in
Impacted Third Molar
Extraction
J.-M. KORBENDAU D.D.S., M.S. | X. KORBENDAU D.D.S. |
Associate Professor Faculty of Dentistry University Paris 5, France |
Private practice Oral Surgery France |
Contributors
Maxillofacial Surgeon
Paris, France
Qualified Orthodontist
Assistant Professor
Faculty of Dentistry
University Paris 5, France
Translation
Periodontist
Assistant Professor
University of Reims, France
Paris, Chicago, Berlin,Tokyo, Copenhagen, London, Milan, Barcelona,
Istanbul, São Paulo, New Delhi, Moscow, Prague, and Warsaw
Jean-Marie KORBENDAU D.D.S., M.S. | |
Associate Professor Faculty of Dentistry University Paris 5, France | |
Xavier KORBENDAU D.D.S. | |
Private practice Oral Surgery France | |
Jean-François ANDREANI M.D. | |
Maxillofacial Surgeon Paris, France | |
Christophe DUNGLAS D.D.S. | |
Qualified Orthodontist Assistant Professor Faculty of Dentistry University Paris 5, France |
First published in French in 2002 by Quintessence International, Paris
L’extraction de la dent de sagesse
© Quintessence International, 2003
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The computerized radiographic images
and the CT examination presented in this textbook
were provided by Drs Pascal Guinet, Alain Lacan,
Philippe Katz and Danielle Pajoni.
We gratefully acknowledge their contribution
and the quality of their documentation.
Cover | |
Table of Contents | |
1 | Third molar extraction: Why and when? |
Embryology and eruption of the third molars Developmental prognosis and eruption axis of the third molar Indications requiring the use of orthodontic techniques Third molar and DMD Therapeutic occlusion and third molars Relapse of anterior tooth crowding and its effect on the third molar | |
2 | Developmental anomalies |
Terminology The follicular cyst Pericoronitis Complications Spread of infection | |
The mandibular third molar | |
3 | Selection of radiographic examinations |
Dental panoramic radiograph Periapical radiograph Computerized tomography | |
4 | Classification: Clinical aspects |
The shape of the tooth The anatomic situation of the tooth | |
5 | Nerve block anesthesia: Technique and failure assessment |
Anesthesia of the inferior alveolar nerve Additional anesthesia Anesthetic procedures for the upper oral regions | |
6 | Surgical protocol: Basic principles |
Instrumentation Incision lines Elevation of a full-thickness flap Bone removal Sectioning the retained tooth Alveolar socket evaluation Suture | |
7 | Germectomy |
Indications for germectomy At what age should treatment start? Surgical protocol | |
8 | The mesially inclined third molar |
Radiographic interpretation Degree of surgical difficulty | |
9 | The horizontal third molar |
Radiographic interpretation Surgical protocol Degree of surgical difficulty | |
10 | The vertical third molar |
Radiographic interpretation Degree of surgical difficulty | |
11 | The distally inclined third molar |
Radiographic interpretation Degree of surgical difficulty | |
The maxillary third molar | |
12 | The maxillary third molar: Examination and extraction |
Anatomic specificities Degree of surgical difficulty Anesthesia in the maxilla Surgical protocol | |
13 | Patient management |
First appointment Surgical phase Postsurgical phase Management of the healing process | |
References | |
Third molar extraction: Why and when? |
Extraction of third molars is one of the most common procedures in dentistry. Studies aimed at obtaining a better understanding of the reasons leading to the extraction of one or several third molars have been reported in the English and Scandinavian literature.
The National Institute of Health (NIH) has published the conclusions of the consensus development conference held in 1979 and, while waiting for an overall consensus on the indications for extractions, made the following recommendations:
• Evidence of hypertrophy, cyst or tumor development of the dental follicle
• Repeated episodes of pericoronitis
• Irreversible carious lesions
• Distal periodontal defect on the second molar
• Distal carious lesion of the second molar in relation to the third molar
Despite the accumulated experience in dealing with diagnosis and treatment of developmental anomalies concerning the third molars, extraction still remains controversial when patients are asymptomatic. Indeed, the proportion of prophylactic extractions is increasing and represents from 18% to 40% of the overall third molar extractions carried out in developed countries (Liedholm et al; Lysel and Rohlin). The majority of third molar extractions take place between the ages of 20 and 29 years (Liedholm et al). The main reasons for deciding on this course of action are:
• To reduce the risk of sequelae, surgical morbidity, and complications involving the neighboring teeth in the elderly patients
• To improve oral health in younger patients who have completed their growth phase
The quality of the outcome of this procedure is determined by a series of factors:
• The relevance of the indication for the prophylactic extraction of one or several third molars
• The stage at which this decision is made, the type of surgical procedure selected, and the skill of the surgeon and the surgical team
However, as yet it has not been possible to establish universal guidelines concerning the relevant indications for prophylactic extractions because of the widely varying criteria used in different countries by different practitioners and different scientific communities (Worrall et al).
Furthermore, even from a review of the current literature, it is not possible to establish a significant risk-benefit ratio. In addition, the decision to proceed with an extraction is often made during a single consultation using only one radiographic examination in young patients who have completed their growth phase.
In order to establish a diagnosis it is essential to fully understand and be able to estimate the stage of eruption of the third molar. The latter is related to the evaluation of the prognosis in terms of impaction, partial retention or enclavement, tooth and periodontal lesions on the second and/or third molar, and the risk of anterior tooth crowding, which should always be avoided.
The English clinical practice consensus committees have suggested three factors that should be considered in the decision-making process for extraction of third molars (Liedholm et al):
• The age of the patient
• The angle formed between the great axis of the tooth and the occlusal plane, as well as the uprighting dynamics of this axis•
• The eruptive position
Some additional factors should also be taken into account:
• Oral hygiene
• Carious and periodontal indexes
The angulation of the axis of the third molar can be classified as follows, depending on the degree of distortion (Liedholm et al; Winter; see chapter 4):
• Mesially inclined
• Horizontal
• Vertical
• Distally inclined
Additionally, the eruptive stage can be specified as follows (Liedholm et al; see chapter 2):
• Totally erupted
• Partially covered with soft tissue
• Totally covered with soft tissue
• Totally covered with bone
The NIH has established that (NIH; Worrall et al):
• The surgical procedure and postoperative effects are more favorable in the case of younger patients.
• However, in the young adolescent, the indication for enucleation of the third molar buds before root formation becomes evident radiographically is not recommended because of the surgical risk that would be incurred.
• Distally inclined molars are more likely to develop complications during eruption than are molars with other angulations.
• Molars that are partially or totally covered with soft tissue are more prone to complications than are totally impacted molars.
In the context of orthodontic treatment, the extraction indication ratios for so-called prophylactic extractions are continually increasing, which naturally leads us to question this indication.
In orthodontics, an indication for third molar extraction usually refers to the third mandibular molar. Many practitioners support the current view of the relationship between the occurrence of anterior mandibular crowding and the eruption of the third molars at the end of adolescence and will therefore often recommend extraction. Once the decision has been made to extract the mandibular molar, this invariably implies the removal of the maxillary molars in order to create a Class I occlusion.
Embryology and eruption of the third molars
Like all human molars, the third molar is an accessional tooth, as distinct from the other teeth, which are known as replacement or successional teeth. The third molar originates from the primitive dental lamina and the bud only becomes evident at around the age of 4 or 5 years. Calcification occurs between 9 and 10 years of age, with full completion of the crown taking place between the ages of 12 and 15 years. As the eruptive movement begins, the tooth establishes an upright axis. The space available for its eruption depends on the growth of the posterior region of the arch. Emergence into the oral cavity occurs between 17 and 21 years of age. The tooth drifts along the distal aspect of the second molar in order to reach the level of the occlusal plane. Root formation is completed between the ages of 18 and 25 years.
The third molar encounters some difficulty in correcting its eruptive curve to the upright position because the direction of its growth often brings it under the cervical line of the second molar, thus causing it to become partially retained within the tissue.
As a general rule, the third mandibular molar usually fills the space formed by the retromolar triangle distal to the second molar.
In the maxilla, the complete absence of any bone obstruction allows the third molar to erupt in either the correct position or a labial position. The only obstacle to the smooth eruption of the third maxillary molar is the muscle-tendon-aponeurotic component (pterygoids, buccinator, or ligaments).
Developmental prognosis and eruption axis of the third molar
Most studies have shown that the eruption of the third molar is a multifactorial mechanism. None of these studies has established any significant correlation between the angulation of mandibular third molar and its impaction.
In the early stages of calcification, the mandibular third molar presents a physiologic mesial and lingual orientation. The change in angulation that leads to the vertical positioning of the tooth should occur between the ages of 14 and 16 years (Richardson, 1978). Establishing this vertical axis may occur during differential growth events in the crown surface and the mesial root in relation to the distal aspect.
According to Richardson, if growth occurs predominantly in the mesial area of the crown, vertical positioning of the tooth will result; but if growth of the distal root predominates, then the tooth bud will develop in a horizontal position (Fig 1-1).
In summary, it appears that the developmental prognosis for the third molar can be established from the age of 16 years.
Björk correlates the lack of appropriate space for the eruption of the third molar with three factors:
• The direction of vertical condylar growth
• Reduced mandibular length
• Backward orientation of tooth eruption
Silling notes that Class II skeletal relationships (ie, mandible positioned in an excessively posterior sagittal position in relation to the maxilla) with a short mandible and a closed mandibular angle are associated with impaction. Conversely, the percentage of impaction decreases in the case of a hyperdeveloped mandible (skeletal Class III).
Indications requiring the use of orthodontic techniques
Some techniques indicate the need for extraction before treatment is initiated.
Importance of posterior crowding
In the Tweed-Merrifield orthodontic technique, the arch is divided into three regions; the second and third molars are located in the posterior region. Crowding is measured by comparing the available space with that required to accommodate the second and third mandibular molars. The available space is the distance between the anterior border of the ramus and the distal aspect of the first molar, parallel to the occlusal plane. The required space is the sum of the respective mesiodistal diameters of the second and third molars as measured with a lateral cephalogram. The difference determines the degree of crowding and the need for extraction.
In a growing patient, starting from the age of 8 years, an average of 1.5 mm per hemiarch per year should be added to the value for the available space, taking into account that cessation of growth occurs approximately at the age of 17 years for boys and 15 years for girls (Tweed). This extra space results from the resorption of the anterior border of the mandibular ramus during growth (Figs 1-2a and 1-2b). However, according to Tweed, estimations of the increase in the available posterior space can be affected by several factors:
• The degree of mesio-occlusal drift of the first mandibular molar
• The degree of resorption of the anterior border of the ramus
• The cessation of mesial molar drift
• Sex
• Age
Applying another orthodontic philosophy, Ricketts (1970) measured posterior crowding on a lateral cephalogram in the following way:
• To assess crowding in the maxilla, the distance between the distal aspect of the first molar and the vertical pterygoid plane, tangential to the posterior edge of the pterygomaxillary notch, is measured. This distance must be equal to the age of the patient + 3 mm ± 2 mm.
• In the mandible, the probability of eruption must be assessed using mean measurements of the Xi distance (ie, the cephalometric point constructed geometrically at the center of the ramus) to the distal edge of the second molar, parallel to the occlusal plane. Turley and Chaconas constructed a curve in order to assess the likelihood of impaction in relation to the available space. The following values are approximations of these mean measurements:
1. 21 mm for impacted teeth
2. 25 mm for marginal third molars
3. 30 mm for third molars in functional occlusion
The need for maximum anchorage preparation
In the Tweed-Merrifield technique, correcting a dental Class II situation in patients who are still growing requires maximum anchorage preparation, ie, therapeutic distal tipping of the mandibular molars before initiation of interarch mechanical treatment, in order to reduce any possible side effects. This leads to the possible risk of impaction of the third molar. The presence of the third molar may indeed limit the possibility of therapeutic distal tipping of the second molar. It thus leads to a dentomaxillary disharmony (DMD) with a secondary or induced posterior position. According to these authors, orthodontic anchorage preparations should only be considered if there is no posterior crowding to jeopardize the success of distal tipping of the first and second molars. The same principle applies to orthodontic distalization of the first maxillary molar.
Third molar and DMD
Spontaneous DMD is the consequence of two biologic mechanisms:
• The growth process, which leads to a decrease in the volume of the face and is species specific and genetically determined
• The genetically determined distance between the teeth and osseous bases
The need for premolar extraction will depend on the size of an anteriorly expressed DMD, anterior tooth crowding, and excessive buccal inclination of the mandibular incisor, regardless of whether there is also a hyperdivergent skeletal pattern, ie, any divergence between the base of the cranium or the Frankfort plane and the inferior edge of the mandibular body as measured radiographically. The extra space made by moving the posterior segment distally will accommodate the third molar. According to Schulhof, each additional millimeter of available space will increase the chance of the mandibular third molar erupting normally by 10%.
Studies undertaken by Ricketts (1979) and Richardson (1975) have shown that a greater percentage of impactions occurred in cases where no extraction was carried out versus cases where premolar extraction had been undertaken and in cases where the first premolars had been extracted compared to those where the second premolars had been extracted.
However, extracting a premolar does not ensure that the third molar will erupt. Thus, there is no evidence to suggest that the extraction of premolars will resolve an anteriorly expressed DMD.
Finally, the decision to extract one or several third molars may depend on whether there are any eruption anomalies of the second molars (Figs 1-3a and 1-3b).
Therapeutic occlusion and third molars
Achieving Class II therapeutic occlusion using maxillary premolar extractions in the presence of posterior mandibular crowding does not automatically require the removal of all third molars. Extraction of only the mandibular third molars may be sufficient in most cases.
Relapse of anterior tooth crowding and its effect on the third molar
Orthodontic treatment should be planned to provide the optimum developmental outcome for the third molars.
Treating DMD, when present, and establishing a functional occlusion does not prevent the occurrence or relapse of tooth malposition, which can quite frequently occur in the anterior region. This leads to the conclusion that other factors may be involved in this partial relapse.
According to Van der Linden, late mandibular growth may be the only factor responsible for anterior crowding and would occur even in the absence of the third molars.
According to Charron, the most plausible explanation for this crowding is the late growth of the mandible at around 17 or 18 years of age. Concomitant changes, mostly in the occlusal relationship, take place at a later stage and are also involved in crowding, probably due to mesial drift and occlusal interference.