A rough outline model for the prosthetic treatment options, single-tooth gap
10.4 Gathering Information
10.4.1 Patient History
10.4.1.1 The Medical History
The patient’s general health must be comprehensively recorded to make sure whether it will affect the selection of treatment procedures or not. The dental procedures or the restoration itself must never be injurious to the health of the patient. Moreover, the caregiver should make sure that no member of the dental team or other patients will be harmed as a consequence of providing dental care to a patient who has an infectious disease.
10.4.1.2 The Social History
It is important to learn about the patient’s lifestyle including eating, drinking and smoking habits. Lifestyle factors can have a big impact on both the treatment itself and the outcome and maintenance of it. In most patients’ lives, the economy plays a major part which prosthetic treatment is affordable.
10.4.1.3 The Dental History
By listening to the patient’s own description of previous experience, it helps the dentist to gain an impression of the patient’s perceptions of dentistry and of their attitude or motivation for dental care. It also gives a hint of the patient’s ability to maintain an acceptable standard of oral hygiene and the previous dental care given.
10.4.2 The Oral Status
This examination encompasses the charting of remaining teeth and their status. An evaluation of the occlusion must be done as well as the health of the masticatory apparatus. Furthermore, the level of oral hygiene should be assessed. Individual teeth may need more specific investigations such as pulp vitality tests or a thorough assessment of the periodontal status. The clinical collection of information and assessment will be accompanied by a more or less extensive radiologic examination.
10.4.3 Radiographic Assessments
There are different imaging techniques and each one has its advantages and disadvantages, which the clinician must be aware of. The patient must not be exposed unnecessarily to ionizing radiation and still there is a need to decide on the best available means to obtain the required and necessary information .
10.4.4 Ridge and Bone Assessment
When selecting between different replacement options, an evaluation of the ridges is essential. This may be done by using a gloved finger to roughly estimate the outline and form. By placing a local anaesthetic and using a sterile probe with a rubber stopper, the thickness of the mucosa from the surface to the bone can be measured . Alternatively, this may be achieved using radiographs via a CT scan, but this is more expensive and not always available for the practising dentist. Bone quality is usually assessed radiographically to determine relative densities.
10.4.5 Space Assessment
Is the available tooth space large enough to incorporate a single tooth? It could very well be that the available space is too large for one single tooth or too small. If it is too large, there is an option to accept the gap as it is or to reduce the space via orthodontics or by reshaping the neighbouring teeth. If the edentulous space is too small, there is an option of increasing the space orthodontically or accepting the gap. Evaluation of the vertical dimensions is mandatory before any prosthetic restoration is placed. Lack of vertical space may require an increase in the occlusal vertical dimensions and can be done in many different ways .
10.5 Extraction and Ridge Augmentation
When a tooth is extracted, it is indisputably followed by a reduction of the alveolar ridge. Moreover, it is well established that both horizontal and vertical changes of hard- and soft-tissue dimensions take place at the edentulous site. The buccal cortical plate of the alveolar process may be resorbed even prior to tooth extraction as a result of inflammatory tooth disease, developmental defects and trauma or a combination of these factors. Recent review studies have shown horizontal bone loss of 29–63% and vertical bone loss of 11–22% after 6 months following tooth extraction and that the most rapid resorption takes place in the first year. The risk of unfavourable bone loss is particularly high in the anterior maxilla which is commonly known to exhibit a thin or even partially absent buccal bone plate [10–13].
The loss of bone often leaves a condition of poor quality and quantity of bone which many times is inadequate for the placement of dental implants but also changes the gingival contours. This can also be critical in determining the usefulness of a tooth-borne fixed bridge. If normal tooth morphology is to be maintained, this will give wide embrasures at the gingiva and may result in problems with speech or eating/drinking. The alternative of blocking the embrasures will lead to a poor aesthetic appearance since the inciso-gingival connectors will be too long [14, 15] (Figs. 10.2 and 10.3).
Bone deficiencies at site 22 after extraction resulting in a long inciso-gingival line and poor aesthetic with a tooth-borne fixed bridge. The gingival outline of pontic 22 will be situated higher compared to the neighbouring teeth. The aesthetics was solved with pre-prosthetic crown lengthening of the front teeth
Staged ridge augmentation at implant site 21 compared to simultaneous ridge augmentation at site 11
Consequently, different measures have been taken to avoid this bone modelling process such as immediate implant placement and bone grafting in order to counteract this catabolic process and preserve the dimensions of the alveolar ridge. Bone augmentation procedures to rebuild deficient ridge contours are mandatory to enable optimal dental implant placement and positioning. Sufficient bone volume, favourable three-dimensional implant positioning and stable peri-implant soft-tissue conditions are considered prerequisites to achieve long-term implant functions and aesthetics [11, 13].
Alveolar ridge rebuilding can be undertaken at different times during treatment and is generally categorized as simultaneous or staged. In the staged approach, the alveolar bone is first reconstructed in an initial surgery. Implant placement is then carried out 2–6 months later. In contrast, in the simultaneous approach, implant placement and alveolar ridge reestablishment are undertaken during the same surgery. The size of the defect affects the healing time. The simultaneous approach is obviously the preferred technique by the patient and clinician alike, since it reduces treatment time and cost. However, if the residual bone volume precludes primary implant stability or results in inadequate prosthodontic implant positioning, the staged approach is recommended [16, 17].
Thus, the clinician is required to carefully plan the extraction of a compromised tooth and to perform the surgical intervention according to a precise schedule and gentle touch in order to promote favourable hard- and soft-tissue conditions at the upcoming edentulous site. In addition, it is possible to reduce healing periods and number of surgical interventions, especially when implant treatment is planned .
The best way to treat a ridge deficiency is to prevent it from occurring!
10.6 No Replacement at All (NRA)
Sometimes “less is more”! Rarely is NRA chosen when a single tooth is missing in the aesthetic zone or in a position which is important to load-bearing zones. Studies have shown that individuals are usually more concerned about replacing missing anterior teeth than posterior teeth, since a great majority of patients find aesthetics more important than function. In some cases, the choice of not replacing a missing tooth could also be due to socio-economic factors . The clinician must also be aware of that drifting and tipping of neighbouring teeth to an extraction site are commonly reported phenomena and make an assessment of the consequences following tooth extraction. In a study by Craddock and co-workers, they found the teeth mesial to the extraction site had a tendency to tip distally. The upper teeth showed a higher degree of tipping and also in subjects with a cusp-to-cusp buccal occlusion. Moreover, the tipping of the tooth distal to the extraction site was more prevalent in individuals with a reduced overbite and in the lower arch. The tipping of the distal tooth could be in some cases extreme . A complete dentition is not always necessary, but the clinician needs to evaluate the risks and consequences with not replacing a missing tooth and explain and inform the patient thoroughly.
10.7 Removable Partial Denture (RPD)
A removable partial denture effectively serves temporarily to stabilize the occlusion and prevent unwanted drifting of the adjacent and opponent teeth into the space of the extracted tooth. The denture is usually made of acrylic or acrylic and metal. The overall treatment time for this option is short and the cost can be very low. There is always a risk of soft-tissue irritation and bone problems. However, in younger patients, it is a good therapy waiting for the right age to place a fixed replacement of the extracted tooth. Sometimes a removable denture suggested as temporary substitute turns out to be very well tolerated as a final treatment and preferred option for replacing a single missing tooth. However, RPDs are mostly used as a temporary replacement or a compromise because of severe problems with surrounding teeth and perhaps general, health or economy.
10.8 Fixed Dental Prosthesis (FDP)
It seems apparent that the most ancient dental prosthetic appliances have been of fixed bridge work and man has for many centuries tried to hold artificial or detached natural teeth from one mouth to another in place by means of wires or ligatures.
10.8.1 Survival and Complication Rates
Fixed dental prosthesis for teeth have taken a variety of designs throughout the history. The initial placement of a fixed dental prosthesis is rarely the end of treatment and many times the patient enters the “cycle of rerestoration” leading to expansion of prostheses carrying increased biological and technical risks and consequently higher costs of dental care. Socio-economic factors and better oral hygiene regimens with patients included in regular recall programmes have led to an increased number of teeth and to a shift from fully to more partially edentulous patients over the past decades. This has resulted in a trend towards higher frequencies of fixed dental prostheses. Fixed dental prosthesis (FDP) are associated with the sacrifice of sound tooth tissue and inherent risks of pulp injury [20–23]. One study conducted amongst 66 practising dentists showed that 70% of treatment recommendations resulted in an increased number of restored surfaces .
A considerable disadvantage with bridgework replacing a single tooth is that the neighbouring healthy teeth have to be involved, affected and damaged. Owing to the variety of techniques employed and materials used, failing reconstructions may be attributed to several causes. Some studies attribute over 50% of failures to the dentists and materials used. Moreover, biological and technical complications have been reported in a variety of studies including secondary caries, loss of retention and marginal defects .
Failure of a FDP is not particularly alarming per se, but the biologic consequences that many times will ensue may be the cause of great concern. Caries is the most reported cause of prosthesis failure and results in loss of dental hard structures, structural compromises and loss of abutment teeth, while loss of retention of the FDP was the most common technical complication . Goodacre and Spolnik  reported that 3–23% of the abutment teeth used requires endodontic treatment after placement of a FDP. Abutment fractures and endodontic failures present additional complications to FDP since abutment teeth that have been further weakened must support larger prostheses . In a meta-analysis conducted by Scurria et al. , prosthesis survival dropped to 69% at 15 years, as in accordance of another study where Lindquist and Karlsson  indicated a survival rate of fixed partial prosthesis that drops significantly after approximately 10 years and after 20 years the survival rate was 65%.
10.8.2 Material Selection
The evolution in material science has led to the introduction of new framework materials, and the tradition with using metal-based reconstructions for fixed dental reconstructions is partially changing in favour for all-ceramic materials, e.g. monolithic materials rather than a framework with a veneer. In a recent systematic review (Pjetursson et al. ) comparing survival rates of all types of all-ceramic FDPs with conventional metal-ceramic FDPs, the incidence of framework fractures was significantly higher for reinforced glass-ceramic FDP as well as infiltrated glass-ceramic FDPs. The incidence for ceramic fracture and loss of retention was significantly higher for densely sintered zirconia FDPs compared to metal-ceramic constructions. In conclusion, the survival rate for all-ceramic FDPs was lower than for metal-ceramic FDPS .
10.8.3 Cantilever Fixed Dental Prostheses
Pjetursson et al.  conducted a review on cantilever fixed partial prosthesis where the cumulative failure rate was 18.2% after a 10-year follow-up time, as compared with the results for conventional end-abutment-supported fixed partial prosthesis which showed a 10.9% failure rate. Of the abutment teeth considered vital at the time of cementation, 32.6% lost their pulp vitality over a period of 10 years, and this was the most common biological complication . In an earlier study by Karlsson , two-thirds of the failed cantilever fixed partial prosthesis had a terminal root-canal-treated abutment indicating that cantilever fixed partial prosthesis was more prone to failure, if based on a nonvital terminal abutment. Randow and Glantz  conducted a study on root-canal-treated teeth and found that the pain threshold was almost twice as high on these nonvital teeth as compared to vital teeth. Comparing one-cantilever pontic with fixed partial prosthesis with multiple extensions, there was no significant difference . Another common biological complication was caries at the abutment teeth, and in several studies an association between loss of retention and secondary caries was noted. This might be debatable which of the two conditions occurred first and led to the other. The most frequent technical complication was loss of retention. In conclusion, it seems that there is a higher risk for biological and technical complications for the cantilever FPP compared to the conventional end-abutment-supported fixed partial prosthesis after 10 years and the estimated survival rate is 81.8% after a 10-year observation period .
10.9 Resin-Bonded Fixed Dental Prosthesis (RBFDP)
The resin-bonded fixed dental prosthesis provides a method for replacing missing teeth or splinting periodontally weakened teeth in the anterior regions of the mouth. This method has both short-term and long-term benefits in that prosthesis can be placed with minimal or no tooth preparation . In the early 1970s, Rochette developed and introduced a more complex procedure compared to the previous bonded acrylic denture tooth. The bridge framework was laboratory-manufactured and perforated with tapering holes in order to lock the framework in place, covering the lingual surfaces and with a more aesthetic pontic . Livaditis and co-workers from Maryland in the USA extended it further to include the posterior region and also developed the etched alloy technique to overcome the shortcomings with the Rochette technique.
10.9.1 Survival and Complication Rates
The survival rates vary widely between studies, but debonding is the most frequent occurring technical complication. When there are no reliable mechanical and chemical bonds between metal/resin and dental/resin surfaces, the retention lock will degrade faster over time being [30, 31]. Pjetursson et al.  has shown a cumulative rate of 19.2% during a 5-year observation time. The debonding was most frequent in the metal-ceramic RBFDPs with a perforated framework, and the posterior bridges showed a higher rate as well with debonding compared to the anterior. Since the development of the first RBBs in the 1970s, there have been significant changes in the design, the materials used and the tooth preparation to improve the longevity of the prosthesis.
10.9.2 Material Selection
The first all-ceramic RBFDPs were introduced in the early 1990s as to benefit from the advantages with a predictable adhesive cementation procedure and debonding was seldom a complication, but they showed a high risk for fracture due to their brittleness. In order to improve their stability, the design was changed from two-retainer to single-retainer cantilever RBFDP, and consequently the survival rates were improved. In a retrospective study of all-ceramic single-retainer cantilever resin-bonded fixed dental prostheses by Sailer et al. , there were no problems with debonding and no catastrophic failures, thus 100% survival after a 6-year follow-up.
10.10 Implant-Supported Single Crown (ISSC)
The use of an implant-supported single crown preserves the adjacent teeth and the surrounding oral tissues. Consequently, there is no risk of loss of vitality of abutment teeth or further weakening of an already weak abutment tooth due to tooth substance loss. Today, many patients also oppose and reject treatments which involve tooth preparations; thus, the osseointegration method has opened up possibilities for implant-supported single crowns for replacing a missing tooth [34–36]. In the early days of implants, the primary goal was osseointegration, but now it is taken for granted and even for the implant to remain in function for years. Today the focus has shifted towards the aesthetics and how to augment and contour the alveolar ridge.