Abstract

This study introduced a new concept of an in situ, custom-made, tooth replica dental implant. It was obtained by injecting a self-set, nonresorbable polymer type bone graft substitute into the tooth socket after extraction. Based on its cited properties, new composite bone cement Cortoss was suggested. The properties were reviewed and evaluated. The technique of application was described with a simulation model presented that appeared simple. Apparently, immediate duplication of tooth anatomy was achieved; thus, the concept might have the potentials of spontaneous adaptation and stabilization, preservation of alveolar bone, increasing implant-bone surface area, better load distribution, and bone stimulation. Modifications were also described to manage cases of resorbed alveolar bone as well as long-standing extracted teeth. Investigations were still required to assess the performance of the material and if modifications would be needed.

Introduction

The tooth anatomy is unique in architecture1 and has been an aspiration to many authors how to duplicate.24 Nevertheless, most of the current practice and research in dental implantology is focusing on endosseous fixture-shape ready-made implants. They are prefabricated, predesigned, and are rigid rod or rod-like in shape with a circular platform. This configuration—unfortunately—dictates to shape off the receptacle bone bed to match that platform of the implants. The bone, on the other hand, is a controlling factor in selection of the appropriate size of the implant. In other words, implant diameter is selected based on the smallest dimension in the horizontal plan of available bone, which in turn, is prepared to confine this rigid implant. Therefore, available bone is deprived of its potential as investing structure and is not utilized to its best.

Few recent trials of tailored implants were introduced. A custom-made implant was reported to be successfully inserted in the root socket of an extracted premolar. This implant took a modified form of the extracted root and was CAD/CAM fabricated of zirconia.3 In another trial, a US patent was published for the invention of custom-machined implant fabrication.5 It described a technique for immediate replacement of an extracted tooth with an implant that had a relative emulation to that tooth and its root. The implant was CAD/CAM generated and was made of titanium. Thus far, these recent trials and the traditional implants alike are fabricated remote from their bed, that is, outside their bony socket and then inserted. Being rigid, their path of insertion dominates the procedure; hence, neither possibility for curved roots nor to fully engage a naturally available root socket is allowed. Application for multi-rooted dental implant was not approached either.

Reviewing the history of dental implants2,69 did not reveal any attempt regarding intrasocket dental implant fabrication.

This study is based on the assumption that if a malleable material with sound biomechanical properties can be delivered into the bony socket where solidification takes place in situ, the preplanned roots shapes—anatomic or modified anatomic—will be obtained.

Bone graft substitutes are basically biocompatible materials and are categorized into several groups based on their structure, mechanical properties, bone response, and hence their applications. Therefore, alternative classifications exist.10,11 Polymer is one group of these materials. Composite polymer is a nondegradable subgroup10 and may exist under the names of composite bone cements, bone filler, or synthetic bone. It is applied by injection into the required site where setting takes place. A new bone cement of this category was recently introduced: Cortoss (Orthovita, Malvern, Pa). The material as described by the manufacturer is a high degree of 3-dimensional, cross-linked resin that is reinforced by ceramic particles. It is a paste-paste system that is packaged sterile in a dual cartridge. The delivery gun and the disposable mixing tips blend the 2 pastes automatically at the time of injection (Figure 1). It is injected in the bone cavity and sets in 3–5 minutes.

Figure 1

Armamentarium required for manipulation and delivering Cortoss into socket. (A) Dual cartridge containing the material. (B) Mixing gun. (C) Mixing tips. (D) Plastic syringes. (E) IV catheters with stopper (arrow). (F) Flexible metal wire.

Figure 1

Armamentarium required for manipulation and delivering Cortoss into socket. (A) Dual cartridge containing the material. (B) Mixing gun. (C) Mixing tips. (D) Plastic syringes. (E) IV catheters with stopper (arrow). (F) Flexible metal wire.

The material is also classified as osteoconductive bioactive glass.11 The scope of use of Cortoss in invasive surgery is wide, among which are vertebral augmentation,12,13 cranioplasty,14,15 femoroplasty,16 and screw augmentation.17,18 Depending on the field of application and the continent, the material has been either cleared for sale or is yet in one phase or another of evaluation. An attractive feature is that it is strong enough to bear the load of body weight.19 Augmentation of load-bearing bones is one of its recommended applications.16,20 Another interesting feature of the material is its bending modulus, which is in the range of 5505 ± 509 MPa21 and can be compared with that of bone as will be discussed later. Moreover, being a composite material makes it possible to adjust some properties if needed.22 Application of Cortoss as dental implant material does not exist and therefore no information is available in this respect.

The reported safety of this material and biologic behavior warrants studying its application as an in situ dental implant material. Extensive investigations are required. This study is part of a research program concerned with a new concept of tooth replication.

The purposes of this study are to describe a new technique for fabrication of an in situ, custom-made tooth replica dental implant from the composite-polymer type bone graft substitute Cortoss and to explore the potentials of the conception and the material.

Technique

The staff should be prepared for and familiar with the steps because of the limitations imposed by the working time of the material. Rehearsal of delivering the material might be advanced so that minimum time is required for the actual process. The armamentarium is shown in Figure 1. Figure 2 represents a model for a tooth upon which the procedure will be conducted. Disinfection of the field is followed by preoperative radiograph and anesthesia. The root length can be estimated beforehand. Simple and conservative incision is made to reflect the gingiva off the tooth in order to expose 1 to 2 mm of the alveolar bone all around the tooth. Impression is prepared while slight pressure is being applied on the field with sterile gauze. Additional silicon or polyether may work well. It is injected around the tooth and the surrounding exposed bone; then the impression is completed with a sectional tray loaded with impression material. The resulting impression is poured with fast-set dental stone into the first cast upon which the desired tooth is disclosed and waxed up to the final tooth shape and contour. Special attention is paid towards obtaining a smooth and highly polished wax up, particularly the cervical area—the area of tooth-gingival junction. The cast is then duplicated twice into the second and third casts. Smooth surfaces can be reproduced by using type IV, high-strength dental stone. The said tooth on the second cast is prepared by reduction for full crown; however, the occlusal surface is overly cut until it has flat surface with 3 mm clearance. The cervical area should be checked again for high smoothness which can still be enhanced by gentle application of a thin layer of composite bonding agent and allowed to cure. A vacuum formed template is then fabricated so that it includes the proposed tooth and at least 1 mesial and 1 distal tooth for secure repositioning. A suitable size access window is cut in the template at the occlusal surface corresponding to the proposed tooth through which the material will be delivered; then the template is disinfected (Figure 3). Profound anesthesia should be examined; otherwise additional doses may be required. Extraction is performed, while another member of the staff is getting ready to start preparation of the material immediately after successful extraction. Every care should be practiced regarding preservation of the alveolar bony plates. A suitable catheter is selected and adjusted. A catheter that is flexible but does not kink upon manipulation can be obtained as radiopaque or can be visualized radiographically by securing a sterile flexible metal wire into its lumen to be withdrawn after the adjustment and verification. Aided with periapical radiograph, the suitable gauge catheter is selected that will extend to the apex of the socket and then cut to the required length (Figures 4 through 6). The wider the catheter, the easier is the flow of the material. Intravenous catheters are available in a range of gauges from 22 to 14 which equals approximately 1.13 mm to 1.80 mm inner lumen with a range of lengths from 25 mm to 45 mm, respectively; the catheters are color coded. They are made of either polyurethane smooth radiolucent or stripped radiopaque, or Teflon, which is radiopaque. Pilot trials have shown the efficiency of gauges 14 and 16 in delivering Cortoss to most of the apices. If, however, a narrower apex is encountered, it could be widened with a suitable surgical bur. Cortoss is auto-mixed with the mixing gun and tips and delivered into a 1 mL Luer Lock syringe; air is released, and then the catheter is locked into it. Luer-locking will act to withstand the pressure of injection (Figure 7). The material is injected into the socket from the apex outward while the catheter is being gradually withdrawn outward paying every care that the tip is kept beneath the surface of the material all the time, thus avoiding entrapment of air or body fluids until complete filling of the socket and the corresponding crown in the template (Figure 8). After setting, the template is removed, the wound is sutured, periodontal dressing is applied, and the patient is given the instructions. Figures 9 and 10 show the outcome. Dressing and sutures are removed after 1 week. During this week, a temporary crown is being fabricated; the tooth stump on the third cast (the cast with full tooth crown) is reduced 2 mm occlusally only; thus, an occlusally relieved provisional soft crown can be vacuum fabricated. After removal of the sutures, the temporary crown is inserted. It will be relined with soft liner, then seated before setting of the liner so that it will adhere to the dried tooth. Excess relining material is trimmed after setting with a sharp blade. The permanent crown is fabricated to the completed form and cemented to the implant as for conventional fixed prosthodontic work after an established period of time.

Figure 2

Illustrative model. (a) A natural lower first molar attached into place in a stone model. (b) Embedded in rubber; bucco-occlusal view. (c) Lingual view. (d) Extraction socket.

Figure 2

Illustrative model. (a) A natural lower first molar attached into place in a stone model. (b) Embedded in rubber; bucco-occlusal view. (c) Lingual view. (d) Extraction socket.

Figure 3

Surgical template. (a) Outer surface showing access opening. (b) Inner surface. (c) Template in place; buccal view. (d) Occlusal view.

Figure 3

Surgical template. (a) Outer surface showing access opening. (b) Inner surface. (c) Template in place; buccal view. (d) Occlusal view.

Figure 4–8

Figure 4,. Catheter with stopper (arrow) and wire (dashed arrow) for assessment of extension. Figure 5,. Catheter adjusted. Figure 6,. Radiograph of Figure 5. Figure 7,. Catheter attached to Luer-lock syringe, loaded with Cortoss and ready for injection. Figure 8 . The syringe is gradually drawn outward as indicated by the stopper (arrow).

Figure 4–8

Figure 4,. Catheter with stopper (arrow) and wire (dashed arrow) for assessment of extension. Figure 5,. Catheter adjusted. Figure 6,. Radiograph of Figure 5. Figure 7,. Catheter attached to Luer-lock syringe, loaded with Cortoss and ready for injection. Figure 8 . The syringe is gradually drawn outward as indicated by the stopper (arrow).

Figure 9

Coronal portion of resulting implant; buccal view (top left) with its radiograph (bottom left) and occlusal view (right).

Figure 9

Coronal portion of resulting implant; buccal view (top left) with its radiograph (bottom left) and occlusal view (right).

Figure 10

The analogous implant after removal from the socket (left) and its corresponding extracted natural tooth (right). (a) Buccal aspect. (b) Lingual aspect. (c) Mesial aspect. (d) Distal aspect.

Figure 10

The analogous implant after removal from the socket (left) and its corresponding extracted natural tooth (right). (a) Buccal aspect. (b) Lingual aspect. (c) Mesial aspect. (d) Distal aspect.

A modified approach is to postpone the implantation process to another visit rather than the visit of extraction. In that case, the socket is plugged with iodoform-soaked cotton gauze after extraction that is to be removed and the socket curetted and irrigated in the subsequent visit before further proceedings.4 

Discussion

The suggested technique describes a method for immediate replacement of a tooth that is undergoing extraction, with duplicate implant of similar anatomic configuration. The anatomy of the crown is known to be geometrically related to its corresponding root/roots and together should be perceived as one unit, the tooth, which is specifically designed and oriented to meet the demands placed upon it23; therefore, both radicular and coronal outlines should be duplicated. Radicularly, the topography of the roots (surfaces, curvatures, cervico-enamel ridges, trunks, furcations, bulges, and depressions) should be paid great concern while restoring the dental arches. Coronally, the occlusal stress points should be geometrically confined to, and should confine the forces generated upon it to the root base outline on one hand and allow for stable occlusion on the other hand.23 Some roots have developmental grooves which give them a kidney or scalloped cross-section at the cervical level and are reflected into surrounding alveolus.24 In agreement with the previously mentioned patent, this would benefit the vascularization of the interdental tissues. Moreover, bone trabeculae are at risk of fatigue failure if loaded off their architectural axis,25 a reason why natural teeth configuration can buffer lateral forces and are much more competent than conventional implants in this respect.26 Furthermore, the width of conventional implant is usually narrower than the corresponding natural root.27 It is agreed that increase in width of the implant increases the surface area of bone contact. Each 0.25-mm increase in diameter increases the surface area of the implant from 5% to 10%28; therefore, duplicating the configuration of the root anatomy would restore root-bone surface area and in turn enhance load distribution and preservation of the integrity of interdental structures.

The technique suggests fabrication of the full tooth in 2 pieces on 2 stages. In the first stage, surgical stage, the root and the reduced crown form are formed as 1 unit by injection and allowed for nonsubmerged transgingival healing. An occlusally relieved provisional soft crown is supplemented 1 week later. Its suggested material will act to minimize the load until the second stage.28 The provisional crown can be easily replaced if the second stage is differed for a longer time. In the second stage, the second piece which is a conventional crown, will be cemented as for conventional fixed prosthodontic work; thus, the technique is simplified, no implant-abutment gap, the need for intraradicular screw is eliminated, such weak junction is avoided, and thickness of the implant is preserved and strength is raised. Fatigue fracture is related to the fourth power of the thickness difference,29 that is, doubling the thickness of a material increases its strength 16 folds, while tripling raises strength 81 folds. If, for example, a root with a 3-mm diameter is compared against 6 mm of the same material, the strength is raised to 16 folds and surface area is increased by 60%–120%.

The contoured anatomy and adaptation to the socket wall will act as a mean of initial stabilization and fixation. The periodontal pack, besides its role in healing and protection of the surgical site, might also act as a temporary splint in the early stage. Splinting to adjacent teeth with composite or acrylic resin might also be advisable. Should increasing initial stability or pull-out force be prejudged, macro tags might be prepared in the lateral walls of the socket or the socket might be widened apically, paying attention to avoid endangering the surrounding vital structures.

With respect to the healing period, it was reported that bone formation would take place around Cortoss after 7 days of incubation in simulated body fluids30 and after 12 weeks in animal study which also showed pull-out strength to be nearly 140 N after 6 and 12 weeks, 340 N after 24 weeks, and 900 N after 1 year.19 The reported values, therefore, exceeded the 500 g (50 N) required anchorage of dental implants.2 Compared with plasma-sprayed hydroxyl appetite coated implants, the latter showed 312 N pull-out strength after 12 weeks and 537 N after 9 months.31 

The proposed technique implies immediate implantation. Immediate implantation can be sought as a predictable treatment modality that has survival rates comparable to implants in healed ridges32; meanwhile, it still has the advantages of early esthetics, function, and comfort.33 Enhancing high levels of bone metabolic activity and decreasing bone loss are added benefits.34 Owing to satisfactory bone anchorage of Cortoss at an early stage, the proposed technique suggests immediate temporization of nonsubmerged tooth replica followed by 8 weeks healing before final restoration is attached. This loading protocol for conventional implantology is considered to be as prosthodontically and esthetically successful as an implant submerged for 26 weeks followed by 8 weeks of healing and final restoration,35 and may therefore be suggested tentatively here until revised otherwise.

Immediate implantation in this technique is not only a tooth replica but also a means of grafting extraction socket with bone graft substitute, which has the benefit of preserving alveolar bone.36,37 

The appropriate timing for attaching the final crown as well as the appropriate crown material should be studied regarding strains that might develop in the implant or surrounding bone. The optimum loading protocol has to be established concerning the new concept of this study.

The properties of the suggested material Cortoss can be summarized from the literature. Cytotoxicity was ruled out in an in vitro study.38 Safety and biologic compatibility were reported in both animal and clinical studies.15,18,19 Immunologic safety with no foreign body reaction was demonstrated in a clinical study in cranioplasty where feasibility of application was also mentioned.18 Bioactivity was reported in an experimental study where it exhibited the formation of apatite layer after 7 days of incubation in simulated body fluids.30 Bone formation was evident in histologic examination conducted on animal study. Bone was formed around Cortoss after 12 weeks of implantation, and the bonding force was found to increase with time.19 Osteosynthesis was also possible in a clinical study on femoroplasty augmentation with Cortoss bone cement and due to its mechanical properties, it was recommended for augmenting load-bearing bones.16,20 

Polymerization of the material was assessed and the degree of conversion was found to be ranging from 76% to 86% experimentally, whereas curing under physiological conditions was postulated to be faster in rate and higher in degree of conversion, and was theoretically calculated to be 95%.39 

The material is yellowish white and is described as being highly radiopaque,20 although quantification of radiographic visualization was not reported.

Regarding trauma on bone, a comparison of trauma imposed on bone by conventional implant technique vs the suggested new technique might be of sensible value. Bone is subjected to trauma during drilling for conventional implant, and this surgical trauma is the primary cause of implant failure.40 This trauma is inevitable and is of both thermal and mechanical origin with a resultant zone of necrotic bone, regardless how much care is given during preparation.40 Meticulous sequential drilling with the controlled use of properly designed incrementally sized drills should be accompanied by copious irrigation cooling so that the heat generated might be lowered to 47°C.41,42 Nevertheless, the temperature of bone drilling may be as high and dangerous as 89°C because of difficulty for the cooling to reach deeply.43 On the other side, the setting reaction of Cortoss bone cement is exothermic with a maximum (in vitro) temperature of 55–58°C and attains this peak of exotherm for 1 minute after setting, then gradually decreases to body temperature in 3–5 minutes.44 

Bone healing on the other hand, depends on adequate bone cells, adequate bone cell nutrition, and adequate stimulus of bone repair. In this respect, healing is explained by 3 mechanisms: cell-to-cell contact, ground substance induction, and electrical stimulus phenomena. Bone cells are at risk if subjected to temperatures above 47°C for 1 minute, but this does not mean the cell-to-cell contact mechanism is stopped.40 Collagen, an important factor in the second healing mechanism, denaturates after prolonged exposure to temperatures above 65°C,45 while denaturation of alkaline phosphatase enzyme occurs above 53°C.46 

It can be inferred that in vitro resulting heat from Cortoss revolves around or below the critical temperature of bone. In vivo, however, like other polymer bone cements, the actual temperature is lower due to the evident cooling effect that can be attributed to blood circulation and poor thermal conductivity of the material.47 Even at 56°C, no adverse effect might be observed.48 Should more cooling be deemed necessary, chilling of the instrumentation just prior to application would be of great value just like what might be recommended for other types of bone cements.49 Therefore, heat resulting from Cortoss reaction appears to be of less traumatic injury to bone than that resulting from bone drilling for fixture insertion.

Again and from the bone injury point of view, for conventional implants, surgical trauma elicited from bone cutting and fixture insertion are additional sources of bone cell disturbance and an added burden.40 

Regarding chemical trauma, Cortoss belongs to a composite subgroup of the polymer group of bone graft substitutes. Hence, Cortoss is a composite polymer in nature but with characteristic features owing to its ceramic content on one hand and to the high molecular weight (286–640 g/mol) monomers on the other.39 This type of monomer makes its high degree of conversion along with minimal leaching at body temperature. Therefore, unlike other types of polymer bone cements, Cortoss may be of limited chemical trauma.

It may sound like a prejudgment to run to conclusion in this early phase of study regarding response of oral tissues. Clinical observations supported by in vitro studies are necessary. Yet, any clinical trial should be justified in advance based on theoretical background, and this is the content of the coming discussion. Cortoss is a polymeric cement with bioactive glass that will form a bond with the host bone tissue, a bond that was found to increase with time, and is comprised of carbonated apatite.11 Stable osteosynthesis was achieved with Cortoss.16,20 The newly formed bone appeared to be in direct contact with Cortoss at 4 weeks in rabbits, and Cortoss was completely surrounded by bone at 24 weeks.19 Direct bone contact alongside the previously mentioned pull-out strength indicates the possibility of osseointegration. It is agreed that osseointegration comprises rigid attachment from the clinical aspect and direct bone contact from the histologic aspect.2,50,51 To retain this osseointegration is left to soft tissue response, biomechanics, and maintenance.

The other possibility is fibro-osseous integration. Periodontal ligaments can regenerate from their formative cellular elements; however, populations of these fibroblasts are necessary for this regeneration to occur.52,53 This is evidenced by the regeneration of periodontal ligaments remaining on replanted teeth.54,55 Cell formation and differentiation were found to be increasing after wounding of periodontal ligaments.53 The ability of periodontal ligaments to proliferate and attach to bioactive glass–modified ceramics was demonstrated in simulated body fluid.56 This is in agreement with the proponents of the role of bioactive glass in clinical improvement of periodontal pockets.57 Therefore, if the bone was not subjected to cutting, there may be a good chance for a good number of progenerator cells and periodontal ligament regeneration and attachment.

It is understood that attachment via periodontal ligaments is the optimum, and that osteointegration is also desirable in the society of osteointegration. However, the American Dental Association Council on Dental Materials, Instruments and Equipments did not state the exact type of attachment required for endosseous implants.58 

From the soft tissue response point of view, no information is available regarding its reaction toward Cortoss. The reason can be easily understood as it was not within the scope of this material yet. Accordingly and undoubtedly, extensive research will be required to assess the behavior of gingival tissues. From previous works in the literature, success of implantation is greatly influenced by permucosal seal—the ability of the junctional epithelium to form a barrier between intrabony and extrabony environments such that if seal was not achieved or was not maintained, the way would be paved for ingestion of microorganisms, inflammation of connective tissue, and pocket formation, and bone resorption would be eventual.59 Controversy exists such that the condition of this seal is a result rather than a cause of the condition of its supporting connective tissue, that is, if implant mobility was taking place, or the connective tissue could not tolerate the forces applied to it, it would be inflamed, and its supported junctional epithelium would proliferate causing disruption of the seal, and invagination would continue apically until exfoliation of the implant.52 Regardless the cascade, both scenarios should be prohibited. If the tooth replica is properly anchored and biomechanically fit, the possibility of the second cascade is eliminated. In order to eliminate the first, a proper permucosal seal is necessary. In order to obtain permucosal seal, the following should be recalled and considered: (1) gingival seal can occur around any surface—biologic or nonbiologic,60,61 but rough surfaces should be avoided because they are detrimental to this seal59; (2) gingival seal around nonbiologic materials is basically due to the potential of junctional epithelium to adhere, closely adapt, and secrete basal lamina onto foreign material62,63; (3) hemidesmosomal gingival attachment is found in relation to natural dentition,59,64,65 and meanwhile its occurrence around implants is questionable59,62,65; (4) the ability of epithelial cells to stick to other surfaces is inversely related to their degree of differentiation,52,66 a favorable phenomenon exhibited by junctional epithelium which is immature epithelium6668; (5) the presence of a zone of attached gingiva; although desirable, it is uncertain if it is essential for gingival seal59,69; and (6) regeneration of dentogingival junction is evidenced by its ability to reformat after gingivectomy.70 Evoking these issues, the proposed technique has underlined the necessity of smoothness of the intracrevicular part of the tooth replica, and the composition of the material has been described and will be highlighted herein. Ceramic content of Cortoss constitutes approximately 68% by weight and 41% by volume. The high degree of conversion of its high molecular weight monomers indicates minimal leaching at body temperature.39 The obtained cervical portion in this study might be tentatively spectacled as an intermediate or a combination of ceramic abutment and plastic healing abutment. Another advantage is the absence of gaps (implant-abutment connection). These features will make this type of superstructure a good candidate for further research. There is a good chance for a potential transgingival seal. This anticipation can be supported by relevant studies which have demonstrated the formation of an almost identical peri-implant junctional epithelium on single-crystal sapphire (alpha-alumina oxide) ceramic implants.63,71 It is noteworthy to point out the maintenance of this type of restoration. Routine subgingival debridement should be performed carefully with the suitable instruments that will not jeopardize the attained smoothness. Rotary interdental brush in adjunct with antimicrobials may be advisable. Home care oral hygiene should also be emphasized.

Because bone cements were intended mainly for applications other than dental implantology, it will be difficult to judge mechanical properties in this study, neither is it the aim of this work. However, some interesting information is available that makes composite bone graft substitute a candidate for further investigations and modifications if necessary. Cortoss has shown a bending modulus of 5505 ± 509 MPa, compressive strength of 146 ± 18 MPa, and a 4-points bending strength of 57 ± 10 MPa.21 As a golden rule, load-bearing capacity of implant should exceed the average maximum occlusal forces within the physiologic strain limit of bone.72 A word of caution: bone will be fractured at 10 000 to 20 000 micro strains and might be resorbed at levels from 2% to 40% of these values.28 Bone strength and modulus vary according to many interacting variables including density,28 microarchitecture,73,74 degree of mineralization,75,76 distribution of minerals,77 and volume fraction.78 These factors are dependent, in part, on adaptive capability and loading history.79 These variables may be the reasonable cause of variation in reported range of modulus of elasticity of cancellous and cortical bone from 0.05 to 2 MPa and from 3.4 to 20 MPa, respectively,80 or say, those of cancellous bone may be 10% of cortical bone.28 Added to the anisotropic feature of trabecular bone,25 these variations may explain the correlation between implant stability and physical properties of bone81 as well as the variation in host response to dental implants.82 

The reported bending modulus of Cortoss appears to be higher than that of cancellous bone but lies in the lower range of that of cortical bone. A lower elastic modulus means fewer forces delivered to bone provided other factors are the same.83 However, elastic deformation is anticipated under function, which may be a source of mechanical stimulation to bone if the stresses developed are within its physiologic capacity.83,84 

Another advantage of the new concept and material in this study is the elimination of the issue of galvanism and corrosion since the proposed material is nonmetal. From this respect and unlike metal implants, no restrictions are imposed on superstructure materials.

Modifications of the technique

The previous technique can be applied in simple and straightforward cases as a starting point. The practitioner may, however, be confronted with cases with deficient alveolar bone due to either periodontal problems or iatrogenic causes during extraction. Therefore, the existing socket might not be sufficient to confine potential volume of roots material. A modified approach will then be needed. The socket(s) ought to be extended toward the basal bone; thus, artificial sockets are created with osteotomy. Accentuation horizontally might also be considered. Radiographic assessment is mandatory. Sketching the radiographs at different angles aided with radiopaque reference markers is of significant help. Vital structures like mandibular canal for incidence can thus be avoided. Extending the artificial sockets buccal or lingual to this canal (though might be sophisticated) will add greatly to this modality. Packing the sockets with cotton gauze soaked with contrast medium (Omnipaque, GE Healthcare Inc, Princeton, NJ) will help radiographic visualization of the artificial sockets. Simply, but not repeatedly, the available bone can be utilized intelligently. In every case, however, understanding of the physiologic anatomy and biomechanics should precede such procedure. The artificial sockets and the resultant roots should take into account the occlusal forces, tooth alignment, and inclination as well as the crown/root ratio. In other words, a working template is needed. The template must represent a well-established shape and contour of the coronal portion of the corresponding tooth. This way, the technique can be applied almost anywhere in the jaws.

Another point of concern where modification is required is the area of root furcation. The interseptal bone has to be reduced to level slightly apical to the buccal and lingual alveolar plates. When Cortoss is injected, the resultant root furcation will follow this level. Worth mentioning, osteotomies carried out in these modifications should adhere to established protocols of bone cutting or drilling regarding torque, speed, and cooling. Bone should always be guarded against unnecessary trauma.

The same principles can be utilized for restoring teeth that have been missed for a long time. A preplanning is a challenge. Difficulty might be encountered because the principal element (natural tooth) is lost. Consequently, rationalization of bio-dynamics is urged. Dynamic occlusion, a functionally generated occlusion, can be initiated as a reference for restructuring the missed tooth. Esthetics regarding teeth display should also be considered.

In the previously mentioned modifications where bone cutting was required, some of the merits would be to some extent scarified, but others would be retained. The original and unique geometry of a tooth might be altered in order to meet the demands placed on it. However, the versatility of the concept of custom-implant allows for restoring the shape and/or function. It is the judgment of the practitioner what to choose. If, for example, a lower molar with resorbed alveolar ridge or a molar that has been missed for a long period of time with the accompanying sequel of atrophied ridge, considerations must be given to obtain properly functioning and stable occlusion. Proper support and retention of this tooth might not be achieved adequately if we were just to rely on the original configuration of the roots because they now lack the original investing structure—the alveolar bone. The available bone should therefore be negotiated to best accommodate altered form(s) of the root(s); broader, longer, altered curves, fused or what so ever. Clinical experience could help determine the optimum and ultimate. To this point, the bone itself is still having the advantage of tailored preparation—a preparation that should consider preservation of proper blood circulation for the mutual benefits of bone and gingiva.

Another concern is scarifying the possibility of periodontal ligament regeneration. Cutting of bone will remove Sharpey's fibers, the outer layer of periodontal ligaments that is adjacent to the bone.64 The trauma elicited by bone drilling may also cause the count of the cellular elements to be diminished. However, the possibility of osseointegration still exists. Research in the area of culturing and planting cells of periodontal ligaments54,85 could certainly synergize this study.

The proposed idea in this study is but an optional approach to dental implantology not to preclude other modalities. Extensive research work is required for assessment of the new approach. Ethical and legal protocols should be prioritized before clinical evaluation.

Summary

Reviewing its cited properties along with analytical discussion, Cortoss composite bone cement may be thought of as an alternative material for an alternative approach in dental implantology. The new approach opens the way for processing custom implants inside the sockets of teeth at the time of extraction, thus restoring each individual tooth to its anatomic morphology. A technique for such an approach was described and appeared to the author simple and convenient. The new concept has the cumulative advantages of immediate implantation, socket grafting, as well as the inherited advantages pertinent to normal tooth morphology and spatial orientation. Furthermore, this versatile concept can be applied to restore old missing teeth as well as periodontally involved teeth. Moreover, galvanism and corrosion are no more a problem.

Inspiring such merits, the behavior of the material has to be investigated further and revised before proceeding into clinical evaluation. Among the encouraged investigations are the following:

  • Radiographic visualization and quantification as well as methodology of clinical assessment.

  • Workability and degree of adaptation to socket walls.

  • Judgment of initial stability.

  • Stress analysis and load distribution inside and around the implant and relevant structures taking into account loading protocol and timing as well as influence of different superstructure materials.

  • Tissue response, bone and soft tissue.

  • Mechanical properties and behavior in conditions similar to those of intrabony, intraoral atmosphere in a lifelike simulation.

  • Changes due to aging.

Should these investigations disclose favorable results or be favorably adjusted, clinical evaluation would then take place. Prior communication to the authorized regulatory, however, must be considered.

References

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