Bicortical Implants Research Articles

ANATOMICAL VARIABILITY OF THE SEGMENTS OF THE INFERIOR ALVEOLAR NERVE IN THE PEOPLE OF SECOND PERIOD OF MATURE AND OLDER AGE

To avoid complications of bicortical implantation, great importance is attached to the study of individual morphological features of the mandible and its structures, in particular, the anatomical variability of the inferior alveolar nerve (IAN) and mandibular canal. The purpose of the study was to fi nd out the peculiarities of the structure, topography and individual anatomical variability of the IAN in persons of the second period of maturity and older age. Cone-beam computer tomography of 54 people of both sexes aged 45-65 years with three- dimensional reconstruction, morphometry and statistical analysis was studied. On the basis of our own research on the topographical and anatomical features of the IAN and its syntopy with the mandible, in particular, with the mandibular canal, we propose to distinguish 4 of its divisions: extra- canal – from the place of formation to the entrance to the mandibular canal; intracanal – from the mandibular foramen to the mental foramen; mental – after exiting the mandibular canal; incisive – after the departure of the mental branch. The topographical and anatomical features and anatomical variability of the IAN were studied. In people of the second period of mature and elderly age, anatomical variability of the macroscopic structure and topography of the IAN was established, which manifested itself in high (4.0-11.0 mm) and low (22.0-33.0 mm) levels, relative to the foramen ovale its beginning and form (one or two trunks) of departure from the mandibular nerve. The largest number of nerve connections with other branches of the mandibular nerve is formed by the extracanal section of the IAN: with the auriculo-t emporal nerve (29 cases – 53.7 %), with the lingual nerve (5 cases – 9.26 %), with the nerve of the medial pterygoid muscle (3 observations – 5.56 %) and with the nerve of the lateral pterygoid muscle (2 specimens – 3.7 %). A diff erent level of departure of the nerve to mylohyoid from the extracanal section of the IAN was established: high (5.0-7.0 mm) and low (27.0-31.0 mm). Anatomical variability of the intracanal part of the IAN was manifested by structural variants: a single trunk (43 cases, 79.6 %), rarely – two trunks (11 observations, 20.4 %) and very rarely – the lower dental plexus (6 specimens, 11,11 %). The proximity of the roots of the 7th and 8th teeth to the IAN can be the cause of severe pain in the pathology of these teeth and cause nerve damage during their removal. Nerve connections occur between the right and left incisive nerves, the knowledge of which is an important practical value for performing anesthesia of the front row of teeth. The number of branches to the teeth, interalveolar septa and gingiva from the IAN signifi cantly decreases with age and with a violation of the integrity of the dentition.

Analysis of the atrophic mandible rehabilitated with fixed total prosthesis on mono or bicortical implants.

Rehabilitation of edentulous atrophic mandibles involves the placement of implants in the anterior segment of the mandible. The primary stability of these implants can be improved using the base of the mandible as complementary anchorage (bicorticalization). This study aimed to analyze the biomechanics of atrophic mandibles rehabilitated with monocortical or bicortical implants. Two three-dimensional virtual models of edentulous mandibles with severe atrophy were prepared. Four monocortical implants were placed in one model (McMM), and four bicortical implants were placed in the other (BcMM). An implant-supported total prosthesis was prepared for each model. Then, a total axial load of 600 N was applied to the posterior teeth, and its effects on the models were analyzed using finite element analysis. The highest compressive stresses were concentrated in the cervical region of the implants in the McMM (-32.562 Mpa); in the BcMM, compressive stresses were distributed in the upper and lower cortex of the mandible, with increased compressive stresses at the distal implants (-63.792 Mpa). Thus, we conclude that axial loading forces are more uniformly distributed in the peri-implant bone when using monocortical implants and concentrated in the apical and cervical regions of the peri-implant bone when using bicortical implants.

Surgical management of traumatic irreducible spondyloptosis of thoracolumbar junction

Introduction. The thoracolumbar junction is the most common location of traumatic spinal injuries. It accounts for 50-60% of all thoracic and lumbar spine injuries. Spondyloptosis is rather rare, but one of the most severe types of traumatic injury, that is characterized by a severe damage of spinal axis in one or more planes. Traumatic spondyloptosis is classified as reducible and irreducible, depending on the possibility of intraoperative restoration of the spinal axis without resection of the damaged vertebra. Objective. To determine the optimal surgical technique for traumatic irreducible spondyloptosis of thoracolumbar junction. Materials and methods. A retrospective analysis of the patients’ database treated at the Romodanov Neurosurgery Institute, Ukraine was performed over the past 4 years (2017 to 2020) to identify all cases with traumatic irreducible spondyloptosis of the thoracolumbar junction. Results. Treatment outcomes of five patients aged 18 to 52 years (mean age 31.2 years) were analyzed. The minimum period from the moment of injury to surgery was 14 days, the maximum was 3 months and 2 days (on average 42.2 days). At the time of admission all patients had a neurological deficit that corresponds to the functional class A on the American spine injury associatin ASIA scale of severity of spinal cord injury. The TLICS (Thoracolumbar injury classification and severity) score was 8 points. All the patients had the injury of lateral spondyloptosis: in three cases as an isolated displacement only in the coronal plane, in two – as a combined one - in the coronal and sagittal plane. Surgical intervention in all cases was performed from the posterior approach. As a body replacement system in 2 patients, a vertical cylindrical implant (Mesh) was used, in 3 patients - a telescopic body replacing implant. The method of bicortical implantation of pedicle screws was applied. The transpedicular system was strengthened by two cross links of the rod-to-rod type. In all cases the restoration of spinal axis was achieved in both the coronal and sagittal planes. Follow-up examinations were carried out 2, 6 and 12-18 months of the postoperative period. Regression of neurological disorders was registered in two patients, in one case to ASIA B, in the other to ASIA C. Conclusions. Isolated posterior approach has demonstrated high efficacy in the surgical management of traumatic irreducible spondyloptosis of the thoracolumbar junction both in restoring the axis of the spine and in ensuring the stability of fusion.

The Use of Computer Guided Tall andTilted Pin Hole Immediately Loaded Implants(TTPHIL) Technique for Severe Atrophic Maxilla Rehabilitation: A One Year Follow-Up

For successful placement of dental implants, the clinician needs adequate bone in three dimensions around endo-osseous implants to enhance Bone Implant Contact (BIC) area and primary stability. The absence of optimum bone calls for complex procedures such as sinus lifts, bone augmentations using grafts that aggravates patient morbidity, dramatically higher costs and limited patient satisfaction. To overcome disadvantages of grafting, graft-less solution used in combination or alone, such as tilted implants, use of long, narrow implants, bi-cortical implants, all-on-4 techniques have enhanced patient acceptance and clinical ease. All-on-4 protocol is one such combination treatment concept whose success has been demonstrated mainly in ideal/moderate osseous structures. Further, it accommodates 10-12 teeth per arch, mostly without second molars compromising chewing efficiency and creating cantilevers especially in rehabilitations opposing complete set of natural teeth. Additionally, optimal number of implants required to support full arch prosthesis remains unclear. Therefore, to circumvent the limitations of all-on-4 technique, 6 long (16-25 mm) and tilted implants have been used to restore 14 teeth in severely atrophic maxillary arch of a healthy 75-year-old female in the following case report. Tall implants engage basal cortical bone aiding in immediate fixation and increase in surface area of osseo-integration. All implants were placed using minimally invasive flapless technique and immediately loaded within 3 days with a screw-retained multiunit DMLS prosthesis. The pterygoid cortex engagement of distal implants does not have any deleterious biomechanical effect eliminating the distal cantilever.

Immediately Loaded Bicortical Implants Inserted in Fresh Extraction and Healed Sites in Patients with and Without a History of Periodontal Disease.

Background:Bicortical screw implants may be used in both healed bone and fresh extraction sockets and loaded immediately. To date, there have not been too many studies reporting clinical results of such screws used in periodontally involved sites. This study aimed to assess many aspects of bicortical screw implants used to retain full-arch and segmental cemented prostheses in the rehabilitation of the mandible and maxilla in patients with or without a history of periodontal disease.Materials and Methods:This retrospective review involved 87 patients, of whom 77 had a history of periodontitis diagnosed before implant placement and 10 did not. They were treated following the same surgical procedure and received a total of 1019 implants which were immediately loaded with fixed prosthetic works.Results:A total of 1019 polished surface, one-piece, bicortical screw implants were used in 87 patients who underwent the same surgical treatment, i.e., tooth extraction and immediate implant placement were investigated, of which 526 were placed in the healed bone and 493 in fresh extraction sockets with the mean follow-up time of 22.2 ± 7.3 months. Results were analyzed using log-rank test, the Kaplan–Meier method, Chi-square test, and t-test. Cumulative survival at 12, 24, and 35 months after placement was 99.3%, 98.6%, and 97.0%, respectively.Conclusion:Bicortical smooth surface implant concept with immediate loading protocol provided predictable outcomes and survival rate of 99% in patients with and without a history of periodontitis. More studies are needed to further support the clinical advantages of bicortical anchoraged smooth surface implants.

Optimal safe implantation corridors in feline cervical vertebrae (C2-T1): CT study in 16 domestic shorthair cats.

The objective of this study was to define safe corridors for the optimal placement of bicortical implants in the feline cervical spine (C2-T1) using CT. CT images of feline cervical spines (n = 16) were reviewed retrospectively. Multiplanar reconstructions were used to define the optimal safe corridors. Safe corridors were defined by their angle of insertion, width and length. The insertion point within the vertebral body was also described. Vertebral measurements were compared between vertebrae using multilevel linear regression, and left and right measurements within vertebrae were compared with the paired samples Wilcoxon signed-rank test. A P value <0.05 was considered significant for all analyses. The safe corridor insertion points were located within the caudal third of the vertebral body in C2 (mean cranial vertebral ratio 0.73) and in the cranial third of the vertebral bodies from C3-T1 (mean cranial vertebral ratios 0.34-0.38). Mean safe corridor widths ranged from 1.04 mm in C2 to 2.30 mm in C7 and T1. The mean right and left optimal angles of implantation were, respectively, 21.79° and 21.49° for C2, 45.26° and 46.19° for C3, 51.48° and 51.04° for C4, 53.52° and 54.30° for C5, 56.36° and 56.65° for C6, 63.40° and 64.92° for C7, and 53.90° and 52.90° for T1. There were statistically significant differences between vertebrae in almost every measurement. Cervical vertebral safe corridors in cats are narrow and differ to those reported in dogs. Safe corridors are located in the caudal third of C2 and cranial third of the C3-T1 vertebral bodies. Current recommendations for implant sizes should be reviewed, as 1.5-2 mm implants would be oversized for bicortical implantation in most of the feline cervical vertebrae.

Alveolar Bone Resorption Evaluation Around Single-piece Designed Bicortical Implants, Using Immediate Loading Protocol, Based on Orthopantomographs

Abstract Background: Inserting dental implants in severely atrophied jawbones is a great challenge for the dental practitioner. There are an increasing number of patients who choose dental implantanchored prosthetic restorations despite compromised bone quality and quantity. There have been numerous attempts in adapting implant design for the atrophic crestal bone. One-piece, needle-type basal implant design is a typical design for these cases. These implants are inserted in the remaining compact bone located in the basal aspect of the jawbones. If high primary stability is achieved, these implants are used for immediate loading protocol. From many points of view, this technique is based on contradictory principles compared to classic implant surgery and loading protocols. The aim of this study was to investigate the long-term success of basal one-piece short-diameter dental implants used for immediate loading protocol. Materials and methods: A total of 56 dental implants were included in this study. Peri-implant bone loss was measured on orthopantomographs. Bone resorption was measured in millimeters in the first 6 and 12 months of functional loading. Results: There were no failing implants in this period; average bone resorption was 1.59 mm after 6 months of functional loading and 2.05 mm after 12 months. Bone resorption was slightly higher in the mandible than in the maxilla. Conclusions: Immediate implant loading protocol might be an attractive solution for fixed fullarch restoration using short-diameter one-stage basal implants, but long-term effects require further investigations.

Changes of the Surfaces of Various Metal Implants after Introduction into Rabbits' Bone Tissue

Screw metal implants with rough or the smooth polished were introduced surface in a tibial bone proximal condyle of not purebred rabbits. Within 6 months after operation the considerable distinctions of radiological data were revealed not. 2 months later after introduction of implants with a rough surface the effort enclosed for its twisting is, much more, than for removal of the polished product. However, stability of fixing of implants was practically made even at 6 months. On remote rough implants there is a set of tissue scraps whereas on products with a smooth surface the tissue remains were much less. Surrounding tissues strongly join a rough surface, grow into cavities, and during removal of such products there is a considerable trauma of tissues round an implantation place. Smooth implants have the smaller area of contact with organism tissues, they are fixed due to bicortical implantation, during removal easily get out and don't break off surrounding tissues.

Some Features of the Dental Metal Implant Changes with Different Character of a Surface After Administration into Bone Tissue of Rabbits

Screw metal implants with rough or the smooth polished were introduced surface in a tibial bone proximal condyle of not purebred rabbits. Within 6 months after operation the considerable distinctions of radiological data were revealed not. 2 months later after introduction of implants with a rough surface the effort enclosed for its twisting is, much more, than for removal of the polished product. However, stability of fixing of implants was practically made even at 6 months. On remote rough implants there is a set of tissue scraps whereas on products with a smooth surface the tissue remains were much less. Surrounding tissues strongly join a rough surface, grow into cavities, and during removal of such products there is a considerable trauma of tissues round an implantation place. Smooth implants have the smaller area of contact with organism tissues, they are fixed due to bicortical implantation, during removal easily get out and don't break off surrounding tissues.

The Tissue Reactions and Changes of a Surface of Various Metal Implants after Their Introduction in a Bone Tissue in Experiment

Screw metal implants (3S, Israel) with rough or smooth polished surface were introduced in a tibial proximal condyle of not purebred rabbits. The condition of surrounding tissues in 2 and 6 months after implantation was compared by light microscopy and X-ray methods. Within 6 months after operation the considerable distinctions of radiological and morphological data were revealed not. 2 months later after introduction of implants with a rough surface the effort enclosed for its twisting is, much more, than for removal of the polished product. However, stability of fixing of implants was practically made even at 6 months. On remote rough implants there is a set of tissue scraps whereas on products with a smooth surface the tissue remains were much less. Surrounding tissues strongly join a rough surface, grow into cavities, and during removal of such products there is a considerable trauma of tissues round an implantation place. Smooth implants have the smaller area of contact with organism tissues, they are fixed due to bicortical implantation, during removal easily get out and don’t break off surrounding tissues. The signs of inflammation and formation of merged multinuclear macrophages were not found at all cases, which give evidence to the inertness of material of the mentioned articles for living organism. In some observations however and by implantation of the rough article and by introduction of polished implants, metal particles were found, but after use of the foreign body with grit-blasted treatment of surface metal was found more frequently, and its fragments had larger volume.

Association between implant apex and sinus floor in posterior maxilla dental implantation: A three-dimensional finite element analysis.

The aim of the present study was to evaluate the effect of the association between the implant apex and the sinus floor in posterior maxilla dental implantation by means of three-dimensional (3D) finite element (FE) analysis. Ten 3D FE models of a posterior maxillary region with a sinus membrane and different heights of alveolar ridge with different thicknesses of sinus floor cortical bone were constructed according to anatomical data of the sinus area. Six models were constructed with the same thickness of crestal cortical bone and a 1-mm thick sinus floor cortical bone, but differing heights of alveolar ridge (between 10 and 14 mm). The four models of the second group were similar (11-mm-high alveolar ridge and 1-mm-thick crestal cortical bone) but with a changing thickness of sinus floor cortical bone (between 0.5 and 2.0 mm). The standard implant model based on the Nobel Biocare® implant system was created by computer-aided design (CAD) software and assembled into the models. The materials were assumed to be isotropic and linearly elastic. An inclined force of 129 N was applied. The maximum von Mises stress, stress distribution, implant displacement and resonance frequencies were calculated using CAD software. The von Mises stress was concentrated on the surface of the crestal cortical bone around the implant neck with the exception of that for the bicortical implantation. For immediate loading, when the implant apex broke into or through the sinus cortical bone, the maximum displacements of the implant, particularly at the implant apex, were smaller than those in the other groups. With increasing depth of the implant apex in the sinus floor cortical bone, the maximum displacements decreased and the implant axial resonance frequencies presented a linear upward tendency, but buccolingual resonance frequencies were hardly affected. This FE study on the association between implant apex and sinus floor showed that having the implant apex in contact with, piercing or breaking through the sinus floor cortical bone benefited the implant stability, particularly for immediate loading.

Pathological mandibular fracture: A severe complication of periimplantitis

Nowadays, dental implant treatment is a very common option for patients even in medical compromised conditons. Some complications related to them have been described. Periimplantitis (PI) is one of the biggest concerns complications of these kind of treatments, probably has a multifactorial aethiology. Usually the consequences of PI are the loss of the implants and prostheses, expenses of money and time for dentists and patients. Very often PI implies the necesity of repeating the treatment . Pathological mandibular fracture due to PI is a severe but infrequent complication after dental implant treatment, especially after PI. In this study we present three cases of mandibular pathologic fractures among patients with different medical and dental records but similar management: two of them had been treated years ago of oral squamous cell carcinoma with surgery and radiotherapy, the other patient received oral bisphosphonates for osteoporosis some years after implantation. We analized the causes, consequences and posible prevention of these fractures as well as the special features of this kind of mandibular fractures and the different existing treatments. Key words:Periimplantitis, pathological mandibular fracture, mandibular atrophy, bicortical implants.

Computed tomographic study of the optimal safe implantation corridors in feline thoraco-lumbar vertebrae

To define the implantation corridors in feline thoraco-lumbar vertebrae (T10-L7) using computed tomography (CT) for optimal safe placement of the implants (screws/pins) in spinal column stabilization. Computed tomographic study. Computed tomography images of feline spinal column (n = 10) were used to define the optimal safe implantation corridors (OSIC) in the transverse plane. The OSIC were defined as corridors allowing the greatest amount of bone purchase with safe margins for implantation of the bicortical implants. They were characterized by their insertion point, optimal angle (from the midsagital plane), maximum and minimum safe angles (from the same insertion points), length, and width. The OSIC are located within the vertebral bodies. Insertion points were situated at the level of the vertebro-costal joint or the base of the transverse process of the vertebral body for thoracic and lumbar vertebrae, respectively. The mean optimal angle of the OSIC was 90.2° with a maximum deviation angle from optimal angle of 10° dorsally and 8.8° ventrally in thoracic vertebrae, and 90.5° with a maximum deviation angle from the optimal angle of 8.4° dorsally and 7.6° ventrally in lumbar vertebrae. Corridors drilled in the vertebral body perpendicular to the midsagital plane (90°) or with a small angle (≤10°) of deviation from the optimal angle provide an optimal safe placement of bicortical implants. However, perpendicular implant placement may not always be feasible due to surrounding soft tissue structures.

Bicortical Implant Insertion in Caudal Cervical Spondylomyelopathy: A Computed Tomography Simulation in Affected Doberman Pinschers

To evaluate the safety of the angle of insertion of bicortical implants in Doberman Pinschers affected by caudal cervical spondylomyelopathy (CCSM) using simulation on computed tomography (CT) images. Doberman Pinschers (n=9) with dynamic spinal compression attributed to CCSM. Dogs had CT evaluation of the cervical vertebral column. Digital images were used to evaluate the safety of bicortical implant insertion from the midline at 30, 35, and 40 degrees inclination by drawing a line simulating implant position. Correct surgical positioning of dogs was evaluated by measuring the degree of rotation of the spine along the longitudinal axis. Insertion of an implant at 30, 35, and 40 degrees inclination was considered safe in 42%, 59%, and 67% of selected sites. Rotation of the spine from 9 degrees counter clockwise to 10 degrees clockwise along the longitudinal axis occurred in 53% of the areas considered. These results suggest that bicortical implants in the caudal cervical area in Doberman Pinschers affected by CCSM carry a high risk of vertebral canal and intervertebral foramina violation. Bicortical implants inserted at 30 and 35 degrees in the caudal cervical area in Doberman Pinschers affected by CCSM carry a high risk of vertebral canal and intervertebral foramina violation. CT planning for individual dogs can facilitate selection of the appropriate insertion plane and vertebral column rotation needs to be considered in surgical planning.

Treatment of an anterior single edentulous space with a bicortical screw implant

Dentistry has undergone many changes during the past quarter century; however, no changes have been more profound than those in the field of implant dentistry. With the introduction of the concept of osseointegration by Per-Ingvar Branemark and continued research in this area, the success rate of implants has been continuously increasing. However, the cost and time factor for healing and tissue integration and the need for ideal ridge forms with good bone in terms of both quality and quantity have been drawbacks of implant dentistry techniques. Bicortical implants minimize these drawbacks and provide an alternative treatment of choice. This article focuses on the placement of a bicortical screw implant to anchor a metal ceramic crown in the missing right lateral incisor region and restoring esthetics with contouring and composite veneering in the upper anterior region of a 21 year-old male patient's mouth.

Influence of Bicortical or Monocortical Anchorage on Maxillary Implant Stability: A 15-Year Retrospective Study of Brånemark System Implants

Influence of Bicortical or Monocortical Anchorage on Maxillary Implant Stability: A 15-Year Retrospective Study of Brånemark System Implants C.J. Ivanoff, K. Gröndahl, C. Berström, et al., Int J Oral Maxillofac Implants. 2000;15:103–110 In the literature, there is considerable debate over the benefits of bicortical stabilization of implants. The purpose of this retrospective study was to evaluate, over a 15-year follow-up period, implant survival and marginal bone loss in the maxilla as a function of either monocortical (MC) or bicortical (BC) implant stabilization. The following selection criteria were used to develop an investigative sample drawn from a patient population treated from 1977 to 1983: edentulous patients were provided with 10-mm long Brånemark implants independent of bone quality. Any patients who were treated with grafts or implants of different length or design were excluded. Based on these selection criteria, a patient population consisting of 20 women and 17 men, having a mean age of 50 years (range 31 to 73 years), was evaluated. The study encompassed 37 maxillary arches giving a total 207 implants for analysis. Radiographic verification via a panoramic image of either monocortical or bicortical stabilization was accomplished by ascertaining if the apical portion of the implant either engaged the anterior or inferior border of the maxillary sinus or floor of the nasal cavity. Following this procedure, three examiners classified 110 implants as MC and 97 as BC. An equal distribution amongst the patient group was found with respect to the ratio of MC or BC implants per patient. Implant survival was assessed by patient records. Marginal bone levels were assessed using intraoral radiographs in relation to a fixed point on the implant. Measurements were made under magnification to the nearest 0.1 mm. Of the original 37 patients, 30 were available after 5 years, 23 after 10 years, and 16 after 15 years. In terms of the drop-out rate’s effect on results, 35% of the MC implants and 45% of the BC implants were lost to follow-up by year 15. Of the 207 implants, a total of 18 (8.7%) failed during the follow-up period. In regards to status of MC or BC stabilization, the survival rates were 96.2% and 84.8%, respectively. The MC group showed four (3.6%) failures out of 110 implants, all four of which fractured. The BC group showed 14 (14.4%) failures out of 97 implants. Of the 14 failures, 11 of the failures were due to fracture (three times higher than MC group), whereas the remaining three failed (all in one patient) due to a loss of integration. Sixteen of the total 18 failures occurred in three patients, who had a high ratio of BC implants. Other variables that may influence implant survival such as smoking, opposing occlusion, cantilever length, and parafunction were not evaluated. As for marginal bone loss, less than 1.0 mm of change was observed over the 15-year period regardless of type of implant anchorage. This study found a four times higher failure rate amongst BC implants versus those with MC stabilization, whereas no difference in marginal bone loss could be observed between the two groups. Although the results of this study should be interpreted with caution, the fact that this paper assesses the concept of either monocortical or bicortical stabilization for implants of equal length is unique.

The stability of bone screws in the os sacrum.

A variety of points of insertion and implantation techniques are recommended for inserting screws into the os sacrum. On the basis of 16 complete human sacrum specimens the following axial pull-out tests were performed: 1. Insertion of convergent measuring screws, 6.0 mm and 7.0 mm in outside diameter respectively, into the body of vertebra S1 using a monocortical and bicortical technique respectively with perforation of the ventral cortex. 2. Insertion of divergent screws into the ala sacralis at the level of S1 with 6-mm and 7 mm screws respectively, using a monocortical technique without perforation of the ventral cortex. 3. Insertion of convergent 6-mm screws into the body of vertebra S2 using a monocortical and bicortical technique respectively with perforation of the ventral cortex. The highest axial pull-out force was reached using convergent 6-mm screws inserted into the body of vertebra S1 using the bicortical technique with perforation of the ventral cortex (2392.4 N). The use of a 7.0-mm screw in the same implantation technique did not result in higher pull-out forces (2274.7 N). The monocortical technique reached a pull-out force of 1657.53 N with a 6-mm screw and 1505.64 N with a 7-mm screw. Convergent insertion of 6-mm screws into the body of S2 resulted in pull-out forces of 537.02 N using a bicortical and only 297.71 N using a monocortical technique. Divergent insertion of screws into the ala sacralis reached a maximal pull-out force of 495.47 N using 6-mm screws and 449.79 N using 7-mm screws. These data resulted from a monocortical implantation technique without perforation of the ventral cortex of the ala sacralis. The results of the present biomechanical study show that convergent bicortical implantation in the body of S1 is the most stable technique for screw fixation in the sacrum. The use of 7-mm rather than 6-mm screws did not lead to increased primary stability. Anatomic studies have shown that a safe area exists in the region of the ventral promontory, so this implantation technique appears to be unobjectionable.

Reintegration of mobilized titanium implants: An experimental study in rabbit tibia

The possibility of re-establishing a rigid bone-implant fixation, i.e. osseointegration, after mechanical loosening of titanium implants, was evaluated in the rabbit tibia. Implants were inserted to engage either one (10 mm long, n=24) or two (16 mm long, n=24) cortical layers and were allowed to heal for six weeks. A re-entry was then made and 12 test implants in each group subjected to a reverse torque procedure until the integration failed. The remaining nonrotated 24 implants were left as controls. Thereafter all implants were allowed to heal for an additional period of six weeks. At the end of the 12 weeks, the degree of integration was assessed by measuring the removal torque for six test and six control implants in each group of implant lengths. Histomorphometric measurements were also performed on ground sections of the remaining test and control implants. A statistically significant higher removal torque was observed for the monocortical test implants than for the corresponding control implants. No differences were seen for the bicortical implants of either kind, however, no morphological differences could be revealed either, when comparing monocortical and bicortical test and control implants. These results indicate that osseointegrated implants that have been mobilized due to a traumatic disruption of the bone-implant interface, may reintegrate if allowed to heal for an additional period of time.

Influence of mono- and bicortical anchorage on the integration of titanium implants: A study in the rabbit tibia

The study aimed to evaluate the removal torque and bone tissue response to titanium implants supported by one or two cortical layers. A total of 72 screw titanium implants, either 10 or 16 mm in length and 3.75 mm in diameter, were inserted in right and left tibiae of 18 adult New Zealand rabbits. The implants engaged either one or two cortical layers, and the animals were allowed a healing period of 6 or 12 weeks. The degree of integration was assessed by measuring the removal torque with a torque gauge manometer. Histomorphometric calculations were also performed in 10-μm-thick ground sections. All implants were clinically stable at the end of the experiment. The removal torque was two times higher for the bicortical implants after 6 weeks, and three times higher after 12 weeks, than for the monocortical ones. The 16-mm implants also showed a statistically higher amount of bone contact and bone area after 6 and 12 weeks, respectively, than the short ones. The results support bicortical anchorage of implants also in the clinical situation.

Damping characteristics of bone‐to‐implant interface; A clinical study with the Periotest® device.

The Periotest device was used to evaluate the damping characteristics of different bone-to-implant interfaces of Brånemark implants. Implant and abutment lengths were found to have a significant influence on Periotest value (PTV). There was no statistical difference between PTVs of implants located in the anterior and posterior areas of the same jaw at abutment connection. No differences were found between PTVs of standard and self-tapping implants. PTVs at abutment connection were highly influenced by the bone quality. The contact with two corticals, one at each extremity of the implant, was of a greater influence in the maxillary than in the mandibular jaw, indicating a firmer anchorage between the bi-cortical implants and the surrounding bone. A progressive decrease of PTVs over time was observed, significant up to 5 years of loading.