An unfavorable relationship between the form and dimension of the dental arch and the number, dimension, and shape of the existing teeth (typical Bolton 6 or 12 discrepancy, Bolton anterior or overall analysis1, malformed or undersized teeth, tooth agenesis, tooth loss due to early trauma) can pose several esthetic, biologic, and functional problems. In many cases, an optimal result cannot be achieved through orthodontic, restorative or reconstructive means alone. Furthermore, patient desires and capacity to comply with the treatment as well as financial considerations are important factors to be included in the treatment concept.
For all options discussed below, the clinical sustainability is well documented in the literature; all show high survival rates and low complication rates in the hands of the experienced clinician.
From the multitude of long-term studies, systematic reviews, and case documentations, it can be extrapolated that both resin-bonded bridges and veneers behave similarly well and may reach 10-year survival rates of 95% or more and 10-year reintervention rates lower than 5% to 10%, given proper indication and handling.
The cost-effectiveness of resin-bonded bridges extrapolated over the lifetime of a patient is also very favorable compared with full-crown bridges and single tooth implants. Since the current standard extension of a resin-bonded bridge is two-unit (one wing), and not three-unit (two wings) as it was before, the risk of secondary caries due to loose wings is no longer relevant.
The standard materials for resin-bonded bridges are either zirconia or lithium disilicate glass-ceramics.
There is certainly still an indication for traditional full-crown and bridge work where existing sound tooth structure is extensively reduced or damaged, but it is no longer the standard of care due to its inherent biologic and technical risks (devitalization, fracture, and caries of abutment teeth). However, the long-term success is excellent, provided the indication is well selected and a conservative preparation concept is used. In contrast to single crowns, all-ceramic bridges seem not to perform as excellently as porcelain-fused-to-metal (PFM) constructions. The overall quality of all the steps involved in the treatment, however, is always crucial for long-term success. Therefore, long-term studies, including reviews, might not reflect the entire potential of traditional crowns and bridgework.
Glass-ceramic veneers seem to perform slightly better than feldspathic veneers, indicating that materials with increased strength show better clinical performance25. There are also attempts by manufacturers to use even stronger materials such as zirconia to fabricate veneers. However, since there are neither long-term results nor sufficient clinical experiences available, these materials should be considered experimental at present.
Direct restorations with composites are today an indispensable and attractive noninvasive way of reshaping teeth. The essential techniques for success are widely available and very well documented. A multitude of parameters such as the type of adhesive materials and procedures, handling properties, curing techniques, and operator skills have an important influence on the outcome. In line with this, a recent systematic literature review showed reasonably inhomogeneous results, although some data reach the same level as veneers. In view of easier modes of reintervention, and given a proper indication, direct composites can no longer be regarded as generally inferior to veneers.
Single-tooth implants are today another indispensable way to replace missing teeth. Implantology is probably one of the best-documented fields in dentistry. However, above all, esthetic problems in the long run still represent a major challenge in the esthetic zone. Due to their ankylotic nature, implants cannot adapt as well as natural teeth do to the changing functional and biologic conditions.
This can lead, over time, to the well-known phenomenon of the apparent intrusion, infraocclusion, and protrusion of implants in relation to the adjacent teeth, when anterior teeth may move downward and simultaneously forward or backward. This may be understood as the lifelong adaptation of the stomatognathic system to the changing functional and physiologic conditions, and may be described as constant adaptation and remodeling.
In addition, the loss of interproximal contact points is also observed. This may not only occur in young patients, but over the entire lifetime of a patient. Therefore, delaying implants in young patients until later in adulthood when skeletal growth is considered to be completed may not completely resolve this problem.
In which incidences and to what extent these changes take place is difficult to predict and is part of an ongoing discussion.
An orthodontic retainer should of course be considered in all these anterior implant cases. Whenever feasible, a fixed lifelong wire retainer is the retention device of choice.
Existing large restorations (for example, full crowns) on adjacent teeth may also make more sense for tooth-supported restorations to close a gap, if these need a replacement anyway.
The following two cases serve to illustrate in an exemplary way the dilemma the clinician faces when looking for a sustainable solution for the patient and being confronted with the lifelong adaptation and remodeling of the oral structures over more than 20 years (in each case).
Case 1-1 shows a patient with a missing right central incisor. The tooth was replaced 30 years previously, when the patient was 22 years old, with an implant-supported all-ceramic crown. The implant type was a soft tissue-level implant with a buccally modified shoulder (scallop) and an adhesively bonded glass-ceramic crown. The left central incisor was restored with a glassceramic veneer to rebuild the deeply fractured incisal edge.
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