Lars Sennerby

Implant stability measurements using resonance frequency analysis: Biological and biomechanical aspects and clinical implications

Osseointegrated implants for prosthetic rehabilitation of the edentulous patient show high success rates if certain preconditions are fulfilled. Implant stability plays a critical role for a successful critical outcome since short implants and implants placed in soft bone are more prone to failure (13, 49). In the original protocols for implant placement, primary implant stability was ensured by new bone formation and remodelling, termed osseointegration, which was accomplished during an initial healing period in which implants remained nonloaded to secure undisturbed bone formation onto the implant surface. The process of osseointegration increases the stiffness of the bone around the implant, and the bony interlock with the implant surface prevents micro-movement and the formation of fibrous scar tissue at the time of implant loading. However, the development of new implant surfaces and clinical techniques has enabled a marked reduction of the initial healing period, even to the point of an immediate ⁄ early loading of implants that show high primary stability (7, 37). Thus, the success of immediate ⁄ early loading implant techniques is dependent on the ability of the clinician to determine the degree of primary implant stability and changes in stability along with new bone formation and remodelling. The clinical perception of primary implant stability is frequently based on the cutting resistance of the implant during its insertion. The feeling of good stability may be accentuated if there is the sense of an abrupt stop at the seating of the implant. Root forms of tapered implants often have a geometry that will provide a firm stop and perhaps a false perception of high stability. A percussion test has also been used to assess implant stability. The percussion test may involve the tapping of a mirror handle against the implant carrier and is designed to elicit a ringing sound from the implant as an indication of good stability or osseointegration. Percussion tests probably provide more information about the tapping instrument, and will at best only yield poor qualitative information. Insertion torque measurements are sometimes used to determine primary implant stability (6). Application of a reverse or unscrewing torque has also been proposed for the assessment of implant stability at the time of abutment connection (53). Implants that rotate under the applied torque are considered failures and are then removed. However, an implant surface in the process of osseointegrating, albeit slowly, may fracture under the applied torque stress. Moreover, as animal experiments have demonstrated the re-integration of loosened and rotationally mobile implants (26), the reverse torque testing has fallen into disrepute. Other techniques, such as the Periotest and resonance frequency analysis, aim to provide an objective measure of implant stability and osseointegration that is noninvasive and does not damage the implant–tissue interface (6, 28). The resonance frequency analysis technique has been extensively used in experimental and clinical research for the last 10 years. The purpose of this

Stability measurements of one-stage Brånemark implants during healing in mandibles: A clinical resonance frequency analysis study

Using a one-stage surgical protocol, 75 implants ad modum Brånemark of three different designs were inserted in 15 edentulous mandibles of high bone density. All implants were followed with repeated stability measurements by means of resonance frequency analysis (RFA) from implant placement to connection of the fixed prostheses (3-4 months), in order to evaluate possible stability changes during healing. It was shown that the resonance frequency (RF) values slightly decreased for the majority of the implants during the study period independent of design. Consequently, the results of the present study indicated that the implants were as stable at time of placement as when measured at 3-4 months post-surgery, i.e. when the prostheses were attached. The available data support the concept of direct loading of implants when inserted between the mental interforaminal regions. One implant failed during healing and the corresponding RF measurement disclosed, at six weeks post-surgery, a value being far below the one registered at implant placement. The lowered RF value indicated the failure several weeks before the mobility was clinically diagnosed. The presence or absence of a fixture/abutment junction did not exert any influence on the marginal bone level, as determined radiographically at the end of the short investigation period.

Influence of implant diameters on the integration of screw implants: An experimental study in rabbits

The influence of diameter on the integration of titanium screw-shaped implants was studied in the rabbit tibia by means of removal torque measurements and histomorphometry. Implants 3.0, 3.75, 5.0, and 6.0 mm in diameter and 6.0 mm long were inserted through one cortical layer in the tibial metaphyses of nine rabbits and allowed to heal for 12 weeks. The implants were then unscrewed with a torque gauge, and the peak torque required to shear off the implants was recorded. The histologic analysis in undemineralized ground sections comprised (1) a gross description of the implant sites and assessments of (2) the total implant length in bone and (3) in the cortical passage, as well as (4) the thickness of the cortical bone adjacent to the implants. From the removal torque values obtained and morphometric measurements, a mean shear stress value was calculated for each implant type. The biomechanical tests showed a statistically significant increase of removal torque with increasing implant diameter. The resistance to shear seemed to be determined by the implant surface in supportive cortical bone, whereas the newly formed bone at the periosteal and endosteal surfaces did not seem to have any supportive properties after 12 weeks. It is suggested that wide diameter implants may be used clinically to increase implant stability.

Bone Formation at the Maxillary Sinus Floor Following Simultaneous Elevation of the Mucosal Lining and Implant Installation Without Graft Material: An Evaluation of 20 Patients Treated With 44 Astra Tech Implants

PURPOSE Restoration of lost dentition in the severely artrophic posterior maxilla has for the last 2 decades been successfully treated with various sinus augmentation techniques and installation of dental implants. The use of graft material is anticipated to be necessary; however, recent studies have demonstrated that the mere lifting of the sinus mucosal lining and simultaneous placement of implants result in bone formation. This study was conducted in order to evaluate simultaneous sinus mucosal lining elevation and installation of dental implants without any graft material. PATIENTS AND METHODS Twenty patients were consecutively included from November 2001 to June 2004. Forty-four Astra ST dental implants (Astra Tech AB, Mölndal, Sweden) with a diameter of 4.5 mm or 5 mm were installed in 27 sinuses. A sinus lift was performed where a cortical window was removed from the maxillary anterior sinus wall. The sinus mucosal lining was elevated and implants installed in the residual subantral bone. The cortical window was thereafter replaced and the incision closed. The remaining bone height was recorded during surgery as well as perforations of the sinus mucosal lining. After 6 months of healing, abutments were connected (the series included 5 1-stage procedures). Clinical and radiological follow-up after loading was performed up to 4 years after implant installation. RESULTS Patients tolerated the procedure well as few complications were observed. Firm primary stability was achieved for all implants at installation with bone levels in residual bone of 2 to 9 mm. Perforations of the maxillary sinus mucosal lining occurred in 11 of the 27 operated sinuses (41%). One implant was lost during a mean follow-up of 27.5 months (range, 14 to 45 months) giving an implant survival rate of 97.7%. The average gain of bone at the sinus floor was 6.51 mm (SD = 2.49, 44 implants) including all measured implants after a minimum of 1 year follow-up. Marked bone formation was observed around long implants and also when the residual bone below the sinus was diminutive. CONCLUSIONS The present study including 20 patients showed consistent bone formation at the maxillary sinus floor following simultaneous mucosal lining elevation and installation of implants. It is suggested that the use of this technique can reduce the risk for morbidity related to harvesting of bone grafts and eliminate costs for grafting materials.

State of the art of oral implants.

Objectives: The aim of this prospective study was to evaluate the Nobel Direct® and Nobel Perfect® one-piece implants (OPIs) when used for immediate function. Material and methods: Forty-eight pati ...

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-microns-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.

Early tissue response to titanium implants inserted in rabbit cortical bone

The tissue response to screw-shaped implants of commercially pure titanium was studied 3–180 days after insertion in the rabbit tibia by means of transmission electron microscopy. Red blood cells and scattered macrophages predominated at the implant surface after 3 days. At day 7 and later intervals, multinuclear giant cells were the cell type found at the implant surface protruding into the bone marrow and in areas with no bone-titanium contact. Osteoblasts or mesenchymal cells were rarely seen at the implant surface at any time period. Two modes of mineralization could be distinguished in the interface. Firstly, the typical mineralization of osteoid seams produced by osteoblasts. Secondly, an accumulation of scattered hydroxyapatite crystals in the unmineralized collagen matrix in the interface. Mineralized tissue was observed close to the implants surface from day 14. However, the innermost 2–20 μm were poorly mineralized although scattered hydroxyapatite crystals were present. The collagen fibrils did not reach the implant surface but were separated from it by an amorphous layer, being 0.3–0.5 μm thick which did not decrease in width with time. An electron-dense lamina limitans-like line containing mineral was observed between the amorphous layer and the bone tissue.

Histologic investigations on 33 retrieved Nobelpharma implants.

Thirty Nobelpharma implants were retrieved from 17 patients despite a remaining clinical stability, after between 1 and 16 years of clinical function. The reasons for implant removal were bone resorption in combination with soft tissue disorders, psychological causes, implant fracture and post mortem cases. When measured at the cortical passage, there was an average of 84.9% direct bone-to-implant contact and 81.8% average surface bone area in individual threads as evaluated in a computerized morphometric system at the light microscopic level.

Is marginal bone loss around oral implants the result of a provoked foreign body reaction

BACKGROUND When a foreign body is placed in bone or soft tissue, an inflammatory reaction inevitably develops. Hence, osseointegration is but a foreign body response to the implant, which according to classic pathology is a chronic inflammatory response and characterized by bone embedding/separation of the implant from the body. PURPOSE The aim of this paper is to suggest an alternative way of looking at the reason for marginal bone loss as a complication to treatment rather than a disease process. MATERIALS AND METHODS The present paper is authored as a narrative review contribution. RESULTS The implant-enveloping bone has sparse blood circulation and is lacking proper innervation in clear contrast to natural teeth that are anchored in bone by a periodontal ligament rich in blood vessels and nerves. Fortunately, a balanced, steady state situation of the inevitable foreign body response will be established for the great majority of implants, seen as maintained osseointegration with no or only very little marginal bone loss. Marginal bone resorption around the implant is the result of different tissue reactions coupled to the foreign body response and is not primarily related to biofilm-mediated infectious processes as in the pathogenesis of periodontitis around teeth. This means that initial marginal bone resorption around implants represents a reaction to treatment and is not at all a disease process. There is clear evidence that the initial foreign body response to the implant can be sustained and aggravated by various factors related to implant hardware, patient characteristics, surgical and/or prosthodontic mishaps, which may lead to significant marginal bone loss and possibly to implant failure. Admittedly, once severe marginal bone loss has developed, a secondary biofilm-mediated infection may follow as a complication to the already established bone loss. CONCLUSIONS The present authors regard researchers seeing marginal bone loss as a periodontitis-like disease to be on the wrong track; the onset of marginal bone loss around oral implants depends in reality on a dis-balanced foreign body response.

Evaluation of a new titanium-zirconium dental implant: a biomechanical and histological comparative study in the mini pig.

BACKGROUND Titanium zirconium alloy with 13-17% zirconium (TiZr1317) shows significantly better mechanical attributes than pure Ti with respect to elongation and fatigue strength. This material may be suitable for thin implants and implant components exposed to high mechanical constraints. PURPOSE The aim of this study was to test the hypothesis that TiZr1317 and Ti implants show comparable osseointegration and stability. MATERIALS AND METHODS The mandibular premolars (P1, P2, P3) and the first molar (M1) in 12 adult miniature pigs were extracted 3 months prior to the study. Six specially designed implants made from Ti (commercially pure, Grade 4) or TiZr1317 (Roxolid®, Institut Straumann AG, Basel, Switzerland) with a hydrophilic sandblasted and acid-etched (SLActive, Institut Straumann AG, Basel, Switzerland) surface were placed in each mandible; three standard implants modified for evaluation of removal torque (RT) in one side and three bone-chamber implants for histologic observations in the contralateral side. RT tests were performed after 4 weeks when also the bone chamber implants and surrounding tissue were biopsied for histologic analyses in ground sections. RESULTS The RT results indicated significantly higher stability (p=0.013) for TiZr1317 (230.9±22.4Ncm) than for Ti implants (204.7±24.0Ncm). The histology showed similar osteoconductive properties for both implant types. Histomorphometric measurements showed a statistically significant higher (p=0.023) bone area within the chamber for the TiZr1317 implants (45.5±13.2%) than did the Ti implants (40.2±15.2%). No difference was observed concerning the bone to implant contact between the groups with 72.3±20.5% for Ti and 70.2±17.3% for TiZr1317 implants. CONCLUSION It is concluded that the TiZr1317 implant with a hydrophilic sandblasted and acid-etched surface showed similar or even stronger bone tissue responses than the Ti control implant.