CHAPTER 5

Decision-making criteria for replacing the missing tooth

1.5.1 Introduction

In this chapter:

■ An evidence-based approach to treatment planning

■ Factor 1 – The patient’s perception

■ Factor 2 – The estimated longevity of the restorations

■ Factor 3 – The neighboring teeth

■ Factor 4 – The evaluation of the tooth gap

■ Factor 5 – The complexity of implant placement

■ Factor 6 – Assessment of risk factors

■ Factor 7 – Multiple risk factors

In their daily practice, dental practitioners routinely face the challenge of making difficult decisions. These are mostly influenced by paradigms, dictated by basic dental education and individual preferences based on many years of clinical practice. One of those decisions is to choose the most appropriate type of restoration to replace a missing tooth for each individual situation. Treatment planning in restorative dentistry was much easier before the era of dental implants. The treatment options to restore edentulous spans in that time were restricted to conventional and cantilever tooth-supported fixed dental prostheses (FDPs) and removable dental prostheses (RDPs). With the emergence of new techniques and computer-aided design and computer-aided manufacturing (CAD/CAM) technologies, the number of treatment options and materials to restore edentulous gaps has increased significantly.

Today when planning a fixed restoration, the first decision to be made is the type of restoration. Should it be tooth-supported (conventional, cantilever, or resin-bonded), a combined tooth-implant-supported, or a solely implant-supported restoration, FDP, or single crown (SC)?

1.5.2 An evidence-based approach to treatment planning

Important decisions in restorative dentistry should preferably be made evidence-based, but the question remains whether evidence-based treatment planning is feasible in prosthetic dentistry. Ideally, treatment decisions should be based on randomized controlled clinical trials (RCTs) or well-conducted systematic reviews with meta-analyses based on RCTs, representing the highest level of evidence1^–3. The evidence-based approach is much more advanced in medicine. The Cochrane organization is an independent body that has promoted evidence-based medicine during the last two decades. It has published over 6700 systematic reviews that analyze the effectiveness of different treatment methods in medicine, while in comparison only 250 such articles have been published in dentistry.

Until now, there is only one RCT that has compared the outcome of different types of fixed restorations. A Swedish research group4^–7 investigated the outcome of combined tooth-implant-supported FDPs and solely implant-supported FDPs in this RCT. The authors included 23 patients with bilateral free-end mandibles and complete maxillary dentures. The edentulous sites in the mandible of each patient were randomly assigned to an FDP supported by either two implants (control) or by one abutment tooth and one implant (test) (Fig 1-5-1). Over a 10-year observation period, 2 out of 23 test implants and 5 out of 46 control implants were lost during function. There was no statistically significant difference between test and control sites and hence, the authors concluded that the combination of teeth and implants in FDPs may be recommended as a predictable and reliable treatment alternative for the restoration of the posterior mandible.

However, this study had clearly not the necessary power to detect smaller but clinically relevant differences with regard to the proportion of lost implants. For example, to detect a clinically relevant difference of a 1% versus 2% annual restoration loss (with 80% power and a significance level of 5%), a two-arm study would need to randomize approximately 1060 patients within 1 year and follow them up for at least 4 years, resulting in a total study time of 5 years. With a longer follow-up time of about 10 years, it would be sufficient to randomize 500 patients. This demonstrates that it is not an easy task to perform a randomized controlled clinical trial with adequate statistical power to compare different types of restorations. Owing to the methodology of systematic reviews and meta-analyses, such clinically relevant questions can be addressed.

The aim of this Chapter is to discuss relevant factors when planning a restoration as replacement for a single or several missing tooth/teeth including the available evidence.

1.5.3 Factor 1 – The patient’s perception

Today, information regarding dental treatment is available to patients from several different sources. An important source is the internet (Fig 1-5-2). Some implant manufacturers even advertise treatment options to directly or indirectly recruit patients. However, most patients still get information regarding dental treatment from dental professionals or from friends and relatives. Two to three decades ago, implant treatment was not so common, but today most patients know someone that has undertaken implant treatment. The implant treatment usually is well-accepted by the patients as shown in a 10-year prospective study8. The authors concluded that more than 90% of the patients were satisfied with the therapy and would be willing to undergo implant treatment again, if necessary. The costs associated with implant therapy were also considered to be justifiable8.

What factors influence the patient’s perception and decision?

Treatment costs

Treatment costs play a major role for a lot of patients. In most European countries, the costs for an implant-supported SC are similar to the costs for a three-unit tooth-supported FDP9. However, this can vary for each individual situation. For example, if there is a need for a complex bone augmentation and/or soft tissue grafting, the price for the implant is significantly increased. Furthermore, if one or both teeth adjacent to the edentulous space require new restorations, the cost-effectiveness of a tooth-supported three-unit FDP is significantly higher9.

Treatment time

The total treatment time is another factor that can influence the treatment plan. For a treatment that is supposed to last for a long period of time it should not really matter whether the treatment duration is 4 weeks or 4 months, especially if teeth have already been missing for a long period of time. Nevertheless, there will always be patients who insist on a very short treatment time and there will be some clinicians trying to meet the demands of these patients. For this reason, treatment protocols like immediate implant placement after tooth extraction and immediate loading of the implant after placement have been established. Shortening the treatment time can however increase the risk of complications and failures10.

Originally it was suggested to wait for 3 months in the mandible and 6 months in the maxilla prior to loading of dental implants11. Owing to developments concerning implant surface and morphology, the healing time of dental implants could be significantly reduced12. The total treatment time for implant-supported SCs is still around 2 months in a standard case though. For complex cases requiring bone augmentation procedures, the total treatment for implant-supported SCs can be prolonged up to 4–6 months. Moreover, in cases where two-stage sinus floor elevations or two-stage lateral bone augmentations are needed, the total treatment time can even extend up to 1 year or longer. Thus, in such cases tooth-supported restorations may be favorable, if time is an important factor for the patient.

The mean total treatment time for tooth-supported FDPs and implant-supported SCs was evaluated in a retrospective study9. The mean treatment time for implant-supported SCs was almost twice as long as for tooth-supported FDPs or 5.9 ± 3.3 months versus 3.2 ± 2.6 months, respectively9.

Thus, tooth-supported FDPs might be the treatment of choice in complex cases, if treatment time is a major consideration, given that less time is generally needed for tooth-supported restorations.

Esthetics

The esthetic outcome is a very important issue for patients. With techniques and materials available today it is possible to make restorations both on teeth and implants that imitate perfectly natural teeth. It must be kept in mind that to achieve the perfect outcome, the clinician needs to have good knowledge of the biology of soft and hard tissues and understand the properties of the material utilized.

Even though it is possible to achieve an excellent esthetic outcome with implant-supported crowns, it must be realized that if something goes wrong with the implants, the effects can be more dramatic for the patient, than if something goes wrong with a tooth-supported restoration (Fig 1-5-3).

For implant-supported SCs, several authors have stated that soft tissue recessions can be expected during the first 3–6 months in function13^,14 and following which, the soft tissue is stable as long as there is no infection around the implant.

A recent systematic review15 which evaluated the esthetic outcome of implant-supported SCs concluded that 7.1% of the crowns had an unacceptable or semi-optimal esthetic appearance. This incidence is, however, difficult to interpret because of a lack of standardized esthetic criteria16 and the fact that neither dental professionals nor patients have evaluated the esthetic outcome. In cases where the neighboring teeth would profit from a crown from an esthetic point of view, a tooth-supported restoration could be the most appropriate treatment choice. Otherwise, from this aspect, restorations that imitate perfectly natural teeth can be accomplished both with tooth-supported and implant-supported restorations.

The provisional phase

For tooth-supported FDPs, the fabrication of a provisional restoration is usually simple, well-accepted by the patients, and comfortable to wear. Provisional restorations that have a similar shape to the final restoration can be used during the whole treatment time. However, during the healing period for dental implants, provisional removable dentures are mostly used. The patients often have problems adapting to them and time is needed for adjustments and repairs.

Long-term survival

When planning a fixed restoration, the patient should be informed about different treatment options, the estimated survival of the restoration, and possible risk factors. Each treatment option has a documented longevity (see Part III). Besides, biological as well as technical risks have to be considered during treatment planning (see Part IV).

1.5.4 Factor 2 – The estimated longevity of the restorations

A group of researchers from the Universities of Iceland, Bern, Geneva and Zurich in Switzerland, and from the National Dental Center in Singapore has published a series of systematic reviews15^,17^–28. These are based on consistent inclusion and exclusion criteria, summarizing the available information on survival and success rates, and the incidence of biological and technical complications of different types of tooth- and implant-supported restorations.

According to the 5-year survival rates, the preferred treatment choices when planning a fixed restoration would be implant-supported SCs, conventional tooth-supported FDPs, with end abutments, or solely implant-supported FDPs, without discriminating the three types (Table 1-5-1). The reason for a relatively low 10-year survival rate of solely implant-supported FDPs (see Part III, Table 3-1-8) is that most of the included studies report on restorations with metal framework and acrylic veneering from which many had to be remade due to esthetic failures. When solely implant-supported FDPs with ceramic veneering were analyzed, the 10-year survival rate increased to 93.9%. As a second treatment option to save tooth substance or due to anatomical reasons or patient-centered preferences resin-bonded prostheses (RBPs), cantilever tooth-supported FDPs, or combined tooth-implant-supported FDPs can be planned.

Table 1-5-1 Estimated 5-year and 10-year survival rates of different types of restoration and the number of restorations that were evaluated

It is important to realize that RBPs have the best outcome when used in the anterior area and when the occlusal relationship is appropriate. The dental literature also shows that tooth-supported cantilever FDPs have a higher risk of failure when supported by endodontically treated teeth. The abutment teeth should ideally be vital, and the preparations should be tilted slightly away from the cantilever unit, to reduce the risk of loss of retention. In addition, the cantilever unit should only have contact in maximum intercuspidation position and no contact in laterotrusion.

1.5.5 Factor 3 – The neighboring teeth

One of the determining factors, whether to plan a tooth-supported or an implant-supported restoration, is the status of the teeth adjacent to the edentulous gap, since those teeth will become the abutment teeth if a tooth-supported restoration is planned.

Teeth can basically be divided into three groups: (1) teeth that are intact or so well-preserved that it would be a huge sacrifice of tooth structure, when preparing them as abutment teeth; (2) teeth with fillings or discolorations that would profit from an improved esthetics and strengthening, if used as abutment teeth; (3) teeth that are doubtful, increasing the risk for larger restorations because in a case of tooth loss, the entire restoration has to be replaced.

Hence, if a tooth is compromised due to substantial loss of tooth substance or with impaired periodontal or endodontic conditions, it might be more reasonable not to use it as an FDP abutment.

An evaluation and a classification of the neighboring teeth has to be based on the following three aspects (see Table 1-5-2).

Table 1-5-2 Pretherapeutic single tooth prognosis: single tooth risk analysis

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