The purpose of this study is to assess the change of crestal bone level at the Titanium Zirconium (TiZr) compared to Titanium (grade IV) implant between surgery and 6, 12, 24, and 36 month post surgery.

This is a clinical trial to compare crestal bone level changes, soft tissue parameters, implant success and survival between small diameter implants in edentulous mandibles restored with removable overdentures.

An initial patient evaluation will be conducted to determine wether a patient meets the study inclusion and exclusion criteria.

The edentulous subjects will undergo surgery for placement of two dental implants, the test and control implant. The implants will be placed in the intraforaminal region.

A gingival former will be inserted in the implant after implant placement to ensures a transmucosal healing. After 6 to 8 weeks the healing abutments will be retrieved and the locator abutments will be connected to the implant.

The removable prosthesis will be prepared and connected to the implants two weeks later.

The study will be blinded until 12 month post surgery and completed with an unblinded follow up period up to 3 years.

Straumann will deliver the randomization envelopes to the sites which had been created by an independent Clinical Research Organization (CRO). The randomization envelopes are marked with a sequential number. The master randomization list will be kept at Straumann.

The success and survival of the implants, soft tissue conditions, success of the prosthesis part and product safety will be assessed after 6, 12, 24, and 36 month after surgery.

Source data verification will be performed by qualified study monitors to assess the accuracy, completeness, or representativeness of registry data by comparing the data to external data sources.

Data will be recorded on standardized Case Report Forms for all study subjects from whom informed consent is obtained. The investigator will be responsible for the accuracy of the data entered on the Case Report Forms. All source documents pertaining to this study will be maintained by the investigator and made available for inspection by authorized persons.

Sample size calculations are proceeded for a given range of clinical relevant differences between test and control implant and a given range of standard deviations with the two sided paired t-test under a significance level of 0.05 and with a power of 80 percent.

To be robust against deviations from the assumption of normality and to take into account possible dropouts it is good clinical practice to increase the calculated sample size by about 10 to 20 percent.

To detect a clinical relevant difference down to 0.1 with a standard deviation of 0.3, one needs 73 plus 15 (88) patients for the study.

Management of dropouts and missing data will depend on their frequency and the particular outcome measure. Any such adjustments will be described completely. All data will be included in the analysis. If outliers are determined to exist, an additional analysis excluding such outliers may be performed and the rationale for such exclusion will be described completely.

A first data analysis including data up to 12 month after surgery is planned after all patients have completed the respective study period. Inferential statistical analysis at this stage will be restricted to the primary efficacy parameter. The final data analysis will be performed after all patients have completed the study.

Categorical data will be described as contingency tables with frequencies and percentage, whereby the dominator for percentages is defined as the number of patients in the respective analysis set. Continuous data will be summarised by mean, standard deviation, minimum, 1st quartile, median, 3rd quartile and maximum. Also the number of missing and nonmissing values will be given.

Tables will be presented by device type and or total, as appropriate. Preabutment connection values will serve as baseline values. Hypothesis tests will be carried out at a two sided significance level of 5 percent, except for the primary efficacy analysis. The confirmatory noninferiority test will be performed at a one sided 2.5 percent significance level.

As usual for secondary, no adjustment os significance level for multiple testing will be performed.

In case of unacceptable deviations from the statistical model assumption, transformations of the data, the use of different distributional models or nonparametric approaches will be considered.

All statistical calculations and analyses will be performed using the Statistical Analysis System (SAS) version 9.1.13 or higher.

Inclusion Criteria:

• Subjects must have voluntarily signed the informed consent form
• Males and females must be 18 years of age.
• Patients must present with an edentulous mandible at the time of surgery.
• The last tooth or teeth in the mandible must have been extracted or lost more than 8 weeks before the date of first stage surgery.
• The opposing dentition must be edentulous with a denture (implant borne or conventional) or natural or restored teeth
• Adequate bone height of at least 9 mm above vital structures (because the minimal available implant lengths is 8mm) in the intraforaminal region. Available bone width should be in such way that 3.3 mm implants can be placed without the use of concurrent bone augmentation techniques. Harvested bone from the drilling sites may be used to cover minor dehiscence defects.
• Patients must be committed to participate in the study for three years of follow-up examinations

Exclusion Criteria:

• Medical conditions requiring prolonged use of steroids
• History of leukocyte dysfunction and deficiencies
• Patients with sever hemophilia
• History of head and neck radiation or chemotherapy
• Patients with history of renal failure
• The application of bisphosphonate medication
• History of uncontrolled endocrine disorders
• Physical handicaps that would interfere with the ability to perform adequate oral hygiene
• Use of any investigational drug or device within the 30-day period immediately prior to implant surgery on study day 0.
• Alcoholism or drug abuse
• Patients with known infection of HIV
• Patients who smoke more than 10 cigarettes per day or cigar equivalents, or who chew tobacco (not greater than 10 cigarette equivalents)
• Fertile females with no adequate method of birth control (contraceptive pill, barrier method, etc.)
• Conditions or circumstances, in the opinion of the investigator, which would prevent completion of study participation or interfere with analysis of study results, such as history of non-compliance, unreliability.