## 1 Introduction  
Dental implants have become a reliable alternative solution for replacing either some or all missing teeth [1].  
In recent decades, the survival rate of dental implants has notably increased. Most studies have reported survival rates between 90% and 95% in the first 10 years and between 51.97 and 75.8% after between 16 and 20 years [2]. Despite these findings, numerous factors can affect implantation success, from patient-related aspects to surgical and prosthetic protocols [1]. An implantation is considered successful when there is no pain, infection, or mobility at the site of the implant or radiolucency around it. If the implant must be removed due to any of these factors, it is considered a failure [3].  
Time-wise, failure can be classified as early or late depending on whether it occurs before loading or after loading. The rate of early failure is estimated at 5% and has been related to local and systemic factors, as well as surgical factors that lead to osseointegration failure. Late failure (accounting for approximately 95% of cases) is related to the presence of bacteria, the mechanical factors of the prosthesis, and patient habits [1].  
Dental implant placement requires an incision in the gums, except in those cases where a flawless intervention is performed [4].  
When an incision has been made, after surgery, the wound margins are brought together and sutured, initiating the healing process. This process has been described as a two-stage sequence in which homeostasis and immune mechanisms are interconnected. Classically, healing is divided into three periods: inflammation, proliferation, and maturation [5]. Some authors additionally distinguish coagulation from the inflammatory phase, thus dividing healing into four periods (coagulation, inflammation, proliferation, and maturation) [6].  
This cascade of events can be affected by soft tissue dehiscence, jeopardizing healing. For this reason, it is very important for the surgeon to manage the flap appropriately and select the ideal type of suture to provide the best stability to the flap without excessive tension [5].  
As mentioned above, various factors can affect the healing process, including patient factors (age, nutritional status), local factors (scarcity of tissues, wound movement, early infection), interventional factors (extension, duration, tension, delicateness), and acquired factors (medication, habits) [5].  
The early detection, and, if possible, early correction of any deviations in tissue healing could increase the rate of dental implant success [7].  
To monitor healing, different types of indices have been developed that can help detect these initial changes. However, there are no clear indications for their use, and their correlation with the degree of well-being of the patient have not been clarified [7].  
The objective of this study was to assess whether there is a correlation between the Wachtel healing index and early dental implant success or failure at the time of loading.  
As secondary objectives, we assessed whether there is any relationship between other variables studied and early success or failure. These variables included:  
* Tobacco use (<10 cigarettes/day)
* Diabetes
* Other systemic diseases
* Ingestion of painkillers
* Inflammation
* Pain
* Guided bone regeneration (GBR) technique