Brånemark System and ITI Dental Implant System for treatment of mandibular edentulism. A comparative randomized study: 3-year follow-up.

In a randomized prospective study, two implant systems were compared in forty consecutive patients treated for mandibular edentulism. The patients were randomly allotted for treatment by the Brånemark two-stage (submerged) system (BRS), or the ITI(R) one-stage (non-submerged) system. In all, 102 Brånemark selftapping implants and 106 ITI hollow screw implants were installed and all patients were treated with full bridges. Biological and prosthodontic parameters, complications, success rates, clinical efficacy, patient satisfaction and resource requirements were evaluated. No differences were found in plaque accumulation, bleeding or complications during the follow-up period. The BRS group showed deeper periimplant sulcus, less attached mucosa, larger bridge-mucosa distance and higher Periotest values. Prosthetic complications were not related to the configuration of the implant systems. After 3 years, the cumulative success rates were 97.9% and 96.8% for the Brånemark and ITI systems, respectively (difference not statistically significant). One implant in the BRS group had failed to osseointegrate at the time of abutment connection, and another was lost after 2 years due to progressive breakdown of bone. In the ITI group, three implants showed progressive bone loss after 1-3 years associated with periimplant infection. All 40 bridges were intact and remained stable throughout the study. There was general patient satisfaction, but about half the Brånemark patients reported difficulty in coping with the surgical procedures. Treatment time was similar for the two systems. It is concluded that both systems meet the current requirements for dental implant systems in the treatment of mandibular edentulism.

Resin-bonded bridges by dental undergraduates: three-year follow-up.

This study was conducted to evaluate performance and longevity of resin-bonded bridges in patients treated by undergraduate dental students. A total of 62 bridges had been constructed for 53 patients by the students at the School of Dentistry, Karolinska Institute, between 1989 and 1997. After a mean observation period of 35.3 months retention had been lost in 13.6% of 59 bridges examined (4.6% per year). The debonding rate was greater in the mandible (8.3 %/year) than in the maxilla (2.7 %/year), and greatest in the mandibular anterior region (13.4%). Thirty-nine patients with 46 bridges (27 maxillary and 19 mandibular bridges), underwent more detailed clinical examination. No significant differences in bleeding and pocket depth were found between abutment teeth and controls. Bleeding was more frequent at the approximal than the lingual surfaces of the abutment teeth. A questionnaire revealed high patient satisfaction, the resin-bonded bridges meeting their expectations. The study suggests that resin-bonded bridges are an acceptable alternative to conventional bridges. Successful outcome is dependent on stringent case selection, an abutment preparation designed to establish retention form, and meticulous bonding procedures.

Evaluation of single-tooth restorations on ITI dental implants. A prospective study of 29 patients.

From January 1992 to March 1997, a total of 30 ITI hollow cylinder implants were installed to replace lost single maxillary incisor teeth. Conical abutments with cemented all-ceramic crowns were used in 10 cases and the Octa-abutment with screw-retained metallo-ceramic crowns in 19 cases. One implant failed due to postoperative infection, and was extracted a month after installation. After a mean observation time of 3.4 years, the cumulative success rate is 96.7%. Only minor bone loss has occurred around the implants, and there have been no other complications to date. The implant system fulfills the requirements for good function and esthetics.

Dental implant installation without antibiotic prophylaxis.

The objective of this study was to retrospectively compare the outcomes of dental implant treatment with and without antibiotic prophylaxis. Two groups of patients with edentulous or partially edentulous maxillas or mandibles (or both) were treated with dental implants. One group, consisting of 147 patients (790 implants), was given prophylaxis with oral phenoxymethylpenicillin; 1 g of antibiotic was administered 1 hour preoperatively, and 1 g was administered every 8 hours for 10 days postoperatively. The other group, consisting of 132 patients (664 implants) was not given any antibiotics preoperatively or postoperatively. There were no significant differences with respect to early and late postoperative infections or with respect to implant survival between the two groups. It appears that antibiotic prophylaxis for routine dental implant surgery offers no advantage for the patient.

Reconstruction of the resorbed edentulous maxilla using autogenous rib grafts and osseointegrated implants.

14 patients with severely resorbed edentulous maxillae underwent reconstruction by the use of autogenous rib graft on-lays and osseointegrated Brånemark System implants in a one-stage procedure. 75 implants were installed. 16 (21.3%) failed to osseointegrate at the abutment connection. After a mean observation period of 5.2 years, 55 (73.3%) of the original implants were osseointegrated. 10 supplementary implants were inserted in 3 patients. At the end of the observation periods, 2 patients had overdentures and 12 had fixed prostheses. The mean marginal bone loss was 2.13 mm (SD 0.47 mm) the 1st year after grafting, and 2.92 mm (SD 1.27 mm) at the end of the follow-up periods. Long-term follow-up did not show any persistent donor site discomfort. The results indicate that this technique is a conceivable alternative for patients with severe maxillary resorption.

Evaluation of three silicoating methods for resin-bonded prostheses.

Three different methods of increasing the bond strength of resin to metal were tested: the original Silicoater technique, the Silicoater MD technique, and the Rocatec system. Metals used for the resin-bonded prostheses were gold, a cobalt-chromium (Co-Cr) alloy, and titanium. Silicoating increased the bond strength to sandblasted specimens. The original Silicoater technique produced the highest bond strengths, especially when used with the Co-Cr alloy and titanium. The Silicoater MD technique showed the lowest bond strengths for all of the test metals. Storage for 7 days with protective film on the silicoated surface did not affect the bond strength, as compared with specimens bonded immediately. The retention of the resin to the gold specimens (Rocatec system) decreased after thermocycling, but retention to the Co-Cr alloy and titanium was not affected. Various resin cements were tested and showed the same retention with the exception of Microfill Pontic, which gave a weaker bond. Scanning electron microscope (SEM) and energy-dispersive X-ray analysis (EDAX) of the specimens before and after the measurements gave no clear explanation of the differences in bond strengths between the test metals. However, it was concluded that silicoating of the metal surfaces contributed to the retention of the resin by chemical action, as no differences in adaptation of the resin to the metal were seen between specimens pretreated by sandblasting and those which were also silicoated.

Clinical evaluation of resin-bonded prostheses.

Resin-bonded prostheses were clinically evaluated following a mean period of 41 months. The abutment teeth were minimally prepared, and one groove was placed on the surface approximating the edentulous space. Retainers were treated using the Silicoater technique. Thirty-four prostheses were made for 32 patients. Four patients were lost from the study and 30 units were re-examined. Two prostheses had debonded. The results suggest that resin-bonded prostheses can be successful if meticulous attention is given to the procedures outlined.

Low concentrations of inorganic mercury inhibit in vitro autonomic transmission in the presence of albumin.

The influence of albumin, 4.5 and 45 g/l, on the effects of Hg2+, 10(-9)-10(-3) M, on the neuromuscular transmission of the isolated guinea-pig ileum and vas deferens was investigated. Hg2+, 10(-9)-10(-6) M, transiently increased the basal tone of the ileum in Tyrode solution without albumin. Albumin, 4.5 g/l, reversed this stimulant effect but enhanced the contractile response to direct muscle stimulation. This contractile response also increased in the vas deferens. Albumin, 45 g/l, obliterated the stimulant effects of Hg2+ on the smooth muscle of the ileum but not of the vas deferens. The effects caused by higher concentrations of Hg2+, 10(-5)-10(-4) M, were only partly inhibited when albumin was present. When neurogenic contractions were elicited in the presence of albumin (45 g/l), Hg2+, 10(-9)-10(-4) M, reduced the contractions in both organs. Consequently, Hg2+ in concentrations presently considered acceptable in blood plasma (10(-9)-10(-8) M) suppressed both cholinergic and adrenergic neuromuscular transmission even in the presence of albumin.

Albumin inhibits effects of Cu2+ on autonomic postganglionic transmission of guinea-pig ileum and vas deferens.

The influence of albumin, 4.5 and 45 g/l, on the effects of Cu2+, 10(-9)-10(-3) M, on the neuromuscular transmission of the isolated guinea-pig ileum and vas deferens was investigated. Low concentrations of Cu2+, 10(-9)-10(-6) M, caused a slight and transient increase of the contractile response to direct muscle stimulation of the vas deferens. Albumin at 4.5 g/l inhibited this effect. The basal tone of the ileum increased transiently when Cu2+ was added in the presence of albumin, 4.5 g/l. A stimulant action of Cu2+, 10(-9)-10(-6) M, was seen on both organs, when contractions were induced by nerve stimulation. All these effects were inhibited by albumin, 45 g/l. Higher concentrations of Cu2+, 10(-5)-10(-4) M, increased the basal tone of the ileum and the vas deferens. In the presence of albumin, 45 g/l, this stimulating effect of Cu2+ appeared in higher concentrations. The results suggest that Cu2+ is more likely to influence the function of neuronal tissues when the concentration of protein is low.

Release of corrosion products from amalgam in phosphate containing solutions.

The effect of phosphate concentration on corrosion was compared for two types of amalgam: a conventional alloy (ANA 68) and a high-Cu admixed alloy (Dispersalloy). The test specimens were stored for 4 months in electrolytes containing 85 mM NaCl and 85 mM NaCl with 2.5, 10, or 100 mM phosphate buffer respectively. The solutions were renewed each month and analyzed for Cu, Zn, Sn, Hg, and Ag in an atomic absorption spectrophotometer. The surfaces and cross-sections of the specimens were studied in a scanning electron microscope (SEM) with an energy dispersive detector (EDAX). The corrosion products, mainly Sn-compounds, at the surface of the amalgams were less in the solutions containing high concentrations of phosphate. In cross-section subsurface corrosion of the high-Cu amalgam was observed especially in specimens immersed in the NaCl solution without phosphate. The conventional amalgam showed surface corrosion only. The decrease in release of elements with time from the conventional amalgam in all the experimental solutions might indicate passivation. For the high-Cu amalgam the release of elements increased with time, except for Cu and Sn in the solution with 100 mM phosphate, indicating that phosphate inhibits corrosion of the Cu-Sn-phases. Release of corrosion products from the high-Cu amalgam was more dependent on the presence of phosphate than the conventional amalgam.

Area ratio effects on metal ion release from amalgam in contact with gold.

The effect of area ratio, chloride concentration and brushing on amalgam in contact with gold was studied by measuring the amounts of elements released in the electrolyte. A type III gold alloy was stored for 4 months in contact with a conventional amalgam, area relations 6/1 and 6/3, in an electrolyte containing 85 mM NaCl with 10 mM phosphate buffer. A specimen with area relation 6/1 was also stored in a 10 mM NaCl solution with 10 mM phosphate buffer. The solutions were renewed each month and analyzed for Cu, Zn, Sn, Hg, and Ag in an atomic absorption spectrophotometer. Cross-sections of the amalgams were studied in a scanning electron microscope. The tendency for Sn and Cu to be released from the amalgam was greater than for the other elements. The Sn-release probably mainly originated from surface corrosion and Cu-release from subsurface corrosion. A stronger galvanic influence enhanced only the release of Cu, and to a less extent Zn. The subsurface corrosion of the amalgam and increasing release of Cu was, in contrast to the other elements, largely dependent on a high chloride concentration in the electrolyte. Light brushing of the specimens had no effect on the amounts of elements released.

In vitro and in vivo experimental studies on single crystal sapphire dental implants.

Successful attachment of the oral tissues to an endosseous dental implant relies in part on its chemical stability, nontoxic properties and maintenance of normal cell functions in the surrounding tissues. The aim of this study was therefore to investigate these 3 factors experimentally. The corrosion resistance of single crystal sapphire (alpha-Al2O3) implants was analysed with respect to the release of aluminium ions; no ions could be detected in the test solutions. The influence of single crystal sapphire on the behaviour of human epithelial cells and fibroblasts derived from biopsies of the oral mucosa, was studied. The cells were cultured in chemically defined or in low serum-containing media. Compared to the corresponding control cultures, no effects on cell morphology and growth characteristics were observed. Sapphire rods were inserted subcutaneously into rats and tissue responses were examined after 4, 8 and 12 weeks post-implantation. None or slight reactions were found in the tissues. The combined evaluation of these experimental approaches indicates that single crystal sapphire is a material well suited for biological implantation.

Marginal microhardness of corroded amalgams: a comparative in vitro study.

One conventional and two high-Cu amalgams were tested for marginal microhardness after 2 months' corrosion in an 85 mM NaCl solution. Amalgams immersed in 200 mM phosphate buffer solution were used as controls. The microhardness tests were conducted on cross-sections of the amalgams 50 microns from the surface edges. The microstructure of the amalgams was studied in SEM and the amounts of Sn, Cu, Zn, Ag, and Hg dissolved in the solutions were analyzed with an atomic absorption spectrophotometer. For the amalgams immersed in the NaCl solution the depth of corrosion after 2 months was between 50 and 400 microns. The specimens immersed in the phosphate solution showed no signs of subsurface corrosion. The marginal microhardness of all the amalgams was reduced after corrosion in the NaCl solution. The greatest microhardness in both the uncorroded and corroded states was shown in the two high-Cu amalgams. The reduction in marginal microhardness after corrosion can probably be attributed mainly to degradation of the gamma-2 phase for the conventional amalgam and to degradation of the eta' phase for the two high-Cu amalgams.

Metal release from plates used in jaw fracture treatment. A pilot study.

This study investigated the occurrence of corrosion associated with the use of metallic implants to stabilize jaw fractures. Three different types of plates, Co-Cr and Ni-Cr alloys and Titanium, were connected in vivo to the mandibular bone surface of monkeys (Cercopithecus aethiops). The animals were killed after 3 and 6 months. The mucous membrane and bone tissue were analysed for concentrations of Co, Cr, Ni, Mo, Al, and Ti by atomic absorption spectrophometry and a radiochemical neutron activation technique. With the exception of Ti, higher concentrations of all the above elements were found in the tissue near the implants when compared with contralateral controls. However, no signs of corrosion, macroscopic or microscopic, were observed on the surface of the implants.

Corrosion of dental amalgam and mercury vapor emission in vitro.

Amalgam specimens were immersed for 30 days in 1) water, 2) 0.9% NaCl in water, 3) 0.9% NaCl and 10 mM phosphate buffer in water, and 4) 0.9% NaCl, 7.7 mM phosphate, and 6.1 mM citric acid in water. The solutions were stored in stoppered glass tubes. Hg-drops were immersed in solutions 1, 2, and 3. The concentration of mercury vapor in the air above the solutions was measured once a day. After 30 days the amounts of Cu, Zn, Hg, and Ag in the solutions were analyzed by atomic absorption spectrophotometry. The results showed that 0.9% NaCl alone or in combination with the additives increased the amounts of elements released into the solutions. The concentration of Hg0 in the glass tubes increased with the amount of Hg in the solutions, with the exception of solution No. 3, from which significantly less Hg0 evaporated. The results indicate that the composition of the saliva, oral hygiene and dietary factors may be determinants of Hg0 emission from amalgams in the oral cavity.

Corrosion behavior and microhardness of three amalgams.

The marginal microhardness of three different types of amalgam was tested after 2 months' immersion in an aqueous solution of NaCl (85 mM) and phosphates (Na2HPO4 100 mM and NaH2PO4 100 mM). Amalgams immersed in distilled water were used as controls. The microhardness tests were conducted at a distance of 50 micron from the margins and at the bulk of each specimen. The solutions were analyzed for Sn, Cu, Zn, Ag, and Hg by means of atomic absorption spectrophotometry (AAS). A statistically significant reduction in the marginal microhardness after immersion in the test solution was found for the conventional and the high-Cu single composition amalgam but not for the high-Cu blended amalgam. SEM-examination of cross-sections of the amalgams revealed small areas of subsurface grain boundary corrosion, no deeper than 10 micron for all the amalgams. The SEM-examination of the specimens and AAS analysis of the solutions indicated that the reduction in marginal microhardness was attributed mainly to corrosion of the Cu-rich phases for the high-Cu single composition amalgam and to corrosion of the gamma 2 phase for the conventional amalgam. The phosphates reduced the corrosion of the amalgams in the presence of NaCl. It is concluded that the marginal strength of dental amalgams in a corrosive environment is largely dependent upon their corrosion resistance.

Electrochemical properties of corroded amalgams.

Three types of amalgam, one conventional, ANA 68, and two with high copper content, Dispersalloy (dispersed type) and ANA 2000 (single composition type), were investigated. The amalgams were immersed for periods of 7 wk at a time, up to 35 wk, in 23 ml (37 degrees C) of 0.9% NaCl aqueous solutions and in 0.9% NaCl solution buffered with NaH2PO4 (8.8 mM) and Na2HPO4 (1.2 mM). The amalgam specimens were embedded in epoxy resin. The surface area of amalgam exposed to the solutions was 0.2 cm2 for each specimen. Every 7 wk the corrosion potential was measured, the amalgam specimens lightly brushed with a soft toothbrush, and the solutions renewed. After 14-21 wk and 35 wk the currents during anodic polarization sweeps over the amalgams were recorded. The corrosion potential for the high-Cu amalgams was somewhat more positive (noble) in the phosphate buffered solution than in the non-buffered solution during the 35 wk of corrosion. The phosphate buffer reduced the reactivity of the amalgams during anodic polarization. Corrosion made the amalgams more passive during the anodic polarization. However, all the elements leached from the amalgams into the solutions throughout the entire experiment.

Effects of mercuric ions on isolated guinea-pig ileum.

The possible physiological significance of low concentrations of Hg2+ in the guinea-pig ileum has been investigated. Responses to nerve stimulation by single electrical shocks, acetylcholine (ACh), and histamine (Hi) and the response to ACh of a depolarized preparation were examined. A stimulant effect of Hg2+, in the concentration range of 10 nM-1 microM, dominated in intestine accommodated in biological saline solution. This excitatory effect was probably mainly due to stimulation of a depolarization-coupled initiation of the contraction. The inhibitory effect of Hg2+, 10 nM-1 microM, observed in depolarized muscle was presumably due to a decreased Ca2+ availability for the contractile process. In the higher concentration range, 1-100 microM, a probably direct action on the contractile elements causing irreversible deterioration of the preparation seems to be present.