Immediate Denture PDF - 5th Year Prosthodontics

Immediate denture 5th year Prosthodontics Lect. Dr. Mustafa Saadi Ali Immediate denture Introduction There are different treatment options for a patient facing loss his or her remaining natural teeth. Immediate denture is one of these options that fulfills an...

Immediate denture 5th year Prosthodontics Lect. Dr. Mustafa Saadi Ali Immediate denture Introduction There are different treatment options for a patient facing loss his or her remaining natural teeth. Immediate denture is one of these options that fulfills an important role in today's treatment modalities by providing patients with esthetics, function, and psychological support after extractions and during the healing phase. Definition An immediate denture is “any complete or partial removable dental prosthesis fabricated for placement immediately following the removal of natural teeth”. Immediate dentures are constructed before all of the remaining teeth have been removed and are inserted immediately following the removal of the remaining teeth. An immediate denture may replace one tooth or all sixteen teeth in either the maxillary or the mandibular arch or in both arches. Indications 1. Educated patient with daily social activity (doctors, lawyers and teachers). 2. Hopeless remaining teeth (caries, periodontal diseases or malocclusion). 3. Patient with stable health condition. 4. Patient does not mind some additional visits or cost. The best patient for immediate dentures is the philosophical type. Their motivation for denture is the maintenance of health and appearance, and they accept replacement of natural teeth that can’t be saved as a normal procedure. Contraindications 1. Patients who are in poor general health (systemic diseases). 2. Patients who are identified as uncooperative, indifferent and unappreciative. 3. Patient at risk from bacteremia. 4. Patient with recurrent history of post extraction hemorrhage. 5. The presence of acute periapical or periodontal diseases and extensive bone loss. 6. Patient don’t mind being edentulous for a period of time till complete healing. 1 Immediate denture 5th year Prosthodontics Lect. Dr. Mustafa Saadi Ali Advantages 1. Maintenance of a patient's appearance because there is no edentulous period. 2. Circumoral support, muscle tone, vertical dimension of occlusion, jaw relationship, and face height can be maintained. The tongue will not spread out as a result of tooth loss. 3. Less postoperative pain is likely to be encountered because the extraction sites are protected. 4. Some researchers have discussed whether immediate dentures reduce residual ridge resorption. 5. It is easier to duplicate (if desired) the natural tooth shape and position, plus arch form and width. 6. The patient is likely to adapt more easily to dentures at the same time that recovery from surgery is progressing. Speech and mastication are rarely compromised, and nutrition can be maintained. 7. Overall, the patient's psychological and social well-being is preserved. The most compelling reasons for the immediate denture prescription are that a patient does not have to go without teeth and that there is no interruption of a normal lifestyle of smiling, talking, eating, and socializing. Disadvantages Immediate denture is a more challenging modality than conventional complete denture because the presence of teeth makes impressions and maxillomandibular positions more difficult to record. Specific disadvantages include the following: 1. The inability to accomplish a denture tooth try-in in advance of extractions precludes knowing what the denture will actually look like on the day of insertion. 2. Because this is a more difficult and demanding procedure, more chair time, additional appointments (relines), and therefore increased costs are unavoidable. 3. The anterior ridge undercut (often severe) that is caused by the presence of the remaining teeth may interfere with the impression procedures. Also capturing a posteriorly located undercut could be inaccurate, which may lead to poor retention. 4. The presence of different numbers of remaining teeth in various locations (anteriorly, posteriorly, or both) frequently leads to incorrectly recording the centric relation position or improperly planning the appropriate vertical 2 Immediate denture 5th year Prosthodontics Lect. Dr. Mustafa Saadi Ali dimension of occlusion. An occlusal adjustment, or even selective pre- treatment extractions, may be needed to make accurate records at the proper vertical dimension of occlusion. 5. Functional activities such as speech and mastication are likely to be impaired; however, this is a temporary inconvenience. Types of immediate dentures According to the case and type of treatment plan, immediate denture can be planned to be: 1. Conventional (or classic) immediate denture (CID) After this immediate denture is placed and after healing is completed, the denture is relined (refitted) to serve as the long-term prosthesis. 2. Interim (or transitional or non-traditional) immediate denture (IID) After this immediate denture is made and after healing is completed, a second (new complete denture) is fabricated as the long-term prosthesis. The interim prosthesis designed to enhance esthetics, stabilization and/or function for a limited period of time, after which it is replaced by a definitive prosthesis. It is a temporary treatment, must be followed by the definite treatment. CID (Definitive) IID (Transitional) Intended as the final or long-term Intended for short term use only prosthesis After healing, it is relined with acrylic After healing, a second denture is made resin The esthetics of the denture cannot be The second denture procedure allows changed an alteration of esthetics, and all other factors, if indicated At the end of treatment, the patient has At the end of treatment, the patient has one denture a spare denture to use in case of extenuating circumstances Contraindication for patients who will Often indicated when the patient will need complicated treatment plans become edentulous in one arch and involving both arches, such as partially edentulous in the opposing periodontal therapy, crowns and fixed, arch for the first time. An interim partial dentures and dentures opposing complete denture can be made. Then removable partial dentures any periodontal procedures, crowns and fixed, partial dentures, can then be done during the initial healing stage 3 Immediate denture 5th year Prosthodontics Lect. Dr. Mustafa Saadi Ali According to the type of restoration, immediate denture can be classified into: 1. Immediate complete denture. 2. Immediate partial denture. 3. Immediate overdenture. According to the flange design, immediate denture can be classified into: 1. Flanged type: A. Complete flange. B. Partial flange. 2. Flangeless type (open face or close fit). Comparisons of flanged and flangeless denture 1. Appearance of flanged denture is not altered after fitting, while the appearance of open face denture (although good initially) can deteriorate rapidly as resorption create a gap between the necks of the teeth and ridge. 2. The flanged denture allows freedom in the positioning of teeth, while, in open face denture teeth have to be positioned in the sockets of the natural teeth so in case of malpositioned teeth, good teeth alignment can be achieved in flanged denture while cannot be achieved in open face type. 3. In upper denture, a flange on an upper denture creates a more effective borders seal, therefore, better retention is achieved than with an open face denture. 4. In lower denture, open face denture is not usually constructed because of poor stability of lower denture during function, so flanged denture is commonly used. Therefore, flanged denture is better from the point of retention and stability. 5. The presence of labial flange produces a stronger denture, labial flange will make the denture stiffer so the midline fatigue fracture caused by repeated flexing across the midline is reduced. So, from the point of strength the flanged denture is better. 6. As the bone resorbed following extraction the denture become loose and a reline is required, so the presence of labial flange make it easier to add either a short-term soft lining materials or a cold curing relining material (as a chair side procedure). The color of some reline materials is not always ideal so they may be visible when used with open face denture. 4 Immediate denture 5th year Prosthodontics Lect. Dr. Mustafa Saadi Ali 7. The flanged denture covers the clot completely and protect them more effectively. The flanged denture exerts pressure on both lingual and labial gingiva reducing post extraction hemorrhage. 8. The consequence of wearing an immediate denture can lead to: a) If it is an open face, will produce a scalloped ridge in the region of the socketed teeth. b) If it is a flanged denture, the distribution of functional loads is more favorable to the underlying ridge, thus minimizing bone resorption. 9. When the patient has got used to an open face immediate denture, there is difficulty to accept a denture with labial flange in future and the patient will complain from the fullness of the lip. If flanged denture had worn from the beginning this problem would not occur. 10.When the ridge morphology produces deeply undercut area, it may not be possible to fit a full labial flange unless there is surgical reduction. In this case, the using of partially flanged denture or open face denture is preferable when surgical procedure is contraindication. Explanation to the Patient Concerning Immediate Dentures 1. They do not fit as well as complete dentures. They may need temporary linings with tissue conditioners and may require the use of denture adhesives. 2. They will cause discomfort. The pain of the extractions, in addition to the sore spots caused by the immediate denture, will make the first week or two after insertion difficult. 3. The esthetics may be unpredictable. Without an anterior try-in, the appearance of the immediate denture may be different from what you expected. 4. Many other denture factors are unpredictable such as gagging tendency, increased salivation, different chewing sounds, and facial contour. 5. Immediate dentures must be worn for the first 24 hours without being removed by the patient. If they are removed, they may not be able to be reinserted for 3 to 4 days. The dentist will remove them at the 24-hour visit. 6. Because supporting tissue changes are unpredictable, immediate dentures may loosen up during the first 1-2 years, or 4-6 months depending on the number of teeth and their location. 5 Immediate denture 5th year Prosthodontics Lect. Dr. Mustafa Saadi Ali Diagnostic steps Good oral hygiene is essential before starting any prosthodontic treatment. Patient's systemic condition, it is very important to check the general health of the patient because multiple extraction may not be tolerated by all the patients, that's why patients with uncontrolled systemic diseases should not be included in this type of treatment. Patients under medical control and do not interfere with the steps of denture construction including several teeth extraction with or without some surgical corrections can be included, medical consultation is advisable. Full dental history must be recorded in the case sheet. Periodontal condition of the remaining teeth must be assessed, this must include teeth mobility, measurement of the pockets; because this might affect surgical step of the treatment course. Severe case of periodontal disease may suggest some surgical correction after extraction to have well contoured residual ridge covered with firmly attached mucosal tissue. Periodontal condition may give a primitive assessment about the bone remodeling subsequent to the surgical phase. Full teeth charting, teeth my help in retention as a partial denture or overdenture abutments must be determined, any soft or hard tissue correction as frenal release or bone reduction must be included after good evaluation. Radiographic examination which is essential for immediate denture patients. Periapical radiograph may be useful for localized area. OPG view give general view for both jaws in single image. Teeth mold and shade must be recorded. Proper communication with the patient about his teeth shade and form is essential. Furthermore, teeth alignment and any individual variations as diastema, spacing, rotation of the teeth if the patient like to preserve same appearance or improvement could be suggested by dentist for better appearance. BUT it is very important to remove any premature contacts because these may interfere with correct jaw relation record, essential changes to improve occlusal plane, midline, overjet and 6 Immediate denture 5th year Prosthodontics Lect. Dr. Mustafa Saadi Ali overbite and any other corrections that help in esthetic and functional requirements. Occlusal plane adjustment is necessary because the factors that necessitate tooth extraction are often associated with occlusal discrepancies. These also interfere with centric relation record as well as with the proper determination of occlusal vertical relation. Proper location of low and high lip lines must be determined to determine the required changes in teeth position or angulations. Presence of any infection or inflammation in the soft and hard tissues. Periapical abscess, granuloma and cysts may make the estimated tissue changes at the time of extraction and healing and remodeling process unpredictable; this may increase of the risk of unfitted immediate denture. Previous prosthesis (if present) must be checked as an additive reference for the jaw relations or teeth selection. It also may help the dentist to explain some of treatment or correct some errors. In many cases of immediate denture, diagnostic casts are essential. These casts could serve a lot in the treatment plan and communication with the patient. The casts also can be used as a pre-extraction record. All immediate denture patients must have good oral prophylaxis, proper scaling and good oral hygiene, this will reduce postoperative edema and infection. Other treatments as restorations or crown and bridges must be done in coincidence with immediate denture planning. In the diagnosis step, with all the collected information, you have to decide type of surgical procedure. Immediate denture can be constructed with one of the surgical procedures: 1. Extraction of teeth only. 2. Extraction of teeth with alveoloplasty. 7 Immediate denture 5th year Prosthodontics Lect. Dr. Mustafa Saadi Ali In some case simple corrections may be needed at the site of extracted teeth to improve the shape of the alveolar process in order to facilitate and improve denture objectives. In these cases, surgical splint construction is important. This splint usually constructed on the master cast after teeth trimming. Cases with excessive bone correction may be end up with rapid bone resorption and unfitted denture, therefore bone removal must be conservative. Consultation with the surgeon is essential in some cases. Steps of immediate denture fabrication 1. Impression Successful impression is governed by proper tray selection, proper material selection and manipulation (usually irreversible hydrocolloid material is used), and well-trained dentist to handle and make the impression in a proper technique. In some cases when the remaining teeth are very loose, there is a risk of teeth extraction during impression making, so try to fix these teeth either by: 1) Applying a lubricant medium to the teeth. 2) In case of adjacent teeth to each other, applying molding soft wax into sub- contact point spaces and around the necks of teeth so that the impression material is prevented from locking into the undercuts. 3) In case of solitary tooth, placing a loose-fitting cupper band over the tooth before taking impression. Primary impression Stock tray (metal or plastic) must extend to cover the intended denture bearing area able to record the vestibule extension, it must cover the retromolar area in the lower arch and extended posteriorly to include tuberosity and hamular notch in the upper arch. Enough space between the tray and the oral tissue to have enough and uniform thickness of the impression material; this does not mean to use oversized tray because it distorts the tissue and leads to incorrect impression recording. Sheet wax may be used to complete minor under extension. The impression must be free of voids and fully extended according to the planned prosthesis design. Primary cast is delivered by pouring the primary impression with any of the gypsum products. This cast helps as a study cast to plan the sequences of the treatment as well as used to construct special tray. Primary impression may be useful as a final impression in case of immediate single tooth replacement with or without short span partially edentulous arch. 8 Immediate denture 5th year Prosthodontics Lect. Dr. Mustafa Saadi Ali Final impression Different tray design and impression techniques were described to deliver final impression. These techniques may range from simple to more complicated depend on tray design and material used. Selection of a suitable technique depends on: 1) Case difficulty. 2) The number and location of teeth included in the immediate denture treatment. 3) Teeth and tissue undercut. 4) Type of impression material used. 5) Dentist skill and experience. The imperative technique is that record the tissues and denture bearing area in a maximum accuracy that minimize the insertion, post-extraction denture adjustment and maintenance phases as possible. The single full arch custom tray technique This technique is used for interim immediate denture and can be used for conventional immediate denture. It is used when the patient has anterior teeth only or anterior and posterior remaining teeth. A custom tray is fabricated on the primary cast using cold cured acrylic resin. The tray should cover all teeth and denture bearing area. It should be 2 mm short of vestibules. A single or double layers of sheet wax (depending of the impression material used) should be placed over the teeth as a spacer before fabrication of the custom tray. After checking the tray in the patient's mouth, border molding is done using tracing compound in the same manner as in conventional complete denture and continue to do final impression. Final impression can be taken with irreversible hydrocolloid or silicone or polysulfide rubber base or polyether as a final impression material. More expert dentist may use 2 impression material (ZOE + alginate) in one tray for maximum accuracy. The sectional impression (split impression tray) technique This technique is used in conventional immediate denture only; and cannot be used in interim immediate denture. 9 Immediate denture 5th year Prosthodontics Lect. Dr. Mustafa Saadi Ali This technique is used mainly when the posterior area is edentulous and only anterior teeth are remaining and need to be replaced with immediate denture. It involves construction of two trays on the same cast; one for the posterior region made as in complete denture and the 2nd is constructed for the anterior region. Indices or references must be made in the tray. The anterior section impression will capture the facial anatomy of the teeth, the vestibular anatomy. The posterior sectional tray (must be tried for proper extension, border molding is made with tracing compound) as in conventional complete denture, then final impression for edentulous area is made by using zinc oxide eugenol impression material, polyvinyl silicon, polysulfide, or polyether. Upon removal of the anterior and posterior sections separately, the two sections are reassembled outside the mouth (using the indices) and prepared for casting. The most important thing in sectional impression tray is the accuracy and proper seating of the trays and reassembling both. Care must be taken not to distorted this assembly during tray removal from the mouth or during pouring therefore it's advisable to bead and box the impression before pouring The impression will record the whole denture bearing area made by two different materials. A modification of the above technique can be made with a full tray covering the denture bearing area with a hole for the teeth area. Again, border molding and impression of the edentulous area is made. Then a proper stock tray over the custom one can be used to capture the teeth area with alginate material. 2. Beading and boxing The impression must be beaded before pouring. Wax may not stick to the alginate impression material; therefore, care must be taken to insure proper beading. Once the beading wax is fixed, boxing wax sheets can be easily stick to the impression. In the sectional impression, be careful to seat the sections properly on the indices. Pour the impression and remove the tray as in the conventional manner. 3. Record base and occlusion rim Bite rims are usually constructed to record jaw relations. If the patient has enough number of remaining anterior and posterior teeth, no need for record base or bite rim as in most of interim immediate denture. 10 Immediate denture 5th year Prosthodontics Lect. Dr. Mustafa Saadi Ali While if there isn't enough number of remaining teeth as in all of conventional immediate denture and some of the interim immediate denture cases, bite rim must be constructed. Before constructing the record base, all teeth and tissue undercuts must be blocked by wax, then cold cure acrylic dough is applied on the edentulous area of the cast. When the material set, record base must be finished and polished. Final evaluation must show a stable properly extended record base. Wax occlusion rim is added to the corresponded edentulous area on the base. Leveling of the wax must depend on some anatomical landmarks as the retromolar area and you may use the remaining teeth but not always. Record base extension and wax rim height must be evaluated clinically. Lip lines; high and low must be determined and marked on the cast, in this way any correction or modifications can be done or marked on the cast to be considered in the teeth setting. 4. Jaw relations record Include vertical and horizontal relations, these usually made as in the conventional denture construction. If we have vertical stops between two opposing posterior teeth, these relations are maintained unless further corrections are needed to improve esthetic or function. Evaluation of the existed vertical dimension of occlusion must be accomplished and dentist must decide if this going to be restored or modified. Uneven tooth loss, teeth wear, loosening of the remaining teeth drifting and extrusion all may indicate correction of vertical relation. In this visit dentist must record the midline, canine lines, ala-tragus line, smiling and high lip line, anterior occlusal plane in relation to the remaining teeth. Face bow transfer and centric Jaw relation must be recorded. Once you record vertical and horizontal relations you are ready to mount the cast on a suitable articulator. Selection of artificial teeth, consider all parameters in teeth selection, in the anterior and posterior segment. Shade, Size, form, an occlusal form of posterior teeth must be selected to fit each case specifically. 11 Immediate denture 5th year Prosthodontics Lect. Dr. Mustafa Saadi Ali 5. Try-in Try in step is not possible in every immediate denture case but even so mounting of the master casts must be confirmed in patient's visit. In most of conventional immediate denture cases posterior teeth are missed so you can set the posterior teeth as in conventional complete denture construction following the rules of teeth arrangement in the centric occlusion. Confirm all the landmarks recorded in the diagnostic step to set the patient's desire as: a) The midline weather it is the same or changed but it is very important to inform the patient if you decide any change, prepare yourself to explain the reasons for the patient. b) The anterior plane of occlusion; teeth may be extruded or over erupted so correct plane of occlusion must be recorded on the casts. Use some of the anatomical landmarks interpupillary line and parallelism with the ala- tragus line. c) High lip line must be determined and marked on the cast. Discussion must be made with the patient about the amount of display of the teeth and gingiva. d) Localized alveoloplasty or some changes in the teeth alignment may be suggested to improve appearance. Make sure that the patient sees and approves this. e) Diastema, rotated teeth, overjet and overbite and other natural variations must be discussed with the patient because some patient may ask for a perfect looking even if they never had, others may like their natural variations (in this way nobody can notice the denture). Dentist may share his experience, knowledge and opinion for best results especially when the patient asks for changes or variations interfere with function and esthetic principles. The patient must be actively involved in the decisions of esthetics. In this visit, further information about the following must be given: surgical procedures, tissue changes as edema and discoloration few days after insertion, local sense of lip puffiness even when the edema dissolved due to the flange extension. Answer all the questions asked by the patient directly and very clear. At the end of the try-in visit you have to check all what is related to the present teeth and mark all what you have to change (teeth and tissues) on the cast. 12 Immediate denture 5th year Prosthodontics Lect. Dr. Mustafa Saadi Ali 6. Cast trimming The remaining teeth now must be trimmed to be replaced with artificial teeth. Trimming of the cast must be done carefully to estimate as possible the shape of the residual ridge after teeth extraction. Final cast ridge must be similar to the contour of the foundation area after teeth extraction. More than one method may be use to trim and set the teeth in immediate denture cases, it depends on: 1) If you decide to duplicate same teeth alignment or not. 2) Esthetic and functional requirement. 3) Amount of changes expected during surgery. Usually, teeth are trimmed by using a saw or a disc bur, sharp knife or wax knife may help. Scribe guidelines on the cast recording the position, angulations and incisal level of the natural teeth (In this step it must follow the rule of third to guide cast trimming). 13 Immediate denture 5th year Prosthodontics Lect. Dr. Mustafa Saadi Ali Note that the amount of grinding is very minimal on the palatal side; this is because the remodeling after extraction is usually minimal in this side. Final ridge form must be round and continuous from the buccal and lingual surfaces. Cast trimming may be done at same time of teeth arrangement. Do not change or trim the essential landmarks as incisive papilla or any frenum. 14 Immediate denture 5th year Prosthodontics Lect. Dr. Mustafa Saadi Ali 7. Surgical guide After complete cast trimming, surgical splint must be constructed. It is a thin transparent form of tissue surface of the immediate denture; it is used to guide the surgical shaping of the alveolar process. It is essential when there is a need to do some alveolar corrections after teeth extraction or ridge recontouring or correction of the inter septal bone or in multiple teeth extraction. The splint is constructed by the following steps: a) Make alginate impression on the cast after trimming. b) Pour the impression (cast duplication). c) Make the clear template processed either by heat or light, vacuum form and sprinkle-on method can be used also. Advantage: splints also help to remove any expected pressure area at the sight of extraction thus minimize insertion time and adjustment at the insertion visit. 8. Setting of anterior teeth Arrangement of anterior teeth can be made in different ways; the dentist has to decide: a) If the teeth are need to be changed in location or alignment to improve the aesthetic. b) The teeth are well aligned, aesthetically and functionally acceptable; then we can reproduce same alignment in the denture. There are two ways to arrange the teeth in the same alignment of the natural teeth First way: Produce a labial index of the natural teeth before they are cut off the cast. The artificial teeth can be set into the index while it is held against the cast preserving same teeth location. In this technique same teeth morphology and location is duplicated. Second way: Remove one tooth from the cast and immediately wax an artificial tooth into position so that the adjacent teeth serve as a guide to the positioning of the artificial replacement. Repeat this procedure alternatively, this is called the alternative method. OR trim all the teeth on one side and use the other side as a reference. 15 Immediate denture 5th year Prosthodontics Lect. Dr. Mustafa Saadi Ali 9. Waxing and flasking In this step, any custom selected personalization criteria must be carved. Processing and flasking are same as in the conventional complete denture. Keep both the denture and the splint template in the disinfectant to delivery. 10.Insertion and post insertion visits At the day of surgery and insertion 1) Examine the patient intraorally to check for any changes. 2) Extraction of the marked teeth; preserve the labial plate and be conservative, no bone trimming is done without guiding; use suture if necessary. 3) Use the surgical template to guide any alveolar corrections. Seat the template: blanch areas seen through the template indicates pressure, then need correction. 4) Insert the denture; remove all the detected over extended flanges and correct any pressure areas. Check the frenum relief. 5) Check occlusion, no gross occlusal interference. 6) Usually, we use the tissue conditioner to retain the denture BUT do not allow the material to extend in the socket areas otherwise normal socket healing will be compromised. 7) At the day of insertion try to reduce the numbers on insertion and removing of the denture to avoid trauma and edema. First 24 hours 1) Avoid removing the immediate denture. 2) Put gentle biting pressure on your denture during the first four hours. 3) Avoid hard food and eat soft healthy food, avoid drinking hot fluids. 4) Using ice pack in the first 24h (20 min on followed by 20 min off) may control inflammation and swelling. 5) Patient should be reminded that the pain from extraction will not reduce by removal the denture. 6) Analgesic, antibiotic, must be prescribed to patient depending on the case. 1st Adjustment must be seen after 24 hours 1) The denture should be kept out of patient mouth only for short time, therefore quickly check the tissue sore spots, over extension and any gross occlusal discrepancy. 16 Immediate denture 5th year Prosthodontics Lect. Dr. Mustafa Saadi Ali 2) On removal the denture may be painful; inform the patient and adjust sore area which appears as deep red areas mostly undercuts as canine eminence, tuberosity, and retro mylohyoid ridge. 3) Adjust occlusion. 4) Assess retention and use tissue conditioner if needed. 1st week after extraction and denture insertion 1) Instruct your patient to wear the denture day and night for first 7 days after extraction or until swelling reduction. 2) Remove the denture 4 or 5 times a day after the first day, and rinse the mouth with warm salt water. Do this for the first week. 3) The denture must be cleaned and rinsed after meal as early as possible and when removal and insertion of the denture is with little or tolerable pain. Further follow up care 1) 2nd week is the next call, this depends on the case. Then the patient should be seen one month later, 4-6 months intervals. 2) A denture adhesive will be necessary to help hold the denture in place. 3) Relining may be necessary to achieve esthetic and occlusion corrections. 4) Frequent or periodic recall mainly for changing temporary liner, this depends on the rate and amount of bone resorption and ability of patient to keep the liner clean. 17