**2. Cemented vs. screw-retained restorations**

The debate between cemented and screw-retained dental implant restorations is old as the implant prosthodontics itself. There are also different opinions in the scientific literature. Studies have shown that there are no significant differences in survival between the two methods, but screw connection has shown a total of fewer technical and biological complications [7]. But, from the clinical perspective, all cemented dental implant restorations should be checked very meticulously for any cement remnants. Even after many years of function, cement remnants can cause peri-implant mucositis which if undetected and untreated can lead to peri-implantitis with severe crestal bone loss around dental implants (**Figure 1**). This bone loss is the

#### **Figure 1.**

*Dental implant with cement-retained PFM crown; left image—immediately after delivery with no cement remnants visible on the radiograph; right image—patient did not come for regular follow-ups until he noticed bleeding while using dental floss, 9 years later. Unfortunately, dental implant needed to be removed due to severe bone loss.*

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

clinical issue which we are trying to avoid by careful treatment planning and precise execution of clinical and laboratory procedures.

Even when using screw-retained restoration, we can witness crestal bone loss around dental implants. This can be caused by the inappropriate size and/or shape of titanium base. Too short or too wide titanium base profile for screw-retained crown can compromise transitional zone of connective tissue and junctional epithelium around dental implant restoration leading to crestal bone loss (**Figure 2**).

The difference in two titanium base height and screw-retained crowns is clearly visible in **Figure 3**. The impact of different titanium base as well the slight changes in emergence profile shape on the crestal bone level and density in a period of 3 months is shown in **Figure 4**.

Nevertheless, the clinical success of dental reconstructions is determined not only by survival rates, but also by the number of technical or biological complications that develop during clinical function. The optimum materials and techniques for

#### **Figure 2.**

*The story of dental implant system, which was newly introduced to the market, with only one available titanium base height at that time (0.5 mm). Subsequent radiographs from top left to bottom right: initial situation; immediately after dental implant placement in augmented socket (two-stage surgery); second stage surgery and healing abutment; at the time of crown delivery (highly polished CAD/CAM zirconia abutment with laboratory cemented screw-retained lithium disilicate crown); 2 years follow-up with crestal bone loss; final radiograph at the time of new crown delivery (1.5 mm high titanium base was available on the market and micro-layered screw-retained zirconia crown with polished subgingival part was made in hope to prevent further crestal bone loss).*

#### **Figure 3.**

*Left: screw-retained crown with 0.5 mm high titanium base; right: screw-retained crown with 1.5 mm high titanium base for the patient in Figure 2.*

**Figure 4.** *Left: final radiograph at the time of new crown delivery; right: 3 months' follow-up radiograph with clearly visible bone remineralization and bone density increase around dental implant neck.*

implant-borne reconstructions are frequently debated to increase clinical outcomes. One of the current discussions is about the best fixation method between the implant and the reconstruction. For a patient-centred clinical approach, it is currently uncertain whether cementation or screw retention is the superior option for restoring dental implants. In clinical practice, both cementation and screw retention appear to have advantages and disadvantages. Clinically and technically, cemented implant reconstructions are quite similar to tooth-borne reconstructions. As a result, they may be easier to make and handle in the mouths of patients. However, prefabricated cementonto or even custom abutments are required. Recently, CAD/CAM (computer-aided design/computer-aided manufacture) technologies enable a wide range of customized abutments to be used, and cemented reconstructions have become the preferred choice in many clinical settings. The difficulty in removing extra cement from cemented crowns and FDPs is one of their drawbacks. More worrying, excess cement has been demonstrated to cause peri-implantitis in the clinical setting [8]. Another notable disadvantage of cemented reconstructions is that, in the event of a problem, they are difficult or impossible to remove without causing damage, such as in the case of technical complications.

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

The retrievability of screw-retained reconstructions, on the other hand, is a big advantage. Furthermore, biological issues are extremely unlikely to arise if the reconstruction is well-fitting. Because the position of the screw access hole and the surrounding material parameters of the suprastructure must be considered, the horizontal and angular positioning of the implant is more delicate and has less tolerance than when employing screw-retained reconstructions. The fixation screw opening should ideally be located in a non-visible palatal or oral location, which is only possible if a suitable implant site and angulation are available. Furthermore, screw-retained reconstructions require more technical production because the reconstruction core must constantly be customized. Technical issues such as retaining screw loosening or veneering ceramic fracture have been clinically observed.

It is indeed difficult to choose between the two types of reconstructions, and it quite often comes down to personal preference rather than scientific data.

In a systematic review published by Sailer et al. [9], it was discovered that cemented restorations cause much higher bone loss than screw-retained restorations. From a total of 4511 titles, 59 clinical studies were chosen for this review, and the data were retrieved and analysed. For cemented single crowns, the estimated 5-year reconstruction survival was 96.5%, for screw-retained single crowns it was 89.3% (*P* = 0.091 for difference). The 5-year survival for cemented partial fixed dental prostheses was 96.9%, similar to the one for screw-retained partial fixed dental prostheses with 98% (*P* = 0.47). For cemented full-arch partial fixed dental prostheses, the 5-year survival was 100%, which was somewhat higher than that for screw-retained FDPs with 95.8% (*P* = 0.54). The projected cumulative incidence of technical problems over a 5-year period was 11.9% for cemented single crowns and 24.4% for screw-retained crowns. In comparison to the cemented partial fixed dental prostheses, a tendency towards decreased complication was observed with the screw-retained partial fixed dental prostheses (partial fixed dental prostheses cemented 24.5%, screw-retained 22.1%; full-arch partial fixed dental prostheses cemented 62.9%, screw-retained 54.1%). Biological problems such as marginal bone loss greater than 2 mm occurred more frequently with cemented crowns (incidence: 2.8%) than with screw-retained crowns (5-year incidence: 2.8%) (5-year incidence: 0%).

This study found that both types of reconstructions had varied effects on clinical outcomes and that neither fixation approach was clearly superior to the other. Screwretained reconstructions had more technical issues, while cemented reconstructions had more substantial biological consequences (implant loss, bone loss >2 mm). Screw-retained reconstructions are more easily retrievable than cemented reconstructions, allowing for easier treatment of technical and biological difficulties. These reconstructions appear to be preferred for this reason, as well as their apparent higher biological compatibility.

In contrary, Nissan et al. published a study that compared the long-term outcomes of cement versus screw-retained implant supported partial dentures in a randomized controlled trial and found that cement-retained FPDs had a better outcome [10]. The study group consisted of consecutive patients with bilateral partial posterior edentulism. In a split-mouth design, implants were placed and cemented or screwretained restorations were randomly assigned to the patients. Examinations for follow-up (up to 15 years) were done every 6 months in the first year and every 12 months in the following years. Ceramic fracture, abutment screw loosening, metal frame fracture, Gingival Index and marginal bone loss were all assessed and reported at each recall appointment. Total of 221 implants were used to support partial prosthesis in 38 individuals. No implants were lost throughout the follow-up period (mean follow-up, 66 47 months [range, 18–180 months] for screw-retained restorations and 61 ± 40 months [range, 18–159 months] for cemented restorations). Ceramic fracture occurred substantially more frequently (P.001) in screw-retained restorations (38% ± 0.3%) than in cemented restorations (4% ± 0.1%). Abutment screw loosening occurred statistically substantially more frequently (P = .001) in screw-retained restorations (32% ± 0.3%) than in cement-retained restorations (92% ± 0.2%). Neither technique of restoration resulted in metal framework fractures. The mean Gingival Index scores for screw-retained (0.48 ± 0.5) restorations were statistically substantially higher (P.001) than for cemented (0.09 ± 0.3) restorations. The mean marginal bone loss was statistically considerably greater (P.001) for screw-retained restorations (1.4 ± 0.6 mm) than for cemented restorations (0.69 ± 0.5 mm).

The long-term clinical and biological outcomes of cemented implant-supported restorations were found to be better to screw-retained restorations in this study. With such contradictory facts, it is difficult to determine which technique is superior. The choice between cement-retained and screw-retained restorations might be philosophical. By opting for cemented restorations, the clinician accepts responsibility for removing all cement residues. Peri-implantitis caused by cement remnants is entirely an iatrogenic condition with no delegation of responsibility to the patient's oral hygiene habits.

Whether we use standard abutments or custom CAD/CAM abutments, the cementation margin is critical. One of the most common causes of cement residues in soft tissues around dental implant restorations is the widespread clinical practice of setting the implant restoration margin too deep subgingival for aesthetic reasons.

This is typically done to conceal the abutment-crown interface and to allow for eventual peri-implant soft tissue recession. When the margin is deeper than 1.5 mm below the soft tissue level, according to one of the Academy of Osseointegration's consensus statements, the risk of cement residues is significant [11]. Furthermore, the American Academy of Periodontology recently included residual cement to the list of risk factors for peri-implant mucositis and peri-implantitis [12]. The key challenge is where to put the cementation margin and how deep it should be?

According to the literature, the margin depth should be deep enough to conceal the margin yet shallow enough to allow residual cement to be removed. Because it is difficult to identify the exact ideal cementation margin depth, this statement does not provide sufficient information for safe and successful everyday clinical practice. To identify a safe margin for cementation, several laboratory and clinical trials were conducted.

The study conducted by Linkevicius et al. sought to determine the amount of cement that remained undiscovered following cementation and cleaning of implantsupported restorations [13]. Fifty-three single implant-supported metal-ceramic restorations were used to treat 53 patients. A periodontal probe was used to assess the subgingival location of each implant's margin mesially, distally, buccaly and lingually, giving 212 measurements. The data were separated into four groups: tissue level (14 samples), 1 mm subgingivally (56 samples), 2 mm (74 samples) and 3 mm (68 samples) below the tissues contour. Metal-ceramic restorations with occlusal holes were made and resin-reinforced glass-ionomer was used to bond them to conventional abutments. After cleaning, a radiograph was taken to determine if all of the cement had been removed. After that, the abutment and crown complex were unscrewed for testing. Adobe Photoshop was used to analyse the photographs of all quadrants of the specimens and peri-implant tissues. Two proportions were determined: (1) the area of

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

cement remnants relative to the overall area of the abutment/restoration; and (2) the area of cement remnants relative to the total area of the implant soft tissue contour.

Excess on the crown groups were group-1 (0.002 ± 0.001); group-2 (0.024 ± 0.005); group-3 (0.036 ± 0.004) and group-4 (0.055 ± 0.007). The amount of undetected excess grew as the margin became deeper subgingivally (P = 0.000), and there was a significant difference between all groups (P 0.05). The soft tissue groups had the following remnants: group-1 (0.014 0.006), group-2 (0.052 0.011), group-3 (0.057 0.009) and group-4 (0.071 0.012). The increase in cement remnants was statistically significant as well as the difference between groups 1 and 2. Radiographic examination revealed cement residues mesially in four cases of 53, or 7.5 %, and distally in six cases of 53, or 11.3 %.

According to the findings of this investigation, the deeper the position of the margin, the more undetected cement was revealed. Dental radiographs should not be considered as a reliable method for cement excess evaluation.

Another study done by Linkevicius et al had the purpose to determine the relationship between patients with a history of periodontitis and development of cementrelated peri-implant disease [14]. Between 2006 and 2011, in private practice, 77 patients with 129 implants were selected for this retrospective study from completed implant cases that were scheduled for routine maintenance or had mechanical or biological issues. Researchers analysed implants with extracoronal cement residues and implants without cement residues. The selected cases were then separated into two groups: implants in patients with a history of periodontitis (1) and implants in persons without a history of periodontitis (2). These groups were chosen based on the patient's treatment history and orthopantomogram. As a control group, a set of 238 screw-retained implant restorations was investigated that were delivered to 66 patients throughout the same period. The incidence of peri-implant disease was assessed in all implant groups.

In 62 of 73 implants with cement residues, peri-implant disease was seen (85%). All implants in group 1 developed peri-implantitis—four cases of early disease and 35 cases of delayed disease. Twenty-one of 30 implants in the periodontally healthy group were diagnosed with peri-implant mucositis, 3 implants developed early peri-implantitis and 11 implants with cement remnants did not develop biological problems. Peri-implant illness was identified in 17 of 56 cases of implants without cement remains (30%). In comparison, just two occurrences of peri-implant disease were discovered in the control group of screw-retained restorations (1.08%).

This study concluded that implants with cement remnants may be more likely to develop peri-implantitis in individuals with a history of periodontitis than in patients without a history of periodontitis.

The literature established that each retention method has a number of advantages and disadvantages. However, there are some clinical situations in which one method of retention is preferable to the other. Shadid and Sadaqa's review of the literature on screw-retained versus cement-retained fixed implant supported reconstruction identifies several clinical situations in which one method of retention is preferable to the other [15].

#### **Clinical situations that prefer screw-retained restoration:**

• Screw-retained large-arch implant reconstructions are preferred, as complications with these long-span prostheses are more common than with short-span prostheses.

