**7. Number of implants in implant-retained overdentures**

Implant-retained overdentures are usually indicated in completely edentulous cases with mild to severe bone resorption in certain regions and therefore go with reduced number of implants. The minimum number of implants needed for an over denture is still in debate.

According to the literature in case of maxillary overdenture with both implant and soft tissue support four to six implants are needed for retention and stability [53–55]. In case of four implants reduction in palatal plate of the denture is reported and recommended (**Figures 9** and **10**) [56, 57].

There are many reports in literature on two implant-retained overdentures in maxilla, too, but it is still the subject of debates (**Figure 11**).

#### **Figure 9.**

*Four dental implants in maxilla. Clinical procedure of adjusting locators in 4 implant-retained maxillary overdenture.*

*Implant-Retained Maxillary and Mandibular Overdentures - A Solution for Completely… DOI: http://dx.doi.org/10.5772/intechopen.99575*

#### **Figure 11.**

*Clinical check-up of the patient five years following the placement of two implants in maxilla and delivery of the 2 implant-retained maxillary overdenture.*

Klemetti et al. concluded that using only two implants in the maxilla did not compromise the dentures longevity or patient satisfaction when compared with four implant overdentures on one hand, but many authors claim that this design of implant-retained overdenture may result in a hinging movement and cause discomfort [58–60].

In mandible, in case of overdenture with both implant and soft tissue support, two implants supported overdenture or single implant retained overdenture is also advisable [61–64].

## **8. Types of attachment systems on implant-retained overdentures**

According to The McGill Consensus Statement on overdentures mandibular twoimplant overdentures (**Figure 12**) are considered to be the first choice standard of care for edentulous patients regardless of the type of attachment system used [41].

Numerous types of attachment systems supporting implant overdentures have been developed over years, such as bars, balls, magnets, different cylindrical attachments etc., made of different materials, according to different concepts and designs [65–71].

#### **Figure 12.**

*Standard implant-prosthodontic procedure in completely edentulous patient according to the McGilly consensus.*

Of the previously listed systems, only bars require mechanically constructed splinting of the implants and the need to connect them via rigid construction or not is still being discussed.

Both splinted and unsplinted overdenture implant attachment systems have unique advantages and disadvantages. Although different in construction, it seems that both systems achieve similar results with regard to marginal bone loss, prosthetic complications and implant survival rate [72]. A systematic research, carried out from 2000. to 2018., investigated the influence of splinted vs. unsplinted designs for 4 implants retained maxillary overdentures in terms of the outcome assessed in implant survival, prosthodontic longevity and patients' satisfaction. The results revealed no influence of the overdenture design on survival rates of both implants and dentures, as well as on patients' satisfaction with implant survival rate higher than 97%, overdenture survival rate of 100% and patients' satisfaction scores higher than 4.5 (on a 1 to 5 Likert scale) for general satisfaction, chewing ability, denture stabilization, esthetic results and speech [73].

Location of the implants in the edentulous jaw serving for the retention and stability of the overdenture as well as each edentulous arch shape highly influence the stress concentration and distribution around the implants and denture bearing area [74, 75].

If it is about splinted overdenture implant attachment systems using bars made from different materials polyetheretherketone (PEEK), titanium and Co-Cr alloys) the question of designing additional distal cantilever arises. Numerous authors confirmed that, if used, the length of the cantilevel should not exceed the anteroposterior span length, with most commonly mentioned length from 7 to 12 mm (**Figure 13**) [76, 77].

Although it has already been proven that cantilevering of the bars in this type of implant prosthodontic restoration may increase bone loss around supporting implants, especially around the implant adjacent to cantilever, without cantilevers there is less retention and stability of the dentures in the function [78–80]. However, not only does the cantilever and its length cause the problems with loss of bone structure around the implants, but increase in bar height can increase stress levels on the peri-implant crestal bone, too [81].

**Figure 13.** *Splinted 4 implant-retained maxillary overdenture with short distal cantilevers.*

*Implant-Retained Maxillary and Mandibular Overdentures - A Solution for Completely… DOI: http://dx.doi.org/10.5772/intechopen.99575*

From the technical point of view, unsplinted overdenture implant attachment systems such as Locators, balls or magnets are much easier to construct, provide more prosthodontic space and require up to 1 cm vertical space for the attachments (**Figures 14**–**16**) [82, 83].

#### **Figure 14.**

*Radiological assessment of implant osseointegration prior to the delivery of 4 implant-retained mandibular overdenture.*

#### **Figure 15.**

*Stone casts with laboratory analogs indicating the position of the locators in the edenetulous mandible.*

**Figure 16.** *Titanium housings on the laboratory analogs.*
