The Journal
11
Boese introduced the concept of lower incisor reproximation to provide broader contact points and increase the available arch space in the mandibular anterior region . In a 4 to 9 year follow-up study of 40 patients , treated with four premolar extractions followed by interproximal reduction and supracrestal fiberotomy , he showed good stability with a post retention irregularity index of only 0.62 mm . The mean interproximal reduction was 1 . 7 mm immediately post treatment and a further 0.8 mm over the retention period . This , however , was a retrospective study that involved continued intervention during the retention period , even in the presence of minor relapse . For this reason , we are unable to compare the results of this study with results from other retention studies .
Role of developing third molars
The role of third molars in lower incisor crowding has been debated for more than a century . The literature is almost equally divided with arguments for both sides . Various studies reported that by the third molars creating space
12-16 to erupt cause anterior teeth to crowd .
17
Woodside postulated that in the absence of third molars , the dentition could settle distally in response to forces generated by growth changes or soft tissue pressures . This implies a passive role of the third molars in the development of late crowding by hindering that adjustment . A study in 1995 shows a statistically significant but not a clinically significant role of third molars in post retention crowding . 18 Broadbent19 was an early advocate of the reproximation to provide broader contact points and increase the available arch space in the mandibular anterior region . In a 4 to 9 year follow-up study of 40 patients , treated with four premolar extractions followed by interproximal reduction and supracrestal fiberotomy , he showed good stability with a post retention irregularity index of only 0.62 mm . The mean interproximal reduction was 1.7 mm
immediately post treatment and a further 0.8 mm over the retention period . This , however , was a retrospective study that involved continued intervention during the retention period , even in the presence of minor relapse . For this reason , we are unable to compare the results of this study with results from other retention studies .
Alteration of arch form
With some notable exceptions , it is generally agreed that arch form and width should be
20,21
maintained during orthodontic treatment . In certain cases , where arch development has occurred under adverse environmental conditions , arch expansion as a treatment goal
22
may be tolerated . Mills found stability after proclination in cases with skeletal deep bites and retroclined incisors in conjunction with a
22 digit or lip entrapment habit .
23
Artun stated that proclination may be successful provided that the lower incisors are initially retroclined , a reason for the retroclination determined , and the cause eliminated during treatment . There is evidence to show that intercanine and intermolar widths decrease during the post retention period ,
24-27
especially if expanded during treatment . For this reason , the maintenance of arch form rather than arch development is generally recommended . Expansion is thought to be better tolerated in Class II Division 2 cases that show a significantly greater ability to maintain intercanine expansion than Class I and Class II
28,29
Division 1 cases . This statement , however , was based on a sample of six patients and was not accepted by Little et al . 30who maintained that intercanine and intermolar width will relapse if expanded in Class II Division 2 cases a s m u c h a s i n o t h e r A n g l e classifications . Another exception to the maintenance of arch width may be found in cases of mandibular expansion concurrent with Rapid Palatal Expansion .
20 Vol . 13 No . 3 Sep-Dec 2017