Subcrestal Level Research Articles

Assessment of Bone Loss Around Platform-Switching Subcrestal Implants: A Quasi-Experimental Study.

Replacement of lost teeth with implants is a well-known and accepted worldwide treatment. A healthy amount of bone surrounding the implant plays a vital role in osseointegration and is required for implant success. This study aimed to evaluate the efficacy of single-crown rehabilitation of subcrestal implants in terms of bone loss (BL) and overall success. Twenty healthy patients requiring implant placement to replace single hopeless teeth or extracted teeth were recruited for this prospective study. In these 20 patients, the implants were placed at the subcrestal level. Bone levels around the implant placement (T0) and one year after loading (T1) were estimated in this study. A paired t-test was used for intra-group comparisons, multivariate linear regression analysis was conducted to analyze the effect of independent variables on BL, and a correlation test was used to correlate various variables. Statistical significance was maintained at a p value of 0.05. The outcomes demonstrated statistically significant BL at the mesial and distal sides of the subcrestal implants at one-year follow-up (p<0.05). Age and sex were not significantly correlated with BL in any region (p>0.05). Brushing frequency, probing depth (PD), and bleeding index (BI) showed statistically significant effects on BL (p<0.05). A weak correlation was observed between age and other variables, with age and mesial BL showing a low correlation of 0.016. Within the parameters of this prospective study, it could be proposed that subcrestal implants caused significant BL. The PD, BI, and brushing frequency were significant predictors of BL.

Comparison of implant placement at crestal and subcrestal levels in aesthetic zone: A finite element analysis.

The success rate of the implant treatment, including aesthetics and long-term survival, relies heavily on preserving crestal peri-implant bone, as it determines the stability and long-term outcomes. This study aimed to demonstrate the stress differences in the crestal bone resulting from dental implant placement at various depths relative to the crestal bone level using finite element analysis. Three study models were prepared for implant placement at the crestal bone level (CL), 1 mm depth (SL-1),and 2mm depth (SL-2). Implants were placed in the maxillary central incisor region of each model, and 100 N vertical and oblique forces were applied. The von Mises, maximum principal (tensile), and minimum principal (compressive) stresses were evaluated. The CL model exhibited the highest stresses on the implant, abutment, and abutment screws under vertical and oblique forces. For maximum principal stress in the crestal bone under vertical force, the SL-2, SL-1, and CL models recorded values of 6.56, 6.26, and 5.77MPa, respectively. Under oblique forces, stress values for SL-1, SL-2, and CL were 25.3, 24.91, and 23.76MPa, respectively. The CL model consistently exhibited the lowest crestal bone stress at all loads and the highest stress values on the implant and its components. Moreover, considering the yield strengths of the materials, no mechanical or physiological complications were noted. Placing the implant at the crestal level or subcrestally beyond the cortical layer could potentially reduce stress and minimize crestal bone loss. However, further studies are warranted for confirmation.

Novel Technique for Alveolar Ridge Expansion: A Comparative Clinical Study

Background: Piezosurgery improved the split approach by making it safer, easier, and less prone to complications when treating extremely atrophic crests. Densah drills, with their unique design, expand the ridge by densifying bone in a reverse, non-cutting mode. Objective: To assess the effectiveness of sagittal piezosurgery, which involves cutting bone to the full implant depth and then expanding it using osseodensification drills. We use this technique to expand narrow alveolar bones and simultaneously place dental implants in the maxillary and mandibular arches. Methods: Fourteen patients received 31 dental implants. The maxillary arch received 19, and the mandible received 12 dental implants. This study will include patients who have narrow alveolar bone ridges (2.5–4 mm). After marking the implant sites with a pilot drill, we used a piezoelectric surgery tip to cut the alveolar crest to the depth of the planned dental implant. We then sequentially used Versah Drills, accompanied by extensive irrigation using cooled, sterile normal saline, and finally inserted the implant into the subcrestal level. Results: This study revealed a significant difference in alveolar ridge width immediately after the procedure, and the significant change in the mandible was slightly higher than that in the maxillary arch. However, all implants in both jaws achieved successful osseointegration. Conclusions: The alveolar ridge width changed a lot more in the mandible than in the maxillary arch after the procedure. These two strategies work well together to properly and simply expand severely atrophied alveolar ridges without affecting bone healing or the osseointegration process.

Effect of supracrestal tissue height on marginal bone level changes at platform-switching dental implants placed crestally and subcrestally: A randomized clinical-trial

ObjectivesThe presence of insufficient peri-implant supracrestal tissue height (STH) may increase marginal bone resorption. This study aims to evaluate the effect of STH on marginal bone level changes (ΔMBC) in platform-switching posterior implants placed crestally and subcrestally. MethodsA total of 80 implants were included in this study. There were two main groups in the study; STH≤2 mm (A) and STH> 2 mm (B) and four subgroups according to the implant placement level, crestally (I) and subcrestally (II): A-I, A-II, B-I, and B-II. Intraoperatively, STH and placement depths of implants were measured from mesial and distal aspects. The mesial and distal peri-implant marginal bone levels were measured on periapical radiographs at immediately (T0), 6 months (T1), 9 months (T2), and 12 months (T3) after functional loading, and the difference between the marginal bone levels was calculated as the ΔMBC. ResultsStatistically significantly more mesial ΔMBC was detected in the A-I than in the B-I at the time of T0–T1. In the group with STH greater than 2 mm, the difference in ΔMBC between the crestally and subcrestally placements was not statistically significant. ConclusionsThis study was found that STH is effective at protecting the marginal bone in the early period, and in cases where the STH is insufficient, subcrestally placement may increase long-term implant success by preventing marginal bone loss from occurring beyond the implant shoulder. The clinical trial number is NCT05595746. Clinical significanceIn this study, it was demonstrated that an STH greater than 2 mm is important for marginal bone stabilization, regardless of crestal and subcrestal levels, and that subcrestally placement is beneficial in cases of insufficient STH.

The influence of bone block graft position on bone dimensional changes in staged onlay horizontal ridge augmentation: A 6-month retrospective cohort study.

To analyze changes in bone dimensions and their modulating factor in bone dimensions 6 months after horizontal ridge augmentation using autogenous bone grafts. Thirty-eight patients with horizontally atrophic alveolar ridges of a single edentulous tooth at the maxillary anterior site were divided into two groups based on the fixation position of the bone block during ridge augmentation surgery (H0, vertical distance from the upper edge of the bone block to the alveolar crest). Patients were classified into a crestal level (CL) group if H0 ≤ 1 mm and a sub-crestal level (SCL) group if H0 > 1 mm. The width and height of the alveolar ridge were recorded using CBCT both before and 6 months after the augmentation procedure. The CL group comprised 20 patients with 23 implants, whereas the SCL group comprised 18 patients with 22 implants. All the augmentation sites exhibited vertical bone resorption. Vertical bone resorption in the SCL group (1.94 ± 2.11 mm) was significantly higher than that of the CL group (0.61 ± 0.64 mm). The SCL group showed significantly lower horizontal bone gain than the CL group (SCL: 1.02 ± 2.30 mm; CL: 3.19 ± 3.17 mm) at the cervical level. Peri-implant marginal bone loss increased significantly in the SCL group (1.00 ± 2.71 mm) compared to the CL group (0.64 ± 0.40 mm). The bone height decreased after horizontal ridge augmentation using autogenous onlay grafting. The fixation position of the bone block was a modulating factor. The SCL group showed more vertical bone loss, less horizontal bone gain 6 months after surgery, and more marginal bone loss after restoration.

Impact of bone levels on stress distribution around all-on-four concept: A 3-D finite element analysis

This study aimed to investigate the impact of implant placement levels within the bone on stress distribution in the context of the All-on-Four concept. In this Finite Element Analysis(FEA), two 4.1 mm x 10 mm implants were axially placed in the anterior region of the jawbone, while two 4.1 mm x 14 mm implants were tilted at 30 ° in the posterior region following the all-on-four concept. In the EC scenario, all implants were inserted at the equicrestal level. In other scenarios, implants were positioned at 1 mm and 2 mm subcrestal levels (SC1, SC2). In all groups, the prosthesis was designed to replicate a group-function occlusion. A total load of 450 N was applied to the prosthesis. Upon deeper implant placement below the crest level, a trend of decreasing Von Mises stresses was observed in both implants and implant fragments. The highest Pmax value in the bone was recorded in SC-2, characterized by the absence of cortical bone support, with values of 3.16 N/mm2 in the anterior region and 1.55 N/mm2 in the posterior region. Conversely, the lowest Pmax values were noted in SC-1 for the anterior implant (2.67 N/mm2) and the EC for the posterior implant (0.87 N/mm2). Implant placements devoid of cortical bone support result in stress transmission from the implant and its components to the peri-implant bone. Optimal stress minimization is achieved by placing anterior axial angle implants deeper than the crest level while retaining cortical bone support and positioning posterior tilted implants at the crest level.

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.

Clinical and radiographic results of crestal vs. subcrestal placement of implants in posterior areas: A split-mouth randomized controlled clinical trial.

The objective of this study was to evaluate the peri-implant soft tissue and marginal bone loss (MBL) around implants with platform-switching and internal conical connection placed at crestal and subcrestal levels in posterior areas. Nineteen partially edentulous patients with at least two adjacent missing teeth in posterior areas unilaterally or bilaterally were included. Forty-two implants were placed randomly at the crestal or subcrestal (1 mm) level in a split-mouth design. Implant-supported fixed dental prostheses with screw retention were delivered after 4 months of healing. Clinical and radiological measurements were performed at implant placement (T0), restoration delivery (T1), and 1-year follow-up after loading (T2). MBL was calculated as the change in distance from the implant-abutment interface to the first radiographically visible bone-implant contact. A repeated-measures mixed ANOVA followed by a paired Student's t-test with the Bonferroni correction was used for statistical analysis. p < 0.05 was considered statistically significant. Eighteen patients with thirty-eight implants completed the study at T2. The MBL was lower in the subcrestal group than in the crestal group (0.04 ± 0.08 vs. 0.17 ± 0.17 mm, p = 0.004). The peri-implant probing depth (PD) was 2.31 ± 0.48 mm in the subcrestal group and 1.92 ± 0.43 mm in the crestal group; this difference was statistically significant (p = 0.002). Intragroup comparison showed no significant differences in MBL, or PD around the crestal group and subcrestal group from T1 to T2. After 1 year of functional loading, subcrestal placement of implants with platform-switching and internal conical connection showed lower MBL and was associated with greater PD and peri-implant soft tissue height than implants placed at the crestal level.

Scanning electron microscopic analysis of adherent bacterial biofilms associated with peri-implantitis.

Peri-implantitis (PI) is caused by bacteria in the peri-implant space but the consensus on microbial profile is still lacking. Current microbial sampling of PI lesions has largely focused on analyzing bacterial species that have been shed from the implant surface and captured in the pocket fluid. The purpose of the present study was to investigate the morphotypes of bacteria in biofilm covering the implant threads and explore whether certain morphotypes were associated with PI. Fourteen failed implants were removed and instantly processed for scanning electron microscope analysis. The implants were imaged at three equally divided sub-crestal levels of the exposed area. Bacterial morphotypes were identified and quantified by three examiners. Mobility and years in function were correlated to the presence of different morphotypes. The implants demonstrated the presence of variable bacterial morphotypes that did not correlate to disease progression in our study. Some implants were dominated by filaments and others showed the presence of combinations of cocci/rods or spirilles/spirochetes. In general, all implants showed variable morphologic biofilm composition. However, individual implants tended to have similar composition throughout the entire implant. Rods and filaments were dominant morphotypes throughout the surfaces and cocci showed increased presence toward the apical third. There were some differences in the biofilm morphology with mobility and time in function. The profiles of bacterial biofilm morphotypes in failing implants with similar clinical presentations were highly variable. While there were significant differences between implants, similar morphotypes in individual implants were often found throughout the entire surface.

Biomechanical influence of narrow-diameter implants placed at the crestal and subcrestal level in the maxillary anterior region. A 3D finite element analysis.

To evaluate the tendency of movement, stress distribution, and microstrain of single-unit crowns in simulated cortical and trabecular bone, implants, and prosthetic components of narrow-diameter implants with different lengths placed at the crestal and subcrestal levels in the maxillary anterior region using 3D finite element analysis (FEA). Six 3D models were simulated using Invesalius 3.0, Rhinoceros 4.0, and SolidWorks software. Each model simulated the right anterior maxillary region including a Morse taper implant of Ø2.9mm with different lengths (7, 10, and 13mm) placed at the crestal and subcrestal level and supporting a cement-retained monolithic single crown in the area of tooth 12. The FEA was performed using ANSYS 19.2. The simulated applied force was 178N at 0°, 30°, and 60°. The results were analyzed using maps of displacement, von Mises (vM) stress, maximum principal stress, and microstrain. Models with implants at the subcrestal level showed greater displacement. vM stress increased in the implant and prosthetic components when implants were placed at the subcrestal level compared with the crestal level; the length of the implants had a low influence on the stress distribution. Higher stress and strain concentrations were observed in the cortical bone of the subcrestal placement, independent of implant length. Non-axial loading influenced the increased stress and strain in all the evaluated structures. Narrow-diameter implants positioned at the crestal level showed a more favorable biomechanical behavior for simulated cortical bone, implants, and prosthetic components. Implant length had a smaller influence on stress or strain distribution than the other variables.

Marginal Bone Loss in Internal Conical Connection Implants Placed at the Crestal and Subcrestal Levels before Prosthetic Loading: A Randomized Clinical Study.

The vertical position concerning the bone in which the implants are placed has been related as one of the factors causing marginal bone loss. The objective of this study was to evaluate the bone loss that occurs before prosthetic loading around tapered internal connection (CIC) implants placed at the crestal (C) and subcrestal (S) levels. Method: A randomized clinical trial (RCT) was carried out, with a sample size of 62 implants placed in 27 patients who underwent radiological controls on the day of placement, at one month, and at 4 months, and stability was measured by resonance frequency analysis (RFA) on three occasions. Results: Bone loss in implants C and S from the time of placement (T0) and the month after (T1) was not significant (p = 0.54) (C = 0.19 mm and S = 0.15 mm). The difference between one month (T1) and four months (T2) (C = 0.17 mm and S = 0.22 mm) was not significant either (p = 0.26). The difference between the day of placement (T0) and the third and last measurement (T2) was almost null (p = 0.94) (C = 0.35 mm and S = 0.36). The overall success rate of the implants was 97.8%. The stability of the implants measured with RFA went from 70.60 (T0) to 73.16 (T1) and 74.52 (T2). Conclusions: No significant differences were found in the bone loss for implants placed at the C and S levels. The millimeters of bone loss detected in both vertical positions did not have a significant impact on the stability of the implants.

Biomechanical Evaluation of Stress Distribution in Equicrestal and Sub-crestally Placed, Platform-Switched Morse Taper Dental Implants in D3 Bone: Finite Element Analysis.

AimThe aim of the study was to assess the effect of implant placement depth on stress distribution in bone around a platform-switched and Morse taper dental implants placed at the equi-crestal and 1 mm and 2 mm sub-crestal levels in a D3 bone using the 3D finite element analysis.MethodologyA mechanical model of a partially edentulous maxilla was generated from a computerized tomography (CT) scan of an edentulous patient, as it can give exact bony contours of cortical bone. Also, from accurate geometric measurements obtained from the manufacturer, 3D models of Morse taper and platform-switched implants were manually drawn. The implant and bone models were then superimposed to simulate implant insertion in bone. Three implant positioning levels such as the equi-crestal, 1 mm sub-crestal, and 2 mm sub-crestal models were created, and meshing was done to create the number of elements for distribution of applying loads. The elastic properties of cortical bone and implant, such as Young's modulus and Poisson's ratio (µ), were determined. A load (axial and oblique) of 200N that simulated masticatory force was applied.ResultsOn comparing stresses within the bone around the equi-crestal and 1 mm and 2 mm sub-crestal implants, it was observed that the maximum stresses were seen within cortical bone around the equi-crestally placed implant (21.694), the least in the 2 mm sub-crestally placed implant (18.85), and intermediate stresses were seen within the 1 mm sub-crestally placed implant (18.876).ConclusionSub-crestal (1-2mm) placement of a Morse taper and a platform-switched implant is recommended for long-term success, as maximum von Mises stresses were found within cortical bone around the equi-crestal implant followed by the 1 mm sub-crestal implant and then the 2 mm sub-crestal implant.

Marginal bone maintenance around implants placed in subcrestal level: a 2 to 9 years retrospective study

Marginal bone maintenance around implants placed in subcrestal level: a 2 to 9 years retrospective study

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.

Treatment of Deep Cusp Fractures: A New Technique.

Cusp fractures occur frequently in endodontically treated teeth with large restorations and no cusp protection. These fractures often lead to challenging clinical decisions, such as whether to undertake complex restorative management or extraction of the affected teeth. This article reports the surgical and restorative management of two teeth with fractures exceeding the biologic width to juxtacrestal and subcrestal levels, respectively, and describes a new technique for such treatment.

Bone Loss in Implants Placed at Subcrestal and Crestal Level: A Systematic Review and Meta-Analysis.

Background: To assess differences in marginal bone loss in implants placed at subcrestal versus crestal level. Methods: An electronic and a manual research of articles written in English from Jaunary 2010 to January 2018 was performed by two independent reviewers. Clinical trials comparing bone loss for implants placed at crestal and subcrestal level were included. Pooled estimates from comparable studies were analyzed using a continuous random-effects model meta-analysis with the objective of assessing differences in crestal bone loss between the two vertical positions. Results: 16 studies were included; 10 studies did not encounter statistically significant differences between the two groups with respect to bone loss. Three articles found greater bone loss in subcrestal implants; while 3 found more bone loss in crestal implants. A meta-analysis for randomized control trial (RCT) studies reported an average and non-statistically different crestal bone loss of 0.028 mm. Conclusions: A high survival rate and a comparable bone loss was obtained both for crestal and subcrestal implants’ placement. Quantitative analysis considering a homogenous sample confirms that both vertical positions are equally valid in terms of perimplant bone loss. However, with respect to soft tissue; in presence of a thin tissue; a subcrestal placement of the implant should be preferred as it may reduce the probability for the implant to become exposed in the future and thus avoid the risk of suffering from peri-implant pathologies.

A Prospective Multicenter Study on Radiographic Crestal Bone Changes Around Dental Implants Placed at Crestal or Subcrestal Level: One-Year Findings.

To compare the peri-implant radiographic crestal bone changes around implants placed at the subcrestal or crestal level. Systemically healthy patients with at least two missing teeth requiring implant-supported fixed prosthetic restorations were enrolled in the study. Implants were randomly placed either 1 mm subcrestally or at the bone crest level. Radiographic examination was performed using the long-cone parallel technique and customized film holders. Digital periapical radiographs were obtained at the time of implant placement (T0), at the time of prosthesis delivery (T1), and 12 months (T2) after prosthetic loading. Marginal bone levels were measured at the mesial and distal aspects of each implant with digital image software. A total of 54 implants were present for the radiographic analysis at the 12-month follow-up. No implant showed mechanical or biologic complications throughout the follow-up period. The implant survival percentage was 100%. After 1 year, the mean bone loss was 0.711 ± 0.721 mm in the subcrestal group and 0.224 ± 0.418 mm in the crestal group. Furthermore, only the subcrestal group showed statistically significant radiographic bone resorption at the end of the follow-up. Within the limitations of this study, implants placed at the crestal level showed greater peri-implant bone stability during the 1-year follow-up. Studies with larger samples and longer follow-up are needed to confirm the results of this investigation.

Effect of implant placement depth on the peri-implant bone defect configurations in ligature-induced peri-implantitis: An experimental study in dogs.

BackgroundThe subcrestal placement of implant platform has been considered a key factor in the preservation of crestal bone, but the influence of implant placement depth on bone remodeling combined with peri-implantitis is not fully understood. The aim of this study was to assess the effect of the crestal or subcrestal placement of implants on peri-implant bone defects of ligature-induced peri-implantitis in dogs.Material and MethodsEight weeks after tooth extraction in six beagle dogs, two different types of implants (A: OsseoSpeed™, Astra, Mölndal, Sweden; B: Integra-CP™, Bicon, Boston, USA) were placed at either crestal or subcrestal (-1.5 mm) positions on one side of the mandible. Ligature-induced peri-implantitis was initiated four weeks after the installation of the healing abutment connections. After 12 weeks, tissue biopsies were processed for histological analyses.ResultsSupra-alveolar bone loss combined with a shallow infrabony defect was observed in crestal level implants while deep and wide infrabony defects were present in subcrestal level groups. Subcrestal groups showed significantly greater ridge loss, depths and widths of infrabony defects when compared to crestal groups (P<0.001).ConclusionsWithin the limitations of the animal study, it can be stated that the implants at subcrestal position displayed greater infra-osseous defect than implants at crestal position under an experimental ligature-induced peri-implantitis. Key words:Subcrestal, peri-implantitis, histology.

Soft tissue changes and crestal bone loss around platform-switched implants placed at crestal and subcrestal levels: 36-month results from a prospective split-mouth clinical trial.

The aim of the present 36-month prospective split-mouth clinical trial was to investigate the peri-implant soft tissue changes and crestal bone loss (CBL) around delayed loaded platform-switched implants placed at crestal and subcrestal levels. Twenty-three individuals with bilaterally missing either mandibular first or second molars were included. The test and control sites were defined as follows: (i) test sites: implants placed 2mm below the alveolar crest (subcrestal); (ii) control sites: implants placed at bone level (crestal). Forty-six implants (23 implants in test sites and 23 in control sites) were placed in the center of the healed alveolar ridge in the posterior mandible. Peri-implant bleeding on probing (BOP), probing depth (PD≥4mm), and CBL was compared at 6, 18, and 36months of follow-up. P<0.05 was considered statistically significant. Sixteen males and seven females with a mean age of 43.5years (29-50) were included. In the control group (n=23), the highest mean percentage of sites that showed BOP and PD≥4mm were at 6months (7.4% and 1.4%, respectively). In the test group (n=23), the highest mean percentage of sites that showed BOP and PD≥4mm were at 6months (2.4% and 1.2%, respectively). The total amount of CBL around crestal and subcrestal implants after 36months of loading was 0.45±0.2 and 0.3±0.2mm, respectively. At all follow-up intervals, all intragroup and intergroup comparisons showed no significant differences in BOP, PD≥4mm, and CBL around implants placed at crestal and subcrestal levels. Up to 36months of follow-up, soft tissue parameters and crestal bone levels can remain equally stable around dental implants placed at crestal and subcrestal levels. The need for long-term follow-up clinical trials is also emphasized.