Abstract
Objective
Implant placement in atrophic mandibles can be challenging due to insufficient bone volume. To overcome this problem, bone grafts are often required to increase bone volume and provide a stable base for the implant. However, bone grafting procedures can be invasive, time-consuming, and costly. Tilted implants are a viable option to bypass the inferior alveolar nerve (IAN) and increase the contact surface and primary stability.
The aim of this study was to evaluate the survival rate of tilted implants in posterior atrophic mandible and complications related to injury of the inferior alveolar nerve (IAN).
Methods
Accepted patients in this study were only those who suffered from teeth loss in the posterior atrophic mandible. The analysis of this study focused on tilted implants to investigate the survival rate following insertion and during the loading stage. Clinical assessment was conducted to analyze any occurrences of IAN injury.
Results
A total of 31 implants were placed in the posterior mandible of 26 patients with insufficient bone volume. Over a 36-month observation period, all implants exhibited a 100 % survival rate. Three patients experienced temporary neurosensory disturbances.
Conclusions
The use of tilted implants is a viable option for patients with atrophic edentulous mandible that lack the required alveolar height for traditional dental implants. Despite limited study observation time, bypassing the IAN during implant placement presents a predictable option for atrophic posterior mandible treatment.
1
Introduction
Before implant surgery, it is important to have an adequate implant bed for optimal implant positioning. Teeth loss leads to resorption of the alveolar bone, which can vary in its type and severity. Resorption can be reduced by treatment methods such as atraumatic tooth extraction and the use of tension-free sutures [ ]. However, if the resorption of the alveolar ridge is progressive, implant surgery becomes more unfavorable [ ]. In such cases, augmentation techniques can be used for bone reconstruction to enable successful oral rehabilitation [ ]. Preparation for implant surgery on such resorbed bone volume includes additive (bone augmentation procedures) [ ] and expansive (bone expansion and splitting) techniques [ ]. Many cases become complicated as neither of the two options for bone grafting are viable due to patient-specific local or systemic conditions [ ].
Smeets et al. (2022) conducted a systematic review of eight studies involving 276 procedures using various bone grafts for horizontal augmentation in the mandible. Their findings indicated an average horizontal bone width gain of 4.8 mm and a low overall bone graft failure rate of 4.4 % [ ].
A systematic review by Elnayef et al. (2017) investigated various techniques for bone augmentation in the posterior mandible, including distraction osteogenesis, inlay block grafting, onlay block grafting, and guided bone regeneration. Their findings indicated that complication rates varied among the techniques, with guided bone regeneration exhibiting the lowest rate. Distraction osteogenesis and inlay block grafting demonstrated higher complication rates. Despite this, distraction osteogenesis achieved the greatest vertical bone gain with an average of 4.49 mm, surpassing the other techniques [ ].
Bone grafting has its disadvantages, such as increased morbidity, treatment costs, and duration. To overcome these difficulties, some researchers have proposed unconventional alternatives like positioning implants buccally or lingually in relative to the inferior alveolar neurovascular bundle [ , ].
This method offers several benefits, including being minimally invasive, shorter treatment duration, and being appropriate for patients who can’t undergo bone augmentation procedures because of relative or absolute contraindications [ ]. Nevertheless, these unconventional and precisely executed procedures come with their own set of risks, with inferior alveolar nerve injury being a significant concern and most commonly injured (64.4 %) in oral surgery procedures followed by lingual nerve (28.8 %) [ ] .
Seddon proposed a three-category system for mechanical nerve injuries based on how long and how well the sensory function recovers [ ] . He called these categories neuropraxia, axonotmesis and neurotmesis. LaBanc applied this system to trigeminal nerve injury cases [ ].
Neuropraxia involves a conduction block without axon degeneration, often due to nerve manipulation, compression, or traction. Severe trauma to the endoneurial capillaries can cause intrafascicular edema, leading to temporary loss of sensation or function, which typically resolves within 1–2 days, with full recovery usually occurring within a week. This injury manifests as paresthesia. Axonotmesis results in axonal injury, degeneration, and regeneration, commonly due to traction or compression, potentially leading to severe ischemia and demyelination. Recovery may take 2–4 months, but full improvement can extend to 12 months. Neurotmesis is a severe injury that disrupts the connective tissue of the nerve trunk, compromising sensory and functional recovery. Causes include traction, compression, injection, chemical injury, laceration, and avulsion. The initial response to these injuries is anesthesia, followed by paresthesia, allodynia, hyperpathia, hyperalgesia, or chronic pain, with a poor prognosis for recovery [ ].
The objective of this retrospective study was to evaluate the survival rate of tilted implants in the posterior atrophic mandible and assess the incidence of complications related to inferior alveolar nerve injury.
The author hypothesizes that tilted implants could provide a simpler and less invasive approach to restoring lost teeth without the need for additional procedures such as augmenting atrophic alveolar bone or performing more complex, uncommon techniques like bone distraction and inferior alveolar nerve lateralization.
The study aims specifically at.
- 1
Evaluating survival rate of loaded dental implants which bypass the IAN
- 2
Subjective evaluation of IAN damage by clinical examination
2
Material and methods
2.1
Study design and sample
The investigation was implemented in accordance with the Declaration of Helsinki as a retrospective study on a sample of 26 patients treated and then observed from January 2020 to February 2023 in Latakia, Syria. This study was approved by the Institutional Ethics Committee of Tishreen University Hospital no. 958/2023(April 19, 2023). Written consent was obtained from each participant.
The study has been reported in line with the STROCSS criteria [ ].
This study is registered with the Research Registry by the identifying number: researchregistry8911 and the reference hyperlink is: https://www.researchregistry.com/browse-the-registry#home/
2.2
Participants
The study sample was composed of patients suffering teeth loss in the posterior mandible who presented for treatment in University Hospital in 2019. All selected patients for this study had atrophic posterior mandible (class 5 and 6 according to Cawood & Howell classification [ ]) with difficulties of bone augmentation procedures due to local (insufficient soft tissue coverage, lack of adequate surrounding bone) or systemic (blood disorders) contraindications. All accepted patients in the study sample were of both genders over 18 years old and indicated for implant placement to restore one or more extracted teeth. Excluded patients from this study were patients who suffer endocrine diseases that affect bone metabolism, oncology patients who receive radiotherapy and/or chemotherapy, pregnant women, and smokers. All patients underwent treatment from the same surgeon N.S., who followed the same surgical protocol for each patient.
To evaluate the position of the inferior alveolar nerve and assess the residual bone volume before
treatment, a Cone Beam Computed Tomography (CBCT) was performed (CS9600 CBCT machine Carestream software for DICOM viewing). The implants used in this study are IBS Implant System® (IBS, Daejeon, South Korea).
2.3
Variables
The primary predictor variable was the treatment protocol included in this study, which is based mainly on placement of tilted implants to restore lost teeth in the atrophic posterior mandible.
Primary outcome variables include.
- 1
3-year survival rate of inserted implants
- 2
Clinical assessment of Neurosensory damage
Covariates include.
- 1
Bone density at the site of drilling
2.4
Surgical technique
All treated patients rinsed out their mouths preoperatively with chlorhexidine gluconate 0.12 % (Biofresh-K mouth rinse®). The skin around the mouth and lips were sterilized with povidone-iodine®. Antibiotic prophylaxis of 2gr amoxicillin with clavulanic acid was taken 1 h before the procedure (Augmentin 1000 mg tab®,Syria).
Buccal and lingual infiltrative local anesthesia was done using lidocaine 2 % with 1:100000 epinephrine (adrecaine®) to maintain sensorial feedback from the patient while drilling near the IAN.
A full thickness mucoperiosteal flap was raised to obtain a complete visual of the alveolar bone. Accurate positioning of the pointer drill was evaluated according to the studied case by CBCT scan. Drilling started with the pointer drill just 2 mm to access through the cortical bone to the sponge bone. A maximum speed of 400 RPM with good cooling irrigation was critical for preventing potential thermal injury to the IAN. A pilot drill of 2.2 mm was then used to prepare the site of the implant until reaching the planned height. To ensure the correct angulation for implant insertion, the technique involved unguided drilling, positioning the drill either buccally or lingually based on the planned implant placement, while keeping the drill parallel to the buccal or lingual plate. In and out motions with light pressure during preparation of the implant site were helpful to pay attention to any pain reflexes from the patient. The sequential drills for the planned diameter were inserted carefully with the same axis of the pilot drill. Any pain sensed by the patients was carefully noticed during the drilling phase. Implant insertion was done manually, and the wound was sutured with 3/0 silk (Unify®) using simple interrupted suture technique. Patients were given a prescription for antibiotics (Augmentin 1000 mg tab, Syria —amoxicillin plus clavulanic acid 1 g/every 12 h) and one tablet of an anti-inflammatory drug (Ibuprofen 600 mg every 8 h) for the following 5 days. Chlorhexidine gluconate 0.12 % was prescribed for daily usage (3 times a day for 1 min). Sutures removal was done after 7 days. Patients’ recall for clinical checkup was done on day 1 after procedure, day 7, 2 weeks, 4 weeks, and monthly until reaching the 39th month. Implants loading was done 3 months after the procedure.
Before the surgery, a CBCT scan (CS9600 CBCT machine –Carestream software for DICOM viewing) was performed to check the position of the IAN and measure bone density in the planned site.
To ensure the safety of implant placement, a minimum of 6 mm of bone width was required adjacent to the inferior alveolar nerve (IAN). A 2 mm safety margin was implemented during drilling to minimize the risk of nerve damage.
Another CBCT scan was done right after the implants were placed to evaluate the location of the tilted implants for each patient. Figs. 1 and 2 .
All implants were loaded 3 months postoperatively.
2.5
Assessment of neurosensory impairment
Subjective evaluation is crucial for assessing neurosensory loss; a questionnaire based on a visual analog scale (VAS) was used as a standardized and quantifiable method as it contains questions with a continuous horizontal line and two descriptive ends where the patients mark it at a point that they feel it represents their status. The horizontal line is 100 mm in length and the score is calculated by the measurement of the millimeters from the left to the right [ ]. The zero measurement means no sensation and the 100 measurement means full normal sensation without any disturbances.The targeted area which corresponds to the IAN anatomy is the lower lip and the chin. The questionnaire was administered on the first day post-surgery. Patients who had any changes in sensation levels filled out the questionnaire again on the seventh day, the fourteenth day, one month, two months, and so on until the twelfth month if sensation problems persisted. Sensation changes that lasted beyond 12 months after the procedure were considered as permanent damage to the IAN.
The following treatment was given to patients with neurosensory disturbance (NSD).
- 1
Prednisolone (Predlone®) oral administration in a 5-day decreasing dose (50-40-30-20-10 mg).
- 2
B vitamins (Betatonic®) for a month, three times daily.
2.6
Data analysis
Statistical analysis was done using IBM SPSS 2020 version 27.0 software for Windows.The distribution of time-to-event (neurosensory disturbance, implant failure) was analyzed using Kaplan-Meier survival analysis to see if it differed based on factors such as implant tilting direction (buccal or lingual), implant diameter, implant length, or implant positioning (premolar, first and second molar). Censoring was considered when no event occurred during the observation period or if the patient dropped out of the study [ ].
Log-rank tests were performed to decide if the distribution of complication/implant survival events varied based on factors such as implant tilting (buccal vs. lingual), implant dimensions, and implant positioning. Descriptive analysis for subjective evaluation of NSD was used.
Spearman correlation test was used to evaluate the relationship between bone density and NSD [ ].
3
Results
Twenty-six participants were included in this study (aged 45.11 ± 8.05) of which 12 were men. Thirty-one implants were placed in the posterior atrophic mandible. Twenty-four implants were directed buccally (74.19 %) and 8 implants lingually (25.8 %). Positioning of implants varied between second premolars (25.8 %), first molars (38.7 %), and second molars (35.4 %).
No failure of any implant happened, and the survival rate of all inserted implants was 100 %. During the assessment period, none of the patients withdrew from the study. All data regarding patients’ details including gender, age, implants dimensions, tilting, and average bone density is shown in Table 1 .
Stay updated, free dental videos. Join our Telegram channel
VIDEdental - Online dental courses
