14

The Atrophic Edentulous Jaw

Augmentations in an atrophied edentulous ridge have some peculiarities compared to the treatmentplanning concept in chapter 11. Augmentations and prosthetic procedures affect not only dental esthetics but also the entire face and perioral skin. The defect size and graft volumes sometimes require extraoral donor regions and inpatient conditions under general anesthesia. The transition from a natural to a prosthetic dentition is a psychologically significant threshold in life for patients, which is respected by careful planning and execution of the dental prosthesis. Careful consideration of conventional as well as augmentation and augmentation-free implant-supported restoration options is required. Great haste and promises of new teeth in a few hours contradict this.

14.1 Function (Mastication and Speech) and Alveolar Ridge Atrophy

The process of alveolar ridge atrophy is physiologic and in this sense not a disease; however, the result—the resorbed alveolar ridges and the limited chewing ability of the edentulous person—must be considered a serious loss of organs, in this case of the masticatory organ. Imagine what an unpleasant experience it is when, in company, the mandibular denture slips into the cup while drinking tea, or what danger can be involved when, while eating in a social situation, an edentulous person tries to swallow unchewed meat out of shame and suffers respiratory distress and possible choking. A study of the chewing ability of test food revealed that patients with overdentures on atrophied ridges had only about 20% of the chewing ability of edentulous patients or patients with fixed dentures (Fig 14-1). Overdentures on dental implants also did not achieve much more chewing ability (40%) than complete dentures, except that the dentures were positionally stabilized.¹ It has been clearly demonstrated that a sufficient number of dental implants increases masticatory strength and masticatory efficiency, both for single-tooth gaps² and for implant-supported complete dentures.³ In patients with atrophied alveolar ridges, implant restoration and masticatory rehabilitation also improved speech function and articulation.⁴

Fig 14-1 Chewing ability was experimentally determined in a study by having participants chew a tough test food (cured impression silicone) and recording the number of chewing cycles and the resulting size of the particles using graduated sieves. This showed that with an overdenture on two implants in the mandible (overdenture on implants), there was only a slight difference in particle size and no advantage at all in chewing duration compared to patients with full dentures on atrophied ridges. Therefore, to be able to chew like dentate patients again, more elaborate prostheses on more than two implants are necessary for edentulous patients. (Adapted from Fontijn-Tekamp.¹)

14.2 Nutrition and Alveolar Ridge Atrophy

Most denture wearers with atrophied alveolar ridges intuitively respond to the question of whether they can chew well that they could eat anything and have hardly any restrictions. This only shows how adaptable people are and how gradually the process of chewing loss occurs. A closer look then reveals that the food is previously divided into small bites on the plate, is gulped down more or less unchewed, and the diet as a whole is very carbohydrate-dominated. Contrary to expectations, patients with poor chewing function are usually not underweight, but rather overweight due to malnutrition. Humans need a certain amount of minerals (eg, calcium and iron) and vitamins and intuitively feel this. If the spectrum of food shifts due to a lack of chewing ability,⁵ if the diet contains fewer fresh vegetables and meat but more mashed potatoes and creamed soups, and if more bananas are consumed instead of apples and carrots, then one has to eat more overall in order to get out of the nutrient-poor diet the required daily amount of nutrients. Lack of exercise reinforces this even further, because if in the past it was possible to extract the nutrients from 3,000 calories per day with physical work, in today’s modern world 1,500 calories per day must suffice as the amount of food required due to a lack of exercise. This does not adequately succeed and is part of the explanation for the high rate of osteoporosis, among other things. Nutrient undersupply is a drive to caloric oversupply, and this is one of the causes of obesity in modern society. Nutrition as a whole suffers from a lack of chewing ability when food cannot be adequately broken down and the food spectrum shifts.⁶ In a comparative study, 22% of denture wearers suffered from malnutrition versus 0% of dentate participants.⁷

A gradual shift in the edentulous person’s food spectrum toward soft carbohydrates may also increase the likelihood of onset of or exacerbate type 2 diabetes. Timely masticatory rehabilitation can therefore prevent nutritional disorders and contribute to general health.

14.3 Dementia and Alveolar Ridge Atrophy

Chewing ability is not a question of old age, but a question of dental status.⁸ It has been known for a long time that the onset of dementia is statistically associated with the loss of chewing ability,⁹ whereby a neuromuscular causal relationship is frequently discussed.¹⁰ In any case, it is plausible that a person with poor masticatory function due to alveolar ridge atrophy may not be able to eat well and may become socially withdrawn, resulting in cognitive deterioration. Timely masticatory rehabilitation may help prevent dementia.

14.4 Quality of Life and Alveolar Ridge Atrophy

There is clear evidence that dental implant-supported restorations improve the quality of life of edentulous patients with alveolar ridge atrophy.¹¹ In a recent study, an Oral Health Impact Profile (OHIP) score improved from 15.89 to 6.18, but not only oral-related quality of life improves with dental implants, but also general health-related quality of life in parallel.¹² The quality of life after augmentation by iliac bone grafts was at a similar favorable level of 8.4, which highlights the good tolerability of the bone augmentation method in edentulous patients with alveolar ridge atrophy.¹³

14.5 Facial Esthetics and Alveolar Ridge Atrophy

The vertical: Occlusal and lower face height

There are many influences over the course of life that lead to a decrease in vertical occlusal dimension. These include abrasion and attrition, intrusion and tooth migration, and orthodontic and other tooth extractions. The reduced occlusal height has consequences. The lower face height decreases, and the face appears wider. The lower face soft tissues, which are sized for a certain bone frame, compress, resulting in thin lips as well as a sharp supramental fold and deepened nasolabial folds. The retracted lips also cause a slightly negative mouth rounding (ie, ).

The positive effect of the bite elevation can already be simulated during the initial consultation by placing cotton rolls on the mandibular dentures of the edentulous patient and blocking the bite by one to two centimeters during the planning consultation. In addition, the lips can be supported from the inside with a little Flexaponal wax (Dentaurum) to simulate the functional and esthetic gain of dental treatment (Fig 14-2). It can be observed whether the lips become fuller and the mouth rounding becomes positive (ie, ).

The horizontal: Pseudoprognathism

In this way, it is also possible to check whether a true prognathism or a pseudoprognathism, which disappears during bite elevation, is present (Fig 14-3). This is because the final occlusal reduction is a consequence of the loss of the last teeth and the subsequent alveolar ridge atrophy. The mandible rotates around the axis of rotation in the temporomandibular joint. This causes the chin and mandibular alveolar ridge to move anterior to the maxilla, resulting in protrusion of the chin and a Class III bite: pseudoprognathism. The muscles of facial expression, often called the mimic muscles, lose their tension in the resting position. This may develop into salivary incontinence with oral angular cheilitis and candidiasis.

Mimic muscles

Atrophy following tooth loss causes the attachment points of the mimic muscles to diminish. Loss of retention of the mentalis muscle, which normally inserts at the root level of the mandibular anterior teeth on the vestibular alveolar ridge, causes the chin soft tissue to descend, which is referred to as chin droop, chin ptosis, or witch’s chin. This deformity cannot be corrected by dental prosthetic measures because the muscle attachment cannot be restored by denture acrylic. The preliminary stage of chin ptosis is greater exposure of the mandibular teeth, which is observed in many elderly people due to a decrease in lip tension. The smile muscles of the upper lip also lose their attachment and tension, so pouting of the lips is eliminated, and the lip becomes narrow and collapsed. The lack of lip support due to alveolar bone and tooth loss leads to fine vertical wrinkling of the upper lip skin in early stages and sagging of the cheek soft tissues into the oral cavity in late stages. This in turn results in a relative protrusion of the nose with lowering of the nasal tip, which then looks oversized compared to the rest of the face.

Fig 14-2 Improvement of masticatory function by increasing the number of implants. a. Initial situation in a 67-year-old patient with atrophic and flabby ridge. b. Existing restoration with overdenture and two dental implants in the mandible. c. Initial situation with curled lips and compressed soft tissues due to the missing lip support from teeth and the alveolar ridge. There is salivary incontinence of the corners of the mouth with a tendency to angular cheilitis. The perioral skin folds are deepened, and the oral fissure shows negative rounding. d. Panoramic radiograph showing Cawood class V atrophy. e. Lateral cephalometric radiograph with especially atrophied anterior alveolar ridge as a combination syndrome due to the hard anterior occlusion with the two mandibular implants. These lead to constant tilting of the maxillary prosthesis with transformation of alveolar bone into flabby tissue. When planning the two mandibular implants, the maxilla could have been included in the implant planning to prevent the combination syndrome. f. Planning simulation of bite elevation and bone augmentation using cotton rolls on the dentures and Flexaponal wax strips on the dentures for lip relining. This causes the red of the lips to roll outward, the perioral wrinkles to disappear, and a positive rounding of the mouth.

Fig 14-2 Improvement of masticatory function by increasing the number of implants. g. Panoramic radiograph after maxillary alveolar ridge augmentation by LeFort interpositional bone grafting. h. Lateral cephalometric radiograph after augmentation. i. Intraoperative image: LeFort I bone graft with interposition of bone substitute material and additional lateral apposition of monocortical autologous iliac bone grafts. j. Panoramic image after implant restoration. k. Lateral cephalometric radiograph after implant restoration. l. Exposed implants before prosthetic restoration.

Fig 14-2 Improvement of masticatory function by increasing the number of implants. m. Panoramic image after restoration with bar prosthesis in the maxilla (Dr Rauch, Melsungen). n. Extraoral image after prosthetic restoration.

Fig 14-3 Improvement of function and facial esthetics by augmentation. a. Initial situation: atrophied maxillary alveolar process with insufficient denture retention in a 55-year-old female patient. b. Lateral cephalometric radiograph showing pseudoprognathism of the mandible.

Fig 14-3 Improvement of function and facial esthetics by augmentation. c. Panoramic image with atrophy of Cawood class V in the maxilla and class IV in the mandible. d. Intraoperative image: LeFort I osteotomy with interposition of bone graft substitutes and additional lateral and anterior apposition of monocortical autogenous iliac bone grafts. e. Panoramic image after maxillary alveolar ridge augmentation by LeFort interpositional bone grafting. f. Lateral cephalometric radiograph after augmentation. Pseudoprognathism is already reduced due to the improved vertical occlusal dimension. g. Osteosynthesis material removal 4 months after Fig 14-3f shows rounding of the edges of the bone grafts and normal low surface resorption, recognizable by the exposed screw heads. h. Augmentation enables prosthetic-friendly, tooth-axis-compliant, and parallel alignment of the maxillary dental implants so that they can later be axially loaded without angled abutments.

Fig 14-3 Improvement of function and facial esthetics by augmentation. i. Panoramic radiograph after implant uncovering 3 months after Fig 14-3 h. j. Lateral cephalometric radiograph after implant uncovering. k. Conical double crowns as retaining elements in the maxilla. l. Same retaining elements in the mandible. m. Prosthetic restoration with overdenture in the maxilla (Dr M. Braun, Kassel). n. Before and after images in profile. Reduction of the pseudoprognathism and unfolding of the lips are noticeable. o. Before and after facial views. A stretching of the facial shape through improved occlusal height as well as a smoothing of the supramental fold and improvement of the lip fullness is recognizable.

All these developments can be reversed by careful dental prosthetic therapy. Cosmetic measures such as permanent makeup to widen curled lips, lip injections, skin resurfacing, facelifts, and the like do not address the problem from the root cause and are therefore usually relatively unsuccessful. At best, they should be performed following occlusal rehabilitation.

14.6 Dental Prosthetic Features in Severe Alveolar Ridge Atrophy

In most cases, dental implants and augmentations are necessary for satisfactory masticatory functional rehabilitation of edentulous patients with ridge atrophy. A conventional denture is often not sufficient.

Maxilla

In the maxilla, support is required for unfolding of the skin around the lips. This usually requires the maxillary anterior and posterior teeth to be positioned anterior or lateral to the alveolar ridge, because the centripetal atrophy of the maxilla has made it too small relative to the mandible. Because of this unfavorable overhang, conventional dentures without implant anchorage would be quickly dislodged. Dislodging of the denture occurs especially with protrusion and guidance contacts, even with a fully balanced tooth setup, resulting in flexing of the anterior maxillary alveolar ridge. This results in increased atrophy of the anterior maxilla with the formation of a rubber-like flabby crest. This influence is particularly extreme in the combination syndrome when a mandibular residual dentition meets a soft tissue-supported full denture in the edentulous maxilla (Fig 14-4). Even more at risk for such a syndrome is the combination of four implants in the mandible with a conventionally rehabilitated maxilla. In these cases, alveolar ridge atrophy is sometimes seen in the anterior region down to the nasal floor, with the alveolar process still present laterally. The final stage of ill-fitting maxillary dentures is usually inflammation of the oral mucosa, chronic pressure sores, and irritation fibromas. Truly effective lip support results only from bone augmentation of the alveolar processes, in which case the mimic muscles find their natural attachment points again and receive proper tension. The alveolar process volume and the sagittal position of the alveolar processes are more important for the lip appearance than the position of the teeth.

Mandible

In the mandible, the problem of increasing alveolar ridge atrophy is initially poor positional stabilization of the denture against shear and pull-off forces. If dental implants are not an option, this problem can be eliminated down to at least 15 mm symphysis height (seen on lateral cephalometric radiograph) by a combination of lowering of the floor of the mouth and coverage by a split-thickness skin graft. These procedures are considered as relative heightening of the ridges, in contrast to a bone augmentation, which is considered absolute heightening of the ridge. After this soft tissue surgical measure, which has unfortunately been largely forgotten in many countries, a mandibular denture usually holds satisfactorily. However, the hold that can be achieved is not comparable with the comfort gain provided by dental implants. In the period of preprosthetic surgery, the indication for an absolute ridge augmentation was below 15 mm. Without dental implants, however, all absolute augmentation measures by bone grafts and visor and sandwich osteotomies were only of short duration, because the amount of elevation disappeared again within a few years due to continued jaw atrophy. Only the combination of bone augmentation measures with dental implants has brought about a real halt to alveolar ridge atrophy, which is referred to as the bone-protective effect of dental implants. However, it is also true for the mandible that the lip appearance is characterized more by the alveolar processes than by the tooth position, because the mimic muscles do not find any attachment points on denture acrylic.

Fig 14-4 Return to a fixed dentition in a case of severe maxillary atrophy. a. Initial situation: 59-year-old female patient with a flabby ridge in the anterior maxilla with inadequate denture fit. b. Panoramic radiograph showing initial situation with combination syndrome due to an almost full dentition in the mandible. The maxilla is severely atrophied anteriorly, which appears as local osteolysis. The posterior maxilla shows a lower degree of atrophy. c. Section of lateral cephalometric image showing negative stepping of the lips and retroposition of the maxilla in relation to the mandible. d. Intraoperative image with LeFort I interpositional osteoplasty under advancement and interposition of bone graft substitute. In addition, lateral and anterior apposition of autogenous iliac bone blocks with corresponding osteosynthesis. e. Panoramic image after augmentation. Two temporary dental implants can be seen for positional stabilization of the provisional prosthesis. f. Section of lateral cephalometric radiograph. The maxillary retroposition has been eliminated.

Fig 14-4 Return to a fixed dentition in a case of severe maxillary atrophy. g. Four months after Fig 14-4d, the dental implants were inserted parallel to each other and in the correct axis for the subsequent prosthetic restoration enabled by augmentation. h. Panoramic image after implant placement with parallel alignment. Without augmentation, the implants would be divergent according to the narrow apical base of the natural maxilla (similar to a bouquet of flowers). i. Section of lateral cephalometric radiograph after implant placement. j. Even before implant uncovering, there is marked improvement in the amount of attached gingiva compared to Fig 14-4a. The flabby ridge has been filled from inside. k. Because the incisions were always made midcrestally and the soft tissue was never detached from the palatal bone during the interpositional bone grafting, in contrast to an onlay osteoplasty, the implants can emerge in that place where already the primary and permanent teeth had erupted. Additional surgical soft tissue management is unnecessary. l. Panoramic image after implant exposure. Bone level up to the implant shoulder is shown.

Fig 14-4 Return to a fixed dentition in a case severe maxillary atrophy. m. The impression copings are parallel in the prosthetic phase thanks to the straight implant alignment. Therefore, little elastic deformation of the impression materials and thus low impression error can be expected. In principle, it would be possible to work with impression plaster as was historically done. n. Fixed prosthesis in crown-bridge technique without acrylic or gingival imitations (Dr J. Tetsch, Münster, Germany). o. Fixed prosthetic restoration after previous extreme atrophy. In a sense, the biologic clock of the ridge has been turned back to the time before edentulism. p. Occlusal view of the prosthesis. q. Smile image. r. Panoramic radiograph 1 year after prosthetic restoration without signs of marginal bone resorption. The prosthetic restoration was modified again, using partial dentures.

A special feature of the atrophic mandible can be the painful pressure on the mental nerve, when the mental foramen seeminigly migrates to the crest over the course of severe atrophy. Here, chronic irritation due to the pressure of the denture and a chronic pain syndrome can occur, which can only be satisfactorily eliminated by bone augmentation.

Another feature of severe alveolar process atrophy of the mandible is the risk of fracture, especially in connection with drilling for dental implants.¹⁴

14.7 Step 1: Differential Indication for Implant-Retained Overdenture Versus Implant-Supported Denture

This differential indication is predominantly a question of chewing performance and chewing habits with the previous restoration. It is also important to assess patients’ previous situation. Do they still have their own teeth, are they already used to removable dentures, or have they been wearing full fixed dentures for a long time? Patients coming from a conventional full denture or overdenture will most likely continue to be satisfied with this solution, with the improvement that a palate-free overdenture can be achieved with dental implants. Patients who previously had their own teeth and until recently were able to chew relatively well would probably be disappointed by a full denture, even if only as a provisional solution. Such patients are more likely to be advised toward implant-supported dentures.

Age and age-related dexterity for hygiene measures as well as wishes for social participation, such as eating food that is difficult to chew in company, also influence the decision. No sharp line can be drawn here, but for those over 80 years of age, the overdenture should at least be seriously considered. However, it should also be mentioned that an overdenture has hygienic disadvantages, because it cannot be rinsed underneath, and severe therapy-resistant denture stomatitis due to candida overgrowth often develops in the covered mucosal areas.

However, the decisive factor for the choice of implant-retained overdentures versus implantsupported dentures is the desire for chewing ability. Edentulous patients with ridge atrophy can first be asked what they can currently eat, followed by the question of what they would like to be able to chew. If there is then no great additional desire for chewing function, the therapy tends to go in the direction of position-stabilized mandibular dentures with two implants and a palate-free overdenture retained on four implants in the canine and first molar positions (Fig 14-5). Sinus elevation also allows secure stabilization in this case and brings many advantages over an overdenture retained on four implants in the intersinus region, because such a solution requires a very wide posterior denture base to absorb the tilting moments. According to the German Society for Implantology (DGI) guidelines, two implants are always too few in the maxilla. In a prospective study, overdentures retained on four mini-implants did not provide any gain in chewing ability compared to conventional full dentures, but only stabilized the position of the denture.¹⁵ Implant-retained or -supported restorations should be recommended in both arches, with a minimum two implants in the mandible and four in the maxilla. If, for reasons of cost, only the mandible is restored with implants, there is a risk of combination syndrome, ie, increased atrophy of the anterior maxilla with formation of a flabby ridge due to the strong occlusive forces in that area. The abutments against the masticatory force should be approximately equally strong in both articulating partners, as in the case of scissors, in order to effectively crush the food.

The chewing comfort of overdentures does not match the chewing power of natural teeth. If the desire is to bite off bread crusts and apples or to eat tough meat, then more effort is required. Then the restoration goes in the direction of a fixed or removable implant-supported prosthesis on at least four interforaminal implants in the mandible and at least four, preferably six, implants in the maxilla.

Fig 14-5 Procedure for implant-retained overdentures. a. Initial situation: denture-incompetent atrophied maxilla in a 74-year-old female patient. b. Panoramic image showing Cawood class V atrophy of the maxillary alveolar process. c. The lateral cephalometric image shows the relatively voluminous bone in the symphysis of the mandible. d. Panoramic image after LeFort I interpositional bone grafting. e. Lateral cephalometric image after augmentation showing bone gain. f. Four months after Fig 14-5d, implant placement takes place. The insertion posts show the prosthetically friendly parallel alignment of the implants.

Fig 14-5 Procedure for implant-retained overdentures. g. The panoramic image shows the recommended number and location of implants for overdenture restorations. h.

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