal bone loss (MBL) is a non-infective remodeling process of variable entity occurring within the first year after implant placement. It has a multifactorial etiology, being influenced by both surgical and prosthetic factors. Their impact remains a matter of debate, and controversial information is available, particularly regarding implants placed subcrestally. The present multicenter prospective clinical study aimed to correlate marginal bone loss around platform-switched implants with conical connection inserted subcrestally to general and local factors. Fifty-five patients were enrolled according to strict inclusion/exclusion criteria by four clinical centers. Single or multiple implants (AnyRidge, MegaGen, South Korea) were inserted in the posterior mandible with a one-stage protocol. Impressions were taken after two months of healing (T1), screwed metal-ceramic restorations were delivered three months after implant insertion (T2), and patients were recalled after six months (T3) and twelve months (T4) of prosthetic loading. Periapical radiographs were acquired at each time point. Bone levels were measured at each time point on both mesial and distal aspects of implants. Linear mixed models were fitted to the data to identify predictors associated with MBL. Fifty patients (25 male, 25 female; mean age 58.0 ± 12.8) with a total of 83 implants were included in the final analysis. The mean subcrestal position of the implant shoulder at baseline was 1.24 ± 0.57 mm, while at T4, it was 0.46 ± 0.59 mm under the bone level. Early marginal bone remodeling was significantly influenced by implant insertion depth and factors related to biological width establishment (vertical mucosal thickness, healing, and prosthetic abutment height). Deep implant insertion, thin peri-implant mucosa, and short abutments were associated with greater marginal bone loss up to six months after prosthetic loading. Peri-implant bone levels tended to stabilize after this time, and no further marginal bone resorption was recorded at twelve months after implant loading.

Influence of Implant Length and Associated Parameters Upon Biomechanical Forces in Finite Element Analyses: A Systematic Review.

The aim of this systematic review is to provide an overview of finite element analyses comparing standard and short dental implants concerning biomechanical properties and to detect the most relevant parameters affecting periimplant stress concentrations. After screening the literature and assessment of studies, 36 studies were included in this review. Eighty-three percent of the studies state that short dental implants have to bear higher stress concentrations compared with standard length implants. At the same time, 44% of articles note that implant diameter can be considered a more effective design parameter than implant length to reduce stress concentrations and to avoid an overload of periimplant bone. Regardless of implant dimension, in all studies, the highest stress concentrations are found in the cortical section around the upper part of the implant. Unaffected of bone quality, implant diameter is found to play a key role to minimize periimplant stress concentrations. Concerning stress reduction implant length gains increasing relevance with decreasing bone density. Furthermore, splinting of short implants constitute an appropriate tool to avoid crestal overloading.

Impact of crestal and subcrestal implant placement upon changes in marginal peri-implant bone level. A systematic review.

BackgroundTo systematically assess studies analyzing peri-implant bone loss in implants placed in crestal and subcrestal position.Material and MethodsFollowing the recommended methods for systematic reviews and meta-analyses (PRISMA), an electronic search was conducted in the PubMed (MEDLINE), EMBASE and LILACS databases to identify all relevant articles published up until April 2017. The search included human studies comparing marginal bone loss (MBL) between a control group and a study group with a minimum of 10 patients and a minimum follow-up of 6 months after prosthetic loading with rough neck implants. Two independent reviewers assessed the risk of bias in the selected studies based on the Newcastle-Ottawa scale for observational studies and the Cochrane Collaboration for clinical trials.ResultsOf 342 potentially eligible items, 7 complied with the inclusion criteria. One article was retrieved through the manual search. Eight articles were finally included: five experimental and three observational studies. The risk of bias assessed by the Cochrane Collaboration and Newcastle-Ottawa showed a high risk of bias. The mean follow-up period was 21 months (range 6-36 months). In four studies, implants placed in a crestal position presented higher MBL than subcrestal implants - the differences being significant in one study, while in three studies, implants placed in a subcrestal position presented greater MBL than crestal implants, with significant differences in only one study.ConclusionsDespite its limitations, the present systematic review did not find better outcomes between crestal and subcrestal implant placement, however, new studies will be needed, involving improved designs and the standardization of protocols to allow statistical comparisons and the drawing of firm conclusions. Key words:Crestal implants, subcrestal implants, placement level, systematic review.

Finite element analysis of peri-implant bone volume affected by stresses around Morse taper implants: effects of implant positioning to the bone crest

Objectives: The purpose of the present study was to evaluate the distribution and magnitude of stresses through the bone tissue surrounding Morse taper dental implants at different positioning relative to the bone crest. Materials and Methods: A mandibular bone model was obtained from a computed tomography scan. A three-dimensional (3D) model of Morse taper implant-abutment systems placed at the bone crest (equicrestal) and 2 mm bellow the bone crest (subcrestal) were assessed by finite element analysis (FEA). FEA was carried out on axial and oblique (45°) loading at 150 N relatively to the central axis of the implant. The von Mises stresses were analysed considering magnitude and volume of affected peri-implant bone. Results: On vertical loading, maximum von Mises stresses were recorded at 6-7 MPa for trabecular bone while values ranging from 73 up to 118 MPa were recorded for cortical bone. On oblique loading at the equiquestral or subcrestal positioning, the maximum von Mises stresses ranged from 15 to 21 MPa for trabecular bone while values at 150 MPa were recorded for the cortical bone. On vertical loading, >99.9vol.% cortical bone volume was subjected to a maximum of 2 MPa while von Mises stress values at 15 MPa were recorded for trabecular bone. On oblique loading, >99.9vol.% trabecular bone volume was subjected to maximum stress values at 5 MPa, while von Mises stress values at 35 MPa were recorded for >99.4vol.% cortical bone. Conclusions: Bone volume-based stress analysis revealed that most of the bone volume (>99% by vol) was subjected to significantly lower stress values around Morse taper implants placed at equicrestal or subcrestal positioning. Such analysis is commentary to the ordinary biomechanical assessment of dental implants concerning the stress distribution through peri-implant sites.

Peri-implant tissue healing at implants with different designs and placement protocols: An experimental study in dogs.

To compare the peri-implant tissue response to subcrestal or crestal placement of implants with or without "platform-switched" implant/abutment connections. On each side of the mandible in six Labrador dogs, two "platform-switched" (PS) implants and two implants with matching implant/abutment diameters (PM) were placed in a crestal or a 1.5mm subcrestal position. Sulcus formers/abutments were connected, baseline radiographs obtained and the distance between the abutment-fixture junction (A/F) and the marginal bone level (B) was determined. Five months later, radiographic and clinical examinations were repeated and biopsies were obtained and processed for histological analysis. The radiographic analysis showed that marginal bone level changes occurred during the first observation period (13weeks). PS-implants showed minor marginal bone level alterations during the full observation period (20weeks), regardless of placement depth. For PM-implants, placement had a significant impact on bone level changes; crestal placement resulted in a mean bone loss of 0.4mm and subcrestal placement in a 1.5mm bone loss. The histometric measurements resulted in a distance A/F-B of 0.6 and 0.0mm for PS implants, placed in a crestal or subcrestal position, respectively. The corresponding distance at PM-implants was 1.5mm irrespective of placement protocol. The peri-implant mucosa was thicker at subcrestally placed implants as compared to a crestal placement. Bone remodeling occurred within the early healing phase. During the full 20weeks of observation, PS-implants demonstrated significantly less crestal bone loss compared to PM-implants.