The implant osteotomy is a key surgical step in implant dentistry. It ends with the insertion of a dental implant that will later supply the patient with a fixed or removable replacement for missing teeth. In this module we will first describe the correct bone preparation technique for implant placement. Subsequently, we will address the adjustments of the protocol that are necessary in different bone densities. Finally we will discuss the potential risks associated with inappropriate osteotomy techniques.

After completing this ITI Academy Module, you should be able to define the sequence, speed and drilling technique and recognize its relationship to primary implant stability and osseointegration, select the appropriate drilling procedure for a given type of bone, and list the effects of inadequate drilling technique and instrumentation on primary implant stability and osseointegration.

The implant osteotomy is technically the preparation of an appropriate space for a dental implant in the edentulous bone ridge. It is performed with two goals in mind: The first goal is to insert the implant in an anatomically and prosthodontically correct position with good primary stability and minimal tissue trauma. The second goal is to achieve its successful osseointegration and function maintained over time. A period of time is required for healing of the bone and soft tissues, and for osseointegration to take place. From a biological perspective, performing an implant osteotomy can be considered a bone injury. This bone injury initiates a cascade of bone-healing-related mechanisms including the resorption of irreversibly damaged bone tissue where necessary and then the apposition of new bone.

Implant osteotomies involve, cutting, heating, compressing or tearing of the bone and the hard tissue. For the healing cascade to end in successful osseointegration, the necessary unavoidable injury created by the implant osteotomy has to be performed with as little trauma as possible. The frictional heat generation during implant osteotomy plays a major role in bone damage. Heating occurs at the interface of the drill to the bone. In an animal study, vital bone showed necrosis if exposed to a heated coil at a temperature of 47º Celsius or 116º Fahrenheit for longer than one minute. In other words, the osteocytes underwent permanent damage at a temperature of only 10º Celsius above the normal body temperature. Despite the methodological differences between the study and the procedures adopted in dental surgery, this temperature-by-time threshold is still considered a valid reference today. Bone damage is further influenced by surgery-related variables, some of them, such as pressure, speed and cooling during drilling, are controlled by the surgeon. Others are dependent on the drill specifications. Primary stability is a prerequisite for the slow-growing bone tissue at the osteotomy walls to generate osseointegration. Movement during healing will compromise implant osseointegration. Although pressure of the implant threads engaging the bone generates a certain amount of necrosis, adequate compression creates primary stability and is beneficial to bone healing. In contrast, excessive squeezing of the bone through the implant threads or even the implant body will cause major and unnecessary bone necrosis. The necrotic bone at the thread level resorbs during postoperative healing and new bone is usually formed on the implant surface.

Several techniques for minimally invasive implant osteotomies have been developed. They are based on rotating drills, oscillating ultrasonic or piezo-electric tips or expansion and compression-based devices enlarging a previously created access hole or gap. This module will discuss the rotary or drilling technique, which is most commonly used and best-documented.

For correct prosthodontically driven three-dimensional positioning of the implant, the preoperatively defined implant position needs to be transferred into the surgical procedure. A surgical template is recommended for this purpose. The surgical template indicates the position of the future prosthesis, thus offering a stable reference in all three spatial dimensions without interfering with the drilling procedure. After perforating the bone surface with a guide drill or round bur, the drilling osteotomy technique is used to create an approximately 2-millimeter-wide pilot hole in the correct position and depth. Afterwards the hole is successively enlarged until the diameter of the implant is reached. In the system shown here, the round bur is used for the superficial perforation, the 2.2-millimeter pilot drill is then brought to the definitive depth and the 2.8-millimeter twist drill enlarges the pilot hole. Each implant system has a recommended sequence of round, pilot and twists drills that the clinician should adhere to.

This stepwise approach has two main advantages that are not present when steps are skipped. The first is minimization of heat generation during the osteotomy: The amount of bone removed with a drill influences heat generation and consequently the risk and degree of bone necrosis. More bone removed at a given time means more friction and thus proportionally more heat generation. The amount of bone removed influences the heat generation more than the drill diameter itself. With increments in drill diameter of less than one millimeter, minimal heat generation can be expected. Secondly, the use of several burs and drills in sequence allows for small corrections of inclination and position before moving to the next instrument in the sequence. In order to detect and correct malpositions early enough, the insertion of a proper direction indicator after each drilling step is strongly recommended. The video sequence demonstrates the insertion of a 2.2-millimeter-wide direction indicator after the corresponding osteotomy. Depending on the manufacturer, direction indicators can also be called alignment pins or depth gauges.

Once the final osteotomy width is reached, some additional steps may be necessary. Depending on the soft and hard tissue level, the collar shape of the chosen implant type and its final vertical position, additional profile drilling in the crestal area may be required. Esthetic, biologic and implant-type-related characteristics determine the necessity of this step. It is recommended to follow the manufacturer's instructions for the correct indication and use of the profile drill. Tapping is necessary in hard bone and serves to control the pressure exerted by the implant threads engaging in low-resilience hard tissue. The implant insertion concludes the osteotomy and can be performed with a hand ratchet or with an insertion device connected to the surgical hand piece or contra-angle.

When preparing and servicing the surgical instruments, some basic principles should be kept in mind. Sharp drills reduce the risk of tearing or unnecessary traumatic removal of tissue parts, and overheating. The drills should be replaced as directed by the manufacturer. The appearance of corrosion or signs of blade damage requires immediate replacement of the drill. Special care needs to be taken when cleaning the drills in order to preserve their sharpness. Soft brushes and mild cleaning agents are recommended. As an alternative to conventional drills, disposable drills may be used.

Original protocols stated the importance of low drilling speeds at 400 to 800 revolutions per minute in order to reduce heat generation. Today, the influence of speed on heat generation is questioned. Cooling and pressure seem to play a more decisive role in heat production. When sharp drills, correct drilling technique and adequate cooling are used, the temperature at the drill-to-bone interface rarely reaches 47º Celsius, irrespective of the drilling speed. Moreover, too-low rotating speeds reduce the cutting effectiveness of the blades and increase the time necessary for the drilling procedure with each instrument. Today, drilling speeds ranging from 400 to 2000 revolutions per minute are considered adequate. The speed of the pilot drilling is set around 800 to 1000 revolutions per minute and then gradually decreased to 400 revolutions per minute while the drill diameter is increased. Higher speeds may be applied to the round bur for more accurate positioning of the initial notch in the cortical bone and low speeds are recommended for tapping and implant insertion. The clinician should observe the manufacturer's recommendation for drill speeds.

A primary factor towards a correct osteotomy is having a stable hold on the surgical contra-angle while drilling. Using the first two or three fingers of both hands to hold the instrument head and using the remaining fingers for stabilization in- or outside the mouth is particularly effective. This helps in reducing drill movements to a purely vertical or up and down movement, without horizontal changes in the position or the axis. Due to the frequently hard cortical bone in edentulous areas, the first drilling with the round bur may challenge the stability of the hands-drill system. In order to accurately position the first mark or notch in the bone surface, horizontal tilting of the round bur can be helpful. After the notch has been drilled in the cortical bone, exclusively vertical movements and controlled finger pressure of maximally twenty Newton or two kilograms are recommended for an accurate and time-efficient drilling. Finally, intermittent drilling movements are recommended. They are also described as pumping or up-and-down lifting of the drill while rotating. This allows for removal and flushing out of the bone chips, thus increasing the cooling effect thanks to the reduced friction and to the cooling solution better reaching the apical part of the drill. It has been demonstrated that the drill head heats faster than the shaft, which demands an even more effective intermittent technique when drilling deep osteotomies.

Today, both internally and externally cooled drills are considered valid options with regard to the long-term outcome. A trend towards external cooling is due to technical limitations such as clogging and the limited relatively wide minimal diameter of the internally cooled hollow drills. When in function, irrigation MUST be abundant and not just drop-wise and MUST hit the bur or drill in order to cool it. The surgical assistant should be instructed not to suction away the irrigation directly from the sprinkler but to allow it to stay in contact with the bone surface for a while. The combination of up-and-down movements and proper contact between coolant and drill allows the irrigation to efficiently cool the entire drill length. Moreover, preoperative chilling of the saline irrigation solution to around 3 to 5 degrees Celsius or 40º Fahrenheit has been demonstrated to further enhance the cooling effect.

When drilling the implant osteotomy, care should be taken not to proceed too slowly. The preparation depth should be reached within a reasonable time through intermittent drilling and moderate pressure. This reduces the likelihood of necrosis in cases where the temperature reaches the threshold of 47º Celsius for longer than one minute. Over-instrumentation and unnecessary re-entries with a drill increase the preparation width, which reduces the primary stability of the implant and increases the risk of malpositioning. Holding the rotating drill at the same depth is particularly dangerous: It increases both the temperature and diameter of the preparation.

Sequence, Speed and Technique of Drilling, Key Learning Points: To achieve long-term success the implant should be placed in a correct position, with good primary stability and minimal tissue trauma. Implant osteotomies involve sequential bone drilling in order to achieve the desired depth and diameter of the planned implant dimension. Stepwise osteotomy allows for a reduction in heat generation and minor corrections to the implant position during the procedure. The risk for heat-related bone necrosis can further be minimized by the correct use of sharp burs, low pressure, intermittent drilling and efficient cooling. Unnecessary re-entries with the drills and excessively slow drill progression should be avoided.

Bone density plays an important role during the osteotomy. It needs to be taken into account during therapy planning, because it often requires an adjustment to the technique. Bone density is patient- and site-specific and thus requires a case and site-specific pre-operative analysis. The most common classification divides bone into four density classes ranging from dense or cortical to soft or cancellous. The bone with the highest density is called D1 and the softest D4. D2 and D3 are intermediate classes and display an increasing ratio of cancellous to cortical bone. This will be referred to as moderately dense bone. Bone density plays a major role in deciding on primary stability and heat generation during drilling: Dense bone allows for more primary stability but causes more friction during osteotomy whereas soft bone shows the opposite effect. These aspects deserve particular attention and specific adjustment of the drilling technique after accurate analysis of the bone density.

The bone density analysis should be performed at two stages: Preoperatively, two-dimensional radiographic imaging such as periapical or panoramic radiography delivers a fairly accurate estimation of the bone density and the cortical thickness. Three-dimensional radiology such as cone beam computed tomography offers the most accurate tool for non-invasive preoperative density estimations. The statistical distribution of bone density is highly variable. As a rule of thumb the following distributions can be considered: Not in every patient, but frequently, D2 bone can be found in the anterior mandible. Very dense D1 bone is usually only present in fully edentulous mandibles. D4 bone is mainly found in the posterior maxilla and D3 in the other areas. Definitive and accurate information on the bone density and cortical thickness can be retrieved during the first deep drilling, the pilot osteotomy. Penetration of this approximately 2-millimeter-thick drill allows a definitive tactile assessment of the bone density and further adaptation of the surgical protocol.

In very dense D1 bone the risk of overheating is the major issue and requires particular care by using all available cooling measures. These are the use of chilled and copious irrigation, intermittent pressure, sharp drills and full drill sequence. The low resilience of this cortical bone type requires bone tapping over the full length of the osteotomy and cervical profiling or countersinking where the implant neck has to be placed lower. Finally, the reduced blood supply of this bone class derives primarily from the periosteum and not from the bone marrow. Minimal flap reflection aids in preventing bone resorption and necrosis.

D2 and D3 bone offer a balance of achievable primary stability and good vascularization. Usually a dense cortical bone plate covers a variably soft cancellous marrow. The engaging implant threads and neck generate appreciable primary stability. The standard drilling protocols of most manufacturers are made for this bone type. Particular care is due in cases where the planned implant position is close to the oral or facial cortical plate. A sudden increase in resistance to drilling is the consequence and this may inadvertently divert the drills or the implant during insertion. Controlled finger forces in all three dimensions are required as well as a tapping of the crestal portion of the osteotomy where necessary. Statistically, the best healing outcome can be expected in sites with moderate bone density due to the optimal blood supply combined with predictable primary stability.

Soft D4 bone has a minimal bone density, resulting in sparse bone trabeculae and a thin or missing cortical plate. Tapping is usually not recommended in D4 bone in order not to further increase the osteotomy diameter. Some manufacturers allow undersizing of the osteotomy hole for an increase in primary stability. Instead of countersinking, the wider neck configuration of many implant types can be set deeper to engage crestal unprepared bone and generate additional stability. Primary closure allows for submerged healing and protection against premature implant loading or movement during healing.

Bone tapping is required in denser bone types. The aim is to prevent the implant threads from excessively engaging the bone walls. This has a two-fold advantage: It reduces pressure-related bone remodeling and thereby the relative drop in implant stability during the early healing phase. Secondly it allows the implant to reach the bottom of the preparation hole in very dense bone. Tapping in D2 and D3 bone should be limited only to the dense portion of the bone in order not to excessively reduce primary implant stability. Thus, tapping of the whole osteotomy depth is only indicated in very dense bone.

Tapping can be performed using either the hand ratchet together with the stabilization instrument or a micro-motor. When using a micro-motor, low speed and high torque are necessary. A speed of 15 revolutions per minute is usually recommended. The surgeon's hand should maintain light but constant and apically directed pressure and respect the original path of the osteotomy for the entire depth. The tap driver has sharp edges and could otherwise deviate from the desired implant position. Bone chips should be gently removed from the tapping threads and either rinsed away or kept for simultaneous bone augmentation if required.

Drilling Procedure for a Given Type of Bone, Key Learning Points: Bone density varies markedly among patients and between different areas of the jaw with the same patient. Extremely high and extremely low bone densities yield a higher risk for surgical complications and implant failures. Preoperative bone density assessment and adjustment of the surgical protocol to the specific density allow for risk reduction and increased outcome predictability. Dense bone is prone to overheating during drilling and requires wider osteotomies. Soft bone has better vascularization than hard bone, offers less primary stability and requires accurate or undersized preparations.

Overheating can be deleterious for bone. Risk of overheating from increased drill friction is expected in dense bone, when high pressure or blunt drills are used and when cooling is insufficient. The consequences range from a decrease in temporary stability due to remodeling of the necrotic bone in the healing course to major site infection and tissue resorption resulting in a fibrous encapsulation.

A further possible complication is reduced or lack of missing primary stability of the implant. It can arise as a result of soft bone, a deviating drill axis while preparing the site or over-instrumentation or a combination of these factors. The latter can be associated with drills deviating from the original path thus creating an oval preparation instead of a round-shaped osteotomy. Preparation with an oval shape or any other shape that does not match the implant section results in an increased likelihood of implant failures.

The result of reduced primary stability could be delay or failure of osseointegration. The reduced primary stability leads to reduction in resistance to force during healing and thus an increased risk of non-osseous healing or fibrous encapsulation. If the healing phase passes without complications, a good long-term outcome can normally be expected. With lack of primary stability successful healing is rare. Lack of primary stability may also have serious consequences and could be potentially dangerous to the patient's health. If left in place, non-stable implants may migrate to adjacent spaces under the influence of oral forces during normal function. Cases of implants displaced into the maxillary sinus as seen in this image, into the floor of the mouth or into cancellous marrow have been reported.

When trying to achieve high primary implant stability, excessively undersized preparations should be avoided. High risk situations include very dense bone combined with a tight, underprepared implant bed and failure to perform a thorough tapping. As a consequence, the implant may not be able to reach the full depth of the preparation due to the excessively high insertion torque and will lock half-way through.

Effects of Inadequate Drilling Technique and Instrumentation, Key Learning Points: High predictability in implant therapy can be expected only if the surgical technique and materials are precise and at the same time adjusted to the site-specific bone characteristics. The use of a poor drilling technique, insufficient cooling or inadequate materials often results in bone necrosis and reduced primary stability. Reduced primary stability may be a potentially dangerous situation with regard to both implant displacement and implant outcome.

Implant Osteotomies, Module Summary: An implant osteotomy is the preparation of bone ending with placement of a dental implant. Its goal is correct implant positioning with primary stability, which enhances the chances for successful osseointegration. Correct hand control, accurate drill direction and sequence are essential to achieve good primary stability of the inserted implant. Overheating and subsequent bone necrosis can be minimized using sharp instrumentation, low pressure, intermittent drilling and copious cooling. Adjustments of the osteotomy technique according to the specific bone density should be considered. An inadequate osteotomy technique can lead to reduced implant success or implant displacement.