An in vivo method for measuring the adsorption of plasma proteins to titanium in humans

A novel method of collecting in vivo plasma proteins of humans from osteotomies prepared during insertion of an oral implant is described. A rod containing a collecting portion with a predetermined surface is introduced into the osteomy, removed, and transferred for enzyme-linked immunosorbent assay analysis. Two experiments were used to examine the feasibility of the method. In the first, titanium (Ti) rods with different roughness were exposed for 10 min to the blood. Blasted and acid-etched surfaces adsorbed four times more and acid-etched surfaces adosorbed two times more plasma proteins as compared to machined surfaces. In the second experiment, blasted and acid-etched rods were wetted for 10 s prior to the insertion. The adsorption for fibronectin, albumin, fibrinogen, and IgG was enhanced significantly compared with nonwetted rods. These results are discussed in the light of previous methods used in studies on adsorption. Thus, use of the collecting instrument enables aspects of human plasma-implant interface to be studied in a more realistic manner.

In vitro CPC retention and VSC adsorption by IPM oil droplets: possible mechanisms of action of a two phase mouthwash

Two phase oil-water mouthwash has been previously shown to efficiently bind oral microorganisms, relying on their cell surface hydrophobicity. The aim of the present in vitro study was to test the cetylpyridinium chloride (CPC) retention and volatile sulfide compounds (VSCs) adsorption abilities of the oil droplets created by mixing of a two phase oil-water solution. VSC adsorption was assayed using a salivary incubation assay and garlic powder solutions, and demonstrated using microscopic sulfide assay. CPC retention was assayed by kinetic and endpoint measurement of Streptococcus salivarius outgrowth using microplate (ELISA) reader. Results showed that the isopropyl myristate (IPM) oil droplets in the two phase solutions were able to adsorb 68-80% of VSCs. CPC at a concentration of 0.05% was most affectively retained by the oil droplets showing a significantly increase in residual antibacterial activity against Streptococcus salivarius. These results taken together, suggests that VSC adsorption and CPC retention by IPM oil droplets may be two additional mechanisms in the activity of the two phase mouthwash formulation.

[Dental implants following trauma in young adults]

Various statistics have shown that avulsion (total displacement of tooth out of its socket) following traumatic injuries is relatively infrequent, ranging from 0.5 to 16% of traumatic injuries in the permanent dentition. The maxillary central incisors are the most frequently avulsed teeth. Avulsion of teeth occurs most often in children from 7 to 9 years of age, when the permanent incisors are erupting. Most frequently, avulsion involves a single tooth; but multiple avulsion are occasionally encountered. Fractures of the alveolar socket wall are often associate with avulsion. After the tooth is lost, an almost certain sequelae is the rapid resorption of alveolar bone. In many cases, only a very thin crestal bony lamella remains after healing of the alveolus, with clinically obvious horizontal and vertical depressions. In a young patient missing an anterior tooth, the operator may find implant insertion, in the proper anatomical position, difficult or impossible, because of inadequate bone volume. This situation aggravates with time because of continuous resorption and relative growth of the adjacent alveolar bone around the teeth. New and predictable bone augmentation techniques allow compensation for bone reduction while waiting for completion of growth. In cases of localized ridge augmentation, the amount of initial bone volume and its shape dictate whether implant insertion and bone augmentation will be performed simultaneously. The indications for this approach are: sufficient bone volume to achieve initial implant stability and a predictably high success rate for the augmentation. When bone volume and shape do not allow for initial stability, there is indication for a staged approach, in which the bone is initially augmented, the results are evaluated and the implant is then inserted. The first stage, the bone regeneration phase, may last between 8-10 months. The second, the implant integration period, may take an additional 6-8 months. The effect of growth on the augmented bone is not quite clear and there is only a paucity of information concerning the use of bone regeneration procedures in growing patients. Clinical decision when to start implant treatment after avulsion is dependent not only on the timing of implant insertion, but also on bone regeneration procedures. When most of horizontal and vertical bony walls of the extraction site is lost, augmentation procedure as a measure to reduce the deficiency, may be considered even in preadolescents. Three cases describing different clinical situations following avulsion, tooth replacement, resorption, regeneration treatment and implant insertion are discussed.

Primary mineralization at the surfaces of implants

Osteogenesis around implants is affected by the physical and chemical characteristics of the biomaterials used. The osteoprogenitor cells must migrate to the implant site and synthesize and secrete a mineralizable extracellular matrix. Because this is neo-bone formation, the mechanism by which the cells calcify their matrix involves extracellular organelles called matrix vesicles in a process termed "primary mineralization". Two different methods for assessing the effects of implant materials on primary mineralization are presented in this report. In the first approach, different implant materials used in dentistry and orthopedic surgery were placed in rat tibial bones after marrow ablation. Two groups of implants were used, bone-bonding and non-bonding materials. We examined the effects of the materials on calcification morphometrically by quantitating changes in matrix vesicle morphology and distribution in endosteal tissue around implants as compared with normal endosteal bone healing. In addition, matrix vesicles were isolated from the endosteal tissue around the implant as well as from the contralateral limb and were examined biochemically. The results demonstrated that bone-bonding materials induced a greater increase in matrix vesicle enzyme activity than did non-bonding materials. However, all materials caused changes in matrix vesicles that were different from those seen in normal endosteal bone formation following injury. The effects of implant materials on biochemical markers of mineralization, including specific activities of matrix vesicle alkaline phosphatase and phospholipase A2 and phosphatidylserine content, demonstrated a high correlation with the morphometric observations with regard to enhancement and/or delay of primary mineralization. In the other approach, we used a radioisotopic method to evaluate the effects of implant materials on primary mineralization. This analysis revealed that implants alter bone healing, as shown by the differential uptake of 99mTc and 32P in different bone compartments. Decreased 32P uptake by the organic phase in the presence of bone-bonding implants suggests that cleavage of 99mTcMD32P into its technetium and methylene diphosphonate moieties was inhibited by the presence of the implants. In summary, these approaches to evaluating the effects of materials on primary mineralization demonstrate that the marrow ablation model can easily distinguish between bone-bonding and non-bonding materials. The use of this model can be valuable in the development of new materials.

Simultaneous and staged approaches for guided bone regeneration

Two approaches for obtaining bone augmentation around implants by guided tissue regeneration are described. In the first, bone is regenerated simultaneously with implant placement, which is a time saving tactic. However, when initial stability of the implant cannot be obtained because of insufficient bone volume, a staged approach must be considered. In the staged approach, the bone is augmented and the implant is inserted later. The staged approach offers improved primary stability, allows the implant to be inserted in mature bone, and enables examination of the newly augmented bone before a decision is made whether or not to use it as an implant site. Two case reports are presented which illustrate the approaches.

Adherence of periodontopathic bacteria to bioabsorbable and non-absorbable barrier membranes in vitro

Guided tissue regeneration (GTR) techniques are increasingly used for the treatment of periodontal defects, or in conjunction with dental implant procedures. As adhesion of bacteria to barrier membranes used in these techniques may lead to failure, a prerequisite for treatment success is an infection-free healing process. The present study examined the adhesion of 3 periodontal pathogenic bacteria: Actinobacillus actinomycetemcomitans, Treponema denticola and Porphyromonas gingivalis, to 3 barrier membranes: Collagen, (Biomend) PTFE, (TefGen-FD) and e-PTFE, (Gore-Tex). The membranes were incubated with 3[H]-thymidine labeled bacteria, and the number of adherent bacteria was calculated using a scintillation counter. The effect of albumin coating on bacterial adherence to the membranes was also studied. Bacterial adherence to the membranes was further examined by scanning electron microscopy (SEM). The results show that the adherence of all bacterial strains to collagen membranes was significantly higher than to the other membranes tested. Precoating of the membranes with albumin did not change the bacterial adherence significantly. These findings are of importance in evaluating the ability of periodontal bacteria to colonize and infect different types of barrier membranes.

Woven bone formation around implants and the effect of bacterial infection

Several implant materials used in dental and orthopedic surgery were placed in rat tibial bones to study their effects on mineralization. The implants consisted of bone bonding and non-bonding materials. Changes in mineralization were defined by morphometric analysis of matrix vesicle distribution at the implant interface and in normal bone healing following marrow injury. Bone-bonding materials induced an increase in matrix vesicle activity. This finding was supported by study of the biochemical changes in the same model that manifested high correlations to the morphometrical observations with regard to enhancement or delay of primary mineralization. In addition, the study of healing using nuclear methods indicated that implants alter bone healing as shown by the different uptakes of 99mTc and 32P in the different bone compartments. Decreased 32P uptake by the organic phase in the presence of bone-bonding implants suggested that cleavage of 99mTc-MD32P into its technetium and methylene diphosphonate moieties was inhibited by administration of implants. Further studies on the effect of bacterial infection on the peri-implant tissues revealed a decrease in woven bone formation due to infection.

Adhesion of periodontal bacteria to titanium, and titanium alloy powders

In this study, the adhesion of radioactively labeled Actinomyces viscosus (A. viscosus), Actinobacillus actinomicetemcomitans (Aa) and Porphyromonas gingivalis (P. gingivalis) to titanium (Ti) and Ti-6-Al-4V alloy (Ti-alloy) coated with albumin or human saliva was investigated. All the tested bacteria displayed greater attachment to Ti-alloy than to Ti. P. gingivalis exhibited less adhesion to Ti and Ti-alloy than did the other bacterial strains. Adhesion of A. viscosus and Aa was greatly reduced when Ti or Ti-alloy were coated with albumin or saliva. P. gingivalis demonstrated a lesser reduction in adhesion to albumin or saliva-coated surfaces. The results show that oral bacteria have different adhesion affinities for Ti and Ti-alloy and that both albumin and human saliva reduce bacterial adhesion.

Mechanism of adsorption of human albumin to titanium in vitro

Our previous studies have shown that human albumin is one of the main salivary proteins that adsorb to titanium (Ti). The goal of the present study was to investigate the role of electrostatic interactions in the adsorption of human albumin to Ti-oxide (TiO2) in vitro. The binding profile of human albumin to Ti was analyzed according to an adsorption isotherm. Purified human serum albumin (HSA) was suspended with native, calcium-, magnesium-, or potassium-treated commercially pure Ti powders, at pH 3.0 and 7.0. The amount of unadsorbed protein in the supernatant fluid was measured. The maximum amount of adsorbed albumin was 0.13 mg/1.0 g Ti. The albumin-Ti association constant was 2.77 mL/mg. Pretreatment of Ti with calcium, or magnesium alone, or combined with increasing pH values (3.0-7.0) resulted in augmented adsorption of HSA to Ti. No increase in adsorption was observed following pretreatment of Ti with potassium. These results point to the involvement of electrostatic interactions in the adsorption of HSA to TiO2.

alpha-Amylase and salivary albumin adsorption onto titanium, enamel and dentin: an in vivo study

In vivo adsorption of salivary albumin and alpha-amylase onto titanium, enamel and dentin was analysed following their exposure to the oral cavity for 2h. Oral appliances in six adults served as a platform for carrying 4-mm discs of the three materials. Adherent proteins were eluted from the discs and the amounts of salivary albumin and alpha-amylase were measured by an enzyme-linked immunosorbent assay. While significant difference between the adsorption of albumin and alpha-amylase onto enamel as compared with dentin was observed, adsorption onto titanium was significantly lower. A sample of whole saliva was also collected from each participant. The mean total amounts of albumin and alpha-amylase in the participants' whole saliva were 0.03 and 0.54 mg ml-1, respectively. Titanium adsorbed significantly less (4.43%) of the total albumin than did enamel (14.30%) or dentin (18.80%). No significant difference was found in the relative amounts of alpha-amylase adsorbed by the three materials. This significantly selective adsorption of proteins may enable the attachment of specific bacteria and thus alter the composition of the dental plaque and its potential pathogenicity.

Effect of axial plane deviation on cross-sectional height in reformatted computed tomography of the mandible

OBJECTIVE

To assess the effect of angular deviation on the measured height of the mandible in reformatted cross-sectional CT scans.

METHODS

Reformatted cross-sectional CT scans were obtained from three dried mandibles, at three angulations, in a special holding and positioning device for perpendicular measurements. The radiographic lengths of 321 measurements were compared with the actual bone length.

RESULTS

The mean difference between actual bone length and image length, with transaxial planes parallel to the lower border, was 0% (s.d. 3.6). Deviations of 10 degrees and 20 degrees from the lower border of the mandible resulted in a mean error of 1% (s.d. 4.5) and 2.8% (s.d. 8.0) respectively. When the angulation between the deviated transaxial plane and the lower border was greater than 10 degrees, the maximum error was about +/- 30%.

CONCLUSION

The use of different transaxial planes along the mandible may result, in a small proportion of cases, in discrepancies in height when measured from the cross-sectional images obtained. This may lead to incorrect interpretation of the depth of bone available for implants.

A combined impression technique for a partial implant-supported fixed-detachable restoration

A passive fit between osseointegrated implants and the prosthesis supported by them is crucial to the correct distribution of the stress exerted on the implants. The accuracy of the impression procedure in duplicating the exact position of the implant abutment is one of the main contributors to passive fit. An impression technique is presented whereby the dentate and edentulous parts are duplicated in elastomeric material, providing both the flexibility needed to remove the impression and the required accuracy. Subsequent duplication of the implant zone with plaster, without removal of the tray, affords a high degree of accuracy.

Atypical incisive nerve: clinical report

A 68-year-old Caucasian man complained of discomfort from two implants placed in the anterior mandibular area. Examination of cross-sectional computerized tomography images revealed the passage of a distinct structure, surrounded by cortical bone, which extended from the right mental foramen anteriorly and passed through the lower part of the right and left implants. The structure, which was identified as the incisive nerve, also emerged from the left mental foramen and advanced toward the midline. This nerve plexus is usually delicate and not detectable by conventional radiography or computerized tomography. The possibility of nerve variations in the anterior region of the mandible must be considered to prevent possible trauma to the adjacent tissues when placing implants.

Uptake and biodistribution of 99mtechnetium methylene-[32P] diphosphonate during endosteal healing around titanium, stainless steel and hydroxyapatite implants in rat tibial bone

Early evaluation of intraosseous implant success and failure is critical, but, until now, there have been no reliable systems of measurement. The present study assessed whether the use of 99mtechnetium methylene-[32P]diphosphonate (99mTcMD32P), a marker for both bone formation and mineralization, can indicate if an implant is bone-bonding or non-bonding. Moreover, this study examined how bone-bonding (titanium and hydroxyapatite) and non-bonding (stainless steel) implants affected the normal healing of bone after marrow ablation, as measured by uptake of 99mTc and 32P. Titanium, hydroxyapatite and stainless steel implants were placed in the right tibiae of Sabra strain rats following ablation of the marrow, and 99mTcMD32P was injected 18 h before harvest. AT 3, 6, 14, 21 and 42 d (and in some experiments, on days 28 and 35) post-injury, the treated and contralateral tibiae were removed and cleaned of soft tissue. The uptake of 99mTc and 32P was measured in the whole bone, as well as in its organic and inorganic phases. Effects of the implants were assessed by comparing the treated to the untreated tibia in each rat. The distribution of 99mTc and 32P varied with each implant. After the insertion of titanium, increased 99mTc uptake was seen in whole bone and in the inorganic and organic phases at days 6-14. 32P uptake in whole bone and in the inorganic phase increased only at day 6, and 32P uptake was decreased in the organic phase at that time. In tibiae implanted with hydroxyapatite, 99mTc and 32P uptake was seen in the whole bone at days 6 and 14. While 99mTc uptake was increased in both the organic and inorganic phases, 32P uptake into the organic phase was decreased at both day 6 and day 14. In tibiae implanted with stainless steel, effects were observed only on day 6. The increased 99mTc uptake in whole bone reflected increases in both the organic and mineral phases. Increased 32P uptake was observed in whole bone as well, due to an increase in the 32P uptake in the mineral phase only; incorporation of 32P in the organic phase was comparable to that found in the contralateral limb. The results of this study indicate that implants alter bone healing, as indicated by the uptake of 99mTc and 32P in the different bone compartments. Moreover, decreased 32P uptake by the organic phase in the presence of bone-bonding implants suggests that cleavage of 99mTcMD32P into its technetium and methylene diphosphonate moieties was inhibited, perhaps as a function of the onset of calcification in the newly synthesized osteoid. The effect of the implants on bone healing was observed on days 6-14, when active bone formation and mineralization were occurring, supporting the hypothesis that these materials events associated with initial calcification. Uptake of 99mTc varies as a function of time, and uptake of 32P varies with time and distribution in the mineral or organic phase of bone, suggesting that these parameters may be useful as indicators of bone-bonding.

Adsorption of salivary proteins onto prosthetic titanium components

In vivo adsorption of salivary proteins onto prosthetic titanium components was analyzed after exposure of titanium abutments to the oral environment for a period of 2 to 6 weeks. Gel electrophoresis and Western immunoblotting were used to separate and identify the proteins, which were mainly alpha-amylase and serum albumin. Selective adsorption of proteins enables attachment of specific oral bacteria and thus may alter the composition of the dental plaque formed on titanium surfaces.

Adsorption of human salivary proteins to titanium powder. I. Adsorption of human salivary albumin

Titanium (Ti) is among the most widely used implant materials in dentistry today. The success of Ti implants is associated with their interactions with the surrounding tissues and biological fluids. In the present study, the adsorption of salivary proteins to Ti and the effect of calcium (Ca) on this process were investigated. Untreated and Ca-treated Ti powders were suspended in human clarified whole saliva. After incubation, the supernatant fluid was collected for protein analysis. The powders were then washed and resuspended in EDTA to desorb proteins from Ti surfaces. Sodium dodecylsulphate polyacrylamide gel electrophoresis and Bradford protein assay were conducted to determine the concentration and type of proteins that adsorbed onto Ti surfaces. The presence of Ca ions enhanced the adsorption of salivary proteins to Ti. A 66 kDa protein, identified by immunoblotting as albumin, was found as the main adsorbed salivary protein. Adsorption of albumin to Ti pretreated with Ca was significantly greater than to native Ti. The Ca-dependent adsorption process was reversed by EDTA. The data suggest that salivary albumin is one of the main constituents of a salivary biofilm formed on Ti dental implants and its adsorption to Ti surfaces is Ca-dependent. The presence of albumin on Ti dental implants may affect plaque accumulation on the implants and the biocompatibility of Ti implants.

Markers of primary mineralization are correlated with bone-bonding ability of titanium or stainless steel in vivo

Critical events in the adaptation of osseous tissues to implant materials involve initial calcification of the newly synthesized bone. Previous studies indicated that bone-bonding but not nonbonding glass ceramics increase the matrix vesicle number, thereby compensating for delayed maturation of the extracellular organelles. The present study assessed whether this was also true for metal implants commonly used in orthopaedics and oral medicine. Bone-bonding titanium (Ti) or nonbonding stainless steel (SS) implants were placed in the right tibias of Sabra rats following ablation of the marrow. At 3, 6, 14, and 21 days postinjury, newly formed endosteal bone in the treated and contralateral limbs was removed and matrix vesicle-enriched membranes isolated. Alkaline phosphatase and phospholipase A2 specific activities and phosphatidylserine (PS) content were determined and compared with those of a nonsurgical control group. Results show that matrix vesicle alkaline phosphatase and phospholipase A2 activity and PS content was increased in the Ti-implanted limbs at 6 (peak), 14, and 21 days, although at levels less than observed in normal healing. Alkaline phosphatase activity remained elevated throughout the healing period. In contrast, these parameters were markedly inhibited in the SS-implanted limbs with respect to Ti or to normal healing. Both implants altered the systemic response associated with marrow ablation, but in an implant-specific manner. The results support the hypothesis that cells adjacent to bone-bonding materials can compensate for negative effects on primary mineralization during osteogenesis, whereas cells adjacent to nonbonding materials either do not compensate or are further depressed. The data support the use of the rat marrow ablation model as a tool for rapid, initial assessment of biomaterials in bone.

Effects of hydroxyapatite implants on primary mineralization during rat tibial healing: biochemical and morphometric analyses

The effect of 40- to 60-mesh hydroxyapatite (HA) granules (Calcitek, Inc., Carlsbad, CA) on the process of primary mineralization during bone healing was examined following insertion of the HA granules into rat tibial bone after marrow ablation. Response to HA was assessed by monitoring morphometric and biochemical changes in matrix vesicles, which are extracellular organelles associated with initial calcification. Following insertion of HA, matrix vesicle-enriched membranes (MVEMs) were isolated from the tissue adjacent to the implant and from the endosteum of the contralateral limb at 3, 6, 14, and 21 days and from a nonimplanted control group (t = 0). MVEM alkaline phosphatase- and phospholipase A2-specific activities were increased on days 6 (peak) and 14; phosphatidylserine content was also elevated on days 6 and 14 (peak). Comparable changes were seen in the contralateral limb but at lesser magnitudes. Morphological changes were observed as well. The number of matrix vesicles/micron2 matrix increased on days 6 (peak) and 14. The mean diameter of the matrix vesicles was elevated on days 6 (peak), 14, and 21. Mean distance from the calcifying front increased on day 6 but was decreased on days 14 and 21. These results indicated that HA behaves like bone-bonding implants in that there is a stimulation of matrix vesicle enzymes, increased phosphatidylserine content, and increase numbers of matrix vesicles. However, the increases occur only after 6 days postimplantation, indicating a delay in response when compared to normal healing. This delay is confirmed by the morphometric measurements. HA causes a reduction in the response associated with marrow ablation. In addition, the effects of HA are comparable locally and systemically but with different intensity. These observations suggest that osteogenic cells are able to compensate for the inhibitory effects of HA and primary calcification involves normal matrix vesicle production and maturation, if somewhat delayed and reduced in magnitude. The ability to support primary mineral formation may contribute to the successful bonding of HA with surrounding osseous tissue.

Complications in the tissue integrated prostheses components: clinical and mechanical evaluation

Cases demonstrating complications in osseointegrated implant supported prostheses are described. These complications occurred in the prostheses framework or veneer, in the fixation screw, in the abutment post or screw as well as in the implant body. The two main reasons for the complications were lack of passive fitting between the restoration and the abutment; and destructive occlusal contacts. The destructive occlusal contacts may develop during the time of wear of the prostheses material or by changes in the opposite restoration. Overloading or bending moments exerted on the prostheses via these occlusal contacts resulted in loosening or fracture in one of the implant-prostheses components. The benefit of acrylic resin or composite material in reducing stresses in the light of the possible long-term, harmful occlusal changes that might develop as a result of their wear should be considered.

In vivo regulation of matrix vesicle concentration and enzyme activity during primary bone formation

In vivo regulation of matrix vesicles (MV) during primary bone formation was examined using tibial marrow ablation in rats as the experimental model. The effects of bone-bonding and nonbonding implants on the number of MV/micron 2 of matrix and the alkaline phosphatase (ALPase) and phospholipase A2 (PA2) activities of MV-enriched microsomes (MVEM) isolated from the healing bone were studied. MV concentration, ALPase, and PA2 were increased by bone-bonding implants by day 3 post-surgery; a similar effect was seen in the contralateral limb, but at a lower magnitude. Nonbonding implants had no effect at day 3 and decreased MV concentration and PA2 activity at later time points; the same behavior was observed in the contralateral limb. These results demonstrate that MVs are influenced in a differential manner by implant materials, both locally and systemically, and can be regulated during primary mineralization.

Effect of titanium implants on primary mineralization following 6 and 14 days of rat tibial healing

The effect of pure commercial titanium implants on the process of primary mineralization was studied. This was examined by insertion of titanium implants into rat tibial bone after ablation. The effects of the titanium were studied through the behaviour of extracellular matrix vesicles (MV). Methods of morphometric analysis at the TEM level were applied. The insertion of titanium implants was followed by an increase in the number of MV as well as vesicular diameter and by a decrease in vesicular distance from the calcified front when compared to normal healing. These results suggest that the process of MV maturation around titanium implants was delayed when compared to normal primary bone formation during bone healing. The delay in mineralization was compensated by an increase in vesicle production, resulting in an enhancement of primary mineralization by the titanium.

Short-term effect of guided bone regeneration and electrical stimulation on bone growth in a surgically modelled resorbed dog mandibular ridge

This study compares the quantitative bone changes that occur in attempting to augment a resorbed mandibular ridge by electrical stimulation and by the guided bone regeneration technique. At the base line three defects resembling an atrophic ridge were created in the mandible of 5 beagle dogs. Concomitantly, a constant current generator producing 20 +/- 2 mA was implanted under the floor of the mouth. Six weeks later a titanium cathode was inserted in the first bony defect and connected to the generator (electrical stimulation = ES); another titanium cathode, not connected to the generator, was inserted in the second defect (non-electrical stimulation = non-ES); the third defect remained without an electrical device (membrane only = MO). All 3 defects were covered with an expanded polytetrafluorethylene membrane, so as to prevent soft tissue proliferation into the defects. Tetracycline bone labelling compounds were administered to mark new bone formation. Four weeks following stimulation, ground sections were prepared for fluorescent microscopy. Differences between ES vs MO and between non-ES vs MO mean scores were statistically significant, indicating that 4 weeks of electrical stimulation resulted in similar bone formation as with non- electrical stimulation when both are confined to a membrane isolated defects.

Surgically modelled reduced ridge in the beagle dog

A reproducible surgical method for the production of reduced alveolar ridge in dogs using guided tissue regeneration principles is described. 3 defects resembling a reduced ridge were formed on both sides of the mandible in 4 dogs. In each of the dogs, a polytetrafluoroethylene membrane was placed on 4 defects, while 2 defects were covered by gingival flaps only. Half of the defects were allowed to heal for 6 weeks and half for 12 weeks. Bucco-lingual width measurements revealed healing up to the membrane. In the uncovered defects, the bony wall width increased during the 12-week healing period. Histological examination showed close adaptation between bone and membrane in well-sealed defects. In cases of incomplete sealing, connective tissue had penetrated into the defect, resulting in unpredictable bone healing. The use of guided tissue regeneration techniques is suggested as a valuable tool in creating experimentally reduced ridges.

Tissue regeneration principles applied to separation of fused teeth

A two-step surgical procedure for separating a central incisor fused to a supernumerary tooth with a 4-year follow-up is described. The fusion was between the crowns and 3/4 of the root length. The roots were connected by web-like radio-opaque tissue. The periodontal ligament could be followed along the lateral aspect of the roots and was continuous along the base of the web. In the first surgical phase, a full-thickness semilunar flap was raised; a fissure bar was cut along and through the web up to the approximate location of the junctional epithelium and the flap was sutured. It was assumed that cells from the bone surrounding the web and/or connective tissue cells from the flap had migrated into contact with the web hard tissue. This resulted in replacement resorption of the web. The connective tissue replacing the web acted as a septum separating the 2 parts of the root. The distal root was extracted. Resorption continued until most of the web disappeared from the wound. At this point, the remaining layer of web tissue was thin enough to allow repopulation of the resorbed surface with periodontal cells from the buccal and palatal sides of the web. The successful clinical outcome supports the assumption that new attachment consisting of periodontal ligament and cementum was formed following the 2-step surgical procedure. Application of the technique is limited by the width of the fusion rather than by its length.

Repairing a crown-sleeve coping prosthesis. Part III

The problem of an abutment tooth that has become carious and an inadequate support for a CSC prosthesis has been presented. The advantages and disadvantages of the various routine restorative techniques have been discussed. A detailed procedure for restoring a carious abutment tooth that also requires periodontal surgery was described.

Surgical exposure, orthodontic movement, and final tooth position as factors in periodontal breakdown of treated palatally impacted canines

Twenty-three patients who had completed orthodontic treatment for the resolution of unilateral palatal canine impactions were examined 2.3 years (mean) after all appliances were discarded. The patients were divided into two groups on the basis of whether the surgical exposure was "light" or "heavy." The whole group was also divided according to the type of orthodontic movement that was carried out--"light" for tipping, extrusive, and rotating movements and "heavy" for root movements. Final position of the teeth was classified as ideal or incomplete if rotations or spaces were present. The results showed marked deteriorative changes where the surgery had been more radical and where the tooth movement involved active alteration of root position. No change due to abnormal tooth position was seen. It is suggested that, in these cases, surgical procedures be limited in scope and that exposure of the cementoenamel junction be avoided.

Periodontal status following the alignment of buccally ectopic maxillary canine teeth

Twenty-nine patients who had completed orthodontic treatment to resolve buccal displacement of maxillary canine teeth were examined 2.9 years (mean) after all appliances had been discarded. Thirteen of these patients had unilateral displacement, and sixteen were bilaterally affected. In the unilateral cases only the width of attached gingiva was significantly less than in the controls. In the bilateral cases the same observation was made, but here the gingival index and pocket depth also showed statistically significant increases, although the expression of these values was found to have doubtful clinical significance. Posttreatment periodontal assessment is recommended for these cases.

Periodontal status following the alignment of palatally impacted canine teeth

Twenty-three patients who had completed treatment to resolve the unilateral palatal impaction of a maxillary canine by orthodontic means were examined 2.3 years (mean) after all appliances had been discarded. Scores were noted for the plaque index, gingival index, attached gingiva, pocket depth, and bone support on each of the affected teeth and also on the contralateral canine which had been unaffected and thus acted as a control. In addition, the teeth immediately adjacent to both canines were similarly scored. The results indicated no significant difference in the plaque index and the amount of attached gingiva, while the gingival index, pocket depth, and particularly the bone support all showed statistically valid differences. It is suggested that in these cases a postorthodontic assessment of the state of the supporting tissues be performed and periodontal treatment instituted in those requiring it.

Temporary space maintainers retained with composite resin. Part II: Fracture load in vitro

The average fracture load during occlusal loading of pontics which were bonded to natural abutment teeth in vitro was found to be 56.1, 57.5 and 74.2 kg for natural, acrylic resin, and Restodent pontics, respectively. Coating the roots of the abutment teeth with a thin layer of silicone rubber before embedding them in stone slightly reduced the strength of the fixed partial dentures. Thermocycling the specimens with coated roots caused a considerable decrease in strength to fracture loads of 33.0, 17.9, and 37.3 kg for natural, acrylic resin, and Restodent pontics, respectively. Fracture of the enamel of natural tooth pontics was observed in a few specimens. The superior strength of the fixed partial dentures with natural tooth and Restodent pontics would indicate that these pontics are superior for clinical trials rather than acrylic resin pontics.

Finish lines in fixed prosthodontics

Ideally, all finish lines should be placed supragingivally. Due to esthetic and carious considerations, however, subgingival placement of the finish line is preferred. No one type of finish line can be used for all crown preparations. In lower anterior teeth or periodontically-treated teeth, the knife-edge finish line appears to be the treatment of choice. In short teeth and preparations for porcelain and porcelain-gold crowns, the full shoulder bevelled preparation is the treatment of choice. In full gold and acrylic veneered gold crowns, as in endodontically-treated teeth, the chamfer preparation is the treatment of choice.