BACKGROUND AND OBJECTIVES: The comparison
of crestal bone loss in relation to implants placed
using conventional drilling osteotomy method and
using bone expansion screws in maxillary region.
METHODS: The crestal bone loss was measured after implant placement and after a period of six months, and the results analyzed. Equal number of male and female patients of comparable age group who opted implant treatment were selected.
RESULTS AND DISCUSSION: After a period of six months of implant placement, a mean value of 1.37 mm of crestal bone loss was noticed for implants placed using conventional osteotomy method while a mean of 0.73 was noticed in relation to implants placed using expansion screws.
CONCLUSION: The implants placed using bone expansion screws show less crestal bone loss compared to implants placed using conventional osteotomy method in maxillary edentulous ridge having less than ideal bone width. It infers that the bone expansion method using expansion screws is more reliable and relatively noninvasive way of implant bed preparation.
Key words: Crestal bone level; Conventional osteotomy; Bone expansion screws; Implants.
Over the past few decades, removable dentures
have given way to fixed prosthetic options due to
the demand for esthetics and comfort. The major
breakthrough; the concept of “osseointegration” in
dentistry by Dr. Per Ingvar Brånemark1
continued research benefited in the rehabilitation
of edentulous patients.
In the maxillary region, the advanced resorption of alveolar bone and relatively lesser bone density poses a challenge for implant placement. Many techniques have been tried for widening edentulous ridge, including osteoinduction2,3 osteoconduction4 , onlay block bone grafting, alveolar distraction osteogenesis5 , guided bone regeneration and splitting to expand the ridge6,7. They come with limitations including harvesting bone from oral sites, highly technique sensitive, lower patient compliance and increased morbidity.
Less invasive techniques using osteotomes and bone expansion screws help to shorten treatment length, avoid additional surgical appointments, reduce trauma to patient and conserve the maximum amount of alveolar bone and decrease morbidity8 . Bone expansion screws utilize a thread former configuration allowing expansion and lateral condensation of bone, when used in increasing diameters inserted with a torque wrench. They allow ‘corticalization’ of the implant site which is advantageous for the primary stability of implants in rather cancellous bone of maxillae according to Lekholm & Zarb9 (1985).
This study was aimed to compare the crestal bone loss which occurred in relation to implants placed by ‘bone spreading technique using bone expansion screws with conventional method of osteotomy preparation. Both methods are employed for placing implants in edentulous ridge with enough bone height as well as a minimum required width. Estimation of peri-implant crestal bone loss is an important parameter for evaluation and prognosis of implant success10.
It is an observational clinical studyconducted
according to the guidelines of the localethical
committee of Thiruvananthapuram dental
This clinical study included patients with healthy remaining dentition, good oral hygiene, no retained roots/pathologic lesions, adequate inter-arch clearance, adequate quality and quantity of bone, no known systemic disease, availability for follow-up. Patients with smoking habit/drug or alcohol abuse, Radiation treatment to head and neck, ongoing chemotherapy, pregnant and lactating women, post-menopausal women, patients under corticosteroids and immune-suppressants, Patients reporting after recent extraction (less than 3 months) were excluded.
Total sample size was 30. Consecutive cases satisfying inclusion and exclusion criteria were selected till the sample size was achieved. The patients were given written information regarding the risks of implant surgery and their written informed consent was obtained.
Based on the evaluation of diagnostic casts and
CBCT (Figure 1,2), titanium root form implant
(GenXT) dimensions were determined for each
patient. A safe distance of minimum 2mm was kept
from anatomical structures such as maxillary sinus.
The surgery was done under antibiotic coverage.
Betadine solution (5%) was used to disinfect the
extra-oral as well as intra-oral tissues. The patient
was asked to rinse with 1.2%mg/ml chlorhexidine
gluconate mouthwash for one minute. The site
of implant surgery was anesthetized by local
infiltration injection of 2% lignocaine with 1:200000
adrenaline (cadila pharmaceuticals).
Group A – Conventional osteotomy method
Initial preparation was done using pilot drill followed by sequential drilling using progressively larger drills. The drilling was done using physio dispensor under copious irrigation of normal saline. The drill depth was assessed using depth gauge. Once the planned implant diameter was achieved, implant was placed with the help of an implant mount.
Group B – Bone expansion screw method
Pilot drill was used on the proposed implant site to reach the desired depth. Bone expansion screws in the order of increasing diameters were inserted into the bone cavity. Screws of diameter 3.5mm, 4.0mm and 4.5mm were used (Figure 3). A torque wrench was used to insert the screw cautiously and slowly upto the desired depth. The last screw spreader used had to be slightly smaller in diameter than the implant diameter. Implant was placed with the help of an implant mount and inserted using torque wrench (Figure 4).
In either of the above methods, immediate loading single stage implants were placed in each patient using immediate loading protocol. An interim restoration was cemented on the day of surgery after implant placement (Figure 5). Digital periapical intraoral radiographs were taken immediately after implant placement and after six months (Figure 6). Regular clinical follow-up was done at one month, three months and six months after implant placement.
From the digital radiographs, the distance from
the mesial crestal bone level to the apex of the
implant was measured with the help of Romexis
software. The measurements were subjected to statistical analysis using Students t –test.
The crestal bone levels in relation to implants placed using both methods were measured immediately and after six monthsof implant placement. Comparison of crestal bone level of implants placed using both the methods were measured immediately and after six monthsof implant placement. After a period of 6 months of implant placement, a mean value of 1.37mm of crestal bone loss was noticed for implant placed using conventional osteotomy method while a mean of 0.73 was noticed in relation to implants placed using bone expansion screws (Graph 1,2). The study was significant at 0.01 level (Table.1.)
Though there are various surgical methods for
implant bed preparation, the conventional drilling
osteotomy technique has been the most used,
irrespective of the quality of bone. A scientific
backup of various studies shows consistent results
with good primary stability and success rate when
performed in good quality bone of adequate
volume11. But the removal of precious bone by
drilling is a major concern particularly in narrow
edentulous maxillary ridge of relatively poor bone
quality (D2, D3 or D4).
The present study was conducted to compare the crestal bone loss that occurred in relation to implants placed using bone expansion screws, with that of conventional osteotomy method using bone drills. Crestal bone loss being an important parameter for the evaluation of success of an implant, it is possible to assess the reliability of using bone expansion screws for implant placement; which is a more conservative procedure. Bone expansion screw method is primarily intended for placing implants in edentulous areas with sufficient bone height but insufficient bone width as well as poor bone quality.
When it comes to implant treatment in narrow edentulous ridges, there are numerous ridge augmentation methods, but most of these surgical procedures are invasive, involves risk of infection and takes longer time period to reach their goal7,12,13.
Bone expansion using screws and osteotomes are two relatively atraumatic methods indicated for implant bed preparation in edentulous ridges of poor bone quality and inadequate width. The concept of bone expansion screws was introduced to overcome the shortcomings of osteotomes such as the difficulty in controlling malleting force as well as the risk of bone fracture. The screws can be engaged into the receptor bone with the help of a ratchet or torque wrench. With the introduction of larger diameter screws, bone is pushed and condensed laterally which allows a slow and gradual expansion of the bone laterally rather than losing bone by drilling.14,15 The implant should be 0.5 mm larger in diameter than the size of the screw last used to expand bone16. The softer bone quality found in type III and type IV maxillary bone is improved by laterally compacting the medullary bone16. The increased bone rigidity achieved by bone condensation results in improved primary stability of implants14. Patient compliance is also more with this method16.
One of the drawbacks of using bone expansion screws is that resilience of bone sometimes requires revision of the osteotomies with final sizing drill before implant placement. Also. a continuous full turn in thin dense bone can lead to excessive osteo- compression16. It can only be performed in cases with cancellous bone within the cortical bone on both sides17.
Immediate loading root form implants were used for the study aiming at a shorter treatment period with a stable and fixed long-term interim restoration on the day of surgery18. This treatment option also aims at maintenance of the hard and soft tissue contour and reducing the waiting period18. The highly acceptable clinical success rate of immediate loading implants has been studied and proved by many pioneers like Maria Chatzistauraw et al19 in 2003, Degidi M20, Piatteli A in 2005, Cannizzaro et al21 in 2011, Yoo et al22 in 2006 etc.
Digital periapical radiographs taken immediately after implant placement and six months later were used for measuring crestal bone loss. The measurements were made from the crest of the bone to the apex of the implant with the help of Planmeca Romexis software. Study by Penarrocha23 et al in 2004 shown that conventional periapical films and digital radiographs were more accurate than orthopantomography in the assessment of perimplant bone loss. In order to reduce any bias in technique, all the radiographs were taken by the same person who is qualified and skilled for the same.
In the present study, analysis of difference in the crestal bone level in relation to implants placed using conventional drilling osteotomy method and using bone expansion screws immediately after implant placement and after a period of six months has been done. Descriptive statistics along with Box plot was used to describe Crestal bone level between two different methods at immediately after and six months after implant placement. Independent sample t-test was used for the comparison of difference in crestal bone level after six months between the two methods. For all statistical interpretations. p<0.05 was considered the threshold for statistical significance. Statistical analysis was performed by using a statistical software package SPSS, version 20.0.
After a period of six months of implant placement, a mean value of 1.37 mm of crestal bone loss was noticed for implants placed using conventional osteotomy method while a mean of 0.73 was noticed in relation to implants placed using bone expansion screws. The mean crestal boneloss for Branemark implants has been determined to be 1.5mm for the first year, followed by a mean bone loss of 0.1 mm per year by Adell et al1 . This value was confirmed by Cox and Zarb24 with their 5-year report.
The present study was statistically significant at 0.01 level. There is significantly lesser bone loss in relation to implants placed using bone expansion screws after a period of six months when compared to implants placed using conventional osteotomy using bone drilling. Here the implants were placed in edentulous maxillary ridge which was classified as belonging to D2, D3 or D4 type bone. Ridges having a minimum of 4.5 mm width were included in the study. The impression made can be that the lateral bone condensation by bone expansion screws improved the quality of porous medullary bone of maxillae14. This technique conserved all of the bone in the surgical site14,15. A study done by Nishioka et.al14 in 2009 showed that the maxilla with insufficient buccolingual width and relatively less dense bone can be managed well by using bone expansion screws.
Bone expansion screws allow the placement of greater diameter implants than when conventional method of osteotomy is used. Each 1 mm increase in diameter of implant increases the surface area by about 20–30%, which in turn decreases crestal stress and eventually crestal bone loss11 Incidence of green stick fractures are minimized and there is no thermal injury to bone16.
The results of the present study indicate that thread-former and “screw-type” design is more appropriate for placing implants in areas of buccal bone resorption and in soft maxillary bone, than the conventional osteotomy drilling. With proper patient selection, evaluation, pre-surgical planning, careful execution of surgical technique and post-operative follow-up, favorable results can be achieved. Long term data regarding the outcome and success rates would require randomized studies to evaluate the predictability of this technique.
Within the limitations of the study, the following conclusions were drawn after analysis of the results: