All PhD Theses

T.S. Leenstra

Cleft palate repair and dento-alveolar development. An experimental and clinical study.

02-06-1997

A scientific essay in Medical Sciences

DOCTORAL THESIS defended in public on 2nd of June 1997

SUMMARY

Chapter 1 elucidates the background of the study and gives a review of clinical aspects and research in the field of orofacial clefts and palatal repair. Scar tissue formation and its attachment to palatal bone after palatal repair, is considered to be one of the major factors of maxillary dento-alveolar growth disturbances. The aim of the present thesis was to evaluate the maxillary dento-alveolar development after palatal surgery when denuded areas are avoided either by covering the denuded areas with biocompatible and biodegradable membranes or by leaving the periosteum onto the bone.

Chapter 2 describes a study on the in vivo behaviour of 5 biodegradable films. This study was performed in order to obtain a suitable material for separation of mucoperiosteum and bone after palatal repair according to von Langenbeck. Non-porous films of poly-(L-lactic) acid (= PLLA), high molecular weight poly-(L-lactic) acid (= HMW-PLLA), poly-(DL-lactic) acid (= PDLLA), poly (E-caprolactone) (= PCL) and a copolymer of poly hydroxybutyrate 80% - hydroxyvalerate 20 % (= PHB-co-HV 80/20) were implanted submucoperiostally on the palate of beagle dogs. After 2, 4, 8 and 12 weeks in situ, the structure of the films and the tissue reactions were evaluated histologically. It was concluded that, in terms of mechanical properties and tissue response, the PHB-co-HV film was the most suitable for use on dogs.

Chapter 3 compares dento-alveolar development in beagle dogs after palatal repair according to von Langenbeck with and without implantation of membranes made from a copolymer of poly hydroxybutyrate 80%- hydroxyvalerate 20% (=PHB-co-HV 80/20). In group 1 (n = 6; age 12 weeks), palatal surgery was performed using the von Langenbeck technique. In group 2 (n = 10; age 12 weeks), the von Langenbeck technique was used, followed by implantation of PHB-co-HV membranes. Six dogs (age 12 weeks) served as unoperated controls. Maxillary arch dimensions were studied by means of dental casts until the age of 25 weeks. It was concluded that palatal surgery according to von Langenbeck followed by implantation of PHB-co-HV membranes had only a slightly positive effect on dento-alveolar development compared with the von Langenbeck procedure only, while wound healing was retarded and most of the membranes were sequestered.

Chapter 4 describes a study in which the wound healing process was evaluated clinically and histologically in growing beagle dogs after palatal repair according to von Langenbeck with and without implantation of membranes of a copolymer of poly hydroxybutyrate 80%- hydroxyvalerate 20% (=PHB-co-HV 80/20). Von Langenbeck's repair was performed in 12 dogs (age 12 weeks) while von Langenbeck's repair followed by implantation of PHV-co-HV membranes was carried out in 11 dogs (age 12 weeks). Four dogs (age 12 weeks) served as unoperated controls. Standardized intra-oral slides of the palate were taken and measurements of the wound surface areas were carried out. Histological sections were prepared at 3 different ages. The animals were studied until the age of 25 weeks. It was found that wound closure after the von Langenbeck's procedure took about 3 weeks while the use of PHB-co-HV membranes after von Langenbeck's repair resulted in complete wound closure after approximately 7 weeks after the membranes had sequestered. At the age of 25 weeks, the histologic results after the von Langenbeck procedure showed that the entire scar tissue covering the former denuded bony areas was attached to the bone by means of Sharpey's fibres, while after implantation of the membranes only local scar tissue attachment by means of Sharpey's fibres was found. Further research is necessary to develop a membrane which allows wound closure without sequestration of it.

Chapter 5 presents a study, on beagle dogs, in which the possibility of preventing the development of Sharpey's fibres by means of a modified surgical technique was investigated. In group 1 (n=2; age 6 months), palatal repair according to von Langenbeck, was simulated. In group 2 (n=4; age 18 months), palatal surgery was performed using a partially split flap technique. Two dogs served as unoperated controls. The palates were histologically evaluated 12 weeks after surgery and compared with the controls group. In group 1, the scar tissue was firmly attached to bundle bone by means of Sharpey's fibres. In group 2 and in the controls, this kind of attachment was not found; the palatal bone was of the larnellar type. It was found that the partially split flap technique had led to the development of vaguely demarcated scar tissue only and it had prevented, to a large extent, development of Sharpey's fibres.

In chapter 6 dento-alveolar development in beagle dogs after palatal repair according to the partially split flap technique and the von Langenbeck method is compared. In group 1 (n=10; age 12 weeks) the partially split flap technique was used. In group 2 (n=6; age 12 weeks), palatal repair according to von Langenbeck was simulated. Six dogs (age 12 weeks) served as controls. Maxillary arch dimensions were studied by means of dental casts until the age of 25 weeks. It was concluded that palatal surgery according to the partially split flap technique resulted in significantly wider transverse maxillary dimensions than after the von Langenbeck procedure and closely resembled that of the control group.

Chapter 7 describes a clinical and histologic evaluation of wound healing in growing beagle dogs after palatal repair according to the partially split flap technique or the von Langenbeck technique. The partially split flap technique was performed in 14 dogs (age 12 weeks). Von Langenbeck repair was simulated in 12 dogs (age 12 weeks). Four dogs (age 12 weeks) served as controls. The animals were studied until the age of 25 weeks. Standardized slides of the palate were taken at 8 occasions and measurements of the wound surface areas were carried out. Histological sections were prepared at 3 different ages. The animals were studied at the age of 25 weeks. It was found that re-epithelialization was completed in approximately 2 weeks in dogs after palatal repair according to the partially split flap technique while re-epithelization time after von Langenbeck's repair took 3 weeks. The histologic features were close to normal while the von Langenbeck procedure results in scar-tissue which was firmly attached to bundle bone by means of Sharpey's fibres. It was concluded that the histologic appearance of the palatal tissues after palatal repair according to the partially split flap technique in growing dogs was close to normal. This is assumed to be the reason for a more favourable dento-alveolar development after the partially split flap technique as compared that after von Langenbeck's repair.

Chapter 8 presents a clinical study in which the peri- and postoperative course and the dento-alveolar development of the deciduous dentition in Japanese ULCP and CP patients up to 5 years after two different types of palatal repair was evaluated. One of the methods, the Kohama supraperiosteal flap technique, is performed without denudation of the bony palate while the other, the Wardill push-back technique, results in areas of denuded bone. It was concluded that the supraperiosteal technique can be performed successfully in almost equal time as the push-back technique. Re-epithelialization of the wound areas after supraperiosteal repair takes about one week, which is one third of the time compared to healing after the pushback technique. Arch depth of the deciduous dentition after the supraperiosteal technique is superior compared to the push-back technique. The question whether or not the supraperiosteal technique produces more favourable dento-alveolar development than the mucoperiosteal technique in the permanent dentition in humans has to be elucidated in future research.

Chapter 9 discusses the results from the previous chapters gives suggestions for future research.