|Year : 2012 | Volume
| Issue : 1 | Page : 47-53
Directions on prosthetic complications in tissue-integrated supported prosthesis
N Sridhar Shetty, D Krishna Prasad, Niranjan Joshi, Aruna M Bhat
Department of Prosthodontics, A. B. Shetty Memorial Institute of Dental Sciences (A.B.S.M.I.D.S), Deralakatte, Mangalore, India
|Date of Web Publication||24-May-2012|
Department of Prosthodontics, A B Shetty Memorial Institute of Dental Sciences, Mangalore
Source of Support: None, Conflict of Interest: None
| Abstract|| |
Advances in medical sciences have brought many patients the gift of longevity of life and we have large percentage of people who are aged and having physiologic, psychologic aging problems. Stomatognathic system is most frequently affected and handicapped with sequelae of oral and dental diseases. Patients are frequently partially dentate or completely edentulous. Restoration of these partially dentate or completely edentulous patients has offered much therapeutic technique. Tissue-integrated supported prosthesis is used effectively to support fixed and removable prosthesis for single and multiple tooth replacements as well as maxillofacial prosthesis. Many patients have been successfully treated with the benefit of tissue-integrated supported prosthesis by permitting diverse prosthodontic treatment. Knowledge regarding the types of complications that can occur with dental procedures is an important aspect of treatment planning, dentistpatient communication, informed consent, and post-treatment care. Success of implant restorations can be described as biologic stability, mechanical stability and hygienic ability. Even though it is not possible to calculate an overall complication incidence for implants and their associated prostheses, there appears to be a greater number of clinical complications associated with implant prostheses than any other types of prostheses evaluated. The purpose of this article is to describe some general mechanical complications that exist during the functional loading phase for other implant systems and prosthesis design for different implant designs.
Keywords: Implant abutment connection, implant failures, prosthetic complications, tissue-integrated supported prosthesis
|How to cite this article:|
Shetty N S, Prasad D K, Joshi N, Bhat AM. Directions on prosthetic complications in tissue-integrated supported prosthesis. J Dent Implant 2012;2:47-53
|How to cite this URL:|
Shetty N S, Prasad D K, Joshi N, Bhat AM. Directions on prosthetic complications in tissue-integrated supported prosthesis. J Dent Implant [serial online] 2012 [cited 2022 Jan 25];2:47-53. Available from: https://www.jdionline.org/text.asp?2012/2/1/47/96574
| Introduction|| |
Advances in medical sciences have brought many patients the gift of longevity of life. We have large percentage of people who are aged, or having physiologic and psychologic aging problems. Stomatognathic system is one organ of the body, which is most frequently affected and handicapped with sequelae of oral and dental diseases. Thus handicapped stomatognathic system by the loss of teeth, affects ingestion, mastication, deglutition and nutrition, which formulates the vital chain for human existence. Patients are frequently partially dentate or completely edentulous and have been successfully treated with benefit of tissue-integrated supported prosthesis.
Implantology belongs to the fast growing area in dental medicine due to its innovations and advancement with regards to medical and technical developments. Out of the various treatment modalities available for replacing missing/unrestorable teeth, treatment with tissue-integrated supported prosthesis have now become an integral and essential part, and today many patients have been successfully treated with benefit of tissueintegrated supported prosthesis.
Rapid technological advances along with the wide use of endosteal implants in dentistry have resulted in a variety of different implant systems. All systems are based on the principle that part of the endosseous implant (abutment) rises into the oral cavity to support or retain the prosthodontic restoration. The implant design should provide the development of physiological contours, fabrication of final restorations with acceptable esthetics, high strength and long-term durability, functional restoration for missing natural teeth and should be cost effective. Quality restorations are the requirement of an implant design and procedures of fabrication are characteristic to each implant system.
During the phase of diagnosis and treatment planning, it is of utmost importance to have knowledge about the possible complications that could be associated with the treatment plan. 
Researchers have tried to calculate the incidence of various complications associated with implant supported prosthesis. Although the results show a varied incidence, it is however indicative of a large number of complications associated with this treatment modality. 
| Prosthetic Complications Related to Tissue Integrated Supported Prosthesis Can be Broadly Grouped As|| |
- Loss of osseointegration.
- Removable prosthesis related complications.
- Misalignment of implants as a prosthodontic complication.
- Screw joint complications.
- Fixed prosthesis related complications.
Loss of osseointegration
Several factors produce systemic changes that have been evaluated for their effect on implant success/failure. These items include smoking, radiation therapy, diabetes, chemotherapy, osteoporosis, hormone replacement therapy, scleroderma, Sjogren's syndrome, Parkinson's disease, multiple myeloma, and an HIVseropositive status. 
The effect of radiation on maxillary implants were loss of around 25% implants and it was around 6% for mandibular implants. 
Cigarette smoking appeared to be detrimental to the success of osseointegrated implants regardless of the amount of cigarette consumption. 
However with the current developments of implant surface treatment such as the Sand Blasted Acid Etched surfaces, the incidence of implant failure due to loss of osseointegration is rare and occurs secondary to systemic factors.
Removable prosthesis related complications
Overdenture clip/attachment fracture
Overdenture clip/attachment fractures constitute around (17%) of the reported complications. 
A study  compared the prosthetic aspects of three different attachment types (ball, bar, and magnets) in two implant-retained mandibular overdentures.
After an observation period of 10 years, the mechanical complications associated with the three groups were as follows: renewal of Oring housing and abutment screw loosening for the ball group; wear and corrosion for the magnet group and need for clip reactivation for the bar group. The magnet and ball groups presented the highest incidence of prosthetic complications as compared to the bar group.
Other studies , demonstrated similar results that the magnetic and ball attachments required frequent maintenance and repair due to corrosion or wear of the magnets, fracture of the ball head and need for reactivation of the ball matrices.
Loss of retention
Loss of retention or adjustment constitutes the highest percentage of mechanical complications associated overdentures with a frequency of around 30%. 
Dudic and Mericske-Stern,  compared the retention mechanism for implant-supported overdentures and found that the rigid group exhibited fractures of bars and retightening of female parts while the resilient group showed broken loose or lost retainers.
van Kampen,  et al. demonstrated that when bars and anchors are subjected to both vertical and oblique forces, solitary anchors provide less retention as compared to the bar group. Implant angulation may compromise the retention of solitary anchors.
However, Chung et al.  showed that in cases of parallel placed implants, solitary attachments such as ocators may match or exceed the Hader bar and metal clip retention.
Gotfredsen  et al. found that patients receiving round bar experienced more problems as compared to those receiving ball attachments.
Zhang  evaluated the retentive characteristics of ANKYLOS SynCone conical crown system over longterm use and observed that under 20 N insertion force, the retentive force of ANKYLOS SynCone conical crown system was between 5 and 10 N. The retentive force kept almost constant during the entire testing cycles. Thus, a constant and adequate retentive force to retain implant-supported overdentures could potentially be provided by the SynCone conical crown system and maybe be considered as an alternative to bar attachments.
Eccellente et al.  evaluated patients with a mandibular overdenture supported by the ANKYLOS SynCone system with metal re-enforced denture base with telescopic retainers and found that after a total observation of 30.3 months (range 12 to 60 months), the prosthesis survival rate was 100%.
Overdenture fracture accounts for 12% of the reported complications associated with implant-supported prosthesis. 
Since implant-stabilized overdentures have much more effective stabilization, they tend to be subjected to greater loads than conventional prostheses. Fractures resulting from masticatory overloads are more common, particularly where the opposing dentition consists largely of natural teeth. Such complications are observed when the applied loads exceed the material's proportional limit or fracture strength. 
In the severely resorbed mandible, implants supporting or retaining an overdenture may be subjected to excessive masticatory forces by the mesial and distal cantilever and also from the occlusogingival lever arm. These forces include off-axis centric contacts, excursive contacts, cantilevered loading, and internal stresses created by both component and framework misfit.  Fracture of the denture base can be prevented by incorporating mental denture base.
Complete and implant-supported mandibular overdenture bases are more prone to fracture because of the increased load transmitted through them. The incidence of their fracture can be substantially reduced by reinforcing them with metal. 
Fractures of the denture can also arise due to rocking around the retainers where suitable spacers have not been used to minimize this problem. Since many implant-stabilized mandibular overdentures have mechanical characteristics similar to a Kennedy Class I partial denture, resorption of the alveolar ridge distally can result in a tendency of the denture to tip anteroposteriorly. This causes rocking around the distal abutments, and can result in fracture of the denture base. Where problems arise as a result of differential support of the prosthesis, this should be controlled as much as possible using selective displacement of the soft tissues in the non-implanted regions. 
Some patients complain of excessive retention with their implant-stabilized prostheses. It can be difficult to remove the dentures, particularly where the patient has reduced manual dexterity or muscle strength. Adjustment of the retainers, or the removal of some of them, can often control this. Patients may benefit from the modification of the flanges of the denture in inconspicuous locations to improve the grip that can be obtained. 
As a result of anatomical constraints, surgical errors, or failure to construct and use diagnostic prostheses and a surgeon's guide, problems can arise where implants are inappropriately located. 
Speech problems are less common when using implant-stabilized removable prostheses than with fixed ones, since the contours can be made more extensive and any gaps covered by gum work. Difficulties are usually related to the changes in tooth position over those to which the patient is accustomed, and can easily be overcome by training. 
Implants placed too far lingually in mandibular overdenture prosthesis will result in encroachment of tongue space and will cause problems with patient comfort and speech. 
In another study,  the influence of immediate loading of implants on speech adaptation was evaluated. They concluded that immediate loading of oral implants does not seem to compromise the normal 36 months speech adaptation period.
Masticatory problems anteriorly are unusual and are usually related to tooth positions and can lead to problems with tipping of the prosthesis or lip biting. Errors in the level of the occlusal plane, a lack of freeway space or buccolingual positioning of the teeth can lead to problems in the posterior region.
Occlusal wear as a prosthodontic complication
When the restoration opposes natural teeth or implant-supported restorations, the use of resinous material of any variety on the occlusal surface of posterior restorations is likely to fail. Rapid wear, chipping of the composite resin, fracture of the resin away from the metal substructure, staining and percolation at the finish lines are the potential complications. 
Misalignment of implants as a prosthodontic complication
Improper alignment of implants through a surgical complication must be handled by the prosthodontist or restorative dentist.
Labially incline implants may compromise the esthetic result when screw access holes exit through the labial or incisal surfaces of teeth.
Encroachment upon the tongue space and soft tissue irritation may result from lingually placed mandibular implants. 
Screw joint complications with single and multiple implants
Abutment implant interface
Loosening or fracturing of the attachment screws is a common problem associated with the prosthetic restoration of dental implants. It occurs mainly because of the magnitude and direction of the oral forces and the strength limitations of the components. Operator error, torsion relaxation, and thermal changes may also contribute to screw loosening. 
Mechanical failures such as loosening or breakage of occlusal screws for the screw-retained restorations, abutment screws or abutments is directly related to the type of the implant-abutment connection.  A study by Mollersten et al.,  showed that short external hexagon design performed particularly poorly.
Da Silva,  et al. compared the influence of the implant design and connector on the implanttoothconnected prostheses. The internal hexagon connection offers greater denture stability due to its greater depth, which results in greater stress on the abutment structures. It is desirable to use an external hexagon connection when connecting an implant to a natural tooth.
Tolman  stated that loose or fractured abutment screws commonly occur repeatedly in the same patient. It usually is an indication that the design concept is inappropriate, the framework is illfitting, the mechanical or material components are incompatible, or the occlusal scheme and masticatory function are not in harmony.
Mangano,  et al. concluded that Morse taperconnection implants provide for a good solution for singletooth restorations, with an incidence of abutment loosening of 0.66%. In another study,  few prosthetic complications at implantabutment interface were reported (0.37%). The use of Morse taper connection implants represented a successful procedure for the rehabilitation of partially and completely edentulous arches.
A study conducted by Sailer  et al. on influence of the type of connection on the fracture load of Zirconia abutments with internal and external implantabutment connections concluded that a secondary metallic component along with an internal connection significantly increased the strength of the Zirconia abutments.
Coppedê  et al. conducted a study on fracture resistance of the implantabutment connection with internal conical connections and internal hex connections under oblique compressive loading and found that the internal conical connection abutments provided greater resistance to deformation and fracture under oblique compressive loading when compared to the internal hex connection abutments due to the strong friction locking mechanics.
Park  compared the effects of abutment screw coating on implant preload and found that non-coated itanium screws provided lesser preload than tungsten carbide carbon screw surface coating. Titanium screws required higher force than tungsten carbide carbon screw for initial removal torque. Post-load removal torque for tungsten carbide carbon screw was greater than itanium screws. Also, Morse taper connections were more effective in maintaining the screw preload in cyclic loads than external-hex butt joint connections.
More mechanical stability has been provided by precisely machined, internaltapered implant-abutment connections than either the external hex connections or butt joint designs. The precision-fit Morse-tapered conical connection of the ANKYLOS implant has been shown to provide better shortterm and longterm clinical performance. 
Screws and screw joints may fracture for many reasons, and by several combinations.  Principal amongst these are over-tightening, poorly aligned components, overload and fatigue failure.
The implant shoulder is the critical factor in influencing the hard and soft tissue response around the implant and proposed restoration. Problems in the restoration implant axis will cause prosthetic complications difficult to restore.
Maintenance of interdental papilla is largely dependent on the presence or absence of the interproximal bone. Restorations with long contact areas will result in restorations with a compromised emergence profile and embrasure form. Horizontally matched implant abutment junctions cause more loss of the adjacent crestal bone as the microbial colonization is in immediate proximity to the bone.
Chou et al.,  have documented that platform-switched implants with Morse taper connection system showed no major crestal bone loss (0.2mm/y from the time of implant placement to 36 months).
According to Weigl,  ANKYLOS implants show an enhanced volume of connective tissue around the neck of the abutment. This is primarily due to the tapered abutment connection of the platform-switched design. The increased volume also helps in hiding the gray metal hue of the titanium abutments leading to an appearance of natural healthy gingival. The shape of these abutments is a critical factor in establishing the emergence profile as it provides a bulk of soft tissue covering the crestal bone. For this reason the ANKYLOS implants are placed equicrestally or 1mm subcrestally to allow development of a thick and wide mucosal layer.
Full mouth fixed prosthesis related complications
Fracture of the veneering material
These constitute around 14 to 22% of mechanical complications. 
Loss of acrylic resin or porcelain facing can occur due to flexure or fracture of the fixed implant superstructure. A survey  conducted showed a high rate of acrylic resin veneer complications as opposed to that of porcelain defects.
Although the frequency of porcelain defects is less, it can occur primarily as a result of poor design, high occlusal loads or the metal ceramic junction placed in extreme shear.
Also if the underlying framework is thin and not adequately rigid, it will exhibit a lot of flexure during function. This will lead to failure of the metal ceramic interface. Acrylic facings, owing to their reduced modulus of elasticity are less likely to debond owing to substructure flexure. 
These constitute around 3% of the failures reported. 
Substructures are fabricated either from gold alloys, cobalt chromium alloys or titanium alloys, which have sufficient rigidity. Substructure fracture are rare and may occur due to faulty design or excessive functional loads resulting from bruxism, inappropriate occlusal schemes, framework misfit or excessive cantilevering. 
Cantilever extensions are a potential risk for prosthetic complications and according to Shackleton,  cantilever extensions >15 mm exhibited dramatically higher failure rates.
In another study by Wenstromm  et al. no differences in the incidence of technical complications were observed over a five-year period in FDPs with or without cantilevers.
Esthetics is crucial in the upper anterior region and such complications frequently occur in this region. These occur as there is a disparity in the position of where the implant has to be placed and the position of the desired prosthetic teeth. The prosthetic teeth should simulate the position of the natural predecessors to achieve an attractive appearance. Since implants have to be placed in resorbed jaws; the corresponding lost tissues have to be replicated in acrylic resin or porcelain with adequate access to oral hygiene. This limits the design of the superstructure leading to compromised esthetics.
Inability of the interdental papilla to fill in the embrasure space often leads to formation of the so called 'black triangles'. These can be corrected to a certain extent by soft tissue surgeries however obtaining satisfactory results is often a challenge. Use of scalloped implant design can be used in these critical esthetic areas to obtain a more desired result.
Changes in the labiolingual and incisocervical position of the anterior teeth is the most common cause of speech problems associated with implant-supported fixed prostheses. Due to the inward and upward resorption of the anterior maxilla, there is a decrease in the anterior tongue space after placement of implants and prosthesis. If a normal emergence profile and minor spatial changes are present, these difficulties are quickly overcome by adaptation. The patients need to be encouraged to read aloud so as to speed up the adaptation process.
In certain cases a gap exists between the soft tissues and the superstructure through which air and saliva can escape and can be a very embarrassing situation for the patient. Use of a palatal elastomeric bung or a removable labial acrylic flange can be used to obdurate the defect. These removable appliances can be removed by the patient to facilitate oral hygiene. 
Problems associated with mastication are rare and occur due to improper occlusal scheme, nature of the opposing dentition or limited distal extensions due to anatomic constraints for implant placement. 
| Summary|| |
The literature describes some general biomechanical, phonetic and esthetic complications of prosthesis design that exist during the functional loading phase for different implant designs and systems.
On the basis of available data, the following conclusions are offered relative to dental implant complications
When it comes to screw joint mechanics, excessive tightening will cause plastic deformation and breakage of the screw, while under-tightening will result in a joint that has more tendency to open up during function. Plastic deformation of the mating screw surfaces, torsional recovery of the screw, cyclical loading, plastic deformation of the joined components and overload of the joint will lead to a fall in the preload of a screw joint following tightening. Forcibly trying to fit a misfitting framework will lead to complete utilization of the preload only in approximating them. Loading such frameworks will increase the risk of screw joint failures.
Frequent loosening of abutments or abutment-retaining screws was observed in horizontally matched implant abutment systems. 
Use of mechanical or electromechanical torque wrenches will help in optimizing the torque required for screw tightening.
Reducing the buccolingual width of the restoration and reducing the cusp angle will reduce the horizontal loads onto the screw joint. However, a cold weld produced by the Morse taper connection provides high strength in the horizontal direction permitting physiologically dimensioned occlusal anatomy. 
Butt joint connections for internal or external hex have shown an inflammatory infiltration of around 0.6mm adjacent to the gap formed at the implant abutment junction. For platform-switched implants, the crestal bone was often located higher than the implant shoulder due to their subcrestal placement. Due to the absence of microgap between the abutment and the implant and its platform-switched design, no crestal bone loss was found around these implants. 
Minimizing cantilever lengths, elimination of non-working contacts, centralization of forces and proper framework design are key factors in success of implant-supported overdentures. 
The use of conical crown concept for overdentures results in predictable retention, improved oral hygiene and easy management of prosthetic phases.
Fabrication of a surgical guide will minimize the problems of misalignment of implants for single or multiple implante supported prosthesis.
Decisions regarding use of cement-retained restoration verses screw-retained restoration is a critical one and several factors need to be considered before either option is considered. Although cement-retained prosthesis are technically simpler, economical and require less expertise, the problem of retrieval of excess cement from deep subgingival areas can preclude its use. However, screw-retained prostheses require increased maintenance, high precision and often lead to increase in the bulk of the prosthesis resulting in over contouring.
Each of these factors need to be carefully considered to prevent or minimize the biomechanical, functional and esthetic failures.
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