1 Preprosthetic SurgeryA. Learning objectives:1. That participants understand the anatomical and physiological factors that impacton the comfortable and effective wearing of dentures.2. That participants understand the process of ridge resorption and the pathologicalfactors that accelerate this process.3. That participants are able to identify the indications for pre-prosthetic surgeryand design surgical procedures to improve denture bearing areas.B. The Dentition Function Curve: a model for understanding dental function overtime.As a patient ages, they generally fall into one of three broad categories of dentalpatient. The fully dentate, the partially dentate (or partially edentulous) and thefully edentulous. Each patient starts out essentially the same, but, as they age,their dentition undergoes erosion of function as a result of the loss of one or manyteeth at a time. It is important to note that the process of loss of function is timedependant. Significant loss of function (the stair steps) accompanies the loss ofteeth.C. The challenge of edentulism:With this model in mind, it is useful to look at denture support and retention from afirst principles point of view. Edentulism, by its very nature, is a significant challengeto both patients and the dental profession. Through the use of artificial materialsand techniques we must call upon tissues to perform functions they were neverdesigned to perform. We ask mucosa and bone to support and retain appliancesand then ask the tongue and lips to adapt to these large foreign bodies and functionessentially normally.We must appreciate that the prosthetically restored dentition is not as functionallyeffective as an intact natural dentition. The artificial dentition does not allow themagnitiude and variety of forces that teeth housed in a PDL and supported byaleolar bone will allow. Hence, chewing efficiency, retention and comfort are allcompromised to a lesser or greater extent.Both the pre-existing conditions that led to the edentuous state as well as the wearand tear of denture use result in worsening of the prothetic condition. The challengeto the profession is to provide an optimal appliance to start with and then throughmaintenance, control the progressive loss of function or through intervention,improve it. A useful place to start is to look at the anatomical and physiologicalfactors that impact on appliance retention and support.D. Factors that affect denture "fit":1. Amount of bone: The more bone, the more surface area available for support ofthe denture (resistance form) and the more complex will be the movement requiredto unseat the denture (retention form).
22. Contour of bone/undercuts/irregularities (examples: lingual or palatal tori, highgenial tubercles, bone spicules, etc): The smoother the contour of the bone, themore uniform will be the loading of the ridge. Irregularities result in "point loading"of the denture bearing ridge with focal areas of excessive pressure. Undercutsprevent close adaptation of the denture to the ridge and therefore loss of uniformloading, again resulting in uneven distribution of forces.3. Height of muscle attachments/depth of sulcus: The height of muscleattachments determine the amount of immobile gingiva/mucosa that is available forsupporting the denture. The higher the attachments (as a function of either originalanatomy or the progressive atrophy of the ridge) the shallower the sulcus andtherefore, less denture bearing area.4. Soft tissue quality (gingiva vs. mucosa): Dense, keratinized gingiva has agreater ability to resist loading and stand up under normal or parafunctional use. Itis less likely to become inflamed and has less tendency for inflammatoryhyperplasia secondary to poor denture fit.5. Tongue/lip habits: Many patients will adapt to complete dentures and willdevelop lip and tongue habits that actually improve retention of dentures. Otherpatients possess adverse habits, such as the "poised" tongue posture that tend todislodge dentures.6. Soft or hard tissue pathoses: Soft tissue pathoses may be independent ofdenture wear or a result of it.Hard tissue pathoses may be primary dental disease in the form of dental caries,periodontal disease or infection associated with residual roots or impacted teeth.Hard tissue pathosis may be residual disease in the form of residual radicular cystsor chronic osteomyelitis or de novo disease in the form of tumours or cysts. Theclinician must also be aware of less common disorders such as Pagets disease ofbone, acromegaly, osteosarcoma, etc.Vesiculobullous disease, dysplasia or neoplasia occur as a result of congenitalpredisposition or as a result of environmental factors (eg. smoking). Their presencemay result in pain, swelling or worse, in the case of cancer, harm to the patientshealth. They must be watched for and managed independently of denturefabrication and management.In contrast, gingival or mucosal hyperplasia is usually a result of denture irritation.This irritation is a function of parafunctional habits (clenching or grinding resulting inpressure sores), day and night wear of the denture resulting in papillary hyperplasiaof the palate or more commonly, irritational rubs secondary to worsening denture fitas the ridge resorbs and the denture is not adjusted (epulis fissuratum).E. Ridge resorption:While other factors impact on ridge quality, the most important factors for denturestability and comfort is the amount and contour of the bone. In general, the amountof bone, the contour of the bone, the sulcus depth and the soft tissue quality are afunction of the inevitable loss of bone to the process of ridge atrophy. This processis more or less rapid from one individual to the next. Bone loss will be accelerated
3in denture wearers as a function of the overall level of inflammation present on themucosa. This inflammation increases with:1. Increased denture wear (worst case: patient leaves dentures in at night)2. Poor denture fit with denture mobility and mucosal ulceration or hyperplasia3. Parafunctional habits: clenching, grinding, etc. resulting in pressure points andincreased loading4. Poor control of forces: unbalanced occlusion, natural dentition against dentureFrom the point of view of control of atrophy, the most effective management tool isdenture maintenance with ongoing adjustment and control of fit by regular relineprocedures. This reduces denture movement and therefore reduces irritation.F. Preprosthetic Surgery:Preprosthetic surgery may be defined as: procedures designed to optimize thestability, retention, support and comfort of removable dentures through the selectivemodification of soft and hard tissues.G. Indications for pre-prosthetic surgery:1. Dental caries and periodontal disease: The extraction of teeth is not alwaysthought of as a presprosthetic procedure nor is it usually thought of as apreventative procedure. The removal of teeth is the definitive preprosthetic surgicalprocedure, particularly if the patient is being edentulated. From this point of view,care during the procedure to minimize bone loss and create an optimal ridge formhas a profound impact on the eventual prosthetic product.From a preventative point of view, the timely extraction of non-restorable orperiodontally doomed teeth prevents the ongoing bone loss that would beassociated with the infection or surgical extraction of decayed teeth or uncontrolledperiodontal disease.2. Pain secondary to point denture loading on ridge irregularities: The eliminationof protruding spicules or points of bone allows for more uniform loading of the ridge.While somewhat more technically demanding, the removal of tori eliminates pointloading in the area of the torus. In the case of lingual tori, removal often allows forextension of the lingual flange with increased retention and resistance.3. Undercuts: Elimination of bony undercuts allows for more intimate contact ofdenture base to bone and therefore more uniform loading of the ridge.4. Flabby ridge tissue: The trimming of flabby ridges allows for more intimateadaptation of denture to mucosa and more uniform loading of ridges. This reducesdenture movement and reduces resultant "rubbing" of the mucosa.5. Papillary hyperplasia of the palate (PHP): PHP is secondary to denture overuseresulting in increased, irregular surface area and the creation of microbiologicalniches that allow for the overgrowth of both bacteria and candidal fungus. Thisleads to increased inflammation of the tissue in reaction to the microorganisms.Excision of PHP may be done with a scalpel (bloody and technically difficult),electrocautery (dryer but more painful because of the depth of the "burn") or arotating handpiece with a large "acrylic" bur (somewhat bloody, technically easy and
4much less painful). In all cases, patient post-op comfort and haemostasis arefacilitated by immediately relining the patients denture with a soft temporary relinematerial.Elimination of PHP eliminates the niches for bacterial and fungal overgrowth andreduces the overall level of inflammation. Should the patient return to day and nightdenture wear post-op, the PHP will likely return.6. Hyperplastic tuberosities: Occasionally, posterior interarch space may bereduced by hyperplasia (usually soft tissue but occasionally osseous) of thetuberosity. This reduces the space available for the placement of a denture baseover the tuberosity or the retro-molar pad. This results in denture heel interference.Soft tissue hyperplasia can be reduced by wedge excision of the tissue followed byundermining of the wound edges and primary closure. Hard tissue reduction iscarried out essentially the same way, with osseous reduction done prior to closure.The amount of bone reduction allowed is a function of the level of the floor of thesinus.7. Small epulis fissuratum (EF): This is essentially the same pathological processas PHP. The denture rubs the mucosa of the depth of the sulcus and causesinflammation and hyperplasia. This again leads to mucosal overgrowth andworsening of denture fit. Excision of EF need to be done at its base. For smallerlesions, simple excision with primary closure is all that is required.8. Large epulis fissuratum (EF): For larger epulis fissuratum lesions, excision andprimary closure would result in elimination of the sulcus. In such cases, placementof a palatal mucosal graft or a skin graft is required in order to maintain sulcusdepth. This requires wiring of the denture in place for approximately two weeks.This is usually done with fixation screws or circummandibular / circumzygomaticwires.9. Decreased retention: Loss of retention as a function of ongoing atrophy isdifficult to regain.b. Vestibuloplasty: With time and bone atrophy, there is a relative loss of vestibulardepth. This is a function of resorption of the ridge crest in a sulcular direction,toward the attachment of the sulcular muscles (mentalis, buccinator, etc.). In afashion similiar to the excision of epulis fissuratum, the sulcus depth can beregained and maintained by the creation of a partial thickness wound (leavingperiosteum intact and on the bone) and then relining the defect with palatal mucosaor a partial thickness skin graft. This procedure is technically demanding andcarries with it increased morbidity (pain, swelling and potential complications. Thisrequires wiring of the denture in place for approximately two weeks. This is usuallydone with fixation screws or circummandibular / circumzygomatic wires.a. Bone grafting to the ridge from hip (iliac crest) or rib is technically verydemanding, and carries with it a high level of morbidity (pain, swelling, risk ofcomplications). Furthermore, it also has a relatively poor prognosis, with a return topre-op bone levels within five years.10. Implants: The other option with respect to regaining retention is the placementof implants. Artificial teeth can then be attached directly to implant abutments(similiar to a bridge) or they may be placed into a relatively standard denture baseand the entire overdenture is then clipped to a bar that is directly attached to the
5implant abutments.H. Summary:1. This discussion has attempted to place the edentulous patient within the contextof a model that looks at the progressive loss of dental function with time, loss ofteeth and loss of bone through alveolar atrophy.2. It is our aim that practitioners may then design preprosthetic surgical proceduresto reverse the ravages of time and disease and therefore improve the ability ofpatients to manage removable appliances.