**4. Materials selection**

Several new dental materials have entered the market over the last decade. They offer an aesthetic, functional and economical alternative to metal-ceramics, the most frequently used material for prosthodontic restorations. This is especially true for zirconium oxide and lithium disilicate ceramics. The incorporation of CAD/CAM manufacturing technology into daily work has resulted in a significant reduction in dental technicians' labour costs. Furthermore, these increased aesthetic standards have resulted in an increase in the use of metal-free restorations at the expense of metal-ceramic restorations. These events also influenced the materials used and the manufacturing process for custom-made dental implant abutments, effectively eradicating stock dental implant abutments. Additionally, the titanium bases for implant abutments have been redesigned to incorporate anti-rotation properties and a cylindrical shape, allowing for more efficient extraoral cementation of prosthodontic restorations. Such prosthodontic restorations, particularly following the introduction of angulated screw access to the abutment screw, resulted in an increase in the proportion of screw-retained restorations versus cemented restorations. All these advancements are now being used more frequently in clinical practice, but they have also prompted scientists to explore new materials and techniques. Given the time, material, human and technical resources required to conduct a high-quality long-term prospective or retrospective study, there is still insufficient solid evidence of these new materials and technologies' clinical benefits and effectiveness. However, prior research and the subjective clinical experience of numerous clinicians indicate that the new materials will eventually justify their partially uncritical use in clinical practice.

#### *Prosthetic Concepts in Dental Implantology DOI: http://dx.doi.org/10.5772/intechopen.104725*

From the clinician's perspective, 5- or 10-year success or survival rates are not the only criterion to consider when planning and implementing implant-prosthodontic treatment. Additionally, the clinician should consider the frequency with which technical and biological issues may emerge when specific materials are used.

With so much conflicting information and data, clinicians may depend on review articles that structurally describe and analyse more scientific studies on a given subject. Pjetursson et al. recently published a statement paper about material selection for implant-supported restorations [24].

#### **4.1 Metal-ceramic implant-supported restorations**

For a long period of time, metal frameworks veneered with feldspathic ceramic have been used in dentistry. They are well-researched and documented restorations that can be used for single crowns and fixed partial dentures. The metal framework provides a high-strength core, protecting the whole restoration against tensile and flexural stress during chewing function. Besides the conventional casting technique, metal framework nowadays can be produced by milling or an additive laser printing process. There are two important published meta-review papers that examine the clinical outcomes, success and survival rates of metal-ceramic implant-supported restorations, as well as the complications rates.

The meta-review analysing metal-ceramic single crowns [25] included 30 studies with a total of 4542 crowns, with 83% of cement-retained crowns and 17% of screwretained crowns, respectively. The meta-analysis estimated an annual failure rate of 0.35% (95% CI: 0.19%–0.66%), which corresponds to a 5-year survival rate of 98.3%. The respective complication rates were 13.3%, which means that one out of eight metal-ceramic single crowns showed some technical, biologic or aesthetic complication or failure. Only 86.7% of the metal-ceramic implant-supported single crowns showed no complications over the 5-year follow-up period. The 5-year incidence rate of peri-implantitis and soft-tissue complications was 5.1%, and significant bone loss of more than 2 mm at marginal bone level was 3.3%. Technical complications, including fracture of abutments or abutment screws, were rare complications, with an incidence rate of 0.2%. Abutment screws loosening was more frequent, with a 5-year complication rate of 3.6%. The incidence of ceramic fractures and chipping was 2.9%, and framework fractures were only reported to be 0.2%.

Another meta-review by Sailer et al was analysing multiple-unit metal-ceramic fixed partial dentures [26] and included 16 studies with a total of 993 fixed partial dentures supported by 2289 dental implant abutments, with 73% of cement-retained fixed partial dentures and 27% of screw-retained fixed partial dentures, respectively. The annual failure rate for metal-ceramic fixed partial dentures was 0.26% (95% CI: 0.10%–0.64%), corresponding to a 5-year survival rate of 98.7%. The respective complication rates were 15.1%, meaning that one out of six fixed partial dentures had some kind of complication. Hence, 84.9% of fixed partial dentures were free of any complications over the 5-year follow-up observation period. The 5-year rate of periimplantitis and soft tissue complications was estimated to be 8.5%. The significant bone loss incidence rate was reported to be 2.6%. Among technical complications, the incidence rate was reported as follows: abutment screws loosening was 5.3%, ceramic fractures or chipping was 11.6% and framework fractures were 0.5%.

Both metal-ceramic single crowns and multiple-unit fixed partial dentures are well researched with very good long-term success rates. They can be used as a treatment option in a wide spectrum of clinical indications, especially in clinical cases with high clinical implant crowns, cantilever types of implant restorations and implantsupported fixed partial dentures with distal units extending more than 8 mm, fixed partial dentures with more than two pontics and in cases with small connector height due to limited interocclusal space.

#### **4.2 Zirconia-ceramic implant-supported restorations**

Increasing aesthetic demands have led to the development of different subtypes of zirconia ceramics. With their appearance, they adequately imitate not only the appearance but also the structure of hard dental tissues. In addition, new generations of zirconia ceramics have excellent biocompatibility and improved mechanical properties. Previous generations of zirconia ceramics had an opaque whitish appearance and had to be veneered to make the restoration look aesthetically pleasing. Newer generations of zirconia ceramics come in multilayer blanks or blocks with different levels of translucency and can be used as monolithic restorations.

The previously mentioned meta-reviews also analysed zirconia-ceramic implantsupported single crowns and fixed partial dentures.

The review by Pjetursson et al [25] analysed eight studies with a total of 912 zirconia-ceramic implant supported single crowns for an average 5-year follow-up period. Of all the included single crowns, 51% were cement retained and 49% were screw retained. The annual failure rate for implant-supported zirconia-ceramic single crowns was 0.49% (95% CI: 0.21%–1.18%), which corresponds to a respective 5-year survival rate of 97.6%. The estimated 5-year complication rate was 16.2%, meaning that only 83.8% of implant-supported zirconia-ceramic single crowns were free of any complications over the complete 5-year observation period. The most frequent complication rates were: 5.3% for peri-implantitis and soft tissue complications, 4.4% for marginal bone loss of more than 2 mm, 2.8% for ceramic fractures or chipping and 2.1% for framework fracture.

Another meta-review by Sailer et al [26] included three studies with a total of 175 zirconia-ceramic fixed partial dentures and an average follow-up period of 5.1 years. Only 15% of all restorations were cement-retained and 75% were screw-retained. The annual failure rate for implant-supported fixed partial dentures was 1.455 (95% CI: 1.06%–1.98%), which corresponds to a respective 5-year survival rate of 93.0%. The most frequent complications were soft tissue complications with a 10.1% incidence rate and framework fracture with a 4.7% rate.

According to the previously mentioned research and numerous other published articles, today we cannot consider veneered zirconia-ceramic as the material of choice for implant-supported fixed partial dentures. They show a high degree of risk of chipping or catastrophic fracture of the restoration framework. The study by Larsson et al. [27] states that the frequency of chipping and framework fractures of fixed partial dentures is up to 50%, which is a clinically unacceptable value. These problems are largely eliminated by the use of monolithic zirconia-ceramic, which with its aesthetic properties satisfies everyday clinical applications. In addition to the lack of chipping, implant-supported restorations of monolithic zirconia-ceramic show greater fracture resistance because the framework of such structures has larger dimensions compared with the framework of coated veneered zirconia-ceramic restorations. Evidence of this is a recent systematic review paper by Pjetursonn et al. [28] that analysed the 3-year survival and failure rates of veneered and monolithic zirconia-ceramic implant-supported restorations. The estimated 3-year survival rates were 96.3% (95% CI: 93.9%–97.7%) for veneered zirconia-ceramic single crowns and 96.1% (95% CI:

93.4%–97.8%) for monolithic zirconia single crowns. Veneered single crowns showed significantly (p = 0.017) higher annual ceramic chipping rates (1.65%) compared with monolithic single crowns (0.39%). Interestingly, the location of the single crowns, anterior vs. posterior, did not influence survival and chipping rates.

When a clinician needs to choose between veneered or monolithic zirconia-ceramic implant-supported restorations, the following factors must be considered: aesthetic demands, location in the dental arch, physical properties of the material, possibility for surface modification and abrasion (wear) properties of the material [24].

## **4.3 Lithium-disilicate reinforced glass-ceramic implant-supported restorations**

To improve the physical properties of glass-ceramic and make it more suitable for prosthetic restorations, lithium disilicate or, in rare cases, leucite fillers were added. Nowadays, there are several techniques for the production of lithium-disilicate reinforced glass-ceramic, such as heat pressing and CAD/CAM milling from prefabricated blanks. Due to its mechanical properties, lithium-disilicate reinforced glass-ceramic can be used for both implant-supported single crowns and short-span fixed partial dentures in the anterior region of the dental arch. A systematic review article by Pjetursson et al. [28] evaluated five studies reporting on veneered leucite or lithium-disilicate reinforced glass-ceramic implant-supported single crowns (a total of 110 crowns) and 14 studies on monolithic leucite or lithium-disilicate reinforced glass-ceramic implant-supported single crowns (a total of 484 crowns). The mean follow-up period for veneered single crowns was 8.1 years and 2.6 years for monolithic single crowns, respectively. Results show a low annual failure rate of 0.80% (95% CI: 0.14%–4.64%) for veneered crowns and 1.02% (95% CI: 0.51%–2.05%) for monolithic reinforced glass-ceramic single crowns. This means that 3-year survival rates were 97.6% for veneered single crowns and 97.0% for monolithic single crowns. The study also reported that monolithic reinforced glass-ceramic crowns had the lowest annual complication rate of 1.7%, and veneered reinforced glass-ceramic crowns had an annual complication rate of 2.6%. In comparison, annual complication rates for monolithic zirconia-ceramic single crowns were 3.6% and for veneered zirconiaceramic single crowns were 4.5%.

Considering these meta-review results, it is reasonable to conclude that lithiumdisilicate reinforced glass-ceramic implant-supported crowns are the treatment of choice for high aesthetic-demanding clinical cases in the maxillary anterior region **Figure 8** shows such a clinical case with tooth #21 replaced by a dental implant where the implant-supported crown was made on a titanium base abutment customized

#### **Figure 8.**

*Clinical case with tooth #21 replaced by a dental implant where the implant-supported crown was made on a titanium base abutment customized with a zirconia CAD/CAM abutment and a lithium-disilicate reinforced glass-ceramic crown.*

with a zirconia CAD/CAM abutment and a lithium-disilicate reinforced glassceramic crown.

## **5. Conclusions**

Proper treatment planning prior to dental implant implantation is just as critical in current implant prosthodontics as the prosthetic components. The wonderful work of the oral surgeon may quickly be destroyed by inadequate prosthodontic execution, resulting in the failure of dental implant treatment.

The controversy between cemented and screw-retained dental implant restorations is as ancient as implant prosthodontics itself. Additionally, there are divergent views in the scientific literature. Although no substantial difference in survival has been shown between the two procedures, screw connection has demonstrated a total of less technical and biological problems. It is presently unknown whether cementation or screw retention is the preferable choice for restoring dental implants from a patient-centred clinical perspective. Both cementation and screw retention seem to have benefits and downsides in practical practice. Choosing between cement-retained and screw-retained restorations may be a matter of philosophy. By choosing cemented restorations, the physician is responsible for completely eliminating all cement residue. Peri-implantitis induced by cement remains is a completely iatrogenic disease with no blame assigned to the patient's oral hygiene practices.

The emergence profile of a tooth or restoration, such as a crown on a natural tooth, a dental implant or a dental implant abutment, is described as the shape of the tooth or restoration in relation to its emergence from restricted soft tissues. Clinically, appropriately designed dental implant restorations are crucial for both the aesthetics and biological effectiveness of the procedure. The biggest difficulty is adapting the circular dental implant to the cervical form of the lost tooth. This shift is made possible by implant abutments. Changes in the critical and subcritical contour zones should be carefully considered in relation to the dental implant location, soft tissue thickness and materials employed. If the crown shape cannot be altered, altering the subcritical zone may significantly enhance the treatment's cosmetic and biological success.

Over the recent decade, many innovative dental materials have reached the market. They provide an attractive, practical and cost-effective alternative to metal-ceramic restorations, the most often used material in prosthodontics. This is particularly true for ceramics made of zirconium oxide and lithium disilicate. Both metal-ceramic single crowns and multi-unit fixed partial dentures have a lengthy track record of success. They can be used to treat a wide variety of clinical indications but are particularly useful in cases requiring high clinical implant crowns, cantilever-type implant restorations, implant-supported fixed partial dentures with distal units extending beyond 8 mm, fixed partial dentures with more than two pontics and cases requiring a small connector height due to limited interocclusal space. When a clinician must choose between veneered and monolithic zirconia-ceramic implant-supported restorations, the following factors must be considered: aesthetic requirements, location in the dental arch, material physical properties, surface modification capability and material abrasion (wear) properties. Considering the findings of this meta-analysis, it is acceptable to infer that lithiumdisilicate reinforced glass-ceramic implant-supported crowns are the treatment of choice for clinical situations requiring a high level of aesthetics in the maxillary anterior area.

*Prosthetic Concepts in Dental Implantology DOI: http://dx.doi.org/10.5772/intechopen.104725*
