Abstract
The purpose of this study was to elucidate the long-term skeletal and dental stability after combined orthodontic and orthognathic surgical treatment of mandibular prognathism with the intraoral vertical ramus osteotomy (IVRO) as the surgical technique followed by 6 weeks of intermaxillary fixation (IMF). Thirty-six patients were included in the study. Mean age at surgery was 21.6 years. Lateral cephalograms and study casts obtained before the start of treatment (T0), and 8 weeks (T1), 1 year (T2), and 12.5 years (T3) after the operation were evaluated. Mean mandibular setback measured at point B was 8.3 mm. Between T1 and T2, a mean anterior relapse of 12% of the setback was observed. Between T2 and T3, the anterior relapse persisted, but decreased to 7% of the setback measured at point B. Despite dental adjustments in both jaws, a statistically significant reduction in overjet was observed during both observation periods. However, the change of the mandible in an anterior direction was small and of minor clinical importance for most of the patients. In conclusion these results indicate that combined orthodontic and orthognathic surgical treatment of mandibular prognathism with the IVRO as the surgical procedure followed by 6 weeks of IMF provides predictable and good long-term clinical results.
In skeletal Class III patients, the sagittal position of the mandible is more anterior than the maxilla when related to the anterior cranial base. This can be the result of a retrognathic maxilla, a prognathic mandible, or a combination of the two. Patients present with an Angle Class III molar relationship, and have a negative overjet or edge-to-edge occlusion. Mild skeletal Class III malocclusions (when the patient is fully grown) can be treated with extractions and fixed appliances as a camouflage treatment. More severe skeletal Class III patients will need combined orthodontic and orthognathic surgical treatment to achieve a satisfying occlusal and aesthetic result.
The first surgical correction of malocclusion was described by Hullihen in 1849. However, it was not until the beginning of the 1950s that orthognathic surgery became a true specialty. During these 100 years, several osteotomy designs to reduce mandibular prognathism were suggested. Today, the two most commonly used surgical techniques for repositioning of the mandible are the sagittal split ramus osteotomy (SSO) and the intraoral vertical ramus osteotomy (IVRO). The SSO technique was first described by Trauner and Obwegeser in 1955 (translated in 1957). In 1964, Moose reported the cases of 25 patients treated successfully by intraoral subcondylar osteotomy. This osteotomy was performed with a medial approach. The first intraoral subcondylar ramus osteotomy with a lateral approach was described by Winstanley in 1968. Subcondylar ramus osteotomies were also performed prior to 1964, but then mainly with an extraoral approach. Winstanley’s arguments for using the intraoral procedure were avoidance of an extraoral retromandibular scar and the minimized risk of damaging the mandibular branch of the facial nerve.
Considerable controversy remains concerning the most favourable treatment of mandibular prognathism. The main advantage of the IVRO over the SSO seems to be the low incidence of injury or damage to the inferior alveolar nerve. In a recently published literature review and meta-analysis comparing skeletal stability and neurosensory function between SSO and IVRO for mandibular setback, it was concluded that both techniques provide good stability, and that IVRO significantly decreases the risk of injury to the inferior alveolar nerve compared to SSO. Other advantages of the IVRO over the SSO include technical simplicity, reduced surgical time, and the ability to reposition the condyle. Several authors have also concluded that the IVRO, or the modified condylotomy, is a method of choice for relieving undesirable temporomandibular joint (TMJ) symptoms.
In both the SSO and the extraoral vertical ramus osteotomy (EVRO), fixation of the proximal and distal segments with miniplates or screws allows almost immediate postoperative function, while the IVRO requires inter-maxillary fixation (IMF) for some weeks after the operation. Thus, for patients not tolerating IMF due to nasal congestion, asthmatic conditions, or mental illnesses, as well as patients who are underweight and for whom adequate nutrition is important, the SSO or EVRO would be beneficial.
Previous studies on skeletal stability after mandibular setback surgery with the use of the IVRO technique have reported both posterior drift and anterior relapse of the mandible. Greebe and Tuinzing found a 16% posterior drift measured at pogonion 1 year after surgery. Other investigations have reported anterior relapse of between 10% and 15.3% of the surgical setback at 12–18 months after the operation. Lai et al. reported a posterior drift of 21% of the surgical movement measured at menton during the IMF period. From removal of the IMF to 1 year after surgery, there was an anterior relapse of the same amount as the initial posterior drift, resulting in a net posterior drift 1 year after surgery of 0.1%. After 2 years of follow-up of the same patients, a further anterior relapse of 10.2% was observed. These results indicate that a 1-year follow-up period is not sufficient to draw conclusions regarding skeletal stability after mandibular setback surgery.
In a meta-analysis performed by Al-Moraissi and Ellis on studies comparing skeletal stability after mandibular setback surgery by either SSO or IVRO, no statistically significant difference between the two techniques was found in the horizontal direction at 6–12 months after surgery. In the vertical direction, the results indicated that SSO showed greater stability than IVRO. However, the differences were small, and both techniques were considered to have good stability. Wisth described the changes in facial morphology and dental arches at 10 years after the surgical correction of mandibular prognathism. He concluded that the stability was fairly good for the majority of patients, but with a tendency towards sagittal relapse throughout the period.
Most previous studies on stability after mandibular setback surgery with the use of the vertical ramus osteotomy have used a follow-up period of 2 years or less. A few studies have used a follow-up period of between 3 and 5 years. It appears that only the one study by Wisth has had a follow-up period of more than 5 years. Even though previous studies have indicated that most relapse occurs within the first year after surgery, it is the long-term skeletal and dental stability that determines whether or not the treatment procedure has been successful. Very few studies have included both dental cast and cephalometric analyses, and the long-term dental and skeletal stability remains unclear.
The aim of this study was, therefore, to elucidate both the short-term and long-term skeletal and dental stability after combined orthodontic and surgical treatment of mandibular prognathism with the IVRO as the surgical technique.
Materials and methods
Patients
Eighty-four patients with genuine mandibular prognathism underwent combined orthodontic and orthognathic surgical treatment during the years 1998–2002. The treatment was planned and coordinated by a regional orthognathic-surgical team, and the surgery was performed in the department of maxillofacial surgery of a university hospital. The mandibular surgical setback procedure was exclusively the IVRO. No maxillary surgery or genioplasty was performed. The pre- and postoperative orthodontic treatment was conducted by private orthodontists according to the treatment plans.
In 2012 the patients were contacted by mail and invited to attend a 10–15-year clinical and radiological follow-up examination. Thirty-seven patients (44.0%) were willing to participate in the study, 39 patients (46.4%) did not respond, six patients (7.1%) wanted to participate but were occupied during the time the data collection took place, and two patients (2.4%) were not interested . One of the 37 patients initially included was excluded due to a history of mandibular fracture during the long post-operation period. However, the fracture was not in relation to the operation site. The final study group of 36 patients comprised 24 females and 12 males. Their mean age at surgery was 21.6 years (range 17.1–45.6 years) ( Table 1 ). For the youngest patients, a hand and wrist radiograph verified completed growth. The mean time between the operation and the long-term follow-up session was 12.5 years (range 9.7–14.5 years). Written informed consent was collected from all of the patients prior to enrolment.
| Mean | SE | 95% CI | Min. | Max. | |
|---|---|---|---|---|---|
| All n = 36 | 21.6 | 0.9 | 19.6–23.5 | 17.1 | 45.6 |
| Male n = 12 | 22.6 | 0.6 | 21.4–23.8 | 20.0 | 25.2 |
| Female n = 24 | 21.0 | 1.4 | 18.2–23.9 | 17.1 | 45.6 |
The long-term follow-up session included a clinical examination of the occlusion, examination of the masticatory musculature and TMJs, sensitivity testing of the lower lip and chin according to Leira and Gilhuus-Moe to detect any damage to the inferior alveolar nerve, clinical photographs, and impressions for study casts. The radiological examination included a panoramic radiograph and lateral cephalogram. The material investigated further in this long-term stability study included dental casts and lateral cephalograms taken before the start of pre-surgical orthodontic treatment (T0), and at 8 weeks (T1), 1 year (T2), and 12.5 years (T3) after the operation.
Inclusion criteria
The inclusion criteria encompassed patients with genuine mandibular prognathism and no skeletal asymmetry or basal open bite. Comprehensive orthodontic treatment was performed before and after surgery for all patients. The surgical procedure was mandibular setback by IVRO technique with subsequent IMF for 6 weeks. No additional maxillary surgery or genioplasty was performed. Syndromic and medically compromised patients were not included. All patients had completed growth before the start of treatment.
Surgical procedure and IMF
All operations were performed by a consultant oral and maxillofacial surgeon. The surgical procedure using the IVRO technique was performed under general anaesthesia for all patients. An intraoral incision was made at the anterior border of the ramus. The lateral aspect of the ramus was exposed sub-periosteally from the sigmoid notch to the angle, and a sub-condylar osteotomy was performed with an oscillating saw. The distal fragment was slid distally and placed medial to the proximal fragments. The distal fragment of the mandible was placed in the planned postsurgical position and was stabilized to the maxillary dental arch by rigid IMF. Running sutures were used to close the wound. The IMF was made with a steel wire between five surgical hooks attached to the archwire in each dental arch. The hooks were placed in the midline, mesial to the canines and mesial to the first molars. The IMF was removed 6 weeks after the operation.
Dental cast variables
The dental cast measurements included overjet and overbite in addition to inter-canine distance, inter-molar distance, and arch depth in both jaws. The measurements were performed with a calliper and a ruler with a 0.5-mm measurement scale. Overjet was defined as the distance in millimetres from the buccal surface of the lower right or left central incisor to the incisal edge of the corresponding maxillary incisor on the occluded models. Overbite was defined as the vertical overlap of the upper central incisor on the corresponding lower central incisor measured in millimetres. The right or left central incisor was chosen depending on the tooth producing the largest value. The inter-canine distance was defined as the linear distance between the cusp tips of the contralateral canines, or in the event of wear, the distance between the centres of the worn surfaces. The inter-molar distance was defined as the linear distance between the tips of the mesiobuccal cusps of the contralateral first molars, or in the event of wear, the distance between the centres of the worn surfaces ( Fig. 1 A). The arch depth was measured as the perpendicular distance from a tangent mesial to the first molars to the contact point between the central incisors ( Fig. 1 B). The dental casts obtained before the start of treatment (T0), and at 8 weeks (T1), 1 year (T2), and 12.5 years (T3) after the operation were analyzed.
Cephalometric variables
Tracings and the collection of data were performed using Facad 3.8.4.1 and Facad Collector 3.8.3.1 (Ilexis AB, Linköping, Sweden). The cephalograms taken at T0, T1, and T2 were analogue. These films were scanned at 300 dots per inch (DPI) resolution using an Epson Perfection V750 Pro scanner (Epson America, Inc. Long Beach, California, USA) and imported into Facad. The lateral head films taken in 2012 (T3) were obtained with a digital cephalostat coupled to Digora for Windows 2.8.109.465 software (Soredex, Tuusula, Finland). From Digora, the cephalograms were exported to Facad. All films were calibrated before tracing was performed.
To quantify the horizontal changes in the cephalometric landmarks, a reference grid was made with the x -axis being the nasion–sella line and the y -axis being a perpendicular through sella. The reference points and variables used are presented in Fig. 2 and Tables 2 and 3 . Only hard tissue measurements were included in this study.
| Anatomical structure | Abbreviation | Definition |
|---|---|---|
| Articulare | Ar | Intersection of posterior ascending ramus and inferior cranial base |
| Sella | S | Centre of sella turcica |
| Nasion | N | Most anterior point of the nasofrontal suture |
| Posterior nasal spine | PNS | The most posterior contour of the hard palate |
| Anterior nasal spine | ANS | The most anterior extremity of the intermaxillary suture |
| Spina marked | Sp′ | Intersection between the nasion–menton line and the nasal line (NL) |
| Point A | A | Deepest point on the anterior curvature of the maxillary alveolar process |
| Apex of upper central incisor | Isa | Most apically positioned point on the root of the most labially positioned upper central incisor |
| Incision superius | Is | Incisal edge of the most labially positioned upper central incisor |
| Incision inferius | Ii | Incisal edge of the most labially positioned lower central incisor |
| Apex of the lower central incisor | Iia | Most apically positioned point on the root of the most labially positioned lower central incisor |
| Point B | B | Deepest point on the anterior curvature of the mandibular alveolar process |
| Pogonion | Pog | Most anterior point on the chin |
| Menton | Me | The lowermost point on the symphysis of the mandible |
| Gonion | Go | The outer point of the angle between the ramus and the corpus of the mandible |
| Variables | Description |
|---|---|
| Sagittal relationships | |
| SNA | Angular description of the maxilla in relation to the anterior cranial base |
| SNB | Angular description of the mandible in relation to the anterior cranial base |
| ANB | Angular measurement of the anteroposterior relationship between the mandible and the maxilla |
| SNPog | Angular description of the chin in relation to the anterior cranial base |
| Pog–NB | Linear measurement of chin protrusion; the distance (mm) between pogonion and the nasion–point B (NB) line |
| hB | The perpendicular distance (mm) from point B to the y -axis |
| hPog | The perpendicular distance (mm) from pogonion to the y -axis |
| Vertical relationships | |
| Gonial angle | Angle between the ramus and the corpus of the mandible |
| ML/NSL | Angular measurement of the lower border of the mandible in relation to the anterior cranial base |
| ML/NL | Angular measurement of the vertical relation between the maxilla and the mandible |
| TFH | Total facial height; distance (mm) from nasion to menton |
| LFH | Lower facial height; distance (mm) from Sp′ to menton |
| Incisor position | |
| Inter-incisal | Angle between the long axis of the most labially upper and lower central incisor |
| Ils/NA | Angle between the long axis of the most labially upper central incisor to the nasion–point A (NA) line |
| Is–NA | Distance (mm) from the incisal edge of the most labially upper central incisor to the NA line |
| Ili/NB | Angle between the long axis of the most labially lower central incisor to the NB line |
| Ii–NB | Distance (mm) from the incisal edge of the most labially lower central incisor to the NB line |
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