Evaluating the risk of post-extraction inferior alveolar nerve injury through the relative position of the lower third molar root and inferior alveolar canal

The aim of this study was to introduce a method to evaluate the risk of inferior alveolar nerve (IAN) injury following the extraction of impacted lower third molars. Two hundred impacted lower third molars adjacent to the IAN were evaluated. These were divided into four classification groups according to preoperative cone beam computed tomography (CBCT) findings: AR, apical region; LT, lateral region of the tapered root; LE, lateral region of the enlarged root; AE, adjacent to the enlarged root. All teeth were dislocated along the long axis or arc of the root by tooth sectioning technique and extracted by a single surgeon. The primary outcome variable was postoperative neurosensory impairment of the IAN. The χ² test was used to evaluate differences in postoperative IAN injury between the classifications. Logistic regression analysis was used to evaluate the risk factors for postoperative IAN injury. The overall incidence of postoperative IAN injury was 7%. Specifically, most injuries involved classification AE (AE 36%, LE 8.6%, LT 3.6%, AR 0%), and the difference was statistically significant (P <  0.05). Logistic regression showed that classification AE was the only risk factor for postoperative IAN injury (P <  0.001). According to preoperative CBCT, the risk of postoperative IAN injury is higher when the IAN is adjacent to the enlarged part of the root.     

Extraction of low horizontally and buccally impacted mandibular third molars by three-piece tooth sectioning

The aim of this study was to investigate the clinical effect of the extraction of low horizontally impacted mandibular third molars by three-piece tooth sectioning. Sixty patients with low horizontally and buccally-impacted mandibular third molars on both sides were operated on under local anaesthesia. Three-piece tooth sectioning was used on one side (n = 60) and the molars were extracted using a high-frequency electric knife, 45° reversed-angle high-speed turbine, and special long crank drill. Each molar was cut into three pieces, which were removed in the following order: middle, root, and crown. One month later, the molars on the other side of each patient’s jaw were removed by conventional extraction (n = 60) with the same equipment. The crown was cut and removed first, and then the remaining piece was extracted. The duration of the procedure, and incidence postoperative swelling, pain, and trismus were compared between the two groups. The procedure was shorter with the three-piece method (10.05 (0.51) min) than with the conventional method (20.15 (0.88) min, p < 0.01). Postoperative swelling, pain, and trismus were all less severe with the three-piece method than with the conventional method (p < 0.01). Three-piece tooth sectioning could be used to remove low horizontally and buccally-impacted mandibular third molars, as it can shorten the duration of the procedure, reduce trauma, and reduce the incidence of postoperative complications.     

Darkening of third molar roots on panoramic radiographs: is it really predominantly thinning of the lingual cortex?

This study investigated the exact intra-alveolar aetiology of a panoramic high-risk sign, darkening of the third molar roots. 83 mandibular third molar surgical removals demonstrating dark bands on the third molar roots in preoperative radiographs were included in this prospective study. Exposure of the inferior alveolar nerve (IAN), the root morphology of the third molar (e.g. groove or hook) and the integrity of the mandibular canal or lingual cortical wall were observed. Differences between single (increased radiolucency alone) and multiple darkening cases (increased radiolucency with accompanying ‘high risk’ signs) and between IAN exposure and groove formation were analysed. In 38 cases (45.8%), the IAN was visible during the operation. Groove was present in 37.4% of cases. 26.5% of the cases showed lingual cortical thinning, while specious root conformation explained the formation of darkening on the radiographic images of an additional 9.6% of the cases. IAN exposure (P < 0.001) and groove formation (P < 0.001) were significantly more frequent in multiple darkening cases than in single darkening cases. According to these findings, darkening of the third molar roots is more often the result of fenestration of the inferior alveolar canal wall or groove formation of the root than lingual cortical thinning.     

微创牵引辅助拔除近中阻生下颌第三磨牙1例报告

近中阻生下颌第三磨牙拔除是口腔外科常见手术。中、低位近中阻生的第三磨牙牙根与牙根位置常与下牙槽神经(inferior alveolar nerve, IAN)关系密切,由于近中邻牙的阻力,拔除时创伤较大,易造成第二磨牙损伤及神经损伤。本文报告1例牙根压迫下牙槽神经的近中阻生下颌第三磨牙患者,采用微创正畸牵引法,直立患牙,牵引完成后顺利拔除。     

Incidence of neurosensory deficits and recovery after lower third molar surgery: a prospective clinical study of 4338 cases

A prospective study of all lower third molar surgery performed in the outpatient extraction clinic of a teaching dental hospital was conducted from January 1998 through October 2005 to determine the incidence of subsequent neurosensory deficit due to inferior alveolar nerve (IAN) and lingual nerve (LN) injury, to examine possible contributing risk factors and to describe the pattern of recovery. 3595 patients were included (61% female, 39% male; age range, 14–82 years). Of the 4338 lower third molar extractions performed by various grades of operators, 0.35% developed IAN deficit and 0.69% developed LN deficit. Distoangular impaction was found to increase the risk of LN deficit significantly (p < 0.001). Depth of impaction was related to the risk of IAN deficit (p < 0.001). Undergraduates caused more LN deficits (p < 0.001). Sex, age, raising of a lingual flap, protection of LN with a retractor, removal of distolingual cortex, tooth sectioning and difficulty in tooth elevation were not significantly related to IAN or LN injury. Postoperative recovery from IAN and LN deficits was noted most significantly at 3 and 6 months, respectively. By the end of the follow-up period, 67% of IAN deficits and 72% of LN deficits had recovered completely.     

Low dose propranolol decreases orthodontic movement

ObjectiveLow dose propranolol has previously been demonstrated to suppress bone remodelling. Therefore, its effect on orthodontic movement was tested.DesignRats were assigned as follows (n = 5): animals with no orthodontic appliance (G1); the remaining groups were fitted with a Ni-Ti closed-coil spring ligated to the upper left first molar and connected to the incisors using metal and resin and received vehicle only (G2), 0.1 mg/kg (G3) or 20 mg/kg (G4) of propranolol orally. Cone Beam Computed Tomography was performed using high resolution for image capture. The distance between the first and second upper molars, both with and without the orthodontic appliance, was measured in millimetres. Gingival tissue was harvested and assessed for IL-1β and IL-6 using ELISA and for ICAM-1 and RANKL by Western blotting.ResultsThe orthodontic appliance induced a significant tooth movement in G2 when compared to the animals without an orthodontic appliance (G1) (p < 0.05). The animals from G3 showed a significantly reduction in tooth movement (p < 0.05) when compared with rats from G2. Animals treated with 20 mg/kg of propranolol (G4) showed tooth movement similar to that of G2. The reduced tooth movement observed in the animals treated with 0.1 mg/kg of propranolol (G3) occurred due to decreased amounts of IL-1β and IL-6, in addition to lower ICAM-1 and RANKL expression.ConclusionsLow dose propranolol inhibits bone remodelling and orthodontic movement.     

Association between impacted third molars and position of the mandibular canal: a morphological analysis using cone-beam computed tomography

Our aim was to assess the association between the angle of impaction of the third molar and the position of the mandibular canal on cone-beam computed tomography (CT). We designed a retrospective study of 100 cone-beam CT images of 173 mandibular third molars that were obtained between January 2012 and December 2015, and recorded the angle of impaction of the third molar, the position of the mandibular canal in relation to the impacted tooth, and the potential contact between the roots of the tooth and the mandibular canal. Most third molars tilted mesially (n = 33), while the mandibular canal was positioned below the roots of the third molar in most cases (n = 73). Contact between the two was most likely when the mandibular canal was between (RR = 1.49; 95% CI 1.27 to 1.75, p < 0.001), or to the lingual side (RR = 1.49; 95% CI 1.27 to 1.75, p < 0.001) of the roots of the tooth. These outcomes indicate a greater likelihood of contact between the canal and the roots when the canal is between, and to the lingual side, of the roots. We found no association between the angle of impaction and the position of the canal. These findings illustrate the importance of surgical planning using complementary imaging tests such as cone-beam CT.     

Measurement of root surface area of permanent teeth in a Chinese population

ObjectivesThe aim of this study was to investigate the relation between the remaining area of periodontal attachment and the attachment levels for each type of permanent teeth in a Chinese population by using micro-computed tomography (micro-CT) scans.DesignA total of 440 extracted permanent teeth (including each tooth type except for the third molars) were collected from a Chinese population and scanned using a micro-CT. The CT data were input into Mimics 15.01 to generate 3D tooth models. To simulate various attachment levels, the roots were virtually cut at 0, 2, 4, 6, 8, and 10 mm from the cemonto-enamel junction (CEJ). The net and percent remaining root surface area (RSA) were measured and calculated, and the data corresponding to attachment level were fitted to a linear function.ResultsA Linear function can perfectly fit in relating the simulated attachment level to the net and percent remaining RSA (R² > 0.99, and p < 0.001 for each tooth type). For net remaining RSA, the slope of the linear function was steepest for maxillary first molars (b₁ = −39.32) and least steep for mandibular central incisor (b₁ = −13.08); whereas for the percentage of remaining RSA, the slopes (b₁) were relatively within a narrow range, from −7.40 (maxillary canine) to −9.64 (maxillary first molars).ConclusionMicro-CT offers simple and precise technique for quantitative analysis of the RSA. The total amount and vertical distribution of the RSA varied by tooth type. Linear formulas can perfectly describe the relation between the attachment level and the net and percent remaining RSA.     

正畸牵引法辅助拔除接触下牙槽神经管的埋伏阻生牙1例报告

阻生下颌第三磨牙拔除是口腔颌面外科的一种常见手术.由于低位阻生的下颌第三磨牙牙根位置常与下牙槽神经(inferior alveolar nerve,IAN)关系密切,神经损伤是该手术的严重并发症之一.目前,国际上主要有3种避免IAN损伤的方法:截冠法、部分牙冠切除术和正畸牵引法.本文报告1例下颌第三磨牙近中斜位低位阻生的患者,采用改良正畸牵引法,分两步将牙根牵离神经管,牵引完成后顺利拔除患牙.     

Stability of miniscrews with different continuous orthodontic forces as measured by cone-beam computed tomography

PurposeMiniscrew stability is a key for successful orthodontic anchorage reinforcement. Light force as 50 g has been proposed to efficiently retract canine; however, for miniscrew stability, its efficiency is still questionable. This study aimed to evaluate and compare miniscrew displacements loaded with 50 and 150 g to retract upper canines.Subjects and methodsTwenty four miniscrews (1.4 mm diameter and 7 mm length) were placed in twelve orthodontic patients (female, 22.55 ± 4.8 years old) who required miniscrews for maximum anchorage. Cone-beam computed tomography (CBCT) was taken to assess the miniscrew displacement in three dimensions. The X, Y, Z coordination points at the miniscrew head and tail with anterior nasal spine as a reference point were recorded and analyzed the displacements during 3 months using one-sample t-test and pair t-test.ResultsMiniscrews were significantly displaced after loading 50 and 150 g at 2 and 3 months compared to baseline (P < 0.001). At 2 months, the displacement of the miniscrews at head and tail had no statistical significance between 50 and 150 g (P > 0.05). However, at 3 months, there were statistically significant displacements between 50 and 150 g. This displacement was found to be greater in 150 g and at head more than at tail (P < 0.05).ConclusionThis study concluded that miniscrews could be significantly displaced with 50 and 150 g during 3 months wherein the heavier loading force essentially caused more miniscrew mobility. Clinically, it is suggested to use proper magnitude of force to miniscrews with care in order to overcome orthodontic anchorage failure.     

Measurement of root surface area of permanent teeth with root variations in a Chinese population—A micro-CT analysis

ObjectivesThis study investigated the influence of root variations on the root surface area (RSA) by using micro-CT scans.DesignA total of 228 extracted permanent teeth (2-rooted and single-rooted maxillary first premolars, mandibular first premolars with non-Tomes’ and Tomes’ roots, 2-rooted and 3-rooted mandibular first molars, and 2-rooted and C-shaped mandibular second molars) were collected in a Chinese population and scanned using a micro-CT. In Mimics 15.01, 3D tooth models were generated, and the net and percent remaining RSA at various simulated attachment levels were measured. The data corresponding to attachment level were fitted to a linear function.ResultsThe mean total RSA for different root forms decreased in the following order: 3-rooted > 2-rooted > C-shaped > single-rooted. However, the differences were statistically significant (p < 0.01) only for 2-rooted vs. single-rooted maxillary first premolars, and 2-rooted vs. C-shaped mandibular second molars. Linear functions can perfectly fit in relating the attachment level to the net and percent remaining RSA.ConclusionMicro-CT combined with Mimics software offers simple and precise technique for quantitative analysis of the RSA. Root variations may affect the total amount and vertical distribution of the net RSA. However, the degree of influence varies with the tooth type.     

Sexual dimorphism,pattern of third molar and mandibular second premolar agenesis in Indian paediatric orthodontic patients

Objective

To determine and compare the prevalence and pattern of agenesis of third molar and mandibular second premolar in paediatric orthodontic patients of age group 9–15 for sexual dimorphism.

Pre-operative assessment of relationship between inferior dental nerve canal and mandibular impacted third molar in Saudi population

ObjectiveTo study the correlation between the position of the inferior dental (ID) nerve canal and the angulation of impacted mandibular third molars using dental cone beam computed tomography (CBCT).Materials and methodsThe study considered 100 impactions in 85 patients (60 males, 25 females), for whom an initial panoramic radiographic assessment had revealed that the ID canal and the lower 3rd molar were in close proximity. A CBCT scan of each patient was carried out to assess how the ID nerve canal position influenced the class and position of impaction, angulation of impaction, and bone contact.ResultsClass I position B impactions were found in the majority of cases, where the position of the ID canal was approximate to the lingual plate and inferior to the 3rd molar (85.7%). The results were statistically significant (p = 0.001). 96% of the ID canals showed bone contact. Of these, 77.1% of ID canals exhibited lingual bone contact, inferior to impaction. The results were statistically significant (p = 0.001). Horizontally angulated impactions were most common in the mandible, and significantly associated with lingual and inferior positioning of the ID canal (76.2%).ConclusionsOur sample population most commonly exhibited horizontally angulated class I position B impactions of the mandible. The position of the ID canal significantly influenced the type of impaction and bone contact.     

Nickel and chromium levels in the saliva of a Saudi sample treated with fixed orthodontic appliances

AimThe aim of this study was to measure the amount of nickel (Ni) and chromium (Cr) released into the saliva of Saudi patients treated with fixed orthodontic appliances.Materials and methodsNinety salivary samples were collected in a cross-sectional manner. Forty samples were collected from patients (17 males, 23 females) with fixed orthodontic appliances after different periods of orthodontic treatment ranging from the first month and up to 32 months into treatment. The fixed orthodontic appliance consisted of 4 bands, 20 stainless steel brackets, and upper and lower nickel titanium or stainless-steel arch wires. The other 50 samples were collected from people without appliances (24 males, 26 females). Samples were analyzed using Inductive Coupled Plasma/Mass Spectrometry and Inductively Coupled Plasma Optical Emission Spectroscopy to measure Ni and Cr levels, respectively. Student’s t-test was used to compare Ni and Cr levels in the treated and untreated control groups.ResultsThe mean Ni level was 4.197 μg/L in the experimental group and 2.3 μg/L in the control group (p < 0.05). The mean Cr level was 2.9 μg/L in the experimental group and 3.3 μg/L in the control group (p < 0.05).ConclusionFixed orthodontic appliances resulted in a non-toxic increase in salivary levels of Ni, but no change in Cr levels. Duration of orthodontic treatment did not affect Ni and Cr levels in the saliva.     

Age of patient at the extraction of the third molar

The purpose of this study was to assess the age of patients at the time of extraction of third molars. Our data included all routine and surgical extractions of third molars (n = 8199 teeth) performed by general and specialist dentists of the public oral health services of the city of Helsinki over the period 2013–2014. Measurements included patient’s age, gender, the identified third molar, the type of anaesthesia, the method of extraction, and the diagnosis at extraction. Patients’ ages ranged from 10 to 99 years. We found significant differences between younger and older age groups: third molar extractions occurred more often for women than for men below the age of 30 years (P < 0.001) and vice versa for patients older than 30. Extractions were more prevalent for the upper jaw (P < 0.001), and surgical extractions were more common than routine extractions (P < 0.001) below the age of 40 years, but the corresponding prevalences reversed after the age of 40 years. Diagnoses at extraction differed between younger and older patients. We conclude that the treatment pattern of third molars at public health services varies greatly over a lifetime, and that a greater variety exists than had been reported previously from oral and maxillofacial units.     

Efficacy of nimesulide versus meloxicam in the control of pain,swelling and trismus following extraction of impacted lower third molar

This study compared the efficacy of nimesulide and meloxicam in the control of pain, swelling and trismus, following the extraction of impacted inferior third molars. Twenty patients with two impacted inferior third molars, in similar positions, were selected. The patients were designated randomly to the meloxicam group (MEL: 7.5 mg twice a day for 5 days) or the nimesulide group (NIM: 100 mg for 5 days). Following the extractions, swelling was more pronounced in the MEL group than in the NIM group (P ≤ 0.001). There were no significant differences in pain intensity between the treatment groups (P > 0.05). At the 72-h evaluation, reduction was significantly larger in mouth opening in the MEL group compared with the NIM group (P < 0.05). In conclusion, pain control was similar in both treatment groups. NIM was more effective than MEL in the control of swelling and trismus following the extraction of impacted lower third molars.     

Comparative effects of tungsten,diamond burs and laser for residual adhesive removal after orthodontic debonding on flexural strength,surface roughness and phase transformation of high-translucent zirconia: An in vitro study

ObjectivesInformation regarding the effects of orthodontic bracket debonding on zirconia restorations, and the preferred method for residual adhesive removal from the zirconia restoration surface is lacking. Thus, this study aimed to assess the effects of different methods of residual adhesive removal after orthodontic bracket debonding on flexural strength, surface roughness, and phase transformation of high-translucent (HT) zirconia.Materials and methodsThis in vitro study evaluated 72 bar-shaped HT zirconia specimens; 18 specimens were assigned to the control group. Metal brackets were bonded to the remaining specimens by resin cement. After bracket debonding, the residual adhesive on the surface of specimens was removed by three methods (n = 18): a 30-flute tungsten-carbide (TC) bur at low speed, an ultrafine diamond bur at high speed, and Er:YAG laser irradiation. The surface roughness (Ra and Rz) was measured. X-ray diffraction (XRD) analysis was carried out, and the flexural strength was measured as well. Data were statistically analyzed (α = 0.05).ResultsBefore polishing, all methods increased the Ra and Rz values (P < 0.05) except for the diamond bur yielding a Rz value comparable to that of the control group. The Ra values of the test groups were comparable after polishing, and still higher than that of the control group (P < 0.05). The flexural strength of all three test groups was comparable (P > 0.05), and significantly lower than that of the control group (P < 0.001). The monoclinic phase was not observed in any group.ConclusionsOrthodontic bracket debonding adversely affects the surface roughness and flexural strength of zirconia despite polishing.     

Response of mandibular condyles of juvenile and adult rats to abnormal occlusion and subsequent exemption

ObjectiveThe adaptation capacities of the mandibular condyle in response to mechanical stimuli might be different between juveniles and adults, but has not been compared. This study aimed to investigate whether abnormal molar occlusion and subsequent molar extraction could lead to different remodeling responses in the mandibular condyles of juvenile and adult rats.MethodsAbnormal molar occlusion (AMO) was established in the 5- and 16-wk old rats by moving their maxillary left and mandibular right third molars distally. AMO was removed in the molar extraction group at 4 weeks but remained in the AMO group. All rats were sacrificed at 8 weeks. Micro-computed tomography, histomorphology, immunohistochemistry and real-time PCR were adopted to evaluate the remodeling of condylar subchondral bone.ResultsCondylar subchondral bone loss and increased osteoclastic activities were observed in both juvenile and adult AMO groups, while increased osteoblastic activities were only seen in the juvenile AMO group. Decreased bone mineral density, bone volume fraction and trabecular thickness, but increased trabecular separation, number and surface of osteoclasts and mRNA levels of TRAP, cathepsin-K, RANKL in the juvenile AMO group were all reversed after molar extraction (all P < 0.05). However, these parameters showed no difference between adult AMO and extraction groups (all P > 0.05).ConclusionsAbnormal molar occlusion led to degenerative remodeling in the mandibular condyles of both juvenile and adult rats, while exemption of abnormal occlusion caused significant rescue of the degenerative changes only in the juvenile rats.     

Evaluation of the efficacy of celecoxib and ibuprofen on postoperative pain,swelling, and mouth opening after surgical removal of impacted third molars: a randomized,controlled clinical trial

The objective of this study was to compare the efficacy of celecoxib and ibuprofen in reducing postoperative sequelae following the surgical removal of impacted mandibular third molars. Ninety-eight subjects who needed surgical extraction of an impacted mandibular third molar were selected for the study. All subjects were randomly allocated to receive one of the following treatments twice a day for 5 days after surgery: placebo (n = 32), ibuprofen (n = 33), or celecoxib (n = 33). The primary outcome chosen was postoperative pain, which was evaluated using the visual analogue scale (VAS) score recorded by each patient. The secondary outcomes chosen were changes in postoperative swelling and maximum mouth opening values compared to preoperative ones. Compared to placebo, treatment with celecoxib and ibuprofen resulted in improvements in the primary outcome. Furthermore, when compared to the other groups, patients in the celecoxib group showed a significant reduction in postoperative pain scores at 6 h (P < 0.001), 12 h (P = 0.011), and 24 h (P = 0.041) after surgery. Regarding swelling and maximum mouth opening values, there were no significant differences between the groups at each follow-up session. This study demonstrated that treatment with celecoxib decreased the incidence and severity of postoperative pain following third molar surgery compared to ibuprofen and placebo.     

Coronectomy of mandibular third molars: a clinical and radiological study of 231 cases with a mean follow-up period of 5.7 years

Coronectomy is a widely accepted treatment for mandibular third molars that are in close relationship to the mandibular canal. However, long-term studies on morbidity following this procedure have not been presented. The aim of this study was to examine the long-term morbidity after coronectomy, with sensory disturbances of the inferior alveolar nerve (IAN) and root migration as the primary outcome variables. A total of 231 mandibular third molar coronectomies were performed in 191 patients with a mean follow-up period of 5.7 years (range 1–12 years). The prevalence of IAN injury was 1.3%, and 3.5% of the retained roots were removed. None of the reoperations to remove the retained roots caused IAN impairment. Infections occurred in 11.7% of the cases and all were treated with antibiotics. Overall, 97% of the retained roots showed signs of migration and 65% showed signs of rotation. Therefore, coronectomy of the mandibular third molars with an intimate relationship to the mandibular canal seems to be a safe treatment modality with a good long-term prognosis.