A Comparison of Dental Implants With Titanium Implants

Transcription

1 Monograph: Dental implants type SEMADOS Active components SEMADOS implants are made of titanium. The component surfaces are Al 2 O 3 blasted. Pharmacology, pharmacokinetics, toxicology Pharmacokinetic studies are not available. Titanium does not have any known physiologic functions [88]. Titanium corrosion has been described as follows: (1) Disadvantages. Susceptibility to complexing agents like fluorides; reduced wear resistance if the α-case is thick. (2) Advantages. Spontaneous passivation and repassivation; quantitatively insignificant solubility product of TiO 2 ; electrical non-conductivity of passive layers; excellent biocompatibility of titanium and its reaction products [131]. In various cell cultures titanium was well tolerated at the cellular level. Cytotoxic effects were absent [1, 2, 4]. Used as implant material, titanium showed insignificant tissue reactions after subcutaneous placement comparable to those of teflon [3]. The effects of long-term orthodontic forces applied to titanium implants (Branemark size 10 x 3.75 mm) on the amount of peri- and para-implant bone and on the percent bone-toimplant contacts were investigated in 2 foxhounds. Six premolars (P3 mandible/maxilla and P4 mandible) were extracted and replaced by 6 implants (P3 and P4) 12 weeks later. After a healing time of 25 weeks the P3 fixtures were used for orthodontic anchorage (test fixtures) to distalize P2 for 26 weeks (continuous force ~N). The P4 fixtures in the mandible served as controls. On histologic analysis the mandibular test fixtures differed from the mandibular controls in several respects: thicker cortical bone; thicker peri-implant bone sheath; thicker partly sclerotic cancellous bone (on the side exposed to compressive Page 1 / 9

2 forces) and thicker trabeculae (on the side exposed to tensile forces). Fluorescence microscopy showed these phenomena to be attributable to extensive deposition of lamellar bone during the application of orthodontic forces. Around the maxillary test implants, by contrast, much less lamellar bone was deposited. The mean percent bone-to-implant contacts were: 40.5% for mandibular controls (n = 4) 51.6% for mandibular test fixtures (n = 4) 42.2% for maxillary test fixtures (n = 4) [120]. In miniature pigs titanium particles were shown to accumulate locally at the implant site. The titanium concentration in the lungs, kidneys and liver were significantly higher than in the controls. The clinical significance of these findings is still poorly understood. Systemic toxicity related to titanium implants has so far not been reported [88]. Biocompatibility Biocompatibility is a function of the chemical species and the ultrastructural surface topography. It is best defined by the ability of a material to perform with an appropriate host response in a specific application [88]. Originally, osseointegration was defined as direct contact between living bone and the implant documented by light microscopy. This definition is no longer considered to be adequate, because the presence of a nonmineralized interface with a thickness of 100 A on the titanium (CPTi, commercially pure titanium) surface does not necessarily imply an inappropriate host response. Clinical longterm results with CPTi fixtures ad modum Branemark [88] argue in favor of an excellent biocompatibility. However, the clinical fate of Branemark fixtures cannot automatically be extrapolated to other systems, even if the base material is the same. [88]. The excellent biocompatibility of CPTi, which has been attributed to the surface oxide layer, is well documented [30, 88]. But the presence of an inert oxide layer does not suggest a static condition between the oxide and the surrounding biologic environment [88]. Page 2 / 9

3 The surface of CPTi is coated with an oxide layer (mainly TiO 2 ). This layer is 3 mm to 5 mm thick. Although TiO 2 is a metal oxide, its surface properties match those of a ceramic material. Several trace elements are present on the implant surface including F, Na, Cl, Ca and Mg. These were detected on the surfaces of Steri-Oss, IMZ and Branemark implants by spectroscopy. Quantitatively, they are in the submonolayer range so that their presence is unlikely to cause any problems clinically [30, 88, 178]. The large amounts of carbon detected on Core-vent, Screw-vent and Osseodent implants were attributed to surface contamination [88]. Various methods are used for cleaning and sterilizing implant surfaces, among them endodontic glass beads, vapor, dry heat, ultrasound plus detergent, chemicals (nitric acid), ultraviolet radiation, argon plasma, etc. All of these methods modify the chemical composition of the surface in one or the other way and may, but need not modify the surface topography [88], (see also [117]. For laser treatment and temperature changes at the bone-to-implant interface, see [32]. In vitro, the cleanliness of implant surfaces can also be assessed by the surface energy. Ceramics and metals are materials with a high surface energy. Organic matter contaminating the implant surface reduces the surface energy. The surface energy of an implant material was studied indirectly with the sessile drop method. UV radiation, argon plasma spraying and other methods increased the surface energy. The increase in surface energy was associated with an increase in cell attachment and implant fixation. Unlike in earlier studies, there was no difference in surface energy and thickness of the oxide layer between autoclaved Branemark fixtures and those sterilized as prescribed in the manufacturer s protocol. The effects of sterilization on cellular reactions were also investigated in animal models. Different sterilizing methods were found to have different effects on bone apposition. But torque analyses failed to show significant differences between variably sterilized titanium implants. In spectroscopic studies, by contrast, the surface composition of implants differed as a function of the method used for sterilization. What these data mean clinically is not yet clear [22, 88]. For bacterial colonization, plaque accumulation and gingivitis with titanium implants, see [26,40,54]. Page 3 / 9

4 For inflammatory reactions of peri-implant soft tissues, see [91]. Albumin is one of the main components of the salivary biofilm formed on titanium implants. Its adsorption depends on Ca. The presence of albumin may affect plaque accumulation and biocompatibility [53]. The calcium phosphate formed on the titanium oxide layer was closer to apatite than other alloys studied (Ti-6A1-4V, Ti-50Ni, 316L-stainless steel, Co-30Cr-5.Ni, Ni-20Cr, Au-9Cu- 6Ag, Ag-20Pd-15Cu-12Au) [88]. For osseointegration and factors affecting bone loss, see [19,21,23,24,25,28,29,31, 38,42,,45,49,60,62,73,74,75,78,79,86,93,103,122,126,128,134,152,172]. Mechanical properties of the bone-to-implant interface are dealt with in [58]. See also [61,80,119]. In an animal model hydroxyapatite (HA) coated cylindrical implants showed more percent bone-to-implant contacts 8 weeks after placement than cylindrical Ti-6Al-4V implants gritblasted with 24-grit Al 2 O 3 particles at 60 to 80 psi for 10 s [88]. In another study the interfacial shear strength of the bone around HA-coated cylindrical implants was higher at 5, 10 and 32 weeks than that around grit-blasted cylindrical Ti-6Al- 4V implants. Other authors found the percent bone-to-implant contacts on HA-coated perforated hollow cylinders (original IMZ coating; Dr. A. Kirsch, DE-Filderstadt) to be higher at 6 weeks than on perforated CPTi hollow cylinders [88]. Although there is considerable evidence suggesting that more bone is deposited on HAcoated implant materials, the clinical relevance still needs to be shown [88]. All in all, the local host bone initially (within the first few months) appears to react earlier to HA-coated implants with more bone-to-implant contacts. This suggests that the HAcoating is osteoconductive. But over time, HA-coated implants appear to show fewer boneto-implant contacts than CPTi implants. The mechanisms underlying this phenomenon are unknown and the clinical implications are still poorly understood [30]. See also [18,20,25,27,44,48,98,118,135,152,163]. For ceramic oxide, see [101]. In [72] the response of the local bone to HA-coated or Al 2 O 3 blasted titanium implants was investigated. Both coatings were found to be highly histocompatible biologically. Page 4 / 9

5 In a more recent definition osseointegration is described as a process leading to asymptotic rigid fixation of alloplastic materials, which is maintained during functional loading [30]. With osseointegrated implants (Branemark) the bone-to-metal interface consists of a TiO 2 layer and a protein (glycosaminoglycane) [30]. Fibro-integration (soft tissue to implant contact) is the term used for normal dense collagenous tissue interposed between the implant and the bone. When fibro-integrated implants are loaded, the fibrous capsule thickens. This may lead to implant mobility or even failure. Even small amounts of fibrous tissue interposed between cylindrical root-form endosseous implants (Branemark fixtures) were shown to be a potential cause of implant failure. Therefore, fibro-integrated implants are increasingly being replaced by osseointegrated systems [30]. The connective tissue sheath forming around fibro-integrated implants is less resistant to plaque and bacterial products [30]. Two types of osseointegration have recently been distinguished, i.e. adaptive osseointegration (bone tissue on the implant surface without a manifest connective tissue interface) and bio-integration (direct biochemical bonding to the surface on electron microscopy). Current interest focuses on whether materials like fibronectin, osteonectin or other growth factors facilitate the attachment of fibroblasts or osteoblasts to implant surfaces and support the implant-to-tissue interface. Preliminary studies with plateletderived growth factor (PDGF) and insulin-like growth factor I showed a positive trend. In other studies bone morphogenetic protein (BMP) and bovine serum albumin (BSA) were examined for their effects on the osseointegration of uncoated cylindrical endosseous implants placed in edentulous dogs. In the BMP-treated group osseointegration was almost complete at no more than 4 weeks. This was much earlier than in the control group treated with BSA. The use of various matrix proteins and growth factors might thus boost the osseointegration of implants [30,59,138,151,153,173]. In Beagles titanium was detected in the regional lymph nodes after placing titanium screws in the maxillofacial region [108]. Page 5 / 9

6 Clinical trials, case reports Repeated overloading of oral implants causes peri-implant bone loss. Overloading is due to parafunctions (bruxism), non-axial forces (poor occlusal scheme, oblique implant axis relative to the occlusal plane, hyperbalances, cantilevers or prosthodontically unfavorable implant position) and poor fit of the suprastructure. To assess the usefulness of titanium frameworks of implant-supported dentures, metal suprastructures of gold were compared clinically with frameworks of titanium. The performance of both suprastructures supported by implants matched that of natural teeth [131, 41]. In a long-term study veneer crowns and titanium bridges were examined for their susceptibility to caries, color fastness and marginal integrity at various time points after cementing, i.e. 0 (= cementing), 14 to 18 months later and 24 to 30 months post cementing. Of 45 units in 22 patients, no more than 2 crowns were lost secondary to ceramic fractures and were rated as failures. Failures due to caries or poor marginal integrity were absent [131]. 173 IMZ two-stage implants placed in the anterior maxilla of 81 patients to replace incisors, canines and premolars were followed clinically and radiologically for 5 years. They were made of titanium and coated with HA and supported either non-removable or removable partial dentures or single crowns. Cumulative implant stability at 3 years was 96.1 % [81]. In a 10-year follow-up study of 136 patients with IMZ and TPS implants placed in the edentulous mandible the 5-year success rate was reported to be 83 % to 97 % [97]. In a controlled clinical trial comparing IMZ implants and Branemark fixtures the mean bone loss after functional loading for 6 to 12 months was 1.68 mm and 0.69 mm, respectively. Whether this difference is attributable to the implant surface, the implant shape or both is unknown [88]. See also [120]. For clinical data, see also [20,39,82,83,85,87,90,96,100,114,115,121,130,136,142, 143,147, 148,149,154,155,156,169]. Page 6 / 9

7 A peri-apical abscess related to a root-form maxillary implant, which necessitated the removal of the implant, was described in a single case report [56]. For local bone grafting with the micro-titanium mesh for alveolar ridge augmentation (Time technique), see [17,92] and for the Procera technique, see [67, 94, 95]. Clinical data (1) Indications For placement in human alveolar bone to support artificial teeth replacing natural teeth. (2) Contraindications None known. (3) Side effects None known. (4) Special precautions for safe use None. (5) Pregnancy and lactation No limitations known. (6) Drug and other interactions Galvanic coupling to dental alloys with a high corrosive potential may induce corrosive reactions. (7) Dosage and mode of application The implants are screwed into cavities formed by drilling. For seating them the self-tapping properties of the threaded component may be used. In hard bone a tap may be used additionally for pretapping the cavity. The implant features a connector accommodating the components needed to support the prosthodontic work. (8) Overdosage Not applicable. (9) Special warnings None. Page 7 / 9

8 (10) Effects on driving vehicles or operating machines None. Note Titanium has become an established implant material. Currently both primary components (implants) and secondary components (suprastructures) are available in titanium. Despite initial problems with brittle margins and poor fit the casting technique is well accepted. Esthetically, the use of titanium may be associated with problems of a metallurgic nature. The massive oxygen reaction of titanium at high temperatures and its passage to the unfavorable cubic spatial ß-phase necessitate the use of low-fusing ceramics. Metallurgic aspects should also be considered for anchoring titanium components. Conventional thermal techniques (e.g. titanium casting) may cause problems attributable to the strong oxygen reactions. These can, however, be overcome by suitable casting techniques [131]. For cast titanium MgO embedding proved to be beneficial [3]. In animal experiments cold-worked titanium was better tolerated than cast titanium [3]. Biologic, mechanical and esthetic criteria are dealt with in a number of publications [43,64,69,76,89,202,258,274,275]. For heat generation during cavity preparation for titanium implants, see [46,99,167]. Titanium and titanium-based alloys are subject to less wear than precious metal alloys [55]. Particle abrasion from the surface of endosseous implants depends on the implant shape and coating. In vitro, longer implants were shown to produce more wear particles than cylindrical implants, and screw-shaped implants produced more wear particles than cylindrical implants. Polished surfaces showed less particle abrasion [109]. For stress analysis of osseointegrated implants, see [110, 113]. A torque of 35 Ncm was recommended for tightening abutments [102]. The relations between Periotest scores, biomaterials and torque were dealt with in a study in baboons designed to shed light on implant stability [105]. A comparative study of antirotation single-tooth abutments showed the hex design to provide the best single-tooth stability [106]. Page 8 / 9

9 The designs and surface properties of 13 commercially available implant systems are described in [150]. In 30 dogs 120 ceramic and titanium implants (cylindrical implants and blades) were compared for one year [166]. To support the distal cantilevers of dentures a new system (JL system) consisting of a short implant and a ball attachment was developed and proved to be superior to conventional dentures [85]. A new system, the Endopore Dental Implant System, which is quite distinct from other systems and designed for easy handling, has recently been described [129]. The ADA/CDMIE (American Dental Association/Council on Dental Materials, Instruments and Equipment) defined guidelines for evaluating implant systems. Under the terms of these guidelines manufacturers are required to furnish data based on 2 independent clinical trials with a patient population of at least 50 each. The variables to be evaluated include mobility, bone loss, gingival health, pocket depth and effects on adjacent teeth. 3-year data are required for provisional acceptance and 5-year data for full acceptance. Since 1992 full acceptance has been granted at a documented 5-year success rate of 85%. 5-year success rates should not be more than 5% lower than the 3-year data. In 1993 the ADA granted full acceptance to 3 endosseous implant systems (Branemark fixtures, IMZ 4.0-mm implant system and One-stage Oratronics Weiss Standard Blade implant system) and provisional acceptance to another 6 systems [88] (Table 1). For mandibular Branemark fixtures the 5-year success rate was reported to be 99 % versus 85 % for maxillary fixtures [30] (Table 1 and pp... ). Based on the evidence available in November 1996 Page 9 / 9